Manufacturing process of large diameter seamless steel tube

The manufacturing process of large diameter seamless steel tube is mainly divided into two types: direct forming method (generally through hot rolling and extrusion), expanding method (thermal expansion), its manufacturing process is more complex than ordinary seamless steel tube, and it needs to combine material characteristics and application requirements, so as to ensure its dimensional accuracy and mechanical properties.

Hot rolling process

The perforated tube is hot rolled, gradually reducing the wall thickness and increasing the diameter until the specified size requirements are reached. In the process of hot rolling, the plastic deformation of the steel tube is sufficient, and the tube with uniform wall thickness and large outer diameter can be manufactured. The main processes are:

Rough rolling: initially reduce the tube wall thickness and adjust the outside diameter.
Finishing: Further accurate sizing, so that the steel tube to meet the design requirements of the diameter and wall thickness.
Sizing and reducing: to ensure the uniformity and dimensional accuracy of the outer diameter of the steel tube through the sizing machine.

Through the hot rolling process, continuous production of steel tubes can be achieved, with high efficiency and suitable for mass manufacturing.

Disadvantages: high requirements for equipment, the need for large rolling machines, complex processes and high production costs, and the size of the processed large-caliber steel tube is limited, can not produce large caliber and special purpose seamless steel pipe.

Extrusion process

The basic principle of extrusion is to put the round billet into the extrusion cylinder and apply pressure through the extrusion rod to make the billet flow and form the desired shape under the restriction of the mold. This process significantly changes the internal structure of the material and improves its mechanical properties. The main processes are:

Heating billet: The billet is heated to a high temperature so that it reaches its optimal plastic state.
Perforation: The blank is processed by the perforator to form a hollow tube.
Extrusion molding: the tube is put into the extrusion cylinder, and the pressure is applied to it by the extrusion rod and the mold, so that it passes through the mold outlet and is formed into a seamless tube.
Cooling and straightening: The extruded tube is cooled and straightened to ensure dimensional accuracy and surface quality.

Thermal expansion process

For ultra-large diameter steel tubes, small-diameter seamless steel pipes are usually expanded by thermal expansion process. The main processes are:

Raw material preparation: Select small and medium diameter seamless steel tube after hot rolling as the master tube.
Heating expansion: The master tube is heated to a high temperature state and the pipe is extended to the desired diameter through a die in the expanding machine.
Cooling and straightening: the expanded steel tube is quickly cooled and straightened.

Extremely large diameter steel tubes (usually up to 1 meter and above) can be produced through the thermal expansion process.

Disadvantages: poor quality uniformity, decreased mechanical properties, reduced accuracy.