Introduction: Preform is an injection molding item. As the intermediate semi-finished product of the subsequent biaxial stretch blow molding, the bottleneck of the preform has been finalized during the injection molding stage, but some problems often occur. In this article, we share the common problems and solutions of the preform for the reference of purchasing friends:
- The bottom of the PET preform is whitish reason: ①Insufficient temperature of hot runner ② Insufficient material temperature Solution: ①Strengthen heat insulation measures ② Increase the temperature of the hot nozzle ③ Properly increase the material temperature ④Increase injection speed ⑤Reduce holding pressure ⑥Slow down the flow rate of cooling water
- PET preforms are opaque reason: ① Insufficient drying of raw materials ② Insufficient plasticization of raw materials ③The wall thickness of the preform is too large or the cooling is insufficient ④ mixed with other plastics ⑤Material temperature is too low Solution: ① Ensure that the material is dry for more than 4 hours ②Increase material temperature ③Increase the screw speed ④ Check whether the temperature of the drying material is too low or the injection volume does not match. It is necessary to ensure that the raw material is dried at 165 degrees until the moisture content is less than 0.02% ⑤Enhance cooling and change the thickness
- PET preform changes from transparent to opaque reason: ①The demoulding temperature is too high Solution: ① Strengthen cooling water ②Extend cooling time ③Change the injection time
- There is fog on one side of the PET preform reason: ① Holding pressure is too high ②Eccentric gate hole of bottom mold Solution: ①Reduce stress ②Correct the mold
- PET preforms have silver streaks or yellowing reason: ①Plastic decomposition Solution: ①Reduce the drying temperature and prolong the drying time ②Adjust the injection speed ③Reduce material temperature ④Reduce the nozzle temperature
- PET preforms have air bubbles reason: ① Insufficient drying Solution: ①Strengthen drying ②Increase material temperature ③Reduce screw speed
- There are irregular ring grooves in the PET preform reason: ①Water vapor condenses in the core cavity Solution: ①Enhance workshop drying ②Increase the cooling water temperature ③Dry the mold
- The PET preform is cracked at the gate reason: ① The hot runner mouth and the gate are not concentric ② Gate undercut ③The gate area is too hot Solution: ①Correct the mold ②Correct the gate ③Extend cooling time ④Increase injection speed or injection time ⑤Enhance gate heat insulation
- The preform mouth is not full or has welded lines reason: ① Poor exhaust ② Eccentric injection Solution: ①Enlarge the exhaust groove ②Clean the lip mold ③Reduce injection speed ④ Correct the gate
- “PET preforms have thick edges and thin edges. The reason for this is poor mold manufacturing, gate hole offset, the injection pressure being too high, and core displacement. The solution is to correct the mold, increase the material temperature, turn down the pressure, and use a mold with high strength and high precision with an adjustable core structure.”
- “Depression on the surface of the preform can be caused by the material temperature being too high, the injection speed being too short, the holding pressure being too short, the injection time being too short, or insufficient cooling. Solutions include reducing the material temperature, reducing the injection speed, increasing the holding pressure, increasing the injection time, and increasing water pressure.”
- “PET preform gate wire drawing can be caused by poor heat insulation, insufficient cooling, pressure in the heat flow, poor check of the screw, or holding pressure being too low. Solutions include ensuring the heat insulation of the gate, increasing cooling, strengthening the inverted cable, cleaning the screw mouth, and increasing the holding pressure.”
- “The preform is bent after demoulding can be caused by gate hole eccentricity or uneven cooling. Solutions include correcting the mold, reducing the holding pressure, increasing the injection speed, extending the cooling time, cleaning up waterways, and increasing the amount of cooling water.”
- “Bending after preform heating can be caused by preform eccentricity, temperature adjustment hole or temperature adjustment seat being eccentric, or preform density varying. Solutions include correcting the mold, correcting the temperature adjustment and positioning parts, and reducing the temperature adjustment, particularly the temperature adjustment temperature of the bending part.”
- “Partial whitening of PET bottle blowing can be caused by insufficient preform temperature regulation. The solution is to increase the PET preform temperature and internal and external uniformity.”
