Screw elements and extrusion systems for screw extruders based on stretching-based reinforcing compounding

Abstract

This invention discloses a screw element for stretch-based reinforced compounding and an extrusion system for a screw extruder. The screw element includes a sleeve with a bottom groove having an outer wall surface twisted by 180° to form a torsional plane. Adjacent bottom grooves have raised ribs, the helical direction of which is consistent with the bottom groove. The height of the raised ribs increases and then decreases helically along the axis of the sleeve, while the width of the raised ribs also increases and then decreases helically along the axis of the sleeve, causing the width of the bottom grooves to decrease and then increase helically. Furthermore, the change in the width of the raised ribs is positively correlated with the change in their height. This invention features unique bottom grooves and raised ribs; the channels formed by the bottom grooves and raised ribs provide stronger stretching action, and the stretching flow field is uniformly distributed in all directions, resulting in superior melting and plasticizing effects on materials.

Description

Technical Field

[0001] This invention relates to extruder technology, and more specifically to a screw element for stretch-based reinforced compounding and an extrusion system for a screw extruder. Background Technology

[0002] In the field of polymer molding and processing, screw extruders are widely used in plastics processing, rubber processing, and composite material processing due to their powerful melt mixing action. As a key component of the extruder, the screw continuously crushes and melts the material by squeezing it against the inner wall of the barrel when the required processing temperature is reached, thus achieving plasticization. In most cases, products produced from a single raw material cannot meet production requirements, and fillers, additives, and other components are often added according to performance requirements. For example, POE can be used to modify and toughen PP, PE, and PA; common additives include plasticizers, toughening agents, crosslinking agents, and heat stabilizers. To ensure that fillers and additives are uniformly dispersed in the matrix, higher requirements are placed on the screw's mixing and compounding capabilities. In addition, in the molding and processing 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 action, which can lead to material discoloration, degradation, melt fracture and other issues that affect the performance of the product. Therefore, the use of screws with shear flow field as the main characteristic is limited.

[0003] Shear flow and tensile flow are two types of processing flow fields in screw extruders, and they usually coexist. In twin-screw and three-screw extruders, the formation of the processing flow field is determined by the rotation direction (co-directional, anti-directional) between the screws, the meshing form (fully meshed, partially meshed, and non-meshing) between the screw elements, and the shape of the screw elements. In contrast, single-screw extruders are only affected by the shape of the screw elements. Traditional single-screw extruders primarily utilize a shear flow field, using the external shear of the screw to provide high shear force to crush the material and achieve melt plasticization. However, excessive shear can lead to localized temperature increases in the melt, making the material prone to degradation and discoloration. Therefore, further research is needed to address the issues of localized overheating and heat transfer in extrusion molding.

[0004] Existing research indicates that, compared to shear flow fields, stretch flow fields possess higher dispersion and mixing capabilities, while also enabling materials to gradually orient themselves during processing, thus improving product performance. For traditional single extruders, the heat generated by the heating rods in each temperature zone of the barrel is transferred radially, and the material extrusion process also drives heat flow conduction. Therefore, by altering the shape of the mixing elements and the screw configuration (the arrangement of screw elements on the screw), the material flow direction can be changed. This not only facilitates dispersion and mixing between materials but also improves the heat flow conduction efficiency within the barrel, thereby reducing the problem of temperature uniformity within the barrel and allowing the material to melt and plasticize better.

[0005] Therefore, further research is needed on how to enhance the material exchange and mixing within the extruder while utilizing a stretching flow field, in order to produce screw components with stable temperature rise, enhanced exchange, and better mixing effects. Summary of the Invention

[0006] The primary objective of this invention is to overcome the shortcomings of the prior art and provide a screw element for stretch-based enhanced compounding. This stretch-based enhanced compounding screw element can have a stronger stretching effect, and the stretching flow field is uniformly distributed in all directions, resulting in superior melting and plasticizing effects on materials.

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

[0008] The objective of this invention is achieved through the following technical solution: This screw element based on stretching and strengthening compounding includes a sleeve, the sleeve having a bottom groove with an outer wall surface twisted by 180° to form a torsion plane, and a protruding ridge between adjacent bottom grooves, the helical direction of the protruding ridge being consistent with that of the bottom groove, the height of the protruding ridge first increasing and then decreasing along the helical direction of the sleeve axis, the width of the protruding ridge first increasing and then decreasing along the helical direction of the sleeve axis so that the width of the bottom groove first decreasing and then increasing along the helical direction, and the change in the width of the protruding ridge is positively correlated with the change in the height of the protruding ridge.

