What Should Be Paied More Attention To Injection Processing Of Rigid PVC ?
Polyvinyl chloride, also called hard PVC, is a polymerized amorphous thermoplastic resin made from vinyl chloride monomer, with certain additives (such as stabilizers, lubricants, fillers, etc.).
In addition to the use of this additive, but also the use of blending with other resin modified method, it has obvious practical value. These resins are chlorinated polyvinyl chloride, polyethylene, ABS, EVA, MBS and so on.
UPVC melt has high viscosity and poor flowability. Even if there is a higher injection pressure and melt temperature, the fluidity will not change much. In addition, the resin molding temperature and thermal decomposition temperature are very close and can form a narrow range of difficult temperatures for forming materials.
1, Plastic processing
After 24 hours at room temperature, less than 0.02% of the water,and therefore no drying. If you must dry, put in a hot air oven of 60-70 DEG C for 3 hours or 80 hours and dry for 1-1.5 hours.When 20% of the recycled material is blended with the new material, the amount of recycled material depends on the final product being used. Injection of abused recycled material may fail, not only by recovering too much of the ingredients, but also by more reprocessing of the material. Recycled materials are recycled for a better drop of water each time.
2, The choice of injection molding machine
UPVC because the melt viscosity is easy to break down and the decomposition products of iron are corrosive. It must be used for plastic injection molding and temperature control system.
3, Mold and gate design
Mold temperature can be set to 40 degrees centigrade. The length of the flow path is short, and there will be a large diameter to reduce the pressure loss and the packing can be transmitted to the cavity. The gate is as short as possible, the cutting surface is circular, the nozzle orifice of 6 mm, minimum diameter, conical, into the 5 degree angle. In the face of the mold gate, a round of negotiations shall be made with a well made cold material, connecting the main channel and the radius gate portion to the diameter of 7mm.
Cut the round face and connect the radius of the plastic parts as much as possible. The application of the door with shorter cutting surface is also very good.
Cold material is a good way to prevent semi - curing material from entering the mold cavity, and its importance is often neglected. The door to the right position, so that in the smooth flow of the flow channel material, not leaving traces of sharp corners, and pieces of metal, in order to avoid compression or decompression, remain in the flow path is smooth.
Chromium plating surface, forming a protective effect of casting stainless steel mold, the chromium content of at least 13%, preferably 16%, at least 55 Rockwell hardness of steel in the mold, application.
After production, be careful to apply mild alkaline cleaning to the mold surface, and then spray oil, spray, or silicone spray quality.
4, melt temperature
Available measurements of airborne emission, ranging from 185-205. The smoothness of the material from the exact melting temperature of the UPVC can be fired. For example, the coarse material after injection, such as by which the material is heterogeneous (less plasticizer), indicates a predetermined temperature too low; such as blowing from the rising and emitting a large amount of smoke, which means that the temperature is too high.
5, injection speed
Slow, otherwise it will cut the material degradation by UPVC, has the extremely smooth, thick wall products, should adopt multi-stage injection filling speed.
6 screw speed
Should be used in conjunction with the molding cycle. The surface speed of the screw shall not exceed 0.15-0.2m / sec
7, back pressure
Up to 150 bars, the lower the better, common for 5 bar.
8, residence time
The temperature of the cylinder residence time is not more than five minutes at about 200. When the temperature is 210 degrees, the barrel residence time shall not exceed three minutes.