PET plate production line and production method

Abstract

The invention relates to a PET plate production line and a production method. The PET plate production line comprises an extruder, a mold and a calender which are arranged in the machining direction. The extruder comprises a machine barrel and a double-screw assembly arranged in the machine barrel. The double-screw assembly comprises two screws meshed with each other, the outer diameter of each screw is decreased in the machining direction, the included angle between the central axes of the two screws ranges from 10 minutes to 1 degree 20 minutes, and the rotation directions of the two screws are opposite. The production line is improved according to the characteristics of PET materials, the plasticizing effect of the PET materials is improved, the quality of PET plates is guaranteed, the productivity of the production line is improved, and energy consumption is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of plate manufacturing, and in particular relates to a PET plate production line and a production method. Background Art

[0002] Currently, the PVC sheets widely used in the market have many shortcomings. First, the environmental friendliness of PVC materials is poor. During production and use, harmful substances may be released, affecting indoor air quality. Secondly, the wear resistance and heat resistance of PVC sheets are relatively low, and they are prone to fading, deformation and other problems after long-term use. In addition, the recycling rate of PVC sheets is low, resulting in waste of resources and environmental pollution. Therefore, seeking more environmentally friendly and durable alternative materials has become an urgent need for the development of the industry.

[0003] As an emerging alternative material, polyester (PET) material has superior performance. First of all, PET material performs well in environmental protection, and the emission of waste gas and harmful substances during the production process is extremely low, which meets the needs of modern green buildings. Secondly, the wear resistance and compression resistance of PET material are better than traditional PVC materials, and it has a longer service life. In addition, PET material has good heat resistance. In addition, PET material has good recyclability, which can reduce the impact of production on the environment and conform to the concept of sustainable development.

[0004] Although PET materials have many advantages, there is currently no high-capacity production line that can be applied to PET sheets. This is mainly because the equipment and processes of existing high-capacity production lines are mainly designed for other types of materials. Due to the unique physical properties of PET materials, when using existing high-capacity production lines for production, the plasticization requirements of PET materials may not be met in the mixing, extrusion and molding links, resulting in unstable product quality and low output. In addition, the existing production lines for PET sheets use co-rotating parallel twin screws in their extruders, which need to run at high speeds, but have low production capacity and high power consumption, and cannot achieve high-capacity production of PET sheets, limiting the promotion and application of PET sheets. Summary of the invention

[0005] In view of at least one shortcoming existing in the related art, the present invention provides a PET sheet production line and a production method, which improves the production line according to the characteristics of PET materials, improves the plasticizing effect of PET materials, ensures the quality of PET sheets, increases the production capacity of the production line and reduces energy consumption.

[0006] On the one hand, the present application provides a PET sheet production line, including an extruder, a mold and a calender arranged along a processing direction, wherein the extruder includes:

[0007] Barrel;

[0008] The twin screw assembly is arranged in the barrel. The twin screw assembly includes two screws meshing with each other. The outer diameter of each screw decreases along the processing direction, and the angle between the central axes of the two screws is 10'~1°

[0009] 20′, the two screws rotate in opposite directions.

[0010] In some embodiments of the first aspect, the two screws have the same size, the average of the maximum and minimum values ​​of the outer diameter of each screw is the median diameter, the ratio of the length of each screw to the median diameter is 25:1 to 35:1, and the length of each screw is 3 to 7 m.

[0011] In some embodiments of the first aspect, each screw includes a preheating section, a first mixing section, a first exhaust section, a compression section, a second mixing section, a plasticizing section, a second exhaust section and a discharging section in sequence along the processing direction; the preheating section is used to stir the material and cooperate with the barrel to heat the material; the first mixing section and the second mixing section are used to mix and crush the material; the barrel is respectively provided with exhaust devices at positions corresponding to the first exhaust section and the second exhaust section, and the exhaust device is connected to the inside of the barrel for discharging waste gas generated during the extrusion molding process of the material; the compression section is used to apply pressure to the material to compress the material; the plasticizing section is used to provide shear force to make the compressed material in a molten state; the discharging section is used to output the molten material from the extruder into the mold.

[0012] In some embodiments of the first aspect, the calender includes a frame and a plurality of calendering roller groups arranged on the frame along a processing direction, and the slab formed by the mold enters the calender for calendering, wherein the calendering roller located above the slab conveying path is the upper calendering roller, and the calendering roller located below the slab conveying path is the lower calendering roller, each group of calendering roller groups includes an upper calendering roller and a lower calendering roller correspondingly arranged above and below, or only includes one lower calendering roller, and a conveying device is provided between at least two adjacent calendering roller groups; the conveying device includes a plurality of rollers arranged between the two adjacent calendering roller groups and a conveyor belt surrounding the plurality of rollers, the upper end surfaces of the plurality of rollers are located on the same plane so that the upper surface of the conveyor belt constitutes a plane, and the plane where the upper surface of the conveyor belt is located is tangent to the roller surface of the lower calendering roller in the two adjacent calendering roller groups.

[0013] In some embodiments of the first aspect, the conveying device also includes a roller mounting member, both ends of each roller are respectively mounted on the frame via the roller mounting member, the roller mounting member is formed with a mounting groove, both ends of each roller are respectively formed with a mounting shaft, the mounting shaft is arranged in the mounting groove and supported by the bottom of the mounting groove to mount the roller on the frame; a bolt hole connected to the bottom of the mounting groove is opened in the roller mounting member, an adjustment bolt is threadedly installed in the bolt hole, and the end of the adjustment bolt extends into the mounting groove from the bottom of the mounting groove and supports the roller.

