Analytical Fluid Flow Models for Tape Casting

Abstract

The details of fluid flow in tape casting of a Newtonian slurry with a parallel blade are analyzed in terms of the relative magnitudes of the driving forces (wall shear and pressure gradient) and the resulting tape thickness. Prior studies are limited to describe the flow under the blade and within the reservoir. Consideration of the flow after the blade exit indicates that the existence of a zero‐shear plane might have a negative effect on particle alignment in the tape. The more common case of a beveled blade is also analyzed using the one‐dimensional flow model, which is shown to be valid for blade angles up to about 45°. The beveled and parallel blades are compared in terms of productivity, minimum thickness, and potential influence on particle alignment.

Texture evolution in tape cast lead metaniobate

“…Since a viscous force is more favorable than a pressure force for particle alignment, variations to the tape casting process that gives lower values should result in a higher degree of texture. 5 In the present study, lead metaniobate ceramics were tape cast with acicular seed particles that serve as templates for subsequent grain growth with a preferred orientation. Lead metaniobate is a ferroelectric ceramic that is isostructural with orthorhombic tungsten bronze where the polar axis is parallel to the crystallographic b-direction.…”

“…where P is the pressure exerted by the slurry head ( P = ρ slurry gH slurry ), H is the blade gap used, μ is the slurry viscosity, L is the length of the doctor blade, and U is the casting velocity. 5 The ratio of the pressure force to shear force determines the flow characteristics and the wet tape thickness for tape casting. Since a viscous force is more favorable than a pressure force for particle alignment, variations to the tape casting process that gives lower values should result in a higher degree of texture.…”

“…5 They employed a parameter, , to quantify the ratio of pressure forces to viscous forces acting on a tape cast slurry during deformation under a doctor blade. Utilizing all process conditions and slurry viscosity, it is possible to calculate and estimate whether a casting operation will be dominated by pressure flow or shear flow.…”

Processing and Properties of Textured Bismuth Layer-Structured Ferroelectrics

“…To make slurry for tape-casting and extrusion, a mixture of platelike and equiaxed particles is mixed with forming aids such as solvent, binder, plasticizer, dispersant, and so forth. The slurry is subject to shear stresses during forming, and the gradient of shear stresses aligns the platelike particles [9,35]. A high degree of particle alignment is essential to obtain highly textured BLSF ceramics, because the orientation of platelike particles in the green compact determines the orientation of grains in the sintered compact.…”

“…to form slurry which is tape-cast by a doctor-blade technique. The shear stresses acting on the slurry during casting align the platelike particles with their plate face parallel to the sheet surface [9,35]. The cast sheet is cut and laminated to form a green compact.…”