Journal of Applied Engineering Science 10(2012)4

Journal of Applied Engineering Science 10(2012)4

I M P R E S S U M

J O U R N A L O F A P P L I E D E N G I N E E R I N G S C I E N C E (J A E S)

The journal publishes original and review articles covering the concept of technical science, energy and environ-ment, industrial engineering, quality management and other related sciences. JAES is Open-Access Journal that follows new trends and progress proven practice in listed fi elds, thus creating a unique forum for interdisciplinary or multidisciplinary dialogue. JAES is part of the electronic journal editing with a transparent editorial and review policy. Provided are:

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All published articles are indexed by international abstract base Elsevier Bibliographic Databases through service SCOPUS since 2006 and through service SCImago Journal Rank since 2011.Serbian Ministry of Science admitted the Journal of Applied Engineering Science in a list of reference journals. Same Ministry fi nancially supports journal’s publication.

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PublisherInstitute for Research and Design in Commerce and Industry - IIPP; www.iipp.rsFor publisher: Prof. dr Branko VasićCopublishersFaculty of Mechanical Engineering - Belgrade University; www.mas.bg.ac.rsFor copublisher: Prof. dr Milorad Milovančević Faculty of Transport and Traffi c Engineering – Belgrade University; www.sf.bg.ac.rsFor copublisher: Prof. dr Branimir StanićEditor in ChiefProf. dr Jovan TodorovićFaculty of Mechanical Engineering, Belgrade;Assistant EditorDr Predrag Uskoković, IIPPEditorial Board Prof. dr Gradimir Danon, Faculty of Forestry, Belgrade; Doc. dr Dušan Milutinović, Institute for Transport and Traffi c CIP, Belgrade; Mr Đorđe Milosavljević, CPI - Process Engineering Center, Belgrade; Prof. dr Miodrag Zec, Faculty of Philosophy, Belgrade; Prof. dr Nenad Đajić,Mining and Geology Faculty, Belgrade; Prof. dr Vlastimir Dedović, Faculty of Transport and Traffi c Engeneering, Belgrade;Prof. dr Mirko Vujošević,Faculty of organizational sciences, Belgrade;Doc. dr Vladimir Popović,Faculty of Mechanical Engineering, Belgrade;Doc. dr Vesna Spasojević Brkić,Faculty of Mechanical Engineering, Belgrade.

ISSN 1451-4117 UDC 33Papers are indexed by SCOPUS

International Editorial BoardProf. dr Vukan Vučić,University of Pennsylvania, USA;Prof. dr Robert Bjeković, Hochschule Ravensburg-Weingarten, Germany;Prof. dr Jozef Aronov, Research Institute for Certifi cation JSC, Russia;Prof. dr Jezdimir Knežević, MIRCE Akademy, England;Dr Nebojša Kovačević, Geotechnical consulting group, England;Adam Zielinski, Solaris Bus & Coach, Poland;Prof. dr Miloš Knežević, Faculty for Civil Engineering, Montenegro;MSc Siniša Vidović, Energy Testing & Balance Inc, USA;Dr Zdravko Milovanović,Faculty of Mechanical Engineering, Banja Luka.Publishing CouncilMilutin Ignjatović,Institute for Transport and Traffi c CIP, Belgrade; Dragan Belić,Transport Company “Lasta”, Belgrade;Dr Deda Đelović, Port of Bar, Bar;Dr Drago Šerović, Adriatic Shipyard, Bijela;Cvijo Babić,Belgrade Waterworks and Sewerage, Belgrade;Nenad Jankov, Power Plant Kostolac B, Kostolac;Miroslav Vuković, Mercator Business System, Belgrade;Dušan Đurašević, Euro Sumar, Belgrade.Editorial Offi ceNada Stanojević, Miloš Vasić, Darko Stanojević,Miloš Dimitrijević, Ivana Spasojević, IIPP, Belgrade;

Journal of Applied Engineeering Science is available at: www.engineeringscience.rs http://scindeks-eur.ceon.rs/index.php/jaeshttp://www.singipedia.com/content/1166-naucni-casopisiPrinted by: Sigrastar, Beograd

Institute for research and design in commerce & industry, Belgrade. All rights reserved. Journal of Applied Engineering Science 10(2012)4

C O N T E N T S

Dr Miroslav Demić, Dr Đorđe DiligenskiA CONTRIBUTION TO RESEARCH OF DEGRADATION OF CHARACTERISTIC

OF VIBRATION PARAMETERS OF VIBRATION ASPECT OF VEHICLE COMFORT185 - 190

Dr Nikola Dondur, Dr Vesna Spasojević-Brkić, Mr Aleksandar BrkićCRANE CABINS WITH INTEGRATED VISUAL SYSTEMS FOR DETECTION

AND INTERPRETATION OF ENVIRONMENT - ECONOMIC APPRAISAL191 - 196

Zoran Petrović, Dr Uglješa Bugarić, Dr Dušan PetrovićUSING ARIMA MODELS FOR TURNOVER PREDICTION IN INVESTMENT

PROJECT APPRAISAL 197 - 200

Dr Radoljub Tomić, Dr Predrag Petrović, Marija PetrovićCONTRIBUTION TO THE EVALUATION OF THE COMPLIANCE FOR NEW

PRODUCTS WITH ASPECT RELIABILITY AND MAINTENANCE201 - 208

Dimić-Mišić Katarina, Dr Paltakari JouniFIBRILLAR MATERIAL AS A COBINDER IN COATING COLORS FORMULATIONS 209 - 220

Dr Vesna Spasojević-Brkić, Dr Slobodan Pokrajac, Dr Nikola Dondur, MSc Sonja Josipović

ALLOCATIVE EFFIENCY AND QM FACTORS COVARIATE IN SERBIAN INDUSTRY

221 - 225

MSc Marija Savić, MSc Predrag Đorđević, Dr Đorđe Nikolić, Dr Ivan Mihajlović, Dr Živan Živković

COMBINATION OF KNOWLEDGE IN SYSTEM SUPPLIERS - MSP - CUSTOMERS IN TRANSITIONAL ECONOMY ENVIRONMENT IN SERBIA

227 - 233

EVENTS REVIEW 234

ANNOUNCEMENT OF EVENTS 235 - 236

BOOK RECOMMENDATION 237

EDITORIAL AND ABSTRACTS IN SERBIAN LANGUAGE 238 - 242


E D I T O R I A L

ALTERNATIVE FUELS AND RENEWABLE ENERGYThe intensive development of world economy and transportation in particularly, caused two big problems: a fast depletion of fossil fuels resources and a severe pollution of the environment. Providing al-ternative fuels and renewable energy resources make, therefore, the main challenges for engineers over the world.

Alternative fuels, known as non-conventional or advanced fuels, are any materials or substances that can be used as fuels, other than conventional fossil fuels (petroleum, coal, propane, and natu-ral gas), as well as nuclear materials. Some well-known alternative fuels are biodiesel, bioalcohol (methanol, ethanol, butanol), chemically stored electricity (batteries and fuel cells), vegetable oil and other biomass sources. One of the best is hydrogen which is practically emission free. The usage of hydrogen as a fuel needs large investment and it is nowadays considered as a fuel for future. Natural gas is another fuel that burns cleanly; cleaner than both gasoline and diesel engines. Renewable energy is energy that comes from natural resources such as hydropower, sunlight, wind, tides, waves and geothermal heat, which are renewable because they are naturally replenished at a constant rate. Biofuels are also considered a renewable source. Biodiesel is made from animal fats or vegetable oils and from plants such as soybean, sunfl owers, sugar cane, corn, etc. Biodiesel will release a smaller number of its pollutants; it burns both cleaner and more effi ciently. Methanol and Ethanol fuel are primary sources of energy; they are convenient fuels for storing and transporting energy. These alcohols can be used in internal combustion engines as alternative fuels. Sunlight is used by photovoltaic cells made from silicon alloys. These cells can convert sunlight into other forms of energy, such as heat and electricity. Geothermal energy is another perspective chance. Technologies used in geothermal production have much in common with those for oil and gas. Wind power is considered the most economical form of electrical power, particularly during night. Fuel cells, a solution to store electricity, are nowadays one of the most realistic perspectives for motorization, particularly with hydrogen as a fuel. In many countries there are already very important improvements in developments of alternative fuels and renewable energy sources. Renewable energy covers in many countries 15 to 20% of all demands (in Norway almost 100%). The most important is hydropower, but there are many wind and sunlight power plants over world, some of them with high power capacity. Biofuels, natural gas and electricity fuels millions of motor vehicles.The development of alternative fuels and renewable energy sources makes a priority task for Ser-bian economy as well. Taking in account our economical and engineering possibilities and natural sources, it is obvious that a priority should be given to further development of hydro powerplatns (riv-ers Drina, Ibar, Danube and a large number of small water fl ows) and to development of new energy sources, such as wind farms, sunlight and geothermal power plants. An attention should be paid to oil shale resources and to an improvement of coal mining sector, regarding capacities and environ-mental protection. In the transportation sector, very important is transfer to natural gas and various types of biofuels that will improve country economy and decrease the environment pollution.

Sincerely yours,Prof.dr Jovan Todorović

Prof. dr Jovan Todorović

Paper number: 10(2012)4, 236, 185- 190

A CONTRIBUTION TO RESEARCH OF DEGRADATION OF CHARACTERISTICS OF VIBRATION PARAMETERS ON VIBRATION

ASPECT OF VEHICLE COMFORTDr Miroslav Demić *University of Kragujevac, Faculty of Engineering Science, Kragujevac, SerbiaDr Đorđe DiligenskiVinča Institute of Nuclear Sciences, Department of Motor Vehicles and IC engines, Belgrade, Serbia

doi:10.5937/jaes10-2244

Dynamic simulation, based on modeling, has a signifi cant role in vehicle development, especially in the early stages of design process, when relevant parameters are being defi ned. In praxis it is usu-ally assumed that vibration parameters are unchangeable, what is basically wrong. All researches indicate that vibration parameters degrade in time of vehicle service, consequently leading to a variation of its dynamic characteristics. This paper, based on preliminary research results, attempts to point out the necessity of taking into consideration this variation in the earliest phases of vehicle design by its implementation in the vehicle simulation model. Key words: Vehicle, Vibration parameters, Degradation, Vibration comfort

INTRODUCTION

Dynamic simulation has important role in devel-opment of motor vehicles, based on modeling, by use of application of numerous vehicle mod-els [05-16,22,24-26,28,29]. It can be assumed that the mechanical model, in the general form, is described by the equation [05, 06]:

(1)where:

Z - vector of generalized coordinates of the vibration system,A - vector of vehicle vibration parameters,U - vector of control functions,Q – time function of excitation (coming from road microprofi le, engine function, unbalanced masses, tire nonuniformities, etc.),L – function that takes into account stochastic variation of characteristics of vibration parameters during the vehicle service life, andt - time.

General solution of vector differential equation (1) can be written in the form [05-06]:

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Z=Z(A,U,L,t) (2)

The simplest case is when there does is no con-trol function (U=0) and when variation of vibra-tion parameters of a vehicle in service is not taken into account (L=0), i.e.:

Z=Z(A,t) (3)

In practice, a simplifi cation given by expression (3) is commonly used, which neglects the infl u-ence of duration of service time on variation of vehicle vibration parameters. However, it repre-sents a major simplifi cation, according to [23], where the existence of the mentioned variation is shown. Therefore, this problem will be consid-ered in details by application of the appropriate vehicle vibration model.

SELECTION OF VEHICLE VIBRATION MODEL

The structure of a vehicle model is chosen with regard to the variables supposed to be analyzed [04, 05]. Therefore, vibration model of various structure and complexity [05-16,20-22,24-31]. The vehicle model should be chosen to be as simple as possible, and to enable simulation of the desired value [05,06]. A vehicle vibration model, often regarded in literature as quarter

185* University of Kragujevac, Faculty of Engineering Science, Sestre Janjić 6, 34000 Kragujevac, Serbia; [email protected]


model [21,22,24,26,28,29], given in Figure 1, has been estimated to be optimal for the obser-vation, bearing in mind that the aim of this re-search was to introduce degradation of vibration parameters in the model.

Figure 1: The equivalent vehicle model

Where the following signs were applied:m1, m2 –unsprung and sprung mass of quar-ter vehicle model, respectively (in this case 27.5 and 250 kg),Fs – force in the spring,Fsh – force in the shock absorber, and Ft – force in the tire.

Force in the tire can be represented by the polynomial equation of the third degree [05-15, 20,21,23,25]:

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where:

c1 and c2 – stiffness parameters, and – spring relative deformation.

Force in the shock absorber depends not only on the relative speed but on the relative motion and acceleration [01, 16]. The analyses have shown that the model defi ned in [01, 16], which applies transcendent functions of acceleration, can hardly be used in modeling of vehicles with more than one degree of freedom. That comes from the fact that the acceleration is covered by the function tangens hyperbolicus, in which case problems of decoupling of differential equations

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(4)

of motion, for model with two or more degrees of freedom of motion. Besides, it appears that the acceleration is of minor infl uence on the force than displacement and velocity, so for further analyses a model [01, 16] has been adopted, where the force is described with the expression:

(5)

where:

and - relative displacement and veloc-ity, respectively, andx1, x2,3, x4, x5 and x6 – parameters of shock absorber model.

Radial force in the tire is also nonlinear [20,21,23,25], and therefore the following ex-pression is used:

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(6)where:

-radial deformation of the tire, andc3, c4 and c5 – parameters of tire radial stiffness.

As it is well known, vertical vehicle vibration de-pend on type of road, velocity and the number of passengers riding in the vehicle. Having that in mind, the analysis is performed for the case that there are two passengers in the vehicle, rid-ing with the characteristic velocity of 30 m/s [32] on a good asphalt road, whose time excitation function is shown in Figure 2 [16]. To be more precise, a polyharmonic excitation function is ap-plied because the analyses have shown that it represents a good approximation of real road micro-profi le, for the applied vehicle velocity of 30 m/s.

Bearing in mind the observed vehicle vibration model, by use of Newton’s law [27,31], the fol-lowing differential equations of vibration motion of vehicle are obtained:

(8)

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(7)

where:

, -accelerations of unsprung and sprung mass measured from the equilibrium position, respectively,Fs – force in the spring given by expression (4),

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Dr Miroslav Demić - A contribution to research of degradation of characteristics of vibration parameters on vibration aspect of vehicle comfort


Fsh – force in the shock absorber given by expression (5), andFt – radial force in the tire given by expression (6).

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Bearing in mind nonlinear and very complex structure of expressions (4,5,6), even in case of such a simple vehicle model, as well as quasis-tochastic character of the excitation function, it appears to be obvious that the vehicle model de-scribed by equations (8,9) is complex and can-not be solved in fi nite form.

The analyses have shown that the argument of the tangens hyperbolicus function in the expres-sion (5) – displacement divided with the triple variation – lies in the domain -1.8 to +1.8 (established on the basis of the experimental results [01, 15].

It can be noted that the argument of the observed function is usually in the interval -1 to +1, and the relative error of approximation of the mentioned function with the Maclaurin polynomial of third degree is approx. 9% [01,16], which is found ac-ceptable.

During the simulation, parameters of the passen-ger car “Zastava 1100” were utilized, provided by the manufacturer [32], and shown in Table 1.

Figure 2: The applied function of road microprofi le excitation for the velocity of 30 m/s

c1, N/m c2, N/m3 c3, N/m c4, N/m2 c5,N/m3

50000 10000 5000 500000 500000x1, 1/N x2,/x3, s/s x4, s2/m x5, N/m x6, N/m

20.25 0.008/0.02 -9.51 -2.091 0.0015

Table 1: Vehicle parameters

It should be pointed out that dimensions of the coeffi cients in Table 1 are within SI unit system.

METHOD

Parameters of elasto-damping elements are variable values during the service life. To be more precise, their values tend to descend. For the illustration, Figure 3 shows a typical example of that variation [23], where it is assumed that values of parameters descend linearly with the duration of service, expressed in km. Data from Figure 3 enable analysis of the infl uence of vi-bration parameters variation on vehicle dynamic characteristics.

For the analysis of the infl uence of vehicle dy-namic cahracteristics due to variation of param-eters of elasto-damping elements in service, two groups of parameters were utilized, taking into account these variations. To be more precise, having in mind Figure 3, after approximation with streight line, any variation is described by the ex-pression:

Figure 3: Variation of vibration parameters in service

(9)

where:

vibpar – value of vibration parameter after service of kilometers,vibpar0 - value of vibration parameter at the beginning of vehicle service, andki – factor that takes into account degrada-tion of vibration parameters during service.

In order to take into account the infl uence of ag-ing on vehicle dynamic characteristics, on the basis of the data given in Figure 3, corrective parameters are adopted and given in Table 2. It should be pointed out that factor k1 refers to

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Dr Miroslav Demić - A contribution to research of degadation of characteristics of vibration parameters on vibration aspect of vehicle comfort


springs, k2 to shock absorbers and k3 to tires, and there were two groups of factors observed: at the beginning of service (group 1) and after 200000 kilometers of service (group 2).

As it has already been pointed out, differen-tial equations (7,8) are solved numerically, by use of method Runge-Kutta, with the sample of increment 0.01s, in 1024 points, which en-abled reliability of the results within the domain 0.1–50 Hz, what is regarded acceptable for this kind of analysis [02-04, 13-15].

On the basis of [02-04], statistical values of errors were calculated. For the signal of 1024 points with the sample of increment 0.01, number of averaging 256, bias errors were obtained 0.003, stochastic error for a single signal 0.10, and for two signals 0.118, for spectra. Such small values of errors indicate that these results enable reli-able analyses.

k1 k2 k3

Group 1 1 1 1Group 2 0,95 0,83 0,70

Table 2: Corrective factors

ANALYSIS OF THE RESULTS

On the basis of the calculated time series of verti-cal vibration of sprung mass, ordinary coherence functions, cross-correlation functions and trans-fer functions for the initial state were calculated, and also for the state of vibration parameters af-ter 200000 km of service, by use of software [17, 18], and presented in Figures 4-7.

Figure 4: Ordinary coherence function

Figure 5: Cross-correlation function

The analysis of the data from the Figure 4 may lead to the conclusion that ordinary coherence function is subject to variation within the interval 0.65 – 1, what indicates that the vehicle model is nonlinear [02-04]. Degradation of vibration pa-rameters also infl uences the value of ordinary coherence function.

Figure 5 presents the variation of cross-correla-tion function with the increment of time duration. To be more precise, it descends with the time increment and gravitates towards zero value, and also indicates that the process of vibration is stationary, what is understandable when the applied function of excitation is stationary value [02-04]. As in previous case, degradation of vi-bration parameters infl uences forced vibration of vehicle sprung mass.

Figure 6: Modulus of transfer function

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The analysis of data from the Figure 6 shows the resonance of sprung mass at approx. 2.5 Hz, and unsprung mass at approx. 7.5 Hz, which confi rms the fact that vehicle parameters are well chosen [21]. It is obvious that degradation of vibration parameters leads to a variation of pa-rameters of resonance of sprung and unsprung masses. I.e., since spring and shock absorber cahracteristics descend with the duration of ser-vice, it is clear that reduced damping leads to a variation of transfer function amplitude [26]. Vari-ation of vibration parameters also infl uences the variation of phase angle, Figure 7.

Figure 7: Phase angle of transfer function

It should be noticed that the variation of pa-rameters of resonant point strongly infl uences parameters of vibration comfort of the vehicle, and degradation of these parameters may lead to a distraction of the vehicle due to unconfort-able ride [12-14, 18]. This effect is often noticed in service when shock absorbers are worn, or suspension characteristics degrade to the extent that makes the vehicle unsafe to use. Therefore, it appears to be a need to introduce a degree of the allowed degradation of vibration parameters, what is not the subject of this paper. It is impor-tant to point out that the infl uence of degrada-tion of vibration parameters should be taken into consideration in the process of creating a vehicle model in the early phase of vehicle design.

