CN206690514U - A kind of special extrusion screw rod of heat-proof polythene - Google Patents

Abstract

The utility model discloses a special extruding screw for heat-resistant polyethylene. The screw includes a feeding section, a compression section, a first metering section, a decompression section, a second metering section, a mixing section and a screw head. The feeding section , the compression section, the first metering section, the decompression section, the second metering section, the mixing section and the screw head are sequentially connected, and the feeding section, the decompression section, the first metering section and the second metering section all adopt single-head threads Structure; the compression section adopts a double thread structure consisting of a main thread and an additional thread, the additional thread intersects the main thread on the side of the feeding section, and does not intersect the main thread on the side of the first metering section; the mixing The segment adopts trapezoidal structure. The utility model has the advantages of simple structure, convenient use, high melting efficiency, uniform plasticization, high conveying capacity, high and stable output under high rotating speed.

Description

A special extrusion screw for heat-resistant polyethylene

technical field

The utility model relates to a plastic extruding screw, in particular to a special extruding screw for heat-resistant polyethylene, which belongs to the production field of heat-resistant polyethylene pipes.

Background technique

As shown in Figure 1, it is a structural schematic diagram of the existing common polyolefin extrusion screw. The screw is a single-flight structure, generally including a feeding section 1, a compression section 2, a metering section 3 and a screw head 4. When the plastic enters from the hopper In the barrel, the material enters the feeding section 1, and under the action of the screw rotation, it is gradually transported forward to the compression section 2 through the friction between the inner wall of the barrel and the surface of the screw. The depth of the screw groove in the compression section 2 becomes shallower, and the solid material is further compressed. At the same time, it is heated outside the barrel, and under the action of friction and shear between the screw and the inner wall of the barrel, the material heats up and begins to melt, and the melted material enters the metering section 3, which quantitatively extrudes the material from the screw head 4. melt.

The Chinese invention patent application with the application publication number CN101774269A discloses a high-speed PB (Polybutene, polybutene) pipe single screw, including a feeding section, a separate melting section, and a mixing extrusion section. The separate melting section is set There is one main flight and two auxiliary flights, which solve the problems that the existing PB pipe screw is difficult to increase productivity at high speed, the plasticizing quality is not good, and the melt temperature is too high, and the plasticizing quality is good and the productivity is high. High (300Kg/hour) PB molten plastic.

The Chinese utility model patent with the authorized announcement number CN201669874U discloses a high-speed extrusion single-screw for polypropylene. The separation section is provided with a main flight and an auxiliary flight. Compared with the prior art, the utility model has the beneficial effects that the geometric compression ratio of the compression section is reduced, the conveying capacity of the material is improved, and combined with the high-speed rotating screw, the plasticizing time of the material from the solid state to the viscous flow state is greatly shortened. , reduce the extrusion temperature of polypropylene, increase the pressure of polypropylene on the machine head, thereby enhancing the material density of the extruded product, not only can realize high-speed and high-yield extrusion of polypropylene, but also can realize low-temperature extrusion of polypropylene .

The Chinese utility model patent with the authorized announcement number CN201317096Y discloses a high-yield extrusion screw for PE (Polyethylene, polyethylene) plastic pipes, which adopts a three-stage structure, which is a feeding section, a melting section, and an extrusion section in sequence. The feeding section adopts Single thread structure, the melting section adopts double-thread separation structure, and the extrusion section adopts mixing structure. The feeding section adopts a single-thread structure, which is conducive to the high-speed and stable transportation of materials; the melting section adopts a double-thread separate structure, which is conducive to the melting and plasticization of materials; the extrusion section adopts a mixing structure, which is conducive to the material Compounding and high-throughput extrusion.

The Chinese utility model patent whose authorized notification number is CN203665916U discloses a plastic extrusion single screw. It includes a feeding section, a melting separation section, a barrier section and a mixing section. The feeding section, the melting separation section, the barrier section and the mixing section are all provided with screw edges, and the feeding section is a double-pitch structure. The utility model can reduce the friction and slipping between the plastic granules and improve the efficiency of the screw conveying material; through the gradual increase of the screw pitch of the double screw edge section, the gradual transition of the melt pressure between the screw edge of the feeding section and the melting separation section is realized, ensuring that The pressure of the melt is stable; the bottom diameter of the helix increases from small to large, and the feeding space formed between it and the blanking bush is reduced, thereby generating greater pressure to push the melt in the melting separation section forward.

