Stretching-based mixing-enhanced screw element and extrusion system of screw extruder

Abstract

The invention discloses a screw element based on stretching and mixing strengthening and an extrusion system of a screw extruder, the screw element comprises a sleeve, the sleeve is provided with a bottom groove which is provided with an outer wall face twisted by 180 degrees to form a twisting plane, a protruding edge is arranged between every two adjacent bottom grooves, the spiral direction of the protruding edges is consistent with that of the bottom grooves, and the protruding edges are arranged in the bottom grooves. The height of the protruding edge is increased and then decreased in the spiral direction of the axis of the sleeve, the width of the protruding edge is increased and then decreased in the spiral direction of the axis of the sleeve so that the width of the bottom groove can be decreased and then increased in the spiral direction, and the width change of the protruding edge is in positive correlation with the height change of the protruding edge. According to the invention, the unique bottom groove and the rib are provided, a channel formed by the bottom groove, the rib and the like can have a stronger stretching effect, and a stretching flow field is uniformly distributed in all directions, so that the material melting and plasticizing effects are more excellent.

Description

Technical Field

[0001] The invention relates to extruder technology, in particular to a screw element for enhanced mixing based on stretching and an extrusion system of a screw extruder. Background Art

[0002] In the field of polymer molding and processing, screw extruders are widely used in plastic processing, rubber processing and composite material processing due to their powerful melt mixing effect. As a key component in the extruder, when the temperature required for material processing is reached in the barrel, the screw continuously extrude and crush the material through the extrusion effect of the screw and the inner wall of the barrel, and melt mixes the material to achieve plasticization of the material. In most cases, products produced by a single raw material cannot meet production needs, and fillers, additives and other ingredients are often added according to performance requirements. For example: POE can be used to modify and toughen PP, PE, PA; common additives include plasticizers, toughening agents, cross-linking agents, thermal stabilizers, etc. In order to make fillers and additives evenly dispersed in the matrix, higher requirements are placed on the mixing and kneading ability of the screw. In addition, in the molding of some shear-sensitive materials and materials with narrow processing temperature windows, such as PA, PC, ABS, PVC and other plastics and rubbers, it is necessary to strictly control the processing parameters to avoid local temperature rise caused by shear, which may cause material discoloration, degradation, melt fracture, etc., affecting the performance of the product. Therefore, the use of screws dominated by shear flow fields is limited.

[0003] Shear flow field and stretching flow field are two types of processing flow fields in screw extruders, and the two usually coexist. In twin-screw and three-screw extruders, the formation of the processing flow field is determined by the rotation direction between the screws (same direction, opposite direction), the meshing form between the screw elements (full meshing, partial meshing and non-meshing), and the shape of the screw elements, while the single-screw extruder is only affected by the shape of the screw elements. The traditional single-screw extruder is mainly based on the shear flow field. The external thread of the screw provides a high shear effect to break the material to achieve the effect of melt plasticization. However, excessive shear will cause the local temperature of the melt to rise, making the material prone to degradation and discoloration. Therefore, there is still room for further research on the problems of local overheating and heat transfer in extrusion molding.

[0004] Existing studies have shown that compared with the shear flow field, the stretching flow field has a higher dispersion and mixing ability, and can gradually orient the material during the processing, which is beneficial to the improvement of product performance. For traditional single extruders, the heat generated by the heating rods in each temperature zone in the barrel is transferred radially, and the heat flow can also be driven during the extrusion of the material. Therefore, the material flow direction can be changed by changing the shape of the mixing element and the screw configuration (the arrangement and combination of the screw elements on the screw), which is not only beneficial to the dispersion and mixing between the materials, but also improves the conduction efficiency of the heat flow in the barrel, thereby reducing the problem of temperature rise uniformity in the barrel, so that the material can be better melted and plasticized.

[0005] Therefore, how to enhance the material exchange and mixing effect in the extruder while using the stretching flow field to produce screw elements with stable temperature rise, enhanced exchange and better mixing effect still needs further exploration. Summary of the invention

[0006] The first purpose of the present invention is to overcome the shortcomings of the above prior art and provide a screw element for strengthening mixing based on stretching. The screw element for strengthening mixing based on stretching can have a stronger stretching effect, and the stretching flow field is evenly distributed in all directions, which has a better effect on material melting and plasticization.

[0007] Meanwhile, a second object of the present invention is to provide an extrusion system of a screw extruder.

[0008] The object of the present invention is achieved through the following technical scheme: the present stretching-based enhanced mixing screw element comprises a sleeve, the sleeve has an outer wall surface twisted 180° to form a bottom groove of a twisted plane, and there are ridges between adjacent bottom grooves, the spiral direction of the ridges is consistent with that of the bottom grooves, the height of the ridges first increases and then decreases along the axial spiral direction of the sleeve, the width of the ridges first increases and then decreases along the axial spiral direction of the sleeve so that the width of the bottom groove first decreases and then increases along the spiral direction, and the change in the width of the ridges is positively correlated with the change in the height of the ridges.

[0009] Preferably, two ends of the convex ridge are provided with cutouts, and the width and height of the cutouts are equal.

