WJM by Dr.kantha Babu

Wear 254 (2003) 763–773

A study on recycling of abrasives in abrasive water jet machining

M. Kantha Babu, O.V. Krishnaiah Chetty∗Manufacturing Engineering Section, Indian Institute of Technology Madras, Chennai 600 036, India

Received 4 October 2002; accepted 20 February 2003

Abstract

This paper reports the effect of recycling of local garnet abrasives (origin: southern India) while cutting aluminium using abrasive waterjet machining. The influence of pressure, traverse rate, and abrasive flow rate on American Foundrymen’s Society grain fineness number,average particle size, depth of cut, top kerf width, bottom kerf width, kerf taper, and surface finish obtained using a specially formulatedoptimised abrasive test sample have been studied. The performance of the test sample has been compared with that of commercial gradeabrasive of mesh size 80. Recycling studies, undertaken with used abrasives after screening out particles less than 90�m size and alsowith all particles without screening are reported. It is found that the test sample performed better than mesh size 80 abrasives, in terms ofachievable depth of cut and surface finish. Recycled abrasives reduces kerf taper, improving the parallelism of cut surface. These resultsindicate that the proper selection of abrasive particle size distribution is necessary for achieving improved results. The reusability percentageof test sample of the local abrasives that can be recycled is determined as 81%.© 2003 Elsevier Science B.V. All rights reserved.

Keywords:Abrasive water jet machining; Abrasive particle size distribution; Recycling; Garnet abrasives

1. Introduction

Abrasive water jet machining (AWJM), an emergingtechnology is experiencing continuous growth. Its industrialusage depends on cost effectiveness. In general, the over-all cost of AWJM systems remains quite high comparedto traditional machining techniques, despite the thrust bythe industry to reduce the equipment cost and increase thesystem reliability. System operating costs have been heldsteady for many years at a high level[1]. The largest com-ponent of operating cost is that of abrasive, constitutingnearly 75% of the total operating expenses. When abrasivedisposal is included, this percentage can be even higher[1,2]. The cost of abrasives has restricted many opportu-nities and usage of this technology. This cost, howevermust be considered along with abrasive performance. Goodabrasive performance is more important than the cost ofabrasive, since any disadvantage in higher abrasive pur-chase cost can be outweighed by the higher cutting speedachieved with a better performing abrasive. Therefore costof abrasive should be weighed against its performance andthe most cost-effective abrasive should be selected[3]. Thecutting efficiency is influenced by the particle size, particlesize distribution, and shape of the abrasive particles.

∗ Corresponding author. Tel.:+91-44-445-8508; fax:+91-44-235-2545.E-mail address:[email protected] (O.V. Krishnaiah Chetty).

Abrasive particles disintegrate during the accelerationand focusing processes and also after cutting. During thecutting process, the breakdown of abrasive particles occursin two stages: (1) particle/particle, particle/water jet andparticle/wall collisions in the mixing chamber/focusing tubeassembly; (2) particle/particle and particle target collisions[4]. With proper cleaning and sorting, an important por-tion of sludge may be recycled and fed back to the cuttingprocess. Only the remaining portion, the microchips of theworkpiece material and the used abrasive material of finersize particles usually less than 90�m are disposed[5].Recycling of the abrasives makes the process more eco-nomical, effective and environmentally friendly. Realisingthe importance of recycling, fully automated systems forabrasive recycling have been recently introduced into themarket.

Natural abrasives are often mined from riverbeds or sanddeposits. Impurities are removed to improve the performanceof cutting. The abrasives are subsequently sized. This mul-tistep process uses metal screen sieves to remove very fineand oversized particles[3]. Among the abrasives, the indus-tries frequently use garnet, as it demonstrated effectivenessof its hardness, sharp edges, flowability, availability, and rea-sonable cost[6]. Comparison of garnet, silica and steel gritindicated improved performance of garnet[6,7]. However,different types of garnet, even when chemically and physi-cally similar, perform quite differently[8].

