| Topic: |
Science > Physics |
| User: |
"Sheri" |
| Date: |
22 Jul 2003 07:12:16 AM |
| Object: |
properties of cut/scored glass? |
I work with glass and several of my co-workers and supervisors are
convinced that glass is a liquid that will "re-fuse" itself together
once scored if you don't immediately break it. i hold my ground that
not only is the whole "flowing phenomenon" a myth, but also that a
cracked piece of glass today will still be a cracked piece of glass in
10 years. however, there certainly is a difficulty in getting a clean
break from a scored piece that has sat around for a while. why does
this happen?
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| User: "Minor Crank" |
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| Title: Re: properties of cut/scored glass? |
23 Jul 2003 02:03:54 AM |
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"Uncle Al" <UncleAl0@hate.spam.net> wrote in message
news:3F1D61C8.DB5F8F6D@hate.spam.net...
2) Press two fused silica optical flats together. They will
irreversibly weld. Johnny blocks are "sticky" toward each other for
the same reason. It has nothing to do with flowing.
Ouch! Very painful memory. Many, many years ago, when I was an ATM (amateur
telescope maker), I ground and polished three 6" optical flats, two of which
tested approximately 1/20 wave accuracy (except for a bit of turned edge).
After acid-cleaning the better two of them in preparation for aluminization
(the university had a professional optical shop), I thought I'd store the
flats face to face to keep them clean...
Minor Crank
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| User: "" |
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| Title: Re: properties of cut/scored glass? |
23 Jul 2003 02:18:49 AM |
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In article <urqTa.113874$sY2.51438@rwcrnsc51.ops.asp.att.net>, "Minor Crank" <blue_whaleANTISPAM@comcast.net> writes:
"Uncle Al" <UncleAl0@hate.spam.net> wrote in message
news:3F1D61C8.DB5F8F6D@hate.spam.net...
2) Press two fused silica optical flats together. They will
irreversibly weld. Johnny blocks are "sticky" toward each other for
the same reason. It has nothing to do with flowing.
Ouch! Very painful memory. Many, many years ago, when I was an ATM (amateur
telescope maker), I ground and polished three 6" optical flats, two of which
tested approximately 1/20 wave accuracy (except for a bit of turned edge).
After acid-cleaning the better two of them in preparation for aluminization
(the university had a professional optical shop), I thought I'd store the
flats face to face to keep them clean...
Well, it sure did keep them clean, forever:-)
Mati Meron | "When you argue with a fool,
meron@cars.uchicago.edu | chances are he is doing just the same"
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| User: "Minor Crank" |
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| Title: Re: properties of cut/scored glass? |
25 Jul 2003 08:39:00 AM |
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<meron@cars3.uchicago.edu> wrote in message
news:tFqTa.56$N4.16603@news.uchicago.edu...
In article <urqTa.113874$sY2.51438@rwcrnsc51.ops.asp.att.net>, "Minor
Crank" <blue_whaleANTISPAM@comcast.net> writes:
"Uncle Al" <UncleAl0@hate.spam.net> wrote in message
news:3F1D61C8.DB5F8F6D@hate.spam.net...
2) Press two fused silica optical flats together. They will
irreversibly weld. Johnny blocks are "sticky" toward each other for
the same reason. It has nothing to do with flowing.
Ouch! Very painful memory. Many, many years ago, when I was an ATM
(amateur
telescope maker), I ground and polished three 6" optical flats, two of
which
tested approximately 1/20 wave accuracy (except for a bit of turned
edge).
After acid-cleaning the better two of them in preparation for
aluminization
(the university had a professional optical shop), I thought I'd store the
flats face to face to keep them clean...
Well, it sure did keep them clean, forever:-)
I never did finish my solar telescope...they were (expensive) titanium
silicate, zero coefficient of expansion so they could be in the sun without
distortion.
