Heating furnaces - furnaces designed to heat metal before subsequent processing under high pressure: stamping, rolling or forging. The ductility of the metal increases with heating, which reduces energy consumption for its deformation. The burnout temperature, at which a liquid phase forms at the grain boundaries of the metal, limits the maximum heating temperature. This allows you to reduce the mechanical bond of the grains and the loss of strength of the metal.
Principle of operation
The temperature difference between the axis of the workpiece and the surface affects the uniformity of heating of the material, which plays a large role in plastic deformation. The plastic properties of the material depend on the heating temperature, and therefore uneven heating can cause deformation. Reducing the temperature difference increases the quality of the rental and the heating time of the billets, reducing the productivity of the furnace and increasing the waste of metal.
Types of furnaces
Heating furnaces are divided into several types:
- Methodical, or continuous.
- Heating wells, or periodic action.
Heating wells
Large workpieces weighing up to 35 tons are heated in heating wells, in which from 5 to 14 ingots can simultaneously be located. Uninterrupted operation of the rolling mill is ensured by a group of heating wells. The melts are issued by steelmaking furnaces at certain time intervals: for open-hearth furnaces it is 4-6 hours, for converters - 1-1.5 hours. The heating furnace stops for repair after its resource has been fully exhausted. During this time, heating wells are used to heat the workpieces stored in the warehouse. Furnaces of this type play the role of a kind of buffer between rolling mills and smelters, while maintaining their continuous operation.
Modern models of heating wells are chamber furnaces with temperature and thermal regimes periodic in time.
Industrial furnaces
In ferrous and non-ferrous metallurgy, industrial-type heating furnaces are used to heat workpieces before forging, pressing or rolling. Furnaces differ in design, ingot loading method and temperature conditions. Fuel oil, electricity or natural gas can be used as an energy source. Heating furnaces are divided into continuous and periodic according to the method of loading workpieces.
In a batch furnace, a specific amount of ingots is loaded, which remain stationary during heating. After reaching the required temperature, the ingots are removed from the furnace and sent for further processing, replaced by a new batch. Chamber heating furnaces are reckoned to this type.
In continuous cycle furnaces, submerged workpieces are constantly moving relative to the heat source, which ensures maximum productivity with the small dimensions of the furnace. This type includes conveyor, methodical and rotary kilns.
Chamber furnaces
The ingots in the chamber furnace remain stationary during heating. Depending on the device, chamber-type heating furnaces are divided into several types:
- Vertical. During heating, loading and unloading of the workpiece are in a vertical position. Used for the manufacture of long and narrow metal.
- Bell-shaped. A movable cap is located above the products, which heats them to the desired temperature. Such designs are used for heating sheet metal.
- Heating well. A vertical-loading furnace with a hatch located on top that allows you to load workpieces. Inside the well, workpieces are held by special mechanical grippers.
The operating mode used for the heating element of the chamber-type furnace classifies the furnace into two types: constant and variable temperature.
Variable temperature furnaces are used to maintain a certain temperature regime to obtain the desired properties of the metal. The blanks go through a full cycle of heating and cooling, and therefore their loading and unloading are carried out simultaneously. Electricity allows you to more accurately control the temperature. Constant temperature furnaces use fuel oil or natural gas as fuel and can heat several workpieces at the same time, while their loading and unloading can be carried out separately.
Methodical furnaces
The workpieces in the methodical heating furnace are constantly moving relative to the heating element. Prevention of mechanical stresses in the metal and ensuring uniform heating is possible due to the passage of the workpieces of three zones:
- Methodical zone in which the ingots are preheated.
- A welding zone in which ingots are heated to the required temperature.
- The languishing zone. Thermal energy is evenly distributed over the workpiece before it is processed.
Features of these zones depend on the size of the workpieces. If the cross section of the ingots is too large, the welding zone includes several sections, each of which has a separate heat source for complete and uniform heating of the workpiece. The thermal energy in small ingots is distributed almost instantly, respectively, they do not need to go through the languishing zone. The power source of such furnaces is liquid fuel or gas. In the walls of the welding zone are nozzles with which heating is carried out.
Industrial gas furnaces
Many industries use gas-type thermal heating furnaces. They are one of the links in the technological cycle in various fields of production - from metallurgy to production of building materials.
For the most part, heating furnaces have the same design, consisting of a working space, a furnace, a chimney, a recuperator, a chimney, and additional devices.
Portable ovens
Compact electric heating furnaces that are easy to use and repair and do not need to install chimneys and foundations. If repair is necessary, the portable furnace is replaced with a new model using an overhead crane, which minimizes downtime of the main equipment.
Mechanized and semi-mechanized furnaces
A variety of furnaces, loading and unloading of workpieces into which is carried out using additional mechanisms.
Mechanized chamber furnaces can be installed in the production line along with other equipment due to the rhythm of the delivery of blanks. The simplest from the point of view of operation and design are pusher furnaces.
Glass Ovens
Rotating spectacle furnaces are used when it is necessary to heat round billets with subsequent disembarkation of bolts and pulling ends. The design of such furnaces is represented by a chamotte muffle of cylindrical shape with holes. The rotation of the muffle is carried out together with the hearth on the hinged ring support. In the central part of the hearth there is a gas burner. Flue gases pass through the holes of the muffle, heating the installed workpieces and leaving the pipeline through an exhaust probe.
Glass stoves are divided into rotary, round, rectangular and fixed depending on the design. More simple to manufacture and large in size are rectangular non-rotary furnaces, which also have only one window.
The metal is heated in such furnaces by an open flame, as a result of which scale forms on its surface. In furnaces of continuous and periodic action, non-oxidizing heating of the workpieces is carried out, which avoids the appearance of scale.