CN115352014A - Continuous extrusion molding method of polychlorotrifluoroethylene bar - Google Patents

Abstract

The invention discloses a continuous extrusion molding method of a polychlorotrifluoroethylene bar, and particularly relates to plasticization of an extruder, molding of an extrusion die, sizing of the bar, damping, heat preservation, cooling and cutting. Compared with the existing mould pressing process, the scheme of the invention can greatly improve the product performance stability and has small performance index fluctuation; the occurrence probability of layering, black spots, bubbles and the like is reduced, and the qualification rate is improved. The production efficiency is greatly improved by more than 10 times of the mould pressing process, the utilization rate of materials for subsequent processing is greatly improved, the waste rate of the materials is reduced by more than 5 times, and the material changing working hour is saved by 1/5.

Description

Continuous extrusion molding method of polychlorotrifluoroethylene bar

Technical Field

The invention relates to a continuous extrusion molding method of a Polychlorotrifluoroethylene (PCTFE) bar, belonging to the technical field of product-grade PCTFE.

Background

Polychlorotrifluoroethylene (PCTFE) is a homopolymer of the monomeric chlorotrifluoroethylene, a polymer of the perhalogenated crystalline type. It is very similar in structure to perfluorinated polymers such as polytetrafluoroethylene. Since the F atom in the molecular structure of PCTFE renders the polymer chemically inert and the Cl atom renders the polymer transparent, thermoplastic and hard, PCTFE is an inert fluoropolymer having high stability, heat resistance, incombustibility, non-hygroscopicity and gas impermeability. PCTFE has excellent dielectric properties, has very high bulk resistance, electrical strength and arc resistance, is hardly affected by temperature or humidity, and is a high-frequency insulating material that can withstand severe conditions better than conventional materials. The PCTFE can be classified into lubricating grease grade PCTFE, film grade PCTFE and product grade PCTFE according to different purposes and molecular weights of the PCTFE, and the invention mainly aims at the product grade PCTFE.

The manufactured grade PCTFE can theoretically be processed by conventional thermoplastic processing methods such as die pressing, extrusion, injection molding, and the like. However, the PCTFE product has a melt viscosity 100 times or more that of ordinary resins, and the melt processing temperature and decomposition temperature are close to each other, so that corrosive substances are likely to be generated during processing. Due to cost and processability limitations, PCTFE has exited from applications such as coatings and injection molded articles. The melt viscosity of PCTFE is extremely high, and the forming process of PCTFE products is basically formed by compression molding similar to powder metallurgy processing at home at present.

Chinese patent CN104987630A discloses a modified polychlorotrifluoroethylene and a molding process thereof, wherein the modified PCTFE prepared by the patent technology increases the hardness peak and the dimensional stability, improves the high temperature resistance, the wear resistance, the thermal conductivity and the creep resistance, changes the friction coefficient of the material, reduces the cost of the original PCTFE, and enlarges the application range of the material. Chinese patent CN206644230U discloses a vertical compression molding die for a polychlorotrifluoroethylene ultra-long rod, and introduces a vertical compression molding technology, which realizes the preparation of an ultra-long rod-shaped PCTFE material by using a mode that the upper end and the lower end of the die are simultaneously fed and pressurized.

At present, the bar extrusion molding process using Polychlorotrifluoroethylene (PCTFE) as a raw material is not reported at home. Extrusion into rods is very difficult, mainly due to the material properties of PCTFE. At present, only a compression molding process can be adopted in China, and the yield of the compression molding process is not high due to the crystallization characteristic of materials. When PCTFE parts are machined actually, due to the fact that the length of a PCTFE molded rod is too short, materials need to be replaced frequently, machining efficiency is low, and excessive waste is caused. And for horizontal type mould pressing PCTFE rod with small diameter, the defect of uneven crystallization at the mould closing gap of the mould also exists, the defect causes the strength defect of parts, and for important occasions, the reliability is difficult to ensure.

Disclosure of Invention

The invention aims to solve the problem of difficult extrusion molding of a PCTFE bar and provides a technical scheme for producing the PCTFE bar by using an extrusion molding process method.

