Continuous extrusion molding method for polytrifluorochloroethylene rod

Abstract

The application discloses a kind of continuous extrusion forming methods of polytrifluorochloroethylene rod, specifically extruder plasticizing, extrusion mold forming, rod shaping, damping, heat preservation, cooling, cutting.Compared with prior art molding process, the application can greatly improve the stability of product performance, and the performance index fluctuation is small;The probability of occurrence of delamination, black spots, bubbles and the like is reduced, and the qualified rate is improved.The production efficiency is greatly improved, which is more than 10 times of the molding process, the utilization rate of the material for subsequent processing is greatly improved, the material waste rate is reduced by more than 5 times, and the material replacement time is saved by 1 / 5.

Description

TECHNICAL FIELD

[0001] The application relates to a continuous extrusion molding method of a polytrifluorochloroethylene (PCTFE) rod and belongs to the technical field of product-grade PCTFE. BACKGROUND

[0002] Polytrifluorochloroethylene (PCTFE) is a homopolymer of monomer trifluorochloroethylene and is a perhalogenated crystalline polymer. Compared with a perfluoropolymer such as polytetrafluoroethylene, the structure is very similar. The F atoms in the molecular structure of PCTFE make the polymer chemically inert, and the Cl atoms make the polymer transparent, thermoplastic and hard, so that PCTFE is an inert fluoropolymer with high stability, heat resistance, non-flammability, non-hygroscopicity and non-permeability. PCTFE has excellent dielectric properties, very high bulk resistance, electrical strength and arc resistance, and is almost not affected by temperature or humidity, and is a high-frequency insulating material that can withstand more severe conditions than traditional materials. According to the different uses and molecular weights of PCTFE, PCTFE can be divided into lubricating grease grade PCTFE, film grade PCTFE and product grade PCTFE, and the application mainly aims at product grade PCTFE.

[0003] Product grade PCTFE can be theoretically processed by traditional thermoplastic processing methods such as molding, extrusion and injection molding. However, the melt viscosity of product grade PCTFE is more than 100 times that of ordinary resins, and the melt processing temperature is close to the decomposition temperature, so corrosive substances are easily generated during processing. Due to the limitations of price and processing performance, PCTFE has withdrawn from application fields such as coating and injection molding products. The melt viscosity of PCTFE is extremely large, and the molding process of PCTFE products currently used in China is basically similar to the powder metallurgy processing of molding.

[0004] Chinese patent CN104987630A discloses a modified polytrifluorochloroethylene and a molding process thereof. The modified PCTFE prepared by using the patent technology increases the hardness peak and the dimensional stability, improves the high-temperature resistance, wear resistance, thermal conductivity and anti-creep property, changes the friction coefficient of the material, reduces the cost of original PCTFE and expands the use range of the material. Chinese patent CN206644230U discloses a vertical molding forming die for polytrifluorochloroethylene super-long rods and introduces a vertical molding forming technology. The technology realizes the preparation of super-long rod-shaped PCTFE materials by using the mode of feeding and pressurizing at the upper and lower ends of the die.

[0005] The bar extrusion molding process using polytrifluorochloroethylene (PCTFE) as raw material has not been reported in China. It is very difficult to extrude PCTFE into a bar due to the material properties. At present, only molding process can be used in China. The qualified rate is not high due to the crystallization properties of the material. When machining PCTFE parts, the length of the molded PCTFE bar is too short, and the material needs to be frequently replaced, resulting in low machining efficiency and waste of excess material. For small-diameter horizontal molded PCTFE bars, there is a defect of uneven crystallization at the joint of the mold, which leads to strength defects of the parts, and the reliability cannot be guaranteed for important occasions. SUMMARY

[0006] The purpose of the present application is to solve the problem of difficult extrusion molding of PCTFE bars, and provide a technical solution for producing PCTFE bars by extrusion molding process.

[0007] The PCTFE bar extrusion molding method adopted by the present application includes plasticizing of the extruder, extrusion molding, bar shaping, damping, heat preservation, cooling and cutting.

