A continuous push forming device for polytetrafluoroethylene tubes

Abstract

The utility model provides a kind of polytetrafluoroethylene pipe continuous push forming device, including pre-press feeding mechanism, multistage screw push system and forming die, wherein multistage screw push system is composed of three axial series and radial phase staggered single screw mechanism, and it realizes no-stop continuous production by the phase relay of push action, pre-press feeding mechanism adopts opposite double screw and conical compression cavity structure, cooperates with spiral groove guide laminar flow in compression cavity, improves material pre-press density.Push system is equipped with gradient pressure, combined with the composite flow channel of helical flow guide vane and honeycomb porous damping plate in pressure equalization cavity, significantly reduces the density deviation of pipe material.Forming die adopts modular design of split type mould segment, compensation ring and locking ring, realizes accurate forming, and guarantees size accuracy by hydraulic jack rod.

Description

Technical Field

[0001] This utility model relates to the technical field of polymer pipe forming equipment, specifically to a continuous push forming device for polytetrafluoroethylene pipe. Background Technology

[0002] The molding processes for polytetrafluoroethylene (PTFE) tubes include the extrusion method and the isobaric method. The extrusion method uses mechanical force to push PTFE paste through a die in a plunger extruder to form a tube. The isobaric method involves filling PTFE powder into an elastic mold and then uniformly compressing the powder into a tube within a high-pressure container using liquid or gas pressure. The extrusion method is less expensive and suitable for continuous production. However, existing extrusion devices, such as those described in the utility model patent with publication number CN214082745U, experience pressure fluctuations during the extrusion process, leading to uneven tube density, poor continuity, and inconsistent product quality. Utility Model Content

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a PTFE pipe forming device that can operate continuously and has uniform pressure distribution.

[0004] To achieve the above objectives, the technical solution provided by this utility model is as follows:

[0005] A continuous extrusion molding device for polytetrafluoroethylene (PTFE) tubes includes a pre-compression feeding mechanism, a multi-stage screw extrusion system, and a molding die connected sequentially along the material conveying direction. The multi-stage screw extrusion system consists of at least three single-screw mechanisms connected in series axially and with radially staggered phases. This device comprises three parts connected in series: the pre-compression feeding mechanism, the multi-stage screw extrusion system, and the molding die. Uninterrupted production is achieved through phase relay extrusion technology. The phase difference time is set by a controller; when the first-stage screw completes 90% of its stroke, the second stage starts; and when the second stage completes 90%, the third stage follows. The power sources of the three screws are independently controlled.

[0006] Furthermore, the pre-compression feeding mechanism includes a twin-screw rotating in opposite directions and a conical compression chamber, wherein the thread pitch of the twin-screw decreases along the pushing direction, and the inner wall of the conical compression chamber is provided with helical grooves.

[0007] Furthermore, the center distance between the twin screws is 1.2-1.8 times the screw diameter, and the length of the thread engagement zone accounts for 40%-60% of the total screw length. The counter-rotating twin screws create a strong shear-tension effect, improving the uniformity of PTFE paste plasticization.

[0008] Furthermore, the single-screw mechanism includes a primary preload screw, a secondary main pressure screw, and a tertiary precision pressure screw.

[0009] Furthermore, the end of the single screw mechanism is provided with a spherical compensator to buffer axial deviation and prevent interruption of the pushing action.

[0010] Furthermore, the multi-stage screw pressing system includes a pressure equalization chamber, the inner wall of which is fixed with continuously spirally arranged guide vanes. The guide vanes are arranged in a continuous spiral to guide the material to flow uniformly.

[0011] Furthermore, the outlet end of the pressure equalization chamber is provided with a honeycomb porous damping plate.

[0012] Furthermore, the molding die includes a modular core mold assembly and an ejection mechanism. The core mold assembly is connected to the mold base via a quick-change interface, and the ejection mechanism includes four sets of symmetrically arranged hydraulic ejector rods.

[0013] Furthermore, the modular core mold assembly includes at least two split mold segments, and a compensation ring and a locking ring are sequentially fitted around the multiple split mold segments.

[0014] Furthermore, each individual screw mechanism of the multi-stage screw pushing system is independently connected to a power source.

[0015] The advantages and beneficial effects of this utility model are as follows:

[0016] 1. This utility model uses a three-stage screw system that is connected in series axially and staggered radially, enabling the three-stage single screw mechanism to achieve phase relay of the pushing action. This breaks through the traditional intermittent pushing mode, improves production efficiency, and eliminates the need for material changing gaps and machine downtime compared to traditional equipment.

[0017] 2. This invention utilizes a twin-screw rotating in opposite directions to create a strong shear-stretching effect, thereby improving the uniformity of the PTFE paste. The spiral grooves within the conical compression chamber guide the material to form a spiral laminar flow, laying the foundation for subsequent high-pressure compression.

