Variable pitch twin screw extruder

Abstract

The application discloses a variable-pitch double-screw extruder, which comprises an extrusion barrel fixedly connected by a plurality of barrel segments, water passing grooves arranged at both ends of the barrel segments, water inlet channels and water return channels arranged on the barrel bodies of the barrel segments, refrigeration fins and heating fins arranged on the outer barrel walls of the barrel segments in an alternating manner, a screw water guide rotatably supported at the feeding end of an extrusion screw, two water guide bolts connected to the screw water guide and leading to the screw water cavity and the water delivery pipe, and the extrusion pitch Tn, the ridge tooth top width Bn and the screw lateral gap Cn of the extrusion screw are continuously reduced from the feeding end to the discharging end of the extrusion screw. The variable-pitch double-screw extruder has the advantages of uniform plasticization of rubber materials, good dispersity, effective control of the working temperature of the screw extruder, and the like, and is particularly suitable for the double-screw extruder for extruding and forming the solar cell packaging film.

Description

Technical Field

[0001] This invention relates to a screw extrusion apparatus, and more particularly to a twin-screw extruder for extruding encapsulation films for solar cells. Background Technology

[0002] Screw extruders are mechanical devices used in the production of solar cell module encapsulation films to melt and plasticize polymer materials such as EVA / POE into a uniform melt. Compared with single-screw extruders, twin-screw extruders have higher melt plasticizing efficiency and mixing quality, and therefore are more widely used in the extrusion film production of solar cell encapsulation films.

[0003] The quality of the extruded film from a screw extruder is not only closely related to parameters such as the screw extruder type and screw geometry, but also extremely important to the operating temperature of the screw extruder. A reasonable and stable operating temperature can effectively improve the plasticizing effect of the rubber compound. If the temperature is too high, the high-viscosity rubber compound will not flow and mix easily in the extrusion system, and may even produce irregular paste-like extrudates, causing serious failure of the extrusion process. If the temperature is too low, the extruded semi-finished product will be undercooked and poorly plasticized.

[0004] To better control the extrusion temperature of the screw, most extrusion screws are currently equipped with a screw water chamber, into which a water supply pipe is inserted to supply cooling water at a certain temperature to ensure the operating temperature of the extrusion screw. However, this structure cannot change or stabilize the operating temperature of the extrusion barrel, so the existing screw barrel structure is difficult to guarantee a stable and reasonable rubber compound temperature throughout the entire extrusion process.

[0005] Meanwhile, since the screw water chamber and the water supply pipe in the screw need to rotate with the screw during extrusion, the current method uses a rubber sealing structure to form the water supply chamber and the water return chamber. For screw extruders that work continuously in a high-temperature environment for a long time, this sealing structure not only has a short service life and limited water supply flow, which is not conducive to controlling the screw extrusion working temperature, but also has unstable sealing performance and is prone to leakage, which directly affects the temperature regulation function of the extrusion screw.

[0006] Currently, most twin-screw extruders use a feeding section, a melting section, and a homogenizing section for the extrusion screw. The pitch and compression chamber volume of the screw remain constant within the same working section. Therefore, there is no significant pressure increase process within the same working section. Furthermore, when transitioning from one working section to another, the extrusion pressure of the screw will change abruptly, resulting in uneven pressure increase and potentially uneven plasticization of the rubber compound. This abrupt pressure increase leads to an unstable pressure increase process and can also generate significant impact vibration, increasing power consumption and reducing working efficiency. Summary of the Invention

[0007] In view of the above-mentioned shortcomings of the existing technology, the technical problem to be solved by the present invention is to provide a variable pitch twin-screw extruder that not only provides uniform plasticization and good dispersion of the rubber compound, but also effectively controls the working temperature of the screw extruder.

[0008] To solve the above-mentioned technical problems, the present invention provides a variable pitch twin-screw extruder, comprising a frame and an extrusion barrel mounted on the frame. Two parallel and meshing extrusion screws are rotatably supported in the extrusion barrel. Each extrusion screw has a water chamber containing a water supply pipe.

