SIMULATION OF ROTATIONAL MOLDING. Abbas TCHARKHTCHI

Transcription

1 SIMULATION OF ROTATIONAL MOLDING Abbas TCHARKHTCHI

2 INTRODUCTION Non-reactive rotational molding Reactive rotational molding

3 NON-REACTIVE ROTATIONAL MOLDING There are not any chemical reactions during rotomolding. The transformation is based essentially on physical state changes The polymer is as powder ( µm) heating cooling Solid molten Solid state Eamples: thermoplastics (PE, PP, PA, PC, )

4 REACTIVE ROTATIONAL MOLDING There are chemical reaction during this processing. Liquid Chemical reactions Solid or heating chemical reactions Solid liquid Solid Eamples: Thermosets, rubbers, polymerization of certain polymers (PA6) chemical modification of certain polymers,

5 DIFFERENT STEPS OF SIMULATION Reactive rotational molding - Chemical reactions (crosslinking, polymerization) - Rheology - Flow of liquid miture Non-reactive rotational molding - flow of particles (powder)? -Sintering - Melting - Rheology - Flow of melted (viscous) polymer - Solidification (crystallization) Heat transfer

6 CYCLE TIME T ( C) C D B A E F I II III IV V time (min) solid Molten polymer solid solid+molten polymer solid+molten polymer

7 HEAT TRANSFER

8 HEAT TRANSFER Heating Oven mold Polymer molten+solid air + powder 1. Convection air of oven / metallic surface of the mold 2. Conduction in the thickness of the mold 3. Transmission mold / polymer 4. Conduction in the thickness of the molten polymer layer 5. Convection polymer / miture of air and powder

9 1 - Convection air of oven / metallic surface of the mold 2 - Conduction in the thickness of the mold 3 - Transmission mold / polymer 4 - Conduction in the thickness of the molten polymer layer 5 - Convection polymer / miture of air and powder HEAT TRANSFER HEAT TRANSFER ( ) T T h T k ov m ov m = / = ρ T k t T C m pm m = + T k H t T C P PP ρ P = T k T k p m ( ) T T h T k pa pa p =

10 RESULTS Evolutions de Ta pour les trois conditions opératoires choisies. Comparaison des courbes epérimentales et numériques (Tfour = 300 C, tchauffe = 20, 25 et 30 min).

11 REACTIVE ROTATIONAL MOLDING

12 REACTIVE ROTATIONAL MOLDING Rheochemistry and rheokinetic of thermosets during rotational molding Chemistry Rheology Fluid Mechanic - Cross-linking mechanism - Kinetic models - Evolution of viscosity - Rhelogical models - Fluid flow models - Finite elements and SPH Heat transfer Eperimental methods, DSC, IR spectrophotometry, Rheometry

13 REACTIVE ROTATIONAL MOLDING Cross-linking reaction [ E ] d dt 2 ( 1 ) k ' + k ([ OH ] + [ E ] ) ( " + k [ ]) = [ E ] 0[ A] HX ,9 450 tau de conversion 130 C 0,8 400 tau de conversion 140 C Rheology η η 0 = * * A+ Bα tau de conversion 0,7 0,6 0,5 0,4 0,3 0,2 0, Viscosité Pa.s tau de conversion 140 C Tau de conversion therorique point de gel à 150 C Point de gel à 140 C Point de gel à 130 C viscosité à 130 C 1Hz viscositéà 140 C 1Hz Viscosité à 150 C 1Hz temps /min

14 SIMULATION (SPH METHOD) SPH is a Lagragian method for simulation of fluid flow. In this method the material at macroscopic scale is considered as a group of particles of masse mi, rate vi avec other properties like pressure, pi, temperature, Ti, internal energy Ui, entropy Si, Central function Smoothing length Conservation of quantity of mouvement Conservation of energy Equation of state Density Schema of integration

15 SIMULATION OF FLUID FLOW A cylinrical mold turning aroude its principal ais

16 SIMULATION OF FLUID FLOW A part with more comple geometry

17 SIMULATION OF FLUID FLOW Cubic mold in rotomolding condition

18 NON-REACTIVE ROTATIONAL MOLDING

19 FORMATION OF DIFFERENT LAYERS Melting + Coalescence Layer by Layer Particle (polymer) Molten Polymer moule moule 1st layer 2nd layer moule 3th layer moule 4th layer

20 FORMATION OF THE FIRST LAYER The following schema shows the mechanism of melting of a particle and its adhesion on the internal surface of the mold. mg Surface mg mg Of the mold The particles fall on the bottom of the mold, will be melted progressively and spread on the internal surface. This spreading depends on the force of gravity and the surface tension.

21 FORMATION OF THE FIRST LAYER γ F mg mg The shear force induced by the weight of particle assures the adhesion between melted particle and the surface of the mold. On the superior part of the mold, the surface tension spreads the melted polymer on the surface

22 NON-REACTIVE ROTATIONAL MOLDING - Flow of particles (powder)? -Sintering (coalescence + densification) support Polymer 1 2 X 1 2 and Different steps of coalescence de grains 1) initial state 2 and 3) growth 4) final state t

23 DIFFERENT MODELS DIFFERENT MODELS - Frenkel Coalescence of 2 particules r t r η γ = ( ) t T K r n = , - Kuckzynski 2 1/ 0 = a t a X η γ - Eshely t e r t η λ = τ Lontz

24 Eample: PVDF - Under optical microscope T = ambiante t = 80 s T = 172,8 C t = 100 s t = 20 s t = 120 s t = 40 s t = 140 s t = 60 s t =160 s

25 Eample: PVDF 1 2 3

26 NON-REACTIVE ROTATIONAL MOLDING - Melting - Rheology - Flow of molten (viscous) polymer - Solidification (crystallization)

27 CONCLUSION Reactive rotational molding Reactive rotational molding Chemical reactions Kinetic model Heat transfer T=f(t) Rheology η=f(t) η=f() X: degree of conversion fluid flow model

28 CONCLUSION Non-reactive rotational molding Non-reactive rotational molding Coalescence Kinetic model Heat transfer T=f(t) Melting X: degree of conversion Densification Formation of layers fluid flow model Rheology Cooling Solidification crystallization