Almen strip
Encyclopedia
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 gages) used in the aerospace industry. The generic requirements can be found in SAE specifications.
Shot peening
Shot peening is a cold working process used to produce a compressive residual stress layer and modify mechanical properties of metals. It entails impacting a surface with shot with force sufficient to create plastic deformation...
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.
- Almen strip of "A" type is predominantly used for shot peening with cast shot or cut wire shotCut wire shotCut wire shot is manufactured from high quality wire in which each particle is cut to a length about equal to its diameter. If required, the particles are conditioned to remove the sharp corners produced during the cutting process....
. - "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 types.
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
AISI steel grades
The Society of Automotive Engineers designates SAE steel grades. These are four digit numbers which represent chemical composition standards for steel specifications. The American Iron and Steel Institute originally started a very similar system...
and have hardness about 45 HRC
Rockwell scale
The Rockwell scale is a hardness scale based on the indentation hardness of a material. The Rockwell test determines the hardness by measuring the depth of penetration of an indenter under a large load compared to the penetration made by a preload. There are different scales, denoted by a single...
.
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.
External links
- Shot Peening Universe FAQ
- Industrial Metal Finishing, Inc. Glossary Comprehensive glossary of Metal Finishing terms and process descriptions, including Almen Strip