What is shot peening?
Shot peening is a process that uses a high-speed rotating impeller to shoot the shot out at high speed, hit the workpiece surface, and clean or strengthen the workpiece surface. The materials used for shot peening include steel shot, aluminum shot, glass ball and ceramic shot.
Characteristics of shot peening
1) High cleaning efficiency, low cost, few operators, easy to realize mechanization, suitable for mass production;
2) No compressed air is used to accelerate the projectile, so there is no need to set up a high-power air compression station, and the cleaned surface is free of moisture;
3) Poor flexibility, limited by the site, some blindness when cleaning the workpiece, and it is easy to produce dead corners on the workpiece surface that cannot be cleaned;
4) The equipment structure is complex, there are many vulnerable parts, especially the blades and other parts wear fast, there are many maintenance hours and high costs;
5) Generally, light and small projectiles cannot be used.
Shot peening process
Shot peening is also the name of a mechanical surface treatment process, similar to sand peening and shot peening. Shot peening is a cold treatment process, which is pided into shot peening cleaning and shot peening strengthening. Shot peening cleaning, as the name implies, is to remove surface oxide and other impurities to improve the appearance quality. Shot peening strengthening is to use high-speed motion of the projectile (60-110m/s) flow to continuously impact the surface of the strengthened workpiece. The target surface and surface layer (0.10-0.85mm) are forced to undergo the following changes during cyclic deformation:
1. Modification of microstructure;
2. Non-uniform plasticized outer surface introduces residual compressive stress and inner surface produces residual tensile stress;
3. The outer surface roughness changes (Ra Rz).
Impact: it can improve the fatigue fracture resistance of materials/parts, prevent fatigue failure, plastic deformation and brittle fracture, and improve the fatigue life.
Structure principle
The two disks in the shot peening device are riveted together to form an impeller body. The impeller body is provided with eight blades, and the impeller body and the shot splitting wheel located in the center of the shot peening wheel are mounted on the main shaft driven by an electric motor. The cover is lined with a guard plate, and the cover shell is provided with a directional sleeve and a shot tube. When working, the shot from the shot tube into the shot peening device. The projectile wheel, which rotates synchronously with the blades, gives the projectile its initial velocity. The projectile flies out of the window of the directional sleeve and is thrown to the high-speed rotating blade outside the directional sleeve. After being further accelerated by the blade, it is thrown onto the surface of the cleaned workpiece. Because the synchronous rotation of the shot wheel and the blade ensures the non-vibration transmission of the projectile to the blade, thus reducing the wear of the blade.
Peening principle is the body of the motor to drive the impeller rotation (direct drive or use the “V” belt drive), by the effect of centrifugal force, the diameter is about 0.2 ~ 3.0 of the projectile (have pills for cast steel, steel cut wire shot, stainless steel, such as different types) to the surface of the workpiece, the workpiece surface reaches a certain roughness, makes the artifacts become beautiful, Or change the welding tensile stress of the workpiece to compressive stress, improve the service life of the workpiece. By improving the surface finish of the workpiece, the film adhesion of the subsequent painting of the workpiece is also improved. Shot peening is almost used in most fields of machinery, such as shipbuilding, automobile parts, aircraft parts, surface of guns and tanks, Bridges, steel structures, glass, steel plate profiles, pipe internal and external wall corrosion and even road surface and so on.
Bring about shot peening machine
Shot peening machine is a kind of processing technology which impacts steel sand and steel shot on the surface of material object at high speed by shot peening device. It is faster and more efficient than other surface treatment techniques, and allows for partial retention or stamping after the casting process.
Shot peening machine can also be used to remove burrs, diaphragms and rust, shot peening machine can also be directed at a partially coated surface to remove surface contaminants and provide an increase in coating adhesion surface profile, to achieve the purpose of strengthening the workpiece.
Shot peening equipment is first applied to the surface of cast steel, cast iron sand and oxide cleaning. Almost all steel castings, gray castings, ductile iron and so on should be shot peening. This is not only to remove the oxide scale and sand on the surface of the casting, but also an indispensable preparation process before the quality inspection of the casting. For example, before the non-destructive inspection of the large gas turbine casing, strict shot peening cleaning must be carried out to ensure the reliability of the inspection results.
Casting shot peening
In general casting production, shot peening is an essential technological means to find surface defects of castings such as subcutaneous pores, slag holes, sand sticking, cold insulation, peeling, etc.
The surface cleaning of non-ferrous metal castings, such as aluminum alloy and copper alloy, in addition to removing the oxide scale and finding the surface defects of the castings, the main purpose is to remove the burr of the die-casting parts by shot peening and obtain the surface quality with decoration significance, so as to achieve comprehensive results.
Mechanical adjustment
The new shot peening device must correctly adjust the position of the directional sleeve window before use, so that the projectile thrown as much as possible to be cleaned on the surface of the workpiece, in order to ensure the cleaning effect, reduce the wear of the indoor wall wear parts. The position of the directional sleeve window can be adjusted by referring to the manual.
Shot peening material
Common shot peening materials are steel shot, aluminum shot, ceramic powder, steel sand, walnut sand, corn cob, glass beads, resin sand, plastic sand and so on.
Source: China Pipe Fittings Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)
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