The oxide film on the surface of seamless steel pipe is thin and dense, not easy to peel off. Normally, seamless steel pipes will generate 0.2-0.3mm oxide scale in the heating furnace. Casting defects within this range can be removed along with the oxide scale of iron. If the defect is outside this range and the surface defect is not dealt with, it will inevitably be brought into the final product.
Stainless steel seamless pipe provided by stainless steel seamless pipe suppliers usually cannot use flame to clean surface defects of castings. Flame cleaning can cause changes in the composition and crystal phase of the cleaned area of the casting, which affects the corrosion resistance of stainless steel products. Therefore, mechanical cleaning is a common and effective means of surface treatment for stainless steel. The general methods include treatment by oxide scale cleaning machine, water blasting, and shot blasting machine.
The oxide scale cleaning machine for seamless steel pipe fittings consists mainly of steel rolls, driving devices, high-pressure water systems, cooling water systems, and clamping devices. Two rolls with steel wires are installed on the roller seat. The steel rolls rotate at high speed in the opposite direction of the casting, using the steel wire to remove the oxide scale attached to the surface of the casting. The oxide scale cleaning machine is suitable for many types of steel, but the cleaning of the oxide scale is not thorough enough.
The water blasting pool uses circulated cold water as the cooling medium. The high-temperature casting is put into the water tank and the oxide scale on the surface of the casting is removed by the "water blast". The principle is that when water encounters high-temperature casting, it vaporizes instantly, causing a "water blast" and producing a large amount of high-pressure steam. The impact force of the steam acts on the surface of the casting, causing the oxide scale to peel off. At the same time, due to the different sizes of stress between the casting and its surface oxide scale, the oxide scale fracture and fall off rapidly due to the cooling of the water in the high-temperature state. The water blasting pool has a low investment, low maintenance, and low production and operation costs. However, it is only suitable for some austenitic stainless steel seamless steel pipe fittings, such as 301 and 304.
The shot blasting machine is commonly used to clean the oxide scale on the surface of the casting. The shot blasting machine mainly consists of a shot blasting chamber, a blasting head, a shot conveying system, a shot cleaning device, a shot supplement device, a dust removal system, a lubrication system, and an electrical control system. The working principle is to use the high-speed steel shots ejected by the shot blaster to impact the oxide scale on the surface of the casting to make it fall off.
The operation rate of shot blasting machine is high and suitable for many types of steel. The removal effect of the oxide scale is good. However, the shot blasting machine cannot handle high-temperature castings, and generally requires the casting temperature to be below 80℃. Therefore, using a shot blasting machine to clean the oxide scale on castings cannot be done online. It requires the casting to be cooled to below 80℃ before shot blasting operation.