h a l f b a k e r yWarm and Fussy
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You still might get a tail, because the molten-glass drop has
to enter the water from a particular direction. Likely you
need a way to spray the molten-glass drop with water from
all directions simultaneously. |
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I wonder if it would be possible to do that on Earth
using one of the ways of simulating microgravity. For
example, you could use freefall, like how lead ball bullets
used to be made in shot towers. (Actually, it wouldn't be
a simulation in that case, but I digress.) |
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Perhaps the following method: Rent the Vomit Comet.
Onboard, levitate glass lumps using a hot air stream, so
that they melt and form spheres. Have the pilot do a
parabola. While in freefall, turn off the hot air streams
and clap clamshells full of cold water over the spheres. |
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A few minutes later, after reading the beginning of
the
linked NASA article, I realized that the Vomit Comet
part of my idea isn't necessary: Just drop the spheres
out
of the levitator (airstreams/acoustic/whatever type)
and
catch them between the clamshells as they fall. Same
effect, though possibly more splashing because the
water will fall
out of the clamshells a little bit if you don't perfectly
coordinate their movements with gravity so that
they're effectively in freefall too. (It might be
necessary to do that anyway, so there's no convection
in the cooling water.) |
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You could probably do the same just using two chilled clamshells to clamp a blob of molten glass. They would form it into a sphere and, at the same time, chill the outside fast enough to create the necessary internal stresses. |
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I suppose to avoid the tail you need to allow time for surface
tension to form a sphere before you start the rapid cooling. |
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Would it work to just drop the glass into water from high
enough? |
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Juvenile prank call to a market from the previous century: |
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" Do you have Prince Rupert in a can ? " |
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One point to bear in mind is that glass (even toughened glass, which is what these would be) is less hard than many steels. |
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Cool. Would that depend on the composition of the glass? |
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Also, I wonder how large a sphere could be attained?
Whether spinning the globule in microgravity would produce more perfect lenses than can be ground?
And if cymatics could be used to create shapes which might not be possible here on Earth?.. perhaps stronger than spherical. |
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// Would that depend on the composition of the glass? // Yes, I think so. Glasses vary quite a lot in hardness (I think pure silica, i.e. quartz is one of the harder ones, but I may be wrong). |
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//I wonder how large a sphere could be attained?// |
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Well, the aim is to put the surface into compression to prevent crack initiation/propagation, whilst the centre is in tension (and isn't vulnerable to scratching, as it's on the inside, and hence approaches its theoretical strength). If you keep increasing the size of the sphere, I guess you will reach a point where the compressive forces cause the outer layers to spall off spontaneously. Alternatively, you'll reach a point where the tensile stress on the inner parts exceeds the breaking stress of the glass, so the inside will crack and relieve the compressive forces on the outer layers. |
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Of the two, my guess is that the second effect will predominate. So, your size limit will be set by the tensile strength of scratch-free glass, which is pretty high (compared to normal glass with surface imperfections), but not astronomically high. |
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It'll also depend on the cooling profile, which will determine how stresses are distributed radially. |
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Toughened sheet glass (as used in car windscreens, glass shelves, glass stairs etc) is basically the same but flat, so the forces are only acting in one plane; so, it's not a perfect model for spherical toughened glass balls. But, to a first approximation, a large ball cooled with the right temperature profile will probably be equivalent to a sheet, meaning that you could make any size you want. |
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On the other hand, there are harder and stronger materials out there. Also, if a toughened glass ball fails, it will fail catastrophically and dump glass powder into the bearing, with disastrously abrasive consequences. If a steel bearing fails, it may just deform and do less damage. |
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what might work on earth is to make a regular ruperts drop, then while the glass is still plastic use sonic vibrations to press the tail into the glass blob creating a sphere. |
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Using the "shot tower" method, rather than dropping in to
water, or using cooled clamshells, have a "puddle" of super-
cooled helium (cold, but still gaseous). It would allow the
drop to maintain it's sphericality (without the impact of
hitting a liquid) while also providing the necessary rapid
cooling to the surface. Experiments would need to be done
to find the optimum temperature/density (or even gas mix).
