Maintenance

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MAINTENANCE

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Introduction to maintenance

Maintenance and reliability is important Maintenance and product quality Maintenance and productivity Maintenance and safety Maintenance and supply chain, JIT Failure cause disruption, waste,

accident, inconvenience and expensive Machine and product failure can have

effect on company’s operation and profitability

Losses due to breakdown

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Failure

Failure – inability to produce work in appropriate manner

Equipment / machine failure on production floor – worn out bearing, pump, pressure leaks, broken shaft, overheated machine etc.

Equipment failure in office – failure of power supply, air-conditioned system, computer network, photocopy machine

Vehicle failure – brake, transmission, engine, cooling system

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Maintenance in Service Industry

Hospital Restaurants Transport companies Banks Hotels and resorts Shopping malls / retail Gas station

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Maintenance in Manufacturing Companies

Electronic Automotive Petrochemicals Refinery Furniture Ceramics Food and beverages

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Maintenance

All actions necessary for retaining an item, or restoring to it, a serviceable condition, include servicing, repair, modification, overhaul, inspection and condition verification

Increase availability of a system Keep system’s equipment in working

order

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Question?

Why do we need maintenance? What are the costs of doing

maintenance? What are the costs of not doing

maintenance? What are the benefits of

maintenance? How can maintenance increase

profitability of company?

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Purpose of Maintenance

Attempt to maximize performance of production equipment efficiently and regularly

Prevent breakdown or failures Minimize production loss from

failures Increase reliability of the operating

systems

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Principle Objectives in Maintenance

To achieve product quality and customer satisfaction through adjusted and serviced equipment

Maximize useful life of equipment Keep equipment safe and prevent

safety hazards Minimize frequency and severity of

interruptions Maximize production capacity –

through high utilization of facility

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Must be consistent with the goals of production (cost, quality, delivery, safety)

Must be comprehensive and include specific responsibilities

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Problems in Maintenance

Lack of management attention to maintenance

Little participation by accounting in analyzing and reporting costs

Difficulties in applying quantitative analysis

Difficulties in obtaining time and cost estimates for maintenance works

Difficulties in measuring performance

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Maintenance Costs

Cost to replace or repair Losses of output Delayed shipment Scrap and rework

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Reduces ReducesMaintenance Policy Frequency

SeverityEmphasize preventive maintenance X XProvide extra machines XReplace machine parts early XInvolve operators in maintenance X XOverdesign machines XDesign machines for maintainability XEnhance maint. dept.’s capability X XIncrease spare parts supply XIncrease standby machines XIncrease in-process inventories X

Maintenance Policies that ReduceFrequency and Severity of Malfunctions

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Types of Maintenance

Maintenance may be classified into four categories:

(some authors prefer three categories- scheduled and preventive maintenances are merged)

Corrective or Breakdown maintenance

Scheduled maintenance Preventive maintenance Predictive (Condition-based) maintenance

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1. Corrective or Breakdown Maintenance

Corrective or Breakdown maintenance implies that repairs are made after the equipment is failed and can not perform its normal function anymore

The unscheduled maintenance or repair to return items/equipment to a defined state and carried out because maintenance persons or users perceived deficiencies or failures

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Quite justified in small factories where: Down times are non-critical and

repair costs are less than other type of maintenance

Financial justification for scheduling are not felt

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Disadvantages of Corrective Maintenance

Breakdown generally occurs inappropriate times leading to poor and hurried maintenance

Excessive delay in production & reduces output

Faster plant deterioration Increases chances of accidents and less

safety for both workers and machines More spoilt materials Direct loss of profit Can not be employed for equipments

regulated by statutory provisions e.g. cranes, lift and hoists etc

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Repair time include

1. Preparation time2. Fault location time3. Spare item obtainment time4. Fault correction time5. Adjustment and calibration time6. Checkout time

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Time reduction in corrective maintenance

1. Efficiency in fault recognition, location, and isolation

2. Effective interchangeability 3. Redundancy4. Effective accessibility5. Human factor considerations

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Types Corrective maintenance

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Types of corrective maintenance

Fail-repair: The failed item is restored to its operational state.

