A method and equipment for extruding ultra-high molecular weight polymers

Abstract

This invention belongs to the field of polymer extrusion molding technology, specifically relating to a method and equipment for extruding ultra-high molecular weight polymers (UHMWPA). During transport in the extruder, the UHMWPA undergoes thermal radiation and frictional heating, becoming a near-melting-point hot powder, consisting of loose, heat-dissipating nascent particles. These particles then enter the transition zone of the molding equipment, where they remain near-melting-point hot powder and are gradually compacted. Next, they enter the compression zone, where the near-melting-point hot powder is further compressed and heated again until it melts. Finally, they enter the setting zone, where the material is uniformly extruded at a constant temperature, quantity, and pressure to obtain the finished product. This invention overcomes the difficulties in melt transport caused by the high viscosity, low critical shear rate, and low coefficient of friction of UHMWPA, and also overcomes the persistent weld lines and quality defects caused by the polymer melt flowing through the mandrel.

Description

Technical Field

[0001] This invention belongs to the field of polymer extrusion molding technology, specifically relating to an ultra-high molecular weight polymer extrusion molding method and molding equipment. Background Technology

[0002] Ultra-high molecular weight polymers, such as ultra-high molecular weight polyethylene (UHMWPE) and polytetrafluoroethylene (PTFE), possess extremely superior properties and have important applications in pillar industries such as medical devices, automobile manufacturing, and textile machinery. For example, UHMWPE generally refers to polyethylene with a relative molecular weight of over 1.5 million. As a new type of engineering plastic with excellent performance, it exhibits superior wear resistance, impact strength, shock absorption and noise reduction, chemical corrosion resistance, and a low coefficient of friction, making it the engineering plastic with the best overall performance. However, due to its extremely high molecular weight, extremely high melt viscosity, almost zero melt flow rate, and low coefficient of friction and thermal conductivity, the intermolecular entanglement and infiltration during molding are more severe than in other engineering plastics. Its high coefficient of thermal expansion and contraction makes it difficult to transport, plasticize, mix, and injection mold. Currently, compression molding is mainly used to produce large sheets with simple structures and various small products. In my country, compression molding accounts for as much as 90% of production. Outdated processing technologies, methods, and monotonous products are far from meeting the consumer demand for ultra-high molecular weight polymer (UHMWPE) extruded products, such as pipelines for conveying various powdered solids and slurry-like solid-liquid mixtures. Existing UHMWPE extrusion molding methods mainly include plunger extrusion and single-screw extrusion. Both methods struggle to overcome the persistent weld lines and quality defects caused by the molten plastic flowing through the mandrel in the molding equipment. Furthermore, the latter method fails to address the difficulties in melt transport caused by the high viscosity, low critical shear rate, and low coefficient of friction of UHMWPE. Summary of the Invention

[0003] To address the problems existing in the prior art, the present invention provides a method and equipment for extruding ultra-high molecular weight polymers, and specifically discloses the following technical solutions:

[0004] A method for extruding ultra-high molecular weight polymers (UHMWPPs) involves the UHMWPP undergoing thermal radiation and frictional heating during transport in an extruder, transforming it into near-melting-point hot powder particles. These loose, heat-dissipating nascent particles then enter the transition zone of the molding equipment. In this zone, the loose, heat-dissipating nascent particles remain near-melting-point hot powder particles and are gradually compacted. Next, they enter the compression zone of the molding equipment, where the near-melting-point hot powder particles are further compressed and compacted, and the temperature is raised again until they melt. Finally, they enter the setting zone, where the material is uniformly extruded at a constant temperature, quantity, and pressure to form a melt and shape it into the final product.

