Several major misunderstandings in steel shot selection

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

　　Is the rounder the cast steel shot is, the better? Editor: No. In the process of making steel shot by granulation, 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 casting castings. The molten steel is partially supplemented, so there are elliptical particles with sunken surface. After sufficient shrinkage, the particles are not round in shape but dense in structure, while steel shots that have not been fully shrunk have good roundness but not dense in structure. , there is shrinkage. Shrinkage cavity and other internal defects. From the effect of use, the rounder the steel shot, the better. Steel shot is usually used in the field of cleaning, and the cleaning efficiency of steel shot with high roundness is lower than that of steel shot with good shrinkage. Throwing energy E=1/2mv2, the shrinkage rate of poor roundness is good, and the structure is dense, so the same volume, mass m is large, the impact energy is high, and it is not easy to break. On the contrary, the steel shot with good roundness is not dense. , the particle quality is small, the kinetic energy is low, and it is easy to break.

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

　　The more uniform the particle size of the steel shot, the better? Editor: No. In the field of cleaning, the surface of the workpiece to be cleaned is blasted or sprayed with steel shot, and pits are formed 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 to reach the overlapping of pits and pits. For steel shots with a certain particle size mixing ratio, large steel shots play a cleaning role, and small steel shots play a role in cleaning large-grained steel shots. The gap is formed, which greatly shortens the blasting time, improves the blasting surface quality, and improves production efficiency.

　　Is the brighter the appearance of cast steel shot, the better? Editor: No. At present, the high-carbon cast steel shots on the market are divided into primary quenching and secondary quenching, which are difficult to distinguish from the composition, hardness, and metallographic structure, but the secondary quenching steel shot has fine grains and high fatigue life. The pellet grains are coarse and the fatigue life is low. The primary quenched steel shot, because there is no further heating and quenching process, the Fe3O4 oxide film formed on the surface is relatively thin, so it looks very bright; and the steel shot after secondary quenching, due to the primary treatment, and After heating and quenching processes, 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 as bright as possible, but attention should be paid to whether it has been subjected to secondary quenching treatment.