![]() At the bottom of the sprue there is a gap called well for the collection of the unwanted sand, which comes with the flowing metal. It should not be small because this enhances rapid solidification in the runner causing a blockage. ![]() The runner should not be big because it will increase the amount of the waste metal. The cope and drag are prepared separately and when they are ready they unites and metal is poured into it through a canal called sprue, which transmits the molten metal via runner into the mold cavity. The upper part of the mold is called the cope and the lower part called the drag. The reason for this is to remove the tasted part easier from the mold. So mold is also made up of two halves, which is separated by a parting line. Filling a metal box having two halves, which is called the flask forms mold. 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. Nails are inserted into thin parts of the mold to reinforce them. Some metal springs called densiments are placed into the mold Io provide uniform solidification of the metal throughout the mold. To ensure that cores retain the correct arrangement core prints are placed into the mold. 3) Yellow indicates that the surface needs machining. 2) Black indicates that the surface needs core and shows the position of the sand core. 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. Patterns have also some identifiers such as colors on them, each of which has different meaning that represent different treatments and requirements for the patterns. Some special coating to prevent their destruction should coat patterns. The size of the pattern depends upon the shrinkage during cooling and the Finishing allowance. So selection of the appropriate pattern material depends to a large extent on the total quality of castings to be made. For example aluminum is the most common metal to be used if" many castings are to be made by the same pattern. Metal patterns are more expensive to make, but they last much longer. Its disadvantages 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). Wood is a common pattern material because it is easily worked into shape. Materials used to make patterns include wood, plastics, aluminum, fiberglass, cast iron and some other metals. 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. Sand Casting is the most important and mostly used casting technique. So for each casting operation you have to form a new mold. ![]() In sand casting expandable molds are used. Sand Casting is simply melting the metal and pouring it into a preformed cavity, called mold, allowing (the metal to solidify and then breaking up the mold to remove casting. It provides us with the possibility of forming wide range of shapes with wide range of materials. ![]() Casting as an old technique is the quickest link between engineering drawing 2nd manufacturing.
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