The technological line of the PCTFE bar extrusion molding method adopted by the invention comprises the steps of extruder plasticizing, extrusion die molding, bar sizing, damping, heat preservation, cooling and cutting.

The extruder plasticizing process is characterized in that the adopted extruder is a single-screw extruder and comprises a screw, a screw cylinder, a variable frequency motor control system, a speed reduction system, a temperature control system, a rack and the like.

The screw barrel and the screw are characterized by being made of nickel-based steel, the outer diameter of the screw is 35-60 mm, and the length-diameter ratio is (20-25): 1, a compression ratio of 2.30 to 2.56.

The difference of the screw and the traditional plastic extruding machine is that the metering section of the screw accounts for 30 percent of the total length of the screw, and the thread depth of the metering section of the screw is 0.04 to 0.06 percent of the diameter of the screw.

The preferable specification of the screw is as follows: an outer diameter of 35mm, a compression molding ratio of 2.30 and a degree of tapering of 0.00720.

The preferable specification of the screw is as follows: an outer diameter of 45mm, a compression ratio of 2.56 and a degree of tapering of 0.00905.

The variable frequency motor driving control system adopts a variable frequency three-phase motor and is controlled by a frequency converter with corresponding power.

The speed reduction system is different from the traditional plastic extruding machine in that a high speed reduction ratio is adopted, and the speed reduction ratio of a screw and a motor is selected to be 20; the belt pulley and the reduction gearbox are adopted to form a series connection speed reduction, and the total speed reduction ratio is up to 50.

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

The extrusion die shaping process is characterized in that a die is made of nickel-based alloy and is characterized by being of a two-stage compression molding structure, so that the problem of die pressure multiplication caused by extremely high viscosity is solved; the compression angle of the inlet of the die is 10-50 degrees, the molding length is 40-300 mm, and the secondary compression angle is 10-40 degrees.

The mould may also be treated with chrome plating.

The bar material shaping process is characterized in that the total length of a shaping die is 100 mm-300 mm.

The cooling process is characterized in that a water-cooling and air-cooling two-section shaping die is adopted, the water-cooling and air-cooling two-section shaping die comprises a water cooling area and a convection air area, the die is firstly cooled by water, the water temperature ranges from 20 ℃ to 80 ℃, and air cooling is negative pressure air which directly passes through a gap formed by the surface of a precooled bar and a die sleeve. The air pressure of the negative pressure air is-0.02 to-0.06 MPa

The damping process is characterized in that the damping device adopts damping laminates and is a friction force assembly consisting of a single sheet or a plurality of temperature-resistant rubber sheets, a hole is formed in the middle of each damping laminate, and the size of the resistance is controlled by the diameter of the hole and the number of the rubber sheets.

The heat preservation process is characterized in that in order to reduce the internal stress of the bar due to rapid cooling, a heat preservation pipeline is used for heat preservation, so that the internal stress of the bar is ensured to be released on line, and the heat preservation temperature is 100-120 ℃.

The insulated pipe is preferably a metal pipe fitted with a heater.

The specific technological operation method comprises the steps of inspection before startup, heating operation, startup operation,

Control and stop operation in the production process.

The inspection work before starting up is as follows: confirming that the equipment is in a good standby state; starting water, electricity and gas sources, and checking whether the equipment leaks water and gas; trial running auxiliary machines (such as a water pump, a tractor, a cutting machine and the like) and confirming that the auxiliary machines are all in a good state; the used mold was checked for integrity.

The temperature raising operation is as follows: properly adjusting the time for turning on the power supply according to different conditions of equipment and a mold so as to ensure that all parts to be heated reach the temperature required by production at the same time; when the temperature rises, the power supply of the extruder is firstly switched on, the temperature control switch is started, and then the set temperature of each zone is adjusted to be 5-10 ℃ higher than the normal production temperature. And checking whether the heating coils generate heat normally. Starting up the die after the die reaches the set temperature and is kept at the constant temperature for about 30 to 50 minutes, wherein the constant temperature time is determined according to the size of the die, and the constant temperature time of the large die is longer than that of the small die; in the heating process, attention should be paid to observe whether the heating speed of each area is normal, and other glass thermometers such as a glass thermometer are used for checking whether the temperature of each area is accurate; the shaping mould is properly opened with cooling water to prevent the sealing ring, the water supply pipe and the water discharge pipe from being damaged due to overhigh temperature.

