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1、The Legacy of Investment CastingInvestment casting, the process used at Hitchiner Manufacturing to produce intricately detailed near-net-shape castings, is one of the oldest and also the most modern of the metallurgical arts. Hitchiner employs the latest scientific advances in CAD-CAM design and man
2、ufacturing, automated systems, conveyorization, robotics, countergravity casting techniques and other innovations to produce the highest quality investment cast parts available today. Hitchiner castings are at work in the fiery combustion chambers of jet aircraft, in the sub-zero vacuum of space, on
3、 the worlds streets and highways and in a myriad of other applications. Yet, the root of this technology, the cire perdue or lost wax process dates back many thousands of years. The artists and sculptors of ancient Egypt and Mesopotamia, the Han Dynasty in China, and the Benin civilization in Africa
4、 used the lost wax method of casting to produce their intricately detailed artwork of copper, bronze and gold. It is remarkable that the art of lost wax casting was so widely known in ancient times. It is not an easy process and calls for considerable skill in its execution. The Aztec gold-smiths of
5、 pre-Columbian Mexico used the lost wax process to create much of their elaborate jewelry. Unfortunately, few examples of this work survived the plunder of the conquistadors. Countless masterpieces were melted down into gold bars to enrich the Spanish treasury. The quality of the few pieces which ha
6、ve survived demonstrate a mastery of the process which must have taken many years of trial and error to develop. Accounts of the methods used are provided in the book by Friar Bernardino de Sahagun, who spent 60 years in an intensive study of Aztec Mexico. Each step in the process, which is describe
7、d and illustrated in his writings, was told to him by the Indians themselves. Some of the finest remaining examples of pre-Columbian Mexican casting were discovered in the 1930s at Monte Alban, the sacred mountain of the ancient Zapotecs near the city of Oaxaca. Many gold artifacts found there were
8、decorated with wirework presumably made by dipping threads into melted wax and applying them to the beeswax pattern prior to casting. In the city of Benin, now a part of Nigeria, brass smiths continue to produce lost wax castings using a method passed down through the ages from one generation to the
9、 next. A study of their methods provides a living example of the early history of the investment casting process. The brass casters at Benin begin with a core of clay kneaded into a mass. They shape the clay into the approximate size and shape of the article to be made. These cores are then allowed
10、to dry thoroughly in the sun for several days. The brass smith creates a pattern for the casting by covering one of these cores with beeswax and carefully modeling it into the exact shape desired. Thus, each casting is a unique hand formed work. When the wax form is finished to the artists satisfact
11、ion, it is covered in a thick coating of clay. Sometimes the cores are made to be self supporting, in other cases small pins are used to keep the core centered. The first layer of clay is applied as a very fine slip. Before the pattern is fully sealed in this coating, a thin roll of wax is added to
12、form a channel into which the molten metal will be poured. Subsequent layers of a thicker clay are added, gradually investing (covering) the form completely, creating a mold. This mold is allowed to air dry thoroughly. When a batch of molds have been created and are ready for casting. they are place
13、d in a fire and heated so that the wax will melt and can be poured off. The clay molds are further heated to a point where they are sufficiently fired to permit the pouring of the molten metal without causing the shell to burst. Meanwhile, pieces of brass are melted in crucibles on a nearby forge fi
14、re. The fire on the force is stoked by a manually operated bellows. Immediately prior to the pour, the molds are taken from the fire and placed upright in spaded earth. A crucible of metal is taken from the forge with long tongs and the molten brass is poured into the open mold. The brass smith hold
15、s a wooden stick in his other hand during the pour and places it on the edge of the crucible to help insure a smooth flow of metal into the shell. Soon after casting, the molds are broken open, the shell knocked off and the final object is cleaned, filed and polished. Benin lost wax castings can be
16、found in museums throughout the world. Shortly after the dark ages in Europe, the industrious sculptor and goldsmith, Benvenuto Cellini began to make use of the lost wax method of casting. He learned this process from the writings of the monk Theophilus Presbyter (circa 1100) whose Schedula Diversarum Artium is the earliest known foundry text. In Cellinis autobiography, considered to be one of the classics of literature, he describes in great detail the c
