video - 1 SAND CASTING Casting as an old technique is the...

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1) SAND CASTING Casting as an old technique is the quickest link between engineering drawing 2nd manufacturing .It provides us with the possibility of forming wide range of shapes with wide range of materials. Sand Casting is simply melting the metal and pouring it into a preformed cavity, called mold, allowing ( t he metal to solidify and then breaking up the mold to remove casting. In sand casting expandable molds are used. So for each casting operation you have to form a new mold. Basic Requirements for metal casting 1. A mold cavity 2. Melting process 3. Pouring technique 4. Solidification process 5. Removal of casting 6. Finishing draft allowance Sand Casting is the most important and mostly used casting technique. To perform sand casting we have to form a pattern (a full sized model of the part), enlarged to account for shrinkage and machining allowances in the final casting. Materials used to make patterns include wood, plastics, aluminum, fiberglass, cast iron and some other metals. Wood is a common pattern material because it is easily worked into shape. Its disadvan t ages are that it tends to warp and the sand being compacted around it abrades it, thus limiting the number of times it can be reused (used for a small number castings). Metal patterns are more expensive to make, but they last much longer. For example aluminum is the most common metal to be used if" many castings are to be made by the same pattern. So selection of the appropriate pattern material depends to a large extent on the total quality of castings to be made. The size of the pattern depends upon the shrinkage during cooling and the Finishing allowance. Some special coating to prevent their destruction should coat patterns. Patterns have also some identifiers such as colors on them, each of which has different meaning that represent different treatments and requirements far the patterns. The color-coding for patterns in sand casting is as follows 1) Red indicates that the surface of the material should be left as it is after casting. 2) Black indicates that the surface needs core and shows the position of the sand core. 3) Yellow indicates that the surface needs machining. The casting will be missing. To ensure that cores retain the correct arrangement core prints are placed into the mold. Some metal springs called densiments are placed into the mold Io provide uniform solidification of the metal throughout the mold. Nails are inserted into thin parts of the mold to reinforce them. After forming the mold cavity, an alcoholic liquid is sprayed aver the cope (The upper part of the mold) and heated with flames to harden and to dry the surface.
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Filling a metal box having two halves, which is called the flask forms mold . So mold is also made up of two halves, which is separated by a parting line . The reason for this is to remove the tasted part easier from the mold. The upper part of the mold is called the cope and the lower part called the drag. The cope
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