A method for maintaining airtightness of an electric resistance welding electrode, the method comprising:
- forming an electrode main body that has a circular cross section by a metal material;
- forming a guide pin that has a circular cross section, projects from an end surface of the electrode main body on which a steel plate component is placed, and penetrates a pilot hole of the steel plate component by a heat-resistant hard material;
- and
- forming a sliding part that has a circular cross section, is fitted into a guide hole formed in the electrode main body in a slidable state, and has a central portion in which the guide pin is inserted, by a synthetic resin material, wherein
- the guide hole is constituted of a large-diameter hole, a medium-diameter hole, and a small-diameter hole,
- a large-diameter portion formed in the sliding part is fitted into the large-diameter hole in a slidable state with no gap,
- a medium-diameter portion formed in the sliding part is fitted into the medium-diameter hole in a slidable state with no gap,
- a ventilation gap through which cooling air passes is formed between the small-diameter hole and the guide pin when the guide pin is pushed down by the guide pin that penetrates the small-diameter hole,
- a movable end surface formed at a boundary portion between the medium-diameter portion and the large-diameter portion of the sliding part is configured to be in close-contact with a stationary inner end surface formed at a boundary portion between the medium-diameter hole and the large-diameter hole of the guide hole, and the stationary inner end surface and the movable end surface are disposed on a virtual plane where a central axis of the electrode main body perpendicularly intersects,
- a length in a direction of the central axis of the electrode main body in which the medium-diameter portion is fitted in the medium-diameter hole is set to be shorter than a length in which the guide pin moves backward during welding,
- a pressurizing unit that presses the movable end surface against the stationary inner end surface is disposed in the guide hole,
- by a width dimension of the movable end surface seen in a diametrical direction of the electrode main body being less than half of a thickness dimension of the large-diameter portion at a position where the guide pin is inserted, an area of the movable end surface is configured to be small to increase a pressurizing force of the movable end surface against the stationary inner end surface, and a minute metal piece that enters a close-contact position of the movable end surface and the stationary inner end surface is pushed from the movable end surface into a base material of the sliding part, and
- by the width dimension of the movable end surface seen in the diametrical direction of the electrode main body being less than half of the thickness dimension of the large-diameter portion at the position where the guide pin is inserted, a thickness dimension of the medium-diameter portion is configured to be set large so as to receive an external force that acts on the guide pin in the diametrical direction of the electrode main body by the medium-diameter portion.