Maintenance policies - Preventive maintenance

1. UNIT - II
MAINTENANCE POLICIES
PREVENTIVE MAINTENANCE
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2. 2
Maintenance Policies
Reliable plant capacity may be defined as an investment
in maintenance which helps in producing a profitable product
and makes a company cost competitive.
In general a company would prefer to have machines
that will run/perform well without any human intervention.
When any new machine is to be installed, it is needed to have
an intellectual group (Engineering and Construction) to work
in team, which is the first step in maintenance effectiveness.
The second step is to be proactive maintenance, once the
machine is installed and operating.

3. 3
Basically there are two types of maintenance tasks. They are
i) Break Down Maintenance
ii) Planned Maintenance
Planned maintenance may further be classified into
(a) Preventive Maintenance
(b) Corrective Maintenance
(c) Predictive Maintenance
(d) Condition Based Maintenance
(e) Reliability Centered Maintenance
TYPES OF MAINTENANCE TASKS

4. 4
Classification Of Maintenance Approach

5. 5
BREAK DOWN MAINTENANCE (OR)
REACTIVE MAINTENANCE
In this category/program, less attention is given to the operating condition of critical
machinery, equipment or system. Here the equipment is allowed to function! operate till
no failure occurs i.e. no maintenance wo rk is carried o ut in advance to
prevent the failure. As long as the equipment is functioning at a minimum
acceptable level, it is
assumed to be effective. This means the people wait till the equipment fails and repair.
This approach of maintenance is ineffective and extremely expensive. The following
factors contribute to high maintenance costs.
i) Poor planning
ii) Incomplete repair
LIMITATION
a) Most repairs are poorly planned due to time constraint caused by reduction
and plant management. This will cost three to four times than the same repair when it
is well planned.
b) This approach focus only on repair or the symptoms of failure and not on
the root cause of failure. This results only in increase in the frequency of repair and
correspondingly the maintenance costs.

6. 6
For example when a bearing fails, it leads to production stop. By this approach only the
bearing will be replaced with a new one, but no attempt will be made to study the cause
of failure or to prevent a recurrence of this failure. This may seriously affect the reliability
of the system.
Breakdown of an equipment or machine or station in a system will have a significant
effect on the production cost, quality and schedules. For each break down, one or more
operations that are to be performed by that particular machine/equipment are idled,
which in turn delays the completion time of the job. Meanwhile, parts waiting for this
equipment / machine are to be diverted and assigned to other competing machines.
Because of this the cost of manufacturing goes up.

7. 7
CORRECTIVE MAINTENANCE
Corrective Maintenance is the program focused on regular planned tasks that will
maintain all critical machinery and system in optimum operating conditions. It is
proactive approach towards maintenance management. The main objective of this
programme
(i) Eliminate breakdowns
(ii) Eliminate deviations from optimum operating conditions.
(iii) Eliminate unnecessary repairs.
(iv) Optimize all critical plant systems.
As per this program, all the repairs are well planned and implemented by properly
trained people and the equipment or system is verified and returned to service.
Prerequisites of Corrective Maintenance
(i) Existence of trained full time maintenance planners for accurate identification of root
cause of all incipient problems.
(ii) Properly trained craftsmen with necessary skill to complete the repair of each
incipient problem.
(iii) Standard maintenance procedure for recurring repairs and maintenance task.
(iv) Allowing sufficient time to maintenance amidst tight production schedules and
management constraints.
(v) A thorough verification process to ensure the completion of repair.

8. 8
Preventive Maintenance
It is a maintenance program which is committed to the elimination or
prevention of corrective and break down maintenance. A comprehensive
preventive maintenance program involves periodical evaluation of
critical equipment, machinery to detect problem and schedule
maintenance task to avoid degradation in operating conditions. It is
designed for day-to-day maintenance like cleaning, inspection,
lubricating, retightening etc. to retain the healthy condition of
equipments.
Benefits of Preventive Maintenance
In general the cost incurred towards breakdown maintenance is Usually higher than the
cost incurred on preventive maintenance.
a) It maintains the equipment in good condition to preventing them from bigger
problems.
b) Prolongs the effective life of the equipments.
c) Detects the problem at earlier stages.
d) Minimizes/eliminates the rework/scrap and helps in reducing the process variability.
e) Significantly reduces unplanned downtime.

