pvc Also known as hard PVC, it is mainly a kind of amorphous thermoplastic resin made by polymerizing vinyl chloride monomer after being added by adding certain additives such as stabilizers, lubricants, fillers and the like product.
In addition to additives, but also with other resins used to blend modified related methods to make it more obvious and practical value of these resins are CPVC, PE, abs , EVA, MBS and so on.
UPVC has a high melt viscosity, poor fluidity, a small change in fluidity even when injection pressure and melt temperature are increased, and the molding temperature of the resin is very close to the thermal decomposition temperature so that the molding temperature range Narrow, it is a more difficult to shape the material.
1, plastic processing
24 hours at room temperature, the amount of water is less than 0.02%, it will form the case of no drying, such as must pass through the drying process, you can put 60-70 ℃ hot air oven for 3 hours, or 80 ℃ About 1-1.5 hours dryer.
Recycled material can be mixed up to 20% with the new material, the amount of recycled material to see the final use of the product to determine. Abuse of recycled materials may result in failure of injection molding, not only the recovery of the composition is too much, more because Because the material is reprocessed several times, the quality of the reclaimed material will show a gradual decline once more.
2, injection molding machine selection
UPVC because the melt viscosity is relatively large, so the decomposition is easier, the decomposition products have a greater corrosion of iron, the injection molding must use a dedicated plastic parts and temperature control system.
Ramada products covered in each of the clamping force models, have a special UPVC plastics injection system, and with the UPVC pipe products core pumping requirements with a dedicated security door device. Under normal circumstances as long as the injection volume to meet the weight requirements , Choose this series of UPVC dedicated injection molding device can be molded into high-quality products.
3, mold and gate design
Mold temperature can be set to 40 ° C. And the entire length of the runway must be short, the diameter is larger, used to gradually reduce the pressure loss and packing can be passed to the mold cavity as short as possible, the die must be cut Round, the minimum diameter of the nozzle mouth is 6mm, into a conical, internal angle of 5.
The mainstream of the die section should also be circular, and the combination of cold well wells, the radius of the section through the main runner and the gate, the diameter of 7mm.
The gate should be connected with the radius of the circular cutout. The shorter the better, the smooth the die cut surface.
The cold well prevents semi-solidified material from entering the mold cavity and its importance is often neglected.
The position of the gate should be correct, so that the material flows smoothly on the runner. It will not stay in the sharp corners, fragments and metal traces, so as to avoid the situation of compression or decompression. The runner should be kept smooth and smooth.
Molds should be 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 molds may be chrome-plated to provide protection.
After the production is finished, use a mild alkali to carefully clean the mold surface and spray with an oily spray or a siliceous spray.
4, melt temperature
Can be measured by the air method, ranging from 185-205 ° C. From the smoothness of the material can be obtained that UPVC accurate melt temperature.If the material is rough after injection, to prove that the material is not uniform (lack of plasticization), said Set the temperature is too low; such as foaming and emit a large amount of smoke after injection, it means that the temperature is too high.
5, injection speed
Slow rate of fire, or excessive shear will make the material degradation, the use of UPVC to produce extremely smooth thick-walled products, should be used multi-level injection mold filling speed.
6, screw speed
Should further cooperate with the molding cycle to determine the screw speed. Screw surface speed should not exceed 0.15-0.2m / s
7, back pressure
Back pressure can reach 150bar, of course, the lower the data the better, the common value is 5bar.
8, residence time
Barrels should not stay longer than 5 minutes at 200 ° C, and should not exceed 3 minutes at 210 ° C.
The above is UPVC plastic raw materials injection molding process analysis summary, to remind everyone that the need for injection speed and back pressure do not pay attention.