CONCLUSIONS

Performed research enabled following conclu-sions:

Degradation of vibration parameters during the service infl uences the variation of charac-teristics relevant for vehicle vibration comfort.The infl uence of degradation of vibration pa-rameters should be taken into account in vehi-cle model in the early phase of vehicle design

REFERENCES

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Paper sent to revision: 24.09.2012.Paper ready for publication: 03.12.2012.

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Paper number: 10(2012)4, 237, 191-196

CRANE CABINS WITH INTEGRATED VISUAL SYSTEMS FOR THE DETECTION

AND INTERPRETATION OF ENVIRONMENT - ECONOMIC APPRAISAL

Dr Nikola Dondur *University of Belgrade, Faculty of Mechanical Engineering, Belgrade, SerbiaDr Vesna Spasojević-BrkićUniversity of Belgrade, Faculty of Mechanical Engineering, Belgrade, SerbiaMr Aleksandar BrkićUniversity of Belgrade, Faculty of Mechanical Engineering, Belgrade, Serbia

doi:10.5937/jaes10-2516

This paper analyses the economic feasibility of production and use of the new generation crane cabins of considerably lighter weight and stiff structure whose interior space necessary for the operator will be developed by using the methods of physical, cognitive and organizational ergonomics with the solved problem of visibility and which will allow higher productivity due to reduction of physical and psychologi-cal stress of the operator, as well as greater safety and security due to the integrated visual system. It is proved that the total economic benefi t of the exploitation of the cabin in the overall exploitation period is signifi cantly higher than the purchase price of the cabin, as well as that the internal rate of return is above the relevant average weighted interest rate and the payback period is less than three years. The analysed project of production and use of crane cabins with integrated visual systems for the detection and interpretation of environment is the project with low economic risk.Key words: Economic feasibility, Cranes, Cabin, Integrity, Products, Operator

INTRODUCTION

As a result of the complicated and constantly changing nature of industrial and construction work, there are very high injury and fatality rates, where cranes contribute to as many as one-third of all fatalities and injuries resulting in permanent disability [01]. The Crane and Hoist Safety report - OSHA reported a death rate of 1.4 deaths per 1000 operators [06]. Human error is the cause of almost 60% of lifting operation related accidents [01]. It is not surprising since crane operators still work in ergonomically unadjusted surrounding with very high visual tension in stressful working conditions due to both physical stress (shocks, vibrations and accelerations), and psychological stress (the sway of the load, extremely low vis-ibility of cranes, etc.). Additionally, the ever grow-ing competitiveness in the international and/or national market makes further improvement in the management, effectiveness and effi ciency of crane operations and crane systems absolutely essential. According to previous research results

[01,06, 05] a new solution for crane cabins is needed to solve the aforementioned problems is needed. The goal is to develop crane cabin as ergonomically adjusted, light weight and inte-grated visual systems for the detection and inter-pretation of environment.

TECHNICAL DESCRIPTION AND FEASIBILITY

We propose the following: 1) To develop smaller and lighter ergonomically adjusted crane cabins with appropriate safety features using physical, cognitive and organizational ergonomics and modelling, and static and dynamic calculations using the fi nite element method; 2) To develop well designed integrated visual systems for the detection and interpretation of environment which will solve the operator’s visibility problems; 3) To develop a simulation crane cabin, based on Virtual Reality technology, to replicate a real crane cabin together with the instrumentation and control of crane operations for the purposes of training and enhancing the cognitive abilities

191* University of Belgrade, Faculty of Mechanical Engineering, Kraljice Marije 16, 11000 Belgrade, Serbia; [email protected] Paper presented at SIE 2012


necessary for the effective and effi cient use of integrated vision systems, and 4) To develop a prototype remote control for cranes which will in-clude a remote control console and associated tracking (sensory) and management information systems. The main innovative idea behind this project consists of synergetic contributions from the following entities as the main fi elds of devel-opment: a) The development of a model with the minimal dimensions of the cabin where the oper-ator will be accommodated in an ergonomically adjusted way based on an anthropometric study; b) The development of a model for the cabin in-terior including well-designed controls and the control station layout according to the principles of ergonomics and biomechanics which will en-sure good safety features, c) The further optimi-zation of the cabin by designing a light weight cab supporting structure with the application of the fi nite element method (FEM) for the analy-sis of load distribution, membrane and bending stresses, strain energy and the distribution of ki-netic and potential energy to groups of elements of cab structure; d) The development of integrat-ed visual systems for the detection and interpre-tation of environment which will solve visibility problems; e) A Virtual Reality based simulation cabin, and f) A crane remote control prototype setup. The benefi ts of this project lie in offer-ing solutions to the following problems: (i) lower productivity due to human-machine interface problems; (ii) large fi nancial and other losses re-sulting from the direct and indirect costs of the accidents caused;(iii) damage to the materials as well as to the material handling equipment; (iv) the unnecessary cost of frequent repairs and consequent loss of production; (v) disturbance in material handling schedules and (vi) an increased work-load on the other equipment and their con-sequent quicker downtime and break down.

ECONOMIC APPRAISAL METHODOLOGY

According to the Global Cranes, Lifting and Han-dling Equipment – Market Opportunities and Business Environment, Analyses and Forecasts to 2015 document produced by World Market In-telligence during the period 2006-2010, the con-sumption value of the global crane, lifting and handling equipment market grew at a CAGR of 2.76%. After witnessing a year of production and consumption decline due to low demand, the market recovered in 2010 to record production growth of 5.9% and consumption growth of 4.7%.

Whilst South America experienced the fastest growth in consumption value during the review period, Asia-Pacifi c and Europe made the high-est contributions to market consumption value in 2010. In terms of construction equipment from emerging nations to support infrastructural and mining investments, global cranes, lifting and handling equipment consumption is expected to record a CAGR of 10.75% in the forecast period - 2015. The European market has experienced a constant and the largest growth, amounting to 46% in 2000, in contrast to 15% in America and 11% in the rest of the world. A European crane cab-ins market is envisaged in this project as this is the area with the lowest transportation costs, thus the highest market growth is expected in this region. For the assessment of economic feasibility of de-velopment, production and use of crane cabins, in practice the most commonly used approach is cost-benefi t (CB) framework. Economic feasibility as-sessment through the cost-benefi t framework can generally be used in the two assumed scenarios:

development, production and sale of a new generation of crane cabins (producer point of view)use /purchase of the above type of crane cabins by the crane owners /lessors.

Economic and fi nancial feasibility in the fi rst assumed scenario foresees defi ning the standard parameters of the assessment from the aspect of a cabin pro-ducer (owner of the crane cabin factory, sharehold-ers, potential creditors) and the overall economy [3]. This approach requires developing complete tables of fi nancial and economic fl ows, necessary for the calculation of the selection criteria (FNPV, FIRR, ENPV, EIRR, pay-back period, BCR).The second approach refers to an assessment of economic feasibility of investing into acquisi-tion of a new generation of crane cabins and/or comparison of such investments (initial invest-ment costs) and discounted additional effects (savings) in the crane exploitation over the en-tire (remaining) lifetime. Thus developed net fl ow serves as a basis for developing the quantita-tive parameters for the justifi cation of investment and/or purchase of the new generation crane cabins from the aspect of the crane owner or user and from the aspect of the entire economy (NPV, IRR, BCR, pay-back period). For creat-ing an economic net fl ow related to a new crane cabin, it is necessary to identify and quantify rel-evant costs and effects. [08, 03].

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Dr Nikola Dondur - Crane cabins with integrated visual systems for the detection and interpretation of environment - economic appraisal


CostsIn the standard terminology that refers to proj-ect analysis, acquisition (purchase price) of the new generation of crane cabin can be seen as an initial investment cost. In the competitive circumstances, purchase price is nearly equal to the marginal production cost, increased by transport, insurance and trade margin. The cost of manufacturing a cabin should include materi-als, labour and energy costs, as well as a portion of dependent fi xed costs. In addition to the costs included in the purchase price (I0 ), it is neces-sary to assemble and test the crane cabin, ensure training for a crane operator, but also disassem-ble the existing cabin if it is already existed on the crane (I1). Initial investment costs, required for the economic assessment of the project of using the new generation crane cabins, would represent a sum of the above-mentioned costs (I0 + I1).

Benefi tsThe exploitation of the new generation of crane cabins has direct and indirect positive effects from the aspect of the owner or user of the crane, but also positive effects on the overall economy. Direct positive effects from the point of view of the crane owner are primarily appeared through increase in productivity of the crane use. The cabin with integrated visual systems for the de-tection and interpretation of environment allows the crane operator to perform work operations faster. Savings of time at one duty allows the crane owner to engage the crane at another job without any additional exploitation costs. Reduc-tion of the annual crane exploitation costs due to the assembly of the new crane cabin, which allows saving of time in performing work operations (Δt) represents benefi t from the aspect of the crane owner. As the exploitation costs depend on the time of the crane operation (t), for the calculation purposes the positive effect for the crane owner represents a product of the sum of all exploitation costs and weight of the average time saving in performing operations (∑CEt· ρt). The annual crane exploitation costs can be de-composed to the costs of depreciation (capital recovery), costs of maintenance and repairs, as well as insurance and registration costs. Formal-ly, these costs can be presented as follows:

(1)

where PC represents a purchase value of the crane, stands for capital recovery factor for the specifi c exploitation lifespan of the crane (n) and interest rate (i). Depreciation of the crane is observed as depreciation of debt and/or future value of equal annual repayments of the amount invested in the purchase of the crane. Weight of the average time saving is determined as a relative ratio of the sum of differences in time of the operations performed by the crane without the new generation cabin and the time of operations with the new cabin and the total time of operations without the cabin with the inte-grated visual crane management system:

(2)

where represents weight of the average re-duction in time of operation of the crane with the new cabin, time of operation (j) without the cabin with the integrated visual system for detec-tion and stands for time of operation (j) with the new generation crane cabin.The following direct benefi t of installing the new generation crane cabins is reduction in labour costs. If we assume that the number of workers and labour cost per hour remain the same, oper-ation time reduction allows the worker to perform in such time reduction an additional work that is benefi cial for the crane owner. Accordingly, time reduction of the operations (ρt) which the crane achieves due to the use of the new generation cabins represents a weight for calculation of the annual savings in labour costs (LSCt) as a prod-uct of the number of workers, cost of labour per hour and number of working hours of the crane:

(3)

where represents savings of labour costs in a year (t), stands for a number of crane op-erators, number of effective working hours of the crane in a year (t), average value of the working hour and is a weight of average savings of time of the crane operation in a year (t).By installing the new generation crane cabin, in-cidence of professional diseases and injuries of crane operators is reduced. This positive effect can be quantifi ed through reduction of number of

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Dr Nikola Dondur - Crane cabins with intergrated visual systems for the detection and interpretation of environment - economic appraisal


working hours which the crane operator spends on a sick leave, during which period a new worker must be hired. This saving can be quantifi ed as a product of the number of workers, number of hours lost due to the crane operator’s absence, labour cost per hour and average weight of time reduction of the crane operations:

(4)

where represents annual savings in labour costs while the crane operator is on a sick leave, n a number of crane operators, number of working hours lost due to sick leaves, repre-sents a cost of the working hour and weight of average time saving of the crane operation in a year (t).Thanks to a better visibility, the use of the new crane cabin reduces a number of breakdowns and slows down wear and tear of the crane mobile parts and/or reduces the costs of crane maintenance and repairs. This positive effect is determined as a product of the crane value and difference in the relative annual maintenance and repair costs:

(5)

where represents savings on the annual costs for maintenance and repairs of the crane , is a purchase value of the crane, is the value of the annual costs for maintenance and repairs of the crane without crane cabin with visual system and is a value of the annual costs for maintenance and repairs of the crane with the new generation crane cabin.Through a more effi cient use of the crane, the new generation crane cabin is supposed to ex-end the assumed crane exploitation lifespan. Ex-tension of the crane exploitation lifespan brings additional benefi ts through reduction of annual depreciation (recapitalisation) costs of the crane which is quantitatively determined as the differ-ence between recapitalised annual write-offs and the lifetime of the crane (n) without the new generation crane cabin and recapitalised annual write-offs with the extended crane exploitation lifespan (n+m):

(6)

where represents annual savings on de-preciation write-offs, purchase value of the crane, capital recovery factor with the as-sumed exploitation lifespan without the new crane cabin (n) with appropriate interest rate (i), whereas represents a capital recovery fac-tor with the extended exploitation lifespan (n+m) due to the use of the new crane cabin with appro-priate interest rate (i).

ECONOMIC APPRAISAL CRITERIA

For the assessment of economic feasibility of the crane cabin with integrated visual systems for the detection and interpretation of environ-ment, the following standard cost benefi t criteria are defi ned: net present value, internal rate of return, cost - benefi t ratio and payback period on investment. Net present value (NPV) of an investment in the new generation crane cabin represents the difference between the sum of initial investment costs and the sum of discount-ed savings over the entire lifetime of the crane, whereby such savings are resulting from the use of the new crane cabin:

(7)

where NPV represents net present value of sav-ings on costs of the crane exploitation achieved by the crane cabin with the integrated visual sys-tem over the crane lifetime (n+m) and (i) repre-sents relevant discount rate. Based on this crite-rion, use of the new crane cabin is acceptable if the net present value is positive.Internal rate of return (IRR) of the investment in acquisition of the new crane cabin is the value of discount rate which equalize the difference of the initial purchase costs of the new crane cabin and the present value of the total savings in op-erating costs with zero. For a project to be eco-nomically justifi ed, this rate should be above the average weighted interest rate. [02, 07].Cost benefi t ratio is a quotient of the total net sav-ings of the crane exploitation and the purchase costs, assembly costs and training costs for the work in that cabin. According to this criterion, purchase of the crane cabin will be economically acceptable if this ratio is greater than one.

ECONOMIC APPRAISAL RESULTS

For the assessment of the economic feasibility of the new generation crane cabin purchase, we

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used the data referring to the bridge crane cabin. Table 1. provides the estimated data and, by us-ing equtions from (1) to (7), calculated values referring to the costs of purchase and savings during the exploitation of the new crane cabin.

Table 1: Economic cost - benefi t appraisal inputs

Variables Values (Euros, %,)Cabin manufacturing costs (costs of materials, labour, energy - I0)

20000 Eur

Costs of assembly, testing, crane operator training and disassembly of the existing cabin if it is already fi tted on the crane (I1)

1500 Eur

Benefi ts ( Savings)Savings in time of operations /cycle reduction / ( ) 10 % (8-12%)

Purchase price of the crane 268000 Eur (20000-500000)

Annual savings on labour costs (LSCt)

1440 Eur

Annual savings due to reduced incidence of professional diseases and injuries of crane operators (LSCt)

400 Eur

Reduction of the crane mainte-nance and repair costs (LSDCt) 4025 Eur

Savings due to the extended exploitation lifespan (from 15 to 18 years) (ELSCt)

1828 Eur

By using the expression (7), we estimated em-pirically net present value of the net effect of the purchase and use of the new generation crane cabin. Net present value as a synthetic measure of absolute economic viability is in the fi rst step calculated on the basis of the best estimates values of variables. Those values are given in Table 1. Net present value is, at the discount rate of 10%, Eur 68350. The total economic ben-efi t of the exploitation of the cabin in the overall exploitation period is higher than the purchase price of the cabin and according to this criterion, the project of installing the new generation cabin is economically viable. Internal rate of return as a relative measure of economic acceptability of the purchase and exploitation of the new crane cabin is signifi cantly above the relevant average weighted interest rate and is equal to 34.30%, which implies high economic profi tability of the investment. Annual savings which are made in the operation of the crane managed from the new generation cabin are Eur 13770 which shows

that the payback period is slightly less than three years. As these are estimated input values ap-plied in the calculation of the relevant criteria for the assessment of acceptability, we used sensi-tivity and risk analysis to test the robustness of the obtained results.

Table 2: Sensitivity analysisNPV IRR(%)

Change (%) +10 -10 +10 -10Purchase value of the crane 77415 59273 37.31 31.26

Cabin price 64708 71980 31.11 38.17Dh (savings in working hours ) 68648 68040 34.4 34.19

Sensitivity analysis shows relative stability of results as the change of the selected critical variables in the range (±10%) does not signifi cantly infl uence the value of the criteria for the assessment of the economic viability of purchase and use of the new generation crane cabin. In risk analysis, we mod-elled fi ve critical uncertain variables (cycle reduc-tion, purchase price of the crane, cabin price, price of the working hour of a crane operator, number of working hours lost due to sick leaves and crane maintenance costs) by triangle probability distri-bution. Figure 1. gives an overview of simulation results (Hypercube sampling).

Figure 1: Distribution of the results195, 237

Dr Nikola Dondur - Crane cabins with intergrated visual systems for the detection and interpretation of environment - economic appraisal


Net present value varies in the range from -16123,6 Eur to 162144 Eur and the internal rate of return ranges from 3% to 72.4%. Probabilities for negative net present values and for internal rates of return below average weighted reference interest rate (10%) are very low. The results of the analysis show that the project of purchase and use of the crane cabin with integrated visual sys-tems for the detection and interpretation of envi-ronment is the project with low economic risk.

CONCLUSION

Techno-economic analysis of the project shows that the total economic benefi t in the overall ex-ploitation period is signifi cantly higher than the purchase price of the cabin and according to this criterion the project of installing the new genera-tion cabin is economically viable. Internal rate of return is above the average weighted interest rate, which implies high economic profi tability of the investment. Annual savings made in the op-eration of the crane which is managed from the new generation cabin have the payback period of less than 3 years. The analyzed project of produc-tion and use of crane cabins with integrated visual systems for the detection and interpretation of en-vironment is the project with low economic risk.

AcknowledgementThe authors wish to acknowledge the fi nancial support from the Ministry of Education and Sci-ence Republic of Serbia through project E!6761.

REFERENCES

Beavers J. E., Moore J. R., Rinehart R., Schriver W. R., (2006), Crane-Related Fatal-ities in the Construction Industry, Journal of Construction Engineering and Management, Vol. 132, No. 9, , pp. 901-910Curry, S. And Weiss, J. (2000). Project Anal-ysis in Developing Countries, MacMillan Press. LondonDobrojević, M., Rakin, M., Medo, B., Omić, S., Sedmak, A.: INTERNET APLIKACIJA ZA UPRAVLJANJE PROJEKTIMA U INDUS-TRIJSKIM SISTEMIMA, (2010), Journal of Applied Engineering Science (Istraživanja i projektovanja u privredi), no. 28, pp. 73-82Dondur, N., (2002). Economic Analysis of Projects, Faculty of Mechanical Engineering, Belgrade (in Serbian)Global Cranes, Lifting and Handling Equip-ment - Market Opportunities and Business Environment, Analyses and Forecasts to 2015, World Market Intelligence,(March2011). (http://www.researchandmarkets.com/reports/1579090/global_cranes_lifting_and_handling_equipment)Neitzel, R. L., Seixas, N. S., and Ren, K. K., (2001), A review of crane safety in the construction industry, Appl. Occup. Environ. Hyg., Vol. 16 No.12, pp. 1106–1117.Potts, D. (2002). Project Planning and Analy-sis for Development, Lynne Rienner Publish-ers, Inc. LondonRosenfeld, Y. and Shapira, A. (1998). Auto-mation of existing tower cranes: economic and technological feasibility, Automation in Construction, vol. 7. pp. 285-298

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Paper number: 10(2012)4, 238, 197-200

USING ARIMA MODELS FOR TURNOVER PREDICTION IN INVESTMENT

PROJECT APPRAISALZoran Petrović *Tecon System d.o.o, Belgrade, SerbiaDr Uglješa BugarićUniversity of Belgrade, Faculty of Mechanical Engineering, Belgrade, SerbiaDr Dušan PetrovićUniversity of Belgrade, Faculty of Mechanical Engineering, Belgrade, Serbia

doi:10.5937/jaes10-2617

In the contemporary investment project analyses, most critical point is how to estimate daily turnover of production, or service, based system. In order to make prediction, for investment in certain type of equipment more accurate, daily turnover in the system for automated car wash was observed, along with weather conditions. According to observation, ARIMA model for daily turnover and weather condition is created, according to Box-Jenkins procedure. Conclusion was made that daily turnover can be analytically expressed through daily weather conditions. Validity of observation is checked on second system that is installed in different town in Serbia. According to compared results, conclusion was made that ARIMA model of system daily turnover, predicted by dependent variable, can be gen-erally used as good predictor in investment analyses, or selective criteria for investment decisions.Key words: Arima, Box-Jenkins, Investments, Predictions, Turnover

INTRODUCTION

Life cycle of project is determined by, at least four phases. In the fi rst phase, also called initial phase, feasibility study is performed and decision for continuing or cancelation of the project, (if not feasible), is made. In the production systems if project is evaluated as feasible, other phases can be carried out (planning and construction, produc-tion and fi nal operational phase), Figure 1. From the Figure 1, it is hard to conclude that fi rst phase of the project is most important one. Con-clusions from the fi rst phase will have vital infl u-ence to the project successful fi nishing [03].

