Maintenance

‘If It Ain’t Broke, Don’t Fix It’, Preventive versus Predicted Maintenance In 1973, the university education is completed, in 1975 your writer entered Ankara Makina factory as a new engineer, after a while became the engineer responsible for the maintenance and repair workshop. The first simple rule of thumb I learned from the foremen of the maintenance and repair workshop is, "You will not interfere with the working machine and the workbench. Let it work, the machine will reveal itself when there is a need for maintenance." This rule has been used for decades all over the world. This is the simplest implementation of maintenance and repair works. Today, more detailed scheduled preventive maintenance is carried out. Preventive maintenance is the one performed after a certain period of time. It is usually done with an oil change. It is like changing the oil of cars after every 15 thousand km. Meanwhile, all filters and spark plugs are replaced. Brake pads are checked. Decreased oil and water levels are completed. Worn out parts are visually inspected, the necessary ones are renewed. Gearbox oils are changed after 5000-10,000 hours in lathe machines. If the machine is not working, or making unusual noises, if the machine is heavy, it is stopped, disassembled, the worn and broken part is found, a new one is made, replaced, and operated again under control. The maintenance person may not be able to replace all the dismantled parts while assembling the machine. While doing a repair job it can break another piece, these are very natural possibilities. After certain flight times, the planes are taken to the indoor hangars, each part is checked manually with a device, worn out parts are replaced, and the aircraft is put back into service after certain tests. In offshore platforms, the structural steels are subjected to load and vibration tests after a certain operating period. If the tests fail, the entire platform is dismantled and rebuilt with new materials. In general, offshore platforms are designed for 25 years and authorised permits are obtained. A test like "Class: A", ABS or Turk Lloyd is applied to the platform, that is, the parts that are underwater. It should be scanned from top to bottom by an authorised surveyor every 5 years. A thickness measurement is made every two years and the amount of rust is measured. When a generator fails too much; it is completely renewed. In factories, things are easier in electrical equipment, usually when overloaded, the fuse of the machine blows and you renew the fuse. You check the cables. The cable may need to be renewed. How to make scheduled preventive maintenance and repair of tens of hundreds of machine lathes in a huge machine factory? You definitely have records of when maintenance was performed, and you have lists of parts that break down frequently and need to be replaced. Protective scheduled maintenance must be done to the machines. You need to know statistically which machine broke down when and where. Selling a lot of spare parts is another way to make good money when you sell some technological machinery and equipment. Turkish Soma and Afşin thermal power plants have very large spare part warehouses. Spare parts have been purchased in quantities that will last a very long time. Although 25- or even 40 years have passed since the first plant operation, the reserves still could not be consumed and spares were sent to other power plants. When we graduated from Ankara METU University Mechanical Engineering in 1973, the alternative to running the machine until it broke down and repairing/maintaining it when it broke down was to replace some parts periodically with preventive maintenance. This method is still used in some areas, especially in the automotive industry. Not much, about 6 years after our graduation, in the Mechanical Vibrations course, which was started in the same department, we started to talk about another option, "predictive maintenance", and to convey its basic principles. In this new maintenance method, the vibrations of the machines are measured at certain intervals (once a week, every two weeks) and from the analysis of the measurement signals obtained, it is determined how close that machine is to failure, which part of it is about to break down, and whether there is another issue in the machine that requires maintenance. There are special measuring devices and software that perform the necessary analysis. In this way, no part is replaced before its life is complete, but an unexpected failure or deterioration of other parts of the machine is not caused. It is more important to apply in sectors where the cost of production loss is high. This predictive maintenance method is especially suitable for machines that may cause disruption of production, or critical machines such that other parts of the machine may be damaged when one part of the machine breaks down. The critical point here is which machine we are talking about. If it doesn't cause secondary failures when it breaks down and the cost of not being able to use the machine is negligible, okay "don't maintain a working machine, let it work". But, for example, if we are talking about machines in an iron and steel factory that will affect production when they break down, preventive maintenance is not the right solution, you will apply "predictive maintenance". Unfortunately, "predictive maintenance" is not yet fully applicable in cars, we are still doomed to preventive maintenance. ‘If It Ain’t Broke, Don’t Fix It’, The Old Saying Needs a Rephrase Ankara, 24 July 2021