Stretching and mixing element for enhancing heat transfer and screw extruder

Abstract

The invention discloses a stretching and mixing element for enhancing heat transfer and a screw extruder, the stretching and mixing element for enhancing heat transfer comprises a sleeve, first beads and second beads, the first beads and the second beads are both fixed on the outer wall of the sleeve, and the first beads and the second beads are alternately arranged; the first protruding edges are evenly distributed relative to the circumference of the axis of the sleeve, a first material flow channel is formed by every two adjacent first protruding edges and the outer wall of the sleeve, and third protruding edges are arranged on the first material flow channels. The second protruding edges are evenly distributed relative to the circumference of the axis of the sleeve, two adjacent second protruding edges and the outer wall of the sleeve form a second material flow channel communicated with the first material flow channel, and the side face contour of each second protruding edge is formed by twisting a sine curve by a certain angle in the circumferential direction. According to the invention, the local melt flow direction is changed to generate convective heat transfer, the dispersion distribution mixing effect is enhanced, local temperature rise caused by strong shearing is favorably diffused, and the applicability of the device in materials and processing equipment is widened.

Description

Technical Field

[0001] The invention relates to extruder technology, in particular to a stretching and mixing element and a screw extruder for enhancing heat transfer. Background Art

[0002] In the field of polymer molding and processing, screw extruders play a very important role. As a key component of the extruder, the screw rotates in the barrel to continuously extrude, crush, mix and transport the materials to achieve the melt processing of the polymer when the barrel wall reaches a certain temperature. In most cases, products produced by a single raw material cannot meet production requirements. Often, a variety of fillers, such as plasticizers, cross-linking agents, stabilizers, etc., need to be added according to the required performance. In order to make these fillers evenly dispersed in the matrix, higher requirements are placed on the mixing and kneading effect of the screw. In addition, for some polymers with a very narrow melt processing range, such as polyvinyl alcohol, it is necessary to strictly control the local temperature rise caused by shearing during the processing process to prevent material decomposition and affect the performance of the extruded product. Therefore, the use of screws dominated by shear flow fields is limited.

[0003] At present, the main mixing and kneading effects in screw extruders are shear flow field and stretching flow field, which usually coexist. In traditional screw extruders, shear flow field is dominant, and the meshing block elements provide high shearing action to extrude and crush the material to achieve the effect of melt plasticization. However, excessive shearing will cause the local melt temperature to rise, which can easily lead to material decomposition. Therefore, further research is urgently needed on the temperature control and local heat diffusion of polymer molding and mixing devices. Summary of the invention

[0004] The first purpose of the present invention is to overcome the shortcomings of the above prior art and provide a stretching and mixing element with enhanced heat transfer. The stretching and mixing element with enhanced heat transfer can reduce the local temperature and improve the disturbance effect.

[0005] Meanwhile, a second object of the present invention is to provide a screw extruder.

[0006] The object of the present invention is achieved by the following technical solution: the stretching and mixing element for enhancing heat transfer comprises a sleeve, a first convex ridge and a second convex ridge, wherein the first convex ridge and the second convex ridge are both fixed to the outer wall of the sleeve, and the first convex ridge and the second convex ridge are arranged alternately;

[0007] The first ridges are evenly distributed around the circumference of the sleeve axis, and two adjacent first ridges and the outer wall of the sleeve form a first logistics channel. A third ridge is arranged in the first logistics channel, and the height of the third ridge is less than or equal to half the height of the first ridge, so that the cross section of the first material channel gradually decreases and then gradually increases;

[0008] The second ridges are evenly distributed around the axis of the sleeve, and two adjacent second ridges and the outer wall of the sleeve form a second logistics channel connected to the first logistics channel. The side profile of the second ridge is formed by twisting a sine curve along the circumferential direction at a certain angle, so that the cross-section of the second logistics channel gradually decreases and then gradually increases.

[0009] Preferably, the first convex ridge includes a rectangular parallelepiped portion and two semi-cylindrical portions integrally formed with the rectangular parallelepiped portion, and the two semi-cylindrical portions are respectively fixed at two ends of the rectangular parallelepiped portion.

