Shot Peening

Many studies have been conducted on fatigue cracks of mechanical parts made of metallic material. These failures normally occur for modest loads, lower than the yield strength of the material, after a period of use of many cycles.

Fatigue cracks generally initiate on the surface at the points of maximum tensile stress. Heat treatments of hardening the material, mechanical processing, welding and grinding can induce tensile stresses which add to the operating stresses of the item. Once initiated, the crack propagates until the breakage, generally of a brittle type. Even in Stress Corrosion Cracking phenomena, the residual tensile stress state generated by the manufacturing processes of the items is decisive for the formation of cracks which, starting from the surface of the metal, propagate, in the case of an aggressive environment and in the presence of modest operating efforts, inside the material.

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The process and the obtainable benefits

The shot peening process consists of hitting the surface of a metallic material item with a perfectly controlled jet of steel, ceramic or glass microspheres, projected at high speed. The impact causes the plasticization of the surface layers, inducing, by balance, residual compressive stresses and exerts a beneficial action on the life of the part by slowing down or preventing the formation of cracks.

Among surface treatments, controlled shot peening (widely used in the aeronautical and automotive sectors) is, in many cases, preferable to more traditional thermochemical treatments due to its greater versatility, better environmental impact and relatively limited cost.

Shot peening then improves the distribution of surface tensions possibly disturbed by mechanical machining or heat treatments and significantly attenuates the concentration of stresses caused by notches, threads and surface decarburizations.

Other benefits are the greater resistance to stress-corrosion, the decrease in porosity and finally the surface, by virtue of the surface dimples, obtained through the impact of the spheres, is able to retain any lubrication oils or greases more effectively.

In general, the treatment makes it possible to prolong the service life of the item, increase load levels during operation, reduce weight and dimensions, use highly resistant materials (but considered too sensitive to notching), and, in certain cases, avoid costly redesigns.

This process, combined with a correct design and an initial stress-relieving treatment in the oven, can be decisive for the service life of many products, for different sectors of use.

Operations of Trater

Trater has an air-conditioned shot peening booth measuring 18 meters x 10 meters x 6 meters high, to be able to process the most critical surfaces of any product.

Trater performs shot peening on:

large carpentry structures subjected to fatigue;

piston rods: which intrinsically have notches and surfaces where the efforts are higher;

shafts for the same reasons previously indicated.


The control parameters of the process, which must be absolutely repeatable, are the speed of the abrasive, its mass in relation to its size and its quantity. Everything translates into a surface compression capacity which is measured in Almen degrees.

Trater, thanks to its residual stress measurement laboratory by using diffractometric and strain gauge equipment, is able to measure the induced compression directly on the surface of the items. The diffractometric method is well suited for this purpose. We have a portable device, designed to be used on field, on any accessible surface, to have the analytical result of the work carried out in a few minutes.

On components in which reliability and accuracy are fundamental, subjected to particularly critical working conditions, it is important that our customers can count on a structured and reliable supplier like Trater, which has personnel and means available to perform the commissioned works in the best possible way.
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