Extruder for producing PET (Polyethylene Terephthalate) plates

Abstract

The invention provides an extruder for producing a PET (Polyethylene Terephthalate) plate. The extruder screw assembly comprises a first screw and a second screw which are used in pairs, each columnar screw comprises a first screw end and a second screw end in the length direction, and the diameter of the first screw end of each screw is larger than that of the second screw end, so that each screw is of a conical structure. The two screws are matched in the direction from the first screw end to the second screw end, and an included angle is formed between the center axis of the first screw and the center axis of the second screw and ranges from 10 minutes to 1 degree 20 minutes. In the PET plate production process, the two screws rotate in opposite directions. The included angle between the double screws of the extruder screw assembly is greatly reduced compared with the included angle between the screws of a conical double extruder in the prior art, the structure similar to that of a flat double extruder is achieved, a certain taper is achieved, the extruder screw assembly has the advantages of the flat double extruder and the conical double extruder, the plasticizing effect and the product machining efficiency can be guaranteed, and the production cost is reduced. The method is especially suitable for production of PET plates.

Description

Technical Field

[0001] The invention relates to the technical field of processing machinery, and in particular to an extruder for producing PET sheets. Background Art

[0002] The production of sheets requires the use of an extruder, which is the front-end equipment of the sheet production line and is used for the initial plasticization treatment of the blank and the extrusion of the blank.

[0003] In the prior art, extruders include single-screw extruders and twin-screw extruders.

[0004] Among them, the single-screw extruder has one screw, which is simpler in structure and easier to operate and maintain than the twin-screw extruder. It has higher production efficiency and lower energy consumption, and is mainly suitable for the processing of various plastic materials, such as polyethylene, polypropylene, polyvinyl chloride, etc., and can meet the needs of large-scale plastic processing.

[0005] Twin-screw extruders are mainly used in the sheet metal processing field. Twin-screw extruders have two screws. According to the structure of the screws and the matching structure of the two screws, they can be divided into parallel twin extruders (parallel twin-screw extruders) and conical twin extruders (conical twin-screw extruders).

[0006] Among them, the two screws of the flat twin extruder are both regular cylindrical, with the same diameter and center distance, so the material is kneaded more evenly. Under the same production capacity, the energy consumption is higher than that of the conical twin extruder. However, due to the small size of the center distance between the two screws, the pressure between the screws is small, resulting in small output torque and poor load resistance. The small end diameter of the conical twin extruder is different from the large end diameter, the two axes are at an angle, and the size of the center distance varies along the axis. The conical twin screw extruder can be equipped with larger radial bearings and thrust bearings, with large working torque and large load-bearing capacity.

[0007] Combined with the characteristics of twin-screw extruders in the prior art, under the same screw size, the parallel twin-screw extruder has low pressure, fast discharge and high efficiency. However, due to the low pressure, the plasticizing effect is poor, and it is necessary to increase the temperature and other means to improve the plasticizing effect. However, too high a temperature can easily cause the material to denature, and in severe cases, the material may be over-burned and become mushy, resulting in over-plasticization. The conical twin-screw extruder has a good plasticizing effect, but low production capacity.

[0008] According to the different materials of sheet processing, the equipment of the sheet production line can be improved in a targeted manner. Polyester (PET) sheets have the advantages of environmental protection and long service life. Different materials show different characteristics during the processing. PET material has high hardness and strength, which makes it brittle and rigid. It has a high glass transition temperature and requires a high processing temperature, but it is environmentally friendly. The existing PET sheet production line uses a co-rotating parallel twin-screw extruder. The screw needs to run at high speed, but the production capacity is low and the power consumption is high. It is impossible to achieve high-capacity production of PET sheets, which limits the promotion and application of PET sheets. Summary of the invention

[0009] The object of the present invention is to solve the above-mentioned technical problems and to provide an extruder for producing PET sheets, which has the advantages of good plasticizing property for PET materials and high processing efficiency.

