Heat treatment furnace:
A heat treatment furnace is normally a box like chamber carrying a refractory lining inside with temperature controls and indication devices outside it. A door is always provided for accessibility. The design of a furnace has to satisfy certain requirements for efficient and economical operation. Uniform heating and cooling is important for better results. So the design of a furnace should ensure uniform heating and cooling of parts in it. Wide ranges of temperatures are employed for various processes and material. So it is very essential to have a close control over temperature. For this heat treatment furnaces should have easy and effective means of temperature control. A furnace should not occupy much of floor space also. When metals are hated to higher temperatures, there are chances for oxidation, scale formation and decarburization to take place. So a furnace has to provide a controlled heating atmosphere inside the heating chamber to avoid such defects. For the heating of load, energy is required, and this may be in the form of fuel or electricity. In both the cases, consumption should be economical. To meet this requirement the furnaces should not take too long for heating up to the required processing temperatures.
1) Classification of Heat Treatment Furnaces
Heat treatment furnaces are classified according to their,
1. Use
2. Source of heat
3. Type of operation and
4. Working environment.
1.1) Classification according to use:
Furnaces are classified according to process, which they are used for, like
a) Annealing furnace
b) Tempering furnace
c) Hardening furnace
d) Carburizing furnace.
The basic difference in all these is based on their capacity to attain the desired temperature and to withstand it with adequate service life. Furnaces, which are capable of working over a wide range of temperatures, are available now. Such furnaces can be used to perform different processes successfully.
1.2) According to source of heat:
According to the source of heat used for heating the load, furnaces can be widely classified in to
A) Fuel fired furnace and
B) Electric furnace.
1.3) According to type of operation:
According to type of operation furnaces are divided in to two groups. These two groups are again subdivided in to different types.
A) Batch furnace
1. Box furnace
2. Muffle furnace
3. Pit furnace
4. Lift off cover furnace
5. Bogie hearth furnace
B) Continuous furnace.
1. Conveyor furnace
2. Rotary hearth furnace
3. Tunnel furnace.
4. Rotary furnace
1.4) According to working environment:
According to working environment, furnaces are classified in to two.
a) Air convection furnace and
b) Controlled atmosphere furnace.
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