Frozen Mercury Shapes Molds
July 1949 Popular Science

July 1949 Popular Science [Table of Contents] Wax nostalgic about and learn from the history of early electronics. See articles from Popular Science, published 1872-2021. All copyrights hereby acknowledged.

As with the health hazards of smoking, in 1949 when this "Frozen Mercury Shapes Molds" article appeared in Popular Science magazine, the severe harm possible from ingestion or absorption of various forms of mercury were not well-established. The history of determination of physiological effects of mercury, both elemental and organic, is abundantly available on the Web, so I won't attempt to replicate it here. Suffice it to say that except under strictly controlled processes, the use of mercury as an agent for forming casting molds would never be done nowadays. Wax and Styrofoam are commonly used materials for the "lost-" technique of molding whereby a solid of easily liquefied material is a "positive" form encased by a secondary material - often sand or plastic - and then removed after the "negative" form has set (become solid). A "refractory material," as mentioned here, is one that remains solid at high temperatures. Here is a 1963 patent for mercury molding.

Frozen Mercury Shapes Molds

Solid mercury metal is one of industry's newest and chilliest materials. Made by cooling quicksilver past its 40-below-zero freezing point, it now replaces wax in precision casting. Applied in the Sperry Gyroscope Co. plant at Great Neck, N.Y., the method yields smoother and more accurate parts of aluminum and stainless steel.

Precision casting turns out quantities of metal parts of complicated shape, or of hard-to-machine alloys, with the advantage of a minimum of machining. The standard, time-honored "lost-wax" process duplicates a steel or brass master pattern by making, first, a master mold and, then, individual patterns of wax. Next, these are coated with refractory material, and the wax is melted out, to make individual molds. Molten, metal is poured into these molds to cast the parts, which are recovered by breaking away the molds. The patented new Mercast™ process follows the same principles.

Filled with liquid mercury, the master mold goes into a fluid refrigerant chilled with dry ice to -76° F., yielding a solid pattern of frozen mercury. Taken from the mold, this is dipped in a similarly cooled liquid mix of refractory material, which dries and hardens around it to form the final mold. Then the mercury is allowed to melt and run out. It is reclaimed for reuse.