CERAMIC CASTING

Slip Casting • Slip casting- process of filling porous (gypsum or plaster of paris) mould

with ceramic slurry

• Water is removed from the slurry via capillary action

• Collection of ceramic particles in the surface of the mould – required thickness

• Green body is dried further and removed from mould

• Sintering and final machining parts

• Slip is a suspension of fine powder in a liquid such as water or alcohol with

small amounts of dispersants, surfactants and binders

•The setting rate will be all the higher as the permeability of the deposited layer

increases (low Rd).

•The powder grain size distribution, which will influence the arrangement of the

particles during the consolidation, varies considerably according to the type of

ceramic and the final properties desired.

• The rheological behaviour and the viscosity of the suspensions in fact depend

directly on the grain size of the powders, the inter- particle interactions

(state of dispersion) and the particle concentration.

Cont…

• Low toughness.

• High porosity, which lowers the strength. If the strength is increased some porosity

must be sacrificed to increase the strength.

• Low strength gypsum molds wear out with time because the pores are eroded from

the water that goes through them.

• Good for producing complex shapes because as the green body loses water and

begins to dry out it shrinks away at edges of the mold for easy removal.

Mold Properties

Advantages

• Low capital investment has to be made for the products

• Highly homogeneous slurries can be produced

• Wide variety of complex shapes can be produced that could not be

produced using other conventional methods.

Disadvantages

• Low dimensional precision

• Low production rate

• Differential shrinkage becoz of packing factor gradient

• low toughness mold- large mould inventory

Pressure casting• The supply of an additional pressure, compared to the low capillary

pressure of the mold (< 0.2 mpa for plaster), decreases the setting time. • The pressure casting consists of applying a pressure, generally Lower than 5 mpa, to the suspension in the porous mold• The pressure gradient thus created (δp) will force the fluid through the

porous network and the formed layer, considerably reducing the setting time compared to traditional casting.

• Pressure casting reduces the water content in the green part and increases its density and its cohesion

• They do not require drying between the various castings• it provides high productivity.

Tape Casting Technology

Tape Casting Technology

Also known as Doctor Blading, Knife Coating

As the name indicates, thin tapes from varying range, 5 micron to 500 micron

are produced.

Thin layers of ceramic loaded polymers used as single layer or stacked and

laminated into multilayer can be fabricated.

Why Tape Casting is required…

Create large, thin and flat ceramic or metallic parts.

Used for fabrication of components which are impossible to produce by

pressing and/or extrusion techniques.

Can be produced in large quantity and in single operation.

To increase capacitance (or to reduce voltage for getting same amount of

strain).

Example: actuators

Advantage is high surface area for same volume high reactivity.

Example : Fuel cells, batteries, armor plate