Moulding and Processing of the Metal - Assignment Example

BULK PROCESSING OF METALS Student’s Name Course Professor’s Name University City Date Question One (510 Words) Metal casting is a practice in which liquid metal, also known as molten, flows by gravity or other forces into a mold. The metal solidifies taking the desired shape of the mold cavity. The mold could be made of sand, ceramic or any other material that can withstand hot liquid metal. Almost all major metals can be cast including aluminum, zinc, steel, iron, and copper-based alloys. The process of casting involves melting the metal, pouring it into a mold, and then letting it freeze (Okayasu et al. 2015, p. 1442). Metal casting is a very important industry because it is used to create large and complex parts such as engine blocks for cars, large pipes, railway wheels, statues, and so on. Additionally, the process also produces small but beneficial products like frying pans, toys and a dental crown. However, the process also has disadvantages such as environmental problems and the limitation of the mechanical properties of the metals used. Herein, we shall address the effects of casting on the material properties of different metals. The heat transfer and fluid flow in metal casting have a direct effect on the formation or suppression of defects. Various defects such as porosity or misruns are controlled by the two factors. Additionally, properties such as the strength of a metal casting or the grain structure depend on the rate and direction of the heat transfer (Okayasu et al. 2015, p. 1442). The effects of metal casting depend on the structure of the metal or alloy. Some of the material properties of metals that are affected by casting include grain structure, strength, ductility, fluidity, temperature and so on. Material properties are improved by an increased solidification rate because the fine grains have a low dislocation density. The molding material plays a very important role in the determining how casting affects the material properties of the metal. If the mold material has a high thermal conductivity, the heat transfer will be more and the molten metal will solidify faster thus impeding on a free flow. The extreme temperatures can also affect the grain size of the metal or alloy. The grain structure may become resistant to deformation. The casting material may elongate some grains making them less strong than others and also affecting the smooth finish of the metal (Okayasu et al. 2015, p. 1445). Casting temperatures also affect the molding material. The casting process affects the tensile strength and ductility of the metals because of the low volume fraction of the metal structures. The material properties of metal also affect the ease into which molten metal can be molded without defects. Therefore, castability depends on two things, the material property and the part design of the metal. It is essential to know the material properties of a metal so as to fully understand their characteristics in different forms and how they can be transformed into different products easily with minimal defects. Therefore, metal casting is an essential process in the formation of different products ranging from large and durable parts to simple materials such as jewelry. Question Two (524 Words) Sand casting is the pouring of molten metal on a mold cavity formed out of natural or synthetic sand. It is the most popular casting process and it is used to make large and complex metal parts. The cavity in the sand mold is formed by duplicating a real part into a pattern. Some of the applications of sand casting include vehicle components like engine blocks and prosthetic hips. This part is a discussion on the suitability of using sand casting as a process to manufacture engine blocks and prosthetic hip replacements. Engine Blocks There are various sand molds and cores used to make the engine block and head. The molds are filled with sand in all the spaces where metal is not needed. The sand casting of the engine block combines different techniques of casting and machining. The mold defines the shape of the engine and the sand mold is used in this process because the special coating on the mold does not allow the sand to stick to the metal (Nguyen 2005, p.11). The sand mold is used in the manufacturing engine block because the sand cast can withstand high temperatures of the molten metals. The mold can also be designed in a way that when the molten metal is poured, it fills all the gaps allowing air to escape through vents and more metal is poured in. The suitability of sand casting is due to its ability to fabricate large locomotive parts and the mold can be designed to reduce flaws in the component because it allows for a certain degree of flexibility and shrinkage when the molten metal is cooling off. Additionally, as the metal cools the sand can be cleared away so that only the metal part is left for use. Prosthetic Hip Replacement Prosthetic hips are one of the major developments in orthopedics because it helps restore patient’s functionality and relieves joint pains. The replacements require significant detail of surface finish