Conductive or Inductive Heating of Large Workpieces at Frequencies of 50 Hz and Below.

The paper reports on studies carried out with the aim of determining the optimum ratio between diameter and depth of penetration as a function of workpiece geometry, material properties and heating conditions and of estalishing on the basis of economic criteria whether preference should be given to inductive or conductive heating of workpieces having a large diameter compared with length. For cylindrical steel ingots conductive heating at mains frequency is preferable up to a diameter of around 230 mm provided the ingot is long compared with its diameter. For diameters between 230 and 300mm the inductive method at mains frequency can be selected which offers increasing advantages as the diameter of the work increases. For diameters between 300 and 700 mm the inductive method at mains frequency is preferable in terms of energy input.