Crucible Furnace – Overview, Parts, Construction, Working, Advantages, and Disadvantages
A crucible furnace is a type of furnace that can be used to melt both ferrous and non-ferrous metals and from this molten metal produced by this furnace, light products are produced. Crucible Furnace is used for melting the metal charges.
Low melting point metals are melted using a crucible furnace.
A crucible furnace is generally used when a low volume of material is to be melted.
A Crucible is actually a pot-like structure that is either made of silicon carbide or graphite or other refractory materials.
Refractory material means a material that is resistant to decomposition by heat.
If more heat is required then the system setup of the crucible furnace is done underground.
Below the ground level, a cylindrical pit is dug. This pit is dug to create space for the furnace.
Small spaces below the furnace are created for the air to pass.
The fuel used in the crucible furnace can be in a solid form such as coke or its fuel can also be in liquid or gaseous form.
Parts Of Crucible Furnace:
1) Crucible Pot:
The crucible pot is the container in which the metal charges to be melted are kept. The crucible pot is packed from all sides with fuel.
Crucible pot is made from graphite or refractory material or high-temperature steel alloy.
It is the outermost layer of the crucible furnace and is made of steel.
2) Refractory Linings:
Inside the shell, there is a refractory lining which helps in reducing the loss of heat and prevents the heat from escaping from the furnace.
This refractory lining maintains the heat inside the furnace for a long period of time.
Whole body of the crucible furnace is placed over the legs. These legs support the full weight of the system of the crucible furnace.
The legs are present in the bottom-most part of the crucible furnace.
From the bottom, the air is supplied to the furnace using the blower. Due to the air supply, more oxygen will be supplied to the system and more fuel will be burned in lesser time.
The air is supplied using soft steel hollow rods. These rods are placed at the bottom of the furnace.
The chimney is used to pass the flue gases produced in the process to the atmosphere.
The cover is present on the top of the crucible furnace and is used to cover the furnace so that the heat does not escape to the environment from the top.
Working Of Crucible Furnace:
1) At first, the metal charges are placed inside the crucible pot. The metal with low melting points is usually placed inside the pot.
2) Then the pot is packed with fuel from both sides.
3) After that, the fuel is ignited and the air is supplied from the bottom so that the fuel burns completely and faster.
4) As the fuel is burned, the heat produced is conducted by the crucible pot and is supplied to the metal charges.
5) As the metal charges start getting a heat, they start melting and the flue gases produced in the process escaped to the environment through the path provided for flue gases to escape.
6) After the metal charges completely melt, the cover is opened and the molten metal is taken out from the top using tongs or tongues.
7) This melted metal can be used for the casting or production of light products.
Types Of Crucible Furnace:
Based on the types of fuel used, crucible furnaces are of three types:-
1) Charcoal Crucible Furnace:
In this type of crucible furnace, charcoal is used as fuel in the furnace. Charcoal crucible furnaces have been used for thousands of years.
2) Oil-Fired Crucible Furnace:
In oil Fired Crucible Furnace, oil is used as a fuel. The burner in this furnace is designed so that the oil drips into the burner tube and ignites.
These furnaces are very fast furnaces that need less capital to operate.
One disadvantage of this type of furnace is that it produces smoke and burners can be fussy as they lack the ease of Gas Crucible Furnaces.
3) Gas Crucible Furnace:
In the Gas Crucible Furnace, gas is used as fuel for the furnace to operate.
It is a little expensive to operate but much more eco-friendly that the other two types of crucible furnaces discussed above.
Crucible furnaces are also classified based on the technique to remove molten metal. Based on the technique to remove molten metal, crucible furnaces are divided into three types:-
1) Lift Out Crucible Furnace:
In this type of furnace, the heat is supplied from the bottom of the furnace. After the metal melts, the crucible can be lifted up and it can be removed, that’s why it is called Lift Out Crucible Furnace. In this type of furnace, molten metal is taken out by lifting up the crucible pot.
2) Stationary Pot Crucible Furnace:
In the Stationary Pot Crucible Furnace, the crucible pot is stationary, and the molten metal is taken out by using some tools like a ladle.
3) Tilting Pot Crucible Furnace:
In this type of crucible furnace, the crucible pot can be tilted. A wheel is provided so that the tilting of the crucible pot can be done easily and the molten metal is taken out by tilting the crucible furnace.
Application of crucible Furnace:
Crucible Furnace is mainly used where a continuous supply of molten metal is not necessary. I.e where molten metal is needed regularly after a certain period of time.
Crucible furnaces are used to melt both ferrous and non-ferrous metals and from this molten metal produced by this furnace, light products are produced.
Advantages Of Crucible Furnace:
1) Less space is required.
2) Less labor is required.
3) less wastage of fuel.
4) Can be operated easily.
5) In this furnace heat can be contained easily.
6) Low investment cost and maintenance costs.
Disadvantages Of Crucible Furnace:
1) only a small amount of metal can be melted at once.
2) continuous supply of molten metal cannot be achieved.
3) Not suitable for high production.
4) As it is operated manually so there are high operation costs.