Salvage: This element of corrective maintenance is concerned with disposal of non repairable material and use of salvaged material from non repairable equipment/item in the repair, overhaul, or rebuild programs.

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Rebuild: This is concerned with restoring an item to a standard as close as possible to original state in performance, life expectancy, and appearance. This is achieved through complete disassembly, examination of all components, repair and replacement of worn/unserviceable parts as per original specification and manufacturing tolerances, and reassembly and testing to original production guidelines.

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Overhaul: Restoring an item to its total serviceable state as per maintenance serviceability standards, using the “inspect and repair only as appropriate” approach.Servicing: Servicing may be needed because of the corrective maintenance action, for example, engine repair can lead to crankcase refill, welding on, etc. Another example could be that the replacement of an air bottle may require system recharging

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2. Scheduled Maintenance Scheduled maintenance

inspection lubrication repair and overhaul of equipments

If neglected can result in breakdown Generally followed for:

overhauling of machines changing of heavy equipment oils cleaning of water and other tanks

etc.

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3. Preventive Maintenance (PM) Principle – “Prevention is better than

cure” All actions carried out on a planned,

periodic, and specific schedule to keep an item/equipment in stated working condition through the process of checking and reconditioning. These actions are precautionary steps undertaken to forestall or lower the probability of failures or an unacceptable level of degradation in later service, rather than correcting them after they occur

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It locates weak spots of machinery and equipments

It provides them periodic/scheduled inspections and minor repairs to reduce the danger of unanticipated breakdowns

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PM may be described as the care and servicing by individuals involved with maintenance to keep equipment/facilities in satisfactory operational state by providing for systematic inspection, detection, and correction of incipient (beginning to happen or develop) failures either prior to their occurrence or prior to their development into major failure

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Elements of preventive maintenance

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Elements of preventive maintenance

Inspection: Periodically inspecting materials/items to determine their serviceability by comparing their physical, electrical, mechanical, etc., characteristics (as applicable) to expected standards

Servicing: Cleaning, lubricating, charging, preservation, etc., of items/materials periodically to prevent the occurrence of incipient failures

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Calibration: Periodically determining the value of characteristics of an item by comparison to a standard; it consists of the comparison of two instruments, one of which is certified standard with known accuracy, to detect and adjust any discrepancy in the accuracy of the material/parameter being compared to the established standard value

Testing: Periodically testing or checking out to determine serviceability and detect electrical/mechanical-related degradation

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Alignment: Making changes to an item’s specified variable elements for the purpose of achieving optimum performance

Adjustment: Periodically adjusting specified variable elements of material for the purpose of achieving the optimum system performance

Installation: Periodic replacement of limited-life items or the items experiencing time cycle or wear degradation, to maintain the specified system tolerance

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Advantages of PM Advantages:

Reduces break down and thereby down time

Less odd-time repair and reduces over time of crews

Greater safety of workersLower maintenance and repair costsLess stand-by equipments and spare parts

Better product quality and fewer reworks and scraps

Increases plant lifeIncreases chances to get production incentive bonus

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4. Predictive (Condition-based) Maintenance

In predictive maintenance, machinery conditions are periodically monitored and this enables the maintenance crews to take timely actions, such as machine adjustment, repair or overhaul

It makes use of human sense and other sensitive instruments, such asaudio gauge, vibration analyzer, amplitude meter, pressure, temperature and resistance strain gauges etc.

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Unusual sounds coming out of a rotating equipment predicts a trouble

An excessively hot electric cable predicts a trouble

Simple hand touch can point out many unusual equipment conditions and thus predicts a trouble

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Maintenance CostsMaintenance Costs

Maintenance Commitment

Cost

Breakdown Cost

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Maintenance CostsMaintenance Costs

Maintenance Commitment

Cost

PM Cost

Breakdown Cost

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Maintenance CostsMaintenance Costs

Maintenance Commitment

Cost

PM Cost

Breakdown Cost

Total Maintenance Cost

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Maintenance CostsMaintenance Costs

Maintenance Commitment

Cost

PM Cost

Total Maintenance Cost

Breakdown Cost

Optimal