Pipe drawing equipment

Abstract

This invention discloses a tube drawing device, belonging to the field of tube processing equipment, which can reduce residual stress in tubes. The tube drawing device of this invention includes an outer mold and an inner mold. The outer mold has a through hole, and the inner mold penetrates the through hole. During tube drawing, the inner mold is located inside the tube. In the drawing direction, the inner mold includes a diameter reduction structure and a diameter expansion structure so that the tube first reduces its diameter and then expands it during the drawing process. During the tube drawing process, the tube passes through the diameter reduction structure and the diameter expansion structure sequentially, so that the tube first undergoes a diameter reduction and then a diameter expansion to offset residual stress.

Description

[Technical Field]

[0001] This invention relates to the field of pipe processing equipment, and more particularly to pipe drawing equipment. [Background Technology]

[0002] Currently, the general process for forming pipes involves the following steps: first, melting the raw material and casting it into a pipe billet; then, drawing the billet to adjust the inner diameter and reduce the wall thickness. There are two methods for adjusting the inner diameter: expansion and reduction. Reduction involves decreasing the inner diameter of the pipe. After reduction, residual stress exists on the pipe, making it prone to cracking. To reduce residual stress, the current practice is to anneal the drawn pipe. However, annealing is time-consuming and costly. Furthermore, annealed pipes often develop red oxide spots and patterns on the surface, making them defective and unsellable. [Summary of the Invention]

[0003] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and propose a tube drawing device that can reduce the residual stress of the tube.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0005] A tube drawing device includes an outer mold and an inner mold. The outer mold has a through hole, and the inner mold passes through the through hole. When the tube is drawn, the inner mold is located inside the tube. In the drawing direction of the tube, the inner mold includes a diameter reduction structure and a diameter expansion structure so that the tube first reduces its diameter and then expands its diameter during the drawing process.

[0006] Based on the above scheme, the minimum size of the diameter reduction structure is D1, the maximum size of the diameter reduction structure is D2, and the maximum size of the diameter expansion structure is D3, wherein D3 is greater than D1 and less than D2.

[0007] Based on the above scheme, the dimensional difference between D3 and D1 does not exceed 2% of D1. The maximum dimension of the expansion structure is slightly larger than the dimension of the sizing section, so that the inner diameter of the pipe will not change significantly.

[0008] Based on the above scheme, in the drawing direction of the tube, the diameter reduction structure includes a guide section, a sizing section and a first transition section connecting the two. The minimum dimension of the sizing section is D1, the maximum dimension of the guide section is D2, and the sizing section and the guide section are cylindrical structures.

[0009] Based on the above scheme, the inner wall of the through hole includes a sizing zone and a transition zone. The sizing zone and the sizing section form a sizing gap. The transition zone and the first transition section form a transition gap. The sizing gap and the transition gap are spliced ​​together to form a drawing gap for changing the inner diameter of the tube. The diameter expansion structure passes through the sizing zone. The size of the sizing zone is D4, and D1 is smaller than D4.

[0010] Based on the above scheme, the diameter reduction structure and the diameter expansion structure are integrally formed.

[0011] Based on the above scheme, the inner mold also includes a first core head and a second core head that are connected to each other, the diameter reduction structure is disposed on the first core head, and the diameter expansion structure is disposed on the second core head.

[0012] Based on the above scheme, the first core head is provided with a first connector, and the second core head is provided with a second connector. The first core head is connected to the second core head through the cooperation of the first connector and the second connector.

[0013] Based on the above scheme, the first core head can be detachably installed on the second core head; or, the second core head can be detachably installed on the first core head.