[0009] The extrusion cylinder is formed by fixedly connecting multiple cylinder sections. Water grooves are provided at both ends of the cylinder section. Water inlet and water return channels are also provided on the cylinder body of the cylinder section. The water grooves at both ends of the cylinder section are staggered relative to each other. The water inlet or water return channel at one end is connected to the water inlet or water return channel at the other end through the corresponding water groove at the other end.

[0010] Cooling plates and heating plates are alternately arranged on the outer wall of the barrel section;

[0011] The feed end of the extrusion screw is rotatably supported by a screw water guide, and two water guide bolts are connected to the screw water guide. The two water guide bolts lead to the screw water chamber and the water delivery pipe, respectively.

[0012] The extrusion pitch Tn, tooth tip width Bn, and screw lateral clearance Cn of the extrusion screw all decrease continuously from the feed end to the discharge end; Tn = To - ΔT

[0013] .n, Bn=Bo-ΔB.n, Cn=Co-ΔC.n; ΔT is the extrusion pitch change rate, ΔB is the tooth tip width change rate, ΔC is the screw lateral clearance change rate, and n is the number of teeth.

[0014] With the above-described structure, the extrusion barrel is composed of multiple barrel sections fixedly connected, and each barrel section has a water channel at both ends. The water channel contains axially oriented water inlet and return channels. This structure allows for direct adjustment and control of the extrusion barrel's operating temperature based on the temperature of the rubber compound within the extrusion screw cavity. Cooling water circulates through the water channel, water inlet, and return channels in a zigzag pattern, significantly increasing the heat conduction area of ​​the cooling water and facilitating stable temperature control within the same barrel section. Furthermore, the presence of cooling and heating elements on the outer wall of the barrel section allows for heating of the barrel section when the barrel and screw operating temperatures are low, and cooling to dissipate heat when the barrel and screw operating temperatures are high, thus achieving a stable barrel and screw operating temperature. Furthermore, because the extrusion screw pitch, tooth tip width, and lateral clearance continuously decrease from the drive end to the discharge end—with the pitch decreasing closer to the discharge end and increasing towards the discharge end—the compression chamber volume formed by the twin screws gradually decreases. Therefore, the internal pressure of the extruded rubber compound increases gradually, effectively eliminating sudden pressure changes. This benefits the extruded rubber compound by ensuring thorough plasticization and uniformity, stabilizing and guaranteeing the quality of the extruded film. Additionally, this continuous, gradual decrease in compression volume ensures smooth screw rotation and reduces screw drive power consumption. The extrusion screw drive end is rotatably supported on a screw water guide, through which cooling water is introduced into the screw chamber via two water guide bolts to stabilize the screw's operating temperature.

[0015] In a further embodiment of the present invention, each of the material cylinder sections is fixedly provided with a cylinder section flange at both ends, and the water passage groove is provided on the outer surface of the cylinder section flange; a water passage section is correspondingly installed at one end of each material cylinder section, and the water inlet pipe and the water outlet pipe on the water passage section respectively lead to the water inlet channel or the water outlet channel through the corresponding water passage groove. This realizes independent water passage and temperature control for a single material cylinder section.

[0016] In a preferred embodiment of the present invention, both the cooling element and the heating element are semiconductor cooling elements. The cold end of the cooling element is attached to the wall of the barrel section, and the hot end of the heating element is attached to the wall of the barrel section. The cooling element and the heating element are attached to the barrel section wall in a staggered, alternating pattern along the axial direction of the barrel section in a strip-like arrangement. The use of semiconductor cooling elements ensures high reliability and allows for convenient adjustment of the barrel section temperature.