9. 9
PREDICTIVE MAINTENANCE
Predictive maintenance is a management technique that
uses regular evaluation of the actual operating conditions of plant equipment,
production systems and plant management functions to optimize total plant
operation. It is not a solution for all the factors that limit total plant performance.
Predictive Maintenance as regard to total plant management can
provide timely actual data that states the operating conditions, critical production
systems and the effectiveness of critical plant function such as purchasing,
engineering and production.
Predictive Maintenance as regard to Production Management is a
useful and an invaluable management tool. It supplies the necessary information
which helps to improve/increase
(i) the production capacity
(ii) product quality
(iii) overall effectiveness of production function
Benefits of Predictive Maintenance
i) Reduced breakdown losses
ii) Reduction of Quality defects
iii) Increased net operating profit
iv) Reduced maintenance cost

10. 10
CONDITION BASED MAINTENANCE
TECHNIQUES
a) Vibration Monitoring- determines the actual
condition of equipments/machines by studying the noise or
vibration produced during functioning.
b) Thermography - determines the condition of plant
machinery, systems etc. by studying the emission of infra red
energy ie . temperature.
c) Tribology - determines the dynamic condition of
bearing Lubrication, rotor support structure of machinery etc. by
adopting anyone of the techniques like lubricating oil analysis,
Spectrographic analysis, ferrography and wear particle analysis.
d) Electrical Motor Analysis- determines the problem
within motors and other electrical equipments.
e) Visual inspection- determines the conditions of
working elements visually based on the experience.

11. LUBRICATION
• Lubrication involves adding a substance
between solid surfaces that are moving against each
other in order to reduce friction and wear.
OBJECTIVES OF LUBRICATION
 To reduce the oxidation and rust formation
 To provide insulation in transformer application
Transmit mechanical power in hydro fluid power
systems
 Seal against dust, dirt and water
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12. PURPOSE OF LUBRICATION
 To prevent wear and premature fatigue by forming the
lubrication film on the surface of load transferring parts to
prevent contacts between metals.
 To enhance the favorable driving characteristics, such as low
noise or friction.
 To prevent overheating of bearings and to prevent lubricant s
own deterioration by radiating the generated heat to outside. It
works particularly well if the circulation lubrication method is
adopted.
 To prevent foreign material penetration, rust, and corrosion.
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13. LUBRICANTS
Any material used to reduce friction between
wearing surfaces with high coefficient of friction
by establishing low viscous film are called
lubricants.
Types of lubricants
Liquid
Solid
Gaseous form
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14. METHODS OF LUBRICATIONS
Hydrostatic lubrication
Hydrodynamic or fluid film lubrication
Boundary lubrication
Elasto hydrodynamic lubrication (EHD)
Extreme pressure (EP) lubrication
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15. HYDROSTATIC LUBRICATION
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16. HYDRODYNAMIC OR FLUID
FILM LUBRICATION
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17. BOUNDARY LUBRICATION
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18. ELASTO HYDRODYNAMIC LUBRICATION
(EHD)
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19. EXTREME PRESSURE (EP) LUBRICATION
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20. AUTOMATIC LUBRICATION
SYSTEM
An automatic lubrication system (ALS), often
referred to as a centralized lubrication system,
is a system that delivers controlled amounts
of lubricant to multiple locations on a machine
while the machine is operating. Even though
these systems are usually fully automated, a
system that requires a manual pump or button
activation is still identified as a centralized
lubrication system.
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21. TYPES OF AUTOMATIC
LUBRICATION SYSTEM
Single Line Parallel systems
Dual Line Parallel systems
Single Line Progressive systems (or Series
Progressive)
Mist Lubrication systems
Multi port direct lubricators
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22. SINGLE LINE PARALLEL SYSTEMS
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23. DUAL LINE PARALLEL SYSTEMS
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24. SINGLE LINE PROGRESSIVE SYSTEMS
(OR SERIES PROGRESSIVE)
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25. MIST LUBRICATION SYSTEMS
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26. MULTI PORT DIRECT LUBRICATORS
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