Linear side wall pass opening design method for controlling ovality of cold-rolled pipe

Abstract

The invention relates to a linear side wall pass opening design method for controlling the ovality of a cold-rolled pipe. The method comprises the steps that the outer diameter and the wall thickness of a pipe blank, the outer diameter and the wall thickness of a finished pipe, a roller gap and a rolling rotation angle gamma are input; the opening angle of the linear side wall hole pattern and the feeding amount in the pipe rolling process can be mutually determined; determining a rolling separation point O of the initial section of the pipe on the hole-shaped section, namely calculating an included angle between an O1O connecting line and an opening angle arc side line; calculating the specific gravity value of the depressed area, and determining the feeding amount and the opening angle when the specific gravity value is smaller than or equal to a threshold value; when the specific gravity value is larger than the threshold value, the feeding amount or the opening angle of the linear side wall hole pattern is adjusted again till the specific gravity value of the screw-down area is smaller than or equal to the threshold value; and finally, calculating to obtain the hole pattern opening width Bx. According to the method, the relation among the feeding amount, the initial pipe specification and the hole pattern opening is obtained through calculation, the ovality of the cold-rolled pipe in the rolling process can be accurately controlled, and the rolling efficiency and the product size precision are improved.

Description

Technical Field

[0001] This invention relates to the field of cold rolling technology for metal tubes, and in particular to a method for designing straight sidewall openings to control the ellipticity of cold-rolled tubes. Background Technology

[0002] Cold-rolled seamless steel pipes, as an important pipe product, are widely used in many fields such as petrochemicals, machinery manufacturing, and aerospace due to their high precision, good surface quality, and excellent mechanical properties. In the production process of cold-rolled seamless steel pipes, the die opening design plays a decisive role in the quality of the pipe.

[0003] Currently, straight-sided sidewall pass openings are common in cold rolling processes. However, this pass design has significant drawbacks: during cold rolling, the deformation zone using straight-sided sidewall pass openings often exhibits a large ellipticity in the tube, with the difference between the major and minor axes at the initial rolling end reaching 20-30 micrometers. This is mainly because the pressure distribution is not uniform when applying pressure to the tube using straight-sided sidewall pass openings, and a relationship between the tube feed rate and the pass opening size has not been established. Therefore, during the rolling process, the rolling force experienced by different positions along the pass opening direction varies significantly, resulting in uneven compression and extension of the tube during deformation, making it difficult to control the ellipticity of the tube.

[0004] Excessive ellipticity in pipes not only affects the product's appearance quality but also reduces its performance in actual use. For example, in applications requiring high pipe concentricity, excessively elliptic pipes can lead to problems such as poor sealing and impeded fluid transport, severely impacting product reliability and lifespan. Therefore, developing a new method to effectively reduce the ellipticity of cold-rolled seamless steel pipes in the deformation zone is of great significance for improving the quality and production efficiency of cold-rolled seamless steel pipes. Summary of the Invention

[0005] To address the aforementioned problems, the present invention aims to provide a method for designing a straight sidewall die opening to control the ellipticity of cold-rolled tubes. By establishing the relationship between the tube rolling feed rate, initial tube specifications, and die opening, the ellipticity of the tube during cold rolling can be precisely controlled, improving the uniformity of rolling force and enhancing the dimensional accuracy and surface roughness of the product.

[0006] The technical solution adopted in this invention is as follows: The present invention proposes a method for designing straight sidewall openings to control the ellipticity of cold-rolled tubes, which specifically includes the following steps: Step 1: Determine the outer diameter of the tube blank and wall thickness Outer diameter of finished pipe and wall thickness Roll gap and rolling rotation angle ; Step 2: Input the opening angle of the straight sidewall hole. Or input the feed rate during the pipe rolling process. ; Step 3: Adjust the feed rate during the pipe rolling process Or straight sidewall hole type opening angle ; Step 4: Determine the pipe material Cross section in hole type Rolling stripping point O on the cross section; Step 5: Calculate the specific gravity of the pressed area using the following formula:

[0007] in: This refers to the ratio of the compressed area of ​​the deformed section of the pipe to its total density. The area of ​​the straight sidewall pressed down; This refers to the pipe area in the opening angle region; Step 6: When the calculated specific gravity of the pressed area is less than or equal to the threshold, the feed rate can be determined. and opening angle When the calculated reduction area ratio exceeds the threshold, the feed rate during the tube rolling process will be readjusted. Or straight sidewall hole type opening angle Continue until the specific gravity of the pressed area is less than or equal to the threshold. Step 7: Determine the feed rate during the tube rolling process and straight sidewall hole opening angle Then, calculate the aperture width using the following formula. :

[0008] in: B x The width of the hole opening; R x Let x be the radius of the bottom arc of the roll groove in the deformation zone x section.

