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J R G Evans - One of the best experts on this subject based on the ideXlab platform.

  • Review: Fabrication of engineering Ceramics by Injection Moulding. I. Materials selection
    International Journal of High Technology Ceramics, 2003
    Co-Authors: M. J. Edirisinghe, J R G Evans
    Abstract:

    Abstract The present article, Part I, reviews the literature on Ceramic powders and organic polymers used to compound Ceramic Injection Moulding mixtures. The intention is to distil, from a somewhat diverse literature, guidelines for the proper selection of materials, with the aim of facilitating the development of the defect-free Moulding of Ceramic components. Part II will examine mixing methods, Moulding techniques and procedures for removal of the organic vehicle prior to sintering.

  • differential sintering in Ceramic Injection Moulding particle orientation effects
    Journal of The European Ceramic Society, 2002
    Co-Authors: S Krug, J R G Evans, J H H Ter Maat
    Abstract:

    Abstract The sintering shrinkage in three orthogonal directions was measured in sections cut from large rectangular Injection moulded Ceramic blocks. Two powders were used: a comminuted alumina and a chemically-derived zirconia. Pronounced anisotropy of shrinkage was observed in the former whereas the equiaxed zirconia showed uniform shrinkage throughout the Moulding. The pattern of shrinkage anisotropy was consistent with that observed by other investigators and indicates that slight particle anisotropy can introduce differential sintering. The sintering shrinkage in the alumina powder was found to be most pronounced perpendicular to the main flow direction.

  • packing and solidification in Ceramic Injection Moulding
    Journal of Materials Research, 2001
    Co-Authors: S Krug, J R G Evans, J H H Ter Maat
    Abstract:

    The occupation of volume in large Ceramic Injection Mouldings solidified under different pressures using two Moulding techniques is considered. Large (60 × 45 × 25 mm) alumina Injection Mouldings were prepared in cavities fitted with conventional (metallic) and insulated [poly(ether ether ketone)] sprues. These provide quite distinct solidification histories which, in turn, influence the physical properties of the Moulding and the extent and type of defects it contains. In the former case, the gate solidified after 26 s whereas, in the latter, the hold pressure could be applied for over 240 s. In insulated sprue Moulding, the advance of the solid liquid boundary during packing and solidification was traced by fractography. Pressure was varied from 5 to 120 MPa. The interdependencies of Moulding mass, apparent density, local density, polymer crystallinity, and microstructure were accounted for as a function of pressure and pressure transmission method. Changes in polymer crystallinity due to different cooling rates at different positions in the Mouldings were insufficient to account for observed density differences. Systematic changes in the mass as a function of hold pressure were related to macroporosity in conventional Mouldings and to microporosity in insulated sprue Mouldings.

  • methods of assessing gate solidification time in Ceramic Injection Moulding
    Ceramics International, 1999
    Co-Authors: S Krug, J R G Evans
    Abstract:

    In Ceramic Injection Moulding, the freezing of the gate separates the contents of the cavity from the barrel of the machine whereupon external control of the pressure on the solidifying Moulding is lost. The gate freezing time can be deduced from analytical or numerical calculation, by reference to Heisler charts, by systematic studies of moulded mass as a function of time or by inference from the cavity pressure decay curve. In this work, a comparison is made between these methods and an experimental technique which allows the diameter of the molten channel to be measured directly as a function of time. It makes use of reverse extrusion of material and accommodates the influence of axial heat transfer from the heated nozzle of the machine.

  • jetting and weld lines in Ceramic Injection Moulding
    British Ceramic Transactions, 1999
    Co-Authors: S Krug, J R G Evans, J H H Ter Maat
    Abstract:

    A multi-thickness mould cavity incorporating replaceable mould face plates of differing thickness was constructed for assessing the integrity of large section Mouldings. The jetting phenomenon, which leads to a Moulding replete with weld lines, was overcome for 15 mm thick Mouldings by adjusting the nozzle and sprue diameters and by changing the angle of impingement of the melt on the opposite face of the cavity. However, for 25 and 35 mm cavities the formation of multiple weld lines during mould filling could not be completely eliminated. The emergence of cracks near the surface in some sintered parts could be traced back to the formation of weld lines in the Injection stage.

