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While some of the methods and techniques used to implement preventive maintenance are optional, we below present those components that are absolute requirements of an effective program.
A typical preventive maintenance procedure...
Delivery Vehicle: 3.0k-mile Oil Change
Purpose: To list cautions and steps required for changing oil.
Ref.: Driver's manual for vehicle.
Cautions: Assure vehicle is blocked securely before going under it.
Hot oil from a recently operating motor can burn.
Assure adequate ventilation when running gas or diesel engine.
Get replacement oil from stockroom. Get tools: catch basin, oil spout, wrench, wipes. Run motor for at least 4 minutes to warm oil and mix contaminant particles. Position vehicle on grease rack, lift, or oil change station. Assure lift lock, blocks, and all safety devices are in safe position. Position catch basin under oil drain. Remove drain plug with wrench and drain oil into catch basin. When oil slows to a trickle, replace drain plug. If engine has a second sump, drain it the same way. Open hood, remove oil fill cap, and fill engine with fresh oil. Run engine for 1 min to circulate oil. Check underneath for any leaks. Check dipstick to assure oil level is full. Clean any spilled oil. Close hood and clean off any oil or fingerprints. Remove any old stickers from driver's door hinge column. Fill out oil change sticker with mileage and stick inside driver's door hinge column. Drive vehicle to parking area. Be alert for indications of other problems. Sign and date this checklist and write in mileage.
Vehicle I.D.#: License: Odometer miles:
Logic for inspection findings.
PLANNING / ESTIMATING
Planning is at the heart of good inspection and preventive maintenance. As described earlier, the first thing to establish is what items must be maintained and what the best procedure is for performing maintenance tasks. Establishing good procedures requires a good deal of time and talent. This can be a good activity for a new graduate engineer, perhaps as part of a training process that rotates him through various disciplines in a plant or field organization. This experience can be excellent training for a future design engineer.
The preventive maintenance procedure should be written by an engineer with excellent writing ability and pragmatic experience in maintenance practices. The language used should be clear and concise; short sentences are preferred. The questions of who, what, when, where, why, and how should be clearly answered. A typical preventive maintenance procedure is illustrated in Ill.1. The following points from this typical procedure should be noted:
1. Every procedure has an identifying number and title.
2. The purpose is stated.
3. Needed tools and parts and reference documents are listed.
4. Safety and operating cautions are prominently displayed.
5. A location is clearly provided for the maintenance mechanic to indicate performance as either okay or deficient. If deficient, details are written in the space provided at the bottom for planning further work.
The procedure may be printed on a reusable, plastic-covered card that can be pulled from the file, marked, and returned when the work order is complete; on a standard preprinted form; or on a form that's uniquely printed by computer, each time a related work order is prepared. Whatever the medium of the form, it should be given to the preventive maintenance craftsman together with the work order so that he has all the necessary information at his fingertips. The computer version has the advantage of single-point control that may be uniformly distributed to many locations. This makes it easy for an engineer at headquarters to prepare a new procedure or to make any changes directly on the computer and have them instantly available to any user in the latest version.
There are two slightly different philosophies for accomplishing the unscheduled actions that are necessary to repair defects found during inspection and preventive maintenance. One is to fix them on the spot. The other is to identify them clearly for later corrective action. This logic is outlined in Ill.2. If a "priority one" defect that could hurt a person or cause severe damage is observed, the equipment should be immediately stopped and "46 red tagged" so that it won’t be used until repairs are made. Maintenance management should establish a guideline such as, fix anything that can be corrected within 10 min but if it will take longer, write a separate work request. The policy time limit should be set, based on:
1. Travel time to that work location
2. Effect on production
3. Need to keep the craftsman on a precise time schedule
The inspector who finds the defects can perform small repairs quickly. This avoids the need for someone else to travel to that location, identify the problem, and correct it. And it provides immediate customer satisfaction. However, more time-consuming repairs would disrupt the inspector's plans, which could cause other, even more serious problems to go undetected. The inspector is like a general practitioner who performs a physical exam and may give advice on proper diet and exercise, but who refers any problems he may find to a specialist.