[0017] In a preferred embodiment of the present invention, the extrusion pitch variation rate ΔT = 1.10~1.20, where To is the pitch of the first adjacent tooth at the feed end of the extrusion screw, Tn is the pitch of the nth adjacent tooth, and n is a natural number. The tooth tip width variation rate ΔB = 0.32~0.33, where Bo is the tip width of the first adjacent tooth at the feed end of the extrusion screw, Bn is the tip width of the nth adjacent tooth, and n is a natural number. The screw lateral clearance variation rate ΔC = 0.10~0.12, where Co is the lateral clearance between the two first teeth at the feed ends of the two extrusion screws, Cn is the lateral clearance between the nth teeth at the feed ends of the two extrusion screws, and n is a natural number. By employing continuously decreasing screw pitch, top width, and side clearance, a smooth and gradual change in internal pressure of the rubber compound is ensured, which is beneficial for homogeneous plasticization. This avoids both the uneven material mixing and plasticization caused by excessive changes in the compression chamber volume of a twin-screw extruder, and the high power consumption and excessively high temperature of the extruded material due to insufficient changes in the compression chamber volume, which can lead to scorching of the molten material. These structural parameters effectively guarantee mixing capacity, dispersion and mixing efficiency, and extrusion stability.

[0018] In a further embodiment of the present invention, the screw water guide includes a water guide housing, within which two water guide rings are disposed. Two water guide bolts are also disposed on the water guide housing, with each water guide ring corresponding to one water guide bolt. The two water guide bolts respectively connect to the screw water chamber and the water supply pipe through their corresponding water guide rings. Water guide holes are provided on the water guide chamber ribs of the water guide rings. The water supply chamber and water distribution chamber located on both sides of the water guide chamber ribs are connected through the water guide holes. The water distribution chamber is connected to the corresponding water guide bolt. Water ring seals are installed at both ends of the water guide rings. Each water ring seal includes a moving ring embedded in the water guide ring, and a stationary ring corresponding to the moving ring is installed on a stationary ring seat. The stationary ring seat is sealed and installed on the water guide housing. An end spring is installed between the stationary ring seat and the end cap. An intermediate spring is installed on the stationary ring seat located inside the water guide ring. The end cap is fixedly installed at both ends of the water guide housing. On the one hand, two water guide rings are used to allow cooling water to be input into or discharged into the screw water pipe and the water supply pipe respectively. On the other hand, the sealing structure of the dynamic and static rings has better sealing performance, longer service life, and is not easily damaged, making it more suitable for the high-temperature operating environment of twin-screw extruders. Attached Figure Description

[0019] The invention of the variable pitch twin-screw extruder will be further described below with reference to the accompanying drawings and specific embodiments.

[0020] Figure 1 A front structural schematic diagram of a specific embodiment of the variable pitch twin-screw extruder of the present invention;

[0021] Figure 2 yes Figure 1 Schematic diagram of the cross-sectional structure along line A-A;

[0022] Figure 3 yes Figure 1 A schematic diagram of the three-dimensional installation structure of the extrusion barrel in the embodiment shown;

[0023] Figure 4 yes Figure 3 A three-dimensional structural diagram of a single barrel section;

[0024] Figure 5 yes Figure 4 A schematic diagram of the structure along direction A;

[0025] Figure 6 yes Figure 4 A schematic diagram of the B-direction structure;

[0026] Figure 7 yes Figure 1 A schematic diagram of the external structure of a single screw in the embodiment shown.

[0027] Figure 8 yes Figure 7 A partially enlarged schematic diagram of the screw;

[0028] Figure 9 yes Figure 1 The diagram shows the relative positional parameters of the two screws in the embodiment shown.

[0029] Figure 10 yes Figure 7 A cross-sectional view of the central screw.

[0030] Figure 11 yes Figure 10 Cross-sectional view of the screw-type water guide;

[0031] Figure 12 yes Figure 11 Cross-sectional view of the central water-conducting ring;

[0032] Figure 13 yes Figure 12 B-B cross-section view.