because they work as integrated body parts. One of the traditional methods used to manufacture hip replacement is sand casting. The process is done through making a model of the implant, imprinting it on two blocks of sand, taking out the model, pouring molten metal on the sand molds and letting it cool. The model is taken out and polished to finish. Through the process, the suitability of the sand casting as a process of manufacturing hip replacements is undermined because it will not give the model an excellent surface finish. The material properties of the metal used are affected, leading to unavoidable defects. The defects make the hip replacement subject to breakage causing other complications to the patient. Additionally, the sand casting method has various inaccuracies, making the whole process expensive. Sand leads to rough features on the model which means that other secondary steps have to be taken to correct the irregularities and achieve uniformity in all the pieces (McKinley 2006, p. 1). Therefore, sand casting is not a suitable method of manufacturing Prosthetic hip replacements because the implant must endure great strain over a long period without having to undergo regular inspection or replacement. Question Three (519 Words) Aluminum is produced from bauxite. The following is the manufacturing process of aluminum tin foil: Refining The bauxite is refined using the Bayer process that has four steps. In the digestion stage, the bauxite is pumped into large pressurized tanks and then mixed with sodium hydroxide. The process applies heat and pressure to saturate the ore into sodium aluminate and other insoluble contaminants. The second step is clarification, and it involves filtering the contaminants by passing the solution through a set of tanks and presses. The remaining filtered solution is sent to a cooling tower. In the third part, precipitation takes place and aluminum oxide is moved into large silos. The fluid is seeded with crystals of hydrated aluminum to help with the formation of aluminum particles into large lumps of aluminum hydrate. The clumps are then filtered out and rinsed (Madehow.com, 2017). The last step in the refining process is calcination whereby the aluminum hydrate is exposed to extreme temperatures so as to dehydrate the material and get the residue aluminum oxide in form of fine white powder. Smelting The process separates the alumina produced in the Bayer process and dissolves it in a smelting cell that is lined with carbon and filled with a heated liquid conductor of cryolite. An electric current is then passed through the cryolite to form a crust on top of the alumina melt. More alumina is gradually added and stirred into the mixture and the crust breaks and is stirred as well. As the alumina dissolves, it decomposes electrolytally to produce a sheet of pure liquid aluminum in the smelting cell. Then, the purified liquid aluminum is drained from the smelting cell and put into crucibles and emptied into the furnace. Foil is made of pure aluminium so the liquid is poured directly into the chill casts where it cools as large slabs called ingots or reroll stock (Madehow.com, 2017). The ingots are heat-treated to enhance workability, and thus, suitable for rolling into the foil. Finishing The Aluminum tin foil is passed through a series of rolling mills that are specially designed for the production of foil. The mills ensure that the foil is uniform, high-tolerant, and has a thin-gauge material. The work rolls machines come after the mill rolls and they guarantee that the foil is flat and has a bright finish. Finally, the foil sheets are trimmed and slit to produce narrow and smooth edges. Some of the mechanical properties of aluminum include linear expansion, machining, formability, and so on. The whole process of manufacturing aluminum tin foil subjects liquid aluminum to extreme conditions that may affect the mechanical properties of the aluminum metal. However, the molecular structure of the metal provides it with a high performance barrier. The metal becomes more malleable in the new state and can be easily deformed, especially when in contact with high temperatures. However, the transformation of the aluminum metal does not interfere with its integrity despite the new form of tin foil. The mechanical properties of the metal are not affected by the transformation of the metal into the foil. Bibliography Madehow.com. (2017). How aluminum foil is made - material, manufacture, making, used, processing, dimensions, aluminium, procedure. [online] Available at: http://www.madehow.com/Volume-1/Aluminum-Foil.html [Accessed 25 Apr. 2017]. McKinley, L. (2006). Metal injection moulding for the production of medical implants. Patent Application Publication. US 20060285991 A1 Nguyen, H. (2005). Manufacturing Processes and Engineering Materials Used in Automotive Engine Blocks. Materials Science and Engineering Section B, EGR250, 1. Okayasu, M., Miyamoto, Y., and Morinaka, K. (2015). Material properties of various cast aluminum alloys made using a heated mold continuous casting technique with and without ultrasonic vibration. Metals, 5(3), 1440-1453. Read More