High-speed extrusion process for flame-retardant polyethylene sheath

Abstract

The invention discloses a flame-retardant polyethylene sheath high-speed extrusion process which comprises the following steps: uniformly mixing low-smoke halogen-free flame-retardant polyethylene and an additive, performing premixing treatment through a double-screw mixing mill, and fully drying the mixed material; the design of the extruder head and the screw rod is optimized; then double cooling is conducted on the screw rod and the screw cylinder; a mold type and a mold material are selected and optimized; and process parameters are adjusted, and the extrusion speed is optimized. By optimizing the temperature setting of each section of the extruder and adopting the advanced mold design, the extrusion speed of the flame-retardant polyethylene sheath is obviously improved, and by adopting the cooling mode of double cooling of the screw and the screw cylinder, the precise control of the temperature of the extruder is realized, and the stability of the material is ensured; the surface defects such as bamboo-like, annular thinning and broken holes in the extrusion process are effectively reduced, the produced flame-retardant polyethylene sheath is smooth and compact in surface and free of air holes, and the section quality is remarkably improved.

Description

Technical Field

[0001] The invention relates to the technical field of sheath preparation, in particular to a flame retardant polyethylene sheath high-speed extrusion process. Background Art

[0002] With the rapid development of the modernization process and the shortening of the distance between cities and rural areas, the demand for wires and cables has further increased. The requirements for wires and cables have also increased accordingly, such as requiring cables to prevent the burning of flames, less smoke and no release of halogen gas in the event of a fire. This has led to the birth of halogen-free, low-smoke, flame-retardant cables, which are widely used in high-rise buildings and crowded places. The revised national standard GB / T12706.1-2020 also includes halogen-free, low-smoke, flame-retardant cables. Competition is in the market, and competitiveness is on site. As a wire and cable manufacturer, how to better control the stability of product quality on site is the goal of the unremitting efforts of the majority of employees. The extrusion process of halogen-free, low-smoke, flame-retardant sheath materials is not equivalent to the extrusion process of polyvinyl chloride, ordinary polyethylene and other materials. In comparison, the former is much more complicated. As long as through a long period of exploration and summary, the problem will always be solved.

[0003] Nowadays, the production technology of low-smoke halogen-free flame-retardant polyethylene is relatively mature, but there are still many technical problems in the actual production process. The production speed is too slow, the glue output is low, the extrusion pressure of the extruder is high, and the current is high during production; when producing the flame-retardant polyethylene outer sheath, the extruder temperature control stability is poor, and the set temperature is quite different from the actual temperature; after the sheath is extruded, the surface of the sheath appears bamboo-like, the surface is rough and hairy, and there are pores. During the extrusion process of the sheath, the material discharge is unstable, and ring-shaped thinning and holes appear. Summary of the invention

[0004] The purpose of this section is to summarize some aspects of embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the specification abstract and the invention title of this application to avoid blurring the purpose of this section, the specification abstract and the invention title, and such simplifications or omissions cannot be used to limit the scope of the present invention.

[0005] In view of the above problems and / or the problems existing in the existing flame retardant polyethylene sheath high-speed extrusion process, the present invention is proposed.

[0006] Therefore, the problem to be solved by the present invention is how to provide a high-speed extrusion process for a flame-retardant polyethylene sheath.

[0007] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0008] The embodiment of the present invention provides a flame-retardant polyethylene sheath high-speed extrusion process, which includes uniformly mixing low-smoke halogen-free flame-retardant polyethylene with additives, premixing through a twin-screw mixer, and fully drying the mixed materials; optimizing the design of the extruder head and the screw; then double cooling the screw and barrel; selecting and optimizing the mold type and mold material; adjusting the process parameters and optimizing the extrusion speed.

