Continuous furnace is a device in which the work enters and leaves the furnace in a continuous stream. Continuous furnaces are mainly used for the high-volume production. With well configurated heating system and good insulation it is used for various purposes.

Types
Continuous furnaces are of different types. They are classified on the basis of function, configuration and applications. Some of the continuous furnaces are as follows:

Pusher-Type Furnaces
Initially these pusher furnace were designed for heating billets and small bloom sections. The pushers were used to push forward the charge of cold billets. However now the longer furnaces are created consisting of top and bottom firing, and contain preheating, heating and soaking zones.

The load to be heated in a continuous furnace can be charged either from the end or through a side door. The heated piece is discharged by several methods, such as through an end door by gravity upon a roller table which feeds the mill etc.

The furnace has certain advantages like they are highly productive, efficient, safe and easy to operate and install. Moreover they are cost effective and consume less energy. The temperature is distributed uniformly and can be regulated. Whole system is well insulated and they have better protection from overheating.

Better means for controlling the rate of heating at all temperature levels. Gradual rise in temperature permits charging all grades of cold steel without cooling furnace. Can be built for any reasonable length of piece to be heated, resulting in higher mill yield.

Rotary-hearth furnace
Rotary hearth furnace are used for for heating rounds in tube mills and for heating short lengths of blooms or billets for forging. In these furnace the external walls and roof to remain stationary while the hearth section of the furnace revolves.

Rotary furnace have better means for controlling the rate of heating at all temperature levels than batch-type furnaces. They also eliminates the manual labor required for rolling rounds forward on horizontal or moderately sloped hearths, or the disadvantages of excessively sloped hearth in continuous furnaces.

Walking-Beam Furnaces
Walking beam furnace consist of water-cooled steel members topped with refractories in such a manner that only the refractories are exposed directly to the heat of the furnace. The beams and supports are normally constructed of water-cooled tubular sections. These furnaces are used to reheat slabs, billets and blooms, etc. The beams are actuated through hydraulic and mechanical methods. Both fuel burners and electricity are used for generating the heat for the furnace.

Walking-Hearth Furnaces
In the walking-hearth furnace, the work rests on fixed refractory piers. When the work is stationary in the furnace these piers extend through openings in the hearth and their tops are above the hearth surface during the time. The furnace gases can thus circulate between most of the bottom surface of the work and the hearth. The hearth is raised vertically to first contact the work and then raise it a short distance above the piers in order to advance the work toward the discharge end of the furnace.

Roller-Hearth Reheating Furnaces
Roller-hearth furnaces are used in many types of heating operations. The advantages of reheating furnace are:

• The control of zone is simple
• They can handle long pieces
• Furnace is self-emptying
• Heating is controlled
• Protection from overheating

General Features
Some of the general features of the continuous furnace are:

• Robust and rugged construction
• The insulation material used is normally ceramic fiber
• Overheat protection
• Cooling is faster
• Reliable and safe operations
• Cost effective as enough power is saved due to sound insulation system

Applications

Pre Heating Annealing Brazing Hardening Brightening

Carburising Sintering Tempering Reheating