From: John De Armond
Subject: Re: exploding glass (on my toad)
Date: Wed, 07 Jun 2000 01:46:57 EDT
Newsgroups: rec.outdoors.rv-travel

DB TECH wrote:
> 
> Tempered glass by it's very nature has a very high degree of
> stress in the sheet.  On rare occasions there can be a weak
> point that can fracture.  Temperature differential can bring
> increased stress to a higher stress point resulting in fracture
> at this small point in the sheet.  When tempered glass fractures
> it fractures into many very small dull edge pieces.
> Again this is a rare event.
> 
> Note: Contrary to popular belief, tempered glass is softer than
> non-tempered glass. (window pane)  (To temper is to soften)

Ah, no.  glass of a given formulation can neither be hardened nor
softened by heat treating because ordinary glass has no crystalline
structure.  Tempered glass appears harder because the internal
stresses make it stronger and thus more resistant to deformation. 
The hardness does not quite extend to the surface.  The outer layer
is still soft.  Indeed, one knows that an unknown piece of glass is
tempered if it will score so deep but no further using ordinary
force.  Force the issue, disrupt the stressed layer and the whole
sheet shatters as the stresses are relieved.  As long as these
stresses are not relieved, tempered glass is amazingly hard, as
anyone who played around with Prince Rupert's Drops in high school
chem class.

To the original question, the window shattered "just because". 
perhaps the process controls weren't quite right on the day that
pane was tempered.  Perhaps there was a scratch that reached the
stressed layer but just barely.  Perhaps all this built up and
combined with direct sunlight to make it let go.  Sometimes it just
happens.  I've learned by experience in installing my wife's stained
glass windows in doors where tempered glass is used as safety
shields that you never ever install such sandwiches too permanently
because some significant minority of tempered glass panes
spontaneously shatter.

John

From: John De Armond
Subject: Re: window glass replacement
Date: Wed, 21 Jun 2000 12:35:05 EDT
Newsgroups: rec.outdoors.rv-travel

GSimcoe wrote:
> 
>  They indicated that the window thickness
> >was not standard and that the glass repair shops will not be able to repair
> >them. They indicated that the entire window system will need to be replaced.
> >
> >Has anyone else experienced this ? Is replacing the window the only solution
> >? Any ideas would be appreciated. I have a 1999 Fleetwood
> >Terry 24J >>
> 
> One of our boys accidentallly broke a rear window on our travel trailer while
> playing around it at home.  When we contacted the trailer shop they told us
> that the cost to fix would be really high and they sent us to the local glass
> dealer who suggested replacing it with a sheet of plexiglass type of material.
> We paid less than 10.00 and were told that real glass would have been sky high.
>  It was only a small window and we were never able to tell the difference
> between it and the real thing.   Good luck

Er, not right away but wait a couple of years.  the previous owner
did that to one window on our rig.  Stood out like a sore thumb. 
Every limb that brushed it left a scratch.  I couldn't wait to get
the rig to the local glass shop to have a tempered pane put back in.

Any glass dealer should be able to cut glass to fit the openings and
then have the glass tempered.  Not very expensive at all.  I've had
dozens of odd-shaped glass pieces tempered to serve as physical
protection in stained glass doors my wife makes.  A typical single
light door panel costs $30.  

It's a good idea to have two pieces of glass cut for each window. 
The tempering process is pretty brutal and breakage is common.  I've
learned to do that so that I always end up with a complete set. 
Whichever ones don't get broken in processing, I give to the
customer as spares.

John

From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Glass Needed
Date: Wed, 07 Dec 2005 00:08:12 -0500
Message-ID: <i2rcp11a3h8dtct9nv38bhkugk83r89rgg@4ax.com>

On Tue, 6 Dec 2005 12:50:07 -0800, "Dave Thompson"
<dave@invalid.invalid> wrote:


>My last purchase of tempered glass was the replacement of a glass coffee
>table top.  I took the measurements to the local glass shop who had to order
>the piece from a glass foundry.  I was told the same.  Glass cannont be cut,
>ground or shaped after tempering.

This is correct.  I've had many pieces of tempered glass made for my
ex's stained glass commercial door projects and one piece for my RV. I
cut my own glass but a glass shop can do it just as well.  The local
foundry recommends sending two pieces since it's about the same price
to two and since some significant percentage of the time, one piece
will shatter during tempering.

Lexan is a really sh*tty replacement for RV windows, particularly if
you don't like the haze, different transparency and reflectance, and
the ease of scratching.  Especially right next to real glass where the
eye quickly catches the difference.