[0009] As a preferred scheme of the flame-retardant polyethylene sheath high-speed extrusion process described in the present invention, the low-smoke halogen-free flame-retardant polyethylene is uniformly mixed with additives, and pre-mixed through a twin-screw mixer, and the mixed materials are fully dried, including: the additives include 25-30% flame retardant, 2-5% carbonizing agent, 0.2-0.5% antioxidant, 0.1-0.3% antistatic agent, 0.2-0.5% lubricant and 2-4% plasticizer; during the initial mixing process, the temperature is controlled below 80°C and the time does not exceed 15 minutes. During the mixing process, the ambient humidity is kept below 50%, the screw speed is set at 200-300rpm, the mixing time is 2-5 minutes, the drying is set at 70-90°C, and the drying time is 4-6 hours.

[0010] As a preferred solution of the flame-retardant polyethylene sheath high-speed extrusion process described in the present invention, the optimization of the design of the extruder head and the screw includes: optimizing the flow channel depth and width of the partial colloid in the head, specifically increasing the depth and width by 5 mm each, and designing the flow channel form to reduce dead angles and optimize the material flow path; the screw uses a screw with a length-to-diameter ratio of 20 and a compression ratio of 1:1.3, optimizing the screw groove depth and spiral angle, increasing the melt cavity between the screw and the barrel, and reducing the shear heat and pressure fluctuations of the material during the extrusion process.

[0011] As a preferred solution of the flame-retardant polyethylene sheath high-speed extrusion process of the present invention, the double cooling of the screw and barrel includes: using 6 750W high-pressure centrifugal fans to air-cool the barrel, and using cooling circulating water to cool the screw to ensure that the extruder temperature is controlled within the set value ±2°C.

[0012] As a preferred solution of the flame-retardant polyethylene sheath high-speed extrusion process described in the present invention, the selection of mold type and mold material and optimization thereof include: using a semi-extrusion tube mold with a core mouth length of 15 mm and a mold sleeve bearing wire length of 8 mm, and placing the core head end at 1 / 2 of the mold sleeve bearing diameter, thereby reducing the stretching of the sheath material, so that the surface wrapping of the sheath is denser and the appearance is brighter under the condition of accelerated production; the mold material is selected to use a mold material with high thermal conductivity and strong wear resistance to reduce the adhesion of the material during the extrusion process.

[0013] As a preferred solution of the flame-retardant polyethylene sheath high-speed extrusion process of the present invention, wherein: the process parameters are adjusted to optimize the extrusion speed, including: adjusting the temperature settings of each section of the extruder according to the material formula, the feed zone is controlled at 145-165°C, the compression zone is controlled at 150-170°C, the metering zone is controlled at 155-175°C, the die zone is controlled at 160-180°C, and the cooling zone is <100°C; gradually increasing the extrusion speed, monitoring the current, voltage and pressure changes, and adjusting the extruder parameters to initially set the extruder speed: 10rpm, current: 142A, pressure: 50bar, glue output: 420kg / h, production speed: 4.6m / min; gradually optimizing the process, the extruder speed is increased to 15rpm, current: 196A, pressure: 75bar, glue output: 578kg / h, production speed: 6.0m / min.

[0014] The beneficial effects of the present invention are as follows: by optimizing the temperature setting of each section of the extruder and adopting advanced mold design, the present invention significantly improves the extrusion speed of the flame-retardant polyethylene sheath, and adopts a cooling method of double cooling of the screw and barrel to achieve precise control of the extruder temperature and ensure the stability of the material; the present invention effectively reduces surface defects such as bamboo-like, ring-shaped thinning, and holes that appear during the extrusion process, and the surface of the produced flame-retardant polyethylene sheath is smooth, dense, and free of pores, and the quality of the section is significantly improved. The optimized screw design and mold material selection reduce the friction between the screw and the barrel during the extrusion process, and reduce the shear heat and flow channel pressure of the material. The mold material used in the present invention has high thermal conductivity and strong wear resistance, which significantly reduces the adhesion and wear of the material to the mold during the extrusion process. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. 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 creative labor. Among them:

[0016] Figure 1 This is the process flow chart of the high-speed extrusion process of flame-retardant polyethylene sheath.

