Seamless steel pipe refers to a steel pipe that is made of a single piece of metal and has no seams on the surface. According to the production method, seamless tubes are divided into hot-rolled tubes, cold-rolled tubes, cold drawn seamless tubing, extruded tubes, jacked tubes, etc. The piercing methods of seamless pipe blanks include pressure piercing, push rolling piercing and skew rolling piercing.
1. Pressure piercing
Pressure piercing is piercing on a press. The raw materials used in this piercing method are square billets and polygonal steel ingots. The working principle is to put the heated billet or steel ingot into the circular die first, and then the press drives the punch rod with the punch to punch out a round hole in the center of the tube blank. The amount of deformation of this piercing method is very small. Generally, the metal that is punched out in the center just fills the gap between the billet and the circular die, so that a circular capillary with almost no extension is obtained, and the maximum elongation coefficient does not exceed 1.1.
2. Push rolling piercing
Push-roll piercing is piercing on a push-roll piercing machine. This piercing method is an improvement of pressure piercing. Change the fixed conical mold into a pair of rolls with round holes. The pair of rolls are driven by the motor to rotate in one direction, and the rotating rolls bite the tube into the pass of the roll, and the punch fixed in the pass punches out a round hole in the center of the tube. In order to facilitate rolling, a back thrust (hydraulic cylinder) is added to the tail end of the billet, so it is called push rolling piercing.
Advantages of push-roll piercing:
1) The center of the billet is in a state of compressive stress. The process is a combination of punching and longitudinal rolling, which will not cause inward folding defects of two-roll cross rolling. The inner surface of the capillary is of good quality and has lower requirements for the quality of the billet;
2) The average unit pressure on the punch is about 50% smaller than that of pressure piercing, so the tool consumption is small;
3) During the piercing process, the metal in the central part of the blank is mainly deformed, which makes the coarse and loose structure in the center well processed and densified. At the same time, under the action of compressive stress, the inner and outer surfaces of the capillary are not easy to crack.
4) The productivity is higher than that of pressure piercing, up to two per minute;
3. Cross rolling piercing
This perforation method is widely used in the production of seamless steel pipes. Generally, round tube blanks are used, and the inner holes are formed by plastic deformation of metals, so there is no loss of metals.
Tips: Pressure piercing and push rolling piercing mostly produce seamless steel pipes of special steel types, and there are few existing units. The amount of deformation is small, and the capillary is short and thick. Therefore, a cross-rolling extension machine is installed in the hot-rolled seamless steel pipe unit to reduce the outer diameter and wall thickness of the capillary and extend the pipe. In addition, it is easy to produce large uneven wall thickness.
1. Pressure piercing
Pressure piercing is piercing on a press. The raw materials used in this piercing method are square billets and polygonal steel ingots. The working principle is to put the heated billet or steel ingot into the circular die first, and then the press drives the punch rod with the punch to punch out a round hole in the center of the tube blank. The amount of deformation of this piercing method is very small. Generally, the metal that is punched out in the center just fills the gap between the billet and the circular die, so that a circular capillary with almost no extension is obtained, and the maximum elongation coefficient does not exceed 1.1.
2. Push rolling piercing
Push-roll piercing is piercing on a push-roll piercing machine. This piercing method is an improvement of pressure piercing. Change the fixed conical mold into a pair of rolls with round holes. The pair of rolls are driven by the motor to rotate in one direction, and the rotating rolls bite the tube into the pass of the roll, and the punch fixed in the pass punches out a round hole in the center of the tube. In order to facilitate rolling, a back thrust (hydraulic cylinder) is added to the tail end of the billet, so it is called push rolling piercing.
Advantages of push-roll piercing:
1) The center of the billet is in a state of compressive stress. The process is a combination of punching and longitudinal rolling, which will not cause inward folding defects of two-roll cross rolling. The inner surface of the capillary is of good quality and has lower requirements for the quality of the billet;
2) The average unit pressure on the punch is about 50% smaller than that of pressure piercing, so the tool consumption is small;
3) During the piercing process, the metal in the central part of the blank is mainly deformed, which makes the coarse and loose structure in the center well processed and densified. At the same time, under the action of compressive stress, the inner and outer surfaces of the capillary are not easy to crack.
4) The productivity is higher than that of pressure piercing, up to two per minute;
3. Cross rolling piercing
This perforation method is widely used in the production of seamless steel pipes. Generally, round tube blanks are used, and the inner holes are formed by plastic deformation of metals, so there is no loss of metals.
Tips: Pressure piercing and push rolling piercing mostly produce seamless steel pipes of special steel types, and there are few existing units. The amount of deformation is small, and the capillary is short and thick. Therefore, a cross-rolling extension machine is installed in the hot-rolled seamless steel pipe unit to reduce the outer diameter and wall thickness of the capillary and extend the pipe. In addition, it is easy to produce large uneven wall thickness.
