Piercing and elongating mill for steel pipes and method of use

Abstract

The application discloses a kind of perforation deformation compensation formula steel pipe rolling mill and use method, belong to seamless steel tube production equipment technical field.It includes rolling mill frame, ejector rod and about ejector rod symmetrical installation can be vertically direction lifting motion lifting plate A and lifting plate B;Lifting plate A inside is sequentially rotatably installed with the upper roll A, upper roll B and upper roll C perpendicular to the ejector rod;Lifting plate B inside is sequentially rotatably installed with lower roll A, lower roll B and lower roll C;The radius of rolling circle C formed by upper roll C and lower roll C is greater than the radius of rolling circle B formed by upper roll B and lower roll B, and less than the radius of rolling circle A formed by upper roll A and lower roll A.The application is a kind of steel pipe rolling mill with reasonable structure, high stability head perforation centricity, realize the perforation and rolling of pipe blank by means of perforation deformation compensation principle, to significantly improve the uniformity of hollow steel tube wall thickness.

Description

A perforation deformation compensation type steel pipe rolling mill and its usage method Technical Field

[0001] This invention mainly relates to the technical field of seamless steel pipe production equipment, specifically a piercing deformation compensation type steel pipe rolling mill and its usage method. Background Technology

[0002] Seamless steel pipes are widely used in pipeline transportation, oil drill pipes, and automotive transmissions due to their advantages such as hollow cross-section, high bending and torsional modulus, and corrosion resistance. Current technology for manufacturing seamless steel pipes involves first piercing a billet to form a rough tube, then inserting the rough tube into a mandrel and rolling it into a blank, and finally using an expansion and sizing device to form the finished steel pipe. While this process can produce stainless steel pipes, the large deformation of the billet during piercing and rolling results in uneven wall thickness in the finished stainless steel pipe. The specific reasons are as follows: 1. The mandrel used in the billet piercing process is a pressure rod with low compressive instability, making it prone to slight bending and causing eccentric piercing; 2. During piercing, the unrestricted flow of material from the center of the billet to the periphery leads to poor wall thickness uniformity in the pierced rough tube; 3. When rolling the rough tube into a blank, one roll in a paired or grouped roll set is usually fixed, resulting in a low degree of overlap between the roll set's centerline and the piercing centerline, leading to eccentric rolling. Therefore, there is an urgent need to design a steel pipe rolling mill that can significantly improve the uniformity of stainless steel pipe wall thickness. Summary of the Invention

[0003] The technical problem to be solved by the present invention is: in view of the technical problems existing in the prior art, the present invention provides a steel pipe rolling mill with reasonable structure, high stability of mandrel piercing concentricity, and realizes piercing and rolling of tube blank by means of piercing deformation compensation principle, thereby significantly improving the uniformity of hollow steel pipe wall thickness.

[0004] To solve the above problems, the solution proposed in this invention is as follows: a piercing deformation compensation steel pipe rolling mill, including a mill stand, a top rod with a top head at one end and fixedly mounted on the mill stand at the other end, a guide column mounted vertically on the mill stand, lifting plates A and B slidably mounted on the guide column and symmetrical about the top rod, upper rolls A, B, and C rotatably mounted inside the lifting plate A from left to right and perpendicular to the top rod, lower rolls A, B, and C rotatably mounted inside the lifting plate B and respectively cooperating with the upper rolls A, B, and C, upper rolls B, and lower rolls C, an upper roll motor driving the upper roll C to rotate clockwise, a lower roll motor driving the lower roll C to rotate counterclockwise, and a lifting plate drive mechanism driving the lifting plates A and B to move closer or further apart.

[0005] The upper rolls A, B, and C are driven together, and the lower rolls A, B, and C are driven together, such that the rolling speed of the roll pairs increases sequentially along the billet's forward direction.

[0006] Furthermore, the radius of the rolling circle C formed by the upper roll C and the lower roll C is greater than the radius of the rolling circle B formed by the upper roll B and the lower roll B, and smaller than the radius of the rolling circle A formed by the upper roll A and the lower roll A; the sum of the maximum circular area of ​​the mandrel and the area of ​​the rolling circle B is equal to the area of ​​the rolling circle A.

[0007] Furthermore, the lifting plate drive mechanism includes a bidirectional threaded rod and a roller opening and closing motor; the bidirectional threaded rod spirally passes through the lifting plate A and the lifting plate B, the roller opening and closing motor is fixedly mounted on the connecting plate, and its output shaft is connected to one end of the bidirectional threaded rod; the connecting plate is fixedly connected to the upper end of the guide column.

