Tube blank perforation process

Perforation is the first process of deformation of hot-rolled seamless steel pipe, and its function is to pierce the solid tube blank into a hollow capillary tube. Since the surface defects or eccentricity (uneven wall thickness) of the pierced capillary tube are difficult to eliminate or reduce in the subsequent deformation process, the quality of the perforated capillary tube has an extremely important influence on the quality of the hot rolled seamless steel pipe. The tube blank perforation method includes pressure punching, push-rolling perforation and cross-rolling perforation. 



1 pressure punching 


Pressure punching is to load a heated billet or wavy ingot into a circular die, and then use a press to drive the punch to punch the inner hole in the central portion of the blank. Generally, the area of the punched hole is equal to or slightly larger than the gap between the blank and the circular die, so the amount of deformation is small, and the elongation coefficient generally does not exceed 1.1. 






2 push and punch 


Push-rolling perforation can be seen as an improved form of pressure punching, that is, changing the fixed circular die at the time of pressure punching into a pair of rolls with a circular hole type, and the rolls are driven by a motor. When the roll is rotated to bite the tube into the hole shape and rolled, the punch fixed at the center of the hole shape penetrates it into a hollow capillary tube. In order to push the rolling, a back thrust is added to the end of the blank, so it is called push-rolling.


Push-rolling and perforation is a method in which the continuous casting process is still not mature. It is necessary to use a square continuous casting blank for perforated rolling. Although it has a larger improvement than pressure punching, the deformation is still small, so the capillary is short and thick. In particular, it is easy to produce large wall thickness unevenness. Therefore, after the perforation, a cross-rolling extension machine is needed to reduce the wall thickness of the capillary tube and the length of the extended capillary tube, and to reduce the uneven thickness of the capillary wall. However, as the round continuous casting blank process matures, the method has gradually Replaced by cross-rolling perforations. 






3 cross-rolled perforation 


The cross-rolling perforation is based on the round tube blank being bitten by two rolls rotating in the same direction and spirally advanced, and the tube blank is hollowed through a hole formed by a roll, a guide (or a guide roll, a guide) and a plug. Hair tube.


In fact, the round billet is bitten by the roll, rotated and compressed and deformed spirally. Before the contact with the plug, the plastic deformation of the central portion of the tube blank under the repeated action of tension and compressive stress gradually develops into looseness, with the gradual loosening. Aggravation will cause the center to rupture and form a "cavity" (also known as the "horizontal forging effect"). Therefore, the front end of the plug needs to be adjusted in a position where the tube blank is loose and does not form a "hole cavity". At this time, the piercing force can be consumed low, the tool wear is small, and the quality of the pierced capillary tube is good. If the tube blank is deformed in contact with the plug after the "hole" has been formed, it is easy to form an "inner fold" in the inner hole of the capillary. 


The two-roll cross-rolling perforation was invented by the German Mannesmann brothers in 1885, and has been improved and perfected by the descendants. Up to now, the cross-rolling perforation has become the most important perforation method for the production of hot-rolled seamless steel tubes.


Type of cross-rolling punching machine: The cross-rolling punching machine can be divided into a two-roll cross-rolling punching machine and a three-roll cross- rolling punching machine according to the number of rolls . 


The three-roll cross-rolling punching machine is easy to form a tail triangle when perforating a thin-walled tube due to poor sealing of the hole type, and thus is limited to a unit for producing a medium-thick-wall steel pipe, such as a three-roll mill.


The two-roll cross-rolling punching machine can be divided into a disc punching machine, a conical roller punching machine and a barrel or Mann punching machine according to the shape of the roll. The difference is that the roll axis is different from the roll centerline, resulting in a large difference in kinematics of the deformation.


The guide plate, the guide roller and the guide disc are guiding devices of the two-roll piercing machine, wherein the guide plate is fixed, the guide roller is a squeezing roller, and the guide plate is driven to rotate by the motor. They not only guide the deformation process of the perforated capillary, but also maintain the stability of the capillary center and rolling, and also play a role in limiting the lateral deformation of the capillary. The guide plates, guide rollers and guide plates together with the roll head form a closed perforated hole type.


The guide plate is the best for the hole type sealing, and is suitable for perforating thin-walled tubes, but the guide plate wears fast and the piercing load is high, which is most commonly used in the two-roll cross-rolling punching machine.


The guide roller and the guide plate have the opposite characteristics, the wear is small, and the piercing load is low, but due to the poor sealing property, it is limited to the perforated large-diameter, thick-walled capillary tube.


In 1932 Diesel introduced the guide into a cross-rolling stretcher (also known as the Diesel mill) and then applied it in a two-roll cross-rolling punch. The guide has the following features.


(1) Due to the active rotation of the guide disc, the axial pulling force on the capillary tube is increased, thereby increasing the axial speed of the capillary tube and improving the perforation efficiency;


(2) The rotation of the guide disc and the relative rolling of the surface of the capillary tube improve the surface quality of the capillary tube. Therefore, the guide disc has a high service life and reduces the time for changing the tool; 


(3) The sealing of the guide plate relative to the guide plate is poor, especially when the capillary tube with a thin wall thickness is perforated, the metal is easily squeezed into the roll gap to cause scratching, chain or broken tail. Therefore, the elongation of the guide disc punching machine should not be too large; 


(4) increased equipment components and weight;


(5) The adjustment of the hole type is relatively complicated.