WO2020244360A1 - 一种感应加热挤出聚四氟乙烯棒材的加工方法 - Google Patents

一种感应加热挤出聚四氟乙烯棒材的加工方法 Download PDF

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Publication number
WO2020244360A1
WO2020244360A1 PCT/CN2020/090083 CN2020090083W WO2020244360A1 WO 2020244360 A1 WO2020244360 A1 WO 2020244360A1 CN 2020090083 W CN2020090083 W CN 2020090083W WO 2020244360 A1 WO2020244360 A1 WO 2020244360A1
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die
polytetrafluoroethylene
plunger
feeder
feeding
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PCT/CN2020/090083
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English (en)
French (fr)
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杨成刚
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浙江松华新材股份有限公司
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Publication of WO2020244360A1 publication Critical patent/WO2020244360A1/zh

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
    • B29C48/03—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor characterised by the shape of the extruded material at extrusion
    • B29C48/06—Rod-shaped
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
    • B29C48/25—Component parts, details or accessories; Auxiliary operations
    • B29C48/78—Thermal treatment of the extrusion moulding material or of preformed parts or layers, e.g. by heating or cooling
    • B29C48/86—Thermal treatment of the extrusion moulding material or of preformed parts or layers, e.g. by heating or cooling at the nozzle zone
    • B29C48/865—Heating

Definitions

  • the invention relates to a processing method for induction heating and extruding polytetrafluoroethylene rods.
  • the widely used PTFE rod extruder is a PTFE extruder heated by resistance wire.
  • resistance wire heating method because the resistance wire heater uses resistance wire to heat the barrel and then transfer the heat to the material, and the barrel is a barrel with a certain thickness, so it is in the radial direction of the barrel. A larger temperature gradient is formed on it.
  • heating with it also takes a long time.
  • resistance wire heaters that use mica sheets as insulating materials are susceptible to oxidation and moisture, which will shorten their life. Since a large amount of mica flakes are used as insulating material, the cost of the heater is also higher.
  • the existing processing methods and equipment have the following defects:
  • the traditional resistance wire heating principle is that the resistance wire itself generates high temperature, and then the heat is slowly transferred from the high temperature area on the outer surface of the barrel to the central low temperature area of the barrel, and the speed is slow. And there is a big error between the actual temperature of the PTFE in the center of the barrel and the surface temperature of the barrel. When the temperature of the PTFE reaches the required temperature, although the resistance wire stops heating, due to the temperature error, the surface of the barrel continues to face the machine.
  • the heating methods used by the barrel in the current extruder equipment are generally traditional electric heaters, electric heating sheets and electric heating tubes Resistance heating.
  • the heating methods used by the barrel in the current extruder equipment are generally traditional electric heaters, electric heating sheets and electric heating tubes Resistance heating.
  • heat is transferred from the surface of the electric heater, electric heating fin and electric heating tube to the surface of the machine, and then the heat is gradually transferred from the surface of the machine barrel to the inner layer of the machine, and finally the heat is transferred from the machine barrel
  • the inner layer is conducted to the PTFE, so that the PTFE can be formed at a temperature. In this process, the heat is gradually transferred from the resistance heating element to the heated medium PTFE in the form of heat conduction, with many intermediate links.
  • the heat dissipation is large. Thermal efficiency is low. Most of the heat outside the electric heater is lost to the air, there is a large amount of heat energy loss, and causes the high temperature and overheating of the workshop; third, the heater on the PTFE extruder is generally set between 300 °C and 380 °C, the traditional Due to the large amount of heat lost in the air, the temperature of the workshop is too high, especially in summer, the workshop is extremely stuffy, and the working environment of employees is very harsh.
  • the purpose of the present invention is to provide a processing method for induction heating extruded polytetrafluoroethylene rods for solving the above technical problems, which has the advantages of rapid heating, real-time and accurate temperature control, high processing efficiency and stable rod quality.
  • the technical solution adopted by the present invention to solve the above-mentioned technical problems is: a processing method of induction heating and extruding polytetrafluoroethylene rods, including the following steps:
  • Step 1 Feeding: Add the polytetrafluoroethylene resin to the feeder set in the extruder;
  • Step 2 Compaction: The plunger compresses the Teflon resin in the feeder to the die set on the extruder;
  • Step 3 Repeat feeding and compaction until the PTFE resin is compacted
  • Step 4 Sintering: The induction coil on the die is energized, and the induction coil generates heat to completely melt the compacted PTFE resin in the die;
  • Step 5 Cooling: The molten polytetrafluoroethylene resin is cooled by an air quenching cooling method to form a polytetrafluoroethylene rod.
  • the cooling method of air quenching means that the product is directly exposed to the air after being extruded from the die.
  • the temperature of the feeder during step one is 5-25°C. If the temperature exceeds 25°C or lower than 5°C, the polytetrafluoroethylene resin is easy to agglomerate and become viscous and hinder the material flow.
  • the optimum temperature of the feeder is 21°C.
  • step two and step three include the following steps:
  • Step 1 Feeding, lasting 0 ⁇ 15s;
  • Step 2 The plunger moves to the die for 3 ⁇ 240s
  • Step 3 Stop the plunger and continue to compress for 0 ⁇ 30s
  • Step 4 The plunger returns for 1-10s.
