Several common misunderstandings in steel shot selection

　　To ensure that the surface treatment is fully up to standard, the two core indicators of metal abrasives are: cleaning efficiency and consumption. Several common misunderstandings in steel shot selection: Are rounder cast steel shots better? Is the more uniform the particle size, the better? Is the brighter the appearance, the better?

　　Are the rounder cast steel shots better? Editor's answer: No. In the process of granulating steel shots, the molten steel is cooled from liquid to solid state and shrinks during the cooling process. This shrinkage is carried out in a free state, and there is no riser to reduce the volume after shrinkage like pouring castings. The molten steel is partially replenished, so oval-shaped particles with concave surfaces appear. Such particles have undergone sufficient shrinkage and are not round in shape but dense in structure. Steel shots that have not undergone sufficient shrinkage have good roundness but not dense in structure. , there is shrinkage porosity. Internal defects such as shrinkage cavities. In terms of usage effect, the rounder the steel shot is, the better. Steel shots are usually used in the field of cleaning. The cleaning efficiency of steel shots with high roundness is lower than that of steel shots with good shrinkage. The throwing energy E=1/2mv2. The shrinkage rate of poor roundness is good and the structure is dense. Therefore, for the same volume and mass m, the impact energy is high and it is not easy to break. On the contrary, the steel shot with good roundness has not dense structure. , the particles have small mass, low kinetic energy, and are easily broken.

　　On the market, the reason why most cast steel shots have good roundness and poor quality is because the manufacturers have limited production conditions, the diameter of the granulation tank is small (8-14 meters), and the drop from the centrifugal disk to the water surface is small (0.2-1 meters). ), that is, the width and height of the workshop are not enough to ensure that the centrifugally formed liquid steel particles have sufficient cooling and shrinkage time. The liquid steel particles instantly enter the water, the surface is cooled, and the roundness is good, but the interior has not yet solidified, resulting in shrinkage and many shrinkage holes. During use Steel shot has a high breakage rate. Only when the diameter of the granulation tank is greater than 20 meters and the forming height is greater than two meters can the steel shots be fully shrunk.

　　Is the more uniform the steel shot particle size, the better? Editor's answer: No. In the field of cleaning, the surface of the workpiece is cleaned by steel shot blasting or spraying, forming pits on the cleaned surface. Only when the pits overlap, the entire surface can be completely cleaned. The more uniform the particle size of the steel shot, the longer it takes for the pits and pits to overlap. For steel shots with a certain particle size mixing ratio, the large steel shot plays a cleaning role, and the small steel shot plays a role in cleaning large-grained steel shots. The formation of gaps greatly shortens the shot blasting time, improves the quality of the shot blasting surface, and improves production efficiency.

　　Is the brighter the appearance of cast steel shot, the better? Editor's answer: No. The high carbon cast steel shots currently on the market are divided into primary quenching and secondary quenching. It is difficult to distinguish from the composition, hardness, and metallographic structure. However, secondary quenching steel shots have fine grains and long fatigue life. The grains of the pills are coarse and the fatigue life is low. Because the primary quenched steel shot has not gone through the heating and quenching process, the Fe3O4 oxide film formed on the surface is thin, so it looks very bright; while the secondary quenched steel shot, on the basis of the primary treatment, has After the heating and quenching process, the Fe3O4 film on the surface becomes thicker, does not reflect light, and does not look bright. Therefore, the appearance of cast steel shot is not the brighter, the better, but attention should be paid to whether it has undergone secondary quenching treatment.