Heating furnaces - furnaces designed to heat metal before further processing under high pressure: stamping, rolling or forging. The ductility of the metal increases with heating, which reduces the energy consumption for its deformation. The burnout temperature, at which a liquid phase is formed at the metal grain boundaries, limits the maximum heating temperature. This allows you to reduce the mechanical bond of the grains and lose the strength of the metal.
The temperature difference between the axis of the workpiece and the surface affects the uniformity of heating of the material, which plays an important 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 rolled products and the heating time of the billets, lowering the productivity of the furnace and increasing the waste of the metal.
Types of ovens
Heating ovens are divided into several types:
- Methodical, or continuous action.
- Heating wells, or intermittent.
Large workpieces weighing up to 35 tons are heated in heating wells, which can simultaneously accommodate from 5 to 14 ingots. Uninterrupted operation of the rolling mill is ensured by a group of heating wells. Melts are given out by steel-smelting furnaces at certain time intervals: for open-hearth furnaces it is 4-6 hours, for converters - 1-1.5 hours. The stop of the heating furnace for repair occurs after the full development of its resource. During this time, the 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 melting furnaces, keeping them running continuously.
Modern models of heating wells are chamber furnaces with periodic temperature and thermal conditions.
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 regime. Oil, electricity or natural gas can be used as a source of energy. Heating furnaces are divided into continuous and intermittent according to the method of loading blanks.
A specific amount of ingots is loaded into a batch furnace, which duringheating remain stationary. After reaching the required temperature, the ingots are removed from the furnace and sent for further processing, replaced by a new batch. This type includes chamber heating furnaces.
In continuous cycle furnaces, the immersed workpieces are constantly moving relative to the heat source, which ensures maximum productivity with a small furnace size. This type includes conveyor, methodical and rotary ovens.
Ingots in a 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 rolled metal.
- Kolpakovye. Above the products is a movable hood, which warms them up to the desired temperature. Such designs are used for heating sheet metal.
- Heating well. A top-loading oven with a hatch located on top that allows you to load blanks. Inside the well, the workpieces are held by special mechanical grippers.
The operating mode of the chamber-type furnace heating element classifies furnaces into two types: constant temperature and variable temperature.
Variable temperature ovens are used to maintain a certain temperature regime in order to obtainspecified properties of the metal. Billets go through a full cycle of heating and cooling, in connection with which they are loaded and unloaded simultaneously. Electricity allows more precise temperature control. Constant temperature ovens use oil or natural gas as fuel and can heat several workpieces at the same time, while loading and unloading can be done separately.
Workpieces in a continuous 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 three zones by blanks:
- Methodical zone in which the ingots are preheated.
- Welding zone in which the ingots are heated to the required temperature.
- Languishing zone. Thermal energy is evenly distributed throughout the workpiece before processing begins.
Features of the listed zones depend on the size of the blanks. If the section of the ingots is too large, then the welding zone includes several sections, each of which has a separate heat source for complete and uniform heating of the workpiece. 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. There are nozzles in the walls of the welding zone, with the help of which heating is carried out.
Industrial gas furnaces
In many industries, gas-type thermal heating furnaces are used. They are one of the links in the technological cycle in various areas of production - from metallurgy to the manufacture of building materials.
Heating furnaces mostly have the same design, consisting of a working space, a furnace, a chimney, a heat exchanger, a chimney and additional devices.
Electric heating furnaces are compact in size, easy to operate and repair and do not require chimneys and foundations. When repairs are needed, the portable oven is replaced with a new model using an overhead crane, minimizing downtime on key equipment.
Mechanized and semi-mechanized ovens
A type of furnace, loading and unloading of blanks into which is carried out using additional mechanisms.
Mechanized chamber furnaces can be installed in a production line along with other equipment due to the rhythmic output of workpieces. Pusher furnaces are the simplest in terms of operation and design.
Rotating spectacle furnaces are used when it is necessary to heat round billets with subsequent upsetting of bolts and tightening of the ends. The design of such furnaces is represented by a cylindrical fireclay muffle withholes. The rotation of the muffle is carried out together with the hearth on a hinged annular support. In the central part of the hearth is a gas burner. Flue gases pass through the openings of the muffle, heating the installed blanks and exiting into the pipeline through the exhaust probe.
Depending on the design, spectacle ovens are divided into rotary, round, rectangular and fixed. Simpler to manufacture and larger in size are rectangular fixed ovens, which also have only one window.
The heating of the metal in such furnaces is carried out by an open flame, as a result of which scale forms on its surface. Oxidation-free heating of workpieces is carried out in continuous and batch furnaces, which makes it possible to avoid the appearance of scale.