High-quality steel shot and steel grit can apply more kinetic energy to the surface of the workpiece, effectively play the role of cleaning and strengthening, have a long enough anti-fatigue life, and reduce consumption in use. Hardness is very important. If the steel shot or steel grit is too low, it will slow down the cleaning speed and reduce work efficiency. The force of low-hardness pellets cannot be compensated by increasing the impact time. If the hardness is too high, it will increase the probability of the projectile being broken, the consumption will be too high, and the equipment will be worn out, which will increase equipment maintenance costs. Therefore, choosing the appropriate hardness is also very important.