Method of making a convoluted tubular envelope for a compact electric discharge lamp

In the manufacture of an electric lamp, the method of forming an envelope of compact triple-U-bent configuration from vitreous tubing that is substantially straight, which method comprises the steps of;

• heating a predetermined length of such substantially straight vitreous tubing in a manner such that the end segments thereof are rigid and the remainder of the tubing is uniformly softened sufficiently to be bent without fracturing or collapsing,
• gripping the rigid end segments of said tubing and swinging them toward one another along a common plane until the heat-softened medial portion of the tubing is bent through an arc such that the tubing is U-shaped,
• immediately placing heated mold means of arcuate configuration against the heat-softened leg portions of the U-shaped tubing and, while maintaining the gripped end segments of the tubing stationary, swinging the U-bent medial part of the tubing through an arc of approximately 180.degree. along a path which is substantially normal to the plane of the first bending operation and thereby simultaneously bending both of the heat-softened leg portions around said mold means and forming two additional U-bends in the tubing which are aligned with one another and position the neck of the first-formed U-bend proximate the gripped end segments of the tubing, and then
• removing said mold means and cooling the resulting triple-U-bent tubular envelope to rigidify and set the vitreous tubing in such configuration.