The boot operation is: confirming whether the temperature of each area reaches the required temperature again; checking whether each connecting screw of the die is fastened or not; confirming that all auxiliary machines are in a standby state again, and adjusting the material rack and the cutting machine system to be in place; starting cooling water normally; starting the motor of the extrusion main machine at a lower rotating speed, slowly adjusting the rotating speed to the reference rotating speed required by the process according to the torque condition, and observing the current and the running noise of the main machine; after the die discharges materials, quickly introducing the material blanks into the damping fin holes; if necessary, the drawing machine is started and the drawing speed is adjusted to match the extrusion speed.

The main molding process parameters of the starting operation are as follows:

(1) the extruder barrel temperature was: c1 is 180-240 ℃, C2 is 200-270 ℃ and C3 is 230-290 ℃;

(2) the rotating speed of the main machine is as follows: 5. -20 Hz;

(3) temperature of the die: 260-290 ℃;

(4) sizing cooling water temperature: 20-90 ℃;

(5) fixed diameter cooling air pressure: -0.02MPa to-0.06 MPa;

(6) damping force: 1. 10 damping fins.

The production process is controlled as follows: after the startup adjustment is normal, entering a stable production state, and performing full inspection on the product quality according to production quality control requirements and related specified requirements during operation; the running condition of the observation equipment is noticed at any time, the current of the host machine is strictly controlled not to exceed a specified value, and each process parameter is within a normal range.

In production, if a problem occurs and production cannot be normally carried out, the main machine is stopped by pressing a stop key, and the main machine is restarted after the main machine is stopped for 1 minute. If an electrical or mechanical fault occurs in the production, a processing mode is selected according to the severity of the consequence caused by the fault, and if the production is unstable, the machine is stopped, and the temperature is reduced. And after the repair is finished, restarting the machine.

The shutdown operation is as follows: closing a blanking port of the hopper; continuing to start the extruder for 3 to 5 minutes, stopping the main motor of the extruder after the current of the extruder is properly reduced, then stopping the power supply after the temperature of the screw cylinder is reduced to be below 150 ℃, and stopping the water source; when the last bar is to be cut, the tractor is shut down (if necessary) after the last bar is completely taken out of the stock mold.

Compared with the existing mould pressing process method, the scheme of the invention can greatly improve the product performance stability, and the performance index fluctuation is small; the occurrence probability of layering, black spots, bubbles and the like is reduced, and the qualification rate is improved. Greatly improves the production efficiency which is more than 10 times of the mould pressing process. The utilization rate of materials for subsequent processing is greatly improved, the waste rate of the materials is reduced by more than 5 times, and the material changing working hour is saved by 1/5.

Drawings

Fig. 1 is a two-stage compression mold head structure.

FIG. 2 shows a water-cooling and air-cooling two-stage cooling sizing sleeve.

Fig. 3 shows a damper, wherein 1 is a supporting circular tube, 2 is a damping lamination, 4 is a supporting frame, 5 is a holding plate, and 6 is a hard film.

Detailed Description

The present invention will be further described with reference to the following examples.

Example 1

The following process of manufacturing a PCTFE round rod with a length of more than 1 meter and a diameter of 20mm is taken as an example, and the method comprises the following steps:

(1) Selecting the following raw materials: PCTFE 300H;

(2) The mold is selected to be 20 in specification, the compression angle of the mold is 50 degrees, and the shrinkage rate is 4.5%;

(3) The screw diameter of the single screw extruder is 35mm, and the extruder parameters are set according to the following parameters: c1:200 ℃, C2:240 ℃ and 280 ℃ of C3; the temperature of the die is 290 ℃; heating, and keeping the temperature for 30 minutes after the temperature is reached.

