Common quality defects of PET preforms and their solutions
1.AA (acetaldehyde) value is too high
(1) Raw material performance has quality problems. Check the quality of raw materials before entering the warehouse.
(2) Poor drying effect. Check the operation of the dryer (such as dew point, drying temperature/time).
(3) The heating temperature of the barrel is too high. Try to reduce the temperature while ensuring quality.
(4) The back pressure of the screw is too high. Set the back pressure to (400-600Psi) while ensuring quality.
(5) The cycle time is too long. Optimize the cycle time (avoid the raw material staying in the screw for too long).
2.The embryo turns yellow
(1) Drying time is too long/temperature is too high. Remove the over-dried raw materials and re-dry them.
(2) The barrel temperature is too high. Lower the temperature (generally, the temperature is increased by 2-5°C when the preform does not produce white fog) to normal temperature.
(3) The mold temperature is too high. Lower the temperature to a suitable temperature (275-280°C).
(4) The raw materials stay in the screw for too long. Empty the high-temperature raw materials in the barrel.
3.Wall thickness change rate is too large
(1) The screw temperature is too high. Adjust the screw temperature appropriately.
(2) The screw back pressure is too high. Adjust the screw back pressure to an appropriate pressure.
(3) The injection speed is too fast. Adjust the injection speed appropriately (usually 3.5 to 4 seconds during injection).
(4) The mold cooling water temperature is too high. Check the cooling circulating water temperature (9 to 11°C ± 2°C).
(5) The cooling time is too short. Increase the cooling time (usually set to 3 to 4 seconds).
4.Surface scratches (body/thread)
(1) The mold has sticky material. Clean the mold.
(2) The mold is damaged. Replace the damaged parts or repair it.
(3) The suction cup of the take-out plate is damaged. Replace the damaged suction cup or repair it.
(4) The ejection position/pressure of the die lip is too high. Adjust the ejection position/pressure to a suitable state.
(5) The position of the take-out plate is improper. Check the distance between the suction cup of the take-out plate and the die lip (generally set to: 22mm).
5.IV (viscosity) drops too much
(1) Raw materials are stored for too long. Raw materials should be used in a first-in-first-out manner.
(2) Poor drying effect. Check whether the dryer is normal, maintain the dryer, and check the use time of the drying beads (usually replace them every 2 to 3 years).
(3) The heating temperature of the barrel is too high. Try to reduce the temperature while ensuring quality.
(4) The back pressure of the screw is too high. Under the premise of quality, the back pressure is generally set to: 400-600 Psi.
(5) The heating temperature of the mold is too high. Reduce the heating temperature of the mold. It is generally set to: 280-285℃.
(6) The preforms are stored for too long or the temperature and humidity of the warehouse are too high. Check the humidity/temperature of the warehouse (usually: below 70%/28), and use the first-in-first-out inventory method.
(7) If there are quality problems with the performance of the raw materials themselves, notify the supplier to handle it.
6.Shrinkage and deformation
(1) Cooling time is too short. Increase cooling time (set to: 3~4S)
(2) Holding time is too short/pressure is insufficient. Increase holding time (set to: total of three levels 6~8S); increase holding pressure (level 1: 800Psi, level 2: 700Psi, level 3: 600Psi)
(3) Mold cooling water temperature is too high. Lower the water temperature (set to: 9~11℃ ±2℃)
(4) Mold circulating water pressure is too low. Increase water pressure (set to: 6~7Kg)
7.Unmelted material
(1) The screw heating temperature is too low. Increase the temperature appropriately.
(2) The screw slips and the raw material cannot be sheared (this phenomenon usually occurs in the production of color oil). Check whether the color oil is too high and replace the color oil.
(3)The screw back pressure is too low. Increase the screw back pressure.
(4)The drying temperature is too low. Check whether the screw feed temperature meets the requirements (normal requirement is 160℃).
8.Lack of material at the bottle mouth
(1) Injection volume is not enough, increase the injection volume (the remaining position after injection is generally 5-8mm)
(2) Injection pressure is too low, increase the injection pressure
(3) Injection speed is too slow, increase the injection speed (optimal injection time: 3.5-4s)
(4) Holding pressure position is too large, reduce the holding pressure position (injection pressure: 900-1200Psi)
(5) Holding pressure is too small, increase the holding pressure
(6) Mold cooling circulation water temperature is too low, increase the cooling water temperature (set to: 8-10℃)
9.Long nozzle, elongated nozzle
(1) The raw material drying effect is poor. Stop and re-dry.
(2) The hot runner valve needle cylinder is blocked. Maintain the hot runner.
(3) The hot runner/nozzle temperature is too high. Adjust the temperature appropriately.
(4) The holding time is too short. Increase the holding time.
(5) The holding pressure is too low. Increase the holding pressure.
(6) The cooling time is too short. Increase the cooling time.