Minor Crank
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| User: "Sheri" |
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| Title: Re: properties of cut/scored glass? |
22 Jul 2003 09:08:14 PM |
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Glass does not flow, even micrscopically, at ambient temps. Sharp
broken edges of glass were recovered from the pyramids. Fiberoptic
does not change its cross-section. Deformed Middle Ages European
windows were originally shaped that way by their fabrication process -
the thick end being near the blowpipe connection. One will note that
striations and thickness variations are radial with divergence, not
linear.
Thanks, but I'm aware of that, I think I referred to flowing as a
"myth" in my original post.
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| User: "Sheri" |
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| Title: Re: properties of cut/scored glass? |
23 Jul 2003 06:55:42 AM |
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Glass has an amorphous structure, no crystalline arrangement. Liquids
have no crystalline structure. So someone decided that makes glass a
liquid, and ever since then people have been repeating this "Gee, whiz!"
notion and thinking it says something about the behavior of glass.
Even metals will age when they sit over a period of months to years,
their properties changing a little. Cool a lump of metal and you'll
probably pass a few solid-solid phase transitions--changes in crystal
structure--on the way to absolute zero. Chocolate is heat treated to
form the desired fat crystals, otherwise it tastes gritty. Just because
something is amorphous doesn't mean it's more prone to flow than
crystalline materials. And just because something is crystalline doesn't
mean nothing happens to it at an atomic level when it's sitting or
hanging there.
Please, I beg of people, answer the question at hand if you post! I
am fully educated on the molecular structure of glass and it's
properties, both liquid and solid. This kind of repititious
information does not help me answer the question, why does a piece of
scored glass become more difficult to break as time goes by?
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| User: "DarkMatter" |
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| Title: Re: properties of cut/scored glass? |
25 Jul 2003 10:24:22 PM |
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On 23 Jul 2003 04:55:42 -0700, (Sheri) Gave us:
Please, I beg of people, answer the question at hand if you post! I
am fully educated on the molecular structure of glass and it's
properties, both liquid and solid. This kind of repititious
information does not help me answer the question, why does a piece of
scored glass become more difficult to break as time goes by?
Look through my replies, and see if my lay person's explanation
helps point you anywhere.
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| User: "Uncle Al" |
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| Title: Re: properties of cut/scored glass? |
23 Jul 2003 09:45:14 AM |
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Sheri wrote:
Glass has an amorphous structure, no crystalline arrangement. Liquids
have no crystalline structure. So someone decided that makes glass a
liquid, and ever since then people have been repeating this "Gee, whiz!"
notion and thinking it says something about the behavior of glass.
Even metals will age when they sit over a period of months to years,
their properties changing a little. Cool a lump of metal and you'll
probably pass a few solid-solid phase transitions--changes in crystal
structure--on the way to absolute zero. Chocolate is heat treated to
form the desired fat crystals, otherwise it tastes gritty. Just because
something is amorphous doesn't mean it's more prone to flow than
crystalline materials. And just because something is crystalline doesn't
mean nothing happens to it at an atomic level when it's sitting or
hanging there.
Please, I beg of people, answer the question at hand if you post! I
am fully educated on the molecular structure of glass and it's
properties, both liquid and solid. This kind of repititious
information does not help me answer the question, why does a piece of
scored glass become more difficult to break as time goes by?
The flaws that rapidly propagate to cause general failure are sharp
microcracks. Crud in the atmosphere and humidity get in there to
blunt the high potential energy tips of the cracks by corrosion. The
best glass-cleaving scratch I have ever seen was done by the edge of a
small crystal plate of boron carbide. The scribed scratch was
essentially invisible. The glass would miraculously soundlessly part
when slightly bent.
In the short term, a drop of spit in a kennametal scratch wedges open
the cracks by capillary action and helps things along.
--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
"Quis custodiet ipsos custodes?" The Net!
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| User: "Bill Vajk" |
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| Title: Re: properties of cut/scored glass? |
24 Jul 2003 12:44:55 AM |
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Littlemanwearingbigboypants makes yet another mistake:
The flaws that rapidly propagate to cause general failure are sharp
microcracks. Crud in the atmosphere and humidity get in there to
blunt the high potential energy tips of the cracks by corrosion.
