Welding head for resistance - welding machine

A welding head adapted for use in a vertical orientation in resistance-welding machines utilizing a welding current, said head comprising a current lead. a housing adapted for the connection of said current lead, a vertical-axis rotor having a lower end and a body mounted rotatingly and non-displaceably in said housing, a roller electrode attached to said lower end of said rotor, and means for supplying said welding current to said roller electrode through said rotor body, said means comprising an interstice filled with mercury, said welding head further comprising a cylindrical central chamber having a wall surface and a base, the base being located adjacent said lower end and extending through almost the entire length of said rotor body, and a current-transmission rod secured to said housing and extending downwards through said central chamber almost to said base thereof, said interstice being formed within said cylindrical central chamber between said wall surface and base thereof and said current-transmission rod free of fluid seals adjacent the lower end portions of said interstice.