[0010] Preferably, there are two third ridges between every two adjacent first ridges, and the two third ridges are symmetrically arranged.

[0011] Preferably, the third convex ridge is semi-conical.

[0012] Preferably, the thickness of both ends of the second ridge is smaller than the thickness of the first ridge.

[0013] Preferably, the sinusoidal curve is: Among them, x is the horizontal axis, y is the vertical axis, and π is the pi.

[0014] Preferably, the side profile of the second convex ridge is a sine curve with a circumferential twist angle of 90° to 120°.

[0015] Preferably, along the axial direction of the sleeve, the end of the first ridge and the end of the second ridge are staggered.

[0016] The screw extruder comprises a barrel, a screw and a stretching and mixing element with enhanced heat transfer according to the first purpose, wherein the screw and the stretching and mixing element with enhanced heat transfer are both arranged in the barrel, and the two ends of the stretching and mixing element with enhanced heat transfer are respectively connected to the screw.

[0017] Preferably, the gap between the maximum diameter of the stretching and mixing element for enhancing heat transfer and the inner wall of the barrel is 0.2 mm to 0.3 mm.

[0018] The present invention has the following advantages over the prior art:

[0019] 1. The heat transfer enhanced stretching and mixing element of the present invention is mainly composed of a sleeve, a first convex ridge and a second convex ridge, and a third convex ridge is added to the first logistics channel formed by the first convex ridge and the sleeve to change the local melt flow direction to generate convective heat transfer, enhance the dispersion distribution mixing effect, and facilitate the diffusion of the local temperature rise caused by strong shear, thereby broadening its applicability in materials and processing equipment.

[0020] 2. The sleeve, the first ridge and the second ridge of the present invention constitute staggered logistics channels (i.e., the first logistics channel and the second logistics channel), and the cross-sections of the logistics channels first gradually decrease and then gradually increase to form a convergent-divergent channel to generate tensile flow, thereby improving the dispersion, distribution, mixing and plasticization effect of the material in the screw channel.

[0021] 3. The present invention changes the melt flow direction and diffuses the local temperature rise by adding a third ridge, and generates a convergence-divergence channel through a sinusoidal profile to reduce viscous heat dissipation, which is beneficial to temperature control and thermal energy management of the entire molding process.

[0022] 4. In the present invention, a plurality of convergent channels are formed in the axial direction between the outer surface of the sleeve and the inner surface of the screw barrel, producing an alternating stretching effect. At the same time, the circumferentially distributed ridges divide the melt into a plurality of parts, which merge between the first and second ridges after passing through the convergent flow channels, so that the material flowing into the mixing element will repeatedly experience homogenization, merging and stretching, thereby improving the dispersion, distribution, mixing and plasticization effect of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic structural diagram of the heat transfer enhanced stretching and mixing element of the present invention.

[0024] Figure 2 The present invention Figure 1 Detailed schematic diagram of two logistics channels.

[0025] Figure 3 It is a front view of the heat transfer enhanced stretching and mixing element of the present invention.

[0026] Figure 4 It is a schematic structural diagram of the heat transfer enhanced stretching and mixing element of the present invention installed in a barrel.

[0027] Figure 5 yes Figure 4 Cross-sectional view along the AA direction.

[0028] Figure 6 It is a schematic structural diagram of the heat transfer enhanced stretching and mixing element of the present invention after installation with the screw.

[0029] Figure 7 It is a schematic diagram of polymer melt flowing from the first logistics channel into the second logistics channel.

[0030] Figure 8 Schematic diagram of the modeling process of the first ridge.

