Abstract: An apparatus for heating a rubber-metal plate composite formed of a plurality of unvulcanized rubber layers and metal plates, each being overlaid alternately, by induction heating, includes an induction coil for applying a magnetic field to the composite and heating the metal plates due to eddy currents generated by the magnetic field, a power unit for applying an alternating current to the induction coil to generate the magnetic field, and a mold to confine the periphery of the composite. The mold is made of a nonmagnetic or weakly magnetic material with electrical conductivity, such as austenitic stainless steel. The mold generates enough heat to function as the heating unit by generating eddy currents in the conductive mold while magnetic flux permeates the mold substantially without loss and reaches the composite therein.

Abstract: A vulcanized rubber-metal plate composite is obtained by overlaying a plurality of unvulcanized rubber layers and metal plates alternately and heating thereof by magnetic induction heating. The vulcanized rubber-metal plate composite is obtained by placing a composite of a plurality of unvulcanized rubber layers and metal plates, each being overlaid alternately, into a place affected by an induction coil; heating the metal plates due to eddy currents formed in the metal plates by applying an alternating current to the induction coil; and vulcanizing the unvulcanized rubber layers due to heat conduction from the heated metal plates.

Abstract: A method and apparatus for automatically tightening and untightening bolts which are assembling and fastening devices for a form used in centrifugal compacting and molding concrete products, in which engaging members are brought into engagement with rotary supports which support the form. A bolt tightening and untightening mechanism is moved with the rotary supports, and the bolts are automatically tightened and untightened during the movement thereof. Engaging members are operated more than a dimensional difference of the rotary supports so that even if dimensions of the rotary supports are different according to the kind of the form, the engaging members can be positively engaged with the rotary supports, or the bolt tightening and untightening mechanism is moved up and down in advance so that a height position thereof becomes a predetermined height with respect to the rotary supports.