Dr. Dmitri Kopeliovich
Sand casting is a method involving pouring a molten metal into a sand mold.
Advantages of sand casting
Disadvantages of sand casting
The typical mold for a sand casting is shown in the picture:
The set of channels through which a molten metal flows to the mold cavity is called gating system.
Typical gating system consists of a pouring cup and a sprue receiving the poured melt, runner – a channel through which the melt is supplied to the gates through which the molten metal enters the mold cavity.
A gating system may include a riser (feed head) – a cavity connected to the gating system feeding the casting when it is shrinking.
Air within the mold cavity and gases formed when a molten metal contacts the mold surface are removed through the vents.
The interior cavities of a casting are formed by a separate inserts called cores.
Cores are usually made of sand and backed.
A mold frame (flask) consists of two parts: cope (the upper part) and drag (the lower part).
A mold cavity is formed in the process of pattern molding, when the pattern (commonly wooden) is embedded in sand in the flask forming an impression of the casting.
After the sand packing the pattern is removed from the flask and the cores and the gating system are arranged.
Cores, runner and gates are arranged in the drag; pouring cap and sprue are placed in the cope.
Then the two parts of the mold are assembled and poured.
Factors determined by sand:
Requirements to sand:
Silica sand with additives is used for sand casting.
Types of sand:
In order to be used repeatedly patterns are made of relatively tough materials.
A parting (release) agent is applied on the pattern surface in order to provide easy removal of the pattern from the mold.
Patterns may be made as one-piece or multiple-piece (split, match plate).
Patterns are commonly made larger than the casting because of the shrinkage effect.
Shrinkage allowances are usually 1-2%.
The pattern surfaces are never made perpendicular to the mold parting surface. The taper of the pattern surface, which provides narrowing the mold cavity towards the mold parting surface is called draft.
Draft allows easy removal of the pattern and the casting from the sand mold.
The draft angle is commonly 1-3%.