Ramiel
Vicious like a ferret
Posts: 484
Registered: 19-8-2002
Location: Room at the Back, Australia
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shaping and crafting glass
Sometimes in a lab with limited money, you have to improvise apparat(-i,-us) because the alternative is too expensive or not available. I was just
wondering if any of you here had techniques, methods or tips on shaping glass and also combining glass (like melting a flask and a tube together to
get a vacuum filter flask FOR EXAMPLE!).
thanks for any input.
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PhewBar
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Glass blowing, forming, fragmenting, etc.
I have had an interest in glass blowing from the first time I watched by grandad blow a crack pipe... just kidding.
In reality pipes are the most common items blown by the beginner. Blowing pipes lets you learn about the behavior of glass and how to heat it, spin
it, etc...
I moved on to more complicated items such as vacuume flasks and condensers, with variable success. What I can tell you for sure is that anything that
joins two pieces of glass together more than once is not practical without an anealing oven. What an anealing oven does is allow the glass to cool
down at a very slow pace.
The reason this matters is that glass expands when it is heated and contracts when it is cooled. Some glass does so more than others, but all glass
does so to some measurable degree. Now since thicker glass(such as where two pieces of glass are joined) cools slower than thinner glass, fast
cooling will lead to large temp differences and therefor unequal contraction leading to stress fractures.
A simple butt T joint of two glass tubes is unlikely to show little signes of stress, but it will still weaken the joint. More complicated items such
as condensers, where one tube is placed inside another and both are joined together at each end will show this affect quite dramatically. I have
fashoned probably a half dozen condensers, each one requiring over an hour and empting two or three bottles of MAPP gas. About half looked good
enough to eat when I was done, but sadly none survived. Even when placed in the oven heated to 500 deg, they all exploded into pieces withing a half
hour.
But I can share a few tips for those who wish to fashon reliable lab equipment, including vacuume flasks and condensers, using glass and other
materials easily available.
To make a vacuume flask; a clear, thick walled wine or champaigne bottle is good starting material. Instead of blowing or drilling a hole in the
bottle, which I have done with mixed results, you should fashon a vacuume connection out of an easily workable material and attach it to the top of
the bottle.
For most compounds being filtered, you can use common PVC pipe and solvent. So take your bottle down to home depot and find a 'natual rubber' (the
black tough, minimally elastic kind) plumbing flange that will fit over the neck of the bottle. These flanges have ring clamps that tighten and
should seal the flange to the bottle. Also find a PVC "T" connection that fits inside the other end of the flange. The "T" connection will be
positioned sideways so the straight through path is vertical and the butt connection sticks out to the side.
Select a PVC reduction flange with 1/2" female threads to reduce the side opening, allowing the connection of a vacuume line. Since the bottom
opening is of course connected to the bottle, only to top opening remains to be connected to a filter mechanism.
I have constructed several different filter setups, depending on what is being filtered. So I would recomend filling the top opening with the largest
female threaded flange that will fit, which allows different filter options to be connected and replaced.
One filtering option I use quite a bit is built from a 4" to 2" natural rubber reduction flange. I like natural rubber because it is very chemical
resistant, and seals well against possitive and negative pressure and can still be removed for cleaning or modifications. The 4" to 2" size would be
perfect for holding a standard round coffie filter, except the hole is so large the filter will be sucked through. I avoid this by draping some
plastic mesh over a short piece of 2" pipe and then slip the flange over that end gripping the mesh between the rubber and pipe. The opposite end of
the pipe goes into a female threaded end that matches the top of the "T" connector.
Now you just drop a coffie filter into the rubber flange, and wet it with clean solvent. This "seals" the filter in place and reduces the amount of
solvated compounds which will be trapped in the filter and thereby lost.
Powering the filter does not take a very strong vacuume. The smallest vacuume I could find, which is used to vacuume out keyboards and cost $15, will
sometimes burst doubled up coffie filters. So you need a way to limit the pressure without hurting the vacuume.
If you partially plug the input or output path of these cheep vacuumes you will soon burn up the motor. I learned that in a dream, or something. So
a better way is use a second "T" connection with the straight through path connected to the vacuume suction port and the butted connection attached to
a small PVC 1/4 turn valve. The remaining opening should be filled with a PVC flange with a 1/2" female threaded connection. This makes it easy to
connect the adjustable vacuume source to the filter flask using two threaded nylon connectors and some 1/2" tygon hose.
