Y. Le Maoult

Modelling of infrared heating of thermoplastic sheet used in thermoforming process

Thermoforming consists of warming a plastic sheet and forming it into a cavity or over a tool using vacuum, air pressure and mechanical means. The process begins by heating a thermoplastic sheet slightly above the glass transition temperature, for amorphous polymers, or slightly below the melting point, for semi-crystalline materials. As the final thickness distribution of the part is drastically controlled by the initial temperature distribution inside the sheet, it is very important to optimise the heating stage. In most of the thermoforming machine, this step is performed using an infrared oven constituted of long waves infrared emitters. The goal of this study is to determine the efficiency of short waves infrared emitters (halogen lamps) for the heating step. The infrared heating of thermoplastic sheets will be modelled following two steps: an experimental set-up developed in our laboratory permits to measure the influence of parameters such as heaters temperature, incidence of the radiation, heat transfer coefficient, etc. An 880 LW AGEMA infrared camera is used to evaluate the surface distribution of the transmitted heat flux by measuring the temperature distribution on the surface of the thermoplastic sheet. In addition, a numerical model using control volume method (software called PLASTIRAD) has been developed to simulate the heating stage. In particular, it takes into account the spectral properties of both heaters and plastic sheet as well as the heaters directivity. Comparisons between experimental data and numerical simulations allow validating the numerical model using different types of emitters and polystyrene (PS).

Experimental study and numerical simulation of preform or sheet exposed to infrared radiative heating

Thermoplastic processing like the injection stretch blow moulding and thermoforming processes provide the heating stage with infrared oven. This is a critical stage of the process, as the final part thickness is strongly dependent on the preform or sheet temperature distribution prior to forming. Optimisation of the infrared oven is therefore necessary. Experiments have been conducted in order to characterise the heat source of the infrared emitter and the interaction between the heaters and a semi-transparent PET sheet. An 880 LW AGEMA infrared camera has been used to determine the surface distribution of the transmitted heat flux by measuring the temperature distribution on the surface of the thermoplastic sheet. In addition, numerical simulations of the temperature distribution using control-volume method have been carried out and compared with experimental data.

Measurement Of Thermal Contact Resistance Between The Mold And The Polymer For The Stretch‐blow Molding Process

In the stretch‐blow molding process, the heat transfer between the polymer and the mold is of prime interest. Although the time of contact is very short (typically around 0.5 s), the heat transfer affects the mechanical properties of the bottle, and the quality of final parts. In order to model heat transfers at the interface, a classical approach — generally adopted in numerical softwares — is to impose the heat flux density boundary condition thanks to a parameter called Thermal Contact Resistance (TCR). This paper focuses on describing the experimental method developed in order to measure evolution of this thermal parameter (TCR) versus time, as well as results obtained on the CROMeP blowing machine. In this study, a mold has been instrumented with two different sensors. The first probe allows to estimate the heat flux density and temperature at the mold surface temperature, using a linear inverse heat condution problem (Function Specification Method). The second device is used to measure the surface t...

Simulation of the Two Stages Stretch-Blow Molding Process: Infrared Heating and Blowing Modeling

In the Stretch‐Blow Molding (SBM) process, the temperature distribution of the reheated perform affects drastically the blowing kinematic, the bottle thickness distribution, as well as the orientation induced by stretching. Consequently, mechanical and optical properties of the final bottle are closely related to heating conditions. In order to predict the 3D temperature distribution of a rotating preform, numerical software using control‐volume method has been developed. Since PET behaves like a semi‐transparent medium, the radiative flux absorption was computed using Beer Lambert law. In a second step, 2D axi‐symmetric simulations of the SBM have been developed using the finite element package ABAQUS®. Temperature profiles through the preform wall thickness and along its length were computed and applied as initial condition. Air pressure inside the preform was not considered as an input variable, but was automatically computed using a thermodynamic model. The heat transfer coefficient applied between the mold and the polymer was also measured. Finally, the G’sell law was used for modeling PET behavior. For both heating and blowing stage simulations, a good agreement has been observed with experimental measurements. This work is part of the European project “APT_PACK” (Advanced knowledge of Polymer deformation for Tomorrow’s PACKaging).

Assessment of the Single-Mixture Gas Assumption for the Correlated K-Distribution Fictitious Gas Method in H2O–CO2–CO Mixture at High Temperature

This paper deals with the comparison of spectral narrow band models based on the correlated-K (CK) approach in the specific area of remote sensing of plume signatures. The CK models chosen may or may not include the fictitious gas (FG) idea and the single-mixture-gas assumption (SMG). The accuracy of the CK and the CK-SMG as well as the CKFG and CKFG-SMG models are compared, and the influence of the SMG assumption is inferred. The errors induced by each model are compared in a sensitivity study involving the plume thickness and the atmospheric path length as parameters. This study is conducted in two remote-sensing situations with different absolute pressures at sea level (105Pa) and at high altitude (16.6km, 104Pa). The comparisons are done on the basis of the error obtained for the integrated intensity while leaving a line of sight that is computed in three common spectral bands: 2000–2500cm−1, 3450–3850cm−1, and 3850–4150cm−1. In most situations, the SMG assumption induces negligible differences. Furthermore, compared to the CKFG model, the CKFG-SMG model results in a reduction of the computational time by a factor of 2.

Load movement measurement using a near-infrared CCD camera for aircraft cargo surveillance

The paper presents a video surveillance system which is able to measure the load displacements in an aircraft cargo area as well as the appearance of fires (hot surfaces, flame and smoke). To benefit from both measurements and cost savings, the system is based on an uncooled CCD camera operating in a near infrared (NIR) spectral band. In this article, we focus on load displacement measurements. The cargo compartment is not pressurized and the temperature is not controlled, thus it may vary from -55/spl deg/C to 85/spl deg/C. The influence of spectral band and temperature variations on a spatial resolution camera is studied using the physical models of a CCD camera. The classical camera geometric model is modified to take into account these variations. After the load detection, the geometric model is used to localize the load in the cargo area. Finally, we present the image processing software which computes the 3D load displacement.

EXPERIMENTAL AND NUMERICAL ANALYSIS OF BUILDING BOUNDARY CONDITIONS

One of the conditions for the determination of conductive heat transfer through building walls is a knowledge of the heat exchanges at their boundaries and particularly the radiative and the convective heat transfer occuring at their surfaces. To study the influence of these two types of heat transfer, the authors have performed a combined experimental and numerical study. The experimental work consisted of building an experimental setup to satisfy a great variety of boundary conditions that may be encountered on building walls. It was composed mainly of an enclosure, a vertical, heated plate in which natural convection heat flow was generated, and a light source that imposed a known radiative flux condition on the solid surface. An inverse heat transfer method has also been developed. This numerical method gives the total heat flux leaving the vertical flat plate by conduction, together with surface temperatures. Then it is possible to use a simple thermal balance to determine the radiative and the convective heat flux variations with time. The results of the study are presented together with the corresponding uncertainty calculations. They show that the method could be useful for following heat exchange variations at the solid surfaces of walls.