Using the Ervin tester students are able to see how coverage develops and how to establish a saturation curve while physically touching and examining the strips during different stages. The Ervin test machine is a great tool for analyzing peening media for durability and the efficiency of transferred kinetic energy. It allows one to compare different media under controlled conditions. The machine consists of a wheel with two blades, a target and re-circulating device, each of which rotate at different speeds around a common centerline. With a weight of only 80 kg and requiring a relatively small workspace (dimensions of 80 x 80 x 60 cm) it fits on almost every workbench. The test media remains in the machine for a predetermined number of cycles and durability is simply determined by the number of passes against the target that are required to reduce the media to an unusable size. Since the completion of such a test is very time consuming (between 1 and 8 hours depending upon the durability of the media that is being tested) it focuses on the effectiveness of kinetic energy. However, the students are theoretically acquainted with the entire procedure. The test machine is equipped with a peening attachment that enables one to mount an Almen test strip and expose it to the shot stream in the chamber. During the presentation Almen A strips are exposed to 0.5 and 0.8 mm peening media at different exposure times. A complete saturation curve is established so the students can see the different arc heights and varied percent of coverage reached at different exposure times. Two different media sizes are purposely chosen to demonstrate the significant influence of the shot size on the intensity and surface roughness.

The machine comes also with a frequency inverter allowing for a change in shot velocity, which in turn allows even more opportunities to duplicate the characteristics of production machines. Only 250 grams of media are needed for a test to accurately predict effects whereas in a production environment you would normally need many tons of media.

The Ervin test machine (named after the developer) is a simple portable piece of equipment that helps to demonstrate the fundamentals of shot peening being taught in the basic course. The training is designed to give students a practical knowledge of how media properties such as hardness, size, density and durability interact and determine the efficiency of energy transfer and consequently the economy of the shot peening process itself.