Paul,
I'm glad you found David's question so vague because it brought out your
wonderful reply.
Perhaps a more specific question is how do I put the anti-scratch coating
back onto my prescription plastic lenses after scratching them and cleaning
it off?
b.t.w. You missed out on the cat content - or was contained within the
'struck by a flying missile' ?
Guy R Day
-----Original Message-----
From owner-spridgets at autox.team.net
[mailto:owner-spridgets@autox.team.net]On Behalf Of Paul Asgeirsson
Sent: 19 July 2004 22:11
To: David Lieb; Spridget List
Subject: Re: Safety glasses and eyeballs NOW a bit longish
Hi David,
I saw it and didn't answer it because there was a dearth of info in the
question. I spent many years in the manufacturing ophthalmic business, with
a lot of that time doing prescription safety glasses.
The ANSI Z-80 standards for safety eyewear are pretty stringent. We had to
test every glass lens and most of the plastic prescription lenses. The
tests were of several types, all equivalent in results. The glass lenses
had to withstand a freefall drop of a 7/8" steel ball onto the unprotected
surface. Or you could do a spring loaded ball trigger device that pounded
the ball onto the surface. Of course, in each of these type tests, the lens
had to survive!
Strengthening of the lens was done either by heating up the glass lens to
just short of it's sag point and then quenching it with cool air to
strengthen it. How it strengthened it was by freezing the outer surfaces
while the inner started to cool and shrink away from the stiffened outer
surface. Much like when you tighten the bicycle spokes on a rim. with no
spokes, you can crush the rim easily, but it becomes very strong when you
place it under tension by the spokes.
The other method was immersing the lens in liquid potassium nitrate,
(Obligatory gun/ammo content!) which was at about 700 degrees F. and it
would leach out sodium ions in the glass and stuff a MUCH larger ion of
potassium in that space, placing the surface under tension. (We got the
highest quality potassium nitrate from Israel!)
Then the plastic lenses were tested in a different manner. You shot a sharp
tipped weighted arrow at the lens and if it penetrated no more than a
specific amount, then that type of material was OK'd. That method destroyed
the lens.
Now, for non prescription wear, nearly the same standards applied. They
were a cinch to make so strong you could hardly destroy them!! All eyewear
had to have a special type of groove in them so the lens wouldn't pop out
into your eye when struck by a flying missile.
All one piece plastic safety eyewear fell into another category, but it's
really safe to say they far exceed the standards.
So, if it's not prescription eyewear, those inexpensive ones at NAPA
counters are as good as they get. If they fit, you'll certainly be well
protected. They are hard to clean though, even with their anti-scratch
coating on them, and keep scratches off them. So what, just get another
pair or 2, they do what they're supposed to do and your eyes damaged by no
safety glasses can be a horrible experience.
What was your question?
Later, Paul A
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