[0008] Furthermore, sprockets A, B, and C, which are connected by a transmission chain A, are fixedly mounted on the central rotating shafts of the upper rolls A, B, and C, respectively. Sprockets D, E, and F, which are connected by a transmission chain B, are fixedly mounted on the central rotating shafts of the lower rolls A, B, and C, respectively.

[0009] Furthermore, the push rod is also equipped with a push rod stiffness strengthening mechanism for increasing the bending stiffness of the push rod; the push rod stiffness strengthening mechanism includes: a sliding sleeve slidably fitted on the push rod, a constraint rod with one end rotatably mounted on the push rod and the other end rotatably mounted with a universal roller, a traction rod with one end rotatably mounted on the sliding sleeve and the other end hinged to the middle of the constraint rod, a return spring with both ends connected to the push rod and the constraint rod respectively, and a sleeve power device for driving the sliding sleeve to slide along the push rod; there are three traction rods, constraint rods and return springs, and they are arranged in a one-to-one correspondence, and the three constraint rods are symmetrically distributed about the axis of the push rod.

[0010] Furthermore, the rolling mill stand is also equipped with a mandrel separation mechanism for driving the mandrel to separate from the hollow steel tube; the mandrel separation mechanism includes: a steel tube push plate fitted outside the mandrel, at least two push-pull rods slidably mounted on the rolling mill stand in the horizontal direction, a force-applying plate fixedly connected to one end of the at least two push-pull rods, and a push-pull trolley for driving the force-applying plate to move horizontally; the steel tube push plate is fixedly connected to the other end of the at least two push-pull rods.

[0011] Furthermore, the mill stand is also equipped with two placement platforms for placing tube blanks and hollow steel pipes, with the two placement platforms located to the left of the lower roll A and to the right of the lower roll C, respectively.

[0012] Furthermore, the top rod and the top head are equipped with cooling water pipes for cooling down.

[0013] Furthermore, the connecting plate is also provided with a hydraulic cylinder A for auxiliary pressurizing the lifting plate A, and the rolling mill stand is also provided with a hydraulic cylinder B for auxiliary pressurizing the lifting plate B.

[0014] A method for using a piercing deformation compensation type steel pipe rolling mill includes the following steps: Step 1: Place the billet to be pierced so that the left end face of the billet is flush with the left end faces of the upper roll C and the lower roll C; Step 2: The lifting plate drive mechanism drives the lifting plate A and the lifting plate B to move closer to each other until the upper roll A and the lower roll A are in the rolling working state; Step 3: Simultaneously start the upper roll motor and the lower roll motor, and the billet moves to the left until the billet is completely pierced to form a hollow steel pipe; during the leftward movement of the billet, the contact between the billet and the mandrel marks the start of piercing. Starting point; Step 4: When the mandrel pierces to half the length of the tube blank, start the sleeve power device to make the sliding sleeve slide to the left to pull the traction rod, thereby making the constraint rod perpendicular to the top rod, and the universal roller rotates and supports the circumferential inner wall of the inner hole of the tube blank; Step 5: Turn off the upper roll motor and the lower roll motor, and drive the lifting plate drive mechanism to drive the lifting plate A and the lifting plate B away from each other, so that the upper roll A and the lower roll A are in the initial non-rolling working state; Step 6: Push the hollow steel tube to the right relative to the mandrel until the mandrel completely leaves the hollow steel tube.

