The Dienes Approach to Practical Slitter Positioning; Manual to Fully Automatic

Market Background:

Most web materials are produced in large, economical roll sizes and at some point converted into to a reduced size for making a final product.

Increasing market demand for final products has pushed traditional slitting technology beyond desired capability.

Final product manufacturing processes have become faster and more automated. Automation and high speed require better accuracy of slit widths, and improved slit edge quality; both being well beyond traditional, operator controlled knife set up methods.

Theory and Practice:

For the converter the importance of understanding shear slitting theory such as blade geometry, blade metallurgy, cant angles, side load force, etc. can not be over emphasized. But the practical side of shear slitting requires changing set up positions and knife blades on machines under demanding production conditions. Web dust, poor ergonomic conditions, and most importantly safety considerations are the daily routine.

Other factors are the type of slitter/rewind (surface, center driven, or other) and whether it is roll to roll or continuous winding, the type of material (paper, nonwovens, plastic, laminates, labels, etc.), the frequency of set up changes, and the slit accuracy and quality requirements.

The Focal Point:

The slitting process is becoming the focal point for improvement. Converters are investigating if they can retrofit existing slitter winding machinery or do they need to purchase new equipment?

This paper looks at different set up technologies. I will present a succeeding range of shear slitting set up technologies, from manual to fully automatic, with factors relating to procedure, accuracy, consistency, effects on knife life, safety, dust, etc.

Shear Slitting Holders:

A common factor for all these technologies is the "pneumatic" top knife holder. This device holds the top rotary knife blade and typically only rotates when in contact with the driven bottom knife. This discussion is about top knife holders with air-powered vertical and horizontal stroke.

Three Key Relationships:

The first is the relationship of each bottom knife to another bottom knife. This determines how wide the web is going to be (given that the winder controls web tension to prevent, or if desired, control material elongation). This bottom knife distance relationship is what slitter manufacturers refer to when providing slit width accuracy statements.

The second is the relationship of the top knife to the bottom knife. This determines slit edge quality, knife blade life, and influences dust levels. Not only in the horizontal plane, but also the vertical plane. Too much overlap depth of the top knife, which introduces an increasing blade width to the material being slit, can cause material damage on one side of the cut.

The third is how much force is applied when the top knife engages the bottom knife in the horizontal plane. Two little force and the knives may not cut, or create excessive dust. Too much force shortens blade life, and when machine vibration is a factor, internal stresses on the knife holder mechanical design can cause premature holder degradation.

Set Up Factors:

Understanding these relationships when selecting which slitting set up method to purchase is important. But there are many factors that should influence what set up methods best suit any operation.

There are four categories to consider:

1. Items that directly effect the final product being slit

• Product material
• Slitting speed
• Slit widths
• Side force applied
• Knife axial run out
• Knife radial run out
• Cant angle

2. Items that improve set up efficiency and longevity of slitting components:

• How many set up change are required daily
• Mounting methods; typically dovetail or linear bearing
• Knife holder rigidity and resistance to vibration; service life
• Knife blade material

3. The cost factor:

• The number of slitters required
• Retrofit or new winder
• Manual or automatic
• Installation costs

4. Safety

TRADITIONAL MANUAL KNIFE SET UP

Procedure: Operators physically position shear bottom knives with ruler or scale. Then the top knife holder is moved and located over the bottom knife. The vertical and horizontal strokes are activated and the holder slid until the top knife engages the bottom knife. The holder is then locked in place.

Accuracy: Bottom knife separation can be 0.025" to 0.032". Top holder position relationship will change from operator to operator resulting in irregular performance and shortened knife life.

Set up Efficiency: Poor, especially with dovetail mount. Set up time for 20 knife sets typically <20 minutes.

Knife life: Shortest due to set up inconsistencies

Cost: Least

Safety: Poorest

DIENES ES-TAB LOCATING SET UP

Procedure: Operators physically position shear bottom knives with ruler or scale. Then the top knife holder is moved across linear bearings and located over the bottom knife. The locating tab is loosened and rotated over the knife blade head until it can contact the bottom knife cutting edge. The top holder is moved gently against the bottom knife and locked into position.

Accuracy: Bottom knife separation can be 0.020" to 0.025". Top knife holder position relationship improved for more consistent set ups and improved knife life.

Set up Efficiency: Improved; linear bearing mounting required. Set up time for 20 knife sets typically <15 minutes.

Knife life: Improved with better set up consistency

Cost: Small increase in cost.

Safety: Improved

DIENES MODULE II-L LASER BEAM AIDED BOTTOM KNIFE SET UP

Procedure: Operators physically position shear bottom knives using two laser beams to locate the knife cutting edge. Digital indicator with direction arrows notifies operator of correct location. The indicator is locked in position.The top knife holder is moved into a mechanical detent area and a lever engages the top knife holder to mechanically position it correctly for the bottom knife.The top knife is locked and the indicator set to zero. The indicator then is moved to the next slit width.

Accuracy: Bottom knife separation can be 0.012" to 0.015". Top knife holder position relationship greatly improved for more consistent set ups and improved knife life.

Set up Efficiency: Greatly improved; linear bearing mounting required. Set up time for 20 knife sets typically <5 minutes.

Knife life: Significantly improved with better set up consistency

Cost: Modest increase in cost.

Safety: Improved

DIENES MODULE IV COMPUTER CONTROLLED, SERVO DRIVEN KNIFE AUTOMATIC SET UPS; AIR SHAFT DRIVE FOR BOTTOM KNIVES

Procedure: Operators selects desired slit set up from menu.Laser scans current knife positions. Top knife holder and bottom knife rings are moved by servo motors; free of operator involvement.

Accuracy: Bottom knife separation can be 0.008". Top knife holder position relationship perfect for consistent set ups and maximum knife life.

Set up Efficiency: Maximum; linear bearing mounting required. Set up time

Knife life: Maximum; 3 to 4 months common.

Cost: Highest

Safety: Maximum

DIENES MODULE IV COMPUTER CONTROLLED SERVO DRIVEN KNIFE AUTOMATIC SET UPS; MOTOR DRIVEN BOTTOM KNIVES

Procedure: Operators selects desired slit set up from menu.Laser scans current knife positions. Top knife holder and bottom knife rings are moved by servo motors; free of operator involvement.

Accuracy: Bottom knife separation can be 0.004". Top knife holder position relationship perfect for consistent set ups and maximum knife life.

Set up Efficiency: Maximum; linear bearing mounting required. Set up time for 20 knife sets typically <2 minutes. 60 knife set up <4 minutes.

Knife life: Maximum; 3 to 4 months common.

Cost: Highest

Safety: Maximum; free of operator involvement.