Here's yet another error by Schwartz. The same effect or
reduction of clean breaking on a scribe line happens to
glass if it is placed in a vacuum or a clean inert gas
atmosphere for a longer period of time. The correct
answer, as I stated it, is stress relief by aging. It
seems to be mechanically similar to aging of cast iron
engine blocks discovered accidentally by Henry Ford
et troupe. On blocks that sat for several years before
use stress cracking and breakage disappeared where
in new engine blocks was at unacceptably high levels.
Chemical process can speed up stress relief in ferrous
products, but you sure can't/don't make stress relieved
"tempered" glass by chemical process.
Now I ask you, how much "corrosion" is there on the
surface of glass from these alleged atmospheric
contaminants over a period of years. Does not a broken
shard of glass keep its extremely sharp edge for
years, if not centuries? Corrosion nuttin.
Humidity, as in water, clearly is an assistant, rather
than a detriment, to the breaking of glass. See this
Argonne discussion directed to a child:
http://newton.dep.anl.gov/askasci/gen01/gen01307.htm
"Because the -OH group of the water molecule and
the -OH groups in the glass are compatible, the
water will penetrate into the parts of the crack
that you cannot see. When the glass is stressed
at the crack, the water assists the fracture along
the crack by aiding the chemistry that occurs when
the bonds between silicon and oxygen are broken."
In future please check your facts before posting nonsense
to usenet.
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| User: "DarkMatter" |
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| Title: Re: properties of cut/scored glass? |
25 Jul 2003 10:30:46 PM |
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On Thu, 24 Jul 2003 05:44:55 GMT, Bill Vajk
<bill9north@hotmailDITCHTHIS.com> Gave us:
It
seems to be mechanically similar to aging of cast iron
engine blocks discovered accidentally by Henry Ford
et troupe.
Grumpy Jenkins preferred aged, old blocks, because if they survived
the aging without cracks, they were not as likely to crack as a new
casting would be, and is. All racers know that OLD aged blocks are
BETTER. If an engine cracks, THAT block is out of the system. The
longer a block lasts, the higher it's reliability rating gets.
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| User: "Gregory L. Hansen" |
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| Title: Re: properties of cut/scored glass? |
26 Jul 2003 07:22:46 AM |
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In article <88t3ivs8mgirg0ogl8oh55k7t9jo2bjdu4@4ax.com>,
DarkMatter <TheBartenderBuyMeADrink> wrote:
On Thu, 24 Jul 2003 05:44:55 GMT, Bill Vajk
<bill9north@hotmailDITCHTHIS.com> Gave us:
It
seems to be mechanically similar to aging of cast iron
engine blocks discovered accidentally by Henry Ford
et troupe.
Grumpy Jenkins preferred aged, old blocks, because if they survived
the aging without cracks, they were not as likely to crack as a new
casting would be, and is. All racers know that OLD aged blocks are
BETTER. If an engine cracks, THAT block is out of the system. The
longer a block lasts, the higher it's reliability rating gets.
A peice of lore I've heard is that you want a block that's been in an
engine fire, then regrind it to remove the warping.
Maybe the heat has something to do with it, maybe blocks that had been in
engine fires tend to be old, maybe it's just myth. But metal can be
artificially aged with heat.
--
"A good plan executed right now is far better than a perfect plan
executed next week."
-Gen. George S. Patton
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| User: "DarkMatter" |
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| Title: Re: properties of cut/scored glass? |
26 Jul 2003 11:12:05 PM |
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On Sat, 26 Jul 2003 12:22:46 +0000 (UTC),
glhansen@steel.ucs.indiana.edu (Gregory L. Hansen) Gave us:
In article <88t3ivs8mgirg0ogl8oh55k7t9jo2bjdu4@4ax.com>,
DarkMatter <TheBartenderBuyMeADrink> wrote:
On Thu, 24 Jul 2003 05:44:55 GMT, Bill Vajk
<bill9north@hotmailDITCHTHIS.com> Gave us:
It
seems to be mechanically similar to aging of cast iron
engine blocks discovered accidentally by Henry Ford
et troupe.
