CN206967928U - Strongly tensile differential multi-screw extruder in the same direction - Google Patents

Abstract

The utility model discloses a multi-screw extruder with strong stretching and differential speed in the same direction. The screw mechanism in the extruder includes a first screw and a second screw that engage with each other, and the first screw includes a first forward conveying that is sequentially connected. element, the first mixing element and the first reverse conveying element, the second screw includes the second forward conveying element, the second mixing element and the second reverse conveying element connected in sequence, the outer diameter of the first screw is the same as that of the second The outer diameters of the two screws are not equal. The processing method is that after the material enters the inner cavity of the machine barrel, the material is conveyed under the joint action of the axial positive displacement conveying force of the screw mechanism and the friction force between the first screw and the second screw; at the same time, the first screw is used to The speed difference and diameter difference between the second screw and the second screw produce a strong stretching effect, so that the material is fully mixed, melted and kneaded and plasticized during the conveying process. The utility model utilizes the strong stretching effect produced by the two screw rods with different rotating speeds and different diameters to strengthen the process of mixing and kneading and heat transfer.

Description

Strong drawing co-rotating differential speed multi-screw extruder

technical field

The utility model relates to the technical field of multi-screw extruders, in particular to a multi-screw extruder with strong stretching and differential speed in the same direction.

Background technique

The co-rotating twin-screw extruder with self-cleaning function is a widely used mixing processing equipment at present. This type of twin-screw extruder only provides disturbance in the meshing area to improve the mixing quality, and lacks a chaotic mixing trigger mechanism away from the meshing area. Moreover, the volume of the material in the left and right screw channels is the same, and the effect of the tensile force field is small. The main part of the volume lacks a structure that can effectively improve the mixing, which will lead to the inability to further improve the distribution mixing effect, and the lack of the tensile force field effect will lead to unsatisfactory dispersion mixing. In addition, most of the processing process of the twin-screw extruder is in a non-full state, and the almost unchanged flow path leads to a great reduction in the plasticization and mixing of materials. In order to improve the mixing effect and increase the output, high speed is often used to achieve high shear in engineering practice. Cutting, the large length-to-diameter ratio screw prolongs the processing process, but this method brings many problems such as high energy consumption, low efficiency and material degradation. In recent years, differential twin-screw extrusion technology has emerged, which uses the speed difference between the two screws to strengthen the melting and mixing during processing. Although chaotic mixing and tensile force field effects have been successfully introduced, it cannot provide stronger tensile strength. Therefore, the processing of micro-scale and nano-materials still faces great challenges.

Utility model content

The purpose of the utility model is to overcome the deficiencies of the prior art and provide a strong stretching multi-screw extruder with differential speed in the same direction. The extruder with this structure can produce a strong stretching force field effect and accelerate the melting efficiency. Achieve excellent dispersion and mixing effect, effectively reduce the particle size of the dispersed phase, and improve processing efficiency.

The technical scheme of the utility model is: a strong stretching co-directional differential multi-screw extruder, including a barrel and a screw mechanism, the screw mechanism is installed in the inner cavity of the barrel, and the screw mechanism includes first screw rods that mesh with each other And the second screw, the first screw includes the first forward conveying element, the first mixing element and the first reverse conveying element connected in sequence, the second screw includes the second forward conveying element, the second mixing element and the second reverse conveying element, the outer diameter of the first screw is not equal to the outer diameter of the second screw. Wherein, the outer diameters of the first screw and the second screw are different, resulting in a greater difference in the linear velocity of the two screws and a greater difference in the flow channel volume of the two screws, which makes the stretching effect of the two screws stronger under the action of the differential speed.

In the first screw, the first forward conveying element, the first kneading element and the first reverse conveying element are all single-start screw structures; in the second screw, the second forward conveying element, the second kneading element and the second reverse conveying element are both double-start thread structures. Both the outer contours of the first screw and the second screw are tangent to the inner wall of the barrel, and a flow channel is formed between the screw mechanism and the inner cavity of the barrel.

As a preferred solution, in the first screw, the outer peripheral edge of the first kneading element is a discontinuous flight structure with a first notch, and the overall outer contour shape of the first kneading element is consistent with the first positive direction Conveying elements are the same;

In the second screw, the outer peripheral edge of the second mixing element is a discontinuous flight structure with a second notch, and the overall shape of the second mixing element is the same as that of the second forward conveying element;

Both the first notch and the second notch are semi-cylindrical groove structures. The mixing element of this structure can provide more powerful distributive mixing ability, but its self-cleaning ability will be reduced compared to the screw structure with smooth edges.

