Almen strip
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An Almen strip is a thin stip of steel used in the control of a shot peening process.
Developed and patented by John O. Almen, the strip was originally supported by 2 knife edges. Later improvement see it being supported on 4 small balls. The strip is placed in the chamber together with the item being shot peened, usually near to an area of the item where the shot peening result is deemed critical. Sometimes special fixtures, simulating the product peening are used for locating the Almen strips. Almen strips are classified into 3 types: 'A', 'N', and 'C'. They differ by their thickness, while they have the same width and length.
- Almen strip of "A" type is predominantly used for shot peening with cast shot or cut wire shot.
- "N" type strips are used usually for glass bead peen and ceramic bead peen.
- "C" type almen strips are used more rarely and are thicker than the other both ones.
Although similar, the specification for almen strip dimensions of the same type slightly vary from one company/organization to another. The almen strips are made from plain carbon steel SAE 1070 and have hardness about 45 HRC.
This test is widely used and the requirements for check are specified in standards. The most rigid requirements are applicable for almen strips and checking devices (almen gages)used in the aerospace industry. The generic requirements can be found in SAE specifications.
