Bottled water production: solve one problem
PET Bottle Base Rocking After Blowing: Find the First Unstable Sample
A PET bottle that rocks on a table may already have an uneven standing surface, may change after a waiting interval, or may only tip during a transfer. Those are different observations. A conveyor jam alone does not establish a blow-molding defect, and a stable empty sample does not qualify its filled condition.
Compare identified bottles on the quality-approved reference surface at a defined age after blowing and again at agreed downstream checkpoints. Keep preform lot, mold cavity and actual empty/filled state linked. Locate the first changed base contact before proposing mold, process, cooling-interface or conveyor work.
Give every rocking sample an age and an identity
Freeze the approved bottle/base drawing, preform revision and lot, mold and cavity identity, and the installed machine configuration. Preserve accepted reference samples. A matching nominal volume or preform weight does not prove equivalent base geometry, resin history or supported operating conditions.
Use the agreed clean reference surface and a defined assessment method, not an arbitrary worn table. Record time after discharge and whether the sample is empty, filled or capped; follow hygiene and safe sampling rules. Do not infer a cooling, pressure or heat cause from appearance alone. Keep as-blown contact different from later handling damage.
Illustration: 10 bottles classified as rocking among 400 examined at the same checkpoint and age equal 2.5%. Record the affected cavity distribution separately. Ten observations of the same bottle are not ten defective bottles. This is not an acceptance limit, a stability certificate or Allot Tech production performance.
Find the first changed support condition
Match cavity, lot and age between checkpoints. A mixed bin of rejected bottles can hide whether the standing surface was already different at discharge or changed only after filling or handling.
| Observed pattern | Evidence to retain | Review boundary |
|---|---|---|
| Rocking is present at the first agreed as-blown check | Cavity-linked samples, approved base reference and fixed inspection age | Bottle formation and serial-specific mold/process review |
| A stable empty sample changes after the agreed wait | Matched specimens and elapsed time under recorded conditions | Time-dependent package/process assessment, not an assumed conveyor cure |
| Empty samples pass but filled samples rock | Linked bottle revision, fill state and base observation | Actual filled-package qualification and responsible specialists |
| Static reference checks pass but bottles tip at transfer | Matched static result and first dynamic handoff observation | Conveyor support/transfer task rather than proven base deformation |
Retest one approved correction without a process recipe
Do not touch hot molds, reach into moving equipment, defeat guards or adjust pressure, heating or stretch timing from this article. Qualified personnel follow stored-energy isolation, OEM procedures and the quality-approved sampling method.
- 01
Preserve original process records, preform lot, cavity mapping and both accepted and adverse bottle samples.
- 02
Agree the reference surface, assessment age, empty/filled states, safe sampling and quality disposition before testing.
- 03
After isolation, have the responsible specialist review the earliest failed boundary and authorize one permitted correction.
- 04
Repeat the same cavity/lot and age comparison, including the downstream condition that originally failed.
- 05
Quality evaluates base contact and any separately required integrity and handling checks; a flat empty bottle alone is not a complete release.
Quote the failed interface, not a universal blowing upgrade
A cavity-linked defect at discharge, a change during the wait and instability limited to a conveyor call for different work. Preserve the evidence that separates them. A faster blow molder or a new conveyor does not demonstrate that the approved filled bottle will stand correctly.
Send Allot Tech the approved preform and bottle drawings, actual samples, cavity/time records and retained interfaces. Ask which molds, base inserts, transfer parts, utilities and acceptance cases are included or retained. Record unknown resin or package information as an open review item rather than assumed compatibility.
Define who owns bottle design, material approval, machine settings and connected acceptance. If a lightweighted preform or different bottle base is proposed, treat it as a new qualification condition. Do not turn a successful short dry run into a claim about all lots, storage intervals or shipping performance.
- Approved bottle/base and preform revisions with lots
- Machine serial, mold and cavity identities
- Accepted and adverse matched sample bottles
- Reference surface, method and exact observation ages
- Empty/filled/capped and downstream handoff observations
- Design, quality, service and acceptance responsibilities
Questions buyers ask
Does a bottle tipping on a conveyor prove the base is malformed?
No. Compare its static base contact using the approved reference method and locate the first dynamic support failure. Formation and transfer evidence must remain separate.
Can one stable empty bottle qualify the filled package?
No. Repeat the agreed sample basis, age and filled condition. Quality must define any further integrity or transport requirements; appearance alone does not establish them.
Related troubleshooting guides
Water filling machine low output
Water filling machine low output →Water bottle shrink-pack problems
Water bottle shrink-pack problems →Cap leaks after capping
Cap leaks after capping →Wrinkled or skewed bottle labels
Wrinkled or skewed bottle labels →Uneven fill levels and underfill
Uneven fill levels and underfill →Conveyor jams and tipping
Conveyor jams and tipping →Missing or unreadable date codes
Missing or unreadable date codes →Wet bottles after drying
Wet bottles after drying →Startup rejects after changeover
Startup rejects after changeover →Missing or extra bottles in packs
Missing or extra bottles in packs →Cap feeder jams and missing caps
Cap feeder jams and missing caps →PET bottle scuffing and scratches
PET bottle scuffing and scratches →Label web breaks and torn liners
Label web breaks and torn liners →Cartons reopening after sealing
Cartons reopening after sealing →Filling valves dripping between bottles
Filling valves dripping between bottles →Reject signal without physical bottle removal
Reject signal without physical bottle removal →Water pallet loads leaning after stacking
Water pallet loads leaning after stacking →Ask Allot Tech to review the evidence
Send your machine identification, package drawing and timed observations. State what is unknown so the proposed scope follows the actual problem.