- “Preform turns white after temperature adjustment can be caused by the temperature adjustment of the preform in the whitish section being too high. The solution is to ensure that PET preforms are blown at 80-110 degrees PP.”
- “PET bottle will not inflate can be caused by insufficient air pressure, insufficient preform temperature regulation, or preform injection defects. Solutions include increasing air pressure, increasing embryo temperature, and using 100 degrees boiling water to check whether the PET preforms are softened evenly.”
- “Pull through the bottom of the embryo can be caused by the embryo bottom temperature being too high, the embryo body temperature being too low, or plastic degradation being serious. Solutions include adjusting the embryo temperature, checking and replacing the original preform, strengthening drying, and slowing down and delaying the blowing time.”
- “Preform eccentricity can be caused by blowing too early, the wind pressure being too high, misalignment between the stretch rod and the bottom of the bottle, serious preform eccentricity, the stretching rod speed being too slow, the distance between the stretch rod and the bottom mold being greater than 1.5mm, or the bottom temperature of the preform being too high. Solutions include slowing down and delaying the blowing time, reducing wind speed, correcting the installation status, checking and correcting the preform condition, adjusting the stretching cylinder pressure, adjusting the end of the stretch rod to the bottom 1-1.5mm, and reducing the bottom temperature adjustment temperature.”
- The bottle body is not fully blown in the vertical direction
Reasons:
- Some preforms that have been heated to too high of a temperature
- Cold blocks present on some preforms
- Insufficient wind pressure and air volume
- Poor exhaust of the bottle blowing mold
- Blowing mold temperature is too high
- The preform wall is too thin
- Insufficient longitudinal stretch ratio of the bottle
Solutions:
- Adjust the temperature of the PET preforms
- Do not touch the heated embryo body, check for cold hard blocks
- Increase the storage pressure and gas volume
- Increase exhaust
- Add cooling water to the blowing mold
- Correct the mold
- Increase the stretch ratio (longitudinal)
- The wall thickness of the PET bottle is uneven in the circumferential direction
Reasons:
- Preform eccentricity
- Uneven temperature regulation
- Poor exhaust
Solutions:
- Improve the preform mold
- Improve the temperature adjustment equipment
- Reduce the temperature of the bad parts of the PET preform
- Increase exhaust
- There is a “crater”-shaped protrusion at the bottom of the bottle
Reason:
- The bottom of the preform is too cold or the temperature in other parts of the preform is too high
Solution:
- Advance the blowing time and adjust the temperature
- Part of the bottle turns white after blowing
Reasons:
- Insufficient local temperature regulation
- The local stretch ratio is too large
- Moisture present in the compressed air
Solutions:
- Increase preform temperature
- Check preform design
- Strengthen water and oil filtration
- Poor vertical bearing capacity of the bottle
Reasons:
- Uneven wall thickness
- Preform heating temperature is too high
- Poor shape of the bottle
Solutions:
- Improve the uniform wall thickness of the bottle
- Mold at low temperature and high pressure as much as possible
- Improve bottle design
- The bottle is easy to break
Reasons:
- The bottom wall thickness is not properly stretched
- Plastic high temperature degradation
Solutions:
- Improve bottom stretch ratio
- Strengthen the drying of raw materials before embryo injection
- Reduce the production temperature
- There are pockmarks and white mist in the bottle
Reasons:
- Blow in dirty air
- High air humidity
Solutions:
- Install an air filter
- Reduce the humidity of the blown air
- The bottle is too soft
Reasons:
- Poor design
- Processing temperature is too high
Solutions:
- Improve design
- Try to inject embryos and blow molding at low temperature
- There is a burnt smell after blowing the bottle
Reasons:
- Heating is too high
- Bad compressed air
- Use of inferior raw materials
Solutions:
- Reduce the blowing temperature
- Arrange the air compressor and filter
- Use regular manufacturer materials
- The water tastes bad after a period of time after the bottle is filled with water
Reasons:
- Acetaldehyde content in the bottle is too high
- Unqualified raw materials
Solutions:
- Use low temperature embryo injection and bottle blowing
- Check the acetaldehyde content of raw materials before processing, and reject inferior raw materials.