Heat Transfer in Polymers Martin Rides, Angela Dawson 6 October 2004
Heat Transfer in Polymers - summary Introduction Heat Transfer Coefficient Thermal Conductivity Industrial Demonstrations NPL s Polymer Processing Website Summary
Aim of the project To help companies measure and model heat transfer in polymer processing This should lead to: Higher productivity (faster processing) Energy saving Fewer failures in service Related project : AIMTECH
Eureka Project: AIMTECH An associated Eureka project (AIMTECH) is progressing Its aim is to improve productivity of injection moulding Main focus is on the moulds - reduce cycle times by using copper alloy moulds in injection moulding NPL Role Measurement of the thermal conductivity of polymer melts (T,P) Understanding the role of the mould/melt interface: Modelling heat transfer and the effect of uncertainties Six UK companies involved 25k co-funding contribution Close fit with the DTI project
Tasks in the DTI Project Heat Transfer Coefficient New facility Thermal Conductivity Uncertainty analysis Extension of method to new materials Simulation To identify the important data To help design equipment Moldflow & NPL s own software Industrial Demonstrations Zotefoams Corus Dissemination Web site, IAGs, PAA Newsletter articles, trade press articles, measurement notes, scientific paper
Heat Transfer Coefficient It is the heat flux per unit area (q) across an interface from one material of temperature T 1 to another material of temperature T 2 : h = q/(t 1 T 2 ) units: Wm -2 K -1 Boundary condition for process simulation In injection moulding & compression moulding Polymer to metal In extrusion & film blowing Polymer to fluid (eg air or water) This project will build apparatus to measure heat transfer coefficient and investigate the significance of different interfaces to commercial processing
Heat Transfer Coefficient (heat transfer across an interface) Features of apparatus being developed Room temperature to 275 C, pressure to at least 500 bar Polymer samples 2 to 25 mm thick Interchangeable top plate to investigate Different surface finishes Effect of mould release agents Option to introduce a gap between polymer & top plate Shrinkage, sink marks Instrumented with thermocouples, fibre optics, heat flux sensors and calorimeter
Heat transfer apparatus Side view cold plate sample hot plate
Heat transfer apparatus fibre optic thermocouple port displacement transducer heater element PTFE seal mould face air gap sample thermocouple ports outer guard ring cooling pipes thermocouples heat flux sensors pressure transducer port
Modelling of key features Effect of vertical thermocouple on distort the temperature field Effect of an air gap
Effect of a thermocouple TherMOL 1.0 Mould at 50 C Polymer at 250 C
Simulation of Heat Transfer with Fibre Optic (left) & Thermocouple (right)
Comparison of thermocouple & fibre optic 50 C 250 C
Air Gap Mould at 50 C with air gap of 0, 0.5 & 1 mm Polymer at 250 C
Pipe T piece and 80 mm diameter disc models
Effect of uncertainties in HTC
Effect of uncertainties in HTC The Effects of Mould-Melt Heat Transfer Coefficient Upon T f Predictions For The 5 mm Thick Disc Model 55 54 Minimum Value Time to Freeze Part, s 53 52 1/10 Default Value x10 51 50 10 100 1000 10000 100000 1000000 Heat Transfer Coefficient, W/(m 2 C)
Effect of uncertainties in HTC The Effect Of Mould-Melt Heat Transfer Coefficient Upon Time To Freeze Part For Discs Of Different Thickness 14 Percentage Variation In Time To Freeze Part From The Standard Simulation Result For The Given Disc Thickness, % 12 10 8 6 4 2 0 Default Mould-Melt Heat Transfer Coefficient Minimum Mould-Melt Heat Transfer Coefficient 1/10 Of Default Mould-Melt Heat Transfer Coefficient *10 Default Mould-Melt Heat Transfer Coefficient -2 0 5 10 15 20 25 30 Disc Thickness, mm