[0005] A molding apparatus for implementing the above-mentioned ultra-high molecular weight polymer extrusion molding method includes a first barrel, a second barrel, a first mandrel, a second mandrel, and a die. The first barrel, second barrel, first mandrel, and second mandrel each have independent temperature-controlled oil chambers. The first barrel covers the outside of the first mandrel. One end of the first mandrel is fixedly connected to one end of the second mandrel. The second barrel and the die are sequentially covered on the outside of the second mandrel from the side closest to the first mandrel to the side furthest from the mandrel. A first cavity is provided between the first barrel and the first mandrel. A second cavity is provided between the second barrel and the second mandrel. A third cavity communicating with the first cavity is provided on the outer periphery of the side of the first mandrel away from the first barrel. A fourth cavity communicating with the second cavity is provided on the outer periphery of the side of the second mandrel away from the second barrel. A fifth cavity is provided between the second mandrel and the die. The first cavity, the third cavity, the fourth cavity, the second cavity, and the fifth cavity are connected in sequence. The locations of the first cavity, the third cavity, and the fourth cavity are transition zones. The location of the second cavity is a compression zone. The location of the fifth cavity is a shaping zone.

[0006] Furthermore, the first barrel includes a first barrel outer layer and a first barrel inner layer, and a first temperature-controlled oil cavity is provided between the first barrel outer layer and the first barrel inner layer. The second barrel includes a second barrel outer layer and a second barrel inner layer, and a second temperature-controlled oil cavity is provided between the second barrel outer layer and the second barrel inner layer. The first mandrel includes a first mandrel outer layer and a first mandrel inner layer, and a third temperature-controlled oil cavity is provided between the first mandrel outer layer and the first mandrel inner layer. The second mandrel includes a second mandrel outer layer and a second mandrel inner layer, and a fourth temperature-controlled oil cavity is provided between the second mandrel outer layer and the second mandrel inner layer. The first temperature-controlled oil cavity, the second temperature-controlled oil cavity, the third temperature-controlled oil cavity, and the fourth temperature-controlled oil cavity are independently arranged and are respectively connected to the corresponding mold temperature controller.

[0007] Furthermore, the outer layer of the first barrel and the inner layer of the first barrel, the inner layer of the first barrel and the outer layer of the first mandrel, the outer layer of the first mandrel and the inner layer of the first mandrel, the inner layer of the first mandrel and the inner layer of the second mandrel, the outer layer of the second mandrel and the inner layer of the second mandrel, the outer layer of the second mandrel and the inner layer of the second barrel, the inner layer of the second barrel and the outer layer of the second barrel, and the outer layer of the second barrel and the die are all fixedly connected by bolts.

[0008] Furthermore, the first mandrel includes a flow divider cone and a connecting portion. The flow divider cone is fixedly disposed at one end of the connecting portion. The first barrel is covered on the flow divider cone. The third cavity is disposed around the connecting portion. The second mandrel includes a large cylindrical portion, a variable diameter portion, and a small cylindrical portion connected in sequence. The end of the large cylindrical portion away from the small cylindrical portion is fixedly connected to the connecting portion of the first mandrel. The fourth cavity is disposed around the large cylindrical portion. The second barrel is covered on the variable diameter portion. The die is covered on the small cylindrical portion.

[0009] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0010] It overcomes the difficulties in melt transport caused by the high viscosity, low critical shear rate and small friction coefficient of ultra-high molecular weight polymers;

[0011] It overcomes the problem of weld lines that are difficult to eliminate when polymer melt flows through the mandrel and the resulting quality defects;

[0012] The lengths of the compression zone and the shaping zone of the molding equipment have been shortened to meet the relaxation time required for unstable molecules to re-entangle and untangle during the flow of the melt through the mandrel.

[0013] Unlike traditional heating methods that use heaters to heat the barrel to transfer heat and achieve temperature control, in this invention, the temperature of each zone is controlled by a mold temperature controller to control the oil temperature in the temperature control oil chamber of each zone, thus achieving controllable temperature rise and fall.

[0014] The method can be applied to the extrusion molding of various ultra-high molecular weight polymers into pipes, sheets, and profiles, and has a wide range of applications. Attached Figure Description

[0015] Figure 1 This is a rotated sectional view of the molding equipment in Example 2.

