1. MAINTENANCE
• Maintenance of facilities & equipment in good
working condition is to achieve specified level
of quality & reliability & efficient working.
plant maintenance is an important service
function of an efficient production system. It
helps in manufacturing & increasing the
operational efficiency of plant facilities & thus,
contributes to revenue by reducing the
operating costs & increasing the effectiveness
of production.
2. MAINTENANCE OBJECTIVES
• Maintenance is any activity is designed to keep the resources in good
working condition or restore them to operating status.
• The objective of plant maintenance are:
1. To increase functional reliability of production facilities.
2. To enable product to be achieved through correctly adjusted, serviced &
operated equipment.
3. To maximize the useful life of the equipment.
4. To minimize the total production or operating costs directly attributed to
equipment service & repair.
5. To maximize the production capacity from the given equipment
resources.
6. To enhance the safety of manpower.
3. MAINTENANCE COSTS
• Breakdown of equipment makes the workers & the machines idle resulting in
loss of production, delay in schedules & expensive emergency repairs. These
downtime costs usually exceed the preventive maintenance costs of
inspection, service & scheduled repairs. Beyond this optimal point an
increasingly higher level of preventive maintenance is not economical
justified & is economical to adopt breakdown maintenance policy. The
optimal level of maintenance activity M,is easily identified on a theoretical
basis, to do this the details of the costs associated with breakdown &
preventive maintenance must be known.
Costs associated with maintenance are:
1. Downtime (IDLE TIME COST) cost due to equipment breakdown.
2. Cost of spares or other material used for repairs.
3. Cost of maintenance labour and overheads of maintenance
departments.
4. 4. Losses due to inefficient operations of machines.
5. Capital requirements required for replacement of machines.
Costs
Maintenance costs
5. Benefits & Limitations of Failure Statistics
Benefits:
1. Helps to diagnose failure when they occur.
2. Provides a valuable information regarding the life & reliability of the equipment to the
design engineer.
3. Failure statistics helps to take maintenance policy decisions as to whether to opts for repair
or replacement options.
4. It is important information for spare parts management.
Limitations:
The wear out failure due to:
1. Failure based on inherent quality & reliability characteristics in design,
manufacturing.
2. Manufacturing defects.
3. The chance failure will occur due to operation included failures, damage of
equipments due to improper handling, accidents etc.
6. Failure
Sudden Failure
Anticipate failure
& prepared to take
remedial
measures
Gradual Failure
Preventive
maintenance
based in condition
monitoring
Strategy Strategy
Failure Analysis
8. 1. Planned maintenance: It is an organized maintenance work carried out as per
recorded procedures having control.
2. Breakdown maintenance: It is an emergency based policy in which the plant or
equipment is operated until it fails & then it is brought back into running
condition by repair. The maintenance staff locate any mechanical, electrical or
any other fault to correct it immediately.
The break down maintenance policy may wok good & feasible for small factories
where,
a) There are few types of equipment.
b) Machines are simple & does not require any specialist.
c) Where sudden failure does not cause any serious financial loss.
3. Corrective maintenance: This is an organized maintenance work intended to
restore a failed unit. It includes different types of actions like typical adjustments
to redesign of equipments. It is a one time job & each corrective maintenance
activity undertaken should be completed fully .Each corrective maintenance job
may differ from the other. The emphasis in corrective maintenance is on
obtaining full information of all breakdowns & their causes. Efforts are made to
identify & eliminate the cause by activities such as improving maintenance
practices, changing frequency of maintenance services & improving process
control procedures.
9. 4. Opportunistic maintenance: When an equipment or system is taken down
for maintenance of one or few worn out parts, the opportunity can be
utilized for changing other parts which are wearing out even though they
have not yet failed. This maintenance system is useful for non-monitored
components.
5. Routine maintenance: It is the simplest form of planned maintenance ,which
is very essential. Routine maintenance means carrying out minor
maintenance jobs at regular intervals. It involves minor jobs such as cleaning,
lubrication, inspection & minor adjustments. Routine maintenance needs
very little investment in time & money.
6. Preventive maintenance: Preventive maintenance is a planned maintenance
of plants & equipments in order to prevent or minimize the breakdown.
7. Predictive maintenance: Predictive maintenance as the name implies simply
means predicting the failure before it occurs, identifying the root causes for
those failures symptoms & eliminating those causes before they result in
extensive damage of the equipment.
8. Condition based maintenance: In this method, the condition of the
equipment or some critical parts of the equipment are continuously
monitored using sophisticated monitoring instruments so that the failure
may be predicted well before it occurs & corrective steps are taken to
prevent failure.
10. 9. Design out maintenance: It is a design oriented curative means aimed at
rectifying a design defect originated from improper method of installation or
poor choice of materials etc. It calls for the strong design & maintenance
interface. Design our maintenance aims to eliminate the cause of
maintenance. It is suitable for items of high maintenance cost.