At present, the disadvantages of the extruding screw in the prior art are: 1) the pressure of the entire screw is established by the pressure of the feeding section. When the head pressure is high, this will reduce the feeding capacity of the screw; 2) the output of the screw is affected by the machine The impact of the head pressure is obvious, and the plastic extrusion fluctuates greatly; 3) The plasticizing effect of the material is not good, the melting efficiency is low, the mixing is not uniform enough, and the output is not high; 4) When the output is high, the plasticization is relatively poor and the melt temperature difference is relatively large , Production volatility is relatively large.

Polyethylene of raised temperature resistance (PE-RT) raw material, as a polyethylene material, has a lower degree of shear thinning than polypropylene (PP) during shearing, so it is used in high-speed production A better shearing effect is needed to meet the plasticizing requirements of the raw material; however, due to the narrow molecular weight distribution of the heat-resistant polyethylene raw material and the small processing temperature range, oxidative degradation will occur in a short time at a temperature higher than the decomposition temperature, so it must be Avoid the situation of strong shear, but it must be fully plasticized during processing. Therefore, the current polyolefin extrusion screw is not suitable for the production of heat-resistant polyethylene pipes. Therefore, it is necessary to design a new type of high-efficiency heat-resistant polyethylene screw to improve production efficiency.

Utility model content

The purpose of this utility model is to overcome the defects of the above-mentioned prior art and provide a special extrusion screw for heat-resistant polyethylene. The screw has simple structure, convenient use, high melting efficiency, uniform plasticization, high conveying capacity, and high The output is high and stable under the rotating speed.

The purpose of this utility model can be achieved through the following technical solutions:

A special extrusion screw for heat-resistant polyethylene, including a feeding section, a compression section and a screw head, and also includes a first metering section, a decompression section, a second metering section and a mixing section, the feeding section, the compression section, the first The metering section, the decompression section, the second metering section, the mixing section and the screw head are sequentially connected, and the feeding section, the decompression section, the first metering section and the second metering section all adopt a single-head thread structure; the compression section A double-start thread structure consisting of a main thread and an additional thread is adopted. The additional thread intersects the main thread on the side of the feeding section, and does not intersect the main thread on the side of the first metering section; the mixing section adopts a trapezoidal structure.

Further, the single-start thread structure on the feeding section forms a feeding groove, the single-start thread structure on the first metering section forms a first metering groove, and the single-start thread structure on the decompression section forms a decompression groove , the single-start thread structure on the second metering section forms a second metering tank, the double-start thread structure on the compression section forms a solid-phase tank communicating with the feeding tank, and a liquid-phase tank communicating with the first metering tank. phase trough.

Further, the bottom of the solid-phase tank extends along the bottom of the feeding tank to the bottom of the first metering tank, and the width of the solid-phase tank gradually decreases from the feeding section to the first metering section. The width of the solid phase tank is the same as the width of the feed tank, and the width of the solid phase tank on the first metering section side is 0.1 to 0.2 times the width of the first metering tank; The outer surface of the thread extends toward the bottom of the first metering tank, and the width of the liquid phase tank gradually increases from the feeding section to the first metering section, and the width of the liquid phase tank on the side of the feeding section is 0.06 to 0.15 times the width of the feeding tank , the width of the liquid phase tank on the side of the first metering section is 0.7 to 0.9 times the width of the first metering tank.

Further, the depth of the feeding tank and the depth of the decompression tank are both greater than the depth of the first metering tank, and the depth of the second metering tank is smaller than the depth of the decompression tank.

Further, the width of the feeding groove is smaller than the outer diameter of the screw, and the widths of the first metering groove, the decompression groove and the second metering groove are all larger than the outer diameter of the screw.

Further, the outer diameter of the additional thread on the compression section is 2.5-5mm smaller than the outer diameter of the main thread.

Further, the lead of the main thread is not equal to the lead of the additional thread, and the lead of the main thread is 1.1-2.1 times of the outer diameter of the screw, and the lead of the additional thread is 0.8-1.8 times of the outer diameter of the screw.