Have a net or something near the bottom of the gas to
catch the drops. |
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Cooling gas could work. Sheet glass is toughened (I believe) using air jets to rapidly cool the surface of the hot glass. |
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They are tough but probably very brittle under constant
pressure, no? |
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// Hard to find the right category for this one // |
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No worries, mate. You nailed it! |
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I wonder if Sapphire would behave the same way? It
would be extremely scratch resistant, but I have no
idea how tough it would be. |
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On another train of thought, I remember seeing ultra
rapidly cooled steel and it became glassy and had
some interesting properties like transparency. It had
to be a ribbon to get the cooling rate, but it would be
interesting if it could be treated in the same way for
another shape. |
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//I remember seeing ultra rapidly cooled steel and it became glassy and had some interesting properties like transparency.// Seriously? Video link? |
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//ultra rapidly cooled steel and it became glassy and had
some interesting properties like transparency// |
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Are you thinking of Metglas or amorphous steel? I'm not
aware of any transparent offerings. Interesting stuff - but
much more difficult and expensive to make than glass. |
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Sounds like the two just need to be incorporated. [link] |
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I can't stop wondering about the properties of various shapes created from the molten glop while suspended, like, why not a Prince Rupert Dodecahedron? |
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...and do the trapped bubbles really contain a hard vacuum?
That's pretty cool. |
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Ah, my mistake...not transparent. Many years ago,
and all that....sorry. I saw it on "Tomorrow's World",
if anyone can remember that program. It
demonstrated a spinning wheel arrangement which
fired out ribbons of metal. |
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"Prince Rupert Spheres" sounds like it should be a
euphemism for something |
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[hippo] or a body piercing. |
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//...and do the trapped bubbles really contain a hard vacuum?// Why would they contain vacuum? |
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Hmm. Well, glass is fairly gas-permeable (at least to oxygen), so I'd expect the voids to contain either oxygen pulled out of solution from the surrounding glass, or (eventually) oxygen diffusing in afterwards. |
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Irrelevant aside: the new building that my old lab moved into has lots and lots of glass. The glass panels are beginning to shatter spontaneously (about a dozen have done so, so far) because the glass contains metallic impurities. Over time, oxygen diffuses in, oxidises the metal particles, and causes them to expand, thereby shattering the glass. It's a crying shame, and I am absolutely not going to laugh at the misfortune of the lab which decided no longer to employ me. No, not even a titter. |
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// The glass panels are beginning to shatter
spontaneously (about a dozen have done so, so far)
// |
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...and this has definitely nothing to do with target
practice? |
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As if I would. Every time I fly over the building, it seems that a few more panels have shattered. Of course, it's hard to tell for sure at Mach 1.1 |
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// "Prince Rupert Spheres" sounds like it should be a euphemism for something // |
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I heard his family had quite the jewels... |
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//Well, glass is fairly gas-permeable (at least to oxygen),// |
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Really?!
Are there ways around this?
I had assumed that since the bubbles form when solidifying that they contained vacuum. I wonder if it could be determined whether the bubbles are air or vacuum by breaking the drop under water to see if any air rises to the surface. If no bubbles rise then the voids must contain vacuum no? |
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I'm tempted to go buy a propane torch right now. |
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//Really?!// Yes, though "fairly" is a relative term. A void that has been sitting around for years (maybe decades - I don't know) will probably lost vacuum. |
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And yes, you could break the glass under water to see if bubbles are released. But unless the voids were large, it would be tricky - the breakage of the glass could cause cavitation, encouraging dissolved gas to come out of the water; or the bubble from the glass might just dissolve in the water and be lost. |
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//I'm tempted to go buy a propane torch right now.// I've tried making small PRDs with soda (common) glass - it's not easy. Most of the time, they shatter on contact with the water. If anyone has made PRDs with greater success, let me know how it's done. |
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Will try. Also, a YouTube video says that you need to keep the torch on the bottom of the drop as it drips, not the neck. |
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I've seen Prince Rupert Drops at an open day at the
Institute of Making in London - they're quite
beautiful |
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Hmm. I'm still not getting anywhere - the drops shatter a moment after hitting the water. I think they're too small - will find some heavier glass rod to melt. |
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hmmm, if you vibrate the container of water with the right wave form then the impact of the drop will be cushioned and much less traumatic for the little droplet. |
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It's not the physical impact; it's the thermal stress. |
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I wonder... Lead shot is (or at least, was) made by dripping molten lead into water, and generates reasonably spherical nodules. As I understand it, the tail of a prince Rupert drop is made by the viscosity of glass- it doesn't seperate cleanly so the tail hasn't quite left the source when the head enters the water. |
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So perhaps you could simply have a device which snips off an extruded lump of glass - perhaps with an extended fall against hot gas before it reaches the cold water. |
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Of course, that's so simple that it probably doesn't work otherwise it'd be done already - so maybe the tail is essential. |
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//what might work on earth is to make a regular ruperts drop, then while the glass is still plastic use sonic vibrations to press the tail into the glass blob creating a sphere.//
//wot?// |
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I think what beanangel is suggesting, in his inimitable way, is almost a Prince Rupert's Klein bottle. You protect the tail by putting it inside the drop. |
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Yes, perhaps he is suggesting making a Klein bottle. The phrase //creating a sphere// sort of threw me off the scent. |
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Shit! I just accidentally deleted [Flying Toaster]'s anno saying; |
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"Why not make a Rupert's torus?"
