Two common industry practices are double-dipping and prewetting. But, how similar or different are they? How much effect upon shell properties does a solids containing prewet dip actually have? Can shell thickness actually be controlled by immersion time? Previous work in this area over the past twenty or so years has suggested that the solids content in a prewet or double dip, or lack thereof, should have marked impact upon a shell strength and permeability. However, actual shell data was somewhat limited. Our previous paper confirmed the effect of all-liquids prewets upon slurry draining, shell drying and shell properties, but did raise questions on the effect of solids containing prewets.

This study reveals some interesting general principles which will be advantageous to foundry men and women where these two dip techniques are used, regardless of slurry system. This paper will address many of the questions that arose on the use of solid containing prewets.

Four shelling techniques will be compared. The first two being a single dip baseline and a double dip shell. The two systems compare all colloidal prewet and a shell prewet by thinned-down slurry. Slurry draining and shell drying differences will be shown. Shell strengths will be then be compared in the green and fired tested cold state as will be permeability and burst strength.