[0015] Compared with the prior art, the present invention has the following advantages and beneficial effects: The piercing deformation compensation type steel pipe rolling mill of the present invention is provided with three pairs of rolls connected in sequence, namely upper roll A and lower roll A, upper roll B and lower roll B, and upper roll C and lower roll C. The three rolling circles formed by the three roll pairs satisfy the piercing compensation relationship: the radius of rolling circle C is greater than the radius of rolling circle B and less than the radius of rolling circle A; the sum of the area of ​​the largest circle at the mandrel and the area of ​​rolling circle B is equal to the area of ​​rolling circle A. This allows for piercing deformation compensation during the piercing and rolling process. The localized material caused by piercing can flow freely and directionally along the radial direction of the tube blank, achieving circumferential uniformity of the hollow steel tube wall thickness. The three roll pairs have different rolling speeds, and the tube blank between two adjacent roll pairs is in a tensile conveying state. The axial tension allows the localized material to flow shear along the axial direction of the tube blank, enabling the thicker tube blanks to elongate and deform uniformly, achieving axial uniformity of the hollow steel tube wall thickness. In addition, the mandrel is equipped with a mandrel stiffness reinforcement mechanism. When the mandrel is pierced more than halfway, the universal rollers of the mandrel stiffness reinforcement mechanism can roll along the inner wall of the hollow steel tube to support the steel tube, thereby increasing the compressive stability and bending stiffness of the mandrel, avoiding mandrel eccentricity caused by mandrel bending, improving the concentricity of the mandrel piercing, and achieving concentricity between the inner hole and outer circle of the hollow steel tube. Therefore, this invention is a steel pipe rolling mill with a reasonable structure, high stability of mandrel piercing concentricity, and the ability to pierce and roll the billet by means of piercing deformation compensation principle, thereby significantly improving the uniformity of the wall thickness of hollow steel pipes. Attached Figure Description

[0016] Figure 1 is a schematic diagram of the structural principle of a perforation deformation compensation type steel pipe rolling mill according to the present invention.

[0017] Figure 2 is a schematic diagram of the relative positions of the tube blank and the three roll pairs in the initial state.

[0018] Figure 3 is a schematic diagram showing the relative positions of the hollow steel pipe and the three roll pairs at the end of piercing.

[0019] Figure 4 is a schematic diagram of the upper roll A and lower roll A in the rolling state of the present invention.

[0020] Figure 5 is a schematic diagram of the top rod stiffness strengthening mechanism in this invention.

[0021] Figure 6 is a schematic diagram showing the connection positions of the three traction rods and the sliding sleeve.

[0022] Figure 7 is a schematic diagram showing the relative positions of the lifting plate A, the two guide columns, and the two bidirectional threaded rods.

[0023] In the diagram, 10—mill stand; 11—lifting plate A; 12—lifting plate B; 13—guide column; 14—double-threaded rod; 15—connecting plate; 16—roll opening and closing motor; 17—placement platform; 2—top rod; 3—top rod stiffness strengthening mechanism; 31—sliding sleeve; 32—traction rod; 33—constraint rod; 34—reset spring; 35—universal roller; 41—upper roll A; 411—sprocket. A; 412—Arc-shaped groove; 413—Rolling circle A; 42—Lower roll A; 421—Sprocket D; 51—Upper roll B; 511—Sprocket B; 52—Lower roll B; 521—Sprocket E; 61—Upper roll C; 611—Sprocket C; 62—Lower roll C; 621—Sprocket F; 7—Tube blank; 71—Hollow steel pipe; 81—Steel pipe push plate; 82—Push-pull rod; 83—Force application plate. Detailed Implementation

[0024] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0025] Referring to Figures 1 to 7, a piercing deformation compensation type steel pipe rolling mill of the present invention includes a mill stand 10, a push rod 2 with a push head at one end and fixedly mounted on the mill stand 10 at the other end, a guide column 13 mounted vertically on the mill stand 10, lifting plates A11 and B12 slidably mounted on the guide column 13 and symmetrical about the push rod 2, and upper rolls A41, B51, and C61 rotatably mounted inside the lifting plate A11 from left to right and perpendicular to the push rod 2. The mill frame 10 comprises a lower roll A42, a lower roll B52, and a lower roll C62, which are rotatably mounted inside the lifting plate B12 and respectively cooperate with the upper roll A41, the upper roll B51, and the upper roll C61; an upper roll motor (not shown in the figure) that drives the upper roll C61 to rotate clockwise; a lower roll motor (not shown in the figure) that drives the lower roll C62 to rotate counterclockwise; and a lifting plate drive mechanism that drives the lifting plates A11 and B12 to move closer or further apart. In a specific implementation, the upper roll motor is mounted on the lifting plate A11, and the lower roll motor is mounted on the lifting plate B12. The mill frame 10 consists of a base plate, a top rod bracket mounted vertically on the base plate, and a platform bracket for mounting two placement platforms 17. The top rod 2 is horizontally set along the X direction, with its left end fixedly connected to the top rod bracket and its right end connected to the top head; the lifting plates A11 and B12 are horizontally set along the XY plane and can move up and down along the vertical direction, i.e., the Z direction; the upper rollers A41, B51, and C61 are horizontally set along the Y direction, and the two ends of the central rotating shafts of the upper rollers A41, B51, and C61 are rotatably mounted on the lifting plate A11 through two rolling bearings; the lower rollers A42, B52, and C62 are respectively installed directly below the upper rollers A41, B51, and C61; to facilitate the installation of the upper and lower rollers, the lifting plates A11 and B12 are both made into detachable U-shaped flat plates.