Figure 1: Project cycle phases [04]

Considering risk distribution across project life cycle, beginning of the project is bearing most of the risk, since in the beginning number of avail-able information is relatively small.

Figure 2: Diagram of project life cycle considering project expenditure and risk [03]

Usually, in investment analyses average daily turnover, measured on existing system is used to estimate turnover for system that is analyzed from the point of investment appraisal. Problem in such approximation is that fl uctuation of aver-age daily turnover of the system that is analyzed as potential investment, can differ signifi cantly from any other, previously installed system.

* Tecon System d.o.o, Antifašističke borbe 21b, 11000 Belgrade, Serbia; offi [email protected] Paper presented at SIE 2012

197


In order to predict daily turnover, two variables were measured on existing system. First variable is Daily turnover and second one is Daily weather condition.

HYPOTHESIS

Hypothesis 1.: H0: Daily turnover is dependent from Daily weather condition.Hypothesis 2.: H0: Measure of dependence can be expressed in analytical form.Hypothesis 3.: H0: Daily weather condition can be used as predictor for estimation of daily turn-over in investment analyses.

METHODOLOGY

Automated car wash was observed in such way that daily records of turnovers and weather condi-tions were registered in research protocol. Case study was created from daily records taken from 25.05.2009. until 21.5.2010. During mentioned time 362 data records were taken.From research protocol two variables were cre-ated – Daily turnover and Daily weather condi-tion. Daily turnovers are represented as values in RSD and Daily weather conditions are represent-ed as one of four different, weather conditions. If weather during most of the day was sunny, num-ber 1 was assigned for Daily weather condition. If weather during most of the day was cloudy, num-ber 2 was assigned. To mostly cloudy with rainy period was assigned number 3 and to the rainy, or snowy, day was assigned number 4. Variables defi ned in research were modeled as ARIMA time series according to Box-Jenkins modeling strategy [01]. Such variables are used for forecasting of turnover on the system [02]. All calculations were done in statistical software IBM SPSS Statistics 20. Dependency between those variables was exam-ined in order to check if daily turnover depends from daily weather condition. In the results, after confi rmation of the Hypothesis 1, analytical mod-el of dependency was created and Hypothesis 2 was confi rmed. For confi rming Hypothesis 3, new system in dif-ferent town was observed. Observation period was defi ned as 100 days, on which both vari-ables (Daily turnovers and Daily weather condi-tions) were recorded and registered in research protocol. Based on the analytic expression of the dependency between variables in fi rst case, daily turnover on second system was modeled, using daily weather conditions as predictor.

Data for both variables were tested against Hy-pothesis that they can fi t to the Normal distribu-tion. Goodness of fi t for both variables was tested with Kolmogorov-Smirnov test, with signifi cance level =0,05. Students T test was used in order to test both variables against Hypothesis 3, that there is no signifi cant differences between distribution of two samples.

RESULTS

According to proposed methodology time series of daily turnover is given on the Figure 3:

Figure 3: Observed daily turnover

Time series of measured data compared to time series of modeled data using ARIMA methodol-ogy is given on the Figure 4.

Figure 4: Observed and modeled daily turnover

According to the calculated data best fi tted mod-el that describes analytical relationship between Daily turnover and Daily weather condition was: ARIMA (1,0,14). Parameters of ARIMA (1,0,14) model are given in the Table 1. Analytical expression for relationship between variables is given as:

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Zoran Petrović - Using arima models for turnover prediction in investment project appraisal


where:

is average turnover for past 14 days. n is number of observation n 1.

Wc is daily weather condition on observed day as categorical variable that can take value 1-4.

ARIMA Model ParametersEstimate SE t Sig.

VA02-Model_1

VAR02 No Transf.Constant 8447,649 557,341 15,157 ,000

AR Lag 1 ,696 ,041 17,070 ,000

VAR01 No Transf.MA Lag 14 -,265 ,055 -5,431 ,000

Num. Lag 0 -1789,317 115,705 -15,464 ,000

Table 1: ARIMA model paramters

According to Ljung-Box procedure, statistical model is good fi tted to observed data. Signifi -cance of the test was 0,081, so difference be-

tween fi tted and measured values are not statis-tically signifi cant. Values of the Ljung –Box test for goodness of fi t are given in the Table 2.

Model Number of Predictors

Model Fit statistics Ljung-Box Q(18) Number of Outliers

Stationary R-squared Statistics DF Sig. R-squaredVAR02-Model_1 1 ,609 23,158 15 ,081 6

Table 2: Model goodnes of fi t

Estimate SE t Sig.

VAR02-Model_1

14 Additive 7889,826 2094,530 3,767 ,000182 Additive 10126,487 1996,093 5,073 ,000300 Additive 10890,786 2045,844 5,323 ,000335 Additive 13578,128 2011,825 6,749 ,000341 Additive 10432,565 2030,952 5,137 ,000

Table 3: Extreme values (outliers)

Number of extreme cases (outliers) is 6, which is less than 2%, of all observed cases. Extreme values (outliers) are given in the Table 3. In order to validate results, newly installed sys-tem was observed in different town. Average turnover form fi rst model was used as starting value for modeling. Rest of time series was mod-eled from analytical expression for relationship between variables, based on weather variable that was recorded on the system, as predic-tor. Data sets from observed real system were tested against Hypothesis that they can be de-scribed with Normal distribution. Data sets from model, were tested against Hypothesis that they can be described with Log Normal distribution. In the fi rst case results are distributed according to Normal distribution N (2671,4912) and in the sec-ond, results were distributed according to Log Nor-mal distribution LogN (0.77,8.2). Histograms for both variables are presented on Figures 5 and 6.

Figure 5: Histogram of data observed from real system

Figure 6: Histogram of data predicted with ARIMA model199, 238



Goodness of fi t was tested with Kolmogorov-Smirnov test, for same signifi cance level =0,05. In the fi rst case, where data on real system were tested against Hypothesis of Normal distribution, critical value for Kolmogorov –Smirnov test was 0,13403 for 100 recorder data sets and value of the test was 0,086. In the second case, where modeled data were tested against Hypothesis of Log Normal distri-bution, critical value for Kolmogorov –Smirnov test was 0,13403 for 100 recorder data sets and value of the test was 0,078. Student’s T test was accomplished in order to test Hypothesis 3, that there is no signifi cant difference between means on two independent samples. According to calculated values of Student’s T test, for signifi cance level of = 0,05 and de-grees of freedom df=198, value of the test was t=0,553. There is no signifi cant difference be-tween means on two variables.

DISCUSION

Hypothesis 1 was tested and results confi rmed stated Hypothesis that variable Daily turnover can be predicted by variable Daily weather con-dition. From the model fi t it can be seen that goodness of the fi t is 60,9%, which is considered as good model fi t [06]. Number of outliers in fi tted model was signifi -cantly small (below 2%), which also indicates goodness of the fi t. Hypothesis 2 was also confi rmed. Analytical formu-lation of dependency was made, which also estab-lished mathematical model for next Hypothesis. Hypothesis 3 was also confi rmed. Based on proposed methodology, record sets of measure-ments from real system and record sets from modeled values were analyzed. Measured val-ues were fi tted to Normal distribution and mod-eled values were fi tted to Log Normal distribution. Reason for this is in the fact that modeled values are dependent from previous record sets, so sudden changes from one weather condition to completely opposite one (from sunny weather to snow for ex-ample) can’t be described completely by model. Never the less model is in the end, for mentioned number of record sets giving good predictive re-sults, with no statistically signifi cant differences between two samples.

CONCLUSION

As described in the paper Daily turnover of auto-mated car wash system depends from observed variable Daily weather condition. Measure of this dependence is calculated through ARIMA time series model. Results from modeling were compared to observed values got from another system. According to these results there is no statistically signifi cant difference between two data sets, which implies that proposed ARIMA method can be used for prediction of daily turn-over of car wash facilities. Similar model can be used for estimation of daily turnover in other industry fi elds. Future analyses will be in the direction of fi nding one or more variables that can be used for pre-diction of daily turnovers in other technical sys-tems and comparing results with one published in this paper.

REFERENCES

Box, G.E.P., Jenkins, G.M., 1987. Time Se-ries Analyses, Forecasting and Control. 2nd ur. San Francisco: Holden-Day.Ho, S.L., 1998. The use of ARIMA models for reliability forecasting and analyses. Computers and industrial engineering, 35 (1-2), 213-216 Jiang, B., Heise, D.R., 2004. The Eye Dia-gram: New Perspective on the Project Life Cycle. Journal of education for Business, pp. 10-16Morris, P. W., 1998. Managing Project inter-faces: Key Points for Project Success. En-glewood Cliffs, New Jersey: Prentice-Hall.Newell, M.W., Grashina, M.N., 2004. The Project Management Question and Answer Book. New York: AMACOM.Tabachnik, B.G., Fidell, L.S., 2007. Using multivariate statistics (5th edn.). Boston: Pearson Education

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* Alfa University, Faculty for Strategic and Operating Management, Staro Sajmište 29, Belgrade, Serbia; [email protected]

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Paper number: 10(2012)4, 239, 201-208

CONTRIBUTION TO THE EVALUATION OF THE COMPLIANCE FOR NEW PRODUCTS WITH ASPECT RELIABILITY AND MAINTENANCE

Dr Radoljub Tomić *Alfa University, Faculty for Strategic and Operating Management , Belgrade, SerbiaDr Predrag PetrovićInstitute Kirilo Savić, Belgrade, SerbiaMarija PetrovićInstitute Kirilo Savić, Belgrade, Serbia

doi:10.5937/jaes10-1688

Development and promotion of the principles of harmonization of new products, it is very important, especially in technical systems and their components, which are applied and exploited in a trans-port vehicle. Quality and reliability of these products have to be high to make the product, and thus the system, fi rst of all was safe, yet competitive in the global market. On the other hand, one of the conditions for the promotion of local products is increasing product competitiveness, while meeting the technical regulations, product quality, reliability and maintenance. When it comes to the proper functioning of the brake system of railway vehicles is a signifi cant benefi t to system maintenance. Bearing in mind that the braking system must fulfi ll a series of conditions in terms of quality of legisla-tion, safety and reliability in all operating and other conditions, this paper describes the dynamics of maintaining a technical system, with special emphasis on the share of costs in relation to the price of the brake system of railway equipment vehicles. It is a new domestic product of IHP “First fi ve” Trstenik-(PPT), with special reference to the component relating to the sealing element, the most sensitive part of the device in the brake system of railway vehicles.Key words: Maintenance, Braking, Availability, Reliable, Railway, Compliance, New product, Costs

INTRODUCTION

When it comes to existing products, but the con-cept of project solutions, the successful opera-tion of the brake system is signifi cantly affected by the maintenance system. The very concept of product design solution, must include all aspects relating to benefi ts for its maintenance. This at-titude almost always have to be aware of the concept of establishing a complex new product confi guration [16,06].Technical system has the design and manufac-ture to be adjusted given environmental condi-tions and system reliability is treated as its inter-nal (inherent) property, which can improve the structural and technological measures. Cancellations technical system represents each event after which the system is unable to perform the required functions. Readiness or availability of a technical system is the probability that the system will successfully take effect and achieve the projected size of the output in minimum re-

quired time period and the circumstances sur-rounding. Reliability theory is the science which deals with the legality of the failures of technical systems and their functional units (system, sub-system, assembly, subassembly, element). From a practical viewpoint term reliability of the easiest and most complete to be considered as a property of the technical system to operate with-out failures in certain conditions and time periods. Reliability analysis involves analyzing continuous technical failure of the system and its functional units, as well as all the factors, which in some way infl uence the occurrence of failures. [01] System maintenance management system is very complex, which applies to the brake system of railway vehicles, and will in this paper only indicate maintenance subsystem elements re-lated to the brakes. The theoretical aspects of this problem are considered in and widely con-sidered in the very knowen books and monogra-phies [16,10,02,15,18].


Dr Radoljub Tomić - Contribution to the evaluation of the compliance for new products with aspect reliability and maintenance

System reliability is the probability that the system by entering in areas tolerances, successfully serve as criteria in the territory of a given, and given the projected weather conditions. It is based on the comparison of the criteria set functions and actual working capacity of the system functions.Brake systems must comply with numerous qual-ity demands, law regulations about safety issues and high reliability in all sorts of work regimes; the logic of maintenance has been described with special review on the share of expenses to the price of brake systems.The sealing system, as the most sensitive as-sembly of the brake devices and system /epecial-ly for this paper, which is produced by Industry of hydraulics and pneumatics »Prva Petoletka«-Trstenik (PPT), will be particularly considered. Analysis of this problem are based on the stan-dards and the system of documentation and pro-duction programme of PPT [18,12,05].

BASIC MAINTENANCE ASPECTS

Main objective technical systems of the railway (MS), refers to the provision of uninterrupted functioning of the system as a whole, provided that its subsystems are functioning properly (PS), and elements (EL). In order to fulfi ll the logical requirements that determine the overall goal, it is necessary to provide an adequate sup-ply of spare parts (RD), and supplies. The level and quality of spare parts and causes the cost to the user invests in procurement, storage and controlled storage reserves [16,06].

Availability of the system is a measure of the state of the system in terms of effi ciency of entry into effect of the realization of output values of the system-level deviations allowed areas set of criteria in a given function, given the time and conditions of use. Size components, availability, caused a number of infl uences, defi nes the dif-ferent parameters of the function linking no can-cellation work and maintainability of the system functions on the basis of: operational, planned and built-in readiness.Operational availability is by defi nition the prob-ability that the system successfully take effect and go in areas tolerances set of criteria function at a given time in the given environmental con-ditions, as determined by the ratio of total time in the system and the total duration (total time in service and cancellation ), as will be shown further on.Planned availability is the time in which it is not required and the effi cient operation of the sys-tem, which is a function of operating conditions and operational levels of the organization and maintenance of the system is dependent on the structural characteristics of the system. Built-availability is determined by structural mea-sures benefi ts and minimum time necessary maintenance procedures. Availability of the system is determined for certain parts of the system as a whole, based on the ratio of total working time (tr), the sum of the total time in service (tu), and the time of failure (to). [08]

Figure 1: Concept of Maintenance Mechanical Systems (MS)

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Current standards ISO 9004 provides event ful-fi llment costs in managing the quality of products and mechanical systems, with most of the tech-nical and production-control demands in terms of effi cient operation of mechanical systems.Proper maintenance is achieved by an effi cient level of reliability and a high level of operational system. Possible concepts maintenance of me-chanical systems are defi ned in Figure 1. [04]Important to maintain the brakes on rail cars are the following:

estimate, measure and record the frequency of the need for spare parts; determination of cases in which it is possi-ble to apply the law of probability, as well as cases where you need permanent removal specifi c groups of causes; minimizing the costs of holding reserves, reserve reconstruction costs and expenses caused by not having a reservation.

Optimization of a new product in terms of techni-cal and economic feasibility of this case is nec-essary for the railway company as a precondi-tion of competitiveness in the market traffi c with other transportation companies. To realize these goals requires research policies, standards, models and tools in the fi eld of Reliability, Avail-ability, Maintainability and Safety (RAMS) and Life Cycle Cost (LCC). Functionality models and tools and their continuous improvement in cer-tain areas allow for effective incorporation into the design stages.Standard EN 50126 defi nes the underlying pro-cesses in the fi eld of railway RAMS is based on the life cycle of the system and the cost (LCC- Life Cycle Cost), and the basic principles of management. When defi ning the parameters of rail systems in the area of RAMS and LCC’s, the standard defi nes the correctness of the factors that may divide into three categories: sources of failure (system requirements), imposed factors during operation (operational requirements), un-desirable, and the real phenomenon of a factor during maintenance (maintenance requirements). All these factors should be identifi ed and assessed qualitatively, to the effect when operating in the life of the system was as effi cient as possible.Defi nition of the system over the RAMS and identify potential risks dangers that need to be analyzed and displayed for example. Frequency or through the matrix to the estimation of a sim-

•

•

•

pler and more effi cient at different levels (unde-sirable, intolerable, unbearable, negligible-(eg undesirable, intolerable, tolerable, negligible). Standard EN 50126 defi nes the system life cycle as a series of stages that cover the overall life-time systems and provide conditions for the plan-ning, management, control and monitoring of all aspects of the system including the RAMS.These stages are: Concept, system defi nition and application Conditions, Risk Analysis, System Requirements, Apportionment of system require-ments, Design and implementation, Manufactur-ing, Installation, System Acceptance, Operation and Maintenance, Performance Monitoring.Annex A gives a principal outline of RAMS speci-fi cations for rolling stock, identifying operating and environmental conditions, reliability targets, system failure modes and mean time between failures, maintenance and repair requirements (e.g. mean time to repair), safety targets, hazardous condi-tions, safety-related functions and failures, safety hazards severity levels, system availability.Annex B gives an outline procedure for a basic RAMS programme and lists some appropriate methods and tools for conducting and manag-ing a RAMS programme. In particular, it refers to some procedures for performing deductive (top-down) and inductive (bottom-up) prelimi-nary, worst case and in-depth RAMS analysis, which are included in separate standards. The most relevant procedures listed are: diagnos-tic testing, (FMEA-Failure Modes and Effect Analysis), (FTA-Fault Tree Analysis), (FMECA–Failure Mode, Effects and Criticality Analysis), reliability block diagram method and Markov techniques.[18]

SPECIAL ASPECTS OF BRAKE MAINTENANCE

Only small parts of theoretical models, for un-derstanding of the problem, will be discussed in this paper. Successful defi nition and realiza-tion of the brake design should prevent prob-lems that may occur during its exploitation. It is clear that constructor should have in mind prod-uct features that will provide easy maintenance for the fi nal user. Therefore, constructors have great responsibility to trace the reliability level (Rd), to defi ne maintenance programme and to establish methodology for analysis of causes for improper functioning of brakes. Afterwards, based on observing concrete brake system, dur-

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ing some period of normal use, constructor has to perform revision of (Rd) and to defi ne control system for the real level of reliability (Rs), Fig. 2, in adequate period of time (three month pe-riod, semiannual, annual), that depends of im-portance of the groups (PS) (subsystems) and

(EL) (elements) for the safety and quality work of brake system. If the value of (RS) is below (Rd), an analysis of causes has to be carried out, and some measures for increasing reliability have to be taken.[16, 05]

Figure 2: Model maintenance elements, method POPS-KNP

Figure 3: Relation of Cu and Crd costs, as a function of allowed reliability level Rd

Maintaining of some elements using method (POPS–KNP - Preventive Maintenance by Condi-tion with the Control Level of Reliability), can be applied in maintenance of (EL) which don’t have essential importance in brake system, but have im-portance in aspect of economy (cost minimization), for fi nding out possibilities of selective application. Such an approach in the literature is generally re-ferred to as POPS-KNP (Preventive Maintenance by Condition with the Control Level of Reliability). Preventive maintenance is a series of actions necessary to prevent it fails, or the maintenance of the criterion function within the permissible deviations in the long term. It is performed on the basis of speculation fails it is studying the weather conditions of the previous period of the same or similar systems Which are based on time intervals prescribed maintenance proce-dures implementation. Depending on the char-acteristics of emergence and implementation of time are adjusted structure and running time of the procedure, Which Enables the adaptive sys-tem for preventive maintenance. This approach is typical of the new systems that do not have enough information from weather conditions or exploitation process. [08]Costs of reserve possession are related, in the fi rst place, on purchase costs of reserve, costs of storage, securing, keeping and maintaining. Costs of reserve renewal are related with the costs of ordering, communication, transport, checking and storage.

