It goes without saying that equipment cannot perform satisfactorily unless it is properly lubricated. Despite this, however, empty, dirty, blocked or leaking reservoirs, grease nipples, lubricators, oil tubes and other lubrication devices are a common sight in many production areas.
Neglecting to lubricate can lead directly to sporadic failures such as bearing seizure. It can also accelerate equipment deterioration by causing wear or overheating, and the effects can spread out to all of the equipment’s units, giving rise to a huge range of different types of failure. Inadequate lubrication can be cited as a typical example of what might be called a psychological latent defect, because it arises from insufficient attention and interest on the part of the people responsible for doing the job.
Many failures are due to nuts, bolts and other fasteners breaking, working loose or falling off. Even a single loose bolt can be a source of failure if it is used to attach an important part such as a bearing unit, die, jig, cutting tool, limit switch, coupling, or flange.
Fastener problems, however, do not usually lead directly to failure but start a chain reaction, which eventually results in a breakdown. When one bolt works loose, for example, the part it is supposed to hold may begin to vibrate, causing another bolt to work loose and create further vibration. Vibration breeds vibration, backlash breeds backlash, and the upshot is a serious breakdown. When one company investigated the causes of its breakdowns, it discovered that 60% of them were due to some form of nut or bolt problem. These kinds of problems account for a surprisingly high proportion of latent defects.
(3) Monitor and control deterioration 1 Observe correct operating conditions
If equipment is to perform its required functions, it must be operated under the correct conditions. In hydraulic systems, for example, the hydraulic fluid must be kept at the correct temperature, volume, pressure, acidity and level of cleanliness, while electrical control systems and measuring instruments must be operated under certain conditions of ambient temperature, humidity, dust level and vibration level. Switches and other devices must be fitted correctly in the right position and satisfy certain parameters (limit switches, for example, must have a dog of the correct shape, together with roller lever and dog contacts of the correct angle and strength). It is essential to set and observe the correct operating, handling and loading conditions for each piece of equipment in use.
Attempting improvements is pointless if the correct operating conditions are not being followed, because the equipment’s accuracy of movement and processing conditions will be unstable and any problems will simply repeat themselves. To eliminate these problems, it is essential to specify the correct operating conditions for each equipment unit and component, and ensure that they are followed.
2 Reverse deterioration
When dealing with failures, attempts are often made to introduce improvements while neglecting to restore deteriorated machines, jigs and tools, or only partially restoring them simply by replacing the broken parts. This will not work. Machines, dies, jigs and tools can only function effectively when the strength and accuracy of their components are properly balanced. If it is clear that a machine’s strength and accuracy are unbalanced from the start because of poor design or fabrication, it may be necessary to remodel it. In other cases, however, if only the broken parts of the machine are remodelled or restored, while other relevant parts are ignored, the problems will merely repeat themselves. In fact, they will go on repeating themselves as long as the deteriorated parts that ultimately cause the failures remain undetected.
For example, if a drive shaft has broken off at a notched section, we should make sure that any defects such as play due to a worn or badly-fitting bearing, or backlash due to worn gears, are eliminated before replacing the shaft or remodelling it to increase the notched section’s radius of curvature.
Equipment deteriorates slowly over and time and its parts eventually begin to fail, starting with the weakest. Simply restoring or remodelling a broken part will not be very successful, because the next weakest part will fail soon after. The quickest way to achieve zero breakdowns is to go back to the drawings, identify the deteriorated parts by checking and testing, and restore the overall balance of the equipment’s strength and precision before thinking about changing its design.
To correct deterioration properly in this way, methods of accurately discovering, predicting and correcting deterioration must be found. Deterioration is detected and predicted by periodic checking and inspecting and through the use of diagnostic techniques, and is corrected by overhauling based on standards. This of course requires a high level of skill on the part of those responsible for maintenance. It also requires the implementation of a preventive maintenance system.
3 Correct design weaknesses
To eliminate breakdowns, it is sometimes necessary to redesign the equipment, changing the materials, dimensions and shapes of its components. If a machine frequently breaks down despite being looked after carefully, and it is impossible to keep it going for long even with regular checks, inspections and overhauls, the maintenance costs become too great, and it may be necessary to eliminate the weaknesses by redesigning. However, it is better not to remodel equipment unless absolutely necessary. There are countless examples of serious mistakes being committed through making hasty decisions, inappropriately copying improvements done on other equipment, or being seduced by attractive new technologies presented in catalogues.
If a machine’s parts are not considered durable enough, the first thing to do is to decide whether it is a design fault. If it is, the weakness should be identified accurately and a plan for remodelling the equipment should be put in place. To do this, the following procedure should be adopted:
(a) Find out exactly what happened before and after the breakdown, and identify the phenomenon precisely.
(b) Check the equipment’s structure and functions.
(c) Check to see whether basic conditions are being maintained, correct operating conditions are being followed, and the equipment has been properly restored. (d) Identify the mechanism by which the phenomenon occurs.
(e) Find the causes (design weakness, some other reason, or both).
(f) Plan an improvement.
(g) Implement the improvement.
(h) Follow up the improvement to see whether it worked or not.
(4) Carry out predictive maintenance
1 Improve operating and maintenance skills
When thinking about how to eliminate breakdowns, we often make the mistake of focusing our attention exclusively on the machines, jigs, tools, materials being processed and other hardware while forgetting about the operating and maintenance skills involved. If the cause of the problem is in fact lack of skill, looking for the causes in the hardware can lead us to repeatedly change the design of a machine or the specifications of the materials used while still failing to reduce the number of breakdowns. If a problem is known to be due to operating or maintenance error, at least we can do something about it; but people are often convinced that the methods they are using are correct when in fact they are not. In such cases, a solution is not easily found. Problems like this can only be solved by working out exactly what skills the operators and maintenance people need to look after their particular equipment, and ensuring that they acquire those skills through comprehensive education and training.