As another preferred solution, in the first screw, the first kneading element is a combined structure formed by connecting multiple first kneading blocks;

In the second screw, the second kneading element is a combined structure formed by connecting multiple second kneading blocks. In addition to providing fully self-cleaning mixing with positive displacement conveying capacity and super large output, the mixing element of this structure also introduces a stronger tensile force field effect to provide more powerful dispersion and mixing capabilities.

In addition, the first mixing element can also adopt the same screw structure as the first forward conveying element, and the second mixing element can also adopt the same screw structure as the second forward conveying element, that is, the first The peripheral edges of both the mixing element and the second mixing element are of smooth helicoidal construction, which provides a fully self-cleaning mix with positive displacement conveying capacity for high throughput.

The first screw and the second screw rotate in the same direction and keep meshing at all times, the speed ratio between the first screw and the second screw is 2 to 7, that is, the speed of the first screw is 2 to 7 times that of the second screw, Or the rotational speed of the second screw is 2-7 times of the rotational speed of the first screw. In this structure, the speed ratio between the first screw and the second screw is 2 to 7 as the optimal solution. Theoretically, the larger the speed ratio is, the smaller the depth of the screw groove between the first screw and the second screw will be. The mixing effect will be better, but when the speed ratio is too large, the depth of the screw groove is close to zero, which cannot be realized geometrically. When the speed ratio is less than 2, the differential speed effect is not obvious, and the stretching effect on the material is considerable. Weak, can not achieve the effect of strong stretching effect.

Among the first screw and the second screw, one of the screws is a large-diameter screw, the other is a small-diameter screw, the ratio of the outer diameter to the inner diameter of the large-diameter screw is 1.1 to 1.8, and the outer diameter of the small-diameter screw is The ratio to the inner diameter is 1.1 to 4.5. It has been proved by experiments that combined with the speed ratio of the first screw and the second screw, the ratio of the inner and outer diameters can better ensure that the groove depth of the two screws and the strong tensile effect on the material are in the best state, thereby maximizing To improve its strong tensile effect.

The radial cross-sectional profile of the first screw is composed of multiple arcs with unequal radii of curvature and multiple non-circular arcs with unequal radii of curvature connected alternately, and the radial cross-sectional profile of the second screw is also composed of multiple segments with unequal radii of curvature Circular arcs and non-circular curved arcs with unequal curvature radii are connected alternately; the total number of circular arcs and non-circular curved arcs that constitute the radial cross-sectional profile of the second screw is equal to the circular arcs and non-circular arcs that constitute the radial cross-sectional profile of the first screw. 2 to 7 times the total number of curved arcs.

The screw mechanism also includes a third screw, the first screw, the second screw and the third screw are engaged in sequence to form a three-screw arrangement of "in-line" or "non-in-line", and the structure of the third screw is the same as that of the first screw. A screw is the same.

The barrel is provided with a conveying section, a melting section, an exhaust section and a mixing and extruding section which are sequentially connected along the material conveying direction. There is an exhaust port connected to the inner cavity of the barrel, and a discharge port is provided at the end of the mixing extrusion section;

In the screw mechanism, the first screw includes the first forward conveying element, the first mixing element, the first reverse conveying element and the first forward conveying element connected in sequence along the material conveying direction, and the second screw includes the first forward conveying element along the material conveying direction. The second forward conveying element, the second kneading element, the second reverse conveying element and the second forward conveying element connected in sequence;

Wherein, the first mixing element and the second mixing element are located in the barrel in the middle of the melting section, and the first reverse conveying element and the second reverse conveying element are located in the barrel at the rear of the melting section.

The processing method realized by the utility model through the above-mentioned strong stretching co-directional differential multi-screw extruder is: after the material enters the inner cavity of the machine barrel, the axial positive displacement conveying force of the screw mechanism and the first screw and the second screw Under the joint action of the friction force between the two screws, the material transportation is realized; at the same time, the speed difference and the diameter difference between the first screw and the second screw are used to generate a strong stretching effect, so that the materials are fully mixed, melted and mixed during the transportation process. plasticizing;

Among them, in the screw mechanism, a stretching effect occurs between the first screw and the second screw; an interface renewal effect occurs between the first mixing element and the first reverse conveying element, and the second mixing element and the second reverse conveying element There is also an interface renewal effect between the conveying elements, thereby enhancing the heat transfer process; coupled with the frictional heat generated by the high-speed rotation of the first screw and the second screw; and the external heating of the barrel; the four factors work together to further melt the material, Accelerate the separation of melt and solid in the material, further accelerate the melting process of the solid, so that all the material forms a melt.