Costs of non-possessing reserves are related to interruption of device or brake system function, profi t loss, risk of major damage and costs of emergency delivery, price increase etc.Relation between spare parts costs (Crd) and to-tal costs (Cu), for allowed reliability level (Rd) is presented on Figure 3.Optimization of guaranteed reserve is for each part separately; expenses level particularly de-pends on:

type of brakes,life cycle of devices and systems,quality system of handling and maintaining,presence of manufacturer of (RD=SP) (spare parts) on the market.

The aim is to accomplish appropriate or wanted reliability level with minimal total maintenance expenses. For the reason of limited size of this paper, only usual functioning scheme of special-ized workshops for maintenance of vital brake devices will be presented, Figure 4.

••••

Figure 4: Functioning scheme of specialized work shops: tu-time of use, tv-idle time, to-repairing time,

ts-free time, ID-correct part, ND-incorrect part

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RESERVE OPTIMIZATION

When a system successfully performs the func-tion of set criteria, it is said that the system meets the and is in operation. Otherwise, when the sys-tem does not satisfy, or does not function suc-cessfully set of criteria, indicates that the system is in failure and determined that it violated the interdependence of the elements and the rela-tionships between them and their features, and it is necessary to take measures to return the system to work. [08]In practice, two of the most frequently used sys-tems for the renewal of the reserves are [16, 02]:

system of periodic renewal,system of renewal according to quantity level of reserve.

System of periodical renewal means renewal of re-serve in equal time intervals and the renewed quan-tities are different. Purchased quantity depends of (Rd), i.e. of reserve achieved by it, Figure 5.This system is applied on the reserves spent in large scale and evenly. Time elapsed from order-ing moment (RD) to their delivery in warehouse

••

is marked with Tp=T1+T2+T3. Therefore, time of vulcanization and entry time of sealing material in warehouse should be considered (Table 1). What defi nes a probability distribution law of distribution according to (Equation 1) is called a Poisson distribution, introduced by Simeon Denis Poisson (1781-1840) as a limiting case of bino-mial distribution provided a large number of ex-periments, and the probability (p) of occurrence of event (A) in each experiment small. [14]Poisson distribution law defi nes the boundary layer binomial model, when the volume of sam-ples of part mechanical system tends to infi nity, provided that the product of the sample size and the probability of the observed events remain limited. So Poisson, the model used to describe the probability of rare mutually independent (requirement for binomial law) events such as failures of individual components of mechani-cal systems. Random variable is the realization of a rare event in a given time interval weight. Random variable (r = 0,1,2,3, .......), a Poisson distribution if in equation (1), value (λ) a positive number.

Figure 5: System of periodic renewal of the reserve Figure 6: System of renewal according to the quantity level of wanted reserve

System of renewal according to quantity level of reserve is shown on the Fig.6. Application of both systems ensures control of costs and pro-vides proper safety of brake system. Managing reserves can be observed as few random values, where rule of distribution is properly described by Poisson’s distribution. In this case reliability can be easily calculated according to equation (1).

(1)

Where:P – reliability achieved with “r” complete sets of elements in reserve,r – number of complete sets in reserve,

•

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- frequency of reserve usage, t – time unit.

User should form nomograph based on experi-ence and analysis, which ensures that determi-nation of guaranteed reserves relies on factors as: ordering time and establishing (RD), costs of reserve elements and expenses of non-pos-sessing reserve. Experienced by the example of the same-type elements of the complex technical system with approximately constant intensity of failure, (POPS-KNP -Preventive Maintenance by Condi-tion with the Control Level of Reliability) concep-tion is recommended, also based on Poisson’s distribution, equation (2) [16]:

••



Where:

N – number of (sub)systems observeda – number of the same-type elements in (sub)systemtsr – average time in element exploitationn – number of element failures during observed

(2)

period of exploitationnggr – upper regulation limit

If n nggr, then usage of (POPS-KNP) model is prolonged. Otherwise steps should be taken to in-crease reliability of elements by testing for causes of failure, revising project, change of exploitation conditions or change scale and frequency of con-trol. If reliability could not be increased by these parameters, some other models of maintenance should be considered [16, 05].

SEALING ELEMENTS APPLIED IN BRAKE SYSTEM DEVICES

Sealing elements must be replaced in devices whether it is planned or not planned intervention on device. Constructor has great responsibility to choose prop-er sealing system. Infl uence of high temperature, aggressive medium, light and ozone, are criteria

for acceptability of construction solution. Also, hard-ness, tensile strength, extensibility, plastic deforma-tion due to pressure, brittleness etc. are pointing to elastomers as adequate sealing material. Elastomers used in brake system devices are based on NBR–caoutchouc, hardness from 45 to 80Sh. Determination of the temperature–time boundary is according to DIN 53546 (temperatures 100 0C to 160 0C and time from 4h to 672h). Artifi -cial aging of standard samples takes place in the stream of hot air according to DIN 53508 [18].Selected physical properties observed during the testing are:

breakdown dilatation, plastic deformation due to pressure,tensile strength.

Considering the request of the constructor that exploitation temperature varies from -40 0C to 80 0C, used methods of selection and testing are guarantee for sealing system to work properly.

EXPLOITATION LIFE TIME

Under normal conditions for storage of sealing elements made of elastomers on NBR basis, maximal recommended intervals of time from their production to entry in warehouse, exit from warehouse to mounting, and their exploitation life time, are presented in the table 1.If the time interval to reduce the installation, ser-vice life for so extended and vice versa.

•••

Element type

Maximal period of time from the quarterly period that follows quarterly period in which vulcanization has been accom-plished Exploitation life time,

counted from the mountingBefore entry in

warehouseBefore exit from

warehouse Before mounting

O–ring, Cuff, Wiper membrane

4quartal/3months 10quartal/3months 16quartal/3 months 20quartal/3 months

Table 1: Number of three month period

With more severe exploitation conditions exploitation life time must be shorter then shown in the table 1.

For example, when the parameter values from table 1, are assigned to equation (1) and requested reliability is defi ned at Pd 0.98(Pd 98%) , the results are below mentioned in-dexes for required complete sets of sealing ele-ments, as guaranteed reserves for reliable ex-ploitation of the brake system [08].

For = 0.200 (reserve is used once in tcr =5 year period) P(r=0) = 0.819, P(r=1) = 0.983, P(r=2) = 0.998 For = 0.111 (reserve is used once in tcr=9 year period)P(r=0) = 0.895, P(r=1) = 0.994, P(r=2) = 0.999 For = 0.087 (reserve is used once in tcr =11.5 year period) P(r=0) = 0.917, P(r=1) = 0.996, P(r=2) = 0.999

1)

2)

3)

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For = 0.080 (reserve is used once in tcr =12.5 year period) P(r=0) = 0.923, P(r=1) = 0.997, P(r=2) = 0.999

Relation between P ( , r, t) based on the above mentioned results is shown in the Figure 7.Practically, with the reserve of one sealing el-ements complete set, Pd=98 can be accom-plished; in the case when mounting is performed immediately after the material left the warehouse, achieved reliability would be at level P Pd, i.e. P=0.99 (P=99%).

4)

Figure 7: Relation between P (λ, r, t)

The conclusion is that it is possible to increase system reliability with minimal reserve only in well–equipped market with spare sealing elements, i.e. with high competition level of reliable producers, and other relevant preconditions for the existence of reliable extern reserves. We have been observ-ing that case, so it is obvious that costs of reserve possessing can be minimized.

SOME INTERNATIONAL EXPERIENCE IN RAILWAY VEHICLES BRAKE The braking system is a very important aspect of the security subsystem rolling stock. The pro-cess of applied technology on the brakes and other systems is very important to the rail service. In China, a group of authors conducted a reli-ability analysis method using FMEA and BCEU (Brake Control Execution Unit) and in doing so revealed some weaknesses in the components of the braking system to the application statisti-cal analysis of stochastic processes signifi cantly improve system reliability evaluation. [11]In order to improve the reliability and scheduled maintenance brake system of railway vehicles, using the relevant techniques, from classic to new models introduced. Some methods and if

they are present for several years, though in practice many are not available because of the extra costs and are increasingly using sophisti-cated control algorithms and the use of special sensors to detect errors in braking systems, and can be used on other mechanical systems. [07]As for the braking systems of railway vehicles, the introduction of the so-called interesting. vor-tex electric brakes, which are essentially based on eddy currents. It is a system ECB (Eddu Cur-rent Brake), which is mainly used for High-Speed Railway Train (HSRT). The system is suitable be-cause it is independent of the point and the con-ditions of adhesion, whose coeffi cients may be variable, changing atmospheric conditions. Such a system reduces maintenance time, increases reliability, without additional electricity demands, as supplied from its own regenerative agregata. was donenumerous simulations regarding the design of the system and the control algorithm of the system uses a linear variation depending on the speed (ECB). Experimental studies have shown that achieving a constant torque on the wheel in the entire operating speed range, with a high degree of reliability. [03,09,01]

CONCLUSION

Theory base of maintenance of the technical sys-tems and DIN 53000 series standard was used for analysis of a model for providing guaranteed reserve of sealing elements for the brake sys-tems of the railway vehicles. [6]. For assigned reliability level Pd 0.98 (Pd 98%), with ap-plication of equation (1), the results have been gathered by identifi cation of the guaranteed re-serves of the sealing material and adequate reli-ability. Practically, with the reserve of one sealing elements complete set, in the case when mount-ing is performed immediately after the material left the warehouse, achieved reliability would be at level P 0.99 (P 99%).The conclusion is that it is possible to increase system reliability with minimal reserve only in well–equipped market with spare sealing ele-ments, i.e. with high competition level of reliable producers, and other relevant preconditions for the existence of reliable extern reserves. We have been observing that case, so it is obvious that costs of reserve possessing can be minimized. Considering application of sealing elements, in same category as in table 1, we can conclude that if the period of time before mounting de-creases, exploitation life time increases for the

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same value and opposite. With more severe ex-ploitation conditions exploitation life time must be shorter then shown in the table 1, so in that case intensity of failures would change, i.e. the number of reserves usage in unit of time would increase, which would affect to guaranteed reserve increase and appropriate expenses. Presented results con-fi rm adequacy of theoretical base and accessibil-ity of the shown concept for identifi cation of model and quantifi cation of indications relevant for refer-ring guaranteed reserves of the brake system seal-ing elements for railway vehicles.

AcknowledgmentThis work was created as a result of the proj-ect, the number of TR 35 031, entitled “Develop-ment and application of methods and laboratory equipment for conformity assessment of techni-cal products,” co-fi nanced by the Ministry of Ed-ucation and Science of Serbia, 2012.

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Jovančić M., Tomić R., Pantić R., „Basic aspects of maintaining the vacuum system for heat treat-ing furnaces“, 2 DQM Conference maintenance management’’ ‘99’’, Čačak, 1999., p.174-178.Luo Min, Wu Meng-lin; Wang Xiao-yan: „Study On Reliability Test For Brake Control Execu-tion Unit Of Rail Transit Vehicle“, Railway &Ur-ban Transit Inst., Tongji Univ., Shanghai, China, Conference Publications, p. 1-4, 2010.Marković Z., Petrović P.:”Primena metode statističke kontrole procesa (SPC) sa aspe-kta kvaliteta proizvoda’’, Journal JUSK-a, No. 2, Vol.26, 1998.,p. 143-147.Pacaiova H., Glatz J., Kacvinsky S., „Pozitive and negative aspect in application of mainte-nance management philosophy“, Journal of Ap-plied Engineering Science (JAES), No. 2, 2012, Vol.10, , ISSN 1451-4117, doi:10.5937/jaes 10-2132, UDC 33, p.99-105.Popović P.: „Technical diagnostics and main-tenance technology “- Analysis of reliability and maintainability engineering systems, Uni-versity Singidunum, Excerpts lectures, 2010S.Vukadinović: „Elementi teorije verovatnoće i matematičke statistike“, drugo izdanje,1978., Privredni pregled.Series of standards ISO 9000 and DIN 53 000.Standard EN 50126.Todorović J., Zelenović D.: „Efektivnost sistema u mašinstvu“, Naučna knjiga, Beograd, 1981.Tomić R., Đurđević Ž.: „Key issues in the maintenance of hydraulic systems based on components and devices of the IHP program’’ ,“PPT’’ Hip-2000, Vrnjačka Banja, p.199–207.Tomić R.,Bijelić S.,Tonić M.:“Basic principles on the quality of maintenance of mechanical systems in terms of optimal management of spare parts“. (special topics, review), OMO, XXV, No. 2-3, Belgrade, 1996., p.101-108.Tomić R.,Jovančić M., Radovanović M., „Contribu-tion to maintenance of brakes of the railway vehicle based on products made in IHP“, “Prva petoletka”, RaDMI 2002.,Vrnjačka Banja, p.1443-1452.Tomić R.:„Appendix objectifi cation of domes-tic developments in relation to the quality system ISO 9000“, 5 DQM Conference “De-pendability and Quality Management”, 2002., Belgrade, p.267–273.

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Paper number: 10(2012)4, 240, 209-220 doi:10.5937/jaes10-2526

FIBRILLAR MATERIAL AS A COBINDER IN COATING COLORS FORMULATIONS

Dimić-Mišić Katarina*Aalto University, Helsinki, FinlandDr Paltakari JouniAalto University, Helsinki, Finland

The micro-fi brillated cellulose (MFC) is a potential material which will at least partly substitute the syn-thetic co- binders, such as carboxymethyl cellulose (CMC), in paper coating color formulations. Co-bind-ers play an important role in controlling both the fl ow properties and the dewatering rate of coating colors during the application process as well as during the subsequent fi lm immobilization [25, 19, 02]. In this study, MFC fi bers are used to substitute standard, synthetic co-binder material, CMC, affecting both dewatering and rheological properties of coating colors. This study was partly attempting to establish standard measurement procedures that can give overall picture of complex rheological behavior of MFC coating colors. Elastic effects of coating color in low shear rate infl uence both the fl ow and blade load [23]. By infl uencing leveling, elasticity, substitution of CMC with MFC infl uences coating color application and immobilization process, as well as the uniformity and optical properties of the coating fi lm [06] . It has been demonstrated that coating colors which contained MFC fi bers as a co-binder had pronounced shear-thinning characteristics which is a desirable property for paper coatings. However, a complete substitution of CMC with MFC fi bers in paper coatings induced low retention properties, longer shear-recovery time and fast immobilization of coating colors, which can have a negative infl uence on leveling and fi nal coating layer uniformity.Coating suspension rheology of the coating infl uences the coating per-formance at high speeds. The quality of the coated and printed papers is also affected by the rheology of the suspension [06,26]. Co-binders play an important role in controlling both the fl ow properties and the dewatering rate of coating colors during the application process as well as during the subsequent fi lm immobilization [23,06]. The micro fi brillated cellulose (MFC) is a potential material which will at least partly substitute the synthetic co- binders, such as carboxymethyl cellulose (CMC), in paper coating color formulations [08,22]. It was expected that the introduction of the MFC material into the coating formulation affects the coating color rheology since the MFC fi bers are highly fl occulated and have reactive groups on their surface [08].Micro-fi brillated cellulose material (MFC), can beproduced through several pre-treat-ment and refi ning routes, each giving products with very differentmorphological and chemical properties [18].It is expected that refi ning and treatment route of MFC infl uence traditional coating layer properties as those designed for special purposes [18]. The observation that MFC could be used in paper coating formulations, as a co-binder, since it is biodegradable and has good shear thinning properties, raises a question about the processability of MFC coatings in a high speed coating process(above 1000m/min) [12]. This work focuses on determining general rheological and dewatering behavior of coating colors that contain MFC fi bers used as co-binders. A thickener is added to prevent an excessive loss of water from coating color into the base paper and to adjust the rheological properties of the color, a thickener is usually added [03,28]. The physical and chemical properties of the thickeners differ, and they can be roughly divided into synthetic and natural polymers [01]. Water retention and immobilization are the key properties for successful paper coating formulations [21,05]. The task of research is to evaluate how the replacement of CMC co-binder with MFC material infl uences the viscoelastic and dewatering properties of the coating color [07]. Correlation of the data matrix obtained from dewatering, low-shear viscoelastic and immobilization time measurements show that there is a pattern providing general un-derstanding of the MFC fi ber performance in coating suspensions. It is important to understand what the typical behavioral pattern of all MFC coatings would be once they are in the coating process. A key characteristic of the response of a viscoelastic material, as are coating colors, to its deformation during dynamic process, is its ability to recover after cessation of the force which causes deformation [13,04].

209* Aalto University, PO Box 110000 Aalto, Finland; [email protected] Paper presented at SIE 2012


Pigment reactivity with binders and co binders has an important effect in viscoelastic behavior of coating color.It has been proved through many previous research papers that more elastic structures of clay coat-ings yield larger elastic moduli than the carbonate coatings [05,14]. Key words: Property, Fiber, Coloration, Coatings, CMC

OBJECTIVES

As micro-fi brillated materials are known to be highly fl occulated gel emulsions, it was neces-sary to examine what kind of reactivity they have with coating pigments and other chemicals in coating formulations. The possible differences in this reactivity with respect to the fi ber fi neness, and pigments types were also to be determined. In order to get a deeper understanding of MFC fi bers used as co-binders and such coating col-ors rheology, this study aim to give in-depth in-vestigation of the rheological behavior of such coatings in shear rates of industrial interest. Ref-erence, standardly used coating formulations having co-binder CMC, were rheologically and in dewatering terms compared with the MFC-con-taining coatings. Two different pigments were used, and coating colors made from carbonate, kaolin, and 50% mixture of kaolin and carbonate.Reactivity of differently charged kaolin(anionic–cationic)) and calcium carbonate (all sides cat-ionic) with MFC fi bers is expected to increase viscoelasticity though interaction with highly re-active hydroxyl groups of MFC fi bers and charg-es on particles. Bridging mechanismis expected to link MFC fi bers and pigments together. After data analysiscorrelationfactorswere calculated between the coating color recipe properties (i.e. solid content, relative amount of nano-fi bers per amount of pigment) and coating performance responses. Static dewatering, viscoelastic and low-shear oscillation rheological measurements were accompanied with an immobilization cell, which uses dynamic dewatering data to mea-sure fi nal immobilization time of the coating layer [09,11]. These measuring techniques make con-nection between the microscopic state of coating suspensions and their macroscopic behavior in process fl ows.