[0014] In some embodiments of the first aspect, at least one calendering roller group among the multiple calendering roller groups includes only one lower calendering roller, and a first baking device is arranged above the calendering roller group including only one lower calendering roller to heat the slab.

[0015] In some embodiments of the first aspect, a displacement sensor for measuring the lifting distance of the upper calendering roller is provided corresponding to each upper calendering roller, and a second drive motor for controlling the lifting and lowering of the upper calendering roller is provided on the frame. The displacement sensor is connected to the second drive motor and is configured to send a signal to the second drive motor to lift the upper calendering roller to a set position.

[0016] In some embodiments of the first aspect, a cooling bracket, a traction machine and a cutting device are provided at the rear end of the calender, and a second baking device is also provided at the front end of the traction machine, and the second baking device is used to heat the PET sheet before cutting.

[0017] The second aspect of the present application provides a method for producing a PET sheet, which is produced by using any PET sheet production line of the first aspect, comprising the following steps:

[0018] Mix the mixture of PET material and auxiliary materials with calcium powder in a ratio of 1:2-5;

[0019] The mixed materials are fed into an extruder for extrusion molding. The two screws of the extruder rotate in opposite directions and the speed is 10-40r / min.

[0020] The material plasticized by the extruder enters the mold for molding;

[0021] The formed slab enters the calender for calendering;

[0022] The slab output from the calender is cut into PET sheets.

[0023] In some embodiments of the second aspect, the screw of the extruder includes a preheating section, a first mixing section, a first exhaust section, a compression section, a second mixing section, a plasticizing section, a second exhaust section and a discharging section in sequence along the processing direction; the temperature of the extruder in the preheating section is 210 to 260°C, the temperature from the first mixing section to the plasticizing section is 230 to 280°C, the temperature from the second exhaust section to the discharging section is 190 to 250°C, and the temperature decreases from the second exhaust section to the discharging section; the temperature of the mold is 220 to 260°C; the temperature of the calendering roller in the calender is 180 to 250°C.

[0024] Compared with the prior art, the advantages and positive effects of the present invention are:

[0025] (1) The production line of PET sheets provided by at least one embodiment of the present invention improves the screw structure in the extruder according to the characteristics of the PET material, thereby providing a suitable shear force for plasticizing the PET material, improving the plasticizing effect and plasticizing efficiency, and reducing the energy consumption of the extrusion process;

[0026] (2) In at least one embodiment of the present invention, a PET sheet production line is provided with a conveying device between adjacent calendering roller groups. The conveying device uses a conveyor belt to convey the sheet, and the inclination of the conveyor belt is adjustable, which can effectively avoid deformation of the sheet surface and ensure the flatness of the final PET sheet;

[0027] (3) The production line of PET sheets provided by at least one embodiment of the present invention is provided with baking devices in the calender and before the traction machine according to the changes in material properties during the production process of the PET sheets, so that the sheet blanks can be heated according to actual needs to avoid the problem of sheet cracking caused by excessive brittleness of the sheet blanks during the calendering and cutting processes;

[0028] (4) The production method of PET sheets provided by at least one embodiment of the present invention adopts an improved production line to produce PET sheets and increases the proportion of calcium powder in the material, thereby realizing low-speed heterogeneous extrusion. At the same time, the temperature of the mold and the temperature of the calender roller are limited to a suitable range according to the characteristics of the PET material, thereby ensuring the quality of the finished PET sheets, while improving production capacity and reducing energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of this application. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0030] Figure 1a A side view of a PET sheet production line provided in an embodiment of the present application;

[0031] Figure 1b A top view of a PET sheet production line provided in an embodiment of the present application;

[0032] Figure 2 This is a schematic diagram of the structure of the extruder in the embodiment of the present application;

[0033] Figure 3 This is a schematic diagram of the structure of a twin-screw assembly in an embodiment of the present application;

[0034] Figure 4a 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;

[0035] Figure 4b for Figure 4aCross-sectional view of the middle AA site;

[0036] Figure 4c for Figure 4a Cross-sectional view of the mid-BB area;

[0037] Figure 5a This is a structural schematic diagram 1 of a calender in an embodiment of the present application;

[0038] Figure 5b The structure of the calender in the embodiment of the present application is shown in FIG. Figure 2 ;

[0039] Figure 5c A side view of a calender in an embodiment of the present application;

[0040] Figure 6 for Figure 5c A partial enlarged view of the middle part C;

[0041] Figure 7 This is a structural schematic diagram 1 of the transmission device in an embodiment of the present application;

[0042] Figure 8 The structure of the transmission device in the embodiment of the present application is shown in FIG. Figure 2 ;

[0043] Figure 9a This is a schematic diagram of the structure of the conveying device after the conveyor belt is removed in the embodiment of the present application, so as to fully illustrate the structure of the roller mounting member;

[0044] Figure 9b for Figure 9a A partial enlarged view of the middle portion D, wherein the roller mounting part is partially cut away to show the internal bolt holes;

[0045] Fig.10 This is a schematic diagram of one side of a calender equipped with a displacement sensor in an embodiment of the present application.

