| Pump shafts that are used in harsh environments | | | | oxide. This creates a mechanical profile on the |
| can get worn out and go out of dimensions. In | | | | surface to which the subsequent coating will |
| the past, such components were simply discarded | | | | properly adhere to. Remember, thermal spray |
| and replaced with new parts. Thermal spray | | | | bonding mechanism is strictly mechanical in nature |
| techniques can be successfully used to rebuild the | | | | and hence proper cleaning and grit blasting are |
| worn surfaces of pump shafts and brought back | | | | essential to ensure good bonding. Then use a |
| to original manufacturer dimensional specifications. | | | | twin-wire material such as |
| Thermal spray build-up involves spraying a surface | | | | nickel-chromium-aluminum wire and build-up the |
| with coating particles that reach the plastic state | | | | surface with coating using the twin-wire-arc |
| and are propelled to the surface where they | | | | process of thermal spraying. |
| form the coating. There are several thermal | | | | In the twin-wire-arc process, an electric arc is |
| spray coating processes available at your disposal. | | | | struck between two wires that melts the material |
| In this article, we will use a simple twin-wire arc | | | | of the wires and the resulting molten particles are |
| thermal spray method to rebuild a worn out | | | | carried by air to reach the substrate surface |
| pump shaft and explain the steps involved in | | | | which in this case is the worn out pump shaft. |
| accomplishing this task. | | | | After coating has been completed, put the shaft |
| The first step is to thoroughly clean the shaft of | | | | on a mechanical lathe and turn it down to the |
| dirt, grease and other foreign matter with a | | | | proper dimensions and you have successfully |
| solvent such as acetone. Then take the | | | | rebuilt the worn out pump shaft! A word of |
| appropriate dimensions to determine how much of | | | | caution: check with the manufacturer if rebuilding |
| a surface build-up is needed to bring back to the | | | | the shaft is acceptable in your application and if |
| original dimensional specifications. Then add to it | | | | the coating material used is acceptable. Some |
| sufficient amount to clean up after machining | | | | very critical applications involving very high speeds |
| because once the coating has been deposited, it | | | | of rotation and very corrosive environments do |
| will have to be machined to the correct | | | | not allow for repairs of this nature; hence it is a |
| dimensions. After ensuring that the surface is | | | | good practice to check with the original equipment |
| clean, it should be grit blasted with an appropriate | | | | manufacturer before proceeding. |
| sand blasting media such as 80 grit aluminum | | | | |