Page 1

WH 2.4

WH 2.4

Slitting

Timothy J. Walker tjwalker@tjwa.com (651) 686-5400 (651) 249-1121 (866) 572-3139

WWW.TJWA.COM

1335 164 Church Stonebridge Street, Road Suite C7

Office Mobile Fax

St Paul, Decatur, Minnesota Georgia55118 30030


WH2.4 Slitting – Outline

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Slitting Qs

How would you cut _____?

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How Would You Cut These?

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How Would You Cut These?

Brittle Thin

Firm Dry

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Soft Sticky

Hard/Soft /Hard Thin

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Brittle Sticky Thin

Strong Abrasive Thin

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Slitting Qs

How is thinking about stress important to slitting?

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Fracture Mechanics Why do things break?

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Break Testing In tensile-elongation testing, a sample is elongated until it breaks. The stress (load over cross-sectional area) and percent elongation are called the break strength and break elongation.

L

dL

…but the break point is uncontrolled.

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T

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Stress Fracture Defined Excessive Stress or Strain will Cause a Break? Stress

brittle break

yield point

x

σ

ductile break

(force/area)

elastic strain

∆σ E= ∆ε

Strain, ε

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x

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(%)

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Controlled Fracture In slitting, we have a specific point where we want fracture to occur, so we need to control it. We use focused geometry to control where we create stresses high enough to fracture the material.

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Fracture Force Once the fracture is started, we want to continue it. Many times, the crack propagation stress is lower than the crack initiation stress.

Fracture is dependent on stress (force over area) so the fracture force will increase with thickness. Tear resistance and toughness are material properties usually dependent on fracture rate, so the fracture force may increase with speed. TJWalker+Associates, Inc., Copyright 2008

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Conventional Slitting Methods All are based on fracturing the tensioned, moving web by mechanical stress concentration. Razor

Crush

Shear

Cuts like a knife.

Cuts like a pizza cutter.

Cuts like scissors.

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Slitting Qs

What are the key variables of traditional slitting?

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Slitting is a Process Process to control MD fracture of web products. Slitting is not just about knives. It’s about knife-product interaction. Web Material Properties Knife Material and Setup Web (and Knife) Speed Control Web Tension Control Web-to-Knife Contact

Slitting Slitting

Goal: Edge Quality Correct Position & Width Minimum Debris TJWalker+Associates, Inc., Copyright 2008

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Slitting Qs

What are the traditional slitting methods?

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Knife Profiles

In Air

In Groove

Razor TJWalker+Associates, Inc., Copyright 2008

Crush Knife and Anvil

Crush www.tjwa.com

Profile Top Shear

Square Shear

Shear WH2.4-16


Crush Slitting = Focusing Stress Web product with target slit point. Crush knife & anvil nip the web at slit point. Stress builds in converging nip point. Fracture occurs within zone of high stress.

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Two Geometries of Shear Slitting Shear can be the most focused slitting method, concentrating stress between two sharp points.

Image courtesy of Dienes Corp. TJWalker+Associates, Inc., Copyright 2008

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Slitting Qs

What defines slitting quality?

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Slitting Quality Quality Slitting = 1. Minimum debris / dust 2. Correct slit position and width (within specifications) 3. Good slit edge quality (without defects listed below) Rough, nicked, or scratched edge Deformed, scalloped, or wavy edge Skiving, angel hair, or double cuts Fusing, smearing, or delaminating coated of laminated products

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Slitting Qs

What causes slitting debris and dust?

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Slitting Debris

In any mechanical slitting method, there are two sources of debris: 1. Fracture cracks that split (bifurcate), releasing particles from the body of the web (Where does the kerf go?)

2. Abrasive wear from the freshly fractured edge rubbing on the side of the knife after the cut point. TJWalker+Associates, Inc., Copyright 2008

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Minimum Debris / Dust Quality Slitting = 1. Minimum debris / dust Minimize slitting kerf by focusing fracture stresses through knife geometry and structural rigidity. Minimize edge-to-knife abrasion through optimized web path, tensioning, and knife geometry. Minimize knife wear. Replace or sharpen worn knives.

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Debris from Slitting Kerf Kerf is defined as the width of a groove made by a cutting tool. A saw blade creates an obvious kerf.

Slitting kerf is less obvious. The entire volume of product under fracture stress levels may turn into slitting debris or dust. Focusing slitting geometry reduces the volume at fracture stress, related dust, ragged edges, and kerf.

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Debris from Abrasion The fresh slit edge is abraded as it passed around the flanks of the blade or knives. Reducing flank contact will improve edge quality and reduce debris generation.

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Fracture Point

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Abrading Contact

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Slitting Qs

Does slitting debris contaminate my coated or laminated product?

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Transport of Slitting Debris Slitting debris tends to stay near a web’s edge. As debris levels increase, dust may fall off the web or become airborne. Always avoid having the web or other debris sensitive equipment under the slitting process to avoid falling dust contamination.

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Slitting Qs

What causes slit width or position variations?

