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Knowledge of injection molding machines

2018/9/26 1:55:59 Viewers:
(1) clamping pressure:
The product projection area is 0.47 to 0.78 tons per square centimeter (cm2) (or 3 to 5 tons per square inch).

(2) machine size:

The weight of the finished product is about 40% to 60% of the capacity of the injection molding machine. For example, when the machine is expressed by polystyrene, the capacity of the injection molding machine should be reduced by 10%, and the beer plastic (polycarbonate) capacity should be used. (1 =28.3).

(3) screw:
Screw length should have at least 15 long diameters, and its L/D is 20:1 best. The compression ratio should be 1.5:1 to 30:1.
The check valve of the front end of the screw should adopt slip ring type, and its resin can flow at least 3.2mm.
(4) nozzle:

The diameter of the nozzle should be at least 4.5 mm. If the weight of the finished product is more than 5.5, the diameter of the nozzle should be more than 9.5.
In addition, the diameter of the nozzle should be 0.5 to 1.0_smaller than the gate, and the shorter the working inlet, the better, the ideal is about 5.0_.
Key points of injection molding conditions:

(a) melting temperature and mold temperature:
The optimum molding temperature is related to many factors, such as injection molding machine size, screw composition, mold and molding product design and molding cycle time.
Generally speaking, in order to melt the plastic gradually, set a lower temperature in the rear section of the tube and the feed area, and set a higher temperature in the front section of the tube.

However, if the screw is not designed properly or the L/D value is too small, the reverse temperature setting is also acceptable.

In terms of mold temperature, high temperature molds provide a better surface appearance, lower residual pressure, and are easier to fill with thinner or longer molds. Low mold temperature can shorten the molding cycle.

(b) screw rotation speed:

Recommendations 40 to 70RPM, but depending on the design of the machine and screw.

(c) back pressure:
The lower the general setting, the better, but for the sake of uniform feeding, it is recommended to use 3 to 14Kg/cm2.

(d) injection speed:

The injection rate is closely related to the gate design. When using direct or edge gate, the slow injection rate is used to prevent sunshine and wave mark.
In addition, if the thickness of the product is above 5, it will help to avoid bubble or sag.

Generally speaking, the principle of fire speed is thin and fast.

(E) injection pressure:

In order to fill the mold quickly, the higher the injection pressure, the better, generally about 850 to 1400 Kg / cm2, can be 2400 Kg / cm2.

(f) keep pressure:

When switching from injection to compression, keep the pressure as low as possible, so as to avoid the residual pressure of molded products.

The residual pressure can be removed or reduced by annealing, if the molding is treated at 120 to 130 degrees Celsius for about 30 minutes to an hour.