PET Bottle Blowing Problem Analysis | How Many Issues Have You Encountered in Blow Molding

  01. Molding Line Flattening (Flat Bottle)

Symptoms:

• Vertical side molding line appears flattened

• Mold separation tendency under blowing pressure

Causes:

1. Gas trapping in exhaust holes along molding line

2. Blocked/leaking mold compensation air pipes

3. Worn mold shell rubber rings

4. Excessive mold gap (>0.2mm)

5. Worn positioning pins/bushings

Solutions:
 Reduce high-pressure air supply rate
 Drill additional vent holes (0.5–0.7mm diameter) along molding line
 Test/replace mold compensation air components
 Adjust mold clamping gap to 0.1–0.2mm
 Replace worn positioning pins and bushings

Pro Tip: Combine pressure reduction with vent hole optimization to prevent cooling time loss.

02. Bottle Bottom Wrinkles (“Volcanoes”)

Symptoms:

• Internal/external creases near preform base

• High explosion/breakage risk

Causes:
External Wrinkles:

• Insufficient pre-blow pressure

• Low preform bottom temperature

Internal Wrinkles:

• Preform base overheating

• Delayed pre-blow timing

Solutions:
 Adjust pre-blow pressure (Typical range: 8-12 BAR)
Optimize bottom temperature (Use IR thermometer to verify)
 Sync pre-blow with stretching start (Max 0.3s delay)

03. Bottle Neck Wrinkles (“Neck Bands”)

Symptoms:

• Internal folds 5–8mm below convex ring

• External palpable creases

Causes:

• Over-stretching of preform’s conical section

• Rapid cooling of thin material during stretching

Solutions:
 Reposition hot spots toward bottle body
 Advance pre-blow timing (Verify solenoid valve function)
 Inspect blow nozzle components:

• Cylinder seals

• Spring tension

• Distributor alignment

04. Bottle Neck Accumulation (“Flower Neck”)

Symptoms:

• Wavy stripes 5–8mm below convex ring

• Irregular/oval-shaped convex ring

Causes:

• Premature preform cooling in mold

• Early pre-blow during stretching

Solutions:
 Reduce pre-blow pressure (Max 25% reduction)
 Delay pre-blow intake by 0.1–0.5s
 Increase Zone 1 heating (+5–10% power)
 Lower lamp frame height (2–3mm increments)
 Balance Zone 2-5 temperatures based on bottle thickness

05. Eccentric Bottle Bottom

Symptoms:

• Non-concentric bottom structure

• White discoloration at bottom corners

• Low stress resistance

Causes:
Mechanical:

• Misaligned preform/mold

• Bent stretching rod

• Improper buffer pad adjustment

Electrical:

• Excessive pre-blow pressure

• Early pre-blow intake

• Solenoid valve issues

Solutions:
 Triple-alignment check:

1. Preform ↔ Mold cavity

2. Blow nozzle ↔ Mold center

3. Stretching rod ↔ Sprue point   

• Replace bowed stretching rods

• Clean/replace solenoid valves

• Clear exhaust silencers

06. Pearlescent White Base Angle

Symptoms:

• Iridescent streaks at bottom corners

• Abnormal material thinning

Causes:

• Excessive stretching beyond material limits

• Insufficient material distribution

Solutions:
 Verify extension gap = ⅔ × Preform bottom thickness
 Extend pre-blow time by 10–20%
 Reduce pre-blow pressure
 Ensure smooth stretching rod operation:

• Lubricate guides

• Replace worn linear bearings

07. Material Distribution Problems

Symptoms:

• Uneven wall thickness

• Weak structural zones

Causes:

• Temperature gradient imbalance

• Incorrect stretch rod speed

• Mismatched pre-blow timing

Solutions:
 Implement zone-specific heating control
 Use thickness mapping software
 Optimize stretch rod acceleration curve

Prevention Framework:  Quality Assurance

1. Daily Checks

   • Mold vent hole inspection

   • Stretching rod alignment verification

2. Weekly Maintenance

   • Solenoid valve cleaning

   • Cooling system flow tests