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Slit Width Variations All slitting methods will have slit width variations due to the web or process control due to tension-related necking, crossweb tension variations of web bagginess, and any nonflatness or gathering in the knives. Perfect web and tension control will still have slit width variations if the knife positions move laterally. This is largely a function of the blade and knife holder deflection and rigidity. Razor & Crush: The blade position determines the cut point. Shear: The bottom blade determines the cut point. Both methods can be pushed open when the product fails to reach critical fracture stress. TJWalker+Associates, Inc., Copyright 2008

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Correct Slit Position and Width Quality Slitting = 2. Correct slit position and width Minimize shaft or crossbar deflection. Minimize blade holder deflection or slop. Minimize axial and radial runout. Minimize tension variations. Ensure taut, flat web at slit point. Set tension high enough to pull out bagginess. TJWalker+Associates, Inc., Copyright 2008

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Knife Positioning Setting the slit spacing ranges from simple ruler-assisted manual positioning to sophisticated electronic-assisted manual or automatic systems. Crush Slitting:

Shear Slitting:

Knife-to-knife spacing determines slit spacing.

The bottom knives are typically fixed and set the slit spacing. The top knives are loaded against the fixed bottom knives.

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Knife Holder or Mount Rigidity

Any looseness in the rotational axis creates slit position and width variations.

Knives on common shaft may tip if there is too much clearance, creating axial runout and slit position / width variations. TJWalker+Associates, Inc., Copyright 2008

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Slitting Failure Mechanical slitting is always about focusing force over a small area to reach a materials fracture stress. If stresses of below the fracture criteria, the product will fail to slit. Low stresses are cause by: 1) Insufficient applied force, or more commonly 2) Insufficient sharpness to focus the force into a high stress. Razor: Low tension, web bagginess, and web flutter lead to insufficient applied force and failure to cut Score & Shear: Both methods can be pushed open when the product fails to reach critical fracture stress. (Fibrous products are especially susceptible to failure to slit.) TJWalker+Associates, Inc., Copyright 2008

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Deflection from Slitting Forces The slitting force will create deflection in both the top and bottom shafts. Knife engagement must be greater than deflection . Deflection creates edge to center slitting differences.

With more knives per width, narrower slitting will have more deflection

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Slitting Qs

How is tension typically controlled at slitting?

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Typical SR Tension Control

TUNWIND

TSLIT

TREWIND

Web drive or brake points

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Tension, Strain, & Necking For solid materials, tension and compression stresses do not significantly change density. Therefore, dimensional increases in one direction are offset by decreases in other directions. Tensioning Increases Length Thickness & Width Decrease

T0 = 0 TJWalker+Associates, Inc., Copyright 2008

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Necking and Slit Width Tension, thickness, width, modulus (stretchiness) and Poisson’s ratio determine how much the web is necked at slitting.

 TX  ε Y = −νε X = −ν    twE 

δwT = w0 (−νε X )

TX

No Tension Tensioned TJWalker+Associates, Inc., Copyright 2008

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Draw Strain and Velocities Draw zone strain alters the incoming web’s strain based on roller surface velocity changes.

ε

Draw Zone Steady-State Strain

V2=V1 V2<V1

A velocity increase will increase draw zone strain and tension. A velocity decrease will decrease draw zone strain and tension. (Too great a drop will make the web go slack.) TJWalker+Associates, Inc., Copyright 2008

V2>V1

Upstream Strain

Length

V2 ε2 TIN ε1 www.tjwa.com

TDRAW

V1 WH2.4-39


Negative Draw Negative draw, where the downstream velocity is less than the input velocity, is often believed to create slack web.

ε

Upstream Strain

Draw Zone Steady-State Strain

0.4%

Draw –0.2%

V2<V1

0.2%

Length

However, if the percent speed drop is less than the input web strain, the web will NOT go slack.

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V2 ε2 TIN ε1 www.tjwa.com

TDRAW

V1 WH2.4-40


Draw Strain and Input Strain V2>V1

Draw zone strain is always relative to the upstream strain.

V2=V1

ε

V2<V1 V2>V1 V2=V1 Draw Zone Steady-State Strain

Upstream Strain

V2<V1

Length

Changes in upstream tension or strain will feed into and change the draw zone tension and strain.

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V2 ε2 TIN ε1 www.tjwa.com

TDRAW

V1 WH2.4-41


Pre-Slit Web Flatness

Any lateral buckling entering the slitting knives will result in a greater post-slit, untensioned strand width.

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Tension Pulls Out Bagginess Loose web will have a poor slit edge quality. Slitting tension should be high enough to pull out any web bagginess or length variation.

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Slitting Qs

How does razor slitting work?

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Crack Propagation Web tension focused onto a small area edge of a razor blade = high stress and fracture. Once a crack is initiated, slitting fracture and separation may occur ahead of the webknife contact point. The knife wedge causes the existing crack to move forward. TJWalker+Associates, Inc., Copyright 2008

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The often crack propagates ahead of the knife tip like ice in front of an icebreaker ship.

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Slitting Qs

How is razor slitting optimized?

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Razor Slitting

Razor-In-Air R-I-A is sensitive to web flutter & bagginess.

Razor-InGroove

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Razor Slitting = Focusing Stress Razor-In-Air

Razor-In-Groove

Web product with target slit point. Razor blade begins to enter the web path. Web stiffness and tension creates stress near razor tip. Fracture occurs within zone of high stress. TJWalker+Associates, Inc., Copyright 2008

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Razor-In-Air vs. Razor-In-Groove

Application Factors

Products

Razor-In-Air

Razor-In-Groove

Easiest installation

Requires grooved roller

Most width flexible

Discrete widths

May create wavy edge in ductile webs

Minimizes wavy edge in ductile webs

Easy to oscillate

Difficult to oscillate

Sensitive to flutter & bagginess

Less sensitive to flutter & bagginess

Needs safety guard

Safer, roller helps guard

Thin, non-extensible films, foils, laminates

Thin extensible films and laminates

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Extending Razor Blade Life • Oscillate blades to expand the wear zone. • Hard coat or ceramic blades. • Avoid overheating blades (reduce speed or product thickness)

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Examples: Razor Blade Holders

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Auto-Positioning Razor Slitting

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Raised Edge, Wavy Edge

Raised Edge

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Wavy Edge

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Razor Slitting Circular Razor

Rotary cutters are commonly used by quilters to cut fabric. The circular razor blades are used similar to crush knives, but against a self-healing mat rather than an anvil.

