In industry, we know several maintenance strategies: reactive maintenance, inspection maintenance, periodic maintenance, preventive maintenance, and finally predictive maintenance. For companies with many machines and installations, it is very important to make a good assessment per machine as to which strategy best suits.
Logically, companies strive to minimize maintenance costs, but on the other hand, the availability of critical machines is also important. The failure of a critical machine results in the shutdown of an entire process. This not only results in repair costs and rush rates (for parts or external expertise), but prolonged downtime will also fail to meet certain delivery conditions. This can lead to customers who have suffered damage enforcing discounts or even filing damage claims.
What is predictive maintenance?
With the advent of new sensors, a lot of data (Big data!) can be obtained about the status of a machine. This data is then analyzed by analysis software from which trends can be identified. By monitoring and interpreting these trends based on threshold values, it can be predicted when maintenance will be needed. In the Netherlands, this form of maintenance is also called predictive maintenance or condition-dependent maintenance (TAO).
This form of maintenance has many advantages:
- The risk of unplanned downtime is greatly reduced
- It can be accurately mapped out which parts need to be replaced during a planned downtime
- The relevant parts can be purchased in advance. This means there are no rush rates when delivering parts or hiring external knowledge.
One of the ways to perform predictive maintenance is by vibration measurements on a machine. Other forms include Thermography / Infrared measurements and oil analysis.
Reactive maintenance (Corrective maintenance)
Actually, there is not really any maintenance involved with reactive maintenance. In this form, the process continues to run until a part actually breaks. After the respective part is replaced, the process will be resumed. Although this may not seem like a logical form of maintenance, in some cases it may well be the most advantageous approach. If it involves a part that is known to be quickly replaceable and not expensive, then this could very well be the best approach.
In some companies, it also happens that a process consists of several steps where one part of the process is carried out one day, and the next part of the process the next day. Even in such a case, reactive maintenance could just be the right approach, because when a malfunction occurs, the staff can easily switch to the other part of the process.
Inspection maintenance
With inspection maintenance, maintenance is really only performed when the operator has observed things that strongly indicate the likelihood of malfunctions. During an inspection round, for example, the status of gears in a gearbox is checked; is there wear present or are there cracks to be observed. If this is the case, then the parts need to be replaced and it should also be looked at if the cause can be traced. This way the cause can be resolved directly, reducing the chance of recurrence.
Periodic maintenance
There are two forms of periodic maintenance: maintenance based on a certain time interval such as weekly, monthly, or annually. Periodic maintenance can also be performed based on the number of operating hours. When a certain part has made a certain number of operating hours, the reliability decreases and the chance of malfunctions increases.
Preventive maintenance
In preventive maintenance, parts of a machine are replaced prematurely before they break and can cause a malfunction. Preventive maintenance is often applied by companies that cannot afford downtime during certain seasons because those are the months when they need to make the most revenue. This form of maintenance is not based on trend data. This form of maintenance is very costly because, on the one hand, a lot of parts are replaced which takes many man-hours, and on the other hand, it costs a lot of money because parts are also replaced that do not need to be replaced at all.