[0033] In the diagram, 1—frame; 2—motor; 3—transmission box; 4—extrusion screw; 401—screw ridge; 402—screw body; 403—ridge teeth; 404—screw water chamber; 405—water pipe; 406—water pipe through hole; 407—water chamber through hole; 408—water chamber filler; 409—end cap; 5—screw water guide; 501—water guide housing; 502—water guide bolt; 503—intermediate spring; 504—water guide ring; 505—end spring; 506—end cap; 507—stationary ring seat; 508—stationary ring; 509—dynamic ring. 510—Water guide hole; 511—Water guide ring rib; 512—Moving ring groove; 513—Water supply chamber; 514—Water distribution chamber; 6—Feeder; 7—Screw barrel cover; 8—Extrusion head; 9—Extrusion barrel; 901—Barrel section; 902—Barrel section flange; 903—Screw chamber; 904—Water passage groove; 905—Flange bolt hole; 906—Refrigeration plate; 907—Heating plate; 908—Water passage section; 909—Water inlet pipe; 910—Drain pipe; 911—Water inlet channel; 912—Water return channel; 10—Temperature control plate; 11—Mixer. Detailed Implementation

[0034] Figure 1 , Figure 2 The variable pitch twin-screw extruder shown has a frame 1 that is movably supported on a ground guide rail via rollers, facilitating the installation, maintenance, and commissioning of the entire production line. An extrusion barrel 9, a motor 2, a transmission box 3, and a feeder 6 are fixedly mounted on the frame 1. The motor 2, fixedly mounted on the frame 1, drives the transmission box 3. The two output shafts of the transmission box 3 are respectively connected to two extrusion screws 4. The two parallel meshing extrusion screws 4 are rotatably supported within the cylinder cavity of the extrusion barrel 9. A screw guide 5 is installed at the drive end of each extrusion screw 4, and a mixer 11 is fixedly connected to the discharge end of the extrusion screw 4. A feeder 6, comprising a feed hopper and a feed motor, is also fixedly mounted on the frame 1. The feed port of the feeder 6 corresponds to the feed end of the extrusion screw 4 through the feed port of the extrusion barrel 9, and the feed end of the extrusion screw 4 is adjacent to its drive end. An extrusion head 8 is fixedly connected to the discharge end of the extrusion barrel 9. A screw barrel cover 7 is provided on the outside of the extrusion barrel 9, and the screw barrel cover 7 is fixedly installed on the frame.

[0035] The extrusion barrel 9 is fixedly connected by 7 extrusion barrel sections 901. Each extrusion barrel section 901 is equipped with an independent water supply and return system to control the temperature of each barrel section 901. A temperature control plate 10 is provided on the outer wall of the barrel section 901. In this embodiment, the temperature control plate 10 includes a cooling plate 906 and a heating plate 907.

[0036] like Figure 3 , Figure 4As shown, a water passage section 908 is fixedly installed between two adjacent barrel sections 901. Each water passage section 908 corresponds to one barrel section 901. A water inlet pipe 909 and a drain pipe 910 are installed on the water passage section 908. The barrel section 901 is a rectangular section. A screw cavity 903 capable of accommodating two parallel extrusion screws 4 is set at the center of the barrel section 901. Barrel flanges 902 are fixedly installed at both ends of the barrel section 901. An arc-shaped flange is provided on the barrel flange 902. 904 trough-shaped water passage.

[0037] like Figure 5 , Figure 6 As shown, each section of the water passage 904 is provided with an inlet channel 911 and a return channel 912 with opposite flow directions. For ease of explanation, Figure 5 , Figure 6 In the diagram, ⊙ and ⊕ represent the water inlet and return channels on the corresponding flange faces, respectively. The water inlet channel ⊙ indicates that the water flows from the near flange to the far flange, while the return channel ⊕ indicates that the water flows from the far flange back to the near flange. However, this does not restrict the actual direction of the water flow. The positions of the water channels 904 at both ends of the barrel section 901 are staggered so that the water flows from the water inlet channel 911 of one flange to the water channel 904 of the other flange and then back to the water inlet channel 911 of the other flange, or from the return channel 912 of one end to the water channel 904 of the other end and then back to the return channel 912 of the other end, and so on. This cycle allows the cooling water from the water inlet pipe 909 on the corresponding water passage section 908 to circulate repeatedly through the water channels 904, water inlet channel 911, and return channel 912 on the barrel section 901, and finally discharges from the drain pipe 910 to carry away the extrusion heat. Several flange bolt holes 905 are provided on the cylindrical flange 902 to fix the flange to the water passage joint 908.