[0010] Preferably, the corners of the cutout are chamfered and rounded.

[0011] Preferably, the side surface of the ridge is a curved surface, and the radius of the curved surface is equal to the width of the bottom of the ridge at the same cross section.

[0012] The extrusion system of the screw extruder comprises a barrel, a core shaft, a screw head and at least two screw elements described in the first purpose, wherein the screw head is installed on one end of the core shaft, the screw element is sleeved on the core shaft, the screw element is arranged in the barrel, and the screw element and the barrel form a plurality of logistics channels, the width of the logistics channels repeatedly decreases and then increases; the incisions between two adjacent screw elements are spliced ​​to form a semicircular hole, and the semicircular hole and the barrel form a guide hole.

[0013] Preferably, the sum of the widths of all the cuts is 1 / 10 of the total length of the mandrel.

[0014] Preferably, the gap between the maximum diameter of the screw element and the inner wall of the barrel is 0.3 mm to 1 mm.

[0015] Preferably, the lead of the screw element is equal to 4 times the pitch.

[0016] The present invention has the following advantages over the prior art:

[0017] 1. The present invention has unique bottom grooves and convex ridges. The channels formed by the bottom grooves and convex ridges can have a stronger stretching effect, and the stretching flow field is evenly distributed in all directions, which has a better effect on material melting and plasticization.

[0018] 2. The present invention has a bottom groove with a twisted plane, which is beneficial to the heat transfer between the melts in the flow channel and promotes uniform melting and plasticization of the material.

[0019] 3. The screw element for enhanced mixing of the present invention has the ability of material exchange. Compared with the independent and non-interfering flow channels, the guide holes are not only conducive to better melting and mixing of the material during the extrusion process, but also can promote the heat flow transfer inside the barrel, improve the temperature uniformity of the melt, and reduce the degradation caused by excessively high local temperature of the material and insufficient plasticization caused by too low temperature.

[0020] 4. The design structure of the present invention is simple and reasonable, the manufacturing cost is low, and it can be applied to the single-screw extrusion molding processing field and the injection system in injection molding. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic structural diagram of the screw element for enhanced mixing based on stretching of the present invention.

[0022] Figure 2 It is a top view of the screw element of the present invention for enhanced mixing based on stretching.

[0023] Figure 3 It is an assembly diagram of the screw element, screw head and mandrel for enhanced mixing based on stretching of the present invention.

[0024] Figure 4 It is a front view of the extrusion system of the screw extruder of the present invention.

[0025] Figure 5 It is a first cross-sectional view of the extrusion system of the screw extruder of the present invention.

[0026] Figure 6 It is a second cross-sectional view of the extrusion system of the screw extruder of the present invention.

[0027] Among them, 1 is a sleeve, 2 is a bottom groove, 3 is a convex ridge, 4 is a cutout, 5 is a curved surface, 6 is a barrel, 7 is a core shaft, 8 is a screw head, 9 is a logistics channel, and 10 is a screw element. DETAILED DESCRIPTION

[0028] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0029] like Figure 1 and Figure 2 As shown, a screw element for enhanced mixing based on stretching includes a sleeve having an outer wall surface twisted 180° to form a bottom groove with a twisted plane, and ridges between adjacent bottom grooves, wherein the spiral direction of the ridges is consistent with that of the bottom grooves, the height of the ridges first increases and then decreases along the axial spiral direction of the sleeve, the width of the ridges first increases and then decreases along the axial spiral direction of the sleeve so that the width of the bottom groove first decreases and then increases along the spiral direction, and the change in the width of the ridges is positively correlated with the change in the height of the ridges.

[0030] Specifically, the sleeve is made of a square steel column, the middle of which is the center with a channel, and the outer wall is four flat planes, which are twisted 180° to form a bottom groove, and both sides of the bottom groove have convex ridges parallel to the bottom groove, and the cross section of the convex ridge is a variable cross section, that is, the cross-sectional area increases first and then decreases along the spiral direction, so that the width of the bottom groove first decreases and then changes. Then the logistics channel composed of the bottom groove and the convex ridges will first decrease and then increase. When the material passes through this material channel, it will undergo a compression-relaxation cycle, which enhances the plasticization of the material. Therefore, when multiple screw elements are set on the core shaft, the material will repeatedly undergo a compression-relaxation cycle. At the same time, the screw element composed of a unique bottom groove and convex ridges is dominated by a tensile flow field, which can promote the melt plasticization of the material and produce a structural orientation. At the same time, the element also has a certain conveying capacity, which reduces the situation of local retention during material mixing, and makes the material uniform and continuous extrusion plasticization. Moreover, the cross section of the ridge changes gradually in the radial direction. This structure can make the volume change in the radial direction produce a stretching flow field when the fluid in the logistics channel flows forward, and it is also beneficial to the diffusion and conduction of heat in the flow channel. From the end face to the middle face of the sleeve, the bottom width of the ridge and the height of the ridge double, which makes the side of the plasticizing flow channel change proportionally, and the melt forms a uniform pressure-relaxation channel when passing through the flow channel. Compared with the bottom groove of the curved flow channel, the plane is more conducive to the flow and transportation of the melt, and the heat flow generated by the heating rods on both sides of the barrel is easier to transfer, which can make the temperature distribution of the entire barrel more uniform, reducing the pain point of local poor plasticization caused by temperature uniformity during the material plasticization process.