  • the pre-forming force generated by the movement of the plunger to the die makes the resin compact, but as long as the plunger has sufficient pressure, the pre-forming force depends on the back pressure, which is caused by the PTFE resin moving in the die The resistance and the braking force applied after the exit mold.
  • the lowest pressure pushed by the plunger is to make the polytetrafluoroethylene resin powder become a compact preform with the least voids; the highest pressure is the pressure that does not cause the polytetrafluoroethylene resin to crack on the adjacent surface of the second feeding. For pre-sintering, it cannot exceed 100MPa.
  • the diameter of the polytetrafluoroethylene rod formed by cooling is 2 to 400 mm.
  • the particles of pre-sintered polytetrafluoroethylene resin are harder, exhibit high density, and still have good fluidity at higher temperatures. It is easy to enter the die and increase the extrusion speed. It can form polytetrafluoroethylene with a diameter of 2 to 400 mm. Vinyl fluoride rods.
  • the extruder includes a die for heating the polytetrafluoroethylene resin, a feeding system for adding polytetrafluoroethylene resin to the die, and compacting the polytetrafluoroethylene resin in the die.
  • the plunger, the power system used to provide pressure for the plunger to compact the PTFE resin, the die is equipped with an electromagnetic induction heater for heating the PTFE resin, and the electromagnetic induction heater is equipped with an induction coil ,
  • the power system, plunger, feeding system, and die are connected in sequence. When the AC power is passed into the induction coil, magnetic lines of force are generated.
  • the magnetic lines of force in the closed circuit have the same frequency as the AC power.
  • the eddy current generates heat when it encounters resistance in the electromagnetic induction heater. Due to the high-frequency induction principle, the induction coil does not directly contact the heated metal, so the thermal radiation temperature of the system itself is close to the ambient temperature, only below 50°C, and the human body can touch it. It has many advantages such as high heat efficiency, fast heat generation, energy saving, safety and reliability.
  • the working principle of electromagnetic induction heater is high-frequency induction. The heated metal is heated by its own current.
  • the heat is generated by the metal of the barrel as a whole, so the preheating time is shorter and the temperature is in the radial direction of the barrel.
  • the gradient is small.
  • the temperature control is real-time and accurate, and the temperature inside and outside the barrel is consistent, which significantly improves the quality of the product and increases the processing efficiency.
  • the electromagnetic induction heater passes high-frequency current to the induction coil to generate a strong magnetic field.
  • the barrel inside the induction coil heats both inside and outside due to the induction of magnetic energy, thereby heating the PTFE in the barrel, which is different from the traditional Compared with heating methods such as resistance wire, the loss of heat conduction and air heat convection is reduced.
  • induction heating has much less intermediate conduction links than resistance heating, and less heat dissipation. High thermal efficiency, thereby saving a lot of electric energy. After the comparison between experimental test and modification, the energy saving is 40%-60%, and the energy saving effect is very obvious.
  • the induction coil of the electromagnetic induction heater is provided with a heat preservation layer
  • the die is provided with a barrel
  • the heat preservation layer is provided on the barrel
  • the heat preservation layer is provided with an induction coil. From the outside to the inside, they are the induction coil, the insulation layer, the barrel, and the PTFE resin.
  • a thermal insulation layer is installed between the induction coil of the electromagnetic induction heater and the barrel. The heat inside the barrel is radiated into the air. The temperature on the surface of the barrel is below 50°C, and the ambient temperature of the workshop is significantly reduced. It can also avoid scalding accidents.
  • the die is provided with a thermostat that cuts off the power to stop heating when the working temperature exceeds a preset value, and the thermostat is provided with a thermocouple for measuring the current working temperature, and the thermocouple is connected to the thermostat.
  • the working temperature of the die can be accurately controlled.
  • the extruder is also provided with a PLC control terminal, and the PLC control terminal is provided with a temperature indicator for checking the current temperature in real time.
  • the operator can know the current temperature data by viewing the temperature indicator, which is used for recording in daily work.
  • the power system includes a cylinder pressure regulator, an intake control valve for controlling air to enter the cylinder, a cylinder for pushing the plunger, and the cylinder pressure regulator, the intake control valve, the cylinder, and the plunger are connected in sequence. Air enters the cylinder through the cylinder pressure regulator and the intake control valve, and the cylinder pushes the plunger to compact the PTFE resin in the die. If voids remain in the polytetrafluoroethylene resin, the appearance is chalk-like.
  • a timer for controlling the movement time of the plunger is provided on the intake control valve. If the pressing speed is too fast and the PTFE resin enters the sintering zone without being fully compressed, the product will also be chalk-like.
  • the timer by controlling the air intake time of the cylinder, the movement speed of the piston in the cylinder can be controlled, and then the pushing speed of the plunger can be controlled.
  • a limit switch for controlling the maximum displacement position of the plunger is provided under the plunger. If the pushing force of the plunger is not large enough and there are voids in the PTFE resin, the product will look like a chalk; the setting of the limit switch can control the pushing force of the plunger.
  • the feeding system includes a feeder for feeding into the die, a feeding pressure regulator for adjusting the pressure in the feeder, a meter for measuring the quantity of raw materials in the feeder, and a meter for controlling the addition to the feeder.
