[TheForge] RE: tempered glass

Tue Mar 16 00:44:13 2004

Dan,

The point I was trying to make is that there is stress between the surface
and the core on the glass.  I used the wrong word for it, you are right it
is compression not tension.

Robert Ehrenberger
Shelbyville, Mo.

++++ Original Message  +++++
From: "Daniel T. Hayes" <[email protected]>
To: <[email protected]>
Subject: RE: [TheForge] RE; Tempering Glass
Date: Mon, 15 Mar 2004 11:00:10 -0500
Reply-To: [email protected]

Robert,

I think you meant to say the surface is in compression, not tension, as a
result of the process.

Dan

-----Original Message-----
From: [email protected] [mailto:[email protected]]
On Behalf Of Bob Ehrenberger
Sent: Monday, March 15, 2004 11:46 AM
To: theforge
Subject: [TheForge] RE; Tempering Glass

Ralph,

While in school I got into glass blowing for a while. It was in the ceramic
engineering dept so they included a lot of information on glass in general.

Basiclly tempered glass is a heat treating process.  Glass shrinks more when
it cools slowly.  So to temper glass they hit the surface with a blast of
cold air to cool the surface quickly. The core then cools slower and puts
the surface under tension.  Thats why you have to cut and drill it before
tempering.  As soon as you penitrate the surface this tension causes the
glass to explode instead of just breaking.

If you look at tempered glass with polorized lenses you can see the dots
where the cold air jets cooled the surface.

Robert Ehrenberger
Shelbyville, Mo.