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Poly (butylene terephthalate) (PBT) POM injection molding process
Date：2010/1/9 10:30:51
Poly (butylene terephthalate) (PBT) POM injection molding process
Molding process
① PBT due process of absorption of stored moisture in the air, high moisture content so that forming a significant decline in physical and chemical properties. Therefore, to be dried before use, drying temperature 105 ○ C ~ 120 ○ C, drying time 4-8 hours. Note: After drying the plastic should be used within half an hour, or be re-dried to prevent further moisture can affect performance.
② Temperature at 220 ○ C ~ 270 ○ C between, PBT molding materials should not stay in the barrel should not exceed seven minutes, such as staying too long, you need to stay too long with the new material to the extrusion. Injection pressure of 300 ~ 700 kg/cm2, for easier molding PBT, so use medium pressure injection pressure, injection speed options speed, screw speed of 60 ~ 100RPM, mold temperature of 30 ○ C ~ 80 ○ C, back pressure is generally Choose 3 ~ 10 kg/cm2.
③ molding material generated in the handle, after the recyclable scrap pieces, PBT has excellent recyclability, material re-used more times back, back with a high and a small impact on the forming quality.
Polyoxymethylene (POM) injection molding process
POM is a crystalline thermoplastic with a high elastic modulus, high hardness and stiffness, good fatigue resistance, low friction coefficient, excellent creep resistance, higher heat distortion temperature. Can work long hours at -40 ~ 140 ○ C temperature. POM production in the humid environment with very good shape, dimensional stability in hot water for a long time with minimal impact on its mechanical properties. In addition to strong acid and oxidation chemicals, but for other inorganic chemicals and oils have superior durability, can be applied to the insert molding, injection molding and metal inserts on the cutting, welding, printing and other high-paying value added processing.
Molding process
① POM melt a very narrow range, showing a poor thermal stability. Barrel temperature of 180 ○ C ~ 210 ○ C, when more than 240 ○ C or heat allowed temperature for a long time, will cause decomposition, coking even black. At 200 ○ C, the decomposition of the barrel retention 60 minutes; and 210 ○ C, 30 minutes to break down. Therefore, if the molding is interrupted, should replace the plastic barrel, lower barrel temperature. If overheating occurs, should immediately reduce the cylinder temperature, overheating with the new plastic replacement materials. Never place hands or face near the nozzle end.
② POM is a high degree of crystallinity of plastic, with a rapid solidification characteristics. The products have a greater shrinkage rate, the value of 1.8% to 3.5%. Shrinkage of the size with product thickness, molding process, mold structure varies.
③ sensitive melting point of POM in the molding process, the filling in order to improve the mobility of POM, the method to increase the injection pressure than to raise the temperature of the method is effective. Injection pressure of 500 ~ 1400 kg/cm2.
④ molded thin, or because the number of flow and dimensional accuracy more strictly, the injection speed should be fast. Thick, hollow molded product due to the problem, issue or flow marks, the injection speed should be slow, back-pressure (gauge pressure) for 5-10 kg/cm2. Back pressure is too low because of the air drawn into the measurement of unstable, but the nozzle back pressure is too high will produce salivation, prolonged plastics problem.
⑤ POM also need drying, the pellets of approximately 0.1% or less water absorption, drying temperature of 80 ~ 90 ○ C, 3-4 hours.
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