  • the raw material feeding controller, the feeding pressure regulator, the meter, the feeding controller, and the feeder are connected in sequence, and the feeder is also connected with the plunger and the die.
  • it also includes an air filter, which is respectively connected with the cylinder pressure regulator and the charging pressure regulator.
  • the setting of the air filter prevents impurities in the air from entering the die through the feeding bin and affecting the molding of PTFE rod products in a high temperature environment.
  • the heating is rapid and the temperature control is real-time and accurate.
  • the working principle of electromagnetic induction heater is high-frequency induction.
  • the heated metal is heated by its own current.
  • the heat is generated by the metal of the barrel as a whole, so the preheating time is shorter and the temperature is in the radial direction of the barrel.
  • the gradient is small.
  • the temperature control is real-time and accurate, and the temperature inside and outside the barrel is consistent, which significantly improves the quality of the product and increases the processing efficiency.
  • the electromagnetic induction heater passes high-frequency current to the induction coil to generate a strong magnetic field.
  • the barrel inside the induction coil heats both inside and outside due to the induction of magnetic energy, thereby heating the PTFE in the barrel, which is different from the traditional Compared with heating methods such as resistance wire, the loss of heat conduction and air heat convection is reduced. It can be seen from this heating process that induction heating has much less intermediate conduction links than resistance heating, and less heat dissipation. High thermal efficiency, thereby saving a lot of electric energy. After the comparison between the experimental test and the modification, the energy saving is 40% to 60%, and the energy saving effect is very obvious.
  • a thermal insulation layer is installed between the induction coil of the electromagnetic induction heater and the barrel. The heat inside the barrel is radiated into the air. The temperature on the surface of the barrel is below 50°C, and the ambient temperature of the workshop is significantly reduced. It can also avoid scalding accidents.
  • the electromagnetic induction heater has a longer life.
  • Figure 1 is a schematic diagram of the structure of the extruder of the present invention.
  • Fig. 2 is a cross-sectional view of the electromagnetic induction heater of the present invention when it is installed on a die.
  • Figure 3 is a schematic diagram of the electromagnetic induction heating of the present invention.
  • a processing method for induction heating extruded polytetrafluoroethylene rods of the present invention includes the following steps:
  • Step 1 Feeding: adding the polytetrafluoroethylene resin 6 to the feeder 21 provided in the extruder;
  • Step 2 Compaction: The plunger 3 compresses the polytetrafluoroethylene resin 6 in the feeder 21 to the die 1 provided on the extruder;
  • Step 3 Repeat feeding and compaction until the PTFE resin 6 is compacted
  • Step 4 Sintering: The induction coil 111 outside the die 1 is energized, and the induction coil 111 generates heat to completely melt the compacted PTFE resin 6 in the die 1;
  • Step 5 Cooling: The molten polytetrafluoroethylene resin 6 is cooled by an air quenching cooling method to form a polytetrafluoroethylene rod.
  • the temperature of the feeder 21 during step 1 is 5-25°C. If the temperature exceeds 25°C or is lower than 5°C, the polytetrafluoroethylene resin 6 tends to agglomerate and become viscous and hinder the flow of materials.
  • the temperature of the feeder 21 is optimally 21°C.
  • Step two and step three include the following steps:
  • Step 1 Feeding, lasting 0 ⁇ 15s;
  • Step 2 The plunger 3 moves to the die 1 for 3 ⁇ 240s;
  • Step 3 Stop the plunger 3 and continue to compress for 0 ⁇ 30s;
  • Step 4 The plunger 3 returns for 1-10s.
  • the diameter of the Teflon rod formed by cooling is 2 to 400 mm.
  • the particles of pre-sintered PTFE resin 6 are harder, exhibit high density, and still have good fluidity at higher temperatures. It is easy to enter the die 1 and increase the extrusion speed. It can be molded with a diameter of 2 to 400 mm. Teflon rods.
  • the extruder includes a die for heating the polytetrafluoroethylene resin 6, a feeding system for adding the polytetrafluoroethylene resin 6 to the die 1, and a feeding system for adding the polytetrafluoroethylene in the die 1.
  • Plunger 3 compacted by resin 6, power system 4 used to provide pressure for plunger 3 to compact the PTFE resin 6, and the die 1 is provided with an electromagnetic induction heater for heating the PTFE resin 6 11.
  • the electromagnetic induction heater 11 is provided with an induction coil 111, and the power system 4, the plunger 3, the feeding system 2, and the die 1 are connected in sequence.
  • the power system 4 includes a hydraulic system and a pneumatic system, and the pneumatic system is adopted in this embodiment.
  • High frequency electromagnetic induction heating is developed on the basis of Faraday's law of induction, which is an application form of Faraday's law of induction. It uses the principle of electromagnetic induction to convert electrical energy into heat, as shown in Figure 3.
  • the heating principle is: the 50Hz/60Hz AC power is converted into DC power through the internal rectification filter circuit, and then the DC power is converted into high frequency low voltage high current power with a frequency of 20-40KHz through the PWM control circuit, and the high-speed changing current will be generated by the coil.