(4) And (4) after the constant temperature time is up, feeding the raw materials into a hopper of the single-screw extruder, and slowly starting the extruder. The rotating speed of the main machine is 10Hz;

(5) Extruding by a single screw, molding and shaping by a mold, wherein the shaping water temperature is 60 ℃, and the cooling air pressure is-0.03 MPa;

(6) Damping: 4 small-hole damping rubber sheet clamping rods are adopted;

(7) And (3) heat preservation: the holding temperature was 120 ℃. Then air cooling, cutting, detecting and packaging.

The obtained bar has the tensile strength of 46MPa and the elongation at break of 120 percent.

Example 2

Taking the manufacturing process of the PCTFE round rod with controllable roundness, length of more than 1 meter and diameter of 15mm as an example, the method comprises the following steps:

(1) Raw materials: PCTFE 300H;

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

(3) The screw diameter of the single screw extruder was 45mm, and the extruder parameters were set as follows: c1:200 ℃, C2:250 ℃ and C3:290 ℃; the temperature of the die is 290 ℃; heating, keeping the temperature for 30 minutes after the temperature is reached;

(4) After the constant temperature time is reached, feeding the raw materials into a hopper of a single-screw extruder, and slowly starting the extruder; the rotating speed of the main machine is 11Hz;

(5) After single screw extrusion, molding and shaping: the water temperature is 30 ℃, and the cooling air pressure is-0.06 MPa;

(6) Damping, 2 small hole damping films are adopted;

(7) Keeping the temperature at 100 ℃, air cooling, cutting, detecting and packaging.

The obtained bar has the tensile strength of 43MPa and the elongation at break of 150 percent.

Claims (5)

1. The continuous extrusion molding method of the polychlorotrifluoroethylene bar comprises the steps of plasticizing an extruder, molding an extrusion die, shaping the bar, damping, preserving heat, cooling and cutting; the method is characterized in that: the extruder adopts a single-screw extruder with the outer diameter of a screw of 35-60 mm, the length-diameter ratio of the screw of 20-25: 1, the compression ratio of 2.3-2.56 and the gradient of 0.00720-0.00905 for plasticization; the extrusion die shaping process adopts a nickel-based alloy die with a two-stage compression molding structure; the bar material shaping process adopts a shaping die with the total length of 100 mm-300 mm; the cooling process adopts a water-cooling and air-cooling two-section shaping structure, and comprises 2 water cooling areas and 2 convective air cooling areas, wherein the water cooling temperature range is 20-80 ℃, and the air cooling adopts negative pressure air with the air pressure range of-0.02 MPa to-0.06 MPa; the damping process adopts a damping fin with a hole in the middle; the heat preservation process adopts a metal pipe provided with a heater to preserve heat of the bar, and the heat preservation temperature range is 100-120 ℃.

2. The continuous extrusion molding method of polychlorotrifluoroethylene bar as claimed in claim 1, wherein: the temperature of the extruder barrel is C1: 180-240 ℃, C2: 200-270 ℃, C3: 230-290 ℃; the rotating speed of the main machine is as follows: 5. -20 Hz; the temperature of the die is 260-290 ℃.

3. The extruder of claim 1, wherein: the extruder comprises a screw, a screw cylinder, a variable frequency motor control system, a speed reduction system, a temperature control system, a rack and the like; the metering section of the screw accounts for 30 percent of the total length of the screw, and the thread depth of the metering section of the screw is 0.04 to 0.06 percent of the diameter of the screw; the variable frequency motor driving control system adopts a variable frequency three-phase motor and is controlled by a frequency converter with corresponding power; the speed reduction system adopts a belt pulley and a speed reduction box to form a series speed reduction screw, the speed reduction ratio of the screw and a motor reaches 20, and the total speed reduction ratio reaches 50.

4. A two-stage compression molding structure according to claim 1, wherein: the compression angle of the mold inlet is 10-50 degrees, the molding length is 40-300 mm, and the secondary compression angle is 10-40 degrees.

5. The damping process according to claim 1, wherein: the damping sheet is a lamination sheet and consists of rubber sheets; the resistance of the damping sheet is determined by the diameter of the opening and the number of the laminated sheets.

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