Method for accurately controlling wall thickness of finished product pipe after tension reduction through pipe jacking unit

Abstract

The invention relates to the field of pipe blank machining, and discloses a method for accurately controlling the wall thickness of a finished pipe after stretch reduction through a pipe jacking unit, which comprises the following steps: S1, feeding a pierced billet: accurately conveying the pierced billet to be machined to a machining area through feeding equipment, and then conveying the pierced billet to the pipe jacking unit; s2, pipe jacking rolling and post-treatment are conducted, specifically, according to preset pipe jacking process parameters, the pierced billet is rolled through a pipe jacking unit; s3, ultrasonic diameter measurement, wherein an ultrasonic detector is used for measuring the diameter of the finished pipe wall; and S4, online thermal detection: thermal detection is mainly based on thermal radiation characteristics of the object, and the thermal radiation characteristics are converted into visible thermal images. According to the invention, a diameter measuring device and a thermal temperature measuring device are additionally arranged, so that a thermal-state core rod size mathematical model and a tension adjusting mathematical model are calculated on line. The method can effectively improve the poor precision of the wall thickness of a finished pipe product caused by uneven core rod temperature, uneven pre-penetrating temperature, uneven cold-state core rod size and the like, and improves the qualified rate and the yield of the product.

Description

Technical Field

[0001] The present invention relates to the technical field of tube blank processing, and particularly to a method for accurately controlling the wall thickness of the finished tube after stretch reducing in a pipe jacking unit. Background Art

[0002] The CPE pipe jacking unit is essentially a fully floating mandrel rolling mill. The wall thickness of the rough tube after pipe jacking is greatly affected by the mandrel size, temperature, etc.

[0003] When rolling thick-walled tubes, a hollow billet is pierced through, and the mandrel is pre-pierced. After pre-piercing, pipe jacking extension is carried out. The head of the mandrel always maintains high-temperature production. At the same time, the head temperature is also higher than the temperature in the middle and at the tail of the extended rough tube, resulting in the head temperature of the mandrel being much higher than the temperature in the middle and at the tail of the mandrel.

[0004] Due to the thermal expansion effect of H13 steel, the size of the mandrel head is large and the size in the middle is small. After pipe jacking rolling, the wall thickness of the head of the rough tube is thinner than that in the middle and at the tail. After stretch reducing tension rolling, this trend is further amplified. In the finished tube, it is manifested as uneven overall wall thickness, thin head, and thick middle, making production control difficult and the cut loss long, and there are great difficulties in product quality and production process control. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the present invention provides a method for accurately controlling the wall thickness of the finished tube after stretch reducing in a pipe jacking unit, which solves the problems that due to the thermal expansion effect of H13 steel, the size of the mandrel head is large and the size in the middle is small, resulting in the wall thickness of the head of the rough tube after pipe jacking rolling being thinner than that in the middle and at the tail. After stretch reducing tension rolling, this uneven wall thickness trend intensifies, causing uneven overall wall thickness of the finished tube, difficult production control, long cut loss, and seriously affecting product quality and production process management and control.

[0006] To achieve the above object, the present invention is realized through the following technical solutions: A method for accurately controlling the wall thickness of the finished tube after stretch reducing in a pipe jacking unit, including the following steps:

[0007] S1. Rough tube feeding: The rough tube to be processed is accurately conveyed to the processing area through a feeding device and then conveyed to the pipe jacking unit;

[0008] S2. Pipe jacking rolling and post-treatment: According to the preset pipe jacking process parameters, the rough tube is rolled through the pipe jacking unit, and subsequent process treatment is carried out on the rolled pipe;

[0009] S3. Ultrasonic diameter measurement: Use an ultrasonic detector to measure the diameter of the finished tube wall. By measuring the time for ultrasonic waves to propagate in the object and the known propagation speed of ultrasonic waves in the object, the thickness or diameter size information of the object can be calculated;

[0010] S4. Online Thermal Inspection: Thermal inspection is mainly based on the thermal radiation characteristics of an object and converts them into visible thermal images, thereby showing the temperature distribution on the surface of the object.