EXPERIMENTAL MATERIALS

MFC fi bers specifi cationMicro fi brillated cellulose was obtained from UPM –Kymmene Corporation. It was prepared from never dried birch pulp by different pretreatment and refi ning methods. Masuko was prepared

, 240

as pulp was passed once through a Voith refi n-er (Voith AG, Germany) and then seven times through Fluidizer M7115 (microfl uidics corp.)The fi rst pass was through a chamber with diame-ter of 500 μm and 200 μm and the rest through chambers with diameters of 500 and 100 μm at a pressure 1,850 bar.The fi nal solid content of suspension was 3 wt%, and the fi bers contained about 25 wt % xylene. Tempo mediated cellulose was obtained as well from UPM –KymmeneCor-poration. It was prepared using tempo-mediated oxidation of native cellulose followed by disinte-gration of the oxidized cellulose fi bers in water using a Warning blender.Transmission electron microscope (TEM)observation of the dispersions showed that mostly individualized cellulose fi brils 3-5 nm in width were obtained, Table 1. Swelling and dispersion behavior of the cellulose in water were studied in detail in terms of carboxylate con-tent by spectroscopic microscopic and viscosity analysis, data property of UPM –Kymmene.

Pigments specifi cationTwo types of pigments were used for both ref-erence (CMC-binder) and MFC coating colors, Tab.1.Coating colors with different pigment pack-ing abilities (Capim RO kaolin and two different carbonate pigments HC-60 and HC-90) were compared in relation to different co-binders.

Tt

Tempo- mediated with 2% pretreatment chemicals

Tf

Tempo-mediated with 4% pretreatment chemical

Mf

Masuko treated, 15% carboxymethylated pretreatment l

Te

Tempo-mediated ethanol- dried with pretreatment chemical

Td Tempo-mediated, dried

Cmd

Masuko treaded, carboxymethylated pretreatment and drying prior refi ning

Tfs

Tempo-mediated, carboxymethilated and dried

Cme

Masuko treaded, carboxymethilated prior to refi ning

Table 1: Pigments specifi cation

210

Dimić-Mišić Katarina - Fibrillar material as a cobinder in coating colors formulations


Pigments were obtained as pigment slurries in cases, carbonate HC-60 , of 35% consistency and HC-90 37% consistency (HC-60 /HC-90 with 60% /90% less 2μm particle size). Kaolin Capim RO was obtained as slurry, 35% consistency.

Water retention value WRVThe wet Tempo-mediated cellulose (Td) and MFC (Mf) were centrifuged at 4500 gravity for 20 min in mixture with reference birch pulp , with different relative consistency, Figure.1

Figure 1: Apparent WRV for MFc fi bers

Relative water retention value calculated by in-terpolation method is presented in Table 2. It is obvious that water retention value for tempo fi -bers is much higher as generally this fi bers are having more reactive groups on fi ber surface and have more swollen cell wall. It is more diffi cult for water to fl ow through such highly swollen fi bers network and go through easily sealed opening of fi lter cake.Rheological measurements Viscoelastic proper-ties of the suspensions were measured with a stress controlled MCR 300 PaarPhysicaRheom-eter rotational rheometer, plate-plate geometry with anPeltier element temperature control, tem-perature during measurements was 23ºC. The gap between plates was 1mm.

consistency of MFC fi bers in fi lter cakesuspention w/w %

WRV, g water/g dry fi ber

Masuko 3 2 9,68Tempo UPM 2 24,024

Table 2: Relative water retention value calculated by interpolation method

Apparent yield stress were determined using amplitude sweep of 1Hz frequency and strain of

0,01-100%). Critical strain of MFC fi bers suspen-sions was determined for consistency of fi bers (1, 1.5, 2 and 2.3%) as a point of the breakage of structure in fi ber suspension, and can be calcu-lated as τ =G0c, were G0 is storage modulus for liner viscoelastic region, Figure 2.Masuko fi bers have higher yield stress as they have less reactive fi ber surfaces, less swollen fi ber walls and there is more friction between fi bers during shearing, which shows as higher storage moduli.

Figure 2: Apparent yield stress of MFC fi bers

211, 240



Ref

eren

ce C

oatin

g co

lor

MFC

Coa

ting

Col

or

Trea

tmen

t/Uni

t10

0%

Kao

lin10

0%

Kao

lin10

0%

Kao

lin50

% C

arb

0% K

aolin

50%

Car

b0%

Kao

lin10

0%

Car

bona

te10

0%

Car

bona

te10

0%

Car

bona

teT f

T tT fs

Cm

eT e

Mf

Cm

dT d

Dry

so

lids

%50

5560

5560

5055

6055

5553

5454

4645

47

Cov

erca

rb

75pp

h

Mira

glos

s-90

00

050

5010

010

010

050

5050

5050

5050

50

Late

x (D

ow

966)

100

100

100

5050

00

050

5050

5050

5050

50

CM

C

(Fin

nfi x

10)

1010

1010

1010

1010

8,5

8,5

8,5

68,

58,

58,

58,

5

Sta

rch

Coa

ting

star

ch0

00

00

00

00

00

00

00

0

T fTe

mpo

4%

C

onsi

sten

cy0

00

00

00

01

00

00

00

0

T tTe

mpo

2%

C

onsi

sten

cy0

00

00

00

00

10

00

00

0

T fsC

arbo

xym

ethy

late

d an

d D

ried

00

00

00

00

00

10

00

00

Cm

eTe

mpo

Eth

anol

pr

etre

ated

00

00

00

00

00

01

00

00

T eM

FC (M

asuk

o) 5

pa

sses

00

00

00

00

00

00

10

00

Mf

Car

boxy

met

hyla

ted

and

Drie

d0

00

00

00

00

00

00

10

0

Cm

dD

ry T

empo

00

00

00

00

00

00

00

10

T d0

00

00

00

00

00

00

00

1

Tabl

e 2:

Stru

ctur

e of

coa

ting

colo

rs

212 , 240



COATING COLORS

Reference coating colors were made in thjree different solid content (50,55 and 60%) and pig-ment types (kaolin, carbonate, blend of 50%ka-olin and 50 % carbonate), Table.2. Carboxymeth-yl cellulose (CMC) was chosen as water soluble thickener in the reference coating colors, making the suspensions susceptible to depletion fl occu-lation. In addition, the pH of each coating mate-rial mixture was adjusted to approximately 9.5 using NaOH. For MFC coating color preparation for thickener was used Finnfi x-10, purifi ed low viscous carboxymethyl cellulose, with degree of substitution of 0.60-0.95, and FF-10 is usually used in coating colors as thickener. MFC coat-ings were made with blend of 50% kaolin and 50% carbonate pigments.Solid content of MFC coatings was adjusted, so that their Brookfi led100 viscosity stayed within coating color viscosity window, recommended for coating colors, 3000 Pas. Coating colors were prepared following the next order; pig-ments, OBA, NFC /CMC, with half an hour mix-ing and then Latex.Testing of the coating colors was fi rst done ac-cording to quick test procedure, dry solid content oven drying, Brookfi eld viscosity 50 and 100 RPM and ÅA-GWR(ÅboAkademi Gravimetric Water Retention Device). Additional dynamical low-shear measurements were performed on a MCR 300 PaarPhysicaRheometer, plate-plate geometry, gap 1mm. The immobilization cell ac-companied on rheometer IMC enables the re-cording of the time to immobilization, i.e. the time for complete build-up of fi lter cake .The immobili-zation cell enables monitoring of the dewatering process of applied layers and controlled shear forces through increase in elastic moduli G` and G`` of suspension [14, 09].

RESULTS

Reference coating colors-carboxymethilated cellulose as co-binderAs can be seen from Figure 3, the gravimetric de-watering of reference coating colors increases in the order: kaolin<CaCO3 , and at the same time decreases with increase in solid content. This is due to the shape and electric charge of carbonate and kaolin pigments [06, 26, 14], as water passes easily through carbonate pigments but platy ka-olin pigments make this passage more diffi cult.

It is obvious that kaolin pigment coating color has a more pronounced shear thinning behavior as kaolin with CMC forms three dimensional struc-ture in a coating dispersion (“house of cards” structure) which brakes when shear is applied, only to be again reconstructed after shear ceas-es [24].Decrease in apparent viscosity measured with increase in spindle rotation rate, from 50 to 100 RPM is shown in Figure 2.

Figure 3: Gravimetric dewatering of reference coating colors

Figure 4: Brookfi eld viscosity of the reference coating colors

213, 240



When measured apparent viscosity on Brook-fi eld viscometer, it is obvious that kaolin pigment coating color has a more pronounced shear thin-ning behavior as kaolin,through molecular bridg-ing with long CMC chains forms three dimen-sional structure in a coating dispersion (“house of cards” structure) which brakes when shear is applied, only to be again reconstructed after shear ceases [11, 24]. Decrease in apparent vis-cosity measured with increase in spindle rotation rate, from 50 to 100 RPM is shown in Figure 4.Within the frequency sweep test( 0,01-100 Hz)

Figure 5.a

within the linear viscoelastic region ( 1% strain), elastic modulus of clays is higher than that for carbonate coatings, Figure 5.Particle fl ocks induced by hydrodynamic and surface interactions group together into a macro scale three-dimensional network which compris-es the elastic structure of the coating dispersions [20]. Same fi gure shows that elasticity expressed as storage modulus G`, is higher for kaolin based than carbonate-based coating colors, for all three consistencies, and elasticity is increasing with solid content with more dense packaging of material.

Figure 5.b

214 , 240



MFC coating colors-micro fi brillated cellulose material (masuko and Tempo based) as a co-binderAs a reference coating for this evaluations was used blend of 50%kaolin 50% carbonate coat-ing color, with 55% consistency, and dewatering band rheological behavior of this particular refer-ence coating color was compared with behavior of MFC coatings.Since MFC fi bers have very high water retention as presented at Figure 2, the gravimetric dewa-tering of MFC based coating colors show higher retention values than for reference coatings, Fig-ure 6. Pretreatment and production route of MFC fi bers has as a product fi bers with different swell-ing of fi ber wall and surface reactivity and thus some fi bers as Mf and Td induced as co-binders drastically increase water retention, while some decrease, as with sample Te.

Figure 6. ÅA-GWR Water retention values for MFC coating colors

For some MFC coatings (Tf, Tt, Cme) apparent (Brookfi eld viscosity at 50 and 100 RPM) is much higher for MFC coatings than for reference one , as a product of reactivity between pigment particles and highly reactive MFC fi bers, while for others (Mf, Td, Tfcs viscosity is lower, Figure 5.a and 5.b. It is important that the coating color immobilizes quickly after metering, and therefore too long immobilization times are not desirable [17, 16]. High solid content normally means a faster immobilization of the coating layer, which reduces the structural changes of the paper ma-

trix under the coating layer, but in the case of MFC faster immobilization is achieved with lower solids than in conventional coatings.

Figure 7: Brookfi eld viscosities for MFC coating colors

Flow behavior of coatings prior to metering and af-ter the exit from the blade nip depend, to a certain extent, on the viscoelastic parameters, as visco-elasticity infl uences consolidation on the wet coat-ings [11, 27]. Wet paper coatings demonstrate a fading memory of recent shearing. The magnitude and rate of recovery after application are defi ned by the formulation and process speed [13].Rheological measurements done in frequency sweep mode ( 0,01-100 Hz) at temperature 23º C on MCR 300 rheometer show complex viscosity de-velopment for coating colors when samples go from low to high shear, in linear viscoelastic region. The double logarithmic plot in Figure 8 depicts the power law shear thinning behavior of the complex viscosity of MFC coatings, typical for a gel like structures.For some MFC coatings (Tf, Tt, Cme) maximal complex viscosity is much higher than for refer-ence coating, while for others(Mf, Td, Tfcs) maxi-mal complex viscosity is lower, Figure 8. Ratio of maximum and minimum complex viscosity within a defi ned frequency sweep was calculated and is presented in Figure 9. Shear thinning behavior, desirable in coating process is obtained when MFC fi bers are replacing traditional CMC co-binder.

215, 240



Figure 8. Complex viscosity curves for NFC and reference (50%. kaolin and 50% carbonate) coating colors; frequency sweep

Figure 9: Shear thinning, ratio of Max/Min complex viscosity for MFC coating colors within a frequency sweep of 0.1- 100 s-1

During frequency sweep measurements MFC coatings have much higher increase on elastic moduli G` at the beginning of measurement, at even very low frequencies, which is because

of their high elasticity, which causes immediate response of coating colors to deformation, as Weissenberg effect as shown in Figure10.

216 , 240



Figure 10: Amplitude sweep ,storage and loss moduli- two different MFC coatings(Tfcs and Cme), compared with reference coating ( 50% carbonate 50% kaolin, solid content 55%)

It is important that the coating color immobilizes quickly after metering, and therefore too long im-mobilization times are not desirable [13]. Inter-

estingly, MFC coating colors immobilize faster although they have a lower solid content than the reference CMC coatings, Figure 11.

Figure 11: Immobilization time for MFC coating colors

A correlation matrix was made comprising data from static, ÅAGWR and dynamical low-shear dewatering with IMC results. Data obtained from these two measurements show a strong cor-

relation, proving the hypothesis that those two measurements correlate [14, 09] as presented in Figure 12.

217, 240



Figure 12: Correlation diagram ÅAGWR vs. Immo time, MFC coatings

Figure 13: First and Second Immobilization time vs. fi nal Storage modulus; MFC coatings

218 , 240



High solid content normally means a faster immo-bilization of the coating layer [13], which reduces the structural changes of the paper matrix under the coating layer, but in the case of MFC faster immobilization is achieved with lower solids than in conventional coatings. Even though faster im-mobilization is desirable in drying process, high elasticity of MFC coatings fi lter cake can cause problems at leveling and metering nip. In several

types of coating units, a more extended dwell time between application and metering leads to the formation of an immobilized coating color pri-or to leveling. It is evident from Figure 13 and 14 that for some types of MFC fi bers, like for those carboxymethylated prior to refi ning (Cmd, Cme), both immobilization time and storage modulus of immobilized layer cake are in better range, more similar to those of reference coating colors.

Figure 14: Immobilization diagrams; MFC coatings vs. 50% carbonate 50% kaolin reference coating color

CONCLUSION

At low frequencies, elasticity of carbonate coat-ings increases with replacement of CMC with MFC fi bers, while shear thinning is higher for MFC coatings which have kaolin inside. Low-shear frequency sweep oscillation measure-ments showed that MFC coating colors have astronger” memory effect” after shear from standard CMC coatings, as having higher elas-tic modulus. Results show that fi ber fi nesse, hence pre-treatment and refi ning route of MFC fi bers determines consolidation, low shear rhe-ology and immobilization time of coating color, as well as there is different reactivity of fi bers in respect to pigment types. MFC samples had different amount of fi brous material depending on the type of pretreatments, with less fi brous material indicating a better refi ning result, higher shear thinning effect, better dewatering /higher

immobilization time with lower fi lter cake elastic-ity. Generally all MFC coatings had lower water retention and much faster immobilization, than reference CMC coating colors.

AcknowledgementThis data is from Author`s Licentiate thesis “ In-fl uence of fi brillar cellulose on pigment coating formulation`s rheology”, supervising professor PaltakariJouni,published at Aalto University, Hel-sinki, 2012.

REFERENCES

Adams P. D andKuszewskiJ., Crystallogra-phy and NMR system: a new software suite for macromolecular structure determination, ActaCrystallogr, 1988, p. 18Åkerholm J., Berg C. and Kirstilä V., An ex-perimental evaluation of the governing mois-

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ture movement phenomena in the paper coating process, Part II, ÅboAkademi Uni-versity, FinlandBackfolkK., Methods for controlling surface contact area of a paper or board structure, Doc-toral Thesis, ÅBO Academy, Finland, 2002BarnessH. A., Hutton J. F., WaltersK., An In-troduction to Rheology, Coating Conference proceedings, Amsterdam, 1998BourneP. andWeissigH., Structural bioinfor-matics A John Wiley & Sons Publication, Fig-ures. 15, 18, 34, 2003BruunS-E., Pigment Coating and Surface siz-ing of Paper, Totally updated version, Paltakari J. ed., Ch. 14, PaperijaPuuOy, Finland, 2009BruunS-E., Pigment Coating and Surface siz-ing of Paper, Totally updated version, Paltakari J. ed., Ch. 6, PaperijaPuuOy, Finland, 2009DreiffenbergI., Lohmander S., Effects of the air content on the rheological properties of coating colors, Advanced Coating Funda-mentals Symposium, 1999Eklund D, Grankvist T., Salahetdin R., Thein-fl uence of viscosity and water retention on blade forces, PTS Coating Symposium, 21stpaper, Munich, GermanyEngströmD. and Ridahl, On the transition from linear to non-linear viscoelastic behavior of CMC /Latex coating colors, Nordic Pulp Paper, 1991EngströmD. and Ridahl, The effect of some polymer dispersions on the rheological prop-erties of coating colors, Tappi press, 1989GrovesR., Ruggles C., Paper Coating Struc-ture – The Role of Latex, PITACoating Con-ference Proceedings, 1993Jäder J. and JärnströmL., Calculation of fi lter cake thickness under conditions of dewatering under shear, Annual transactions of the Nordic Rheological Society, vol. 9, p. 113-117, 2001Jäder J., Engström G, and Järnström L., Ex-tensional Viscosity of paper coating Suspen-sions studies by converging Channel-fl ow and fi lament stretching, Annual transactions of the Nordic Rheology Society, vol. 12, 2004

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JäderJ., Consolidation and Rheology at High Solid Content, Dissertation; Karlstad Univer-sity Studies, 2004Kugge C., Consolidation and structure of pa-per coating and fi ber systems, Doctoral dis-sertation, Stockholm, 2003Kugge C., DaicicJ. and Furo, Compressional rheology of model paper coatings, funda-mental research paper symposium, Pira in-ternational, Oxford, 2001Leino M., VeikkolaT., A New Board Coating Meth-od, TappiCoating Conference Proceedings, 1998Lepoutre P., Coating structure and surface coverage, Symposium on Surface Cover-age, Helsinki, Finland, 1999Lepoutre P., Substrate Absorbency and Coat-ing StructureTappi Journal, 61[5], 1978Li J., Tanguy P., Carreau J., Moan M., Effect of thickener structure on paper-coating color properties, Colloid Polymer Sci. 2001Paltakari J., Puu-21. 3060 Pigment Coating Technology, Aalto University, FinlandPigment Coating and Surface sizing of Pa-per, Totally updated version, Paltakari J. ed., Ch. 5, PaperijaPuuOy, Finland, 2009Triantafi llopoulos N., Paper coating Visco-elasticity, Tappi press, 1996Watanabe J. andLepoutre P., A Mechanism for the Consolidation of the Structure of Clay-latex Coatings Appl. Polym. Sci., 1982Willenbacher N., Wagner H., High Shear Rhe-ology of Paper Coating colors-More than just viscosity , Chem. Eng. Technol. 20, 1997Young T, Fu E., Associative behavior of cel-lulose thickeners and its implementation on coating structure and rheology, Coating Con-ference Proceedings Tappi pressZeyringer E. and EichingerR., A new method to determine the water retention of coating colours and its impact on mottling of coated paperTappi Advanced Coating Symposium, October, 2010

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16)

17)

18)

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20)

21)

22)

23)

24)

25)

26)

27)

28)


220 , 240


Paper number: 10(2012)4, 241, 221-225

ALLOCATIVE EFFICIENCY AND QM FACTORS COVARIATE IN SERBIAN INDUSTRY

doi:10.5937/jaes10-2517

* Faculty of Mechanical Engineering, Kraljice Marije 16, 11000 Belgrade; [email protected] Paper presented at the SIE 2012

Dr Vesna Spasojević-Brkić*University of Belgrade, Faculty of Mecahical Engineering, Belgrade, SerbiaDr Slobodan PokrajacUniversity of Belgrade, Faculty of Mecahical Engineering, Belgrade, SerbiaDr Nikola DondurUniversity of Belgrade, Faculty of Mecahical Engineering, Belgrade, SerbiaMSc Sonja JosipovićUniversity of Belgrade, Faculty of Mecahical Engineering, Belgrade, Serbia

Trends of allocative effi ciency and covariate of fi rm size and effi ciency of quality management(QM) factors in the Serbian industry were tested on the unbalanced panel sample of 48 industrial fi rms from 12 industrial sectors in the period 2004-2009. The obtained results show that 10 of 12 sectors have a positive covariate of participation in the output market and multi-factor productivity. Covari-ates of fi rm size and effi ciency of all QM factors record the same direction in the chemicals sector (positive) and motor vehicles (negative), which means that in those two sectors larger companies had above-average and/or below-average effi cient TQM. The same (positive) trend of allocative ef-fi ciency and covariates of all QM factors was recorded in manufacture of chemical industry.Key words: Allocation, Allocative effi ciency, Covariation, Industry, QM

INTRODUCTION

The more recent literature brings a limited num-ber of studies which analyse the relationship between fi rm performances and quality man-agement. [01], [05], [12]. Results are mixed and often do not support the hypothesis on positive correlation between productivity and effi ciency of some critical QM factors [13]. Reallocation of resources signifi cantly infl uences the level of aggregate productivity of industry from less pro-ductive to more productive fi rms. In this type of studies, aggregate industry pro-ductivity is determined as weighted average of fi rm level total (multi-factor) productivity with market share in industry output as a weight. This method of defi ning productivity allows decompo-sition of industry productivity on average produc-tivity and covariate part as sum of cross product of fi rm size and fi rm productivity. Such decom-position gives insight into correlation of fi rm size (market share) and fi rm level productivity. If the sum of cross product positive industry productiv-ity is improved, the sector resources are allocat-ed towards more productive fi rms and industry is allocative effi cient.

