The Rockwell hardness test was developed as an alternative to Scleroscope, Vickers and Brinell tests. Stanley P. Rockwell invented the test when he found that the other three methods were too time consuming, too big for certain parts and difficult to use. A Rockwell tester is required to complete the assessment of metal rigidity levels. The basic sequence regarding the application of test force advanced the field of hardness testing significantly. The user was finally able to perform and exact hardness test on a multitude of different sized parts in mere seconds. The test methods are defined with three standards: ASTM E18 and ISO 6508 metals and ASTM D785 plastics.
There are two basic types of Rockwell tests: the Rockwell and the Superficial Rockwell. The difference is in measurements. The Superficial Rockwell has a drastically reduced level of minor and major loads than the Rockwell. A Rockwell tester is used with many varying factors, one of which is scales. Rockwell hardness values are represented as a joining of hardness numbers and scale symbols illustrating the indenter along with the minor and major loads. The hardness number is represented by the HR symbol and the scale designation. The Rockwell B and C scales encompass most applications. These scales are used for testing a variety of metals. If no specification is present or if there is uncertainty regarding the compatibility of a certain scale, an examination of material type, thickness of specimen, test location and scale limitations should be made.
There are certain principals that occur when using a Rockwell tester. First, the indenter slides into its position on the part surface. Next, a zero reference position is made when a minor load is used. A dwell time beyond zero applies when using a major load. The minor load is left after the major load is released. The final Rockwell number displays the contrast in depth from the zero reference position. This is an outcome of the major load’s application.
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