Further, the cross-sectional shape of the mixing section is rectangular, and the area of the bottom surface is larger than the area of the top surface. The trapezoidal structure is composed of a plurality of trapezoidal bodies, and the distance between any two adjacent trapezoidal bodies is the same. Each trapezoidal body is divided into multiple rows in the axial direction of the screw rod, and the trapezoidal bodies in each row are arranged circularly on the circumference of the screw rod.

Further, the effective length of the screw is 34 to 40 times the outer diameter of the screw, the length of the feeding section is 5 to 10 times the outer diameter of the screw, and the length of the compression section is 10 to 21 times the outer diameter of the screw , the length of the first metering section is 2 to 6 times the outer diameter of the screw, the length of the decompression section is 1 to 5 times the outer diameter of the screw, and the length of the second metering section is 5 times the outer diameter of the screw. ~11 times, the mixing section is 2~8 times the outer diameter of the screw.

Compared with the prior art, the utility model has the following advantages and beneficial effects:

1. In the extrusion screw of the present utility model, the feeding section adopts a single-head thread structure, which improves the feeding capacity. The compression section adopts a double-head thread structure composed of a main thread and an additional thread. The additional thread is on the side of the feeding section and the main thread. Intersecting, the side of the first metering section does not intersect with the main thread, the optimized double-start thread structure enhances the melting and plasticizing effect, improves the blockage of materials in the compression section, and improves the plasticizing capacity. The mixing section adopts trapezoidal shape The solid structure has a mixing effect on the material, the distribution and mixing ability of the screw is strengthened, the uniformity in the vertical and horizontal directions is improved, the mixing effect is good, and the dispersion is good.

2. In the extrusion screw of the present utility model, the single-head thread structure of the feeding section forms a feeding groove, the single-head thread structure of the first metering section forms the first metering groove, and the double-head thread structure of the compression section forms a connection with the feeding groove. The solid phase tank and the liquid phase tank connected with the metering tank, the solid phase material entering from the feeding tank can enter the compression section smoothly without hindering the feeding. Under the operation of the screw and the external heating of the barrel, the solid phase After melting, the material enters the liquid phase tank through the additional thread, which improves the melting and plasticizing effect of the material in the barrel, and the material in the solid phase tank can be continuously heated to increase the heat exchange area of the solid phase material, and a small amount of unmelted The solid phase material can also enter the metering section smoothly, without strong shear force or hindering the feeding, shortening the melting length and relatively lowering the temperature of the melting material as a whole, which is conducive to low-temperature extrusion and avoiding overheating of the material.

3. In the extrusion screw of the present utility model, the single-head thread structure of the decompression section forms a decompression groove, and the depth of the decompression groove is greater than the depth of the first metering groove. Because the decompression groove is deep, the impact of the pressure on the machine head is reduced. The influence of the feeding capacity of the feeding section reduces the pressure in the barrel and reduces the wear of the screw and the barrel.

4. The effective length of the extrusion screw of the utility model is 34 to 40 times of the outer diameter of the screw. It can be seen that the ratio of length to diameter is relatively large, which can increase the speed of the screw and ensure the residence time of the material in the barrel under the state of high speed of the screw. , to make it fully plasticized, thereby increasing the extrusion volume.

5. The extrusion screw of the utility model has a simple structure and a reasonable design, and can obtain heat-resistant polyethylene pipes with high rotational speed, high specific output, good plasticizing quality, accurate measurement, and low melt temperature, and the maximum extrusion volume can reach 550kg /h, compared with the general-purpose single-screw of the same specification, the melt temperature is lowered by 3°C, which can achieve better dispersion and distribution effects. The masterbatch can be mixed evenly with raw materials, and the coloring effect is good. The produced durable The appearance quality of thermal polyethylene pipe is good, the outer wall is bright without lines, the inner wall is smooth without fusion lines, and the end face has no appearance quality defects such as black spots.

Description of drawings

Fig. 1 is the structural representation of extruding screw rod in the prior art

Fig. 2 is a structural schematic diagram of the special extrusion screw for heat-resistant polyethylene in Example 1 of the present invention.

Fig. 3 is a structural schematic diagram of the feeding section of the special extrusion screw for heat-resistant polyethylene in Example 1 of the present invention.

