Zenith Aluminum & Brass Casting Foundry
China sand casting and gravity casting manufacturer

Sand casting technique

Sand casting uses natural or synthetic sand (lake sand) which is mostly a refractory material called silica (SiO2). The sand grains must be small enough so that it can be packed densely; however, the grains must be large enough to allow gasses formed during the metal pouring to escape through the pores. Larger sized molds use green sand (mixture of sand, clay and some water). Sand can be re-used, and excess metal poured is cut-off and re-used also.

Typical sand molds have the following parts (see Figure 2):

• The mold is made of two parts, the top half is called the cope, and bottom part is the drag.
• The liquid flows into the gap between the two parts, called the mold cavity. The geometry of the cavity is created by the use of a wooden shape, called the pattern. The shape of the patterns is (almost) identical to the shape of the part we need to make.
• A funnel shaped cavity; the top of the funnel is the pouring cup; the pipe-shaped neck of the funnel is the sprue ­ the liquid metal is poured into the pouring cup, and flows down the sprue.
• The runners are the horizontal hollow channels that connect the bottom of the sprue to the mould cavity. The region where any runner joins with the cavity is called the gate. 4
• Some extra cavities are made connecting to the top surface of the mold. Excess metal poured into the mould flows into these cavities, called risers. They act as reservoirs; as the metal solidifies inside the cavity, it shrinks, and the extra metal from the risers flows back down to avoid holes in the cast part.
• Vents are narrow holes connecting the cavity to the atmosphere to allow gasses and the air in the cavity to escape.
• Cores: Many cast parts have interior holes (hollow parts), or other cavities in their shape that are not directly accessible from either piece of the mold. Such interior surfaces are generated by inserts called cores. Cores are made by baking sand with some binder so that they can retain their shape when handled. The mold is assembled by placing the core into the cavity of the drag, and then placing the cope on top, and locking the mold. After the casting is done, the sand is shaken off, and the core is pulled away and usually broken off.

Read more Comments(0) 07th Mar., 2009

Casting methods

Metal casting process begins by creating a mold, which is the reverse shape of the part we need. The mold is made from a refractory material, for example, sand. The metal is heated in an oven until it melts, and the molten metal is poured into the mould cavity. The liquid takes the shape of cavity, which is the shape of the part. It is cooled until it solidifies. Finally, the solidified metal part is removed from the mould.

A large number of metal components in designs we use every day are made by casting. The reasons for this include:

• (a) Casting can produce very complex geometry parts with internal cavities and hollow sections.
• (b) It can be used to make small (few hundred grams) to very large size parts (thousands of kilograms)
• (c) It is economical, with very little wastage: the extra metal in each casting is re-melted and re-used
• (d) Cast metal is isotropic ­ it has the same physical/mechanical properties along any direction.

Common examples: door handles, locks, the outer casing or housing for motors, pumps, etc., wheels of many cars. Casting is also heavily used in the toy industry to make parts, e.g. toy cars, planes, and so on.

Table 1 summarizes different types of castings, their advantages, disadvantages and examples.

Read more Comments(0) 20th Feb., 2009