Common quality failures and solutions for PET bottle blow molding machines

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Update:Jan, 02 /2024
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PET bottle blow molding machines

PET bottle blow molding machines are complex and require precise control of various parameters to produce high-quality bottles. Despite best efforts, quality failures can still occur. Here are some of the most common issues and potential solutions:

1) High AA Value:

  1. Quality issues with raw material performance → Conduct quality inspection of raw materials before entering the warehouse.
  2. Poor drying effect → Check the operation of the drying machine (e.g., dew point, drying temperature/time).
  3. Barrel heating temperature too high → Lower the temperature while ensuring quality.
  4. Screw back pressure too high → Set the back pressure to (400 to 600 Psi) while maintaining quality.
  5. Excessive cycle time → Optimize cycle time (avoid excessive residence time of raw materials in the screw).

2) Yellowing of Preform:

  1. Excessive drying time/temperature → Release over-dried raw materials and redry.
  2. Barrel temperature too high → Reduce the temperature (generally increase by 2 to 5℃ without producing white mist in preforms).
  3. Mold temperature too high → Reduce it to the appropriate temperature (275 to 280℃).
  4. Prolonged residence time of material in the screw → Empty high-temperature material from the barrel.

3) Excessive Wall Thickness Variation:

  1. Screw temperature too high → Adjust the screw temperature appropriately.
  2. Excessive screw back pressure → Adjust the screw back pressure to the appropriate level.
  3. Injection speed too fast → Moderately reduce injection speed (usually 3.5 to 4S).
  4. Mold cooling water temperature too high → Check cooling water temperature (9 to 11℃ ± 2℃).
  5. Short cooling time → Increase cooling time (generally set to 3 to 4S).

4) Surface Scratches (Body/Thread):

  1. Mold with adhesive residue → Clean the mold.
  2. Damaged mold → Replace damaged components or repair.
  3. Damaged ejection plate suction tube → Replace or repair the damaged suction tube.
  4. Excessive mold lip ejection position/pressure → Adjust to the appropriate state.
  5. Improper ejection plate position → Check the distance between the ejection plate suction tube and the mold lip (generally set to 22mm).

5) Excessive IV Drop:

  1. Long storage time of raw materials → Use the first-in, first-out method.
  2. Poor drying effect → Check if the drying machine is normal, maintain the drying machine, and check the usage time of drying beads (replace every 2 to 3 years).
  3. Barrel heating temperature too high → Lower the temperature while ensuring quality.
  4. Excessive screw back pressure → Set the back pressure to 400 to 600 Psi while maintaining quality.
  5. Mold heating temperature too high → Reduce the mold heating temperature, usually set to 280 to 285℃.
  6. Prolonged storage time or high temperature/humidity in the warehouse for preforms → Check warehouse humidity/temperature (generally 70%/28 or below) and adopt a first-in, first-out inventory method.
  7. Quality issues with raw material itself → Notify the supplier for resolution.

6) Shrinkage Deformation:

  1. Short cooling time → Increase cooling time (set to 3-4S).
  2. Insufficient holding pressure time/pressure → Extend holding pressure time (set to a total of 6-8S for all stages); increase holding pressure (Stage 1: 800Psi, Stage 2: 700Psi, Stage 3: 600Psi).
  3. Mold cooling water temperature too high → Reduce water temperature (set to 9-11℃ ± 2℃).
  4. Low mold circulating water pressure → Increase water pressure (set to 6-7Kg).

7) Unmelted Material:

  1. Screw heating temperature too low → Increase the temperature appropriately.
  2. Screw slippage causing inability to shear the material → (This phenomenon generally occurs in the production of colored oil) Check if the colored oil has excessive oil content, replace the colored oil.
  3. Low screw back pressure → Increase screw back pressure.
  4. Low drying temperature → Check if the screw feed temperature meets the requirements (normal requirement is 160℃).

8) Missing Material at the Bottle Neck:

  1. Insufficient injection volume → Increase injection volume (remaining position after injection is generally 5-8mm).
  2. Low injection pressure → Increase injection pressure.
  3. Slow injection speed → Accelerate injection speed (optimal injection time is 3.5-4s).
  4. Holding pressure position too large → Reduce holding pressure position (injection pressure: 900-1200Psi).
  5. Holding pressure too small → Increase holding pressure.
  6. Mold cooling water temperature too low → Increase cooling water temperature (set to 8-10℃).

9) Long Nozzle, Elongated Nozzle:

  1. Poor raw material drying effect → Stop and redry.
  2. Hot runner valve needle cylinder blockage → Maintain the hot runner.
  3. Hot runner/nozzle temperature too high → Appropriately lower the temperature.
  4. Short holding pressure time → Extend holding pressure time.
  5. Holding pressure too small → Increase holding pressure.
  6. Short cooling time → Increase cooling time.

