MAINTENANCE PHILOSOPHIES
There are three basic maintenance philosophies:
1. Breakdown or run-to-failure maintenance
2. Preventive or time-based maintenance
3. Predictive or condition-based maintenance
1. Breakdown or Run-to-Failure Maintenance
The basic principle of this maintenance philosophy is to allow the machinery to operate or run until failure occurs. The corrective action is to repair or replace the damaged machinery part. It is very obvious that this maintenance technique is not suitable for critical machine. This maintenance philosophy has its advantages and disadvantages.
Breakdown maintenance has two advantages. The first advantage is that it does not need periodic maintenance activity. In this technique, corrective action will be done after the machine fails. Thus, the maintenance cost for this philosophy is low. It has been discussed in the previous paragraph that the corrective action is to repair or replace the damaged part of the machine which is not critical for production process. So, the second advantage is it does not interrupt the production process.
On the other side, this maintenance philosophy has some disadvantages. The first disadvantage is it can cause the production process stopped if it is applied to the critical machine. The second disadvantage is people in industry tend to increase the number of spare parts and this condition will lead industry to the increase of spare part procurement cost. In addition for the two previous disadvantages, the late corrective action can cause another failure.
From the previous explanation, it can be concluded that breakdown maintenance philosophy has big risk to be applied in industry. Because of that, people in industry prefers to use preventive and predictive maintenance.
2. Preventive or Time-Based Maintenance
This maintenance philosophy is suitable for critical machine. In this philosophy, overhaul is done at certain time which is scheduled before. Similar to the breakdown maintenance, preventive maintenance has advantages and disadvantages.
The first advantage of this method is it lengthens the machinery lifetime. By applying scheduled inspection, machinery fault can be avoided and this condition makes the machinery lifetime becomes longer. The second advantage is the number of spare parts can be reduced and the procurement cost is lower than the cost in the previous philosophy. This advantage makes preventive maintenance is preferable to breakdown maintenance.
Preventive maintenance also has several disadvantages. The first disadvantage is unnecessary overhaul can happen. Unnecessary overhaul means corrective action which is done when there is no machinery fault exists. This overhaul is wasteful and can trigger another machinery fault. In addition, the second disadvantage is failure can occur because of imperfect reparation.
3. Predictive or Condition-Based Maintenance
Predictive maintenance is maintenance method which is based on actual machinery condition. This method has several characteristics. The first characteristic is predictive maintenance replaces scheduled overhaul with periodic machinery condition based monitoring activity. Another characteristic is overhaul is done if the machine diagnostic process shows dangerous result. Similar to the two previous method, predictive maintenance has advantages and disadvantages too.
The first advantage is by applying this maintenance method, machinery fault can be detected earlier and failure can be avoided. In addition, the second advantage is predictive maintenance reduces number of unnecessary overhaul. Thus, it can reduce the maintenance cost and lengthen the machine operational time.
On the other hand, this method has also disadvantages. The first disadvantage is this method need early investment related to machinery diagnostic tools and equipments. The last disadvantage is industrial training is needed for employee who takes a part in this predictive activity. Thus the factory must spend some money for this training cost.