[0026] Upper rolls A41, B51, and C61 are driven together, as are lower rolls A42, B52, and C62, such that the rolling speed of the roll pairs increases sequentially along the forward direction of the billet 7. Specifically, the rolling speed of the upper rolls B51 and B52, which rotate in opposite directions at the same speed, is less than the rolling speed of the upper rolls A41 and A42, which rotate in opposite directions at the same speed, but greater than the rolling speed of the lower roll C62, which is paired with the upper roll C61, which rotates in opposite directions at the same speed. Preferably, sprockets A411, B511, and C61, connected by a drive chain A (not shown in the figure), are fixedly mounted on the central rotating shafts of the upper rolls A41, B51, and C61, respectively. Similarly, sprockets D421, E521, and F621, connected by a drive chain B (not shown in the figure), are fixedly mounted on the central rotating shafts of the lower rolls A42, B52, and C62, respectively. In a specific implementation, the output shaft of the upper roll motor is connected to the central rotating shaft of the upper roll C61. Thus, the upper roller C61 rotates clockwise, driving the upper rollers B51 and A41 to rotate synchronously via the transmission chain A; the output shaft of the lower roller motor is connected to the central rotating shaft of the lower roller C62, causing the lower roller C62 to rotate counterclockwise, driving the lower rollers B52 and A42 to rotate synchronously via the transmission chain B; since the upper roller rotates clockwise and the lower roller rotates counterclockwise, their rotation speeds are equal to those of the upper roller, thus causing the tube blank 7 to be subjected to a resultant force to the left, causing the tube blank 7 to move to the left relative to the push rod 2.

[0027] Referring to Figures 1 and 7, the lifting plate drive mechanism includes a bidirectional threaded rod 14 and a roll opening / closing motor 16. The bidirectional threaded rod 14 spirally passes through the lifting plates A11 and B12. The roll opening / closing motor 16 is fixedly mounted on a connecting plate 15, and its output shaft is connected to one end of the bidirectional threaded rod 14. The connecting plate 15 is fixedly connected to the upper end of the guide post 13. In a specific implementation, two guide posts 13 and two bidirectional threaded rods 14 are provided. The two guide posts 13 are respectively located on one diagonal line of the lifting plate A11, and the two bidirectional threaded rods 14 are respectively located on the other diagonal line of the lifting plate A11, to increase the smoothness of the lifting movement of the lifting plates A11 and B12. The guide posts 13 slide through the lifting plates A11 and B12. The lifting plates A11 and B12 are respectively provided with left-hand threaded holes and right-hand threaded holes that mate with the threads of the bidirectional threaded rod 14. The left-hand thread and the right-hand thread on the bidirectional threaded rod 14 spirally pass through the left-hand threaded hole of the lifting plate A11 and the right-hand threaded hole of the lifting plate B12, respectively. The two bidirectional threaded rods 14 can be driven by two independent roller opening and closing motors 16, or they can be driven synchronously by one roller opening and closing motor 16 with the help of a transmission device. When the roll opening and closing motor 16 rotates in the forward direction, the lifting plates A11 and B12 move closer to each other under the limiting action of the two guide columns 13, so that the upper rolls A41, B51, and C61 move closer to the lower rolls A42, B52, and C62 respectively, until they form the rolling circles A413, B (not shown in the figure), and C (not shown in the figure) in the rolling working state respectively. When the roll opening and closing motor 16 rotates in the reverse direction, the lifting plates A11 and B12 move away from each other under the limiting action of the two guide columns 13, and the upper rolls A41, B51, and C61 move away from the lower rolls A42, B52, and C62 respectively, so that the upper rolls and the corresponding lower rolls are in the non-rolling working state.

[0028] By appropriately setting the relative radii of sprockets A411, B511, and C611, and appropriately setting the relative radii of sprockets D421, E521, and F621, the rolling linear speed of the roll pair can be sequentially increased along the forward direction of the tube blank 7. This sequentially increasing rolling linear speed can be achieved as follows: when the tube blank 7 moves to the left during rolling, the upper roll A41 and lower roll A42 will exert an axial tensile force on the tube blank 7 located between rolling circles A413 and B, and the upper roll B51 and lower roll B52 will exert an axial tensile force on the tube blank 7 located between rolling circles B and C. This results in axial shear-type directional flow of the material during rolling, improving the uniformity of the wall thickness of the hollow steel tube 71.

