Finishing Process

Roughening is the process of pre-treating the surface of a workpiece by using a shot blasting machine or a sand blasting machine to increase its roughness and improve the adhesion of subsequent coatings. Shot blasting machines use high-speed rotating impellers to project steel shots onto the surface, forming a uniform micron-level concave-convex structure through impact. For example, before painting, shot blasting can achieve a surface roughness of 90μm for concrete (using S330 steel shots). Sand blasting uses compressed air to spray abrasives such as quartz sand or corundum, and adjusts the sand particle size and pressure according to demand to achieve controllable roughness. Both are widely used in aerospace, automotive manufacturing and other fields.

Both shot blasting and sand blasting can remove burrs caused by machining. Shot blasting machines use the high-speed impact force of steel shots to remove sharp edges of metal parts, and are particularly suitable for batch processing. Sand blasting (such as air pressure spray guns) is more suitable for thin-walled workpieces or complex structures. It can accurately remove fine burrs after die casting and stamping without damaging the substrate. For example, impeller shot blasting machines can automatically process burrs on forgings, while dry sand blasting is often used for precision parts.

Wet blasting mixes water and micro-powder abrasives (such as glass beads) into a slurry, which reduces dust and controls the accuracy to 0.0001 inches. It is suitable for the final finishing of precision parts (such as gears and tools). Compared with dry blasting, its surface texture is finer, but the processing time is longer.

Shot blasting can achieve surface finishing through small-size steel shots (such as S110), while introducing compressive stress to enhance wear resistance. 

Sand blasting (such as glass sand) is used for matte treatment of aluminum alloy or plastic parts to enhance the appearance texture.

For example, stainless steel tableware often uses dry sandblasting to obtain a uniform matte surface.

Degreasing is often required before sandblasting. Spraying degreasing agent can remove mineral oil and enhance the subsequent sandblasting effect.

Some sandblasting processes directly integrate degreasing functions, such as chemical additives in wet sandblasting can simultaneously degrease.

Shot peening uses high-speed shot streams (cast steel shot, glass shot) to impact the workpiece surface, introducing residual compressive stress to improve fatigue resistance. It is suitable for key components such as springs and gears.

Different from shot blasting, shot peening power mostly comes from compressed air, which is suitable for thin-walled parts, but deformation needs to be controlled.

For example, aircraft engine blades are strengthened by shot peening to extend their service life.

Shot blasting uses continuous impact of steel shot to smooth sharp edges, form uniform rounded corners, and improve workpiece safety and fatigue strength. Sand blasting (such as ceramic shot) can also achieve similar effects, especially suitable for edge processing of precision parts such as medical devices.

Shot blasting can remove the oxide scale and welding slag of hot-rolled steel plates. The impact force of the steel shot can penetrate the dense scale layer.

Sand blasting (such as white corundum) is suitable for descaling stainless steel or aluminum alloy to avoid chemical corrosion.

For example, shot blasting machines are used in steel structure production lines to remove the rolling oxide layer on the surface of steel plates.

Sand blasting machines are widely used to remove residual sand from the surface of castings. High-speed sand streams (such as corundum) can penetrate deep into the pores and remove sand casting residues.

Shot blasting machines can also process castings, but they focus more on strengthening and descaling.

For example, automotive castings often use impeller blasting to remove sand particles and improve surface quality.

Sandblasting is an effective method for removing old coatings. High-speed abrasives (such as glass sand and steel balls) hit the surface, stripping the paint layer without damaging the substrate. Wet sandblasting reduces dust by mixing water and micro powder into a slurry, which is suitable for scenes with high environmental requirements. Shot blasting can also be used to remove coatings over large areas, but the hardness of the steel shot needs to be controlled to avoid excessive wear.

Both shot blasting and sand blasting can effectively remove rust. Shot blasting machines remove scale and rust by impacting steel shots, and are suitable for large steel structures (such as bridges and ships). Sand blasting is more flexible. Quartz sand or garnet can clean scale after heat treatment and can handle complex shapes. For example, manually operated spray guns in shot blasting rooms can be used to specifically treat weld rust.