In the above method, the processing of the material in the barrel is as follows:

(1) After the material enters the corresponding flow channel of the conveying section from the feed port, the first screw and the second screw rotate in the same direction and at a differential speed along their respective screw axes; when the axial positive displacement of the first screw and the second screw The conveying force and the frictional force between the first screw and the second screw realize the feeding and conveying, and force the material to move to the direction of the flow channel corresponding to the melting section;

(2) When the material moves to the flow channel corresponding to the melting section, due to the stretching effect of the first screw and the second screw; at the same time, between the first mixing element and the first reverse conveying element, the second mixing element The interface renewal effect is generated respectively with the second reverse conveying element, thereby strengthening the heat transfer process; coupled with the frictional heat generated by the high-speed rotation of the first screw and the second screw; and the external heating of the barrel; the four work together to make The material further melts, accelerates the separation of the melt and the solid in the material, further accelerates the melting process of the solid, and makes the material all form a melt;

(3) After the material that becomes the melt enters the flow channel corresponding to the exhaust section from the flow channel corresponding to the melting section, the first forward conveying element and the second forward conveying element corresponding to the first screw and the second screw adopt The large-lead conveying element (that is, the lead L/D of the conveying element is greater than or equal to 3), expands the exhaust surface area of the material, and the gas is discharged from the exhaust port under the action of strong stretching, and the molten material is first The action of the screw and the second screw further moves to the direction of the flow path corresponding to the mixing extrusion section;

(4) After the melted material enters the flow channel of the mixing extrusion section, the molten material is subjected to the flow channel formed by two screws (that is, between the screw mechanism and the inner cavity of the barrel, and the screw grooves of the two screws). The periodical compression and expansion effect and the differential rotation of the two screws result in a strong stretching effect, so that the melt material is further mixed and plasticized, and the melt material is stabilized It is extruded from the discharge port; at the same time, the mutual wiping action between the first screw and the second screw realizes the self-cleaning effect.

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

In the strong stretching co-directional differential multi-screw extruder and its processing method, the strong stretching effect produced by the different speeds and diameters of the first screw and the second screw is used to strengthen the mixing and heat transfer process, The thermal history and mechanical history of material plasticization are greatly shortened, thereby effectively reducing the energy consumption of the extruder.

In the screw mechanism of this strong stretching co-directional differential multi-screw extruder, the first screw and the second screw are connected in sequence by corresponding forward conveying elements, mixing elements and reverse conveying elements. It can provide a stronger tensile force field, which can significantly reduce the critical capillary number of material dispersion, making the particle size of the dispersed phase smaller, suitable for micro-nano-scale material processing, and can significantly improve product quality; at the same time, the positive conveying elements and The reverse conveying element ensures that the first screw and the second screw are tightly meshed and rotate in the same direction at a differential speed, and the two screws wipe each other to realize the self-cleaning effect in the processing process.

Description of drawings

FIG. 1 is a schematic structural view of the screw mechanism in Embodiment 1.

Fig. 2 is the structural representation of screw mechanism and barrel in embodiment 1.

Fig. 3 is a cross-sectional view of the screw mechanism in Fig. 1 .

Fig. 4 is a schematic structural view of the first mixing element and the second mixing element in Fig. 1 .

Fig. 5 is a schematic structural view of the first forward conveying element and the second forward conveying element in Embodiment 2.

Fig. 6 is a schematic structural view of the first mixing element and the second mixing element in Example 3.

Fig. 7 is a structural schematic diagram of the screw mechanism in embodiment 4.

Fig. 8 is a structural schematic diagram of the screw mechanism in Embodiment 5.

detailed description

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

Example 1

In this embodiment, a strong stretching co-directional differential multi-screw extruder, as shown in Figure 2, includes a barrel 1 and a screw mechanism, the barrel 1 is provided with an inner cavity 2, and the screw mechanism is installed in the inner cavity, As shown in Figure 1, the screw mechanism includes a first screw 3 and a second screw 4, the first screw and the second screw are engaged with each other, and the outermost edges of the first screw and the second screw are tangent to the inner wall of the cavity; The first screw, the second screw and the inner cavity of the barrel form a flow channel; the first screw is composed of the first forward conveying element 5, the first mixing element 6, the first reverse conveying element 7 and the first forward conveying element 5 are connected in sequence, and the second screw is composed of the second forward conveying element 8, the second kneading element 9, the second reverse conveying element 10 and the second forward conveying element 8 in sequence.

