How The Molten Metal Must Be Poured In Sand Casting?
Around the casting methods especially in metal casting methods, sand casting is the most prominent and used method to cast metals in industry. The place where sand casting operations are done are called as foundry. Because of the greatness of market, there are lots of kinds of foundries around the, nearly every county. So, sand casting market is very big. In here, we explain the general characteristics and technical details of sand casting methods.
There is a general terminology that is used in sand casting tecniques.
In sand casting operations or processes, molten metal is poured from a mouth, then this poured molten material fill the cavity inside the sand casting mold. This is the most basic explanation of sand casting operations.
As you see at the above illustration, there are bunch of terms related to sand casting methods. General sand casting equipments are have cope and drag sections. In most basic aspects, cope is the upper part of sand casting mechanism. Drag is the lower part of the sand casting mechanism. And these two halves of sand casting system is divided by parting line.
Parting line is very important, because the cavity of the mold is placed symmetrically generally inside the mold. These cope, drag and parting line system is placed inside a flask that hold the sand together. This flask also can be divided into two parts from parting line.
The pouring cup is where molten metal is poured into the cavity of sand mold. Pouring cup must be designed to prevent turbulent flux inside the gate system. Turbulation can lead to the porosities becuase of trapped gases.
Downsprue is where molten metal is travelled vertical direction to reach mold cavity. Also downsprue must be designed to obtain required flux characteristics from molten material.
Runner is the horizontal gate that molten materials pass from it to reach mold cavity. This is an another part of gating system of sand casting system. It must be designed also to obtain enough flux characteristics from molten metal. These runner, downsprue and pouring cup constitute the gating system that molten metal travels into the mold cavity.
Riser is a very important part of sand casting system. Riser provides molten metal into the cavity in solidification phase. So, the riser must be designed to solidify after the metal inside the mold cavity solidifies. When the all system solidifies, riser is cut.
In a part that produced with sand casting method, there can be internal cavities that can not be produced only with mold cavity. To obtain these internal shapes and cavities, cores are used. Cores are also produced from sand, and also can be produced from other materials such as ceramics etc. Placement of cores inside the mold cavity is an also very important thing to obtain decent part.
Patterns of produced parts are also produced to obtain sand cavity that molten metal will poured inside it. These patterns are generally produced from wood, polymer foams etc.
These designed patterns are slightly bigger than the original sand cast metal part. This is because in the phase of transition from liquid to solid, metals shrink. This phenomenon is called as ‘shrinkage’ in casting. Shrinkage must be considered, when mold and the mold cavities are designed. Shrinkage calculations are generally done by engineers, and very detailed designs must be made to obtain required shapes in required dimensions. After these shrinkage calculations, patterns are produced.
The produced patterns are placed into the flasks, and sand with binders are spilled to fill the all flask. The model is placed symmetrically around parting line. When the binders inside sand, packs the sand, pattern is removed by unmantling the cope and drag sides of flasks.
With the addition of this pattern, a proper gating and riser systems are also designed to obtain succesful sand casting operation.
When the molten metal is poured inside the mold, air is trapped inside the sand. This trapped air can lead a problem of porosities inside the produced cast part. Because of these porosities, the mechanical properties of produced part can be affected adversely. Self ventilating system of sand mold, lets the trapped air go out from mold cavity.
In permanent metal molds, special venting holes are drilled to take the trapped air out.
These are the general characteristics, terminology of sand casting method to produce metal parts. Do not forget to leave your comments and questions about sand casting method and terminology of sand casting method below.
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