  • the high-speed changing magnetic field when the heated metal object is placed in the middle, the heated metal object cuts the alternating magnetic field lines and generates countless alternating currents (ie eddy currents) inside the heated metal object.
  • the eddy current causes the The iron molecules move randomly at high speed, and the molecules collide and rub against each other to generate heat energy, so that the heated metal object itself heats up at a high speed. Because the metal object heats itself, the heat conversion rate is particularly high.
  • the plunger 3 is composed of a standard-sized cylinder and a fixed-shaped top.
  • the top is in contact with PTFE resin and is often made of high temperature resistant plastic.
  • the outer diameter of the plunger 3 is smaller than the inner diameter of the die 1.
  • PTFE resin refers to polytetrafluoroethylene resin.
  • Die 1 is a metal tube with a very uniform cross-section over the entire length and a smooth inner surface. Because the die 1 is heated, corrosion-resistant stainless steel materials are often used. In this embodiment, the die 1 is heated by electromagnetic induction.
  • the basic molding of the plunger 3 is the continuity of compression molding, which can continuously mold PTFE resin, which is a method of sintering and cooling under pressure.
  • PTFE resin which is a method of sintering and cooling under pressure.
  • the PTFE resin is compressed into a preform, and then sintered in the die 1 and cooled.
  • the back pressure that makes the product strong during the extrusion process comes from the friction between the material itself and the wall of the die 1, as well as the braking force exerted on the product after the cooling section.
  • the induction coil 111 of the electromagnetic induction heater 11 is provided with a thermal insulation layer 112, the die 1 is provided with a barrel 113, the thermal insulation layer 112 is provided on the barrel 113, and the thermal insulation layer 112 is provided with an induction coil 111.
  • the power system 4 includes a cylinder pressure regulator 41, an intake control valve 42 for controlling air to enter the cylinder 43, a cylinder 43 for pushing the plunger 3, a cylinder pressure regulator 41, an intake control valve 42, a cylinder 43, a column
  • the plugs 3 are connected in sequence.
  • a timer 421 for controlling the movement time of the plunger 3 is provided on the intake control valve 42.