8.3 The 5 Main Factors that Cause Equipment to Fall, and the Priority Issues
The seven concepts behind achieving zero failures have been described. The fact that actions (3) through (7) are required indicates that neglecting to carry them out is a common cause of failure. These actions are so important that they are identified as the 5 Zero-Breakdown Countermeasures. Neglecting a single one of them can lead directly to a failure, but more often than not, failure is due to neglecting several in combination, as shown in Figure 4.28. This means that it is not always possible to eliminate a particular kind of failure by implementing only one or two of the countermeasures. Sometimes, even after numerous improvements have been made, failures continue to happen. The fastest way to achieve zero breakdowns is to implement all five countermeasures in order to identify and deal with every latent problem. Figure 4.29 shows the usual priorities within the countermeasures. This figure has been generalised to make it applicable to any kind of equipment and can be used for ensuring that all aspects have been covered.
Figure 4.28 Overlapping Causes of Breakdowns
Figure 4.29 The 5 Zero-Breakdown Countermeasures
8.4 The 4 Phases to Zero Breakdowns
The 5 Zero-Breakdown Countermeasures will not work well if they are introduced in a rush or if more than one is implemented at a time. The best approach is to introduce them progressively in four phases. The main thrusts of the four phases, outlined in Table 4.12, are explained below. If this approach is followed, breakdowns are certain to get closer and closer to zero.
Table 4.12 The 4 Phases to Zero Breakdowns
Phase 1: Eliminate forced deterioration
1. Correct neglected deterioration. The first thing that needs to be done is to reverse any obvious deterioration that has been left untreated.
2. Eliminate forced deterioration. Forced deterioration, which results from omitting to sustain basic equipment conditions and observe correct operating standards, is the biggest cause of variation in equipment failure intervals. Sustaining basic equipment conditions and adhering to operating standards will eliminate this variation.
Phase 2: Extend lifetimes through corrective maintenance
1. Correct design weaknesses. Eliminating forced deterioration will bring the service life of equipment closer and closer to its natural lifespan (i.e. the length of time it would last for if subjected only to natural deterioration). If it still does not last long enough, this indicates a problem with the original design. In such cases, the lifetime of the equipment must be extended by correcting its inherent weaknesses. This approach to improving equipment reliability is called
‘ corrective maintenance’.
2. Eliminate sporadic breakdowns. Although most sporadic breakdowns result from misoperation, many are also due to faulty repair work. They are the most difficult kind of failure to deal with, since they are unpredictable and therefore cannot be prevented by checking or inspecting; moreover, they are often caused by excessive stress acting on a part which, under normal conditions, would never be expected to be subjected to it. They must be eliminated by reducing human error, which can be achieved by raising operating and maintenance skills, installing error-proofing devices, improving maintenance tools and procedures, and introducing fail-safe designs.
3. Reverse visible deterioration. In phase 2, all relatively obvious external deterioration must be reversed, and the equipment restored to its original, pristine condition. Generally, more than 50% of all breakdowns can be avoided by eliminating visible deterioration.
Phase 3: Monitor and control deterioration
1. Periodically reverse deterioration. Deterioration must be corrected regularly to maintain and further reduce the level of breakdowns attained in Phase 2. To accomplish this, parts life must be estimated, standards for periodically checking, inspecting and replacing them must be established, and equipment must be restored carefully on the basis of these standards. The most important thing when doing this is first to improve the maintainability of the equipment through corrective maintenance. If standards are set while the maintainability of the equipment is still poor, dismantling the equipment for checking or replacing parts will be excessively time-consuming and costly and in the end will not get done.
2. Learn how to detect signs of internal deterioration. It is impossible to prevent every type of breakdown just by periodically reversing external, visible deterioration; operators must learn to use their five senses to detect warning signs of internal deterioration as well. Not every type of internal deterioration gives out such signs, but many do; and trained operators are often able to detect it by noticing unusual temperature, vibration, noise, light, colours, smells and movements. They should do all they can to sharpen their ability to detect the warning signs of abnormality.
Phase 4: Carry out predictive maintenance
1. Predict equipment life using diagnostic techniques. When equipment life remains highly variable, or when the warning signs of breakdowns are not detectable by the five senses, cannot be detected reliably, or cannot be detected early enough, the only remaining approach is to use diagnostic techniques to predict equipment lifetimes – that is, to analyse deterioration parameters quantitatively using diagnostic equipment. Even with parts of the equipment that are on a time-based maintenance regime, it is often possible to reduce maintenance costs by the application of condition-based maintenance using diagnostic technology; in fact, it is essential to consider moving from time-based to condition-based maintenance whenever possible.
2. Analyse catastrophic failures. Catastrophic failures are totally unpredictable, sudden failures that result in a total loss of function. Once the level of failures has been driven down by the application of the measures described above, almost all of the remaining failures will be of this type, or close to it. To prevent such failures from recurring, the causes of each should be subjected to a technical analysis (investigating the physics of fracture surfaces, materials fatigue, gear-tooth faces, stress concentrations, etc.), steps should be taken to increase the lifetimes of the relevant parts, and deterioration should be periodically reversed based on an estimate of those lifetimes. Table 4.13 shows a programme for achieving zero failures that summarises the points described in this section.
Table 4.13 A Programme for Achieving Zero Breakdowns
Chapter 4. Focused Improvement. Part 3