[0017] Figure 2 This is a structural schematic diagram of a medium-voltage cross-linked polyethylene insulated PVC inner sheathed steel belt armored low-smoke halogen-free flame-retardant polyethylene outer sheath power cable.

[0018] Figure 3 This is a schematic diagram of the glue dispenser structure before the process technology upgrade.

[0019] Figure 4 This is a schematic diagram of the glue dispenser structure after the process technology is upgraded. DETAILED DESCRIPTION

[0020] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the drawings of the specification. Obviously, the described embodiments are part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary persons in the art without creative work should fall within the scope of protection of the present invention.

[0021] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0022] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0023] At the same time, in the description of the present invention, it should be noted that the directions or positional relationships indicated by the terms "upper, lower, inner and outer" are based on the directions 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 direction, be constructed and operated in a specific direction, and therefore cannot be understood as limiting the present invention. In addition, the terms "first, second or third" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0024] Example 1

[0025] Reference Figures 1-2 , which is an embodiment of the present invention.

[0026] A flame retardant polyethylene sheath high-speed extrusion process:

[0027] The low-smoke halogen-free flame-retardant polyethylene and the additives are uniformly mixed, and pre-mixed by a twin-screw mixer, and the mixed materials are fully dried; the additives include 25% flame retardant, 2% carbonizing agent, 0.2% antioxidant, 0.1% antistatic agent, 0.2% lubricant and 2% plasticizer; in the initial mixing process, the temperature is controlled at 80°C for 15 minutes, the ambient humidity is maintained at 48% during the mixing process, the screw speed is set at 200rpm, the mixing time is 2 minutes, the drying is set at 70°C, and the drying time is 4 hours;

[0028] The extruder head and screw design are optimized. The depth and width of the flow channel of the colloid in the head are optimized. The specific depth and width are increased by 5mm respectively. At the same time, the flow channel form is designed to reduce dead angles and optimize the material flow path. The screw uses a screw with an aspect ratio of 20 and a compression ratio of 1:1.3. The screw groove depth and spiral angle are optimized to increase the melting cavity between the screw and the barrel, reducing the shear heat and pressure fluctuations of the material during the extrusion process.

[0029] The screw and barrel are double-cooled, using 6 750W high-pressure centrifugal fans to cool the barrel, and cooling circulating water to cool the screw, ensuring that the extruder temperature is controlled within the set value ±2℃;

[0030] The mold type and mold material are selected and optimized. A semi-extrusion tube mold is used, with a core mouth length of 15mm and a sleeve bearing line length of 8mm. The core head is placed at 1 / 2 of the sleeve bearing diameter, which reduces the stretching of the sheath material. As a result, the sheath surface is more densely wrapped and the appearance is brighter when the production speed is increased. The mold material is selected to use a mold material with high thermal conductivity and strong wear resistance to reduce the adhesion of the material during the extrusion process.

[0031] Adjust the process parameters, optimize the extrusion speed, adjust the temperature settings of each section of the extruder according to the material formula, control the feed zone at 145°C, the compression zone at 150°C, the metering zone at 155°C, the die zone at 160°C, and the cooling zone at 100°C; gradually increase the extrusion speed, monitor the changes in current, voltage and pressure, and adjust the extruder parameters to initially set the extruder speed: 10rpm, current: 142A, pressure: 50bar, glue output: 420kg / h, production speed: 4.6m / min; gradually optimize the process, the extruder speed is increased to 15rpm, current: 196A, pressure: 75bar, glue output: 578kg / h, production speed: 6.0m / min.