[0009] Furthermore, in step 1, the pipe is a small-diameter, thin-walled seamless steel pipe with a straight sidewall aperture angle. The rolling rotation angle is 15°-35°; to ensure uniform circumferential deformation of the pipe, the rolling rotation angle γ must be greater than twice the opening angle; the roll gap is 1mm-2mm.

[0010] Furthermore, in step 2, the opening width of the straight sidewall hole is... B xThere are two ways to determine the opening angle of the straight sidewall hole: Or input the feed rate during the pipe rolling process. Determine the order of priority.

[0011] Furthermore, in step 3, the feed rate during the pipe rolling process... Or straight sidewall hole type opening angle It needs to be adjusted according to the specific gravity of the pressed area.

[0012] Furthermore, in step 4, controlling the initial ellipticity of the pipe ensures the dimensional accuracy and quality of the finished pipe, thus determining the pipe material... The cross section in the hole The rolling stripping point O on the cross section; wherein, the location of the rolling stripping point O is determined according to the following formula:

[0013] in: The angle between the line connecting O1O (where O1 is the center of the arc of the pipe section) and the edge of the arc of the opening angle; Deformation zone The radius of the bottom arc of the groove in the cross-section roll; The radius of the bottom arc of the roll groove in the initial cross section of the deformation zone.

[0014] Furthermore, in step 5, the area of ​​the straight sidewall is pressed down. Calculated using the following formula: .

[0015] Furthermore, in step 5, the pipe area in the opening angle region... Calculated using the following formula:

[0016] in: The radius of the outer contour arc of the mandrel in the initial cross-section of the deformation zone is given.

[0017] Furthermore, in step 5, the specific gravity threshold for the pressed area must meet the following condition: The specific gravity of the pressed area calculated at that time .

[0018] Compared with the prior art, the present invention has the following advantages: This invention, by adopting the above technical solution, reduces the outer diameter of the tube blank. and wall thickness Outer diameter of finished pipe and wall thickness Roll gap and rolling rotation angle γGiven the given information, the opening angle of the straight sidewall hole type Feed rate during pipe rolling process They can be mutually confirmed; pipes need to be found. Cross section in hole type The rolling release point O on the cross-section is calculated by determining the angle between the line connecting O1O and the edge of the opening angle arc; then, the specific gravity of the reduction area is calculated. When the specific gravity is less than or equal to the threshold, the feed rate can be determined. and opening angle When the specific gravity exceeds the threshold, the feed rate during the pipe rolling process will be readjusted. Or straight sidewall hole type opening angle The process continues until the specific gravity of the pressed area is less than or equal to the threshold; finally, the orifice opening width is calculated. B x Compared to traditional methods, the determination of the straight sidewall opening takes into account factors such as feed rate and initial tube specifications, which can reduce uneven deformation of the material metal, thereby improving rolling efficiency and reducing production costs. It also plays an important role in reducing the ellipticity of the tube during rolling and in the finished tube. Attached Figure Description

[0019] Figure 1 This is a flowchart of a method for designing straight sidewall hole openings to control the ellipticity of cold-rolled tubes, as proposed in this invention. Figure 2 This is a schematic diagram of the longitudinal and transverse sections of a cold-rolled seamless steel pipe; Figure 3 A schematic diagram of the transverse cross-section of the cold-rolled tube at position x=t after it has been fed in; Figure 4 This is an enlarged schematic diagram of the opening area of ​​the die in a cold-rolled tube. Figure 5 This is an enlarged schematic diagram of the roll opening and roll gap area of ​​cold-rolled tubes. Detailed Implementation