The inspection or preventive maintenance procedure form should have space where any additional action required can be indicated. When the procedure is completed and turned into maintenance control, the planner or scheduler should note if any additional work is required and , if so, see that it gets done according to priority.
How to Estimate Time
Since inspection or preventive maintenance is a standardized procedure with little variation, the tasks and time required can be accurately estimated. Methods of developing time estimates include consideration of such resources as:
1. Equipment manufacturers' recommendations
2. National standards such as Hayne’s or Chilton's on automotive or Means' for facilities
3. Industrial engineering time-and-motion studies
4. Historical experience
Experience is the best teacher, but the procedure determined from historical experience must be care fully critiqued to make sure that it truly is the "best way" and that the pace of work is reasonable.
The challenge in estimating is to plan a large percentage of the work (preferably at least 85%) so that the time constraints are challenging but achievable without a compromise in high quality. The trade-off between reasonable time and quality requires continuous surveillance by experienced supervisors. Naturally, if a maintenance mechanic knows that his work is being time studied, he will follow every procedure specifically and will methodically check off each step of the procedure. When the industrial engineer goes away, the mechanic will do what he feels are necessary items, in an order that may or may not be satisfactory. As discussed earlier, an experienced preventive maintenance inspector mechanic, depending on motivation, can vary performance as much as 45% either way from the standard without most maintenance supervisors recognizing a problem or opportunity for improvement. Periodic checking against national or time-and-motion standards, as well as trend analysis of repetitive tasks, will help keep preventive task times at a high level of effectiveness.
Estimating Labor Cost
Cost estimates can be determined from time estimates simply by multiplying the estimated hours required by the required labor rates. Beware of coordination problems where multiple crafts are involved. For instance, one "Fortune 100" company has trade jurisdictions that require the following personnel in order to remove an electric motor: a tinsmith to remove the cover; an electrician to disconnect the electrical supply; a millwright to unbolt the mounts; and one or more laborers to remove the motor from its mount. That situation is fraught with inefficiency and high labor costs since all four trades must be scheduled together with at least three people watching while the fourth is at work. The cost will be at least four times what it could be and is often greater if one of the trades does not show up on time. The best a scheduler can hope for, if he has the latitude, is to schedule the cover removal at say 8:00 a.m. and the other functions at reasonable time intervals thereafter: electrician at 8:00, millwright at 9:00, and laborers at 10:00.
It’s recommended that estimates be prepared on "pure" time. In other words, the exact hours and minutes that would be required under perfect scheduling conditions should be used. Likewise, it should be assumed that equipment would be immediately available from production. Any delay time should be reported and scheduling problems should be identified so that they can be addressed separately from the hands-on procedure times. Note that people think in hours and minutes, so 1 hr and 10 min is easier to understand than 1.17 hr.
Most parts and materials that are used for preventive maintenance are well known and can be identified in advance. The quantity of each item should be multiplied by the cost of the item in inventory.
The sum of those extended costs will be the material cost estimate. Consumables such as transmission oil should be enumerated as direct costs, but grease and other supplies used from bulk should be included in overhead costs.
Feedback from Actual
The time and cost required for every work order should be reported and analyzed to provide guidance for more accurate planning in the future. It’s important to determine what causes the task and times to change. Blindly assuming that the future will be like the past, or even that things were done perfectly in the past, may be an error. Comparisons should certainly be made between different individuals doing the same tasks in order to evaluate results in the amount of time required, what was accomplished during that time, quality of workmanship, and equipment performance as a result of their efforts.
Some people will argue that setting time standards for preventive maintenance is counterproductive. They feel that the mechanic should be given as much time as he desires in order to ensure high quality work. This is generally not true. In fact, the required tasks will generally expand or contract to fit the available time. Preventive maintenance inspection and lubrication can in fact be treated as a production operation with incentives for both time performance and equipment uptime capability.
