Abstract: A high frequency heating coil device having sufficient flexibility and heating ability is provided. Coils 2 are contained in outer jacket 1. The coils 2 are made of steel, copper or brass tubing which is annealed sufficiently to be flexible. Plural pieces of magnetic substance 10 are arranged in series between the coils 2. Flexible spacer 9 is arranged between a magnetic substance 10 and the coils 2. Upper and lower end faces of each piece of the magnetic substance 10, make direct contact with other adjacent pieces, and are made with curved faces a. Heating coil device is so constructed that when inserted into a hole of an object to be heated and high frequency current is supplied to the coils to the coils 2 from electric source 6, eddy currents are generated in an inner surface of the hole in order to heat the object. The heating coil device, while being bent to avoid obstructions, can still be inserted into and drawn out of the hole.

Abstract: An automatic plate bending system using high frequency induction heating has many universal poles for bearing a steel plate, a member to be heated, by supporting it from below, the height positions of front end portions of the universal poles themselves being adjustable, and automatically moves a high frequency heating coil of a high frequency heating head above the steel plate, which is placed on the universal poles, along predetermined heating lines while retaining a constant clearance between the high frequency heating coil and the surface of the steel plate, whereby the steel plate is heated and automatically bent into a desired shape.

Abstract: An automatic plate bending system using high frequency induction heating has many universal poles for bearing a steel plate, a member to be heated, by supporting it from below, the height positions of front end portions of the universal poles themselves being adjustable, and automatically moves a high frequency heating coil of a high frequency heating head above the steel plate, which is placed on the universal poles, along predetermined heating lines while retaining a constant clearance between the high frequency heating coil and the surface of the steel plate, whereby the steel plate is heated and automatically bent into a desired shape.

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.

Abstract: A high frequency bar type heater can be inserted into a hole of an object to be heated even if there is an obstruction above the hole. The high frequency bar type heater has a flexible and slender heat resisting and insulating tube (2) having both its ends closed so as to form a water-tight container. A flexible and slender conductor coil (3) is inserted in the heat resisting and insulating tube (2). A magnetic core (5), sectioned in plural pieces in its longitudinal direction, is contained on an inner side of the conductor coil (3). A flexible cooling water pipe (6) is inserted in the heat resisting and insulating tube (2) so as to cool the interior thereof. The high frequency bar type heater thus has flexibility as a whole. The magnetic core may also be formed of a flexible material.

Abstract: A high frequency bolt heater is provided which can heat up the inside of a narrow hole much faster than a conventional bolt heater employing a resistance wire. The high frequency bolt heater includes an induction heating coil made of a copper tube bent in a hairpin fashion and whose shape is made approximately circular in section by pinching a magnet between opposed portions thereof. The heater can be inserted into a hole bored in the axial direction of a metallic bolt. A length of the coil is made approximately equal with that of the bored hole, and the magnet is omitted from a region of the heater which corresponds to a screw portion of the bolt for mounting a nut. An adjustable stopper made of a heat resistant electrical insulator is provided for setting a necessary length of the induction heating coil to be inserted into the hole, and a heat resistant insulator is provided on the surface of the induction heating coil.

Abstract: An information transmission method using arc and apparatus thereof are applied to a loudspeaker and the like having the function of illumination. The information transmission method is characterized in that arc current supplied to an arc generating device is modulated by a signal based on information to vibrate arc column so that at least one of audible waves, ultrasonic waves and arc light is employed to transmit the information. Arc having small mechanical inertia is employed as a sound producing device and accordingly can be used as a loudspeaker having a good frequency characteristic and large output. It can be used as a sound producing device having the function of illumination by utilizing strong light emitted from arc column.