best practices for web handling in & out of corona treaters

Presented by

Enercon Industries Corporation

Best Practices for Web Handling In & Out

of Corona Treaters

Enercon Technical Forum Series

Presentation Agenda Types of Problematic Thin Films

Understanding the Tensile Stress-Strain Relationship

Web Handling Issues Through Corona Treaters Wrinkling/Puckering EffectsBackside TreatmentWeb “Drag”

Troubleshooting Recommendations Low friction RollsNip RollRoll Drive Spreader Rolls Process Speeds

© Enercon Industries 2013

Types of Problematic Thin Films


All polymer films driven by mechanical instabilitywhen stress exceeds a critical value.

Highly elastic, thin films

Typical Modulus of Elasticity for Films:

Flexible PVC 350-560 kg/cm2 5-8 kpsi LDPE 1000-1800 kg/cm2 15-25 kpsi LLDPE 1400-2100 kg/cm2 20-30 kpsi BOPP 7700-24000 kg/cm2 110-350 kpsi OPET 35000-42000 kg/cm2 500-600 kpsi

Source: Nitto Denko

Treater Lamination Rewind Unwind Coater

Dryer

Film

Treater

Source: Nitto Denko


Treater Lamination Rewind Unwind Coater

Dryer

Film

Treater

Maximum Web Tension – 60 in. wide, 2 mil. LDPE Film

Must calculate tension-to-stress to 1.5% of elastic modulus

Ave. modulus of 20 kpsi for LDPE: 1.5%x 20,000psi = 300psi Cross-sectional area = 60 in. x 0.002 in. = 0.12 sq. in.

Max. web tension = 300 psi x 0.12 sq. in. = 36 lbs.

Understanding the

Tensile Stress-Strain Relationship


Films are subjected to dynamic tension

Mechanical behavior of most films depends strongly on the “strainrate” (rate of film deformation relative to time).

Tension that exceeds the strength of the film damages it at load celland non-load cell locations.

Every roller on a line will alter web tension - Increasing web tension accelerates roller rotation. Drive will relieve a web’s tension

Drag inertia

Drive Web tension changes as webs traverse over rolls


Roller Drag – Idler rolls, Ground rolls, Nip rolls

Opposes motion, increasing web tension Rolls move air, affected by air resistance Rolls in nip - rolling resistance hysteresis Driven rolls – drive transmission losses at belts, bearings, etc.

Inertial Tension – Torque that accelerates/decelerates rolls

“Mass Moment of Inertia” of rolls determined primarily bymachine width

Web tension build-up to accelerate idler rolls (accelerationvariations from 1 ft/min/s to 300 ft/min/s)

Tension Tension + ∆ Tension

Tension + 2 ∆ Tension





Web Handling Issues Through

Corona Treaters

Web Handling Issues Through Corona Treaters Wrinkling/Puckering Effects

Most common and costly web defect with primarilylightweight materials, wider webs.

Improper web management can cause treatmentvariation.

Gauge control and managing static are also keyapproaches to wrinkling


Compressive Buckling Amount of compression a web can withstand determined primarily by caliper3

Reason why wrinkles are common for webs < 10 mil. Adding CD compression to web tension = wrinkles in the MD

Adding shear stress to web tension = angled wrinkles

Misalignment of rolls


Constrained Expansion

Thermal expansion effect with polymer film or foil

Hygroscopic expansion with paper webs

Drop in line tension

Excessive roll/roller deflection Keep < 0.015% of roll width Slenderness ratio (length/diameter)

10-15 if nipped 15-20 if un-nipped

MD


Other Causes of Diagonal Web Wrinkles

Caliper (gauge band) variation Non-uniform nip pressure on deformed roll Baggy web Material skew Non-uniform tension Web slippage over rollface

CD Wrinkles

Air entrapment (type of nip, web permeability,caliper, web width, speed)

Web Handling Issues Through Corona Treaters Backside Treatment

Web Handling Issues Through Corona Treaters Web Drag

Thermal Effects Hot web will conductively heat up the roller shell.

Creates axial load against locked bearing collars.

Oxidation Effects Oxidation degrades bearing performance.

Moving web will entrain ozone gases not removed fromcorona treaters.

High Wrap, Cantilevered Rollers Torsional load from cantilevered shaft’s deflections mayincrease bearing load, wear rate.

Troubleshooting Recommendations Low Friction Rolls

Designed for reduced weight and high critical speed

Key Advantages for Corona Treating Reduced mass moment of inertia by up to 80% Less web drag, wrinkling Reduce vibration Less roll deflection, web bagginess Easier roll acceleration Less bearing wear, web drag More accurate transducer measurements.

Troubleshooting Recommendations Nip Rolls

High speed webs - boundary layers of air can cause web

float over treater ground roll

Air ionizes in gap, producing a corona and backside treat.

Adding a nip roll breaks-up any boundary layer air,squeezed out entrapped air without high nip pressure.

Types include Hypalon, Nitrile rubber, Ethylene PropyleneDiene Monomer (EPDM), Silicone, Polychloroprene andPolyurethane.

60 durometer Hypalon preferred Ozone-resistance Heat resistance to 140 °C

Troubleshooting Recommendations Nip Rolls

Position of nip roll to ground roll critical to web tension and uniform treatment.

Ground roll Nip Roll

Ground roll web wrap below the nip


Ground roll web wrap above the nip


Opening nip affects line load cells

Load cell

Wrong Right

Troubleshooting Recommendations Spreader Rolls

Key to avoiding wrinkles coming into treater

Bowed Rollers Very aggressive, high frictionCan cause web stretching/distortion in many webs.

Expanding Surface Rollers High friction; polymer band designCan require separate drive

Rubber Spreader Rollers Outward-spiraling grooves with angled soft polymerAs web exits roll, compression force goes to zero and the rubberlands go back to where they started.

Reverse Taper Rollers Larger diameter at the outer edges and smaller diameter at rollcenterline. Creates surface speed differential at each roll diameter, resultingin the material climbing outward toward the larger diameter edges of the roll.

Troubleshooting Recommendations Process Speeds

High speed webs coming into corona treaters can introduce entrained air, CD wrinkles, backside treatment. Integrate incoming nip roll to treater Install spreader roll prior to treater Calculate material tension-to-stress, max web tension Maximize web wrap angle to ground roll

Slow Speed High Speed

Treater Ground Roll

Treater Ground Roll

Contact Area

Contact Area

……………………………………..

……………………………………..

Boundary Air Boundary Air

Contamination Contamination

Problems Attributed to Station Cleanliness

Dirty ground roll surface Back side treatment Variations in web treat levels

Reduced flow of cooling air Over heating of electrodes

Residue Accumulation Arcing

Ceramic Electrodes & Ground Rolls

Tough Stains 3M Scotch-Brite Pad with Household ceramic

cleaner Wash, rinse, wipe surface with alcohol

Presented by

Enercon Industries Corporation

Best Practices for Web Handling In & Out

of Corona Treaters

Enercon Technical Forum Series

"Certain information contained in this presentation reflects the Company's assessment of possible results and is dependent upon many factors over which the Company has no control. Nothing in this presentation shall constitute a warranty regarding any product. The only warranties granted by the Company are contained in the Company's terms and conditions of sale, which shall constitute the entire agreement between the Company and any buyer of Company products. Nothing contained in this presentation that is not contained in the Company's terms and conditions of sale shall be valid or binding with respect to any sale of products."

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best practices for web handling in & out of corona treaters

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