0043-1648/03/$ – see front matter © 2003 Elsevier Science B.V. All rights reserved.doi:10.1016/S0043-1648(03)00256-4

764 M. Kantha Babu, O.V. Krishnaiah Chetty / Wear 254 (2003) 763–773

Literature indicates that only limited attempts weremade to study the influence of particle size distributionparameters in AWJM. For the first time Momber and Ko-vacevic [9] studied the influence of two different particlesize distribution parameters; size modulus of 150–400�mand a distribution modulus of 1–4, while machining ofaluminium. The distribution parameters are derived froma Rosin–Rammler–Sperling grain size distribution. Theinfluence of these parameters on the depth of cut is notsignificant in the selected parameter range, whereas surfacefinish in the smooth cutting zone is sensitive to changes inboth of the particle size distribution parameters.

In our ongoing research, garnet abrasives obtained fromsouthern India are being tested for utility. Preliminary re-search on AWJM with these abrasives[10–12]has concen-trated on depth of cut, top and bottom kerf width, kerf taper,surface finish, and fragmentation of abrasive particles mea-sured by American Foundrymen’s Society grain finenessnumber (AFS no.) as well as average particle sizes (a.p.s.)proposed by Guo et al.[2]. Since commercial grades ofmesh sizes supplied by various vendors vary in their particlesize distribution[4,13], a specially formulated test samplewith five equally distributed particle sizes rather than singleor three equally distributed sizes is recommended for usebased on optimisation studies[12].

The present work attempts to study the recycling capabil-ities and reusability of local abrasive particles with differentparticle size distribution. Specially formulated optimisedabrasive test sample of five equally distributed particle sizeswas compared with abrasive particles of commercial grademesh size 80 having AFS no. and a.p.s., similar to test sam-ple. Recycling studies are undertaken with used abrasivesafter screening out particles less than 90�m and also withall particles without screening.

The target parameters considered are depth of cut (d),top kerf width (KWT), bottom kerf width (KWB), kerf taper(KT), surface finish (Ra) (Figs. 1 and 2), and the fragmen-

Fig. 1. Schematic of workpiece.

tation of abrasives during various stages of recycling stud-ied using AFS no. and a.p.s. The AFS no. is defined as thesum of product (consists of weight of abrasive particles re-tained in each sieve in percentage multiplied by previoussieve mesh number) divided by the total percentage of abra-sives retained in the set of sieves and the pan. The a.p.s. iscalculated based on momentum method; defined as the sumof product (consists of particles retained on each sieve inpercentage is multiplied with average mesh size of the sieve)divided by the total percentage of abrasives retained in theset of sieves and the pan.

2. Experimental set-up and procedure

An injection jet type abrasive water jet machine consist-ing of pressure intensifier, an abrasive machining head, anx–y positioning system and a catcher tank has been used forexperimentation. The equipment details are given inTable 1.

Table 1Details of the equipment

Item Description

AWJM system Pressure intensifier, injectiontype nozzle

Power 22 kW, 50 HzMaximum discharge pressure 360 MPaAbrasive feeding system Vibratory conveyor with

heating facilityCNC work table Two-axis control (X = 1000,

Y = 1000)British standard sieves, mesh

number30, 36, 44, 52, 60, 72, 80, 100, 120

Surface finish measuringequipment

Perthometer, cutoff length:0.8 mm, traverse length:4.8 mm

Kerf width measurement Optical microscope, 0.5�m accuracyScanning electron microscope JEOL JSM-5300

M. Kantha Babu, O.V. Krishnaiah Chetty / Wear 254 (2003) 763–773 765

Fig. 2. A typical cut surface.

Table 2Constant process parameters

Parameter Description

Abrasive material Garnet (origin: southern India)Abrasive particle shape Angular (random)Primary nozzle diameter (mm) 0.25, sapphireSecondary nozzle diameter (mm) 0.8, carbideSecondary nozzle length (mm) 70Standoff distance (mm) 3Jet impact angle (◦) 90Workpiece material Aluminium 6063 T6Pressure (MPa) 225Traverse rate (mm/min) 50Abrasive flow rate (g/s) 1.5