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] The Pilger cold rolling mill is the main cold rolling equipment for producing small-diameter, thin-walled, thick-walled seamless steel pipes. Its upper and lower rolls, along with the mandrel in the middle, constrain the pipe material. For example... Figure 2As shown, with the feeding of the tube, a large tube cross-section is fed into a relatively small die. Under the extrusion of the bottom contour 1 of the roll groove and the outer contour 2 of the mandrel, the tube 3 undergoes metal extrusion deformation. For the straight sidewall die opening 4, if the feed rate is too large, the metal will deform violently in the die opening area. This not only makes the inner surface of the tube prone to defects such as cracks, but also increases the ellipticity of the tube in the rolling deformation zone, which is detrimental to subsequent stable rolling. When the feed rate is too small, the rolling cycle will be prolonged, and the rolling efficiency will be significantly reduced.

[0022] When the pipes are sent in After length, x Specific parameters of the transverse cross section of the pipe at the location are as follows: Figure 3 As shown, the area of ​​the straight sidewall is reduced. The metal will flow towards the opening angle region. Therefore, controlling the straight sidewall reduction area becomes a key factor in solving the pipe ellipticity problem. Finding the relationship between the feed rate, initial pipe specifications, and orifice opening can control the straight sidewall reduction area. Therefore, it is necessary to calculate the straight sidewall reduction area. Pipe area in the opening angle region The specific parameters and their positional relationships are as follows: Figure 4 As shown.

[0023] By comparing the specific gravity of the pressed area with the threshold value, the feed rate during the pipe rolling process is continuously adjusted. Or straight sidewall hole type opening angle The feed rate during the pipe rolling process can be determined once the specific gravity of the pressed area is less than or equal to the threshold value. and straight sidewall hole opening angle Finally, the width of the straight sidewall opening can be calculated. B x The specific parameters and their positional relationships are as follows: Figure 5 As shown.

[0024] Example 1 See appendix Figure 1 This embodiment proposes a method for designing the straight sidewall die opening to control the ellipticity of cold-rolled tubes, based on the known feed rate during the tube rolling process. The design scheme includes the following steps: Step 1, determine the outer diameter of the tube blank. and wall thickness Outer diameter of finished pipe and wall thickness Roll gap and rolling rotation angle γ ; Step 2: Input the feed rate for the pipe rolling process. ; Step 3, adjust the opening angle of the straight sidewall hole. ; Step 4, determine the pipe material Cross section in hole type The rolling release point O on the cross section; x is the axial coordinate from the starting position of rolling; Step 5, calculate the specific gravity of the pressed area using the following formula:

[0025] in: This is the ratio of the compressed area of ​​the deformed section of the pipe to its density. The area of ​​the straight sidewall pressed down; This represents the area of ​​the pipe material in the opening angle region.

[0026] Step 6: When the calculated specific gravity of the pressed area is less than or equal to the threshold, the feed rate can be determined. and opening angle When the calculated reduction area ratio exceeds the threshold, the feed rate during the tube rolling process will be readjusted. Or straight sidewall hole type opening angle This continues until the specific gravity of the pressed area is less than or equal to the threshold.

[0027] Step 7: Determine the feed rate for the pipe rolling process. and straight sidewall hole opening angle Then, calculate the aperture width using the following formula. B x :

[0028] in: B x The width of the hole opening; R x Let x be the radius of the bottom arc of the roll groove in the deformation zone x section.

[0029] The pipe is a small-diameter, thin-walled seamless steel pipe. To better control the dimensional accuracy and surface quality of the steel pipe and reduce problems such as ovality and uneven wall thickness during rolling, the opening angle of the straight sidewall die is [not specified]. The rolling rotation angle should be between 15° and 35° to ensure uniform circumferential deformation of the pipe. γ The opening angle should be greater than twice the opening angle; the roll gap should be 1mm-2mm.

[0030] After determining the feed rate during the pipe rolling process Then, the opening angle of the straight sidewall hole needs to be adjusted according to the specific gravity of the pressed area. .

