Shot Peening Equipment
Shot peening is a cold metalworking process that seeks to subtly deform a surface in order to induce compressive stresses and relieve tensile stresses. These compressive stresses help the surface of the metal to become stronger, more resistant to fatigue and, most notably, more resistant to cracking.
Quick links to Shot Peening Equipment Information
Purpose of Shot Peening Equipment
Shot peening is also considered a blasting process, but unlike the one to which it is most similar, sandblasting, it does not deform through abrasion, but rather the mechanism of plasticity. Shot peening equipment provides valuable strengthening services for metal products in a variety of industries, most notably aerospace, automotive manufacturing, architecture, construction and general manufacturing.
Application of Shot Peening Equipment
Peening is performed after the primary fabrication of metal products, such as camshafts, gear parts, clutch springs, turbine blades and connecting rods. Shot peening equipment can additionally be used in foundries, where it performs descaling, sand removal, decoring and surface finishing services on castings like cylinder heads and engine blocks.
The equipment’s descaling capabilities are also used on steel products like bar stock, wire, strips, sheets and plates. In addition to clutch springs, shot peening helps finish other springs that are important to automotive function, such as engine valve springs (compression springs), extension springs, OEM valve springs and leaf springs. In aerospace, shot peening equipment provides aircraft repairs by relieving those tensile stresses that built up during the grinding process and replacing them with useful compressive stresses.
Design of Shot Peening Equipment
No matter the media type most shot peening equipment incorporates either as an air blast system or a centrifugal blast wheel to work. The main component of an air blast system is the nozzle. Through this nozzle, the media, after it has been introduced into the path of high pressure, flies toward its target. The main component of a centrifugal blast wheel, on the other hand, is a high speed paddle wheel. Its other components include workpiece holding equipment like loading and unloading robots, rotating tables and jigs that can hold more than one workpiece at a time.
Blast wheel systems can be reverse-belted models, overhead monorail systems, satellite rotation models or have any number of other designs. To work, shot media are placed in the center of the spinning wheel, where the paddles also spin, creating a centrifugal force that propels the media towards the surface to be peened. Moments of release are timed by the adjustment of the media entrance location. Other, less common methods used by shot peening equipment include laser peening (which does not use media), ultrasonic peening and wet peening.
The two main factors that impact the performance of shot peening equipment are coverage and intensity. Coverage, in this context, is the percentage of the surface indented by peening media. It varies based on the angle at which the blast stream hits it, exposure time, shot properties, shot flow (number of impacts), shot properties (chemistry and size) and workpiece properties. Intensity is measured by the Almen strip, which is a strip of SAE 1070 steel placed on the workpiece. The intensity of the blast stream is calculated by measuring the deformation on the Almen strip after shot peening. If the method and media are well-chosen, shot peening can be incredibly beneficial to manufacturers and end-users alike. According to a study commissioned by the SAE Fatigue Design and Evaluation Committee, welds that have not been peened will fail on average after 250,000 cycles, whereas those welds that have been peened can withstand around 2.5 million cycles before giving out.
Types of Shot Peening Equipment
Shot peening equipment uses small pellets, exerted with varying levels, as media. This media may be formed from cast steel, glass bead, ceramic bead or rounded cut wire. Of these, perhaps the most popular is the last one on the list, cut wire shot. Cut wire shot has risen in popularity above cast shot because, able to retain its roundness as it is degraded, it can last up to five times longer. Cast shot, on the other hand, tends to break into sharp pieces as it is applied, causing damage to the workpiece.
Things to Consider When Choosing Shot Peening Equipment
The decision of which blast media to use depends on the nature of the surface being peened. For example, non-metal peening media like ceramic or glass materials are usually reserved for use with softer surfaces that could be damaged from heavier or more angular media.
Accessories of Shot Peening Equipment
This necessitates additional equipment, like shot separators, to remove shot pieces from the workpiece throughout.