Stretching and mixing elements for enhanced heat transfer and screw extruders

Abstract

The application discloses a stretching and mixing element for enhancing heat transfer and a screw extruder, and belongs to the technical field of polymer processing equipment. The stretching and mixing element for enhancing heat transfer comprises a sleeve, a first protruding rib and a second protruding rib, the first protruding rib and the second protruding rib are fixed to the outer wall of the sleeve, and the first protruding rib and the second protruding rib are arranged alternately; the first protruding rib is uniformly distributed relative to the circumference of the axis of the sleeve, and two adjacent first protruding ribs and the outer wall of the sleeve form a first flow channel, and a third protruding rib is arranged in the first flow channel; the second protruding rib is uniformly distributed relative to the circumference of the axis of the sleeve, and two adjacent second protruding ribs and the outer wall of the sleeve form a second flow channel which is communicated with the first flow channel, and the side profile of the second protruding rib is formed by twisting a sine curve by a certain angle in the circumferential direction. The application changes the direction of local melt flow to generate convective heat transfer, strengthens the mixing effect of dispersion distribution, is beneficial to local temperature rise caused by diffusion and strong shear, and widens the applicability of the application to materials and processing equipment.

Description

TECHNICAL FIELD

[0001] The present application relates to extruder technology, in particular to a stretching mixing element for enhancing heat transfer and a screw extruder. BACKGROUND

[0002] In the field of polymer forming processing, screw extruder plays a very important role, in which screw as a key component in the extruder, through the rotating movement in the barrel, constantly extruding, crushing, mixing and conveying the material to achieve the melt processing of polymer. In most cases, the products produced by a single raw material cannot meet the production demand, and various fillers such as plasticizers, crosslinking agents and stabilizers need to be added according to the required performance. In order to make these fillers uniformly dispersed in the matrix, higher requirements are put forward for the mixing and mixing effect of the screw. In addition, for some polymers with very narrow melt processing interval, such as polyvinyl alcohol, the local temperature rise caused by shear action needs to be strictly controlled during processing to prevent material decomposition and affect the performance of the extruded product, so the use of screw dominated by shear flow field is limited.

[0003] At present, the mixing and mixing effect in the screw extruder is mainly realized by shear flow field and stretching flow field, which usually coexist. In the traditional screw extruder, the shear flow field is mainly dominated, and the high shear effect is provided by the meshing block element to extrude and crush the material, so as to achieve the effect of melt plasticization. However, too high shear will cause local melt temperature rise, which is easy to cause material decomposition. Therefore, further research is needed on temperature control and local heat diffusion of polymer forming processing mixing device. SUMMARY

[0004] The first object of the present application is to overcome the shortcomings of the prior art and provide a stretching mixing element for enhancing heat transfer. The stretching mixing element for enhancing heat transfer can reduce local temperature and improve disturbance effect.

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

[0006] The object of the present application is achieved by the following technical scheme: the stretching mixing element for enhancing heat transfer comprises a sleeve, a first protruding rib and a second protruding rib, the first protruding rib and the second protruding rib are fixed to the outer wall of the sleeve, and the first protruding rib and the second protruding rib are arranged alternately;

[0007] The first protruding rib is uniformly distributed around the axis of the sleeve, and the outer wall of the sleeve and the adjacent two first protruding ribs form a first material flow channel. A third protruding rib is arranged in the first material flow channel, and the height of the third protruding rib is less than or equal to half the height of the first protruding rib, so that the cross section of the first material flow channel gradually decreases and then gradually increases.

[0008] The second convex edges are circumferentially and evenly distributed relative to the axis of the sleeve, and the outer wall of the sleeve and the two adjacent second convex edges form a second material flow channel which is in communication with the first material flow channel, and the side profile of the second convex edge is formed by twisting a sinusoidal curve by a certain angle in the circumferential direction, so that the cross section of the second material flow channel first gradually decreases and then gradually increases.

[0009] Preferably, the first convex edge comprises a cuboid part and two semicylindrical parts integrally formed with the cuboid part, and the two semicylindrical parts are respectively fixed at the two ends of the cuboid part.

[0010] Preferably, the number of the third convex edges between every two adjacent first convex edges is two, and the two third convex edges are symmetrically arranged.

[0011] Preferably, the third convex edge is semicone-shaped.

[0012] Preferably, the thickness of the two ends of the second convex edge is smaller than the thickness of the first convex edge.

[0013] Preferably, the sinusoidal curve is: wherein x is the horizontal coordinate axis, y is the vertical coordinate, and π is the circular constant.

[0014] Preferably, the side profile of the second convex edge is twisted by a sinusoidal curve by an angle of 90-120 degrees in the circumferential direction.

[0015] Preferably, the end of the first convex edge is arranged in a staggered manner with the end of the second convex edge in the axial direction of the sleeve.

