Shaping Overview of shaping technologies method product geometry

Shaping Overview of shaping technologies method product geometry Starting material mold costs product examples axial die pressing simplecomplex granulate high ferrite cores, piezo ceramics isostatic pressing simple granulate medium tubes, spark plug, pistons tape casting simple (tape) conc. suspension very low condensator substrates extrusion simple plastic mass low tubes pressure slip casting simple conc. suspension low sanitary ceramics slip casting complex conc. suspension low sanitary ceramics injection molding complex plastic mass high turbine blades Liquid content of the starting material for the different shaping processes • Compaction of granulates ca. 5% • Extrusion, injection molding ca. 25 -30 • Casting ca. 60 -70% increasing liquid content

Shaping Pressure forming methods Compaction of powders is used for shaping simple forms. pump oil rubber bag 100 isostatic pressing Compaction process: 1. sliding and rearrangement of particles/granules 2. Deformation (elastic and plastic) of particles/granules (3. Densification of granules) Problems: - Unhomogeneous density distribution - Residual large pores (hollow granules) - Ejection problems KBr powder 80 Density (%) uniaxial pressing tile body 60 40 alumina granules 20 20 40 60 Pressure(Mpa) Yanagida et al. : p. 158 - 160 80

Shaping Isostating pressing Pressure vessel with liquid Elastic, shape stable form The advantage of isostatic compaction is a more homogeneous density distribution. The complexity of the mold is, however, limited. Green body

Shaping Die pressing: flow chart Process flow diagram for shaping by die pressing.

Shaping Compaction of granules density stage 3 stage 1 stage 2 End stage II pressure Compaction behavior of granulated powders stage I granule flow and rearrangement stage II granule deformation stage III granule densification End stage III Evolution of the green-body microstructure during compaction of granules

Shaping Densification defects Pressure distribution in a die at the beginning and at the end of the second compaction stage. The spring back behavior after pressure is released is directly proportional to the pressure in a certain area. The differential pressure is mainly due to friction of the punch. Densification defects occurring on die pressed green bodies.

Shaping Die pressing additives Reed, 1995

Shaping Die pressing powders Reed, 1995

Shaping Products shaped by axial die pressing

Shaping Slip casting I a) The slurry is poored into the mold made of plaster of Paris (Ca. SO 4 � 0. 5 H 2 O). b) The mold absorbs the liquid, while the powder particles are deposited on the walls of the mold. c) The surplus suspension is drained and d) the greenbody is removed from the mold. Steps in slip casting of ceramics. (Source: From Modern Ceramic Engineering, by D. W. Richerson, p. 462, Fig. 10 -34. Copyright © 1992 Marcel Dekker. Reprinted by permission. )

Shaping Hollow molds The holding time will the wall thickness greenbody. Typical times are between 5 minutes. dictate of the holding and 30

Shaping Slip casting of sanitary ceramics

Shaping Rheology in slip casting Viscosity (m. Pa sec) Slip casting of porcellaine 1500 1250 1000 750 500 V 250 0 20 40 60 80 100 spindle speed (rpm) The rheology of the cast is shear thinning. Before mixing, pumping and pouring the slurry has to be stirred % sodium silicate Influence of the viscosity on the shape of the slip casted white ware part

Shaping Kinetics of slip casting The thickness of the cake deposited on the mold walls depend on mold and suspension characteristics. The wall thicknes growth is a parabolic.

Shaping Slip casting examples Slip casted silicon nitride turbine (Allied Signal)

Shaping Tape casting I slurry doctor blade green body in form of a film liquid absorbing, porous film Compositions of a alumina and titanate tape cast (vol%) Powder Solvent Al 2 O 3 Trichlorethylene Ethylalcohol Deflocculant Menhaden oil Binder Polyvinylbutiral Plasticizer Polyethylene glycol Octyl phthalate Wetting agent Cyclohexanone 27. 0 42. 0 16. 0 1. 8 4. 4 4. 8 4. 0 1. 2 Ba. Ti. O 3 Methylketone Ethylalcolhol Menhaden oil Acryllic emulsion Polyethylene glycol Butylbenzlphtalate 28. 0 33. 0 16. 0 1. 7 6. 7 Such slurries exhibit also shear thinning. The quality and thickness of the tape is controlled by the size of the blade oppening, the speed of the tape, the rheology of the slurry and the shrinkage during drying. Industrial tape casting machines are up to 25 m long, several meters wide and run with speeds. Up to 1. 5 m/min to produce tapes with thicknesses between 25 and 1250 mm.

Shaping Tape casting II Example of a tape drying on the Mistler laboratory-scale batch tape caster. Industrially the process is often continuous with the tape being force dried prior to removal from the carrier, dicing and further processing. A doctor blade assembly. The ceramic slurry is held in the reservoir behind the blade [middle of the micrograph]. The twin micrometers [right] control the blade height above the carrier film. More sophisticated versions feature double blades and pumped metered slurry flow to keep the height of the slurry reservoir constant.

Shaping Pressurized slip casting I 1. Closing of the mold 2. Injection of the slurry into the mold

Shaping Pressurized slip casting II 3. Pressurizing the slurry 4. Draining of surplus slurry

Shaping Pressurized slip casting III 5. Opening of the mold 6. Removal of the component

Shaping Pressurized slip casting examples Pressurized slip casting mold for sinks Finished products

Shaping Injection molding Process flow diagram for shaping by injection molding

Shaping Injection molding products Most products shown in the picture are guiding elements used in thread manufacturing

Shaping Extrusion casting slurry Yanagida et al. : p. 160 cylindric greenbody Industrial pug mill ith deairing chamber and extrusion auger

Shaping Drying of greenbodies I Drying geometry moving drying air Boundary layer (air + vapour) Particles Suspension liquid Drying kinetics will depend on the rate of heat transfer into the body and mass (liquid) transport out of the body. Four rate determining processes can be distinguished: 1. Boundary layer mass transfer 3. Boundary layer heat transfer 2. Pore mass transfer 4. Pore heat transfer Each of the above steps are rate determining for some time during drying, the boundary layer process at the beginning, the pore processes towards the end. Mass and heat transfer rates are obviously coupled and equal to the evaporation rate E:

Shaping Drying of greenbodies II as cast Moisture cont. Shrinkage and deformation Moisture content at the surface const. Rate determining step: heat and mass transport through boundary layer No further shrinkage, all particles are in contact, leatherhard greenbody constant rate Partially filled pores. Rate determining step: pore mass and heat transfer completely dry decreasingt rate Typincal drying curve time The boundary processes are linear functions of the greenbody size (radius for spheres, cylinders, thickness for plates), whereas the pore processes go with the square of the greenbody dimension. The overall rate is ± a square function of the greenbody size. Example for a spherical Zr. O 2 greenbody: Diameter: drying time 1 cm 5. 8 h 10 cm 20 days

Shaping Drying shrinkage Linear and volume shrinkage of a greenbody can be defined by: The shrinkage can be influenced by the moisture content (Dl) amd the particle dimensions (N) shrinkage defects due to 1. Unhomogeneous drying of a homogeneous greenbody 2. Homogeneous drying of unhomogeneous green body shrinkage drying rate critical moist. cont. warping cracking delamination moisture content Unhomogeneities: - uneven moisture distribution - preferred orientation of particles