COBEM99

S25 Métodos Numéricos

Title:

VISCOELASTIC EFFECTS OF DEFORMABLE ROLL COVER

Summary :

ROLL COATING IS DISTINGUISHED BY THE USE OF ONE OR MORE GAPS BETWEEN ROTATING CYLINDERS TO METER A CONTINUOUS LIQUID LAYER AND TO APPLY IT TO A FLEXIBLE SUBSTRATE. OF THE TWO ROLLS THAT MAKE A FORWARD-ROLL COATING GAP, ONE IS OFTEN COVERED BY A LAYER OF DEFORMABLE ELASTOMER. LIQUID CARRIED INTO THE GAP DEFORMS THE RESILIENT ROLL COVER. THE COMPLETE UNDERSTANDING OF THE COUPLING BETWEEN THE LIQUID FLOW AND ROLL COVER DEFORMATION IS VITAL TO THE OPTIMIZATION OF THIS WIDELY USED COATING METHOD. EARLIER WORKS ON DEFORMABLE ROLL COATING ANALYZED THE ACTION WITH BOTH ONE-DIMENSIONAL AND PLANE-STRAIN TWO-DIMENSIONAL ELASTIC MODELS OF THE ROLL COVER DEFORMATION. HOWEVER, RUBBER AND RUBBER-LIKE MATERIALS USED AS ROLL COVERS DO NOT BEHAVE PURELY ELASTICALLY. CARVALHO AND SCRIVEN (1996) ANALYZED THE PERFORMANCE OF DEFORMABLE ROLL COATING NIPS BY MEANS OF LUBRICATION APPROXIMATION AND A SET OF INDEPENDENT, RADIALLY ORIENTED VISCOELASTIC ELEMENTS, THE CLASSIC SPRING-DASHPOT COMBINATION FROM LINEAR VISCOELASTICITY THEORY. IN ORDER TO TEST THE ACCURACY OF THIS SIMPLE APPROACH AND TO EVALUATE THE RELATIONSHIP BETWEEN THE EMPIRICAL CONSTANTS USED IN THE MODEL TO THE RELEVANT PHYSICAL PARAMETERS, A COMPLETE, TWO-DIMENSIONAL, VISCOELASTIC MODEL HAS TO BE USED. IN THIS WORK, THE FLOW BETWEEN A RIGID AND A DEFORMABLE ROTATING ROLL WAS EXAMINED BY SOLVING THE COMPLETE NAVIER-STOKES SYSTEM COUPLED WITH A PLANE-STRAIN VISCOELASTIC MODEL OF THE ROLL COVER DEFORMATION. THE STRESS AT EACH LOCATION OF THE ROLL COVER WAS EVALUATED BY AN INTEGRAL OF THE DEFORMATION ALONG THE MATERIAL PATH OF THE POINT BEING ANALYZED. THE MODEL PERMITS MULTIPLE RELAXATION TIME WITHOUT EXTRA COMPUTATIONAL EFFORT. THE EQUATION SYSTEM WAS SOLVED BY THE GALERKIN / FINITE ELEMENT METHOD. RESULTS SHOW HOW THE VISCOELASTIC PROPERTIES OF ROLL COVER AFFECT THE PERFORMANCE OF DEFORMABLE ROLL NIPS. KEY WORDS: ROLL COATING, DEFORMABLE COVER, ELASTOHYDRODYNAMICS, FINITE ELEMENT METHOD.

Author :

Carvalho, Márcio S.

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