What factors affect the quality of plasticizing the injection molding machine

Update:14 Mar 2019
Summary:

The aspect ratio, tightening ratio, back pressure, scre […]

The aspect ratio, tightening ratio, back pressure, screw speed, and barrel heating temperature of the injection molding machine screw are the main factors affecting the quality of plasticization.

1. Length to diameter ratio: the ratio of the useful working length to the screw diameter of the injection molding machine screw.

a, the ratio of long diameter to diameter is easy to eat;
b. Plastics with better thermal stability can be used for longer mixing and non-burning of the screw of the injection molding machine. Plastics with poor thermal stability can be used without a thread of a shorter injection molding machine screw or screw end. Considering the characteristics of plastics, the general flow length is as follows: thermoset is 14\'16, hard PVC, high viscosity PU and other heat sensitivity is 17\'18, general plastic is 18\'22, PC, POM and other high temperature stability plastics are 22\'24.

2. Tightening ratio: the ratio of the final groove depth of the feed section to the first groove depth of the metering section.
a. Considering the effects of shrinkage, filling degree, reflow, etc., the product should be dense, heat transfer and exhaust;
b. Appropriate tightening ratio can increase the density of plastics, make the combination of molecules and molecules more tight, help reduce the air, reduce the temperature rise caused by pressure, and affect the difference of output, improper tightening Than will damage the physical properties of the plastic;
c. The higher the tightening ratio, the higher the temperature rise during the plasticizing process of the plastic in the material tube, and the better the uniformity of the plastic in the plasticizing process, and the relative discharge amount is greatly reduced.
d, high tightening ratio is suitable for non-melting plastics, especially low melt viscosity, heat stable plastic; low shrinkage ratio is suitable for fusible plastics, especially high melt viscosity, heat sensitive plastics.

3, back pressure
a. Adding back pressure can add the work done by the injection molding machine screw to the molten resin, eliminate the unmelted plastic particles, and increase the density and uniformity of the material in the material tube;
b. Back pressure is used to advance the temperature of the barrel, which is the most obvious;
c. The back pressure is too large, and the plastic with high heat sensitivity is easy to be decomposed. For low-viscosity plastics, the phenomenon of runny may occur, and the back pressure is too small, and the products injected may have air bubbles.
4, screw speed
a, the rolling speed of the injection molding machine screw directly affects the shear of the plastic in the spiral groove;
b. The screw groove of the small injection molding machine absorbs the heat source quickly. It is satisfactory to promote the softening of the plastic during the tightening period. The resistance between the screw and the wall of the barrel is low. It is suitable for high-speed rotation and plasticization.
c. The screw of the large injection molding machine should not be rotated quickly to prevent uneven plasticization and constitute excessive resistance to heat;
d. For plastics with high heat sensitivity, if the screw speed is too large, the plastic will be easily decomposed;
e. Generally, the screw of the standard injection molding machine has a certain speed scale, the general speed is 100\'150rpm; if it is too low, the plastic cannot be melted, and if it is too high, the plastic is burnt.

5, electric temperature setting
a. Melting the chilled plastic staying in the barrel and the screw of the injection molding machine to facilitate the screw rolling, and supplying the plastic to obtain a part of the heat required for melting;
b. Set the temperature lower than the melting temperature by 5\'10 °C (partially due to the thermal energy supply);
c. The adjustment of the nozzle temperature can also be used to control problems such as flow, condensate (plug), and wire drawing;

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