Analysis of Reliability and Maintenance in Order to Get Rid of Breakdowns and Frequent Stoppages:
A breakdown is a situation in which stress has reached a maximum in intensity. When machinery is designed, it is given adequate safety margin against stress (the power added to mechanical facilities) and the intensity level raised so that the machine will not be damaged quickly when used. The intensity level and functions, however, become lower with time and the machine stops sometimes. Finally, it stops due to a sporadic breakdown. This becomes a frequent stoppage or a breakdown.
Mechanisms which trigger breakdowns and frequent stoppages:
Stress and time are the immediate causes of breakdowns. These trigger the process for a real breakdown, and a breakdown phenomenon occurs.
This relationship can be seen a follows:
Stress : The process in which a breakdowns occurs > Breakdown phenomena
Trash: Blocked filter > Oil cutoff > Metal burns
Shock: Loose bolt > Position slip
Number of times operated: Worn out spring> Spring breaks> Damage occurs
The stress in this chart can be divided into two large categories: operational stress and environmental stress. Operational stress is due to electrical load or mechanical load, and environmental stress is due to temperature, humidity and vibrations etc.
Measures for breakdowns and frequent stoppages:
Considering breakdown measures based on the above relationships, there are three possibilities.
The first is to raise the level of intensity by changing materials, making the materials thicker, or heavier. The second is to lower stress by using 5S activities to take quick action. This is extremely important.
The third is to not lower intensity itself, but to exchange parts which have worn out.
Looking at breakdown measures from the cause:
There are two major reasons why breakdowns and frequent stoppages do not decrease.
Reason1: The operations department is indifferent about daily preventive activities.
Reason 2: Breakdown measures are left to the discretion of the maintenance department.
Unless the operations department and the maintenance department cooperate, breakdown phenomena cannot be grasped accurately, the pursuit of the causes becomes lax, almost all potential defects are over looked, and five mistakes are repeated over and over. These five mistakes are as follows:
(1) Mistake of not making preparation for basic condition – there is no “Seiso” or measures against abnormalities, oil depletion, or loose parts.
(2) Mistake of not considering use conditions for enhancing the correct functions of mechanical facilities and structural parts.
(3) Mistake of making partial improvements and not dealing with degradation.
(4) Mistake of taking measures which leave a weak point in design as it is – taking measures without sufficiently analyzing the breakdown phenomena.
(5) Being concerned only with machinery, jigs, tools, materials, etc., and forgetting to consider how human behavior (functions) ought to be.
Reliability analysis and maintenance analysis:
During which conditions wilh breakdowns and frequent stoppages occur, when will they occur, and how much time will it take to rehabilitate them (difficulty of repairs)? When this is understood steps can be taken before a breakdown or frequent stoppage occurs. The quantitative analysis for this is called reliability analysis and maintenance analysis.
1. Reliability means a nature in which breakdowns do not occur.
2. The gauges of reliability are MTBF (Mean time between failures) and ratio of breakdown frequency.
3. When MTBF is small and ratio of breakdown frequency is large, improvements are necessary.
4. Maintainability represents the ease of maintenance
5. MTTR (Mean time to repair) and breakdown intensity rate are the gauges for measuring.
6. If the MTTR and the breakdown intensity rate are large improvements are necessary.