Grumpy Jenkins preferred aged, old blocks, because if they survived
the aging without cracks, they were not as likely to crack as a new
casting would be, and is. All racers know that OLD aged blocks are
BETTER. If an engine cracks, THAT block is out of the system. The
longer a block lasts, the higher it's reliability rating gets.
A peice of lore I've heard is that you want a block that's been in an
engine fire, then regrind it to remove the warping.
Maybe the heat has something to do with it, maybe blocks that had been in
engine fires tend to be old, maybe it's just myth. But metal can be
artificially aged with heat.
It gets relaxed, or "stress relieved".
A real good example is car disc rotors. After a while of driving,
one should go out, and get them suckers hot... real hot, and then hit
some water. If they warp, that's a GOOD thing. You can go get them
turned again, and they will likely *never* warp again.
You should always get your rotors turned on the first brake pad
replacement on any new set of rotors. Once you have, you only need to
do it again generally if the thing gets gouged. Unlikely it will warp
again, but of course, it is possible.
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| User: "tj Frazir" |
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| Title: Re: properties of cut/scored glass? |
24 Jul 2003 11:20:16 PM |
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Sound not age ,,,,sound allone relax the stress.
Its not age unless it was sound over a time.
Time would do nothing .
Sound bends as its conducted.
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| User: "tj Frazir" |
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| Title: Re: properties of cut/scored bust? |
24 Jul 2003 12:27:00 AM |
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SOUND bends the glass and the stress gets eleastic .
If you said sound stress fracture or sound bends glass you got me.
Sound reduces stress in glass.
Bending glass will reduce stress in directions in glass but sound will
in all directions.
Sound will bend glass in evry direction.
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| User: "Bill Vajk" |
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| Title: Re: properties of cut/scored glass? |
23 Jul 2003 07:46:56 AM |
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Sheri wrote:
Please, I beg of people, answer the question at hand if you post! I
am fully educated on the molecular structure of glass and it's
properties, both liquid and solid. This kind of repititious
information does not help me answer the question, why does a piece of
scored glass become more difficult to break as time goes by?
Asked and answered: Message-ID: <3F1D5282.80001@hotmailDITCHTHIS.com>
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| User: "DarkMatter" |
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| Title: Re: properties of cut/scored glass? |
25 Jul 2003 10:21:45 PM |
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On Tue, 22 Jul 2003 17:40:27 +0000 (UTC),
glhansen@steel.ucs.indiana.edu (Gregory L. Hansen) Gave us:
Even metals will age when they sit over a period of months to years,
their properties changing a little. Cool a lump of metal and you'll
probably pass a few solid-solid phase transitions--changes in crystal
structure--on the way to absolute zero.
Some of them "stick" when it comes back up to ambient.
There is a super chill method of taking ordinary hardened tool steel
tooling, and chilling it to a specified temperature.
Two high speed drill bits. One chilled one not.
Both at room temp at start of drilling process, the chilled bit will
last longer, by far. Is that
"Crystallize Further and Stay That Way"? What's up wit dat chit, man?
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| User: "Bill Vajk" |
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| Title: Re: properties of cut/scored glass? |
25 Jul 2003 10:27:48 PM |
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DarkMatter wrote:
On Tue, 22 Jul 2003 17:40:27 +0000 (UTC),
glhansen@steel.ucs.indiana.edu (Gregory L. Hansen) Gave us:
Even metals will age when they sit over a period of months to years,
their properties changing a little. Cool a lump of metal and you'll
probably pass a few solid-solid phase transitions--changes in crystal
structure--on the way to absolute zero.
Some of them "stick" when it comes back up to ambient.
There is a super chill method of taking ordinary hardened tool steel
tooling, and chilling it to a specified temperature.
Liquid Nitrogen is boiled off and used in a dry process
chilling of the product, then heat cycled to ~300F several
times afterwards.
