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Maintenance Engineering(Ch. E – 405)

Izzat Iqbal CheemaLecturer

Maintenance Engineering (Ch. E – 301)CH 17 (Supp.): Maintenance

Maintenance

All activities that maintain facilities and equipment in good working order so that a system can perform as intended.

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Maintenance

It is consider as a combination of actions carried out in order to replace, repair, service (or modify) the components, or some identifiable grouping of components, of a manufacturing plant so that it will continue to operate to specified availability for specified time.

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Function of Maintenance

The function of maintenance is the control of plant availability.

timeOutageoperationofTime

operationofTimetyAvailabili

)()(

)(

MrepairtotimeMeanMTTFfailuretotimerunningMean

MTTFfailuretotimerunningMeantyAvailabili

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Maintenance Categories

• Buildings and Grounds• Equipment Maintenance

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Reasons for Maintenance

• Avoid production disruptions• Not add to product cost• Maintain high quality• Avoid missed delivery dates• Increase in equipment life• Hazards to employees + environment avoid• Placebo

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Types of Maintenance

1. Breakdown Maintenance2. Preventive Maintenance

Periodic Maintenance Predictive Maintenance

3. Corrective Maintenance4. Maintenance Prevention

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Decision Makers: Trade-off

Total Cost

Preventive Maintenance Cost

Breakdown& Repair Cost

Optimum

Amount of Maintenance

Mai

nten

ance

Cos

t

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Types of Maintenance

• Breakdown Maintenance• Preventive maintenance

oPeriodic maintenance oPredictive maintenance

• Corrective maintenance• Maintenance prevention

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Breakdown Maintenance

It means that people wait until equipment fails and repair it. Such a thing could be used when the equipment failure does not significantly affect the operation or production or generate any significant loss other than repair cost.

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Preventive Maintenance

It is a daily maintenance ( cleaning, inspection, oiling and re-tightening ), design to retain the healthy condition of equipment and prevent failure through the prevention of deterioration, periodic inspection or equipment condition diagnosis, to measure deterioration. It is further divided into periodic maintenance and predictive maintenance. Just like human life is extended by preventive medicine, the equipment service life can be prolonged by doing preventive maintenance.

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a. Predictive Maintenance

This is a method in which the service life of important parts are predicted based on inspection or diagnosis, in order to use the parts to the limit of their service life. Compared to periodic maintenance, predictive maintenance is condition based maintenance. It manages trend values, by measuring and analyzing data about deterioration and employs a surveillance system, designed to monitor conditions through an on-line system.

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b. Periodic Maintenance

Time based maintenance consists of periodically inspecting, servicing and cleaning equipment and replacing parts to prevent sudden failure and process problems.

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Corrective Maintenance

It improves equipment and its components so that preventive maintenance can be carried out reliably. Equipment with design weakness must be redesigned to improve reliability or improving maintainability.

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Maintenance Prevention

It indicates the design of new equipment. Weakness of current machines are sufficiently studied ( on site information leading to failure prevention, easier maintenance and prevents of defects, safety and ease of manufacturing ) and are incorporated before commissioning a new equipment.

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Consequences of Breakdown

1. Production capacity is reduced2. Orders are delayed3. There is no production4. Overhead Continues5. Increasing the cost per unit6. Quality issues7. Safety issues8. Environmental issuesCH 17 (Supp.): Maintenance

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Breakdown Maintenance

It is to deal with the problems after they have taken place.

Reactive Approach

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Preventive Maintenance

It is to deal with the problems through certain programs.

Proactive Approach

Examples:• Lubrication• Adjustment• Cleaning• Inspection and replacement of worn parts

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Decision Makers: Trade-off

Total Cost

Preventive Maintenance Cost

Breakdown& Repair Cost

Optimum

Amount of Maintenance

Mai

nten

ance

Cos

t

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Concepts of Preventive Maintenance

Goal: To reduce the incidence of breakdowns or failures in the plant or equipment to avoid the associated cost.

Costs: Loss of outputs, idle works, schedule disruptions, injuries, damage, products or facilities, repairs.

Periodic: Scheduled according to maintenance personnel and avoid interference with operating hours.

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Scheduling of Preventive Maintenance

• Results; planned inspection• Calendar; passage of time• No. of operating hours

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Example - 1

The frequency of breakdown of a machine per month is shown in the table.Cost of a breakdown = $ 1,000 / month

Cost of preventive maintenance is $1,250 / monthManager should do preventive maintenance, or would it be cheaper to repair the machine when it breaks down?

Number of breakdowns 0 1 2 3

Frequency of occurrence 0.20 0.30 0.40 0.10

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Example – 1 (Solution)

Breakdown cost = 1.40 x 1000 = $ 1,400 / monthSavings = $ 150 / month (Preventive Maintenance)

No. of Breakdowns Frequency of Occurrence Expected No. of Breakdowns

0 0.20 0

1 0.30 0.30

2 0.40 0.80

3 0.10 0.30

1.00 1.40

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Problem - 1

The probability that equipment used in hospital lab will need recalibration is given in the following table;

A service firm is willing to provide maintenance and provide any necessary calibrations for free for a fee of $ 650 per month. Recalibration costs $ 500 per time. Which approach would be most cost effective, recalibration as needed or the service contract?

No. of recalibration 0 1 2 3 4

Probability of occurrence 0.15 0.25 0.30 0.20 0.10

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Predictive Maintenance

It is an attempt to determine when to perform preventive maintenance activities.

Historical Data:Installation, operating hours, dates, types of insurance and types of repairs.

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Approaches used to dealwith breakdowns

1. Standby or backup equipment2. Inventories of spare parts3. Operators based minor repairs4. Repair people

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Replacement

• What is the cost of replacement compared with the cost of continued maintenance?

• Technology change• Forecasts of demand

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Example - 2

The average time before breakdown is normally distributed and has a mean of 3 weeks and a standard deviation of .60 weeks. If breakdown cost averages $1,000 and preventive maintenance costs $250, what is the optimal maintenance interval?

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Example – 2 (Solution)

weeksDSzmeant

DS

meantz

CostBreakdownCosteventive

Costeventive

5.2)60.0(84.03.).(

..

20.01000250

250

Pr

Pr

From Appendix Table – B; z = - 0.84

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Problem - 2The frequency of breakdown of machine that issues lottery tickets is given in the following table. Repairs cost an average of $240. A service firm is willing to provide preventive maintenance under either of two options. #1 is $500 and covers all necessary repairs for free, and #2 is $350 and covers any repairs after the first one, for free, provide any necessary repairs. Which option would have the lowest expected cost, pay for all repairs, service option #1, or service option #2?

No. of breakdowns/month 0 1 2 3 4

Frequency of occurrence 0.10 0.30 0.30 0.20 0.10

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Problem - 3Determine the optimum preventive maintenance frequency for each of the pieces of equipment if breakdown time is normally distributed:

Equipment Average Time (days) between Breakdowns

Standard Deviation

A 201 20 2B 400 30 3C 850 40 4

Equipment Preventive Maintenance Cost ($) Breakdown Cost ($)

A 201 300 2,300

B 400 200 3,500

C 850 530 4,800

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