[0029] Referring to Figures 1 and 4, preferably, the sum of the maximum circular area of ​​the mandrel and the area of ​​the rolling circle B is equal to the area of ​​the rolling circle A413. This causes the portion of the material on the tube blank 7 whose cross-section is equal to that of the rolling circle B to expand outward during the mandrel piercing process, thereby filling the rolling circle A413 formed by the upper roll A41 and the lower roll A42. This transforms the circular cross-section of the tube blank 7 from the rolling circle B to the rolling circle A413. The radius of the rolling circle C formed by the upper roll C61 and the lower roll C62 is greater than the radius of the rolling circle B formed by the upper roll B51 and the lower roll B52, and smaller than the radius of the rolling circle A413 formed by the upper roll A41 and the lower roll A42. In specific implementation, both the upper roll A41 and the lower roll A42 have arc-shaped grooves 412 circumferentially arranged on their outer circumferential sidewalls, as shown in Figure 4. Specifically, the intersection of the arc-shaped grooves 412 and the longitudinal section of the rolls along the axes of the upper roll A41 and lower roll A42 forms a circular arc. During rolling, the two arc-shaped grooves 412 form a complete rolling circle A413. The end faces of the two arc-shaped grooves 412 do not completely contact each other, thus ensuring no motion interference occurs during the rotation of the upper roll A41 and lower roll A42. The structural characteristics of the upper roll B51 and lower roll B52, and the upper roll C61 and lower roll C62 are similar to those of the upper roll A41 and lower roll A42. The axis of the mandrel 2 is collinear with the axis of the mandrel, and the centers of the rolling circles A413, B, and C are all located on the axis of the mandrel.

[0030] Referring to Figures 1, 5, and 6, preferably, the push rod 2 is further equipped with a push rod stiffness strengthening mechanism 3 to increase the bending stiffness of the push rod 2. The push rod stiffness strengthening mechanism 3 includes: a sliding sleeve 31 slidably fitted on the push rod 2; a constraint rod 33 with one end rotatably mounted on the push rod 2 and the other end rotatably mounted with a universal roller 35; a traction rod 32 with one end rotatably mounted on the sliding sleeve 31 and the other end hinged to the middle of the constraint rod 33; a return spring 34 with both ends connected to the push rod 2 and the constraint rod 33 respectively; and a sleeve power device (not shown in the figures) for driving the sliding sleeve 31 to slide along the push rod 2. There are three traction rods 32, three constraint rods 33, and three return springs 34, and they are arranged in a one-to-one correspondence. The three constraint rods 33 are symmetrically distributed about the axis of the push rod 2. Specifically, when installing the push rod stiffness strengthening mechanism 3, the distance between the push head and the push rod stiffness strengthening mechanism 3 can be equal to half the length of the hollow steel pipe 71. The sleeve power unit can be either a motor with a winding wheel or a piston cylinder, as long as it can drive the sliding sleeve 31 to slide left and right. When the sliding sleeve 31 slides to the left, the traction rod 32 pulls the constraint rod 33, making the constraint rod 33 perpendicular to the axis of the top rod 2. At this time, the universal roller 35 can rotate and support the inner wall of the hollow steel pipe 71, thus supporting the top rod 2. Setting three axisily distributed constraint rods 33 can better balance the radial force of the top rod 2 and effectively prevent the top rod 2 from bending in one direction. Since one end of the top rod 2 is fixedly connected to the rolling mill stand 10 and the other end is equipped with a mandrel, when the mandrel pierces the billet 7, the top rod 2 is a compression rod under pressure. By setting the top rod stiffness strengthening mechanism 3, the compressive stability of the top rod 2 can be increased, and the bending stiffness of the top rod 2 can be increased, thereby improving the centering of the mandrel piercing.