Two high speed drill bits. One chilled one not.
Both at room temp at start of drilling process, the chilled bit will
last longer, by far. Is that
"Crystallize Further and Stay That Way"? What's up wit dat chit, man?
The claim is: "Transforms almost all soft retained austenite
to hard martensite."
http://www.300below.com/cryprocessingadvantage.htm
The evidence that's been presented to me looked reasonable.
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| User: "DarkMatter" |
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| Title: Re: properties of cut/scored glass? |
29 Jul 2003 08:38:52 AM |
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On Sat, 26 Jul 2003 03:27:48 GMT, Bill Vajk
<bill9north@hotmailDITCHTHIS.com> Gave us:
The claim is: "Transforms almost all soft retained austenite
to hard martensite."
http://www.300below.com/cryprocessingadvantage.htm
The evidence that's been presented to me looked reasonable.
You are correct. here's another...
http://www.cszinc.com/industrial/t-tf-v-series.htm
Just scroll down to the T Chambers, they are like the second model
down.
BTW, these guys are the best chamber makers around.
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| User: "DarkMatter" |
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| Title: Re: properties of cut/scored glass? |
26 Jul 2003 10:36:12 PM |
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On Sat, 26 Jul 2003 03:27:48 GMT, Bill Vajk
<bill9north@hotmailDITCHTHIS.com> Gave us:
The evidence that's been presented to me looked reasonable.
I can tell you first hand that it works. I used to work at
Cincinnati Sub Zero, and they were the first chamber makers to offer
chambers to tool makers for the process. I'm not sure that there
process involved multiple cycles or elevated heating cycles at all.
I'm not sure that the process created is the same. I know it works.
Hehehe.. we made chambers 150 feet long for rocket and missile
testing.
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| User: "tj Frazir" |
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| Title: Re: properties of cut/scored glass? |
26 Jul 2003 11:34:29 PM |
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The seel can be hardend by dipping in flux and baking ,,then cooling
then heating then cooling.
The colder the better max to max.
Graining the steel by quenching it.
Getting the most carbon out and using the chill of the outside to
compress the steel inside.
The next extream would be heating the inside to compress the inside.
The big block and the mercury chamber
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| User: "Bill Vajk" |
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| Title: Re: properties of cut/scored glass? |
29 Jul 2003 09:07:03 AM |
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DarkMatter wrote:
On Sun, 27 Jul 2003 00:34:29 -0400 (EDT), (tj
Frazir) Gave us:
The seel can be hardend by dipping in flux and baking ,,then cooling
then heating then cooling.
The colder the better max to max.
Graining the steel by quenching it.
Getting the most carbon out and using the chill of the outside to
compress the steel inside.
The next extream would be heating the inside to compress the inside.
The big block and the mercury chamber
You're an idiot. The process is where ALREADY hardened steel is
further hardened without heat at all. No flux here, dimgledorf.
http://www.cszinc.com/industrial/t-tf-v-series.htm
Heat treatment itself is a mosnomer, it should probably
called quench treatment since the outcome is established
by the quenching process after some necessary temperature
level has been achieved.
Quenching does not stop at 70 degrees F ambient. It continues
through lower temperatures, even if the process is time
displaced.
In this case, as others, internal stresses build to
destructive levels if the temperature drops too rapidly.
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| User: "DarkMatter" |
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| Title: Re: properties of cut/scored glass? |
29 Jul 2003 05:44:43 PM |
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On Tue, 29 Jul 2003 14:07:03 GMT, Bill Vajk
<bill9north@hotmailDITCHTHIS.com> Gave us:
Quenching does not stop at 70 degrees F ambient. It continues
through lower temperatures, even if the process is time
displaced.
The granite "flows" and "folding" in mountain sides are one of the
long, hot, high pressure variety, rendered exposed. It's pretty hard
to fold rocks, and huge crystalline growths like taffy.
Meteorites, and asteroid makeup is an interesting study topic.
How well "treated are those "alloys"? Hehehehe...
