Objective
Injection moulding of ceramics is already widely used in industrial applications and is considered to be the most feasible shaping technique for producing large quantities of rather small parts of complex shape, like exhaust pipes, precombustion chambers or rocker arm tips. The method consists of mixing the ceramic powder with organic plasticizers and binders in order to obtain thermoplastic behaviour suitable for injection moulding. Currently the industrial limiting stage concerns the burn-out step. In order to avoid defects such as cracks and blisters, the heating rate has to be kept very small (typically 2C/H) in some temperature ranges where critical mechanisms take place. Thus, complete removal times can reach several hundred hours. This chosen binder formulation is based on polystyrene, and the ceramic is silicon nitride. The objectives and the corresponding achievements of the proposed work are: Basic understanding of the physico-chemical transformations taking place during the burn-out: - TGA and mass spectrum measurements led to consider two types of reactions (pyrolysis and thermo-oxidation); a kinetic based model was built on TGA isothermal experiments of polystyrene thermo-degradation; - the physical state of the sample (porosity, mean pore size, gas permeability) was settled at different thermodegradation stages, through gas permeametry and Hg porosimetry; ultrasonic waves velocity through parts is continuously measured during dewaxing, to be correlated to physical or chemical phenomena occurring during this process. Modelling and numerical simulation of pressure build-up in the body: a model considering both kinetic and gas flow through porous media during debinding was written. A finite element programme is under development. Assessment of optimal cycles for any given point: simple parts have been submitted to the rate-loss weight controlled furnace. At this time, satisfying results have been obtained with cylindrical injected parts up to 3.7 mm thick and 40 mm wide.
This study is divided into kinetic analyses (TGA and kinetic mechanisms) and physical measurements (porosimetry, permeametry, BET and ultrasonic testing) and finally this leads to a numeric modelling with a finite element discretisation (thermodynamical approach). Some interesting correlations result from these different methods.
OPTIMUM CYCLES WILL BE GIVEN THROUGH NUMERICAL CALCULATIONS, USING A MAXIMUM INTERNAL PRESSURE CRITERION AND WITH THE RATE CONTROLLED BINDER REMOVAL TECHNIQUE PRECEDINGLY DEVELOPED BY THE SWEDISH INSTITUTE FOR SILICATE RESEARCH.
THE METHODOLOGICAL WORK IS EXPECTED TO LEAD TO THE FOLLOWING INDUSTRIAL CONSEQUENCES:
- HIGHER PRODUCTIVITY THROUGH REDUCED BINDER REMOVAL TIMES.
- IMPROVEMENT OF QUALITY AND RELIABILITY OF INJECTED COMPONENTS.
Fields of science (EuroSciVoc)
CORDIS classifies projects with EuroSciVoc, a multilingual taxonomy of fields of science, through a semi-automatic process based on NLP techniques. See: The European Science Vocabulary.
CORDIS classifies projects with EuroSciVoc, a multilingual taxonomy of fields of science, through a semi-automatic process based on NLP techniques. See: The European Science Vocabulary.
- engineering and technology materials engineering amorphous solids organic amorphous solids
- social sciences economics and business economics production economics productivity
- natural sciences chemical sciences inorganic chemistry metalloids
- engineering and technology materials engineering ceramics
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Coordinator
91003 Evry
France
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