This paper discusses technical problems related with casting of titanium alloys in centrifugal vacuum furnaces. The potentials of an analysis of the centrifugal casting process carried out in the ...Flow3D software CFD (Computational Fluid Dynamics) were presented. Simulations were carried out on a model set, which enables casting of two connecting rods for an I.C. engine. Changes in the mould filling process were examined for the three selected spinning velocities of the casting arm. The ranges of the metal flow velocity in mould were calculated as well as metal pressure in mould after reaching a predetermined spinning velocity. The results and the adopted mould geometry enabled determination of the magnitude of stress occurring in mould at the time of filling it with liquid titanium alloy. The paper presents a methodology for testing of the ceramic material strength using a four-point loading arrangement. The strength of the ceramic material was determined on samples heated at different temperatures. The obtained results enabled a thesis to be formulated that for pouring of moulds in a centrifugal vacuum furnace, the layered foundry ceramic moulds can be safely used, and the use of moulds that will provide the directional solidification of metal should be possible as well.
In this work an approach for rapid prototyping and manufacturing of metallic as well as ceramic parts is presented. By using Mold Shape Deposition Manufacturing (MoldSDM), a wax mold is fabricated ...which is filled with a slurry containing the final part material in powder form. The wax mold is manufactured by first decomposing the desired part geometry into machinable compacts. In a next step the mold is built up in a series of layers by machining either the wax or a sacrificial support material. The surface quality of the final mold is only limited by the abilities of the CNC machine. After casting a ceramic or metallic slurry, the wax mold is removed and the obtained green part debinded and sintered. In this work the mechanical and microstructural properties of the parts obtained by this method are presented. The materials which have been investigated are silicon nitride and stainless steels. Due to the high mold quality the process is suitable for a variety of applications in rapid prototyping and manufacturing where parts made of engineering materials are required.
The viscosity and shear rate as a function of 2–24% volume concentration of solids was determined for alumina and kaolin slurries. A model of viscosity as a function of volume concentration of a ...dispersed phase in a matrix and a bidimensional balance of forces acting on a particle in suspension is presented. The theoretical model was compared with experimental data accomplished with a double concentric cylinders rheometer. A good correlation of the proposed model with the measured data could be verified. The forces of mechanical origin that cause restrictions to particle rotation and translation appear to remarkably influence the variation of viscosity.
Rheology of Glaze Suspensions Savarmand, Saeid; Golkar-Narenji, Mohammad-Reza; Saedi, Kourosh
Canadian journal of chemical engineering,
October 2003, Letnik:
81, Številka:
5
Journal Article
Recenzirano
Rheological properties of suspensions and ceramic glaze slurries under steady flow conditions have been considered. Colloidal forces play an important role in the rheology of such ceramic slurries. ...Since the potential function characterizes the rheology of colloidal systems, a new dimensionless group, viz. potential number, is introduced within a dimensional analysis representing the relative significance of the potential to the Brownian energy. In order to relate the relative viscosity to other dimensionless groups, a new model is proposed by the inclusion of an extra term in addition to that of the hard‐sphere theory owing to the fact that the presence of colloidal forces always increases the fluid viscosity with respect to that predicted by the hard‐sphere. Steady viscosity measurements have been carried out on ceramic glaze suspensions at different volume fractions, particle diameters, and shear rates. Experimental results have been used to modify the model relating the relative viscosity to the Péclet number, potential number, volume fraction, and maximum packing fraction.
On a examiné les propriétés rhéologiques de suspensions et de boues d'émail céramique dans des conditions d'écoulement stationnaires. Les forces colloïdales jouent un rôle important dans la rhéologie de telles boues. Vu que la fonction potentielle caractérise la rhéologie des systèmes colloïdaux, un nouveau groupe adimensionnel, soit le nombre potentiel, est introduit au sein d'une analyse dimensionnelle représentant l'importance relative du potentiel pour l'énergie brownienne. Afin de relier la viscosité relative aux autres groupes adimensionnels, un nouveau modèle est proposé par l'inclusion d'un terme additionnel en plus de celui de la théorie des sphères dures étant donné que la présence des forces colloïdales augmente toujours la viscosité du fluide par rapport à celle qui est prédite par la théorie des sphères dures. Des mesures de viscosité stationnaire ont été effectuées sur des suspensions d'émail céramique à différentes fractions volumiques, diamètres de particules et vitesses de cisaillement. Les résultats expérimentaux nous ont permis de modifier le modèle reliant la viscosité relative au nombre de Péclet, au nombre potentiel, à la fraction volumique et à la fraction de garnissage maximale.
•DLP technology was used to manufacture lattices with CAD designed struts of 200–500 μm.•The slurry prepared with the pre-treated powder showed appropriate properties for successful processing on the ...Admaflex 130.•The cure depth necessary for successful manufacturing was found to be inversely proportional to the exposed area.•DOE showed the most significant parameters that influence the dimensional accuracy were the exposure time, the exposure power and their interaction.•The broadening parameters were found to be dependent on the layer thickness as well as the energy dose and the feature size.
Digital Light Processing (DLP) technology demonstrates the potential for manufacturing parts with complex structures for various engineering applications. The purpose of this study is to evaluate Al2O3 ceramic slurry preparation techniques, establish optimal processing window and assess the manufacturability and dimensional accuracy of lattice structures with CAD strut diameters of up to 500 μm. Two preparation techniques of the ceramic slurry were investigated. The slurry with the pre-treated powder showed appropriate rheological and photopolymerization behaviour. Full factorial Design of Experiments (DOE) was conducted to generate an experimental plan and assess the influence of the printing parameters on the dimensional accuracy. Analysis of Variance (ANOVA) revealed the exposure time, the exposure power, and the interaction effect of both had a significant influence on the dimensional accuracy of lattice strut diameters. The excess cure width was found to be dependent on the feature size, the energy dose and the layer thickness.
Stereolithography is one of the most widely used additive manufacturing techniques for preparing high precision and complex ceramic components. Due to the high optical absorbance and refractive index ...of SiC powder, the rapid stereolithography of SiC ceramics components has become a key challenge. Here, we innovatively use graded silica to improve the curing thickness, rheological and settling performance of the slurry. And we presented a preparation method of SiC ceramic slurry for stereolithography with high solid content, low viscosity, low sedimentation rate and high curing thickness. The printable precision of the slurry is more than 75 μm, the dynamic viscosity is less than 2 Pa·s, and the 24 h sedimentation height is less than 5%. This strategy demonstrates a tantalizing possibility and promising prospect to rapid stereolithography of large size SiC ceramic green body.
PDF