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| User: "DarkMatter" |
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| Title: Re: properties of cut/scored glass? |
29 Jul 2003 05:40:06 PM |
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On Tue, 29 Jul 2003 14:07:03 GMT, Bill Vajk
<bill9north@hotmailDITCHTHIS.com> Gave us:
Heat treatment itself is a mosnomer, it should probably
called quench treatment since the outcome is established
by the quenching process after some necessary temperature
level has been achieved.
To be sure.
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| User: "Randy Poe" |
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| Title: Re: properties of cut/scored glass? |
22 Jul 2003 12:03:23 PM |
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Sam Wormley <swormley1@mchsi.com> wrote in message news:<3F1D2CAD.4B4C906A@mchsi.com>...
Sheri wrote:
I work with glass and several of my co-workers and supervisors are
convinced that glass is a liquid that will "re-fuse" itself together
once scored if you don't immediately break it. i hold my ground that
not only is the whole "flowing phenomenon" a myth, but also that a
cracked piece of glass today will still be a cracked piece of glass in
10 years. however, there certainly is a difficulty in getting a clean
break from a scored piece that has sat around for a while. why does
this happen?
See: http://math.ucr.edu/home/baez/physics/General/Glass/glass.html
That doesn't appear to answer the second question about
why an old scored glass might be harder to break than
a newly-scored piece.
I think that all materials have a tendency to diffuse
into each other a little bit, and so there might be
some healing of the fault line. This has nothing to do
with glass "flow", which is all but nonexistant, but with a
property common to all solids. Breaking glass requires
the existence of a sharp continuous fault that goes
all or most of the way through. After a while, there
are probably points of adhesion formed. Same way
something heavy sitting on a counter gets stuck
after a while. Something heavy sitting on a painted
surface gradually bonds with the paint.
This is about 50% WAG (wild-***** guess). Somebody more
knowledgeable might have a better answer.
- Randy
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| User: "Edward Green" |
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| Title: Re: properties of cut/scored glass? |
25 Jul 2003 04:45:25 PM |
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(Randy Poe) wrote in message news:<585ab5d8.0307220903.3b03cf15@posting.google.com>...
Sam Wormley <swormley1@mchsi.com> wrote in message news:<3F1D2CAD.4B4C906A@mchsi.com>...
Sheri wrote:
I work with glass and several of my co-workers and supervisors are
convinced that glass is a liquid that will "re-fuse" itself together
once scored if you don't immediately break it. i hold my ground that
not only is the whole "flowing phenomenon" a myth, but also that a
cracked piece of glass today will still be a cracked piece of glass in
10 years. however, there certainly is a difficulty in getting a clean
break from a scored piece that has sat around for a while. why does
this happen?
See: http://math.ucr.edu/home/baez/physics/General/Glass/glass.html
That doesn't appear to answer the second question about
why an old scored glass might be harder to break than
a newly-scored piece.
I agree with you -- I noticed the same thing.
I think the best comment on this may be the following:
Bill Vajk <bill9north@hotmailDITCHTHIS.com> wrote in message news:<3F1D5282.80001@hotmailDITCHTHIS.com>...
If you score glass and let it sit around for a while it
experiences stress relief by aging.
Now let's see, you suggest:
(Randy Poe) wrote in message news:<585ab5d8.0307220903.3b03cf15@posting.google.com>...
I think that all materials have a tendency to diffuse
into each other a little bit, and so there might be
some healing of the fault line. This has nothing to do
with glass "flow", which is all but nonexistant, but with a
property common to all solids. Breaking glass requires
the existence of a sharp continuous fault that goes
all or most of the way through. After a while, there
are probably points of adhesion formed. Same way
something heavy sitting on a counter gets stuck
after a while. Something heavy sitting on a painted
surface gradually bonds with the paint.
The problem with this is, The fault doesn't go all the way through the
material after the score. The function of the score is to create a
local stress concentrator, so that when _further_ stressing the glass
we will get a stress peak and crack initiation at that location. Once
the crack is started, it serves as its own stress concentrator. At
least that's a well known story.
