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The purpose of the page is to give miscellaneous information
about the subjects at the top of the page without pretending that I am doing
them or know very much about them. So far, omitted from this page is
Scientific Lampworking which is a specialized area all its own.
----- Original Message -----
From: "Kenny Greenberg" <neonshop.com>
Newsgroups: rec.crafts.glass
Sent: Tuesday, January 18, 2005 1:52 PM
Subject: Re: Neon Signmaking Books
> On Mon, 17 Jan 2005 17:29:51 -0500, Mark Jones wrote:
>>>Mike Firth wrote:
>>> I know enough that the process of bombarding (a word that eluded me in my
>>> previous reply) involves sucking down a phenomenal vacuum and then cooking
>>> the inside with a special bombarding transformer that can put a couple of
>>> amps (or more?) into the plasma so the molecules of gas that will cause
>>> problems later are cooked out. Then, a tiny amount of the illuminating gas
>>> is added to the vacuum to get the result desired. Sealing is simply a
>>> matter of applying a torch to the neck and watching the vacuum suck the
>>> glass down tight. The transformers used for lighting, while not cheap, are
>>> much less costly than the bombarding transformer.
>>>
>>
> Bombarders are typically 12 to 15kva. The processing current is at first typically 250 to 300 ma. The voltage across the tube will be whatever it requires - on average 10kv + or - a few thousand volts.
> Most of the processing happens in the 2 to 4 torr range. The heat releases impurities from the glass wall. Near the end of the process at around 250'C the pressure is lowered some more and the current is raised. This electro-chemically 'converts' the electrodes so that the cathode fall is reduced. The tube is then pulled down to about 1 to 2 microns and cooled somewhat before backfilling to approximately 10 or more torr.
>
>
> Kenny Greenberg www.neonshop.com
>
Translating that paragraph to my experience, bombarding involves
about 3,000 watts (250 ma being a quarter amp times 12,000 volts).
Atmospheric pressure is 760 torr, so 2 torr is 2 mmHg or 0.039 psi or 5/8 ounce
per sq.in. and 1-2 torr is about 1/1000th atmospheric. The temp goes up to
482F, above the ignition point of paper. It is then pulled down to one
thousandth the previous pressure, or about 1 millionth of atmospheric.
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