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melting pyrex for blanks

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#51 KenScharf

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Posted 27 December 2012 - 04:40 PM

I hope that some ATM'ers with kilns will make some extra blanks from surplus glass (either low expansion or just plan old plate), and see fit to sell them to others at a fair price. Not all of us want to make monster Dob's, and you really need to make a number of good small mirrors to hone your optical skills in order to make a good large mirror. I'd be happy if I could make a good mirror around 12" or so. That's about the largest scope I could use that would be portable and not require a ladder to use.

#52 dan_h

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Posted 27 December 2012 - 05:10 PM


The density of 7740 Pyrex is about 2.23 grams/cc where as the density of soda-lime about 2.44gm/cc. If one has a reasonably accurate scale one can use the Archimedes principle to determine the density with sufficient accuracy. In the lab at work, I have a digital scale with a capacity of 15Kg that measures to 0.1 gram, I have used this with mirrors up to 16 inches to measure the density of the glass.

Jon


I took a crack at this with my old, old Pyrex measuring pitchers (I have gram-accurate digital scales), but found that my attempts to measure displacement with kitchen equipment were less precise than required to distinguish the densities (I tried both measuring volume change, and the mass of overflow).

I have a digital luggage scale (suspension hook type) that I will break out to see if I can distinguish the weight change from immersion without trying to measure displacement. It may not be accurate enough though.


I have done this determination without the use of an accurate scale to measure the mass. I set up a balance arrangement where I could immerse the article of interest and measure the balance point along the beam with the article in air and in water. I used an accurate measuring ruler to determine the balance positions on the beam and was able to work out the densities needed. I could detect pyrex from BK7 pretty easily.

dan

dan

#53 Mark Harry

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Posted 27 December 2012 - 06:46 PM

Instead of doing a displacement of volume, just calculate volume instead. I used this to identify a pyrex blank that was moulded in a KzFS4 mould with those initials on the glass. I came out to within 3 places of the decimal point of pyrex value---close enough.
M.

#54 danjones

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Posted 28 December 2012 - 12:13 AM

i'm currently using plate glass in my kiln. its everywhere. i already got a list of ppl who just want me to come get their old tabletops out their basement. i tested the kiln just to see how hot it could get, since i was doing that, i went ahead and threw a mold together and some plate to see what happened. the kiln well exceeded what i need for temp, melting the glass easily along the way. while i did get a rough blank, i didnt anneal it at all so its no good, that wasnt my test. i'm building a ramp/soak controller now to control the firing/annealing stages. so until its done, just melting experiments. i was just wondering if 'pyrex' pie plates would work, but thinking not. thanks for all the feedback.

#55 KenScharf

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Posted 28 December 2012 - 10:59 AM

Even if those 'pyrex' pie plates are really 'soda' glass they might still make a good blank (as good as plate glass anyway). You just want a source of good quality glass. There is nothing wrong a well annealed plate glass disk for a mirror, at least up to 18" or so in diameter. Port holes are of this stuff and John Dobson has made countless telescopes from them.

#56 Mark Harry

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Posted 28 December 2012 - 07:08 PM

I think that's the key with plate glass- if the anneal is good, you're all set.
M.

#57 sopticals

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Posted 28 December 2012 - 07:10 PM

I think that's the key with plate glass- if the anneal is good, you're all set.
M.


Yup. :bow:

#58 astrobeast1

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Posted 28 December 2012 - 07:40 PM

Wow ! that,s good new,s for me then . anneal it well, =excellent blank.anyone want a mirror ?

#59 sopticals

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Posted 28 December 2012 - 11:25 PM

Wow ! that,s good new,s for me then . anneal it well, =excellent blank.anyone want a mirror ?


Yup. :bow:

#60 Chuck Jennings

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Posted 30 December 2012 - 06:22 AM

I'm a little late to the conversation, but a friend and I have successfully fused and annealed a 14" plate blank in our kiln, and figured the blank to F4.3 at the last Delmarva mirror making session. We used Mike's work as a starting point, and modified slightly. Although we have yet to try it, I don't see why borosilicate wouldn't work with an adjustment of the temps. There are some pictures of our project as well as our ramp/soak schedule in the following thread.

http://www.cloudynig...5138637/page...

#61 mark cowan

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Posted 01 January 2013 - 01:20 AM

Instead of doing a displacement of volume, just calculate volume instead. I used this to identify a pyrex blank that was moulded in a KzFS4 mould with those initials on the glass. I came out to within 3 places of the decimal point of pyrex value---close enough.
M.


Yup. I did this to ID a suspected Zerodur blank (oh, like the color isn't a giveaway - :lol: - but they've come in all shades). Measurement and an accurate scale gets to digits.

Best,
Mark

#62 FlorinAndrei

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Posted 01 January 2013 - 06:49 PM

Dan, how many watts (or amps) are required by the 17" kiln at peak temperature?

#63 John Carruthers

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Posted 03 January 2013 - 03:40 AM

or immerse the suspected Pyrex in vegetable oil, if it 'disappears' it's pyrex (or something with a similar RI).