[0031] Preferably, the mill stand 10 is also equipped with a mandrel separation mechanism for driving the mandrel to separate from the hollow steel tube 71. The mandrel separation mechanism includes: a steel tube push plate 81 fitted outside the mandrel 2; at least two push-pull rods 82 slidably mounted on the mill stand 10 in the horizontal direction; a force-applying plate 83 fixedly connected to one end of the at least two push-pull rods 82; and a push-pull trolley (not shown in the figure) that drives the force-applying plate 83 to move horizontally. The steel tube push plate 81 is fixedly connected to the other end of the at least two push-pull rods 82. When the push-pull trolley moves to the right, the push-pull rods 82 move to the right, and the steel tube push plate 81 moves to the right, pushing the hollow steel tube 71 to move to the right relative to the mandrel and mandrel 2, thereby causing the mandrel to gradually separate from the hollow steel tube 71. When the push-pull trolley moves to the left, it drives the steel tube push plate 81 to move to the left until it returns to its initial position. The push-pull trolley is prior art, and its structure and working principle will not be described in detail here.

[0032] Preferably, the mill stand 10 is also equipped with two placement platforms 17 for placing the billet 7 and the hollow steel tube 71. The two placement platforms 17 are located to the left of the lower roll A42 and to the right of the lower roll C62, respectively. When the billet 7 is initially placed, its left end is located between the upper roll C61 and the lower roll C62, and its right end is located on the right placement platform 17, with the axis of the billet 7 collinear with the axis of the push rod 2. After the billet 7 is pierced to form the hollow steel tube 71, its left end is located on the left placement platform 17, and its right end is located between the upper roll A41 and the lower roll A42. To increase the stability of the billet 7 and the hollow steel tube 71 on the placement platform 17, an arc-shaped platform groove (not shown in the figure) is partially opened on the placement platform 17 along the X direction to accommodate the billet 7 and the hollow steel tube 71.

[0033] Preferably, the push rod 2 and the push head are equipped with cooling water pipes inside for cooling, so as to reduce the temperature rise of the push rod 2 during the piercing process and maintain the initial stiffness of the push rod 2 as much as possible. The cooling water pipe is prior art, and its structure and working principle will not be described in detail here.

[0034] Preferably, the connecting plate 15 is further provided with a hydraulic cylinder A (not shown in the figure) for auxiliary pressurization of the lifting plate A11, and the mill stand 10 is further provided with a hydraulic cylinder B (not shown in the figure) for auxiliary pressurization of the lifting plate B12. In specific implementation, hydraulic cylinder A is fixedly installed on the connecting plate 15, and its output rod is in contact with the lifting plate A11 in the auxiliary pressurization state, and moves away from each other in the non-pressurization state; hydraulic cylinder B is fixedly installed on the bottom of the mill stand 10, and its output rod is in contact with the lifting plate B12 in the auxiliary pressurization state, and moves away from each other in the non-pressurization state. Since the rolling force required for rolling tube blanks 7 of different diameters is different, hydraulic cylinders A and B need to be activated to apply auxiliary pressure to the corresponding lifting plates A11 and B12 when the following two situations occur: First, the double-threaded rod 14 is insufficient to drive the lifting plates A11 and B12 to generate sufficient rolling force; Second, although the double-threaded rod 14 can drive the lifting plates A11 and B12 to generate sufficient rolling force, the reaction force of the rolling force causes the lifting plates A11 and B12 to undergo significant bending deformation.

[0035] A method for using a piercing deformation compensation type steel pipe rolling mill includes the following steps: Step 1: Place the billet 7 to be pierced on the placement platform 17 located on the right side, ensuring that the left end face of the billet 7 is flush with the left end faces of the upper roll C61 and the lower roll C62. To facilitate the extrusion and driving of the billet 7 by the upper roll B51 and the lower roll B52, the left end of the billet 7 can be made into a cone shape, with the minimum radius of the cone being smaller than the radius of the rolling circle B.

[0036] Step 2: In the forward direction, start the roll opening and closing motor 16 to drive the lifting plates A11 and B12 closer together until the upper roll A41 and lower roll A42 are in the rolling working state; if necessary, start hydraulic cylinders A and B to apply auxiliary pressure to the lifting plates A11 and B12. Here, "if necessary" refers to the two situations where hydraulic cylinders A and B need to be started.

[0037] Step 3: Simultaneously start the upper and lower roll motors. The billet 7 moves horizontally to the left until it is completely pierced to form a hollow steel tube 71. During the leftward movement of the billet 7, the piercing starting point is when the billet 7 contacts the mandrel. Since the upper rolls C61, B51, and A41 rotate clockwise, the outer surface of the upper half of the billet 7 is subjected to a leftward frictional force. The lower rolls C62, B52, and A42 rotate counterclockwise, so the outer surface of the lower half of the billet 7 is also subjected to a leftward frictional force. Therefore, starting the upper and lower roll motors can drive the billet 7 to move horizontally to the left.

