Forming by Powder Pressing

The primary particle size distribution of the powder, as well as the granule shape, has an influence upon the attainable density and strength of the molded article. The static friction between the individual particles and the compression mold can be reduced by lubricating additives, which largely suppress the development of structural stress. 

Compression pressures of up to 2 kbar are used depending of the composition of the powder and the required green density of the unsintered molded article. 

Highly mechanized plants can produce up to 300 unsintered articles/min/press. The achievable dimensional precision of the molded article is very high with tolerances down to several tens of microns in thickness and ca. 1 % in weight. Greater tolerances are allowable for large format refractory products. 

Dry pressing process utili/.able for simple geometric forms and long production runs. Stringent demands placed on the powder properties 

The molded article should have as high density and strength as possible 

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From the above discussion, it should be clear why objects formed by powder pressing exhibit virtually no shrinkage in drying (only several tenths of a per cent). In this case, the mix contains so little water that there are no water layers to separate the particles. However, even these products may be damaged by excessively rapid drying as a result of high pressure of steam which cannot escape through the pores. 

Porosimetry The determination of the open pore volume in a material. Example Mercury porosimetry, where mercury is hydrostatically forced into the pores and the weight change is measured. Porosimetry can be used in the specification of sputtering targets formed by powder pressing processes. 

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