Patent ID: 7805962

Claim:
A device for thermally pre-stressing an elongated hollow glass tube having an elongated interior surface, comprising: a heater for heating the tube to be pre-stressed; a holder configured for holding the tube to be pre-stressed at one end thereof; a rotary drive for rotating said holder about a longitudinal axis; a support body having a fluid inlet; a pressure line connected to said fluid inlet for feeding a cooling agent into said fluid inlet; a plurality of fluid lines communicating with said fluid inlet; and a plurality of outlet openings communicating with said fluid lines, said outlet openings being arranged concentrically to said longitudinal axis and being configured for directing a flow of cooling agent against an outer surface of the tube held within said holder; wherein one of said fluid lines is a central tube having an end face which is axially aligned with a first upper axial end of said tube and terminates immediately adjacent said first upper axial end of the tube, said central tube having an inner diameter of 2 to 20 mm and substantially equal to an inner diameter of the tube to be pre-stressed and being configured for directing cooling agent in the first upper axial end and along the entire elongated interior surface of the tube held within said holder.