10) Stringing at the Nozzle:

  1. Hot runner nozzle unable to close or nozzle worn out → Maintain hot runner cylinder or replace with a new nozzle.
  2. Hot runner nozzle temperature too high → Reduce nozzle heating temperature.
  3. Delayed closing time of water mouth valve → Reduce the delay closing time of the water mouth valve.
  4. Valve needle control valve malfunction → Maintain the valve needle control valve.

11) Water and Air Traces:

  1. Mold cooling water temperature too low → Increase the mold circulating water temperature.
  2. High workshop environmental temperature or excessive humidity causing mold condensation → Lower the air conditioning temperature.
  3. Mold leakage → Investigate and eliminate the cause of mold leakage.

12) Bottom Crystallization:

  1. Low temperature of hot runner and nozzle → Increase the temperature of the nozzle and hot runner.
  2. Excessive holding pressure → Reduce the holding pressure of the third stage.
  3. Mold cooling water too low or too high → Check if the cooling water temperature is reasonable before adjusting.
  4. Blockage in the mold's cold water channel → Maintain the mold's water circulation channel.

13) White Haze on the Bottle Body:

  1. Insufficient raw material drying → Stop and redry the raw material.
  2. Screw heating temperature too low → Increase the screw heating temperature.
  3. Screw slippage → (Generally occurs in the production of colored oil preforms) Increase the barrel temperature.
  4. Low back pressure → Increase back pressure.

14) Black Spots/Contamination on Preform:

  1. Contaminated raw material or impurities present → Release materials with impurities (Material handling personnel should always check for contamination).
  2. Contamination during drying → Discard materials with quality issues during drying.
  3. High temperatures in barrel/heating channels/nozzle → Lower the temperature to an appropriate level.
  4. Poor cleanliness of production environment or equipment → Maintain cleanliness in the workshop and equipment.
  5. Contaminated preforms in the warehouse → Maintain cleanliness in the warehouse environment and ensure intact packaging.

15) Flashing:

  1. Damaged mold lip, core seat, or mold cavity → Replace or repair damaged components.
  2. Excessive injection pressure → Reduce injection pressure.
  3. Excessive holding pressure → Reduce holding pressure or holding position.
  4. High heating temperature → Lower heating temperature.
  5. Low mold clamping pressure → Increase mold clamping pressure (usually 200-230Psi).
  6. Excessive residence time of raw material in the heating section → Shorten the production cycle.

16) Bottom Peeling:

  1. Nozzle temperature percentage too high or too low → Adjust nozzle temperature to a moderate level.
  2. Worn-out nozzle mouth → Replace with a new nozzle and a new nozzle insulating sleeve.
  3. Deformation or wear of hot runner valve needle → Replace with a new valve needle.
  4. Excessive holding pressure in the third stage → Reduce holding pressure.

17) Internal Shrinkage at the Bottom:

  1. Scale or rust in the mold core cooling channel → Clean the mold core cooling channel.
  2. Loose water conduit for the mold core → Disassemble the mold and re-tighten the water conduit.
  3. Insufficient water pressure → Increase water pressure (usually 6-7 bar).
  4. Water temperature too high → Adjust the cooling water machine's inlet temperature.

18) Scorch Marks:

  1. Nozzle temperature too high → Reduce the nozzle heating percentage.
  2. Aging of the nozzle insulating sleeve → Replace with a new nozzle insulating sleeve.
  3. Blockage in the mold cavity bottom cooling water channel → Disassemble the mold and clean the mold cavity bottom.
  4. Insufficient water pressure → Increase water pressure.
  5. Water temperature too high → Lower water temperature.

19) Fishbone-like Stripes:

  1. Mold hot runner temperature too high → Lower the hot runner temperature.
  2. Mold nozzle heating temperature too high → Reduce nozzle temperature.
  3. Aging of the mold nozzle insulating sleeve → Replace the nozzle insulating sleeve.
  4. Inefficient movement of the nozzle valve needle → Maintain the hot runner or replace the valve needle.

20) Nozzle Pinholes:

  1. Mold nozzle temperature too high → Lower the nozzle temperature.
  2. Small material withdrawal position → Adjust the material withdrawal position appropriately.
  3. Mold hot runner temperature too high → Lower the hot runner temperature.
  4. Poor raw material drying effect → Stop and redry (approximately 2-3 hours).
  5. Excessive injection speed → Slow down the injection speed.
  6. Insufficient holding pressure and time → Extend holding pressure and time.

21) Bottom Shrinkage:

  1. Insufficient injection volume → Increase injection volume (remaining position is usually 5-8mm).
  2. Holding pressure position too large → Adjust the holding pressure.
  3. Cooling water temperature too high → Lower cooling water temperature.
  4. Short cooling time → Increase cooling time.
  5. Holding pressure too small → Increase holding pressure.

TAG:  Blow Molding Machine  PET Bottle Blow Molding Machine

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