The core of the component remains unaffected by the treatment and its physical properties are those of the bar from which it was machined, whilst the hardness of the case can be within the range 37/58 HRC.
[1] A large alternating current is driven through a coil, generating a very intense and rapidly changing magnetic field in the space within.
Many mechanical parts, such as shafts, gears, and springs, are subjected to surface treatments after machining in order to improve wear behavior.
[3] Induction surface hardened low alloyed medium carbon steels are widely used for critical automotive and machine applications which require high wear resistance.
[4] Early last century the principles were explored as a means to melt steel, and the motor generator was developed to provide the power required for the induction furnace.
It was already understood that the depth of current penetration in steel was a function of its magnetic permeability, resistivity and the frequency of the applied field.
Engineers at Midvale Steel and The Ohio Crankshaft Company drew on this knowledge to develop the first surface hardening induction heating systems using motor generators.
Modern day induction heating units use the latest in semiconductor technology and digital control systems to develop a range of powers from 1 kW to many megawatts.
Often the use of ferrite or laminated loading materials is required to influence the magnetic field concentrations in given areas thereby to refine the heat pattern produced.
Another drawback is that much more power is required due to the increased surface area being heated compared with a traverse approach.
[7] In traverse hardening systems the work piece is passed through the induction coil progressively and a following quench spray or ring is used.
It is normal when hardening round shafts to rotate the part during the process to ensure any variations due to concentricity of the coil and the component are removed.
Once this has been established then a variety of methods can be used to calculate the power density required, heat time and generator operating frequency.
The above table is purely illustrative, good results can be obtained outside these ranges by balancing power densities, frequency and other practical considerations including cost which may influence the final selection, heat time and coil width.
It can be seen from the above table that the selection of the correct equipment for any application can be extremely complex as more than one combination of power, frequency and speed can be used for a given result.