Me401metalcasting.files.wordpress.com



Devin Ford0820933July 25, 2012ME 401 Research PaperLost-Wax Casting and its HistoryLost-wax casting is one of the most simple, common, and early casting techniques that is still used today. This casting process has to do with a metal sculpture being created from a wax mold that was sculpted by an artist. The wax is then removed leaving a hollow portion in the mold to form the metal. Completing this process requires a few simple steps that were created thousands of years ago. Lost-wax castings can be seen through ancient findings and in many techniques that are still used today.Lost-wax casting can be described in six main steps. The first step is to create a wax mold. This can be done with any sort of wax. Different waxes come in different colors and each has a different hardness. Currently, these casts use petroleum based products. However, in the past, bees wax and tree resins were used. The next step is to add sprues, which are also known as gates and vents. The gates act as a passageway for metal to flow into the mold while the vents allow air and other gasses to escape when the pour is occurring. Gates should be rectangular or triangular while vents should be circular. Vents are only required on some molds. For example, jewelry usually does not require vents because the mold material is usually porous enough to let gas escape and the pieces are not large enough to need extra vents. The third step is to cover the model and sprue in a material that can withstand the heat of the molten metal that will be poured into the cast. Some earlier historical examples of these investments include clay mixed 25% of horse manure or mixing clay with frayed cloth. The excretion and frayed cloth were added in order to increase porosity of the mold and also too add strength before it was fired. Ceramic shells or plasters are now mainly used to replace the clay mixtures. These shells or plasters can consist of gypsum mixed with quarts of other additives for lower heat pours or silicon-dioxide can be used for higher temperature pours such as platinum. Some molds may be reinforced by adding wires or other metal into the molds too increase the strength [Sias, 2005]. Wax is then needed to be burnt out of the molds. The molds are placed on a grate with the vents faced down and heated either by an oven or by an open flame. This process not only burns the wax out, but also helps harden the molds and helps the mold to become more porous by burning out the wax that could have soaked into the investment. The next step is to cast the mold. This can be done in several ways. The first way is to pour the metal into the vent and let gravity and the vents act to make the metal flow through the mold. A few other ways for casting include centrifugal casting and vacuum assisted casting. Centrifugal casting drives the metal to the edges of the mold by spinning it and allowing the centrifugal force to assist the gravity. Vacuum assisted casting is when a vacuum is used to extract air from the bottom of the mold so that a vacuum force is created to help suck the metal down and assist the force of gravity [Sias, 2005]. The final step is the removal of the investment. One way to do this is to plunge the mold into a bucket of water. This works mostly for small gold casts but allows the mold to disintegrate leaving just the gold behind although this technique can leave cracks in other metals [Sias, 2005]. The more common removal of the investment is to allow the mold to cool and remove the investment with a mechanical device such as a chisel. This can cause harm to the cast if not carefully done. Finally the sprues are cut off and the casting is cleaned up with tools such as saws, files, and sandpaper. The procedure described above is the method that is used today and it is similar to the lost wax casting that has been used throughout history.Lost-wax casting can be dated back over 6000 years ago. The first evidence of lost-wax casting was dated to 4200 BCE. This piece was a gold stud found in Syria also known as a terminal and could have been used as a gate in the casting process. Six more pieces were found in the Amung Plain in Syria, one of those pieces included a gold statue of a woman. These pieces were created around 4000 BCE. Gold was thought to be one of the earliest metals to be cast, even though the findings of gold casts in the present are very rare. This is due to the fact that gold can be so easily re-melted and reworked that would allow it to be made into modern day objects. Another huge finding occurred near Israel in a cave in Masada. Most of these other objects that were found are made of a bronze alloy of copper, antimony, and arsenic [Sias, 2005].Although the use of lost-wax casting was thought to be originated near the Tigris and Euphrates Rivers, it was also invented in several other locations shortly after its origin with no known contact with the place of origin. Some of these places include Egypt, China, South America, and Africa. Egyptians used the lost-wax technique near 2200 BCE. They cast tools and parts out of bronze and used the more valuable gold castings to make statues that would be stored in tombs. The Chinese were in the Brass Age from 2000 BCE to 500 BCE. Although the Chinese were in the Brass Age for this long period of time, they didn’t adopt the lost-wax techniques until the very end of the period. For the majority of this period they used clay molds in order to make their bronze statues. The lost- wax casting methods found in South America and Africa are dated to 1000 CE. Most of the castings made in South and Central America were gold, and thus thought to be melted down and shipped back to Europe in the Columbus and post Columbus ages. The techniques used to create castings found in Africa were thought to be adopted from Europe and are now known as Ashanti casting and are still practiced today [Sias, 2005]. The Ashanti technique consists of a wax mold placed around a clay base. A slip is first applied that is made from charcoal and clay and then the investment is added and is made out of a mixture of sand, tree palms, and clay. The mold is then attached to a crucible and placed in a kiln metal side down. After it is heated it is removed and flipped so that the metal can flow into the mold. The clay is then removed with chisels and hammers to reveal the casted object [West, 2012].The lost-wax casting techniques used in Greece between 600-500 BCE are the first signs of using similar techniques that are used today. They were the first civilization to use lost-wax molds to create very large castings. An example of this the creation of the 105 foot tall hollow bronze statue the Colossus of Rhodes, which is one of the seven wonders of the world. Many pieces of this were created from lost-wax molds and it stood for 65 years until it fell from an earthquake and the bronze was melted and sold to merchants [Sias, 2005].Currently lost-wax casting is used to produce things such as engine parts, sculptures and jewelry. The main automotive parts that are created are valves, gears, and lever arms. It is very common in this industry because it can create parts with a very smooth surface and also need very little finishing touches []. Lost-wax casting is one of the most common practices in making jewelry. This is due to the fact that wax is very cheap and jewelry artists can go into greater detail with the tools used. The process is normally done by carving away from a block of hard wax and then using a softer wax as an additive to build upon the harder wax when needed. The tools used by jewelers are normally a wax file, a spiral saw blade, dental picks, and wax pens. These tools can be heated up by a heat candle or torch in order to create easier working on the wax. A small sprue or vent is then attached to the piece and it is ready to cover and attached to a base. It is then covered with an investment solution which is normally a plaster-like substance rather than clay which was used in the more ancient techniques. Lost-wax casting again gives a very precise ending piece that needs very little clean up besides the removal of the sprue. [Loney, 2009]. Lost-wax casting is a technique that has stood the test of time. It can be accomplished in six simple steps and artifacts that have been made from this technique have been discovered dating back 6000 years ago. The procedure of lost wax casting was also thought to be created in various parts of the world with no contact between these very different cultures. This ancient art form has only been slightly modified to create items such as jewelry and automotive parts in the present day.ReferencesLost Wax Casting: Old, New, and Inexpensive Methods, Fred R Sias, 2005Metal Jewelry made Easy, Jan Looney, 2009 of Metal Casting, Laura west, 2012 ................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download