[0046] In the figure:

[0047] 1. Loading machine;

[0048] 2. Extruder; 21. Barrel; 211. Barrel sleeve; 22. Screw; 221. Preheating section; 2211. Feeding section; 2212. First heating section; 2213. Second heating section; 222. First mixing section; 223. First exhaust section; 224. Compression section; 225. Second mixing section; 226. Plasticizing section; 2261. Reflux section; 2262. Blocking section; 2263. Reflux trough; 227. Second exhaust section; 228. Discharging section; 2281. First discharging section; 2282. Second discharging section; 229. First transition section; 2210. Second transition section; 23. Stirring assembly; 231. Tooth-shaped protrusion; 24. Exhaust device; 25. Heating coil;

[0049] 3. Mould;

[0050] 4. Calender; 41. Frame; 42. Calender roller group; 421. Upper calender roller; 422. Lower calender roller; 43. Conveyor; 431. Support roller; 4311. Mounting shaft; 432. Conveyor belt; 433. Support roller mounting member; 4331. Mounting groove; 4332. Bolt hole; 434. Adjusting bolt; 435. First driving motor; 436. Driving roller; 437. Guide roller; 44. First baking device; 45. Lifter; 46. Connecting rod; 47. Displacement sensor; 48. Second driving motor;

[0051] 5. Cooling bracket;

[0052] 6. Second baking device;

[0053] 7. Traction machine;

[0054] 8. Cutting device;

[0055] 9. Ground running track. DETAILED DESCRIPTION

[0056] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0057] Reference to "embodiments" in this application means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those of ordinary skill in the art that the embodiments described in this application may be combined with other embodiments without conflict.

[0058] In the description of the present invention, it should be understood that the terms "upper", "lower", "front", "back", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings, and are 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 limiting the present invention. The terms "first" and "second" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features.

[0059] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0060] In a first aspect, the present application provides a PET sheet production line, which is particularly suitable for producing PET sheets, but it is understandable that other types of sheets can also be produced according to actual conditions. Figure 1a and Figure 1b As shown, in some embodiments, the PET production line includes a feeder 1, an extruder 2, a mold 3, a calender 4, a cooling bracket 5, a traction machine 7, a cutting device 8, etc. along the processing direction.

[0061] The materials are mixed by the feeder 1 and then enter the extruder 2 for processing. The extruder 2 used in the embodiment of the present application is a twin-screw extruder, and the materials are transported forward in the extruder 2 by the rotation of the screw. In the process of the forward movement of the materials, the materials are fully mixed, melted and plasticized through heating, shearing and compression of the screw, providing the prerequisite for the subsequent molding of the plate.

[0062] Different materials present different characteristics during processing, for example, PET material has higher hardness and strength, making it brittle and rigid, with higher glass transition temperature, requiring higher processing temperature, but good environmental protection. When PET material is extruded by existing extruder, the plasticizing process is difficult to control, and the problem of insufficient or over-plasticizing of plasticizing is prone to occur, and the current fluctuation is large, the product quality is unstable and the production capacity is low. In view of the above problems, the application first starts with extruder 2 to improve the production line, improves the plasticizing effect of PET material, and is conducive to improving the quality of subsequent sheet forming.

[0063] like Figure 2 and Figure 3 As shown, the extruder 2 includes a barrel 21 and a twin-screw assembly disposed in the barrel 21. The twin-screw assembly includes two screws 22 meshing with each other, the outer diameter of each screw 22 gradually decreases along the processing direction, and the angle α between the central axes of the two screws 22 is 10′ to 1°20′, and the two screws 22 rotate in opposite directions, that is, one screw 22 rotates clockwise and the other screw 22 rotates counterclockwise. Figure 3 FIG. 1 is a schematic diagram of the structure of a twin-screw assembly. In order to more clearly illustrate the inclination of the screw 22, Figure 3 The threads on the screw 22 are not shown. Figure 3As shown, the two screws 22 have a very small taper close to that of a flat screw (i.e., a cylindrical screw with the same outer diameter), and the taper is very small relative to the length of the screw 22. The angle between the central axes of the two screws 22 is α, and the value range of α is 10′ to 1°20′. The final value of α can be determined according to the composition of the material and the processing conditions, for example, α can also be 30′, 35′, 40′, 1°, 1°10′, etc. Optionally, α is 10′ to 1°.

[0064] In some embodiments, the two screws 22 have the same size, the average of the maximum and minimum values ​​of the outer diameter of each screw 22 is the median diameter, the ratio of the length of each screw 22 to the median diameter is 25:1 to 35:1, and the length of each screw 22 is 3 to 7 meters. In this solution, the taper and length of the screw 22 are limited. The screw 22 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 22 and the action time on the PET material is optimized, the plasticization process of the PET material is more sufficient, the plasticization effect is improved, and the desired processing state is obtained. For example, the ratio of the length to the median diameter of each screw 22 can be 26:1, 27:1, 28:1, 29:1, 30:1, 31:1, 32:1, 33:1, 34:1, etc., and the length can be 3.5m, 4m, 4.5m, 5m, 5.5m, 6m, 6.5m, 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 discharging end of the screw 22 can be determined, thereby determining the outer dimensions of the screw 22.