[0031] Therefore, it is necessary to determine the pipe material first. Cross section in hole type The rolling break point O on the cross-section can be determined using the following formula:

[0032] in: The angle between the line connecting O1O (where O1 is the center of the arc of the pipe section) and the edge of the arc of the opening angle; Deformation zone The radius of the bottom arc of the groove in the cross-section roll; The radius of the bottom arc of the roll groove in the initial cross section of the deformation zone.

[0033] The area of ​​the straight sidewall compression Calculated using the following formula:

[0034] Pipe area in the opening angle region Calculated using the following formula:

[0035] in,: The radius of the outer contour arc of the mandrel in the initial cross-section of the deformation zone is given.

[0036] The specific gravity threshold of the pressed area must meet the following requirements: The specific gravity of the compressed area calculated from the simulation results. .

[0037] After obtaining the feed rate during the pipe rolling process and straight sidewall hole opening angle Then, the width of the straight sidewall hole opening can be determined. B x The designed straight sidewall opening will facilitate the extrusion deformation of the metal and improve the ellipticity of the pipe.

[0038] The following specific examples will further illustrate this embodiment: A method for designing straight sidewall die openings to control the ellipticity of cold-rolled tubes includes the following steps: Step 1, determine the outer diameter of the tube blank. and wall thickness Outer diameter of finished pipe and wall thickness Roll gap and rolling rotation angle ; Step 2: Input the feed rate for the pipe rolling process. ; Step 3, adjust the opening angle of the straight sidewall hole to ; Step 4, determine the pipe material Cross section in hole type Rolling stripping point O on the cross section; Step 5: Calculate the specific gravity of the pressed area using the following formula. The relevant calculation formula is:

[0039] Step 6, calculate the specific gravity of the pressed area. Less than the threshold The feed volume can then be determined. and opening angle The requirements are met; Step 7: Determine the feed rate for the pipe rolling process. and straight sidewall hole opening angle Then, the initial width of the aperture is calculated using the following formula. The calculation method for the opening width of the holes in other locations is the same, and the relevant calculation formula is as follows:

[0040] Among them, in determining the pipe material Cross section in hole type When the rolling release point O is on the cross-section, the angle between the line connecting O1O (where O1 is the center of the arc of the tube cross-section) and the edge of the arc of the opening angle is calculated using the following formula. The relevant calculation formula is:

[0041] The area of ​​the straight sidewall compression is calculated using the following formula. The relevant calculation formula is:

[0042] The pipe area in the opening angle region can be calculated using the following formula. The relevant calculation formula is:

[0043] The specific gravity threshold of the pressed area must satisfy... The specific gravity of the pressed area calculated at that time .

[0044] Design results: Table 1. Location of the deformation section during pipe rolling and ellipticity of the finished pipe.

[0045] Experimental measurement data shows that when the feed rate is 2mm and the opening angle is 25°, the difference between the major and minor axes of the tapered tube at the initial position is only 0.14mm. During the rolling process, the ellipticity of the tube gradually decreases, and the ellipticity of the finished tube reaches 0.392%. Currently, the ellipticity of high-precision metal tubes is generally required to be controlled within 0.5% - 1.0%. Therefore, the straight sidewall die opening design method for controlling the ellipticity of cold-rolled tubes plays an important role in improving the ellipticity of the tubes.

[0046] Example 2 This embodiment proposes a method for designing straight sidewall die openings to control the ellipticity of cold-rolled tubes, specifically for cases where the opening angle of the straight sidewall die is known. The design scheme includes the following steps: Step 1, determine the outer diameter of the tube blank. and wall thickness Outer diameter of finished pipe and wall thickness Roll gap and rolling rotation angle γ ; Step 2, input the opening angle of the straight sidewall hole. ; Step 3: Adjust the feed rate during the pipe rolling process. ; Step 4, determine the pipe material Cross section in hole type Rolling stripping point O on the cross section; Step 5, calculate the specific gravity of the pressed area using the following formula:

[0047] in: This refers to the ratio of the compressed area of ​​the deformed section of the pipe to its total density. The area of ​​the straight sidewall pressed down; This represents the area of ​​the pipe material in the opening angle region.