[0016] The screw extruder comprises a barrel, a screw and the reinforced heat transfer stretching mixing element of the first aspect, the screw and the reinforced heat transfer stretching mixing element are arranged in the barrel, and the two ends of the reinforced heat transfer stretching mixing element are respectively connected with the screw.

[0017] Preferably, the gap between the largest diameter of the reinforced heat transfer stretching mixing element and the inner wall of the barrel is 0.2-0.3 mm.

[0018] Compared with the prior art, the present application has the following advantages:

[0019] 1. The reinforced heat transfer stretching mixing element of the present application mainly comprises a sleeve, a first convex edge and a second convex edge, and a third convex edge is additionally arranged in the first material flow channel formed by the first convex edge and the sleeve, so that the flow direction of the local melt is changed to generate convective heat transfer, the dispersion and distribution mixing effect is strengthened, the local temperature rise caused by diffusion and strong shear is facilitated, and the applicability of the material and the processing equipment is widened.

[0020] 2、The sleeve, the first ridge and the second ridge of the present application constitute staggered flow channels (i.e. the first flow channel and the second flow channel), and the cross sections of the flow channels are gradually reduced and then gradually increased, forming converging-diverging channels, to generate elongational flow, thereby improving the dispersion distribution mixing and plasticizing effect of the material in the screw channel.

[0021] 3、The present application changes the melt flow direction, diffuses the local temperature rise, and generates converging-diverging channels through sinusoidal profile, reduces viscous dissipation heat, which is beneficial to the temperature control and thermal energy management of the entire molding process.

[0022] 4、The present application forms several converging channels in the axial direction between the outer surface of the sleeve and the inner surface of the screw barrel, generating alternating stretching effect. At the same time, the circumferentially distributed ridges divide the melt into several parts, which converge between the first and second ridges after passing through the converging flow channel, so that the material flowing into the mixing element will repeatedly experience homogenization, convergence and stretching effect, thereby improving the dispersion distribution mixing and plasticizing effect of the material. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a structural schematic diagram of the present application of the elongational mixing element for enhancing heat transfer.

[0024] Figure 2 is a detail schematic diagram of two flow channels in the present application Figure 1 .

[0025] Figure 3 is a front view of the elongational mixing element for enhancing heat transfer of the present application.

[0026] Figure 4 is a structural schematic diagram of the elongational mixing element for enhancing heat transfer of the present application installed in the barrel.

[0027] Figure 5 is Figure 4 a sectional view in the A-A direction.

[0028] Figure 6 is a structural schematic diagram of the elongational mixing element for enhancing heat transfer of the present application after installation with the screw.

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

[0030] Figure 8 is a modeling process schematic diagram of the first ridge.

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

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

[0033] like Figures 1 to 3 As shown, the heat-enhancing stretching and mixing element includes a sleeve, a first protrusion, and a second protrusion. Both the first and second protrusions are fixed to the outer wall of the sleeve, and the first and second protrusions are alternately arranged. The first protrusions are evenly distributed circumferentially relative to the axis of the sleeve, and two adjacent first protrusions and the outer wall of the sleeve form a first material flow channel. A third protrusion is provided in the first material flow channel, and the height of the third protrusion is less than or equal to half the height of the first protrusion, so that the cross-section of the first material flow channel gradually decreases and then gradually increases. The second protrusions are evenly distributed circumferentially relative to the axis of the sleeve, and two adjacent second protrusions and the outer wall of the sleeve form a second material flow channel that communicates with the first material flow channel. The side profile of the second protrusion is formed by twisting a sine curve circumferentially at a certain angle, so that the cross-section of the second material flow channel gradually decreases and then gradually increases.

[0034] Specifically, the first protrusion has multiple ridges, which are evenly distributed to form a first material flow channel at the front end of the sleeve. Before the polymer melt enters this first material flow channel, it is initially diverted and segmented by the first protrusions. Due to the influence of the third protrusion, the cross-section of the first material flow channel gradually decreases and then gradually increases. As the polymer melt passes through the first material flow channel, its volume gradually thins and then gradually thickens, generating tensile flow to promote mixing and compounding. That is, when the polymer melt enters the front section of the first material flow channel (i.e., before passing the narrowest point between the two third protrusions), due to the guiding effect of the third protrusion, part of the melt will generate radial flow, first outward and then inward, such as... Figure 2 As shown, the radially flowing melt and the normal axially flowing melt engage in convection, which enhances the mixing and compounding of the polymer melt in the mixing system. At the same time, it can disperse the locally heated melt and enhance the heat transfer.

[0035] When the polymer melt enters the latter part of the first flow channel (i.e., after passing the narrowest part between the two third convex ridges), the polymer melt is diverted a second time because the ends of the second convex ridge are relatively sharp and the second convex ridge is misaligned with the first convex ridge.

