Heat expanded seamless carbon and alloy steel pipe

The maximum outer diameter of the hot rolled seamless steel pipe produced is less than 530mm; Continuous rolling pipe less than 460mm; Large Pilger less than 660mm. When a larger diameter steel pipe is needed, in addition to the use of pipe jacking method and extrusion method, the thermal expansion method of steel pipe can be used, which can currently produce the largest seamless steel pipe with an outer diameter of 1500mm thin-walled pipe.

There are three methods for thermal expansion of steel pipes: skew rolling, drawing and pushing, these three methods started in the 1930s, and the skew rolling and drawing need to heat the steel pipe as a whole before deformation processing, while the pushing type does not need to heat the whole steel pipe.

Diagonal rolling expanding machine:

The process of expanding in diagonal rolling is as follows: the heated pipe material is transported to the expanding machine in diagonal rolling. The expanding mill consists of two rolls of the same shape. The axis of the two rolls is at a 30° Angle with the rolling line, and the two rolls are driven separately by the motor to rotate in the same direction. In the expanding deformation area, the top head participates in the deformation, the steel pipe makes spiral movement in the deformation area, and the pipe wall is rolled by the roll and the top head, so that the expanding diameter is expanded, the wall thickness is thinned, and the axial force of the top head is borne by the top rod, which can be arranged at the entrance side or installed at the exit.

The steel pipe with wall thickness of 6 ~ 30mm and maximum outer diameter of 710mm can be produced by diagonal rolling and expanding. The disadvantage is that there are residual helical traces on the inner and outer surfaces of the steel pipe, which reduces the surface quality, so it is necessary to set the whole machine and the sizing machine. This kind of expanding machine has huge equipment, high investment cost, and the variety is limited to a certain extent, and can not produce thick wall pipe.

Draw-type expanding machine

Draw-type expanding is a production method with low production capacity, but it is still used because of its simple equipment and processing and easy mechanization. Drawing type expanding machine can be both cold drawing and hot drawing expanding, when the expanding amount is not large and it is required to improve the physical and mechanical properties and dimensional accuracy of the steel pipe, cold drawing expanding can be used. The process of hot drawing and expanding of steel pipe is: heating of pipe material, expanding of pipe end, expanding of pipe, straightening, cutting of head and tail, inspection. The expansion rate of each heating is 60 ~ 70%, and the maximum diameter of 750mm steel pipe can be produced.

The main working principle of drawing type thermal expansion is: through a group (generally 1 to 4) of gradually increasing diameter of the head, inserted and through the full length of the inner hole of the steel pipe, so that the diameter of the steel pipe is expanded, the wall thickness is reduced, and the length is slightly shortened.

The main tools of the drawing type expanding machine are the expanding head, the expanding pipe head and the lifting rod. The advantages are simple equipment, easy to operate, easy to master; Wide range of product varieties, specifications, can also produce rectangular shaped steel pipe. The disadvantages are long production cycle, low productivity, and large consumption of tools and metals.

Propulsive expanding machine

The working principle of the propulsive expanding machine is to place the raw steel pipe in the medium frequency induction coil, after the medium frequency induction heating, by the movement of the hydraulic cylinder piston or the pushing head of the hoist, push the tail of the steel pipe to make the steel pass through the axially fixed conical mandrel from the tube head in order to achieve the purpose of expanding the meridian; When the end of the steel pipe is pushed into the mandrel, a new steel pipe to be processed is added after the pusher head returns and continues to push the tail of the new steel pipe, and the head of the new steel pipe pushes the tail of the previous steel pipe over the mandrel, thus completing the expanding of a steel pipe. Since only the steel pipe in the deformation section is heated, the steel pipe after deformation is easy to bend, and the wall thickness and length of the expanding pipe are limited, the advantages of the propulsive expanding machine are high metal recovery rate, simple equipment, low energy consumption, and the disadvantage is that the performance consistency of the steel pipe in the length direction is slightly poor, and the production efficiency is low. Because of its small investment, it has recently built many new sets in North China. At present, it can produce steel pipes with wall thickness of 6 ~ 30mm and maximum outer diameter of 860mm.