Recommendations 1. Distortion allowance Vertical edges will be curved or distorted, this is prevented by shaped pattern converge slightly inward so that the casting after distortion will have its side vertical. Prevention also can be done by providing sufficient machining allowance to cover the distortion effect and by providing suitable allowance on the pattern called camber or distortion allowance.
2. Ramming a mold Few inches of sand over the pattern should be carefully rammed and tightly packed. Soft spots, packets should be rammed properly. The mould should be rammed layer by layer. Besides ramming should be done as close to vertical surfaces of pattern. 3. Moulding sand preparation and moisture content determination The moisture content controls practically all other properties of the sand. It is a varying property since water content constantly evaporates during mold preparation. So water should be add sufficiently to bring the moisture content to within desired limits and uniform distribution of water all over the sand so that all part of the sand receive has same moisture property. Do not let the sand dry out. Use sand riddle to cover the first layer just the pattern only and make sure there is no lumps. The riddle fluffs the sand up so it can be packed properly and avoid defects. If the sand is too wet torch the casting area about a minute, this will dry out excess moisture. 4. Gases in metals The gases in metal is important in deciding the defect free castings. In metal castings, gases may be mechanically trapped, due to variation in their solubility at different temperatures and phases and mechanical reaction with surrounding air during melting and pouring of the metal. So precaution had to take to overcome this for example by bubbling dry insoluble gases through molten melt. Do not overheat any metal that use in the melting process. 5. Pouring and gating design A good design gating design should be made to ensure proper distribution of molten metal without excessive temperature loss, turbulence, gas trapping and slags. Molten metal should be poured very slowly, since time taken to fill the mould cavity will become longer, solidification will start even before the mould is completely filled. A steady rate of pouring should be use. Molten metal also should not be poured very faster because it can erode the mouled cavity. So gating design is important and it depends on the metal pouring and molten metal composition.
6. Additives Additives like coal dust, pulverized slag, manganese dioxide and others should be added to the sand mixture to improve surface finish and avoid thermal cracking during pouring. The lubricants such as calcium stearate can be added to improve the flowability of the sand and permit easy release of the shell from the pattern. 7. Avoid and overcome defects Shrinkage – use large sprue and riser to promote directional solidification. Locate risers and gating systems in correct positions. Gates to be cut as wide as possible. Porositiy – avoid excess ramming of mould and provide proper vent holes. Avoid use of excess carbonaceous or other organic material in the sand /core binders, because these materials react with the molten metal producing large amount of gases. Misrun – fluidity of metal should be high. Pouring rate and time should be controlled. Penetration – sand should be properly rammed and moulding sand should not be too coarse to promote metal penetration and control the metal temperature. Hot tears – provide adequate fillets at sharp corners. Proper metallurgical and pouring temperature. Place gates and risers at proper locations.
Conclusion
The molding operation aboard ship depends primarily on the molder and ability on certain people. A molding technique based on careful attention to the various details involved in making a mold. As a conclusion this experiment should have the following qualities to a degree suitable for the purpose intended: 1. Refractoriness to withstand the casting heat. This is obtained by selection material and proper processing. 2. Strength to withstand handling and casting forces. This is obtained by the use of the proper amount of binders and by good internal structural supports. 3. Collapsibility to permit breakdown during contraction of the casting and ease of cleaning. By avoiding the use of sands bonded too strongly and by hollowing out the center or filling it with coke, cinders, gravel, or weak sand, this quality may be obtained. 4. Smooth strong surface to provide a good casting finish, internal cleanliness, and ease of cleaning. This quality is obtained by the use of an adequately bonded refractory sand, uniformly hard rammed, baked immediately after being made, and used shortly after baki.ng. 5. Low gas content to prevent unsoundness in the casting. This quality is obtained by using the minimum of organic binding materials, baking well, and venting thoroughly. All of the above features are essential in core making and are regularly obtained only by good core practice Molding consists of all operations necessary to prepare a mold for receiving molten metal. Molding usually involves placing a molding aggregate around a pattern held with a supporting frame, withdrawing the pattern to leave the mold cavity, setting the cores in the mold cavity and finishing and closing the mold. The preparation of molten metal for casting is referred to simply as melting. Melting is usually done in a specifically designated area of the foundry, and the molten metal is transferred to the pouring area where the molds are filled. In a nutshell, the principles and terminology underlying the sand casting process has been investigated. Overall, this experiment has been done well and all the understanding and knowledge about molding preparation and pouring are obtained.
