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The extrusion molding process conditions of the chlorinated polyvinyl chloride pipe ( CPVC pipe ) are similar to those of the ordinary polyvinyl chloride pipe, and the difference is that the quality requirements of the parts for extrusion molding are higher; the process temperature The fluctuation range control requirements are more stringent.
(1) Extrusion molding process of chlorinated polyvinyl chloride tube: According to the formula of CPVC pipe forming material, the raw materials are metered separately → the raw materials are put into the mixer, stirred and mixed uniformly → the mixed homogeneous material is cooled and cooled, and the extruder is plasticized. Make it in a molten state → mold forming tube blank → vacuum sizing cooling setting → cooling water tank to cool the pipe → traction → trademark printing → cutting → pipe end flaring → inspection → packaging into the warehouse.
(2) Equipment selection: High-speed mixer for mixing raw materials, the required speed is 800~1000r/min, the upper cover has exhaust device, and the transfer can be adjusted. After mixing the raw materials evenly, the mixer is used for cooling, the rotation speed is low, and the cooling water can be cooled by the circulating cooling water.
The plasticizing raw material can be a single screw extruder or a twin screw extruder. For pellet forming, if a single-screw extruder is used, the screw structure should be gradually deepened in thread depth (ie, equidistant unequal gradient snail), and the aspect ratio L/D=22-25; such as twin-screw extrusion machine.
It should be used in the same direction rotation type, the working speed is low 20r/min, and the molding die temperature is about 200°C; if it is extruded by powder, it should be extruded by a counter-rotating twin-screw extruder. When the single-screw extruder extrudes the plasticized raw material, the screw can be tempered by the circulating oil, and the equipment should have a better exhausting device; the barrel is cooled by circulating water or circulating oil, and the process temperature fluctuation is controlled at ±5. °C or so. It is more suitable to extrude CPVC powder by ordinary parallel twin-screw extruder. There is no perforated plate between the barrel of the extruder and the forming die; the screw working place should be equipped with an overload protection device.
In the mold structure, the shrinkage angle of the core uranium is required to be less than 60°; the length of the straight section should be about twice the diameter of the extruded pipe, and at this time, there should be a heating and cooling cooling device capable of controlling the temperature of the mandrel to maintain this section. The temperature control is smooth and the inner wall of the pipe is smooth. In order to improve the corrosion resistance of the mandrel, the working faces of the melt channels in the mandrel and the mold should be chrome-plated.
(3) Molding process operation and temperature control:
1CPVC resin should be dried in an 80° oven for 2 to 4 hours before being put into production to remove moisture from the raw materials.
2 The metered raw materials are put into a high-speed mixer and mixed, and the material temperature is about 115 °C.
3 The high temperature compound after high speed compounding is cooled in the low speed mixer until the material temperature reaches about 40 °C.
4 extruder extrusion raw materials in the molten state process temperature is as follows:
Single screw extruder extrusion temperature:
The feeding section of the barrel is 160 ° C, the plasticizing section is 170 ° C, the homogenization section is 180 ° C, and the molding die temperature is 185 ° C to 190 ° C. Twin-screw extruder extrusion temperature: barrel feeding section 188 ° C ~ 195 ° C, plasticizing section 180 ° C ~ 188 ° C, homogenization section 175 ° C ~ 180 ° C, forming mold temperature 175 ° C ~ 190 ° C. Mandrel operating temperature 160 ° C ~ 170 ° C; screw circulating oil temperature: 100 ° C ~ 120 ° C.
(4) Process operation points: The extrusion molding of chlorinated polyvinyl chloride tube is more difficult than the extrusion molding of polyvinyl chloride tube, because the viscosity of chlorinated polyvinyl chloride melt is high (about 2 times greater than the viscosity of PVC resin). The fluidity is poor, the molding is difficult, and the melt is easily decomposed during the production process. Therefore, the following problems should be noted in the extrusion molding production of the chlorinated polyvinyl chloride resin.
The chlorinated polyvinyl chloride resin must be dried before being put into production, and dried in an oven at 80 ° C for 2-4 hours. If necessary, the raw materials after high-speed mixing are also sieved once with a 40 mesh sieve, and then put into the extruder. Production in the hopper (Note: it is not advisable to heat up when mixing high-speed mixers).
2 The raw material formula of the formed pipe should pay attention to the selection of stabilizers and other processing aids, which should be mainly to improve the melt flow and improve the thermal stability of the raw materials. Mix the formula first if necessary. Take a small sample test and place it in an oven at 230 °C for 2 h. If there is no obvious discoloration and decomposition phenomenon, it indicates that the auxiliary material selection is reasonable and reasonable (the temperature of the material after high-speed mixing is in the range of 115 °C to 120 °C).
The process temperature for extrusion molding of 3 chlorinated polyethylene pipes is slightly higher than the extrusion process temperature of PVC pipes. However, it should be noted that the temperature control fluctuation cannot be greater than ±5 °C.
4 In the process of producing CPVC pipe, if there is a power outage, equipment failure, signs of possible decomposition of the melt or smoke from the die mouth, immediately stop feeding into the barrel, and use PVC resin to remove the machine and the mold. CPVC melt, then stop again to troubleshoot.
The HCI gas released when the 5CPVC melt is decomposed is harmful to the human body, and attention should be paid to the ventilation of the production workshop.
6 Extruder barrel for the production of CPV resin, the melt flowing through the surface of the screw and the forming mold shall be treated with anti-corrosion treatment to prolong the service life of the equipment parts.
7 The raw material mixing and kneading machine top cover should have a vent (with a 400 mesh copper mesh or cloth bag to seal the vent) to facilitate the discharge of water vapor.
8Use CPVC pipe extrusion molding extruder. Pay attention to the performance conditions such as exhaust gas and process temperature control stability when the extruder barrel is working. If these two conditions fail to meet the production requirements, the extrusion molding of the CPVC pipe will be difficult or even impossible to produce.
9 When producing CPVC pipe, the screw should be cooled by circulating oil; the core shaft of the mold should have heating and cooling devices, and the stability of the process temperature of these two parts should be properly adjusted during the work to improve the fluidity of the molten material and ensure the fluidity of the molten material. The molding quality of the product (the control of the mandrel temperature has a great influence on the molding quality of the inner wall of the pipe).
10 When the inner wall of the formed pipe is uneven, the acrylate processing aid (also available as methyl methacrylate copolymer) should be added or appropriately added to the raw material formulation to improve the melting temperature of the mixture of CPVC and PVC. Close; at the same time, pay attention to the stability control of the mandrel temperature.
In the formulation of CPVC pipe extrusion molding, CPVC and PVC resin can be used in combination. However, it is to be noted that the Vicat softening temperature of the mixed resin decreases as the amount of the PVC resin added increases. If the PVC in the formulation is 10 parts and the CPVC is 90 parts, the Vicat softening temperature is about 110 °C; when the PVC is 20 parts and the CPVC is 80 parts, the Vicat softening temperature is about 105 °C; the PVC resin and the CPVC resin are each At 50 parts, the Vicat softening temperature is about 90 °C.