Abstract: A helical band is produced by applying a layer of heat-settable material on to a rotating support to one side of the axis of rotation. Heat is applied to the layer, as by the support while it rotates, for a length of time sufficient for the material in the layer to set to a required extent to form the band. The band is removed before it comes into contact with the material being applied on the support. The band is preferably made of electrically-insulating material so that it can be wound helically round and bonded to a cylindrical rod of electrically-insulating material to form a helically flanged insulator for use in an overhead electric power transmission line, the flange-forming band defining along the rod a helical leakage path of substantially uniform width.

Abstract: An apparatus for fabricating a plastic insulator having helical-shaped shields or screens, these shields radially protruding from an insulator rod. Two oppositely rotating rolls coact to form an infeed gap for the material forming the shields which is infed in a kneadable condition in transverse direction to the rolls. According to a first embodiment drive means serve to rotate the rolls about their axes and the insulator rod about its lengthwise axis. Means provide relative mutual movement of the pair of rolls and the insulator rod in the direction of the lengthwise axis of the insulator rod or parallel thereto, in order to simultaneously form the shield and apply the same to the insulator rod. According to a further embodiment both of the rolls have peripheral grooves and these rolls, with the exception of such peripheral grooves, bear against one another at their outer surfaces, and drive means serve for rotating the rolls for forming a shield or screen rod.