[0038] Cooling elements 906 and heating elements 907 are alternately attached to the outer wall of the barrel section 901. Both cooling elements 906 and heating elements 907 are semiconductor cooling elements. The cold end of the semiconductor cooling element is attached to the outer wall of the barrel section 901 to form the cooling element 906, and the hot end of the semiconductor cooling element is attached to the outer wall of the barrel section 901 to form the heating element 907. The cooling elements 906 and heating elements 907, arranged in a strip structure along the axial direction of the barrel section 901, are each composed of several semiconductor cooling elements. When the barrel screw operating temperature is too high, the cooling element 906 operates; when the barrel screw temperature is low, the heating element 907 operates. Therefore, the cooling elements 906 and heating elements 907 operate alternately to ensure a reasonable and stable extrusion temperature.

[0039] like Figure 8As shown, each extrusion screw 4 adopts a single-head screw structure. The screw ribs 401 of the extrusion screw 4 are spirally arranged on the screw body 402. The rib teeth 403 are the cross-sectional tooth profiles of the screw ribs along a plane passing through the axis of the extrusion screw 4. The rib tooth number n = 0, 1, 2---, where n is the natural number of rib teeth. The extrusion pitch Tn, the rib tooth tip width Bn, and the screw lateral clearance Cn of the extrusion screw 4 gradually decrease continuously from the feed end to the discharge end of the extrusion screw.

[0040] The main parameters of the extrusion screw 4 are: Tn = To - ΔT.n; Bn = Bo - ΔB.N; Cn = Co - ΔC.n.

[0041] In the above, To is the distance between the first tooth 403 and the first tooth 403 at the feed end of the extrusion screw, T1 is the distance between the first tooth 403 and the second tooth 403 at the feed end of the extrusion screw, and correspondingly, Tn is the distance between the nth tooth and the (n+1)th tooth at the feed end of the extrusion screw, and ΔT is the extrusion pitch change rate, the unit of which is the length value per tooth (e.g., mm / tooth).

[0042] Bo is the tooth tip width between the first tooth and the first tooth at the feed end of the extruder screw, B1 is the tooth tip width between the first tooth and the second tooth at the feed end of the extruder screw, and correspondingly, Bn is the tooth tip width between the nth tooth and the (n+1)th tooth at the feed end of the extruder screw, and ΔB is the tooth tip width change rate, the unit of which is the length value per tooth (e.g., mm / tooth).

[0043] like Figure 9 As shown, the lateral clearance Co is the clearance between the first teeth of two meshing extrusion screws. Specifically, Co is the lateral clearance between the first teeth at the feed end of one extrusion screw and the first teeth at the feed end of the other extrusion screw. C1 is the lateral clearance between the first teeth at the feed end of one extrusion screw and the first teeth at the feed end of the other extrusion screw. Correspondingly, Cn is the lateral clearance between the nth teeth at the feed ends of the two extrusion screws. ΔC is the rate of change of the screw lateral clearance, and the unit of the rate of change of the lateral clearance is the length value per tooth (e.g., mm / tooth).

[0044] like Figure 7 As shown, a screw water guide 5 is rotatably supported at the feed end of the extrusion screw 4, and two water guide bolts for injecting or discharging cooling water are connected to the screw water guide 5. A mixer 11 is fixedly connected to the discharge end of the extrusion screw 4.