The piece for my RV was where the previous owner had installed Lexan
rather than go to the extra effort of tempered.  It easily scratched,
had hazed from sun exposure, was much colder in the winter and let in
more heat in the summer.  I hated it.

There is a sheathed version of Lexan available, coated with some sort
of thin film hard stuff, maybe silicon dioxide or whatever. It's
almost as scratch resistant as glass but it still solarizes (hazes
from sun exposure) and costs more than glass.

Just take the RV over to the local glass shop, pay  him his $50 or
$100 and let him do it right with a new piece of tempered glass.  If
the RV is used in cold weather and the foundry can do it, I recommend
getting it E-glassed, coated with an infrared reflectance coating.
That makes a world of difference in heat gain.

John

From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Glass Needed
Date: Wed, 07 Dec 2005 00:56:58 -0500
Message-ID: <n9ucp1hg6iom6ofgi8shdva5tv50e0p509@4ax.com>

On Wed, 07 Dec 2005 03:55:07 GMT, "Bill  McKee"
<bmckeespam@ix.netcom.com> wrote:

>I thought they could diamond saw the glass.
>

I tried that once just for sh*ts'n'grins.  Spectacular. As the saw cut
through the skin layer, suddenly a loud pop and the piece of glass I
was holding just disappeared in a cloud of gravel.  I was still
cleaning bits of that experiment from my shop months later.

Once tempered, about all you can do to glass is look at it, mildly
etch it or anneal it again for rework.  Or scratch it and watch it
break, of course :-)

John

From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Glass Needed
Date: Thu, 08 Dec 2005 14:04:30 -0500
Message-ID: <fg0hp1hpjmej6moj8dkf07qpqs9s1n5i35@4ax.com>

On 8 Dec 2005 06:18:27 -0800, "dmartin" <dmartin@newarts.com> wrote:

>Prince Rupert's Drops....
>
>Just let hot glass droplet fall into water.
>
>A great demonstration of strengthing by prestressing.

Those are fun to play with and I make 'em frequently for visitors to
my glass shop.  However, what Elliot is trying to remember is the
Bologna Bottle.  This is a thick walled bulbous hand blown bottle that
is tempered like Rupert's drops by plunging it into water while still
soft.

The bottle is hard enough to drive nails and yet if a crystal of
carburundum or other hard abrasive is dropped into the bottle, the
scratch causes it to shatter with a loud noise.

These things are VERY hard to make.  I've only succeeded a few times.
Pyrex or other low expansion coefficient glass works best, as does
boiling water.  The idea is to chill the thing as rapidly as possible
without actually shattering the glass.

Here's a photo of one:

http://www.phys.appstate.edu/demos/mechanics/1r20_60.html

From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Glass Needed
Date: Thu, 08 Dec 2005 15:27:21 -0500
Message-ID: <ug5hp1ptrkorbc8c55e7ej0ihuua8m2nrq@4ax.com>

On Thu, 08 Dec 2005 20:05:46 GMT, Elliot Richmond
<xmrichmond@xaustin.xrr.xcom> wrote:


>>>Prince Rupert's Drops....
>>Those are fun to play with and I make 'em frequently for visitors to
>>my glass shop.  However, what Elliot is trying to remember is the
>>Bologna Bottle.  This is a thick walled bulbous hand blown bottle that
>>is tempered like Rupert's drops by plunging it into water while still
>>soft.
>
>You are absolutely correct. I had combined the two quite different
>objects into one.
>
>As I now remember, the Prince Rupert's Drops were so fragile that you
>could break off the tip with a fingernail and the whole thing would
>shatter.

Not really fragile but highly stressed.  The intact drop is harder
than steel.  In fact, I've demonstrated that by pressing a drop
between two smooth steel plates in a press.  The drop will indent the
steel without breaking.

OTOH, breaking off the tail causes it to shatter.  I usually use an
old pair of dykes to snip the tail because at some point along the
tail the tempering stops and the glass is brittle again.  If your
finger happens to end up there, you get a good poke.

I've found that the trick to making a highly stressed tail is a) to
work in absolutely still air and b) as the drip of glass starts
falling off the punty, plunge the whole affair into water.  That way
the tail is still hot enough to be tempered.  If I allow the glass to
drip all the way off, the fine tail will have cooled enough not to
temper and will remain sharp.

Pyrex is easier to make but leaded glass Drops are more spectacular
because of leaded glass's high COE.

John