Patent ID: 7387000

Claim:
A method for producing a hollow cylinder from silica glass, said method comprising: depositing SiO 2 particles onto an elongate support that rotates about a longitudinal axis thereof, said support having a first longitudinal section with a first outer diameter and a second longitudinal section with a second outer diameter, the first outer diameter being larger than the second outer diameter, so as to produce a porous blank with an inner bore defined by a first cylindrical surface extending over a first length of the blank and having a first inner diameter, and by a second cylindrical surface extending over a second length of the blank and having a second inner diameter, and an area therebetween, the first inner diameter being larger than the second inner diameter so that said area between the first longitudinal section and the second longitudinal section has a constriction in said inner bore of said blank, said constriction being formed by said support by shaping the inner bore during said SiO 2 deposition, and vitrifying the blank suspended in vertical orientation in a furnace using a suspension that engages with said constriction, said constriction being in an upper region of the blank; said suspension having an upper portion and a lower portion, said upper portion being smaller than the second inner diameter, and said lower portion having a size between the first inner diameter and the second inner diameter, and wherein during said vitrification said suspension extends into the inner bore and supports the blank by engagement with said blank in said area of said constriction, said suspension having no contact with said first cylindrical surface of the inner bore of the blank during said vitrification.