US2508127A - Method of bending sealed glass tubes - Google Patents

Description

1950 H. E. VALENTINE 2,508,127

METHOD OF BENDING SEALED GLASS TUBES Filed June 1, 1949 lrwveh lrorz Harold E. VaLen=tine, Jog fiat A? His A=irirorne5.

Patented May 16, 1950 METHOD OF BENDING SEALED GLASS TUBES Harold E. Valentine, New Malden, England, assignor to General Electric Company, a corporation of New York Application June 1, 1949, Serial No. 96,445 In Great Britain June 25, 1948 2 Claims.

This invention relates to the manufacture of hermetically sealed lengths of glass tubing bent to a desired shape and the pressure within which is either below or is above atmospheric. More particularly, but not exclusively, the invention relates to the manufacture of low pressure tubular electric discharge lamps which are bent to a desired shape.

The bending of the glass tubing in such manufactures has hitherto been performed prior to the evacuation or pressure-filling and the sealing of the tubes, usually by wrapping an electric heating coil around the part of the tube to be bent, passing current through the coil to heat and soften the glass, and bending the tube to shape around a former.

But in some cases, especially with long tubes, the manipulation of the bent tube for evacuation or pressure-filling and for sealing is very inconvenient and the object of this invention is to provide a method whereby the bending may be effected after the evacuation or pressurefilling and the sealing despite the low or high pressure within the tube.

According to the invention, in order to effect the bending after the evacuation or pressurefilling and the sealing, the already sealed, evacuated or pressure-filled tube is enclosed within a flexible and substantially gas-tight jacket at least at the part at which the bending is to be eflected, the pressure within the jacket is adjusted to substantially the pressure within the tube, part of the tube is softened by heating in any suitable manner and the softened part of the tube and corresponding part of the jacket are then bent together to give the required bending for the tube.

The jacket is preferably of cross section not much larger than that of the tube so that the bending of the glass tube in the softened state may be easily effected and controlled. A former may be used in the usual manner to provide the requisite shape.

The heating means by which the glass is softened is preferably an electric heating coil lying within the jacket and wound around the part of the tube which it is desired to soften.

For a further understanding of my invention reference may be had to the accompanying drawing wherein Fig. 1 is an elevation, partly in section, of a tube enclosed in a suitable jacket preparatory to bending the tube, and Fig. 2 is a plan view showing the bending of the assembly of tube and jacket around a suitable form.

In one method in accordance with the invention, and illustrated in the drawing, for manufacturing a low pressure tubular electric discharge lamp bent to a desired shape, a straight tubular glass envelope i, already sealed with the electrodes (not shown) and required low pressure filling therein, is mounted so that part of the tube having an electric heating coil 2 wound around it lies within a flexible bellows type tubular metal jacket 3 of the vacuum-tight kind already known for use in connection with pumping systems and whose cross section is not much larger than that of the tube l. The ends or" this jacket 3 are vacuum tightly closed by rubber bungs l, 4 which fit closely in brass sleeves 5, 5 soldered or brazed to the ends of the jacket 3, and the leads to the heating coil 2 are taken vacuum tightly through insulating tubes or beads 6, 5 in the bungs 4. In addition a pump connection l is made through one or both of the bungs 4. Preferably the heater wire 2 is covered with braided asbestos to insulate it from the metal jacket 3; and the said wire may be made in strip form. as disclosed, for example, in Patent 2,135,775 to Walker.

In the process of manufacture the flexible jacket 3 is evacuated to the pressure within the tube by pumping and then the pump connection is closed, a current is passed through the heating coil 2 and when the associated part of the tube I is softened sufficiently the outer jacket and the tube are together bent around a former 8 (Fig. 2) to the desired shape at this part.

Alternatively, if the jacket 3 is not completely vacuum-tight it may be continuously pumped to maintain the desired low pressure within it during the softening and bending operation.

It will be appreciated that the invention may be applied to the manufacture of bent fluorescent discharge lamps as well as to the non-fluorescent type of lamp, and to lamps having hot cathodes as well as to lamps having cold cathodes.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. The process of bending sealed glass tubing the pressure within which is substantially different from atmospheric pressure which comprises enclosing the tubing within a substantially gastight and flexible jacket closely fitting the tubing, adjusting the pressure within the jacket to correspond substantially to the pressure within the tubing, heating the tubing to soften it, and then bending the assembly of tubing and jacket to the desired shape.

2. The process of bending sealed glass tubing the pressure within which is substantially different from atmospheric pressure which comprises wrapping an electric heating coil around the tubing and enclosing the tubing within a substantially gas-tight and flexible jacket closely fitting the tubing, adjusting the pressure within the jacket to correspond substantially to the pressure within the tubing, heating the tubing to soften it by passing an electric current through said heating coil, and then bending the assembly of tubing and jacket to the desired shape.

HAROLD E. VALENTINE.

No references cited.

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