[0016] Figure 2 for Figure 1 Cross-sectional view of the connection part of the first core rod.

[0017] Figure 3 This is a front sectional view of the molding equipment in Example 3.

[0018] Figure 4 This is a top sectional view of the molding equipment in Example 3.

[0019] 1-Outer layer of the first barrel, 2-Inner layer of the first barrel, 3-Outer layer of the first mandrel, 4-Inner layer of the first mandrel, 5-Inner layer of the second barrel, 6-Outer layer of the second barrel, 7-Outer layer of the second mandrel, 8-Inner layer of the second mandrel, 9-Die. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Example 1

[0022] A method for extruding and molding ultra-high molecular weight polymers (UHMWPPs) specifically involves the following steps: During transport by the extruder, the UHMWPP undergoes thermal radiation and frictional heating, transforming it into a near-melting-point hot powder, which is a loose, heat-dissipating nascent particle. This powder then enters the transition zone of the molding equipment, where it remains a near-melting-point hot powder and is gradually compacted. Next, it enters the compression zone of the molding equipment, where the near-melting-point hot powder is further compressed and compacted, and then reheated until it melts. Finally, it enters the setting zone, where the material is uniformly extruded at a constant temperature, quantity, and pressure to obtain the final product.

[0023] Example 2

[0024] Reference Figure 1-2 A molding apparatus for extruding ultra-high molecular weight polymers includes a first barrel, a second barrel, a first mandrel, a second mandrel, and a die 9. Each of the first barrel, second barrel, first mandrel, and second mandrel has an independent temperature-controlled oil chamber. The first barrel covers the outside of the first mandrel. One end of the first mandrel is fixedly connected to one end of the second mandrel. The second barrel and the die 9 are sequentially arranged on the outside of the second mandrel from the side closest to the first mandrel to the side furthest from the mandrel. A first cavity is formed between the first barrel and the first mandrel. A second cavity is provided between the second barrel and the second mandrel. A third cavity communicating with the first cavity is provided on the outer periphery of the side of the first mandrel away from the first barrel. A fourth cavity communicating with the second cavity is provided on the outer periphery of the side of the second mandrel away from the second barrel. A fifth cavity is provided between the second mandrel and the die 9. The first cavity, the third cavity, the fourth cavity, the second cavity, and the fifth cavity are connected in sequence. The locations of the first cavity, the third cavity, and the fourth cavity are transition zones. The location of the second cavity is a compression zone. The location of the fifth cavity is a shaping zone.

[0025] In this embodiment, the first barrel includes an outer layer 1 and an inner layer 2, with a first temperature-controlled oil chamber disposed between the outer layer 1 and the inner layer 2. The second barrel includes an outer layer 6 and an inner layer 5, with a second temperature-controlled oil chamber disposed between the outer layer 6 and the inner layer 5. The first mandrel includes an outer layer 3 and an inner layer 4, with a third temperature-controlled oil chamber disposed between the outer layer 3 and the inner layer 4. The second mandrel includes an outer layer 7 and an inner layer 8, with a fourth temperature-controlled oil chamber disposed between the outer layer 7 and the inner layer 8. The first, second, third, and fourth temperature-controlled oil chambers are independently configured and each is connected to a corresponding mold temperature controller. By controlling the oil temperature in each temperature-controlled oil chamber, the temperature of the ultra-high molecular weight polymer in the corresponding mold cavity can be controlled separately.