Yikes! These are scary safety-wise.

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Slitting Qs

How does crush slitting work?

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Crush and Shear Dovetailed Holders Crush knives with individual dovetail holders.

Knife holders for increasingly demanding applications.

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Slitting Qs

What is the difference between crush slitting and rotary die cutting?

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Two Approaches to Crush Slitting Individual pneumatically loaded circular blades and common anvil roller

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Rotary converting die: rigid or flexible tooling in tight tolerance gap vs. anvil roller

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Slitting Qs

How does shear slitting work?

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Shear Slitting = Focusing Stress Web product with target slit point. Shear knives nip the web at slit point. Stress builds in converging nip point.

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Shear Slitting = Focusing Stress Web product with target slit point. Shear knives nip the web at slit point. Stress builds in converging nip point. Fracture occurs within zone of high stress. Post-fracture abrasion of edge edge.(and knives).

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Slitting Qs

Whatâ&#x20AC;&#x2122;s the difference between wrap and tangential shear slitting?

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Wrap vs. Tangential Shear Slitting Wrap Shear

Tangential Shear

More suitable for thin, flexible webs

Especially suitable for thick, more rigid webs

Wrap curvature opposes vertical deflection

Flat web geometry doesnâ&#x20AC;&#x2122;t inhibit vertical deflection

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Slitting Qs

How does top shear knife setup affect shear slitting?

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Passing the Top Knife There are two extremes of how the top knife web will pass by the knife, via lateral compression or vertical deflection.

pre-cut

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lateral compression

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vertical deflection

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Top Shear Blade Geometry Recommendations by Rheinhold Schable, Tidland Corp. Schable considers seven factors: Caliper Density

Recommended top blade setup and profile is a function of each of these factors as they vary from low to high extremes,

Elongation The key top blade parameters are: Grind Angle, Rim Width, and Cant Angle

Stiffness Tensile Abrasiveness Compressibility TJWalker+Associates, Inc., Copyright 2008

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Tangential Shear Top Blade Profiles Some typical top blade profiles for tangential shear. Width-Angle = 0.8 mm - 45º, 2 mm - 25º, 9 mm - 5º Default tangential shear top blade

For stiff, high density webs

For thicker, low density webs

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0.8 mm

2 mm

45º

25º

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9 mm

5º WH2.4-67


Top Shear Blade Geometry General trend of recommendations: Primary Angle = 0-10o

Primary Angle = 20-45o or 45-60o

Rim Width = Wide

Rim Width = Narrow

Cant Angle = 0-0.5o

Low High Low Low High Low High

Wimpy

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Cant Angle = 0.5-1.0o

Caliper Density Elongation Stiffness Tensile Compressibility Abrasiveness www.tjwa.com

Hefty

High Low Med-High High Low High Low WH2.4-68


Top Blade Geometry Back Side Face

Cutting Face

Secondary Grind Angle

Undercut Primary Grind Angle Rim Width TJWalker+Associates, Inc., Copyright 2008

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Passing the Top Knife There are two extremes of how the top knife web will pass by the knife: lateral compression or vertical bending. Lateral compression will be encouraged by a narrower, smaller angle top blade

Vertical bending is encouraged by a wider, larger angle top blade.

Soft webs will easily compress, stiff webs will buckle. Look out for increased side abrasion TJWalker+Associates, Inc., Copyright 2008

Stiffer webs will bend and recover. Look out for top face abrasion. www.tjwa.com

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Wrap Shear Top Blade Profiles Typical top blade profiles for wrap shear. Width = 0.7 mm, Primary angle of 25, 45, or 60 degrees. Default tangential shear top blade

For stiff, high density webs

For thicker, low density webs

60ยบ TJWalker+Associates, Inc., Copyright 2008

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45ยบ

25ยบ WH2.4-71


Cant Angle The cant angle is designed to force the shear knife contact to the overlap entrance point.

Top View Cant Angle

Cut occurs here

Most slitters where the top knives are all on a common shaft donâ&#x20AC;&#x2122;t have this adjustment. +

Front View

Side View +

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Cant Angle on Common Shaft Knives Itâ&#x20AC;&#x2122;s difficult to create a cant angle when the top knives share a common shaft.

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Top Knife Geometry and Tilting With no concave angle, engagement tilting shifts contact to the high center of the overlap zone.

Contact occurs here.

Gap on bottom

With a concave geometry the engagement tilting shifts contact to overlap entrance and exit points (as long as tilt angle is less than the concave angle). TJWalker+Associates, Inc., Copyright 2008

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Contact at entrance and exit

Gap on top WH2.4-74


Knife Overlap The overlap is set by how far the top bladeâ&#x20AC;&#x2122;s tangent point is engaged beyond the bottom bladeâ&#x20AC;&#x2122;s tangent point.

