The Impact

Source:   Release time:2018-09-25 10:13:36  Visit:
The impact of vertical injection molding machine plastic extrusion process factors are temperature, melt pressure and melt conveying speed.

(1) temperature. Temperature has a significant effect on the performance of vertical injection molding machine plastic extrusion and parison. Lifting the extruder heating temperature results in the following: the ability to lower the melt viscosity, improved melt flow, reduce the power consumption of the extruder; may be appropriate to enhance the screw speed, without affecting the effect of mixing plastics materials; help to improve the intensity with the brightness of the final product; help to improve the transparency of the final product. However, the melt temperature is too high, the extruded parison prone to sagging weight, causing uneven thickness longitudinal parison; Parison inflation will extend the cooling time; will expand the shrinkage of the final product; make pvc and other heat-sensitive plastic degradation parison strength Pc and other engineering plastics is significantly reduced. Therefore, we should follow this principle to set the heating temperature of the extruder, extrusion that is both smooth and uniform parison, and not leave under the premise of the transmission system overload, in order to ensure a higher melt parison strength, should be possible to adopt a lower heating temperature.

When setting the extruder heating temperature, the temperature of the feed zone should be relatively low, to prevent blockages in the transportation of materials affect the charging port; the higher temperature compression section, help mixing plastics materials; extrusion temperature ranges may be less than the compression section, and higher than the feed zone, is conducive to stability and uniform feed to the head.

Heating means of the extruder, generally adopt an electric heater, while placement of air-cooled machine, for adjusting the heating temperature of the extruder. To control the heating temperature deviation extruder, often adopt proportional (P) Integral (I) derivative (D) temperature controller. Their role is to:

① proportional action. Heating current with temperature deviation proportional relationship exists, the smaller the heating current, temperature deviation is also smaller.

② integral action. Heating current is proportional to the time integral of the temperature deviation. Thus, even if the deviation is very small, after a certain time, can also eliminate the static error, improve temperature control system static accuracy.

③ derivative action. Heating current is proportional to the temperature difference of the time differential. Then, the temperature deviation occurs sooner, and the corresponding amount of change in the heating current is also larger, can enhance the ability of the heating system to the outside world suddenly interference.

Because of these effects, PID temperature controller can control the temperature of the extruder deviation within ± 1 ℃, the power consumption is also reduced by about half.

(2) melt pressure. Vertical injection molding machine into the nose should melt pressure evenly. Appropriate to enhance the melt extruder, pressure, mixing materials can even make the parison and stable performance of the final product. For high molecular weight polyethylene, high density polyethylene with a blend of low density polyethylene, with colored polymer masterbatch, a sufficient melt pressure allows the parison has a good appearance, reduce the "crystallization point" with clouds like pattern. However, due to debris blocking stencil nose, causing the melt pressure is too high, it will increase the load and damage the extruder machine, should be replaced, cleaning stencils, so to maintain a stable pressure melt into the nose. Adoption of a resin of low melt flow rate, decrease the extruder heating temperature, to enhance the speed of the extruder screw, etc., can enhance the melt pressure of the extruder.

To control the pressure of the melt extrusion, melt pressure measuring devices can be installed in the feed section of the extruder. Melt pressure measuring instrument used a mechanical pressure gauges, hydraulic (oil, grease, mercury) gauges, pneumatic and electrical gauges, pressure gauges, and so on.

(3) a melt conveying speed. Melt conveying speed is large, the extruder extrusion volume. Enhance the melt conveying speed, the weight can improve sagging parison, increasing the wall thickness of the parison. With a screw diameter of the melt conveying speed increases, less affected by the head pressure. Lifting the extruder screw speed with the heating temperature, the melt can be improved accordingly conveying speed. However, when the screw speed upgrade to a certain value, easy to produce melt fracture phenomenon. In the vertical injection molding machine plastic extrusion experience, these three factors are interdependent. Meanwhile, these three factors require low volatility. If the temperature, pressure, melt conveying speed greater volatility, not only the parison wall thickness uniformity, repeatability subsequently deteriorated, but also the mechanical properties of the final product, and dimensional stability with greater performance difference fell.
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