Sand casting

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There are several stages that make up a typical sand casting system.  
There are several stages that make up a typical sand casting system.  
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1. The hopper -
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1. Pattern construction-
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The plastic enters the machine as either plastic beads or some other form of plastic granule. This is stored into the hopper until it is needed.
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The object to be cloned is made of different materials such as wood or metals. They are used to create the sand mold.
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2. Injection Barrel-  
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2. Molding-  
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Typically the hopper feeds into the injection barrel by way of gravity. The injection barrel is heated in order to begin melting the plastic on its way to be injected. Any color is typically added to the plastic at this stage.
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Sand which is self-hardening, air-setting is used and is imprinted by the pattern
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3.The Injector -  
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3. Pouring-  
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The plastic is driven through the barrel through one of two different means. Either a reciprocating screw drives the plastic forward into the injector, or there is a hydralic ram. With current technologies the reciprocating screw drive has a much higher precision for injection and is used more frequently, especially with smaller components.
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The material of which the copy is to be made of is then poured into the hardened sand mold.  The mold is filled using a network of runner troughs designed in accordance to the specifications of each casting.
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4. The Mold -  
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4. Removal and Cleaning-  
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The mold is the component that contains an empty volume (cavity) in the negative shape of the object desired. This is where the plastic is injected to recieve it's permanent shape. Typically the mold is cooled so that the plastic hardens evenly and quickly. The mold contains two parts which seperate to allow the part to be retrieved after the process is done.  
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Once the material has solidified and cooling period is over, the casting is lifted out of the mold and the sand is recovered to start the molding cycled again.
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5. Ejector Pin -  
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5. Final Treatment-  
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Some components do not simply fall out of the mold when completed so an additional ejector pin is added in these cases to knock the part out of the mold
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The casting is then further finalized by processes such as thermal treatment, machining, and painting depending on what the design calls for.
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Revision as of 06:29, 12 February 2007

Definition


What & How:
Casting is a manufacturing process used to produce objects by pouring molten material in to a cavity called a mold which is the negative of the object, and allowing it to cool and solidify. Sand casting is the specific casting process in which the mold is usualy made from sand formed around the object to be copied.


Top and bottom halves of a sand mold.


Two sets of castings (bronze and aluminum) from the above sand mold.

Process

Steps of Sand casting: There are several stages that make up a typical sand casting system.

1. Pattern construction- The object to be cloned is made of different materials such as wood or metals. They are used to create the sand mold.
2. Molding- Sand which is self-hardening, air-setting is used and is imprinted by the pattern
3. Pouring- The material of which the copy is to be made of is then poured into the hardened sand mold. The mold is filled using a network of runner troughs designed in accordance to the specifications of each casting.
4. Removal and Cleaning- Once the material has solidified and cooling period is over, the casting is lifted out of the mold and the sand is recovered to start the molding cycled again.
5. Final Treatment- The casting is then further finalized by processes such as thermal treatment, machining, and painting depending on what the design calls for.

Image:injection_molding_process.jpg

A diagram of injection molding

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