Glass tube

Glass tubed or glass tubing are hollow pieces of various glass types (like borosilicate, flint, aluminosilicate, soda lime, lead or quartz glass) with a large variety of applications which are laboratory glassware, lighting applications , solar thermal systems and pharmaceutical packaging to name the largest. Glass tubing is frequently attached to rubber stoppers.

In the past, scientists constructed their own laboratory apparatus prior to the ubiquity of interchangeable ground glass joints. Today, commercially available parts connected by ground glass joints are preferred; where specialized glassware are required, they are made to measure using commercially available glass tubes by specialist glassblowers. For example, a Schlenk line is made of two large glass tubes, connected by stopcocks and smaller glass tubes, which are further connected to plastic hoses.

Until the 19th century glass tubes were exclusively produced by mouth blowing, thus discontinuously manufactured from a batch or a glass melt. In 1912, E. Danner (Libbey Glass Company) developed the first continuous tube drawing process in the USA, which works in horizontal direction. In 1918 he received a patent. In 1929 a vertical drawing process was developed by L. Sanches-Vello in France.

Glass tubes are produced in various types of glass and in diameters ranging from a few millimeters to several centimeters. In most production processes, an "infinitely long" glass tube is drawn directly from the melt, from which approximately 1.5 m long pieces are chopped off after passing a roller track up to the drawing machine.

The three common methods differ regarding the drawing direction:

In the Danner process, the molten glass runs from the feeder as a belt onto an obliquely downwardly inclined, rotating ceramic hollow cylinder, the Danner pipe. Through the hollow pipe, compressed air is blown to prevent the glass tube from collapsing. At the tip of the pipe the so-called drawing onion is formed, from which the glass tube is drawn off in the free sag on a horizontal pulling line.

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