I'm melting
February 25, 2010 12:43 PM   Subscribe

I am looking for a torch to melt pyrex (borosilicate glass).

I want to seal a small pyrex tube for lab reasons. Since we do not have a torch, I need to get one that will get to an appropriate temperature. I don't know what this temperature is and My googlefu is not helping me figure out what kind of torch I need (butane, propane, acetylene, oxy-acetylene, etc).

Added levels of difficulty:

The sealing will need to happen in a fume hood so the torch set up must be portable.

The tube in question is pretty tiny so we'd like to have a needle point flame.

We're in the US so extra points for suggesting a US-based website where we can get this.

Thank you.
posted by sciencegeek to Technology (11 answers total) 2 users marked this as a favorite
Best answer: I made hash oil pipes several years ago from Pyrex tubes and used one of these with MAPP gas. It involved sealing one end completely then heating until malleable enough to blow a bowl.
posted by buggzzee23 at 1:00 PM on February 25, 2010

If it's small an ordinary blow torch or laboratory bunsen burner will do the job. People join pyrex tubing that way all the time.
posted by Kid Charlemagne at 1:00 PM on February 25, 2010

Best answer: Some random email says Pyrex's thermal properties are:

1. Strain Point ( 515C ) = viscosity of 10^13.5 Ns/m2 (10^14.5 poise)
2. Annealing Point ( 565C ) = viscosity of 10^12.4 Ns/m2 (10^13.4 poise)
3. Softening Point ( 820C ) = viscosity of 10^6.6 Ns/m2 (10^7.6 poise)
4. Working Point ( 1245C ) = viscosity of 10^3.0 Ns/m2 (10^4.0 poise)

I would guess that MAPP gas is your best bet, too. Cheap, readily available, and hot.
posted by rusty at 1:07 PM on February 25, 2010

Best answer: an ordinary blow torch or laboratory bunsen burner will do the job

Not borosilicate, not with just lab gas, in my experience. Sodium glass, sure, but borosilicate needs something hotter like MAPP to soften enough to work. More commonly an oxygenated torch, either methane or propane, is used.
posted by bonehead at 1:10 PM on February 25, 2010

Response by poster: And now for the updates:

My mentor's former lab used these torches but the company which bought them doesn't actually want to sell them to us for no apparent reason.

The glass in question is ASTM Type 1 Class A Borosilicate Glass (link goes to NMR tubes that we're trying to seal, 5mm).

Thank you all for the pointers so far. You're awesome.
posted by sciencegeek at 1:16 PM on February 25, 2010

Best answer: You're pretty much going to have to buy locally. Shippers don't like having to move gas around (but it is possible if you pay enough). I'd try industrial plumbing supply stores or a tool supply. Benzomatic sells MAPP in standard torch size containers and heads like one buggzzee23 links to above are easy to find.
posted by bonehead at 1:26 PM on February 25, 2010

I think we've been able to seal NMR tubes with a butane torch, although maybe they were just sodium glass. Hardware stores (Canadian Tire up north is where we get ours) sell portable ones that can get pretty hot and with a pretty thin flame.
posted by beepbeepboopboop at 1:35 PM on February 25, 2010

Natural gas/oxygen will do just fine for pyrex. Probably the hardest part will be getting a well-tempered flame in the high-flow enviroment of the hood.

Otherwise: your lab might have natural gas plumbed already, so you'll just need to find a spot to chain up your oxygen bottle/cylinder that is pretty far from your workspace. I'd recommend hanging a sheet of stainless steel as a "backsplash" in the hood where you're planning to work.
posted by janell at 3:26 PM on February 25, 2010

Best answer: A good swirl tip air-propane torch will reach 1700F+ or so and propane is way cheaper than MAPP1 gas especially in refillable 6 or 20lb. tanks.

Benzomatic sells a compact little torch using their MAPP replacement Max/Power fuel called the Quickfire. It would be ideal if you don't need to do this on a regular basis.

1MAPP is a trade name and I've been told it isn't being made anymore. It's being replaced with other products that mostly interchange despite having different chemical compositions like MAP/Pro.
posted by Mitheral at 3:28 PM on February 25, 2010

Check your local welding supply. They'll have whatever you need and be able to provide knowledgeable advice.
posted by buggzzee23 at 3:36 PM on February 25, 2010

Response by poster: I think we're going to get the Cutting, Welding and Brazing Torch Kit (OX2550KC). And maybe get a tip with a smaller aperture.

janell: sadly we do not have gas lines in the building. Nor do we have vacuum lines. Or CO2 lines. I run my bunsen burner from a propane tank the size of a loaf of bread.

Thank you all for your help.
posted by sciencegeek at 3:42 PM on February 25, 2010

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