[0065] The twin screw assembly used in the extruder 2 is a new type of screw structure between a flat twin screw and a conical twin screw. The existing conical twin screw has a large taper, and the diameter of the screw from the feeding end to the discharging end varies greatly. For example, the maximum diameter is about twice the minimum diameter, the length is small, and the aspect ratio is between 22:1 and 28:1. The space for the material to move forward inside the screw will become smaller and smaller, and the pressure on the material will become greater and greater. The plasticizing ability is good, but when used to process PET materials, it is easy to over-plasticize or paste if it is not well controlled. In addition, the pressure needs to be controlled during the production process. If it is not well controlled, it will fluctuate, resulting in poor stability. The existing parallel twin screws have the same outer diameter and no taper. Compared with the tapered twin screws, their plasticizing capacity is slightly worse. Therefore, it is necessary to increase the length of the screw to improve the plasticizing effect. The aspect ratio of the existing parallel twin screws is generally above 30:1, and some may reach 38:1 or even above 40:1. Since the parallel twin screws do not have taper, the material will not generate pressure and fluctuation during the forward advancement process. Therefore, the production process is easier to control and has good stability. However, when used for processing PET materials, the plasticizing process will not be sufficient and the PET materials cannot reach a good plasticizing state. The twin-screw assembly designed in the present application is designed and developed based on the above two existing screw structures. By retaining and reducing the appropriate taper of the conical twin screw, the disadvantage of the conical twin screw being easily over-plasticized is avoided. By retaining appropriate pressure, the advantage of the conical twin screw being easy to plasticize is controlled within an appropriate range. Correspondingly, due to the reduction in taper, the plasticizing ability is relatively weakened. The required degree of plasticization is achieved by appropriately increasing the length of the screw. Compared with the existing conical screw, it has a smaller taper and a longer length, and can provide suitable shear force for the plasticization of PET materials, so that the PET material can be more fully plasticized without over-plasticization. It is easier to control during the production process and has good stability. It also combines the advantages of a conical twin screw and a flat twin screw.

[0066] In one embodiment of the present application, the twin screw assembly is designed based on the existing 92 conical twin screw, the maximum diameter of the existing 92 conical twin screw is 188 mm, and the minimum diameter is 92 mm. The average value of the maximum diameter and the minimum diameter of the existing conical twin screw is (188+92) / 2=140. Optionally, 190 mm and 145 mm are respectively taken as the minimum diameter of the maximum diameter of the screw in the twin screw assembly in one embodiment of the present application, and the ratio of length to median diameter is taken as 33:1. The length of the screw is (190+145) / 2*33=5527.5 mm. Therefore, the length is taken as 5527 mm, and this form of twin screw assembly is named 168 light conical flat twin screw.

[0067] In addition, the existing PET material extrusion molding process is restricted by the structure of the screw. During 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. Based on the improvement of the screw structure, the extruder 2 can adopt a scheme of rotating in opposite directions with two screws 22. Compared with the existing scheme of rotating in the same direction, the rotation speed can be lower, for example, the rotation speed can be 25-40r / min, resulting in lower energy consumption but increased production capacity.

[0068] In some embodiments, Figure 4a As shown, each screw 22 includes a preheating section 221, a first mixing section 222, a first exhaust section 223, a compression section 224, a second mixing section 225, a plasticizing section 226, a second exhaust section 227 and a discharge section 228 in the processing direction. The initial state of the material when it is added to the extruder 2 is solid, granular or powdery. The barrel 21 of the extruder 2 is provided with a heating ring 25 corresponding to each section of the screw 22 to control the temperature inside each section of the barrel 21. 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.

[0069] The functions of each section of the screw 22 are achieved through the design of the screw ridges on the screw 22 in conjunction with the temperature control of the barrel 21. 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 screw structure is improved, rather than on how to specifically achieve the functions of each section. In order to achieve the corresponding functions of each section, technical personnel in this field can refer to the prior art to achieve it. Anything not described in this application should not be considered as insufficient disclosure of this application.

[0070] The barrel 21 continuously heats the material in the preheating section 221, and the preheating section 221 of the screw 22 continuously turns the material so that the material can be heated evenly to ensure the preheating effect. The first mixing section 222 and the second mixing section 225 are used to mix and crush the material so that the dispersed phase size of the material is smaller and the distribution is more uniform. During the rotation of the screw 22, the material is subjected to the shear force between the screw 22 and the barrel 21 and between the different flow layers inside the material to achieve mixing. During the material processing process, the air, water vapor and low-molecular volatiles entrained in the material will be discharged. If they are not discharged in time, defects such as bubbles and voids will be formed in the product, resulting in a decrease in product quality. Figure 2As shown, the barrel 21 is provided with exhaust devices 24 at positions corresponding to the first exhaust section 223 and the second exhaust section 227. The exhaust device 24 is connected to the inside of the barrel 21 and is used to discharge the waste gas generated during the extrusion molding process of the material. The screw 22 adopts a large pitch in the first exhaust section 223 and the second exhaust section 227, so that the material is in a loose state, increasing the contact area between the material and the air, and facilitating exhaust. The compression section 224 compresses the material to increase the density of the material. The screw 22 has a smaller pitch and a shallower thread depth in the compression section 224, which reduces the space occupied by the material and realizes the compression function. The preheated and compressed material enters the plasticizing section 226 for further heating and shearing, so that the material is completely melted, forming a uniform viscous flow state, and achieving a plasticizing effect. The plasticized material is smoothly transported forward through the discharge section 228, and outputs the extruder 2 into the mold 3.

[0071] In some embodiments, Figure 4a and Figure 4b As shown, the first mixing section 222 and the second mixing section 225 have multiple groups of stirring components 23 distributed along the axial direction on the outer surface of the screw 22, each group of stirring components 23 includes multiple tooth-shaped protrusions 231 distributed along the circumference of the screw 22, the interval between adjacent stirring components 23 is 20-35 mm, the length of each tooth-shaped protrusion 231 in the axial direction of the screw 22 is 20-35 mm, the distribution and size of the stirring components 23 on the first mixing section 222 and the second mixing section 225 are the same, and the length of the second mixing section 225 is greater than that of the first mixing section 222. In this embodiment, the design of the stirring components 23 in the mixing section of the screw 22 can disrupt the flow of the material, increase the lateral mixing of the material, and through two-stage mixing before plasticization, the material is more fully mixed to prepare for plasticization.