[0026] In this embodiment, the molding equipment can be combined with the extruder conveying equipment. During the conveying process, the ultra-high molecular weight polymer (UHMWPP) is heated by thermal radiation and friction, becoming a near-melting-point hot powder, i.e., loosely dissipating nascent particles. The UHMWPP remains in powder form throughout the entire conveying process, overcoming the difficulties in melt conveying caused by the high viscosity, low critical shear rate, and small friction coefficient of UHMWPP. The nascent particles entering the transition zone of the molding equipment are still in a near-melting-point powder state, which is conducive to conveying and overcomes the weld lines that are difficult to eliminate when the polymer melt flows through the mandrel of the molding equipment, as well as the quality defects caused by them. After entering the compression zone of the molding equipment, the temperature of the UHMWPP rises until it melts, eliminating the weld lines of the UHMWPP. This greatly shortens the length of the compression zone and the shaping zone of the molding equipment, which require relaxation time for unstable molecules to re-entangle and untangle during the flow of the melt through the mandrel. Finally, the UHMWPP is shaped and formed in the shaping zone.

[0027] In this embodiment, the first outer layer 1 of the barrel and the first inner layer 2 of the barrel, the first inner layer 2 of the barrel and the first outer layer 3 of the mandrel, the first outer layer 3 of the mandrel and the first inner layer 4 of the mandrel, the first inner layer 4 of the mandrel and the second inner layer 8 of the mandrel, the second outer layer 7 of the mandrel and the second inner layer 8 of the mandrel, the second outer layer 7 of the mandrel and the second inner layer 5 of the barrel, the second inner layer 5 of the barrel and the second outer layer 6 of the barrel, and the second outer layer 6 of the barrel and the die 9 are all fixedly connected by bolts, thereby facilitating the assembly and disassembly of the molding equipment.

[0028] In this embodiment, the first mandrel includes a flow divider cone and a connecting portion. The flow divider cone is fixedly disposed at one end of the connecting portion. The first barrel covers the flow divider cone. The third cavity is disposed around the connecting portion, and a plurality of connecting partitions are disposed within the third cavity to fix the inner and outer layers of the connecting portion, thereby ensuring the integrity of the connecting portion. The second mandrel includes a large cylindrical portion, a variable diameter portion, and a small cylindrical portion connected in sequence. The end of the large cylindrical portion away from the small cylindrical portion is fixedly connected to the connecting portion of the first mandrel. The fourth cavity is disposed around the large cylindrical portion, and a plurality of connecting partitions are also disposed within the fourth cavity to fix the inner and outer layers of the large cylindrical portion, thereby ensuring the integrity of the large cylindrical portion. The second barrel covers the variable diameter portion, and the die 9 covers the small cylindrical portion.

[0029] Example 3

[0030] refer to Figure 3-4 This embodiment also uses equipment capable of implementing the extrusion molding method described in Embodiment 1. It includes a connecting transition section I, a sheet extrusion die transition section II, and a sheet extrusion die forming section III connected sequentially. Each section has a cavity at its center, and these cavities are sequentially connected. The cross-section of the cavity in the connecting transition section I is circular at the end furthest from the sheet extrusion die transition section II and rectangular at the end closest to it. In other words, the cavity in the connecting transition section I transitions from a circle to a rectangle. A fluid-blocking device is installed inside the cavity of the sheet extrusion die transition section II. Each of the connecting transition section I, sheet extrusion die transition section II, and sheet extrusion die forming section III has an independent temperature-controlled oil chamber, which is connected to a mold temperature controller to control the temperature of each section. The mold temperature controller controls the temperatures of the connecting transition section I and the sheet extrusion die transition section II, ensuring that the temperature of the ultra-high molecular weight polymer material inside their cavities is slightly lower than the material's melting point. The mold temperature controller controls the temperature of the sheet extrusion die forming section III, ensuring that the temperature of the ultra-high molecular weight polymer material inside its cavity is higher than the material's melting point but lower than its degradation temperature. The ultra-high molecular weight polymer is a near-melting-point hot powder when passing through the extruder conveying equipment, the connecting transition section I, and the sheet extrusion die transition section II, which is conducive to transportation. When the powder passes through the connecting transition section I, the shape of its transport cross section changes from circular to rectangular, resulting in compression and compaction. When the powder passes through the sheet extrusion die transition section II, it flows through the resistance fluid of the sheet extrusion die transition section II (in section A of II) and reaches the die lip of the sheet extrusion die transition section II (section B of II), where the powder fluid pressure is basically uniformly distributed. In the sheet extrusion die forming section III, the near-melting-point hot powder is further heated and melted, and after passing through the sheet extrusion die forming section III, it is shaped and formed.

