Bombarder I - what is it

Sent: 	Wednesday, June 18, 1997 8:16 PM
To: 	Tesla List
Subject: 	Re: Bombarder I - what is it

        There is one other reason for the bombarder.  The fabrication of the
glass tubing into the neon sign introduces significant cooling stress into
the joints and bends.  The classical glassworking solution is to place the
entire piece into an "annealing" oven, bring it to the annealing temperature
for that type of glass (just before it gets plastic), and slowly cool.  This
relaxes the several tons of stress built into the work.  Ovens that will
take a large variety of work are expensive to build and operate.  Early on,
neon sign makers found that they could dispense with the oven if they ran
far too much current through the tube.  This got the entire tube and its
electrodes very hot, and relieved the stress.  A tube bender will usually
mark the tube with a heat-indicating crayon selected to change appearance at
the annealing temperature, toast it till the crayon mark melts, while
pumping, of course, and let it cool.  All of the below is true also, the
high heat helps remove water vapor and other contaminants and the greater
purity of the vacuum prolongs the life of the tube.  Some of the electrodes
have a nitro-cellulose coating with mixtures of salts like strontium and
calcium nitrate, and these are baked into the proper state by the heat.  The
reduced metals assist in the emission of electrons.
        Neon sign work is very variable.  Some work is many feet in length,
other pieces much shorter.  Hence the bombarder, a high voltage transformer
without current limiting, and capable of significant power output, is always
marketed with some kind of choke current limiter.  In practice, the
bombarder is connected to the sign, the choke core fully in (max impedance)
and the choke withdrawn to increase the current until the proper temperature
is reached.


At 08:35 AM 6/16/97 -0500, you wrote:
>Subject:      Re: Bombarder I - what is it
>       Date:  Mon, 16 Jun 1997 06:27:52 -0700
>       From:  Bert Hickman <bert.hickman-at-aquila-dot-com>
>Organization: Stoneridge Engineering
>         To:  Tesla List <tesla-at-pupman-dot-com>
> References:  1
>Tesla List wrote:
>> Subject:  RE: Bombarder I - what is it
>>   Date:  Sun, 15 Jun 97 23:37:28 UT
>>   From:  "William Noble" <William_B_Noble-at-msn-dot-com>
>>     To:  "Tesla List" <tesla-at-pupman-dot-com>
>> I've been reading the posts about the bombarder transformer and it's
>> attributes, but I don't have a clear idea of what you are talking about
>> or what it's intended (original) purpose is - I understand that this is
>> a pretty large open frame transformer, and that neon sign shops have
>> them, but beyond that I'm in the dark (e.g. the plasma is out)  Can
>> someone elucidate??
>These transformers are used to provide a source of high current and high
>voltage during the manufactue of neon signs - 10 or more times the
>current used in lighting the tube. Typical range is 50 to 750 mA, and
>these devices are thus in the 5 KVA power range. The whole idea is to
>heat the glass tubing and electrodes to remove any surface impurites.
>During bombarding, the glass will be brought up to a temperature that
>will scorch paper(!). This is done prior to the stage where the final
>lighting gas mixture is put into the tube. Bombarding prevents these
>impurities from later changing the operational characteristics of the
>tube, thereby extending the its useful life.
>Hope this helps!
>-- Bert --
Jack Herron - Editor
Society for Amateur Scientists
8118 E. 20th St.
Tucson, AZ 85710 USA
520 885-6933