UPVC, also known as hard PVC, is an amorphous thermoplastic resin made by the polymerization of vinyl chloride monomer plus certain additives (such as stabilizers, lubricants, fillers, etc.).
In addition to the use of additives, the use of blends with other resins has been modified to give them significant practical value. 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 does not change much. In addition, the molding temperature of the resin is close to the thermal decomposition temperature, and the temperature range in which molding can be performed is very narrow. A material that is difficult to form.
1, plastic processing
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 placed in a hot gas oven at 60-70 °C for 3 hours, or a dryer at 80 °C for 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 products. Abuse of recycled materials can cause injection molding failure, not only the excess components are recycled, but also because of the excess material. Reprocessing. The more the quality of the recycled material is recovered, the more it is recycled.
2, injection molding machine selection
UPVC has a high melt viscosity, easy to decompose, and the decomposition products have a corrosive effect on iron. The plastic injection parts and temperature control system must be used for injection molding.
Each type of clamping force model covered by Ramada has a special UPVC plastic injection system, and special safety door device is required for the core pulling of UPVC pipe fittings. 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. The length of the flow channel should be short, the diameter should be large to reduce the pressure loss and the pressure can be transferred to the cavity. The shorter the gate, the better, the die-cut surface should be round, the nozzle mouth The diameter is at least 6mm, it is conical, and the internal 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, the diameter can be 7mm.
The gate should be applied with a radius of tangent to connect the plastic parts. The shorter the better, the smooth cutting surface should be smooth.
Cold material wells prevent semi-solidified material from entering the mold cavity. Its importance is often overlooked.
The position of the gate should be correct, so that the material can flow smoothly on the flow path, and it will not stay in the corners, fragments and metal traces, so as to avoid compression or decompression, the flow path should be kept smooth and smooth.
The mold is cast in stainless steel. The content of chromium is at least 13%, preferably 16%. The Rockwell hardness is at least 55. The hard steel mold can be chrome-plated to form a protective effect.
After production, use mild alkali to carefully clean the mold surface and spray with oil spray or siliceous spray.
4, melt temperature
It can be measured by the air-launch method, ranging from 185-205 ° C. The exact melting temperature of UPVC can be known from the smoothness of the injected material. If the material is rough after injection, it proves that the material is not uniform (insufficient plasticization), indicating The set temperature is too low; if it foams after injection and emits a lot of smoke, it means 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
It should be matched with the molding cycle. The screw surface speed should not exceed 0.15-0.2m/s.
7, back pressure
Up to 150bar, the lower the better, the common 5bar.
8, detention time
At 200 ° C, the barrel retention time can not exceed 5 minutes. When the temperature is 210 ° C, the barrel retention time can not exceed 3 minutes.