10.Sprue drawing
(1) The hot runner nozzle cannot be closed or the nozzle mouth is worn. Maintain the hot runner cylinder or replace the nozzle with a new one.
(2) The hot runner nozzle temperature is too high. Reduce the nozzle heating temperature.
(3) The gate valve delay closing time is too long. Reduce the gate valve delay closing time.
(4) The valve needle control air valve fails. Maintain the valve needle control valve.
11.Traces of moisture
(1) The mold cooling water temperature is too low. Increase the mold circulating water temperature.
(2) The workshop environment temperature is too high or the humidity is too high, causing water droplets to form on the mold. Lower the air conditioning temperature.
(3) Check the mold for water leakage. Causes and solutions for mold leakage
12.Bottom crystallization
(1) The temperature of the hot runner and nozzle is too low. Increase the temperature of the nozzle and hot runner.
(2) The holding pressure is too high. Reduce the holding pressure to level 3.
(3) The cooling water of the mold is too low or too high. Check whether the cooling water temperature is reasonable and adjust it.
(4) The cooling water channel of the mold is blocked. Maintain the water circulation channel of the mold.
13.White mist on the bottle
(1) If the raw material is not dry enough, stop the machine and dry the raw material again.
(2) If the screw heating temperature is too low, increase the screw heating temperature.
(3) If the screw slips (usually occurs when producing color oil embryos), increase the barrel temperature.
(4) If the back pressure is too low, increase the back pressure.
14.Black spots/contamination on preforms
(1) The raw materials are contaminated or have impurities. Remove the impurities (the material collector should always pay attention to whether the raw materials are contaminated).
(2) The raw materials are contaminated during drying. Remove the raw materials with quality problems.
(3) The barrel temperature/hot runner/nozzle temperature is too high. Lower the temperature to an appropriate temperature.
(4) The production environment or equipment is too clean and hygienic. Keep the workshop and equipment clean and hygienic.
(5) The preforms are contaminated during storage in the warehouse. Keep the warehouse environment clean and the packaging intact.
15.Flying edge
(1) If the die lip, core seat or cavity is damaged, replace or repair the damaged parts.
(2) If the injection pressure is too high, reduce the injection pressure.
(3) If the holding pressure is too high, reduce the holding pressure or the holding position.
(4) If the heating temperature is too high, reduce the heating temperature.
(5) If the clamping pressure is too low, increase the clamping pressure (usually 200-230 Psi).
(6) If the raw material stays in the heating section for too long, shorten the production cycle.
16.Bottle bottom peeling
(1) The nozzle temperature percentage is too high or too low. Adjust the nozzle temperature to a moderate level.
(2) The nozzle mouth is worn. Replace the nozzle and the nozzle insulation sleeve.
(3) The hot runner valve needle is deformed or worn. Replace the valve needle.
(4) The third level of holding pressure is too high. Reduce the holding pressure.
17.Internal shrinkage of the bottle bottom
(1) Excessive scale or rust on the core cooling channel Clean the core cooling channel
(2) The core water pipe is loose Remove the mold and tighten the water pipe again
(3) Insufficient water pressure Increase the water pressure (usually: 6 to 7 bar)
(4) The water temperature is too high Adjust the water inlet temperature of the chiller
18.Scorch marks
(1) The nozzle temperature is too high. Reduce the nozzle heating percentage.
(2) The nozzle insulation sleeve is aging. Replace it with a new one.
(3) The cooling water channel at the bottom of the mold cavity is blocked. Remove the mold and clean the bottom of the mold cavity.
(4) The water pressure is insufficient. Increase the water pressure.
(5) The water temperature is too high. Reduce the water temperature.
19.Fishbone Stripes
(1) The mold hot runner temperature is too high. Lower the hot runner temperature.
(2) The mold nozzle heating temperature is too high. Lower the nozzle temperature.
(3) The mold nozzle insulation sleeve is aging. Replace the nozzle insulation sleeve.
(4) The nozzle valve needle is not moving smoothly. Maintain the hot runner or replace the valve needle.
20.Sprue pinhole
(1) The temperature of the mold nozzle is too high. Lower the nozzle temperature.
(2) The glue extraction position is too small. Increase the glue extraction position appropriately.
(3) The temperature of the mold hot runner is too high. Lower the hot runner temperature.
(4) The drying effect of the raw material is poor. Stop the machine and dry it again (about 2 to 3 hours).
(5) The injection speed is too fast. Slow down the injection speed.
(6) The holding pressure and time are too small. Increase the holding pressure and time.
21. Embryo base shrinkage
(1) Insufficient injection volume Increase injection volume (remaining position: 5-8mm)
(2) Holding pressure position is too large Increase holding pressure
(3) Cooling water temperature is too high Reduce cooling water temperature
(4) Cooling time is too short Increase cooling time
(5) Holding pressure is too low Increase holding pressure