[0010] To achieve the above object, the present invention adopts the following technical solution:

[0011] An extruder for producing PET sheets, comprising a barrel and a screw assembly arranged in the barrel, a first screw and a second screw used in pairs, the first screw and the second screw both being columnar, each columnar screw including a first screw end and a second screw end along the length direction, the diameter of the first screw end of each screw being greater than the diameter of the second screw end, so that each screw forms a tapered structure;

[0012] The outer peripheral wall of each screw is provided with a thread, and the two screws are matched from the first screw end to the second screw end, and the central axis of the first screw and the central axis of the second screw form an angle, and the range of the angle is 10' to 1°20';

[0013] The first screw is connected to the output shaft 1 of the driving gear reducer, and the second screw is connected to the output shaft 2 of the driving gear reducer. The driving rotation direction of the output shaft 1 of the driving gear reducer is opposite to that of the output shaft 2 of the driving gear reducer. In the process of producing PET sheets, based on one side of the second screw end, the first screw on the left side rotates counterclockwise, and the second screw on the right side rotates clockwise.

[0014] In some embodiments of the present invention, along the length direction of each screw, from the first screw end to the second screw end, each screw includes: a first screw segment, a first mixing segment, a second screw segment, a second mixing segment and a third screw segment; the screw where each screw segment is located has a spiral thread, and the screw where each mixing segment is located has multiple circles of toothed threads, and the toothed threads are arranged circumferentially around the circumference of the screw, and each circle of toothed threads includes a plurality of toothed protrusions arranged at intervals along the circumferential direction.

[0015] In some embodiments of the present invention, from the first screw end to the second screw end, the first screw section includes a feed section, a first temperature rise section and a second temperature rise section, the number of threads of the feed section, the first temperature rise section and the second temperature rise section are equal, and the pitch and the screw ridge dimensions in the axial direction of the screw decrease successively.

[0016] In some embodiments of the present invention, in the direction from the first screw end to the second screw end, the second screw section includes a first exhaust section and a compression section; an exhaust assembly is provided at the barrel corresponding to the position of the first exhaust section, which is used to discharge the gas inside the barrel to the outside of the barrel.

[0017] In some embodiments of the present invention, the number of threads of the first exhaust section and the compression section is equal, and the pitch and the dimensions of the screw flight in the axial direction of the screw decrease successively.

[0018] In some embodiments of the present invention, in the direction from the first screw end to the second screw end, the third screw section includes: a plasticizing section, a second exhaust section and a discharging section; an exhaust assembly is provided at the barrel corresponding to the position of the second exhaust section, which is used to discharge the gas inside the barrel to the outside of the barrel.

[0019] In some embodiments of the present invention, the plasticizing section includes a reflux section and a material blocking section, and a reflux groove is formed on at least part of the screw fins in the reflux section.

[0020] In some embodiments of the present invention, the lead of the material-blocking section is smaller than the lead of the reflow section, and the length of the reflow section is larger than the length of the material-blocking section and smaller than twice the length of the material-blocking section.

[0021] In some embodiments of the present invention, along the length direction of each screw, the third screw section includes a plasticizing section, a second exhaust section and a discharge section, and along the length direction of each screw, the discharge section includes a first discharge section and a second discharge section, the pitch of the first discharge section is greater than the pitch of the second discharge section and the number of heads in the first discharge section is less than the number of heads in the second discharge section, and a reflux groove is formed on at least part of the screw ridges of the first discharge section.

[0022] In some embodiments of the present invention, the temperature of the extruder in the first screw section is 210-260°C, the temperature from the first mixing section to the second screw section is 230-280°C, the temperature in the second exhaust section and the discharge section is 190-250°C, and the temperature decreases gradually from the second exhaust section to the discharge section.

[0023] Compared with the prior art, the technical advantages of the present invention are:

[0024] 1. The twin screw structure in the present invention is defined as a light cone flat twin screw structure. The angle between the twin screws of the screw assembly in the present invention is greatly reduced compared with the angle between the screws of the cone twin extruder in the prior art, reaching a structure similar to that of a flat twin extruder, but with a certain taper, thereby making it have the advantages of both flat twin and cone twin, and can ensure the plasticizing effect and product processing efficiency.