  • the die 1 is equipped with a thermostat 12 that cuts off the power to stop heating when the working temperature exceeds a preset value.
  • the thermostat 12 is equipped with a thermocouple 13 for measuring the current working temperature, a thermocouple 13 and a thermostat 12 connection.
  • the extruder is also provided with a PLC control terminal (not shown), and the PLC control terminal is provided with a temperature indicator (not shown) for checking the current temperature in real time, and temperature indicators are all sold in the market.
  • the PLC control terminal can control the charging controller 24 and the air intake control valve 42.
  • the PLC control terminal is connected to the charging controller 24, the air intake control valve 42 and the thermostat 12.
  • the PLC control terminal displays the temperature of the die 1 on the temperature indicator through the temperature controller 12.
  • a limit switch 31 for controlling the maximum displacement position of the plunger 3 is provided under the plunger 3.
  • the feeding system 2 includes a feeder 21 for feeding the die 1, a feeding pressure regulator 22 for adjusting the pressure in the feeder 21, a meter 23 for measuring the quantity of raw materials in the feeder 21, and a meter for controlling the feeder 21.
  • the feeding controller 24 for adding raw materials in the feeder 21, the feeding pressure regulator 22, the meter 23, the feeding controller 24, and the feeder 21 are connected in sequence, and the feeder 21 is also connected with the plunger 3 and the die 1 respectively.

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Abstract

本发明公开了一种感应加热挤出聚四氟乙烯棒材的加工方法，包括以下步骤：步骤一：加料：将聚四氟乙烯树脂加入到设在挤出机的加料器中；步骤二：压实：柱塞将处于加料器中的聚四氟乙烯树脂向设在挤出机上的口模压缩；步骤三：重复加料和压实，直到聚四氟乙烯树脂被压实；步骤四：烧结：将口模上的感应线圈进行通电，感应线圈产生热量将口模内压实的聚四氟乙烯树脂完全熔融；步骤五：冷却：将熔融的聚四氟乙烯树脂采用空气淬火的冷却法进行冷却，形成聚四氟乙烯棒材。本发明具有加热迅速，温度控制实时准确，加工效率高、棒材质量稳定的优点。

Description

一种感应加热挤出聚四氟乙烯棒材的加工方法 技术领域
本发明涉及一种感应加热挤出聚四氟乙烯棒材的加工方法。
背景技术
目前广泛使用的聚四氟乙烯棒材挤出机是电阻丝加热的聚四氟乙烯挤出机。采用电阻丝加热的方式，由于电阻丝加热器是采用电阻丝加热机筒后再把热传到的物料上，而机筒又是一个具有一定厚度的筒体，因此在机筒的径向方向上便形成较大的温度梯度。另外，用它加热也需要较长的时间。同时，使用云母片作绝缘材料的电阻丝加热器，其电阻丝易氧化受潮等，也会使其寿命缩短。由于要使用大量的云母片作绝缘材料，加热器的成本也较高。
现有的加工方法及设备有如下缺陷：一是传统的电阻丝加热原理是电阻丝本身产生高温，然后热量再慢慢的从机筒外表面高温区传导到机筒的中心低温区，速度缓慢，并且位于机筒中心的聚四氟乙烯实际温度和机筒表面温度有较大误差，当聚四氟乙烯温度达到要求时虽然电阻丝停止加热，由于存在温度误差，机筒表面仍然继续向机筒内部传导热量，导致温度控制不准确，既影响了成型质量也降低了加工效率；二是目前挤出机设备中的机筒所使用的加热方式普遍为传统的电热器、电热片和电热管等电阻式加热。通过接触传导，热量从电热器、电热片和电热管等的表面把热量传到机简的表面上，然后，热量由机筒的表面逐步传导到机简的内层，最后热量才从机筒的内层传导给聚四氟乙烯，使聚四氟乙烯得到可以以成型的温度，在这一过程中，热量主要以热传导的形式由电阻发热体逐步传导给被加热介质PTFE，中间环节多。热量耗散大。热效率低。电热器外侧的热量大部分散失到空气中，存在大量的热能损失，并造成车间高温过热；三是聚四氟乙烯挤出机上面的加热器一般设定在300℃～380℃之间，传统的电阻式加热由于其有大量的热量散失在空气中，造成车间温度过高，尤其足夏季车间异常闷热，员工的工作环境非常恶劣。
