Best Practices for Sharpening and Replacing Blades of Folding and Cutting Machine

For an industrial tissue factory, the blade is the most critical consumable. Whether you are operating a high-speed interfolding machine for facial tissues or an orbital log saw for toilet rolls, the precision of your sharpening and the timing of your replacements directly impact your bottom line. Poorly maintained blades lead to “napping” (fiber pulling), increased dust, and downstream packaging jams.

Below is a technical guide on the best practices for maintaining the cutting edge of your folding and cutting machinery.

1. Establishing a Systematic Sharpening Protocol

Modern tissue machines are typically equipped with integrated sharpening units. However, “automatic” does not mean “maintenance-free.”

• Continuous vs. Intermittent Sharpening: For high-speed log saws, intermittent sharpening is often preferred over continuous contact. Continuous sharpening can lead to excessive heat buildup, which tempers the steel and makes the blade brittle.
• The Burring Edge: The goal of sharpening is to maintain a specific bevel angle (usually between $15^{\circ}$ and $22^{\circ}$ depending on the GSM of the paper). Operators should visually inspect for a “wire edge” or burr. If a burr forms and is not honed off, it will break off during production, causing a jagged cut.
• Stone Management: Ensure that sharpening stones are clean and free of paraffin or paper dust. Glazed stones will “rub” the metal rather than cut it, creating friction heat without improving sharpness.

2. Monitoring Blade Diameter and Wear Limits

Every blade has a “discard diameter.” As a circular log saw blade is sharpened, its diameter decreases.

• The Reach Factor: Once a blade falls below a certain diameter, it can no longer penetrate the entire log, leaving “tails” or uncut sections at the bottom of the roll.
• PLC Calibration: Ensure your machine’s PLC is updated with the current blade diameter. Advanced machines automatically adjust the orbital path or the feed depth as the blade wears down, but this must be verified weekly to prevent “under-cutting.”

3. Best Practices for Blade Replacement

Replacing a blade is a high-risk maintenance task that requires strict adherence to safety and precision.

• Thermal Equilibrium: Never install a “cold” blade onto a machine that has been running at high speeds. Allow the machine components to reach a stable temperature to avoid misalignment due to thermal expansion.
• Flange Cleaning: Before mounting a new blade, the mounting flanges must be cleaned with a solvent to remove all traces of grease and paper dust. Even a 0.05mm speck of debris trapped behind the flange can cause “blade wobble” (axial runout), leading to uneven cuts.
• Torque Specifications: Always use a calibrated torque wrench to tighten the mounting bolts. Under-tightening leads to vibration; over-tightening can stress the steel and lead to catastrophic blade failure (shattering) at high RPMs.

4. Special Considerations for Folding Machine Slitters

In interfolding machines (V-fold or Z-fold), the “slitting” is often done by a pair of shear-cut blades (top and bottom).

• The Overlap Setting: The overlap between the top and bottom circular knives should be minimal—typically between 0.5mm and 1.0mm. Excessive overlap increases friction and “nicks” the blades.
• Cant Angle (Side Pressure): The “spring” or side pressure between the blades is what creates the clean snip. Too much pressure causes rapid wear and heat; too little pressure causes the paper to “fold” between the blades instead of cutting.

Summary Maintenance Checklist

Conclusion: The ROI of Sharpness

For the factory owner, a strict blade management program reduces energy consumption (as sharp blades require less torque to cut) and extends the life of the machine’s motors and bearings. By treating the blade as a precision instrument rather than a simple consumable, you ensure a premium product that stands out in a crowded market.