In this type the jet is formed by accelerating abrasive par-ticles through contact with a high velocity water jet. Thewater jet is formed in an orifice on top of the head, whilethe abrasives enter the head through a separate entry. Themixing of abrasives, water jet, and air take place in a mix-ing chamber, and the acceleration process occurs in an ac-celeration tube. The particles leave the nozzle at velocitiesof several hundred meters per second. A large number ofabrasive particles impinge on target and cut the material[6].The process parameters kept constant are shown inTable 2.The details of abrasive test sample containing particles of

Table 3Details of abrasive samples

Abrasive sample Percentage of abrasive mesh designation (particle size, mm) AFS no. Averageparticlesize (mm)#44

(0.355–0.400)#52(0.315–0.355)

#60(0.250–0.315)

#72(0.200–0.250)

#80(0.180–0.200)

#100(0.160–0.180)

#120(0.125–0.160)

Test sample 20 20 20 20 20 – – 52.8 0.282Mesh size 80 8.3 29.1 36 1.1 23.7 1.4 0.4 53.8 0.281

five different mesh sizes and the commercial grade abrasiveof mesh size 80 are shown inTable 3.

A trapezoidal workpiece has been cut and the depth of ma-chining (d = ABsin 25◦) is determined as shown inFig. 1.Each combination of parameters can achieve certain depthof cut, indicated to the operator by splashing of jet. Thelength of cut over the test runs is therefore, a variable (inthis work it depends on the conditions of the abrasives; freshabrasives are expected to cut longer than recycled abrasives).The top and bottom kerf widths (width of the cuts) are mea-sured at three locations on the cut length, viz, at the start ofcut, middle and at the end of cut and then averaged (Figs. 1and 2). The kerf taper (ratio of top kerf width to bottom kerfwidth) is computed. In an AWJM cut surface, the upper sec-tion consists of smooth cutting zone (SCZ) characterised byroughness, while the lower section consists of rough cuttingzone (RCZ) characterised by waviness (Fig. 2). Therefore inthis experimentation work, the middle region is selected formeasurement and comparison of surface finish. Three mea-surement of surface finish (Ra) in the direction of cut aremade and averaged.

To study the disintegration behaviour of abrasives(through AFS no. and a.p.s.), abrasive particles have beencollected at the exit of the focusing nozzle, and also af-ter cutting. Collection is done through a special catcher,


consisting of a cylindrical drum with a screening cloth.The collected abrasives are cleaned (aluminium debris isdissolved by adding 20% NaOH solution), dried and thensieved. Scanning electron microscope (SEM) is used tostudy the changes in particle size and shape of abrasives atnozzle exit and after cutting aluminium material with allparticles during various stages of recycling.

Automated recycling equipment, screen out particles lessthan 90�m. Researchers[2,13–15]have preferred elimina-tion of finer particles less than 90�m for improved cuttingperformance and repeated use. Therefore the present worksdeals with recycling studies with particles more than 90�msize. In order to understand the behaviour of recycled localabrasives in the presence of finer particles, studies are alsoundertaken with all particles including particles less than90�m size (without screening) for possible reduction in re-cycling costs.

3. Experimental results and discussion

The following subsections detail the results of recyclingstudies with particles more than 90�m size and also withall particles.

3.1. Recycling of abrasive particles with size morethan 90µm

3.1.1. AFS no./average particle sizeTable 4as well asFigs. 3 and 4indicate the influence of

recycling on the AFS no. and a.p.s. of test sample and meshsize 80. The AFS no. and a.p.s. for fresh abrasives and forrecycled ones at nozzle entry, nozzle exit, and after cuttingare shown inTable 4andFigs. 3 and 4. Table 5indicate thedetails of particle size distribution of the abrasives at variousstages. It can be observed that the AFS no. increases withrecycling, both with the test sample and mesh size 80.