[0011] S5. Online Numerical Simulation to Calculate the Hot Dimensions of the Mandrel in Real Time: Use numerical simulation to calculate the hot dimensions of the mandrel in real time.

[0012] S6. Adjust the Tension Coefficient of the Stretch Reducer: After knowing the hot dimensions of the mandrel, use this as a reference to adjust the tension coefficient of the stretch reducer.

[0013] S7. Final Inspection and Feedback of the Finished Product: Re-inspect the wall thickness, outer diameter dimensions, and surface quality of the finished pipe after stretch reducing treatment to ensure that all indicators of the finished pipe meet the production standards.

[0014] Preferably, the raw pipe mentioned in step S1 refers to the steel pipe billet that has undergone preliminary processing such as piercing and has not yet undergone further finishing and deep processing.

[0015] Preferably, the processing area mentioned in step S1 includes: ring heating, piercing, necking down, and pre-piercing.

[0016] Preferably, the subsequent process treatment in step S2 is specifically as follows: First, perform the operations of loosening the mandrel and removing the mandrel to separate the raw pipe from the mandrel; then cut the raw pipe with a hot saw; subsequently, send the raw pipe into a reheating furnace to raise the temperature, perform water descaling to remove the surface scale, and then use intermediate frequency heating to make the raw pipe reach the appropriate tension reducing temperature.

[0017] Preferably, in step S5, the numerical simulation is specifically as follows:

[0018] L t = L0(1 + αΔT)

[0019] Where: Lt is the hot dimension, L0 is the initial dimension, α is the linear expansion coefficient of the material, ΔT is the temperature change, T2 - T1, T2 is the hot temperature, and T1 is the initial temperature.

[0020] Preferably, in step S6, the adjustment of the tension coefficient of the stretch reducer is specifically as follows:

[0021] Basic formula: According to the equality of the metal mass flow rate, at the inlet and outlet of the stretch reducer, where A1 and A2 are the cross-sectional areas at the inlet and outlet respectively, v1 and v2 are the speeds at the inlet and outlet respectively. Assuming that the deformation of the strip steel in the stretch reducer is uniform and the spread is ignored, A2 = π(D2 - t2)t2, where D1 and D2 are the pipe diameters at the inlet and outlet, t1 and t2 are the wall thicknesses at the inlet and outlet. The speeds v1 and v2 are related to the rotational speed and diameter of the rolls and can be expressed as v1 = ω1R1, where ω1 and ω2 are the angular velocities of the rolls, and R1 and R2 are the radii of the rolls. From this, the expression for the tension T can be derived: T =v2ρv12A1(v2-v1) , where ρ is the density of the material;

[0022] Calculation steps: First, according to the process parameters of the tension-reducing machine, determine the inlet and outlet pipe diameters, wall thickness, roller speed and diameter, etc., calculate the metal cross-sectional areas A1, A2 and speeds v1, v2, and then calculate the tension T according to the material density ρ;

[0023] Given the hot size of the mandrel and the size of the finished rack of the pipe jacking machine (according to the arrangement of the pipe jacking machine rack), the outer diameter of the rough pipe is approximately equal to the size of the finished rack, and the wall thickness of the rough pipe at a single point can be calculated as (size of the finished rack - hot size of the mandrel at a single point) / 2;

[0024] Adjust the tension coefficient according to the wall thickness of the raw pipe at the inlet, reduce the tension at thinner points and increase the tension at thicker points;

[0025] Adjustment principle: Take the hot size of the middle section of the mandrel as the benchmark, and the size of the mandrel at the head and tail as the adjustment point, increase or decrease the tension according to the percentage conversion, and send the converted tension coefficient to the tension-reducing machine. The tension at different positions is accurately adjusted through the steel biting position of the tension-reducing machine, so as to ensure the uniform wall thickness of the finished pipe after tension-reduction and improve the product qualification rate and yield rate.

