An Almen strip is a thin strip of SAE 1070 steel used to quantify the intensity of a shot peening process.
Developed and patented by John O. Almen, the strip was originally supported by 2 knife edges; later improvements see it being supported on 4 small balls. The strip is placed in the chamber in place of the item to be shot peened, usually near to an area of the item where the result is deemed critical, sometimes located by a special fixture. Compressive stress introduced by the peening operation causes the strip to deform into an arch, which is measured using a gauge.
Almen strips are classified into 3 types: 'A', 'N', and 'C'. They differ in their thickness, while they have the same width and length.
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 gauges) used in the aerospace industry. The generic requirements can be found in SAE specifications.
Another operation to gauge the intensity of a shot peening process is the use of an Almen round, developed by R. Bosshard.
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An Almen round is a thin round disk used to quantify the intensity of a shot peening process. Developed in 1994 by Rudolf Bosshard in Switzerland, it is a modification of the Almen strip method, which is used worldwide as a surface treatment testing method in the field of shot peening. The basic principle is the same, but due to the simple shape and minimized size, the Almen round is more suitable for automated processing and installation on dummy rigs. Also instead of the Almen block according SAE J442, here a matching device is used and if connected to electronic processing unit, the Almen value according AMS-S-13165 can be evaluated in one run.
Shot peening can be used to recondition distorted steel conveyor belts. The shot peening process is quick and cost-effective compared with other methods and does not interrupt daily production. A deformed steel belt has the following disadvantages:
In metallurgy, peening is the process of working a metal's surface to improve its material properties, usually by mechanical means, such as hammer blows, by blasting with shot, focusing light, or in recent years, with water column impacts and cavitation jets. With the notable exception of laser peening, peening is normally a cold work process tending to expand the surface of the cold metal, thus inducing compressive stresses or relieving tensile stresses already present. It can also encourage strain hardening of the surface metal.