FROM THE FOREIGN JOURNALS
T H E G R O W I N G ROLE OF G L A S S P. J. E h m a n ,
American
Glass
Review
No. 3 (1956)
The article is a review of the state of the glass industry of the United States at the end of the first half of 1956. The annual production of all types of glass now exceeds q,000,000 tons. New glasses (coated or subjected to special surface treatments) have been developed, of very low reflecting power, speefany stable to abrasion, of high strength, and with transparent couducting coatings. Furnaces have been Improved by increase of volume, service life, and efficiency, and as a result the performance of glass furnaces has improved 3 to 4-fold during the past 25 years. Research is carried on in three directlon~ improvement of materials, production of new and improvement of existing ware, and development and improvement of production processes. New research centers have been established for these purposes. The output of container glass, television tubes, foam glass, glass fibers, fluorescent lamps, sheet glass, etc. is growing. There is an increased demand for curved automobile glass of larger area. A new treatment process Is two-sided grinding, which gives glass with almost ideally parallel surfaces. In building and architecture there is a tendency toward an increase in the use of glass in all types of buildings. Glass Is used as a material for walls, ceilings, and panels, in the form of decoreated and enameled sheets, c lored blocks, foam glass and glass fiber insulation, and tiles. Laminated and wire-reinforced glass is also used, It is stated that 8fi~ of the dwelling houses under construction will have one or more walls glazed from floor to ceiling. Doors made of double (packet) glass and various glass articles for mirrors, doors, shelves, etc. are widely used. Glass walls are extensively used in school construction. Prismatic glass panels are used in institutions and shcools~ the amount of incoming light can be regulated and scattered uniform illumination is provided. The production of fault-free curved glau for automobiles and aircraft has been achieved by means of strict temperature control and improved mold and lehr design. The resistance to abrasion of glass containers (bottles, jars, etc.) in use has been increased by the use of organosillcon coatings. Tests have shown that the organosllicon fllmretains its protective action for 15-20 cycles of use. Organosilicon compounds are also used as lubricants for glass molds. Glass plastic laminates are used for manufacture of protective visors for cars ro reduce risk of injury in eollis ions, and for protective inserts above and in front of the passengers. An almost unbreakable material, used in place of window glass, is made from glass fibers. In accordance with the new theory of industrial lighting, light panels of three types are made from glass fibers: pale pink for darkened buildings, green for strongly illuminated buildings, and pale blue for normal factory conditions. A four-seater airplane with a cruising speed of about 250 kin/hour has been built entirely from glassreinforced plastics. Glass paper made from glass microfibers about 0.25 mm thick is used in electrical engineering and in the plastics industry. In addition to high strength, this paper is more absorbent. ,
184
Considerable advances have been made tn the production of glass with special properties for electronic equipment. Among other applications of glass, mention should be made of a new type of luminous panels of green, bluish green, and yellow tints, glass-reinforced plastics for military sledges, Instrument knobs, bicycle frames, secttom of swimming pools, and production of molds for metal casting.
DEBITEUSE WITH UNSYMMETRICAL
S L O T FOR S H E E T G L A S S
DRAWING French Patent No, 1, 111, 688 (Saint-Gobaln Company Verres et Refraetatres (France), September and October 1956, p. 299
A debltense with an unsymmetrical slot is recommended for improvement of the quality of verticaldrawn glass. The top of the slot Is In the center of the dehiteuse, but the widened lower end is displaced from the central vertical plane In the direction of the working channel along which the melt flows under a wall Immersed in It Into the work pit. The walls of this unsymmetrical slot should be streamlined In form. The authors claim that me of debltenses of this type decreases deformation of the edges of the glass rtbbon, Increases its useful width by 3%, reduces variations of the sheet thickness to 0.1 mm (from the usual 0.3 or 0.4 mm), and raises the drawing speed by 10%,
ELECTRODES
AS T O O L S
L. P e n b e r t h y ,
Glass
IN C O N V E C T I O N Industry
(USA),
CURRENT CONTROL January
1956
One way of Influencing convection currents in the melt In glass tanks is by booster heating. The influence of booster heating on convection currents depends matnly on the following five factors: electrode materlal (contact resistance relative to glass), electrode size and current density, total power, location of the electrodes, and their position. The electrode material Influences heat transfer in accordance with the contact resistance, which in Its turn depends on the degree of wetting of the electrodes by the melt. Oxidizing metals and their oxides, such as molybdenum and Iron, are wetted well and therefore have low contact resistance. The contact resistance of platinum is higher than that of molybdenum or iron, while carbon and graphite have even higher contact resistance, as they are wetted extremely badly by glass melt. The electrode dimensions are chosen In accordance with the size of the tank, their Influence on current density at the electrode surface being taken Into account. In a tank containing Iron electrodes in the form of large blocks running the whole length of the tank there are rising convection currents parallel to the side walls of the tank, and descending currents along the center line of the tank, where the melt is cooled especially strongly by the batch. If small electrodes are used, local Intensive ascending currents are formed immediately over the electrodes. The current density alters with the electrode dimensions, and this, of course, Influences conveotion currents, Decrease of electrode size results in a corresponding Increase of heat transfer per unit electrode area.
185
