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TOTAL PRODUCTIVE MAINTENANCE
7.4.4 SCHEDULED AND MONITORED PREVENTIVE MAINTENANCE
Preventive maintenance can be divided into two basis categories: schedule and
monitored.
7.4.4.1 SCHEDULED MAINTENANCE
Schedule maintenance is the process of periodic overhauls or service of the
equipment. This may be anything from a lubrication routine to a time frame for
replacement of component parts on a piece of equipment; the point is that
maintenance is set to a time period, much the same as service to a car is tied to
mileage. The time may be in hours of operation, number of shifts of operation, or a
given service period in days, weeks, or months. Once the schedule has been set,
periodic checks should be run from time to time to ensure that the times set up are
correct, and that the equipment is not being inspected too frequently or not often
enough.
7.4.4.2 MONITORED MAINTENANCE
Monitored maintenance uses sophisticated testing equipment to help predict when the
equipment components will fail. This testing equipment wear rates for even better
estimations of equipment condition. Such a system allows logical decisions to be made
as to replacement of worn parts without causing lost production hours, for the
equipment can be changed on scheduled repair turns. This helps take the guess work
out of component replacement. Figure 7.3 illustrates how a control limit is set defining
the amount of wear that is acceptable. Once this point is exceeded, the component
should be changed. If it isn’t replaced, then the failure area will be reached resulting
in a breakdown. If changed when the control limit is reached, it can be scheduled so
as not to interfere with production.
As we progress through the preventive maintenance program, notice that all of the
previous types of maintenance have their place in the organisation. The cost of the
equipment, lost production, wasted man hours, and repair times will be weighed
against the cost of preventive maintenance to see what equipment needs it and what
doesn’t.
Any properly designed and operated preventive maintenance program will more than
pay itself. The initial set up and operation will increase the overall cost; but after a
period of time, the maintenance cost will drop off below the original level (see Figure
7.4).
BPLK 82 DMQ 40392
