As we stated in the both permanent mold metal casting methods and expandable mold metal casting methods, the common factor is the molten metal. In general casting operations, molten metal is poured or pressed inside casting molds.
This procurement of molten metal must be established inside the casting sites right in time. So, a manufacturing site that makes casting operations must have special furnaces to supply molten metal for casting operations. There are various types of melting furnaces that are avaliable in casting market. A proper selection of the melting furnace is very important.
In the selection phase of proper melting furnace equipment for a foundry, the important parameters are;
- Type of metal or metal alloy that is being cast,
- Melting temperature of metal or metal alloy in foundry. This can vary according to the types of cast metals that are used in that foundry.
- Environmental restrictions are very important. A comprehensive research must be done whether the selected melting furnace equipments are proper for the environmental regulations in that country or region.
- Production capacity of the foundry is very important parameter.
- Investment cost of selected melting furnace system and maintenance and operational costs such as workforce required are very important parameters.
Here you can find summary information about the types of melting furnace types for casting operations;
Crucible furnaces are generally used for melting the non-ferrous metal alloys because of their low melting temperatures. In the mechanism crucible melting furnaces, there is a melting pot which is made from refractory materials. These melting pot is placed inside the crucible furnace which is heated with the application burning fuel. These crucible furnaces generally have enclosed structures which keeps the heat inside. The general fuel types that are used in crucible furnaces coal and natural gas.
There are three types of crucible furnaces avaliable;
- Stationary pot crucible furnaces: The pot is stationary inside furnace that molten metal is taken from it with the use of tap at the bottom of furnace.
- Lift-out pot crucible furnace: When the metal inside pot is fully melt, the pot is lifted with the help of cranes inside manufacturing site to serve the molten metal to the molds.
- Tilting pot furnace: Pot is stationary inside crucible furnace, and the whole furnace system is tilted to pour the molten metal inside it.
For one service, several hundred kilograms of molten metal can be served by using crucible furnaces.
Induction furnaces are the most succesful technique to obtain high quality and pure metals and metal alloys. In induction furnaces, electric charge is used to produce induction which produces electromagnetic field. This electromagnetic field vibrates the atoms of metal, then is vibration creates heat. Eventually, metal inside induction furnace is completely molten.
Because of there is no direct connection of metal and the melting equipments, the state of metal can be controlled in a very good way. Thus, very accurate compositions can be obtained in high quality.
All types of metals can be melted inside induction furnaces such as cast irons, ferrous and non-ferrous metals and metal alloys etc.
Cupola furnaces are the big vertical and round structures that has ‘charge’ inside them to produce required molten metal. Cupolas are the biggest type of melting furnaces produces highest tonnage of molten metal. In generali cupolas are used for melting of cast irons. Charge is placed inside the big cylinder which is coated with refractory liner inside. The constituents of charge;
- Coke: Coke is used as fuel to melt the material inside cupola furnace.
- Limestone: With the addition of proper amount of limestone which is also called as ‘flux’, ash and other impurities reacted with it and form ‘slag’. This slag on molten material form a protective layer to prevent oxidizing environment inside cupola furnace.
- Metal parts and other alloying elements: Required metal parts and other alloying elements are provided into cupola furnace from charging hole. Metal parts can be leftovers or scraps produced from other casting processes, such as in the form of risers, sprues etc.
At the bottom of cupola furnaces, there is a tapping hole that the molten metal is taken from the cupola furnace.
Cupola furnaces are general application for cast iron casting operations for very high amounts.
Direct Fuel-Fired Melting Furnaces
Unlike crucible furnaces that we stated above, there is a direct interaction of fire that are produced with combustion of fuel which is generally natural gas, with the metal. This process takes place inside a structure called ‘hearth’ which has a closed structure to melt the material inside it. When the metal is melt inside direct fuel fired furnace, metal is tapped from bottom of hearth. Melting processes of non-ferrous metals are generally made with direct-fuel fired melting furnaces.
Electric Arc Furnaces
Electric arc furnaces are one of the biggest furnaces that they can produce molten metal up to 25-45 tonnes per hour. Becuase of that, they are used for very high production rates in foundries. The working principle of electric arc furnaces is very easy. Electric arc is produced with electric current to produce heat. But the energy consumption is very high compared with other technologies.
This article about metal melting technologies which are generally used in metal industry, can be very good starting point for your research about them. You can decide the required metal melting technologies for your manufacturing site.
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