Method for precisely controlling wall thickness of pierced billet of pipe jacking unit and reducing cutting loss under pressure

Abstract

The invention relates to the technical field of steel pipe manufacturing methods, in particular to a method for precisely controlling the wall thickness of a pierced billet of a pipe jacking unit and reducing the cutting loss through reduction, which comprises the following steps: adding reduction racks: in the pipe jacking step, the pipe jacking unit is adopted for pipe jacking, two reduction racks are added behind a pipe jacking unit bed, and the two reduction racks are respectively placed in a forward and reverse manner and are used for rounding; establishing a pipe-jacking digital-analog calculation system; determining a pressing position of a pressing rack through the digital-analog calculation system; and pressing operation is controlled, specifically, the two pressing racks are controlled to operate according to the determined pressing position, and the high-temperature section of the head of the pierced billet is avoided. The two screw-down racks convenient to control are additionally arranged on a traditional CPE pipe jacking unit, accurate control is achieved through the pipe jacking digital-analog calculation system, the wall thickness trends of the head, the middle and the tail of a pierced billet are consistent under the pressure of the low-temperature section by avoiding the high-temperature section, and the cutting loss of the wall thickness of the original low-temperature section can be effectively reduced after tension reduction.

Description

Technical Field

[0001] The invention relates to the technical field of steel pipe manufacturing methods, and in particular to a method for reducing cutting loss by accurately controlling the wall thickness of a rough pipe of a pipe jacking unit. Background Art

[0002] In order to develop small-size seamless steel pipes, the use of advanced continuous rolling mills and CPE pipe jacking mills will become a trend. The commonly used methods of traditional rolling are pipe blanks → annular heating → piercing → shrinking → pre-piercing → pipe jacking → loosening rods → stripping rods → hot sawing → reheating furnace → water descaling, medium frequency heating → tension reduction → cooling bed cooling pipe → sawing.

[0003] The existing Chinese patent with publication number CN102366767A discloses a method for manufacturing a steel pipe, which includes melting a rough ingot → heating and punching the rough ingot → reheating → wall uniformity in an oblique rolling and stretching machine → pipe jacking in a pipe jacking unit → rod removal after pipe jacking → head and tail cutting → reheating → sizing and straightening in a sizing machine. The process flow is characterized in that shrinking is required before pipe jacking. The shrinking process is specifically as follows: after the mandrel is inserted into the rough pipe, the shrinking machine tightly holds the end of the rough pipe on the mandrel head, and the jacking machine rolls it. The shrinking section must withstand the jacking force of the first 2 to 3 die seats rolling deformation, and the jacking force generated by the subsequent deformation is borne by the rough pipe already held on the mandrel and the shrinking part.

[0004] With regard to the above-mentioned related technologies, it is found that in the manufacturing process of existing steel pipes, when rolling thick-walled pipes, holes are punched out of hollow rough pipes, and the mandrel is pre-pierced. After pre-piercing, the top pipe is extended. The head of the mandrel is always kept at high temperature during production. At the same time, the temperature of the head is also higher than the temperature of the middle and tail of the rough pipe after extension, resulting in the temperature of the mandrel head being much higher than the temperature of the middle and tail of the mandrel. Due to the effect of thermal expansion, the head size of the mandrel is large and the middle size is small. After the top pipe is rolled, the wall thickness of the rough pipe head is thinner than that of the middle and tail. After tension reduction rolling, this trend is further amplified, which is reflected in the finished pipe as uneven overall wall thickness, thin head, thick middle, difficult production control and long cutting loss, which poses great difficulties in product quality and production process control. Summary of the invention

[0005] The invention solves the problems in the related art and provides a method for reducing cutting loss by precisely controlling the wall thickness of a rough pipe of a pipe jacking unit.

[0006] In order to solve the above technical problems, the present invention is realized by the following technical scheme: a method for reducing cutting loss by accurately controlling the wall thickness of the rough pipe of a pipe jacking unit, the method comprising the steps of heating the pipe blank, perforating, inserting rods, shrinking, jacking, loosening rods and removing rods, and further comprising:

[0007] Add a press-down rack: In the pipe jacking step, a pipe jacking unit is used for pipe jacking. Two press-down racks are added behind the bed of the pipe jacking unit. The two press-down racks are placed upright and inverted respectively for returning to a circle;

[0008] Establish a digital-analog calculation system for jacking pipes: determine the pressing position of the pressing frame through the digital-analog calculation system;

[0009] Control the pressing operation: control the operation of the two pressing racks according to the determined pressing position, avoid the high-temperature section at the head of the rough pipe, start the first pressing in the middle of the rough pipe, and perform the second pressing in the low-temperature section at the tail of the rough pipe.