Fig. 4 is a structural schematic diagram of the compression section in the extrusion screw dedicated to heat-resistant polyethylene in Example 1 of the present invention.

Fig. 5 is a structural schematic diagram of the first metering section in the special extrusion screw for heat-resistant polyethylene in Example 1 of the present invention.

Fig. 6 is a structural schematic diagram of the decompression section in the extrusion screw dedicated to heat-resistant polyethylene in Example 1 of the present invention.

Fig. 7 is a structural schematic diagram of the second metering section and the mixing section in the special extrusion screw for heat-resistant polyethylene in Example 1 of the present invention.

Among Fig. 1, 1-feeding section, 2-compression section, 3-metering section, 4-screw head;

In Fig. 2 to Fig. 7, 5-feeding section, 51-feeding tank, 6-compression section, 61-solid phase tank, 62-liquid phase tank, 63-main thread, 64-additional thread, 7-first metering section , 71-first metering tank, 8-decompression section, 81-decompression tank, 9-second metering section, 91-second metering tank, 10-mixing section, 11-screw head.

detailed description

The utility model will be further described in detail below in conjunction with the embodiments and accompanying drawings, but the implementation of the utility model is not limited thereto.

Example 1:

As shown in Figures 2 to 7, the special extrusion screw for heat-resistant polyethylene in this embodiment includes a feeding section 5, a compression section 6, a first metering section 7, a decompression section 8, a second metering section 9, and a mixing section 10 With the screw head 11, the feeding section 5, the compression section 6, the first metering section 7, the decompression section 8, the second metering section 9, the mixing section 10 and the screw head 11 are connected successively, and the outer diameter of the screw is 70mm. The effective length is 38 times the outer diameter of the screw, and the larger aspect ratio (the ratio of the length of the screw to the outer diameter of the screw) can ensure the residence time of the material in the barrel under the condition of high screw speed, so that it can be fully plasticized.

The feeding section 5 adopts a single thread structure, and the single thread structure forms a feeding groove 51, the width of the feeding groove 51 is smaller than the outer diameter of the screw rod, and remains unchanged, and the depth of the feeding groove 51 is 0.12 times the outer diameter of the screw rod, and remains unchanged. The thread width is 0.08 times the outer diameter of the screw, and the length of the feeding section 5 is 6 times the outer diameter of the screw. Due to the single-start thread structure, the feeding capacity can be improved.

The first metering section 7 adopts a single-start thread structure, and the single-start thread structure forms a first metering groove 71. The width of the first metering groove 71 is greater than the outer diameter of the screw rod and remains unchanged. The depth of the first metering groove 71 is 0.1 times the outer diameter of the screw, less than the depth of the feeding tank 51, and remains unchanged, the thread width is 0.08 times the outer diameter of the screw, and the length of the first metering section 7 is 3 times the outer diameter of the screw; because the depth of the feeding tank 51 is greater than the first metering The depth of the groove 71 can form an appropriate compression ratio.

The compression section 6 adopts a double-start thread structure consisting of a main thread 63 and an additional thread 64. The lead of the main thread 63 is not equal to the lead of the additional thread 64, and the lead of the main thread 63 is 1/2 of the outer diameter of the screw 64. 1.1 to 2.1 times, the lead of the additional thread is 0.8 to 1.8 times the outer diameter of the screw, the pitch of the main thread 63 of the entire compression section 6 is different, and the pitch of the additional thread 64 is also different, and the additional thread 64 is in the feeding section 5 One side intersects with the main screw thread 63, and does not intersect with the main screw thread 63 on the first metering section 7 side, forming a solid phase tank 61 communicated with the feeding tank 51, and a liquid phase tank 62 communicated with the first metering tank 71 , the solid phase material entering from the feeding tank 51 can smoothly enter the compression section 6 without hindering the feeding. Under the operation of the screw and the external heating of the barrel, the solid phase material melts and crosses the additional thread 64 to enter the liquid phase tank 62. The melting and plasticizing effect of the material in the barrel is improved, and the material in the solid phase tank 61 can be continuously heated to increase the heat exchange area of the solid phase material, and a small amount of unmelted solid phase material can also enter smoothly In the first metering section 7, there will be no strong shearing force or impeding feeding, shortening the melting length and relatively lowering the temperature of the melting material as a whole, which is beneficial to low-temperature extrusion and avoiding overheating of the material;