[0036] Similarly, the second convex ridges are arranged in a circumferential array, and the two sides of the second convex ridges are formed by twisting a sine curve in the circumferential direction at a certain angle. This causes the second material flow channel formed by the adjacent second convex ridges and the sleeve to first decrease and then increase in the axial direction, forming a convergent-divergent channel. When the melt flows through the second material flow channel, it generates a stretching flow, which enhances the mixing effect of the melt.

[0037] The modeling process for 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] Where x is the horizontal axis, y is the vertical axis, and π is the value of pi.

[0039] Specifically, the side profile of the second convex ridge is established in the xoy plane based on the sine curve equation. This curve is mirror-symmetric about the y-axis and forms a closed surface, which is then stretched along the z-axis, as shown in the figure, to establish the initial model. Next, the initial model is distributed in a circular array on the side wall of the sleeve. Then, the model is twisted by 100° to obtain the final model of the second convex ridge, thus completing the model, as shown. Figure 8 As shown.

[0040] The second convex ridge and sleeve obtained by the above modeling can form a convergent-divergent second material flow channel. The outline of the second material flow channel can be changed by changing the period and amplitude of the sine function, thereby controlling the strength of the tensile flow field of the second material flow channel and adjusting the mixing effect.

[0041] The height of the apex of the third convex ridge does not exceed half the height of the first convex ridge. If the height of the third convex ridge is too high, the polymer melt will tend to move towards 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 protruding ridge includes a cuboid portion and two semi-cylindrical portions integrally formed with the cuboid portion, with the two semi-cylindrical portions respectively fixed at both ends of the cuboid portion. This structure is simple and easy to manufacture.

[0043] There are two third protruding ridges between every two adjacent first protruding ridges, and these two third protruding ridges are symmetrically arranged. The third protruding ridges are semi-conical. Specifically, the third protruding ridges are arranged between two adjacent first protruding ridges to adjust the shape of the first material flow channel, so that the vertical first material flow channel becomes a convergent-divergent first material flow channel, thereby improving the mixing effect. Moreover, the shape of the third protruding ridge is not limited to semi-conical; it can also be other shapes, such as spherical.

[0044] The thickness at both ends of the second protruding ridge is less than the thickness of the first protruding ridge. This design facilitates the cutting and diversion of the polymer melt, allowing it to flow smoothly into the second material flow channel.

[0045] like Figure 7 As shown, along the axial direction of the sleeve, the ends of the first and second protruding ribs are offset. Specifically, the circumferential arrays of the first and second protruding ribs employ different array angles to offset the ends of the first and second protruding ribs, thereby performing secondary cutting and diversion of the polymer melt and improving the mixing effect.

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

[0047] The above specific embodiments are the preferred embodiments of the present application, and cannot limit the present application, and any changes or other equivalent replacement manners without departing from the technical solutions of the present application are included in the protection scope of the present application.

Claims

1. A stretch mixing element for enhanced heat transfer, characterized by: The sleeve, the first ridge and the second ridge are fixed to the outer wall of the sleeve, and the first ridge and the second ridge are arranged alternately; The first ridges are evenly distributed around the axis of the sleeve, and the outer wall of the sleeve and two adjacent first ridges form a first material flow channel, a third ridge is arranged in the first material flow 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 flow channel gradually decreases and then gradually increases; The second ridges are evenly distributed around the axis of the sleeve, and the outer wall of the sleeve and two adjacent second ridges form a second material flow channel which communicates with the first material flow channel, and the side profile of the second ridge is formed by twisting a sine curve in the circumferential direction by a certain angle, so that the cross section of the second material flow channel gradually decreases and then gradually increases; The first ridge comprises a cuboid part and two semicylindrical parts integrally formed with the cuboid part, and the two semicylindrical parts are respectively fixed to the two ends of the cuboid part; The number of third ridges between every two adjacent first ridges is two, and the two third ridges are symmetrically arranged; The third ridge is semicone-shaped; The thickness of the two ends of the second ridge is less than the thickness of the first ridge; The sinusoidal curve is: where x is the horizontal axis, y is the vertical axis, and π is the ratio of a circle's circumference to its diameter. The side profile of the second ridge is twisted by an angle of 90°-120° in the circumferential direction of the sine curve; The end of the first ridge is arranged in a staggered manner with the end of the second ridge along the axis direction of the sleeve.

2. Screw extruder, characterized in that The screw and the heat transfer enhanced stretching and mixing element are arranged in the barrel, and the two ends of the heat transfer enhanced stretching and mixing element are respectively connected with the screw.

3. The screw extruder of claim 2, characterized in that: The gap between the largest diameter of the heat transfer enhanced stretching and mixing element and the inner wall of the barrel is 0.2-0.3 mm.

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