Insulator and Heat Exchanger for Ultra High Vacuum,
High Voltage Discharge Chamber,
W. J. Wheeler
Glass Technician
University of Wisconsin
Madison, Wisconsin
whee112923@aol

Fabrication of 18" Diameter Glass Tube

A 4 foot deep, 3 foot high and 2 foot wide Lydon annealing oven is currently in use in the glass shop facilities, and it was decided that if a "snorkel" were built to accommodate the additional length of tubing, a suitable annealing operation could be performed. An 8-foot by 2-foot steel table was constructed, set on casters, and an extension, 2 foot square and 8 foot long was constructed of Thermobestos (See Editor Note Below *) insulation 4 inches thick and set on this table to retain the heat of the oven. The distance from either end of the 18 inch tube to the sealed area was 4 feet, and all seals on the heat exchanger were at the ends, therefore no additional heating was used in the "snorkel". It merely served to seal the oven door and extend the heated space. (See Figure 5 and 6).

Measurements of the temperature showed the range to be 375 C. at the outboard end, and 555° C. in the oven proper. The tubes were held at this temperature for one hour and subsequent viewing with polarized light showed the seals to be strain free.

(Editor Note* : The Thermobestos and Transite materials referenced in this article have been banned from use
since the early 1980's. Each material contains asbestos fibers that are a health hazard. Currently, there are many
comparable high temperature products available that do not contain asbestos. Refer to the ASGS Safety and
Hazards section of this web site for a full report on asbestos replacements.)

Rings were made by sealing sections of an arc of 1 inch I.D. heavy wall tubing, generating a glass ring 16 inches O.D. A fixture to hold short sections of 1 inch I.D. tubing was made, and twenty one 3 inch long sections of 1 Inch I.D. tubing were "T"d into the rings, seals made with a hand torch, and annealed. (See Figure 7, 8, and 9).

The ends of the 3-inch glass sections were cut off evenly with a hot wire cut off and the whole assembly annealed. Then, ten- foot long sections of 1 inch I.D. tubing were strapped to Transite forms with bands of stainless steel. Spacing of the ten-foot tube was determined by the spacing of the "T"s in the end rings. Closed circuit seals were then made between the parallel tubes and the end rings.

Three Transite spool forms were used, supported by a central 3-inch steel pipe, giving us a means of transporting the assembly to the annealing oven. The Transite spools were designed so that they could be dismantled and drawn out from between the parallel tubes at the completion of all sealing operations

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