Manufacturing method of seamless steel pipe

　　Seamless steel pipe is a kind of long steel with hollow section and no joint around. The seamless steel pipe has hollow section and can be used as the pipeline for conveying fluid, such as oil, natural gas, gas, water and some solid materials. Compared with solid steel such as round steel, seamless steel pipe is lighter in weight when its bending and torsion strength is the same. It is a kind of economic section steel, which is widely used in the manufacture of structural parts and mechanical parts, such as oil drill pipe, automobile transmission shaft, bicycle frame and steel scaffold used in construction. Using seamless steel pipe to make annular parts can improve the material utilization rate, simplify the manufacturing process, save materials and working hours, such as rolling bearing rings, Jack sleeves and so on. Steel pipe is also an indispensable material for all kinds of conventional weapons. Gun barrel and barrel should be made of steel pipe.

　　According to different production methods, it can be divided into hot-rolled pipe, cold-rolled pipe, cold drawn pipe, extruded pipe, etc.

　　1. Hot rolled seamless steel pipe is usually produced on the automatic pipe mill. After checking and removing the surface defects of the solid tube blank, it is cut into the required length, centring on the end face of the piercing end of the tube blank, and then sent to the heating furnace for heating and piercing on the piercing machine. In the process of piercing, a cavity is gradually formed inside the tube blank under the action of the roller and the plug, which is called the blank tube. Then it is sent to the automatic pipe rolling mill to continue rolling. Finally, the wall thickness is adjusted by the whole machine, and the diameter is calibrated by the sizing machine to meet the specification requirements. It is an advanced method to produce hot rolled seamless steel tube by continuous pipe mill.

　　2. In order to obtain smaller size and better quality seamless tubes, cold rolling, cold drawing or a combination of both must be used. Cold rolling is usually carried out on a two high mill. The steel tube is rolled in an annular pass composed of a variable cross-section circular groove and a stationary conical plug. Cold drawing is usually carried out on 0.5-100t single chain or double chain cold drawing machines.

　　3. In extrusion process, the heated tube blank is placed in a closed extrusion cylinder, and the piercing rod and the extrusion rod move together to extrude the extruded part from the smaller die hole. This method can produce small diameter steel pipe.