[0072] It is understandable that, except for the first mixing section 222 and the second mixing section 225, the outer surfaces of the other sections of the screw 22 are all provided with helical threads, and the corresponding functions are achieved by designing the pitch, lead, screw ridges, etc. of the helical threads.

[0073] In some embodiments, the length of the preheating section 221 accounts for 30% to 40% of the total length of the screw 22, the pitch of the preheating section 221 is 50 to 65 mm, and the preheating section 221 includes the feeding section 2211, the first heating section 2212, and the second heating section 2213 in the processing direction, the length of the feeding section 2211 is ≥ the length of the first heating section 2212, and the length of the first heating section 2212 is > the length of the second heating section 2213, the number of threads of the feeding section 2211, the first heating section 2212, and the second heating section 2213 is equal, and the pitch and the screw ridges in the axial direction of the screw 22 are reduced in sequence. In this embodiment, the preheating section 221 occupies a longer length, so that the material can be fully heated before mixing, and by dividing the preheating section 221 into three functional sections and reducing the pitch and screw ridge size of each section in sequence, the material can be heated more fully and better transition to the mixing section.

[0074] In some embodiments, the pitch of the compression section 224 is smaller than the pitch of the first exhaust section 223 and larger than the spacing between the stirring components 23 of the first mixing section 222 and the second mixing section 225, and the dimension of the screw fins of the compression section 224 in the axial direction of the screw 22 is smaller than the length of the tooth-like protrusions 231 of the first mixing section 222 and the second mixing section 225 in the axial direction of the screw 22. The small pitch and small dimension of the screw fins of the compression section 224 can enhance the extrusion effect of the material, so that the material is compressed more tightly.

[0075] In some embodiments, the pitch and spiral ridge of the first exhaust section 223 and the second exhaust section 227 are the same, and the pitch and spiral ridge of the first exhaust section 223 and the second exhaust section 227 in the axial direction of the screw 22 are larger than the pitch and spiral ridge of the other sections of the screw 22 in the axial direction of the screw 22, and the length of the second exhaust section 227 is larger than the length of the first exhaust section 223 and smaller than twice the length of the first exhaust section 223. 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 222 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 227 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.

[0076] In some embodiments, three exhaust devices 24 are provided, wherein one exhaust device 24 is provided at the first exhaust section 223, and two exhaust devices 24 are provided side by side in the processing direction at the second exhaust section 227. The exhaust device 24 can adopt any device in the prior art that can realize the exhaust of the extruder, for example, the solution provided in Chinese patent application 202422531684.X can be referred to.

[0077] In some embodiments, the plasticizing section 226 includes a reflux section 2261 and a material blocking section 2262. Figure 4c As shown, a reflow groove 2263 is formed on at least part of the spiral edges in the reflow section 2261, the lead of the material blocking section 2262 is smaller than the lead of the reflow section 2261, and the length of the reflow section 2261 is greater than the length of the material blocking section 2262 and less than twice the length of the material blocking section 2262. The reflux section 2261 can make part of the material reflux in the screw 22. During the reflux process, the materials entering the screw 22 at different levels and times can be fully mixed, which increases the residence time of the material in the plasticizing section 226, 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 2261 can be 80-100mm (for example, 90mm), and the lead of the blocking section 2262 is smaller, which can be 40-55mm (for example, 50mm). The axial advancement speed of the material in the blocking section 2262 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 2261 can be orderly and stably advanced in the blocking section 2262 according to the predetermined direction, making the plasticization process more stable. In addition, the design of the length of the reflux section 2261 and the blocking section 2262 can find a balance between the plasticization efficiency and the plasticization effect, so that the material can be fully processed and the extrusion process can be completed efficiently.

[0078] In some embodiments, a first transition section 229 is provided between the first mixing section 222 and the first exhaust section 223, and a second transition section 2210 is provided between the second mixing section 225 and the plasticizing section 226; the pitch of the first transition section 229 is greater than the spacing of the stirring components 23 of the first mixing section 222 and less than the pitch of the first exhaust section 223; the pitch of the second transition section 2210 is greater than the spacing of the stirring components 23 of the second mixing section 225 and greater than the pitch of the plasticizing section 226.

[0079] In some embodiments, the discharge section 228 includes a first discharge section 2281 and a second discharge section 2282 disposed at the rear end of the second exhaust section 227 along the processing direction, the pitch of the first discharge section 2281 is greater than the pitch of the second discharge section 2282, the number of heads of the first discharge section 2281 is less than the number of heads of the second discharge section 2282, and the length of the first discharge section 2281 is greater than twice the length of the second discharge section 2282. The design of the first discharge section 2281 and the second discharge section 2282 in the discharge section 228 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.

[0080] The present application also improves the calender 4 in the sheet production line to make it more suitable for producing PET sheets. Figure 5a-5cAs shown, the calender 4 includes a frame 41 and a plurality of calendering roller groups 42 arranged on the frame 41 along the processing direction. The slab formed by the mold 3 enters the calender 4 for calendering, wherein the calendering roller located above the slab conveying path is the upper calendering roller 421, and the calendering roller located below the slab conveying path is the lower calendering roller 422. Each calendering roller group 42 includes an upper calendering roller 421 and a lower calendering roller 422 correspondingly arranged above and below, or only includes a lower calendering roller 422. A conveying device 43 is provided between at least two adjacent calendering roller groups 42. Figure 6-Figure 8 The conveying device 43 includes a plurality of rollers 431 arranged between two adjacent calendering roller groups 42 and a conveyor belt 432 surrounding the plurality of rollers 431. The upper end surfaces of the plurality of rollers 431 are located on the same plane so that the upper surface of the conveyor belt 432 constitutes a plane. The upper surface of the conveyor belt 432 is tangent to the roller surface of the lower calendering roller 422 in the two adjacent calendering roller groups 42.

