Factories that produce metal castings are called foundries. At these factories, metals are cast into various shapes by melting them into liquids, pouring them into a mould and then, when the metal has cooled and solidified, removing the mould. These factories can produce items from metals such as bronze, brass, steel, magnesium, zinc, aluminium and cast iron, however the last two mentioned are most commonly used.
These foundries use specialised furnaces to melt the metal. Electrical arc furnaces, induction furnaces, cupolas, reverberatory and crucible furnaces are some furnace types which are used most commonly in today’s industry. The type of furnace which a factory will use is dependent on the type of alloy used as well as the amount which needs to be produced.
In some cases, such as when using an aluminium alloy, it can be necessary to reduce the amount of hydrogen dissolved in the liquid metal. In these instances, a degassing process has to be implemented. When there is too much hydrogen in the liquefied metal the finished product becomes porous when it cools and solidifies. This is very bad as a porous metal produces a much weaker finished product than is acceptable.
Degassing involves bubbling argon or nitrogen through the liquefied metal. As the argon or nitrogen bubbles go up through the liquid metal they gather the dissolved hydrogen and take it to the surface. The foundry needs a range of different types of equipment to do this.
It is sometimes necessary to change the physical and sometimes chemical properties of a material. Most of the time heat treatment can be used to achieve this. The heat treating processes can also be used to manufacture some materials such as glass. This process involves heating or chilling a material, sometimes to the extremes, to achieve either a hardened or softened result.
In foundries, workers also grind, sand and machine the produced castings before they are ready to be used. In this process, the desired dimensions are accurately achieved and imperfections are removed. Sometimes it is necessary to improve the visual appeal of the product. The foundry needs certain equipment to polish the product to make it look better.