scope:

Surface temper etch inspection ("acid etch" testing) for thermal damage as a result of hard finishing (typically, grinding) operations is the most prevalent inspection method in gear manufacturing. The acid etch method relies on contrast in color, resulting from nitric acid severity of attack on thermally affected areas versus those areas that are not thermally affected. There are known issues with maintaining proper nitric acid baths, HCl baths, wash baths, and rinse baths. Assurance that an acid etch system and method is working correctly requires a standard sample. This paper discusses a unique method of producing a sample that has a very consistent amount of thermal damage. Multiple degrees of burn are applied to the sample to ensure that the etch inspection can detect all levels of potential burn on the piece parts. The sample can then be reliably used to test an acid etch system and method to ensure the proper amount of contrast for threshold levels of thermal damage. The developed sample, with standardized burns, may be processed through the etch tanks at frequent intervals (or even simultaneously with piece parts) to ensure the etch system is able to detect any burn that may be present on the actual piece parts. The method of producing the sample is described, and methods of quality control using the standard are proposed.