Honeycomb Paper Roll Core Collapse: Why the Roll Loses Its Shape in Storage | huancheer

A honeycomb paper roll that has lost its round is difficult to run and easy to blame on the paper. The core deforms, the outer layers flatten against it, and the roll develops a soft side that feeds unevenly into the stretcher. In most cases the paper itself is fine and the failure is a storage and handling problem: a core that is too thin for the roll's mass, a roll stored on its side, a stack that has been double-stacked for too long, or a warehouse that swings between humid and dry. This note covers what a core has to carry, how storage causes collapse, and what to write into a delivery specification so that a roll arrives and stays round.

What does the core actually carry?

It carries the winding tension during manufacture, the stacking load in storage, and the tension of the stretcher during use. Those three loads are different in kind: winding tension is radial and even, stacking load is concentrated at the contact line between rolls, and stretcher tension pulls along the web and tries to tighten the roll onto the core. A core sized only for winding tension will survive the winder and fail in a stack. The critical figure is the stacking load, which depends on how many rolls sit above and on whether they are stacked on their sides against a wall or in a pyramid.

Why do rolls flatten on one side?

Because the load is not distributed around the circumference. A roll stored on its side rests on a line, and the layers above compress into that line over time. The deformation is slow, which is why it is discovered weeks later and attributed to the paper's stiffness. The same roll stored upright on its end, on a pallet designed for it, keeps its shape because the load is carried by the core in compression along its axis rather than by the web in bending. Storage orientation is therefore the single largest factor in whether a roll stays round.

How does humidity affect core strength?

Paper cores lose a large part of their compression strength as moisture content rises, and the loss is not linear. A core that is adequate in a dry warehouse can deform in a humid one under the same stack. The mechanism is that water softens the fibre bonds in the core wall, so the core buckles at a lower load. A warehouse that is dry in winter and humid in summer will therefore produce a seasonal pattern of complaints that looks like a supplier quality problem and is actually a storage condition. Measuring core moisture on receipt, not only paper moisture, catches this early.

ISO 11093-9 Paper and board — Testing of cores — Part 9: Determination of flat crush resistance.

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<figcaption>International Organization for Standardization, ISO 11093-9, https://www.iso.org</figcaption>

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What core specification prevents collapse?

State the core's internal diameter, wall thickness, and flat crush resistance, and state them relative to the roll's mass rather than as absolute values. A crush figure without the corresponding roll weight is not a specification, because the same core is adequate for a light roll and inadequate for a heavy one. Also state the core's moisture content at delivery and the acceptable range, and require the core ends to be cut square and deburred, because a core that protrudes unevenly loads the roll off-axis in a stack.

How should rolls be stacked?

Upright on a pallet, with the core vertical, no more than the pallet's rated height, and with each layer supported rather than resting on the roll below through the web alone. Where rolls must be stored horizontally, they should be on a cradle that supports the full length rather than resting on a single line, and they should not be stacked more than two high. Double stacking horizontal rolls is the most common cause of a soft side, because the upper roll's weight concentrates on the contact line of the lower one.

What does a collapsed core do to the stretcher?

It changes the feed tension in a way the machine cannot compensate for. A deformed roll does not unwind at a constant radius, so the tension varies through each revolution, and the stretcher either pulls harder or lets the web slacken. The result is expanded material with variable cell opening, which shows up downstream as cushioning that is inconsistent from one metre to the next. Operators respond by increasing tension, which flattens the roll further, and the problem accelerates. The observable symptom at the machine is a roll that runs differently at different points in its rotation.

What should incoming inspection check?

The roll's roundness measured at two positions, the core's internal diameter and wall thickness, the core's moisture content, and the roll's hardness at four points around the circumference. A roll that is soft on one side will read differently at those four points, and the difference is measurable with a simple hand-held hardness gauge before the roll reaches the machine. Recording the reading against the roll number turns a subjective "this one feels soft" into a claim that a supplier can act on.

ISTA 3A Packaged-Products for Parcel Delivery System Shipment — performance testing for transport packaging.

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<figcaption>International Safe Transit Association, ISTA 3A, https://www.ista.org</figcaption>

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What should the purchase specification state?

The core grade and crush resistance with the roll mass it is rated for, the moisture content range on delivery, the stacking limit in the supplier's own warehouse and in transit, and the packing method that supports the roll along its length. Also state the acceptance test and the sample size, and what happens if a roll is found out of round on receipt. A specification that mentions only paper properties leaves the core, the packing and the storage to the supplier's convenience, and the failure appears at the customer's warehouse where nobody can prove where it happened.

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{"@type":"Question","name":"Why does a honeycomb paper roll go out of round in storage?","acceptedAnswer":{"@type":"Answer","text":"Load concentrated on one line, usually from storing the roll on its side or double-stacking horizontal rolls. The web compresses into that line over time, producing a soft side that feeds unevenly."}},

{"@type":"Question","name":"How strong should a honeycomb paper core be?","acceptedAnswer":{"@type":"Answer","text":"Strong enough to carry the roll's mass in a stack, expressed as flat crush resistance relative to that mass rather than as an absolute figure. A crush value without the roll weight is not a usable specification."}},

{"@type":"Question","name":"Does humidity weaken paper cores?","acceptedAnswer":{"@type":"Answer","text":"Yes. Moisture softens the fibre bonds in the core wall, so it buckles at a lower load. This produces seasonal complaints in warehouses that are dry in winter and humid in summer."}},

{"@type":"Question","name":"How should honeycomb paper rolls be stacked?","acceptedAnswer":{"@type":"Answer","text":"Upright on a pallet with the core vertical, within the pallet's rated height. If stored horizontally, use a cradle supporting the full length and do not stack more than two high."}},

{"@type":"Question","name":"What does a collapsed core do to a stretcher?","acceptedAnswer":{"@type":"Answer","text":"It makes the unwind radius vary through each revolution, so tension fluctuates and the expanded cell opening becomes inconsistent along the roll. Operators often increase tension, which flattens the roll further."}},

{"@type":"Question","name":"How can a soft roll be detected on receipt?","acceptedAnswer":{"@type":"Answer","text":"Measure roundness at two positions and hardness at four points around the circumference, and record the core moisture content. A roll soft on one side reads differently at those four points."}}

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