发明内容
本发明的目的在于提供一种用于解决上述技术问题的感应加热挤出聚四氟乙烯棒材的加工方法，具有加热迅速，温度控制实时准确，加工效率高、棒材质量稳定的优点。
本发明解决上述技术问题采用的技术方案是：一种感应加热挤出聚四氟乙 烯棒材的加工方法，包括以下步骤：
步骤一：加料：将聚四氟乙烯树脂加入到设在挤出机的加料器中；
步骤二：压实：柱塞将处于加料器中的聚四氟乙烯树脂向设在挤出机上的口模压缩；
步骤三：重复加料和压实，直到聚四氟乙烯树脂被压实；
步骤四：烧结：将口模上的感应线圈进行通电，感应线圈产生热量将口模内压实的聚四氟乙烯树脂完全熔融；
步骤五：冷却：将熔融的聚四氟乙烯树脂采用空气淬火的冷却法进行冷却，形成聚四氟乙烯棒材。
当将交流电源通入感应线圈时，就产生了磁力线，磁力线在封闭回路中具有与交流电源相同的频率，当磁通发生变化时，就会在封闭回路中产生感应电动势，从而引起二次感应电压及感应电流，亦叫电的涡流。涡流在电磁感应加热器中遇到阻力就产生热量。由于是高频感应原理，感应线圈不和被加热金属直接接触，所以系统本身热辐射温度接近环境温度，只有50℃以下，人体完全可以触摸。它以热效高、发热快、省电节能、安全可靠等诸多优点。
空气淬火的冷却法是指将制品从口模挤出后直接暴露于空气中。
作为优选，步骤一加料时加料器的温度为5～25℃。温度超过25℃或低于5℃聚四氟乙烯树脂就容易结团变粘使料流受阻。加料器的温度为21℃最适宜。
作为优选，步骤二和步骤三包括以下步骤：
步骤1：加料，持续0～15s；
步骤2：柱塞向口模移动3～240s；
步骤3：柱塞停止，持续压缩0～30s；
步骤4：柱塞返回，持续1～10s。
柱塞向口模移动产生的预成型力使树脂压实，但只要柱塞有足够的压力，预成型力的大小取决于反压力，反压力由聚四氟乙烯树脂在口模内移动时的阻力和出口模后外加的制动力所构成。柱塞推动的最低压力是使聚四氟乙烯树脂粉末成为致密的、空隙最少的预成型物；最高压力是不使聚四氟乙烯树脂在2次加料的邻接面上产生碎裂的压力。对预烧结的不能超过100MPa。
作为优选，步骤五中，冷却形成聚四氟乙烯棒材的直径为2～400mm。预烧结聚四氟乙烯树脂的颗粒较硬、表现密度大，在较高的温度下仍有较好的流动性，容易进入口模而提高挤出速度，可以成型直径为2～400mm的聚四氟乙烯棒材。
作为优选，挤出机包括用于加热聚四氟乙烯树脂的口模、用于将聚四氟乙 烯树脂添加到口模中的加料系统、用于将口模中的聚四氟乙烯树脂压实的柱塞、用于为柱塞提供压力将聚四氟乙烯树脂压实的动力系统，口模上设有用于加热聚四氟乙烯树脂的电磁感应加热器，电磁感应加热器上设有感应线圈，动力系统、柱塞、加料系统、口模依次连接。当将交流电源通入感应线圈时，就产生了磁力线，磁力线在封闭回路中具有与交流电源相同的频率，当磁通发生变化时，就会在封闭回路中产生感应电动势，从而引起二次感应电压及感应电流，亦叫电的涡流。涡流在电磁感应加热器中遇到阻力就产生热量。由于是高频感应原理，感应线圈不和被加热金属直接接触，所以系统本身热辐射温度接近环境温度，只有50℃以下，人体完全可以触摸。它以热效高、发热快、省电节能、安全可靠等诸多优点。电磁感应加热器的工作原理是高频感应，被加热的金属是通过自身的电流发热，热能是由机筒金属整体产生，因此预热升温的时间较短，在机筒的径向方向上温度梯度较小。温度控制实时准确，机筒内外温度一致，明显改善了产品的质量和提高了加工效率。电磁感应加热器是给感应线圈通以高频率的电流，使其产生强磁场，感应线圈内的机筒因感应到了磁能而内外一起发热，从而实现对机筒内的PTFE进行加热，与传统的电阻丝等加热方式相比减少了热传导和空气热对流的损耗。从这一加热过程可以看出，感应加热比电阻式加热的中间传导环节少了许多，热量耗散少。热效率高，从而节约了大量的电能。经过实验测试和改装之后的对比，节约电能在40％～60％，节能效果非常明显。
作为优选，电磁感应加热器的感应线圈内设有保温层，口模上设有机筒，保温层设在机筒上，保温层上设有感应线圈。由外到内依次为感应线圈、保温层、机筒、聚四氟乙烯树脂。电磁感应加热器的感应线圈和机筒之间加装一层隔热保温层，机筒内部的热量微量辐射到空气中，机筒表面的温度在50℃以下，车间的环境温度明显降低很多，还可避免烫伤事故的发生。
作为优选，口模上设有当工作温度超过预设值时断开电源停止加热的温控器，温控器上设有用于测量当前工作温度的热电偶，热电偶与温控器连接。通过热电偶和温控器的设置，可以将口模的工作温度进行精确控制。
作为优选，挤出机上还设有PLC控制终端，PLC控制终端上设有用于实时查看当前温度的温度指示器。操作人员可以通过查看温度指示器知道当前温度的数据，用于日常工作中的记录。
作为优选，动力系统包括气缸压力调节器、用于控制空气进入气缸的进气控制阀、用于推动柱塞的气缸，气缸压力调节器、进气控制阀、气缸、柱塞依次连接。空气经气缸压力调节器、进气控制阀进入气缸，气缸推动柱塞压实口 模中的聚四氟乙烯树脂。若聚四氟乙烯树脂内残留空隙，则外观呈粉笔状。
作为优选，进气控制阀上设有控制柱塞运动时间的计时器。若推压速度过快，聚四氟乙烯树脂未经充分压缩就进入烧结区，则产品也会呈粉笔状。通过计时器的设置，通过控制气缸进气的时间，从而控制气缸内活塞的运动速度，进而可以控制柱塞的推压速度。
作为优选，柱塞下方设有控制柱塞最大位移位置的限位开关。若柱塞的推压力不够大，聚四氟乙烯树脂内残留空隙，则产品外观呈粉笔状；通过限位开关的设置，可以控制柱塞的推压力。
