Common faults and solutions for blow molding and bottle blowing (1)

Introduction:

The production of PET bottles through blow molding is a delicate process that demands precision and control over various parameters. However, even with meticulous oversight, common faults can occur, affecting the quality of the final product. Understanding the root causes of these issues and implementing effective solutions is crucial for maintaining product integrity and production efficiency. In this comprehensive guide, we will delve into these common problems and provide practical methods for their elimination, ensuring your PET bottle manufacturing process runs smoothly.

Fault 1: Poor transparency of PET bottle

Reason:

1. Heating temperature is too high

2. Heating time is too long

3. Compressed air contains moisture

4. The injection molded embryo tube itself is opaque

5. Improper embryo tube design

6. The inflation ratio is too small

Method of exclusion:

1. Cool down

2. Shorten heating time

3. Use a dryer to remove water

4. Improve the quality of embryonic tubes, select materials and improve the dryness of raw materials.

5. Improve embryo tube size design

6. Reduce the diameter of the embryo tube

Fault 2: The PET bottle appears pearly and white.

Reason:

1. Heating temperature is too low

2. Uneven wall thickness of embryo tube

3. The thickness of the embryo tube is too thick and the heating penetration is insufficient.

Method of exclusion:

1. Raise the temperature or slow down the revolution speed

2. Improve embryonic tube quality

3. Reduce the thickness of the embryo tube, or try to raise the outer cover of the heating device to increase the temperature dissipation from the surface of the embryo tube.

Fault 3: The position of the water outlet at the bottom of the PET bottle is offset

Reasons:

1. Start blowing too early

2. The stretching rod is not lowered to the bottom.

3. Offset of the center line of the stretching rod and the bottle axis

4. The embryo tube wall thickness is uneven or the injection density is uneven.

5. Uneven heating

Method of exclusion:

1. Delay the blowing time or increase the descending speed of the stretch rod.

2. Adjust the position of the magnetic pole switch

3. Adjust the position of the stretching rod

4. Improve embryonic tube quality

5. Improve the heating conditions, or check whether there are any problems with the rotation of the embryo tube.

Fault 4: Uneven wall thickness of PET bottles

Reason:

1. The position of the stretching rod is not in the center of the embryo tube

2. The blowing holes are asymmetrical and have different diameters.

3. The stretch ratio is too low or the blow-up ratio is too small.

4. The embryo tube does not rotate in the heating furnace.

5. The embryo tube wall thickness is uneven or the injection density is uneven.

Method of exclusion:

1. Adjust the position of the stretching rod

2. Adjust the position and diameter of the blowing hole

3. Increase the stretch ratio or blow-up ratio

4. Check the rotation device

5. Improve embryonic tube quality

Fault 5: The upper part of the bottle is too thick

Reason:

1. The upper temperature is too low

2. The position of the mold exhaust hole is too far from the upper part.

3. The stretch ratio is too low

4. The inflation ratio of the upper part of the bottle is too low

5. The stretching rod speed is too slow

Method of exclusion:   

1. Upper heating

2. Adjust the position of the exhaust hole

3. Increase the stretch ratio

4. Change bottle shape

5. Adjust stretch rod speed

Fault 6: The bottom of the bottle is too thin

Reasons:

1. Start blowing too early

2. The bottom temperature is too high

3. The bottom of the embryo tube is too thin

Method of exclusion:   

1. Delay the start time of blowing

2. Reduce the bottom temperature

3. Increase the thickness of the bottom of the embryo tube

Fault 7: The bottle mold closing line is obvious

Reasons:

1. Insufficient mold clamping pressure

2. Sealing time is too early

3. Mold problem

4. The size of the embryonic tube mouth does not match the mold.

Method of exclusion:   

1. Increase the mold closing pressure and adjust the mold closing support rod angle (<5 degrees)

2. Move the mold closing stroke switch position backward

3. Repair the mold or check the assembly position of the mold, such as whether the guide pillar is loose or the mold is not pressed tightly.

4. Repair the matching position of the mold teeth

Fault 8: The bottom or neck of the bottle is rolled up and material accumulates

Reason:

1. The delayed blowing time is too long

2. One roll, one good

3. The temperature of the accumulation area is too low

4. The operating air pressure is unstable, which affects the descending speed of the stretch rod.

Method of exclusion:   

1. Shorten the delayed air blowing time or reduce the descending speed of the stretch rod.

2. Reduce the air volume on one side of the roller bottle

3. Increase the heating temperature of the embryo tube

4. Add a gas storage tank to the operating gas source, or shorten the gas supply pipeline

Fault 9: The bottom of the bottle is stretched and perforated

Reason:

1. The temperature is not enough and there is no penetration.

2. The delayed stretching time is too long

3. The stretch ratio is too large

4. The bottom of the embryo tube is too thin

5. The stretching rod head is too sharp

Method of exclusion:   

1. Heating

2. Shorten the delayed stretching time

3. Reduce stretch ratio

4. Improve the bottom design of the embryo tube

5. Rounding and stretching the club head

Fault 10: The bottom of the bottle explodes

Reason:

1. The delayed blowing time is too short

2. The delayed mold opening time is too short

3. The temperature is too high

4. The exhaust valve does not work

Method of exclusion:   

1. Extend the delayed air blowing time or increase the descending speed of the stretch rod.

2. Extend the delayed mold opening time

3. Cool down

4. Clean the exhaust valve with gasoline

Conclusion:

Blow molding PET bottles is a complex endeavor that requires attention to detail and a keen understanding of the process. The occurrence of common faults such as poor transparency, pearlescence, offset water outlets, uneven wall thickness, and others can disrupt production and compromise product quality. By employing the troubleshooting methods outlined in this guide, manufacturers can overcome these challenges, optimize their processes, and consistently produce high-quality PET bottles. With regular maintenance and continuous improvement, achieving excellence in blow molding becomes attainable.