The Polycarbonate injection molding process

1. Material processing

   Polycarbonate injection molding has high water absorption. So before injection molding, it must be preheated and dried. The pure polycarbonate is dried at 120 °C, and the modified PC should generally be dried for more than 4 hours at a temperature of 110 °C. The drying time should not exceed 10 hours. Generally, you can use the method of air extrusion to determine whether it’s dry enough. The utilization of recycled materials can reach 20%. In some cases, the utilization of recycled materials can be 100%; the actual quantity is subject to the quality requirements of the products. Recycled materials can’t mix different masterbatch simultaneously, or it will seriously damage the nature of the finished product.

   

   PC-spuitgieten

2. Selectie van een spuitgietmachine

   Now, for cost and other reasons, PC often uses modified materials, especially electrical products, which should increase fireproof performance. When the flame-retardant PC and other plastic alloy products are molded, it should make sure the plasticizing system of the injection molding machine mixes well and is corrosion-resistant. It is unachievable for the conventional plasticizing screw. So when choosing, you should state in advance that, usually, there are special PC screws for customers to choose from.

3. Design of mold and gate for polycarbonate injection molding

   The common mold temperature is 80–100 °C, and the temperature of mold adding glass fiber is 100–130 °C. Small products can use the pinpoint gate; the gate depth should be 70% of the thickest part; and other gates are circular and rectangular. If the gate is bigger, it’s better, which can reduce the defects caused by excessive shear. The depth of the vent should be less than 0.03-0.06 mm; the runner should be short and round. The ejection gradient is generally about 30′-1.

4. Melt temperature for Polycarbonate material

   You can use the gas injection method to determine the processing temperature. Generally, the polycarbonate injection molding processing temperature is 270–320 °C. The temperature of the PC with some modification or low molecular weight is 230–270 °C.

5. Injectiesnelheid

   When molding, relatively fast injection speeds are usually adopted, such as for electrical switch parts. Commonly, it is from slow to rapid injection molding.

6. Verpakking

   Packing is 10 bars around; it can be appropriately reduced without the gas lines and color mixing.

7. Verblijftijd

   If the materials stay at high temperatures for a long time, they will degrade, emit CO2, and turn yellow. You should use PS to clean the cylinder, not LDPE, POM, ABS, or PA.

8. Special notes

   Some modified PC injection molding material, as being recycled many times (the molecular weight decreased) or an uneven mix of ingredients, would easily produce the dark brown liquid bubble.

Produce high-quality polycarbonate injection molding parts that need a special injection barrel because polycarbonate has a high density. Nominal injection barrels make it hard to mold polycarbonate materials. If you are looking for high-quality polycarbonate injection molding parts, you need to look for a professional polycarbonate molding company to support you. You could contact us to make your PC molding parts.

The key point to select injection molding machine for PC Plastic Injection molding parts

Clamping force:

The finished projected area per square centimeter is multiplied by 0.47 to 0.78 tons (or per square inch by 3 to 5 tons).
The size of the machine: A finished weight is approximately 40–60% of the capacity of the injection molding machine. If the machine puts polystyrene as the capacity (oz), which needs to be decreased by 10%, At the beginning, which is used as GUANG DA’s capacity, 1 ounce is 28.3 grams.

Screw: Screw length should be at least 15 diameters long; L/DD of 20:1 is the best. The compression ratio is preferably between 1.5:1 and 30:1. The stop valve in front of the screw should be set into a sliding ring. The flowing gap of resin should be at least 3.2 mm.

Nozzle: The tip opening should be at least 4.5 mm (diameter); if the weight of the finished product is over 5.5 kg, the diameter of the nozzle should be 9.5 mm or above. Besides, the tip opening should be less than 0.5–1 mm smaller than the gate diameter, and the segment road is shorter, which is better; it’s about 5 mm.

The key point on molding conditions for PC injection molding:

Melt temperature and mold temperature:

The best molding temperature setting is related to many factors, such as size presses, screw configuration, the mold and the molded article in the design, the molding cycle time, etc. In general, to make plastic gradually melt, you should set a lower temperature in the rear section of the feed tube or feeding area. And set a higher temperature in front of the feed tube. However, if the screw is designed defectively or the L/DD value is too small, you can also set the reverse temperature.

For the mold temperature, the high mold temperature may provide a better surface appearance, and the residual stress will be smaller. For the thinner or longer-finished PC plastic injection molding products, it’s easy to fill. However, low mold temperatures can shorten the molding cycle.

The speed of rotation of the screw is suggested at 40 to 70 rpm, but it’s subject to the design of the machine and screw.

Injection pressure: to fill the mold as soon as possible, the injection pressure should be bigger, which is better. Generally, it’s about 850 to 1,400 KG/CM2, up to 2,400 KG/CM2.

Packing: Generally, the lower, the better. For the sake of uniformity in feeding, it is suggested to use 3 to 14 KG/CM2.

The speed of injection molding: firing rate has a great relation with gate design; when using a direct gate or edge gate, in order to avoid the day sunshine phenomenon and the phenomenon of wave and current marks, you should use the slow firing rate. What’s more, if the thickness of finished products is above 5 mm, you can use slow injection to avoid air bubbles or recesses.

In general, the principle of firing rate is faster for the thin and slower for the thick. From injection to holding pressure, holding pressure is as low as possible to avoid molding products appearing to have residual stress. However, you can use the annealing method to remove or alleviate the residual stress. The condition is 120 to 130 degrees Celsius for approximately half to one hour.

PC plastic injection molding