Melting furnace
The important part of every country’s heavy industry is its metal smelting industry. The basis of smelting industry is furnace industry. Here, different types of furnaces and the importance of furnace industry will be discussed.
What is a melting furnace ?
A melting furnace is a device that has the ability to generate the heat that is needed to melt a certain weight of metal or alloy with the required speed and acceptable costs. The choice of furnace is determined by cost, metal quality, production needs and type of alloy. The versatility of the furnace in different conditions is an advantage for different types of production.
Types of melting furnaces
Based on their application, furnaces are categorized into three groups of ; reheating / melting / holding furnaces. In terms of energy consumption, they are divided in two main categories ; [fossil fuel furnaces / electric furnaces ]
In general, the following furnaces are used in casting and smelting metals.
1- cupola furnace
2- crucible furnaces [ fixed and rotary]
3- air furnaces [ fixed and rotary ]
4- electric arc furnaces
5- siemens- martin furnace
6- induction furnaces in low frequency and high frequency
6a- coreless induction furnaces
6b- pouring furnaces
Crucible furnace
Crucible furnaces are one of the most common furnaces that are used in foundry since the old days. And Due to their simplicity of construction and suitable price, they are one of the most important furnaces in metal smelting and they are used in large factories as auxiliary furnaces.
The different parts of crucible furnaces :
1- metallic body
2- bottom plate
3- lining refractory
4- top furnace
5- ventilator
6- gas burner
7- refractory block
Crucible furnace advantages
– The ability to melt various metals
– Low waste
– Low manufacturing cost
– Simplicity of usage
Crucible furnace disadvantages
– Low capacity
– Efficience of 10-15%
Induction furnce
An induction furnace is an electrical device in which the heat is applied by induction heating of metal. There is a copper coil inside these furnaces, and by passing electricity through it, a high amount of electric current is induced on the metallic surface inside the block. The electric current generates a high amount of heat which leads to rapid melting of metal. The passage of water in the copper coil prevents the coil from melting.
Based on consumed power, these induction furnaces are divided into three types of low /medium and high frequency furnaces and based on transferring heat and converting electrical heat into heat, they are divided into two types of
coreless induction furnaces and cupolas,rotary furnaces.The operating frequency range of induction furnaces is from 50HZ to 400HZ or higher.
Electric arc furnace
The electric arc furnace [ EAF ] consists of a large bath with acid or base with refractory layer and carbon electrode on top of the melt’s surface. When the furnace is charged with scrap, the electrodes are lowered and an electric current flows. The electrodes rise and an electric arc is established from the electrode to the metal and then melting process begins. Iran is the sixth developed country using the electric arc technology in melting furnaces.
Application of electric arc furnace
1- Manufacturing many grades of steel
2- Ribbed rebar used for reinforcing concrete, all types of commercial steel made in the form of studs, rods and belts.
3- High quality grades of bar used in the automotive and oil industry
4- Common source of supplying molten steel for mini-rods that are used to produce rods or sheets.
Siemens-Martin furnace
The heat required to melt the charge in a Siemens-Martin furnace is provided by gas or solid fuels such as coal or liquid fuels. The fuel is ignited in the combustion chambers that are located on the two sides of the Siemens-Martin furnace and enters the Siemens-Martin furnace through burners.
The two burners on either side of the Siemens-Martin furnace do not work together, One works for about 15 to 20 minutes; and the other one stops working . Then the other side works for the same amount of time . This operation is repeated alternately.
Siemens – Martin furnace charging material
– Lime
– Calcium fluoride [fluorine]
– Bauxities
– Broken chamotte bricks
– Iron ore
– Steel scrap
– Raw cast iron
Cupola furnace
Cupola furnace is the most common way of melting cast iron.
This furnace was first built and used in china in 403-221 BC.
Cupola furnace has a simple operation mechanism and this furnace is mostly used for melting cast iron scraps.
The operation of this furnace is very similar to a high furnace.
The difference is that high furnaces are used to regenerate iron ore.
This type of smelting furnace is available in various sizes with a melting power in the range of 100 kg and several tons of cast iron.
The cupola furnace is devided into two parts; The main part including metallic body / refractory materials / charge chamber / air inlet and melt outlet. Ancillary parts including;
Charge chamber / exhaust gas purifier / preheating air and charging valve.
