SAND CASTING
Sand Casting
Casting is the process of production of objects by pouring molten into the cavity called a mould which is the negative, or mirror image of the object, and allowing it to cool and solidify. Sand casting is means of producing rough metal casting using a mould usually made from sand formed around a replica of the object to be cast (called a pattern) that is removed once the sand has been compacted. Sand castings not further worked by polishing are readily recognized by the sand-like texture imparted by the mould. As the accuracy of casting is limited by imperfections in the mould making process there will be extra material to be removed by grinding or machining, more than is required by other more accurate casting processes. Furthermore because the mould is destroyed in order to retrieve the object, a new mould must be made for each casting. Casting is a manufacturing process by which a liquid material such as suspension of minerals as used in ceramics or molten metal or plastic is introduced into a mould, allowed to solidify within the mould, and then ejected or broken out to make a fabricated part. Casting is used for making parts of uneconomical to make by other methods, such as cutting form solid material.
Casting may be used to form hot, liquid metals or meltable plastics (called thermoplastics), or various materials that cold set after mixing of components such as certain plastic resins such as concrete or plaster, and materials that become liquid or paste when moist such as clay, which when dry enough to be rigid is removed from the mould, further dried, and fried in a kiln or furnace.
Substitution is always a factor in deciding whether other techniques should be used instead of casting. Alternatives include parts that can be stamped out on a punch press or deep-drawn, forged, items that can be manufactured by extrusion or by cold bending, and parts that can be made from highly active metals.
Sand:
Product of the disintegration of rocks over long periods of time.
Most sand casting operations use silica sand (SiO2). A great advantage of sand in manufacturing applications is that sand is inexpensive. Another advantage of sand to manufacture products by metal casting processes is that sand is very resistant to elevated temperatures. In fact, sand casting is one of the few processes that can be used for metals with high melting temperatures such as steels, nickel, and titanium. Usually sand used to manufacture a mould for the casting process is held together by a mixture of water and clay. A typical mixture by volume could be 89% sand, 4% water, 7% clay. Control of all aspects of the properties of sand is crucial when manufacturing parts by sand casting, therefore a sand laboratory is usually attached to the foundry.
Use of Binder in Sand Casting:
A mould must have the physical integrity to keep its shape throughout the casting operation. For this reason, in sand casting, the sand must contain some type of binder that acts to hold the sand particles together. Clay serves an essential purpose in the sand casting manufacturing process, as a binding agent to adhere the moulding sand together. In manufacturing industry other agents may be used to bond the moulding sand together in place of clay. Organic resins, (such as phenolic resins), and inorganic bonding agents, (such as phosphate and sodium silicate), may also be used to hold the sand together. In addition to sand and bonding agents, the sand mixture to create the metal casting mould will sometimes have other constituents added to it in order to improve mould properties.
Types of Sand Used In Sand Casting:
There are two general types of sand used in the manufacturing process of sand casting
Naturally Bonded:
Naturally bonded sand is less expensive but it includes organic impurities that reduce the fusion temperature of the sand mixture for the casting, lower the binding strength, and require higher moisture content
Synthetic Sand:
Synthetic sand is mixed in a manufacturing lab starting with a pure (SiO2) sand base. In this case, the composition can be controlled more accurately, which imparts the casting sand mixture with higher green strength, more permeability, and greater refractory strength. For these reasons, synthetic sand is mostly preferred in sand casting manufacture.
Casting is the process of production of objects by pouring molten into the cavity called a mould which is the negative, or mirror image of the object, and allowing it to cool and solidify. Sand casting is means of producing rough metal casting using a mould usually made from sand formed around a replica of the object to be cast (called a pattern) that is removed once the sand has been compacted. Sand castings not further worked by polishing are readily recognized by the sand-like texture imparted by the mould. As the accuracy of casting is limited by imperfections in the mould making process there will be extra material to be removed by grinding or machining, more than is required by other more accurate casting processes. Furthermore because the mould is destroyed in order to retrieve the object, a new mould must be made for each casting. Casting is a manufacturing process by which a liquid material such as suspension of minerals as used in ceramics or molten metal or plastic is introduced into a mould, allowed to solidify within the mould, and then ejected or broken out to make a fabricated part. Casting is used for making parts of uneconomical to make by other methods, such as cutting form solid material.
Casting may be used to form hot, liquid metals or meltable plastics (called thermoplastics), or various materials that cold set after mixing of components such as certain plastic resins such as concrete or plaster, and materials that become liquid or paste when moist such as clay, which when dry enough to be rigid is removed from the mould, further dried, and fried in a kiln or furnace.
Substitution is always a factor in deciding whether other techniques should be used instead of casting. Alternatives include parts that can be stamped out on a punch press or deep-drawn, forged, items that can be manufactured by extrusion or by cold bending, and parts that can be made from highly active metals.
Sand:
Product of the disintegration of rocks over long periods of time.
Most sand casting operations use silica sand (SiO2). A great advantage of sand in manufacturing applications is that sand is inexpensive. Another advantage of sand to manufacture products by metal casting processes is that sand is very resistant to elevated temperatures. In fact, sand casting is one of the few processes that can be used for metals with high melting temperatures such as steels, nickel, and titanium. Usually sand used to manufacture a mould for the casting process is held together by a mixture of water and clay. A typical mixture by volume could be 89% sand, 4% water, 7% clay. Control of all aspects of the properties of sand is crucial when manufacturing parts by sand casting, therefore a sand laboratory is usually attached to the foundry.
Use of Binder in Sand Casting:
A mould must have the physical integrity to keep its shape throughout the casting operation. For this reason, in sand casting, the sand must contain some type of binder that acts to hold the sand particles together. Clay serves an essential purpose in the sand casting manufacturing process, as a binding agent to adhere the moulding sand together. In manufacturing industry other agents may be used to bond the moulding sand together in place of clay. Organic resins, (such as phenolic resins), and inorganic bonding agents, (such as phosphate and sodium silicate), may also be used to hold the sand together. In addition to sand and bonding agents, the sand mixture to create the metal casting mould will sometimes have other constituents added to it in order to improve mould properties.
Types of Sand Used In Sand Casting:
There are two general types of sand used in the manufacturing process of sand casting
Naturally Bonded:
Naturally bonded sand is less expensive but it includes organic impurities that reduce the fusion temperature of the sand mixture for the casting, lower the binding strength, and require higher moisture content
Synthetic Sand:
Synthetic sand is mixed in a manufacturing lab starting with a pure (SiO2) sand base. In this case, the composition can be controlled more accurately, which imparts the casting sand mixture with higher green strength, more permeability, and greater refractory strength. For these reasons, synthetic sand is mostly preferred in sand casting manufacture.
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