[0032] Example 2

[0033] A flame retardant polyethylene sheath high-speed extrusion process:

[0034] The low-smoke halogen-free flame-retardant polyethylene and the additives are uniformly mixed, and pre-mixed by a twin-screw mixer, and the mixed materials are fully dried; the additives include 26% flame retardant, 3% carbonizing agent, 0.3% antioxidant, 0.15% antistatic agent, 0.25% lubricant and 2.4% plasticizer; in the initial mixing process, the temperature is controlled at 75°C, the time is 13min, the ambient humidity is maintained at 45% during the mixing process, the screw speed is set at 220rpm, the mixing time is 3min, the drying is set at 75°C, and the drying time is 4.2h;

[0035] The extruder head and screw design are optimized. The depth and width of the flow channel of the colloid in the head are optimized. The specific depth and width are increased by 5mm respectively. At the same time, the flow channel form is designed to reduce dead angles and optimize the material flow path. The screw uses a screw with an aspect ratio of 20 and a compression ratio of 1:1.3. The screw groove depth and spiral angle are optimized to increase the melting cavity between the screw and the barrel, reducing the shear heat and pressure fluctuations of the material during the extrusion process.

[0036] The screw and barrel are double-cooled, using 6 750W high-pressure centrifugal fans to cool the barrel, and cooling circulating water to cool the screw, ensuring that the extruder temperature is controlled within the set value ±2℃;

[0037] The mold type and mold material are selected and optimized. A semi-extrusion tube mold is used, with a core mouth length of 15mm and a sleeve bearing line length of 8mm. The core head is placed at 1 / 2 of the sleeve bearing diameter, which reduces the stretching of the sheath material. As a result, the sheath surface is more densely wrapped and the appearance is brighter when the production speed is increased. The mold material is selected to use a mold material with high thermal conductivity and strong wear resistance to reduce the adhesion of the material during the extrusion process.

[0038] Adjust the process parameters, optimize the extrusion speed, adjust the temperature settings of each section of the extruder according to the material formula, control the feed zone at 150°C, the compression zone at 155°C, the metering zone at 160°C, the die zone at 165°C, and the cooling zone at 95°C; gradually increase the extrusion speed, monitor the changes in current, voltage and pressure, and adjust the extruder parameters to initially set the extruder speed: 10rpm, current: 142A, pressure: 50bar, glue output: 420kg / h, production speed: 4.6m / min; gradually optimize the process, increase the extruder speed to 15rpm, current: 196A, pressure: 75bar, glue output: 578kg / h, production speed: 6.0m / min.

[0039] Example 3

[0040] A flame retardant polyethylene sheath high-speed extrusion process:

[0041] The low-smoke halogen-free flame-retardant polyethylene and the additives are uniformly mixed, and pre-mixed by a twin-screw mixer, and the mixed materials are fully dried; the additives include 27% flame retardant, 4% carbonizing agent, 0.4% antioxidant, 0.2% antistatic agent, 0.3% lubricant and 3% plasticizer; in the initial mixing process, the temperature is controlled at 70°C for 10 minutes, the ambient humidity is maintained at 41% during the mixing process, the screw speed is set at 250rpm, the mixing time is 4 minutes, the drying is set at 80°C, and the drying time is 5 hours;

[0042] The extruder head and screw design are optimized. The depth and width of the flow channel of the colloid in the head are optimized. The specific depth and width are increased by 5mm respectively. At the same time, the flow channel form is designed to reduce dead angles and optimize the material flow path. The screw uses a screw with an aspect ratio of 20 and a compression ratio of 1:1.3. The screw groove depth and spiral angle are optimized to increase the melting cavity between the screw and the barrel, reducing the shear heat and pressure fluctuations of the material during the extrusion process.

[0043] The screw and barrel are double-cooled, using 6 750W high-pressure centrifugal fans to cool the barrel, and cooling circulating water to cool the screw, ensuring that the extruder temperature is controlled within the set value ±2℃;

[0044] The mold type and mold material are selected and optimized. A semi-extrusion tube mold is used, with a core mouth length of 15mm and a sleeve bearing line length of 8mm. The core head is placed at 1 / 2 of the sleeve bearing diameter, which reduces the stretching of the sheath material. As a result, the sheath surface is more densely wrapped and the appearance is brighter when the production speed is increased. The mold material is selected to use a mold material with high thermal conductivity and strong wear resistance to reduce the adhesion of the material during the extrusion process.

