High frequency heating method of a bolt with hole

Abstract

A high frequency heating method of a bolt sets a maximum achievable temperature Tmax in an inner surface of the bolt with hole to a value which is not higher than a final heat treated temperature To. A maximum thermal stress .sigma.max occurring in the bolt with hole is set to a value which is not more than a yield stress .sigma.ys of the bolt material. From the maximum thermal stress .sigma.max, a temperature difference .DELTA.T is obtained between Tmax and a mean temperature Tmean along an entire cross section of the bolt, under the condition that .DELTA.T is to be not more than a permissible maximum temperature difference .DELTA.To obtainable from the yield stress of the material. The maximum suppliable power by Tmax, .DELTA.T and dimensions of the bolt are obtained, and then a heater is inserted into a small diameter hole of the bolt with hole and the maximum suppliable power, which value is obtained by the above operation, is supplied to the heater so that the bolt with hole is heated to be elongated. The temperature of the bolt with hole, while it is being heated, is not higher than To, and hence lowering of the material strength can be prevented. The thermal stress is not higher than .sigma.ys, hence the life consumption due to fatigue can be suppressed and loosening of the bolt with hole within a short time becomes possible.