A tube-in-tube forming die and method

Abstract

The application discloses a pipe-in-pipe forming die and method, which comprises a die body, the die body comprises a support die, a mouth die, a core die and a middle die, the end of the support die is provided with the mouth die, the middle die is arranged in the mouth die and close to the end, the inside of the support die, the mouth die and the middle die which form an integral whole is provided with the core die, the middle die comprises a middle die body, an annular ring is arranged on the front end of the middle die body, the annular ring is supported on the middle die body through a group of supports, a middle die temperature control medium channel one is arranged in the support, a group of middle die temperature control medium channels two are arranged on the middle die body, at least one middle die temperature control medium inlet and one middle die temperature control medium outlet are arranged on the inlet and the outlet of the middle die temperature control medium channel one, and the technical scheme is adopted, on one hand, the middle die temperature control can be realized, and on the other hand, the problem that the pipe material is pressed flat by external air pressure due to insufficient internal cavity pressure during pipe extrusion can be avoided.

Description

Technical Field

[0001] This invention belongs to the field of plastic pipe extrusion technology, specifically relating to a pipe-in-pipe forming mold and method. Background Technology

[0002] A pipe-in-pipe system refers to a system consisting of an inner pipe, an outer pipe, and supports or ribs that fix the inner pipe inside the outer pipe. Due to its unique structure, it can be used to transport toxic, flammable, and explosive media. When the inner pipe ruptures and leaks, the outer pipe can collect the media within the pipe to prevent leakage to the outside, and can also monitor the media inside the outer pipe for timely maintenance and repair. Additionally, pipe-in-pipe systems can be used for insulation, noise reduction, and saving space by sharing a single inlet and outlet pipe.

[0003] In existing technologies, pipes are generally sized using vacuum cooling, which cools the outer surface. PVC hollow pipes, due to their thin inner and outer walls and small gaps, cool and solidify quickly, allowing for good molding. However, if materials with slower cooling and solidification are used, or if a single-piece pipe with thick inner and outer walls and large gaps is formed, the same technology often results in problems with timely shaping of the inner tube and ribs. The inner tube sags and deforms after extrusion, and the ribs are squeezed by the inner and outer tubes and deform irregularly during cooling. This leads to significant pipe non-roundness, rib distortion, uneven wall thickness, and even partial adhesion between the inner and outer tubes, causing the cavity to shrink or disappear, thus failing to meet installation requirements.

[0004] Furthermore, because the wall thickness and rib thickness of the inner and outer tubes in a tube-in-tube design often differ according to requirements, and the die clearance also varies, mismatches in the speeds of these three components can easily occur during extrusion. This can lead to circumferential and axial creases, unevenness, and high internal stress in the formed tube. These two major technical problems significantly limit the types of materials, dimensions, and application range of tube-in-tube designs.

[0005] Chinese patent CN201821702238.9 discloses a tube-in-tube extrusion die, which is formed by side feeding, air cooling cavity and ribs. It is not suitable for extruding materials that are shear-sensitive, easily thermally decomposed and have poor flowability. In addition, the cooling efficiency is relatively low, the extrusion speed is limited, and the wall thickness uniformity of the inner tube cannot be adjusted.

[0006] In addition, there is the split-type pipe-in-pipe, which assembles inner and outer pipes of different specifications together to form a pipe-in-pipe. This solution involves a large amount of installation and welding work, low forming efficiency, and the support that fixes the inner pipe hinders the flow of the medium in the outer pipe, which can even cause blockage of the outer pipe in severe cases. Summary of the Invention

[0007] In view of the problems existing in the prior art, the purpose of the present invention is to provide a tube-in-tube forming mold and method, which on the one hand can realize temperature control of the middle mold, and on the other hand can avoid the problem of the tube being flattened by external air pressure due to insufficient internal pressure during tube extrusion.

[0008] The technical solution of the present invention is as follows:

[0009] A tube-in-tube forming mold includes a mold body, which includes a support mold, an orifice mold, a core mold, and a middle mold. The support mold has an orifice mold at its end, and a middle mold is located near the end of the orifice mold. The support mold, orifice mold, and middle mold together form a core mold inside the mold body. The middle mold includes a middle mold body, and an annular ring is sleeved on the front end of the middle mold body. The annular ring is supported on the middle mold body by a set of supports. A middle mold temperature control medium channel one is opened inside the supports, and a middle mold temperature control medium channel two is opened on the middle mold body. The middle mold temperature control medium channel one has at least one middle mold temperature control medium inlet and one middle mold temperature control medium outlet. The middle mold temperature control medium inlet is sequentially connected to the middle mold temperature control medium channel one, the middle mold temperature control medium channel two, and the middle mold temperature control medium outlet.