[0045] Adjust the process parameters, optimize the extrusion speed, adjust the temperature settings of each section of the extruder according to the material formula, control the feed zone at 155°C, the compression zone at 160°C, the metering zone at 165°C, the die zone at 170°C, and the cooling zone at 91°C; gradually increase the extrusion speed, monitor the changes in current, voltage and pressure, and adjust the extruder parameters to initially set the extruder speed: 10rpm, current: 142A, pressure: 50bar, glue output: 420kg / h, production speed: 4.6m / min; gradually optimize the process, increase the extruder speed to 15rpm, current: 196A, pressure: 75bar, glue output: 578kg / h, production speed: 6.0m / min.

[0046] Example 4

[0047] A flame retardant polyethylene sheath high-speed extrusion process:

[0048] The low-smoke halogen-free flame-retardant polyethylene and the additives are uniformly mixed, and pre-mixed by a twin-screw mixer, and the mixed materials are fully dried; the additives include 28% flame retardant, 4.5% carbonizing agent, 0.45% antioxidant, 0.25% antistatic agent, 0.4% lubricant and 3.5% plasticizer; in the initial mixing process, the temperature is controlled at 65°C for 8 minutes, the ambient humidity is maintained at 38% during the mixing process, the screw speed is set at 280rpm, the mixing time is 4.5 minutes, the drying is set at 85°C, and the drying time is 5.5 hours;

[0049] The extruder head and screw design are optimized. The depth and width of the flow channel of the colloid in the head are optimized. The specific depth and width are increased by 5mm respectively. At the same time, the flow channel form is designed to reduce dead angles and optimize the material flow path. The screw uses a screw with an aspect ratio of 20 and a compression ratio of 1:1.3. The screw groove depth and spiral angle are optimized to increase the melting cavity between the screw and the barrel, reducing the shear heat and pressure fluctuations of the material during the extrusion process.

[0050] The screw and barrel are double-cooled, using 6 750W high-pressure centrifugal fans to cool the barrel, and cooling circulating water to cool the screw, ensuring that the extruder temperature is controlled within the set value ±2℃;

[0051] The mold type and mold material are selected and optimized. A semi-extrusion tube mold is used, with a core mouth length of 15mm and a sleeve bearing line length of 8mm. The core head is placed at 1 / 2 of the sleeve bearing diameter, which reduces the stretching of the sheath material. As a result, the sheath surface is more densely wrapped and the appearance is brighter when the production speed is increased. The mold material is selected to use a mold material with high thermal conductivity and strong wear resistance to reduce the adhesion of the material during the extrusion process.

[0052] Adjust the process parameters, optimize the extrusion speed, adjust the temperature settings of each section of the extruder according to the material formula, control the feed zone at 160°C, the compression zone at 165°C, the metering zone at 170°C, the die zone at 175°C, and the cooling zone at 88°C; gradually increase the extrusion speed, monitor the changes in current, voltage and pressure, and adjust the extruder parameters to initially set the extruder speed: 10rpm, current: 142A, pressure: 50bar, glue output: 420kg / h, production speed: 4.6m / min; gradually optimize the process, increase the extruder speed to 15rpm, current: 196A, pressure: 75bar, glue output: 578kg / h, production speed: 6.0m / min.