[0018] 3. By setting the gradient speed of the three-stage single screw, combined with the composite flow channel of the spiral guide vane and the honeycomb damping plate, the density deviation of the pipe can be reduced. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of this utility model;

[0020] Figure 2 This is a cross-sectional structural schematic diagram of the present invention;

[0021] Figure 3 This is a schematic diagram of the cross-sectional structure of this utility model;

[0022] In the picture:

[0023] Pre-compression feeding mechanism 1, twin screws 11, conical compression chamber 12, spiral groove 121, gear 13;

[0024] 2. Multi-stage screw pushing system, 21. Single screw mechanism, 21. First-stage pre-compression screw, 211. Second-stage main pressure screw, 212. Third-stage fine pressure screw, 213. Spherical compensator, 214. Pressure equalization chamber, 22. Guide plate, 221. Honeycomb porous damping plate, 222. Opening, 23. Recess, 24. Power source, 25.

[0025] 3. Molding mold, 31. Modular core mold assembly, 311. Quick-change interface, 312. Split mold piece, 313. Compensation ring, 314. Locking ring, 32. Ejection mechanism, 32. Hydraulic ejector rod, 321. Detailed Implementation

[0026] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and examples. The following examples are only used to more clearly illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention.

[0027] Example 1:

[0028] like Figure 1-2 As shown, a continuous extrusion molding apparatus for polytetrafluoroethylene (PTFE) tubes includes a pre-compression feeding mechanism 1, a multi-stage screw extrusion system 2, and a molding die 3, connected sequentially along the material flow direction. The multi-stage screw extrusion system consists of a primary pre-compression screw 211, a secondary main compression screw 212, and a tertiary precision compression screw 213 connected axially in series, with adjacent single screw structures 21 radially staggered by 120°. The outlet flange of the conical compression chamber 12 of the pre-compression feeding mechanism is bolted to the inlet of the primary pre-compression screw 211. The outlet flange of the pressure equalization chamber 22 is sealed to the inlet of the molding die 3 using a metal spiral wound gasket.

[0029] The pre-compression feeding mechanism has a feed inlet at its end. A pair of twin screws 11 inside the feed inlet rotate in opposite directions via meshing gears 13. One of the twin screws 11 is connected to a motor. The discharge end of the twin screws 11 is sealed to the inlet of the conical compression chamber 12 using a transition sleeve. The primary pre-compression screw 211, the secondary main compression screw 212, and the tertiary precision compression screw 213 are axially offset via a series base, which is fixed with a locating pin. The outer wall of the conical compression chamber 12 has an opening 23, and the opening 23 has a recess 24 extending into the cylinder. Supported by the recess 24, the primary pre-compression screw 211, the secondary main compression screw 212, and the tertiary precision compression screw 213 all pass through the outer wall of the conical compression chamber 12, through the recess 24, and are independently connected to the power source 25 via a gear set, belt set, coupling, or other devices to transmit power. At the end of the first-stage preload screw 211, the second-stage main pressure screw 212 pushes, and at the end of the second-stage main pressure screw 212, the third-stage fine pressure screw 213 continues to push, forming a continuous relay pushing action.

[0030] Example 2:

[0031] Based on Example 1, the twin screws have a center distance of 120mm (screw diameter of 80mm) and are driven to rotate in opposite directions by a reducer (speed ratio 15:1). The thread pitch of the twin screw 11 decreases along the feeding direction to increase the compression ratio. The discharge end of the twin screw 11 is inserted into the inlet sleeve of the conical compression chamber 12. The inner wall of the conical compression chamber 12 has helical grooves with a depth of 3mm, extending along the helix angle of 15° to the outlet of the conical compression chamber 12. The total length of the twin screws is 1200mm, of which 600mm is the meshing zone. The root diameter of the screw is 50mm, the thread height is 15mm, and the thread width is 8mm, forming a progressive compression ratio of 3:1.

[0032] Each single-screw mechanism 21 is equipped with a spherical compensator 214 at its end to buffer the axial deviation of the preload cylinder 211. The maximum pressure of the first-stage preload screw 211 is 30 MPa, the maximum pressure of the second-stage main pressure screw 212 is 80 MPa, and the maximum pressure of the third-stage fine pressure screw 213 can reach 120 MPa. Each single-screw mechanism is independently connected to a power source 25, which is electrically connected to a controller. The single-screw mechanism 21 is set in a pressure equalization chamber 22. The inner wall of the pressure equalization chamber 22 is provided with guide vanes 221, which are continuously arranged in a helix angle of 30°. The outlet end of the pressure equalization chamber 22 is provided with a honeycomb porous damping plate 222, which has a pore diameter of 1.5 mm and an opening ratio of 40%.

[0033] Example 3:

[0034] like Figure 2 As shown, the twin screws 11 in the pre-compression feeding mechanism 1 have a diameter of Φ80mm, a center distance of 120mm, and a thread pitch that decreases from 60mm at the feed end to 20mm at the discharge end. The meshing zone length accounts for 50% of the total screw length. The spiral grooves 121 on the inner wall of the conical compression chamber 12 have a lead of 200mm, a depth of 3mm, and a helix angle of 15°, guiding the material to form a laminar flow.

