Implementation of Condition Based Maintenance

The procedure for implementation of CBM is detailed in the following steps:

• Listing and numbering all machines, so as to have their identification and location.
• Selecting critical machines. A critical machine is that whose shutdown would cause production losses or dangerous to personnel. This distinction does not depend only on quantity but also on product quality. The degree of criticality of the machine is one of the factors influencing examination frequency.
• Establishing program and methods specifying the parts to be examined.
• Reliability of CBM depends not only on instrument but also mostly on the skill and sense of responsibility of the examiner who is entrusted with a group of machines.
• Establishing for each part of the machine the severity limits of the machine condition parameter (vibration, sound, temperature, contamination, etc.) to be measured.
• Selecting proper examination frequencies. To arrive at the best frequency of examination, we must consider for each machine.

1. Its criticality in the process flow chart.
2. The availability of the standby machines.
3. The standardisation of items.
4. The operating conditions.
5. The failure statistics (MTBF-MTTR).
6. The cost of examination.
7. The overall cost of failure.
8. The cost of maintenance.

The following formula has been suggested in order to optimize examination frequency.

                              e^{-λ t}  - λ t = 1 + λ (C₁ / C₂ )

Where   λ = failure rate,

t = examination interval,

C₁ = examination cost, and

C₂ = unitary down time (maintenance cost + production losses).

This formula is valid only in the cases of constant failure rate (FR), while in the case of a variable FR the formula is more complicate, therefore the empirical methods are applied.

• Recording data.
• Training examiners.

The examiners should have a high standard of experience, a thorough knowledge of machinery and particularly endowed with analytical skill. However it is necessary to train the personnel for this job by:

1. Making clear the objectives of CBM
2. Illustrating the principle and working of the instruments.
3. Going through essential mathematics and principles of physics to perform the job.
4. Attending refresher courses on professional matters, like lubrication, ball bearing assembly, vibration analysis, etc.