The basic parameters of an injection molding machine are the basis for designing, manufacturing, purchasing and using the injection molding machine, including three aspects of injection, mold clamping and comprehensive performance.

Theoretical injection volume

The injection volume reflects the processing capacity of the injection molding machine to a certain extent, and it marks the maximum quality of the plastic products that can be produced. Generally, there are two representation methods of theoretical injection volume and injection quality.

1) Theoretical injection volume

The volume of melt shot by the screw or plunger during the maximum injection stroke of an injection molding machine in air is expressed in cm3. The calculation formula for the theoretical injection volume VL is:

In the formula: VL ― theoretical injection volume, cm3;

D — diameter of screw (or plunger), cm

S ― Maximum injection stroke of screw (or plunger), cm

During the injection process, on the one hand, the density of the melt will change with changes in temperature and pressure, and on the other hand, there will be a small amount of melt backflow under the effect of pressure. The contraction amount is supplemented, so the actual injection volume is smaller than the theoretical injection volume. Correction with injection coefficient. The injection coefficient is usually selected in the range of 0.7-0.9.

In the formula: VS ― actual injection volume, cm3; α ― injection coefficient.

2) Theoretical injection quality

The maximum mass of polystyrene (PS) melt that is ejected when the screw or plunger makes a maximum injection stroke when the injection molding machine is air-injected, is expressed in grams (g). When the material of plastic products is different from PS, the injection volume should be converted according to the following formula:

Where ρ―the density of the plastic, g / cm3;

M-injection quantity expressed in PS plastic, g.

According to actual production experience, the total quality of plastic products (the sum of the product quality and the quality of the gate system) is best controlled within 85% of the injection volume, which can be large for non-crystalline plastics and small for high viscosity plastics value.