Concurrently, deregulation and market liberali-sation may have positive impact on QM practice as companies are trying, in the conditions of in-creased competition, to have more effective QM. Therefore, thanks to reallocation of resources, more productive fi rms can be expected to grow bigger and at the same time have more effective QM. Average QM effi ciency may be, similarly to productivity, decomposed to average effi ciency of critical QM factors and a sum of cross product of fi rm size and fi rm QM effectiveness (QM fac-tors covariate). If a covariate is positive, QM ef-fectiveness of the industry is improved. The aim of this research is to examine the trend of al-locative effi ciency and QM factors covariate.

METHODOLOGYAllocative effi ciencyMarket reallocation of resources represents one of key channels for identifying the change in pro-ductivity at the level of an industry. [02],[07],[11]. Aggregate multi-factor productivity in industry is average weighted productivity of fi rms, whereby a weight is share of a fi rm in the output market:

(1)

221


where represents aggregate productivity in industry (j) in time (t), is market share of plant (i), in industry (j) in time (t), fi rm level productivity and N represents a number of fi rms in the sector (j).Industry productivity may vary through changes in allocation of productivity and market share re-allocation between incumbent (surviving) fi rms,

(2)

or

(3)

but also through contributions entering and exit-ing fi rms [10]. Contribution of resource realloca-tion to the change in aggregate productivity can be captured through decomposition of productiv-ity of industry to the product of the deviation of market share of plant from the average market share and fi rm productivity from average un-weighted productivity at the level of the industry:

where represents average unweighted productivity, average unweighted sales par-ticipation, difference between participa-tion in company sales and average sales participation and difference between company productivity and average pro-ductivity at the level of the industry .Sum of cross product represents productivity covariate (covprod) and contains contribution of resource reallocation to the change in aggregate productivity.If it is positive, industry has a positive allocative effi ciency where resources in the industry follow more productive incumbent (surviving) fi rms.

QM factors covariateThe covariate of effi ciency of QM and fi rm size comes down to a question whether fi rms with above-average scale of dimensions of the spe-cifi c critical QM factor have bigger output market participation. QM effi ciency is measured as an average value of the dimension scale for specifi c critical QM factor. Effi ciency of the specifi c QM factor at the industry level is a weighted average of fi rm-level effi ciency (scale of QM factor at fi rm level) with market share of industry as weights:

(4)

where represents a weighted scale of the factor (n), sector (j) in time (t), represents a market share of the fi rm (i), in the market of the sector (j) and time (t), scale of the factor (n) of the fi rm (i) sector (j) in time (t) and N repre-sents a number of fi rms in the sector (j).

Weighted effi ciency of the specifi c QM factor in the sector (j) can be decomposed to average un-weighted effi ciency of factor (n) and the sum of cross product deviation of fi rm size (i) and effi -ciency (scale) of the factor (n) in a fi rm (i):

(5)

where represents average unweighted effi -ciency of factor (n), sector (j) in time (t), whereas represents average unweighted market share as a measure of average size of a company in the sector (j) in time (t).If covariate of QM factor (QM cov) and fi rm size is positive, effi ciency of QM factor at the industry level increases. Companies with higher market share (larger companies) had in the observed time a more effi cient QM factor.

Analysis procedure and results The sample is a stratifi ed random sample drawn from the population of Serbian industrial fi rms certifi ed according to ISO 9000. The information referring to the determination of MFP and effi -ciency of QM factor cover the period 2004-2009. The information on company productivity comes from the offi cial fi nancial reports and informa-tion about QM practice comes from a question-naire. Quality management elements or critical QM factors, as the components that will lead to the successful application of the QM concept, were considered for the fi rst time by [03] and the number of available works reported to date is not negligible. Following an analysis of frequency in-cidence in available literature the QM critical fac-tors shown in Table 1. can be segregated.

222 , 241

Dr Vesna Spasojević-Brkić - Allocative effi ciency and QM factors covariate in Serbian industry


CRITICAL QM FAC-TORS

DIMENSIONS FOR CRITICAL QM FACTORS

Leadership and man-agement support for quality program (LID)

L2: Care of Department manager for qualityL3: Efforts of company management to improve qualityL4: Goal setting and quality policyL5: Establishing regulation for quality

Training and involve-ment of employees

(OB)

OB2: Employees training as priority of the companyOB3: Existence of fi nancial resources for employees trainingOB4: Employees training to apply methods and techniques (tools) for quality improvement

Systemic approach and documentary

evidence for quality system (SIST)

SIST1: Availability of data on quality to each employeeSIST2: Analysis of collected data on quality in order to improve itSIST3: Existence of Department of qualitySIST4: Possession of documents for quality system

Process approach (PROC)

PROC1: Differentiation and description of each process in the companyPROC2: Continuous monitoring of key processes in the company and their improvementPROC3: Determination of quality measure for each process in the companyPROC4: Participation of machine operator in maintenance

Benefi cial interaction with suppliers (ISP)

ISP1: Relying upon a small number of reliable suppliersISP2: Selection of certifi ed suppliersISP3: Participation of supplier in program developmentISP4: Participation in employees training in quality fi eld at supplier’s fi rm

Permanent quality improvement (PK)

PK1: Permanent tendency to eliminate internal process leading to waste of time or moneyPK3: Application of advanced IT to better analyze data and determining priorities to improve qualityPK4: Revision of documents for quality system if necessaryPK5: Application of methods and techniques to improve quality

Product design according to user

demands (PP)

PP1: Coordination of employees from different organizational units in product development processPP2: New product quality as priority in its design and manufacturePP3: Analysis of possibility for manufacture and cooperation in product development

Table 1: The dimensions of critical QM factors after factor and reliability analysis [13]

The research instrument proposed initially con-tains 7 factors with 31 dimensions (Table 1.), which is substantially the lowest of all offered to date. Using recommendations by [13] to recode 25 – 50% of the questions (posed in reverse or-der relative to other questions), 45.88% of the questions were recorded. All questions had a fi ve-level Likert scale. The majority of questions in the research instrument were taken from or designed using previous research (which is of critical importance in research of this kind as stated in [12, 14]. The information from fi nancial statements is used for the determination of MFP at the indus-

try level through neoclassical production func-tion, whereby LP algorithm is applied in order to avoid simultaneity. [04]. The data due to QM practice were exposed to factorial analysis to en-sure that they constituted reliable indicators of QM constructs. [13]. Based on the determined MFP and selected reliable QM factors by apply-ing algorithms (2),(3),(4) and (5), allocative effi -ciency and QM covariate of all 12 industrial sec-tors were determined.

223, 241



The results show that 10 of 12 sectors have positive covariate of output market participation and multi-factor productivity and in those sectors market allocates most resources towards com-panies with factor productivity above average productivity of the sector. Allocative effi ciency in these sectors is increasing in the observed pe-riod. Covariates of fi rm size and effi ciency of all QM factors show the same trend in the sector of chemical industry (positive) and motor vehicles (negative), which means that in these two sec-tors larger companies had QM effi ciency above average. In other sectors, the trends of covariate of fi rm size and scale of QM factor are different. In food-manufacturing industry, an increase of quality with negative covariate is visible, which means that larger companies had effi ciency of quality increase below sector average. Training of employees has positive covariate in leather sector, while it is negative in non-metal industry. Metal sector shows a positive covariate of prod-uct design, while the sector of machine manu-

Figure 1: Allocative effi ciency and QM factors covariate

facturing has positive covariate of training and negative covariate of quality improvement. In the production of TV sets, values of covariate are very low. In the electrical sector, there is a posi-tive covariate of suppliers, whereas in the con-struction sector a positive covariate of systemic approach should be noted. In the transport sec-tor, there is a very negative covariate of leadership. If a covariate of fi rm size and effi ciency of all ana-lysed QM factors and a covariate of fi rm size and MFP are observed only in the sector of manu-facture of chemicals and chemical products, the same trends are recorded. It is only in that sector that larger fi rms record a higher factor productiv-ity and more effi cient TQM as well.

CONCLUSIONS

The chemical industry’s predominant use of batch manufacturing processes is in sharp con-trast to the use of assembly line production in automotive or computer industries, so it can be expected that these differences infl uence the re-

224 , 241



lationship between QM implementation [6]. Ac-cording to the same authors the strongest con-tributor to variation in total effects of QM across groups was industry type, followed by size and then QM duration. Typical risks associated with the work in chemical industry require high level of organisation, documented, transparent and effective management systems and therefore, greater attention is given to the standardisation of various management systems. On the other hand, motor vehicles industry in Serbia is in most cases only learning about ISO/TS 16949: 2009, whereby larger manufacturers are for many years in the phase of restructuring and produc-tion programme adjustment.

Therefore, our result is expected. Work thus of-fers managers the possibility to allocate avail-able resources subject to the type of industry and size of the company. An important result of this research is also a fact that majority of the sectors have positive covariate of output market participation and multi-factor productivity so that in those sectors the market directs most of the resources towards companies that have factor productivity above average productivity of the relevant industrial sector.

REFERENCES

Agus A., Ahmad M.S., Muhammad J., (2009) An Empirical Investigation on the Impact of Quality Management on Productivity and Profi tability: Associations and Mediating Ef-fect, Contemporary Management Research, Vol. 5, No. 1, pp. 77-92.Baily, M., Hulten, C., and Campbell, D. (1992). Productivity dynamics in manufac-turing plants. In Brookings Papers on Eco-nomic Activity: Microeconomics, Brookings Institute. Vol. 4, pp. 187-267.Benson G, Saraph J, Schroeder R (1991). The effects of oranizational context on qual-ity management: An Empirical Investigation. Manag. Sci. 37(9): pp. 107-1124.Dondur, N., Pokrajac, S., Spasojevic Brkic, V., and Grbic, S. (2011) Decompisition of Productivity and Allocative Effi ciency in Ser-bian Industry, FME Transactions, Vol. 39, N0 2, pp.73-78.Feng M., Terziovski M., Samson D., (2008) Relationship of ISO 9001:2000 quality sys-tem certifi cation with operational and busi-ness performance - A survey in Australia

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and New Zealand-based manufacturing and service companies, Journal of Manufactur-ing Technology, Management, Vol. 19. No. 1, pp. 22-37.Grandzol JR, M Gershon, 1997. “Which TQM Practices Really Matter: An Empirical Inves-tigation”, Quality Management Journal, Vol 4 No 4, pp. 43-59.Griliches, Z. and Regev, H. (1995). Firm pro-ductivity in Israeli Industry: 1979-1988. Jour-nal of Econometrics, 65, pp. 175-203.Jayaram J., Ahire S.L., Dreyfus P., (2010) Contingency relationships of fi rm size, TQM duration, unionization, and industry context on TQM implementation - A focus on total effects, Journal of Operations Management 28. pp. 345–356.Madu, C., (1998). An Empirical Assessment of Quality: Research Consideration, Inter-national Journal of Quality Science, 3(4). pp.348-355.Melitz, M. and Polanec, S. (2009). Dynamic Oley-Pakes Decomposition with Entry and Exit, manuscript.Olley, S. and Pakes, A. (1996) The Dynam-ics of Productivity in the Telecommunications Industry. Econometrica, 64(6), pp. 1263-1298.Spasojevic Brkic, V,. Djurdjevic T,. Omic, S,. Klarin, M,. and Dondur, N., (2011). An Em-pirical Examination of Quality Tools Impact on Financial Performances: Evidence from Serbia, Serbian journal of Business Manage-ment, 7(1), pp.77-88.Spasojevic Brkic, V., Dondur, N., Klarin, M., Komatina, M., & Curovic, D. (2011). Effec-tiveness of quality management and total factor productivity. African Journal of Busi-ness Management, 5(22), pp. 9200–9213.Spasojevic-Brkic, V., Klarin, M., Curovic, D. (2009): Dimenzije menadžmenta kvalitetom isporučioca u industrijskim preduzećima Srbije. Journal of Applied Engineering Sci-ence (Istraživanja i projektovanja za privre-du), no. 23/24, pp. 67-70

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Paper sent to revision: 10.08.2012Paper ready for publication: 06.12.2012.


Paper number: 10(2012)4, 242, 227-233

COMBINATION OF KNOWLEDGE IN THE SYSTEM SUPPLIERS - MSP - CUSTOMERS IN THE

TRANSITIONAL ECONOMY ENVIRONMENT IN SERBIA

MSc Marija Savić*University of Belgrade, Tehnical Faculty in Bor, Bor, SerbiaMSc Predrag ĐorđevićUniversity of Belgrade, Tehnical Faculty in Bor, Bor, SerbiaDr Đorđe NikolićUniversity of Belgrade, Tehnical Faculty in Bor, Bor, SerbiaDr Ivan MihajlovićUniversity of Belgrade, Tehnical Faculty in Bor, Bor, SerbiaDr Živan ŽivkovićUniversity of Belgrade, Tehnical Faculty in Bor, Bor, Serbia

doi:10.5937/jaes10-2522

The paper presents the results of research of the combination of knowledge in the system: suppli-ers - SMEs - consumers in case of SMEs in Eastern Serbia. A theoretical model of a combination of knowledge was established in the investigated system. By using the statistical analysis of the results a satisfactory statistical signifi cance of acquired results was determined, which allowed the testing of the defi ned model using LISREL software package. The results show the importance of the established hypotheses for the impact of the cooperation with suppliers on a combination of knowledge, as well as the combination of knowledge of customers and suppliers on the creation of the new knowledge in SMEs. The hypothesis about the positive infl uence of the sharing of knowledge with customers on the combination of the knowledge in SMEs has not been proven. These facts suggest that SMEs in Serbia do not collaborate with their customers. The cause of such a situation is the lack of system quality (SQ) in the SME sector in Serbia, as well as not applying the principles of TQM practices, which provides the best explanation of the short life cycle of SMEs in Serbia and the inability of their internationalization.Key words: SMEs, Customers, Suppliers, Knowledge, Combination, LISREL

INTRODUCTION

The concept of small and medium enterprises (SMEs) is particularly developed in the U.S., and has recently been experiencing an expan-sion in Europe [01].The development of SMEs in Europe is slower because of the barriers in the process of starting a new business and the fear of failure [02, 17]. SMEs in developed econ-omies are complementary to large companies, which provides them with safety in their work, growth and development [10, 02]. In transition economies in post-communist countries (coun-tries of the former USSR, the countries of the former Warsaw Pact, countries that emerged from the disintegration of Yugoslavia....) there is a great desire, among entrepreneurs, to create

their own businesses and to start new SMEs, but many attempts have been unsuccessful. Unsuc-cessful attempts were usually caused by a lack of knowledge of entrepreneurs, who gained their experience in the state-owned companies. In the educational systems in these countries, until re-cently, there were no elements pertinent to the fi eld of private enterprise, therefore the knowl-edge to start and run a private business was ob-viously lacking among entrepreneurs [03, 04].In Serbia, which has been going through the transitional process for a long period of time, the expansion of the starting SMEs actually takes place after the year 2000. The motiva-tion for the creation and development of SMEs is growing during 2009 and onwards, due to the global economic crisis and high unemployment.

227* Tehnical Faculty in Bor, Vojske Jugoslavije 12, 19210 Bor, Serbia; [email protected] Paper presented at the SIE 2012


In such conditions, the survival of SMEs during the period of economic crisis is becoming more diffi cult, which causes many SMEs to fail. De-velopment Strategy for SMEs can be defi ned as the creation of knowledge and the concepts of utilizations and adaptation of knowledge artifacts (knowledge artifact) which are necessary for the key elements of the SMEs functioning (Jarzab-kowski and Wilson, 2006). Many studies show that the knowledge is transferable in certain or-ganizational systems such as TQM [18].According to the theory of entrepreneurship, SMEs innovative behavior is conditioned by a combination of knowledge that is widespread, which means that different individuals know dif-ferent things [26]. Science has established net-works of knowledge [05] through the various concepts, such as learning through a network, relationship memory [07, 22]. Within the concept of entrepreneurial activities, innovative behavior is caused by a combination of knowledge which can be created within the concept of knowledge networks of SMEs with their customers and sup-pliers [23], which in many cases can lead to the creation of the new knowledge [22] In terms of globalization of the market, many SMEs become more international [28, 17] and the terms of the concept of creating a network of development produce good results, leading to the emergence of entrepreneurial fi rms with high technological performance as a consequence of the accumu-lation of knowledge in the process of combining knowledge [26].The system suppliers - SMEs - customers, if the activity of SMEs is internationalized, creates good opportunities for the creation of a network of different knowledge whose combination can create a new knowledge which presents a ba-sis for growth and development of SMEs (Street and Cameron, 2007). In terms of transitional economy in Serbia, with high entropy in the sys-tem suppliers - SMEs - customers, the creation of the new knowledge, by combining existing knowledge in certain areas of the defi ned sys-tem, can be a good starting point for improving the performance of SMEs in Serbia.

THEORETICAL BACKGROUND AND HYPOTHESES

Many SMEs have a problem with limited re-sources, which limits their business activity on the market, where they operate in one way in ac-tivities on domestic market, and in different way

in the process of internationalization of business. Very often the missing resources cannot be pro-vided through the proprietary possession, there-fore SMEs become dependent on the resources they utilize from the network with customers and suppliers [28] In accordance with the substan-tive arguments of this study, SMEs are depen-dent on the knowledge network of clients and the knowledge networks of suppliers, because these categories provide different knowledge which is the instrument for combining the knowledge [27]. Knowledge derived from these networks, in the case of SMEs, may consist mainly of market knowledge (consumer preferences, market con-ditions) and technological innovation [25].Market knowledge is usually associated with a network of consumers, but may be associated with the network of suppliers. Technological knowledge is usually associated with a network of suppliers, but may be also connected to the network of consumers. Knowledge within the networks of SMEs with customers and suppliers can be acquired by reacting to exogenous situa-tions, as well as through conscious and planned efforts by SMEs [26]. Modern SMEs should be actively operating in the network capabilities of customers and suppliers, which implies that they must work to change the existing combination of knowledge and to fi nd new ones. These fi ndings enable defi nition of the following hypotheses:H1 Supplier knowledge positively affects the combination of the knowledge in SMEs.H2 Customer knowledge positively affects the combination of the knowledge in SMEs.Research suggests that knowledge-based view serves as an important tool for understanding the spread of entrepreneurial fi rms [21] Current knowledge is not suffi cient and requires constant accumulation regardless of whether SME oper-ates at the local level or the international level [16].Therefore, SME performance depends on its ability to create knowledge, to combine it order to achieve the objectives required by the market [28]. It was determined that the business oppor-tunities are improving more rapidly and develop-ing more innovatively with the knowledge that is being actively developed as opposed to the knowledge gained by experience over time [08].Activities that take place through a combination of knowledge adjusted dynamics of the SMEs with the dynamics of the market. Therefore, the combination of knowledge will enhance the ac-

228

MSc Marija Savić - Combination of knowledge in the system suppliers - MSP - customers in the transitional economy environment in Serbia

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cumulation of knowledge which will enhance the performance of SMEs. These facts allow the defi nition of the following hypotheses:H3 Combining knowledge of suppliers and cus-tomers has a positive impact on the creation of the knowledge in the SMEs.Based on the defi ned hypothesis it is possible to defi ne a theoretical model of a combination of knowledge in the system suppliers-SME-cus-tomers to increase the knowledge, in order to in-crease the performance of SMEs, Figure 1.