[0026] The present invention provides a method for a pipe jacking unit to accurately control the wall thickness of a finished pipe after tension reduction. It has the following beneficial effects:

[0027] 1. The present invention adds a diameter measuring device, a thermal temperature detection device, an online calculation of the hot mandrel size digital model, and an online calculation of the tension adjustment digital model. It can effectively improve the poor wall thickness accuracy of the finished pipe caused by uneven mandrel temperature, uneven pre-piercing temperature, and uneven cold mandrel size, thereby improving the product qualification rate and yield rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a flow chart of the method of the present invention;

[0029] Figure 2 It is a schematic diagram of the expansion curve of the present invention. DETAILED DESCRIPTION

[0030] The following will be combined with the drawings of the present invention specification to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. 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.

[0031] Example:

[0032] Please see attached Figure 1 - AttachmentFigure 2 , an embodiment of the present invention provides a method for accurately controlling the wall thickness of the finished pipe after stretch reducing by a pipe jacking unit, including the following steps:

[0033] S1. Blank pipe feeding: Accurately convey the blank pipe to be processed to the processing area through feeding equipment and then to the pipe jacking unit. The blank pipe refers to the steel pipe billet that has undergone preliminary processing such as piercing and has not yet undergone further finishing and deep processing. The processing area includes: ring heating, piercing, necking, and pre-piercing;

[0034] S2. Pipe jacking rolling: Pipe jacking rolling and post-treatment: Roll the blank pipe through the pipe jacking unit according to the preset pipe jacking process parameters, and perform subsequent process treatment on the rolled pipe. The subsequent process treatment is specifically as follows: successively perform the operations of releasing the mandrel and removing the mandrel to separate the blank pipe from the mandrel; then cut the blank pipe with a hot saw; subsequently send the blank pipe into a reheating furnace to raise the temperature, perform water descaling to remove the surface oxide scale, and then use intermediate frequency heating to make the blank pipe reach the appropriate stretch reducing temperature;

[0035] S3. Ultrasonic diameter measurement: Use an ultrasonic detector to measure the diameter of the finished pipe wall. When ultrasonic waves propagate in a medium, they will reflect and refract when encountering the interface of different media. The ultrasonic diameter measurement device precisely utilizes this characteristic. When ultrasonic waves are emitted from the transmitting transducer and propagate to the surface of the object to be measured, reflection waves will be formed on the surface and inside of the object. After the receiving transducer receives these reflection waves, by measuring the propagation time of the ultrasonic waves in the object and the known propagation speed of the ultrasonic waves in this object, the thickness or diameter size information of the object can be calculated;

[0036] S4. Online thermal inspection: Thermal inspection is mainly based on the thermal radiation characteristics of objects. Any object with a temperature higher than absolute zero will radiate infrared rays, and different temperatures result in different infrared ray energies and wavelengths. The thermal inspection equipment captures these infrared rays and converts them into visible thermal images, thereby showing the temperature distribution on the surface of the object;

[0037] S5. Online digital simulation calculation of the real-time hot size of the mandrel: Use digital simulation to calculate the real-time hot size of the mandrel. The digital simulation is specifically as follows:

[0038] L t = L0(1 + αΔT)

[0039] where: Lt is the hot size (i.e., the size after temperature change), L0 is the initial size (usually the size at room temperature), α is the linear expansion coefficient of the material, and ΔT is the temperature change amount (T2 - T1, T2 is the hot temperature, and T1 is the initial temperature);

[0040] 1. Detection method:

[0041] When the linear expansion coefficient α is defined as the relative change rate of the length of an object per unit temperature change, the mathematical expression is:

[0042] α = ΔL / (L0 * ΔT)

[0043] Where: ΔL is the change in length of the object when the temperature changes by ΔT, and L0 is the length of the object at the initial temperature.

