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Home SAND CASTING:
Over View:
Sand casting use ordinary sand as the primary mold material. The sand grains are mixed with small amount of other materials, such as clay and water, to improve moldability and cohesive strength, and then packed around a pattern that has a shape of desired casting. A pattern should be removed before poring the molten metal, the mold is usually made in two pieces. An opening called the sprue hole is cut from the top of the mold. The molten metal is pored through the sprue hole in the mold, and enters the mold cavity through the opening called gate. Gravity flow is most common means of introducing the metal in the mold. After solidification, the mold is broken and the finished casting is removed. Because the mold is broken therefore it must be made for each casting.
Patterns:
The first step in casting is the design and construction of a pattern. This is the duplicate of the part to be cast.
Types Of Patterns:
There are many types of patterns used in the foundry, some of them are listed below:
In his type, the pattern is in one piece.
In this type pattern is in two pieces, and this type is used where one piece pattern is no applicable.
3)Match-plate-Pattern:
This type is similar to split type pattern, the only difference is that the pattern is mounted on the metal plate. The plates are used to aligned the two metals.
4)Lose Piece Pattern:
Pattern is made in pieces and they are assembled and cavity is made. When the cavity is ready and the metal is casted then they are disassembled.
Types Of Sand Used For Making Mold:
It has high refractory ness. It can withstand high temperature. It has low cost and can be re useable. It is available in wide range of grain sizes and shapes.
Silica sand is added with binders and make the mold cavity.
Rather silica sand have many advantages it has few draw bakes. It
has high expansion rate. It has tendency to fuse with metal. It can cause health hazards.
It is also used for making mold but it has larger number of organic compound in it and it reduce the mold ness of sand.
It is composed of washed sharp grain silica, to which 3-5% of clay is added to make mold cavity.
Sand Conditioing:
The sand used to make the molds must be carefully prepared it is to provide satisfactory and uniform results. Sand are added with additives to meet four requirements:
The ability to with stand high temperature.
The ability to retain a given shape when packed into a mold.
The ability to permit gasses to escape through it.
The ability to permit the metal to shrink after it solidifies and ultimately to free the casting by disintegration of the surrounding mold.
Type Of Sand Molds:
There are three basic types of sand mold used in the industry.
The above discussed facts were in our mind when we visited the production site. Now we will discuss the facts that we seen in the factory.
Observation:
After we reached the in-house production site the workers explained and showed us the process.
Products to cast:
There are different products which the workers are casting in the factory for automobiles, such as head, pulleys etc.
Pattern:
A metal pattern of the products was provided by the company, who given them the task to made the cast product.
Sand & Mold:
In the casting process first we have to decide which kind of mold is required. The workers in the factory that we have visited are using the green sand mold.
They are also adding " Molasses" as binders. The worker told us that by
adding molasses we can reuse the mold for several times.
Furnace:
Another basic requirement of casting is to melt the metal. For this purpose they were using the furnace.
The furnace they were using was heated by burning the crude oil or diesel oil.
The temperature may reach around 1100-1400 C.
The Process:
The metal i.e. cast iron is melted to a molten form in the furnace. In the meantime the flask’s upper and lower parts i.e. the cope and drag are prepared. The cope is filled with sand and so is the drag. Salt or powder is also sprayed so that metal and sand do not stick to each other. On the drag the pattern is kept and cope is placed above it tightly. Then the pattern is taken out forming a mold cavity. Arrangement for riser and gating system is done. Both cope and drag are fixed again .The sprue is formed by using a funnel or cylindrical shape metal that’s pierced or made to go in the and meeting the gating system.
From the furnace through a ladle ,the molten cast iron is brought and is poured into the flask through a sprue on cope. Molten metal which is filled till top of sprue is allowed to solidify. The gases are seen escaping from the top (cope) showing the permeability of mold.
There are many other flasks with the same mold too and the same procedure is followed in them.
After sometime the flask is opened and the formed product is taken out .The unwanted parts are removed by hammering and scrubbing and thus comes out the required product.
