Preventive Maintenance | Forms | Elements | Objectives

What is Preventive Maintenance?

Preventive maintenance consists of routine actions taken in a planned manner to prevent breakdowns. Lubrication and inspection are the two constituents of preventive maintenance. Lubrication ensures long and safe working of the equipment without mishaps. Inspection facilitates detection of faults in an equipment so that repairs and replacements may be undertaken before the faults assume the proportion and shape of a breakdown.

Preventive Maintenance Activities

Direct and Indirect Activities of Preventive Maintenance

Preventive Maintenance of Plant Services

The preventive maintenance function is sub-divided as

  1. Preventive maintenance of production departments and
  2. Preventive maintenance of plant services.

Preventive maintenance of production departments includes anticipatory inspection and servicing of equipment besides routine maintenance. Preventive maintenance is equally important for the various types of plant services. Though they do not directly contribute to the production like other production departments, they play a key role in the production operations.

The important plant services requiring preventive maintenance are building, power plant, material handling equipment, fleet of transport vehicles, water supply, waste disposal systems, store-room, tool-room, time keeper’s office, fire fighting facilities, etc.

Forms of Preventive Maintenance

A formal preventive maintenance may take four different forms:

a. Time-based preventive maintenance

Refers to conducting maintenance at regular intervals, e.g., every two months, etc. It is easy to monitor time and this form is used when deterioration is likely to be time rather than usage-dependent, or when usage cannot easily be measured.

b. Work-based preventive maintenance

Maintenance performed after a set number of operating hours of volume of work produced, e.g., every 40,000 photocopies in a xerox machine, etc. Usage can be more difficult than time to monitor and some form of ‘auto-counting’ of output should be used, if possible.

c. Opportunity-based preventive maintenance

Repair or replacement takes place when the equipment or system is devoid of work, e.g., during a holiday.

d. Condition-based preventive maintenance

This method often relies unplanned inspection to reveal when maintenance is prudent, e.g., replacement of a brake pad when it has worn to 2mm thickness. This is dependent on monitoring the equipment condition which can be difficult, and impractical if a time-consuming strip-down precedes any examination or inspection. These various forms of maintenance often operate together, overlap or coincide.

For example, time-based and work-based maintenance will coincide if the rate of work is constant; condition-based replacement may occur during a work-in-progress or opportunity-based maintenance activity may be resorted to whenever convenient.

Several other terms which are often used as synonym for preventive maintenance are:

1. Running Maintenance

In running maintenance the preventive maintenance work is carried out while the equipment is in service.

2. Shutdown Maintenance

In shutdown maintenance the preventive maintenance work is carried out when the equipment is out of service.

3. Servicing

In servicing, the minor activities like cleaning, lubrication, etc., are carried out at planned intervals.

4. Scheduled Maintenance

Scheduled maintenance system provides for inspection, overhauling, lubrication, and servicing of certain machines at predetermined dates. For example, overhauling of machines, cleaning of tanks and white washing of buildings are normally done in this manner. This type of maintenance is, therefore, practiced to a certain extent, even in those companies where breakdown maintenance is otherwise a rule.

Pre-determination of dates of commencement of maintenance work ensures comparatively better allocation of manpower, keeping in view the requirements of production and other activities of the maintenance crew. Mere scheduling, however, is not sufficient. It cannot ensure completion of work in time because the nature and details of work required to be done remain unknown. It consequently leads to an increased down-time due to non-availability of requisite skill and materials. For the same reason, allocated manpower may also remain underutilized.

5. Planned Maintenance

Planned maintenance represents an advancement over the above mentioned types of maintenance practices. Briefly stated, planned maintenance visualizes the work contained in a future job, determines the best method to be adopted and skills required for its execution, estimates the time, material and costs involved in assigned jobs and programmes the work to specific time periods on the basis of priority. Planned maintenance also provides for a system of feed back of information for necessary changes in the original plan.

6. Predictive Maintenance

A new type of preventive maintenance known as predictive maintenance is becoming popular. It involves the use of sensitive instruments to predict trouble. Such maintenance helps in determining the need for and time of overhauling.

Elements of Preventive Management

The various elements of a preventive maintenance system in an industry are as follows:

1. An inventory of all the plant and equipment need to be maintained.

2. Categorization of equipment to assess the relative importance and thereby determine the equipment requiring preventive maintenance.

3. A well designed inspection system.

4. A good lubrication system i.e., regular cleaning, greasing and oiling of the moving parts.

5. Maintenance of adequate records and analysis of the same.

6. Planning of maintenance work.

7. Control of maintenance stores and spares.

8. Organization for preventive maintenance work.

9. Replacement of worn-out parts before they fail to operate.

10. Provision of stand-by machines for critical equipment.

Objectives of Preventive Maintenance

Important objectives of preventive maintenance are as follows.

1. To minimize the possibility of unanticipated production interruptions by locating or uncovering any condition which may lead to it.

2. To make plant equipment and machines always available and ready for use.

3. To maintain the value of the equipment and machinery by conducting periodic inspection, repairs, overhauling, etc.

4. To reduce the work content of maintenance jobs.

5. To ensure safety of life and limbs of the workmen.