Overlap

Top Knife Radius

Bottom Knife Radius

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Tilt in Spring-Loaded Top Knives The lateral load is set by adjusting the lateral shift of the top knives relative to the bottom knives.

Rake Angle

This motion can be measured with a dial indicator. This motion compresses the top knife springs.

Top Knife Springs

More engagement motion create more lateral force and more rake angle.

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Slit Width, Knife Spacing, & Web Tilt Knives are setup and adjusted to achieve the target web slit width. Actual slit width will be greater than knife spacing for two reasons: 1.The Poissonâ&#x20AC;&#x2122;s effect â&#x20AC;&#x201C; The web is slit under tension and recovers width when tension is removed. (This effect is extremely small with the high modulus, thick, low tension products.)

Any lateral buckling here will result in a greater post-slit, tension-free width.

2.Buckling - If the web has any lateral buckling at the knives the post-slit, unbuckled width will be greater. TJWalker+Associates, Inc., Copyright 2008

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Other Shear Slitting Considerations • Relative speed of web, bottom knife, and top knife • Interaction of these factors with overlap and overspeed • Setting knife overlap • Knife wear causes

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Example: Knifeholder Loads *

Tidland CLASS I knifeholders loads are roughly ½ of CLASS II Image courtesy of Tidland Corp. TJWalker+Associates, Inc., Copyright 2008

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More on Top Shear Knife Profiles

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More on Bottom Shear Knife Profiles

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Knife Mounting Options Top knives on a common axis and support shaft.

Top knives with individual holders on a dovetail shaft.

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Shear Slitting on Dovetail Mount Top and bottom knives on individual dovetail mounted holders.

Top knives with individual holders on a dovetail shaft.

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Auto-Positioning Shear Knives

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Individual Top Knife Blade Holders

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Individual Driven Bottom Shear Knife

Bottom Shear Knife Holder with Servo Motor

Images courtesy of Dienes Corp.

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Slitting Qs

What is stripe slitting and why is it challenging?

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Stripe / Pattern Slitting The goal seems simple enough. 1) Unwind a patterned web, 2) Slit relative to the pattern, and 3) Wind it up.

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Stripe Slitting Registration Factors 1. Good input stripe and splice consistency

3. Accurate stripe detection

7. Stable bottom knife spacing and axial runout

2. Uniform tensioning

6. Minimum and consistent preslit puckering

8. Top knives follow bottom knives.

5. Stable postguide tracking

4. Good web guide mechanics

T

Sidelay Unwind Unit

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Standard vs. Stripe Slitting Look out for tolerance stacking! Tolerance Factor

Standard

Stripe

n/a

+/- 0.010”

1. Input Material 2. Consistent Tensioning

TTOTAL = ∑ Ti

+/- 0.005***

+/- 0.020”

3. Pattern Detection

n/a

+/- 0.005”

4. Web Guide Performance

n/a

+/- 0.010”

5. Guide-to-Knives Tracking

n/a

+/- 0.020”

6. Pre-Slit Web Flatness

+/- 0.002”***

+/- 0.005”

7. Knife Performance

+/- 0.005”

+/- 0.005”

+/- 0.012”

+/- 0.075”

*** Variability from these factor is smaller with standard slitting since the error doesn’t stack crossweb.

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Potentially SIX times worse! WH2.4-90


1. Input Material

Stripe-to-Stripe Error Position Error

Single Stripe Error Width Error TJWalker+Associates, Inc., Copyright 2008

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2. Consistent Tensioning For solid materials, tension and compression stresses do not significantly change density. Therefore, dimensional increases in one direction are offset by decreases in other directions.

T =0

0 TJWalker+Associates, Inc., Copyright 2008

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T1 = 0

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2. Consistent Tensioning For solid materials, tension and compression stresses do not significantly change density. Therefore, dimensional increases in one direction are offset by decreases in other directions. Tensioning Increases Length

Thickness & Width Decrease

T =0

0 TJWalker+Associates, Inc., Copyright 2008

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T1 > 0

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2. Consistent Tensioning Poisson’s ratio determines to what degree machine direction strain creates web necking.

 TX  ε Y = −νε X = −ν    twE 

δwT = w0 (−νε X )

TX

No Tension

Tensioned TJWalker+Associates, Inc., Copyright 2008

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2. Consistent Tensioning Tension upsets create slit width variations. With standard slitting, all errors are equal.

In stripe slitting, the slit-to-stripe error is additive, increasing with each cut.

No Tension

Tensioned

Low Tension Error High Tension Error TJWalker+Associates, Inc., Copyright 2008

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3. Pattern Detection Detecting a central pattern reduces lateral error stacking.

+4

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-2

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+2

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3. Pattern Detection “Noisy” or “ragged” pattern edges can create detection variation. -2

+2

Sensor “deadband” is another tolerance stacking variable.

Since pattern sensors are inherent optical, they are sensitive to ambient light and dust. TJWalker+Associates, Inc., Copyright 2008

www.tjwa.com

WH2.4-97


4. Web Guide Performance

Web Guide Limitations** 1. Maximum Actuation Rate 2. Range 3. Structural Rigidity 4. Unstable Control ** Web guide limits covered Lateral Control section TJWalker+Associates, Inc., Copyright 2008

www.tjwa.com

WH2.4-98


5. Guide-to-Slitting Tracking Accurate stripe position at the sensor must be transferred to accurate stripe position at slitting. Pay special attention to alignment, cylindricity, and traction in this section of the web path.