[0008] The plasticizing process of the extruder is characterized in that the extruder used is a single screw extruder, which is composed of a screw, a screw cylinder, a variable frequency motor control system, a speed reduction system, a temperature control system, a rack, etc.

[0009] The screw cylinder and the screw are characterized in that they are made of nickel-based steel material, the outer diameter of the screw is 35 mm to 60 mm, the length-diameter ratio is (20 to 25):1, and the compression ratio is 2.30 to 2.56.

[0010] The screw is different from the conventional extruder in that the metering section of the screw accounts for 30% of the total length of the screw, and the thread depth of the metering section of the screw is 0.04 to 0.06 of the diameter of the screw.

[0011] The preferred specification of the screw is that the outer diameter is 35 mm, the compression ratio is 2.30, and the gradual change degree is 0.00720.

[0012] The preferred specification of the screw is that the outer diameter is 45 mm, the compression ratio is 2.56, and the gradual change degree is 0.00905.

[0013] The variable frequency motor drive control system uses a variable frequency three-phase motor controlled by a corresponding frequency converter.

[0014] The speed reduction system is different from the conventional extruder, which adopts a high speed reduction ratio, and the speed reduction ratio of the screw and the motor is selected to be 20; the belt pulley and the speed reduction box are used to form a series speed reduction, and the total speed reduction ratio reaches 50.

[0015] The temperature control system is composed of a temperature controller, a thermocouple and a relay, and the temperature controller adopts PID technology.

[0016] The extrusion die forming process is characterized in that the die is made of nickel-based alloy, and the die is characterized by two-stage compression molding structure, which solves the problem of die pressure multiplication caused by high viscosity; the die inlet compression angle is 10°-50°, the forming length is 40 mm-300 mm, and the secondary compression angle is 10°-40°.

[0017] The die can also be plated with chromium.

[0018] The rod forming process is characterized in that the total length of the forming die is 100 mm-300 mm.

[0019] The cooling process is characterized in that a two-stage forming die of water cooling+air cooling is used, including a water cooling zone and a convection air zone, the die is first cooled by water, the water temperature ranges from 20℃ to 80℃, and the air cooling is negative pressure air directly passing through the gap formed between the pre-cooled rod surface and the die sleeve. The air pressure of the negative pressure air is -0.02 to -0.06 MPa.

[0020] The damping process is characterized in that the damping device adopts damping laminations, which are friction force components composed of single or multiple temperature-resistant rubber sheets, the damping laminations are provided with holes in the middle, and the resistance is controlled by the hole diameter and the number of rubber sheets.

[0021] The heat preservation process is characterized in that in order to reduce the internal stress of the rod formed by rapid cooling, a heat preservation pipeline is used for heat preservation to ensure online release of the internal stress of the rod, and the heat preservation temperature is 100℃-120℃.

[0022] The heat preservation pipeline is preferably a metal pipeline provided with a heater.

[0023] The specific process operation method of the present application includes pre-starting inspection, temperature rising operation, starting operation,

[0024] Production process control and shutdown operation.

[0025] The pre-starting inspection includes confirming that the equipment is in good standby state, turning on the water, electricity and gas sources, checking whether the equipment leaks water and gas, testing the auxiliary machines (such as water pump, traction machine, cutting machine, etc.), confirming that the auxiliary machines are in good condition, and checking whether the used die is intact.

[0026] The temperature rising operation is: according to the equipment and the mold case is different to adjust the time of opening the power supply appropriately, to ensure that each part that must be heated reaches the required temperature for production at the same time; the power supply of the extruder is turned on first when the temperature rises, the temperature control switch is turned on, and then the temperature of each zone is set to be 5-10℃ higher than the normal production temperature. Check whether the heating of each heating ring is normal. After the mold reaches the set temperature, it can be started after constant temperature for about 30-50 minutes. The constant temperature time is determined according to the size of the mold. The constant temperature time of large mold is longer than that of small mold; attention should be paid to the normal temperature rising speed of each zone during the temperature rising process, and the temperature of each zone should be checked for accuracy with other temperature meters such as glass temperature meter; the cooling water of the shaping mold is appropriately turned on to prevent the damage of the sealing ring caused by high temperature, and the water supply and drainage pipes.