DISCUSSION OF RESULTS

The studies presented in this paper were carried out through a questionnaire given in Appendix A [28]. Studies were conducted in the Eastern Serbia in a total of 536 SMEs, by surveying entrepreneurs during the visit to their fi rms. The questionnaire was administered in a way that the interviewer conducted an interview with the entrepreneur. The questionnaire has four groups of dependent vari-ables (DV) supplier knowledge (DV-1), customer knowledge (DV-2), knowledge combination (DV-3) and the creation of knowledge (DV-4), within which 10 independent variables are contained.

Figure 1: The theoretical model of the combination of knowledge in the system:

suppliers - SMEs – customers

The demographic structure of the sample is as follows: with the sample of entrepreneurs, in the most devastated part of Serbia, 71% were men and 29% were women entrepreneurs. Most of the SMEs were as follows: 75% had up to 10 employees, 22% had 10-30 employees and 3% had 50-250 employees. Time from starting a business: 11% up to 1 year; 18% 1-3 years; 25% 3-5 years; 24% 5 – 10 years and 22% over 10 years. Investigated SMEs belong to the sector of: agriculture - 11%; transport - 24%; industry - 5%; tourism - 7%; service sector - 45% and healtservice - 8%. Demographic characteristics of the sample indicate that the dominant struc-

ture in the SMEs belongs to the service sector, the existence of most companies was noted to be up to fi ve years and that the dominant struc-ture of entrepreneurs male.Likert’s fi ve-point scale (1 - completely disagree, 2 - disagree, 3 - undecided, 4 - agree and 5 - completely agree) was used for testing, with re-sults presented in this paper. This methodology has been used in numerous previous studies [18, 14, 24, 15], which justifi es the validity of the utilized methodology.A statistical analysis of the results obtained in our research and validation of theoretical models defi ned in Figure 1. were performed by using the software packages SPSS v18 and LISREL (Lin-ear Structural Relationship) v16. For the empiri-cal validation of the hypothetical model, Figure 1., a SEM [22]. In the statistical analysis of the validation of the defi ned models, fi rstly one-di-mensionality was confi rmed, using factor analy-sis (PCA), across all 10 groups of latent variables in the considered model. The values obtained by factor analysis are shown in Table 1. To ensure the reliability and validity of the research model a control measurement model was defi ned on which confi rmatory factor analysis (CFA) was performed. CFA analysis confi rmed the good fi t of the control model, which practically verifi es that 10 defi ned variables describe, in a reliable way, the four latent class variables, defi ned in the research model, Figure 1.Consistency of variables, defi ned in the frame-work of latent classes in the investigated model, was measured by the size of the Crombach’s al-pha [09]. Acquired values of the Crombach’s alpha > 0.7, Table 1, show good consistency of certain variables within the four defi ned latent groups of variables in the investigated models. Crombac’h alpha value for the whole population is 0.98, so the obtained data can be considered reliable for the testing of the proposed model [06].The values of the t-tests are used to test the hy-pothesis that the sample does not differ from the population, which shows the tendency of the normal Gaussian distribution; t values should be greater than 2. Results obtained in Table 1 show that in all cases t - values are greater than 2, with the signifi -cance level of p < 0.05, which indicates that values in the tested model, are statistically reliable [12].To study the discriminant validity of various groups of questions the Structural Equation Modeling (SEM) was performed, by comparing pairs of latent class-

229


, 242


defi ned questions on the principle of two by two. Ta-ble 2 shows the results of discriminative validity and the correlation between the four groups of questions.Positive values of Pearson’s coeffi cient were obtained

with statistical signifi cance of p < 0.05, which indicates that the correlation of random pairs of groups of latent variables are true [19].

Groups of questions

Considered variable

Factor analysis (EFA) Confi rmatory factor analysis (CFA)

PCA Reliability Convergent validity

% of variance explained by

one-dimensional factor

Factor loading Cronbach`s alpha Factor

loading t -statistics

Supplier knowledge:

ZV-1

L1L2 67.343

0.9110.804 0.891

0.8300.703

4.13*

8.19*Client

knowledge: DV-2

L1L2

82.3920.8610.906 0.942

0.8360.932

6..56*6.14*

Knowledge combination:

DV - 3

L1L2L3L4

49.9370.7180.8420.8720.975

0.9560.6310.7750.7690.845

6.53*4.04*5.10*6.74*

Knowledge creationDV - 4

L1L2 89.236

0.8810.801 0.956

0.8870.775

8.02*4.75*

Table 1: The results of the factor analysis and CFA analysis of the investigated model

Correlations between pairs of latent classes of variables, associated to the defi ned model, Fig-ure 1. have values of Pearson’s coeffi cients gen-erally above 0.12 (coeffi cients marked bold in Table 2). The highest value of correlation exists between knowledge of suppliers and knowledge combinations (0.44 with p < 0.05), indicating that entrepreneurs perceive the dominant infl uence on customer knowledge on the knowledge com-bination in SMEs. The lowest correlation with the value of Pearson’s coeffi cient of 0.12 with p < 0.05 refers to the infl uence of a combina-tion of knowledge of customers and suppliers on the creation of the new knowledge, indicating a poorly developed mechanisms for combining knowledge with the goal to create new knowl-edge in terms of SMEs operation under the con-ditions of transitional economy in Serbia.

* p < 0.05

Groups of variables DV- 1 DV- 2 DV- 3 DV-4

DV- 1 1DV- 2 0.39* 1DV- 3 0.14* 0.44* 1

DV- 4 0.31* 0.33* 0.12* 1

Table 2: Analysis of the discriminant validity correlation of the latent class-defi ned questions

To test the validity of the model defi ned in Figure 1. software package LISREL v16 was used for statistical data analysis, considering that the sta-tistical reliability of the data for the model valida-tion is satisfactory.Firstly, the values of indicators were determined, which determine whether the proposed model adequately fi ts the input data. The results of the analyzed fi tting indicators are shown in Table 3. Goodness-of-fi t index (GFI) is the extent to which the model is applicable in comparison with the case where a model does not exist. Good fi tting is indicated with GFI value above 0.90 [18]. In this case the value of GFI of 0.96 is above the threshold. V Indicator Root Mean Square Error of Approxi-mation (RMSE) shows the errors that occur dur-ing the approximate connection of populations. Good value of the RMSA indicators is within the limits of 0.08 – 0.10. The obtained value of this indicator 0.081 shows, together with the GFI in-dicator, a satisfactory coincidence.In addition to GFI and RMSA indicators for as-sessing the quality of fi tting the following indica-tors are also being used: Normed fi t index (NFI), Comparative fi t index (CFI), Incremental Fit In-

230


, 242


dex (IFI) Relative Fit Index (RFI). Following val-ues were obtained in the tested model : 0.92, 0.92, 0.93 and 0.92, respectively. The values were above 0.9 therefore they can be regard-ed as absolutely satisfactory. Also, an indicator of Minimum Fit Function Chi-Square/Degre of Frededom X2/d.f. should be considered, which in this case has a value of 1.93, where the re-quired value should be less than 3.

Indicators of the fi tting statistics

Values obtainedin the model

Recommended values

X2/d.f. 59.97/31 = 1.93 < 3.0RMSEA 0.081 0.08 – 1.0

GFI 0.96 > 0.9NFI 0.92 > 0.9CFI 0.92 > 0.9IFI 0.93 > 0.9RFI 0.92 > 0.9

Table 3: Summary values for the fi tting indicators

The obtained values of the considered fi tting in-dicators of indicate a satisfactory level of fi tting in the suggested model which suggests that the regression coeffi cients of the paths can be calcu-lated in the defi ned theoretical model in Figure 1.By using LISREL v16 the path-regression coef-fi cients were determined (correlations between the latent class variables defi ned in the model which is shown in Figure 1) and the obtained re-sults are shown in Figure 2. The results in Figure 2. indicate that the hypotheses H1 and H3 in the defi ned model have positive values of path co-effi cients with the values for t above 2 and the statistical signifi cance of p < 0.05, indicating that these hypotheses are confi rmed. The obtained value of - 0.10 for the path coeffi cient of the H3 hypothesis is negative and t = - 0.29, indicating that H3 is not proven.

CONCLUSION

Bearing in mind the proposed hypothetical model of knowledge creation by combining knowledge in the system suppliers - SME - customers in SMEs in the transition economy in Serbia, Figure 1., and obtained results in Figure 2., hypothesis H1 and H2 were confi rmed while the hypothesis H3 is not confi rmed. Hence, it was confi rmed that knowledge has a positive effect on the combination of entrepreneurial skills of a com-pany, as well as on developing the dependence on supplier knowledge networks which have a

positive effect on the entrepreneurial combining of knowledge of fi rms and the creation of new knowledge, which in accordance with the results of the investigation of SMEs in Sweden [26].

Figure 2: Structural model of the combination of knowledge in the system:

suppliers - SMEs – customers in Serbia (t - values in parenthesis)

Level of signifi cance: * < 0.05

Our research has shown that information ob-tained from clients do not have a positive effect on the combinations of entrepreneurial fi rms knowledge, which means that manufacturers do not rely on knowledge of clients (consumers) be-cause it does not contribute to new knowledge in entrepreneurial fi rms.This result can be explained by under-developed marketing function in the investigated SMEs in Serbia, which indicates a low level of compliance with the requirements of clients, including the lack of TQM practices in investigated SMEs. Transi-tional conditions in Serbia: the reforms, restruc-turing, price liberalization, the establishment of a strong private sector and the fulfi llment of the EU requests, still holds Serbian borders closed for major business projects, which is slowing down the internationalization of Serbian SMEs.Due to the confusing situation in the market cus-tomers have lost their vision of what they want in the market, and suppliers use this as an opportu-nity to sell to the market what they have, by pro-viding favorable terms of payment of purchased goods. Most entrepreneurs are determined to purchase goods offered by suppliers, while not being informed if customers have a demand for it or not. Due to the organizational and business culture in Serbia overloaded with transitional re-strictions, client’s culture, and primarily due to a lack of quality standards, most of the SMEs are

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confi dent that they will sell on the Serbian mar-ket whatever they offer.

APPENDIX A

QUESTIONNAIREDV-1 (Supplier knowledge)

Your relationships with key suppliers depend on information, knowledge and experience you acquire from them.Your relationships with other suppliers in the market depend on information, knowledge and experience you acquire from them.

DV - 2 (Client knowledge)Your relationships with key clients depend on information, knowledge and experience you get from them.Your relationships with other clients in the market depend on information, knowledge and experience you get from them.

DV-3 (combination of knowledge)Business partners (customers and suppliers) are a source of information, knowledge and experience to you. The relationship with your business partners (customers and suppliers) is characterized by mutual adjustmentsThe relationship with your business partners (customers and suppliers) is characterized by an exchange of information, knowledge and experience. How familiar are you with the business part-ner’s (customers and suppliers) information, knowledge and experience?

DV-4 (Knowledge creation)The relationship with your business partners (customers and suppliers) result in the cre-ation of new products/new services.The relationship with your business partners (customers and suppliers) result in new pro-cedures, practices of the organizational de-tails etc. in your company.

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Kayank, H., (2003) The relationship betwen total quality management practices and their effects on fi rm performance, Journal of Op-erations Management 21(4), 405 – 435.Knight G.A., Cavusgil, T., (2004) Innova-tion organizational capabilities and the Born-global fi rm, Journal of International Business Studies, 35(1): 124-141.Moen, O., (2002) The born globals: A new generation of small European exporters, In-ternational Marketing Review, 19: 156 – 175.Molina, L.M., Montes, L.J., Moreno, A.R., Relathionship betwen quality management practices and knowledge transfer, Journal of Operations Management, 25: 682-701.Moris, H. DeGroot, Mark S. Schervish (2002) Probabiolity and Statistics, Addison – Wes-ley, p.485.Omerzel, G.D., Antončič, B., (2008) Criti-cal enterpreneur knowledge dimensions for SME performance, Industrial Management & Data systems, 108(9): 1182 – 1199.Rialp, A., Rialp, J., Knight, G.A., (2005) The phenomenon of early internationalizing fi rms: what do we know after decade (1993-2003) of scientifi c linquiry , International Business Review, 14(2):147-166.Soda, G., Usai, A., Zaheer, A., (2004) Net-work memory: the infl uence of past and cur-rent networks on performance, Academy of Management Journal, 47(6): 893-906.

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E V E N T S R E V I E W

The Province Secretariat for Energy and Mineral Resources for many years focus its activities to the promotion of the energy sector, particularly renewable energy, energy effi ciency improvement and cooperation with potential investors who wants to direct their resources in the energy sector. There-fore, Secretariat actively participated in both the exhibition and the congress event INVESTEXPO, which is traditionally held in late October at the Novi Sad Fair.

During the mentioned event ENERGY DAYS, that were held from 23-25. October 2012 in the Master Center of Novi Sad Fair, following conferences has been held:

Conference “The potential of investments in the energy” (23.10.2012.) that presented pos-sibilities for realization of projects in renewable energy and energy effi ciency sector, as well as examples of good practice of investing in various forms of renewable energy, with special focus to models of public-private partnership and potential investors.Scientifi c Conference “Natural Gas” (24.10.2012.) that discussed the current issues: ensuring supply security, investment opportunities and increase potential of the natural gas consumption over other fuels, natural gas quality, the new legislation, the protection of fi re in the fi eld of natural gas, possibilities of natural gas use in combination with renewable energy sources, as well as the possibility of using compressed natural gas, especially as fuel for motor vehicles.Scientifi c Conference “Energy and agro-processing” (24.10.2012.) that presented topics related to the use of all forms of biomass for energy purposes such as solid biomass, liquid (bio-diesel) and gaseous (biogas). In cooperation with the Ministry responsible for the Diaspora, this event provided a video conference with the presentations of international experience in the fi eld of biomass.6th International Forum on Renewable Energy “Serbian Energy Challenge 2020-30-50” (24-25.10.2012.). The subject of the Forum was future of energy in Europe and in Serbia. Partner of the Forum was the Republic of Finland that presented the best practices of the use of various forms of renewable energy. First year of the use of photovoltaic power plant at FTS building was presented, as well as a new program for renewable energy in schools.

The event ENERGY DAYS gathered large number of representatives of energy companies, local governments, businesses, citizens and all interested to hear the positive case studies due to the fact that future investment in the energy sector could be best implemented through available technical, production, implementation and fi nancial capacity.

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ENERGY DAYS23rd-25th October 2012

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A N N O U N C E M E N T O F E V E N T S

IIPP QUALITY MANAGEMENT SCHOOL

Considering business conditions of European market, quality has a signifi cant role, not only in pro-viding new markets, but also in maintaining the existing ones. Nowadays, customers do not only expect a quality product, but they require a proof that the company is capable to produce high quality products and provide quality services. Obtaining of this evidence should be the fi rst goal for each company that has high aspirations when it comes to new markets but also standard’s procedure in order to maintain its reputation. Implementation is not complete if employees are not familiar with standards.

With the aim to closer inform the employees of the meaning and signifi cance of ISO standards, Insti-tute for research and design in commerce & industry – IIPP organize training “School of Quality”.

During the training participants will:expend their knowledge about implementation of ISO standards,learn how to maintain and improve quality level of companies learne how to verify and improve business performance of companies

Training will be held during four days in two locations. First lectures will be held at the Faculty of Mechanical Engineering in Belgrade, while the fi nal lecture and the test will take place in attractive location in Serbia - Zlatibor.

ProgrammeFundamentals of quality concepts, defi nitions, approachesStandards, review and interpretationManagement ResponsibilitySystem and process approachData management, information systemStatistical methods (engineering methods, quality

management methods)RISK, FMEA, FTASupply and storage, evaluation of supplier MaintenanceEvaluation, audit, certifi cation Examples, practice, Deming management experimentPAS 99 - Integrated Management Systems

ResultAfter implemented training, Qiipp consultant is able to assume responsibility for independent work in the following fi elds of activity:

Implementation of quality standardsMaintaining a high level of qualityConstant improvement of the quality systemAssessment and audits of own companies and their suppliers

Candidates who passe the test will get a diploma “Qiipp consultant for implementation, maintenance, analysis, evaluation and testing, design and improvement of the quality system”.

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Institute for research and design in commerce & industryPhone: 011/6300750; Fax: 011/6300751; E-mail: offi [email protected]; web: www.iipp.rs

Time and location:March 2013, Belgrade, Faculty of Mechanical Engineering

info: www.iipp.rs

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A N N O U N C E M E N T O F E V E N T S

IIPP MAINTENANCE MANAGEMENT SCHOOL Maintenance Management School presents practical experience in combination with adopted theo-retical knowledge, thus creating maintenance management experts capable to perform and coordi-nate the maintenance of complex technical systems. Use unique opportunity to expand knowledge in the fi eld of technical systems maintenance.

During fourdays training focus will give to the following topics:

Result: More than 240 national certifi cates and 16 internationally recognized certifi cates:European Maintenance Manager.

Time and location: March 2013, Belgrade, Faculty of Mechanical Engineering

Info: www.dots.rs

Maintenance Objectives and PoliciesMaintenance ConceptsMaintenance TerminologyLaws and RegulationsCondition MonitoringFault Finding TechniquesSpare Part Management

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Corporate/Company EnvironmentWork PlanningTeam Working and CommunicationsInformation TechnologyQuality Assurance (Systems)Environment and Occupational Health and Safety

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The school program merges best local knowledge and experience modernized and harmonized with the recommendations of European Federation of National Maintenance Societies.Since Maintenance Management School connected and unifi ed local tradition and experience in the maintenance process with the European norms and requirements, it’s result is thus twofold - to all who signed up gives a chance to gain national certifi cate ’’Expert for maintenance management” and to those who can and want more, Maintenance management school opens the possibility of obtaining the International certifi cate “European maintenance manager”.

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B O O K R E C O M M E N D A T I O N

237

This book is devoted to engineering problems in decision-making and management. It is a result of the author’s long time research in the area of optimization methods and their application in en-gineering practice. The accent is put on planning and decision problems. The operations research and system engineering methodology is used.

The monograph is designed to professionals, practitioners who use or should use contempo-rary scientifi c methods in studying and solving management problems in complex systems. Some parts of the text might be useful for stu-dents of academic master and doctoral studies in the area of management, engineering, economy, artifi cial intelligence and applied mathematics. It consists of fi ve chapters: Introduction to optimiza-tion (28 pages), Integer programming (37 pages), Constraint programming (42 pages), Multi-crite-ria optimization (20 pages), and Computational complexity (30 pages). The text is written in clear style and simple examples are used as illustra-tion of main optimization and solving ideas.

