Induction Heating

What is Induction Heating?

Induction heating is a process where electrically conductive components are heated in a strong magnetic field utilising the principle of electromagnetic induction discovered by Michael Faraday. The magnetic field creates a flow of electrical current in the component which by means of the electrical losses in the component generates heat.

Heat Treatment Hardening of 100mm Pin

Heat Treatment Hardening of 100mm Pin

Induction Heating - 100mm pin being hardened to a depth of 5mm using 350Kw D Type medium frequency induction heater and horizontal traverse.

The magnetic field is generated in a copper coil which is fed by an AC current. The depth at which the current flows is governed by a multitude of factors including the magnetic permeability and resistivity of the material in combination with the power density. However a major parameter is also the frequency of the AC supply to the coil and therefore rate of change of the magnetic field.

The selection of the correct frequency for any application is one of the key elements of any successful system. As with all subjects frequency selection can become extremely complicated as in some cases many factors need to be considered and these often vary with the application. Fortunately experience of past applications together with some simple calculations and practical trials can often be used as the basis for selection. In more complicated cases modelling using finite element analysis can be used.

The selection of the power output is similar to frequency selection as many factors need to be considered and these can again vary with the application. Similar processes are used in the selection process.

Heat Treatment Hardening of 100mm Pin

Induction Heating treatment Hardening of Lawnmover Blades

Induction Heating - Purpose-built system for edge hardening of lawnmower bottom blades. Power is from 12Kw Ultratec RF Induction Heater.

What can be heated?

Induction heating can be used to heat many conductive materials including Ferrous metals, Non Ferrous metals, Carbon, Carbon Based composites, Conductive Gasses, Molten Glass etc.

Applications of Induction Heating

From a user point of view induction heating is the most flexible way of heating electrically conductive objects to a given temperature in a specific, due to the heat being generated within the component power delivery is very accurate and repeatable. Further control can be gained by the use of infra red pyrometers and closed loop systems in relevant applications.

1 - Induction Heat Treatment

Traditionally one of the main applications for Induction heating. Most steel parts can be heated by this method.

The controllability of the induction process and its ability to produce pin point heat in selective areas is utilised for the selective zone and case hardening of components in a multitude of industries. In recent years induction annealing and tempering have been used extensively to increase throughput and reduce floor area requirements when compared with more traditional methods.

The Automotive industry uses Induction heating extensively to harden, temper and anneal selective areas on various components including drive shafts, engine vales ,tappet adjusters, selector forks, rocker arms, clutch diaphragm springs, clutch bearings, etc. The advantage with using Induction is that it can be incorporated in existing flow line techniques. Also by selecting the correct power and frequency, it is possible to produce very accurate case depths with complete repeatability.

The small tool and saw industries extensively use induction hardening for hammers, axes, chisels, saw teeth, pruner blades, shear blades etc.

The list of hardening applications is truly endless and we regularly find new applications some examples of other induction hardened parts include, power tool shafts, Sealant gun shafts, leather knives, paper knives, rolling mill rolls, screw threads, gun drills, pump parts, motor parts etc.

Due to the high power density, the heat cycle can be very short allowing rapid throughput combined with a heat pattern which can be very accurately controlled reducing distortion, scale and damage to other metallurgical properties.

2 - Induction Brazing and Soldering

Due to the precision and controllability of the heat produced by induction heating it is particularly suited to a whole range of Brazing Soldering and Metal Joining applications.

Given the added advantage that the process is clean and intrinsically safe, it utilises no gasses or external heat sources removing the concerns of naked flames and explosive atmospheres. Induction heating represents technologically advanced solution to metals joining.

Typical parts joined include:-

  • Electrical contacts
  • Cutting tools for machine tools lathes and millers
  • Coal cutter picks
  • Carbide teeth to saws
  • Immersion heaters elements
  • Tubular sections for cycles
  • Hydraulic tubes
  • Capacitor leads to studs
  • Masonry drill bits
  • carbide tiles to plough shares
  • Heat exchanger tubes

With induction it is possible to join materials under atmosphere or in vacuum ensuring no contamination of the welded joints or where copper joining alloys are used.

In most cases the inductors used for brazing are low impedance single turn often machined and fabricated. This type of coil in conjunction with our safe-braze work-head ensures the output voltage will be low enough to allow the operator to work safely within the coil with no risk.

Typical power units for brazing and soldering are from 1kW up to 30kW at frequencies from 50kHz up to 200kHz. Extensive use of twin head systems allows many applications to be carried out manually as they ensure full utilisation of the power unit.

In situations where high volume fully automated solutions are required these include conveyors, rotary tables, shuttle units and other tailor made systems.

3 - Induction Forging

A whole range of components are now forged utilising Induction heating as the heat source.

Complete billets or bar ends can be heated to a precise temperature very quickly ensuring accurate metal flow and reducing scaling. The final forging is cleaner, more accurate and less prone to other metallurgical defects than with gas or other types of heating.

The range of shapes and sizes of materials being heated not only includes the traditional such as round bars, square billets, hexagonal bars but is constantly expanding and now includes complex geometries such as railway rails which are heated to produce points, switch blades etc.

The end product can vary from small fasteners used in the aerospace sector up to crankshafts, axles and larger components.