The standard maintenance estimating and scheduling techniques of time slotting, use of ranges, and calculations based on the log-normal distribution may be followed as reliable data and analytical competence are established. Since preventive maintenance time and costs will typically comprise 20 to 50 percent of the maintenance budget, accurate planning, estimating, and scheduling are crucial to holding down costs and improving profits.
Scheduling is, of course, one of the advantages to doing preventive maintenance over waiting until equipment fails and then doing emergency repairs. Like many other activities, the watchword should be PADA, which stands for Plan a Day Ahead. In fact, the planning for inspections and preventive activities can be done days, weeks, and even months in advance in order to assure that the most convenient time for production is chosen, that maintenance parts and materials are available, and that the maintenance workload is relatively uniform.
Scheduling is primarily concerned with balancing demand and supply. Demand comes from the equipment's need for preventive maintenance. Supply is the availability of the equipment, craftsmen, and materials necessary to do the work. Establishing the demand has been partially covered in sections on on-condition, condition monitoring, and fixed interval preventive maintenance tasks.
Those techniques identify individual equipment as candidates for preventive maintenance.
There must be a procedure for identifying the order in which tasks are to be done. Not everything can be done first. First in-first out (FIFO) is one way of scheduling demand. Using FIFO means that the next preventive task picked off the work request list, or the next card pulled from the file, is the next preventive maintenance work order. The problem with this "first come, first served" method is that the more desirable work in friendly locations tends to get done while other equipment somehow never gets its preventive maintenance. The improved method is Priority _ Need Urgency _ Customer Rank _ Equipment Criticality. The acronym NUCREC will help one remember the crucial factors.
NUCREC improves upon the Ranking Index for Maintenance Expenditures (RIME) in several ways:
1. The customer rank is added.
2. The most important item is given the number-one rating.
3. The number of ratings in the scale may be varied according to the needs of the particular organization.
4. Part essentiality may be considered.
A rating system of numbers 1 through 4 is recommended. Since most humans think of number 1 as the first priority to get done, the NUCREC system does number 1 first.
Need urgency ratings include:
1. Emergency; safety hazard with potential further damage if not corrected immediately; call back for unsatisfactory prior work
2. Downtime; facility or equipment is not producing revenue
3. Routine and preventive maintenance
4. As convenient, cosmetic Customers are usually ranked in the following order:
1. Top management
2. Production line with direct revenue implications
3. Middle management, research and development facilities, frequent customers
4. All others
The equipment criticality ratings are:
The product of the ratings gives the total priority. That number will range from 1 (which is 1 _ 1 _ 1) to 64 (4 _ 4 _ 4).
Work given the lowest number will have first priority. Priority 1 work is a first-class emergency. When several work requests have the same priority, labor and materials availability, locations, and scheduling fit may guide which is to be done first.
The priorities should be set in a formal meeting of production and maintenance management at which the equipment criticality number is assigned to every piece of equipment. Similarly, a rank number should be applied to every customer and the need urgency should be agreed on. With these predetermined evaluations, it’s easy to establish the priority for a work order either manually by taking the numbers from the equipment card and the customer list and multiplying them by the urgency, or by having the computer do so automatically. Naturally, there may be a few situations in which the planner's judgment should override and establish a different number, usually a lower number so that the work gets done faster.
Ratings may rise with time. A good way to assure that preventive maintenance gets done is to increase the need urgency every week. In a computer system that starts with preventive maintenance at 3, a preventive task that's to be done every month or less can be elevated after one week to a 2, and finally to a 1 rating. Those increases should assure that the preventive task is done within a reasonable amount of time. If preventive maintenance is required more often, the incrementing could be done more rapidly.
Dispatch of the preventive maintenance work orders should be based on the demand ordered by priority, consistent with availability of labor and materials. As discussed earlier, predictive maintenance provides a good buffer activity in service work since time, to within a few days, is not normally critical. The NUCREC priority system helps assure that the most important items are done first.