[0035] Example 4:

[0036] like Figure 3As shown, based on Example 2, the modular core mold assembly 31 in the molding die 3 comprises four split mold segments 312. A quick-change interface 311 is provided between the modular core mold assembly 31 and the split mold segments 312. The quick-change interface includes, but is not limited to, flanges, chucks, and clamps. A compensation ring 313 and a locking ring 314 are sequentially fitted around the four split mold segments 312. The compensation ring 313 is made of shape memory alloy Ni-Ti alloy with a phase change temperature of 120℃. After heating, it expands to compensate for the gap between the mold segments by 0.1-0.3mm. The locking ring 314 has a 1:10 taper and a hydraulic locking force of 15MPa to ensure tight mold segment closure. After the split mold segments release the locking ring, the four sets of hydraulic ejector rods 321 of the ejection mechanism 32 simultaneously eject the mold segments for mold replacement. Here, the compensation ring 313 needs to be preheated to 130℃ during installation to achieve phase change expansion.

[0037] In the above embodiments, in actual control, it is necessary to set the second-stage cylinder to start pushing when the first-stage cylinder has completed 90% of its stroke, and the phase difference time = single-cylinder pushing time × 10%.

[0038] The spiral groove 121 preferably has a trapezoidal cross-section (2mm top width, 4mm bottom width, and 3mm depth) to avoid material residue. The guide vanes 221 are arranged with equal lead and equal helix angle to prevent uneven flow resistance. The compensation ring 313 needs to be activated at 120-150℃ to match the PTFE processing temperature.

[0039] The working principle of this utility model lies in the synergistic effect of the phase relay of the multi-stage screw pressing system, the material pretreatment optimization of the pre-pressing feeding mechanism, and the dynamic compensation mechanism of the forming mold. The material is first subjected to forced shearing and mixing by the counter-rotating twin screws 11 of the pre-compression feeding mechanism. The decreasing screw pitch, combined with the spiral grooves 121 in the conical compression chamber 12, guides laminar flow and improves the pre-compression density. Then, it enters the pushing system composed of a three-stage phase-interlaced single screw mechanism 21. Through the adaptive correction of the ball compensator 214 of the first-stage pre-compression screw and the high-pressure precision pressing of the third-stage precision pressing screw 213, the pushing action is continuously relayed. The pressure distribution is balanced by the composite flow channel of the spiral guide vanes 221 and the honeycomb damping plate 222 in the pressure equalization chamber 22. Finally, the material is shaped by the split mold 312 of the forming mold 3. The shape memory alloy compensation ring 313 expands to compensate for the gap at the processing temperature. The tapered locking ring 314 ensures the closing accuracy through hydraulic locking force. The four sets of hydraulic push rods 321 are synchronously fine-tuned by the controller connected to the reversing valve to ensure dimensional consistency. Thus, the process goal of continuous production of PTFE pipes without downtime, low density deviation, and high outer diameter accuracy is achieved.

[0040] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A continuous extrusion molding apparatus for polytetrafluoroethylene (PTFE) tubes, characterized in that: It includes a pre-pressing feeding mechanism (1), a multi-stage screw pressing system (2) and a forming mold (3) connected in sequence along the material conveying direction. The multi-stage screw pressing system (2) consists of at least three single screw mechanisms (21) connected in series axially and with radial phases interlaced.

2. The apparatus according to claim 1, characterized in that: The pre-compression feeding mechanism (1) includes a twin screw (11) rotating in opposite directions and a conical compression chamber (12), wherein the thread pitch of the twin screw (11) decreases along the pushing direction, and the inner wall of the conical compression chamber (12) is provided with a spiral groove (121).

3. The apparatus according to claim 2, characterized in that: The center distance of the twin screws (11) is 1.2-1.8 times the screw diameter, and the length of the thread engagement area accounts for 40%-60% of the total screw length.

4. The apparatus according to claim 1, characterized in that: The single screw mechanism (21) includes a primary pre-compression screw (211), a secondary main compression screw (212), and a tertiary fine compression screw (213).

5. The apparatus according to claim 4, characterized in that: The single screw mechanism (21) is provided with a spherical compensator (214) at its end.

6. The apparatus according to claim 1, characterized in that: The multi-stage screw pushing system (2) includes a pressure equalization chamber (22), the inner wall of which is fixed with guide vanes (221) arranged in a continuous spiral.

7. The apparatus according to claim 6, characterized in that: The outlet end of the pressure equalization chamber (22) is provided with a honeycomb porous damping plate (222).

8. The apparatus according to claim 1, characterized in that: The molding die (3) includes a modular core mold assembly (31) and an ejection mechanism (32). The core mold assembly (31) is connected to the mold base through a quick-change interface (311), and the ejection mechanism (32) includes four sets of symmetrically arranged hydraulic ejector rods (321).

9. The apparatus according to claim 8, characterized in that: The modular core mold assembly (31) includes at least two split mold segments (312), and a compensation ring (313) and a locking ring (314) are sequentially fitted on the outside of the multiple split mold segments (311).

10. The apparatus according to claim 1, characterized in that: Each single screw mechanism (21) of the multi-stage screw pushing system (2) is connected to a power source.

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