Recommended by prof. dr Slobodan Vujić

METODE OPTIMIZACIJE U INŽENJERSKOM MENADŽMENTUOPTIMIZATION METHODS IN ENGINEERING MANAGEMENT

Author: prof. dr Mirko Vujošević, University of Belgrade, Faculty of organizational sciences

Language: Serbian

Format B5, 165 pages, ISBN 978-86-87035-06-5 (AINS)

Publishers: Serbien Academy of Engineering Science and Faculty of Organizational Sciences (2012)


S A D R Ž A J

Prof. dr Jovan TodorovićUVODNIK 239

REZIMEI RADOVA

Dr Miroslav Demić, Dr Đorđe DiligenskiPRILOG ISTRAŽIVANJU DEGRADACIJE KARAKTERISTIKA OSCILATORNIH

PARAMETARA NA OSCILATORNU UDOBNOST VOZILA240

Dr Nikola Dondur, Dr Vesna Spasojević-Brkić, Mr Aleksandar Brkić KABINE KRANA SA INTEGRISANIM VIZUELNIM SISTEMOM ZA DETEKCIJU I

INTERPRENTACIJU EKONOMSKE PROCENE SREDINE240

Zoran Petrović, Dr Uglješa Bugarić, Dr Dušan PetrovićUPOTREBA “ARIMA” MODELA ZA PROMET PREDVIĐANJA U PROCENI

INVESTICIONOG PROJEKTA240

Dr Radoljub Tomić, Dr Predrag Petrović, Marija PetrovićPRIlOG OCENI USAGLAŠAVANJA NOVIH PROIZVODA SA ASPEKTA

POUZDANOSTI I ODRŽAVANJA241

Dimić-Mišić Katarina, Dr Paltakari JouniFIBRILARNI MATERIJAL KAO ZAMENA KO-VEZIVU U BOJI ZA KOTIRANJE PAPIRA 242

Dr Vesna Spasojević-Brkić, Dr Slobodan Pokrajac, Dr Nikola Dondur, MSc Sonja Josipović

ALOKATIVNA EFIKASNOST I KOVARIJANTNI FAKTORI MENADŽMENTA KVALITETA U SRPSKOJ INDUSTRIJI

241

MSc Marija Savić, MSc Predrag Đorđević, Dr Đorđe Nikolić, Dr Ivan Mihajlović, Dr Živan Živković

KOMBINACIJA ZNANJA U SISTEMU DOBAVLJAČI-MSP-KUPCI U USLOVIMA TRANZICIONE EKONOMIJE U SRBIJI

242

OD UREĐIVAČKOG ODBORA

238


O D U R E Đ I V A Č K O G O D B O R A

239

ALTERNATIVNA GORIVA I OBNOVLJIVI IZVORI ENERGIJE

Intenzivan razvoj svetske privrede, a posebno sektora transporta, stvorio je dva velika problema: sve veće iskorišćavanje rezervi fosilnih goriva i velika zagađenja okoline. Stoga su razvoj alternativnih goriva i obnovljivih izvora energije glavni izazovi za inženjera u celom svetu.

Alternativna goriva, poznata još i kao nekonvencionalna ili napredna goriva, predstavljaju materi-jale ili supstance koje mogu da se koriste da goriva, pored konvencionalnih fosilnih goriva (nafta, ugalj, propan, prirodni gas), kao i nuklearni materijali. Najpoznatija alternativna goriva su biodizel, bioalkohol (metanol, etanol, butanol), elektricitet hemijski uskladišten (akumulatori i gorivne ćelije), biljna ulja i drugi oblici biomasa. Jedan od najboljih je vodonik, koji sagoreva praktično bez emisije štetnih gasova. Primena vodonika zahteva velike investicije i zato se danas još uvek smatra gorivom budućnosti. I prirodni gas je takodje gorivo koje sagoreva čisto, sa manjim emisijama od benzina i dizel goriva.Obnovljiva energija se dobija iz prirodnih izvora, kao što su hidroelektrane, sunčeva energije, vetar, plima, talasi i geotermijska energija. Ova energija je obnovljiva pošto se prirodno stalno obnavlja. Biogoriva su takodje obnovljivi izvori energije. Biodizel se dobija iz životinjskih masti ili biljnog ulja, kao i od biljaka, kao što su soja, suncokret, kukuruz, šećerna trska, itd. Biodizel ima manju emisiju zagađivača i sagoreva čistije i ekonomičnije. Metanol i etanol su primarni izvori energije i pogodni su za skladištenje i primenu u transportu. Ovi alkoholi mogu da se koriste i za motore sa unutrašnjim sagorevanjem. Sunčeva energije se koristi pomoću fotoćelija koje se izrađuju od legura silikona. Ove ćelije pretvara-ju sunčevu energiju u toplotu ili elektricitet. Geotermalna energija je druga mogućnost. Tehnologije koje se koriste u proizvodnji geotermalne energije slične su onima koje se koriste za naftu i gas. En-ergija vetra se smatra najekonomičnijim vidom proizvodnje električne energije, posebno preko noći. Gorivne ćelije, kao vid akumuliranja elektriciteta, danas su jedna od najperspektivnijih alternativa za motorna vozila, posebno sa vodonikom kao gorivom.U mnogim zemljama već su ostvareni značajni rezultati u razvoju alternativnih goriva i obnovljivih iz-vora energije. Obnovljiva energija danas zadovoljava 15 do 20% ukupnih poteba (u Norveškoj skoro 100%). Najvažnija je energija koja se dobija iz hidroelektrana, ali ima sve više i postrojenja koja energiju proizvode pomoću vetra i solarnih ćelija, ponekad sa velikim instalisanim snagama. Danas su u svetu milioni vozila koja rade na biogoriva, prirodni gas i elektopogon. Razvoj alternativnih goriva i obnovljivih izvora energije predstavlja primarni zadatak i za srpsku eko-nomiju. Uzimajući u obzir naše privredne i tehničke mogućnosti i prirodne resurse, očigledno je da prednost treba da se da gradnji novih hidroelektrana (na Drini, Ibru, Dunavu i brojnij manjim vodenim tokovima), a i razvoju novih izvora energije, vetro i solarnim postrojenjima, kao i korišćenju geoter-malne energije. Pažnja treba da se usmeri i na uljne škriljce, kao i na dalje unapređenje rudnika uglja, u pogledu kapaciteta i zaštite okoline. U sektoru transporta veoma važno je veće korišćenje prirodnog gasa i različitih vrsta biogoriva, što može da doprinese poboljšanju ekonomije i većoj zaštiti okoline.

S poštovanjem,Prof.dr Jovan Todorović


R E Z I M E I R A D O V A

PRILOG ISTRAŽIVANJU DEGRADACIJE KARAKTERISTIKA OSCILATORNIH PARAMETARA NA OSCILATORNU UDOBNOST VOZILA

Broj rada: 10(2012)4, 236doi:10.5937/jaes10-2244

240

Dr Miroslav Demić-Univerzitet u Kragujevcu, Fakultet inženjerskih nauka, Kragujevac, SrbijaDr Đorđe Diligenski-Institut Vinča, Centar za motorna vozila i motore, Beograd, Srbija

Tokom razvoja motornih vozila, značajnu ulogu ima dinamička simulacija, koja je zasnovana na modeliranju. Uloga modeliranja je veoma značajna u prvim fazama projektovanja, tokom defi nisanja opredeljujućih parametara. U praksi se obično pretpostavlja da su oscilatorni parametri vozila to-kom eksploatacije nepromenljivi, što u osnovi nije tačno. Naime, sva istraživanja pokazuju da to-kom eksploatacije dolazi do degradacije oscilatornih parametara i, zbog toga, promene dinamičkih karakteristika motornih vozila. U ovom radu će biti učinjen pokušaj da se, na osnovu preliminarnih rezultata, ukaže na neophodnost da se i u najranijim fazama projektovanja te promene uključe u razmatranje tokom modeliranja vozila.Ključne reči: Vozilo, Vibracioni parametri, Degradacija, Vibraciona udobnost

Broj rada: 10(2012)4, 237

Dr Nikola Dondur-Univerzitet u Beogradu, Mašinski fakultet, Beograd, SrbijaDr Vesna Spasojević-Brkić-Univerzitet u Beogradu, Mašinski fakultet, Beograd, SrbijaMr Aleksandar Brkić-Univerzitet u Beogradu, Mašinski fakultet, Beograd, Srbija

doi:10.5937/jaes10-2516

Rad analizira ekonomsku opravdanost i upotrebu nove generacije kabina krana znatno manje težine i krutosti čiji će unutrašnji prostor neophodan za rukovaoca biti razvijen korišćenjem metode fi zičkog, kognitivnog i ergonomskog organizovanja sa rešenim problemom vidljivosti i koji će omogućiti veću produktivnost, usled smanjenja fi zičkog i psihičkog stresa rukovaoca, kao i veću bezbednost i sigurn-ost usled integrisanja vizuelnog sistema. Dokazano je da ukupna ekonomska prednost eksploatacije kabine u ukupnom eksploatacijskom period značajno veća, nego upotrebna cena kabine, kao i da je interna stopa prinosa iznad prosečne ponderisane kamatne stope i da je vreme povratka uloženog manje od 3 godine. Analizirani proizvodni projekat i upotreba kabine krana sa integrisanim vizuelnim sistemom za detekciju i interpretaciju sredine je projekat niskog ekonomskog rizika.Ključne reči: Ekonomska opravdanost, Kran, Kabina, Integritet, Proizvodi, Operator

UPOTREBA “ARIMA” MODELA ZA PROMET PREDVIĐANJA U PROCENI INVESTICIONOG PROJEKTA

U savremenim analizama investicionih projekata, najkritičnija tačka je kako proceniti dnevni promet proiz-vodnje, ili usluga, na bazi sistema. Da bi ostvarili predviđanje, za precizno ulaganje u određenu vrstu opreme analiziran je dnevni promet za automatko pranje vozila u skadu sa vremenskim uslovima. Prema analizama, napravaljen je ARIMA model i vremensko stanje u skladu sa “Box-Jenkins” procedurom. Zaključak je da se dnevni promet može analitički izraziti kroz dnevne vremenske uslove. Ispravnost sistema je proverena na drugom sistemu koji je postavljen u drugom gradu Srbije. Prema upoređenim rezultatima,zaključak je da se ARIMA model za sistem dnevnog prometa, predviđen zavisnom promenljivom, generalno može koristiti kao dobar za predviđanje u analizama investicija ili za kriterijum izbora u investicionim odlukama.

Paper number: 10(2012)4, 238 doi:10.5937/jaes10-2617

Zoran Petrović-Tecon Sistem d.o.o, Beograd, SrbijaDr Uglješa Bugarić-Univerzitet u Beogradu, Mašinski fakultet, Beograd, SrbijaDr Dušan Petrović-Univerzitet u Beogradu, Mašinski fakultet, Beograd, Srbija

Ključne reči: Arima, Box-Jenkins, Investicije, Predviđanja, Promet

KABINE KRANA SA INTEGRISANIM VIZUELNIM SISTEMOM ZA DETEKCIJU I INTERPRENTACIJU EKONOMSKE PROCENE SREDINE



PRIlOG OCENI USAGLAŠAVANJA NOVIH PROIZVODA SA ASPEKTA POUZDANOSTI I ODRŽAVANJA

241

Paper number: 10(2012)4, 239

Dr Radoljub Tomić-Alfa Univerzitet, Fakultet za strateški i operativni menadžment , Beograd, SrbijaDr Predrag Petrović-Institut Kirilo Savić, Beograd, SrbijaMarija Petrović-Institut Kirilo Savić, Beograd Srbija

doi:10.5937/jaes10-1688

Razvoj i unapređenje principa usaglašavanja novih proizvoda, je veoma bitno, posebno kod tehničkih sistema i njihovih komponenata, koje se primenjuju i eksploatišu u saobraćajnim sredstvima.Nivo kvaliteta i pouzdanosti takvih proizvoda, mora biti visok, kako bi proizvod, a time i sistem, pre svega bio bezbedan, a istovremeno konkurentan na globalnom tržištu. S druge strane, jedan od uslova za promociju izvoza domaćih proizvoda je povećanje konkurentnosti proizvoda, uzistovremeno ispun-javanje tehničkih propisa, kvaliteta proizvoda, pouzdanosti i održavanja. Kada je u pitanju pravil-no funkcionisanje kočionog sistema železničkih vozila značajna je pogodnost održavanja sistema. Imajući u vidu da kočioni sistem mora da ispuni niz kvalitativnih uslova sa aspekta zakonodavst-va, bezbednosti, pouzdanosti rada na svim režimima i drugih uslova, ovaj rad opisuje dinamiku održavanja jednog tehničkog sistema, sa posebnim osvrtom na učešće troškova u odnosu na cenu uređaja kočionog sistem železničkih vozila. Radi se o domaćemnovom proizvodu Industrije hidrau-like i pneumatike „Prva petoletka” Trstenik-(PPT), sa posebnim osvrtom na komponentu koja se odnosi na zaptivnielement, kao najosetljivijem delu uređaja na kočionom sistemu železničkih vozila

Ključne reči: Održavanje, Kočenje, Raspoloživost, Pouzdanost, Železnica, Usaglašenost, Novi proizvod, Troškovi

Trendovi alokativne efi kasnosti i kovarijati veličine preduzeća i efi kasnosti faktora menadžmenta kv-litetom u srpskoj industriji su testirani na nebalansiranom panel uzorku od 48 industrijskih preduzeća iz 12 industrijskih sektora u periodu 2004-2009. Dobijeni rezultati pokazuju da 10 od 12 sektora ima pozitivan kovarijat učešća u outputu tržišta i multi-faktorskoj produktivnosti. Kovarijat veličine preduzeća i efi kasnosti svih faktora menadžmenta kvalitetom pokazuju isti smer u hemijskom sektoru (pozitivno) i sektoru motornih vozila (negativno), što znači da u ta dva sektora veće kompanije imaju natprosečnu i/ili ispodprosečnu efi kasnost menadžmenta kvalitetom. Isti (pozitivan) trend alokativne efi kasnosti i kovarijata svih faktora menadžmenta kvalitetom je zabeležen u hemijskoj industriji.

Paper number: 10(2012)4, 241doi:10.5937/jaes10-2517

Dr Vesna Spasojević-Brkić-Univerzitet u Beogradu, Mašinski fakultet, Beograd, SrbijaDr Slobodan Pokrajac-Univerzitet u Beogradu, Mašinski fakultet, Beograd, SrbijaDr Nikola Dondur-Univerzitet u Beogradu, Mašinski fakultet, Beograd, SrbijaMSc Sonja Josipović-Univerzitet u Beogradu, Mašinski fakultet, Beograd, Srbija

Ključne reči: Raspodela, Alokativna efi kasnost, Kovarijantnost, Industrija, QM

ALOKATIVNA EFIKASNOST I KOVARIJANTNI FAKTORI MENADŽMENTA KVALITETA U SRPSKOJ INDUSTRIJI



242

Ključne reči: SMEs, Potrošači, Snabdevači, Znanje, Kombinacija, LISREL

FIBRILARNI MATERIJAL KAO ZAMENA KO-VEZIVU U BOJI ZA KOTIRANJE PAPIRA


Dimić-Mišić Katarina, Aalto University, Helsinki, FinlandDr Paltakari Jouni, Aalto University, Helsinki, Finland

Ključne reči: Svojstva, Vlakno, Bojenje, Premazi, CMC

Mikrofi brilarna celuloza (MFC) je novi materijal koji ima tendenciju da se koristi u formulaciji boja za kotiranje papira, kao delimična substitucija sintetičkim ko-vezivima, kao što je karboksimetil celuloza (CMC). Ko vezivo je važan sastojak u smeši boja za kotiranje papira jer kontroliše fl uidnost i brzinu kojom voda ističe na papirnu podlogu, neposredno posle primene ove suspenzije na papir koji se kotira. U ovoj studiji, MFC vlakna su se koristila da zamene uobičajno ko-vezivo CMC, u suspenziji boja za kotiranje papira i na taj način uticala na promenu reoloških karakteristika smeše i brzine oti-canja vode iz smeše nakon primene. Ova studija pokušava da bar delimično utvrdi standardnu met-odologiju kojom bi reološka ispitivanja ovakvih boja za kotiranje papira bilo moguće. Veoma izražen elasticitet ovih suspenzija pri niskim naponima utiče na fuidnost istih i napon samog noža zaravn-janja pri upotrebi. Raznim reološkim metodama je pokazano da boje za kotiranje papira koje sadrže MFC vlakna imaju izraženu osobinu smanjenja viskoziteta kada su izložene naponima, što je željeno ponašanje u proizvodnji istih. Ovim radom je pokazano da u slučaju kompletne zamene ko-vezivnim vlaknima suspenzija bi imala veoma nizak nivo retencije vode, mnogo duže vreme povratka viskoz-iteta i to po prestanku delovanja napona i veoma brzu imobilizaciju, osobine koje negativno utiču na sam mehanizam primene. S obzirom da reologija boje za kotiranje papira utiče na fl uiditet pri velikim brzinam a pri primeni, i sam kvalitet kotiranog sloja zavisi od istih parametara. Zamena ko-veziva MFC vlaknima bi uticala na viskozitet i reologiju preko mehanizma visoke fl okulacije ovih vlakana i velike reaktivnosti hidroksilnih grupa na površini MFC. Postoje razne metode za proizvodnju MFC vlakana, u zavisnosti od kojih se hemijske osobine vlakana veoma razlikuju. Njihova primena kao sastojka kotiranog sloja treba da bude najrasprostranjenija za one vrste kotiranja papira koje se ko-riste u specijalne namene. Naravno, postavlja se pitanje da li i pored njihovih povoljnih osobina,jer su prirodnog porekla, njihov uticaj na fl uiditet i reologiju može da izađe u susret visokim zahtevima koje sam proces primene postavlja (sa brzinama primene preko 1000 m/min).

U radu se prezentuju rezultati istraživanja kombinacije znanja u sistemu: Dobavljači – MSP – Kupci za slučaj MSP u Istočnoj Srbiji. Uspostavljen je teorijski model kombinacije znanja u ispitivanom sistemu. Statističkom obradom dobijenih rezultata utvrđena je zadovoljavajuća statistička značajnost dobijenih re-zultata, što je omogućilo testiranje defi nisanog modela korišćenjem LISREL softverskog paketa. Dobijeni rezultati pokazali su važnost postavljenih hipoteza za uticaj saradnje sa dobavljačima na kombinaciju znanja, kao i kombinacije znanja kupaca i dobavljača na stvaranje novog znanja u MSP. Hipoteza o pozi-tivnom uticaju razmene znanja sa kupcima na kombinaciju znanja u MSP nije dokazana. Ove činjenice ukazuju da MSP u Srbiji nemaju saradnju sa svojim klijentima. Uzrok ovom stanju je nepostojanje siste-ma kvaliteta (SQ) u MSP u Srbiji, kao ni primene principa TQM prakse, što na najbolji način objašnjava činjenicu kratkog životnog ciklusa MSP u Srbiji i nemogućnost njihove internacionalizacije.

MSc Marija Savić, University of Belgrade, Tehnical Faculty in Bor, Bor, SrbijaMSc Predrag Đorđević, University of Belgrade, Tehnical Faculty in Bor, Bor, SrbijaDr Đorđe Nikolić, University of Belgrade, Tehnical Faculty in Bor, Bor, SrbijaDr Ivan Mihajlović, University of Belgrade, Tehnical Faculty in Bor, Bor, SrbijaDr Živan Živković, University of Belgrade, Tehnical Faculty in Bor, Bor, Srbija


KOMBINACIJA ZNANJA U SISTEMU DOBAVLJAČI-MSP-KUPCI U USLOVIMA TRANZICIONE EKONOMIJE U SRBIJI

Journal of Applied Engineering Science 10(2012)4

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