China plastic injection molding machine back pressure knowledge

China Plastic Injection Molding Machine backpressure

The backpressure is one of the critical parameters, it is controlled melt quality and product quality in the plastic injection molding process. The right backpressure plays an important role in improving product quality.

First, the backpressure of the formation

Plastination process in the plastic melt, melt constantly move the barrel front end (measuring indoor), and more and more. And gradually from 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 backpressure.

China plastic injection molding machine backpressure, 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 a backpressure valve. It was adjusting the injection cylinder when the back of the drain screw rotation speed. So that the fuel tank to maintain a certain pressure. To traverse the whole motor screw ( resistance) is controlled by an AC servo valve.

Second, the appropriate adjustment to the backpressure benefits

1, It can barrel melt compaction, increase density, improve the stability of the injection amount the weight and size of products.

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 product blending phenomenon.

3, Appropriate to enhance the back-pressure, it can improve shrinkage and product around the product surface to go plastic.     China plastic injection molding machine can improve the melt temperature, melt plasticization to improve the quality and improve mobility in the melt filling the product surface cold glue pattern.

Parameter and Pressure

the pressure is too low, prone to the following questions

1.Backpressure is too low, the screw back too fast。 Flowing into the barrel the front of the melt density (loose), the folder into the air.     This will lead to poor quality of plastics and injection volume instability, product weight, product size changes.

2. The product surface will appear to shrink, spent gas, cold feed grain, gloss unevenness, and other undesirable phenomena.

3. the inside of the product is prone to bubbles, the product of peripheral and bone bit easy to walk, dissatisfied with glue.     The high back pressure, prone to the following questions.

In a barrel the front of the melt pressure is too high, the high melt temperature, viscosity decreases. The melts in the screw slot counter-current barrel and screw clearance leakage flow rate increases, which 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.

 the backpressure is too high, slow screw back, pre-plastic material back for a long time.

It will increase the cycle time, resulting in decreased productivity.

1, High back pressure, high melt pressure injection nozzle prone to melt salivation phenomenon; the next injection nozzle flow tract of cold material can clog the nozzle or products of a cold material spot.

2, In the pre-plastic process, often due to backpressure is too large, nozzle leakage glue phenomenon. A waste of raw materials and lead to burn near the nozzle heaters.

3, pre-plastic bodies and mechanical wear of the screw tube increases.

Tuning

China plastic injection moulding machine 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. The product size, weight changes may be appropriate to increase the backpressure. Drooling, salivation, melt thermal decomposition of the product color. Return the material is too slow when the nozzle may be considered appropriate to reduce the backpressure.

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