[0025] 2. Improving the screw structure in the extruder according to the characteristics of PET materials can provide suitable shear force for plasticizing PET materials, improve the plasticizing effect and efficiency, and reduce the energy consumption of the extrusion process. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0027] Figure 1 This is a schematic diagram of the structure of a twin-screw assembly in an embodiment of the present invention;

[0028] Figure 2 This is a schematic diagram of the distribution of each section along the axial direction of the screw in the embodiment of the present application;

[0029] Figure 3 for Figure 2 Cross-sectional view of the middle AA site;

[0030] Figure 4 for Figure 2 Cross-sectional view of the mid-BB area;

[0031] Figure 5 It is a structural schematic diagram of an extruder in an embodiment of the present invention;

[0032] In the above figures:

[0033] 1- barrel, 101- heating ring;

[0034] 2-first screw, 201-feeding section, 202-first heating section, 203-second heating section, 204-first mixing section, 205-first exhaust section, 206-compression section, 207-second mixing section, 208-toothed protrusion, 209-reflux section, 2091-reflux groove, 210-blocking section, 211-second exhaust section, 212-first discharging section, 213-second discharging section, 214-exhaust device, 215-first transition section, 216-second transition section;

[0035] 3- Second screw. DETAILED DESCRIPTION

[0036] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0037] It should be noted that when an element is referred to as being "disposed on", "connected to", another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element.

[0038] It should be understood that the orientation or positional relationship indicated by the terms "upper", "lower", "bottom", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0039] The terms "first" and "second" are used for descriptive purposes only and are not used to imply relative importance.

[0040] In the prior art, each screw of a conical twin extruder is a conical screw. The structural dimensions of common conical twin extruder screws include the following types:

[0041] In the prior art, each screw of the conical twin extruder is a conical screw, including an end with a larger diameter and an end with a smaller diameter. The structural dimensions of the common conical twin extruder screws include the following types. The diameter of the larger end is 100mm, and the corresponding diameter of the smaller end is about 50mm; the diameter of the larger end is 132mm, and the corresponding diameter of the smaller end is about 65mm; the diameter of the larger end is 188mm, and the corresponding diameter of the smaller end is about 92mm; the diameter of the larger end is 220mm, and the corresponding diameter of the smaller end is about 110mm. According to the design idea of ​​the existing conical twin extruder screw, usually, the diameter of the larger end is usually designed to be about 2 times the diameter of the smaller end. The characteristics of this design structure are: the taper of the screw is large, and the shear force between the twin screws is large, so the material is easier to plasticize. But the disadvantage is that it is easy to cause excessive plasticization. Especially for the processing of some materials with high requirements for plasticization indicators, the use of the conical twin extruder in the prior art will have the problem of difficult control of processing quality.

[0042] The material travel will also affect the plasticization time. Therefore, in order to solve the problem of excessive plasticization, the screw of the conical twin extruder is usually designed to be shorter. The aspect ratio is generally less than 22:1 of the middle diameter. However, a screw that is too short will affect the extruder's capacity.

[0043] Because the conical twin-screw extruder has a taper of nearly half, the space for materials to move forward inside the screw will become smaller and smaller, so the pressure will become greater and greater. In this way, the main machine needs to work hard to control the pressure during the production process. If it cannot be controlled, it will fluctuate, resulting in poor stability. The above is a description of the advantages and disadvantages of the conical twin-screw extruder.

[0044] The present invention provides an extruder for producing PET sheets, comprising a barrel 1 and a screw assembly arranged in the barrel 1. In the present invention, a twin-screw assembly is used in the extruder.

[0045] Structural reference of screw assembly Figure 1 , including a first screw 2 and a second screw 3 used in pairs, the first screw 2 and the second screw 3 are both columnar, and each columnar screw includes a first screw end and a second screw end along the length direction, and the diameter of the first screw end of each screw is greater than the diameter of the second screw end, so that each screw forms a conical structure.