By adjusting the 1/4 turn valve outside air is allowed to bypass the filter which drastically reduces affective pressure. A nylon 1/2" threaded to
1/4" barbed hose adapter will partially plug the valve opening leaving a 1/8" diameter opening which can be further impeded by the valve.
If people are interested, I can describe the construction of condensers for distillation/reflux and several other interesting devices. That is when
my fingers recover from the longest post I have ever typed.
PhewBar out.
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Polverone
Now celebrating 21 years of madness
Posts: 3186
Registered: 19-5-2002
Location: The Sunny Pacific Northwest
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wow
I would be interested in hearing more about improvised/home manufactured laboratory equipment. You certainly seem to have some knowledge of it. You
say that natural rubber is very chemical resistant. I'm rather surprised by this. I had the impression that chlorinated solvents, strong oxidizers,
and strong bases would all have an adverse affect on it. I've made rubber bands swell up like monstrous space spaghetti in hot conc. NaOH solution.
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PhewBar
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I may be wrong in labeling the black dense rubber used on plumbing flanges as 'natural rubber'. I don't really remember where I heard that
information, but that is what I believe them to be.
I havn't found anything, except THF, that I have run through the device to greatly affect the rubber. I have filtered most of the common solvents
including; toluene, xylene, diethel ether, MeOH, IPA, acetone and THF. The only thing that showed signs of damage was the THF. I don't know if you
have ever had the pleasure of dealing with THF, but it could desolve the corpses of the east german olympic power lifting team including their
fillings over a long weekend.
I have not had as consistant results from PVC, which is well fucked by half the organic chemicals listed above. I also have not filtered DCM, tri/di
cloro/floro -anything, so these may slag the device apon contact.
I have a variation of this device that did survive THF, and I would imagine almost anything else, which uses a glass funnel as the filter holder fit
through a off white rubber single hole stopper. The stopper is wedged into a 3/4" hole drilled through a 1 1/4" x 1 1/4" teflon block that I rounded
on a grinder. I then drilled a 5/16" hole from the side intersecting the vertical path, which I threaded with a standard 3/8" tap.
The rounded teflon adapter can be 'fixed' to the top of a glass container using one of the rubber flanges, but teflon thread sealant made by LOCTITE
can be used to seal the crack between the teflon block and the lip of the glass container to prevent any contact between the filtered compound and the
flange.
The only materials in contact with the filtered compound(s) are the glass funnel, filter, teflon block, teflon sealant and the underside of the single
holed stopper. Since the glass funnel neck will certainly extend will below the stopper, it will only come into contact with vapor which should
reduce the severity of any attack.
If the compound being filtered is agressive enough for the vapor alone to eat through a rubber stopper, then you should probably be killed before you
can hurt anyone anyway.
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Ramiel
Vicious like a ferret
Posts: 484
Registered: 19-8-2002
Location: Room at the Back, Australia
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Mood: Semi-demented
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I'm very glad you're around!
So do I need any special glass flux or secret-grandmaster-gung-fu technique to join two glass pipes together?
Also, if i want to bend or shape two joined pieces of glass, would that exacibate stresses in joins?
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PhewBar
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Registered: 30-10-2002
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Let me first say that I am not very practiced at making glass joints, but I have made them. Most of them were air tight, but I'm sure all of them had
significant internal stress weaknesses that made them easily broken. I will likely sound more skilled in the art than I am because I had the luck to
find a fifty year old book on scientific glass blowing at half priced books. So I am mostly parating what I have read without being able to add much.
I was able to successfully achieve butt-joins, which are 90 deg connections of two pieces of glass tube, on small diameter glass tubes on my first
try.
The 'trick' is to heat the side of a glass tube that has one end plugged while gently blowing in the other end. You blow while the tube is in the
flame, but immediately remove it from the flame when the bubble pooches out from the glass. It is important to blow gently or else the buble will
pop, and you do not want that to happen. What you want to do is blow out a bubble, then without blowing use the flame to shrink the bubble back down
to a flat unbroken surface. This surface will be much thinner than the original tubing wall, and the missing glass will be collecting around the edge
of the 'hold' as a kind of lip. Now return the tube to the fire, heating the exact same spot and blow another bubble in the same place. Try to again
stop before it pops, then shrink it down flat. Repeat this step several times until the bubble finally pops.
