Avoiding Core Damage and Out-of-Roundness in Paper rolls

Problems such as core damage and out-of-roundness frequently affect paper rolls during handling and transport.Causes include excessive clamping force, incorrect positioning, or deformation from contact with another object.

“To avoid this, operators should set the right clamp force using the pressure selection valve, pick the right friction surface on contact pads, or use automated paper roll clamps,” said Hansjörg Freund, Regional Sales Manager at Cascade Corporation, during a WPF/OPHAL webinar.Cascade offers attachments, forks, masts, and related tools to help improve productivity in the supply chain.

From the papermaking side, some rolls become out-of-round more easily during handling. Different paper grades serve different end uses and have specific characteristics.

What influences out-of-roundness

“One simple way to categorise paper is by its basis weight, measured in grams per square meter (gsm),” said Martin Schorn, Director of Technical Customer Service, UPM.

Newsprint is usually 40-45 gsm. Magazine paper ranges from 48 to 100 gsm. Premium papers for covers can go up to 150 gsm.

“The raw material and its properties impact winding hardness, which can range from soft to hard. Softer rolls deform more easily, especially during handling. The raw material mix also affects roll softness,” Schorn said.

Roll width influences out-of-roundness too, especially if narrow rolls are not clamped or lifted at the center.

Properties such as brightness and print quality increase with grade. Softer wound rolls – especially in lower grades such as newsprint, machine-finished speciality paper (MFS), or supercalendered paper (SC) – are more prone to out-of-roundness, but all grades require proper handling, he added.

The bulk of the sheet is the major factor in out-of-roundness. Bulk refers to thickness at a given basis weight.

“Bulkier sheets are more compressible and usually softer when wound. Raw material matters here too. Chemical pulp and virgin fibres are bulkier than recycled ones, making rolls softer and more vulnerable to deformation during handling,” he said.

Measuring out-of-roundness is complex

One method to measure out-of-roundness uses a device called the spider. The roll is placed on its side with the device centred in the core, while a laser arm circles it, measuring surface distance at several points.

It’s time-consuming, especially for wide rolls, and perhaps hazardous, Schorn said.A simpler method uses a mechanical device. The roll rests on its side while a spring-loaded gauge circles it, measuring radius deviations. This method only measures the edges, not the centre.

Another cause is eccentricity, which can happen during production, not just handling. If winding stations vibrate, the core may shift, causing eccentric rolls that act like out-of-round rolls in printing.

though rare, eccentricity can occur in 100 percent recycled rolls.

Handling Damage: What Printers Need to Know

Roll handling is a critical, yet often overlooked, part of the printing process. Damaged rolls can cause important downtime and waste. But how do you prevent these issues? Understanding the forces at play is the first step.

According to a recent presentation by Dr. Michael Freund at the World Association of Newsprint Producers (WAN-IFRA), several factors contribute to roll handling damage. It’s more complex than just being careful.

Here’s a breakdown of the key elements:

1. roll weight and inertia: Heavier rolls have more momentum.
2. Acceleration and deceleration: Rapid changes in speed create stress.
3. Impact forces: dropping or bumping rolls causes immediate damage.
4. Clamp force: This is the pressure holding the roll in place.
5. Contact pad surface pressure: This is clamp force per unit area of pad surface. It helps minimise damage.
6. Dynamic forces: Handling generates forces (hoisting, braking, rough terrain, collisions) that affect the roll.

“All six factors influence handling. Correct clamp force is key: too much causes damage and deformation, while too little can lead to roll drops, injury, or telescoping,” Freund said.

Though, Freund suggests three key steps to avoid handling damages.

• Set initial hydraulic pressure
• Verify and fine-tune pressure
• Perform daily equipment checks

Consequences of out-of-round rolls at the print shop

• Increased web breaks, especially during splicing.
• Wasted material and production delays.
• Potential for damage to printing equipment.
• Reduced print quality.

Preventative maintainance and a thorough understanding of these forces aren’t just good practice-they’re essential for a smooth, efficient, and safe printing operation. Don’t underestimate the impact of proper roll handling.