T Zhang - One of the best experts on this subject based on the ideXlab platform.

  • the orientation of binders and particles during Ceramic Injection Moulding
    Journal of The European Ceramic Society, 1997
    Co-Authors: T Zhang, S Blackburn, J Bridgwater
    Abstract:

    By annealing sections of thick, Injection-moulded Ceramics, the orientation of the organic binder was studied. A modified calculation method for X-ray diffraction analysis was used for evaluation of particle orientation. Using a finite difference method, the temperature distribution in a mould system was related to the structure found. Fine plate-like particles became highly oriented during Injection Moulding and the oriented particles restricted the binder orientation and subsequent relaxation of the extended chains.

  • Debinding and sintering defects from particle orientation in Ceramic Injection Moulding
    Journal of Materials Science, 1996
    Co-Authors: T Zhang, S Blackburn, J Bridgwater
    Abstract:

    The causes of the defects in Injection-moulded Ceramic bars during debinding and sintering were investigated using density and shrinkage measurements in combination with macroscopic observation. Differential shrinkage during sintering is the main cause of post-debinding defects. Particle shape, mould geometry and gate position have a large effect on this differential shrinkage, while the volumetric shrinkage is almost constant and the influences of Moulding conditions are relatively small. Particles with plate-like morphology orientate during Moulding and contribute markedly to defect formation during debinding and sintering.

  • computation of volume flow in modulated pressure Ceramic Injection Moulding
    Ceramics International, 1993
    Co-Authors: T Zhang, Jrg Evans
    Abstract:

    Abstract The volume of Ceramic suspension involved in oscillatory flow through the sprue and runners during modulated hold pressure Moulding was calculated using the cooling characteristics of the Moulding and the equation of state for the suspension. With single-gated moulds, the displaced volume is limited by the mould dimensions and the compressibility of the suspension. This restricts the heat dissipated from viscous losses in the core of the sprue and hence the extension to sprue solidification time. The calculation facilitates preliminary estimations of heat fluxes.

  • mechanical properties of Injection Moulding suspensions as a function of Ceramic volume fraction and temperature
    Journal of The European Ceramic Society, 1991
    Co-Authors: T Zhang, J R G Evans
    Abstract:

    Abstract The elastic modulus of Ceramic Injection Moulding compositions with Ceramic volume fractions from 0 to 0·56 were measured in the temperature range from 20°C to the softening point of 144°C. The uniaxial fracture strength of the most concentrated suspension was measured in the same temperature range. Poisson's ratio was obtained by a train gauge method in which the electrical heating effect of the gauge was controlled. The results are compared with model predictions in order that such data can be obtained for diverse suspensions from a minimum of measurements. Such results are necessary for the analysis of residual stress and hence cracking during the solidification stage of Ceramic Injection Moulding.

  • the properties of a Ceramic Injection Moulding suspension based on a preCeramic polymer
    Journal of The European Ceramic Society, 1991
    Co-Authors: T Zhang, J R G Evans
    Abstract:

    Abstract A Ceramic suspension incorporating fine sinterable silicon carbide powder in a polycarbosilane vehicle has been modified by additions of paraffin wax to make it suitable for plastic forming operations. The diluent enables higher volume fractions of Ceramic to be incorporated and lowers the softening point of the suspension. The danger of temperature-induced crosslinking in processing machinery is alleviated.

Jrg Evans - One of the best experts on this subject based on the ideXlab platform.

  • transient effects during catalytic binder removal in Ceramic Injection Moulding
    Journal of The European Ceramic Society, 2001
    Co-Authors: S Krug, Jrg Evans, J H H Ter Maat
    Abstract:

    Abstract This work is part of a comprehensive study of the incidence and cause of defects in large section Ceramic Injection Mouldings. In previous related work, the defects associated with mould-filling and with solidification and packing in the cavity were identified. Such defects sometimes manifest themselves only after binder removal or after sintering and so may be causally connected with those stages by mistake. In the present work, defects which do indeed arise from the binder removal stage itself as a result of minor process interruptions are isolated. These are identifiable by a pattern of defects which are distinct from those due to solidification and are independent of solidification conditions. This work reports on the systematic study of perturbations to conditions in the binder removal oven in order to track the origin of these defects and hence distinguish them from shrinkage-related defects.

