External internal channels in glass tubing

Abstract

A method for forming integral internal channels defined by a wall with an annular cross-section inside high softening temperature glass tubing is described. In particular, a reduced pressure is provided inside a rotating tube with heating outside which softens the glass for deformation by the reduced pressure while a smaller tube is maintained in position in contact with the inside walls of the larger tube. The pressure in the smaller tube is usually the same as that in the larger tube and is such that it can collapse at the point of contact to form at least one fusion band along the inside wall of the larger tube. The position of the smaller tube is maintained such that the larger tube has concave depressions between the fusion bands. Usually the heating is accomplished by a gas flame ring burner positioned under the larger tube and moved progressively along the larger tube until the desired fusion of the tubes is completed. The next step which is preferred is to provide a positive pressure in the larger tube with heating to soften the glass to move the concave depressions out and mold them against a platen provided in spaced relation to the depressions outside of the larger tube. This can also be progressively accomplished with the ring burner. While the glass tubes are being manipulated, the sections being fused and molded are maintained above the strain point temperature of the glass. The glass is then usually annealed and then it is cooled. The articles produced are strain free, compact, durable and particularly useful for heat transfer applications such as reflux, still-head and take-off condensers used in conducting chemical reactions and liquid distillation operations. Preferably the channels form a helical coil inside the tube. In addition an electrical resistance wire can be provided in the channels to produce reaction vessels suitable for heating liquids and for conducting chemical reactions.

Dependencies are inferred from the claim text.