[0009] Preferably, the two ends of the protruding ridge are provided with cuts, the width and height of which are equal.

[0010] Preferably, the edges of the cut are chamfered and rounded.

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

[0012] The extrusion system of the screw extruder includes a barrel, a mandrel, a screw head, and at least two screw elements as described in the first purpose. The screw head is mounted on one end of the mandrel, and the screw elements are sleeved on the mandrel. The screw elements are disposed inside the barrel, and the screw elements and the barrel form multiple material flow channels. The width of these material flow channels repeatedly decreases and then increases. The cuts between two adjacent screw elements are joined to form a semi-circular hole, and this semi-circular 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 a unique bottom groove and convex ridge. The channel formed by the bottom groove and convex ridge can have a stronger stretching effect, and the stretching flow field is evenly distributed in all directions, resulting in a better melting and plasticizing effect on materials.

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

[0019] 3. The screw element of the present invention for enhanced mixing has material exchange capability. Compared with the independent and non-interfering flow channels, the guide hole not only facilitates better melting and mixing of materials during the extrusion process, but also promotes heat flow transfer inside the barrel, improves the temperature uniformity of the melt, and reduces degradation caused by excessively high local temperature of the material and insufficient plasticization caused by excessively low temperature.

[0020] 4. The present invention has a simple and reasonable design structure, low manufacturing cost, and can be applied to the field of single-screw extrusion molding and injection systems in injection molding. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of the screw element for tension-based reinforced compounding according to the present invention.

[0022] Figure 2 This is a top view of the screw element of the present invention based on stretching and strengthening compounding.

[0023] Figure 3 This is an assembly diagram of the screw element, screw head and mandrel based on the stretching-reinforced compounding of the present invention.

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

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

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

[0027] Among them, 1 is the sleeve, 2 is the bottom groove, 3 is the protruding ridge, 4 is the notch, 5 is the curved surface, 6 is the barrel, 7 is the mandrel, 8 is the screw head, 9 is the logistics channel, and 10 is the screw element. Detailed Implementation

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

[0029] like Figure 1 and Figure 2 As shown, a screw element for tensile-reinforced compounding includes a sleeve having a bottom groove with an outer wall surface twisted 180° to form a torsion plane, and a ridge between adjacent bottom grooves. The helical direction of the ridge is consistent with that of the bottom groove. The height of the ridge increases and then decreases helically along the axis of the sleeve, and the width of the ridge increases and then decreases helically along the axis of the sleeve so that the width of the bottom groove decreases and then increases helically. The change in the width of the ridge is positively correlated with the change in the height of the ridge.

[0030] Specifically, the sleeve is made of a square steel column with a central channel and four flat planes on the outer wall. These four flat planes are twisted 180° to form a bottom groove, and both sides of the bottom groove have protruding ridges parallel to the groove. The cross-section of the protruding ridges is variable, meaning the cross-sectional area first increases and then decreases along the spiral direction, thus causing the width of the bottom groove to first decrease and then change. The material channel formed by the bottom groove and protruding ridges will first decrease and then increase. When the material passes through this channel, it undergoes a compression-relaxation cycle, enhancing the plasticizing effect on the material. Therefore, when multiple screw elements are set on the mandrel, the material will repeatedly undergo a compression-relaxation cycle. Simultaneously, the screw element, composed of a unique bottom groove and protruding ridges, is dominated by a stretching flow field, which can promote the melting and plasticizing of the material and generate structural orientation. This element also has a certain conveying capacity, reducing local stagnation during material mixing and ensuring uniform and continuous extrusion plasticizing of the material. Furthermore, the radially varying cross-section of the convex ridge allows for a stretching flow field due to the radial volume change as the fluid flows forward in the material channel. This also facilitates heat diffusion and conduction within the channel. From the end face to the middle face of the sleeve, the width and height of the convex ridge double, resulting in a proportional change in the side of the plasticizing channel. This creates a uniform pressure-relaxation channel as the melt passes through it. Compared to curved channel bottom grooves, flat surfaces are more conducive to melt flow and transport. The heat generated by the heating rods on both sides of the barrel is also more easily transferred, leading to a more uniform temperature distribution throughout the barrel and reducing the problem of poor localized plasticization caused by uneven temperature distribution during the material plasticization process.