[0045] Figure 9 The relative positions and structural parameters of the meshing teeth of two extrusion screws are shown. The two meshing screws have the same screw tip diameter D, screw root diameter d, screw tip height H, and screw tip clearance h. The screw tip cross-section of extrusion screw 4 is an isosceles trapezoid with a lateral inclination angle α.

[0046] Because the structural parameters of the extrusion screw need to comprehensively consider factors such as rubber compound properties, melt plasticizing efficiency, mixing performance, operational stability, and energy consumption, the applicant company has conducted extensive theoretical analysis, simulation design, and practical experiments. The main structural parameters of the extrusion screw of the twin-screw extruder for extruding solar cell encapsulation films of this invention are as follows:

[0047] The extrusion pitch Tn = To - ΔT.n = To - (1.10 - 1.20)n, where ΔT = 1.10 - 1.20.

[0048] The tooth tip width Bn = Bo - ΔB.n = Bo - (0.32 - 0.33)n, where ΔB = 0.32 - 0.33;

[0049] The lateral clearance of the toothed teeth is Cn = Co - ΔC.n = Co - (0.10 - 0.12)n, where ΔC = 0.10 - 0.12.

[0050] The outer diameter of the extrusion screw is D = 135-140 mm; the screw height is H = 28-30 mm; the screw tip clearance is h = 3-5 mm; the center distance between the two screws is a = D - H + h; the root diameter of the screw is d = D - 2H; the isosceles trapezoidal side inclination angle of the screw edge of the extrusion screw is α = 5°-10°.

[0051] Example 1:

[0052] The extrusion screw 4 has a total of 43 teeth, i.e., the sequential number of teeth along the longitudinal direction of the screw is n = 0, 1, 2, 3, ... n... 43. To = 110 mm; the last screw pitch T43 = 60 mm, ΔT = 1.16 mm / tooth. Bo = 38 mm, B43 = 24 mm, ΔB = 0.325 mm / tooth; Co = 8.3 mm, C43 = 3.6 mm, ΔC = 0.109 mm / tooth. H = 30 mm, h = 5 mm, D = 140 mm, d = 80 mm, α = 8°. The center distance between the two extrusion screws is a = 115 mm.

[0053] Example 2:

[0054] The extrusion screw 4 has a total of 40 teeth, i.e., the sequential number of teeth along the longitudinal direction of the screw is n = 0, 1, 2, 3, ... n..., 40. To = 108 mm; the last screw pitch T40 = 63 mm, ΔT = 1.125 mm / tooth. Bo = 37 mm, B40 = 24 mm, ΔB = 0.325 mm / tooth; Co = 8.1 mm, C40 = 3.6 mm, ΔC = 0.1125 mm / tooth. H = 30 mm, h = 5 mm, D = 140 mm, d = 80 mm, α = 8°. The center distance between the two extrusion screws is a = 113.5 mm.

[0055] Example 3:

[0056] The extrusion screw 4 has a total of 38 teeth, i.e., the number of teeth arranged sequentially along the longitudinal direction of the screw is n = 0, 1, 2, 3, ... n... 38. To = 106 mm, T38 = 62 mm, ΔT = 1.158 mm / tooth. Bo = 36 mm, B38 = 23.6 mm, ΔB = 0.326 mm / tooth. Co = 7.9 mm, C38 = 3.6 mm, ΔC = 0.113 mm / tooth. H = 28 mm, h = 4.8 mm, D = 136 mm, d = 80 mm, α = 7°; the center distance between the two extrusion screws is a = 112.8 mm.