The complex process of mixing within the mixing cham-ber and focusing nozzle results in an increase in AFS no.(reduction in the a.p.s.) at the nozzle exit. It can also be ob-served fromTables 4 and 5that tremendous disintegrationoccurs with the fresh abrasives in the mixing chamber andfocusing nozzle, as compared to recycled abrasives. This isto be expected, since fresh abrasives has particles of larger

Table 4Effect of recycling of abrasives on AFS no. and a.p.s. of test sample and mesh size 80 with particles more than 90�m

Fresh abrasives Recycle-I Recycle-II Recycle-III

Test sample Mesh size 80 Test sample Mesh size 80 Test sample Mesh size 80 Test sample Mesh size 80

AFSno.

a.p.s.(mm)

AFSno.

a.p.s.(mm)

AFSno.

a.p.s.(mm)

AFSno.

a.p.s.(mm)

AFSno.

a.p.s.(mm)

AFSno.

a.p.s.(mm)

AFSno.

a.p.s.(mm)

AFSno.

a.p.s.(mm)

Nozzle entry 53 0.282 54 0.281 65 0.200 63 0.200 66 0.171 65 0.192 71 0.168 70 0.176Nozzle exit 94 0.192 87 0.195 111 0.170 101 0.171 114 0.168 105 0.162 115 0.161 114 0.160After cutting 105 0.174 100 0.186 113 0.169 103 0.165 114 0.167 109 0.161 115 0.157 117 0.153

Fig. 3. Effect of recycling of abrasives on AFS no. of (a) test sample and(b) mesh size 80 with more than 90�m particles.

size. During the cutting process further disintegration takesplace and the AFS no. is further increased (a.p.s. further re-duces). Guo et al.[2] observed that larger particles disinte-grate more than smaller particles. The increase in AFS no.(reduction in the a.p.s.) is found to be more with test sampleas compared to mesh size 80. It is because the test sampleabrasives contains more number of larger particles and there-fore higher fragmentation due to inter particle collisions andalso with abrasive/water jet and as well with abrasive/targetcollisions. The same phenomenon has been observed withthe recycled particles at every cycle.

With the test sample (Fig. 3a and b) it is found that theincrease in AFS no. of recycled particles before and aftercutting is marginal, while with mesh size 80 this increaseis significant. This may be attributed to the particle size


Tabl

e5

Dis

trib

utio

nof

all

part

icle

size

sof

test

sam

ple

and

mes

hsi

ze80

atva

rious

stag

es

Abr

asiv

esa

mpl

eP

erce

ntag

eof

abra

sive

reta

ined

onm

esh

desi

gnat

ion

(par

ticle

size

,m

m)

AF

Sno

.A

vera

gepa

rtic

lesi

ze(m

m)

#44

(0.3

55–0

.400

)#5

2(0

.315

–0.3

55)

#60

(0.2

50–0

.315

)#7

2(0

.200

–0.2

50)

#80

(0.1

80–0

.200

)#1

00(0

.160

–0.1

80)

#120

(0.1

25–0

.160

)#1

70(0

.09–

0.16

0)#2

40(0

.063

–0.0

9)P

an

Test

sam

ple

Fre

shab

rasi

ves

2020

2020

20–

––

––

52.8

0.28

2A

fter

Icu

t1.

53.

211

.310

.97.

420

.414

11.9

109.

410

4.8

0.17

4R

ecyc

le-I

0.9

0.7

5.7

10.3

5.3

17.6

1914

.49.

416

.712

0.9

0.15

7R

ecyc

le-I

I0.

70.

55.

51.

316

.417

.418

.314

.311

.514

.112

2.6

0.15

2R

ecyc

le-I

II0

02.

49.

59.

217

.321

.717

.312

.510

.212

4.9

0.14

7

Mes

hsi

ze80

Fre

shab

rasi

ves

8.3

29.1

361.

123

.71.

40.

4–

––

53.8

0.28

1A

fter

Icu

t0.

21.

613

.824

10.4

13.1

11.5

8.6

511

.899

.50.

186

Rec

ycle

-I0.

10.

57.

319

.27.

216

.916

11.6

7.5

13.7

110.

70.

167

Rec

ycle

-II

00.

33.

217

.67.

420

.417

.911

.88.

113

.311

2.8

0.16

0R

ecyc

le-I

II0

0.2

3.4

10.1

7.6

17.2

27.5

14.3

7.1

12.7

115

0.15

3

Fig. 4. Effect of recycling of abrasives on a.p.s. of (a) test sample and(b) mesh size 80 with more than 90�m particles.

distribution and presence of larger size particles in the testsample. This is also influenced by the removal of finer sizeparticles. The results of the AFS nos. and the a.p.s. (Table 4)indicated that the test sample has superior recycling capacitythan mesh size 80, when the particles less than 90�m areremoved. This further increases recycling capabilities of theabrasives.

