Apparatus for manufacturing a vitreous silica article

Apparatus for manufacturing a vitreous silica article, comprising:

• a linear burner which comprises at least five slots opening to an exit face of the burner and extending side-by-side in the elongate direction of the linear burner, and means to supply a separate gas flow to each of said slots, wherein said supply means comprises an assembly of separator plates disposed between opposed casing parts, the separator assembly defining the slots and at least one of the casing parts defining at least part of a respective plenum chamber for each gas flow, each plenum chamber communicating with a different one of said slots in the separator assembly, and
• a bait piece situated adjacent to the linear burner to enable deposit of silica synthesized in a reaction in the flame of the linear burner wherein at least one of the innermost slots of the burner is adapted to carry a central flow of a hydrolyzable silicon containing feedstock, said at least one innermost slot being surrounded on either side by further slots adapted to carry gas flows, which do not react directly with the central flow, the latter two flows being flanked outwardly by two further slots adapted to carry further flows of another gas such that the combined flows lead to combustion via the creation of a primary synthesis flame and the formation of a sheet-like plume of silica fume suitable for depositing silica soot on the bait piece, the overall dimension of the primary synthesis flame in the elongate direction of the slots being at least 5 times the total thickness of the primary synthesis flame at the exit face of the burner.