RE: GLASS Flows? (getting way OT!)

["Hladky, John" <John_Hladky at tdytsi.com>]

>We all make mistakes, once in a while. ;-)

All would be well if I only made mistakes once in a while :-o

I wish I had some rare killies.  Actually, I wish I had any killies.  I
stopped at a LFS over lunch (PetCo).  They had some "Golden wonder" killies.
Looked like A. lineatus (Spelling?).  Any info?  Are they suitable for a
rank beginner?  I have had aquariums for years, even bred some killies, but
never successfully raised the young.
John



-----Original Message-----
From: Wright Huntley [mailto:jwwiii at pacbell_net]
Sent: Friday, August 15, 2003 1:39 PM
To: killietalk at aka_org
Subject: Re: GLASS Flows? (getting way OT!)




Hladky, John wrote:
> I did a little research yesterday, AFTER (unfortunately) I sent the e-mail
> on glass flow.  Although it is a well known scientific fact that glass
does
> flow if given enough time, it is apparently a WRONG fact.  Does anyone out
> there have a good recipe for crow?  Does it go well with killies?
> John

Hey John,

We all make misteaks, once in a while. ;-)

I posted a little fun response and Charles thought I was accusing him of 
originating your original glass-flow post. Guess I should apologize to 
him, and anyone who misunderstood my poorly-worded note. I knew that 
Charles was posting *no-flow* information, but re-reading my answer I can 
see where it wasn't obvious what I meant by it. Sorry.

Another little goof. I said glass was stable to a part in ten to the 
eighth, which is nonsense, as stated. It was better than a part in ten to 
the eighth *per year*, according to the engineers (at -- I think it was -- 
Ferranti of England), who did those studies. That is, it was more stable 
than we knew how to measure it, if left unstressed.

We took advantage of the fact that glass is way softer than steel -- it 
has a modulus of elasticity only about 1/3 that of steel. By attaching 
both ends of a glass measuring scale to a steel mount that was at least 
three times as big in cross section as the glass scale, the steel 
dominated (by 9:1) so the glass just stretched and compressed to follow 
whatever the steel did. El cheapo way to make a glass scale with exactly 
the same thermal expansion coefficient as steel, for measuring bearings 
and other critical automotive parts.

Unfortunately, in that nit-picky business, it was well known that most 
steel shinks at about 1ppm/year, due to metallic crystal phase changes. We 
had to nitride and grind the steel mount in a process similar to that used 
to make guage blocks, to assure the scale wasn't changing, too. Then we 
had to have the centroids of the glass and steel mount exactly aligned, so 
we didn't create the equivanent of a bi-metallic strip that would bend 
with temp. changes. Nutty business!

Why so fussy? Our Holograf scales gave an analog sine/cosine signal pair 
that had a period of 10 microinches (or a quarter of a micron in the 
metric version). One customer, who made optical-disc-mastering equipment, 
divided that signal into 256 parts, for a digital least count down around 
1 nanometer, which is pretty small. Such accuracy is why you get so many 
MB on your DVD (original tracks written accurately) and why they get so 
many transistors on an IC (good, accurate photomasks).

Look John, just send be three pairs of any really rare killifish and I'll 
forget the whole thing. Otherwise, expect a long treatise on metallic 
crystaline phase change. :-)

Wright
> 
> 
> 
> -----Original Message-----
> From: Wright Huntley [mailto:jwwiii at pacbell_net]
> Sent: Thursday, August 14, 2003 9:45 PM
> To: killietalk at aka_org
> Subject: Re: GLASS Flows?
> 
> 
> There is probably some limited cold flow, under enough stress, of almost 
> any amorphous material (i.e., glassy solid) but the mythology of windows 
> slumping with age is just that -- mythology.
> 
> Most big store windows, and other large sheets, were made with float 
> glass, on float tables that were deliberately tilted. This gave a thicker 
> end that was thought to be stronger as the load-bearing base. [Ill-trained

> grad students probably applied impecable post-hoc-ergo-propter-hoc logic 
> to look at old windows, as old builings were torn down, and start the 
> myth. It continues, obviously, to this day.]
> 
> No big telescope has ever been refigured due to cold flow, AFAIK.
> 
> About 40 years ago, extensive studies on the stability of glass for 
> optical scales and gratings was done, and the final conclusion was that 
> glass is inherently more stable than our ability to know the velocity of 
> light was at that time (about a part in ten to the eighth).
> 
> Acrylic (i.e., "Plexiglas") does not usually warp unless uneven moisture 
> is involved. Look in your rubber book, Charles and see just how much it 
> expands when exposed to moisture. It stays very flat over a terrarium if 
> the humidity is the same inside and out. [Few other plastics have that 
> problem, BTW.]
> 
> Wright
> 
> Charles Harrison wrote:
> 
>>>I believe the reason the covers are bending is that despite it's solid
>>>appearance, plastics have some properties of liquids, i.e. they flow.  
>>>Even
>>>glass exhibits this behavior.  It can be observed in the windows of 
>>>200 year
>>>old houses.  They are slightly thicker at the bottom than at the top.  
>>>Also,
>>>the big optical telescopes lose their focus after a few decades unless
>>>something is done to compensate for the glass flow.  I suspect that if we
>>>leave our aquariums set up long enough, in a few 1000 years the tops 
>>>will be
>>>so thin that they will break!
>>>John
>>
>>
>>It is strange from a physical chemistry point of view, considering the 
>>*non-solid* nature of glass, but the windows in many of the oldest 
>>churches in Florida and Cuba - put into place by the Spanish 
>>missionaries back in the 1500's have been measured to determine the 
>>amount of flow which can occur over a period of four centuries.
>>
>>I will have to go back into the Chemical & Eng News to find the issue, 
>>it has been a dozen years ago -  but, the results of the survey was that 
>>there was no measurable flow. Actually, this was a complete surprise to 
>>me and many scientists who have some training in glass blowing and 
>>constructing glass devices.
>>
>>I wonder if anyone has laid lengths of these various plastics over empty 
>>aquariums or shelves or whatever to determine: does the stuff bend 
>>without water involved???
>>
>>Charles H
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> 
> 

-- 
Wright Huntley -- 760 872-3995 -- Rt. 001 Box K36, Bishop CA 93514


Physics is the study of frictionless elephants whose masses may be ignored.




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