TJWalker+Associates, Inc., Copyright 2008

Sensor Sensor

www.tjwa.com

Slitting Slitting

WH2.4-99


6. Pre-Slit Web Flatness

Any lateral buckling entering the slitting knives will create an unintentionally wide strand width.

TJWalker+Associates, Inc., Copyright 2008

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WH2.4-100


Cutting On Target

After jumping all the hurdles to get the striped web in position to be cut, one hurdle remains.

The knives must cut the web in the correct spot. TJWalker+Associates, Inc., Copyright 2008

www.tjwa.com

WH2.4-101


7. Knife Performance Knives may be setup on a common shaft or dovetail. The mount to the common cross-element must be rigid and accurate.

Score on Shaft

Score on Dovetail

Shear on Shaft

Shear on Dovetail

TJWalker+Associates, Inc., Copyright 2008

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WH2.4-102


7. Knife Performance Any looseness in the rotational axis creates slit position and width variations. Knives on common shaft may tip if there is too much clearance, creating axial runout and slit position / width variations. TJWalker+Associates, Inc., Copyright 2008

www.tjwa.com

WH2.4-103


7. Knife Performance Some knives are setup in a stack using a precision machined width and small spacers. Other knives are set independently on a common shaft, using an optical comparator or other precision measurement device.

TJWalker+Associates, Inc., Copyright 2008

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WH2.4-104


Visual Referencing The best reference to visually detect stripe position error or wander is a short full-width strip of the striped web. Hang a stripe of reference material near the web guide to check web guide and input material variations. Hang another reference strip near the knives to check guide-to-slit tracking. TJWalker+Associates, Inc., Copyright 2008

Error

www.tjwa.com

WH2.4-105


Slitting Qs

Why isnâ&#x20AC;&#x2122;t your slitter running?

TJWalker+Associates, Inc., Copyright 2008

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WH2.4-106


Why Isn’t Your Slitter Running? You have excess capacity. (Good idea for a slitter) It’s not scheduled this shift. You have no material to run. The operator is busy: • Busy getting the slitter ready to run. ☺ • Busy with other stuff?!

TJWalker+Associates, Inc., Copyright 2008

www.tjwa.com

WH2.4-107


Slitter Operations An operators day includes many activities. Jumbo Jumbo Inventory Inventory

Jumbo Jumbo Staging Staging

Knife Knife Setup Setup

Inspection Inspection &&Flagging Flagging

Core Core Cutting Cutting

Core Core Loading Loading

Roll RollLoad Load &&Unload Unload

Tabbing Tabbing&& Core CoreStarts Starts

Splicing Splicing

Roll Roll Unloading Unloading

Shaft Shaft Handling Handling

Packing Packing

Web Web Threading Threading

Acceleration Acceleration

TJWalker+Associates, Inc., Copyright 2008

Running Running

Deceleration Deceleration

www.tjwa.com

Trim Trim

Paperwork Paperwork

WH2.4-108


Critical Path Slitter Operations Slitter operation activities fall into 5 categories: Per Jumbo

Jumbo Jumbo Inventory Inventory

Jumbo Jumbo Staging Staging

Roll RollLoad Load &&Unload Unload

Per Product

Knife Knife Setup Setup

Web Web Threading Threading

Core Core Cutting Cutting

Running Time

Acceleration Acceleration

Running Running

Deceleration Deceleration

Per Cut

Roll Roll Unloading Unloading

Core Core Load Load&&Align Align

Tabbing Tabbing&& Core CoreStarts Starts

Per Order

Pallet Pallet Handling Handling

Paperwork Paperwork

TJWalker+Associates, Inc., Copyright 2008

www.tjwa.com

Splicing Splicing

Packaging Packaging Rolls Rolls

WH2.4-109


Slitting Qs

How can time studies and critical path analysis help with slitter productivity?

TJWalker+Associates, Inc., Copyright 2008

www.tjwa.com

WH2.4-110


Reducing Non-Running Times What is required to get the slitter running again?

Identify activities on the critical path! Focus 1st operator on critical path activities. Use 2nd operator to: > complete non-critical activities. > complete critical activities simultaneously. > work together on critical activities (w/ #1). Reduce time to perform any critical activity. TJWalker+Associates, Inc., Copyright 2008

www.tjwa.com

WH2.4-111


Critical Path Slitter Operations Which activities are on the critical path?: Per Jumbo

Jumbo Jumbo Inventory Inventory

Jumbo Jumbo Staging Staging

Roll RollLoad Load &&Unload Unload

Per Product

Knife Knife Setup Setup

Web Web Threading Threading

Core Core Cutting Cutting

Running Time

Acceleration Acceleration

Running Running

Deceleration Deceleration

Per Cut

Roll Roll Unloading Unloading

Core Core Load Load&&Align Align

Tabbing Tabbing&& Core CoreStarts Starts

Per Order

Pallet Pallet Handling Handling

Paperwork Paperwork

TJWalker+Associates, Inc., Copyright 2008

www.tjwa.com

Splicing Splicing

Packaging Packaging Rolls Rolls

WH2.4-112


Critical Path Operations? Critical path activities Per Jumbo

Roll RollLoad Load &&Unload Unload

Splicing Splicing

Per Product

Knife Knife Setup Setup

Web Web Threading Threading

Running Time Per Cut

Non-critical path activities Jumbo Jumbo Inventory Inventory

Jumbo Jumbo Staging Staging

Core Core Cutting Cutting

Accel Accel––Running Running- -Decel Decel Roll Roll Unloading Unloading

Core Core Load Load

Core Core Starts Starts

Per Order TJWalker+Associates, Inc., Copyright 2008

Pak’g Pak’g Rolls Rolls Pallet Pallet Handling Handling

www.tjwa.com

Paperwork Paperwork WH2.4-113


Critical Path Operations? Sharing critical path activities Slitter #1 Operator Per Jumbo

Completed at same time.