[0031] The two ends of the ridge are provided with notches, and the width and height of the notches are equal. Specifically, after two adjacent screw elements are spliced ​​together, the two adjacent notches form a semicircular hole, which then cooperates with the barrel to form a unique guide hole. This guide hole allows the material between the two adjacent logistics channels to exchange, thereby promoting heat flow conduction in the entire device and reducing insufficient plasticization or degradation of the material due to low or high local heat.

[0032] The edges and corners of the cutout are chamfered and rounded. The chamfering and rounding make the material exchange between two adjacent logistics channels smoother. At the same time, in order to further improve the smoothness of the exchange, the direction of the cutout is perpendicular to the rotation direction of the convex edge.

[0033] The side of the ridge is a curved surface, and the radius of the curved surface is equal to the width of the bottom of the ridge at the same cross section. The side of the ridge is set as a curved surface, so that the cross section of the ridge is hill-shaped, which further strengthens the stretching effect of the logistics channel to enhance the plasticization effect on the material.

[0034] like Figures 3 to 6The extrusion system of the screw extruder shown includes a barrel, a mandrel, a screw head and at least two screw elements described in the first purpose, wherein the screw head is mounted on one end of the mandrel, the screw element is sleeved on the mandrel, the screw element is arranged in the barrel, and the screw element and the barrel form a plurality of logistics channels, the width of which is repeatedly reduced and then increased; the cuts between two adjacent screw elements are spliced ​​to form a semicircular hole, and the semicircular hole and the barrel form a guide hole. The sum of the widths of all the cuts is 1 / 10 of the total length of the mandrel. The gap between the maximum diameter of the screw element and the inner wall of the barrel is 0.3 mm to 1 mm. The lead of the screw element is equal to 4 times the pitch.

[0035] From the perspective of the entire extrusion process, the material is first sent to the barrel through the conveying element and initially melt-mixed. Then, when the polymer melt is conveyed to the screw element, the melt is diverted by four convex ridges and enters the arched logistics channels respectively, and each is plasticized, mixed, and oriented under the action of the stretching flow field. As the material is extruded forward to the guide hole in the screw element, the melt between adjacent logistics channels is exchanged and mixed under the melt pressure, further enhancing the mixing effect of the melt. In this way, after a dynamic cycle of melting, plasticizing, stretching, and exchange, it is finally extruded and formed through the screw head, and the final product has a better oriented structure, which is conducive to the improvement of the mechanical properties of the product. At the same time, the combination of the unique convex ridge and the flat bottom groove can improve the effect of the stretching flow field, coupled with the material exchange capacity of the guide hole, the extrusion system of the present application promotes the mixing effect of the material processing process, and at the same time can improve the problem of excessive local temperature rise caused by shear heat during screw extrusion.

[0036] 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 screw element for enhanced mixing based on tension, characterized in that: The invention comprises a sleeve, which has an outer wall surface twisted 180° to form a bottom groove of a twisted plane, and convex ridges are arranged between adjacent bottom grooves, the spiral direction of the convex ridges is consistent with that of the bottom grooves, the height of the convex ridges first increases and then decreases along the spiral direction of the axis of the sleeve, the width of the convex ridges first increases and then decreases along the spiral direction of the axis of the sleeve so that the width of the bottom groove first decreases and then increases along the spiral direction, and the change in the width of the convex ridges is positively correlated with the change in the height of the convex ridges.

2. The screw element for enhanced mixing based on stretching according to claim 1, characterized in that: The two ends of the convex edge are provided with cutouts, and the width and height of the cutouts are equal.

3. The screw element for enhanced mixing based on stretching according to claim 2, characterized in that: The edges and corners of the cutout are chamfered and rounded.

4. The screw element for enhanced mixing based on stretching according to claim 1, characterized in that: The side surface of the ridge is a curved surface, and the radius of the curved surface is equal to the width of the bottom of the ridge at the same cross section.

5. The extrusion system of the screw extruder is characterized by: It comprises a barrel, a core shaft, a screw head and at least two screw elements according to any one of claims 1 to 4, wherein the screw head is mounted on one end of the core shaft, the screw element is sleeved on the core shaft, the screw element is arranged in the barrel, and the screw element and the barrel form a plurality of logistics channels, the width of the logistics channels repeatedly decreases and then increases; the cutouts between two adjacent screw elements are spliced ​​to form a semicircular hole, and the semicircular hole and the barrel form a guide hole.

6. The extrusion system of the screw extruder according to claim 5, characterized in that: The sum of the widths of all the cuts is 1 / 10 of the total length of the mandrel.

7. The extrusion system of the screw extruder according to claim 5, characterized in that: The gap between the maximum diameter of the screw element and the inner wall of the barrel is 0.3mm to 1mm.

8. The extrusion system of the screw extruder according to claim 5, characterized in that: The lead of the screw element is equal to 4 times the pitch.

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