[0010] A gas channel is provided next to the temperature control medium channel of the middle mold, and a gas channel is provided on the middle mold body. The inlet of the gas channel is an air inlet, and the end of the middle mold body is an air outlet. The air inlet is connected to the gas channel, the gas channel, and the air outlet. The air inlet is connected to the outside, so that when the tube is extruded, air enters from outside the mold to fill the cavity between the tube blank ribs, preventing the cavity from being flattened by external air pressure due to insufficient internal pressure.

[0011] Furthermore, a set of groove one and groove two are respectively opened on the first end face and the last end face of the middle mold body. A sealing plate is welded on the second groove. The thickness of the sealing plate is less than the depth of the second groove, so that the end and the first end of the adjacent middle mold temperature control medium channel two are connected, forming a reciprocating tortuous middle mold temperature control medium channel.

[0012] Furthermore, the middle mold body is provided with rib forming channels in the same circumferential direction as the finished tube ribs, and the distance from the starting position of the rib forming channel to the first end face of the middle mold body is greater than the depth of the second groove.

[0013] Furthermore, the front end of the middle mold body is fixedly provided with a middle mold front end, which is a conical structure. The rear end face of the middle mold front end is provided with a protrusion that matches the groove, wherein the height of the protrusion is less than the depth of the groove. The middle mold front end and the middle mold body are welded together after the protrusion and the groove are engaged.

[0014] Furthermore, the number of supports is the same as the number of finished pipe ribs; both the inlet and outlet of the temperature-controlled medium in the intermediate mold are connected to pipes and joints, wherein the pipes are threadedly connected to the intermediate mold or welded and sealed.

[0015] Furthermore, the die includes die one, die two, and die three, the core die includes core die one and core die two, die one is fixedly provided at the end of the support die, die two is fixedly provided at the end of die one, die three is fixedly provided at the end of die two, the two ends of the middle die are respectively connected to die two and die three, and the support die, die one, die two, die three, and the middle die together form an integral whole in which core die one and core die two are provided, one end of core die one is fixedly connected to the support die, and the other end of core die two is connected to core die one by a thread.

[0016] Furthermore, the central portions of the first and second core molds are hollow structures. The end of the second core mold extends out of the third and middle molds. The outer surface of the second core mold has spiral core mold oil channels one and two, which are staggered to form a DNA-like double helix meandering flow channel structure. The middle and rear section of the outer surface of the second core mold has a set of vacuum slits or pores. The slits or pores are connected to the central hollow structure from the outer surface. The slits or pores are located at the center of the partition wall between the DNA-like double helix meandering flow channel structures, so that they do not come into contact with the temperature control medium.

[0017] Furthermore, the support mold is provided with an air extraction outlet, which is connected to the hollow center of the two core molds, so that the inner tube adheres to the outer surface of the second core mold during extrusion, thereby cooling and controlling the temperature of the inner surface.

[0018] Furthermore, it includes a core mold oil pipe one and a core mold oil pipe two. The oil inlet of the core mold oil pipe one is used to introduce a temperature control medium. The oil outlet of the core mold oil pipe one passes through the air extraction outlet inside the support mold and the two core molds in sequence, and then connects to the right end inlet of the spiral core mold oil channel one through an oil pipe joint. The left end outlet of the spiral core mold oil channel one is connected to the left end inlet of the spiral core mold oil channel two.

[0019] The right end outlet of the spiral core mold oil channel two is connected to the oil inlet of the core mold oil pipe two through an oil pipe joint. The oil outlet of the core mold oil pipe two then passes through the air extraction outlet inside the support mold and the center between the two core molds in sequence.

[0020] This invention proposes a method for preparing a tube-in-tube using a tube-in-tube forming mold, comprising the following steps:

[0021] 1) After the tube blank material enters the forming front end from the rear end of the mold, it is first melted and extruded. After the material flow stabilizes, the screw one set in the circumferential direction of the die one is adjusted, and the die two and the middle die are moved to adjust the uniformity of the inner tube wall thickness. Then the screw two set in the circumferential direction of the die two is adjusted, and the die three is moved to adjust the uniformity of the outer tube wall thickness.

