Cross rolling is a rolling method between longitudinal rolling and cross rolling. The rolling of the rolled piece rotates along its own axis, deforms and advances between two or three rolls whose longitudinal axes intersect (or incline) in the same direction of rotation. Cross rolling is mainly used for piercing and rolling of pipes (such as the production of thermal expansion seamless pipes
), and periodic section rolling of steel balls.
The cross rolling method has been widely used in the production process of heat-expanded seamless steel pipes. In addition to the main thermal expansion process of piercing, it is also used in rolling, leveling, sizing, elongation, expansion and spinning, etc. in the basic process.
The difference between cross rolling and longitudinal rolling and cross rolling is mainly in the fluidity of metal. The main direction of metal flow during longitudinal rolling is the same as that of the roll surface, and the main direction of metal flow during cross rolling is the same as that of the roll surface. Cross rolling is between longitudinal rolling and cross rolling, and the flow direction of deformed metal is Forming an angle with the direction of movement of the deformation tool roll, in addition to the forward movement, the metal also rotates around its own axis, which is a spiral forward movement. There are two types of skew rolling mills used in production: two-roll and three-roll systems.
The piercing process in the production of thermal expansion seamless steel pipe is more reasonable today, and the piercing process has been automated. The whole process of cross-rolling piercing can be divided into 3 stages:
1. Unstable process. The metal at the front end of the tube blank gradually fills the deformation zone stage, that is, the tube blank and the roll begin to contact the front metal and exit the deformation zone. In this stage, there are primary bite and secondary bite.
2. Stabilization process. This is the main stage of the piercing process, from the metal at the front end of the tube blank to the deformation zone until the metal at the tail end of the tube blank begins to leave the deformation zone.
3. Unstable process. The metal at the end of the tube blank gradually leaves the deformation zone until all the metal leaves the roll.
There is a clear difference between a stable process and an unstable process, which can be easily observed in the production process. For example, there is a difference between the size of the head and tail and the middle size of a capillary. Generally, the diameter of the front end of the capillary is large, the diameter of the tail end is small, and the middle part is consistent. Large head-to-tail size deviation is one of the characteristics of an unstable process.
The reason for the large diameter of the head is that as the metal at the front end gradually fills the deformation zone, the friction force on the contact surface between the metal and the roll increases gradually, and it reaches a maximum value in the complete deformation zone, especially when the front end of the tube billet meets the plug At the same time, due to the axial resistance of the plug, the metal is resisted in the axial extension, so that the axial extension deformation is reduced, and the lateral deformation is increased. In addition, there is no outer end restriction, resulting in a large front diameter. The diameter of the tail end is small, because when the tail end of the tube blank is penetrated by the plug, the resistance of the plug drops significantly, and it is easy to extend and deform. At the same time, the lateral rolling is small, so the outer diameter is small.
The front and rear jams that appear in production are also one of the unstable features. Although the three processes are different, they are all realized in the same deformation zone. The deformation zone is composed of rolls, plugs and guide discs.
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