Automatic conveying sand blasting machine

1. Workpiece surface roughness

The factors affecting the surface roughness include the strength and hardness of the part material, the sandblasting diameter, the angle and speed of sandblasting, and the original surface roughness of the parts.

Under the same other conditions, the higher the strength and surface hardness value of the part material, the more difficult the plastic deformation, the shallower the crater and the smaller the surface roughness value; the smaller the diameter of sandblasting, the slower the speed, the shallower the crater, and the smaller the surface roughness value; the larger the spraying angle, the smaller the normal component of sandblasting speed, the smaller the impact force, the shallower the crater and the tangential velocity of sandblasting The larger the grinding effect of sand blasting on the surface is, the smaller the surface roughness value is. The coarser the original surface is, the smaller the reduction of roughness is after sandblasting; on the contrary, the smoother the surface is, the rougher the surface becomes after sandblasting. When the parts are sandblasted with high strength, the deep crater will not only increase the surface roughness, but also form a large stress concentration, which seriously weakens the effect of sandblasting.

2. Strength of sandblasting machine

The main process parameters affecting the sand blasting strength are: sand blasting diameter, sand blasting flow rate, sand blasting time, etc. The larger the sandblasting diameter is, the faster the speed is, the greater the collision momentum between sandblasting and workpiece is, and the greater the sandblasting strength is. The residual compressive stress formed by sandblasting can reach 60% of the tensile strength of the parts. The depth of residual k stress layer is usually 0.25 mm, and the maximum limit value is imm. The sand blasting strength needs a certain sandblasting time to ensure. After a certain period of time, the sand blasting strength reaches saturation, and then the sandblasting time is prolonged, and the strength will not increase significantly. In Almen test of sandblasting strength, the characterization of sandblasting strength is the improvement of specimen deformation.

In Almen test, the sandblasting strength is measured by the test piece (used for non-ferrous metal test), test piece a (most commonly used), and test piece C (higher strength). The relationship between test piece a and test piece C is approximately three times. If the strength measured by C specimen is 0.15 ~ 0.20tmn, it is equivalent to 0.45 ~ 0.60mm of specimen a. During the test, the original deformation of the test piece is measured first, and then the tooling for clamping the test piece is placed in the sandblasting box, and the same process as the workpiece is used for spraying. After sandblasting, take down the test piece and measure the deformation arch height.

Automatic rotary sand blasting machine

3. Sand blasting coverage

Measurement of coverage: apply a layer of colored glaze or fluorescent glaze on the surface of the workpiece, and then sandblast the workpiece according to the process parameters. After sandblasting the workpiece surface once, take out the workpiece, and observe the proportion of residual coating on the surface under the microscope (magnifying glass). If the residual coating is 20%, the sand spraying coverage rate is 80%. When the residue is only 2%, that is, the coverage rate is 98%, it can be regarded as completely removed, that is, the coverage rate is 100%, and there is a required time. To achieve 400% coverage, it takes four times as long.

The factors that affect the coverage rate include the hardness of parts material, sandblasting diameter, spraying angle and distance, sandblasting time, etc. When the hardness of the parts is lower than or equal to the hardness of the standard test piece, the coverage rate can reach 100%; otherwise, the coverage rate will decrease. Under the same sandblasting flow rate, the longer the distance between the nozzle and the workpiece, the smaller the spraying angle and the smaller the sandblasting diameter, the shorter the time to meet the coverage requirements. During sand blasting strengthening, proper size of sand blasting, spraying angle and distance should be selected to make the sand blasting strength and coverage reach the required value at the same time.