TOUGHENED GLASS
METHOD OF MANUFACTURE
Toughened- ;glasshas an outer skin of: great" hardness and a ;soft inner core. The'inner .core is in tension while the surfaces are in' compression. Glass breaks/when it is in tension but not in compression. .■■■■■■■• "■lt is -possible to-make- a toughened glass" that will "do anything required of it,' bend -and- twist and resist fracture up to a pre-arranged impact. When it fractures, .each= particle is divided by. a series of minute" cracks.. The space be-•tweenH-hemV-or:the-size of.the granules 'into-which it will be distributed, can be predetermined in.manufacture. The first essential is a uniform quality • and purity of the basic glass. During the toughening process the flass alters in size so that very exact nowledge of variations is necessary. The plate glasr; is first cut to the required shape by skilled operators using templates;, but each. operator varies; some-undercut, some go wide. So the template for each series of jobs has to be made to suit the operator! »
There follow the grinding and polishing of the edges of the glass. Each sheet is- then chemically cleaned be^ fore '■■passing to the furnace room. The glass is lowered into the furnace, between banks of elements, for a certain period. Exactly at the rigljt moment the glass is raised, glowing red, and the frame in which' it is held is given a rotary - oscillation while compressed air-Is blown .on it. ."-'..." .'.'
The force of the air is important, because it has to overcome the repelling effect, :of the heat of the glass itself; so also are its temperature and purity. The effect of-the impact of cold air on the red-hot glass suddenly cooling it causes the surfaces' to contract and harden and 1 puts them into a state of compression.
Air' is a most expensive commodity in the works.. It,has to .be.-scrubbed, literally washed with water, cooled, and purified, before passing to the electric compressors.
Each individual piece of glass is given an impact and a polariscope test. A steel ball weighing 1.681b dropped from a'height of less than lft would: break Jin plate glass and scatter
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https://paperspast.natlib.govt.nz/newspapers/EP19370306.2.183.3
Bibliographic details
Evening Post, Volume CXXIII, Issue 55, 6 March 1937, Page 28
Word Count
347TOUGHENED GLASS Evening Post, Volume CXXIII, Issue 55, 6 March 1937, Page 28
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