Introduction to Maintenance 2 Maintenance • Action necessary for retaining an item/restoring it to a serviceable condition which include servicing, repair, modification, inspection and condition verification. • Combination of actions carried out to replace, repair, or modify the components, items, items & units of a plant so that it will continue to operate at specified availability over a specified time. 3 QUESTIONS • • • • • 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? 4 Maintenance Lathe Maintenance Lathe maintenance involves maintenance of • Drive belt • cross slide & compound rest • Adjusting tailstock clamp After 8 hours of work, ▫ Cleanliness of slideway, slideway lubrication After 40 hours of work, ▫ Tightness of screws, inside cabinet dirt oil After 1000 hours of work, ▫ Drive belt wear, refill oil reservoir 5 Maintenance Objective • • • • • To increase availability of a system To maximize performance of production equipment efficiently and regularly To prevent failure/ breakdown To increase reliability of the system To minimize frequency & severity of interruptions 6 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 7 Maintenance in Service Industry • Hospital • Restaurants • Transport companies • Banks • Hotels and resorts • Shopping malls / retail • Gas station Maintenance in Manufacturing Industry • Electronic • Automotive • Petrochemicals • Refinery • Furniture • Ceramics • Food and beverages 8 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 9 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 • 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 10 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. 11 Scheduled Maintenance • Scheduled maintenance is a stitch-in-time procedure and incorporates ▫ 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. 12 Preventive Maintenance (PM) • Principle – “Prevention is better than cure” • Procedure - Stitch-in-time • It ▫ Locates weak spots of machinery and equipments ▫ Provides them periodic/scheduled inspections and minor repairs to reduce the danger of unanticipated breakdowns 13 Candidates for Preventive Maintenance Frequency of Failure Good candidates have more normal distribution with low variability Mean Time Between Failure (MTBF) 14 Advantages of PM • Advantages: ▫Reduces break down and thereby down time ▫Lass odd-time repair and reduces over time of crews ▫Greater safety of workers ▫Lower maintenance and repair costs ▫Less stand-by equipments and spare parts ▫Better product quality and fewer reworks and scraps ▫Increases plant life ▫Increases chances to get production incentive bonus 15 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 as ▫audio gauge, vibration analyzer, amplitude meter, pressure, temperature and resistance strain gauges etc. 16 Predictive Maintenance (Contd.) • 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 17 Maintenance Costs Cost Breakdown Cost Maintenance Commitment 18 Maintenance Costs Cost PM Cost Breakdown Cost Maintenance Commitment 19 Maintenance Costs Cost Total Maintenance Cost PM Cost Breakdown Cost Maintenance Commitment 20 Maintenance Costs Cost Total Maintenance Cost PM Cost Breakdown Cost Optimal Maintenance Commitment 21 Maintenance Strategy • Maintenance Strategy is concerned with identifying the components of the plant which might require maintenance, determining the most appropriate maintenance procedure and then listing the procedures in the form of a schedule for the plant 22 Maintainability Diagrams • Deal with replaceability and repair characteristics • Maintainability diagrams are an aid to determining a maintenance strategy. The diagram includes only those parts that might require maintenance during the life of the unit • Parts are usually classified as ▫ Complex replaceable items: replace & repair ● Ex: Gearbox ▫ Simple replaceable items: replace & discard ● Ex: Drive belt 25 Fixed Time Maintenance (FTM) • Maintenance actions are taken at regular intervals or after a fixed cumulative output, fixed number of cycles of operation, etc. • Actions: Item replacement, repair and major strip-down for inspection • It is effective only when failure mechanism is age related (i.e. item failure predictable) The implication of the above is that FTM is an appropriate procedure for simple items (e.g. air filters) but is usually difficult to justify in the case of complex items (e.g. electric motors) because of the high cost of maintenance 26 Condition based Maintenance (CBM) • Appropriate when the approach to failure is readily detectable by a monitorable parameter • The monitored-parameter can provide information about a single component (e.g. the wear of a brake pad) or provide information that can indicate a change in any number of different components (e.g. vibration from a turbo-generator). 27 Condition based Maintenance (CBM) • Three ways of condition monitoring: (i) Simple inspection (Qualitative checks based on look, listen and feel, Usually cheap and carried out as part of a routine ) (ii) Condition checking (Done routinely and measuring some parameter which is not recorded but is only used for comparison with a control limit, Such checking only has value where there is extensive experience of identical systems) (iii) Trend monitoring (Measurement and graphical plotting of a performance or condition parameter in order to detect gradual departure from a norm) 28 Design out maintenance (DOM) • Aims to eliminate the cause of maintenance rather than minimizing effect of failure • For items of high maintenance cost arising from poor maintenance, poor design 29 Systematic Approach to Establish Maintenance Strategy In order to establish an effective maintenance strategy, a systematic approach is needed that takes into consideration: 1. Understand the characteristics of plant operation. ▫ ▫ ▫ ▫ ▫ Construct a process flow diagram Understand the production policy Rank the units by criticality Identify the maintenance scheduling characteristics Identify the existing maintenance objective and strategy 2. Establish a maintenance plan for each unit 3. Establish a maintenance schedule for the plant 4. Establish the initial policy for spare parts and reconditioning Thanks To all