3.1.2. Depth of cutFig. 5 indicates the effect on the depth of cut for both of

test sample and mesh size 80. Abrasive particles disintegrate

Fig. 5. Effect of recycling of abrasives on depth of cut of test sampleand mesh size 80 with more than 90�m particles.


during cutting. Recycling leads to further disintegration. Therole of finer abrasives in reduction of cutting is well estab-lished[2]. Hence recycling leads to decreased depth of cut.With the test sample the percentage reduction in depth of cutwith first recycling as compared to fresh abrasives is foundto be 18% and with mesh size 80 it is found to be 22%. Withtest sample, reduction in depth of cut due to further recy-cling is found to be from 0.5 to 3%, while with mesh size80 it is 3–4%. The performance of the test sample (Fig. 5)indicates that an increase of 12–20% in depth of cut can beachieved with the test sample as compared to mesh size 80.This indicates superior performance of test sample and maybe attributed to the presence of larger size particles in thefresh sample (Tables 4 and 5). Thus particle size distributionplays a key role in improving the cutting efficiency.

3.1.3. Kerf width and kerf taperAverage of three measurements of kerf parameters (Figs. 1

and 2) have been recorded.Fig. 6a indicates the influenceof recycling of test sample on top kerf width, bottom kerfwidth, and kerf taper. After the first recycling, the kerf pa-rameters have reduced considerably. This can be attributedto the availability of larger particles with the fresh abrasives.On further recycling, it is found that there is a consider-able reduction in top kerf width as compared to bottom kerfwidth. The decrease in kerf widths (top and bottom) is due to

Fig. 6. Effect of recycling of abrasives on kerf parameters of (a) testsample and (b) mesh size 80 with more than 90�m particles.

Fig. 7. Effect of recycling of abrasives on surface finish of test sampleand mesh size 80 with more than 90�m particles.

increase in the AFS no. (decreased a.p.s.) and hence reducedcapability to cut. The reduction in kerf taper is also observedwith further recycling. Reductions in kerf taper obtained withrecycled abrasives are advantageous in machining since par-allelism of a cut surface increases, leading to quality cuts.

Fig. 6b indicates the influence of recycling of mesh size80 on kerf parameters. Though observations similar to testsample have been made (both with the top and bottom kerfwidth), the kerf widths decreases cycle after cycle, the topkerf width indicates lower values for mesh size 80 than forthe test sample. This is due to smaller size abrasives presentin the mesh size 80. However the bottom kerf width and thekerf taper for mesh size 80 are more than those obtainedwith the test sample. This supports the fact that particle sizedistribution influences these parameters.

3.1.4. Surface finishThe surface finish (Ra) at the middle section of the work-

piece is measured by Perthometer at three places in thedirection of cut and the average is recorded (Fig. 2). Fig. 7shows the influences of recycling on surface finish,Ra,obtained with the test sample and with mesh size 80. Thesuperior performance of test sample results in increased sur-face finish with recycling when compared to mesh size 80 inevery cycle. The improvement in surface finish is attributedto increase in AFS no. of abrasive particles (reduction ina.p.s.) (Tables 4 and 5). Though the AFS no. of mesh size 80also increases with recycling, it is less than that for the testsample (Tables 4 and 5), hence the surface finish is inferiorto that of the test sample. Therefore, the particle size distri-butions seem to play a role in controlling the surface finish.

3.2. Recycling studies with all particles

The following subsections detail the results of recyclingstudies with all particles up to three cycles. The abrasivescould be reused three times, and could not be continued dueto erratic and discontinuous cutting. Due to disintegration ofabrasives with reuse, the abrasive particles become finer andfiner, and as a result blockage of the flow channel was noticed


Fig. 8. Effect of recycling of abrasives on AFS no. of (a) test sample and(b) mesh size 80 with all particles.

and the cutting has been erratic. Hence further recycling hasbeen discontinued.