[0038] Step 4: When the mandrel is pierced to half the length of the tube blank 7, start the sleeve power device to make the sliding sleeve 31 slide to the left and pull the traction rod 32, thereby making the constraint rod 33 perpendicular to the top rod 2, and the universal roller 35 rotates and supports the circumferential inner wall of the inner hole of the tube blank 7.

[0039] Step 5: Turn off the upper roll motor and the lower roll motor, and start the roll opening and closing motor 16 in reverse to drive the lifting plate A11 and the lifting plate B12 away from each other, so that the upper roll A41 and the lower roll A42 return to the initial non-rolling working state; if necessary, start the hydraulic cylinder A and the hydraulic cylinder B in reverse to return their output rods to the initial position; start the sleeve power unit in reverse to return the sliding sleeve 31 to the initial position.

[0040] Step 6: Start the push-pull trolley, push the force plate 83 to the right, and then push the hollow steel pipe 71 to the right relative to the mandrel through the steel pipe push plate 81 until the mandrel completely leaves the hollow steel pipe 71; start the push trolley in the opposite direction, drive the force plate 83 to the left so that the steel pipe push plate 81 returns to the initial position, and remove the rolled hollow steel pipe 71.

[0041] The principle of piercing deformation compensation for the tube blank is as follows: Under the rolling action of the upper roll C61 and the lower roll C62, the tube blank 7 is locally rolled from an initial larger circular cross-section to a smaller circular cross-section equal to that of the rolling circle C. As the tube blank 7 moves to the left, the local circular cross-section of the tube blank 7, which is the rolling circle C, is further reduced by the rolling action of the upper roll B51 and the lower roll B52. The local circular cross-section becomes the rolling circle B and then enters the rolling circle A413. Since the radius of the rolling circle A413 is smaller than the radius of the rolling circle B, and the sum of the maximum circular area of ​​the mandrel and the area of ​​the rolling circle B is equal to the area of ​​the rolling circle A413, the material in the center of the tube blank 7 flows freely outward radially during piercing until the outer wall of the tube blank 7 touches the inner wall of the upper roll A41 and the lower roll A42. This causes the local circular cross-section of the tube blank 7 to change from the rolling circle B to the rolling circle A413, thereby achieving piercing deformation compensation.

[0042] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions conceived without creative effort should fall within the scope of protection of the present invention.

Claims

1. A piercing deformation compensation type steel pipe rolling mill, comprising a mill stand (10), a push rod (2) having a push head at one end and a push rod (2) fixedly mounted on the mill stand (10) at the other end, characterized in that: It also includes a guide post (13) mounted vertically on the mill stand (10), a lifting plate A (11) and a lifting plate B (12) slidably mounted on the guide post (13) and symmetrical about the top rod (2), an upper roll A (41), an upper roll B (51) and an upper roll C (61) rotatably mounted inside the lifting plate A (11) from left to right and perpendicular to the top rod (2), and a rotatably mounted inside the lifting plate B (12). The upper roller A (42), lower roller B (52) and lower roller C (62) respectively cooperate with the upper roller A (41), upper roller B (51) and upper roller C (61), the upper roller motor drives the upper roller C (61) to rotate clockwise, the lower roller motor drives the lower roller C (62) to rotate counterclockwise, and the lifting plate drive mechanism drives the lifting plate A (11) and lifting plate B (12) to move closer or further apart from each other; The upper rolls A (41), B (51), and C (61) are connected by a drive, and the lower rolls A (42), B (52), and C (62) are connected by a drive, such that the rolling linear speed of the three roll pairs formed by the cooperating upper and lower rolls increases sequentially along the forward direction of the billet (7); the radius of the rolling circle C formed by the upper roll C (61) and the lower roll C (62) is greater than the radius of the rolling circle B formed by the upper roll B (51) and the lower roll B (52), and smaller than the radius of the rolling circle A (413) formed by the upper roll A (41) and the lower roll A (42); the sum of the maximum circular area of ​​the mandrel and the area of ​​the rolling circle B is equal to the area of ​​the rolling circle A (413).

2. The piercing deformation compensation type steel pipe rolling mill according to claim 1, characterized in that: The lifting plate drive mechanism includes a bidirectional threaded rod (14) and a roller opening and closing motor (16); the bidirectional threaded rod (14) spirally passes through the lifting plate A (11) and the lifting plate B (12), the roller opening and closing motor (16) is fixedly mounted on the connecting plate (15), and its output shaft is connected to one end of the bidirectional threaded rod (14); the connecting plate (15) is fixedly connected to the upper end of the guide post (13).