[0031] Among them, 1 is a sleeve, 2 is a first convex rib, 3 is a second convex rib, 4 is a first logistics channel, 5 is a third convex rib, 6 is a second logistics channel, 7 is a barrel, and 8 is a screw. DETAILED DESCRIPTION

[0032] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0033] like Figures 1 to 3 As shown, the heat transfer enhanced stretching and mixing element includes a sleeve, a first ridge and a second ridge, the first ridge and the second ridge are both fixed to the outer wall of the sleeve, and the first ridge and the second ridge are alternately arranged; the first ridge is evenly distributed relative to the circumference of the axis of the sleeve, and two adjacent first ridges and the outer wall of the sleeve form a first logistics channel, a third ridge is arranged in the first logistics channel, and the height of the third ridge is less than or equal to half of the height of the first ridge, so that the cross-section of the first material channel gradually decreases and then gradually increases; the second ridge is evenly distributed relative to the circumference of the axis of the sleeve, and two adjacent second ridges and the outer wall of the sleeve form a second logistics channel connected to the first logistics channel, and the side profile of the second ridge is formed by twisting a sine curve along the circumferential direction at a certain angle, so that the cross-section of the second logistics channel gradually decreases and then gradually increases.

[0034] Specifically, there are multiple first ridges, and the multiple first ridges are evenly distributed to form a first logistics channel at the front end of the sleeve; before the polymer melt enters this first logistics channel, it is initially diverted and divided by the first ridge to enter the first logistics channel. Because under the influence of the third ridge, the cross-section of the first material channel first gradually decreases and then gradually increases. In the process of the polymer melt passing through the first logistics channel, the volume of the melt will first gradually become thinner and then gradually become thicker, generating stretching flow to promote the mixing and kneading of the melt. That is, when the polymer melt enters the front section of the first logistics channel (that is, before passing through the narrowest part between the two third ridges), due to the guiding effect of the third ridge, part of the melt will produce radial flow, first outward and then inward, such as Figure 2 As shown, the radially flowing melt and the normal axially flowing melt undergo convection, which enhances the mixing and kneading effect on the polymer melt in the mixed system, and at the same time can disperse the locally heated melt and enhance heat transfer.

[0035] When the polymer melt enters the rear section of the first flow channel (i.e. after passing through the narrowest part between the two third ridges), the polymer melt is diverted for the second time because the thickness of both ends of the second ridge is sharper and the second ridge is staggered with the first ridge.

[0036] Similarly, the second ridges are arrayed along the circumferential direction, and the contours on both sides of the second ridges are formed by twisting a sine curve along the circumferential direction at a certain angle, so that the second logistics channel formed by adjacent second ridges and the sleeve first decreases and then increases along the axial direction, forming a convergent-divergent channel. When the melt produces tensile flow through the second logistics channel, the mixing effect of the melt is enhanced.

[0037] The modeling process of the second convex ridge is as follows. In this embodiment, the side profile of the second convex ridge adopts the following sine curve equation:

[0038] Among them, x is the horizontal axis, y is the vertical axis, and π is the pi.

[0039] Specifically, the side profile of the second ridge is established based on the sine curve equation in the xoy plane, the curve is mirrored about the y-axis to enclose a closed surface, and stretched in the z-axis direction, and the initial model is established as shown in the figure; then the initial model is distributed in a circular array on the side wall of the sleeve; then the model is twisted at a magnitude of 100° to obtain the final model of the second ridge, and the model is completed, as shown in FIG. Figure 8 shown.

[0040] The second ridge and sleeve obtained by the above modeling can form a convergent-divergent second logistics channel. The profile of the second logistics channel can be changed by changing the period and amplitude of the sine function, thereby controlling the strength of the stretching flow field of the second logistics channel to adjust the mixing effect.

[0041] The top height of the third ridge does not exceed half of the height of the first ridge. If the height of the third ridge is too high, the polymer melt will tend to move toward the middle of the first flow channel, the radial flow trend will be weakened, and the heat dissipation effect caused by forced convection will be reduced.

[0042] The first convex edge comprises a rectangular parallelepiped portion and two semi-cylindrical portions integrally formed with the rectangular parallelepiped portion, and the two semi-cylindrical portions are respectively fixed at two ends of the rectangular parallelepiped portion. This structure is simple and convenient to manufacture.

[0043] The number of third ridges between each two adjacent first ridges is two, and the two third ridges are symmetrically arranged. The third ridge is semi-conical. Specifically, the third ridge is arranged between two adjacent first ridges to adjust the shape of the first logistics channel so that the vertical first logistics channel becomes a convergent-divergent first logistics channel to improve the mixing effect. And the shape of the third ridge is not limited to a semi-conical shape, but can also be other shapes, such as a spherical shape.

