A paper board caliper profile shows how measured thickness changes across a reel, sheet or sampled production group. One center reading can miss edge-to-center patterns that affect blank feeding, seam overlap or bottom-paper handling. The map must preserve location and use a controlled thickness method.
This guide supports diagnostic mapping and supplier discussion. It does not reproduce ISO 534, set a universal thickness limit or establish that caliper caused a forming problem. Apply the purchased material specification and current approved test method.
Diagnostic decision table
| Profile pattern | Follow-up | Do not assume |
|---|---|---|
| Edge differs from center | Repeat mapped locations and reel identity | One reading describes the full width |
| Results change after conditioning | Control atmosphere and equilibrium | Instrument drift is the only cause |
| Single-sheet and pack values differ | Use the specified method consistently | Methods are interchangeable |
| Pattern follows converted blanks | Trace sheet orientation and nesting | Machine adjustment created the material pattern |
Define the material population and coordinates
Identify supplier lot, reel or pallet, grade, coating construction and dimensions. Establish machine direction and cross direction. Create a location scheme before cutting samples so every result maps back to an edge, center, sheet or reel position.
State whether the objective is average conformity, cross-web variation or diagnosis of selected blanks. These questions require different sampling. Do not call a few convenient edge strips representative of an entire delivery. Preserve links from gross sample to test piece and from converted blank to finished cup where practical.
Use the specified thickness method
ISO 534 describes single-sheet thickness and, for paper, bulking thickness; its abstract notes that the methods can give different results and that bulking thickness is unsuitable for board. Use the current purchased standard and the method named in the material agreement.
Control the measuring-face condition, applied pressure, dwell or reading procedure and instrument verification through the laboratory method. Board structure can compress under contact, so two gauges with different geometry or pressure may not be comparable. Record calibration status and avoid mixing instruments without a correlation study.
Condition and protect specimens
Apply the agreed conditioning atmosphere and procedure. ISO 187:2022 specifies standard atmospheres and monitoring for pulp, paper and board. Record actual temperature, relative humidity and conditioning history. Keep specimens flat, clean and protected from edge crushing or fingerprints.
Randomize or balance measurement order where practical so instrument drift does not align with cross-web position. Mark specimens outside the measured area. If production urgency requires an unconditioned screening check, label it as such and do not compare it directly with conditioned laboratory acceptance data.
Plot the profile without hiding variation
Retain individual readings by coordinate and replicate. Plot position against caliper and distinguish reels or sheets. Review abrupt local changes, gradual edge-to-center trends and repeatability. An overall average can appear acceptable while a spatial pattern remains operationally important.
Check whether apparent patterns exceed measurement uncertainty and repeat-setup variation. Investigate outliers with sample condition and instrument events. Do not discard a high point because it disrupts a smooth profile unless a predefined invalidity rule applies. Report both the map and the intended summary statistic.
Connect material evidence to conversion and forming
Trace mapped material through printing, cutting and forming when a controlled trial is feasible. Compare blank feeding, seam geometry and bottom handling using identified positions. Block or randomize other factors so time and machine warm-up are not confused with material location.
Send HANNAI the material specification, sampling diagram, conditioning record and profile with finished-cup outcomes. This can show whether a defect aligns with a board pattern, but final material acceptance remains governed by the buyer-supplier agreement and qualified laboratory results.
Related equipment and next checks
Review the 850 roll die cutting machine and the related guide to online gauge and laboratory correlation. The Engineering Notes archive connects these checks with wider machine planning.
Technical reference
- ISO 534: paper and board thickness, density and specific volume — general reference; confirm applicability to the installed equipment.
- ISO 187: conditioning and testing atmosphere — general reference; confirm applicability to the installed equipment.
Frequently asked questions
Can one center reading represent a reel?
Not when the objective is to investigate a cross-web profile.
Are single-sheet and pack thickness interchangeable?
No. Use the method specified for the material and decision.
Why preserve machine and cross direction?
It keeps the measured pattern linked to converting and forming orientation.
Does a caliper pattern prove it caused a cup defect?
No. Use a controlled trace-through trial and other evidence.
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.