[0081] In the above scheme, one or more conveying devices 43 may be provided, and the specific number may be determined according to the distance between adjacent calendering roller groups 42. For example, if the distance between two adjacent calendering roller groups 42 is large, a conveying device 43 may be provided, and if the distance between two adjacent calendering roller groups 42 is small, a conveying device 43 may not be provided. The conveying device 43 is in the form of a conveyor belt 432 surrounding a plurality of rollers 431, and the upper surface of the conveyor belt 432 supported above the plurality of rollers 431 is a plane. Since the rigidity of the PET slab is relatively large, the temperature of the calender 4 is relatively high during the calendering process, so that the PET slab is in a relatively soft and easily deformable state. When the PET slab is being transported between the calendering roller groups 42, the flat conveyor belt 432 may provide a flat support for the PET slab, thereby avoiding the corrugated deformation of the PET slab and ensuring the flatness of the PET sheet.

[0082] The plane where the upper surface of the conveyor belt 432 is located is tangent to the roller surface of the lower calendering rollers 422 in the two adjacent calendering roller groups 42, so that the conveyor belt 432 forms a good docking with the calendering rollers at both ends. The slab output from one calendering roller group 42 can be transported to the top of the conveyor belt 432 in a flat state, and then transported to the next calendering roller group 42 from the top of the conveyor belt 432 in a flat state, thereby ensuring the flatness of the slab. The upper surface of the conveyor belt 432 may be horizontal or inclined, which is specifically determined by the height of the lower calendering rollers 422 at its front and rear ends. The inclination of the upper surface of the conveyor belt 432 is determined by the arrangement height of the above-mentioned multiple rollers 431.

[0083] In some embodiments, Figure 9a and Figure 9bAs shown, the conveying device 43 further includes a roller mounting member 433, and both ends of each roller 431 are respectively mounted on the frame 41 via the roller mounting member 433, and the roller mounting member 433 is formed with a mounting groove 4331, and both ends of each roller 431 are respectively formed with a mounting shaft 4311, and the mounting shaft 4311 is arranged in the mounting groove 4331, so as to mount the roller 431 on the frame 41. The roller mounting member 433 can be a sheet structure or a block structure, and the mounting groove 4331 is formed through the sheet structure or the block structure, and the shape of the mounting groove 4331 can be an upward opening shape or a hole shape.

[0084] In some embodiments, Figure 9a and Figure 9b The roller mounting member 433 is provided with a bolt hole 4332 connected to the bottom of the mounting groove 4331. An adjusting bolt 434 is installed in the bolt hole 4332 in a threaded manner. The end of the adjusting bolt 434 extends from the bottom of the mounting groove 4331 into the mounting groove 4331 and supports the mounting shaft 4311 of the roller 431. When the height of the roller 431 needs to be adjusted to adjust the flatness and inclination of the upper surface of the conveyor belt 432, the height of the roller 431 can be adjusted by rotating the adjusting bolt 434 and adjusting the height of the end of the adjusting bolt 434 exposed from the bottom of the mounting groove 4331. This is simple and easy to achieve.

[0085] In some embodiments, Figure 5c-Figure 8 As shown, the conveyor 43 also includes a first drive motor 435 and a drive roller 436 installed on the frame 41, and the conveyor belt 432 surrounds a plurality of rollers 431 and the drive roller 436. The output shaft of the first drive motor 435 is connected to the drive roller 436, and the first drive motor 435 drives the drive roller 436 to rotate to drive the conveyor belt 432 to rotate. In this solution, the first drive motor 435 only needs to drive one drive roller 436 to rotate to realize the transmission of the entire conveyor 43, and there is no need to drive each roller 431 to rotate separately, thereby improving the driving efficiency and ensuring the stability of the slab conveying. The first drive motor 435 can be a servo motor, etc.

[0086] In some embodiments, the conveying device 43 further includes two guide rollers 437, which are installed between the driving roller 436 and the plurality of rollers 431. The two guide rollers 437 are located between the two lower calendering rollers 422 in the two adjacent calendering roller groups 42. The conveyor belt 432 surrounds the plurality of rollers 431 and is guided to the driving roller 436 via the opposite side of the two guide rollers 437. In this solution, the driving roller 436 is installed on the frame 41 near the bottom of the frame 41, and the direction of the conveyor belt 432 is adjusted by means of the guide rollers 437 to avoid interference between the conveyor belt 432 and the calendering rollers.

[0087] In some embodiments, Figure 5a-5cAs shown, at least one of the multiple calender roller groups 42 includes only one lower calender roller 422, and a first baking device 44 is provided above the calender roller group 42 including only one lower calender roller 422 to heat the slab. The first baking device 44 can be a device that can achieve heating, such as an oven or a heating lamp, and the length of the first baking device 44 can be equivalent to the length of the calender roller, so as to cover the entire slab width and ensure uniform heating. Since the PET material is highly rigid, it may become brittle as the temperature decreases during processing. In order to prevent the PET slab from becoming brittle and having defects such as cracks during the calendering process, the first baking device 44 is provided in the calender 4, and heating can be performed as needed according to the change in performance of the PET slab during the calendering process.