The "shop" explanation of why an old score loses its punch is not that
far off the mark, though tainted by association with the flowing glass
myth.
OTOH, you may be right. :-) (I'm trying out for the wishy washy
award). Since we agree that there may be such a thing as solid state
welding of clean surfaces, and since local internal crack surfaces
formed by the score are clean surfaces, they may indeed weld.
Evidence that "star cracks don't heal" and so forth doesn't really
contradict this -- typical black and white thinking. If a crack is
visible from the surface it represents an actual void, not clean and
touching but debonded atomic surfaces. Not all cracks have to heal to
allow _some_ cracks to heal.
You know ... Aristotle is the whipping boy of emprical science, but he
_is_ given credit for codifying elementary logic. And if he heard some
of the "arguments" made here, he could certainly return some of the
compliments!
P.S. It occurs to me some of Uncle's Anecdotes tending to show the
lack of atomic movement in glass at room temperature are self
contradictory.
Uncle Al <UncleAl0@hate.spam.net> wrote in message news:<3F1D61C8.DB5F8F6D@hate.spam.net>...
1) Support a ten foot length of glass cane at its edges. Over a
period of months it will deform into a catenary curve. Warm it in an
oven (below its strain point temp!!) laying on its side and it will
spontaneously undeform - it didn't flow.
4) Internal strain visible between crossed linear polarizers does
not dissipate over time unless thermally annealed.
OK ... take that deformed length of cane, and force it straight. It
is now stressed, no? Warm it ... or better, simply wait a comparable
number of months at RT, and the stress will now presumably be relieved
by the same mechanism which first relieved the stresses in the
catenary hung rod.
Everything is nuance, not slogan. This effect may represent the
movement of interstitials: material flow, stress relieving, but not
changing the shape of the matrix. "Slogans are for suckers!!!" ;-)
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| User: "Sheri" |
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| Title: Re: properties of cut/scored glass? |
22 Jul 2003 08:37:02 PM |
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How 'bout;
The microscopic cracks along the score have more time
to propagate?
SWAG. (silly wild-***** guess) :)
Jim
This is actually the most common and reasonable answer I've been able
to find. My theory was that the score creates a division in weight,
therefore gravity would simply pull each side in a different manner,
causing the scored edges to torque just enough that the break will
break unevenly after time. Anyone care to take a gander on that?
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| User: "Edward Green" |
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| Title: Re: properties of cut/scored glass? |
25 Jul 2003 04:55:26 PM |
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(Sheri) wrote in message news:<128c7a35.0307221519.32bf49e9@posting.google.com>...
How 'bout;
The microscopic cracks along the score have more time
to propagate?
SWAG. (silly wild-***** guess) :)
Jim
This is actually the most common and reasonable answer I've been able
to find. My theory was that the score creates a division in weight,
therefore gravity would simply pull each side in a different manner,
causing the scored edges to torque just enough that the break will
break unevenly after time. Anyone care to take a gander on that?
Yes. You may know about the microscopic structure of glass, but you
don't know quite as much as you think. :-( Gravity? Trying weakening
and stress concentration in the region of the score: all effects start
there.
I'm no expert on this, but I know a well informed opinion when I see
one: and that opinion is -- the world of Bill Vajk. Read and study.
If he's wrong, by the time you've studied his answers sufficiently and
followed them up, you will necessarily know more than he does, hence
know the answer. But it's going to take awhile.
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| User: "Bill Vajk" |
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| Title: Re: properties of cut/scored glass? |
25 Jul 2003 05:12:57 PM |
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Edward Green wrote:
I'm no expert on this, but I know a well informed opinion when I see
one: and that opinion is -- the world of Bill Vajk. Read and study.
If he's wrong, by the time you've studied his answers sufficiently and
followed them up, you will necessarily know more than he does, hence
know the answer. But it's going to take awhile.
Thank you.
If I knew it all there'd be nothing left to live for. I
continue to have busy times ahead.
