Accurate roll width is fundamental for downstream converting operations, ensuring slit rolls nest properly in packaging machines and minimizing edge waste. Mills establish roll width tolerances based on customer specifications, machine capabilities, and slit-knife positioning accuracy. Rigorous on-site setup and maintenance preserve these tolerances throughout production.
1. Establishing Tolerance Specifications
Customer requirements
Typical tolerances range from ±0.5 mm for graphic and medical grades to ±2.0 mm for corrugating mediums.
Machine capability studies
During commissioning, mills perform trial slitting runs, measuring as-built roll widths across the web to determine achievable CD accuracy (often ±0.3 mm).
2. Knife Positioning and Calibration
CNC-controlled arbor positioning
Servo-driven arbors position shear, crush, or score knives with ±0.1 mm repeatability. Regular calibration against gauge blocks maintains accuracy.
Vision-based alignment
Laser-vision cameras verify knife edge alignment in real time, auto-correcting drift caused by thermal expansion or mechanical play.
3. Tension’s Role in Width Control
Web stretch
High tension can elastically stretch the paper web, causing roll widths to undercut nominal setpoints. Proper pre- and post-slit tension zoning prevents this effect.
Live tension compensation
Tension sensors upstream of the slitter inform servo compensations, adjusting knife positions to offset web deformation.
4. Maintenance and Wear Management
Knife wear monitoring
Regular inspections detect edge dulling, which can deflect the web and alter cut positions. Scheduled knife replacements preserve tolerance.
Slitter frame alignment
Periodic laser-scan alignment of slitter frames ensures arbor skew and parallelism remain within ±0.05°.
5. On-Site Validation and SPC
Continuous width measurement
Laser micrometer arrays downstream of the slitter sample width at multiple CD points, feeding SPC charts with real-time pass/fail status.
Manual roll checks
QA technicians measure roll widths using calibrated laser tape measures at run start and every 500 m, reconciling inline data and addressing any drift.
By combining precise CNC knife positioning, tension control, wear management, and continuous measurement, mills set and maintain roll width tolerances that align with customer and converter requirements. On-site calibration and SPC-driven adjustments ensure consistent roll widths—minimizing waste and maximizing downstream productivity.
