UPVC, also known as hard PVC, is an amorphous thermoplastic resin made by polymerizing vinyl chloride monomer with certain additives (such as stabilizers, lubricants, fillers, etc.).
In addition to the use of additives, it is also used in blending with other resins to make it have obvious practical value. These resins are CPVC, PE, ABS, EVA, MBS, and the like.
UPVC has a high melt viscosity and poor fluidity, and 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 very close to the thermal decomposition temperature, and the temperature range in which molding can be performed is narrow, which is a material that is difficult to mold.
After 24 hours at room temperature, the amount of 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 the new material, depending on the end use of the product. Abuse of recycled materials can cause injection molding failure, not only because of the excessive recovery of components, but also because the materials are reprocessed many times. The more the quality of the recycled material is recovered, the more the quality is reduced.
Selection of injection molding machine
UPVC has a high viscosity and easy decomposition, 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 DAYA MACHINERY 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.
The mold temperature can be set to 40 °C. The length of the flow path is short and the diameter is large to reduce pressure loss and pressure holding energy to the cavity. The shorter the gate, the better, the die-cut surface should be round, the diameter of the nozzle mouth is at least 6 mm, and the shape is 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 then spray an oily spray or a siliceous spray.
Heating temperature/ melt temperature
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 material being shot. 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.
injection speed should be 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.
Up to 150bar, the lower the better, the common 5bar.
At a 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.