[Laser] Cutting and bonding mirrors

[Chuck Hast]

On Wed, Oct 12, 2011 at 15:58, Tom Becker <GTBecker at rightime.com> wrote:
>> How does that theory differ...
>
> I don't know that it does.  If a stress line creates a plane of
> vibrating molecules perhaps the two notions are the same.  If it is a
> plane of constant attractive or repulsive molecular force, perhaps not.

Glass is an amorphous solid, i.e. it has not crystalline structure, so indeed
it is just like very cold honey or other very cold liquids, if it sets the small
fractures in the cut will start to close up and you loose a lot of the ability
to make the break at the score line.

If you have worked in a glass plant (I used to service glass container
inspection machines in bottle plants) you will notice that they talk about
a melting point but is is more or less the point at which the glass is not
too thin to mould and not too thick to go down the guides into the mould
and make a decent bottle. Same holds for flat glass, as all of it cools it
just gets thicker and thicker until it no longer will "move" at any noticeable
rate. But very small micro-fissures will heal if not in this case used after
the scoring process to finish the break.

As with any liquid if those fissures are small enough the molecular
attraction will re-bind them and it does not take long.  Giving the impression
that something is "cooling" or slowing down, when in reality it is rebinding
or "healing" as I have heard the old bottle makers call it in the hot end of
the bottle plant. This is why the inspection machines have to do all kinds
of optical inspections, cracks that may develop in the moulding process
may heal as the bottle goes through the lehr (annealing process), where
the bottle is heated back up and allowed to slowly cool down uniformly.
Those healed fissures leave stress lines and may make your bottle of
brew break when subjected to abuse usually of the thermal type.

In truth, the score needs to be broken as soon as possible or it may not
break as planned. Or become harder to break.




-- 

Chuck Hast  -- KP4DJT --
To paraphrase my flight instructor;
"the only dumb question is the one you DID NOT ask resulting in my going
out and having to identify your bits and pieces in the midst of torn
and twisted metal."
---
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