[0022] 2) After the outer tube wall thickness is adjusted in step 1), observe and measure the flow rate of the inner tube, outer tube and rib. If the inner and outer tubes are inconsistent, the design of the front end of the middle die is modified, and the flow rate entering the outer tube and inner tube flow channels is redistributed. If the flow rate of the rib is inconsistent with that of the inner and outer tubes, the design of the flow channel of the main rib of the middle die is modified to make the extrusion speed of the three consistent.

[0023] 3) After step 2) is completed, gradually reduce the set temperature of the three-part die, the two-part core die, and the middle die. The mold is vacuumed and opened. The core die adsorbs the inner tube, so that the ribs of the tube-in-tube, the inner tube, and the outer tube are initially cooled and shaped at a lower temperature. Then, it enters the sizing sleeve for final cooling and shaping of the outer surface.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] 1) By adopting the technical solution of the present invention, a medium temperature control medium channel one is opened inside the bracket, and a set of medium temperature control medium channels two are opened on the medium mold body. The first end face and the last end face of the medium mold body are respectively provided with groove one and groove two. A sealing plate is welded on the groove two. The thickness of the sealing plate is less than the depth of the groove two, so that the ends or the first ends of adjacent medium temperature control medium channels two are connected, forming a reciprocating tortuous structure of medium temperature control medium channels, which can realize medium mold temperature control.

[0026] 2) In this invention, a gas channel is provided next to the temperature control medium channel, and a gas channel is provided on the main body of the middle mold. Gas channel one and gas channel two are connected to the outside, so that when the pipe is extruded, especially during traction, air enters from outside the mold to fill the cavity between the ribs of the pipe blank, preventing insufficient pressure inside the cavity from being flattened by external air pressure.

[0027] 3) The present invention provides a vacuum function on the surface of the second flow channel of the core mold and provides a temperature control medium channel and an air channel in the second core mold, which can adsorb the inner tube while cooling it, thus solving the problem of non-roundness of the inner tube.

[0028] 4) In this invention, the end of the core mold two extends out of the outlet mold three and the middle mold, which can support the inner tube and prevent it from sagging until the inner tube and the rib cool and solidify before being removed from the core mold. At this time, the rib can support and fix the inner tube in the center of the outer tube and drive the inner tube forward.

[0029] 5) The intermediate mold set in this invention meets the requirements for matching the flow rates of the inner and outer tubes and ribs; it realizes the cooling and temperature control of the intermediate mold and the ventilation requirements of the cavity, and combined with the cooling and temperature control of the third mold and the second core mold, it can fully and evenly shape the inner tubes and ribs. Attached Figure Description

[0030] Figure 1 This is a schematic cross-sectional view of the mold of the present invention;

[0031] Figure 2 This is a schematic diagram of the three-dimensional structure of the mold of the present invention;

[0032] Figure 3 This is a schematic diagram of the three-dimensional structure of the intermediate mold of the present invention;

[0033] Figure 4 This is a schematic diagram of the main structure of the intermediate mold of the present invention. Figure 1 ;

[0034] Figure 5 This is a schematic diagram of the main structure of the intermediate mold of the present invention. Figure 2 ;

[0035] Figure 6 This is a cross-sectional view of the main body of the intermediate mold of the present invention;

[0036] Figure 7 This is a top view of the main body of the intermediate mold of the present invention;

[0037] Figure 8 This is a schematic diagram of the front end structure of the middle mold of the present invention.

[0038] In the diagram: 1. Support mold; 2. Middle mold; 3. Middle mold body; 301. Groove 1; 302. Groove 2; 4. Middle mold front end; 401. Protrusion 1; 5. Annular ring; 6. Support; 7. Middle mold temperature control medium channel 1; 701. Middle mold temperature control medium inlet; 702. Middle mold temperature control medium outlet; 8. Middle mold temperature control medium channel 2; 9. Gas channel 1; 10. Gas channel 2; 11. Air inlet; 12. Air outlet; 13. Sealing plate; 14. Rib forming flow channel; 15. Mouth mold 1; 16. Mouth mold 2; 17. Mouth mold 3; 18. Core mold 1; 19. Core mold 2; 20. Air gap; 21. Air extraction outlet; 22. Core mold oil pipe 1; 23. Core mold oil pipe 2; 24. Pressure plate 1; 25. Pressure plate 2; 26. Screw 1; 27. Screw 2; 28. Clearance seam. Detailed Implementation

[0039] The present invention will be further described below with reference to the accompanying drawings, but the scope of protection of the present invention is not limited to the scope described.

