Analysis of eight key points of the hottest UPVC P

Analysis of eight key points of UPVC Plastic injection process

upvc, also known as hard PVC, is an amorphous thermoplastic resin made of vinyl chloride monomer through polymerization plus certain additives (such as stabilizers, lubricants, fillers, etc.)

in addition to using additives, it also adopts the method of blending and modifying with other resins, so that it has the practical value of Ming · thermosetting/thermoplastic carbon fiber composite prepreg molding process. The introduction of our experimental machine to ensure the quality of self-adhesive. These resins include CPVC, PE, ABS, EVA, MBS, etc

upvc has high melt viscosity and poor fluidity. Even if the injection pressure and melt temperature are increased, the fluidity changes little. In addition, the molding temperature of the resin is very close to the thermal decomposition temperature, and the temperature range that can be molded is very narrow, so it is a kind of material that is difficult to be molded

1. Plastic treatment

after 24 hours at room temperature, the water absorption is less than 0.02%, so there is no need to dry. If it must be dried, it can be put into a hot gas furnace at ℃ for 3 hours, or a dryer at 80 ℃ 5 hours

recycled materials can be mixed with new materials by up to 20%. The amount of recycled materials depends on the end use of the products. The abuse of recycled materials can make injection molding fail, not only because there are too many recycled components, but also because the materials have been reprocessed many times. The more recycled materials are recycled, the more the quality decreases

2. The injection molding machine adopts

upvc. Because the melt viscosity is large and easy to decompose, and the decomposition products have corrosive effect on iron, its injection molding must have special plasticizing parts and temperature control system

3. The melt temperature

can be measured by air injection method, ranging from ℃. The accurate melt temperature of UPVC can be known from the smoothness of the injected material. If the material is rough and uneven after injection, it proves that the material is not homogeneous (insufficient plasticization), indicating that the set temperature is too low; If there is foam and a large amount of smoke after shooting, it means that the temperature is too high

4. The injection speed

the injection speed should be slow, otherwise excessive shearing will degrade the material. When using UPVC to produce extremely smooth thick wall products, multi-level injection mold filling speed should be used

5. The screw speed

should be determined according to the molding cycle. The screw face speed should not exceed 0 2m/s

6. The back pressure

can reach 150bar. The more attention should be paid to the running direction of the motor and the direction 1 shown by the arrow on the pulley cover, the better. It is usually 5bar

7. Retention time

at 200 ℃, the retention time of the barrel shall not exceed 5 minutes at most. When the temperature is 210 ℃, the retention time of the barrel cannot exceed 3 minutes

8. Mold and gate design

mold temperature can be set to 40 ℃. The length of the runner should be short and the diameter should be large to reduce the pressure loss and transfer the pressure retaining energy to the mold cavity. The shorter the gate, the better. The cutting surface of the die should be round. The diameter of the nozzle should be at least 6mm, conical, and the internal angle should be 5

the die cutting surface of the sprue should also be circular, which is combined with the cold charging well. The diameter of the die cutting surface can be 7mm, which connects the sprue and the gate through the cutting radius

the gate should be used to connect the plastic parts with the radius of the tangential plane, the shorter the better, and the cutting surface of the mold should be smooth

cold charging well can prevent semi solidified materials from entering the mold cavity, and its importance is often ignored

the position of the gate should be correct, so that the materials can flow smoothly on the runner, and will not stay in sharp corners, debris and metal traces, so as to avoid compression or decompression. The runner should be kept smooth and smooth

the mold shall be cast with stainless steel. The chromium content shall be at least 13%, preferably 16%, and the Rockwell hardness shall be at least 55. The hard steel mold can be chrome plated to form a protective effect

after production, the mold surface shall be carefully cleaned with mild alkaline solution, and then sprayed with oil spray or silicon spray

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