NPL Report DEPC-MPR 001 The Effect of Uncertainty in Heat Transfer Data on The Simulation of Polymer Processing J. M. Urquhart and C. S. Brown http://libsvr.npl.co.uk/npl_web/search.htm
Heat Transfer Coefficient Summary Investigate effect of: Different surface finishes/mould materials Mould release agents Air gap between polymer & top plate Shrinkage, sink marks
THERMAL CONDUCTIVITY MEASUREMENT Angela Dawson
Thermal Conductivity Line source probe apparatus Measures at temperature and pressure conditions found in industrial polymer processing Sample Heater bands Thermal conductivity probe Measurement cylinder Guiding bar Lower Piston Distance holder
Uncertainty Budget For NPL Line-Source Thermal Conductivity Probe (Atmospheric Pressure) Type A Repeatability Reproducibility Type B Non- uniformity of Value ± % 15.6@ 2 std de vs 13.6@ 2 std de vs Probability Distribution Divisor C i Uncertainty Contribution ± % Uncertainty Squared ±% Normal 2 1 7.815 @ 1 std dev 61.07 89 Normal 2 1 6.801 @ 1 std dev 46.25 89 0.002 Rectangular 1.73 1 0.00116 1.34E-06 heat input Non-uniformity of 0.0 Rectangular 1.73 1 0.000 0.000 temperature Sample height 0.0 Rectangular 1.73 1 0.000 0.000 Time 0.0 Normal 1 1 0.000 0.000 Calculation of Uncertainty Sum of squares 107.3 % Square root of 10.4 % sum of squares Multiplication by ±20.7% k= 2 for 95% Fin al confidence level Uncertainty Value V i or V eff
Thermal Conductivity of PDMS (Atmospheric Pressure)
Thermal Conductivity of HDPE (Atmospheric Pressure)
Thermal Conductivity of HDPE (Atmospheric and 1000 bar Pressures) 0.50 0.45 0.40 Repeatability (95% confidence level) of thermal conductivity test data for one operator testing HDPE HCE000 from 170 C to 50 C at 1000 bar pressure (green) and at ambient pressure (blue) Thermal Conductivity, W/mK 0.35 0.30 0.25 0.20 0.15 1000 bar repeatability 8% ambient pressure repeatability 16% 0.10 40 60 80 100 120 140 160 180 Temperature, C
Thermal Conductivity Uncertainty Analysis Summary Picking data from literature expect uncertainty value +/- 50% Measurement of a typical thermoplastic at atmospheric pressure - total uncertainty value +/- 20.7% Measurement of a typical low viscosity polymer +/- 1.4% (repeatability) Measurement of a typical thermoplastic at atmospheric pressure expect +/- 16% (repeatability) Measurement of a typical thermoplastic at 1000 bar +/- 8% (repeatability) Conclusion: Can improve on +/- 20.7% total uncertainty value Action: Incorporate +/- 8% repeatability value into uncertainty budget Investigate repeatability contribution at elevated pressure and incorporate result uncertainty budget What is the commercial significance of this? Illustrated by Moldflow simulation
Moldflow model of HDPE Pipe T-piece
Changes In Cooling Times With Increasing Thermal Conductivity Values For T- Piece From Moldflow Simulation
Thermal Conductivity Extending the scope of the measurement (at least six) Nanoclay filled PPs 3 Rubber toughened PMMA 3 Rubber samples (Avon) softness project link 3 HDPE (Durapipe grade) used for uncertainty analysis 1 HDPE powder (rotational moulding grade) 1 Thermosets (Railko polyesters) 2 Glass filled nylon 1 PC 1 PS 1 ABS 1 Total 13 + 4 = 17
Nano-materials Thermal Conductivity (200 bar) Thermal Conductivity, W/mK 0.55 0.50 0.45 0.40 0.35 0.30 0.25 0.20 Comparison of thermal conductivity behaviour on cooling of virgin polypropylene (AAATJ000) with two polymer nanocomposites (AAATJ001 and AAATJ002) at 200 bar pressure AAATJ000 200bar AAATJ001 200bar AAATJ002 200bar 0 50 100 150 200 250 Temperature, C
Nano-materials Thermal Conductivity (800 bar) Thermal Conductivity, W/mK 0.55 0.50 0.45 0.40 0.35 0.30 0.25 Comparison of thermal conductivity behaviour on cooling of virgin polypropylene (AAATJ000) with two polymer nanocomposites (AAATJ001 and AAATJ002) at 800 bar pressure AAATJ000 800bar AAATJ002 800bar AAATJ001 800bar 0.20 0 50 100 150 200 250 Temperature, C