[0088] In some embodiments, a lift 45 is installed on the first baking device 44, and the lift 45 is installed on the frame 41. Starting the lift 45 can adjust the distance between the oven and the slab and adjust the heating effect. Since the first baking device 44 is relatively long, two lifts 45 can be respectively provided at both ends in the length direction, and the two lifts 45 are connected by a connecting rod 46 to ensure synchronous movement. The lift can be implemented by any structure that can realize the lifting function.

[0089] In some embodiments, the frame 41 of the calender 4 is installed on the ground walking rail 9 to facilitate the adjustment of the position of the calender 4 in the production line.

[0090] In some embodiments, Fig.10 As shown, a displacement sensor 47 for measuring the lifting distance of the upper calendering roller 421 is respectively provided corresponding to each upper calendering roller 421, and a second drive motor 48 for controlling the lifting of the upper calendering roller 421 is provided on the frame 41. The displacement sensor 47 is connected to the second drive motor 48 and is configured to send a signal to the second drive motor 48 to lift the upper calendering roller 421 to a set position, thereby realizing precise adjustment of the gap between the calendering roller group 42.

[0091] In some embodiments, Figure 1a and Figure 1b As shown, a cooling bracket 5, a tractor 7 and a cutting device 8 are provided at the rear end of the calender 4, and a second baking device 6 is also provided at the front end of the tractor 7. The second baking device 6 is used to heat the PET sheet before cutting. Considering that the PET sheet may become brittle after passing through the cooling bracket 5, in order to avoid defects such as cracks during the cutting process, the PET sheet is heated before cutting to ensure the cutting effect. The specific setting of the second baking device 6 can refer to the above-mentioned first baking device 44, which will not be repeated here.

[0092] In some embodiments, a coating assembly (not shown in the figure) can be provided at the rear end of the calender 4 as needed to coat the PET slab. The coating assembly can be provided with one or more sets of coating rollers as needed. For details, please refer to the prior art.

[0093] The PET sheet production line provided in the embodiment of the present application mainly improves the extruder 2 and the calender 4 in combination with the characteristics of the PET material. The production capacity of the production line can reach a high capacity of more than 1600kg / h, and the quality of the obtained PET sheets is stable, with few defects and a high yield.

[0094] The second aspect of the present application provides a method for producing a PET sheet, which is produced by using the PET sheet production line as described in any one of the first aspects above, comprising the following steps:

[0095] Mix the mixture of PET material and auxiliary materials with calcium powder in a ratio of 1:2-5;

[0096] The mixed material is fed into the extruder 2 for extrusion molding. The two screws 22 of the extruder 2 rotate in opposite directions and at a speed of 10 to 40 r / min.

[0097] The material plasticized by the extruder 2 enters the mold 3 for molding;

[0098] The formed slab enters the calender 4 for calendering;

[0099] The slab outputted from the calender 4 is cut into PET sheets.

[0100] In the above-mentioned PET sheet production method, production is carried out based on the improved PET sheet production line. By increasing the mixing ratio of calcium powder, the state of the material in the extruder 2 can be adjusted. The two screws 22 of the extruder 2 can be operated in different directions at low speed to improve the plasticizing effect, reduce energy consumption and increase output. Molding and calendering are carried out under the premise that the material has a good plasticizing state, which can improve the molding and calendering effect of the sheet and ensure the quality of the finished PET sheet.

[0101] In the above embodiment, the mixing ratio of the mixture of PET material and auxiliary materials to calcium powder can be 1:3-5, specifically 1:4; the auxiliary materials may include, for example, one or a combination of two or more of plasticizers, heat stabilizers, lubricants and flame retardants, which can be determined according to needs. The speed of the screw 22 during the extrusion molding process can be 15r / min, 18r / min, 20r / min, 25r / min, 28r / min, 30r / min, 35r / min, etc., which can be determined by those skilled in the art according to actual needs.

[0102] In some embodiments, the temperature of the extruder 2 is 190-280° C. Specifically, the extruder 2 is provided with a barrel sleeve 211 corresponding to each section of the screw 22, and a heating ring 25 is provided on the barrel sleeve 211 for heating the barrel 21, wherein the temperature of the extruder 2 in the preheating section 221 is 210-260° C. (for example, it can be 220° C., 230° C., 240° C., 250° C., etc.), the temperature from the first mixing section 222 to the plasticizing section 226 is 230-280° C. (for example, it can be 240° C., 250° C., 260° C., 270° C., etc.), the temperature in the second exhaust section 227 and the discharge section 228 is 190-250° C. (for example, it can be 200° C., 210° C., 220° C., 230° C., 240° C., etc.), and the temperature decreases from the second exhaust section 227 to the discharge section 228. The extruder 2 sets corresponding temperatures for each functional section of the screw 22 so that each section of the screw 22 can better perform its function at the corresponding temperature, so that the material is fully mixed and plasticized.

[0103] In some embodiments, when the material extruded by the extruder 2 enters the mold 3 for molding, the temperature of the mold 3 is 220-260°C, for example, it can be 230°C, 240°C, 250°C, etc., and technicians in this field can adjust it according to the state of the extruded material.

[0104] In some embodiments, the temperature of the calendering roller in the calender 4 is 180-250°C, for example, it can be 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, etc., and technical personnel in this field can adjust it according to the state of the slab after forming.

[0105] According to the characteristics of the PET material during processing, the temperature of the mold 3 and the temperature of the calender roller 4 are limited to a suitable range, so that the temperature is adjusted according to the state of the PET sheet during production, the quality of the finished sheet is improved, the occurrence of defects is reduced, and the production capacity of the production line is further improved.

