4. Carrying out Effective Maintenance
4.1 The Structure of Equipment Maintenance
Equipment maintenance can be defined as preventing machines from breaking down by selecting what type of maintenance should be used on which parts of which machines, formulating maintenance standards, and then systematically maintaining and controlling the machines in accordance with a maintenance calendar.
This definition can be split into the following five component elements, which form the structure of equipment maintenance:
• Which machines
• Which parts
• What type of maintenance
• Formulating maintenance standards
• Systematically maintaining and controlling the machines
Each of these elements will now be explained
(1) Which machines
The equipment should be scored in terms of its importance from the standpoints of productivity, quality, cost, delivery, safety and morale, and ranked as AA, A, B, or C depending on its score, in order to prioritise the maintenance effort.
(2) Which parts
In practice, the decision as to which parts of the equipment to maintain will become progressively clearer during the Autonomous Maintenance and Effective Maintenance process. The maintenance of existing equipment depends very greatly on experience.
(3) What type of maintenance
This is also decided on the basis of experience in most cases.
(4) Formulating maintenance standards
Once the decision has been reached as to which parts of which machines to maintain, and what types of maintenance to use, the details are written into standards (equipment maintenance activity standards) in 5W1H format.
(5) Systematically maintaining and controlling the machines
Effective maintenance is all about maintaining the equipment systematically. To accomplish this, the maintenance tasks are recorded on a maintenance calendar which is then rigorously implemented.
Figure 6.9 The Structure of Equipment Maintenance
4.2 Zero-failure Programmes
Effective maintenance is progressed by initiating activities designed to reduce failures and gradually building up a preventive maintenance system.
4.2.1 Basic thinking
The starting-point for creating an Effective Maintenance system is to try to eliminate sporadic breakdowns through a comprehensive programme of restoration and improvement. To do this, the production and maintenance departments must work hand in hand to develop the activities described below.
To begin with, the production department must:
• Encourage the painstaking restoration and improvement of the equipment through its Autonomous Maintenance programme
• Develop equipment-competent operators and institute thorough routine management of the equipment
Meanwhile, as a body of professionals, the maintenance department should aim to eliminate breakdowns through the following approaches:
• Identify the causes of forced deterioration and restore and improve the equipment (Prolonging equipment lifetimes, Phase 1)
• Further prolong the intrinsic lifetime of the equipment by applying corrective maintenance to the necessary parts (Prolonging equipment lifetimes, Phase 2)
• Study the natural deterioration patterns of the equipment’s functional sections and components
• Begin preventive maintenance, starting with periodic maintenance
• In addition, keep the equipment from breaking down by performing predictive maintenance on parts that still exhibit widely varying lifetimes, and by keeping their deterioration within specified limits
Figure 6.10 The Concept of Zero Failure
4.2.2 Approaching zero failure, and the 4 Phases
The conceptual approach to zero failure is built on the concepts of maintenance and prevention. However, as described earlier, there are various approaches to the practical realisation of zero failures.
This section explains the procedure to be adopted, in the sense of supplementing the conventional approach, by focusing on how to identify the deterioration of functional parts of the equipment and what parameters to use in order to measure it.
Phase 1: Eliminate forced deterioration
The idea here is to establish equipment environments and conditions that permit only natural deterioration. This is done by eliminating the causes of forced deterioration and reversing any deterioration that has been left unchecked, as well as by improving the equipment.
Phase 2: Extend lifetimes through corrective maintenance
However assiduously deterioration is reversed and equipment is improved, machines with inherent design weaknesses will require a commensurate amount of corrective maintenance. The decision as to whether corrective maintenance is required is usually based on the frequency with which maintenance is needed and the variation in the equipment’s lifetime.
Phase 3-a: Monitor deterioration
In principle, maintenance should be restricted to those parts of the equipment that exhibit some kind of functional deterioration with the passage of time. In fact, all functional parts, i.e. all parts subject to stress, are always changing with time in some way or another. It may be more accurate to say it is just that our current level of expertise does not yet allow us to identify all these changes.
Figure 6.13 Monitor and Control Deterioration
Phase 3-b: Control deterioration
Once a deterioration pattern has been recognised, the next stage is to find out what parameter (specifically, what physical quantity) can be used to measure that deterioration. This step requires diagnostic expertise, and is where the whole range of sensors and other diagnostic devices come into play.
Phase 4: Carry out predictive maintenance
Equipment can be prevented from failing by appropriate periodic maintenance, but if we are seeking to extend its lifetime as far as possible, then predictive maintenance must form the basis for all our maintenance activities.
