Dyescan Tracers as a Quality Control Tool for Coverage Determination in Controlled Shot Peening

The Shot Peening process is not new, but like most forms of technology, its application and development has accelerated in recent times by greater knowledge of what is happening at and beneath the surface and how the process should be applied. It has become clear that the uniformity of surface indentation is critical to achieving the best increase in fatigue strength and on production, maintaining that degree of cold work on subsequent parts once the parameters and acceptable life are established. The accepted method of determining uniform complete indentation or coverage is by visual means using a 10-power magnifying glass. However, it is difficult and time consuming to visually examine large areas, hardened steel parts, fillets, cavities, grooves or holes with that glass since many areas are inaccessible to visual instrumentation. A recent development is the use of Dyescan Tracers which compliment the 10-power glass and are applied before peening to form a thin brittle film which breaks up under the action of peening. An ultra-violet (U.V.) light is then used to examine for coverage with fully peened areas appearing deep purple and partially peened areas appearing white, or speckled white.