Defects In The Quality Of Hot Expanded Steel Tubes

The expansion of hot-rolled seamless steel pipe has two methods: vertical rolling expansion and cross-rolling expansion. The quality defects of longitudinal rolling expansion mainly include surface cracks of steel pipes and cracking of pipe body, uneven wall thickness, inner straight road, inner pit, wrinkles and bending. The quality defects of the cross-rolling tube expansion are basically the same as those of the two-roll cross-rolling tube mill, including uneven wall thickness, surface cracks and scratches, rolling, spiral and spiral inversion, and inner pit. Wait.

There are pull-type and push-pull tube expansion processes in the process of longitudinal rolling expansion. The deformation process is divided into three stages: under the action of the cone surface of the head, the tube wall of the blank tube first bends and deforms; as the diameter of the head increases gradually, the spiral submerged arc tube and the seamless tube are expanded and reduced; The trunk pipe after the expansion is sizing and straightening by the cylindrical section of the head. Obviously, the expansion is mainly in the second stage. The main product defects in the vertical rolling expansion process are: cracking of the surface of the steel pipe and cracking of the pipe body, uneven wall thickness, internal straight road, wrinkles, internal pits, and bending.

The cross-rolling tube expansion process originates from the secondary perforation process. It is a cross-rolling machine with two tapered rolls and arranged horizontally. The diameter of the roll gradually increases from the inlet to the outlet of the deformation zone. The roll axis intersects the rolling line in a space to form a feed angle and a roll angle. The two rolls are single-supported and are separately driven by two motors, and the transmission mechanism is located at the outlet side of the rolling mill. The position of the rolls can be adjusted along the axis of the rolling line. The guide plates are arranged up and down. The deformation is divided into three parts: the flattening and reducing area, the reducing area and the rounding area.

Flattening and reducing the deformation: The blank tube first contacts the tapered roller in the state of the cantilever beam and advances under the action of friction. At this point, the blank tube is only in contact with the rolls and is not in contact with the plug. The deformation is mainly the flattening and reducing the deformation. When the diameter reduction is too large, the wall of the steel pipe sometimes thickens. The size of the flattening and reducing area is related to the position of the head. The position adjustment of the head is mainly to achieve a bite of the blank tube and create good mechanical and kinematic conditions for the secondary biting and the wall expansion.

Reduced wall expansion and deformation: It is the main deformation zone of the cross-rolling expansion pipe. In this area, the blank tube is reduced in diameter and expanded. Since the elongation coefficient is close to 1, according to the law of metal volume invariance, almost all of the metal thinned by the steel pipe wall becomes a metal that needs to be replenished due to an increase in the outer diameter.

The deformation of the metal mainly occurs in the circumferential and radial directions of the blank tube. Since both the roll and the plug can be moved in the respective axial directions, the specifications of the expanded steel pipe can be changed by changing the position of the roll and the plug. When the position of the roll and the head is adjusted, the amount of deformation in the reduced wall area does not change any more.

A worker from a steel pipe company, which is located in China.