3.2.1. AFS no./average particle sizeTable 6as well asFigs. 8 and 9indicate the details of AFS

nos. and a.p.s. of test sample and mesh size 80. The AFS no.and a.p.s. for fresh abrasives and for recycled ones at nozzleentry, nozzle exit, and after cutting are shown inTable 6,andFigs. 8 and 9. Table 5indicate the details of particle sizedistribution of the abrasives of test sample and mesh size 80at various stages of recycling (with fresh abrasive, after I cut,recycle-I, recycle-II and recycle-III). These results indicatethat the increase in AFS no. (reduction in a.p.s.) in everystages of recycling. The increase in AFS no. resulted in veryfine particles and blocked the flow channel.

Table 6Effect of recycling of abrasives on AFS no. and a.p.s. of test sample and mesh size 80 with all particles

Fresh abrasives Recycle-I Recycle-II Recycle-III

Test sample Mesh size 80 Test sample Mesh size 80 Test sample Mesh size 80 Test sample Mesh size 80

AFSno.

a.p.s.(mm)

AFSno.

a.p.s.(mm)

AFSno.

a.p.s.(mm)

AFSno.

a.p.s.(mm)

AFSno.

a.p.s.(mm)

AFSno.

a.p.s.(mm)

AFSno.

a.p.s.(mm)

AFSno.

a.p.s.(mm)

Nozzle entry 53 0.282 54 0.281 105 0.174 100 0.186 121 0.157 111 0.167 123 0.152 113 0.160Nozzle exit 94 0.192 87 0.195 109 0.158 106 0.174 122 0.155 112 0.166 124 0.150 114 0.159After cutting 105 0.174 100 0.186 121 0.157 111 0.167 123 0.152 113 0.160 125 0.147 115 0.153

Fig. 9. Effect of recycling of abrasives on a.p.s. of (a) test sample and(b) mesh size 80 with all particles.

Fig. 10shows the SEM photographs of abrasive test sam-ple and mesh size 80 at nozzle entry, nozzle exit and aftercutting. It can be generally observed that the larger parti-cles when fractured are likely to yield sharp edged prod-ucts. Finer particles that are unable to fracture have roundededges in the process of machining. These photographs aretypical of the process and indicate process complexity.

3.2.2. Depth of cutFig. 11 shows the effect of recycling, wherein with re-

peated abrasive use (both with the test sample as well asmesh size 80) the depth of cut reduces. Abrasive particlesdisintegrate (leading to increase in AFS no.) during mixingand cutting processes. With the test sample, the percentagereduction in depth of cut with first recycling is found to be22% and with mesh size 80, it is 26%. The reduction in


Fig. 10. SEM photographs.


Fig. 10. (Continued).

depth of cut due to further recycling is found to range from3.9 to 5.5% with test sample, while in the case of mesh size80 it is 3–3.9%.Fig. 11indicates that an increase of 12–16%in depth of cut is achieved with the test sample as com-pared to mesh size 80. This indicates superior performanceof test sample and may be attributed to the presence of largersize particles in it. However the depth of cut achieved withremoval of finer particles (less than 90�m) is marginallyhigher (Fig. 5) than that of all particles.

Fig. 11. Effect of recycling of abrasives on depth of cut of test sampleand mesh size 80 with all particles.

3.2.3. Kerf width and kerf taperAverage of three measurements of kerf parameters have

been recorded.Fig. 12a indicates the influence of recyclingon top kerf width, bottom kerf width, and kerf taper achievedwith the test sample. It can be observed that the top kerfwidth as well as bottom kerf width achieved with recycledabrasives is lower than those with fresh abrasives. This is dueto the increase in the AFS no. of recycled abrasives as com-pared to fresh abrasives. Similar behaviour is also observedin the recycling studies with particles more than 90�m.However the results obtained with all particles (Fig. 12a),indicate lower values than that of recycling of abrasives hav-ing particles, more than 90�m particles (Fig. 6a). It mayalso be observed that the continuous recycling of the testsample results in decrease of top kerf width, bottom kerfwidth, while kerf taper decreases and then increases.