3. The piercing deformation compensation type steel pipe rolling mill according to claim 1, characterized in that: The upper rollers A (41), B (51), and C (61) are respectively fixedly mounted on their central rotating shafts and connected by a transmission chain A. The lower rollers A (42), B (52), and C (62) are respectively fixedly mounted on their central rotating shafts and connected by a transmission chain B.

4. A piercing deformation compensation type steel pipe rolling mill according to claim 1, characterized in that: The top rod (2) is also equipped with a top rod stiffness strengthening mechanism (3) for increasing the bending stiffness of the top rod (2); the top rod stiffness strengthening mechanism (3) includes: a sliding sleeve (31) slidably mounted on the top rod (2); a constraint rod (33) with one end rotatably mounted on the top rod (2) and the other end rotatably mounted with a universal roller (35); a traction rod (32) with one end rotatably mounted on the sliding sleeve (31) and the other end hinged to the middle of the constraint rod (33); a return spring (34) with both ends respectively connected to the top rod (2) and the constraint rod (33); and a sleeve power device for driving the sliding sleeve (31) to slide along the top rod (2); the traction rod (32), the constraint rod (33) and the return spring (34) are all three and are arranged in a one-to-one correspondence, and the three constraint rods (33) are symmetrically distributed about the top rod (2).

5. A piercing deformation compensation type steel pipe rolling mill according to claim 1, characterized in that: The mill stand (10) is also equipped with a mandrel separation mechanism for driving the mandrel to separate from the hollow steel pipe (71); the mandrel separation mechanism includes: a steel pipe push plate (81) fitted outside the mandrel (2), at least two push-pull rods (82) slidably mounted on the mill stand (10) in the horizontal direction, a force-applying plate (83) fixedly connected to one end of the at least two push-pull rods (82), and a push-pull trolley for driving the force-applying plate (83) to move horizontally; the steel pipe push plate (81) is fixedly connected to the other end of the at least two push-pull rods (82).

6. A piercing deformation compensation type steel pipe rolling mill according to claim 1, characterized in that: The mill stand (10) is also equipped with two placement platforms (17) for placing tube blanks (7) and hollow steel pipes (71), and the two placement platforms (17) are located on the left side of the lower roll A (42) and the right side of the lower roll C (62), respectively.

7. A piercing deformation compensation type steel pipe rolling mill according to claim 1, characterized in that: The top rod (2) and the top head are equipped with cooling water pipes for cooling.

8. A piercing deformation compensation type steel pipe rolling mill according to claim 2, characterized in that: The connecting plate (15) is also provided with a hydraulic cylinder A for assisting in pressurizing the lifting plate A (11), and the mill stand (10) is also provided with a hydraulic cylinder B for assisting in pressurizing the lifting plate B (12).

9. The method of using a piercing deformation compensation type steel pipe rolling mill according to claim 4, characterized in that, The process includes the following steps: Step 1: Place the tube blank (7) to be pierced so that the left end face of the tube blank (7) is flush with the left end faces of the upper roll C (61) and the lower roll C (62); Step 2: The lifting plate drive mechanism drives the lifting plate A (11) and the lifting plate B (12) to move closer to each other until the upper roll A (41) and the lower roll A (42) are in the rolling working state; Step 3: Simultaneously start the upper roll motor and the lower roll motor, and the tube blank (7) moves to the left until the tube blank (7) is completely pierced to form a hollow steel tube (71); During the process of the tube blank (7) moving to the left, the piercing starting point is when the tube blank (7) contacts the mandrel; Step 4: When the mandrel is pierced to half the length of the tube blank (7), start the sleeve power device to make the sliding sleeve (31) slide to the left to pull the traction rod (32), thereby making the constraint rod (33) perpendicular to the top rod (2), and the universal roller (35) rotates and supports the circumferential inner wall of the inner hole of the tube blank (7); Step 5: Turn off the upper roll motor and the lower roll motor, and drive the lifting plate drive mechanism to drive the lifting plate A (11) and the lifting plate B (12) away from each other, so that the upper roll A (41) and the lower roll A (42) are in the initial non-rolling working state; Step 6: Push the hollow steel tube (71) to move to the right relative to the mandrel until the mandrel completely leaves the hollow steel tube (71).

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