Plastic Deformation of Powder Mixtures

Plastic deformation of a mixture Extrusion Injection molding Moist mixture of powder and binder solution Granulated mixture of powder and solid binder Elongated shapes with uniform cross section Small intricate shapes... 

Plastic deformation of a moldable powder-additive mixture is employed in several forming methods for ceramics. Extrusion of a moist clay-water mixture is used extensively in the traditional ceramics sector for forming components with a regular cross section (e.g., solid and hollow cylinders, tiles, and bricks). The method is also used to form some oxide ceramics for advanced applications (e.g., catalyst supports, capacitor tubes and electrical insulators). A recent development is the repeated co-extrusion of a particle-filled thermoplastic polymer to produce textured microstructures or fine-scale structures. Injection molding of a ceramic-polymer mixture is a potentially useful method for the mass production of small ceramic articles with complex shapes. However, the method has not yet materialized into a significant forming process for ceramics mainly because of two factors ... 

Compacted powder mixtures of titanium and titanium dihydride demonstrate the hydrogen-enhanced plasticity effects on deformation over 500 C, like titanium alloys hydrogenated from the gas phase. 

Two basic requirements must be satisfied for plastic forming to be successful. First, the mixture must flow plastically (above a certain yield stress) for formation of the desired shape. Second, the shaped article must be strong enough to resist deformation under the force of gravity or under stresses associated with handling. These two requirements are particularly important in extrusion, where the powder mixture contains a limited amount of binder and the shaped article must be dried after forming. As in casting methods, the... 

The plastic forming of ceramic shapes is based on the application of external forces to a mixture of ceramic powder and binder. The plastic mixture deforms and flows under applied stresses. The external forces cause the plastic mix to be adjusted to any die or mold, which dictates the eventual shape. Therefore, the flow behavior of such mixes during plastic forming has a major effect on the quality of the ceramic parts. Again, the flow stability of the mix during forming depends on the homogeneity of the ceramic powder and binder mixture. 

In this chapter, the effect of hydrophobic lubricant (i.e, stearic acid, magnesium stearate and sodium steaiyl fumarate), their concentration and blending time on the powder and compaction properties of a plastic deforming (sorbitol) and fragmenting material (lactose monohydrate) alone and in mixtures with spironolactone was assessed. 

Plastic forming methods in which a mixture of the ceramic powder and additives is deformed plastically through a nozzle or in a die provide a convenient route for the mass production of CCTamic green bodies. Extrusion is used extensively in the traditional ceramics industry and to a lesser extent in the advanced ceramics sector. Injection molding has been the subject of intense investigation in recent years, but it has not yet made any significant inroads in the forming of ceramics for industrial applications. 

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