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| FERROUS & NON FERROUS ALLOY SAND CASTING |
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| HOW IT WORKS |
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Sand casting is used to make large parts (typically Iron, but also Bronze, Brass, Aluminum). Molten metal is poured into a mold cavity formed out of sand (natural or synthetic). The processes of sand casting are discussed in this section, include patterns, sprues and runners, design considerations, and casting allowance.
The Sand Casting (Green Sand) molding process utilizes a cope (top half) and drag (bottom half) flask set-up. The mold consists of sand, (usually silica), clay and water. When the water is added it develops the bonding characteristics of the clay, which binds the sand grains together. When applying pressure to the mold material it can be compacted around a pattern, which is either made of metal or wood, to produce a mold having sufficient rigidity to enable metal to be poured into it to produce a casting. The process also uses coring to create cavities inside the casting. After the casting is poured and has cooled the core is removed.
The material costs for the process are low and the sand casting process is exceptionally flexible. A number of metals can be used for castings in sizes from ounces to many thousand pounds. The mold material is reclaimable, with between 90 and 95% of the sand being recycled, although new sand and additions are required to make up for the discarded loss. These features, combined with the relative ease of mold production, have ensured that the green sand molding process has remained as the principal method by which castings are produced |
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| PROCESS |
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Sand Casting is the most commonly used Casting Process, in the entire Casting Industry.
The Sand Casting Concept The top and the bottom of the mold form the flask. This top and bottom, are also called the flask assembly, and this flask assembly "holds the whole thing together." The upper or top-most section of the flask is called the cope, while the bottom of the flask is called the drag. There is always an impression device, in the middle of the flask assembly. This is called the pattern. The sand around the pattern is called the, holding medium.
These are the basic, universal casting components, which can be applied to all Casting and Molding Processes.
To cast an object, the mold maker, uses the pattern to make the impression in the holding medium, the sand. He then sets the pattern aside. At that point, the molder closes the cope and drag, to complete the flask, and forms the mold, with the impression of the pattern captured in the sand. What the mold maker wants is the potential "CASTING" or the void left from the impression of the pattern, in middle of the sand. To get that "CASTING," the mold maker fills that void with a molten material; which could be almost anything, but here just imagine the material is aluminum. |
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| POURING CUP: |
This is where the metal is poured into the mold. |
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| SPRUE: |
The vertical channel from the top of the mold to the gating and riser system. Also, a generic term used to cover all gates, runners and risers. |
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| RUNNER: |
The portion of the gate assembly that connects the sprues to the casting in gate or riser. |
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| GATE: |
The end of the runner in a mold where molten metal enters the mold cavity. |
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| RISER: |
A reservoir of molten metal provided to compensate for the contraction of the metal as it solidifies. |
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| MOLD CAVITY: |
The impression in a mold produced by the removal of the pattern. When filled with molten metal it forms a casting. |
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| COPE: |
Upper or top most section of a flask, mold or pattern. |
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| PARTING LINE: |
A line on a pattern or casting corresponding to the separation between the parts of a mold. |
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| DRAG: |
Lower or bottom section of a flask, mold or pattern. |
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Solid pattern - A solid pattern is a model of the part as a single piece. It is the easiest to fabricate, but can cause some difficulties in making the mold. The parting line and runner system must be determined separately. Solid patterns are typically used for geometrically simple parts that are produced in low quantities. |
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Split pattern - A split pattern models the part as two separate pieces that meet along the parting line of the mold. Using two separate pieces allows the mold cavities in the cope and drag to be made separately and the parting line is already determined. Split patterns are typically used for parts that are geometrically complex and are produced in moderate quantities. |
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Match-plate pattern - A match-plate pattern is similar to a split pattern, except that each half of the pattern is attached to opposite sides of a single plate. The plate is usually made from wood or metal. This pattern design ensures proper alignment of the mold cavities in the cope and drag and the runner system can be included on the match plate. Match-plate patterns are used for larger production quantities and are often used when the process is automated. |
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Cope and drag pattern - A cope and drag pattern is similar to a match plate pattern, except that each half of the pattern is attached to a separate plate and the mold halves are made independently. Just as with a match plate pattern, the plates ensure proper alignment of the mold cavities in the cope and drag and the runner system can be included on the plates. Cope and drag patterns are often desirable for larger castings, where a match-plate pattern would be too heavy and cumbersome. They are also used for larger production quantities and are often used when the process is automated. |
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| Another piece of tooling used in sand casting is a core-box. If the casting requires sand cores, the cores are formed in these boxes, which are similar to a die and can be made of wood, plastic, or metal just like the pattern. The core-boxes can also contain multiple cavities to produce several identical cores. |
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| PHOTO GALLERY |
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Investment Casting Ferrous Non Ferrous Castings Gravity Pressure Die Casting Graded Casting for Pump Electric Motor Valves |
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