Once the bubble pops, use the flame to melt the thin whisps of glass back into the lip of the hole in the side of the glass tube. This process builds
up a lip of extra glass around the hole which is important to a strong joint be possible.
I failed to mention that the size of the hole created should be about the size of the internal diameter of the glass rod being connected to the hole.
The next, last and most difficult step is to heat the two pieces of glass at the same time, most likely in the same flame and connect them together.
The hotter you get the two pieces of glass the more time and care you can take lining them up and connecting them. If you miss or don't get them
completely connected, them all the molecules on the planet will simultainiously reverse and then explode at the speed of light, so make sure you get
both sides fairly hot before you try.
Once both sides are as hot as your torch well get them, gently touch the tip of the glass tube being heated to the top or bottom of the hole you made.
Hold the tube being connected at a 45 deg angle, so that only the edge will initially connect. Then once you see that everything has lined up, shift
the tube being connected to slightly more than 90 degrees. This will push the remaining part of the joint together, but it must be done before the
glass cools. If not, your children are certain to certain to be born deformed and vote republican their entire lives.
Since you will sooner or later fuck up this highly intuitive process, your best bet is to heat the partial connection and then while hot touch the
corner of a wet sponge to the point you wish to seperate. This is my own contribution to the art, and for me at least, tends to seperate the two
pieces without fucking things up to much. Reheat both tubes well to smooth the surfaces before risking additional offspring.
I will get out the book and look for anything I missed later today, good luck. And buy plenty of glass, sticking to smaller sizies at first. 10mm to
18mm is easiest, 12-14 makes the best pipes.
If anyone is interested I can describe pipe blowing, I am shamefully adept at that.
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NERV
Hazard to Others
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Registered: 22-9-2002
Location: USA
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I am intrested in pipe blowing. I had a friend whos uncle made glass pipes for a living, and ever since I saw one of them I have been intrested in the
art. There are other resions I like pipe blowing to that I wont go into though 
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vulture
Forum Gatekeeper
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I have no experience with shaping glass, but how about dipping the still hot joined together pipes in a crucible with a bit of molten glass to get a
thicker layer there?
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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Shotgun Man
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Bullseye Glass Co. approach to glass blowing
I highly recommend watching this 20 minute presentation on the updated science behind glass blowing, but for those not wanting to sit down for 20
minutes I will still spoon feed you brief information to satisfy your curiosity, get the gist or crush your dreams...
http://www.bullseyeglass.com/methods-ideas/recommended-annea...
Essentially Bullseye Glass Co. have found that unacceptable levels of stress develop when any one part of the glass differs from another by 5 degrees
Celsius during cooling from 482 - 427 degrees Celsius. In practice, hold time at 482 degrees Celsius is irrelevant and merely needs to achieve this
temperature throughout the glass before cooling to 427 degrees Celsius.
In theory, you could flash heat the glass to 482 degree Celsius and then flash chill the glass to room temperature provided there is at no point a
deviation in 5 degree Celsius through any part of the glass. From a practical perspective with the correct equipment, 1/8 inch thick glass can be
cooled to 427 degrees Celsius within 15 minutes and be acceptably annealed.
To conclude, this indicates that temperatures above the recommended 482 degree Celsius are unnecessary, amounting to only being a waste of energy and
one's time. Aside from reaching this temperature, temperature and time held at said temperature becomes completely irrelevant. From 482 degrees
Celsius, the only factor you must consider for annealing glass is being able to maintain less than 5 degrees Celsius temperature deviation throughout,
until you reach 427 Celsius.
