Trivia about steel shot and steel grit: the difference between shot peening, shot peening, and sandblasting surface treatment

Shot peening is mainly the use of mechanical equipment, high-speed operation of a certain size of the steel shot by the centrifugal force of the head thrown, was thrown out of the steel shot and the components of the violent collision blow so as to achieve the purpose of getting rid of steel surface corrosion of a method.

It uses a variety of steel shot: cast iron shot, steel wire cut shot, cast steel shot, stainless steel shot and so on.

Cast steel shot and cast iron shot is the use of dissolved iron in the jet and rapid cooling of the formation of the particle size of 0.8 ~ 5mm iron shot, the surface is very round. It is relatively cheap but slightly less durable. In the shot blasting process by repeated impact iron shot is crushed and excluded as dust.

Steel wire cut shot is used to waste steel wire rope steel wire cut into 2mm small sections and become, its surface with sharp corners, rust removal effect is relatively high and not easy to break the service life is extended, but the price has increased. The latter shot blasting surface is more rough.

Sandblasting rust removal is the use of high-pressure air to bring out the quartz sand jet to the surface of the components to achieve a method of rust removal. The sources of quartz sand are: river sand, sea sand and steel sand, artificial sand and so on. The cost of sand is low and the source is wide, but it is very polluting to the environment; the descaling is operated completely by hand, and the roughness of the surface of the components after descaling is small, and it is not easy to meet the requirement of coefficient of friction. Sea sand should get rid of its salt before use.

The above two descaling methods require the environment humidity to be less than 85%. Requirements for the standard of descaling grade of descaling machine National Standard GB8923-88 “Steel Surface Modification Grade and Descaling Grade before Painting” divides the descaling grade into three types: jet or parabolic descaling, manual and power descaling, and flame descaling. Jet or spray descaling is indicated by the letter “Sa”. There are four grades: Sa1 Light spray or jet descaling. There is no visible grease or dirt on the surface of the steel, and there is no poorly adhered oxidized skin, rust, paint coatings, etc. Sa2 Thoroughly sprayed or blasted descaling. The steel surface should be free of visible grease and dirt, oxidized skin, rust and other attachments have been basically removed, and its residue should be firmly attached. The surface of the steel is uniformly arranged after blasting the formation of blast indentations, anti-slip coefficient of 0.35 ~ 0.45. Sa2.5 very thoroughly sprayed or blasted descaling. The steel surface shall be free of visible adherents such as grease, dirt, oxide skin, rust and paint coatings, and any residual traces shall be only dots or strips of slight discoloration. The surface of the steel is uniformly arranged with blast indentations formed after blasting, and the anti-slip coefficient reaches 0.45 to 0.5.Sa3 Jet or blast descaling to make the steel apparently clean. The surface of the steel shall be free from visible adherents such as grease, dirt, oxidized skin, rust and paint, and this surface shall show a uniform metallic luster.

Shot blasting is the use of high-speed rotation of the impeller to throw the small steel shot or small iron shot high-speed impact on the surface of the parts, so you can remove the surface of the parts of the oxidized layer. At the same time, steel shot or iron shot high-speed impact parts surface, resulting in parts surface lattice distortion deformation, so that the surface hardness increases, is a method of cleaning parts surface, shot blasting is often used to clean the surface of the casting or parts surface strengthening treatment. General shot blasting is used for regular shapes, etc., several throwing head up and down, left and right together, high efficiency, small pollution. Repair, shipbuilding industry, shot blasting, sandblasting is commonly used.

Shot blasting is the use of high-speed rotating impeller to throw the abrasive out; sandblasting is the use of compressed air to blow the abrasive out at high speed. Of course, not shot blasting is not necessary to use high-speed rotation of the impeller can not be. In repair, shipbuilding industry in general, shot blasting (small steel shot) used in the pretreatment of steel plate (rust removal before painting); sandblasting (repair, shipbuilding industry with mineral sand) used in the molding of the ship or segment, the role is to remove the old paint and rust on the steel plate, and then re-painted. In the repair and shipbuilding industry, the main role of shot blasting, sand blasting is to increase the adhesion of the paint on the steel plate coating. Studies have shown that, in terms of destruction, the presence of tensile stress on the surface of metal materials is much easier than compressive stress, the surface is compressive stress, the fatigue life of the material is greatly improved, therefore, for shafts and other components that are easy to fatigue fracture usually use shot blasting to form surface compressive stress, improve product life, in addition, metal materials are very sensitive to stretching, which is the reason why the tensile strength of the material is much lower than the compressive strength, which is also Metallic materials generally use tensile strength (yield, tensile) to indicate the reason for material properties.

The working surfaces of the steel plates of the automobiles we ride in every day are peened by shot peening, which can significantly improve the fatigue strength of the material. Shot blasting is a motor-driven impeller body rotation, relying on the role of centrifugal force, the diameter of 0.2 ~ 3.0 pills (cast pills, cut pills, stainless steel pills, etc.) thrown to the surface of the workpiece, so that the workpiece becomes beautiful, or to change the welded tensile stress of the workpiece to compressive stress, improve the service life of the workpiece. Almost used in most fields of machinery, repair, shipbuilding, automobile parts, aircraft parts, guns and tanks surface, bridges, steel structure, glass, steel plate, pipeline and so on. Sandblasting (pill) is the use of compressed air as a driving force will be in the diameter of 40 ~ 120 mesh sand or 0.1 ~ 2.0 or so of the pill sprayed to the surface of the workpiece, so that the workpiece to achieve the same effect, the size of the pill particles are different, to achieve the same treatment effect is not the same.

Focus on: shot blasting can also play a role in strengthening, and now the domestic equipment into a misunderstanding that only shot blasting can achieve the purpose of strengthening. The United States, Japan, the enterprises used to strengthen the shot blasting and use, each with its own advantages. For example, such as gears, such as the workpiece, shot blasting can not change the angle of the shot, can only use frequency conversion to change the initial speed. But it deals with the amount of large, fast, and shot blasting is just the opposite of the effect of shot blasting is not as good as the effect of shot blasting.

Sandblasting is the use of compressed air to the quartz sand blown out at high speed on the surface of the parts to clean up a method. Factory also called blowing sand, not only to rust, but also incidental oil removal, very useful for painting. Commonly used in parts surface rust; parts surface modification (the market sells small wet sandblasting machine is the purpose, the sand is usually corundum, the medium is water); in the steel structure, the application of high-strength bolts for the coupling is a more advanced method, due to the high-strength coupling is the use of the friction between the bonding surface to the transmission of force, so the bonding surface of the quality of the requirements of the combination are very high, this time it is necessary to sandblast on the surface of the bonding Processing.

Sand blasting is used for complex shapes, easy to remove rust manually, low efficiency, bad site environment, uneven rust removal. General sand blasting machine has various specifications of sand blasting gun, as long as it is not particularly small box, you can put the gun in to play clean. The matching product of pressure vessel - head uses sand blasting to remove the oxidized skin on the surface of the workpiece. There is a kind of processing is the use of water as a carrier, driving diamond sand to process parts, is a kind of sandblasting. Shot blasting and sandblasting can play on the workpiece to clean up the purpose of decontamination, the purpose of the next sequence of preparation, that is, to ensure that the roughness requirements of the next process, but also in order to be the consistency of the surface, shot blasting on the workpiece has a reinforcing effect, sandblasting is not obvious. General shot blasting for small steel balls, sand blasting for quartz sand. According to different requirements, the number of subheads. Precision casting almost every day with sandblasting, shot blasting.