Furnace is a device use for heating or It is equipment to heat material to change their shape like rolling and forging or to change the properties of the material. Most of the time furnace is used for melting metals for casting.
Types and Classification of Different Furnaces
On the basis of generating heat furnace is classified in to following types
In combustion type furnace, it is further classifies in to oil fired, gas fired and coal fired
Furnaces are classified in to the following two types on the basis of mode of material charged in to it.
- Batch type or periodic type or intermittent furnace
Batch furnaces are further classified into
- Forging furnace
- Re rolling mill furnace
- Pot furnace
- Continuous furnace
Furnace are classifies in to the following two types based on the method of waste heat recovery
- Recuperative furnace
- Regenerative furnace
Furnace is classified in to the following types based on the mode of heat transfer
- Open fire place furnace
- Heated through medium
Characteristics of an efficient furnace
Furnaces should be designed in such a way to consume less fuel and heat as much material as possible in given time requiring less labor cost. To achieve the goal following parameters can be considered
- Determination of the amount of heat to be given to the material or change
- There should be sufficient liberation within the furnace to heat the stock.
- There much be proper heat transfer from the furnace gases to the surface of the heating stock
- Temperature should be equal within the stock.
- Try to minimize the heat loss from the furnace as much as possible
Energy supple of furnace
In furnace, the product of the flue gases directly comes in contact with the stock. So it is important to choice the type of fuel wisely. For example some material does not tolerate sulphur content in the fuel. Using solid fuel will generate particulate that can strike the stock. Hence, liquid, gaseous and electric mode of heat input is used generally.
Oil fired furnace
For reheating and treatment of materials, furnace oil is commonly used in oil fired furnace. Sulphur content is undesirable in many heating stock therefore light diesel oil is used. The efficiency of furnace depends upon complete combustion of fuel with minimum excess air.
The efficiency of furnace is in range between 7 to 90 percent. This is because of the high temperature at which furnace have to operate to meet the require demand. For example a furnace heating the stock to 1500 °c will have its exhaust gases leaving at least at 1200°c resulting in huge heat loss through the stack. By preheating the stock, preheating combustion air and other waste heat recovery system, improvement in furnace efficiency have been made.
Typical furnace system
To preheat billets and ingots, forging furnaces is used. In this furnaces forge temperature is attained. The temperature maintained inside these furnaces is around 1200 to 1250°c. an open fire place system is used thorough which most of the heat is transmitted via radiation. The furnaces operate around 16 to 18 hours a day. The typical loading in forging furnace is 5 to 6 tones. The operations take place in forging furnace is
- Heat up time
- Soaking time
- Forging time
The consumption of fuel depends upon type of feed and number of reheat require.
Re rolling mill furnace
This furnace is used to heat scrap, small ingots. The temperature maintained inside is 1200°c. the charging and discharging is done manually. The product is taken out in the form of rods and strips. The operation take place in re rolling furnace is
- Heat up time
- Rerolling time
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