Paper cup bottom paper curl can change how a strip approaches the punch and how a released disc sits during transfer. A roll that feeds correctly near its outside may behave differently closer to the core. Record the strip shape and roll position before treating every missed disc as a timing fault.
This guide separates a material-shape comparison from machine adjustment. Follow the approved reel path and coated-face orientation. Do not reverse a production roll merely to flatten the strip if that would place the wrong surface against the sealing interface.
Diagnostic decision table
| Observed pattern | Compare | Record |
|---|---|---|
| Curl increases near the core | Outer and inner roll samples | Roll identity and approximate position |
| Disc lifts after cutting | Strip curl and transfer support | Released-disc shape |
| Only one roll behaves poorly | Matched approved stock | Storage and converting history |
| Several rolls fail at one guide | Machine path and constraint | Guide condition and route |
Map the roll and coating orientation
Label the reel, supplier lot, slit width, coated face and unwind direction using the material and machine drawings. Record which side contacts each relevant guide without adding marks to product-contact surfaces. Photograph a retained strip outside the machine so its natural bend can be related to the installed path.
Identify whether the complaint occurs at startup, throughout the roll or only near the core. Record actual roll-position information available from production; avoid inventing an exact remaining diameter from memory. Retain material from both a good period and the affected period with labels that survive storage and handling.
Observe free shape without introducing a new bend
Use the same sample length, handling procedure and conditioning time for each comparison. Place retained strips on a defined clean support and record their orientation and shape. If measuring curl height, agree the support points and measurement method first; different sample lengths can produce different heights from similar curvature.
Do not pull one sample flat while allowing another to relax. Avoid heating, wetting or reverse-bending the stock as an informal correction. Such treatment changes the material state and may affect the coating. Treat photographs as comparative shape evidence unless a validated dimensional method and scale have been used.
Separate feeding from released-disc behavior
During guarded operation, distinguish strip entry instability, an incomplete cut and a disc that cuts correctly but fails to settle. These events can lead to the same final reject count while requiring different inspections. Use the normal diagnostic view or approved observation arrangement; never reach into a punch or transfer station to hold the paper.
Inspect retained discs after the safe collection procedure, preserving their production identity. Compare the direction of dish or curl with the incoming strip. A distorted disc can also result from cutting or handling, so a visual similarity supports a hypothesis rather than proving that the reel alone caused the fault.
Run a controlled material comparison
Compare approved reference stock and suspect stock with the same tooling, recipe and verified threading route. Record attempts, missed transfers and accepted cups, not just a short video of successful cycles. Keep the roll position and any stop or splice events visible in the trial record.
If supplier-authorized guide or support changes are needed, record those as a separate trial condition. Do not simultaneously change winding orientation, guide pressure and timing. That may restore output temporarily but leaves no clear explanation of which change mattered or whether the next roll can use the same configuration.
Define an incoming check and a release boundary
Agree the accepted roll construction, orientation, conditioning and any curl-assessment method with the converter and machine supplier. Use successful representative trials to support the requirement. Do not set a universal curl tolerance from one sample or extend approval to a different coating construction without review.
Send HANNAI the labelled strip and disc images, roll-position comparison and trial counts. Include the bottom-paper and cup drawings so the transfer condition can be evaluated in context. Keep suspect material segregated until the agreed review is complete, and confirm finished-cup bottom quality after any feeding improvement before releasing routine production.
Related equipment and next checks
Review the HN-M100 forming equipment and the related guide to bottom feed and transfer diagnosis. The Engineering Notes archive connects these checks with wider machine planning.
Frequently asked questions
Can reversing the roll solve curl?
Only if the approved material orientation and machine route remain correct; obtain supplier guidance first.
Is a curl-height photograph a certified measurement?
No. It needs a defined method and suitable scale to support a dimensional decision.
Does a missed disc always mean incorrect timing?
No. Distinguish strip feeding, cutting and transfer behavior.
Should samples be taken only from the roll outside?
Include the roll positions associated with the complaint and a comparable good period.
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.