  • Residual stresses and cracking in large Ceramic Injection Mouldings subjected to different solidification schedules
    Journal of The European Ceramic Society, 2000
    Co-Authors: S Krug, Jrg Evans, J.h.h. Ter Maat
    Abstract:

    In Ceramic Injection Moulding, the Moulding dimensions and the residual stresses are related to the hold pressure history during solidification in the cavity. In conventional Moulding, the residual stresses are generally compressive at the surface. In this work, an insulated sprue device was made. It allows prolonged pressure transmission to the Moulding and this can result in residual tensile stresses at the surface of thick section Mouldings. At very low holding pressures (

  • Control of fibre orientation in Injection moulded Ceramic composites
    Composites Part A-applied Science and Manufacturing, 1998
    Co-Authors: Tao Zhang, Jrg Evans, Michael J. Bevis
    Abstract:

    A Ceramic Injection Moulding suspension containing 60 vol% solids of which 12 vol% was in the form of short-staple fibres was prepared by twin screw extrusion. The material was moulded in the form of large and small end-gated rectangular bars using a machine which applied modulated pressure after mould filling. The orientation of fibres in conventional and modulated pressure Moulding was compared. The former showed the well-known arrangement of sub-skin alignment and disorder near the centre. In the latter, the fibres were preferentially oriented in the flowing direction throughout the Moulding. The uniformity of preferred orientation throughout the bar was sensitive to oscillation frequency. This is because of the high thermal diffusivity and hence rapid solidification of the Ceramic suspensions compared to unfilled polymers. The solidification front progresses rapidly to occlude fibres which were incompletely oriented during the period in each cycle when the melt was stationary.

  • computation of volume flow in modulated pressure Ceramic Injection Moulding
    Ceramics International, 1993
    Co-Authors: T Zhang, Jrg Evans
    Abstract:

    Abstract The volume of Ceramic suspension involved in oscillatory flow through the sprue and runners during modulated hold pressure Moulding was calculated using the cooling characteristics of the Moulding and the equation of state for the suspension. With single-gated moulds, the displaced volume is limited by the mould dimensions and the compressibility of the suspension. This restricts the heat dissipated from viscous losses in the core of the sprue and hence the extension to sprue solidification time. The calculation facilitates preliminary estimations of heat fluxes.

  • Computer modelling of the origin of defects in Ceramic Injection Moulding
    Journal of Materials Science, 1991
    Co-Authors: K N Hunt, Jrg Evans, N. J. Mills, J Woodthorpe
    Abstract:

    Thermal stress profiles were calculated for Injection-moulded flat discs of a zirconia-polystyrene suspension by considering the heat flow in, and elastic properties of, the suspension in the solid state. The calculated maximum tensile stress in the centre of the moulded discs could be used to predict the incidence of cracking in Moulding experiments. The computer model allows the influence of material and machine parameters on residual stress profile to be explored for the simple case of an infinite flat plate. In particular, high tensile stresses are induced by low mould temperatures and high Injection pressures.

S Blackburn - One of the best experts on this subject based on the ideXlab platform.

  • Comparison of paste rheology and extrudate strength with respect to binder formulation and forming technique
    Journal of Materials Processing Technology, 1999
    Co-Authors: O. Draper, K. Smalley, S Blackburn, Gaynor Dolman, A. Griffiths
    Abstract:

    Two series of Ceramic Injection Moulding (CIM) pastes were prepared using three different mixing methods. Two Newtonian binder systems, were employed composed of EVA-paraffin wax and EVA-vegetable fat mixed in varying proportions to give a wide range of binder viscosities. The powder loading of each paste system was adjusted using the Chong equation to compensate for the variation in binder viscosity. The mixing methodologies employed were convectional Z blade mixing, twin roll milling (TRM), and Extrumixing (a combination of Z blade mixing and single-screw extrusion). The rheology of the pastes was characterised by extrusion, with the data being rheologically analysed by the Benbow/Bridgwater and Herschel/Bulkley models. The most rheologically favourable systems produced relatively low yield values and were not highly velocity dependent. Extrudates from these two paste systems were mechanically tested after undergoing identical debinding and sintering regimes, and found to posses strengths of 360 and 580 MPa, respectively. The most promising mixing methodology employed was Extrumixing due to the high shear mixing action in combination with the extrusion action used in removing the paste from the mixer.

  • A Water-based System for Ceramic Injection Moulding
    Journal of the European Ceramic Society, 1997
    Co-Authors: R. J. Huzzard, S Blackburn
    Abstract:

    Water-based binders for Injection Moulding of Ceramics use low Moulding temperatures allowing Moulding and die temperatures to be similar. Most of the binder system can be driven off as water vapour, cutting process time, reducing burn-out problems and causing less environmental pollution. The difficulties with removing moulded articles from the die must be overcome. To address this problem, gel strength was measured on solutions up to 8 wt% of ten commercially available cellulose derivatives at four temperatures between the gel temperature and the boiling point of water. A paste with rheology that permits mould filling was made from the binder that showed highest gel strength. This was used in Moulding trials. A similar formulation based on a low-strength binder was also studied for comparison. The paste based on the highest gel strength binder showed significantly less deformation on release from the die, allowing the processing advantages of the system to be realised. © 1996 Elsevier Science Limited.

  • a water based system for Ceramic Injection Moulding
    Journal of The European Ceramic Society, 1997
    Co-Authors: R. J. Huzzard, S Blackburn
    Abstract:

    Water-based binders for Injection Moulding of Ceramics use low Moulding temperatures allowing Moulding and die temperatures to be similar. Most of the binder system can be driven off as water vapour, cutting process time, reducing burn-out problems and causing less environmental pollution. The difficulties with removing moulded articles from the die must be overcome. To address this problem, gel strength was measured on solutions up to 8 wt% of ten commercially available cellulose derivatives at four temperatures between the gel temperature and the boiling point of water. A paste with rheology that permits mould filling was made from the binder that showed highest gel strength. This was used in Moulding trials. A similar formulation based on a low-strength binder was also studied for comparison. The paste based on the highest gel strength binder showed significantly less deformation on release from the die, allowing the processing advantages of the system to be realised.

  • the orientation of binders and particles during Ceramic Injection Moulding
    Journal of The European Ceramic Society, 1997
    Co-Authors: T Zhang, S Blackburn, J Bridgwater
    Abstract:

    By annealing sections of thick, Injection-moulded Ceramics, the orientation of the organic binder was studied. A modified calculation method for X-ray diffraction analysis was used for evaluation of particle orientation. Using a finite difference method, the temperature distribution in a mould system was related to the structure found. Fine plate-like particles became highly oriented during Injection Moulding and the oriented particles restricted the binder orientation and subsequent relaxation of the extended chains.

  • Debinding and sintering defects from particle orientation in Ceramic Injection Moulding
    Journal of Materials Science, 1996
    Co-Authors: T Zhang, S Blackburn, J Bridgwater
    Abstract:

    The causes of the defects in Injection-moulded Ceramic bars during debinding and sintering were investigated using density and shrinkage measurements in combination with macroscopic observation. Differential shrinkage during sintering is the main cause of post-debinding defects. Particle shape, mould geometry and gate position have a large effect on this differential shrinkage, while the volumetric shrinkage is almost constant and the influences of Moulding conditions are relatively small. Particles with plate-like morphology orientate during Moulding and contribute markedly to defect formation during debinding and sintering.

S Krug - One of the best experts on this subject based on the ideXlab platform.

