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Problems of shot blasting in aluminium castings should be paid attention to

Shot blasting is also the name of a mechanical surface treatment process. Similar processes include sand blasting and shot blasting. Shot blasting is a cold treatment process, which is divided into shot blasting cleaning and shot blasting strengthening. As the name suggests, shot blasting cleaning is to remove surface oxide scale and other impurities and improve appearance quality. Shot blasting strengthening is to continuously impact the strengthened workpiece surface with high-speed projectile (60-110m / s) flow, forcing the target surface and surface (0.10-0.85mm) The following changes occurred during cyclic deformation: 1. The microstructure was modified; 2. Residual compressive stress is introduced into the non-uniform plastic deformation outer layer, and residual tensile stress is generated in the inner surface layer; 3. The outer surface roughness changes (RA RZ). Effect: it can improve the fatigue fracture resistance of materials / parts, prevent fatigue failure, plastic deformation and brittle fracture, and improve fatigue life.

The principle of shot blasting is to use the motor to drive the impeller body to rotate (directly or driven by V-belt), and by the action of centrifugal force, throw the projectile with diameter of about 0.2 ~ 3.0 (including cast steel shot, steel wire cutting shot, stainless steel shot and other types) to the surface of the workpiece, so as to make the surface of the workpiece reach a certain roughness, make the workpiece 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 paint film adhesion of the subsequent painting of the workpiece is also improved. Shot blasting is almost used in most fields of machinery, such as shipbuilding, auto parts, aircraft parts, gun and tank surface, bridge, steel structure, glass, steel plate profile, anti-corrosion of inner and outer walls of pipeline and even road surface.

Improper selection of steel shot will affect the normal operation of shot blasting machine and may also cause machine failure. Steel shot for shot blasting machine generally includes steel wire cutting shot, alloy shot, cast steel shot, iron shot, etc.

Customers who use shot blasting machines want to find suitable steel shot. Choosing good quality steel shot can not only improve the service life of shot blasting machines and their vulnerable parts, but also improve the surface quality of products. Generally speaking, the type and size of steel shot mainly depends on the workpiece you want to clean:

Non ferrous metals generally use aluminum shot or stainless steel shot; Steel shot shall be selected for ordinary steel and its weldments, castings and steel;

The larger the steel shot diameter, the higher the surface roughness after cleaning, but the cleaning efficiency is also high;

The cleaning efficiency of steel grit or steel wire cutting shot with irregular shape is higher than that of spherical shot, but the surface roughness is also higher;

The projectile with high cleaning efficiency also wears the equipment quickly (relatively), which is only calculated by the service time, but it is not fast compared with the production efficiency.

a) The hardness is directly proportional to the cleaning speed, but inversely proportional to the service life. Therefore, the hardness is high, the cleaning speed is fast, but the service life is short and the consumption is large. Therefore, the hardness should be moderate (about HRC40-50 is appropriate) and the use effect is the best.

b) Moderate hardness and excellent rebound, so that the steel shot can reach every place in the cleaning room and reduce the processing time.

c) Internal defects of projectiles, such as pore cracking and internal shrinkage, can affect their service life and increase consumption.

d) If the density is greater than 7.4g/cc, the internal defects tend to be the smallest.
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