Per Product

Web Web Threading Threading

Running Time

Accel Accel––Running Running- -Decel Decel

Per Cut

Roll Roll Unloading Unloading

Per Order TJWalker+Associates, Inc., Copyright 2008

Core Core Load Load

Slitter #2 Operator Roll RollLoad Load &&Unload Unload

Splicing Splicing

Knife Knife Setup Setup

Core Core Starts Starts

Roll Roll Unloading Unloading

More help on rewind end with no jumbo change. www.tjwa.com

Core Core Load Load

Core Core Starts Starts

#2 Assists #1 WH2.4-114


No. of Cuts per Order Calcs. Slit strands per jumbo

Knives per cut

Cuts (passes) per order

Jumbos to fill order

 (WJUMBO − 2WTRIM )  = ROUNDUP   W SLIT  

N SLIT CUT

N KNIVES CUT = N SLITS CUT + 1 N CUTS ORDER

N JUMBOS ORDER

 N ROLLS ORDER  = ROUNDUP   N  SLITS ORDER 

 N SLITS CUT × LSLIT  = ROUNDUP   L JUMBO  

N = Number of… W = Width of… TJWalker+Associates, Inc., Copyright 2008

www.tjwa.com

L = Length of… INT = Whole Nos. WH2.4-115


Number of Cuts, Slits Roll and core handling are reasonable.

Roll and core handling eat up your operatorâ&#x20AC;&#x2122;s efficiency (and life) TJWalker+Associates, Inc., Copyright 2008

www.tjwa.com

WH2.4-116


Bottleneck and Non-BN Times Operation Times Each Jumbo Each Knife Change

Critical Path Time

Non-Critical Time

10 * NJ

10 * NJ

1 * (NS/O+1)

(0.1*NS/O+1) x NC/O

Each Cut core load,

+(0.2*NS/O + 3)

run,

+V/LS + tACC/DEC

roll unload

+0.4*NS/O +4) x NC/O

These numbers are only found by an extensive time study.

0

10 * NJ

Post Run

2 * NC/O

Time (in minutes) per activity are based on production time study (given here for example). TJWalker+Associates, Inc., Copyright 2008

www.tjwa.com

WH2.4-117


Slitting Qs

Why is percent running time the wrong measure for a slitter?

TJWalker+Associates, Inc., Copyright 2008

www.tjwa.com

WH2.4-118


Increasing Speed W=5in. Slitter Time vs. Speed No. Rolls = 100 Length of Cuts = 1000 yds.

20 18

Total Time

16

Running Time

Time,hrs

14 12 10 8 6 4 2 0 0

500

1000

1500

2000

2500

Slitter Speed TJWalker+Associates, Inc., Copyright 2008

www.tjwa.com

WH2.4-119


Increasing Speed Percent Run Time and Speed

W=5in. No. Rolls = 100 Length of Cuts = 1000 yds.

2500

60%

2000

40%

1500

30% 1000

20%

500

10% 0%

0 1

2

TJWalker+Associates, Inc., Copyright 2008

3

4 www.tjwa.com

Speed, fpm

% Run Tim

50%

Increasing speed makes percent run time look worse!

5 WH2.4-120


Increasing Speed Order Time and Speed

W=5in. No. Rolls = 100 Length of Cuts = 1000 yds.

2500

9.0 8.0 7.0

2000

6.0 5.0 4.0 3.0

1500 1000

2.0 1.0 0.0

Speed, fpm

Order Time

Increasing speed reduces order time, but with diminishing returns

500 0 1

2

TJWalker+Associates, Inc., Copyright 2008

3

4 www.tjwa.com

5 WH2.4-121


Increasing Width Slitter Time vs. Width Each case has total rolls of 50â&#x20AC;? wide by 20,000 yds. at 500 fpm

60

Time,hrs,%

50 40 Time Saved, %

30

Total Time, hrs 20

Crit. Time Shared, hrs

Wider product take less time.

10 0 0

10

20

30

40

50

60

Slit Width TJWalker+Associates, Inc., Copyright 2008

www.tjwa.com

WH2.4-122


Increasing Length per Roll Slitter Time vs. Length

Each case has total rolls of 2â&#x20AC;? wide by 100,000 total yds. at 500 fpm

30.0

Total Time Crit. Path Time

Time,hrss.

25.0

Crit. Time shared

20.0 15.0 10.0 5.0 0.0 0

200

400

600

800

1000

1200

Slit Length TJWalker+Associates, Inc., Copyright 2008

www.tjwa.com

WH2.4-123


Slitting Qs

How do speed, slit width, and slit roll length affect slitting related costs?

TJWalker+Associates, Inc., Copyright 2008

www.tjwa.com

WH2.4-124


Cost Benefits - Assumptions

+ Material costs are fixed (so not included in cost or saving calculations).

