Ceramic mold casting

I I Process does not normally operate within this region 

7CC Ceramic mold casting process capability chart. 

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Slip casting of metal powders closely follows ceramic slip casting techniques (see Ceramics). SHp, which is a viscous Hquid containing finely divided metal particles in a stable suspension, is poured into a plaster-of-Paris mold of the shape desired. As the Hquid is absorbed by the mold, the metal particles are carried to the wall and deposited there. This occurs equally in all directions and equally for metal particles of all sizes which gives a uniformly thick layer of powder deposited at the mold wall. 

Most important, this bronze vessel has seams which show it to have been cast from a mold made in four separated sections. This wine cup required a complex ceramic mold, which sets the early Chinese bronze technology apart from the lost-wax process used in the West. 

Preliminary experiments on the ultrasonic treatment of solidifying precise castings (into ceramic molds) have shown that significant warming of a melt in a mold occurs with development of cavitation and introduction of acoustic power above 100 W. As the volume of a casting is not large and the melt mass is hardly above 0.2 kg, the data obtained allow one to follow the improved filling of thick channels under ultrasonic action. 

Besides royal gold jewelry, they made artistic brass weights, spoons, and boxes. They also worked copper, zinc, tin, lead, and nickel. They cast objects in brass by the lost wax method. In this process, shapes were carved in wax, then encased in clay and baked. The hot wax was poured out, leaving a ceramic mold. 

The process as it is practiced now actually produces a ceramic shell of modest thickness (about 0.2-0.5 in. thick) around the wax pattern. The relatively thin shell when compared to solid mold casting not only saves material but also allows for more uniform and rapid cooling of the metal parts. This is an important factor in maintaining fine grain size that results in stronger parts. 

Rusher, R.L. Strength Factors of Ceramic Shell Molds , Cast Metals Research Journal, Vol. 10, No. 4 December 1974 and Vol. 11, No. 1 March 1975. 

Observations indicate that particle morphology and PSD greatly influence the quality of slurries in the reproduction of details and thin sections of ceramic molds. Consequently, good cast-metal quality may be obtained. It is clear from the results... 

Ceramic precision casting for aluminum molds should only be used when a milling process is not economical. It should not be forgotten that the cast models have to be manufactured in the milling process. 

The use of mold shells manufactured in an aluminum casting is advantageous for large and deep mold shells or for necessary follow-on molds. For the manufacture of aluminum casting mold shells, the casting molds made from sand or sand/ceramic molds have to be manufactured first. The aluminum casting process, shown in Figure 1.179, is done by hand. 

A mold is used to generate a wax pattern of the shape required. A refractory material zircon, then a ceramic slurry and finally a binder is used to coat the pattern which is slow fired in an oven to cure. The wax is melted out and the metal cast in the ceramic mold. The mold is then destroyed to remove the casting. Process often known as the Lost Wax process (see 1.6F). 

During the Chalcolithic period, copper was produced in clay-lined furnaces. Ceramic containers were made to hold and refine molten metal, and ceramic molds were used to cast the metal. Colored ceramic glaze was made... 

Large quantities of zinc are used to produce die castings, which are used extensively by the automotive, electrical, and hardware industries. An alloy called Prestal(R), consisting of 78 percent zinc and 22 percent aluminum, is reported to be almost as strong as steel and as easy to mold as plastic. The alloy said to be so moldable that it can be molded into form using inexpensive ceramics or cement die casts. 

Nickel—beryllium casting alloys are readily air melted, in electric or induction furnaces. Melt surface protection is suppHed by a blanket of argon gas or an alumina-base slag cover. Furnace linings or cmcibles of magnesia are preferred, with zirconium siUcate or mullite also adequate. Sand, investment, ceramic, and permanent mold materials are appropriate for these alloys. Beryllium ia the composition is an effective deoxidizer and scavenger of sulfur and nitrogen. 

Slip Casting. SHp casting (38,40—42,45,59—62), the process in which a cast is formed from a slurry using a porous mold, is used to form sinks and other sanitary ware, figurines, refractory cmcibles, porous thermal insulation, fine china, and complex shape stmctural ceramics such as multivane rotors. 

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