Wherein, as shown in Figure 3, the cross-sectional profile of the first screw rod is made up of 2 sections of circular arcs and 2 sections of non-circular curved arcs, and the cross-sectional profile of the second screw rod is composed of 4 sections of circular arcs and 4 sections of non-circular curved arcs (the non-circular The curved arc can be straight or cycloidal); and the first screw is a single thread, and the second screw is a double thread, when the first screw and the second screw rotate in the same direction, the speed of the first screw is the second The rotation speed of the two screws is twice that of the two screws, and the two screws always keep in contact with each other to realize the self-cleaning function.

As shown in Figure 1 or Figure 4, the main structure of the first mixing element is the same as that of the first forward conveying element, except that a first notch 18 is provided on its screw edge; the main structure of the second mixing element is the same as that of the first forward conveying element. The two forward conveying elements are the same, except that a second notch 19 is provided on the screw flight; and both the first notch and the second notch are semi-cylindrical groove structures.

The inner cavity of the barrel is composed of two connected cylindrical grooves, and the cross-sectional shape of the inner cavity is a lying "8".

As shown in Figure 3, the distance between the rotation center O1 of the _first screw and the rotation center _O2 of the second screw is C, and the maximum outer diameter _of the _first screw is D1, the minimum inner diameter is d1, and the second The maximum outer diameter of the screw is D ₂ , and the minimum inner diameter is d ₂ . In order to ensure the two meshing rotations, it is required:

D ₁ -d ₁ =D ₂ -d ₂

C=(D ₁ +d ₂ )/2

And 1.1≤D ₁ /d ₁ ≤1.8, 1.1≤D ₂ /d ₂ ≤4.5. There is a characteristic angle β:

As shown in Figure 3, the cross-sectional profile of the second screw is symmetrical about the O ₁ O ₂ axis, and is also symmetrical about the line passing through O ₂ and perpendicular to the O ₁ O ₂ axis, and the four arcs included are N ₁ N ₂ , N ₃ N ₄ , N ₅ N ₆ and N ₇ N ₈ , N ₁ N ₂ , N ₅ N ₆ these two arcs have a radius of d ₂ /2, corresponding to the central angle γ/2, and N ₃ N ₄ , N ₇ N ₈ , the radii of these two arcs are both D ₂ /2, and the corresponding central angles are both α/2, and the arcs N ₃ N ₄ , N ₇ N ₈ are both in contact with the inner wall of the barrel cut. The central angles α and γ corresponding to the arc satisfy:

α+γ=2π-2β

The other four non-circular arcs are N ₂ N ₃ , N ₄ N ₅ , N ₆ N ₇ and N ₈ N ₁ , among them, N ₂ N ₃ , N ₄ N ₅ , N ₆ N ₇ and N ₈ N ₁ The shapes are exactly the same, and the arcs can be straight lines or cycloidal arcs, or circular arcs can be used according to actual needs, and the corresponding central angles are both β/2.

The cross-sectional profile of the first screw consists of two sections of circular arcs M ₁ M ₂ , M ₃ M ₄ and two sections of non-circular curved arcs M ₂ M ₃ , M ₄ M ₁ . Among them, the arc M ₁ M ₂ has a radius of D ₁ /2, and the corresponding central angle γ meshes with N ₁ N ₂ and N ₅ N ₆ ; the arc M ₃ M ₄ has a radius of d ₁ /2, The corresponding central angle α meshes with N ₃ N ₄ and N ₇ N ₈ . The other two non-circular arcs are respectively M ₂ M ₃ and M ₄ M ₁ , which are symmetrical about the O ₁ O ₂ axis, and their shapes are determined by cutting the cross-section of the second screw meshed with them.

The pitches L of the first screw and the second screw are both 0.01D˜10000D.