#64 danjones

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Posted 05 January 2013 - 11:24 PM

hi florin. thanks for the interest. i'd have to go out and look at the label of the kiln, but i'm sure it's requires 30 amps for peak temp topping out at near 2300 degrees. for melting plate glass, it can be just melted enough at 1700-1725 or so. melting broken chunks or strategically cut chunks in a stack, needs more 1800. other substrates like pyrex and others need more, but well within my kiln's max. it needs 230v to operate fully, but requires more technology than the onboard temp control. glass is finicky, and the temp needs to be controlled precisely. i'm working on a ramp/soak controller to exactly control the kiln's temp operation. the ramp up heat and soak times need to be controlled, especially to well anneal the glass and take out any strain, even in the thickest of blanks. :)

#65 Babaloo

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Posted 30 November 2013 - 07:18 PM

Boy, you can tell a lot of you guys haven't been doing much of the cooking! The new 'Pyrex' has a greenish tinge to the cookware edges, extremely noticeable. And it is just tempered glass. The real Pyrex cookware (which may be different from the Pyrex used in labware) has no tinge (termed colorless). I think one would be safe in scrounging up a lot of old colorless Pyrex cookware from garage sales and melting it all together (better yet, some old labware.) It would also be advisable to cast/slump a test piece from the molten batch, anneal it, and run it through some heat shock tests to make sure. But if the melt can be mixed thoroughly (stirred?), that might very well negate any slight differences in C.O.E.s of the constituents, if different.

#66 ccaissie

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Posted 01 December 2013 - 07:02 AM

A 16 x 3.25 would make a 24 x 1.5?


Interesting. I've got a few of the old yellow monsters.

#67 ccaissie

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Posted 01 December 2013 - 07:07 AM

Isn't the old way of mixing glass to cast/break/re-cast several times?


I think they melt a raw batch, shatter it, select for homogeneity and correct dispersion, then remelt for greater quality as needed. I've got a 10" piece of BK7 that is "A/PK" and that must've been gone through several times to reach such quality.

#68 steveastrouk

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Posted 01 December 2013 - 09:42 AM

European 'PYREX' IS 100% borosilicate, I used to supply equipment to the UK factory, before it moved to France. I did negotiate a deal to buy broken returns, in ton lots, for around $2000, but when I punted the idea in forums like this, the silence was deafening. I have the actual glass formulation used written somewhere.

LCD monitors have boro glass faces too.

#69 Napersky

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Posted 02 December 2013 - 09:27 AM

Awesome I hope making optical glass is the next trend for ATMs. The major glass companies have been gouging the community to the max!

#70 JohnH

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Posted 02 December 2013 - 10:19 AM

I have a pair of these huge 16" X 3 /14" blanks and a better use of them would be to cut them into 2 1 1/2" blanks.

I found the cost of around $150 to cut without any other work (lapping or diamond generation) quite reasonable

#71 Napersky

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Posted 02 December 2013 - 10:25 AM

You can buy authentic Corning Pyrex 1" rod for $8 a pound (a 4 foot 1" rod weighs 3 lb) from glass blowing supply places:

http://www.waleappar...&showprevnext=1

It appears the Pyrex brand name was sold to World Kitchen just for the cookware product line.

http://www.corning.c...ces/product_...



I would guess that there is quite a difference between optical Pyrex and Kitchen glass which is still manufactured. Only the former was discontinued.

#72 Napersky

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Posted 02 December 2013 - 10:34 AM

http://www.newportgl...om/pyrexmkt.htm

"From a distributor and a fabricator perspective, both Newport Glass Works, Ltd. and Newport Industrial Glass, Inc., will continue to offer “Pyrex” parts and sheets from equivalent replacement material. Newport will be stocking and distributing Schott’s Supremax 33 and Borofloat in lieu of “Pyrex”. They will also offer “Pyrex” replacement material in strip form made by other manufacturers."

http://www.matweb.co...8524e79a5030...

#73 Napersky

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Posted 02 December 2013 - 10:41 AM

Apparently Corning sells a ULE that's better than Pyrex and in bulk.

http://www.pgo-onlin...atalog/ule.html

#74 careysub

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Posted 02 December 2013 - 10:49 AM

You can buy authentic Corning Pyrex 1" rod for $8 a pound (a 4 foot 1" rod weighs 3 lb) from glass blowing supply places:

http://www.waleappar...&showprevnext=1

It appears the Pyrex brand name was sold to World Kitchen just for the cookware product line.

http://www.corning.c...ces/product_...



I would guess that there is quite a difference between optical Pyrex and Kitchen glass which is still manufactured. Only the former was discontinued.


Laboratory Pyrex is still manufactured, and actual Corning Pyrex rod would be this same material.

This is exactly the material wanted for mirror manufacture since it has the very low thermal expansion property (one does not want a beaker of acid shattering from thermal stress).

The discontinuation of the production of Pyrex mirror blanks would be a separate issue.

The original kitchenware borosilicate Pyrex with the same low thermal expansion was discontinued when the tradename for that product line was sold to World Kitchen in the late 1990s. World Kitchen sells cheap soda lime glass that has been tempered through a heat heating process under the name "Pyrex" (essentially the same as that produced by Anchor Hocking).

http://www.consumerr...home-garden/...

World Kitchen makes a business out of buying famous high quality kitchen brands, then selling cheap knock-offs under that old famous name.

They did this with Magnalite cookware also, replacing the original magnesium with cast aluminum; and with Revere Ware, replacing the clad copper disk which provided excellent heat distribution with thin copper plating which quickly comes off in a most unsightly manner.

#75 TxStars

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Posted 02 December 2013 - 11:37 AM

One could also remelt Zerodur sheets.
http://www.capovani....m?itemno=105019






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