[0046] The improvement of the present invention is to improve the taper structure of the screw in the prior art so that the twin screws have the advantages of a flat twin extruder and a conical twin extruder after being matched. It should be understood that the first screw 2 and the second screw 3 are of the same structure. The structure of the screw is specifically described below by taking the structure of one screw as an example.

[0047] Each screw has a very small taper close to that of a flat screw (i.e., a cylindrical screw of equal outer diameter), and the taper is very small relative to the length of the screw. The outer peripheral wall of each screw is provided with threads, and the two screws are matched from the first screw end to the second screw end. The central axis of the first screw and the central axis of the second screw form an angle, and the angle α ranges from 10′ to 1°20′. In the preferred implementation structure, the angle is 30′ to 50′. In the prior art, in order to pursue the effect of extrusion and shearing, the angle range of the conical twin extruder screw is usually designed to be relatively large. The angle between the twin screws of the screw assembly in the present invention is greatly reduced compared to the angle between the screws of the conical twin extruder in the prior art, achieving a structure similar to that of a flat twin extruder, but with a certain taper, so that it has the advantages of both a flat twin and a conical twin.

[0048] It should be understood that the twin screw structure of the present invention is a new type of screw structure between a flat screw and a conical screw. The twin screw structure of the present invention is defined as a light conical flat twin screw structure.

[0049] The existing conical screw has a large taper, and the diameter of the screw changes greatly from the feeding end to the discharging end, which generates a large shear force on the material. However, if it is not well controlled when used to process PET materials, it is easy to cause over-plasticization or paste. The existing flat screw has an equal outer diameter, and the shear force on the material is relatively stable, but the shear force is limited. When used to process PET materials, it will lead to insufficient plasticization process and the PET material cannot reach a good plasticization state. The flat twin-screw structure in this application has a smaller taper and a longer length than the existing conical screw, which can provide suitable shear force for the plasticization of PET materials, so that the PET material can be more fully plasticized without over-plasticization.

[0050] Usually, the screw end with a smaller diameter (corresponding to the second screw end in the present invention) of the conical twin screw is the discharge end, and the screw end with a larger diameter (corresponding to the first screw end in the present invention) is the feed end.

[0051] Usually, the extruder screw is driven by a reduction gear box. In some embodiments of the present invention, the first screw is connected to the output shaft 1 of the driving gear reduction box, and the second screw is connected to the output shaft 2 of the driving gear reduction box, and the driving rotation direction of the output shaft 1 of the driving gear reduction box is opposite to that of the output shaft 2 of the driving gear reduction box. In the process of producing PET sheets, with one side of the second screw end as the reference (i.e., observed from the discharge end), the first screw on the left side rotates counterclockwise, and the second screw on the right side rotates clockwise.

[0052] In the prior art, the extrusion molding process of PET materials is restricted by the structure of the screws. In the extrusion process, both screws rotate in the same direction and must run at high speed, resulting in high energy consumption but low production capacity. In the production of PET materials, the present invention adopts a scheme of rotating two screws in opposite directions. Compared with the existing scheme of rotating in the same direction, the rotation speed can be lower, for example, the rotation speed can be 10-40r / min, resulting in lower energy consumption but increased production capacity.

[0053] In some embodiments of the present invention, the diameter of the first screw end of each screw is in the range of 130 to 250 mm, and the diameters of the two screws at the first screw ends are the same.

[0054] In some embodiments of the present invention, the diameter of the second screw end of each screw is in the range of 100 to 190 mm, and the diameters of the two screws at the second screw ends are the same.

[0055] Generally, the capacity of an extruder is related to the length of the screw. Therefore, in some embodiments of the present invention, in order to ensure the capacity of the screw equipment, the length of the screw is 3 to 7 m.

