A system of equations is established describing how variations in powder characteristics and process parameters are related to the quality of the sintered product.The basic assumption is that a cylindrical body is to be fabricated by cold pressing and sintering. It is also assumed that the allowable variations in the diameter, the bulk density, and/or the linear density of this sintered body are specified.The powder material is characterized by the slope, K, of the curve of green density vs. sintered dem,ity. Values near unity give least variation in sintered diameter. An important parameter of the process is the variation, Bg, of the green density.Variation of the parameters, B of bulk density, L of linear density, and D of sintered diameter are dependent on two groups of variables. The total variation may be composed of variations in the powder quality and the sintering conditions (group 1) or of variations in the green density (group 2).Taking a practical example, equations are derived for the ...

Equations describing dimensional and density variations in sintered bodies: application for predicting optimum production practice

As explained mathematically, the magnitude of the ‘diabolo’ effect in sintered nuClear-fuel pellets is a function of the slope and position of the sinterability curve and the density gradient existing in the green pellets. If sinterability is representedby a straight line passing through the origin, the diabolo effect is negligible; this condition can be fulfilled when using a deactivated powder.In any other case, the density gradient must be kept as low as possible to produce sintered pellets of regular shape. This is discussed as a function of powder roughness, lubricant quality, lubrication technique, and compaction characteristics.When the sinterability curve cannot be adapted and powder quality and lubrication conditions are fixed, the possibility still exists of minimizing irregularities in sintered diameter by using a single-action press and compacting the powder in an adapted conical die with a moving lower punch.

A. Smolders

Papers

Factors controlling the shape regularity of sintered u02 pellets