What is shot blasting and sandblasting, and what is the difference?

Shot blasting process

Shot blasting, also is the name of a mechanical surface treatment process, similar to sand blasting and shot peening. The principle is to use a motor to drive the impeller to rotate, and rely on centrifugal force to throw abrasives with a diameter of 0.2 to 3.0 (such as cast shot, cut shot, stainless steel shot, etc.) to the surface of the workpiece, so that the surface of the workpiece reaches a certain degree of roughness. , Make the workpiece beautiful, or change the welding tensile stress of the workpiece to compressive stress, and improve the service life of the workpiece. Shot blasting is almost used in most fields of machinery, such as shipbuilding, auto parts, aircraft parts, gun and tank surfaces, bridges, steel structures, glass, steel plates, pipes, and so on. In terms of form, abrasives are projected on the surface of parts at high speed and long distance by mechanical methods, collectively called shot blasting. It includes: projecting abrasives to castings with sand, removing sand and core shot blasting, and projecting abrasives to casting, forging, welding and heat treatment parts to remove black skin, nodules, oxide films, and rust spots surface cleaning; Strike abrasives to the surface of steel plates and various shapes for shot blasting pretreatment; For parts such as springs, leaf springs and gears subjected to variable stress, shot blasting to eliminate stress and improve surface fatigue strength; Perform shot blasting to enhance the color of the decorative parts of household appliances or the surface of tableware. But in terms of process classification, shot blasting is limited to a cleaning process for the purpose of removing cast, forging, welding and heat treatment parts. The shot blasting referred to in this article is this concept. For those who use abrasives to project to the surface of the workpiece to achieve the relevant technological goals, they are directly named after their technological requirements, such as: Blasting shakeout, Shot peening, Blasting brighten, etc., to distinguish it from shot blasting.

When the parts are shot blasted, the facilities that can make the parts to be cleaned continuously in the jet stream to achieve uniform shot blasting requirements are called shot blasting equipment, or shot blasting machines. Because of the ever-changing workpieces to be cleaned, the shot blasting equipment is also diverse. Shot blasting equipment of a certain specification is only suitable for cleaning parts within a certain range. The special equipment is suitable for a certain kind of parts.

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Sandblasting process

Sandblasting is a method of using compressed gas to spray the material (commonly used spray materials are copper ore, quartz sand, emery sand, iron sand, Hainan sand, etc.) onto the surface at high speed to clean the part. It not only removes rust, but also removes oil incidentally, which is very useful for painting. It is often used to remove rust on the surface of parts; to modify the surface of parts (the small wet industrial sandblasting equipment sold in the market is for this purpose, the sand is usually corundum, and the medium is water); in the steel structure, the application of high-strength bolts for connection is a relatively advanced Because the high-strength connection uses the friction between the bonding surfaces to transmit force, the quality of the bonding surface is very high. At this time, the bonding surface must be treated by sandblasting. The blasting process is divided into dry blasting and wet blasting.

Dry sandblasting has two types: mechanical sandblasting and air pressure sandblasting, each of which is divided into manual, non-automatic or continuous automatic methods. The manual air pressure sandblasting machine is widely used in China, which also uses various complex shapes. Of small and medium-sized parts.

The abrasive used in wet sandblasting is the same as dry sandblasting. The abrasive can be mixed with water to form a mortar. The abrasive generally accounts for 20%-35%, and it is constantly stirred to prevent settling. Use compressed air into the nozzle to spray the parts, or sand and water Put them into tanks separately, mix them before flowing to the nozzle, and spray them on the parts. To prevent corrosion of steel parts, sodium nitrite and other corrosion inhibitors must be added to the water. In addition, the sand should be dried before next use.

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The difference between shot blasting and sand blasting

But whether it is shot blasting or sand blasting, they are all available in the form of compressed air. Of course, it is not necessary to use a high-speed rotating impeller instead of shot blasting. Generally speaking, shot blasting (small steel shots) is mostly used in steel plate pretreatment (rust removal before painting); sand blasting (ore is used in shipbuilding and repairing industries) is mostly used in forming ships or sections. The function of sand shot blasting machine is to remove the old paint and rust on the steel plate and repaint it. In the ship repair and shipbuilding industry, the main function of shot blasting and sand blasting is to increase the adhesion of the steel plate coating paint.