The bottom of the solid-phase tank 61 extends along the bottom of the feeding tank 51 to the bottom of the first metering tank 71, and the width of the solid-phase tank 61 gradually decreases from the feeding section 5 to the first metering section 7. In the feeding section 5 The width of the solid phase tank 61 on one side is the same as the width of the feeding tank 51, and the width of the solid phase tank 61 on the first metering section 7 side is 0.1～0.2 times of the width of the first metering tank 71; The additional thread outer surface on one side of the feeding section extends towards the bottom of the first metering tank 71, and the width of the liquid phase tank 62 gradually increases from the feeding section 5 to the first metering section 7, and in this embodiment gradually increases from 3 mm to Close to the width of the first metering tank 71, the width of the liquid phase tank 62 on one side of the feeding section is 0.06 to 0.15 times the width of the feeding tank 51, and the width of the liquid phase tank 62 on the side of the first metering section 7 is the first metering tank. 0.7 to 0.9 times the width of 71; the width of the solid phase tank 61 gradually decreases, and the width of the liquid phase tank 62 gradually increases, which can effectively improve the stability of the material running in the screw and is conducive to high-speed operation;

The outer diameter of the additional thread 64 is 4.0mm smaller than the outer diameter of the main thread 63, which will not generate strong shear force and is conducive to the high-speed rotation of the screw; the width of the main thread 63 is 0.08 times the outer diameter of the screw, and the width of the additional thread 64 is 0.05 times the outer diameter of the screw, the length of the entire compression section 6 is 17 times the outer diameter of the screw, which is beneficial to ensure that the main thread 63 pushes the solid-phase material to move and promotes its melting, and at the same time facilitates the separation of the melted solid-phase material by the additional thread 64.

The decompression section 8 adopts a single thread structure, the decompression section 8 separates the first metering section 7 and the second metering section 9, and the compression ratio and thread depth can be independently designed. The purpose of the decompression section 8 is to reduce extrusion The pressure in the barrel of the machine can have a constant specific flow rate even at a very high speed, which is suitable for high-speed extrusion; the single-thread structure forms a decompression groove 81, and the width of the decompression groove 81 is larger than the outer diameter of the screw. The embodiment is 1.2 times of the outer diameter of the screw, and remains unchanged. The depth of the decompression groove 81 is 2mm larger than the depth of the first metering groove 71, and remains unchanged. The output of the screw is stable under the high rotating speed, and is not affected by pressure and speed. Influence; the thread width is 0.08 times the outer diameter of the screw, and the length of the decompression section 8 is 2 times the outer diameter of the screw.

The second metering section 9 adopts a single-start thread structure, which forms a second metering groove 91, and the width of the second metering groove 91 is greater than the outer diameter of the screw, which is 1.2 times the outer diameter of the screw in this embodiment, and remains unchanged , the depth of the second metering groove 91 is 0.08 times the outer diameter of the screw, less than the depth of the decompression groove 81, and remains unchanged; the thread width is 0.08 times the outer diameter of the screw, and the length of the second metering section 9 is 7 times the outer diameter of the screw .

The cross-sectional shape of the mixing section 10 is a rectangle, and the area of its bottom surface is greater than the area of the top surface. The mixing section 10 adopts a trapezoidal (trapezoidal polyhedron) structure, and the trapezoidal structure is composed of 48 trapezoidal bodies. The spacing between the adjacent trapezoids is the same, and the 48 trapezoids are divided into 6 rows in the axial direction of the screw, and each row has 8 trapezoids arranged circularly on the screw circumference; the length of the mixing section 10 is 3 times the outer diameter of the screw.