[0014] The beneficial effects of this invention are:

[0015] This invention discloses a tube drawing device for drawing tubes to change their inner diameter, outer diameter, and wall thickness. During the tube drawing process, the inner die is located on the inner wall of the tube, and the outer die can clamp the inner die to restrict its movement, allowing the tube to move relative to both the inner and outer dies. The tube sequentially passes through a diameter reduction structure and a diameter expansion structure, undergoing a diameter reduction followed by a diameter expansion. Since the tube is made of metal, after diameter reduction, tensile stress, or residual stress, is generated that tends to expand outwards. By setting a diameter expansion pass after the diameter reduction pass, the residual stress is offset, eliminating the need for annealing to eliminate it. This reduces the time required for the annealing process, improving tube production efficiency. Furthermore, the tube does not require multiple transfers, reducing scrap during transfer and increasing the yield rate, while also lowering production costs.

[0016] The minimum dimension of the diameter reduction structure is D1, the maximum dimension of the diameter reduction structure is D2, and the maximum dimension of the diameter expansion structure is D3, where D3 is greater than D1 and less than D2. After the pipe undergoes the diameter reduction pass, its inner diameter is D1. The purpose of setting the diameter expansion structure is to reduce residual stress; therefore, the diameter expansion structure only needs to be greater than D1. If it were D2, the inner diameter of the pipe would be greater than its original size.

[0017] The dimensional difference between D3 and D1 does not exceed 2% of D1. The maximum dimension of the expansion structure is slightly larger than that of the sizing section, thus preventing significant changes in the inner diameter of the tube. During the drawing process, the inner die needs to pass through the outer die; if the size of the expansion structure is too large, it will hinder its fit with the outer die.

[0018] These features and advantages of the present invention will be disclosed in detail in the following specific embodiments and accompanying drawings. [Attached Image Description]

[0019] The invention will be further described below with reference to the accompanying drawings:

[0020] Figure 1 This is a schematic diagram of the drawing equipment during the tube drawing process in an embodiment of the present invention;

[0021] Figure 2 This is a schematic diagram of the inner mold structure in an embodiment of the present invention;

[0022] Figure 3 This is a schematic diagram of the drawing device in an embodiment of the present invention;

[0023] Figure 4 This is a schematic diagram of another internal mold structure in an embodiment of the present invention;

[0024] Figure 5 This is a schematic diagram showing the connection between the first and second core heads in an embodiment of the present invention;

[0025] Figure 6 This is a schematic diagram showing the connection between a first core head and a second core head in an embodiment of the present invention.

[0026] Figure label:

[0027] Outer mold 100, through hole 110, sizing band 111, transition band 112;

[0028] Inner mold 200, diameter reduction structure 210, guide section 211, sizing section 212, first transition section 213, diameter expansion structure 220, second transition section 221, cylindrical section 2211, frustum section 2212, first core head 230, opening 231, second core head 240, second core head body 241, connector 242, locking component 243;

[0029] The sizing clearance is 300 mm and the transition clearance is 310 mm.

Detailed Implementation Methods

[0030] The technical solutions of the embodiments of the present invention will be explained and described below with reference to the accompanying drawings. However, the following embodiments are only preferred embodiments of the present invention and not all of them. Other embodiments obtained by those skilled in the art based on the embodiments in the implementation methods without creative effort are all within the protection scope of the present invention.

[0031] The terms "exemplary" and "some embodiments" used below are meant to be "used as examples, embodiments, or illustrations," and any embodiment described as "exemplary" is not necessarily to be construed as superior to or better than other embodiments. Numerous specific details are set forth in the following detailed description to better illustrate the invention, and those skilled in the art will understand that this disclosure can be practiced without certain specific details.

[0032] Reference Figures 1 to 6 The present invention discloses a tube drawing device, including an outer mold 100 and an inner mold 200. The outer mold 100 is provided with a through hole 110, and the inner mold 200 passes through the through hole 110. When the tube is drawn, the inner mold 200 is located inside the tube. In the drawing direction of the tube, the inner mold 200 includes a diameter reduction structure 210 and a diameter expansion structure 220 so that the tube first reduces its diameter and then expands its diameter during the drawing process.

[0033] Tube drawing equipment is used to draw tubes to change their inner diameter, outer diameter, and wall thickness.