Depending on the volumes required, the system can be manual fed or completely automated utilising pneumatic pushers, conveyors, rocket launchers, rotary tables, traditional pinch wheel fed in line billet feeders and robots.

Using Induction heating, the temperature and position of the heated area can be controlled extremely accurately leading to a high quality of finish and repeatability. As the heat is generated within the component energy efficiency is optimised thus reducing production costs.

As most forging operations require a through heated component at temperatures between 1100° to 1300°, the coil has to be insulated with special materials to contain and withstand the radiated heat. To increase the wear characteristics of continuously fed billet heating coils water cooled, hard faced stainless steel rails can be utilised on which the billets slide.

4 - Induction Melting

Induction melting systems are used widely in the metals casting and metals processing industries industry. Sizes of installations vary from a few grams to many tonnes.

There are a number of techniques available and selection is based on the individual needs of the customer and the individual application.

The larger production units in the 50kg to 10 tonne range generally consist of a high power (typically up to 100kW), low frequency (typically less than 3kHz) power source and a coreless refractory lined furnace where the magnetic field not only melts the metal but can also be used to stir the molten charge.

Due to the combined weight of the furnace body and its contents a hydraulic tilt mechanism is utilised to pour the metal although some systems can feature a pop up furnace.

Smaller systems in the 250g to 30kg typically use a clay graphite, silicon carbide or pure graphite crucible. The principle advantage of such units is that the crucible act as a susceptor therefore the power unit sees the crucible and not the charge material. This makes the systems extremely flexible as they can melt a range of metals of differing geometries in the same system with no changes in set up. Furnaces are often pop-up type or small manual tilting arrangements. These units are found in Universities, Scrap Metal Companies, Assay Offices and Jewellers. A typical Inductelec "Mini Melt" system is shown on the home page.

Typical power of a Mini-Melt generator is between 5kW and 36kW with an operating frequency of between 30 and 200kHz. Comprising induction power unit (5kW up to 30kW depending on sample size) and pop-up furnace. The Unit can also be supplied with one power unit and two furnaces. In this case a special changeover switch is also provided. This means one furnace can be loaded whilst the other is melting, resulting in greater utilisation and more product.

Specialist melting systems for laboratory and scientific use are available with vacuum chambers and cold crucible technology and are often used for producing extremely pure samples or for melting metals where oxidisation can present problems.

5 - Induction Bending

Induction heaters are extensively used in the tube and metal bending industries where the accurate zone heating and controlled temperatures ensure consistency of product.

Rapid heat cycles reduce scaling and other surface defects to a minimum reducing the need for fettling and downstream processes. Typical bending applications include forklift forks, medical implements, railway rail clips etc.

6 - Shrink Fitting and Expansion

Due to its controllability, surface power density and accuracy of application Induction heating can be used to expand a range of products prior to fitting or assembly.

Typical applications include assembly of high quality roller bearings, fitting starter rings to flywheels, timing gears to crank shafts, turbines to shafts, motor stators to motor bodies etc. In many cases the same unit is also utilised to remove old or damaged components before replacement with new.

Due to the accuracy required in the assembly phase it is common to have a jig or press of some type to ensure accurate alignment. These range from simple fly-press arrangements to fully automated pneumatic and hydraulic units capable of generating forces of up to 10 tonnes pressure.

7 - Hot Staking

Hot staking refers to the heating of a metal product to allow its insertion into a plastic object. The precise and controllable heat generated by the induction heating process allows accurate control over the flow of the plastic and therefore the bond achieved.

Typical applications include fitting handles to knives, medical implements and decorating tools. The technology is also extensively used to insert threaded parts into automotive lighting bezels and mobile phone cases.

8 - Curing and Bonding

Adhesives, paints and exotic coatings have all been cured onto metal surfaces using a variety of induction heating techniques.

Curing is achieved by heating the metallic substrate to a temperature which accelerates the cure. This can be in the form of a continuous process on tubes, strips or wires or in a static process e.g. setting the adhesive which attaches rubber handles to a metal hammer shaft. Bonding equipment is extensively used in the automotive industry for securing trim to panels.

9 - Induction Tube Welding

Seam welded tubes used in the metals fabrication and construction industries are often welded utilising Induction heating technology.

Current which is induced in the tube will run along the open edges of the seam creating a temperature to enable the two edges to be welded together. The coil is normally wound around the outside of the tube and an intensifier can be used in the bore of the tube. At this point the edges are forced together resulting in a continuous weld. Typically tube welding units have very high power outputs often into the 100's of kW and frequencies typically above 200kHz. Post welding it is possible to utilise lower frequency units with iron loaded coils to anneal the weld.

10 - Induction Sealing

Cap sealing of bottles and other containers can be carried out using relatively small low powered generators. Other typical products are toothpaste tubes and cosmetic tube products.

11 - Hi Tech and Scientific

Fibre-optic cables, semiconductors, plasma generation, medical research, nuclear industry etc many hi tech industries rely on the induction heating process. The highly controllable, clean, non contact nature of induction heating makes it extremely attractive to many laboratory applications.

Please browse our website for more information about Induction Heating then contact us on 0114 272 3369 to speak to a member of our team or e-mail us on info@inductelec.co.uk.