[0053] Example 5

[0054] A flame retardant polyethylene sheath high-speed extrusion process:

[0055] The low-smoke halogen-free flame-retardant polyethylene and the additives are uniformly mixed, and pre-mixed by a twin-screw mixer, and the mixed materials are fully dried; the additives include 30% flame retardant, 5% carbonizing agent, 0.5% antioxidant, 0.3% antistatic agent, 0.5% lubricant and 4% plasticizer; in the initial mixing process, the temperature is controlled at 60°C for 6 minutes, the ambient humidity is maintained at 35% during the mixing process, the screw speed is set at 300rpm, the mixing time is 5 minutes, the drying is set at 90°C, and the drying time is 6 hours;

[0056] The extruder head and screw design are optimized. The depth and width of the flow channel of the colloid in the head are optimized. The specific depth and width are increased by 5mm respectively. At the same time, the flow channel form is designed to reduce dead angles and optimize the material flow path. The screw uses a screw with an aspect ratio of 20 and a compression ratio of 1:1.3. The screw groove depth and spiral angle are optimized to increase the melting cavity between the screw and the barrel, reducing the shear heat and pressure fluctuations of the material during the extrusion process.

[0057] The screw and barrel are double-cooled, using 6 750W high-pressure centrifugal fans to cool the barrel, and cooling circulating water to cool the screw, ensuring that the extruder temperature is controlled within the set value ±2℃;

[0058] The mold type and mold material are selected and optimized. A semi-extrusion tube mold is used, with a core mouth length of 15mm and a sleeve bearing line length of 8mm. The core head is placed at 1 / 2 of the sleeve bearing diameter, which reduces the stretching of the sheath material. As a result, the sheath surface is more densely wrapped and the appearance is brighter when the production speed is increased. The mold material is selected to use a mold material with high thermal conductivity and strong wear resistance to reduce the adhesion of the material during the extrusion process.

[0059] Adjust the process parameters, optimize the extrusion speed, adjust the temperature settings of each section of the extruder according to the material formula, control the feed zone at 165°C, the compression zone at 170°C, the metering zone at 175°C, the die zone at 180°C, and the cooling zone at 85°C; gradually increase the extrusion speed, monitor the changes in current, voltage and pressure, and adjust the extruder parameters to initially set the extruder speed: 10rpm, current: 142A, pressure: 50bar, glue output: 420kg / h, production speed: 4.6m / min; gradually optimize the process, increase the extruder speed to 15rpm, current: 196A, pressure: 75bar, glue output: 578kg / h, production speed: 6.0m / min.

[0060] Comparison example

[0061] The actual production conditions before and after the implementation of the invention method were compared, as shown in Table 1 and Table 2;

[0062]

[0063] Table 1: Before the implementation of the invention method

[0064] Table 1 shows the WDZA-YJV22 26 / 35kV 3×240mm produced before the implementation of the invention method 2 When the extruder speed is set to 25 rpm, the cable surface becomes rough and uneven, and there are a large number of pores on the cross section.

[0065]

[0066] Table 2: After implementation of the invention method

[0067] Table 2 shows the production of WDZA-YJV22 26 / 35kV 3×240mm after replacing the die head, upgrading the colloid flow channel, using a new low-smoke, halogen-free, flame-retardant screw, and a semi-extrusion mold with a low stretch ratio. 2 From the table, it is analyzed and summarized that for the production of cables of the same model and specification, after upgrading the colloid flow channel and using a new low-smoke halogen-free flame-retardant screw and a semi-extrusion die with a low stretch ratio, the current and pressure of the extruder at the same speed have been significantly reduced, and the glue output, production speed and surface quality have been significantly improved.

[0068] In summary, the research and development method of the flame-retardant polyethylene sheath high-speed extrusion process of the present invention, by changing the depth, width and flow channel form of the partial colloid flow channel in the head of the sheath extruder, adopts a cooling method of double cooling of the screw and barrel, uses a length-to-diameter ratio (L / D) of 20, a compression ratio of 1:1.3, deepens the screw groove depth, increases the screw helix angle, and is equipped with a low-stretching ratio semi-extrusion tube mold. It solves the problems of slow production speed, low glue output, high extrusion pressure and high current of the extruder during production of low-smoke halogen-free flame-retardant polyethylene; poor extruder temperature control stability, large difference between the set temperature and the actual temperature, bamboo-like extrusion surface, rough hair, and pores; unstable material discharge during extrusion, and a series of problems such as ring-shaped thinning and holes, truly achieving the goal of high-speed and stable production of low-smoke halogen-free flame-retardant polyethylene.

