Abstract: The method of manufacturing a preform having a supporting core by effecting successive passes with a plasma torch while material is being supplied, and by effecting at least one glazing step with the plasma torch and without material being supplied includes:a) a first glazing step effected at slow speed from a first end of the preform to the second end thereof;b) pre-separation of the preform adjacent to the first end, thereby reducing its diameter to substantially that of the supporting core;c) a second glazing step effected from the first end to the second end of the preform; andd) complete separation of the preform at the place of pre-separation.

Abstract: The invention relates to a method of performing surface treatment on a preform manufactured in an installation for manufacturing or building up preforms having supporting cores, the installation including at least rotation means having a horizontal axis of rotation and two mounting points between which the supporting core of the preform to be manufactured or built up is mounted, plasma-torch and material-supply means disposed radially relative to the supporting core and mounted to move in axial translation relative to and parallel to the supporting core so as to make the preform around the supporting core, the preform being manufactured or built up by effecting successive passes with the plasma torch while material is being supplied.