[0056] In some embodiments of the present invention, the aspect ratio of each screw is 30:1 to 35:1, where the aspect ratio is the ratio of the length of the screw to the median diameter of the screw, and the median diameter of the screw is the average of the diameter of the first screw end and the diameter of the second screw end. For example, the diameter of the first end of the screw is 190 mm, the diameter of the second end is 150 mm, and the median diameter of the screw is 170 mm. The length of each screw can be further selected according to the aspect ratio of the screw.

[0057] For example, the ratio of the length to the median diameter of each screw can be 31:1, 32:1, 33:1, 34:1, etc., and the length can be 4m, 4.5m, 5m, 5.5m, etc. According to the length of the screw and the ratio of the length to the median diameter, the outer diameter value (maximum outer diameter) of the feeding end and the outer diameter value (minimum outer diameter) of the discharge end of the screw 22 can be determined, thereby determining the outer dimensions of the screw.

[0058] The light cone parallel twin-screw machine proposed in the present invention can make the screw of the cone twin extruder longer and the taper smaller, which can solve the problem of over-plasticization of the cone twin. It should be understood that the size ratio of the two screw head parts of the twin screw is improved, and the size ratio of the two screw heads is no longer close to 2, but is reduced. For example, the first screw end adopts 200mm and the second screw end adopts 150mm, thereby controlling the taper. By reducing and retaining the appropriate taper of the conical twin screw, the appropriate pressure will be retained, and the advantage of the conical twin screw that is easy to plasticize will be controlled within an appropriate range. Since the screw taper is small, the degree of plasticization will be reduced. The present invention achieves the plasticization requirements by increasing the appropriate length.

[0059] Based on the above screw length configuration structure, it is proposed to manufacture PET sheets by rotating the screw in opposite directions, which can ensure the plasticizing effect, processing quality and processing efficiency of the PET sheets. In addition, the taper and length of the screw are limited in this scheme. The screw has a longer length and a smaller taper than the existing conical screw, so that the combination of the shear force provided by the screw and the action time on the PET material is optimized, the plasticizing process of the PET material is more sufficient, the plasticizing effect is improved, and the required processing state is obtained.

[0060] The present invention further designs the structure of each thread segment of the extruder screw. The design of the thread segment on the first screw 2 is taken as an example to illustrate the structure of the thread segment. The structure of the thread segment on the second screw 3 is the same as that of the first screw 2, and will not be repeated.

[0061] The functions of each section of the screw are realized by the design of the screw fins (including pitch, lead, and number of heads) on the screw, the design of the screw length, and the temperature control of the barrel 1. It can be understood that the focus of this application is on the adjustment of the distribution of each functional section on the screw after the improvement of the screw structure, rather than on how to specifically realize the functions of each section. In order to realize the solutions for the corresponding functions of each section, those skilled in the art can refer to the prior art. Anything not described in this application should not be considered as insufficient disclosure of this application.

[0062] In some embodiments of the present invention, along the length direction of the first screw 2, from the first screw end to the second screw end, the first screw 2 includes: a first screw segment, a first mixing segment 204, a second screw segment, a second mixing segment 207 and a third screw segment. The first mixing segment 204 and the second mixing segment 207 are used to mix and crush the materials.

[0063] The initial state of the material when it is added to the extruder 2 is solid, granular or powdery. The barrel 1 of the extruder is provided with a heating coil 101 corresponding to each section of the screw to control the temperature inside each section of the barrel 1. In this embodiment, based on the improvement of the screw structure, the functional sections of the screw from the feed end to the discharge end are rearranged, and two mixing sections and two exhaust sections are provided, so that the PET material is mixed more fully before entering the plasticizing section and the exhaust is more thorough.

[0064] The screw where each screw segment is located has a spiral thread, and the screw where each mixing section is located has multiple turns of toothed threads, which are arranged circumferentially around the circumference of the screw, and each turn of toothed threads includes a plurality of toothed protrusions 208 arranged at intervals along the circumferential direction.

[0065] When applied to an extruder, the first screw segment is located near the feeding end of the extruder and is used to preheat the material. The length of the first screw segment accounts for 30% to 40% of the total length of the first screw 2, and the pitch of the first screw segment is 50 to 65 mm. From the first screw end to the second screw end, the first screw segment includes a feeding segment 201, a first heating segment 2021 and a second heating segment 2022.