[0057] like Figure 10 As shown, a screw water cavity 404 is provided at the axial position of the extrusion screw 4, extending all the way to the mixer 11 and forming a blind hole structure. A water supply pipe 405 is inserted into the screw water cavity 404, with a gap between the water supply pipe 405 and the cavity wall of the screw water cavity 404. The water supply pipe 405 is fixedly supported on the screw body 402 by a water cavity filler 408, and an end cap 409 is installed on the extended end of the water cavity filler 408. A water pipe through hole 406 and a water cavity through hole 407 are respectively provided radially on the screw body 402. The bolt holes of the two water guide bolts 502 on the screw water guide 5 are respectively connected to the water supply pipe 405 and the screw water cavity 404 through the water pipe through hole 406 and the water cavity through hole 407.

[0058] like Figure 11 , Figure 12 and Figure 13 As shown, the screw water guide 5 includes a water guide housing 501. Two water guide rings 504 are provided in the cavity of the water guide housing 501. The two water guide rings 504 are fixedly installed on the screw body 402, and a rubber sealing ring 515 is placed between the water guide rings 504 and the screw body 402. Therefore, the water guide rings 504 rotate together with the extrusion screw 4.

[0059] Each water guide ring 504 has a water ring seal installed at both ends. The water ring seal includes a moving ring 509 embedded in the water guide ring 504, and a stationary ring 508 forming a sealing pair with the moving ring 509, which is installed on a stationary ring seat 507. The moving ring 509 and the stationary ring 508 are made of silicon carbide material. The stationary ring seat 507 is fixedly installed in the cavity of the water guide housing 501, and a rubber sealing ring 515 is also placed between the stationary ring seat 507 and the inner wall of the cavity of the water guide housing 501.

[0060] A water guide ring 504 is provided with a water guide ring rib 511. The two sides of the water guide ring rib 511 are a water supply chamber 513 and a water distribution chamber 514, respectively. The water guide ring rib 511 has eight water guide holes 510, which connect the water supply chamber 513 and the water distribution chamber 514. An end spring 505 is installed between the stationary ring seat 507 and the corresponding end cap 506 to press the stationary ring 508 against the moving ring 509 to form a friction seal pair. An intermediate spring 503 is installed on the stationary ring seat 507 inside the water guide ring 504, i.e., the intermediate spring 503 is positioned between two opposing stationary ring seats 507. Both the end spring 505 and the intermediate spring 503 are helical compression springs.

[0061] Two water guide bolts 502 are screwed onto the water guide housing 501. Each water guide bolt 502 corresponds to a water guide ring 504. The water guide hole on the water guide bolt 502 is connected to the water distribution cavity 514 on the water guide ring 504, so that the water guide bolt 502 leads to the water pipe through hole 406 or water cavity through hole 407 on the screw body 402 through the water distribution cavity 514, water guide hole 510 and water supply cavity 513 on the corresponding water guide ring 504. In this way, cooling water can enter the water supply pipe 405 through one water guide bolt 502 and water pipe through hole 406. The cooling water in the water supply pipe 405 returns from the screw water cavity 404 to the water cavity through hole 407 and flows out through the other water guide bolt 502, thereby carrying away the extrusion heat of the screw.

