Paper cup base rocking inspection addresses a cup that does not sit steadily on its intended support ring. The symptom can come from the cup, the test surface or damage introduced after forming. A controlled rotation and contact check helps locate the problem before bottom tooling is adjusted.
This guide describes comparative inspection. The customer must define the relevant use condition and acceptance requirement. A rocking check does not establish leak resistance, bottom-seal strength or overall cup safety, and it should not be used as a substitute for those separate evaluations.
Diagnostic decision table
| Observation | Useful next check | Avoid assuming |
|---|---|---|
| Rocking follows the cup when rotated | Map the support-ring orientation | The bottom disc alone is responsible |
| Rocking stays at one table location | Check the test surface and debris | Every tested cup is defective |
| Only packed cups show the symptom | Compare handling and stack history | The forming station caused all damage |
| Behavior differs after filling | Use the agreed loading condition | Empty-cup results represent every use |
Establish a suitable reference surface
Use a clean, rigid reference surface with a suitability check defined by the quality team. Remove loose debris without altering the cup. Do not rely on a visibly worn desk or flexible conveyor belt for a dimensional conclusion. Record the surface identity and the region used for the inspection.
Compare a known satisfactory cup at the same locations as the suspect cup. Rotate and relocate both samples in a planned sequence. If the instability stays with a surface location rather than the cup orientation, investigate the surface before classifying production. Preserve photographs that show both the cup orientation and the reference area.
Map the contact ring and direction
Mark a reference orientation on the cup away from the support area, using the sidewall seam as a traceable feature where appropriate. Record the direction in which rocking occurs and whether the behavior repeats after rotation. Apply only the light, defined contact needed by the agreed inspection method.
Avoid pressing the rim until the cup deforms and then describing that movement as base rocking. If a gap measurement is needed, have the metrology specialist choose a method that does not lift or distort the support ring. A visual shadow can identify a location to investigate but is not automatically a calibrated gap value.
Keep the original condition intact
Inspect the support ring for local crushing, trapped material, scuffing or an irregular formed edge. Photograph the condition before cleaning or manipulation that could remove evidence. Distinguish the actual supporting surface from the recessed bottom panel; their shapes play different roles in how the cup rests on the table.
Compare cups collected safely near machine discharge with cups taken after stacking and packing. Keep time, lot and handling histories linked. If only downstream samples are affected, investigate the transfer and packing conditions as well as forming. Do not straighten a damaged base before the original failure has been documented.
Use loading conditions that match the question
Agree whether the relevant assessment concerns empty cups, a specified fill condition or another customer-defined use. Keep temperature, fill amount and time after filling consistent when those variables are part of the test. Follow the approved test arrangement for any hot-liquid work rather than improvising an operator demonstration.
Record observations before and after loading without mixing them into one undifferentiated verdict. A cup can behave differently as its loading and material condition change. If the symptom develops with time, preserve the sequence and test conditions so the investigation can distinguish initial geometry from behavior during use.
Relate repeated defects to production evidence
Map confirmed cup-related defects to production time and forming position where that identity can be retained. Review bottom support geometry, tooling condition and handling evidence with the machine supplier. Do not alter knurling or forming settings solely because one cup rocks; the responsible feature must first be located.
Verify any authorized correction with representative cups and the unchanged inspection method. Include the separate bottom-seal and other required quality checks. Send HANNAI the orientation map, reference-surface comparison, cup drawings and pre-packing versus post-packing observations so the next inspection targets a supported cause.
Related equipment and next checks
Review the HN-M100 cup forming equipment and the related guide to bottom knurling and base-seal inspection. The Engineering Notes archive connects these checks with wider machine planning.
Frequently asked questions
Does a rocking cup necessarily leak?
No. Stability and liquid integrity are different characteristics that need separate checks.
Can a table defect make good cups appear unstable?
Yes. Use reference cups, rotation and relocation to investigate that possibility.
Should the bottom panel be pressed flat before checking?
No. Preserve the original condition and use the approved inspection method.
Can one photograph establish a gap tolerance?
No. A dimensional decision requires a suitable method and an agreed requirement.
Review the evidence with HANNAI
Send your machine model, component identification and the observations described in this guide. Include the drawing or material reference and any before-and-after measurements so the required next check can be identified.