Induction heating occurs when an electrically conducting material is placed within a varying magnetic field. The heating is due to eddy-current losses within the material (in magnetic materials such as iron, some heat is also generated by hysteresis losses). Let’s have a look at needs for capacitors in this application field.
An important aspect of the process is that the heat is generated by the material itself without the need for an external radiant heat source. This means that induction heating is clean and fast. It also highly repetitive; once the equipment has been set up, part after part can be heated with identical results.
Induction heating finds applications in many industries for heat treating activities such as annealing, forging, welding, brazing, curing and sealing.
What is induction heating?
Induction heating is a process which is used to bond, harden or soften metals or other conductive materials. For many modern manufacturing processes, induction heating offers an attractive combination of speed, consistency and control.
The basic principles of induction heating have been understood and applied to manufacturing since the 1920s. During World War II, the technology developed rapidly to meet urgent wartime requirements for a fast, reliable process to harden metal engine parts. More recently, the focus on lean manufacturing techniques and emphasis on improved quality control have led to a rediscovery of induction technology, along with the development of precisely controlled, all solid state induction power supplies.
What makes this heating method so unique? In the most common heating methods, a torch or open flame is directly applied to the metal part. But with induction heating, heat is actually "induced" within the part itself by circulating electrical currents.
Induction heating relies on the unique characteristics of radio frequency (RF) energy - that portion of the electromagnetic spectrum below infrared and microwave energy. Since heat is transferred to the product via electromagnetic waves, the part never comes into direct contact with any flame, the inductor itself does not get hot, and there is no product contamination. When properly set up, the process becomes very repeatable and controllable.
Induction heating industries and applications
Induction heating is a natural fit for automated production lines and, because magnetic fields can permeate glass and similar materials, it works in controlled environments.
Some of the industries that use induction heating in a big way are:
l The automotive industry for treating bearings, brakes, drive trains, gears joints and shafts. Frames, seats, bumpers and steering wheels are also heat treated.
l The bus and truck industry for similar, albeit physically larger, applications and the ship-building industry for larger still; It is also used for repairing and reshaping damaged hulls. The commercial and recreational marine engine industry uses induction heating processes in production.
l The sports and fitness industry for golf clubs, goal posts and exercise equipment.
l The wind-turbine industry for gear-handling systems.
l The aeronautics and aerospace industries for heat treating components and producing special alloys.
l The oil and mining industries for pipe and tool manufacture.
l The railroad industry for an array of locomotive parts.
The commercial, residential and industrial construction industries for the production of structural sections.
Induction heating process introduction
How induction heating works?
How exactly does induction heating work? It helps to have a basic understanding of the principles of electricity. When an alternating electrical current is applied to the primary of a transformer, an alternating magnetic field is created. According to Faraday's Law, if the secondary of the transformer is located within the magnetic field, an electric current will be induced.
In a basic induction heating setup, a solid state RF power supply sends an AC current through an inductor (often a copper coil), and the part to be heated (the workpiece) is placed inside the inductor. The inductor serves as the transformer primary and the part to be heated becomes a short circuit secondary. When a metal part is placed within the inductor and enters the magnetic field, circulating eddy currents are induced within the part.
Eddy currents flow against the electrical resistivity of the metal, generating precise and localized heat without any direct contact between the part and the inductor. This heating occurs with both magnetic and non-magnetic parts, and is often referred to as the "Joule effect", referring to Joule's first law – a scientific formula expressing the relationship between heat produced by electrical current passed through a conductor.
Secondarily, additional heat is produced within magnetic parts through hysteresis – internal friction that is created when magnetic parts pass through the inductor. Magnetic materials naturally offer electrical resistance to the rapidly changing magnetic fields within the inductor. This resistance produces internal friction which in turn produces heat.
In the process of heating the material, there is therefore no contact between the inductor and the part, and neither are there any combustion gases. The material to be heated can be located in a setting isolated from the power supply; submerged in a liquid, covered by isolated substances, in gaseous atmospheres or even in a vacuum.
Induction heating process
The use of induction heating for surface hardening and localized hardening of metal parts allows a considerable saving of time compared to the traditional oven hardening process.
The possibility to choose the power and the frequency of operation allows to concentrate the treatment in a very specific area, as well as to facilitate the control of all the parameters, in order to be able to produce certified pieces with high repeatability.
Furthermore, the induction hardening process of metals has the characteristic of being easily included in automatic systems, in such a way as to significantly reduce the necessary manpower.
The use of induction to temper a component significantly reduces processing times. Induction heating generates heat directly in the material in a few seconds, an activity that otherwise, for example with an oven, would require much longer times.
Furthermore, the induction metal tempering process has the characteristic of being able to be easily included in the line and possibly in automatic systems, in such a way as to significantly reduce the necessary manpower.
The execution of induction annealing processes has numerous advantages over the classic use of an oven. The heat is generated by transferring the energy directly to the material, a method that increases the efficiency of the system and reduces energy costs.
Using induction it is possible to perform localized annealing in a very small area, respecting production tolerances and preserving the metallurgical characteristics of the material.
Furthermore, the induction annealing process of metals has the characteristic of being easily included in the line and possibly in automatic systems, in such a way as to significantly reduce the necessary manpower.
The execution of induction brazing of metal parts has some important advantages compared to the classic use of flame systems.
First, with induction, the operator has greater control over heating, reducing the risk of overheating.
In addition, by exploiting the induction characteristic of transmitting energy directly to the piece, the risks of cold brazing are reduced and production speeds are increased.
Last, but not least, the safety aspect: induction eliminates the need to use gas generate open flames.
Induction systems are used, for example, for brazing tools, pipes, fittings and values for the hot / cold sector.
Plastic / metal welding
Where there is the need to make a joint between a plastic component and a metal component, induction can be the technology suitable for the purpose.
Typical applications in this sector are, for example, welding of plastic terminals on broom handles, joining threaded metal inserts inside a plastic component, etc.
The procedure consists of the cold assembly of the components, and a subsequent localized and controlled induction heating of the metal part. The heat generated on the metal melts the plastic, which drowns the knurls and inlets of the metal insert itself. A joint is obtained with mechanical characteristics that are difficult to achieve using other technologies.
The application can be easily integrated into automated systems, in such a way as to significantly reduce the necessary manpower and reduce the cost of processing.
Induction forging and molding
The induction heating of metals for forging and stamping has considerable strengths in the application sector:
l Quick heating of the pieces
l High yield and reduction of energy costs
l High process cleanlines, with reduced oxidation
l High degree of control of the heating process, high uniformity of heating
l Elimination of gas and flame systems
Furthermore, the heating process for forging and induction molding has the characteristics of being easily included in the line and possibly in automatic systems, in such a way as to significantly reduce the labor required.
Induction billet heating
The induction heating process of billets has the characteristics of being easily included in the line and possibly in automatic systems, in such a way as to significantly reduce the necessary manpower.
In the event that it is necessary to mechanically assemble metal components, induction heating technology can be useful for this purpose.
By exploiting the physical principle of thermal expansion, the piece to be assembled is heated to increase the passage diameter. The subsequent assembly operations will be facilitated, also leading to a reduction in non-conformities.
Hot pressing is adopted especially in the electric motor sector, for which we cite some typical applications below: shrink fit of the shaft into the rotor, insertion of the stator block in the relative housing casing, keying of ball bearings in the appropriate seats.
Induction heating equipment
The design and manufacture of induction heating equipment is a major industry in itself, and machine types are many and varied.
Some types are:
1. Large industrial heat treatment and processing systems
2. Mobile heat generators
3. Solid state welders
4. Modular forging systems
5. Custom configurations, etc.