Infrared and Its Application For Drying Coatings On Webs

AIMCAL FALL TECHNICAL CONFERENCE2005

By: Bob NarangRadiant Energy Systems, Inc.

www.radiantenergy.com

Water or solvent based wet coatings applied on webs,are generally dried using three technologies:

1. Convection – such as a hot airimpingement or flotation dryer

2. Conduction –oil or steam heated drums

Heated Drum

Web Path

3. Infrared or Radiant Heating

IR Emitter

Web Path

Electric/Gas Infrared Heating System

Typical Conduction Heating System

Exhaust Air Plenum

Web Path

Recirc/ Exhaust

Heated Supply Air

Direct Impingement Convection Dryer

•• Theory of InfraredTheory of Infrared

•• Different types of infrared heatersDifferent types of infrared heaters

•• ApplicationsApplications

•• Advantages and LimitationsAdvantages and Limitations

•• AcknowledgementsAcknowledgements

Infrared Drying

Theory of InfraredTheory of Infrared

Electromagnetic Spectrum showing varioustypes of energy based on wavelength

Infrared SpectrumInfrared Spectrum

The Infrared spectrum can beThe Infrared spectrum can bedivided into three divided into three

categories:categories:1. Short Wave Length2. Medium Wave Length3. Long Wave Length

3 Basic Laws of Radiation3 Basic Laws of RadiationWienWien’’s Laws Law

The peak wave length of The peak wave length of emission of an infrared heater emission of an infrared heater can be calculated by Wiencan be calculated by Wien’’s Laws Law

λ = C/T

λ – wavelength in microns

C - Constant 2898

T - Source temperature (ºK)

Stefan Boltzman LawStefan Boltzman Law

W = kTW = kT44

W – Emitted Power

k - Constant

T – Source temperature (°K)

PlanckPlanck’’s Laws Law

Spectral Characteristics of InfraredSpectral Characteristics of Infrared

-- Absorbed by the object (A)Absorbed by the object (A)

-- Reflected by the object (R) Reflected by the object (R)

-- Transmitted through the Transmitted through the object (T) object (T)

A + R + T = 100% of A + R + T = 100% of energy received.energy received.

Absorption Curves for Different ProductsAbsorption Curves for Different Products

Types of HeatersTypes of Heaters

Short Wavelength Quartz Tube Short Wavelength Quartz Tube Emitter (TEmitter (T--3 lamp)3 lamp)

Medium Wavelength Quartz Tube Emitters

Medium Wavelength Stamped Foil Type Heaters

Types of HeatersTypes of Heaters

Long Wavelength Infrared Long Wavelength Infrared HeatersHeaters

Gas Fired Infrared Heaters

ApplicationsApplications

Infrared Air & Hot Air Dryeron a Coating Line

Infrared Air Pre-dryer

Advantages of Infrared DryersAdvantages of Infrared Dryers

§§ High efficiency conversion of electrical energy into heat for High efficiency conversion of electrical energy into heat for electrical IRelectrical IR

§§ Higher rate of heat transferHigher rate of heat transfer§§ Floor space savings due to smaller sizeFloor space savings due to smaller size§§ Heats only the object without heating the surroundingsHeats only the object without heating the surroundings§§ Easy to zone for uniform heating of the productEasy to zone for uniform heating of the product§§ Faster response to changing process conditionsFaster response to changing process conditions§§ Quick start up and shut downQuick start up and shut down§§ Easy to have cut off zones for narrow widthsEasy to have cut off zones for narrow widths§§ Ease of controlEase of control§§ Lower capital and installation cost Lower capital and installation cost §§ Can be easily be added to existing conventional dryers to Can be easily be added to existing conventional dryers to

increase line speedincrease line speed§§ Infrared Air dryers suitable for solvent based coatingsInfrared Air dryers suitable for solvent based coatings

Limitations of Infrared DryersLimitations of Infrared Dryers

§§ Some coatings may not be able to take advantage Some coatings may not be able to take advantage of of higher rates of heat transfer and may skin and higher rates of heat transfer and may skin and blisterblister

§§ Difficult to work with temperature sensitive Difficult to work with temperature sensitive substrates substrates

§§ Scaling up of the heaters is not always Scaling up of the heaters is not always straightforwardstraightforward

§§ Since IR is basically a surface phenomenon, Since IR is basically a surface phenomenon, harder to harder to dry heavier coatingsdry heavier coatings

§§ Almost essential to run trials in lab or on the pilot Almost essential to run trials in lab or on the pilot line toline to

confirm designconfirm design

AcknowledgementsAcknowledgements

§§ Infrared Process Heating Handbook by Industrial Infrared Process Heating Handbook by Industrial Heating Equipment AssociationHeating Equipment Association

§§ Handbook of Industrial Drying by Arun MujumdarHandbook of Industrial Drying by Arun Mujumdar

§§ Watlow IR HandbookWatlow IR Handbook

§§ Phillips Lighting HandbookPhillips Lighting Handbook

§§ Litex Infrared Lamps Litex Infrared Lamps

§§ Electric Process Heating by Maurice OrfeuilElectric Process Heating by Maurice Orfeuil

§§ Hydro QuebecHydro Quebec

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