A number of different methods have been introduced to the Investment Casting Industry for determining whether or not a coat of stucco has dried adequately enough to apply another coat. Although many of these have proven to be very successful where visual contact is possible, the areas that require extra drying generally are not easily seen. This presents a problem for foundrymen in trying to determine if the previous coat of stucco has dried completely in these conspicuously concealed areas. The result is that we have to be more than creative, to say the least, in attempting to take out the guesswork. One solution is to determine relevant conductivity of the previous stucco application prior to the next coat. Colloidal silica is a water based material making it a highly conductive element and being the primary constituent of the slurry, the slurry therefore becomes a conductive material as well. As the coat begins to dry it becomes less and less conductive and eventually becomes neutral with relation to conductivity. The question then is to determine the intended method for successfully measuring conductivity of the outer coat. One quick and simple idea is to use a conductivity meter measuring megohms of resistance indicating an acceptable range in a manner that shell room employees can read and understand. Any instrument designed to measure conductivity that offers a simple good or bad reading is ideal for this purpose. Attached is a photo of exactly this type of instrument.
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