Anyone had success with lost wax in a cement shell? ... Lost wax investment casting Book by C. W. Ammen "Cement Molds Cement investment molds are made in either two-part, cylindrical metal flasks or in rosin-paper flasks. The investment cannot be poured; it must be tamped down around the pattern. The investment consists of 10 parts (by volume) of 100- mesh silica sand to one part Hi-Early cement. The pattern should be made of three parts pine rosin (by weight) to one part victory wax. The cement and sand are mixed dry, and then tempered on the heavy side to about 8 percent moisture. The pattern is embedded in 4 or 5 inches of cement and sand and tamped down in the bottom of the flask. Then the mold is progressively built up by tamping to the required height and leveled off. The mold is allowed to set overnight, then inverted and dewaxed at 600 F. The cement mold does not require calcining at all, only dewaxing. The mold, when cold, can be filled with any metal or alloy up to 2800 F. in its molten state. Large cast-iron fountains and architectural pieces are often made this way. The mold is clamped together and dewaxed. After dewaxing, the mold is separated. The entire cavity, which at this point is exposed, is washed with a core wash, such as Zirc-O-Graph mixed with naptha. The naptha is ignited and burns off, setting the wash. The mold is then re- assembled, clamped together, and filled. If the piece is to be cored, it is lined with clay to the desired metal thickness and provided with the necessary prints for support. The core is made of the same mix used for the mold. The reason for using a rosin-wax pattern is that in dewaxing a cement mold, you do not calcine; heat is only used to melt the wax out. Thus, some wax is absorbed back into the mold face, making it soft during this operation. However, when the mold cools to room temperature, the rosin will re-harden the mold face. Extremely large castings have been successfully cast in bronze and iron this way, some of 20 tons or more in weight. Cement molds are best poured through bottom gating with several whistler vents on top, because wax left in the mold will ignite and burn and the fumes must have free passage out." ...
