Resistance Ovens & Furnaces: General Construction & Heating Chambers

Resistance Ovens And Furnaces

  • Low temperature heating chamber with provision for ventilation is termed as “oven”.
  • Resistance ovens are used for drying and baking potteries, drying varnish coatings, vulcanizing and hardening of synthetic materials and commercial and domestic heating.
  • The indirect resistance heating chamber for temperature of heat treatment process applied to steel above 7000 C except for tempering below that temperature is termed as “resistance furnace”.
  • The oven is constructed of firebricks or other heat resisting material supported on metal frame work.
  • The resistance furnace is an enclosure with a refractory lining i.e. a surrounding layer heat insulation and outer casing of steel plates, bricks or tiles.
  • The inside proportions of a heating chamber are to suit the character of the charge and type of furnace or oven.
  • The nature of material required for the insulation is determined by the maximum temperature of the inner face of the layer of insulation of a heating chamber.
  • The heating elements are mounted on top, sides or bottom of the oven as the circumstances permit.
  • An oven may be of ‘batch” or “continuous” type. In the former the charge is fed intermittently and in the latter the charge travels continuously on a moving platform through the oven.

Heating Chambers

  • An enclosure of a charge to be heated by radiation or convection or by the joint effect of these modes of heat transfer is known as heating chamber.
  • Apart from mechanical consideration, the design of the chamber is related primarily to temperature and the major mode of heat transfer to be used. The function of the chambers are :
    1. To control the distribution of heat within the chamber.
    2. To control the cooling rate of charge, if required.
    3. To confine the atmosphere around the charge.
    4. To store as much of the heat supplied as may be practicable and economical.
  • A cylinder with an inside diameter equal to its height is an ideal shape and of ideal proportions heating chamber, keeping only the utilization of material and rate of heat loss from the exterior surfaces in view.
  • The ideal is seldom attained because of many practical considerations.

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