[0040] like Figure 1-2 As shown, a tube-in-tube forming mold includes a mold body, which includes a support mold 1, a middle mold 2, a first mold 15, a second mold 16, a third mold 17, a first core mold 18, and a second core mold 19. The first mold 15 is fixedly provided at the end of the support mold 1, and the second mold 16 is provided at the end of the first mold 15. A pressure plate 24 is provided between the second mold 16 and the first mold 15. The second mold 16 is pressed and sealed onto the first mold 15 by screws on the pressure plate 24. The third mold 17 is fixedly provided at the end of the second mold 16. The two ends of the middle mold are connected to the second mold 16 and the third mold 17 respectively. The middle mold 2 is fitted with the first mold 15 and the second mold 16 through tolerance to ensure that the concentricity remains unchanged.

[0041] A pressure plate 25 is provided between die 2 16 and die 3 17. The middle die 2 is pressed onto die 2 16 by screws on the pressure plate 2 25, and die 3 17 is pressed onto the middle die 2 by screws on the pressure plate 2 25. Die 3 17 is provided with a die 3 temperature control medium flow channel, which is connected to a mold temperature controller to realize temperature control of die 3 17.

[0042] The support mold 1, along with the first mold 15, the second mold 16, the third mold 17, and the middle mold 2, has a core mold 18 and a core mold 29 inside. One end of the core mold 18 is fixedly connected to the support mold 1, and the other end of the core mold 29 is connected to the core mold 18 by a thread.

[0043] Several screws 26 are arranged circumferentially on the outer side of die 15, which can be used to move die 2 16 and middle die 2 together to adjust the concentricity with the core mold, thereby adjusting the uniformity of the inner tube wall thickness; several screws 27 are arranged circumferentially on the outer side of die 2 16, which can be used to adjust the concentricity of die 3 17 and the core mold, thereby adjusting the uniformity of the outer tube wall thickness.

[0044] In this embodiment, the support mold 1 is provided with an air extraction outlet 21, which is connected to the hollow center of the two core molds. This allows the inner tube to adhere to the outer surface of the second core mold 19 during extrusion, thereby cooling and controlling the temperature of the inner surface. At the same time, the extended section of the core mold can also support the inner tube to prevent it from sagging until the inner tube and the rib have cooled and solidified before being removed from the core mold. At this point, the rib can support and fix the inner tube in the center of the outer tube and drive the inner tube forward.

[0045] The central part of core mold 18 and core mold 2 19 is a hollow structure. The oil pipe can be connected from the hollow hole at the rear end of the mold. The oil pipe is made of high temperature resistant copper pipe or other high temperature resistant flexible pipe such as polytetrafluoroethylene pipe. The oil pipe includes core mold oil pipe 1 22 and core mold oil pipe 2 23.

[0046] The end of the core mold 2 19 extends out of the outlet mold 3 17 and the middle mold 2, which can support the inner tube and prevent it from sagging until the inner tube and the rib cool and solidify before detaching from the core mold. At this time, the rib can support and fix the inner tube in the center of the outer tube and drive the inner tube forward, thus solving the problem of sagging and deformation of the inner tube after extrusion.

[0047] The outer surface of the second core mold 19 has two spiral core mold oil channels, namely spiral core mold oil channel one and spiral core mold oil channel two. The spiral core mold oil channel one and spiral core mold oil channel two are arranged alternately to form a DNA-like double helix meandering flow channel structure. The middle and rear section of the outer surface of the second core mold 19 has a set of vacuum air gaps 20 or air holes. The air gaps 20 or air holes are connected to the hollow structure in the center from the outer surface. The air gaps 20 or air holes are located in the center of the partition wall between the DNA-like double helix meandering flow channel structures, so that they do not come into contact with the temperature control medium.