[0010] As a preferred solution, the pressing frame is a three-roller frame, which is controlled by three oil cylinders.

[0011] As a preferred solution, the strokes of the three oil cylinders on the pressing frame are 0-22mm, 0-22mm and 0-14mm respectively.

[0012] As a preferred solution, the pipe jacking digital-analog calculation system includes an input end and an output end, and uses an equal volume algorithm to obtain data at the output end based on data at the input end.

[0013] As a preferred solution, the input end is used to input the rough pipe size, rough pipe size, jacking pipe rack size, jacking pipe rack size, planned pressing amount and planned pressing area into the system, and the output end is used to display the position and amount of the cylinder pressing.

[0014] As a preferred solution, the capillary tube size and rough tube size both include outer diameter, wall thickness and length.

[0015] As a preferred solution, the size of the pipe jacking frame is used to calculate the cross-sectional area of ​​the roller.

[0016] As a preferred solution, the equal volume algorithm specifically includes: determining the cross-sectional area of ​​the rough pipe before and after passing through the jacking rack by the dimensions of the front and rear rough pipe racks, calculating the elongation after passing through the rack by the volume invariance principle, and then determining the pressing position.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention adds two easily controlled pressing frames to the traditional CPE pipe jacking unit, and accurately controls it through a pipe jacking digital-analog calculation system, avoids the high-temperature section, and presses down in the low-temperature section to make the wall thickness trend of the head, middle and tail of the rough pipe consistent. After tension reduction, the cutting loss of the original wall thickness in the low-temperature section can be effectively reduced. At the same time, the overall wall thickness tends to be consistent, reducing the risk of wall thickness in the high-temperature section. DETAILED DESCRIPTION

[0018] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0019] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0020] Unless otherwise specifically stated, the relative arrangement of the parts and steps, numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present invention. The techniques, methods and equipment known to those of ordinary skill in the relevant art may not be discussed in detail, but in appropriate cases, the techniques, methods and equipment should be considered as a part of the authorization specification. In all examples shown and discussed here, any specific value should be interpreted as being merely exemplary, rather than as a limitation. Therefore, other examples of exemplary embodiments may have different values.

[0023] In addition, it should be noted that the use of terms such as "first" and "second" to limit components is only for the convenience of distinguishing the corresponding components. If not otherwise stated, the above terms have no special meaning and therefore cannot be understood as limiting the scope of protection of the present invention.

[0024] This application studies the pipe rolling process of traditional seamless pipes, especially the pipe jacking process through the CPE pipe jacking unit, and finds that the CPE pipe jacking unit is essentially a full floating mandrel rolling unit, and the wall thickness of the rough pipe after the pipe jacking is greatly affected by the mandrel size, temperature, etc. When rolling thick-walled pipes, the hollow rough pipe is pierced through the hole, the mandrel is pre-pierced, and the pipe jacking extension is performed after the pre-piercing. The head of the mandrel is always kept at high temperature, and the head temperature is also higher than the middle and tail temperatures of the rough pipe after extension, causing the temperature of the mandrel head to be much higher than the middle and tail temperatures of the mandrel. Due to the thermal expansion of H13 steel, the head size of the mandrel is large and the middle size is small. After the pipe jacking rolling, the wall thickness of the rough pipe head is thinner than the middle and tail. After the tension reduction rolling, this trend is further amplified, which is reflected in the finished pipe as uneven overall wall thickness, thin head, thick middle, difficult production control, long cutting loss, and great difficulty in product quality and production process control.

[0025] Therefore, a method for reducing cutting loss by precisely controlling the wall thickness of the rough pipe of the pipe jacking unit is designed, by adding two pressing racks behind the bed of the traditional pipe jacking unit, and the two pressing racks are placed upright and inverted respectively. The pressing rack is a three-roll rack controlled by three oil cylinders. The strokes of the three oil cylinders are 0-22mm, 0-22mm and 0-14mm respectively. The pipe jacking digital analog calculation system is provided with an input end and an output end. The input end is used to input the rough pipe size (outer diameter size, wall thickness and length), the rough pipe size (outer diameter size, wall thickness and length), the pipe jacking rack size (used to calculate the roller cross-sectional area), the pressing rack size, the planned pressing amount and the planned pressing area into the system, and the output end is used to display the position and amount of the cylinder pressing. Then, the cross-sectional area of ​​the rough pipe before and after passing through the pipe jacking rack is determined by the front and rear rough pipe rack sizes, and the elongation after passing through the rack is calculated by using the volume invariance principle, and then the pressing position is determined.