[0062] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A variable pitch twin-screw extruder comprising a frame (1) and an extrusion barrel (9) mounted on the frame (1), two parallel meshing extrusion screws (4) being rotatably supported in the extrusion barrel (9), a screw water cavity (403) being arranged in each extrusion screw (4), a water delivery pipe (404) being arranged in the screw water cavity (403), characterized in that: the extrusion barrel (9) is fixedly connected by a plurality of barrel segments (901), water passing grooves (904) being arranged at both ends of the barrel segments (901), water inlet channels (911) and water return channels (912) being further arranged on the barrel body of the barrel segments (901), the water passing grooves (904) at both ends of the barrel segments (901) being oppositely and staggeringly arranged, the water inlet channels (911) or the water return channels (912) at one end being connected to the water inlet channels (911) or the water return channels (912) at the other end through the corresponding water passing grooves (904) at the other end; refrigeration fins (906) and heating fins (907) being alternately arranged on the outer barrel wall of the barrel segments (901); a screw water guide (5) being rotatably supported at the feed end of the extrusion screw (4), two water guide bolts (502) being connected to the screw water guide (5), the two water guide bolts (502) being respectively connected to the screw water cavity (403) and the water delivery pipe (404); the extrusion pitch Tn, the tooth top width Bn and the screw lateral clearance Cn of the extrusion screw (4) being continuously reduced from the feed end to the discharge end of the extrusion screw (4); Tn = To - ΔT*n, Bn = Bo - ΔB*n, Cn = Co - ΔC*n; ΔT is the extrusion pitch change rate, ΔB is the tooth top width change rate, ΔC is the screw lateral clearance change rate, and n is the tooth number; the extrusion pitch change rate ΔT = 1.10-1.20, To is the pitch of the first adjacent tooth at the feed end of the extrusion screw (4), Tn is the pitch of the nth adjacent tooth, and n is a natural number; the tooth top width change rate ΔB = 0.32-0.33, Bo is the tooth top width of the first adjacent tooth at the feed end of the extrusion screw (4), Bn is the tooth top width of the nth adjacent tooth, and n is a natural number; the screw lateral clearance change rate ΔC = 0.10-0.12, Co is the tooth lateral clearance between the two first teeth at the feed end of the two extrusion screws (4), and Cn is the tooth lateral clearance between the nth tooth at the feed end of the two extrusion screws, and n is a natural number. a barrel segment flange (902) being fixedly arranged at both ends of each barrel segment (901), the water passing grooves (904) being arranged on the outer side surface of the barrel segment flange (902); a water passing segment (908) being correspondingly mounted at one end of the barrel segment (901), a water inlet pipe (909) and a water outlet pipe (910) on the water passing segment (908) being respectively connected to the water inlet channel (911) or the water return channel (912) through the corresponding water passing grooves (904).

2. A variable pitch twin screw extruder according to claim 1, characterized in that: ​ 3. The variable pitch twin screw extruder of claim 1, wherein: The refrigeration sheet (906) and the heating sheet (907) are both semiconductor refrigeration sheets, the cold end of the refrigeration sheet (906) is attached to the barrel wall of the cartridge section (901), and the hot end of the heating sheet (907) is attached to the barrel wall of the cartridge section (901); the refrigeration sheet (906) and the heating sheet (907) are alternately attached to the barrel wall of the cartridge section (901) at intervals, and the refrigeration sheet (906) and the heating sheet (907) are attached to the barrel wall in a strip shape along the axial direction of the cartridge section (901).

4. The variable pitch twin screw extruder of claim 1, wherein: The screw water guide (5) comprises a water guide shell (501), two water guide rings (504) are arranged in the shell cavity of the water guide shell (501), two water guide bolts (502) are further arranged on the water guide shell (501), each water guide ring (504) corresponds to a water guide bolt (502); the two water guide bolts (502) are respectively connected to the screw water cavity (403) and the water delivery pipe (404) through the corresponding water guide ring (504).

5. A variable pitch twin screw extruder according to claim 4, characterized in that: The water guide cavity rib plate (511) of the water guide ring (504) is provided with a water guide hole (510), the water supply cavity (513) and the water distribution cavity (514) located on both sides of the water guide cavity rib plate (511) are connected through the water guide hole (510), and the water distribution cavity (514) is connected with the corresponding water guide bolt (502).

6. A variable pitch twin screw extruder according to claim 5, characterized in that: The water guide ring (504) is provided with a water ring seal at both ends, the water ring seal comprises a movable ring (509) embedded in the water guide ring (504), a static ring (508) corresponding to the movable ring (509) is mounted on a static ring seat (507), and the static ring seat (507) is sealingly mounted on the water guide shell (501).

7. A variable pitch twin screw extruder according to claim 6, characterized in that: The static ring seat (507) and the end cover (506) are provided with an end spring (505), the static ring seat (507) located on the inner side of the water guide ring (504) is provided with an intermediate spring (503), and the end cover (506) is fixedly mounted on both ends of the water guide shell (501).

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