  • differential sintering in Ceramic Injection Moulding particle orientation effects
    Journal of The European Ceramic Society, 2002
    Co-Authors: S Krug, J R G Evans, J H H Ter Maat
    Abstract:

    Abstract The sintering shrinkage in three orthogonal directions was measured in sections cut from large rectangular Injection moulded Ceramic blocks. Two powders were used: a comminuted alumina and a chemically-derived zirconia. Pronounced anisotropy of shrinkage was observed in the former whereas the equiaxed zirconia showed uniform shrinkage throughout the Moulding. The pattern of shrinkage anisotropy was consistent with that observed by other investigators and indicates that slight particle anisotropy can introduce differential sintering. The sintering shrinkage in the alumina powder was found to be most pronounced perpendicular to the main flow direction.

  • transient effects during catalytic binder removal in Ceramic Injection Moulding
    Journal of The European Ceramic Society, 2001
    Co-Authors: S Krug, Jrg Evans, J H H Ter Maat
    Abstract:

    Abstract This work is part of a comprehensive study of the incidence and cause of defects in large section Ceramic Injection Mouldings. In previous related work, the defects associated with mould-filling and with solidification and packing in the cavity were identified. Such defects sometimes manifest themselves only after binder removal or after sintering and so may be causally connected with those stages by mistake. In the present work, defects which do indeed arise from the binder removal stage itself as a result of minor process interruptions are isolated. These are identifiable by a pattern of defects which are distinct from those due to solidification and are independent of solidification conditions. This work reports on the systematic study of perturbations to conditions in the binder removal oven in order to track the origin of these defects and hence distinguish them from shrinkage-related defects.

  • packing and solidification in Ceramic Injection Moulding
    Journal of Materials Research, 2001
    Co-Authors: S Krug, J R G Evans, J H H Ter Maat
    Abstract:

    The occupation of volume in large Ceramic Injection Mouldings solidified under different pressures using two Moulding techniques is considered. Large (60 × 45 × 25 mm) alumina Injection Mouldings were prepared in cavities fitted with conventional (metallic) and insulated [poly(ether ether ketone)] sprues. These provide quite distinct solidification histories which, in turn, influence the physical properties of the Moulding and the extent and type of defects it contains. In the former case, the gate solidified after 26 s whereas, in the latter, the hold pressure could be applied for over 240 s. In insulated sprue Moulding, the advance of the solid liquid boundary during packing and solidification was traced by fractography. Pressure was varied from 5 to 120 MPa. The interdependencies of Moulding mass, apparent density, local density, polymer crystallinity, and microstructure were accounted for as a function of pressure and pressure transmission method. Changes in polymer crystallinity due to different cooling rates at different positions in the Mouldings were insufficient to account for observed density differences. Systematic changes in the mass as a function of hold pressure were related to macroporosity in conventional Mouldings and to microporosity in insulated sprue Mouldings.

  • Residual stresses and cracking in large Ceramic Injection Mouldings subjected to different solidification schedules
    Journal of The European Ceramic Society, 2000
    Co-Authors: S Krug, Jrg Evans, J.h.h. Ter Maat
    Abstract:

    In Ceramic Injection Moulding, the Moulding dimensions and the residual stresses are related to the hold pressure history during solidification in the cavity. In conventional Moulding, the residual stresses are generally compressive at the surface. In this work, an insulated sprue device was made. It allows prolonged pressure transmission to the Moulding and this can result in residual tensile stresses at the surface of thick section Mouldings. At very low holding pressures (

  • methods of assessing gate solidification time in Ceramic Injection Moulding
    Ceramics International, 1999
    Co-Authors: S Krug, J R G Evans
    Abstract:

    In Ceramic Injection Moulding, the freezing of the gate separates the contents of the cavity from the barrel of the machine whereupon external control of the pressure on the solidifying Moulding is lost. The gate freezing time can be deduced from analytical or numerical calculation, by reference to Heisler charts, by systematic studies of moulded mass as a function of time or by inference from the cavity pressure decay curve. In this work, a comparison is made between these methods and an experimental technique which allows the diameter of the molten channel to be measured directly as a function of time. It makes use of reverse extrusion of material and accommodates the influence of axial heat transfer from the heated nozzle of the machine.