The warm tightening and loosening of nuts & bolts are actually performed by means of radiant heating rods An operators’ priority is the reduction of the time needed to carry out this operation. We developed an induction heating system that improves the achievement times and the security of both the operators and the material to be tightened.


Induction heats the steel in depth, contrarily to a radiant heating source. This characteristic of the induction allows to reduce consequently

  • The heating time
  • The temperature needed to obtain the required stretch
  • The cooling time
  • The heater element breaks
  • The risks related to the security of both the staff and the heated parts


Trials (between induction and radiant heating) performed on a M64 bolt (body length 350 mm, stretch 0,18%) have shown:

  • A gain of 2/3 in heating time for both tightening and loosening. On site, the gain of time lies between 2/3 and 1/2
  • A gain of 50% in cooling time. The difference of temperature for an induction and radiant heated bolt is of about 90¡
  • A gain in time of change from one bolt to another (immediate coming out of the heater element once the required stretch obtained).
  • A few seconds are needed to change from a bolt to another, no jamming of the inductor inside the bolt.
  • A gain as regards the heater element. The inductors can be easily repaired.
  • A simple use (only one operator per machine)
  • An appreciable improvement of the security. Both heater element and bolt are cold (manual tightening without glove)
  • A maximal security for the tightened material. Curie point impossible to exceed
  • An autonomy of the whole heating set. There is just one plug to connect (autonomous and integrated cooling system)