Fig. 12b indicates the influence of recycling on kerf pa-rameters achieved with mesh size 80. Though observationssimilar to test sample are made with regard to the top andbottom kerf width, the top kerf width is found to be smallerthan that with the test sample. This is due to the presence oflarger sized particles in the test sample. However the bottomkerf width is larger than that of the test sample. The kerftaper is found to increase initially and then decrease. Thejet instability at the bottom cut surface is responsible for an


Fig. 12. Effect of recycling of abrasives on kerf parameters of (a) testsample and (b) mesh size 80 with all particles.

increase in bottom kerf width and could influence the kerftaper. The variations observed in kerf taper confirm the jetfluctuations and may be attributed to the particle size distri-bution. It is because the final penetration process controlledby erosion wear at larger angles of attack is associated withan upward deflection of the jet, increasing the local rate ofchange of momentum[6].

3.2.4. Surface finishFig. 13indicates the influence of recycling on surface fin-

ish (Ra), both with the test sample and mesh size 80. The

Fig. 13. Effect of recycling of abrasives on surface finish of test sampleand mesh size 80 with all particles.

test sample has resulted in decreased surface finish with firstand second recycling and remains unaltered with third recy-cling. The reduction in finish can be attributed to increasein the AFS no. of finer particles of abrasives. It is also ob-served that the performance of mesh size 80 is more fluc-tuating than the test sample. The mesh size 80 is found toyield higher surface finish with fresh abrasives as well as re-cycled abrasives. Though the AFS no. of mesh size 80 alsoincreases with recycling (Tables 4 and 5), the surface finishis found to fluctuate widely. Hence the particle size distri-bution seems to play a role in controlling the surface finish.This indicates a superior performance of the test sample ascompared to mesh size 80.

4. Reuse of abrasives

Tests have been carried out to estimate the amount of reuseof local abrasives of test sample and mesh size 80, whenthe limit for the reusable size is 90�m. Fig. 14a shows therecycling capacity of test sample after every use. It indicatesthat 81% of abrasives can be reused after the first cut, 49%after the second cut, 26% after the third cut, and 15% afterthe fourth cut. This result indicates that test sample of localabrasives is found to be having superior recycling capacitythan the 60% reported by Guo et al.[2]. Fig. 14b shows the

Fig. 14. Recycling capacity of local garnet abrasives with (a) test sampleand (b) mesh size 80 with more than 90�m particles.


recycling capacity of mesh size 80. It indicates that 83% oflocal abrasives can be reused after the first cut, 55% afterthe second cut, and 31% after the third cut, 13% after thefourth cut.

5. Summary and conclusions

This paper reports the findings of research on recyclingof garnet abrasives available in southern India. Tests con-ducted on aluminium using optimised abrasive test sample,indicate improved performance of the abrasives comparedto commercial abrasive with mesh size 80. The results aresummarised as follows:

• Particle size distribution, if controlled will yield improvedperformance of fresh as well as recycled abrasives. Thetest sample showed advantages in cutting as well as recy-cling. These are analysed using studies on AFS no. anda.p.s. along with SEM photographs.

• Fragmentation is more pronounced in the mixing chamberand focussing nozzle than after cutting and it is higherwith fresh abrasives than recycled abrasives.

• Recycling if continued beyond three cycles, discontinuouscutting will result due to blockage of the flow channelwith finer abrasive particles.

• Depth of cut is higher by 12–20% with test sample withparticles more than 90�m than mesh size 80.

• Test sample with particles greater than 90�m performsbetter compared to when all particles are used. Also itperforms better compared to mesh size 80.

• Improved surface finish is obtained with test samplethan mesh size 80. However the surface finish decreaseswhen particles less than 90�m are removed (both withtest sample as well as mesh size 80) compared to allparticles.

• Recycled abrasives cause reduction in kerf taper. It is ad-vantageous in machining because of the improvement inparallelism of cut surfaces.

• The reusability of abrasives of test sample with more than90�m will be 81, 49, 26 and 15% after the first, second,third, and fourth cut, respectively.

Acknowledgements

The authors express their sincere thanks to Science andEngineering Research Council, Department of Science andTechnology, Government of India, for the financial support

for the equipment. They also acknowledge the financial as-sistance for research interactions with German counterpartsunder the DST-DAAD project based personnel exchangeprogram 1999.

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WJM by Dr.kantha Babu

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