作为优选，加料系统包括用于给口模内加料的加料器、用于调节加料器内压力的加料压力调节器、用于测量加料器内原料数量的计量表、用于控制向加料器内添加原料的加料控制器，加料压力调节器、计量表、加料控制器、加料器依次连接，加料器还分别与柱塞、口模连接。
作为优选，还包括空气过滤器，空气过滤器分别与气缸压力调节器、加料压力调节器连接。通过空气过滤器的设置，防止空气中的杂质通过加料仓进入口模在高温环境下影响聚四氟乙烯棒材产品的成型。
本发明具有的有益效果是：
1、当将交流电源通入感应线圈时，就产生了磁力线，磁力线在封闭回路中具有与交流电源相同的频率，当磁通发生变化时，就会在封闭回路中产生感应电动势，从而引起二次感应电压及感应电流，亦叫电的涡流。涡流在电磁感应加热器中遇到阻力就产生热量。由于是高频感应原理，感应线圈不和被加热金属直接接触，所以系统本身热辐射温度接近环境温度，只有50℃以下，人体完全可以触摸。它以热效高、发热快、省电节能、安全可靠等诸多优点。
2、加热迅速，温度控制实时准确。电磁感应加热器的工作原理是高频感应，被加热的金属是通过自身的电流发热，热能是由机筒金属整体产生，因此预热升温的时间较短，在机筒的径向方向上温度梯度较小。温度控制实时准确，机筒内外温度一致，明显改善了产品的质量和提高了加工效率。
3、节能效果明显。电磁感应加热器是给感应线圈通以高频率的电流，使其产生强磁场，感应线圈内的机筒因感应到了磁能而内外一起发热，从而实现对机筒内的PTFE进行加热，与传统的电阻丝等加热方式相比减少了热传导和空气热对流的损耗。从这一加热过程可以看出，感应加热比电阻式加热的中间传导环节少了许多，热量耗散少。热效率高，从而节约了大量的电能。经过实验测试和改装之后的对比，节约电能在40％～60％，节能效果非常明显。
4、环保效果好，明显降低车间温度。电磁感应加热器的感应线圈和机筒之 间加装一层隔热保温层，机筒内部的热量微量辐射到空气中，机筒表面的温度在50℃以下，车间的环境温度明显降低很多，还可避免烫伤事故的发生。
5、在正确的冷却和使用的情况下，电磁感应加热器的寿命比较长。
附图说明
图1是本发明的挤出机的结构示意图。
图2是本发明的电磁感应加热器设在口模上时的剖视图。
图3是本发明的电磁感应加热原理图。
图中：1、口模，11、电磁感应加热器，111、感应线圈，112、保温层，113、机筒，12、温控器，13、热电偶，2、加料系统，21、加料器，22、加料压力调节器，23、计量表，24、加料控制器，3、柱塞，31、限位开关，4、动力系统，41、气缸压力调节器，42、进气控制阀，421、计时器，43、气缸，5、空气过滤器，6、聚四氟乙烯树脂
具体实施方式
以下结合附图和实施方式对本发明作进一步的说明。
如图1-3所示，本发明一种感应加热挤出聚四氟乙烯棒材的加工方法，包括以下步骤：
步骤一：加料：将聚四氟乙烯树脂6加入到设在挤出机的加料器21中；
步骤二：压实：柱塞3将处于加料器21中的聚四氟乙烯树脂6向设在挤出机上的口模1压缩；
步骤三：重复加料和压实，直到聚四氟乙烯树脂6被压实；
步骤四：烧结：将口模1外侧的感应线圈111进行通电，感应线圈111产生热量将口模1内压实的聚四氟乙烯树脂6完全熔融；
步骤五：冷却：将熔融的聚四氟乙烯树脂6采用空气淬火的冷却法进行冷却，形成聚四氟乙烯棒材。
步骤一加料时加料器21的温度为5～25℃。温度超过25℃或低于5℃聚四氟乙烯树脂6就容易结团变粘使料流受阻。加料器21的温度为21℃最适宜。
步骤二和步骤三包括以下步骤：
步骤1：加料，持续0～15s；
步骤2：柱塞3向口模1移动3～240s；
步骤3：柱塞3停止，持续压缩0～30s；
步骤4：柱塞3返回，持续1～10s。
步骤五中，冷却形成聚四氟乙烯棒材的直径为2～400mm。预烧结聚四氟乙烯树脂6的颗粒较硬、表现密度大，在较高的温度下仍有较好的流动性，容易 进入口模1而提高挤出速度，可以成型直径为2～400mm的聚四氟乙烯棒材。
挤出机包括用于加热聚四氟乙烯树脂6的口模1、用于将聚四氟乙烯树脂6添加到口模1中的加料系统2、用于将口模1中的聚四氟乙烯树脂6压实的柱塞3、用于为柱塞3提供压力将聚四氟乙烯树脂6压实的动力系统4，口模1上设有用于加热聚四氟乙烯树脂6的电磁感应加热器11，电磁感应加热器11上设有感应线圈111，动力系统4、柱塞3、加料系统2、口模1依次连接。动力系统4包括液压系统和气压系统，本实施例采用的是气压系统。
高频电磁感应加热是在法拉第感应定律基础上发展起来的，是法拉第感应定律的一种应用形式。它是利用电磁感应原理将电能转换为热能，如图3所示。其发热原理是：通过内部整流滤波电路将50Hz/60Hz的交流电变为直流电，再经过PWM控制电路将直流电转换成频率为20-40KHz的高频低压大电流电，高速变化的电流通过线圈会产生高速变化的磁场，当被加热金属物体放置在中间时，被加热金属物体即切割交变磁力线而在被加热金属物体内部产生无数交变的电流(即涡流)，涡流使被加热金属物体内的铁分子高速无规则运动，分子互相碰撞、摩擦而产生热能从而使被加热金属物体本身高速发热，由于是金属物体自身发热，所以热转化率特别高。
柱塞3由标准尺寸的圆柱及固定形状的顶部组成，顶部与PTFE树脂接触，常由耐高温塑料制成，柱塞3外径小于口模1内径。PTFE树脂是指聚四氟乙烯树脂。
口模1是在整个长度上截面非常均匀、而内表面光滑的一根金属管，因口模1是加热的，常采用耐腐蚀的不锈钢材料。本实施例采用电磁感应加热口模1。
柱塞3基础成型是模压成型的连续化，能连续成型PTFE树脂，属于压力下烧结和冷却的方法。柱塞基础成型时，把PTFE树脂压缩成预成型物后，在口模1中烧结并冷却。挤出过程中使产品结实的反压力来自物料自身和物料与口模1壁之间的摩擦，以及出冷却段后施加于制品上的制动力。
电磁感应加热器11的感应线圈111内设有保温层112，口模1上设有机筒113，保温层112设在机筒113上，保温层112上设有感应线圈111。