[0048] Step 6: When the calculated specific gravity of the pressed area is less than or equal to the threshold, the feed rate can be determined. and opening angle When the calculated reduction area ratio exceeds the threshold, the feed rate during the tube rolling process will be readjusted. Or straight sidewall hole type opening angle This continues until the specific gravity of the pressed area is less than or equal to the threshold.

[0049] Step 7: Determine the feed rate for the pipe rolling process. and straight sidewall hole opening angle Then, calculate the aperture width using the following formula.B x :

[0050] in: B x The width of the hole opening; R x Let x be the radius of the bottom arc of the roll groove in the deformation zone x section.

[0051] The finished tube is a small-diameter, thin-walled seamless steel pipe. To better control the dimensional accuracy and surface quality of the steel pipe and reduce problems such as ovality and uneven wall thickness during the rolling process, the opening angle of the straight sidewall die is [not specified]. The rolling rotation angle should be between 15° and 35° to ensure uniform circumferential deformation of the pipe. γ The opening angle should be greater than twice the opening angle; the roll gap should be 1mm-2mm.

[0052] After determining the opening angle of the straight sidewall hole... Then, the feed rate during the tube rolling process needs to be adjusted according to the specific gravity of the pressed area. .

[0053] Therefore, it is necessary to determine the pipe material first. Cross section in hole type The rolling stripping point O on the cross-section can be determined using the following formula:

[0054] in: The angle between the line connecting O1O (where O1 is the center of the arc of the pipe section) and the edge of the arc of the opening angle; Deformation zone The radius of the bottom arc of the groove in the cross-section roll; The radius of the bottom arc of the roll groove in the initial cross section of the deformation zone.

[0055] The area of ​​the straight sidewall compression Calculated using the following formula:

[0056] Pipe area in the opening angle region Calculated using the following formula:

[0057] in: The radius of the outer contour arc of the mandrel in the initial cross-section of the deformation zone is given.

[0058] The specific gravity threshold of the compressed area must meet the following condition. The specific gravity of the compressed area calculated from the simulation results. .

[0059] After obtaining the feed rate during the pipe rolling process and straight sidewall hole opening angle Then, the width of the straight sidewall hole opening can be determined. B x First, determine the opening angle of the straight sidewall hole. Then, by adjusting the feed rate during the pipe rolling process... The sequential approach is more practical and can better improve the ellipticity of the pipes.

[0060] The following specific examples will further illustrate this embodiment: A method for designing straight sidewall die openings to control the ellipticity of cold-rolled tubes includes the following steps: Step 1, determine the outer diameter of the tube blank. and wall thickness Outer diameter of finished pipe and wall thickness Roll gap and rolling rotation angle ; Step 2, input the opening angle of the straight sidewall hole. ; Step 3: Adjust the feed rate during the pipe rolling process. ; Step 4, determine the pipe material Cross section in hole type Rolling stripping point O on the cross section; Step 5: Calculate the specific gravity of the pressed area using the following formula. The relevant calculation formula is:

[0061] Step 6, calculate the specific gravity of the pressed area. Less than the threshold The feed volume can then be determined. and opening angle The requirements are met; Step 7: Determine the feed rate for the pipe rolling process. and straight sidewall hole opening angle Then, the initial width of the aperture is calculated using the following formula. The calculation method for the opening width of the holes in other locations is the same, and the relevant calculation formula is as follows:

[0062] Among them, in determining the pipe material Cross section in hole type When the rolling release point O is on the cross-section, the angle between the line connecting O1O (where O1 is the center of the arc of the tube cross-section) and the edge of the arc of the opening angle is calculated using the following formula. The relevant calculation formula is:

[0063] The area of ​​the straight sidewall compression is calculated using the following formula. The relevant calculation formula is:

[0064] The pipe area in the opening angle region can be calculated using the following formula. The relevant calculation formula is:

[0065] The specific gravity threshold of the pressed area must satisfy... The specific gravity of the pressed area calculated at that time .

[0066] Design results: Table 2. Location of the deformation section during pipe rolling and ellipticity of the finished pipe.

