Thermal spray masking materials
Thermal spray coatings processing involves the use of masking materials as a significant step prior to coating. The masking process exposes only the coating required areas to the abrasive grit blasting gun and subsequently to the coating gun. Inappropriate masking materials behavior by way of failure can cause rejection of the coated part. Many aerospace and medical components are naturally very expensive and so one cannot to take chances and deal with masking failures due to poor engineering functional performance of thermal spray masking.
Firstly, thermal spray masking materials need to lend themselves to be easily applied on to the component surface. They must exhibit sufficient adhesive strength. The adhesives used must have the capability to withstand the tremendous heat generated during the thermal spray process. If thermal spray tape is used, then the material of the tape needs to be able to withstand the pressures of abrasive grit blasting and the erosion caused by the grit blasting media. Sometimes, sprayed on compounds that are subsequently cured at low to moderate temperatures are used. Such compounds need to lend themselves for easy scribing and cut off to enable proper exposure of coat only surfaces.
Masking materials need to be easily removable after thermal spray coating in subsequent de-masking and de-burring operations. When cured compounds are used, they usually are re-useable but care must be taken to avoid using past the useful life of these off the part cured masking materials. Chemical compounds used in such cases usually have a very limited shelf life and should not be used past this date. The material data sheet that comes with these compounds usually details this very clearly and also spells out the proper methods and safety precautions to use.
Poor performance of thermal spray masking materials can result in improper grit blasting by way of over blasting the required coating area and potentially enabling coating in no-coat allowed areas. They can also result in shadows. Additionally, they may pose a real problem in the masking removal and de-burring and finishing departments. The engineering and technical functional requirements of thermal spray masking materials are quite extensive and hence only the highest quality materials need to be employed to avoid processing and quality problems.
The author invites you to learn more about thermal spray masking tapes as well as about grit blasting parameters by visiting the links above.
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