UPVC is also called hard PVC. In addition to additives, UPVC is also blended with other resins to make it more practical. These resins are PE, ABS, EVA, CPVC, MBS, etc. UPVC has a high melt viscosity and poor fluidity, and even if the injection pressure and the melt temperature are increased, the change in fluidity is small. In addition, the molding temperature of the resin is almost close to the thermal decomposition temperature, and the temperature range in which the molding can be performed is narrow, which is a material which is difficult to mold.
1, plastic processing
If the water absorption amount is less than 0.02% after 24 hours at room temperature, the plastic does not need to be dried. If it has to be dried, it can be placed in a hot gas oven at 60-70 ° C for 3 hours, or a dryer at 80 ° C for about 1-1.5 hours.
Recycled materials can be mixed with up to 20% of new materials. The amount of recycled materials depends on the end use of the product. Abuse of recycled materials may cause the injection molding job to fail, not only because of the excessive recovery of the components, but also because the materials are processed several times. The quality of the recycled material will gradually decline every time it is recycled.
2, the selection of injection molding machine
UPVC has a relatively high melt viscosity, so it is easy to decompose. The decomposition products have a great corrosive effect on iron. The injection molding must use special plasticized parts and temperature control system.
Each type of clamping force model covered by Ramada has a special UPVC plastic injection system, and a special safety door device is required for the core pulling of UPVC pipe products. Under normal circumstances, as long as the injection volume can meet the weight requirements, this series of UPVC special injection molding equipment can be used to form high quality products.
3, mold and gate design
The mold temperature can be set to 40 °C. Moreover, the entire length of the flow path must be short, and the diameter is relatively large, which is used to gradually reduce the pressure loss and the pressure holding energy can be transmitted to the cavity. The shorter the gate, the better. The die-cut surface must be round. The diameter of the nozzle mouth is 6mm minimum, conical, and the inner angle is 5.
The die-cut surface of the main channel is also round, combined with a cold well, connected to the main channel and gate by the radius of the cut surface, and the diameter can be 7mm.
The gate is connected to the plastic part by the radius of the rounded surface. The shorter the better, the smoother the die cut surface.
Cold wells prevent semi-solidified materials from entering the mold cavity, and its importance is often overlooked.
The position of the gate should be correct so that the material flows smoothly on the flow path and does not stay in the traces of sharp corners, debris and metal, so as to avoid compression or decompression, the flow path should be kept smooth and smooth.
The mold is cast in stainless steel with a chromium content of at least 13%, preferably 16%, and a Rockwell hardness of at least 55. The hard steel mold can be chrome-plated to form a protective effect.
After production, use a mild lye to carefully clean the mold surface and spray an oily spray or a siliceous spray.
4, the temperature of the melt
It can be measured by the air-launch method and varies from 185-205 °C. The exact melt temperature of the UPVC can be known from the smoothness of the injected material. If the material is rough after the injection, it proves that the material is not uniform (insufficient plasticization), indicating that the temperature is too low; if the foam is emitted after the injection and a large amount of smoke is emitted, the temperature is too high.
5, injection speed
The rate of fire is slow, otherwise excessive shearing will degrade the material. When UPVC is used to produce extremely smooth thick-walled products, multi-stage injection mold filling speed should be used.
6, screw speed
The screw speed should be determined further in conjunction with the molding cycle. The screw surface speed should not exceed 0.15-0.2m/s
7, back pressure
Back pressure can reach 150bar, of course, the data is as low as possible, the common value is 5bar.
8, staying time
Under the temperature of 200 ° C, the cylinder residence time can not exceed 5 minutes. When the temperature is 210 ° C, the barrel residence time can not exceed 3 minutes.
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