Tubular glass
Tubular glass is glass that is produced in tubular form.
history
Tubular glass was manufactured exclusively by mouth-blowing until the 19th century , i.e. discontinuously from a batch or a batch of glass. In 1912 E. Danner (Libbey Glass Company) developed the first continuous tube drawing process in the USA , it works in a horizontal direction. In 1918 he received a patent for it . In 1929 L. Sanches-Vello worked out a vertical drawing process in France .
production method
Tubular glass is produced in various types of glass (e.g. borosilicate , aluminosilicate , soda lime, lead or quartz glass ) and in diameters from a few millimeters to several centimeters. In most production processes, an "infinitely long" glass tube is drawn directly from the melt, from which pieces about 1.5 m long are cut off after passing through a roller conveyor to the drawing machine.
The three common methods differ in the direction of drawing:
Horizontal drawing direction
Danner method
With the Danner process, the molten glass runs out of the feeder as a belt onto a rotating ceramic hollow cylinder, the Danner pipe , which is inclined downwards . Compressed air is blown through the hollow pipe to prevent the glass tube from collapsing. The so-called draw onion forms at the tip of the pipe, from which the glass tube is pulled in free slack on a horizontal draw path.
If the drawing speed is kept constant, an increase in the blowing air pressure results in larger diameters and smaller wall thicknesses; If, on the other hand, the drawing speed is reduced while the air supply is constant, tubes with greater wall thicknesses result.
With this method, pipe diameters between 2 and 60 mm can be achieved.
Vello method
In the Vello process, the glass runs through an annular slot out of the bottom of the feeder. This slot is formed between the round outlet nozzle of the feeder and a height-adjustable, hollow needle (also mandrel). Here, too, the tube is "blown up" with compressed air. The glass tube, which initially emerges in a vertical direction, is then deflected horizontally in free slack.
The nozzle mandrel must be set eccentrically to the drawing nozzle in order to avoid uneven wall thicknesses. The resulting pipe therefore initially has different wall thicknesses, which even out after being bent.
With this process, pipe diameters between 1.5 and 70 mm can be produced; the throughput is higher than with the Danner process. It is also possible to use glasses with highly volatile components such as borates ( borosilicate glass ) and lead oxides ( lead glass ), since the temperatures at the drawing nozzle are lower than in the Danner muffle.
Glass rods can also be produced without a needle, with the diameter being adjusted via the nozzle and the drawing speed. Because of the vertical glass exit, draw-down procedures are sometimes used today under the collective term Vello, although these do not necessarily have to be deflected horizontally.
Danner and Vello processes are used for the production of thin-walled glass tubes with a relatively small diameter, with throughputs of up to 55 tons per day being achieved.
Direction of drawing vertically downwards (draw-down)
The draw-down process is basically the same as the Vello process, but here the glass tube is not deflected, but pulled off in a vertical direction.
Pipes with a maximum diameter of 350 mm and wall thicknesses of 2 to 10 mm can be created in the draw-down. A drawing speed of 0.3 m / min can be achieved for borosilicate glass (35 mm diameter).
Drawing direction vertically upwards (vertical tube drawing)
Here, the glass tube is not shaped with a mandrel, but pulled from the free surface of the bath. A nozzle protrudes from below into a drawing nozzle, through which the air is blown into the glass tube. The nozzle also gives the pulling onion a hold so that it doesn't wander to the side. Since the quality and drawing speed achieved with vertical tube drawing are relatively low, this process has almost no practical significance today.
Further procedures
Glass tubes with very large diameters (20 to 100 cm), as required for systems in the chemical industry, are produced by centrifugation or blowing . However, only the production of relatively short pipe sections of up to one meter, so-called pipe sections, is possible.
Major manufacturers
Schott-Rohrglas in Mitterteich is one of the world's leading manufacturers of special glass tubes ; Another producer of tubular glass was Technischen Glaswerke Ilmenau (TGI) in Ilmenau ( Thuringia ), which was declared bankrupt in 2014. The Duran Group GmbH in Wertheim is an important processor of tubular glass in Germany .
application
Tubular glass is processed, for example, into housings for electronic components, light sources , pharmaceutical products (e.g. ampoules, medicine bottles or high-quality syringes), laboratory equipment and for industrial applications (e.g. glass bodies for sprinkler systems and much more).
literature
- H. Hessenkemper, A. Berg, G. Nölle, H. Uhe, R. Weißmann: Forming of glass . Ed .: HVG - Metallurgical Association of the German Glass Industry. 2nd Edition. 1997.
- Dieter Schumann, Jan Peter Müller, Hermann Schier: Machines of glass technology . Ed .: Central Office for Vocational Training of the Ministry of Glass and Ceramics Industry, Ilmenau. 2nd Edition. VEB German publishing house for basic industry, 1980.