动力系统4包括气缸压力调节器41、用于控制空气进入气缸43的进气控制阀42、用于推动柱塞3的气缸43，气缸压力调节器41、进气控制阀42、气缸43、柱塞3依次连接。
进气控制阀42上设有控制柱塞3运动时间的计时器421。
口模1上设有当工作温度超过预设值时断开电源停止加热的温控器12，温控器12上设有用于测量当前工作温度的热电偶13，热电偶13与温控器12连接。 挤出机上还设有PLC控制终端(未示出)，PLC控制终端上设有用于实时查看当前温度的温度指示器(未示出)，温度指示器在市场上均有销售。PLC控制终端可以控制加料控制器24、进气控制阀42，PLC控制终端与加料控制器24、进气控制阀42、温控器12连接连接。PLC控制终端通过温控器12将口模1的温度在温度指示器上显示。
柱塞3下方设有控制柱塞3最大位移位置的限位开关31。
加料系统2包括用于给口模1内加料的加料器21、用于调节加料器21内压力的加料压力调节器22、用于测量加料器21内原料数量的计量表23、用于控制向加料器21内添加原料的加料控制器24，加料压力调节器22、计量表23、加料控制器24、加料器21依次连接，加料器21还分别与柱塞3、口模1连接。
还包括空气过滤器5，空气过滤器5分别与气缸压力调节器41、加料压力调节器22连接。
说明书中各个实施例采用递进的方式描述，每个实施例重点说明的都是与其他实施例的不同之处，各个实施例之间相同相似部分互相参见即可。
对所公开的实施例的上述说明，使本领域专业技术人员能够实现或使用本发明。对这些实施例的多种修改对本领域的专业技术人员来说将是显而易见的，本文中所定义的一般原理可以在不脱离本发明的精神或范围的情况下，在其它实施例中实现。因此，本发明将不会被限制于本文所示的这些实施例，而是要符合与本文所公开的原理和新颖特点相一致的最宽的范围。

Claims (10)

  1. 一种感应加热挤出聚四氟乙烯棒材的加工方法，其特征在于：包括以下步骤：
    步骤一：加料：将聚四氟乙烯树脂(6)加入到设在挤出机的加料器(21)中；
    步骤二：压实：柱塞(3)将处于加料器(21)中的聚四氟乙烯树脂(6)向设在挤出机上的口模(1)压缩；
    步骤三：重复加料和压实，直到聚四氟乙烯树脂(6)被压实；
    步骤四：烧结：将口模(1)上的感应线圈(111)进行通电，感应线圈(111)产生热量将口模(1)内压实的聚四氟乙烯树脂(6)完全熔融；
    步骤五：冷却：将熔融的聚四氟乙烯树脂(6)采用空气淬火的冷却法进行冷却，形成聚四氟乙烯棒材。
  2. 根据权利要求1所述的感应加热挤出聚四氟乙烯棒材的加工方法，其特征在于：步骤一加料时加料器(21)的温度为5～25℃。
  3. 根据权利要求1或2所述的感应加热挤出聚四氟乙烯棒材的加工方法，其特征在于：步骤二和步骤三包括以下步骤：
    步骤1：加料，持续0～15s；
    步骤2：柱塞(3)向口模(1)移动3～240s；
    步骤3：柱塞(3)停止，持续压缩0～30s；
    步骤4：柱塞(3)返回，持续1～10s。
  4. 根据权利要求3所述的感应加热挤出聚四氟乙烯棒材的加工方法，其特征在于：步骤五中，冷却形成聚四氟乙烯棒材的直径为2～400mm。
  5. 根据权利要求1或2或4所述的感应加热挤出聚四氟乙烯棒材的加工方法，其特征在于：挤出机包括用于加热聚四氟乙烯树脂(6)的口模(1)、用于将聚四氟乙烯树脂(6)添加到口模(1)中的加料系统(2)、用于将口模(1)中的聚四氟乙烯树脂(6)压实的柱塞(3)、用于为柱塞(3)提供压力将聚四氟乙烯树脂(6)压实的动力系统(4)，口模(1)上设有用于加热聚四氟乙烯树脂(6)的电磁感应加热器(11)，电磁感应加热器(11)上设有感应线圈(111)，动力系统(4)、柱塞(3)、加料系统(2)、口模(1)依次连接。
  6. 根据权利要求5所述的感应加热挤出聚四氟乙烯棒材的加工方法，其特征在于：电磁感应加热器(11)的感应线圈(111)内设有保温层(112)，口模(1)上设有机筒(113)，保温层(112)设在机筒(113)上，保温层(112)上设有 感应线圈(111)。
  7. 根据权利要求6所述的感应加热挤出聚四氟乙烯棒材的加工方法，其特征在于：动力系统(4)包括气缸压力调节器(41)、用于控制空气进入气缸(43)的进气控制阀(42)、用于推动柱塞(3)的气缸(43)，气缸压力调节器(41)、进气控制阀(42)、气缸(43)、柱塞(3)依次连接。
  8. 根据权利要求1或2或4或6或7所述的感应加热挤出聚四氟乙烯棒材的加工方法，其特征在于：口模(1)上设有当工作温度超过预设值时断开电源停止加热的温控器(12)，温控器(12)上设有用于测量当前工作温度的热电偶(13)，热电偶(13)与温控器(12)连接。
  9. 根据权利要求8所述的感应加热挤出聚四氟乙烯棒材的加工方法，其特征在于：柱塞(3)下方设有控制柱塞(3)最大位移位置的限位开关(31)。
  10. 根据权利要求5所述的感应加热挤出聚四氟乙烯棒材的加工方法，其特征在于：加料系统(2)包括用于给口模(1)内加料的加料器(21)、用于调节加料器(21)内压力的加料压力调节器(22)、用于测量加料器(21)内原料数量的计量表(23)、用于控制向加料器(21)内添加原料的加料控制器(24)，加料压力调节器(22)、计量表(23)、加料控制器(24)、加料器(21)依次连接，加料器(21)还分别与柱塞(3)、口模(1)连接。
PCT/CN2020/090083 2019-06-03 2020-05-13 一种感应加热挤出聚四氟乙烯棒材的加工方法 WO2020244360A1 (zh)

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