All You Need to Know About Almen Strips

Almen strips are mainly used for quantifying the intensity of the shot peening procedure. Shot peening is mainly a cold-working procedure that is used for producing compressive residual stress layer on metal parts and also to modify its mechanical properties. These strips were developed and patented by John O Almen and originally, they were supported by two knife edges. With time, some improvements were made and now these strips are supported on four small balls. The strip deforms into an arch due to the compressive stress caused by shot peening procedure. This deformation can be easily measured with the help of a gauge. Under defined peening conditions, these strips always show the same arc height.

There are three types of strips: A, N and C and even though the width and length is the same, they differ in thickness. Predominantly, the A type strip is used in the shot peening procedure with cut wire shot or cast shot. Use of C type strip is very rare and compared to other two types, these are thicker. The third and last type N is usually used for ceramic bead peen or glass bead peen.

What are these strips made of?

The strips are made from plain carbon steel SAE 1070. Carbon steel is mainly a type of steel in which carbon is the interstitial alloying constituent in the 0.12-2.0% range. Hardness of these strips is about 45 HRC.

Apart from the chemical and mechanical properties, flatness is a key value for these strips. If the tolerance for the flatness of a strip is small, the quality and cost of the strip will go higher. Measuring flatness of the strip before the treatment is important because bending of the strip is measured only after peening.

For many years, these strips have been used in the shot peening industry for monitoring the amount of compressive stress the peening operation produces. It is held in a fixture and blasted on one side. The blasting ‘bows’ up the strip due to the uneven stress applied on it from one side. Specifications such as AMS S13165 and SAE 5442 govern this procedure. This deflection can also be related to amount of residual stress in the part itself. When it doesn’t represent a thick part, it is considered a good measure of peening control and intensity.

Importance of choosing a reliable manufacturer

There are several shot blasting machine manufacturer in India that also make these strips from high quality materials. It is recommended to do some research before buying these strips because only a high quality strip will ensure how effective the shot peening procedure will be. Some of the renowned manufacturers offer a variety of strips that are durable and highly effective. They are perfect to be used as a specimen for measurement of arc height and coverage in the shot peening procedure. Only a reputed company will manufacture strips that are tested on all parameters before being delivered in the market.

Carlsen is a professional avid blogger who writes articles related to latest technologies