Investigation into the rapid manufacture of investment casting moulds through accelerated drying

Douse, Elliot (2020). Investigation into the rapid manufacture of investment casting moulds through accelerated drying. University of Birmingham. Eng.D.

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Abstract

The manufacture of ceramic moulds for investment casting turbine blades is time consuming due to the accumulation of successive periods of drying between layers. Each layer is composed of a ceramic slurry onto which ceramic grains are deposited. Substitution of conventional non-porous ceramic grains for porous ceramic grains containing up to 60 vol% pore volume was conducted which reduced the amount of time required to dry a layer by up to 50%. After firing to casting temperature, moulds containing porous stucco display flexural deformation and an increase in flexural strength of up to 20%, both of which can cause casting defects. Through selective thermo-mechanical analysis of materials comprised within the ceramic mould, it was identified that defects originated primarily from large volumetric contraction of porous grains at casting temperature. To counteract this, composite ceramic materials were developed containing a porous and non-porous component to produce a material capable of absorbing water from the slurry upon contact but remain dimensionally stable at casting temperature. An alternative solution was also evaluated which minimised defect formation by constraining contraction within the layers containing porous grains. Both of these solutions successfully produced a reduction in drying time whilst maintaining the integral properties of the ceramic mould. The mechanism of accelerated drying when utilising porous ceramic grains was also investigated and it was hypothesised that a rate limited step prevents the utilisation of the complete pore volume of the porous grain.

Type of Work:

Thesis (Doctorates > Eng.D.)

Award Type:

Doctorates > Eng.D.

Supervisor(s):