Sorry dude. |
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I was honestly thinking about this today.
It might be possible to create torus shaped molten drops... whether they would hold together is debatable. |
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//It's not the physical impact; it's the thermal stress.// |
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Are you sure it's not a combination of the two?
Breaking the surface tension of still water must throw a wider impact and deform the droplet more than say aerated water would, so maybe there exists a ratio which allows for fastest cooling with minimal stress to the structure. |
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You could probably make a setup whereby several
powerful jets of hot air suspend the drop after it's
separated from the Glass rod. Think 3 or 4 burners
carefully controlled to levitate the drop above the
quenching liquid surface, then suddenly turn them off. A
tail wouldn't get a chance to form. May not be spherical,
but there would be no tail. Perhaps you could induce
spinning if you carefully align the jets, this might help
with the sphericity. |
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[Max] - you could try a light oil perhaps, instead of water,
the shock wouldn't be as sudden. Another idea would be
to get the water nearly boiling, that way the leidenfrost
effect would be stronger, again reducing the shock. Of
course what means you'll get less internal stress, but I'm
sure you could then refine your process. |
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//Are you sure it's not a combination of the two?// |
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Never ask me if I'm sure. I'm always sure. |
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hmmm, I wonder if it would be possible to extrude the molten glass at a rate which remains constant so that Rupert Rods are formed? |
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p.s. thanks for the category pick.
: ] |
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//I wonder if it would be possible to extrude the molten glass at a rate which remains constant so that Rupert Rods are formed?// |
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Yes, you can make toughened glass rods by extrusion. I think the problem is cutting them to length. |
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// You could probably make a setup whereby several powerful jets of hot air suspend the drop [...]//
Yeah, but I already said that. |
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// - you could try a light oil perhaps, instead of water, the shock wouldn't be as sudden. [...] Of course what means you'll get less internal stress, but I'm sure you could then refine your process.// |
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Hmm. I think the sudden drop in temperature is essential to the process.
But this makes me think - what if you used _very cold glass_ to catch the drip in a little container? There would be no issue with evaporative gas slowing the cooling. You could make for example cubes... with a fragile tail if essential.
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If so, there are two possibilities - either the glass sticks to the container, or it doesn't.
If it doesn't, I suppose you could certainly make hexagons and pentagons. Probably you could make them taper inward towards the back. Since they're loose, you could put them together in such a way that the fragile ends are on the inside of an almost spherical conglomeration. |
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Alternatively, if they stick to the support - what if you had a continuous process, where each drip was caught by the previous one? You'd need to keep the tails out of the way of course, so you could end up with a row or sheet of drips which was ridiculously tough on one side, but hilariously fragile on the other. |
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// // You could probably make a setup whereby several
powerful jets of hot air suspend the drop [...]//
Yeah, but I already said that. // |
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//No, I did.// (notexactly)
Yeah, you did. Well, kinda. You were trying to do some wierd clamping thing too.
I'm not convinced the tail isn't essential to the successful development of the drip. |
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Hey, does everyone agree with me that the inside of the drip isn't that important for function? Perhaps we could create glass drips with inclusions.
"In case of emergency, break glass" |
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You could include a bubble, or maybe a round object. |
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If you make a cavity (or include an object) with sharp corners, those corners will act as stress concentrations in glass which is under extreme tension. The whole point of a PRD (or toughened glass generally) is that the tension forces are confined to a region of the glass which has no scratches or re-entrants to act as crack initiators. |
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[mb]'s annotation is interesting. if you used lasers to differentially warm the different, possibly onionlike layers of the sphere you might be able to concentrate all the stress at an inner layer, or even the surface of a bubble. |
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Have you visited theonion.com recently? I miss the paper version. |
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Isn't the paper version called theonionskin? |
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Onions are just ions with zero charge. |
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// Well, glass is fairly gas-permeable (at least to oxygen)
// |
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Then how is it glass ampoules are used to contain chemical
samples that must not mix with any external gases? |
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" glass is fairly gas-permeable (at least to oxygen) " |
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Sounds like a long term phenom ... |
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" I've tried making small PRDs with soda (common) glass - it's not easy. Most of the time, they shatter on contact with the water. " |
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Have you tried raising the water temperature as high as possible? |
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//how is it glass ampoules are used to contain chemical samples that must not mix with any external gases?// |
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Permeable is a relative term. But it's more permeable than many other solid materials. |
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Wow! Very interesting stuff! [+] |
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