(1) Mold locking pressure:
Multiply 0.47 to 0.78 tons (or 3 to 5 tons per square inch) per square centimeter (cm2) of the projected area of the finished product.
(2) Machine size:
The weight of the finished product is about 40 to 60% of the capacity of theinjection molding machine. If the capacity of the machine is represented by polystyrene, it needs to reduce by 10% to use the capacity of beer plastic (polycarbonate). (1 Jans = 28.3 g).
(3) Screw:
The length of screw should be at least 15 diameters long, and its L / D ratio is 20:1. The compression ratio should be 1.5:1 to 30:1.
The stop valve at the front end of the screw shall be of the sliding ring type, with a minimum flow clearance of 3.2mm.
(4) Nozzle:
The diameter of nozzle hole shall be at least 4.5mm. If the weight of finished product is more than 5.5kg, the diameter of nozzle hole shall be more than 9.5mm.
In addition, the diameter of the nozzle hole should be 0.5-1.0mm smaller than the gate, and the shorter the working water inlet section, the better, the ideal is about 5.0mm.
Key points of injection molding conditions:
(a) Melting temperature and mold temperature:
The best molding temperature is related to many factors, such as the size of injection molding machine, screw composition, mold and molding product design and molding cycle time.
Generally speaking, in order to make the plastic melt gradually, a lower temperature is set in the rear section of the feed pipe and the feed area, while a higher temperature is set in the front section of the feed pipe.
However, if the screw design is improper or the L / D value is too small, the reverse temperature setting can also be done.
In terms of mold temperature, high temperature mold can provide better surface appearance, lower residual pressure and easier filling for thinner or longer shaped products. Low mold temperature can shorten the molding cycle.
(b) Screw rotation speed:
40 to 70 rpm is recommended, subject to machine and screw design adjustments.
(c) Back pressure:
Generally, the lower the setting is, the better it is, but in order to achieve uniform feeding, it is recommended to use 3-14kg / cm2
(d) Injection speed:
There is a great relationship between the injection rate and the gate design. When using direct gate or edge gate, in order to prevent the phenomenon of sunlight and wave mark, the slower injection rate is used.
In addition, if the thickness of the finished product is more than 5.0mm, in order to avoid bubbles or depressions, slow injection will be helpful.
Generally speaking, the principle of shooting speed is that the thinner is faster, the thicker is slower.
(e) Injection pressure:
In order to fill the mold quickly, the higher the injection pressure is, the better it is. Generally, it is about 850-1400kg / cm2, and 2400KG / cm2.
(f) Pressure maintaining:
When switching from injection molding to pressure maintaining, the pressure maintaining shall be as low as possible to avoid residual pressure of molding products.
The residual pressure can be removed or reduced by annealing, provided that the molding product is humidified at 120 to 130 ℃, about 30 minutes to an hour.
