Most companies use time-based maintenance as their primary method of discovering failures and addressing issues. Time-based maintenance is a program of inspections or repairs that are performed according a time schedule or cycles: once a week, once a month, or once a year. This approach also involves costly semiannual or annual shutdowns for maintenance repairs and overhauls.

In many cases, time-based maintenance is not the correct approach to eliminating component failures. Often, equipment fails shortly after the preventative maintenance was completed. This is not the fault of the operators or the maintenance professionals, however, it can be blamed on traditional mindsets in the foundry business. For many decades, there has been a belief that all failures are age-related; in other words, it is commonly assumed that every piece of equipment has a useful life, and after the end of this life has reached, the equipment needs to be overhauled, or replaced.  This assumption still exists and Figure 1, known as a “bathtub curve,” demonstrates the frequency of age-related failures.

The bathtub curve indicates that at the beginning of its service life, the equipment has a high chance of failure; this could be understood as “start-up issues.” Then, it has an equal chance of failure for some time, and once the equipment reaches its useful life, the likelihood of failures increases, at which point it needs either to be replaced or overhauled.

In the early 1980s a comprehensive study of this concern was completed, but it never was adopted by many industries. The study showed that 89% of all failures in any industry are random incidents, and do not follow the bathtub curve. This was a revelation in many industries, and then it was realized that the traditional preventative maintenance is not effective for preventing random failures.

This finding holds true for foundries, too. However, most foundries still use the traditional time-based maintenance, which is why failures keep occurring even though the PM programs are completed.

Every time I ask operators how we should eliminate downtime in foundries, I receive the similar answers: Better preventative maintenance programs; more inspections; keeping spare parts on hand; implementing Total Productive Maintenance; better operating procedures; more operator training; more maintenance training; buy better parts; and dedicate more time to perform the required maintenance.

None of these replies can really answer the basic question: How to eliminate equipment failures.  In fact, all these answers are premised on the traditional understanding of equipment maintenance.

The only effective answer to this question is, in order to eliminate equipment failures we must make the equipment 100% reliable.