[0066] The number of threads of the feed section 201, the first temperature rising section 2021 and the second temperature rising section 2022, the feed section 201, the first temperature rising section 202 and the second temperature rising section 203 are equal, and the pitch and the spiral flight in the axial direction of the screw are reduced successively. The length of the feed section 201 is ≥ the length of the first temperature rising section 2021, and the length of the first temperature rising section 202 is > the length of the second temperature rising section 2022, the number of threads of the feed section 201, the first temperature rising section 2021 and the second temperature rising section 2022 are equal, and the pitch and the spiral flight in the axial direction of the first screw 2 are reduced successively. In this embodiment, the first screw section occupies a longer length, so that the material can be fully heated before mixing, and by dividing the first screw section into three functional sections and reducing the pitch and spiral flight size of each section successively, the material can be heated more fully and better transition to the first mixing section 204.

[0067] In a preferred implementation structure, the number of heads of the feeding section 201, the first temperature rising section 202 and the second temperature rising section 203 are all 3, the lead is between 140-190 mm, and the pitch is between 45-70 mm.

[0068] In some embodiments of the present invention, from the first screw end to the second screw end, the second screw segment includes a first exhaust segment 205 and a compression segment 206; an exhaust assembly is provided at the barrel 1 corresponding to the position of the first exhaust segment 205, which is used to discharge the gas inside the barrel 1 to the outside of the barrel 1. The compression segment 206 is used to apply pressure to the material to compress the material.

[0069] In some embodiments of the present invention, the number of threads of the first exhaust section 205 and the compression section 206 is equal, and the pitch and the size of the screw ridges in the axial direction of the screw are successively reduced. The pitch of the compression section 206 is smaller than the pitch of the first exhaust section 205 and larger than the interval between the stirring components of the first mixing section 204 and the second mixing section 207, and the size of the screw ridges of the compression section 206 in the axial direction of the first screw 2 is smaller than the length of the tooth-like protrusions 231 of the first mixing section 204 and the second mixing section 207 in the axial direction of the first screw 2. The small pitch and small size of the screw ridges of the compression section 206 can enhance the extrusion effect on the material, so that the material is compressed more tightly.

[0070] In some embodiments of the present invention, along the length direction of each screw, the third screw section includes a plasticizing section, a second exhaust section and a discharge section, the plasticizing section is used to provide shear force so that the material compressed by the compression section 206 is in a molten state, and the discharge section is used to output the molten material from the extruder into the mold, and along the length direction of each screw, the discharge section includes a first discharge section 212 and a second discharge section 213, the pitch of the first discharge section 212 is greater than the pitch of the second discharge section and the number of heads in the first discharge section 212 is less than the number of heads in the second discharge section 213, and a reflux groove is formed on at least part of the screw ridges of the first discharge section 212.

[0071] In some embodiments of the present invention, from the first screw end to the second screw end, the plasticizing section further includes a reflux section 209 and a material blocking section 210, and a reflux groove 2091 is formed on at least part of the screw ribs in the reflux section 209. The lead of the material blocking section 210 is smaller than the lead of the reflux section 209, and the length of the reflux section 209 is greater than the length of the material blocking section 210 and less than twice the length of the material blocking section 210. The reflux section 209 can make part of the material reflux in the first screw 2. During the reflux process, the materials entering the first screw 2 at different levels and times can be fully mixed, which increases the residence time of the material in the plasticizing section, promotes heat transfer, further promotes the plasticization of the material, and ensures that the material reaches a good plasticized state; the lead of the reflux section 209 can be 80-100mm (for example, 90mm), and the lead of the blocking section 210 is smaller, which can be 40-55mm (for example, 50mm). The axial advancement speed of the material in the blocking section 210 is relatively slow, and the pressure can be adjusted to prevent excessive reflux of the material, so that the material flowing out of the reflux section 209 can be orderly and stably advanced in the blocking section 210 in a predetermined direction, making the plasticization process more stable. In addition, the design of the length of the reflux section 209 and the blocking section 210 can find a balance between plasticization efficiency and plasticization effect, so that the material can be fully processed and the extrusion process can be completed efficiently.