[0027] The start operation is: confirm again whether the temperature of each zone reaches the required temperature; check whether the connecting screws of the mold are tightened; confirm again that each auxiliary machine is in standby state, the material rack and the cutting machine system have been adjusted to the position; normally turn on the cooling water; start the main motor of the extruder at a low speed, adjust the speed to the reference speed required by the process slowly according to the torque, and pay attention to the current and running sound of the main machine; after the mold discharges the material, quickly introduce the material blank into the damping piece hole; if necessary, turn on the traction machine and adjust the traction speed to match the extrusion speed.

[0028] The main process parameters of the start operation are as follows:

[0029] ①The temperature of the extruder barrel is: C1: 180-240℃, C2: 200-270℃, C3: 230-290℃;

[0030] ②The speed of the main machine is: 5-20Hz;

[0031] ③The temperature of the mold is: 260-290℃;

[0032] ④The temperature of the sizing cooling water is: 20-90℃;

[0033] ⑤The air pressure of the sizing cooling air is: -0.02MPa to -0.06MPa;

[0034] ⑥The damping force is: 1-10 damping pieces.

[0035] The control of the production process is: after the normal adjustment of the start, enter the stable production state, and the product quality should be fully inspected according to the requirements of production quality control and relevant regulations during operation; pay attention to the running condition of the equipment at any time, and strictly control the current of the main machine not to exceed the specified value, and each process parameter should be within the normal range.

[0036] In production, if there is a problem, the production cannot be carried out normally, the host should be stopped first, and the host should be restarted after 1 minute. If there is an electrical or mechanical failure in production, the treatment method should be selected according to the severity of the consequences caused by the failure. If it causes unstable production, it should be stopped and the temperature should be reduced. After repair, restart the machine.

[0037] The stop operation is: close the hopper discharge port; continue to start for 3-5 minutes, and then stop the extruder main motor after the current of the extruder is appropriately reduced; then stop the power supply after reducing the barrel temperature to below 150 DEG C; and close the water source; when cutting the last rod, the traction machine is turned off after completely walking out of the shaping mold (if necessary).

[0038] Compared with the existing mold pressing process, the scheme can greatly improve the performance stability of the product, the performance index fluctuation is small; reduce the probability of delamination, black spots, bubbles and other phenomena, and improve the qualified rate. The production efficiency is improved by more than 10 times of the mold pressing process. The utilization rate of the material for subsequent processing is greatly improved, the material waste rate is reduced by more than 5 times, and the material replacement time is saved by 1 / 5. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 It is a two-stage compression molding die structure.

[0040] Figure 2 It is a water-cooled + air-cooled two-section cooling shaping sleeve.

[0041] Figure 3 It is a damping machine, wherein 1 is a support circular pipe, 2 is a damping sheet, 4 is a support frame, 5 is a holding plate, and 6 is a hard rubber sheet. DETAILED DESCRIPTION

[0042] The application will be further described below in combination with examples.

[0043] Example 1

[0044] The following is an example of the production process of a PCTFE round rod with a length of more than 1 meter and a diameter of 20 mm, including the following steps:

[0045] (1) Select raw materials: PCTFE 300H;

[0046] (2) The mold is selected to be 20 specifications, the mold compression angle is 50 degrees, and the shrinkage rate is 4.5%;

[0047] (3) The screw diameter of the single screw extruder is 35 mm, and the extruder parameters are set as follows: C1: 200 DEG C, C2: 240 DEG C, C3: 280 DEG C; the mold temperature is 290 DEG C; after heating and reaching the same temperature, keep the temperature for 30 minutes.