[0034] In existing technologies, after the tubing is drawn, its mechanical properties, surface condition, and surface hydrophilicity are all satisfactory, but the residual stress is relatively high, generally between 6 and 8 kgf / mm². 2 However, the requirement for usable pipe material is less than 5 kgf / mm². 2 Using traditional stress-relief annealing methods, the residual stress in the pipe material can be reduced to 3–4.5 kgf / mm² after annealing. 2 However, after annealing, red oxide spots and patterns often appear on the surface of the tubes, which are defective products and cannot be sold.

[0035] When using the tube drawing equipment of this application to draw tubes, the process includes the following steps: annealing / casting – diameter reduction – diameter expansion – annealing – secondary drawing – sawing; or, annealing / casting – diameter reduction – diameter expansion – sawing.

[0036] In existing technologies, the drawing process is usually as follows: annealing / casting - diameter reduction - annealing - secondary drawing - annealing - sawing; or, annealing / casting - diameter reduction - annealing - sawing.

[0037] When drawing tubes using the tube drawing equipment of this application, the inner die 200 is located on the inner wall of the tube, and the outer die 100 can lock the inner die 200 to restrict its movement, allowing the tube to move relative to the outer die 100 and the inner die 200. The tube will sequentially pass through the diameter reduction structure 210 and the diameter expansion structure 220, so that the tube undergoes a diameter reduction once and then a diameter expansion once. Since the tube is made of metal, after diameter reduction, tensile stress, i.e., residual stress, will be generated, which tends to cause the tube to expand outward. By setting a diameter expansion pass after the diameter reduction pass, the residual stress is offset, thus eliminating the need to eliminate residual stress through annealing. This reduces the time required for the annealing process and improves the tube production efficiency. Therefore, the tube does not need to be transferred multiple times, reducing the scrapped tubes during the transfer process, increasing the tube yield, and also reducing the tube production cost.

[0038] The table below shows the properties of the tubes after being drawn using the tube drawing equipment described in this application:

[0039]

[0040] As shown in the table, using the same type of tube blank as raw material and processing it with different processing objectives, the residual stress of each type of formed tube is less than 5 kgf / mm² after adopting the floating mandrel of this application. 2 .

[0041] The minimum dimension of the diameter reduction structure 210 is D1, the maximum dimension of the diameter reduction structure 210 is D2, and the maximum dimension of the diameter expansion structure 220 is D3. D3 is greater than D1 and less than D2, and the difference between D3 and D1 does not exceed 2% of D1. After the diameter reduction pass, the inner diameter of the pipe is D1. The purpose of setting the diameter expansion structure 220 is to reduce residual stress. Therefore, the diameter expansion structure 220 only needs to be greater than D1. If it is D2, the inner diameter of the pipe will be greater than the size before processing. The maximum dimension of the diameter expansion structure 220 is slightly larger than the dimension of the sizing section 212, so that the inner diameter of the pipe will not change significantly. During the drawing process, the inner die 200 needs to pass through the outer die 100. If the dimension of the diameter expansion structure 220 is too large, it will be detrimental to the fit with the outer die 100. If the dimension of the diameter expansion structure 220 is too small, its stress relief effect will not be significant. Preferably, D3 is 0.5% to 1.5% larger than D1.

[0042] In the drawing direction of the tube, the diameter reduction structure 210 includes a guide section 211, a sizing section 212, and a first transition section 213 connecting the two. The sizing section 212 has a size of D1, and the guide section 211 has a size of D2. The sizing section 212 and the guide section 211 are cylindrical structures. The inner wall of the through hole 110 includes a sizing band 111 and a transition band 112. The sizing band 111 and the sizing section 212 form a sizing gap 300, and the transition band 112 and the transition section form a transition gap 310. The sizing gap 300 and the transition gap 310 are spliced ​​together to form a drawing gap for changing the inner diameter of the tube. The diameter expansion structure 220 passes through the sizing band 111. The sizing band 111 has a size of D4, and D1 is smaller than D4.

