Construction and Working of Furnace
Points : Construction and Working of Furnace, Definition Definition Furnace may be divided into two general classes with respect to the environment, which they provide for the metal to be treated. In the first type there is no particular attempt to control the environment. It will be whatever gas happens to be present. A piece of steel can be heated for hardening ‘in a blacksmith’s forge, and there it will he in contact with products of combustion of the fuel used in the forge.
In an open furnace of any kind where products of combustion can circulate, what chemical reaction will take place at the surface of the steel, or other metal, depends a great deal on the exact composition of the product of combustion. The second general type of furnace has means of control of the medium in contact with the metal. For example, the chemical composition of salt bath can he quite easily regulated so that it may supply carbon to the steel or be neutral with respect to the surface of the steel. Although usually an undesirable practice a salt bath may even be made oxidizing in nature. In furnaces which do not have liquid medium in contact with the steel, the analysis of the atmosphere may be regular and controlled to produce whatever condition of surface is desired. In the operations of gas carbonizing and nitriding gases are delivered to the furnace and to the hot steel for the definite purpose of changing the analysis of the surface to produce harder constituents. In most heat treatments, it is not desired to change the analysis but merely to retain, without change in the metal, whatever the composition may be as the metal is sent to heat treatment. Atmospheres produced for that purpose are known as neutral atmospheres. Bottled gases such methane, propane, and ammonia as well as city gas are available, and by burning these gas under proper conditions an atmosphere neutral to the steel at heat-treating temperature can he produced and caused to surround the metal, independently of the source of heat.
Points : Construction and Working of Furnace, Definition Definition Furnace may be divided into two general classes with respect to the environment, which they provide for the metal to be treated. In the first type there is no particular attempt to control the environment. It will be whatever gas happens to be present. A piece of steel can be heated for hardening ‘in a blacksmith’s forge, and there it will he in contact with products of combustion of the fuel used in the forge.
In an open furnace of any kind where products of combustion can circulate, what chemical reaction will take place at the surface of the steel, or other metal, depends a great deal on the exact composition of the product of combustion. The second general type of furnace has means of control of the medium in contact with the metal. For example, the chemical composition of salt bath can he quite easily regulated so that it may supply carbon to the steel or be neutral with respect to the surface of the steel. Although usually an undesirable practice a salt bath may even be made oxidizing in nature. In furnaces which do not have liquid medium in contact with the steel, the analysis of the atmosphere may be regular and controlled to produce whatever condition of surface is desired. In the operations of gas carbonizing and nitriding gases are delivered to the furnace and to the hot steel for the definite purpose of changing the analysis of the surface to produce harder constituents. In most heat treatments, it is not desired to change the analysis but merely to retain, without change in the metal, whatever the composition may be as the metal is sent to heat treatment. Atmospheres produced for that purpose are known as neutral atmospheres. Bottled gases such methane, propane, and ammonia as well as city gas are available, and by burning these gas under proper conditions an atmosphere neutral to the steel at heat-treating temperature can he produced and caused to surround the metal, independently of the source of heat.
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