Whenever trying to reproduce an Almen specification, it is necessary to determine the short saturation peculiar to the variables (material, particle size, distance, pressure or turbine speed etc.) involved, as a function of the relatively small time (t), measuring the resulting strain (Almen Intensity). The test should be repeated using a time equal to 2t. The operation is repeated successively until twice the intensity increases less than 10%. The previous time may be considered as saturation time or 100% coverage and shall be within the range of specified intensities.
If it is outside of it, the operation must be repeated correcting the variables to make it happen. The resulting curve must be filed and the operating conditions recorded for future guidance. In very long operations or in serial productions, the measurement should be repeated every six or eight hours when working with steel shot and every hour or two with glass balls.
2 °) Usually the coverage is specified. When omitted, it is recommended to provide 100%.
3 °) Restrictions regarding contamination problems, roughness limits, etc., lead to complementary specifications of the nature of the material and / or particle size.
4 °) Finally, in special cases methods and detailed devices are indicated to ensure the accurate reproduction of the process.
Whatever the degree of detail of the specification, the first step is to position the Almen plate on the same level as the surface of the part to be treated, reproducing the same automatism conditions as for the process application. For example, for “peening” on an inner corner of a crankshaft bearing (figure), it is usual to modify a discarded part by machining a support block housing cavity with an Almen plate, locating it exactly at the point to be hit. The part is mounted on a rotating device and the test is performed with all the automation features for future reproducible reproduction parts. It is common to use simple devices designed with the sole care of correctly positioning the nameplate and reproducing the movements in front of the pistols or turbines, such as the surface to be blasted.
As already said, it is not enough that the intensity to be reproduced is equal to the specified. It has to be obtained in the saturation area of the intensity / time curve, which requires the observance of a working method.