Nano-materials Thermal Conductivity (1200 bar) Thermal Conductivity, W/mK 0.55 0.50 0.45 0.40 0.35 0.30 0.25 Comparison of thermal conductivity behaviour on cooling of virgin polypropylene (AAATJ000) with two polymer nanocomposites (AAATJ001 and AAATJ002) at 1200 bar pressure AAATJ000 1200bar AAATJ001 1200bar AAATJ002 1200bar 0.20 0 50 100 150 200 250 Temperature, C
Summary of Thermal Conductivity Study of Nano-clay Filled Polypropylene Can measure thermal conductivity of polymer nanocomposites at range of temperatures and pressures Addition of nano-clay filler to polypropylene increases the crystallisation temperature of the polymer Addition of nano-clay filler to polypropylene can increase the thermal conductivity of the polymer across the processing range of temperatures New area of work would be to look at addition of nanoclays to range of polymers to determine effects of nanoclays on thermal conductivity and other physical properties of polymers
Thermal Conductivity of Rubber Thermal Conductivity, W/mK 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05 0.00 thermal conductivity of AAATH000 rubber powder on heating and cooling from 50 C to 250 C at atmospheric pressure 0 50 100 150 200 250 300 Temperature, C 300304 AAATH000 1bar heating 300304 AAATH000 1bar cooling 310304 AAATH000 200 bar heating 310304 AAATH000 200 bar cooling
Thermal Conductivity of PMMA Thermal Conductivity, W/m K 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05 0.00 thermal conductivity of AAATH001 PMMA bead polymer on heating and cooling from 50 C to 250 C at atmospheric pressure 310304 AAATH001 200bar heating 310304 AAATH001 200bar cooling 010404 AAATH001 1bar heating 010404 AAATH001 1bar cooling 0 50 100 150 200 250 300 Temperature, C
Thermal Conductivity of Rubber/PMMA Compound Thermal Conductivity, W/m K 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05 0.00 thermal conductivity of AAATH002 rubber/pmma granular compound on heating and cooling from 50 C to 250 C at atmospheric pressure 010404 AAATH002 1bar heating 010404 AAATH002 1bar cooling 300404 AAATH002 200bar heating 300404 AAATH002 200bar cooling 0 50 100 150 200 250 300 Temperature, C
Summary of Thermal Conductivity Study on Rubber, PMMA and Rubber/PMMA Compound Thermal conductivity measurements on powders, beads and granules are possible at range of temperatures and pressures Thermal conductivity measurements at atmospheric pressure depend on compaction of sample best results achieved with powder sample Thermal conductivity measurements of rubber samples can be made in the pre-crosslinked powder form (atmospheric pressure) and after crosslinking (200 bar)
Effect of Pressure on PP Thermal Conductivity 0.35 0.33 0.31 Thermal conductivity of polypropylene (AAATK004) on cooling from 250 C to 50 C at pressures of 200, 800 and 1200 bar Thermal Conductivity, W/mK 0.29 0.27 0.25 0.23 0.21 0.19 0.17 0.15 200 bar 800 bar 1200 bar 0 50 100 150 200 250 300 Temperature, C
Effect of Pressure on PE Thermal Conductivity Thermal conductivity, W/mK 0.45 0.40 0.35 0.30 0.25 0.20 Thermal conductivity of polyethylene (AAATK005) on cooling from 250 C to 50 C at pressures of 200, 800 and 1200 bar 200 bar 800 bar 1200 bar 0.15 0 50 100 150 200 250 300 Temperature, C
Effect of Pressure on PC Thermal Conductivity Thermal Conductivity, W/mK 0.55 0.50 0.45 0.40 0.35 0.30 0.25 0.20 Thermal conductivity of polycarbonate (AAATK001) on cooling from 200 C to 50 C at pressures of 200 and 800 bar 200 bar 800 bar 0 50 100 150 200 250 Temperature, C