+ Each operator = $50K for salary and benefits + Each slitter costs = $500K depreciating over 5 years ($100K per year)

+ Sharing critical path activities cuts non-run time by 40% whether 1 or 0.5 operators are added per slitter.

+ Your slitter runs 2000 hrs/yr at the conditions listed in speed, width, and length comparisons. TJWalker+Associates, Inc., Copyright 2008

www.tjwa.com

WH2.4-125


Benefits: Output MM Sq Yds per Year

Single Operator Crit.Path Shared

30.0

Increasing Speed

Increasing Width

Increasing Length

25.0

MM SqYd/y

20.0 15.0 10.0 5.0 0.0 1

2

3

TJWalker+Associates, Inc., Copyright 2008

4

5

6

7

8

www.tjwa.com

9

10

11

12

13

14

15

16 WH2.4-126


Benefits: Costs/Area Cost per Square Foot 1.80

Single Operator CPS, 2 op/slitter CPS 1.5 op/slitter

Increasing Speed

Increasing Width

Increasing Length

1.60 1.40

Obviously, costs are higher at low speed, narrow width, and short lengths.

$$/ ft^2d

1.20 1.00 0.80 0.60 0.40 0.20 0.00 1

2

3

TJWalker+Associates, Inc., Copyright 2008

4

5

6

7

8

www.tjwa.com

9

10 11 12 13 14 15 16 WH2.4-127


Benefits: Savings/Area Savings per Square Foot

CPS, 2 op/slitter CPS 1.5 op/slitter

0.90 0.80

Increasing Speed

Increasing Width

Increasing Length

0.70

More cost benefits at narrow widths and short lengths.

0.60 $$/ ft^2

0.50 0.40 0.30 0.20 0.10 0.00 -0.10

1

2

3

TJWalker+Associates, Inc., Copyright 2008

4

5

6

7

8

www.tjwa.com

9

10 11 12 13 14 15 16 WH2.4-128


Reducing Critical Path Times Per Jumbo

Roll RollLoad Load &&Unload Unload

Splicing Splicing

Per Product

Knife Knife Setup Setup

Web Web Threading Threading

Running Time Per Cut

Accel Accel––Running Running- -Decel Decel Roll Roll Unloading Unloading

TJWalker+Associates, Inc., Copyright 2008

Core Core Load Load

Core Core Starts Starts

www.tjwa.com

WH2.4-129


Reducing Critical Path Times Per Jumbo

• • • •

Roll RollLoad Load &&Unload Unload

Splicing Splicing

Use a second shaft or turret unwind. Mount splicing tape on slitter. Use rotary coupling to fill pneumatic bladders. Have all rolls ready to go (unwrapped and prepped).

Per Product Running Time Per Cut

Knife Knife Setup Setup

Web Web Threading Threading

Accel Accel––Running Running- -Decel Decel Roll Roll Unloading Unloading

TJWalker+Associates, Inc., Copyright 2008

Core Core Load Load

Core Core Starts Starts www.tjwa.com

WH2.4-130


Reducing Critical Path Times Per Jumbo

Roll RollLoad Load &&Unload Unload

Splicing Splicing

Per Product

Knife Knife Setup Setup

Web Web Threading Threading

• Use second knife shaft for set up • Use cartridge style knife systems. • Have winding recipes ready or in controller. Running Time Per Cut

Accel Accel––Running Running- -Decel Decel Roll Roll Unloading Unloading

TJWalker+Associates, Inc., Copyright 2008

Core Core Load Load

Core Core Starts Starts www.tjwa.com

WH2.4-131


Reducing Critical Path Times Per Jumbo

Roll RollLoad Load &&Unload Unload

Splicing Splicing

Per Product

Knife Knife Setup Setup

Web Web Threading Threading

Running Time

• • • •

Accel Accel––Running Running- -Decel Decel

Optimize accel-decel. Use rough rollers and winding nip to run faster. Encourage customers to buy long length rolls. Don’t run so fast yield suffers. Per Cut

Roll Roll Unloading Unloading

TJWalker+Associates, Inc., Copyright 2008

Core Core Load Load

Core Core Starts Starts www.tjwa.com

WH2.4-132


Reducing Critical Path Times Per Jumbo

Roll RollLoad Load &&Unload Unload

Splicing Splicing

Per Product

Knife Knife Setup Setup

Web Web Threading Threading

Running Time Per Cut

• • • • •

Accel Accel––Running Running- -Decel Decel Roll Roll Unloading Unloading

Core Core Load Load

Core Core Starts Starts

Stage cores in core boxes. Use second shafts or turret rewind. Use tape clamp bar to hold tails ready for new cores. Use two people for roll unload and core loading. Use cantilevered shafts and roll unload stands.

TJWalker+Associates, Inc., Copyright 2008

www.tjwa.com

WH2.4-133


Why Isnâ&#x20AC;&#x2122;t Your Slitter Running? Your slitter runs narrow, short rolls at high speed, so run time is a small percent of overall time. Your operator spends too much time on non-critical activities. Your operator has to do all critical activities alone. You havenâ&#x20AC;&#x2122;t reduced the time to complete critical path activities.

TJWalker+Associates, Inc., Copyright 2008

www.tjwa.com

WH2.4-134


Other Uses for These Calcs? Forecast slitter process times from order info. Predict costs of slitting new products. Cost justify upgrades to improve productivity or new equipment. Predict benefits (or lack thereof) for increasing slitter speed. Compare actual slitter order times to predicted: â&#x20AC;Śidentify difficult to slit materials â&#x20AC;Ś(or operator improvement opportunities) TJWalker+Associates, Inc., Copyright 2008

www.tjwa.com

WH2.4-135


Slitting Qs

What are alternate slitting methods?

