Preventive maintenance is time-based maintenance, a routinely scheduled, time-based activity. (To define the word “time” used here, it can mean calendar-based, time-based, interval-based, or usage-based, whatever the set parameter is.) What needs to be understood is that PM tasks can be proactive or reactive depending on how they are utilized. PM, just like predictive maintenance (PdM), helps to find and identify symptoms and faults earlier within the failure curve. Reactivity treats those symptoms and faults, whereas proactivity gets to the root cause and puts methods in place to prevent the failure from occurring.
In a reactive environment, the idea of doing a preventative maintenance task (i.e., a PM) is to look over the machine to change parts as seen fit. Normally what happens is that the mechanic begins the PM and the first defect they come to, they stop the inspection, replace the part and neglect to finish the inspection because it took too long to replace the part. Then the PM is issued the next week and the same thing occurs, eventually leading to mechanics doing a PM and the machine still fails at start up, ruining the confidence that management and operators had in the maintenance department.
This ends up a run-to-failure strategy although PM is utilized to some extent. What’s more is the PMs are often very generic, containing statements like “Check the oil” or “Check the chain” creating more variability and inducing more failure into the machine. To make matters worse, there are normally multiple PM types forged into one PM, and the mechanic is given 8 hours to complete the PM with the expectation that they do the job as if they had 40 hours. Then, management gets mad at them when they do not get it completed, or if the machine fails that next day.
To my knowledge there are seven timed-based activities: inspections, adjustments, rebuild/overhaul, replacement, testing, calibration, and lubrication. These activities take place regardless of asset condition. In order to optimize PM work, there needs to be standardization within each PM: the types need to be separated, procedures need to be created for each activity, and it needs to be drilled into the mechanic to stick to the script as much as possible. This is a long and drawn out process and is not easy to do, but the way I look at it is that it is just work. It is not complicated work, just hard work.
This is the most common PM type, and the overall goal of an inspection PM is to identify defects. Failures and defects found during an inspection constitute a work order to be generated whether by an operator or a mechanic. A work order will be generated for each failure found, along with the part needing replaced entered into the work order. These work orders then will be planned and scheduled to be completed when parts and time are available. This is corrective maintenance.
When you are in the reactive hole, it is a bit overwhelming at first, because of the number of defects that are found and loaded into the system. The ultimate goal is to restore all critical assets to basic conditions and put procedures in place to then maintain the assets at basic condition. Until your assets are at basic condition, you will never dig yourself out of the hole.
Also, there are normally two types of inspections (in the proactive world): operator inspections and maintenance inspections. Any inspection with the frequency of 30 days or less should be given to the operator. Any inspection greater than 30 days goes to the maintenance department. Speaking from a Total Process Management (TPM) perspective, the operator inspections focus on three areas: Cleaning, Inspection and Lubrication (i.e., CILs).
Mechanics, regardless of experience, are considered by most organizations as the Subject Matter Experts (SME) of the equipment within the facility. What I have reiterated to my mechanics is the importance of completing each inspection. If they do happen to come across a showstopper of a defect, then come back to it later or hand it off to the next shift if need be, but by all means, complete the inspection! I also tell them that that most defects come down to two things: the way an operator runs a machine and workmanship failures on behalf of maintenance. When you just change parts, most of the time you are introducing new defects without even knowing it!
How to optimize: Inspections are one of the most important PM types. It is critical that defects are identified as early as possible to give you time to plan and schedule the work. It is also important that the mechanic has certain tools to use during the inspection. For example, if the activity is to check the chain for elongation, it is critical that the mechanic has the tools and training to execute what you are asking.
A great way to do this is with the use of a chain wear gauge. So now, on your inspection PM, where the activity states to check the chain for elongation, you would put “see attached procedure.” With it you will have the procedure on how to check the chain for wear, with the set standard of an acceptable range of wear, along with the next steps if anything were outside that range (Figure 1).
The next thing is to have mechanics take pictures of sections of machines and identify the wear points. Put that picture in a spreadsheet and have them write out each inspection point step. When completed, share it with other mechanics in the shop to make sure nothing is missed and have them all sign off that it is completed. Then this can be given to the planner/scheduler for updating in the system (Figure 2).