[0106] In some embodiments, the calender 4 is provided with a first baking device 44, which heats the slab during the slab calendering process, and the temperature of the first baking device 44 is 180-220° C. The temperature of the first baking device 44 can be 190° C., 200° C., 210° C., etc. After the slab is heated by the first baking device 44, the temperature increases, the brittleness decreases, and the risk of fracturing during the calendering process is reduced.

[0107] Finally, it should be noted that: the various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0108] The above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or some technical features can be replaced by equivalents without departing from the spirit of the technical solution of the present invention, which should be included in the scope of the technical solution for protection of the present invention.

Claims

1. A PET sheet production line, comprising an extruder, a die and a calender arranged along a processing direction, characterized in that: The extruder comprises: Barrel; A twin screw assembly is arranged in the barrel, and the twin screw assembly includes two screws meshing with each other, the outer diameter of each screw decreases along the processing direction, and the angle between the central axes of the two screws is 10' to 1°20', and the two screws rotate in opposite directions.

2. The PET sheet production line according to claim 1, characterized in that: The two screws have the same size, the average value of the maximum and minimum values ​​of the outer diameter of each screw is the median diameter, the ratio of the length of each screw to the median diameter is 25:1 to 35:1, and the length of each screw is 3 to 7 meters.

3. The PET sheet production line according to claim 1, characterized in that: Each of the screws includes a preheating section, a first mixing section, a first exhaust section, a compression section, a second mixing section, a plasticizing section, a second exhaust section and a discharging section in sequence along the processing direction; the preheating section is used to stir the material and cooperate with the barrel to heat the material; the first mixing section and the second mixing section are used to mix and crush the material; the barrel is provided with exhaust devices at positions corresponding to the first exhaust section and the second exhaust section, respectively, and the exhaust devices are connected to the inside of the barrel to discharge the waste gas generated during the extrusion molding process of the material; the compression section is used to apply pressure to the material to compress the material; the plasticizing section is used to provide shear force to make the compressed material in a molten state; The discharging section is used to discharge the molten material out of the extruder and into the mold.

4. The PET sheet production line according to claim 1, characterized in that: The calender includes a frame and a plurality of calendering roller groups arranged on the frame along the processing direction. The slab formed by the mold enters the calender for calendering, wherein the calendering roller located above the slab conveying path is the upper calendering roller, and the calendering roller located below the slab conveying path is the lower calendering roller. Each calendering roller group includes an upper calendering roller and a lower calendering roller correspondingly arranged above and below, or only includes one lower calendering roller. A conveying device is provided between at least two adjacent calendering roller groups; the conveying device includes a plurality of rollers arranged between the two adjacent calendering roller groups and a conveyor belt surrounding the plurality of rollers, the upper end surfaces of the plurality of rollers are located on the same plane so that the upper surface of the conveyor belt constitutes a plane, and the plane where the upper surface of the conveyor belt is located is tangent to the roller surface of the lower calendering roller in the two adjacent calendering roller groups.

5. The PET sheet production line according to claim 4, characterized in that: The conveying device also includes a roller mounting member, both ends of each of the rollers are respectively mounted on the frame via the roller mounting member, the roller mounting member is formed with a mounting groove, both ends of each roller are respectively formed with a mounting shaft, the mounting shaft is arranged in the mounting groove and supported by the bottom of the mounting groove, so as to mount the roller on the frame; a bolt hole connected to the bottom of the mounting groove is formed in the roller mounting member, an adjustment bolt is threadedly mounted in the bolt hole, an end of the adjustment bolt extends into the mounting groove from the bottom of the mounting groove and supports the roller.

6. The PET sheet production line according to claim 4, characterized in that: At least one of the multiple calendering roller groups includes only one lower calendering roller, and a first baking device is arranged above the calendering roller group including only one lower calendering roller to heat the slab.

7. The PET sheet production line according to claim 4, characterized in that: A displacement sensor for measuring the lifting distance of the upper calendering roller is provided corresponding to each upper calendering roller. The frame is provided with a second drive motor for controlling the lifting and lowering of the upper calendering roller. The displacement sensor is connected to the second drive motor and is configured to send a signal to the second drive motor to lift the upper calendering roller to a set position.

8. The PET sheet production line according to claim 1, characterized in that: A cooling bracket, a traction machine and a cutting device are arranged at the rear end of the calender, and a second baking device is arranged at the front end of the traction machine. The second baking device is used to heat the PET sheet before cutting.

9. A method for producing a PET sheet, which is produced by using the PET sheet production line described in any one of 1 to 8 above, characterized in that: The following steps are involved: Mix the mixture of PET material and auxiliary materials with calcium powder in a ratio of 1:2-5; 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; The material plasticized by the extruder enters the mold for molding; The formed slab enters the calender for calendering; The slab output from the calender is cut into PET sheets.

10. The method for producing a PET sheet according to claim 9, characterized in that: The screw of the extruder includes a preheating section, a first mixing section, a first exhaust section, a compression section, a second mixing section, a plasticizing section, a second exhaust section and a discharging section in sequence along the processing direction; the temperature of the extruder in the preheating section is 210-260°C, the temperature from the first mixing section to the plasticizing section is 230-280°C, the temperature in the second exhaust section and the discharging section is 190-250°C, and the temperature decreases from the second exhaust section to the discharging section; the temperature of the mold is 220-260°C; the temperature of the calendering roller in the calendering machine is 180-250°C.

Images