Shot peening s used primarily to prevent fatigue failures that originate on the surface of a part. It is a process used to produce a compressive residual stress layer and modify the mechanical properties of metal. It requires a surface to be impacted with shot media (usually round metallic, glass or ceramic material) with force whereby it creates plastic deformation. Plastic deformation induces a residual compressive stress in a peened surface along with tensile stress in the interior. The process is similar to sandblasting but instead of etching, each of the particles functions similar to a ball-peen hammer thus changing the mechanical properties of the surface. The particles are applied with such force which usually means that less material is removed and less dust is created. PEENING PROCESSES AND EQUIPMENT Popular methods for peening include air blast systems and centrifugal blast wheels systems. With the air blast systems, shot media is introduced by various methods into the path of high pressure air and accelerated through a nozzle directed at the part. The centrifugal blast wheel systems consist of a high speed paddle wheel. Shot media is introduced in the center of the spinning wheel and propelled by the centrifugal force by the spinning paddles towards the part by adjusting the media entrance location, effectively timing the release of the media. Wheel blast systems include satellite rotation models, rotary through-feed components and other manipulator designs. There are overhead monorail systems as well as reverse-belted models. Work piece holding equipment includes rotating index tables, loading and unloading robots and jigs that hold multiple work pieces. For larger work pieces, there are manipulators available to reposition them to expose features to the shot blast stream. Other peening methods include ultrasonic peening and wet peening. Another method is laser peening which doesn’t use any media. SHOT PEEN MEDIA Media options include spherical cast steel shot, ceramic bead shot, glass bead shot or conditioned (rounded) cut wire shot. Cut wire shot is preferred because it maintains its roundness as it is degraded, unlike cast shot which tends to break up into sharp pieces that can damage the work piece. This shot can last five times longer than cast shot. Because peening requires shot to be of a consistent hardness, diameter and shape, a mechanism for removing shot fragments throughout the process is suggested. Types of equipment available include various types of separators to clean and recondition the shot, and feeders to add new shot automatically to replace any damaged material. PEENING APPLICATIONS AND EFFECTS Shot peening is used on cams and camshafts, clutch springs, connecting rods, crankshafts, gearwheels, gear parts, leaf, coil and suspension springs, air-suspension beams, rock drills, wheels and turbine blades. It is also used in foundries for sand removal, de-coring, de-scaling and surface finishing of castings such as engine blocks and heads. The de-scaling action can be used in the manufacturing of steel products such as strip, plates, sheets, wire and bar stock. Shot peening is often used in aircraft repairs to relieve tensile stresses built up in the grinding process and replace them with beneficial compressive stresses. Depending on the size and shape of the part, the material the part is made of, the type of shot material used, the quality of the shot, the intensity the shot is applied and the application coverage area, shot peening can increase fatigue life over 800%. Some sources claim the process can increase it to 1000%. Shot peening may also be used for cosmetic effects. The surface roughness resulting from the overlapping dimples causes light to scatter upon reflection. Because peening typically produces larger surface features than sand-blasting, the resulting effect is more pronounced. KEY PARAMETERS Intensity is a key parameter of the shot peening process. This refers to the velocity of the media and how it impacts the work piece. It is suggested to determine what is referred to as the "intensity of the blast stream" by measuring the deformation of the material that is created in the shot peening process. Coverage, which refers to the amount of the surface peened, is variable due to how the shot blast stream is applied to the work piece. The stream is typically cone-shaped which allows for the shot to be applied at varying angles. Processing the surface with a series of overlapping passes improves coverage but bear in mind that variation or striping will still be present. Incomplete impact coverage creates the risk of fatigue cracking of the work piece. Overpeening will cause excessive cold working of the surface of the piece which can also cause fatigue cracks. USED PEENING MACHINES Liberty Machinery buys and sells Used peening machines. They are classified as S5054 and B2754. These cover Air/Shot Blast Peening, Centrifugal Shot Blast Peening, Ultrasonic Peening, Wet Peening, Laser Peening and Blast Cleaning machines. Used Shot Peening Machines in stock: Progressive, Clemco and Zero Blast-N-Peen See our Used Shot Peening Machines For Sale Back