[0026] According to the determined pressing position, the operation of the two pressing racks is controlled to avoid the high temperature section at the head of the rough pipe, and the first pressing is started in the middle of the rough pipe, and the second pressing is carried out in the low temperature section at the tail of the rough pipe. The wall thickness of the head, middle and tail of the rough pipe is uniform through the hydraulic pressing of the oil cylinder. The tension reduction loss after compensating pressing is significantly reduced, and the wall thickness of the finished pipe is uniform, which reduces the probability of excessive thickness at the end and negative wall at the head of the pipe body (high temperature section of the mandrel head), and improves the product quality. Working principle: During actual rolling, the two pressing racks are named K1 and K2, and the normal jacking rack before K2 is named K3. The spacing between K1 and K2 is set to 1400mm, and the spacing between K2 and K3 is set to 1500mm. Input the rough pipe size (outer diameter, wall thickness, length), the rough pipe size (outer diameter, wall thickness, length), the size of each jacking rack (used to calculate the roller cross-sectional area), the size of the jacking rack, the planned reduction amount and the planned reduction area. The cross-sectional area of ​​the rough pipe before and after passing through the jacking rack is known (the dimensions of the rough pipe racks before and after are known, and the cross-sectional area is calculated approximately as a circle). The elongation after passing through the rack is calculated using the volume invariance principle, and the reduction position is determined. When the rough pipe reaches the last two reduction racks after passing through the normal jacking rack, the reduction rack performs three-roll reduction at the output reduction position, and the reduction amount is equal to the set reduction value.

[0027] The above are preferred implementation modes of the present invention. Those skilled in the art to which the present invention belongs can also change and modify the above implementation modes. Therefore, the present invention is not limited to the above specific implementation modes. Any obvious improvements, substitutions or modifications made by those skilled in the art on the basis of the present invention belong to the protection scope of the present invention.

Claims

1. A method for reducing cutting loss by accurately controlling the wall thickness of a rough pipe of a pipe jacking unit, the method comprising steps of heating the pipe blank, perforating, inserting a rod, shrinking the pipe, jacking the pipe, loosening the rod and removing the rod, characterized in that: Also includes: Add a press-down rack: In the pipe jacking step, a pipe jacking unit is used for pipe jacking. Two press-down racks are added behind the bed of the pipe jacking unit. The two press-down racks are placed upright and inverted respectively for returning to a circle; Establishing a pipe jacking digital model calculation system: Determine the pressing position of the pressing frame through the pipe jacking digital model calculation system; Control the pressing operation: control the operation of the two pressing racks according to the determined pressing position, avoid the high-temperature section at the head of the rough pipe, start the first pressing in the middle of the rough pipe, and perform the second pressing in the low-temperature section at the tail of the rough pipe.

2. According to claim 1, a method for reducing cutting loss by accurately controlling the wall thickness of the rough pipe of a pipe jacking unit, characterized in that: The pressing frame is a three-roller frame and is controlled by three oil cylinders.

3. The method for reducing cutting loss by accurately controlling the wall thickness of the rough pipe of a pipe jacking unit according to claim 2 is characterized in that: The strokes of the three oil cylinders on the pressing frame are 0-22mm, 0-22mm and 0-14mm respectively.

4. The method for reducing cutting loss by accurately controlling the wall thickness of the rough pipe of a pipe jacking unit according to claim 1 is characterized in that: The pipe jacking digital-analog calculation system comprises an input end and an output end, and uses an equal volume algorithm to obtain data at the output end according to data at the input end.

5. The method for reducing cutting loss by accurately controlling the wall thickness of the rough pipe of a pipe jacking unit according to claim 4 is characterized in that: The input end is used to input the rough pipe size, rough pipe size, jacking rack size, jacking rack size, planned jacking amount and planned jacking area into the system, and the output end is used to display the position and amount of the cylinder jacking.

6. The method for reducing cutting loss by accurately controlling the wall thickness of the rough pipe of a pipe jacking unit according to claim 5 is characterized in that: The capillary tube size and rough tube size both include outer diameter, wall thickness and length.

7. The method for reducing cutting loss by accurately controlling the wall thickness of the rough pipe of a pipe jacking unit according to claim 6 is characterized in that: The pipe jacking stand dimensions are used to calculate the roll cross-sectional area.

8. The method for reducing cutting loss by accurately controlling the wall thickness of the rough pipe of a pipe jacking unit according to claim 7 is characterized in that: The equal volume algorithm specifically includes: determining the cross-sectional area of ​​the rough pipe before and after passing through the jacking frame by the dimensions of the front and rear rough pipe frames, calculating the elongation after passing through the frame by using the volume invariance principle, and then determining the pressing position.