[0072] In some embodiments of the present invention, the lead of the material blocking segment 210 is smaller than the lead of the reflow segment 209 , and the length of the reflow segment 209 is larger than the length of the material blocking segment 210 and smaller than twice the length of the material blocking segment 210 .

[0073] In some embodiments, the pitch and spiral ridge of the first exhaust section 205 and the second exhaust section 211 are the same, and the pitch and spiral ridge of the first exhaust section 205 and the second exhaust section 211 in the axial direction of the screw 22 are larger than the pitch and spiral ridge of other sections of the screw 22 in the axial direction of the screw 22, and the length of the second exhaust section 211 is larger than the length of the first exhaust section 205 and smaller than twice the length of the first exhaust section 205. The large pitch and large spiral ridge of the exhaust section can increase the residence time of the material in the exhaust section and reduce the pressure, which helps the gas in the material to be discharged out of the barrel 21. In addition, the two exhaust sections are designed at the rear end of the first mixing section 203 and the rear end of the plasticizing section 226, which helps to improve the plasticizing effect of the PET material, and the second exhaust section 211 has a longer length, which helps to fully discharge the gas in the plasticized material, further reducing the defects such as bubbles in the product.

[0074] In some embodiments, three exhaust devices are provided, wherein one exhaust device 214 is provided at the first exhaust section 205 , and two exhaust devices 214 are provided side by side at the second exhaust section 211 in the processing direction.

[0075] In some embodiments, a first transition section 215 is provided between the first mixing section 203 and the first exhaust section 205, and a second transition section 216 is provided between the second mixing section 207 and the plasticizing section; the pitch of the first transition section 215 is greater than the spacing of the stirring components 23 of the first mixing section 203 and less than the pitch of the first exhaust section 205; the pitch of the second transition section 215 is greater than the spacing of the stirring components 23 of the second mixing section 207 and greater than the pitch of the plasticizing section 226.

[0076] In some embodiments, the discharge section 228 includes a first discharge section 212 and a second discharge section 213 disposed at the rear end of the second exhaust section 227 along the processing direction, the pitch of the first discharge section 212 is greater than the pitch of the second discharge section 213, the number of heads of the first discharge section 212 is less than the number of heads of the second discharge section 213, and the length of the first discharge section 212 is greater than twice the length of the second discharge section 213. The design of the first discharge section 212 and the second discharge section 213 in the discharge section can efficiently convey materials and establish a stable pressure, so that the materials are smoothly conveyed forward, and quality problems of the product caused by pressure fluctuations are avoided.

[0077] In some embodiments of the present invention, the temperature of the extruder in the first screw section is 210-260°C, the temperature from the first mixing section to the second screw section is 230-280°C, the temperature in the second exhaust section and the discharge section is 190-250°C, and the temperature decreases from the second exhaust section to the discharge section. This temperature configuration can be more suitable for the production of PET material sheets.

[0078] The process of using the present invention for the production of PET sheets is as follows.

[0079] Mix the mixture of PET material and auxiliary materials with calcium powder in a ratio of 1:2 to 1:5;

[0080] The mixed material is fed into the extruder for extrusion molding, and the two screws of the extruder rotate in opposite directions and at a speed of 10 to 40 r / min;

[0081] The material plasticized by the extruder enters the mold for forming, and the temperature of the mold is 220-260°C;

[0082] The slab after the mold forming process enters the calender for calendering. The temperature of the calendering roller of the calender is 180-250℃.

[0083] The slab output from the calender is cut into PET sheets.

[0084] The present invention can improve the problem that when PET materials are extruded by an existing extruder, the plasticization process is difficult to control, insufficient plasticization or over-plasticization is likely to occur, the current fluctuation is large, the product quality is unstable and the production capacity is low, and the production quality of PET sheets is improved.

