Pump shafts that are used in harsh environments can get worn out and go out of dimensions. In the past, such components were simply discarded and replaced with new parts. Thermal spray techniques can be successfully used to rebuild the worn surfaces of pump shafts and brought back to original manufacturer dimensional specifications.

Thermal spray build-up involves spraying a surface with coating particles that reach the plastic state and are propelled to the surface where they form the coating. There are several thermal spray coating processes available at your disposal. In this article, we will use a simple twin-wire arc thermal spray method to rebuild a worn out pump shaft and explain the steps involved in accomplishing this task.

The first step is to thoroughly clean the shaft of dirt, grease and other foreign matter with a solvent such as acetone. Then take the appropriate dimensions to determine how much of a surface build-up is needed to bring back to the original dimensional specifications. Then add to it sufficient amount to clean up after machining because once the coating has been deposited, it will have to be machined to the correct dimensions.

This creates a mechanical profile on the surface to which the subsequent coating will properly adhere to. Remember, thermal spray bonding mechanism is strictly mechanical in nature and hence proper cleaning and grit blasting are essential to ensure good bonding. Then use a twin-wire material such as nickel-chromium-aluminum wire and build-up the surface with coating using the twin-wire-arc process of thermal spraying.

In the twin-wire-arc process, an electric arc is struck between two wires that melts the material of the wires and the resulting molten particles are carried by air to reach the substrate surface which in this case is the worn out pump shaft. After coating has been completed, put the shaft on a mechanical lathe and turn it down to the proper dimensions and you have successfully rebuilt the worn out pump shaft! A word of caution: check with the manufacturer if rebuilding the shaft is acceptable in your application and if the coating material used is acceptable. Some very critical applications involving very high speeds of rotation and very corrosive environments do not allow for repairs of this nature; hence it is a good practice to check with the original equipment manufacturer before proceeding.

The use of thermal grease is indispensable. Generally, a cooler is used to remove the heat of the processors and each processor warrants smooth functioning with the specific type of cooler. If a wrongly dimensioned cooler is used, it causes overheating problems. And it promotes heat transfer between the processor and the cooler because of the air gaps formed by the imperfect physical contact between the processor and the cooler. This leads to overheating of the processor. This problem is solved by applying between them, thereby filling the tiny gaps of air.