[0044] 2. Test plan:

[0045] And heat the test material to 1000 °C at a heating rate of 5 °C / s, hold for 10 min, and then cool at a rate of 5 °C / s.

[0046]

[0047]

[0048] S6. Adjust the tension coefficient of the pipe reducer: After knowing the hot-state mandrel size, use this as a reference to adjust the tension coefficient of the pipe reducer. The specific calculation of the tension coefficient is as follows:

[0049] Basic formula: According to the equal metal mass flow rate, at the inlet and outlet of the pipe reducer, where A1 and A2 are the cross-sectional areas at the inlet and outlet respectively, and v1 and v2 are the speeds at the inlet and outlet respectively. Assuming that the deformation of the strip steel in the pipe reducer is uniform and the spread is ignored, A2 = π(D2 - t2)t2, where D1 and D2 are the pipe diameters at the inlet and outlet, and t1 and t2 are the wall thicknesses at the inlet and outlet. The speeds v1 and v2 are related to the rotational speed and diameter of the rolls and can be expressed as v1 = ω1R1, where ω1 and ω2 are the angular velocities of the rolls, and R1 and R2 are the radii of the rolls. From this, the expression for the tension T can be derived: T = v2ρv12A1(v2-v1) , where ρ is the density of the material;

[0050] Calculation steps: First, according to the process parameters of the pipe reducer, determine the pipe diameters, wall thicknesses, rotational speeds and diameters of the rolls at the inlet and outlet, calculate the cross-sectional areas A1 and A2 and speeds v1 and v2 of the metal, and then calculate the tension T according to the density ρ of the material;

[0051] Knowing the hot-state mandrel size and the finished product frame size of the pipe mill stand (according to the arrangement of the pipe mill stands), the outside diameter of the semifinished pipe is approximately equal to the finished product frame size, and the single-point semifinished pipe wall thickness can be calculated as = (finished product frame size - single-point hot-state mandrel size) / 2;

[0052] Adjust the tension coefficient according to the wall thickness of the semifinished pipe at the inlet. Reduce the tension at the thin point and increase the tension at the thick point;

[0053] Adjustment principle: Take the hot size of the middle section of the mandrel as the benchmark, and the size of the mandrel at the head and tail as the adjustment point, increase or decrease the tension according to the percentage conversion, and send the converted tension coefficient to the tension-reducing machine. The tension at different positions is accurately adjusted through the steel biting position of the tension-reducing machine, so as to ensure the uniform wall thickness of the finished pipe after tension-reduction, and improve the product qualification rate and yield rate;

[0054] S7. Finished product re-inspection and feedback: The finished pipes after the tension reduction treatment are re-inspected for wall thickness, outer diameter, and surface quality to ensure that all indicators of the finished pipes meet the production standards.

[0055] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for precisely controlling the wall thickness of the finished pipe after stretch-reducing by a pipe jacking unit, characterized in that, The following steps are involved: S1. Raw pipe loading: The raw pipe to be processed is accurately transported to the processing area through the loading equipment, and then transported to the pipe jacking unit; S2, pipe jacking rolling and post-processing: according to the preset pipe jacking process parameters, the rough pipe is rolled through the pipe jacking unit, and the rolled pipe is subjected to subsequent process treatment; S3. Ultrasonic diameter measurement: Use an ultrasonic detector to measure the diameter of the finished pipe wall. By measuring the propagation time of the ultrasonic wave in the object and the known propagation speed of the ultrasonic wave in the object, the thickness or diameter size information of the object can be calculated; S4. Online thermal inspection: Thermal inspection is mainly based on the thermal radiation characteristics of the object and converts it into a visible thermal image, thereby showing the temperature distribution on the surface of the object; S5. Online digital model calculation of real-time core rod hot size: Use digital model to calculate the core rod hot size in real time; S6. Adjust the tension coefficient of the tension reducing machine: after the hot mandrel size is known, use it as a reference to adjust the tension coefficient of the tension reducing machine; S7. Finished product re-inspection and feedback: The finished pipes after the tension reduction treatment are re-inspected for wall thickness, outer diameter, and surface quality to ensure that all indicators of the finished pipes meet the production standards.

