Aqueous electrophoretic deposition as a method for producing an investment casting shell mould ceramic face-coat. Part 1: formation of a carbon-filled investment casting wax electrode material

P J Roach,C B Ponton

doi:10.1007/s10853-013-7562-8

P J Roach, C B Ponton

Open Access

https://doi.org/10.1007/s10853-013-7562-8

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Abstract

Aqueous electrophoretic deposition (EPD), using a zircon, i.e., zirconium silicate (ZrSiO4) suspension, has been investigated as an alternative to the conventional slurry dip-coating process for producing the face-coat of investment casting ceramic shell moulds. This is because EPD has the potential to (a) increase dimensional tolerances in the resultant casting, and (b) form a uniform face-coat on the entire mould-surface of complex shell moulds, including the small and/or complex cavities that are a problem for conventional dip-coating. Part 1 of this work addresses the formation of carbon-filled investment casting wax composite electrode materials. A carbon black powder and a micronised graphite powder were used as the alternative fillers in a water-emulsified pattern wax, an unfilled pattern wax and an unfilled runner wax. The runner wax composites exhibited consistently higher resistivities for both filler types and across the range of filler concentrations. Electrical resistivities of 1200 and 240 Ω cm were attained for the 16 vol% micronised graphite-filled and carbon black-filled straight pattern wax composites, respectively. The higher conductivity values associated with the use of carbon black filler are attributed to its high-surface area and hierarchical agglomerated structure. Rheologically, the micronised graphite-filled runner wax and water-emulsified pattern wax composites followed the Krieger–Dougherty model, which is helpful given that investment casting waxes are invariably injection moulded. In summary, these results confirm, in conjunction with Part 2, the feasibility of developing EPD as a promising technique for forming the investment casting shell mould ceramic face-coat.

Highlights

The production of complex investment cast metal components requires complex and accurately dimensioned ceramic shell moulds
These scanning electron microscopy (SEM) observations are borne out by the laser diffraction particle size distribution analysis (LDPSA) results, which are shown in Figs. 4, 5, 6 and 7
While it is acknowledged that (a) laser diffraction particle size distribution analysis (LDPSA) techniques cannot distinguish between dispersed particles and particle agglomerates, and (b) the particle size distribution results become subject to increasing bias and error as the particle morphology deviates further from the assumed spherical morphology, it is the comparative particle/agglomerate size distributions that are of particular interest in the present work, rather than the absolute particle sizes or agglomerate sizes

Summary

Introduction

The production of complex investment cast metal components requires complex and accurately dimensioned ceramic shell moulds. The addition of electroconductive filler markedly increased the working temperature range and viscosity of the A7-11 wax matrix composite materials; it was effectively only used in the experiments described in the ‘‘Electrical resistivity measurements’’ section for the reasons explained in the ‘‘Rheology measurements’’ section.

Results

Conclusion