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Casting is a manufacturing process by which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify. The solidified part is also known as a casting, which is ejected or broken out of the mold to complete the process. Casting materials are usually metals or various cold setting materials that cure after mixing two or more components together; examples are epoxy, concrete, plaster and clay. Casting is most often used for making complex shapes that would be otherwise difficult or uneconomical to make by other methods. |
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| Investment Casting (Lost-wax casting) |
| Investment casting (known as lost-wax casting in art) is a process that has been practised for thousands of years, with the lost-wax process being one of the oldest known metal forming techniques. From 5000 years ago, when beeswax formed the pattern, to today’s high technology waxes, refractory materials and specialist alloys, the castings ensure high-quality components are produced with the key benefits of accuracy, repeatability, versatility and integrity. Investment casting derives its name from the fact that the pattern is invested, or surrounded, with a refractory material. The wax patterns require extreme care for they are not strong enough to withstand forces encountered during the mold making. One advantage of investment casting is that the wax can be reused. The process is suitable for repeatable production of net shape components from a variety of different metals and high performance alloys. Although generally used for small castings, this process has been used to produce complete aircraft door frames, with steel castings of up to 300 kg and aluminium castings of up to 30 kg. Compared to other casting processes such as die casting or sand casting, it can be an expensive process, however the components that can be produced using investment casting can incorporate intricate contours, and in most cases the components are cast near net shape, so requiring little or no rework once cast. |
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| Stainless steel couplings by SME Lost-wax casting | |||
| 1. Prior to wax pattern making, we produce a master pattern: our mould-maker creates an original pattern from wax (clay, wood, plastic, steel, or another material). Then Mouldmaking: A mould, known as the master die, is made of the master pattern. The master pattern may be made from a low-melting-point metal, steel, or wood. If a steel pattern was created then a low-melting-point metal may be cast directly from the master pattern. Rubber moulds can also be cast directly from the master pattern. The first step may also be skipped if the master die is machined directly into steel. SME employs craftsmen of over 20-year experiences who make patterns in strict compliance with the designed drawings. We are mostly careful with our pattern precision and its secrecy. Customer-owned patterns are trackable and unique with definite markings. Any copy or violence of supply elsewhere is strictly prohibited. SME has been living up to its good fame of accurate patterning capacity and customer-oriented management of molding storage systems. |
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| 2. Produce the wax patterns: Wax patterns may be produced in one of two ways. In one process the wax is poured into the mold and swished around until an even coating, usually about 3 mm (0.12 in) thick, covers the inner surface of the mould. This is repeated until the desired thickness is reached. Another method is filling the entire mould with molten wax, and let it cool, until a desired thickness has set on the surface of the mould. After this the rest of the wax is poured out again, the mould is turned upside down and the wax layer is left to cool and harden. With this method it is more difficult to control the overall thickness of the wax layer. Starting pattern process, SME applies 100% checking machanism. Every single piece of wax pattern is examined by inspectors due to the fact that wax patterns are the actual base of end products in respect of the surface quality, dimensional accuracy and so on. |
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3. Assemble wax patterns: The wax pattern is then removed from the mould. Multiple patterns are attached to a wax sprue, with the result known as a pattern cluster, or tree; as many as several dozen patterns may be assembled into a tree depending on products. The wax patterns are attached to the sprue or each other by means of a heated metal tool. Each day, no less than three thousand wax patterns are assembled in SME foundries, keeping the continuous supply chain of qualified products. |
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| 3. Investment: Investment is produced by three repeating steps: coating, stuccoing, and hardening. The first step involves dipping the cluster into a slurry of fine refractory material and then letting any excess drain off, so a uniform surface is produced. This fine material is used first to give a smooth surface finish and reproduce fine details. In the second step, the cluster is stuccoed with a coarse ceramic particle, by dipping it into a fluidised bed, placing it in a rainfall-sander, or by applying by hand. Finally, the coating is allowed to harden. These steps are repeated until the investment is the required thickness, which is usually 5 to 15 mm (0.2 to 0.6 in). Note that the first coatings are known as prime coats. 5~7 layers are applied in SME Stainless couplings casting procedures, in pursuit of the finest surface and the strongest mechanical parameters. |
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| 4. Dewax: The investment is then allowed to completely dry, which can take 16 to 48 hours. Drying can be enhanced by applying a vacuum or minimizing the environmental humidity. It is then turned upside-down and placed in a furnace or autoclave to melt out the wax. Most shell failures occur at this point because the waxes used have a thermal expansion coefficient that is much greater than the investment material surrounding it, so as the wax is heated it expands and induces great stresses. In order to minimize these stresses the wax is heated as rapidly as possible so that the surface of the wax can melt into the surface of the investment or run out of the mold, which makes room for the rest of the wax to expand. Any wax that runs out of the mold is usually recovered and reused. | |||
| 5. Burnout: The mold is then subjected to a burnout, which heats the mold between 870 °C and 1095 °C to remove any moisture and residual wax, and to sinter the mold. | |||
| 6. Pouring: The investment mold is then placed cup-upwards into a tub filled with sand. The metal may be gravity poured, but if there are thin sections in the mold it may be filled by applying positive air pressure, vacuum cast, tilt cast, pressure assisted pouring, or centrifugal cast. | |||
| 7. Removal: The shell is hammered, media blasted, to release the casting. The sprue is cut off and recycled. The casting may then be cleaned up to remove signs of the casting process, usually by grinding. | |||
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| SME is managed to build up our own manufacturing flow, starting reliable raw materials source to developing diversified ways of casting techniques, including investment casting, gravity casting, low-pressure casting and die-casting, etc. Well control at the starting point of couplings manufacture grants SME enormous vantages against small-scale producers. Staying open-minded to leading casting technologies, SME keeps fast reacted to the market trends with a good care of user experiences. | |||
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