[0048] (4) After the constant temperature time arrives, the above raw materials are sent into the single screw extruder hopper, and the extruder is slowly opened. The main machine speed is 10 Hz;

[0049] (5) After single screw extrusion, the rod is shaped and shaped by mold, with water temperature of 60°C, cooling air pressure of -0.03 MPa;

[0050] (6) Damping: 4 pieces of small hole damping film clamping rods are used;

[0051] (7) Heat preservation: the heat preservation temperature is 120°C. Then air cooling, cutting, detection and packaging are carried out.

[0052] The tensile strength of the obtained rod is 46 MPa, and the elongation at break is 120%.

[0053] Example 2

[0054] The following takes the production process of PCTFE round rod with controllable roundness size, length size of more than 1 meter and diameter of 15 mm as an example, which includes the following steps:

[0055] (1) Raw material: PCTFE 300H;

[0056] (2) The mold is selected to be 15 specifications, the mold compression angle is 45 degrees, and the shrinkage rate is 6%. The sizing sleeve is cooled by water and air;

[0057] (3) The screw diameter of the single screw extruder is 45 mm, and the extruder parameters are set as follows: C1: 200°C, C2: 250°C, C3: 290°C; The mold temperature is 290°C; After heating, the temperature is kept for 30 minutes;

[0058] (4) After the constant temperature time arrives, the above raw materials are sent into the single screw extruder hopper, and the extruder is slowly opened. The main machine speed is 11 Hz;

[0059] (5) After single screw extrusion, the rod is shaped and shaped by mold, with water temperature of 30°C, cooling air pressure of -0.06 MPa;

[0060] (6) Damping: 2 pieces of small hole damping film are used;

[0061] (7) Heat preservation, heat preservation temperature is 100°C, air cooling, cutting, detection and packaging.

[0062] The tensile strength of the obtained rod is 43 MPa, and the elongation at break is 150%.

Claims

1. A continuous extrusion molding method for polychlorotrifluoroethylene rods, comprising extruder plasticizing, extrusion die forming, rod shaping, damping, heat preservation, cooling, and cutting; characterized in that: The extruder plasticizing process uses a single-screw extruder with a screw outer diameter of 35-60mm, a screw length-to-diameter ratio of (20-25):1, a compression ratio of 2.3-2.56, and a gradient of 0.00720-0.00905. The extrusion die forming process uses a nickel-based alloy die with a two-stage compression molding structure. The bar shaping process uses a shaping die with a total length of 100mm-300mm. The cooling process employs a two-stage shaping structure of water cooling and air cooling, including two water cooling zones and two convection air cooling zones. The water cooling temperature range is 20℃-80℃, and the air cooling uses an air pressure range of -0.02MPa to -0.06MPa. The negative pressure air; the damping process uses a damping sheet with a central opening; the heat preservation process uses a metal tube equipped with a heater to heat the rod, with a heat preservation temperature range of 100℃~120℃; the extruder barrel temperature is C1: 180℃~240℃, C2: 200℃~270℃, C3: 230℃~290℃; the main machine speed is 5~20Hz; the nickel-based alloy die inlet compression angle is 10°~50°, the forming length is 40 mm~300 mm, and the secondary compression angle is 10°~40°.

2. The continuous extrusion molding method for polychlorotrifluoroethylene rods according to claim 1, characterized in that: The extruder consists of a screw, a barrel, a variable frequency motor control system, a reduction system, a temperature control system, and a frame. The metering section of the screw accounts for 30% of the total screw length, and the thread depth of the metering section is 0.04~0.06 of the screw diameter. The variable frequency motor control system uses a variable frequency three-phase motor controlled by a frequency converter of corresponding power. The reduction system uses a series reduction screw composed of a pulley and a reduction gearbox, with a reduction ratio of 20 between the screw and the motor, and an overall reduction ratio of 50.

3. The continuous extrusion molding method for polychlorotrifluoroethylene rods according to claim 1, characterized in that: The damping sheet is a stacked sheet composed of rubber sheets; the resistance of the damping sheet is determined by the diameter of the opening and the number of stacked sheets.

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