The working principle of the special extrusion screw for heat-resistant polyethylene in this embodiment is as follows:

1) The material enters the feeding section 5 of the screw from the hopper, and is gradually pushed to the screw head 11 and compacted under the action of the screw speed under the action of the screw speed, and is gradually melted under the shear of the screw and the barrel and the action of the external heater;

2) In the compression section 6 of the screw, the material starts to melt during the conveying process. Under the push of the screw, the melted material crosses the additional thread 64 and enters the liquid phase tank 62, while the unmelted solid particles are blocked by the additional thread 64, Still in the solid phase tank 61, thereby realizing the separation of the melted material and the unmelted material, forming a melt material at the place where the solid phase tank 61 and the liquid phase tank 62 meet, the melting is basically completed at this time, and the melted plastic and solid The plastic is separated, so that the shearing of the melted plastic is reduced, thereby realizing low-temperature extrusion, which also provides conditions for realizing the high-speed operation of the screw;

3) After passing through the first metering section 7 and the decompression section 8, in the second metering section 9 of the screw, under the push of the thread, due to the longer length, it is easy to establish a higher melt pressure, which can be as accurate as a metering pump, Quantitative delivery of melt materials, increase positive flow, reduce pressure flow and leakage flow, and make plasticization more fully and uniformly;

4) In the mixing section 10 of the screw, on the one hand, the trapezoidal body breaks the solid material, destroys the melt, disrupts the two-phase flow of solid and liquid, and repeatedly separates and merges the material flow, changing the material flow in the barrel The internal direction and velocity distribution make the solid phase and the liquid phase fully mixed, increase the heat transfer area between the solid phase and the liquid phase, and generate a certain resistance and friction shear to the material, so that the solid phase melts. On the other hand, it is The material is divided, divided and merged multiple times to increase the dispersion of additives and color masterbatches.

According to the experiment, compared with ordinary screw, the radial temperature difference of the extrudate can be reduced by 1-3°C, and the lateral temperature difference can be reduced by 2-5°C; the solid phase continuously absorbs heat from the melt during the melting process, and it is possible The temperature of the melt is lowered, the material is divided, divided and merged multiple times, and the direction and position of the material change during the movement, so that the different components in the material can be well dispersed and mixed, so that the mixture can be uniform and low temperature extrudates.

Example 2:

The main feature of this embodiment is that the outer diameter of the additional thread 64 on the compression section 6 is 2.5 mm smaller than the outer diameter of the main thread 63 . All the other are with embodiment 1.

Example 3:

The main feature of this embodiment is that the outer diameter of the additional thread 64 on the compression section 6 is 5mm smaller than the outer diameter of the main thread 63 . All the other are with embodiment 1.

Example 4:

The main features of this embodiment are: the effective length of the screw is 34 times, the length of the feeding section 5 is 5 times of the outer diameter of the screw, the length of the compression section 6 is 11 times of the outer diameter of the screw, and the length of the first metering section 7 is The length is 6 times of the outer diameter of the screw, the length of the decompression section 8 is 5 times of the outer diameter of the screw, the length of the second metering section 9 is 5 times of the outer diameter of the screw, and the mixing section 10 is 2 times of the outer diameter of the screw. All the other are with embodiment 1.

Example 5:

The main features of this embodiment are: the effective length of the screw is 40 times, the length of the feeding section 5 is 4 times of the outer diameter of the screw, the length of the compression section 6 is 15 times of the outer diameter of the screw, and the length of the first metering section 7 is The length is 6 times of the outer diameter of the screw, the length of the decompression section 8 is 5 times of the outer diameter of the screw, the length of the second metering section 9 is 6 times of the outer diameter of the screw, and the mixing section 10 is 4 times of the outer diameter of the screw. All the other are with embodiment 1.

In summary, the extrusion screw of the utility model has a simple structure and a reasonable design, and can obtain heat-resistant polyethylene pipes with high rotational speed, high specific output, good plasticizing quality, accurate measurement, and low melt temperature. It can reach 550kg/h. Compared with the general-purpose single-screw of the same specification, the melt temperature is lowered by 3°C, which can achieve better dispersion and distribution effects. The masterbatch can be mixed evenly with raw materials, and the coloring effect is good. Production The heat-resistant polyethylene pipe produced has good appearance quality, with bright outer wall without lines, smooth inner wall without fusion lines, and no black spots on the end surface and other appearance quality defects.

The above is only a preferred embodiment of the utility model patent, but the scope of protection of the utility model patent is not limited thereto, any skilled person familiar with the technical field within the disclosed scope of the utility model patent, according to The technical scheme of the utility model patent and the equivalent replacement or change of the utility model patent concept all belong to the protection scope of the utility model patent.