The Phases to Zero
What the Operating
Department Should Do (in
What the Maintenance
Department Should Do (in
1 Eliminate forced
Detect minor equipment
problems through cleaning;
establish basic conditions
deterioration due to lack of
appropriately, and retighten);
and observe correct operating
Instruct and advise on
detecting minor equipment
problems; establish and
teach correct conditions of
use; eliminate hidden forced
deterioration; and rapidly
correct any deterioration
2 Extend lifetimes
Improve equipment to make
basic conditions easier to
sustain (act against sources of
contamination and hard-toaccess
Identify and correct design
weaknesses; consider ways
of prolonging equipment
lifetimes; and improve
maintenance standards; check
and repair the equipment
using checklists; and detect
and correct equipment
problems through General
(identify lifetimes of
machines and components);
reverse deterioration; and
clarify relationships between
equipment precision and
Enhance visual management
4 Carry out
Perform condition monitoring
and trend control through
Identify deterioration and
predict lifetimes through
Figure 6.15 The Concept of Zero Failure
4.3 Prioritising the Equipment and Selecting the Maintenance Regime
(1) Prioritising the equipment
Each factory should determine its own machines’ priorities, depending on their effect on the factory’s overall production (volume and quality) and factors such as how much damage the machines would sustain if they broke down.
Generally speaking, machines are assessed in terms of the following six aspects, with each aspect being scored and the total score determining whether the equipment is ranked AA, A, B or C. The appropriate maintenance regime is then selected in accordance with this priority ranking.
Machines with no standby
Machines that fail frequently
Machines whose failure leads to drastic cuts in production
Machines that are less productive than those of competitors
Machines whose output fluctuates widely
Machines that greatly affect quality
Machines whose output quality fluctuates widely
Machines whose failure leads to changes in quality
Machines fed with expensive raw materials
Machines that require a lot of manual input
Machines that consume large amounts of heat, power, etc.
Machines whose failure would lead to large consumption
and yield losses
Machines that many other machines depend on
Machines near the end of the production line
Machines critical to production timing
Machines whose failure would slow down the factory’s
Air conditioning equipment
Pollution control equipment
Other equipment whose failure would adversely affect the
P: production volume (loading status, availability of alternative equipment)
Q: effect on quality
C: effect on cost
D: effect on delivery lead times and equipment damage
Although, as shown in the table, there are various practical ways of evaluating equipment, the ultimate decision depends on the company’s business judgment, and there is little point in pedantically insisting on a ranking system based on scoring alone. As a guideline, the percentage of equipment within each rank should be in the region of 5-7%
for AA, 25% down to A, 60% down to B, and the rest C.
Table 6.3 Example of Equipment and Priority Ranking for Selecting Maintenance Regime
Table 6.4 Example of Criteria for Prioritising Equipment
(2) Selecting the maintenance regime
Once the equipment and the parts to be maintained have been prioritised, the maintenance regime to be applied to the equipment within each rank must be decided.
The parts to be maintained should ideally be identified at the design and fabrication stages by using techniques such as FMEA and FTA. In practice, however, they are usually identified through the experience of repairing many breakdowns while the equipment is in use.
When deciding which maintenance regime to use, the two principal factors described below must be taken into account:
1 The equipment’s priority
2 The causes of the equipment’s deterioration.
As well as determining the causes of deterioration, it is also important to establish whether or not the speed with which the machine deteriorates is proportional to a parameter such as time, production volume, number of strokes, etc. If a proportional relationship exists, time-based maintenance can be used; if not, condition-based
maintenance or periodic overhaul must be used. In practice, the above two factors are considered together when deciding on the maintenance regime.
A general approach to selecting the maintenance regime is outlined below
1 Is the service life between one overhaul and the next guaranteed? If the service life can be relied on, the machine can be periodically overhauled at appropriate intervals, as long as it is operated under conditions of zero forced
2 If the lifetime is not guaranteed, have any causes of forced deterioration been left untreated? This means verifying whether or not the equipment is being properly managed on a daily basis. If any causes of forced deterioration have been overlooked, go back to basics and eliminate them.
3 If the equipment is being properly managed, is its service life acceptable? Check whether there are any design problems making the lifetime unacceptable. If there are, carry out corrective maintenance to prolong the lifetime.
4 If the service life is acceptable, is it stable? Examine the equipment’s history and decide whether or not its lifetime varies significantly. If it is stable, choose TBM.
5 If the service life is not stable, can the deterioration pattern be identified? In other words, does the part to be maintained deteriorate in an identifiable way with time? If the deterioration pattern cannot be identified, study the relevant part until it can.
6 If the deterioration pattern can be identified, is there a parameter by which the deterioration can be measured?
If no parameter can be identified, study the situation until one can. If a parameter can be identified, choose CBM.
Figure 6.16 Flowchart for Selecting General Maintenance Regime
Table 6.5 Prioritizing Equipment and Selecting Maintenance Regime
Chapter 6. Planned (Effective) Maintenance. Part 3