[0044] The thickness of the two ends of the second convex ridge is less than the thickness of the first convex ridge. This arrangement facilitates cutting and diverting of the polymer melt, so that the polymer melt flows smoothly into the second logistics channel.

[0045] like Figure 7 As shown, along the axial direction of the sleeve, the end of the first ridge is staggered with the end of the second ridge. Specifically, the first ridge and the second ridge are arranged at different array angles so that the end of the first ridge and the end of the second ridge are staggered, thereby performing secondary cutting and diversion on the polymer melt to improve the mixing effect.

[0046] like Figures 4 to 6 As shown, the screw extruder comprises a barrel, a screw and a stretching and mixing element with enhanced heat transfer according to the first purpose, wherein the screw and the stretching and mixing element with enhanced heat transfer are both arranged in the barrel, and the two ends of the stretching and mixing element with enhanced heat transfer are respectively connected to the screw. The gap between the maximum diameter of the stretching and mixing element with enhanced heat transfer and the inner wall of the barrel is 0.25 mm.

[0047] The above specific implementation modes are preferred embodiments of the present invention and cannot be used to limit the present invention. Any other changes or other equivalent replacement methods that do not deviate from the technical solution of the present invention are included in the protection scope of the present invention.

Claims

1. A stretching and mixing element with enhanced heat transfer, characterized in that: It comprises a sleeve, a first convex ridge and a second convex ridge, wherein the first convex ridge and the second convex ridge are both fixed to the outer wall of the sleeve, and the first convex ridge and the second convex ridge are alternately arranged; The first ridges are evenly distributed around the circumference of the sleeve axis, and two adjacent first ridges and the outer wall of the sleeve form a first logistics channel. A third ridge is arranged in the first logistics channel, and the height of the third ridge is less than or equal to half the height of the first ridge, so that the cross section of the first material channel gradually decreases and then gradually increases; The second ridges are evenly distributed around the axis of the sleeve, and two adjacent second ridges and the outer wall of the sleeve form a second logistics channel connected to the first logistics channel. The side profile of the second ridge is formed by twisting a sine curve along the circumferential direction at a certain angle, so that the cross-section of the second logistics channel gradually decreases and then gradually increases.

2. The heat transfer enhanced stretching and mixing element according to claim 1, characterized in that: The first convex ridge includes a rectangular parallelepiped portion and two semi-cylindrical portions integrally formed with the rectangular parallelepiped portion, and the two semi-cylindrical portions are respectively fixed at two ends of the rectangular parallelepiped portion.

3. The heat transfer enhanced stretching and mixing element according to claim 2, characterized in that: The number of third ridges between every two adjacent first ridges is two, and the two third ridges are symmetrically arranged.

4. The heat transfer enhanced stretching and mixing element according to claim 1, characterized in that: The third convex edge is semi-conical.

5. The heat transfer enhanced stretching and mixing element according to claim 1, characterized in that: The thickness of both ends of the second convex ridge is smaller than the thickness of the first convex ridge.

6. The heat transfer enhanced stretching and mixing element according to claim 1, characterized in that: The sinusoidal curve is: Among them, x is the horizontal axis, y is the vertical axis, and π is the pi.

7. The heat transfer enhanced stretching and mixing element according to claim 1, characterized in that: The side profile of the second convex ridge is twisted by a sine curve in the circumferential direction at an angle of 90° to 120°.

8. The heat transfer enhanced stretching and mixing element according to claim 1, characterized in that: Along the axial direction of the sleeve, the end of the first ridge is staggered with the end of the second ridge.

9. Screw extruder, characterized in that: It comprises a barrel, a screw and a stretching and mixing element with enhanced heat transfer as claimed in any one of claims 1 to 8, wherein the screw and the stretching and mixing element with enhanced heat transfer are both arranged in the barrel, and the two ends of the stretching and mixing element with enhanced heat transfer are respectively connected to the screw.

10. The screw extruder according to claim 9, characterized in that: The gap between the maximum diameter of the stretching and mixing element for enhancing heat transfer and the inner wall of the barrel is 0.2 mm to 0.3 mm.

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