Some pressure will be encountered from production people who want a particular work request filled right away instead of at the proper time in the priority sequence. It can be helpful to limit the "criticality 1" equipment and "rank 1" customers to 10 percent, since, according to Pareto's Principle of the Critical Few, they will probably account for the majority of activity. If rank 2 is the next 20 percent, rank 3 is 30 percent, and the balance is 40 percent for rank 4, the workload should be reasonably balanced. If temporary work needs exist for selected equipment or a customer needs to be given a higher priority, then one equipment should be moved to a lower criticality for each equipment that's moved higher. After all, one objective of prioritization is to assure that work gets done in the proper sequence. A preventive maintenance action that's done on time should assure that equipment keeps operating and that emergency work is not necessary.
Coordination with Production
Equipment is not always available for preventive maintenance just when the maintenance schedulers would like it to be. An overriding influence on coordination should be a cooperative attitude between production and maintenance. This is best achieved by a meeting between the maintenance manager and production management, including those at the foreman level, so that what will be done to pre vent failures, how this will be accomplished, and what production should expect to gain in uptime may all be explained.
The cooperation of the individual machine operators is of prime importance. They are on the spot and most able to detect unusual events that may indicate equipment malfunctions. Once an attitude of general cooperation is established, coordination should be refined to monthly, weekly, daily, and possibly even hourly schedules. Some preventive maintenance work will require a "cold" shutdown of equipment. These major shutdowns should be carefully planned. Maintenance will often find that they must do this on weekends and holidays, when other persons are off-site. Normal maintenance should be coordinated according to the following considerations:
1. Maintenance should publish a list of all equipment needing inspections, preventive maintenance, and modifications; and the required time to perform these tasks.
2. A maintenance planner should negotiate the schedule with production planning so that a balanced workload is available each week.
3. By Wednesday of each week, the schedule for the following week, broken down by days, should be negotiated and posted where it’s available to all concerned.
4. By the end of the day before the preventive activity is scheduled, the maintenance person who will do the preventive maintenance should have seen the first-line production supervisor in charge of the equipment to establish a specific time for the preventive task.
5. The craftsman should make every effort to do the job according to schedule.
6. As soon as the work is complete, the maintenance person should notify the production supervisor so that the equipment may be put back into use.
Overdue work should be tracked and brought up to date. Preventive maintenance scheduling should make sure that the interval is maintained between preventive actions. For instance, if a preventive task scheduled for May is done on the thirtieth of the month, the next monthly task should be done during the last week of June. It’s foolish to do a preventive maintenance task on May 30 and again on June 1, just to be able to say one was done each month. In the case of preventive maintenance, the important thing is not the score but how the game is played.
Opportunity Preventive Maintenance Activities
It’s often helpful to do preventive maintenance when equipment suddenly becomes available, which may not be on a regular schedule. One method called techniques of routine interim maintenance (TRIM) was covered in the preceding section. TRIM means generally that specified cleaning, inspection, lubrication, and adjustments are done at every service call. TRIM can be very effective.
Another variation is to convert (or expand) a repair call to include preventive activities. A good work order or service call system will quickly show any preventive maintenance, modification, or other work due when equipment work is requested. The system should also check parts availability and print pick lists. Parts required for preventive maintenance replacement can then be taken to the site and all work done at one time. Unless production is in a hurry to use the equipment again as soon as possible, doing all work on an equipment during the single access is much more efficient than having to gain access several times in order to perform a few tasks each time.
A formal record is desirable for every inspection and preventive maintenance job. If the work is at all detailed, a checklist should be used. The completed checklist should be returned to the maintenance office on completion of the work. Any open preventive maintenance work orders should be kept on report until the supervisor has checked the results for quality assurance and signed off approval. Modern computer technology with handheld computers and pen-based electronic assistants permit paperless checklists and verification. In many situations, a paper work order form is still the most practical medium for the field technician. The collected data should then be entered into a computer system for tracking.