2. The method for precisely controlling the wall thickness of the finished pipe after stretch-reducing in a pipe jacking unit according to claim 1, characterized in that The rough pipe in step S1 refers to the steel pipe blank that has undergone the initial perforation processing but has not yet undergone further finishing and deep processing.

3. A method for accurately controlling the wall thickness of the finished pipe after tension reducing of a pipe jacking unit according to claim 1, characterized in that, The processing areas in step S1 include: annular heating, perforation, shrinkage, and pre-piercing.

4. A method for precisely controlling the wall thickness of the finished pipe after tension reducing in a pipe jacking unit according to claim 1, characterized in that, The subsequent process described in step S2 is specifically as follows: Carry out the rod loosening and rod removing operations in sequence to separate the rough pipe from the core rod; Then the rough pipe is cut by hot saw; The rough pipe is then sent to the reheating furnace for heating, water descaling is performed to remove the surface oxide skin, and then medium frequency heating is used to make the rough pipe reach the appropriate tension reducing temperature.

5. A method for accurately controlling the wall thickness of the finished pipe after tension reducing in a pipe jacking unit according to claim 1, characterized in that, In step S5, the digital mold body is: L t = L0(1 + αΔT) Where: Lt is the hot size, L0 is the initial size, α is the linear expansion coefficient of the material, ΔT is the temperature change, T2 - T1, T2 are the hot temperatures, and T1 is the initial temperature.

6. A method for precisely controlling the wall thickness of the finished pipe after stretch reducing by a pipe jacking unit according to claim 1, characterized in that, In step S6, the tension coefficient of the tension reducing machine is adjusted as follows: Basic formula: Based on the equal metal flow rate per second, at the inlet and outlet of the stretch reducing mill, where A1 and A2 are the cross-sectional areas at the inlet and outlet respectively, and v1 and v2 are the speeds at the inlet and outlet respectively. Assuming that the deformation of the strip in the stretch reducing mill is uniform and the spread is ignored, A2 = π(D2 - t2)t2, where D1 and D2 are the pipe diameters at the inlet and outlet, and t1 and t2 are the wall thicknesses at the inlet and outlet. The speeds v1 and v2 are related to the rotational speeds and diameters of the rolls and can be expressed as v1 = ω1R1, where ω1 and ω2 are the angular velocities of the rolls, and R1 and R2 are the radii of the rolls. From this, the expression for the tension T can be derived: T = v2ρv12A1(v2-v1) , where ρ is the density of the material; Calculation steps: First, according to the process parameters of the tension-reducing machine, determine the inlet and outlet pipe diameters, wall thickness, roller speed and diameter, etc., calculate the metal cross-sectional areas A1, A2 and speeds v1, v2, and then calculate the tension T according to the material density ρ; Given the hot size of the mandrel and the size of the finished rack of the pipe jacking machine (according to the arrangement of the pipe jacking machine rack), the outer diameter of the rough pipe is approximately equal to the size of the finished rack, and the wall thickness of the rough pipe at a single point can be calculated as (size of the finished rack - hot size of the mandrel at a single point) / 2; Adjust the tension coefficient according to the wall thickness of the raw pipe at the inlet, reduce the tension at thinner points and increase the tension at thicker points; Adjustment principle: Take the hot size of the middle section of the mandrel as the benchmark, and the size of the mandrel at the head and tail as the adjustment point, increase or decrease the tension according to the percentage conversion, and send the converted tension coefficient to the tension-reducing machine. The tension at different positions is accurately adjusted through the steel biting position of the tension-reducing machine, so as to ensure the uniform wall thickness of the finished pipe after tension-reduction and improve the product qualification rate and yield rate.

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