As shown in Figure 2, barrel 1 is provided with delivery section 14, melting section 15, exhaust section 16 and mixing extrusion section 17; delivery section 14, melting section 15, exhaust section 16 and mixing extrusion section 17 Arranged sequentially from the moving direction of the processed materials; the upper part of the conveying section is provided with a feed port 11 connected with the inner cavity, and the upper part of the exhaust section is provided with an exhaust port 12 connected with the inner cavity; The end is provided with a discharge port 13. In the screw mechanism, the first mixing element and the second mixing element are located in the barrel in the middle of the melting section, the first reverse conveying element and the second reverse conveying element are located in the barrel at the rear of the melting section, and the conveying section, The first forward conveying element and the second forward conveying element are arranged in the barrel corresponding to the front part of the melting section, the exhaust section and the kneading extrusion section, and the first forward conveying element and the second forward conveying element located in the exhaust section The second forward conveying element adopts a large lead conveying element.

The processing method realized by the above-mentioned strong stretching co-rotating differential multi-screw extruder comprises the following steps:

(1) After the material enters the flow channel of the conveying section from the feed port, the first screw and the second screw rotate in the same direction and at a differential speed along their respective screw axes; the axial positive displacement conveying force of the first screw and the second screw and the The frictional force between the first screw and the second screw realizes the feed transportation and forces the material to move towards the flow channel of the melting section;

(2) When the material moves to the flow channel corresponding to the melting section, due to the stretching effect of the first screw and the second screw; at the same time, between the first mixing element and the first reverse conveying element, the second mixing element The interface renewal effect is generated respectively with the second reverse conveying element, thereby strengthening the heat transfer process; coupled with the frictional heat generated by the high-speed rotation of the first screw and the second screw; and the external heating of the barrel; the four work together to make The material further melts, accelerates the separation of the melt and the solid in the material, further accelerates the melting process of the solid, and makes the material all form a melt;

(3) After the material that becomes the melt enters the flow channel corresponding to the exhaust section from the flow channel corresponding to the melting section, the first forward conveying element and the second forward conveying element corresponding to the first screw and the second screw adopt The large-lead conveying element (that is, the lead L/D of the conveying element is greater than or equal to 3), expands the exhaust surface area of the material, and the gas is discharged from the exhaust port under the action of strong stretching, and the molten material is first The action of the screw and the second screw further moves to the direction of the flow path corresponding to the mixing extrusion section;

(4) After the melted material enters the flow channel of the mixing extrusion section, the molten material is subjected to the flow channel formed by two screws (that is, between the screw mechanism and the inner cavity of the barrel, and the screw grooves of the two screws). The periodical compression and expansion effect and the differential rotation of the two screws result in a strong stretching effect, so that the melt material is further mixed and plasticized, and the melt material is stabilized It is extruded from the discharge port; at the same time, the mutual wiping action between the first screw and the second screw realizes the self-cleaning effect.

Example 2

This embodiment is a kind of strongly stretched co-directional differential multi-screw extruder. Compared with Embodiment 1, the difference is that: as shown in Figure 5, the outer diameter of the first screw is smaller than the outer diameter of the second screw , that is, the ratio between the outer diameter and the inner diameter of the second screw is 1.1-1.8, and the ratio between the outer diameter and the inner diameter of the first screw is 1.1-4.5.

Example 3

This embodiment is a strong stretching co-directional differential multi-screw extruder. Compared with Embodiment 1, the difference is that: as shown in Figure 6, in the first screw, the first mixing elements are multiple The combined structure formed by connecting the first kneading blocks; in the second screw, the second mixing element is a combined structure formed by connecting multiple second kneading blocks. In addition to providing fully self-cleaning mixing with positive displacement conveying capacity and super large output, the mixing element of this structure also introduces a stronger tensile force field effect to provide more powerful dispersion and mixing capabilities.

Example 4

This embodiment is a kind of strongly stretched co-directional differential multi-screw extruder. Compared with Embodiment 1, its difference is that: as shown in Figure 7, the screw mechanism also includes a third screw 20 (its center of rotation is O ₃ ), the first screw, the second screw and the third screw are meshed in sequence to form an "inline" three-screw arrangement, and the structure of the third screw is the same as that of the first screw.

Example 5

This embodiment is a kind of strongly stretched co-directional differential multi-screw extruder. Compared with Embodiment 1, its difference is that: as shown in Figure 8, the screw mechanism also includes a third screw 20 (its center of rotation is O ₃ ), the first screw, the second screw and the third screw are meshed in sequence to form a "non-inline" three-screw arrangement, and the structure of the third screw is the same as that of the first screw.

