High Precision Plastic Injection Molding

high precision injection molding plastic industrial and housing machining components and parts

Gate halo may occur in high precision injection molding
Gate halo, also known as sun spots, refers to the circle-shaped discoloration near the gate.
cause:
1. The mold temperature is too low;
2. The gate is too small or the cavity at the glue inlet is too thin. When the cross-sectional area of the gate is small or the wall thickness of the product is too thin, the shear rate of the melt is high, and the shear stress increases, so that the melt molecules break and the phenomenon of gate halo occurs.
solution:
1. Increase the melt temperature and mold temperature, especially near the gate;
2. Adjust the position and size of the gate, increase the size of the gate, and arrange the gate at the thick wall of the product.
3.9. Scorch marks
Scorch marks are also called scorched, burns, manifested in the form of black spots and black stripes, which are dark, black dots or stripes on the surface of the product.
Reasons for formation:
Material:
1. The particles are uneven and contain powder;
2. High volatile matter content in raw materials;
3. Excessive amount of volatile lubricants and release agents;
4. Excessive impurities, excessive or polluted recycled materials;
5. Mix black pigment into the raw material.
Mold:
1. The surface of the mold is polluted (oil, grease and other foreign matter);
2. The gate is too small or the gate position is improper;
3. Poor exhaust, dead angle in the runner system;
4. The local resistance of the cavity is large, which makes the material flow confluence slower and makes exhaust difficult.
Injection molding machine:
1. The barrel is not cleaned;
2. Due to the loss of control of the heating control system, the overheating of the barrel caused
components decompose and turn black;
3. Due to the defects of the screw or barrel, the molten material is stuck and stored, and it is decomposed after long-term fixed heating;
4. Some plastics such as ABS are cross-linked and coked by high heat in the barrel. It is difficult to melt when the original particle shape is almost maintained, and it is crushed by the screw and entrained into the product;
5. The nozzles in the feeder, the thread of the screw, the check valve and other parts cause the stagnation of the resin, and it is brought into the product after decomposition and discoloration.
Process:
1. The temperature of barrel and nozzle is too high;
2. Injection pressure or pre-molding back pressure is too high;
3. The injection speed is too fast or the injection cycle is too long;
4. The screw speed is too fast, resulting in overheating;
5. The residence time of the molten resin in the barrel is too long, resulting in overheating and decomposition of raw materials.
solution:
1. Ensure the cleanliness of injection molding workshop, injection machine and mold;
2. After injecting heat-sensitive plastic, clean the barrel;
3. Reduce the temperature of the melt and shorten the residence time of the material in the barrel to prevent the material from decomposing and turning black due to overheating in the barrel;
4. Improve the exhaust of the injection machine and the mold, ensure that the screw has an appropriate speed during the metering process, and suppress the gap between the plasticized materials and the inflow of gas to the greatest extent with suitable back pressure, so as to ensure that the materials during the injection molding process The gas generated when filling into the mold is smoothly discharged to the outside of the mold;
5. Reduce injection pressure and screw pre-molding back pressure;
6. Reduce the injection speed and shorten the injection cycle;
7. Adjust to the appropriate screw speed.

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