Patent attributes
A yoke is produced by rolling up Zn—Al—Mg platinized steel plate of corrosion-resistance treatment where both ends thereof are tightly mated. On the outer peripheral surface of the yoke, plural linear grooves extending in the axis direction of the yoke are formed at a constant interval in the rolling step. Because the steel plate of corrosion-resistance treatment is prepared before initiating the rolling step, it is not necessary to perform coating and electroplating after making a cylindrical shaped yoke, namely, not necessary to perform any coating and electroplating after making the yoke, and the grooves are not filled with reaction products. This increases the radiation capability of the yoke because of increase of the entire surface area of the yoke. The Zn—Al—Mg platinized steel has a silver color and hardly absorbs radiant heat from an engine of a vehicle, and suppresses the increasing of the yoke temperature.
