Thermal spraying is a technique whereby a metal, a metal alloy or metal compound in wire or powder form, is melted and sprayed onto a surface using a thermal spray gun. This is done so that the component's usability is enhanced by the addition of coatings with improved properties.
With only one exception, thermal spraying is a cold process. That is to say that the workpiece undergoes a slight rise in temperature due to the heat transfer from the molten droplets when they land the surface. The conventional workpiece temperature of between 50° to 200° C cannot cause any deformation, change in structure or dilution. As a result, the base material always retains its original mechanical properties.
The structure of a cold-sprayed layer is lamellar, which is somewhat similar to a cast iron structure. Micro pores and oxide inclusions are partly the reason why some sprayed metal layers have a low frictional coefficient and high hardness. Microporous sprayed layers are also very good at retaining certain lubricants, thus preventing wear caused by metal/metal contact.
The thermal spraying technique uses a group of materials that are known as self-fluxing alloys or hard metals, and, after spraying, are given a heat treatment at 1050° - 1150° C. The structure of these hot-sprayed layers is homogeneous and, as a result, the mechanical strength is significantly higher.
The base material for hot-sprayed layers is nickel, chromium, or cobalt, possibly with the addition of tungsten carbides, and these can be supplied in a hardness of Rc 30 to 75. These types of fused layers have a very high resistance to chemical corrosion, abrasion, heat oxidation, impact and/or heavy mechanical stress.
There are 5 main thermal spray techniques for applying the coatings. Griekspoor has the in-house expertise to apply every one of these techniques.
These are: