Thanks to the advent of affordable electronic and insulating components in modern manufacturing, the field of application of induction heating is becoming ever wider. This technology is used not only in metallurgy, but also in the development of household appliances.
Induction heating principle
The operation of the induction furnace is based on the transformer principle of energy exchange. The inductor is made of a copper tube, which is then twisted into a multi-turn coil. An alternating current is supplied to the primary circuit of the inductor, which leads to the formation of an alternating magnetic field around it. Under the influence of a magnetic field in a body placed inside the inductor, an electric field arises, which subsequently leads to a heating process. The power and, accordingly, the heat generated by the induction crucible melting furnace directly depend on the frequency of the alternating magnetic field. Therefore, for efficient operation, the furnace needs high frequency currents.
The use of induction furnaces
Induction heating can be used to work with any material: metal, slag, gas, etc. The main advantage of its application is non-contact heat transfer. Also, induction heating allows you to achieve almost any heating rate - it all depends on the power of the generator that feeds the furnace. The heat loss during such heating is minimal. The maximum temperature to which an object can be heated in an oven is limited only by the resistance of the refractory material. The process of non-contact heat transfer to the heated material makes it possible to produce heating in a vacuum environment.
According to the reviews of metallurgists, the scope of induction furnaces is somewhat limited due to existing shortcomings. The disadvantages of the crucible furnace include:
- high price for electrical equipment;
- cold slags complicating the refining process;
- reduced lining stability during temperature jumps between melts.
Scheme of a crucible induction furnace
Induction crucible furnace has the following design.
The main element of the furnace is the crucible (7), covered with a lid (1). The crucible is located inside the heating inductor (3), made in the form of a multi-turn coil. The coil is a copper tube inside which, for the purpose of cooling, water is constantly circulating. The magnetic flux from the inductor passes through the magnetic cores (4), which are made of special transformer steel. A swivel assembly (2) is provided for tilting the furnace during the spill of molten liquid. The furnace is installed on a mild structure (5). Cooling is done using water cooling hoses (6). An auxiliary platform (8) is used to service the furnace.
The scheme of the crucible furnace also includes a transformer, capacitors, a control unit and a gas evacuation system. The crucible electric furnace is powered by currents with a frequency of 50 Hz.
Features of internal structural elements
Most often, the inductor is made of a circular tube. But there are situations in which a round copper pipe is not applicable. In certain cases, profiled elements are used to design an induction crucible furnace, due to which the magnetic flux of dispersion is reduced. The inductor tubes are insulated between each other with fiberglass impregnated with a special varnish. Protected coils are compressed by blocks made of dielectric material. An inductor and a crucible placed inside the coil are mounted on a pallet made of refractory bricks or heat-resistant concrete. In industrial conditions, the crucible manufacturing process takes place directly in the furnace. In this case, the inductor is assembled installed on a pallet and insulated with asbestos. After that, the pallet is filled with refractory powder, which is sealed using a pneumatic installation. The gap between the template installed on the bottom and the inductor is filled with powders from refractory materials.
The lining of the zone above the inductor is provided by refractory bricks. The collar and drain gutter are also lined with heat-resistant brick. The operation of the induction crucible furnace takes place under the most difficult conditions, therefore, high demands are made on the quality of the heat-resistant materials used. The lining durability is affected by the composition of the refractory mass, the mode of operation and the applied frequency of the electric current. Typically, a crucible withstands up to 100 swimming trunks, and then fails.
Design of external elements
The frame of the melting crucible furnace is a base to which all its elements are attached. On large industrial devices, the frame has the form of a continuous casing. All frame parts must have high strength, due to the influence of the electromagnetic field of the inductor on them. The casing under certain conditions can heat up in the same way as the material in the furnace. To reduce heating, the frame is rationally made from non-conductive materials. However, since dielectric materials are expensive, steel usually serves as the material for the frame. The steel structure is divided into several elements, which, in turn, are isolated from each other. Screens are used to reduce the electromagnetic field near the frame. A shield is installed between the inductor and the furnace body. The screen has the shape of a cylinder and is made of aluminum or copper.
The swivel assembly is an important structural element. The main requirement for the rotation mechanism is to provide a tilt for complete discharge of the metal. Swing mechanisms can be used different. Small ovens use a manual or electric hoist. Industrial furnaces are tilted using a crane beam. Large furnaces can be equipped with a hydraulic tilt drive.
The cover that covers the crucible for melting serves to maintain the temperature inside the unit at a higher level. However, given that it is possible to cover the furnace only after the charge has completely melted, the use of a cover is not necessary.
DIY stove making
Induction furnaces are widely used not only in industry, but also in everyday life. You can find schemes of a large number of home-made devices, but some of them, at best, simply will not work, and at worst, they will harm the health of their creator. Many lovers warn of such consequences. In everyday life, the induction heating method is used in such devices:
- channel furnace for metal melting;
- crucible induction furnace - the easiest to design, and in this regard, the most popular among enthusiasts, judging by the reviews;
- a water boiler, the operation of which is based on the induction method;
- induction hobs competing with popular gas stoves.
Channel oven
This type of furnace is used to produce high-quality cast iron, as well as for melting duralumin and non-ferrous special alloys. A channel furnace with a capacity of up to 3 kW is made independently from a welding transformer, the frequency of which corresponds to the industrial one. Such a furnace allows melt a blank of bronze or copper weighing up to half a kilogram. The channel furnace also allows remelting duralumin, but it must be taken into account that the process of “aging” should follow the melting process. The time of this process can be up to 2 weeks and depends on the composition of the alloy.
For the manufacture of the furnace, the primary winding of the welding transformer is left unchanged, and a ring-type crucible is placed in place of the secondary winding. The best material for the crucible of a small channel furnace is electrophore. Other options are not suitable due to low strength and dielectric loss. According to amateur metallurgists, the problem is that it is not possible to process the electric porcelain independently, and it is very unlikely to find a suitable item on sale. It is because of a deficit crucible that the channel furnace was not widely used by enthusiasts, although this type of furnace has an efficiency of more than 90%.
Crucible induction furnace
A self-made crucible furnace is used primarily for the purification of valuable metals. For example, having a radio connector made in the Soviet Union, you can get a certain amount of gold from its contacts. Using external heating, such a result is impossible to achieve.
In addition to gold mining, such a furnace is often used to uniformly heat the metal, which is required for high-quality quenching. By changing the position of the part in the inductor and adjusting its power, it is possible to achieve a given temperature in a specific section of the metal. It is important that the use of such a furnace will be quite budgetary, because almost all the energy is directed to the process of heating the part.
Induction boilers
Induction water heating boilers have every chance in the future to displace conventional boilers. The minus of such a water heater is the users consider the high price, but at the same time, systematizing numerous reviews, several advantages can be highlighted:
- Reliability. There is no electric coil in the boiler, which is a weak link in a conventional boiler.
- The efficiency is almost 100%.
- Security. Access to electricity to the boiler body is not possible due to the design features.
- The device does not need special grounding.
- Resistant to power surges.
- Does not form scale.
- Durability. The boiler is able to work without maintenance for about 30 years.
Homemade Water Boiler
The basis of such a water heater is a power transformer with a capacity of up to 1.5 kW, the primary winding of which is designed for a voltage of 220 V. A transformer from a lamp color TV is perfect. The secondary winding should be removed, and the number of turns of the primary must be increased.
Craftsmen advise and warn: the use of such a home-made device is unsafe, so the transformer should be grounded, and the device itself must be connected via a high-speed RCD.
Inductor in the kitchen
Induction kitchen hobs are no longer surprising and are widely used in everyday life. The device is based on the same principles as an induction furnace, with the only difference being that the secondary winding is the metal bottom of the dishes.
The use of such plates was made possible due to the appearance of a dielectric in production, which, in addition to performing the task of insulating the inductor, must also have strength and hygienic characteristics. Material satisfying all the requirements has appeared relatively recently, and its cost is a significant part in the total price of the plate.
Users unanimously say: the independent manufacture of an induction cooker does not make sense for two reasons. First, cooking on such a cooking surface requires fine tuning for each type of food. For the necessary adjustment of all electrical parameters during the preparation process, a microcontroller is required. The second reason is the price of the electronic parts that make up the stove. In total, all elements will cost much more than the cost of a finished device.
Induction cooker has the following positive qualities:
- the absence, in contrast to microwave ovens, of third-party radiation;
- the ability to program the stove according to your style of cooking;
- Cooking dishes such as caramel without overheating and burning;
- profitability due to the rational use of heating energy.