[0031] The two ends of the protruding ridge are provided with slits, the width and height of which are equal. Specifically, after two adjacent screw elements are spliced ​​together, the two adjacent slits form a semi-circular hole, which, in conjunction with the barrel, forms a unique flow guide hole. This flow guide hole allows material exchange between two adjacent material flow channels, thereby promoting heat conduction throughout the device and reducing insufficient plasticization or degradation of materials due to excessively low or high local heat.

[0032] The cut edges are chamfered and rounded. These chamfering and rounding treatments facilitate smoother material exchange between adjacent material flow channels. Furthermore, to further improve the smoothness of the exchange, the cut direction is perpendicular to the spiral direction of the convex edge.

[0033] The side surface of the protruding ridge is curved, and the radius of this curved surface is equal to the width of the bottom of the protruding ridge at the same cross-section. The side surface of the protruding ridge is set as a curved surface, so that the cross-section of the protruding ridge is hill-shaped, which further enhances the stretching effect of the material flow channel and enhances the plasticizing 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 as described in the first objective. The screw head is mounted on one end of the mandrel, and the screw elements are sleeved on the mandrel. The screw elements are disposed inside the barrel, and the screw elements and the barrel form multiple material flow channels, the width of which repeatedly decreases and then increases. The cuts between two adjacent screw elements are joined to form a semi-circular hole, which, together with the barrel, forms a guide hole. The sum of the widths of all 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 screw pitch.

[0035] From the perspective of the entire extrusion process, the material is first fed into the barrel by the conveying element and undergoes preliminary melting and mixing. Then, when the polymer melt is conveyed to the screw element, the melt is diverted by four protruding ridges and enters the arched material flow channels respectively. Under the action of the stretching flow field, each channel is plasticized, mixed, and oriented. As the material is extruded forward by the screw element to the guide hole, the melt between adjacent material flow channels exchanges and mixes under melt pressure, further enhancing the mixing effect of the melt. Through this dynamic cycle of melting, plasticizing, stretching, and exchange, the material is finally extruded through the screw head, resulting in a product with a better orientation structure, which is beneficial to the improvement of the product's mechanical properties. At the same time, the combination of the unique protruding ridges and the flat bottom groove enhances the effect of the stretching flow field. Combined with the material exchange capacity of the guide hole, the extrusion system of this application promotes the mixing effect of the material processing and can also improve the problem of excessive local temperature rise caused by shear heat during screw extrusion.

[0036] The above-described specific embodiments are preferred embodiments of the present invention and are not intended to limit the present invention. Any other changes or equivalent substitutions made without departing from the technical solution of the present invention are included within the protection scope of the present invention.

Claims

1. A screw element based on tensile-strengthened compounding, characterized in that: The sleeve includes a bottom groove with an outer wall surface twisted by 180° to form a torsion plane, and a protruding rib between adjacent bottom grooves. The helical direction of the protruding rib is consistent with that of the bottom groove. The height of the protruding rib increases and then decreases along the helical direction of the sleeve axis, and the width of the protruding rib increases and then decreases along the helical direction of the sleeve axis so that the width of the bottom groove decreases and then increases along the helical direction. The change in the width of the protruding rib is positively correlated with the change in the height of the protruding rib.

2. The screw element based on stretching and reinforcing compounding according to claim 1, characterized in that: The two ends of the protruding ridge are provided with cuts, the width and height of which are equal.

3. The screw element based on stretching and reinforcing compounding according to claim 2, characterized in that: The edges of the cut are chamfered and rounded.

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

5. The extrusion system of a screw extruder, characterized in that: The device includes a barrel, a mandrel, a screw head, and at least two screw elements as described in any one of claims 1 to 4. The screw head is mounted on one end of the mandrel, the screw elements are sleeved on the mandrel, the screw elements are disposed inside the barrel, and the screw elements and the barrel form multiple material flow channels, the width of which repeatedly decreases and then increases; the cuts between two adjacent screw elements are spliced ​​to form a semi-circular hole, and this semi-circular 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 0.3 mm to 1 mm.

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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