Effect of Pressure on PS Thermal Conductivity 0.35 0.33 0.31 Thermal conductivity of polystyrene (AAATK002) on cooling from 250 C to 50 C at pressures of 200, 800 and 1200 bar Thermal conductivity, W/mK 0.29 0.27 0.25 0.23 0.21 0.19 0.17 0.15 200 bar 800 bar 1200 bar 0 50 100 150 200 250 300 Temperature, C
Summary of Pressure Effects on Thermal Conductivity of Polymers Increase in thermal conductivity with increase in pressure across temperature range for all crystalline and amorphous polymers Increase in crystallisation temperature with increase in pressure for crystalline polymers (PP and PE) Decrease in thermal conductivity with cooling for amorphous polymers (PS and PC) across temperature range Step increase in thermal conductivity with cooling for crystalline polymers (PP and PE) across temperature range
INDUSTRIAL TRIALS Corus & Zotefoams
Industrial Demonstrations Aim is to demonstrate practical benefits of heat transfer measurements and modelling Corus Thermal conductivity of plastisol coated steel before and after solidification Zotefoams Heat transfer during cooling of polyolefin foam
Corus Use DSC method to measure thermal conductivity of bilayer Plastisol/steel Measure before and after solidification Data useful in predicting optimum line speeds Earlier work had shown that the polymer layer was significant in terms of heat transfer
DSC method for thermal conductivity DSC pan Indium or eutectic Mulitlayer sample
DSC method for thermal conductivity 65 Heat Transfer for sapphire 60 K x mx = Ki mi 2 h h x i (Khanna et al (1988)) Heat Flow (mw) 55 50 45 145 150 155 160 165 170 175 Temperature ( C)
Zotefoams Model heat transfer Measure (T, heat flux) over time Model/measure shrinkage Calculate internal stresses Use bending theory to predict curvature
Zotefoams Key Air Flow Steel or aluminium plate u amb m& h plate h gap Foam h foam h plate L width = W
Stress relaxation of a two layer section after cutting L set Cut foam layers from foam sheets Layer 1 Layer 2 cut cut L set L top Release of stresses at the free surfaces Layer 1 Layer 2 h strip L bottom L top Onset of bending Layer 1 Layer 2 L bottom
Thermal Conductivity Standards ISO TC61 SC5 WG8 Thermal Properties Thermal conductivity and diffusivity: General Principles - New Work Item Proposal (NWIP) prepared Hot Wire Techniques: Hot Wire (S. HEYEZ, Belgium) (ISO 8894) Line Source (H. LOBO, USA) (D 5930 ASTM) Hot Disk (S. GUSTAFSSON, Sweden) - NWIP prepared Wave and Pulse methods: Temperature Wave Analysis (J. MORIKAWA, Japan) - NWIP prepared Laser Flash (B. HAY, France) (ISO 18755) Steady State methods: Guarded Hot Plate (G. SIMS, UK) (ISO 8302) cross referenced Guarded Heat Flux (G. SIMS, UK) (ISO 8301/E 1530 ASTM) cross referenced Temperature Modulated DSC (in DSC ISO 11357 series)
Polymer Processing Website http://www.npl.co.uk/npl/cmmt/polyproc/
http://www.npl.co.uk/npl/cmmt/polyproc/
http://www.npl.co.uk/npl/cmmt/polyproc/
http://www.npl.co.uk/npl/cmmt/polyproc/
http://www.npl.co.uk/npl/cmmt/polyproc/
The next 6 months Commission and commence trials on heat transfer coefficient equipment Continue to extend thermal conductivity measurement procedures to new types of material thermosets, rubbers, powders, nano-materials, glass filled scientific paper Industrial demonstrations (Corus / Zotefoams) to complete/continue
Deliverable extensions Heat transfer coefficient apparatus M2/d2 Delivery of equipment: Jan 05 M3/d1 & d2 Test procedure and commissioning: March 05 Thermal conductivity measurement M6/d3 Scientific paper: November 04
Summary Heat Transfer Heat transfer coefficient apparatus designed and now being manufactured Assisted by modelling studies Effect of uncertainties investigated (report available) Melt thermal conductivity Nano-fillers Powders/granules Effect of uncertainties investigated (report available) Standards active New website - IAG members facility http://www.npl.co.uk/npl/cmmt/polyproc