[0067] Experimental measurement data shows that when the feed rate is 3mm and the opening angle is 30°, the difference between the major and minor axes of the tapered tube at the initial position is 0.13mm. During the rolling process, the ellipticity of the tube gradually decreases, and the ellipticity of the finished tube reaches 0.389%. Furthermore, for tubes with pre-determined straight sidewall opening angles... Then, by adjusting the feed rate during the pipe rolling process... The sequential approach is more practical, requiring only a small number of tube blanks to determine the optimal approach, and can better improve the ellipticity of the tube.

[0068] All matters not covered in this invention are common knowledge.

[0069] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for designing straight sidewall opening profiles to control the ellipticity of cold-rolled tubes, characterized in that, The method includes the following steps: Step 1: Determine the outer diameter of the tube blank and wall thickness Outer diameter of finished pipe and wall thickness Roll gap and rolling rotation angle ; Step 2: Input the opening angle of the straight sidewall hole. Or input the feed rate during the pipe rolling process. ; Step 3: Adjust the feed rate during the pipe rolling process Or straight sidewall hole type opening angle ; Step 4: Determine the pipe material Cross section in hole type Rolling stripping point O on the cross section; Step 5: Calculate the specific gravity of the pressed area using the following formula: in: This is the ratio of the compressed area of ​​the deformed section of the pipe to its density. The area of ​​the straight sidewall pressed down; This refers to the pipe area in the opening angle region; Step 6: When the calculated specific gravity of the pressed area is less than or equal to the threshold, the feed rate can be determined. and opening angle When the calculated reduction area ratio exceeds the threshold, the feed rate during the tube rolling process will be readjusted. Or straight sidewall hole type opening angle Continue until the specific gravity of the pressed area is less than or equal to the threshold. Step 7: Determine the feed rate during the tube rolling process and straight sidewall hole opening angle Then, calculate the aperture width using the following formula. : in: B x The width of the hole opening; R x Let x be the radius of the bottom arc of the roll groove in the deformation zone x section.

2. The method for designing a straight sidewall opening for controlling the ellipticity of cold-rolled tubes according to claim 1, characterized in that: In step 1, the pipe is a small-diameter, thin-walled, seamless steel pipe with a straight sidewall opening angle. The rolling rotation angle is 15°-35°; to ensure uniform circumferential deformation of the pipe, the rolling rotation angle γ must be greater than twice the opening angle; the roll gap is 1mm-2mm.

3. The method for designing a straight sidewall opening for controlling the ellipticity of cold-rolled tubes according to claim 1, characterized in that: In step 2, the width of the straight sidewall hole type opening is... B x There are two ways to determine the opening angle of the straight sidewall hole: Or input the feed rate during the pipe rolling process. Determine the order of priority.

4. The method for designing a straight sidewall opening for controlling the ellipticity of cold-rolled tubes according to claim 1, characterized in that: In step 3, the feed rate during the tube rolling process Or straight sidewall hole type opening angle It needs to be adjusted according to the specific gravity of the pressed area.

5. The method for designing a straight sidewall opening for controlling the ellipticity of cold-rolled tubes according to claim 1, characterized in that: In step 4, controlling the initial ellipticity of the pipe ensures the dimensional accuracy and quality of the finished pipe; therefore, the pipe material is determined... The cross section in the hole The rolling stripping point O on the cross section; wherein, the location of the rolling stripping point O is determined according to the following formula: in: The angle between the line connecting O1O (where O1 is the center of the arc of the pipe section) and the edge of the arc of the opening angle; Deformation zone The radius of the bottom arc of the groove in the cross-section roll; The radius of the bottom arc of the roll groove in the initial cross section of the deformation zone.

6. The method for designing a straight sidewall die opening to control the ellipticity of cold-rolled tubes according to claim 5, characterized in that: In step 5, the area of ​​the straight sidewall is pressed down. Calculated using the following formula: 。 7. The method for designing a straight sidewall opening for controlling the ellipticity of cold-rolled tubes according to claim 6, characterized in that: In step 5, the pipe area in the opening angle region... Calculated using the following formula: in: The radius of the outer contour arc of the mandrel in the initial cross-section of the deformation zone is given.

8. The method for designing a straight sidewall opening for controlling the ellipticity of cold-rolled tubes according to claim 7, characterized in that: In step 5, the specific gravity threshold of the pressed area must meet the following condition: The specific gravity of the pressed area calculated at that time .

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