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| User: "Edward Green" |
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| Title: Re: properties of cut/scored glass? |
26 Jul 2003 12:49:18 AM |
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Bill Vajk <bill9north@hotmailDITCHTHIS.com> wrote in message news:<3F21A9C2.9010608@hotmailDITCHTHIS.com>...
Edward Green wrote:
I'm no expert on this, but I know a well informed opinion when I see
one: and that opinion is -- the world of Bill Vajk. Read and study.
If he's wrong, by the time you've studied his answers sufficiently and
followed them up, you will necessarily know more than he does, hence
know the answer. But it's going to take awhile.
Thank you.
If I knew it all there'd be nothing left to live for. I
continue to have busy times ahead.
You're welcome.
I had intended to write "the word of Bill Vajk", but my typo seems to
work just as well. :-)
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| User: "DarkMatter" |
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| Title: Re: properties of cut/scored glass? |
25 Jul 2003 10:13:02 PM |
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On Tue, 22 Jul 2003 17:06:43 GMT, Jim <lose30lb@workfromhome.com> Gave
us:
On 22 Jul 2003 10:03:23 -0700, (Randy Poe) wrote:
Sam Wormley <swormley1@mchsi.com> wrote in message news:<3F1D2CAD.4B4C906A@mchsi.com>...
Sheri wrote:
I work with glass and several of my co-workers and supervisors are
convinced that glass is a liquid that will "re-fuse" itself together
once scored if you don't immediately break it. i hold my ground that
not only is the whole "flowing phenomenon" a myth, but also that a
cracked piece of glass today will still be a cracked piece of glass in
10 years. however, there certainly is a difficulty in getting a clean
break from a scored piece that has sat around for a while. why does
this happen?
See: http://math.ucr.edu/home/baez/physics/General/Glass/glass.html
That doesn't appear to answer the second question about
why an old scored glass might be harder to break than
a newly-scored piece.
I think that all materials have a tendency to diffuse
into each other a little bit, and so there might be
some healing of the fault line. This has nothing to do
with glass "flow", which is all but nonexistant, but with a
property common to all solids. Breaking glass requires
the existence of a sharp continuous fault that goes
all or most of the way through. After a while, there
are probably points of adhesion formed. Same way
something heavy sitting on a counter gets stuck
after a while. Something heavy sitting on a painted
surface gradually bonds with the paint.
This is about 50% WAG (wild-***** guess). Somebody more
knowledgeable might have a better answer.
- Randy
How 'bout;
The microscopic cracks along the score have more time
to propagate?
SWAG. (silly wild-***** guess) :)
The fresh score breaks better. You need to explain more thoroughly.
The cracks finish out, and there are not as many left when the old
score gets stressed for the break. The odds of a bad skew are higher.
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| User: "Bill Vajk" |
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| Title: Re: properties of cut/scored glass? |
22 Jul 2003 10:09:42 AM |
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Sam Wormley wrote:
Sheri wrote:
I work with glass and several of my co-workers and supervisors are
convinced that glass is a liquid that will "re-fuse" itself together
once scored if you don't immediately break it. i hold my ground that
not only is the whole "flowing phenomenon" a myth, but also that a
cracked piece of glass today will still be a cracked piece of glass in
10 years. however, there certainly is a difficulty in getting a clean
break from a scored piece that has sat around for a while. why does
this happen?
See: http://math.ucr.edu/home/baez/physics/General/Glass/glass.html
As a practical matter I discovered for myself long ago
that old glass is much harder to cut (break on a scored
line) than new glass. In fact, sometimes I was unable to
get a proper cut in old glass after several tries.
The reason ordinary glass is cut by scoring is a matter of
creation of localized stressing and having the glass break
along that line. It is similar to stone and brick cutting
by creating a scored line and introducing a sudden increase
in stress. And it provides the reason why stress relieved
"tempered" glass cannot be cut by scoring it.
If you score glass and let it sit around for a while it
experiences stress relief by aging. There's an interesting
related discussion at
http://focus.aps.org/story/v6/st24
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