Industrial furnaces for heat treatment of metal parts. The temperature is generally lower than that of the heating furnace. Heat treatment furnace can adopt various types of heating furnace, but it is required to strictly control furnace temperature and furnace atmosphere. Most of the heat treatment furnaces use gas fuel for heating. In order to control the furnace temperature accurately, some heat treatment furnaces use electric heating. Modern heat treatment (especially chemical heat treatment) process is becoming more and more complex, and there are many forms of heat treatment furnace. For continuous heat treatment process, appropriate continuous heat treatment furnace shall be equipped; for periodic heat treatment process, forced circulation control atmosphere shall be adopted, and operation of furnace shall be mechanized and automated. The following heat treatment furnaces are commonly used in metallurgical plants.
Bell type furnace
A periodic heat treatment furnace in which the heated material is heated in a hood. It is mainly used for annealing of sheet stacks or steel coils. The bell type furnace is usually composed of an outer cover, an inner cover and a furnace platform. The heated object is placed in the inner cover (muffle cover), and heat is supplied between the inner cover and the outer cover. Generally, control atmosphere is introduced into the inner cover. After the completion of the heating, heat preservation and slow cooling process, the outer cover shall be lifted away, and the plate stack or steel coil shall be cooled in the inner cover; after the cooling to the given temperature, the inner cover shall be removed, and the plate or steel coil shall be cooled in the air, and then discharged. Fig. 1 is a bell type annealing furnace for processing sheet stacks, and the burners are arranged on the hearth. There are two types of bell type furnaces for cold-rolled steel coils: single stack type and multi stack type. The multi stack type can put 2-8 stacks of steel coils on a rectangular furnace platform, and each stack is respectively fastened with a separate circular inner cover. A circulation fan is installed at the lower part of the inner cover to strengthen the control atmosphere and promote the convective heat transfer between the steel coils.
Roller hearth furnace
Heat treatment materials shall be transported by roller table in the furnace. A roller shall be installed every certain distance along the whole length of the furnace. Materials shall run on the roller. Burners can be arranged in the furnace above and below the roller for heating (Fig. 2). There are two kinds of rollers: ring roller (with disc-shaped roller ring) and flat roller. The former can only be used to heat plates, while the latter can be used to heat plates, sections, pipes and bars. The outer layer of the roller sleeve is usually made of heat-resistant steel, some of which are also made of silicon carbide. The furnace with high temperature (1000-1150 ℃) adopts heat-resistant steel furnace roll with water-cooling shaft and heat insulation lining, or fully water-cooled furnace roll. In order to prevent the furnace roll from bending, the roller working at high temperature must rotate continuously; when the furnace is empty or does not discharge, it should also swing or rotate at a low speed of 0.5-1.5 weeks per minute. The roller hearth furnace is widely used in heat treatment processes such as normalizing, annealing, quenching and tempering due to its fast and even heating on both sides of the material.
Chain furnace
The utility model relates to a conveyor belt type heat treatment furnace, in which a chain is used as a conveyor belt to transport workpieces. The chain is generally set in the groove under the furnace, and the "furnace claw" made of heat-resistant steel or heat-resistant cast iron is installed between the chain links, on which the thin slab or sheet is placed. Generally, the steel can be heated to 900 ℃, and the furnace length is not more than 25 meters. In nonferrous metal processing, machinery, enamel and other industries, chain furnaces are also commonly used for heat treatment of various workpieces and mold drying. The chain of some chain furnaces is installed on the top or side of the furnace, and the hook or suspender is extended into the furnace through the gap to hang the workpiece. Some low-temperature heat treatment furnaces put the chain in the furnace, and the workpiece is directly placed on the chain for heating.