[0048] The oil inlet of the core mold oil pipe 22 is used to introduce the temperature control medium. The oil outlet of the core mold oil pipe 22 passes through the air extraction outlet 21 in the support mold 1 and the two core molds in sequence, and then connects to the right end inlet of the spiral core mold oil channel 1 through the oil pipe joint. The left end outlet of the spiral core mold oil channel 1 is connected to the left end inlet of the spiral core mold oil channel 2.

[0049] The right end outlet of the spiral core mold oil channel 2 is connected to the oil inlet of core mold oil pipe 23 through an oil pipe joint. The oil outlet of core mold oil pipe 23 then passes through the air extraction outlet in the support mold 1 and the center between the two core molds in sequence.

[0050] Depend on Figure 3 It can be seen that the intermediate mold 2 includes the intermediate mold body 3 and the intermediate mold front end 4 fixedly disposed at the front end of the intermediate mold body 3. The front end of the intermediate mold body 3 is provided with an annular ring 5, and the annular ring 5 is supported on the intermediate mold body 3 by a set of brackets 6. The number of brackets 6 is the same as the number of finished pipe reinforcements. In this embodiment, the number of brackets 6 is 4.

[0051] The support 6 has an internal intermediate mold temperature-controlled medium channel 7, and the intermediate mold body 3 has a set of intermediate mold temperature-controlled medium channels 8. The intermediate mold temperature-controlled medium channel 7 has at least one intermediate mold temperature-controlled medium inlet 701 and one intermediate mold temperature-controlled medium outlet 702. Figure 7 It is understood that the present invention has two intermediate mold temperature control medium inlets 701 and two intermediate mold temperature control medium outlets 702. The intermediate mold temperature control medium inlet 701 is sequentially connected to the intermediate mold temperature control medium channel 1 7, the intermediate mold temperature control medium channel 2 8, and the intermediate mold temperature control medium outlet 702.

[0052] like Figure 4-5 As shown, a set of groove 1 301 and groove 2 302 are respectively opened on the first end face and the last end face of the middle mold body 3. A sealing plate 13 is welded on the groove 2 302. The thickness of the sealing plate 13 is less than the depth of the groove 2 302, so that the end and the first end of the adjacent middle mold temperature control medium channel 2 8 are connected, forming a reciprocating tortuous middle mold temperature control medium channel.

[0053] Both the inlet and outlet of the temperature-controlled medium in the middle mold are connected to pipes and joints. The pipes are either threaded or welded to the middle mold. When threaded, the pipes need to be removed before the middle mold 2 can be taken out. When welded, the middle mold 2 16 must be provided with a clearance joint 28 to avoid the pipes when it is removed from left to right.

[0054] like Figure 1 and Figure 6As shown, a gas channel 9 is provided next to the temperature control medium channel 7 of the middle mold, and a gas channel 10 is provided on the middle mold body 3. The inlet of the gas channel 9 is an air inlet 11, and the end of the middle mold body 3 is an air outlet 12. The air inlet 11 is connected to the gas channel 9, the gas channel 10 and the air outlet 12. The air inlet 11 is connected to the outside, so that when the tube is extruded, especially during traction, air enters from outside the mold to fill the cavity between the tube blank ribs, preventing the cavity from being flattened by external air pressure due to insufficient internal pressure.

[0055] Depend on Figure 3 It can be seen that the middle mold body 3 is provided with the same number of rib forming channels 14 as the finished tube ribs in the circumferential direction. Each rib forming channel 14 is chamfered or rounded around its perimeter except for the outlet, so as to match the extrusion speed of the finished tube ribs with that of the inner and outer tubes. The distance from the starting position of the rib forming channel 14 to the first end face of the middle mold body 3 is greater than the depth of the groove 302.

[0056] like Figure 8 As shown, the front end 4 of the middle die has a conical structure. The sharp corner position and slope shape of the front end 4 of the middle die can adjust the flow distribution of the material entering the inner tube and the outer tube flow channel, so as to match the speed of the inner tube and the outer tube during extrusion.

[0057] The front end face of the middle mold 4 is provided with a protrusion 401 that matches the groove 301. The height of the protrusion 401 is less than the depth of the groove 301. The front end face of the middle mold 4 and the middle mold body 3 are welded together after the protrusion 401 and the groove 301 are matched, so that the beginning and end of the adjacent middle mold temperature control medium channel 8 are connected.

