PET Bottle Base Is Deformed or Rocks on the Conveyor

The cost of deformed PET bottle bases and unstable standing bottles is not limited to the visible reject. It can include product giveaway, rework, unstable downstream operation and hours spent correcting the wrong variable.

A PET bottle defect can originate in preform quality, heating, stretching, pre-blow, final blow, mould cooling or transfer. The location and symmetry of the defect usually reveal which process window moved. For this fault, the first distinction is between incorrect base thermal profile and stretch-rod endpoint error. The procedure below moves from non-invasive checks to controlled repair and restart.

What operators usually see

The failure pattern narrows the search more quickly than replacing parts. Mark samples and record which of these conditions are present: For this case, preserve evidence that shows whether bottle feet are uneven and the container rocks.

• Bottle feet are uneven and the container rocks
• The gate area is stretched off-center
• Bases push upward after filling
• One cavity produces a repeatable base shape

Make the equipment safe and protect the product

Isolate high-pressure air, electrical power, heating circuits and motion energy before entering the guarded area. Treat hot oven components and pressurized blowing circuits as stored-energy hazards.

Keep samples by cavity and timestamp. Record preform lot, resin or rPET content, oven profile, pre-blow timing and pressure, final pressure, stretch-rod position, mould temperature and cooling-water conditions. Explicitly record whether bottle feet are uneven and the container rocks.

Most likely causes, in practical checking order

1. Incorrect base thermal profile

Too much or too little heat prevents the feet and push-up from forming correctly To test this explanation without guessing, inspect bottles immediately at mould discharge and again after conveying and filling Record the result before moving to the next cause.

2. Stretch-rod endpoint error

The rod stops short, overtravels or is off-center at the base A practical confirmation step is to map defects by cavity and time. Compare the finding with a known-good run.

3. Mould-base or cooling fault

Position drift and poor cooling release an unstable hot base Do not compensate for this condition in the recipe. First, measure base temperature and cooling-water flow or differential temperature Keep the original setting and measured result in the fault record.

4. Downstream thermal or mechanical load

Hot bottles are squeezed, filled or accumulated before the base stabilizes Separate this cause from the others with one controlled check: verify stretch-rod home, endpoint and alignment Use the same product, format and speed for the comparison.

Step-by-step diagnostic procedure

The aim is to eliminate whole groups of causes with each check. Record actual values rather than “normal” or “looks good.”

1. Inspect bottles immediately at mould discharge and again after conveying and filling
2. Map defects by cavity and time
3. Measure base temperature and cooling-water flow or differential temperature
4. Verify stretch-rod home, endpoint and alignment
5. Inspect mould-base movement, seating and vent cleanliness
6. Check downstream rails and hot-bottle accumulation for pressure on the base

Corrective actions that address the root cause

A reset is not a repair. Complete the mechanical, process or controls work indicated by the evidence and document the as-left state.

• Rebalance base heating within the qualified recipe
• Correct stretch-rod position and mechanical condition
• Repair mould-base actuation and restore cooling flow
• Reduce harmful hot handling and correct guides or residence time

How to verify the repair before full-speed production

Restart at reduced speed with normal production materials, then increase output in steps. The first acceptance check is: Confirm that deformed pet bottle bases and unstable standing bottles is absent for multiple consecutive cycles, not only for one sample. Review the alarm history and keep diagnostic product segregated until the site’s quality procedure releases it.

• Confirm that deformed pet bottle bases and unstable standing bottles is absent for multiple consecutive cycles, not only for one sample.
• Compare the repaired result for “Bottle feet are uneven and the container rocks” with the approved quality limit and the last known-good baseline.
• Check adjacent stations and downstream package quality for side effects associated with incorrect base thermal profile.
• For “PET Bottle Base Is Deformed or Rocks on the Conveyor”, record the final settings, measurements, parts used and restart authorization.

Prevent the problem from returning

The most effective preventive action is an observable limit with a named response, not a general instruction to “check regularly.”

• Use a base-rock or stability gauge at startup
• Trend cooling conditions
• Inspect stretch-rod position
• Keep mould vents clean
• Link blower cavity data to filler and conveyor rejects

When to stop troubleshooting and call a specialist

Stop and contact the machine or component supplier when deformed pet bottle bases and unstable standing bottles cannot be isolated with non-invasive checks, when it returns after an approved repair, or when calibration requires protected service tools. Stop local work when safe diagnosis requires protected service tools, energized access or a change to a validated process. Send the service engineer the fault history, photos, samples, trend data, recipe revision and work already completed.

Relevant equipment for this application

Where deformed PET bottle bases and unstable standing bottles reveals an application mismatch rather than a maintenance fault, review the Automatic Water Bottle Blowing Molding Machine. A useful technical discussion includes the real bottle, closure, product properties, pack format and site conditions.

Frequently asked questions

What should be checked first when deformed PET bottle bases and unstable standing bottles?

Separate blow-process base defects from post-blow heat or handling damage. Check base heating, stretch-rod endpoint, mould-base position, cooling-water flow, ejection temperature and downstream guide pressure. Preserve the original settings and take representative samples before repair work begins.

How can we distinguish incorrect base thermal profile from stretch-rod endpoint error?

Too much or too little heat prevents the feet and push-up from forming correctly In contrast, the rod stops short, overtravels or is off-center at the base Compare the two mechanisms under the same operating condition by completing these checks: inspect bottles immediately at mould discharge and again after conveying and filling Then map defects by cavity and time

Can production continue while deformed PET bottle bases and unstable standing bottles?

Only when the plant’s documented risk assessment and quality procedure allow it. For deformed PET bottle bases and unstable standing bottles, stop and segregate production when package integrity, sanitation, validated processing, pressure safety, electrical protection or an uncontrolled reject trend is involved.

What evidence will help the equipment supplier respond faster?

Provide the model and serial number, product and format, target speed, first fault, timestamps, photos or video, affected station pattern and maintenance history. For this issue, also include bottle feet are uneven and the container rocks and the measured result from this check: check downstream rails and hot-bottle accumulation for pressure on the base