We expect a great deal from our investment casting slurries. They are called upon not only to build a uniform shell, flow into narrow passage ways, fill through holes and allow fine lettering detail in castings. They are called upon to also build shell in an increasingly more rapid pace for greater production efficiencies. These two requirements commonly work against each other. Typically, slurries are either thin for detail or thick for rapid shell building! Although some new slurries can accomplish this dual role quite well, prewet dips can also be used successfully for those slurries which do not handle the twin requirements well.,p>

The objective of this paper is to equip investment casters with a more complete understanding upon how the use of prewets affects their drying times and shell properties. The questions we will attempt to address here include the following: “How is my shell thickness affected by all liquid prewet dips?” and “How is shell strength, and permeability affected by one or multiple prewet dips?” We will attempt to answer others such as: “To what degree is my required shell dry time affected by single or multiple prewet dips?”

This report compares the affect of an ‘all-liquid” (no flour) prewet upon drying, as well as how several shell building characteristics are affected thru retained slurry and stucco amounts. The report then covers the affect upon standard shell strengths in the green, hot-wet, fired tested cold and fired tested hot conditions. Additional data is then presented which covers the affect of prewet use upon burst strength and shell permeability. Differences are shown between no prewet use and one thru as many as five prewets and the resultant trends in drying and shell properties.