This comprehensive guide describes roll defects and presents their causes along with possible corrective actions. Understanding these defects is crucial for maintaining product quality, reducing waste, and optimizing manufacturing processes.
Roll defects can occur at various stages of production and can significantly impact downstream processes. Early identification and proper corrective action are essential for maintaining operational efficiency and product quality.
Core and Structural Defects
Body Damage
Refers to the body of a roll. Such defects as gouges and cuts are not common, however, they do occur. The damage will always be observable when the roll wrapper has been removed and often before.
Possible Causes:
- Transit damage
- Mishandling of rolls
Corrective Actions:
- Better packaging and/or load preparation
- Check tractors and conveyors — remedies depend on handling methods
Crushed Core
When the core within a roll of paper has collapsed.
Possible Causes:
- Excessive compressive pressure from the web
- Sharp outside blow or other mishandling
- Core is not strong enough
Corrective Actions:
- Softer start
- Avoid mishandling of rolls
- Use cores of adequate strength
Loose Core
When the core rotates at a different rate than the surrounding roll. Rotational displacement may cause the web to tear free from the core and can cause tension and draw control problems in subsequent processing.
Possible Causes:
- Start of wound roll too soft with respect to remainder of the roll
Corrective Actions:
- Wind harder at start of roll
Offset Core
A core that is not evenly aligned with the edge of the roll.
Possible Causes:
- Core not properly aligned with edge of roll at the winder
Corrective Actions:
- Align cores prior to starting the winder
Winding Defects
Poor Start
When there is an obvious difference in appearance between the paper near the core and the remainder of the roll.
Possible Causes:
- Web wrinkling during start of the roll
- Web slack during start of the roll
- Web weaving during start of the roll
- Winding too soft near the core
- Poor quality cores
Corrective Actions:
- Reset sheet spreading equipment
- Fasten web to core securely prior to winder startup
- Reduce web cross-deckle caliper variation
- Wind tighter near the core
- Change to better cores
Dished Roll
A progressive roll edge misalignment that can be concave or convex. Observed immediately upon unwrapping.
Possible Causes:
- Non-uniform cross-deckle caliper
- Winding too soft at same radius of the roll with respect to other radius
- Cores not stationary with respect to web while roll is being wound
Corrective Actions:
- Reduce cross-deckle caliper variation
- Control hardness of wind throughout the problem area
- Keep cores from shifting
Telescoped Roll
A progressive roll edge misalignment that can be concave or convex. Observed only after the roll has started to be unwound.
Possible Causes:
- Non-uniform cross-deckle caliper
- Winding too soft at same radius of the roll with respect to other radius
- Excessive web tension while winding
Corrective Actions:
- Reduce cross-deckle caliper variation
- Control hardness of wind throughout the problem area
- Reduce web tension
Out-of-Round Roll
A defect that can be identified because of a flat section on the outside of the roll. The core is not in the center of the roll.
Possible Causes:
- Roll wound too soft
- Severe impact
- Non-uniform roll structure
Corrective Actions:
- Wind roll tighter
- Provide for proper handling, storage and transport of roll
- Pay attention to winding controls and recipes
Starred End
Identified by observing the "star" pattern on the end of the roll. Often the star is symmetrical, but frequently one or more rays are missing.
Possible Causes:
- Tightly wound paper above paper that is loosely wound
- Thin web thickness at the edge of the roll causing a soft end
- Severe impact
Corrective Actions:
- Wind tight at the start of the roll or gradually soften as the diameter increases
- Keep cross-deckle caliper variation to a minimum
- Provide for proper handling, storage and transport of roll
Slitting Defects
Poor Slitting
Poor slitting results in a rough or fuzzy roll edge appearance. When the web edge is examined closely, it is not straight. The edge often appears to be nicked or dented.
Possible Causes:
- Dull slitters
- Slitters not adjusted or set properly
- Speed differential between web and slitters too great
Corrective Actions:
- Sharpen slitters
- Set slitter at proper shear angle, depth, etc.
