When to Use Thermal Plasma Spray Coatings
Thermal plasma spray is a specialised coating process that is suited to particular demanding situations. In contrast, other processes such as chrome plating, nickel plating or paint coating are general purpose coating processes suitable for almost all situations.
Parts Facing Extreme Surface Temperatures
Turbine blade coatings and combustion liner coatings are examples of coatings that can run at surface temperatures of over 1,000° C hours after application. Typically these are made of a ceramic thermal barrier coating, such as yttria-stabilised zirconia, that is applied by Thermal Plasma Spray.
Components Needing High Hardness at Tight Tolerances
Pump sleeves, rollers and wear faces on other components, such as shafts and seals, can be hard surfaced with a coating of chromium oxide or alumina. The material is typically applied by Thermal Plasma Spray in a controlled thickness deposit. The coating is then ground back to size, providing a surface hardness similar to hard chrome plating, but without the usual environmental problems associated with chrome plating.
Heat-Sensitive Base Materials
Some substrates, such as certain aluminium alloys, thin-walled steel sections or components with composite backing, cannot be exposed to the high temperatures that weld-based hard-facing processes develop. The low temperature process of Thermal Plasma Spray allows the substrate temperature to remain low during the spraying process and thus the mechanical properties of the base material are not compromised and the geometry is not affected.
Where Electrical Insulation Is the Primary Requirement
In instances where a dense, non-conductive surface is required, such as for bearing housings or induction tooling, an alumina coating that has been plasma sprayed provides a reliable dielectric insulation surface.
Restoring Worn or Undersized Dimensions
Shafts and bores that have worn or oversized dimensions can be restored by building up a thick, machinable deposit by plasma spray. The deposit can then be finished-machined to the required dimensions. This is an alternative to re-manufacturing a new part.
Matching the process to the application is what differentiates a good coating from a poor covering.