Preform defects and solutions

Update:27-12-2019
Summary:

Preform is yellow Cause: The resin is thermally or oxid […]

Preform is yellow

Cause: The resin is thermally or oxidatively degraded, but the carbonization point is not reached

1. Reduce the drying temperature, the maximum drying temperature is 175 °C; 2. Confirm whether the specifications of the raw materials meet the requirements; 3. Confirm that the drying parameters range from 160 °C (6h) to 175 °C (4h); 4. Reduce the melting temperature to 280 ° C ± 10 °C; 5. Reduce the% control as much as possible, because the% control has no feedback; 6. Reduce the extrusion back pressure. Large extrusion back pressure can make the liquid mix uniformly, too small will produce bubbles, the range is 15-20 bar; 7. Confirm The screw buffer is not too much, at least 25mm; 8. Check whether the thermocouple and its mechanism are damaged.

Dark spots on the preform

Reason: Overheated degradation of raw materials to carbonization point

1. Reduce the melting temperature to 280 °C ± 10 °C; 2. Reduce the% control as much as possible, because the% control has no feedback; 3. Reduce the injection speed and control the range between 10 ~ 12g / s / cavity; 4. Reduce the extrusion back pressure, Extrusion back pressure ranges from 15 to 20 bar; 5. Reduce screw speed to reduce shear force, but within the period; 6. Confirm whether the specifications of the raw materials meet the requirements; 7. Check whether there is impurities in the head, Then remove it; 8. Confirm whether the thermocouple and its mechanism are damaged.

Air bubbles in the preform head

Cause: Gas trapped in the melt cannot be ruled out

1. Reduce the dew point or increase the drying temperature; 2. Make sure that the drying parameters range from 160 °C(6h) to 175 ° C (4h); 3. Make sure that the melting temperature is 280 °C ± 10 °C; 4. Make sure that the melt does not exceed the extrusion screw If it exceeds, you need to increase the extrusion temperature or increase the cycle time; 5. Increase the head cooling temperature (minimum 160 °C) 6. Make sure that the barrel is not blocked; 7. Increase the extrusion back pressure; 8. Increase the screw buffer and screw The buffer should be at least 25mm; 9. Reduce the return time and position, time = -1s, distance = -10mm; 10. If using recycled materials, the particles should not be too large; 11. Check if there is impurities in the machine head, and remove them ;

Slight depression inside the bottle

Reason: As the preform is still inside the mold, the cavity cools faster than the core, which causes the inside to shrink after the outside is solidified

1. Make sure that the cooling water temperature is between 7 °C ~ 10 °C; 2. Make sure that the cooling water is flowing properly; 3. Make sure that the valve stem opens normally; 4. Make sure that the pressure is enough to open the valve, and the pressure range is 8-10bar; 5. Reduce the cooling time, Cooling time 1s ~ 3s, determined by wall thickness; 6. Increase the holding time; 7. Increase the holding pressure; 8. Increase the melting temperature to 280 ℃ ± 10 ℃; 9. Reduce the return time and position, time = -1s Distance = -10mm; 10. Make sure that the mouth of the mold is clean and tidy, so that the exhaust can be smooth; 11. Make sure there is no condensation water, and the dew point should be lower than the cooling water temperature

0