PREVENTIVE MAINTENANCE SYSTEM
The preventive maintenance policy is a system of planned scheduled
maintenance. The basic principal involved in this system is “prevention is
better than care". Preventive maintenance includes :
1. Proper identification of all items, their documentation & coding.
2. Inspection of plant & equipments at regular interval
3. Proper cleaning, lubrication of equipments.
4. To upkeep the machine through minor repairs, major overhauls etc.
5. Failure analysis & planning for their elimination.
Preventive maintenance schedules are normally of two categories:
1. Fixed time maintenance(firm) schedule.
2. Condition based maintenance.
11. PREVENTIVE VERSUS BREAKDOWN MAINTENANCE
Preventive maintenance is the routine inspection & service activities
designed to detect potential failure conditions & make major adjustments
or repairs that will help prevent major operating problems where as,
breakdown maintenance is the emergency repair & it involves higher cost of
facilities & equipments that have been used until they fail to operate.
An effective preventive maintenance program for equipments requires
properly trained personnel, regular inspection & service & should maintain
regular records. It is planned in such a way that it will not disturb the normal
operations, hence no down time cost of equipment. Breakdown
maintenance stops the normal activities & the machine as well as the
operators is rendered ideal till the equipment is brought back to normal
condition of working.
12. CONDITION BASED MAINTENANCE(CBM) SYSTEM
Predictive maintenance is more feasible today because of technology that
available for equipment surveillance & diagnose of problems while the
machines are still operating. The condition of a machine can be monitored
by several means. Sensors may be instaled,or periodic readings may be
taken with portable units to measure vibration or temperature. Vibration
sensors & ultrasonic sensors are used to feed data in to a computer for
analysis. The deviation from the normal vibration pattern are recorded when
the machine is running properly are analyzed to determine where the
problem is developing & when it will become serious. A problem of this type
prevents unplanned downtime that disrupts production schedules.
The objectives of condition- based maintenance are:
To detect the failure before they occurs.
To carry out maintenance only when required.
To reduce the maintenance costs & downtime costs.
• The methodology of C.B.M consists of following steps:
1. Proper identification & location of machines by codification.
2. Selection of critical machine 7 systems.
3. Identifying components.
14. 2. Maintenance planning & scheduling
Once the list of the defect is known & the type of the maintenance is
decide, the next step is to plan & schedule the maintenance jobs in order
to execute the jobs properly & to get the desired results. planning &
scheduling of maintenance jobs are the important components of
maintenance functions.
3. Job planning
Maintenance planning basically deals with answering two questions “What
"jobs to be done & “how” these activities are done.
The various steps in job planning includes-
i. Knowledge about equipment job, available technique & facilities.
ii. Development of the repair plan- preparation of a step by step
procedure which would accomplish the work with the most
economical use of time, manpower & material.
iii. Preparation of list of materials required
iv. Preparation of list special tools & equipments.
v. Estimation of the time required to accomplish the job or work.
vi. Provision of necessary safety devices & safety instructions.
15. Job Manuals
Job manuals are also permanent records about methodology, spares, tools
& facilities etc. for all maintenance jobs, which may have to be done for
the future.
The following steps are generally involved in preparing the job manuals:
i. List of all majors & medium maintenance jobs of the plant are prepared &
they are property coded for identification.
ii. For each coded job, a separate job manual is to be prepared which
includes the following:
– Sequence wise break of the job in to activities with instructions to
carry out those jobs.
– List of tools, tackles, spares & consumables needed to perform the
activity
– List of jigs & fixtures & handling for each activity
– Safety instructions
– Time estimation for the job activities.
iii. Make available the manuals to all the users & update the manuals as
when needed.
16. Job Scheduling
Scheduling of maintenance job basically deals with answering the two
questions “who” & “when” of the job that is who to do the job & when the
job is to be started.
Realistic schedules are the functions of realistic thinking, availability of the
data & records.
The scheduler should obtain knowledge about the following facts before
starting his job.
i. Availability of component manpower-by trade,location,shifts etc.
ii. Availability of equipments ,spares & paper tools where the work is to
be carried out.
iii. Starting data for the job & past schedules & charts.
Scheduling techniques like bar charts & network techniques are used.
Systematic maintenance:
The various elements of systematic maintenance are:
• Codification & Cataloguing.
• Equipment history cards & sheets.
• Instructions manuals & operating manuals.
• Standard operating practices & work instructions.
17. •Maintenance time standards(MTS).
•Maintenance work order & work permit
•Job cards & job cards procedures
•Job execution ,monitoring,feed back & control.
•Maintenance records & documentation.
BASIC MAINTENANCE DECISIONS
1.Centralized versus decentralized maintenance.
2.Contract versus in-house maintenance.
3.Repair versus replacement.
4.Individuals versus group replacement.
5.Standby equipments,
6.Amount of maintenance capacity.
7.Preventive versus predictive maintenance.
18. MAINTENANCE PERFORMANCE EVALUATION
The following criteria can be used for measuring the effectiveness of
maintenance function.
1. Total plant maintenance productivity(TPMP)
TPMP= Plant output in the given period
Total maintenance cost in the given period
2. Down time index = Down time hours 100
Production hours
3. Maintenance cost index = Maintenance cost 100
Capital cost
4. Equipment utilization = Total man hour actually worked on the job
Hours the equipment was available to run
at capacity during evaluation period.
5. Man power efficiency = Total man hour actually worked on the job
Total man hour scheduled for these jobs