Claims (9)

1. A special extrusion screw for heat-resistant polyethylene, comprising a feeding section, a compression section and a screw head, characterized in that: it also includes a first metering section, a decompression section, a second metering section and a mixing section, the feeding section , the compression section, the first metering section, the decompression section, the second metering section, the mixing section and the screw head are connected sequentially, and the feeding section, the decompression section, the first metering section and the second metering section all adopt single-head threads Structure; the compression section adopts a double thread structure consisting of a main thread and an additional thread, the additional thread intersects with the main thread on the side of the feeding section, and does not intersect with the main thread on the side of the first metering section; the mixing The segment adopts trapezoidal structure. 2. A special extrusion screw for heat-resistant polyethylene according to claim 1, characterized in that: the single-start thread structure on the feeding section forms a feeding groove, and the single-start thread structure on the first metering section The first metering groove is formed, the single-start thread structure on the decompression section forms a decompression groove, the single-start thread structure on the second metering section forms a second metering groove, and the double-start thread structure on the compression section A solid phase tank communicated with the feeding tank and a liquid phase tank communicated with the first metering tank are formed. 3. A special extrusion screw for heat-resistant polyethylene according to claim 2, characterized in that: the bottom of the solid phase tank extends along the bottom of the feeding tank to the bottom of the first metering tank, and the solid phase The width of the phase tank gradually decreases from the feeding section to the first metering section, the width of the solid phase tank on the side of the feeding section is the same as the width of the feeding tank, and the width of the solid phase tank on the side of the first metering section is the width of the first metering tank 0.1 to 0.2 times of that of the liquid phase tank; the bottom of the liquid phase tank extends from the additional threaded outer surface on the side of the feeding section to the bottom of the first metering tank, and the width of the liquid phase tank gradually increases from the feeding section to the direction of the first metering section Large, the width of the liquid phase tank on the side of the feeding section is 0.06 to 0.15 times the width of the feeding tank, and the width of the liquid phase tank on the side of the first metering section is 0.7 to 0.9 times the width of the first metering tank. 4. A heat-resistant polyethylene special-purpose extrusion screw according to claim 2 or 3, characterized in that: the depth of the feeding tank and the depth of the decompression tank are greater than the depth of the first metering tank, and the depth of the first metering tank is The depth of the second metering groove is less than the depth of the decompression groove. 5. A heat-resistant polyethylene special-purpose extrusion screw according to claim 2 or 3, characterized in that: the width of the feeding groove is smaller than the outer diameter of the screw, and the first metering groove, the decompression groove and the second The width of the metering grooves is larger than the outer diameter of the screw. 6. A special heat-resistant polyethylene extrusion screw according to any one of claims 1-3, characterized in that: the outer diameter of the additional thread on the compression section is 2.5-5mm smaller than the outer diameter of the main thread. 7. A special heat-resistant polyethylene extrusion screw according to any one of claims 1-3, characterized in that: the lead of the main thread is not equal to the lead of the additional thread, and the lead of the main thread is 1.1 to 2.1 times the outer diameter of the screw, and the lead of the additional thread is 0.8 to 1.8 times the outer diameter of the screw. 8. A heat-resistant polyethylene special-purpose extrusion screw according to any one of claims 1-3, characterized in that: the cross-sectional shape of the mixing section is rectangular, and the area of its bottom surface is greater than that of its top surface, so The trapezoidal structure is composed of multiple trapezoidal bodies, the distance between any two adjacent trapezoidal bodies is the same, the multiple trapezoidal bodies are divided into multiple rows in the axial direction of the screw, and the trapezoidal bodies in each row are arranged circularly on the circumference of the screw rod . 9. A special extrusion screw for heat-resistant polyethylene according to any one of claims 1-3, characterized in that: the effective length of the screw is 34 to 40 times the outer diameter of the screw, and the The length is 5 to 10 times the outer diameter of the screw, the length of the compression section is 10 to 21 times the outer diameter of the screw, the length of the first metering section is 2 to 6 times the outer diameter of the screw, and the decompression section The length of the second metering section is 5 to 11 times the outer diameter of the screw, and the length of the mixing section is 2 to 8 times the outer diameter of the screw.