[0043] The first transition section 213 is frustum-shaped. The end of the first transition section 213 that connects to the guide section 211 has a dimension of D2, and the end of the first transition section 213 that connects to the sizing section 212 has a dimension of D1. The frustum-shaped first transition section 213 will not damage the inner wall of the tube during the drawing process, and allows the inner diameter of the tube to change gradually.

[0044] Reference Figure 2 , Figure 4 Based on the above embodiments, in one embodiment of the present invention, the diameter reduction structure 210 and the diameter expansion structure 220 are integrally formed. The inner mold 200 is a floating mandrel, which has both a diameter reduction portion and a diameter expansion portion. It can be processed in one drawing pass without having to perform a diameter reduction step and then a diameter expansion step. This eliminates the need for two head making processes, reducing losses. Furthermore, the hardness of the tube increases between the two drawing passes, which is detrimental to the second diameter expansion step.

[0045] In this embodiment, the expansion structure 220 is disposed at one end of the sizing section 212 away from the first transition section 213, which can ensure that the pipe material is fully processed after passing through a sufficiently long sizing section 212.

[0046] The expansion structure 220 is a raised rib that surrounds the outer wall of the sizing section 212. The side wall of the raised rib in the radial direction of the sizing section 212 is an arc surface. The contact surface between the raised rib and the inner wall of the tube is an arc surface. The expansion structure 220 extends outward from the outer wall of the sizing section 212 in its radial direction and can protect the inner wall of the tube during the drawing process.

[0047] Alternatively, the expansion structure 220 can be a columnar structure, with a second transition section 221 between the expansion structure 220 and the sizing section 212. The second transition section 221 is frustum-shaped, with one end connecting to the sizing section 212 having a dimension of D1, and the other end connecting to the expansion structure 220 having a dimension of D3. As the pipe passes through the second transition section 221, its inner diameter gradually increases, preventing significant dimensional changes in the inner wall of the pipe within a short period, which could affect the pipe quality. The frustum-shaped second transition section 221 also prevents damage to the inner wall of the pipe during drawing and allows for a gradual change in the inner diameter.

[0048] Reference Figure 5 and Figure 6 In another embodiment of the present invention, the inner mold 200 further includes a first core head 230 and a second core head 240 connected to each other, a diameter reduction structure 210 is disposed on the first core head 230, and a diameter expansion structure 220 is disposed on the second core head 240.

[0049] Preferably, the first core head 230 and the second core head 240 are detachably connected so that the second core head 240 can be replaced to select a suitable second core head 240 according to factors such as tube size.

[0050] The second core head 240 includes a second core head body 241 and a connector 242 disposed on the second core head body 241. The first core head 230 is provided with an opening 231 through which the connector 242 passes. The connector 242 passes through the opening 231 and cooperates with the locking member 243 to clamp the first core head 230 between the second core head body 241 and the locking member 243. After the locking member 243 cooperates with the connector 242, there will be no relative wobbling between the first core head 230 and the second core head 240, so as to ensure the quality of the tube. The size of the locking member 243 is smaller than the minimum size of the second core head 240. The small size of the locking member 243 will not contact the inner wall of the tube and cause wear to the inner wall of the tube.

[0051] The connector 242 is a columnar structure with an external thread at the end furthest from the second core head body 241. The locking member 243 is a nut that mates with the external thread. During engagement with the connector 242, the nut applies a force to the first core head 230 in the direction of the second core head 240 to ensure the overall stability of the inner mold 200. During the drawing process, the force exerted on the first core head 230 by the tube material is along the axial direction of the opening 231. For the connector 242 to separate from the nut, a force along the circumferential direction of the opening 231 is required, thus preventing the first core head 230 and the second core head 240 from separating during the tube material drawing process.

