Knowledge of back pressure for china plastic injection molding machine

china plastic injection molding company machine chooice

China Plastic Injection Molding Machine

The back pressure is one of the important parameters for the control of melt quality and product quality in china plastic injection molding process, the right back pressure plays an important role for improving product quality.    First, the back pressure of the formation    Plastination process in the plastic melt, melt constantly move the barrel front end (measuring indoor), and more and more, and gradually form a pressure to push the screw to the back. In order to prevent screw back too fast, to ensure uniform melt and compacted to provide a pressure in the opposite direction, you need to screw the opposite direction to prevent screw back pressure known as the back pressure.    Back pressure, also known as the plasticization pressure, its control by regulating the injection cylinder back to the oil throttle. The back of the injection cylinder pre-plasticizing screw injection molding machines are equipped with back pressure valve to adjust the injection cylinder when the back of the screw rotation speed of the drain, so that the fuel tank to maintain a certain pressure (shown below); traverse the whole motor screw ( resistance) is controlled by AC servo valve. Second, the appropriate adjustment to the back pressure benefits     1, can barrel melt compaction, increase density, improve the stability of the injection amount of the products weight and size.     2, the gas within the melt can be squeezed out, reduce product surface air spend, internal bubbles, improve gloss uniformity.     Slow down the screw astern speed, so that the melt inside the barrel fully plasticized by Toner, Color Masterbatch and melt mixed, to avoid products blending phenomenon.     Appropriate to enhance the back-pressure, can improve shrinkage and product around the product surface to go plastic.     5, can improve the melt temperature, melt plasticization to improve the quality and improve mobility in the melt filling the product surface cold glue pattern.

China Plastic injection molding parameter and pressure

Two, the back pressure is too low, prone to the following questions     A back pressure is too low, the screw back too fast, flowing into the barrel the front of the melt density (loose), the folder into the air.     Will lead to poor quality of plastics and injection volume instability, product weight, product size changes.     3, the product surface will appear to shrink, spent gas, cold feed grain, gloss unevenness and other undesirable phenomena.     4, the inside of the product is prone to bubbles, the product of peripheral and bone bit easy to walk, dissatisfied with glue.     Third, the high back pressure, prone to the following questions     A barrel the front of the melt pressure is too high, the high melt temperature, viscosity decreases, the melt in the screw slot counter current barrel and screw clearance leakage flow rate increases, will reduce the plasticizing efficiency (per unit time plasticizing The feeding amount).     Poor thermal stability of plastic (such as: PVC, POM, etc.) or coloring agents, due to increased melt temperature and heating time growth in the barrel caused by thermal decomposition, or the degree of increase of colorants color, the product surface color / gloss worse.     3, the back pressure is too high, slow screw back, pre-plastic material back for a long time, will increase the cycle time, resulting in decreased productivity.     4, high back pressure, high melt pressure injection nozzle prone to melt salivation phenomenon; next injection nozzle flow tract of cold material can clog the nozzle or products of cold material spot.     5, in the pre-plastic process, often due to back pressure is too large, nozzle leakage glue phenomenon, a waste of raw materials and lead to burn near the nozzle heaters.     6, pre-plastic bodies and mechanical wear of the screw tube increases.     Fourth, the back pressure tuning     Injection back pressure adjustment should be considered the performance of raw materials, dry conditions, product mix and quality status the, backpressure general adjustment in 3-15kg/cm3. When the product surface to spend a little gas, blending, shrink and product size, weight changes may be appropriate to increase the back pressure. Drooling, salivation, melt thermal decomposition of the product color and return the material is too slow when the nozzle may be considered appropriate to reduce the back pressure.

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