[0058] This invention also proposes a method for preparing a tube-in-tube using the tube-in-tube forming mold of this invention, comprising the following steps:

[0059] 1) After the tube blank material enters the forming front end from the rear end of the mold, it is first melted and extruded. After the material flow stabilizes, the screw 26 set in the circumferential direction of the die 15 is adjusted first, and the die 26 and the middle die 2 are moved to adjust the uniformity of the inner tube wall thickness. Then the screw 27 set in the circumferential direction of the die 216 is adjusted, and the die 317 is moved to adjust the uniformity of the outer tube wall thickness.

[0060] 2) After the outer tube wall thickness is adjusted in step 1), observe and measure the flow rate of the inner tube, outer tube and rib. If the inner and outer tubes are inconsistent, the design of the front end 4 of the middle die is modified, and the flow rate entering the outer tube and inner tube flow channel is redistributed. If the flow rate of the rib is inconsistent with that of the inner and outer tubes, the design of the flow channel of the rib of the middle die body 3 is modified to make the extrusion speed of the three consistent.

[0061] 3) After step 2) is completed, gradually reduce the set temperature of the die 3 17, core die 2 19, and middle die 2. The mold is vacuumed and opened. The core die adsorbs the inner tube, so that the ribs of the tube-in-tube, the inner tube, and the outer tube are initially cooled and shaped at a lower temperature. Then, it enters the sizing sleeve for final cooling and shaping of the outer surface.

Claims

1. A pipe-in-pipe forming die comprising a die body, the die body comprising a support die (1), a mouth die, a core die and a middle die (2), the end of the support die (1) being provided with a mouth die, the mouth die being provided with a middle die (2) near the end, the inside of the support die (1) being provided with a core die in an integral manner with the mouth die and the middle die (2), characterized in that The middle die (2) comprises a middle die body (3), the front end of the middle die body (3) is provided with an annular ring (5), the annular ring (5) is supported on the middle die body (3) through a group of supports (6), the inside of the support (6) is provided with a middle die temperature control medium channel one (7), a group of middle die temperature control medium channels two (8) are arranged on the middle die body (3), the middle die temperature control medium channel one (7) has at least one middle die temperature control medium inlet (701) and one middle die temperature control medium outlet (702), the middle die temperature control medium inlet (701) is in sequence through with the middle die temperature control medium channel one (7), the middle die temperature control medium channel two (8) and the middle die temperature control medium outlet (702). The middle die temperature control medium channel one (7) is provided with a gas channel one (9) beside, a gas channel two (10) is arranged on the middle die body (3), wherein the inlet of the gas channel one (9) is an air inlet (11), the end of the middle die body (3) is provided with an air outlet (12), the air inlet (11) is through with the gas channel one (9), the gas channel two (10) and the air outlet (12), wherein the air inlet (11) is communicated with the outside, so that when the pipe is extruded, air enters the cavity between the pipe blank rib and the rib from the outside of the die, to prevent the cavity from being crushed by external air pressure due to insufficient internal pressure.

2. A tube-in-tube forming die according to claim 1, characterised in that The first end face and the end face of the middle die body (3) are respectively provided with a group of grooves one (301) and grooves two (302), wherein the grooves two (302) are welded with a sealing plate (13), the thickness of the sealing plate (13) is less than the depth of the grooves two (302), so that the end and the first end of the adjacent middle die temperature control medium channel two (8) are through, forming a reciprocating circuitous structure of the middle die temperature control medium channel.

3. A tube-in-tube forming die according to claim 2, characterised in that The middle die body (3) is provided with a rib forming flow channel (14) which is the same as the number of finished pipe ribs, the distance from the starting position of the rib forming flow channel (14) to the first end face of the middle die body (3) is greater than the depth of the grooves two (302).

4. A tube-in-tube forming die according to claim 3, wherein The front end of the middle die body (3) is fixedly provided with a middle die front end (4), the middle die front end (4) is a conical structure, the rear end face of the middle die front end (4) is provided with a protrusion one (401) matched with the grooves one (301), wherein the height of the protrusion one (401) is less than the depth of the grooves one (301), the middle die front end (4) and the middle die body (3) are welded after the protrusion one (401) and the grooves one (301) are matched.

