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Sylvia Andrieu
Abstract
Experimental and numerical infrared heating of thermoplastic sheet during thermoforming process
Sylvia Andrieu - 25 march 2005
Thermoforming includes a heating stage of thermoplastic sheets
by infrared heaters. The temperature distribution on the surface
and through the thickness of the sheet conditions the eventual
thickness distribution over the thermoformed part. Our objective
is to understand the heat transfers between the infrared heaters
and the thermoplastic sheets.
For that we developed an infrared heating device which makes
possible to carry out temperature measurements of a sheet during
the heating with an infrared oven. An AGEMA 880 LW infrared
camera allows measuring the back surface (non-directly exposed
to the radiation) temperature distribution of the sheet. An
indication of temperature discrepancy through the thickness is
given by a RAYTEK Thermalert TX pyrometer, measuring the
temperature on a local area of the sheet front side. Two types
of infrared ovens (halogen lamps and ceramics heaters)
representative of two typical infrared bandwidths (short and
long wave-infrared respectively), were studied on a polymer
widely used on the thermoforming market (white PS 3mm-thickness
sheets).
These experimental measurements allow validating the numerical
models. A method of radiative transfer based on ray tracing is
indeed used to simulate the irradiance with heater
reflectors. The Rosseland approximation is introduced to take
into account the optical properties of the polymers that were
measured using infrared spectrometry. The transient heat balance
equation (including 3D radiative diffusion) is solved.
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