As mentioned above, the utility model can be better realized, and the above-described embodiment is only a preferred embodiment of the utility model, and is not used to limit the scope of implementation of the utility model; that is, all equal changes made according to the contents of the utility model and modifications are all covered by the scope of protection required by the claims of the present utility model.

Claims (9)

1. Strong stretch co-directional differential multi-screw extruder, including a barrel and a screw mechanism, the screw mechanism is installed in the inner cavity of the barrel, and it is characterized in that the screw mechanism includes a first screw and a second screw that mesh with each other , the first screw includes the first forward conveying element, the first mixing element and the first reverse conveying element connected in sequence, and the second screw includes the second forward conveying element, the second mixing element and the second Reverse conveying elements, the outer diameter of the first screw is not equal to the outer diameter of the second screw. 2. The strong drawing co-directional differential multi-screw extruder according to claim 1, characterized in that, in the first screw, the first forward conveying element, the first mixing element and the first reverse The conveying elements all have a single-start thread structure; in the second screw, the second forward conveying element, the second mixing element and the second reverse conveying element all have a double-start thread structure. 3. The strong drawing co-directional differential multi-screw extruder according to claim 1, characterized in that, in the first screw, the outer peripheral edge of the first mixing element is an intermittent groove with a first notch Type screw flight structure, the overall outer contour shape of the first mixing element is the same as that of the first forward conveying element; In the second screw, the outer peripheral edge of the second mixing element is a discontinuous flight structure with a second notch, and the overall shape of the second mixing element is the same as that of the second forward conveying element; Both the first notch and the second notch are semi-cylindrical groove structures. 4. The strong drawing co-directional differential multi-screw extruder according to claim 1, characterized in that, in the first screw, the first mixing element is a combined structure formed by connecting a plurality of first kneading blocks ; In the second screw, the second kneading element is a combined structure formed by connecting multiple second kneading blocks. 5. The strong drawing co-directional differential multi-screw extruder according to claim 1, characterized in that, the first screw and the second screw rotate in the same direction and keep meshing at all times, the first screw and the second screw The speed ratio between them is 2-7. 6. The strongly stretched co-directional differential multi-screw extruder according to claim 1, wherein, among the first screw and the second screw, one of the screws is a large-diameter screw, and the other screw is a small screw. diameter screw, the ratio between the outer diameter and the inner diameter of the large-diameter screw is 1.1-1.8, and the ratio between the outer diameter and the inner diameter of the small-diameter screw is 1.1-4.5. 7. The strong drawing co-directional differential multi-screw extruder according to claim 1 is characterized in that, the radial cross-sectional profile of the first screw rod is composed of multi-section unequal arcs and multi-section curvature radii. Equal non-circular curved arcs are connected alternately, and the radial cross-sectional profile of the second screw is also composed of multiple circular arcs with unequal radii of curvature and multiple non-circular curved arcs with unequal radii of curvature; the radial cross-section of the second screw is formed The total number of circular arcs and non-circular curved arcs of the profile is 2 to 7 times the total number of circular arcs and non-circular curved arcs constituting the radial cross-sectional profile of the first screw rod. 8. The strong stretching co-directional differential multi-screw extruder according to claim 1, wherein the screw mechanism also includes a third screw, and the first screw, the second screw and the third screw are meshed in sequence to form "In-line" or "non-in-line" three-screw arrangement, the structure of the third screw is the same as that of the first screw. 9. The strong drawing co-directional differential multi-screw extruder according to claim 1, wherein the barrel is provided with a conveying section, a melting section, an exhaust section and a mixing section connected successively along the material conveying direction. In the refining and extrusion section, the conveying section is provided with a feed port connected to the inner cavity of the barrel, the exhaust section is provided with an exhaust port connected with the inner cavity of the barrel, and the end of the mixing extrusion section is provided with a discharge port ; In the screw mechanism, the first screw includes the first forward conveying element, the first mixing element, the first reverse conveying element and the first forward conveying element connected in sequence along the material conveying direction, and the second screw includes the first forward conveying element along the material conveying direction. The second forward conveying element, the second kneading element, the second reverse conveying element and the second forward conveying element connected in sequence; Wherein, the first mixing element and the second mixing element are located in the barrel in the middle of the melting section, and the first reverse conveying element and the second reverse conveying element are located in the barrel at the rear of the melting section.