About preventive and corrective maintenance

In high-production plants, the maintenance of the manufacture means probably occupies one of the first three places in the company's priorities, perhaps together with the training of personnel and attention to variable costs, i.e., the cost of raw materials and / or purchase parts that appear in the bill of materials of products. It is a fact, as well as a situation that I have witnessed several times, that when production programs are pressing (when there is exuberance of customer orders), there is a temptation to "ignore" a maintenance stop to send more product to the warehouse. It is an evil temptation to which one must not give in. There are a few reasons why scheduled maintenance might be disregarded.

1- To give a simple example, no Ducati owner would dare to skip the scheduled maintenance of the desmodromic or ignore the change of the distribution chain in a car: in fact, damage to these mechanisms would cause much greater and expensive ones soon after.

2- Moreover, it would be an action that is hardly justifiable in front of all those who really believe in the benefits of effective, well-planned and efficient maintenance.

3- Another key reason is that preventive maintenance (and the name is self-explaining) moves the needle of business operations to the side of prevention / proactivity rather than to the side of corrective actions, important but to be avoided.

4- Finally, it would be a behavior clearly contrary to the principles of quality: what position should we hold in front of a customer who claims a quality problem due to a maintenance not performed or poorly carried out? Isn’t it better to always be on the side of reason, or at least of deontological correctness?

The time dedicated to preventive maintenance is essential for the training of operators and supervisors: in fact, during cleaning, repair, replacement and restart operations, they should work alongside the technicians. In this way, the following maintenance job will take shorter and we’ll increase the level of involvement of those who work with that equipment most of the time.

A good preventive maintenance plan, combined with the optimal management of corrective maintenance, can really increase the level of productivity of the plant by up to 20%, without improvement actions.

Corrective maintenance, according to the logic of the continuous improvement, must flow into preventive maintenance, as long as "unexpected" problems occur and are resolved. My advice is to manage corrective maintenance in a simple way, that is, within everyone's reach: after a problem is identified (better if not yet "exploded"), it is evaluated whether you can continue with a temporary repair until the next preventive maintenance. The classic white board method is fine, as long as they are checked at least daily by the technical maintenance manager. Each "new" problem must trigger a monitoring action over time (typically control of wear, coupling or plays) and ensure that as soon as possible this criticality is absorbed by periodic (preventive) maintenance activities. The dream of any maintenance manager is to see the "sudden" and "unexpected" problems disappear gradually, to devote almost all the resources to planning maintenance activities.

It is necessary to make a premise: there are sophisticated maintenance systems that are based on the number of cycles performed and that require a maintenance stop at the end of the set number of operations. Although excellent in principle, this method lends itself to being disregarded; just think of a maintenance intervention that pops up during a shift when the technical coverage is thin, or when the technician is busy elsewhere; however, a system clocked by cycles instead of time will surely give alarms during the less manned shifts, with the risk of having unfulfilled maintenance. Without going into the merits of corporate ethics, avoiding temptations puts everyone on the side of reason.

That's why over time I have re-evaluated a lot of the maintenance planning systems based on time and not on cycles. The important thing is the preparation stage: initially, all equipment maintenance sheets are individually examined and adapted according to the “ON” time. It translates the interval between two successive maintenance jobs (through cycle time) from number of cycles to time. Frequencies are determined that approximately make all maintenance coincide with certain days of the week, and that's it.

A piece of advice that I would like to give is to intersperse preventive and corrective maintenance.

Staggered corrective maintenance sessions have a threefold purpose:

1- to permanently fix the problems listed on the correspondent whiteboards,

2- to give technicians time to introduce improvements and

3- to be able to conclude any maintenance works still pending from the previous preventive maintenance session.

Personally, I would avoid preventive maintenance on Mondays and Fridays: the first is typically dedicated to the restart of the plant; as for the second, it is always better to finish the working week with machinery in motion.

The executive phase of the preventive maintenance session takes place during the central shift, when all company resources are present, especially technical ones. The maintenance manager prints the booklet of the works to be performed: every page is dedicated to different machines and the processes to be taken care are listed; each page is then physically attached to the machine under PM and all activities are inspected by the manager simultaneously as they proceed.

Depending on the number of projects to be performed, it is easier to plan and "book" the necessary resources to complete the activities within 6 hours, to dedicate the remaining 2 hours to the restart and qualitative tuning phase.

I’d like to attach to this article a tool that I have used with satisfaction for several years: the production rhythms and maintenance cards favoured periodicity of 4 weeks as a minimum interval.

Preventive_Maintenance_EffBee_2

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