Silver streaks are mainly caused by moisture or volatile components due to the incomplete drying of the raw materials. When silver filaments are produced, firstly use thoroughly dried pellet diets to perform a pla injection molding test. If this cannot eliminate the silver streak, check for other reasons.
1. In terms of injection molding machine:
(1) The barrel and screw are worn out, or there are dead angles in the material flow of the rubber head and rubber ring, which will be decomposed by long-term heating.
(2) The heating system is out of control, thus causing the temperature to be too high and leading to decomposing. Check whether there are any problems with the heating elements such as thermocouples and heating coils. If the design of the screw is improper, it will cause improper exhaust or the air will be easy to be brought in.
2. In terms of injection moulding dies:
(1) Poor venting;
(2) The frictional resistance of the runner, pouring gate, and cavity in the mold is high, causing local overheating and leading to decomposition;
(3) Unbalanced distribution of the pouring gate and cavity and unreasonable cooling system will all cause unbalanced heating, thus leading to local overheating or obstruction of air passages;
(4) Water that leaks from the cooling path enters the cavity;
(5) There is some unplasticized cold plastic on the electronic plastic parts, which will increase the size of the cold slug well. Expand the end of the runner to form an additional plastic cold slug well. Use electric heating nozzles and nozzle sleeves;
(6) The runner and pouring gate are too small or their length is too long, which will cause the plastic to condense during its transportation. If necessary, increase the runner diameter and the depth of the pouring gate.
3. In terms of the craft:
(1) If the setting of the temperature, pressure, speed, back pressure, the motor speed of melting glue is too high, it will cause decomposition. Or if the pressure and speed are too low, injection time and pressure holding are insufficient, and the backpressure is too low, silver streaks will appear because the gas cannot be melted and the density is insufficient due to failure to obtain high pressure. To solve it, appropriate temperature, pressure, speed and time should be set and multi shot plastic injection molding speed should be adopted.
(2) Low backpressure and fast speed will make it easy for air to enter the barrel and then enter the injection moulding die with the molten material. If the cycle is too long, the molten material will be heated in the barrel for too long and then decompose. The plastic stays in the injection cylinder for too long. Reduce the total cycle time. The injection volume is too small for injection molding requirements.
(3) Insufficient amount of material, too large buffer pad, too low temperature of the material or the mold will affect the flow of the material and molding pressure, thus promoting the formation of bubbles.
(4) If the surface temperature of the collosol is too high, it will reduce the temperature of the injection cylinder. If the temperature of the collosol is too low, causing the mold filling time unstable, increase the temperature of the injection cylinder; Increase the nozzle temperature; Increase the filling speed of the mold.
(5) Since too much mold release agent on the surface of the injection moulding die, you can use ethanol to clean the mold surface thoroughly.
4. In terms of plastics:
(1) If the plastic has high humidity, the proportion of added reworked materials is too large or harmful scraps are included, the plastic should be fully dried and the scraps should be removed.
(2) Absorb moisture from the atmosphere or from the colourant. Then the colourant should also be dried. It is best to install a dryer on the machine.
(3) The amount of lubricants, stabilizers added to the plastic is too much or the mixing of them is uneven, or the plastic itself contains volatile solvents.
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