TJWalker+Associates, Inc., Copyright 2008

www.tjwa.com

WH2.4-136


Alternate Slitting Methods Separating processes not included in â&#x20AC;&#x153;conventionalâ&#x20AC;? description.

Waterjet

Lathe

Laser

Ultrasonic

TJWalker+Associates, Inc., Copyright 2008

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WH2.4-137


Waterjet Slitting High pressure water supplied through a ruby nozzle delivers a concentrated a load over a small area, generating high enough stress to fracture the web. Applications: Typically thick, stiff materials. Advantages: No sharpening, debris is transported away, easy to reposition. Disadvantages: Expensive, ragged edge on many materials.

TJWalker+Associates, Inc., Copyright 2008

www.tjwa.com

WH2.4-138


Laser Slitting High energy focused coherent light will burn, melt, or ablate the web. Two general types are CO2 (infrared) and Excimer (UV) gas lasers. Applications: Thinner webs, flexible electronics, perforating, contoured parts. Advantages: No sharpening, easy to reposition or cut nonlinear shapes. Disadvantages: Rate limited by energy, expensive, IR laser may leave edge bead. TJWalker+Associates, Inc., Copyright 2008

www.tjwa.com

WH2.4-139


Lathe Slitting Full width, target length rolls are cut, product and core together, using circular or guillotine blade. (Similar to a core or baloney cutter.) Applications: Rolls with small buildup or low hardness able to deflect away from the blade. Advantages: Width flexibility, good for delicate webs, good product and core alignment, reduced winding and handling. Disadvantages: Limited product applications, may have poor slit edge, may require lubricants. TJWalker+Associates, Inc., Copyright 2008

www.tjwa.com

WH2.4-140


Ultrasonic Slitting High frequency (ultrasonic) vibrations are concentrated using horn and roller geometry to bond or fracture the web. Applications: More common as patterned or spot bonding of laminates. Advantages: Combined slitting and laminating process. Disadvantages: Rate limited by energy, required thermoplastic materials, expensive, may create poor or undesired fused edges. TJWalker+Associates, Inc., Copyright 2008

www.tjwa.com

WH2.4-141


Slitting Qs

What are some interesting slitting related processes?

TJWalker+Associates, Inc., Copyright 2008

www.tjwa.com

WH2.4-142


Slitting-Related Processes Slitting integrated or altered from conventional methods. Delamination / Slit / Re-Lamination Hot Slitting Control Depth Cut Perforate and Tear Stripe Slitting

TJWalker+Associates, Inc., Copyright 2008

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WH2.4-143


Delamination / Slit / Re-Lamination Slitting may be integrated with delamination and re-lamination to provide a peel point for a liner or labelstock.

Delamination

Slit

Re-Lamination

Tension control must keep the two webs elongations in sync to prevent curl or transverse wrinkling. TJWalker+Associates, Inc., Copyright 2008

www.tjwa.com

WH2.4-144


Hot Slitting

Heated slitting blades are typically used to prevent debris buildup. Hot slitting, like IR laser slitting, can separate a web via melting. Hot slitting laminates may create desirable or undesirable edge bonding, similar to ultrasonic slitting. Image courtesy of Dienes Corp. TJWalker+Associates, Inc., Copyright 2008

www.tjwa.com

WH2.4-145


Control Depth Cut A control depth cut does not fracture through the entire thickness of a web or laminate product. Traditionally, score or rotary die has been used for control depth cutting.

TJWalker+Associates, Inc., Copyright 2008

www.tjwa.com

Recently, lasers have gained in popularity, especially for easy tear flexible packaging.

WH2.4-146


MD Perforation Either a perforating score knife or a pulsed laser can perforate a web.

(a.k.a. Pinking Score Knives) TJWalker+Associates, Inc., Copyright 2008

www.tjwa.com

WH2.4-147


MD Perforate and Tear A perforated web can be â&#x20AC;&#x153;slitâ&#x20AC;? by tearing along the perforations (like a postage stamp).

TJWalker+Associates, Inc., Copyright 2008

www.tjwa.com

WH2.4-148


Best Guiding: Slitting The most accurate web positioning method is slitting. Immediately after slitting, the exact web position is known better than any automatic guide can deliver. Any web length between slitting and winding only promotes sidewall error and the need for guiding.

TJWalker+Associates, Inc., Copyright 2008

www.tjwa.com

WH2.4-149


Sidewall Error from Slit-to-Wind Tracking These factors will determine if the post-slit lateral registration is maintained into the winding roll. 1. Neighboring strand contact. There Thereisisanother another 2. Slackness from web bag. set of variables set of variables that 3. Slackness from winding accumulation thatcan canshift shift the theweb webwithin within variation. the thewinding windingroll! roll! 4. Wander from web skew. 5. Web-roller attraction / uneven â&#x20AC;&#x153;peelingâ&#x20AC;?. 6. Tracking from roller or winding roll/core diameter variation. 7. Tracking from roller or winding roll/core alignment. TJWalker+Associates, Inc., Copyright 2008

www.tjwa.com

WH2.4-150

TJWA WH2.4 Slitting  

TJWalker, TJWA Inc. tjwalker@tjwa.com Presentation on Slitting Process Technology April 2008

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