Reduce the frequency and severity of interruptions due to malfunctions
Extend the useful life of equipment
Reduce the total cost of maintenance by substituting PM costs for repair costs
Provide a safe working environment
Improve product quality by keeping equipment in proper adjustment
Tradeoff Between Repairs and PM Annual Cost Degree of Preventive Maintenance Minimum Total Maintenance Cost Preventive Maintenance Cost Breakdown and Repair Cost Total Maintenance Costs Minimum Level of Preventive Maintenance
In design out maintenance, the aim is to minimize the effect of failures and in fact eliminates the cause of maintenance. The equipment with design-out maintenance are so designed that they perform their useful economic life without any maintenance need. This is also called “ Run to Destruction ”.
PROACTIVE MAINTENANCE :- Identify as to What can go wrong. i.e monitor the parameters that can cause failure.
RCM [Reliability Centered maintenance)- the type of maintenance is chosen with reliability of the system in consideration, i.e. system functions, failures relating to those functions and effects of the dominant functional system failures. This strategy in the beginning was applied to critical systems such as aircrafts, nuclear and space applications. At present, this is being extended to critical systems in the plant.
TPM :- Total Productive Maintenance :-TPM, a Japanese concept, involves total participation of all concerned. The aim is to have overall effectiveness of the equipment with participation of all concerned using productive maintenance system.
Following are the major functions of a maintenance department
Maintenance of installed equipment and facilities
Installations of new equipment and facilities
PM tasks – Inspection and lubrication of existing equipment
CM tasks – monitoring of faults and failures using appropriate techniques
Modifications of already installed equipment and facilities
Management of inventory
Supervision of manpower
An effective maintenance system includes the following elements
Get equipment back into operation as quickly as possible.
Control cost of repairs crews.
Control cost of the operation of repair shops.
Control the investment in replacement spare parts.
Control the investment in standby or backup machines.
Perform the appropriate amount of repairs at each malfunction.
How Speedy Should Repairs Be? Cost Speed of Making Repairs 0 Minimum Total Cost of Repairs Cost of Repair Crews & Shops, Spare Parts, and Standby Machines Cost of Interruptions to Production Total Costs of Repairs Slow Fast Cost of repair as a function of MTTR
Breakdowns Trigger Repairs and Corrective Actions
An equipment breakdown should trigger two actions:
Fast repair of the malfunction equipment
Development of a program to eliminate cause of the malfunction and need for such repairs in the future
Modification/redesign of malfunctioning machine
Modification/redesign of part or product being processed
Training of operators to improve machine care
More frequent preventive maintenance/inspection
Advantages of Letting Workers Repair Their Own Machines
Greater variety may make job more satisfying
May be more sensitive to potential malfunctions
Can make minor repairs faster
Can avoid minor repairs by cleaning, lubricating, adjusting and servicing machines
The probability that an item will perform a required function without failure under stated conditions for a stated period of time .
Why Reliability :
When you can measure what you are speaking about and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it with numbers, your knowledge is of a meager and unsatisfactory kind. -- Lord Kelvin, 1883, May 3
A study, in the 80’s, showed that when a customer is satisfied with a product he might tell 8 other people, whereas, a dissatisfied customer will tell 22 people.
Capability: Item’s ability to satisfy functional needs.
Efficiency: Item’s ability to effectively utilized the energy supplied
Quality: Item’s Fitness to a particular purpose
Reliability: The item’s ability to start or continue to operate.
Maintainability: The item’s ability to quickly start following its failure.
Understanding Few Related Key Concepts
System Reliability The main objective of system reliability is the construction of a model (life distribution) that represents the times-to-failure of the entire system based on the life distributions of the components R 1 R 2 R Series System R 2 R 1 R Parallel System- Standby System failure = Failure of any component At least one of the units must succeed for the system to succeed
In modern day business environment where the impetus is placed on reduction of manufacturing cost and improving overall plant efficiency and reliability , thus directly affecting the profitability and customer’s satisfaction.
To know when an equipment is reaching its useful life cycle, the key is not its age but its condition. Plant equipments may be old but most of equipments are continually upgraded and maintained in order to keep up with evolving manufacturing and production requirements. However a few considerations applicable are as follows.
GOVERNMENT LEGISLATIONS :- Externally imposed changes such as those required by Govt. Legislations (Stack Emission, Noise Pollution , Waste Disposal etc) are sometimes the major reason for replacement of equipments /processes.
Example :- Open Hearth Furnaces for Steel Making.
MARKET FORCES :- If the present equipment is not able to produce to the quality standards required by the market , there is no point in producing the goods which can’t be marketed. In such condition replacement of equipment becomes imperative to meet the market demand.
As each organisation looks for ways and means to reduce cost ,and if the present equipment can not meet production requirement in Quantity and Quality , then it needs to be replaced. However before new equipment is bought , detailed study of life-cycle cost and reliability to be done and strategy developed.