- Slitters should move at the same speed as the web or faster, not slower
Slitter Edge Curl
Slitter edge curl results in a wavy edge at the slit which gives the roll edge a wavy or shaggy appearance.
Possible Causes:
- Edge of web stretched because bottom or top slitter is too far into the sheet
Corrective Actions:
- Set slitters at proper depth
- Reduce web tensions through slitter section
Cracked Edge
Cracked edge refers to a broken edge of the web. It usually extends in only a short distance and is sometimes termed "edge tear".
Possible Causes:
- Slitter equipment in poor working order
- Slitters improperly set
- High sheet caliper at edge
- Rolls stored on end with single or multiple sheet run-out
Corrective Actions:
- Get slitters in good working condition
- Set slitters properly
- Maintain uniform sheet caliper at the edge
- Eliminate sheet run-out particularly at splices
Tension and Stress Defects
Cross-Machine Tension Burst
An irregular separation or rupture of the web. While the defect is normally in the machine direction, the fiber separation is in the cross machine direction. Normally this defect is not visible at the edge of the roll.
Possible Causes:
- An abrupt change in cross-machine caliper
- Winding too tight
Corrective Actions:
- Minimize cross-machine sheet caliper variation
- Wind softer
Full Machine-Direction Tension Burst
A complete separation or rupture of the web. While the defect is normally in the cross machine direction, the fiber separation is in the machine direction. It is often visible at the edge of the roll, appearing as a stickout or offset.
Possible Causes:
- Winding too tight — causes wound-in tension to exceed the ultimate strength of the paper
Corrective Actions:
- Soften winding
Partial Machine-Direction Tension Burst
Partial machine direction tension burst refers to a partial, irregular separation or rupture of the web. Internal stress of the reel has locally exceeded the ultimate strength of the paper.
Possible Causes:
- Non-uniform cross-deckle caliper variation
- Winding too tight
Corrective Actions:
- Reduce cross-deckle caliper variation to a minimum
- Soften winding
Baggy Paper
Refers to a web with non-uniform draw. The web width does not uniformly support web tension. There are slack and tight sections across the width of the sheet.
Possible Causes:
- Non-uniform cross-deckle web thickness
- Winding too tight
- Tight winding in a local area across the web
- Incorrect setting of the web spreading device
Corrective Actions:
- Reduce cross-deckle caliper variation to a minimum
- Wind as soft as practical
- Adjust spreading device properly
Specialized Defects
Blister Cut
A cut in the web, usually at an angle to the machine direction. It is normally a result of excess paper accumulating as a "blister" at the entrance of a nip.
Possible Causes:
- Excess paper accumulating in front of a nip
- Corrugations in wire or wet felt
- Non-uniform basis weight
- Non-uniform moisture
- Non-uniform nip pressure
Corrective Actions:
- Tighten draw
- Address specific causes once identified
Rope Marks
Bands of relatively uniform width around the roll at a constant distance from the edge. Usually uniform diagonal markings are present within the band.
Possible Causes:
- Non-uniform cross-deckle web caliper
- Tight winding
Corrective Actions:
- Minimize cross-machine sheet caliper variations
- Wind softer
Crepe Wrinkle
A web defect that looks like an accordion. Usually there are several wrinkles gathered in or folded immediately next to each other at an angle to the axis of the roll.
Possible Causes:
- Roll wound too soft at or near core
- Abrupt change in hardness of the wind
Corrective Actions:
- Wind harder near core
- Change hardness of wind slowly as roll diameter increases
How RollTagger Prevents These Defects
Many of these roll defects can be prevented through continuous monitoring and precise control. RollTagger's advanced tracking system helps manufacturers:
- Real-time monitoring of tension variations and winding parameters
- Early detection of developing defects before they become critical
- Precise tracking of defect locations for targeted removal
- Data analysis to identify patterns and prevent recurring issues
- Quality documentation for continuous improvement programs
- Automated alerts when parameters exceed acceptable ranges
By implementing comprehensive roll tracking and monitoring, manufacturers can significantly reduce defect rates, improve product quality, and optimize their production processes.