Metal shadow masks are placed approximately two to three times the total coating thickness away from the part to be sprayed and in front of the spray torch, shielding selected areas from the direct spray stream. The targeted spray area may be stationary or rotating. The mask is typically stationary and securely affixed. As the spray stream is traversed across the target area and onto the mask, the unwanted spray collects on the mask and is prevented from reaching the substrate.
The coating will end in a narrow feathered band rather than as a sharply defined line. In contrast to the feathered edge, note that a contact mask, similar to the tape that is discussed in this section, leaves a sharp edge, which may act as a stress raiser that often leads to disbonding of the coating. Metal masks can be reused, subject to the amount of coating buildup and/or distortion due to heat from the spray process.
Volume 5A, Thermal Spray Technology -> Introduction to Coating Design and Processing -> Processing Prior to Coating