[0031] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the technical scope of the present invention. Therefore, any minor modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A method for extruding ultra-high molecular weight polymers, characterized in that, When ultra-high molecular weight polymers are transported through the extruder conveying equipment, they become near-melting-point hot powders after being heated by thermal radiation and friction. These are loose, heat-dissipating nascent particles. They then enter the transition zone of the molding equipment, where they remain near-melting-point hot powders and are gradually compacted. Next, they enter the compression zone of the molding equipment, where the near-melting-point hot powders are further compressed and compacted, and the temperature is raised again until they melt. Finally, they enter the setting zone, where the material is uniformly extruded into a melt at a constant temperature, quantity, and pressure, and then shaped to obtain the finished product. The molding equipment includes a first barrel, a second barrel, a first mandrel, a second mandrel, and a die. Each of the first barrel, second barrel, first mandrel, and second mandrel has an independent temperature-controlled oil chamber. The first barrel covers the outside of the first mandrel. One end of the first mandrel is fixedly connected to one end of the second mandrel. The second barrel and the die are sequentially arranged on the outside of the second mandrel from the side closest to the first mandrel to the side furthest from the mandrel. A first cavity is provided between the first barrel and the first mandrel. A second cavity is provided between the second barrel and the second mandrel. A third cavity, communicating with the first cavity, is located on the outer periphery of the first mandrel away from the first barrel. A fourth cavity, communicating with the second cavity, is located on the outer periphery of the second mandrel away from the second barrel. A fifth cavity is provided between the second mandrel and the die. The first, third, fourth, second, and fifth cavities are sequentially connected. The locations of the first, third, and fourth cavities form a transition zone, the location of the second cavity forms a compression zone, and the location of the fifth cavity forms a shaping zone.

2. The method for extruding ultra-high molecular weight polymers according to claim 1, characterized in that, The first barrel includes an outer layer and an inner layer, with a first temperature-controlled oil chamber disposed between the outer and inner layers. The second barrel includes an outer layer and an inner layer, with a second temperature-controlled oil chamber disposed between the outer and inner layers. The first mandrel includes an outer layer and an inner layer, with a third temperature-controlled oil chamber disposed between the outer and inner layers. The second mandrel includes an outer layer and an inner layer, with a fourth temperature-controlled oil chamber disposed between the outer and inner layers. The first, second, third, and fourth temperature-controlled oil chambers are independently configured and each is connected to a corresponding mold temperature controller.

3. The method for extruding ultra-high molecular weight polymers according to claim 1, characterized in that, The outer layer of the first barrel and the inner layer of the first barrel, the inner layer of the first barrel and the outer layer of the first mandrel, the outer layer of the first mandrel and the inner layer of the first mandrel, the inner layer of the first mandrel and the inner layer of the second mandrel, the outer layer of the second mandrel and the inner layer of the second mandrel, the outer layer of the second mandrel and the inner layer of the second barrel, the inner layer of the second barrel and the outer layer of the second barrel, and the outer layer of the second barrel and the die are all fixedly connected by bolts.

4. The method for extruding ultra-high molecular weight polymers according to claim 1, characterized in that, The first mandrel includes a flow divider cone and a connecting portion. The flow divider cone is fixedly disposed at one end of the connecting portion. The first barrel is covered on the flow divider cone. The third cavity is disposed around the connecting portion. The second mandrel includes a large cylindrical portion, a variable diameter portion, and a small cylindrical portion connected in sequence. The end of the large cylindrical portion away from the small cylindrical portion is fixedly connected to the connecting portion of the first mandrel. The fourth cavity is disposed around the large cylindrical portion. The second barrel is covered on the variable diameter portion. The die is covered on the small cylindrical portion.

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