[0069] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A flame retardant polyethylene sheath high-speed extrusion process, It is characterized in that include: The low-smoke halogen-free flame-retardant polyethylene and the additives are uniformly mixed, and pre-mixed by a twin-screw mixer, and the mixed materials are fully dried; Optimize the design of extruder head and screw; Then double cooling the screw and barrel; Select mold type and mold material and optimize them; Adjust process parameters and optimize extrusion speed.

2. The flame retardant polyethylene sheath high speed extrusion process as claimed in claim 1, It is characterized in that The low-smoke halogen-free flame-retardant polyethylene and the additive are uniformly mixed, and pre-mixed by a twin-screw mixer, and the mixed material is fully dried, including: The additives include 25-30% flame retardant, 2-5% carbon former, 0.2-0.5% antioxidant, 0.1-0.3% antistatic agent, 0.2-0.5% lubricant and 2-4% plasticizer; during the initial mixing process, the temperature is controlled below 80°C for no more than 15 minutes, the ambient humidity is kept below 50% during the mixing process, the screw speed is set at 200-300rpm, the mixing time is 2-5 minutes, the drying is set at 70-90°C, and the drying time is 4-6 hours.

3. The flame retardant polyethylene sheath high speed extrusion process as claimed in claim 1, It is characterized in that The optimization of the extruder head and screw design includes: The depth and width of the flow channel of some colloids in the die are optimized, with the specific depth and width increased by 5mm respectively. At the same time, the flow channel form is designed to reduce dead angles and optimize the material flow path. The screw uses a screw with a length-to-diameter ratio of 20 and a compression ratio of 1:1.

3. The screw groove depth and spiral angle are optimized, the melt cavity between the screw and the barrel is increased, and the shear heat and pressure fluctuations of the material during extrusion are reduced.

4. The flame retardant polyethylene sheath high speed extrusion process as claimed in claim 1, It is characterized in that The double cooling of the screw barrel comprises: Six 750W high-pressure centrifugal fans are used to cool the barrel, and cooling circulating water is used to cool the screw to ensure that the extruder temperature is controlled within the set value ±2°C.

5. The flame retardant polyethylene sheath high speed extrusion process as claimed in claim 1, It is characterized in that The method of selecting and optimizing the mold type and mold material includes: A semi-extrusion tube die is used, with a core nozzle length of 15mm and a die sleeve bearing wire length of 8mm. The core head is placed at 1 / 2 of the die sleeve bearing diameter, which reduces the stretching of the sheath material. As a result, the surface of the sheath is more densely wrapped and the appearance is brighter when the production speed is increased. The mold material is selected with high thermal conductivity and strong wear resistance to reduce the adhesion of the material during the extrusion process.

6. The flame retardant polyethylene sheath high speed extrusion process as claimed in claim 1, It is characterized in that The process parameters are adjusted to optimize the extrusion speed, including: According to the material formula, the temperature settings of each section of the extruder were adjusted, the feed zone was controlled at 145-165°C, the compression zone was controlled at 150-170°C, the metering zone was controlled at 155-175°C, the die zone was controlled at 160-180°C, and the cooling zone was <100°C; the extrusion speed was gradually increased, and the current, voltage and pressure changes were monitored. By adjusting the extruder parameters, the initial settings were: extruder speed: 10rpm, current: 142A, pressure: 50bar, glue output: 420kg / h, production speed: 4.6m / min; the process was gradually optimized, and the extruder speed was increased to 15rpm, current: 196A, pressure: 75bar, glue output: 578kg / h, production speed: 6.0m / min.

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