Common quality failures and solutions for PET bottle blow molding machines

Update：Jan, 02 /2024

Author： Beverage Packaging Machine Manufacturer

Pageviews：108

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:

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

2) Yellowing of Preform:

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

3) Excessive Wall Thickness Variation:

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

4) Surface Scratches (Body/Thread):

Mold with adhesive residue → Clean the mold.
Damaged mold → Replace damaged components or repair.
Damaged ejection plate suction tube → Replace or repair the damaged suction tube.
Excessive mold lip ejection position/pressure → Adjust to the appropriate state.
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:

Long storage time of raw materials → Use the first-in, first-out method.
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).
Barrel heating temperature too high → Lower the temperature while ensuring quality.
Excessive screw back pressure → Set the back pressure to 400 to 600 Psi while maintaining quality.
Mold heating temperature too high → Reduce the mold heating temperature, usually set to 280 to 285℃.
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.
Quality issues with raw material itself → Notify the supplier for resolution.

6) Shrinkage Deformation:

Short cooling time → Increase cooling time (set to 3-4S).
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).
Mold cooling water temperature too high → Reduce water temperature (set to 9-11℃ ± 2℃).
Low mold circulating water pressure → Increase water pressure (set to 6-7Kg).

7) Unmelted Material:

Screw heating temperature too low → Increase the temperature appropriately.
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.
Low screw back pressure → Increase screw back pressure.
Low drying temperature → Check if the screw feed temperature meets the requirements (normal requirement is 160℃).

8) Missing Material at the Bottle Neck:

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

9) Long Nozzle, Elongated Nozzle:

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

10) Stringing at the Nozzle:

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

11) Water and Air Traces:

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

12) Bottom Crystallization:

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

13) White Haze on the Bottle Body:

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

14) Black Spots/Contamination on Preform:

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

15) Flashing:

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

16) Bottom Peeling:

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

17) Internal Shrinkage at the Bottom:

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

18) Scorch Marks:

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

19) Fishbone-like Stripes:

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

20) Nozzle Pinholes:

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

21) Bottom Shrinkage:

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

TAG: Blow Molding Machine PET Bottle Blow Molding Machine