5. A tube-in-tube forming die according to claim 4, characterised in that The number of the supports (6) is the same as the number of finished pipe ribs; the middle die temperature control medium inlet (701) and the middle die temperature control medium outlet (702) are connected with pipes and joints, wherein the pipes are threadedly connected or welded with the middle die.

6. A tube-in-tube forming die according to claim 5, wherein The die includes a die one (15), a die two (16) and a die three (17), the core die includes a core die one (18) and a core die two (19), the end of the support die (1) is fixedly provided with the die one (15), the end of the die one (15) is fixedly provided with the die two (16), the end of the die two (16) is fixedly provided with the die three (17), the two ends of the middle die (2) are connected with the die two (16) and the die three (17) respectively, the inside of the whole formed by the support die (1), the die one (15), the die two (16), the die three (17) and the middle die (2) is provided with the core die one (18) and the core die two (19), one end of the core die one (18) is fixedly connected with the support die (1), the other end of the core die two (19) is connected with the core die one (18) through a threaded connection.

7. A tube-in-tube forming die according to claim 6, characterised in that The center part of the core die one (18) and the core die two (19) is a hollow structure, the end of the core die two (19) extends out of the die three (17) and the middle die (2), the outer surface of the core die two (19) is provided with a spiral core die oil channel one and a spiral core die oil channel two, wherein the spiral core die oil channel one and the spiral core die oil channel two are arranged in an interlaced and spaced manner to form a DNA-shaped double helix circuit flow channel structure, a group of air slots (20) or air holes for vacuumizing are arranged on the middle and rear sections of the outer surface of the core die two (19), the air slots (20) or air holes are in communication between the outer surface and the hollow structure in the center, and the air slots (20) or air holes are located in the center of the partition wall between the DNA-shaped double helix circuit flow channel structures, so that they are not in contact with the temperature control medium.

8. A tube-in-tube forming die according to claim 7, characterised in that The support die (1) is provided with an air outlet (21), the air outlet (21) is in communication with the hollow centers of the two core dies, so that the inner tube is adhered to the outer surface of the core die two (19) during extrusion, and the inner surface is cooled and temperature-controlled.

9. A tube-in-tube forming die according to claim 8, characterised in that The core die oil pipe one (22) and the core die oil pipe two (23) are included, the oil inlet of the core die oil pipe one (22) is used for introducing the temperature control medium, the oil outlet of the core die oil pipe one (22) sequentially penetrates the air outlet (21) in the support die (1) and the two core dies, and is connected with the right end inlet of the spiral core die oil channel one through an oil pipe joint, the left end outlet of the spiral core die oil channel one is connected with the left end inlet of the spiral core die oil channel two; The right end outlet of the spiral core die oil channel two is connected with the oil inlet of the core die oil pipe two (23) through an oil pipe joint, and the oil outlet of the core die oil pipe two (23) is sequentially penetrated from the air outlet in the support die (1) and the center between the two core dies.

10. A method of making a pipe-in-pipe using the pipe-in-pipe forming die of claim 1, characterized by The method includes the following steps: 1) After the pipe blank material enters the forming front end from the rear end of the mold, it is first melted and extruded, after the material flow is stable, the screw one (26) arranged in the ring of the die one (15) is first adjusted, the die two (16) and the middle die (2) are moved, and the uniformity of the inner pipe wall thickness is adjusted; then the screw two (27) arranged in the ring of the die two (16) is adjusted, the die three (17) is moved, and the uniformity of the outer pipe wall thickness is adjusted; 2) After the outer tube wall thickness adjustment in step 1) is completed, the flow rates of the inner tube, the outer tube and the rib are observed and measured. If the inner and outer tubes are inconsistent, the front end (4) of the middle die is designed to be corrected, and the flow rates into the outer tube and the inner tube flow channel are redistributed. If the flow rate of the rib is inconsistent with the inner and outer tubes, the flow channel of the rib of the middle die body (3) is designed to be corrected, so that the extrusion speeds of the three are consistent; 3) After step 2) is completed, gradually lower the set temperature of the die (17), the core die (19) and the middle die (2), the mold is vacuumized and opened, the core die absorbs the inner tube, and the rib, the inner tube and the outer tube of the tube-in-tube are preliminarily cooled and shaped at a lower temperature, and then enter the sizing sleeve for final cooling and shaping of the outer surface.

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