Abstract: A charging base includes: a base seat installed on a floor surface; a columnar tower part provided on the base seat; a first support provided on the tower part and capable of supporting a vertical first electric vacuum cleaner; and a second support provided on the tower part and capable of supporting a vertical second electric vacuum cleaner. An electric vacuum cleaner system includes the charging base configured as described above, the vertical first electric vacuum cleaner, and the vertical second electric vacuum cleaner.

Abstract: A method of heat-treating a rail for obtaining a variety of strength levels from medium value to high value. The method has the steps of: preparing a steel rail maintained at a high temperature region not lower than the austenite field, and disposing a nozzle means around the head of the rail such that the nozzle means can direct a gaseous cooling medium toward the head of the rail; determining the distance between the nozzle means and the head of the rail in accordance with both the hardness level to be attained in the head of the rail and the carbon equivalent of the steel constituting the rail; moving the nozzle means such that the distance is attained between the nozzle means and the head of the rail; and directing the gaseous cooling medium towards the head at a predetermined flow rate and for a predetermined time so as to cool the head of the rail thereby attaining the desired hardness level in the head of the rail.