[0052] The inner wall of the opening 231 is also provided with internal threads, and the external threads on the connector 242 can cooperate with the internal threads so that the second core body 241 will not wobble relative to the core body in the radial direction of the through hole 110. In addition, the cooperation between the internal and external threads also limits the assembly direction of the connector 242 and the through hole 110.

[0053] The second core body 241 also includes a second transition section 221 connected between the expansion structure 220 and the connector 242. When the tube passes through the second transition section 221, its inner diameter will gradually increase, so as to avoid the inner wall of the tube from undergoing obvious dimensional changes in a short period of time, which would affect the quality of the tube.

[0054] like Figure 5 As shown, the outer wall of the second transition section 221 gradually widens from the connector 242 toward the diameter expansion structure 220, and the dimension of one end of the second transition section 221 connecting to the diameter expansion structure 220 is D3. The outer wall of the second transition section 221 can be a conical surface or an arc surface. Preferably, the outer wall of the second transition section 221 is an arc surface, and it forms a nearly spherical second core body 241 with the diameter expansion structure 220.

[0055] Or, such as Figure 6 As shown, the second transition section 221 includes a cylindrical section 2211 and a frustum section 2212. One end of the cylindrical section 2211 is connected to the connector 242, and the other end of the cylindrical section 2211 is connected to the frustum section 2212. The other end of the frustum section 2212 is connected to the expansion structure 220. The dimension of the cylindrical section 2211 is D1, and the dimension of the end of the frustum section 2212 connected to the cylindrical section 2211 is D5. D5 is slightly smaller than D1 so that the edge of the frustum section 2212 will not scratch the inner wall of the pipe during the process of leaving the sizing section 212. The dimension of the end of the frustum section 2212 connected to the expansion structure 220 is D3.

[0056] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that the present invention includes, but is not limited to, the contents described in the accompanying drawings and the specific embodiments above. Any modifications that do not depart from the functional and structural principles of the present invention will be included within the scope of the claims.

Claims

1. A pipe material drawing apparatus comprising an outer die and an inner die, the outer die having a through hole formed therein, the inner die being inserted through the through hole, the inner die being located inside a pipe material during drawing of the pipe material, characterized in that, The inner mold comprises a necking structure and an expanding structure in the drawing direction of the pipe material, so that the pipe material is first necked and then expanded during drawing, and the expanding structure is arranged outside the through hole; wherein the minimum size of the necking structure is D1, the maximum size of the necking structure is D2, the maximum size of the expanding structure is D3, the D3 is greater than the D1 and less than the D2, and the size difference between the D3 and the D1 is not more than 2% of the D1.

2. The tube shell drawing apparatus of claim 1, wherein, In the drawing direction of the pipe material, the necking structure comprises a guide section, a sizing section and a first transition section connected between the two, the minimum size of the sizing section is D1, the maximum size of the guide section is D2, and the sizing section and the guide section are cylindrical structures.

3. The tube shell drawing apparatus of claim 2, wherein, The inner wall of the through hole comprises a sizing band and a transition band, the sizing band and the sizing section form a sizing gap, the transition band and the first transition section form a transition gap, the sizing gap and the transition gap are spliced to form a drawing gap for changing the inner diameter of the pipe material, the expanding structure passes through the sizing band, the size of the sizing band is D4, and the D1 is less than the D4.

4. The tube shell drawing apparatus of claim 1 wherein, The necking structure and the expanding structure are integrally formed.

5. The tube shell drawing apparatus of claim 1 wherein, The inner mold further comprises a first core head and a second core head connected to each other, the necking structure is arranged on the first core head, and the expanding structure is arranged on the second core head.

6. The tube shell drawing apparatus of claim 5, wherein, The first core head is provided with a first connecting piece, the second core head is provided with a second connecting piece, and the first core head is connected to the second core head through the cooperation of the first connecting piece and the second connecting piece.

7. The tube shell drawing apparatus of claim 5 wherein, The first core head can be detachably installed on the second core head; or, the second core head can be detachably installed on the first core head.

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