Perfectly annealed glass has less than 100 PSI of stress, while dangerous levels of stress are greater than 1000 PSI. The formula for this obviously
requires that you have a pyrometre to measure the temperature of the centre and outer surfaces of the glass product, but is expressed as:
Stress of glass in PSI = E * alpha * Delta T
Where:
E = Young's modulus
alpha = Coefficient of Thermal Expansion
Delta T = variance in temperature throughout glass during cooling
An example calculation:
Known values:
Young's modulus of soda lime glass = 10 200 000
Coefficient of Thermal Expansion of soda lime glass = 0.000009
Delta T of soda lime glass = 1.7
PSI of annealed glass = 10 200 000 * 0.000009 * 1.7 = 156.1 PSI
Having gone through the basic theory and math for the spoon feeders out there, it becomes apparent that if you own a small glassblowing kiln (I did
some brief price checks, some run for under $200 US) it is simple to anneal homemade laboratory glassware in as little as 20 minutes. However, I
understand some here and not interested in purchasing a kiln and for them denies their sense of victory being able to produce glassware without one.
Obviously annealing glass was done historically and so must be possible with only heat and some basic earthen materials.
If anyone here owns a pyrometre, I challenge you to find a cheap method. I hear campfires burn roughly 500 degrees, perhaps you could heat a large
steel drum filled with perlite until the internal perlite is 500 degrees, insert freshly made glassware and then leave to cool. This would require you
to position the glassware in the centre and ensure that the steel container is of equal dimensions in order to allow for the perlite to cool as
equally as possible.
When I have $40 to waste, I myself will try to use my propane furnace as a kiln by heating glowing hot, inserting glassware on a pedestal, heat the
glass for a brief while using guesswork and then shut off and seal. My hopes is that the residual heat will radiate from the furnace walls, creating
an environment with an even application and slow decline in heat. However, I have more important, much more challenging experiments to complete first.
"While all other sciences have advanced, that of government is at a standstill - little better understood, little better practiced now than three or
four thousand years ago." - John Adams
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elementcollector1
International Hazard
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Quote: Originally posted by Ramiel  | I'm very glad you're around!
So do I need any special glass flux or secret-grandmaster-gung-fu technique to join two glass pipes together?
Also, if i want to bend or shape two joined pieces of glass, would that exacibate stresses in joins? |
Everyone stop, and think about that last paragraph. Put together an image in your head of a man karate-chopping two pieces of glass together.
I'm interested in flameworking mainly because I have a few useful parts which just don't connect to ground glass, and I'd like to fix that.
Elements Collected:52/87
Latest Acquired: Cl
Next in Line: Nd
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watson.fawkes
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One word of warning. This company does soda-lime
glass, not borosilicate. The idea that ΔT has to be minimized during cooling is correct, but the specific temperatures won't apply to
borosilicate or other glass compositions.
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Pyro
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I have a little experience with glass. I mainly butt-seal Pasteur pipettes together to make longer tubes.
this is how I do it: I have a roaring flame on my teclu burner (I imagine that a MAPP torch would be better). then I take 2 pasteur pipettes, one in
each hand, and hold them at the base of the flame, just out of the light blue cone (I do this to have a very fine line of heat so I just heat the
outer 1mm) when it starts glowing, just before it starts collapsing I press them together so there is a bead at the joint, I then keep in in the flame
and gently pull them apart until the OD is the same.
I have found this very effective, Just yesterday I dropped a joined tube on the ground from table level and it was intact.
I hope this helped
all above information is intellectual property of Pyro.  |
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Dr.Bob
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| Quote: Originally posted by Polverone | | I would be interested in hearing more about improvised/home manufactured laboratory equipment. You certainly seem to have some knowledge of it. You
say that natural rubber is very chemical resistant. I'm rather surprised by this. I had the impression that chlorinated solvents, strong oxidizers,
and strong bases would all have an adverse affect on it. I've made rubber bands swell up like monstrous space spaghetti in hot conc. NaOH solution.
|
The black rubber in most plumbing parts is a Viton or chlorinated rubber, which holds up far better than any natural rubber. But even it will swell
in many solvents. If you design things to not expose the rubber directly to solvents it will last a while in a lab, like a rubber stopper on a
filter flask, with a glass tube in it. They can last years, as long as the flask does not get full or the solvent does not splash. Natural rubber
does not last long in a lab, even NOT exposed to solvents, as the gases in the air are enough to oxidize it. Not sure about lungs, but they seem to
fare better, thankfully.
Viton is very good, compared to most, and for good rubber tubing, buy fuel line tubing at a auto parts place, it is usually Viton, and it will do
pretty well.
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