[0085] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. An extruder for producing PET sheets, characterized in that: The invention comprises a barrel and a screw assembly arranged in the barrel, a first screw and a second screw used in pairs, the first screw and the second screw are both columnar, and each columnar screw comprises a first screw end and a second screw end along the length direction, and the diameter of the first screw end of each screw is greater than the diameter of the second screw end, so that each screw forms a tapered structure; The outer peripheral wall of each screw is provided with a thread, and the two screws are matched from the first screw end to the second screw end, and the central axis of the first screw and the central axis of the second screw form an angle, and the range of the angle is 10' to 1°20'; The first screw is connected to the output shaft 1 of the driving gear reducer, and the second screw is connected to the output shaft 2 of the driving gear reducer. The driving rotation direction of the output shaft 1 of the driving gear reducer is opposite to that of the output shaft 2 of the driving gear reducer. In the process of producing PET sheets, based on one side of the second screw end, the first screw on the left side rotates counterclockwise, and the second screw on the right side rotates clockwise.

2. The extruder for producing PET sheets according to claim 1, characterized in that Along the length direction of each screw, from the first screw end to the second screw end, each screw includes: a first screw segment, a first mixing segment, a second screw segment, a second mixing segment and a third screw segment; the screw where each screw segment is located has a spiral thread, and the screw where each mixing segment is located has multiple circles of toothed threads, and the toothed threads are arranged circumferentially around the circumference of the screw, and each circle of toothed threads includes a plurality of toothed protrusions arranged at intervals along the circumferential direction.

3. The extruder for producing PET sheets according to claim 2, characterized in that From the first screw end to the second screw end, the first screw section includes a feed section, a first temperature rise section and a second temperature rise section. The number of threads in the feed section, the first temperature rise section and the second temperature rise section is equal, and the pitch and the screw ridge dimensions in the axial direction of the screw decrease successively.

4. The extruder for producing PET sheets according to claim 2, characterized in that From the first screw end to the second screw end, the second screw section includes a first exhaust section and a compression section; an exhaust assembly is provided at the barrel corresponding to the position of the first exhaust section, which is used to discharge the gas inside the barrel to the outside of the barrel.

5. The extruder for producing PET sheet according to claim 5, characterized in that The number of threads of the first exhaust section and the compression section is equal, and the pitch and the dimensions of the screw flight in the axial direction of the screw decrease successively.

6. The extruder for producing PET sheets according to claim 2, characterized in that In the direction from the first screw end to the second screw end, the third screw section includes: a plasticizing section, a second exhaust section and a discharging section; an exhaust assembly is provided at the barrel corresponding to the position of the second exhaust section, which is used to discharge the gas inside the barrel to the outside of the barrel.

7. The extruder for producing PET sheets according to claim 6, characterized in that The plasticizing section comprises a reflux section and a material blocking section, and a reflux groove is formed on at least part of the screw edges in the reflux section.

8. An extruder for producing PET sheets as claimed in claim 6 or 7, characterized in that The lead of the material blocking section is smaller than the lead of the reflow section, and the length of the reflow section is larger than the length of the material blocking section and smaller than twice the length of the material blocking section.

9. The extruder for producing PET sheet according to claim 2, characterized in that: Along the length direction of each screw, the third screw section includes a plasticizing section, a second exhaust section and a discharge section. Along the length direction of each screw, the discharge section includes a first discharge section and a second discharge section. The pitch of the first discharge section is greater than the pitch of the second discharge section and the number of heads in the first discharge section is less than the number of heads in the second discharge section. A reflux groove is formed on at least part of the screw ridges of the first discharge section.

10. The extruder for producing PET sheets according to claim 9, characterized in that The temperature of the extruder in the first screw section is 210-260° C., the temperature from the first mixing section to the second screw section is 230-280° C., the temperature in the second exhaust section and the discharge section is 190-250° C., and the temperature decreases gradually from the second exhaust section to the discharge section.

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