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Author: Subject: Hairline Crack - Repair With Epoxy?
lastlokean
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mad.gif posted on 18-4-2013 at 13:17
Hairline Crack - Repair With Epoxy?


So... I got a new distillation setup after my last one became a pile of dust due to an unfortunate incident with moving.

First few distillations = No issues.

Then I decide I need to do a vacuum distillation... Mostly for fun. Sadly the vaccum take-off adapter hairline cracked instantly after vacuum was applied. :(

The crack is under an inch short, seemingly water tight. Thankfully it is not by the joint, but in the middle of the 'bend'.

My initial thought was... Throw this POS away. Last time I get glassware from China. On second thought I'm thinking of trying to seal the hairline crack from both sides with a high quality epoxy. Obviously this is 'madness'.

Anyone have any words of advice on sealing a hairline glass fracture with epoxy? Could it ever hold up to a vacuum?




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DraconicAcid
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[*] posted on 18-4-2013 at 13:21


Repaired or not, I would not trust it under vacuum. Rather than epoxy, I'd wrap it in duct tape. If it does break, it prevents it from shattering in such a way that it throws shards all over the place, and makes it easier to clean up.



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lastlokean
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[*] posted on 18-4-2013 at 13:27


Thanks for the advice. I think I'm going to:

1: Epoxy it.
2: Sand it smooth.
3: Wrap it in duct tape.
4: Epoxy over duct tape.

I will order a replacement as well... From someplace other than china.




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bahamuth
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[*] posted on 18-4-2013 at 13:38


Why bother with such a cheap piece of glassware. Cracks tend to propagate in glass as it is thermally cycled, sometimes instantly without any warning. I'd go with safety, instead of it breaking when it really shouldn't.

As a comparison, you won't screw a crack whore with a rubber that has been in you wallet for ten years now would you...




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lastlokean
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[*] posted on 18-4-2013 at 13:50


Rofl.... I suppose you have a point. Obviously I would never trust the piece of glass under any volatile or extreme situation...

Mostly because it will be a few weeks before I can order more glassware. I was mostly hoping to just get it functioning for the output of a condenser again. As in the piece would not really be exposed to any thermal stress.

I was mostly curious to see if anyone had experience repairing glassware with epoxy. Mostly because I was under the impression that epoxy was ~ as strong as glass...




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watson.fawkes
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[*] posted on 18-4-2013 at 15:10


Quote: Originally posted by lastlokean  
As in the piece would not really be exposed to any thermal stress. [...] Mostly because I was under the impression that epoxy was ~ as strong as glass...
Thermal stress is only one source for mechanical stress. Pressure differentials, such as drawing vacuum, are another. Any kind of cyclic mechanical stress will cause a crack tip in glass to propagate and thus a crack to elongate.

Epoxy is strong, but not strong enough to deal with the forces generated at the tip of a crack. That's why cracks propagate in the first place. The only way to counteract this force to prevent the two sides of the crack from moving with respect to each other. You can do that with concrete (more or less) but it's basically impossible with glass. You have to (1) have an adhesive of such low viscosity that it can get between the two sides of a crack, (2) of sufficient strength once it cures, and (3) have a way of opening the crack up to all the adhesive to penetrate. Just go try getting all three at once on glass only 1-2 mm thick. Instead, what you have to do is to eliminate the crack tip by fusing the two sides of the crack together with heat.
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Oscilllator
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[*] posted on 25-4-2013 at 02:24


I think I've posted this somewhere else before, but I once repaired a hairline crack in a test tube by heating it red hot with a propane lamp. The hairline crack completely disappeared. Now it was probably under a fair bit of stress, but it held up well for a few months until it came to its demise in an unrelated incident :(.
Not saying you should conduct this on that bigger and more complex piece like a take-off adapter, but it can be done.




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Organikum
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[*] posted on 25-4-2013 at 08:38


I have used, Oh! No! I actually still use from time to time glassware which is held together mostly by strong PTFE-tape.
Mostly broken grounded joints.

Never had a problem with it even vacuum was fine.

I sometimes think just find something what gives PTFE tape (thick one) structural integrity and to build everything from this, just one or two times use and throw out.
I strongly dislike cleaning glassware.

/ORG

[Edited on 25-4-2013 by Organikum]
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CycloKnight
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[*] posted on 27-4-2013 at 11:58


Quote: Originally posted by Oscilllator  
I think I've posted this somewhere else before, but I once repaired a hairline crack in a test tube by heating it red hot with a propane lamp. The hairline crack completely disappeared. Now it was probably under a fair bit of stress, but it held up well for a few months until it came to its demise in an unrelated incident :(.
Not saying you should conduct this on that bigger and more complex piece like a take-off adapter, but it can be done.


^^This.

I have done many times, whenever I see a crack in a small item the glassware just goes under the blowlamp for a while. No sweat. The glass will anneal thus neutralising stresses, but should be cooled slowly. I think it works okay for small items, for large items (RBF, desiccator, etc) I'd just replace.
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Pyro
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[*] posted on 27-4-2013 at 12:13


I thought one needed temperatures in excess of 500*C for that to happen at an appreciable rate.



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[*] posted on 22-5-2013 at 14:31



Hi,

Just a couple of thoughts on the use of epoxies for glass repairs. Over the years I have repaired literally hundreds glass and ceramic objects for museums and private collectors. Many of these have had to confer strength sufficient that the object could be actually put back into use, and not only cosmetically.

The epoxies I most often use are Epotek 301-2 or 301, and HXTAL NYL- 1 - depending on the refractive indices of the glass involved and the degree of acceptable yellowing that will occur over time.

The HXTAL NYL- 1, and Epotek 301-2 are not the easiest materials to use but have remarkable properties. The cure rate of the HXTAL NYL- 1 at RT is about a week and for the 301-2 overnight. When properly cured these materials will be stronger than the glasses they applied to, i.e. the glass will fail before the join (at RT...).

The operational useful range of the 301-2 is - 55°C to 200°C and the HXTAL is probably less than 100° (depending or the Temperature/cure schedule)

Both have Tgs of around 80° C and water-white and low viscosities

http://www.epotek.com/sscdocs/datasheets/301-2.PDF

the information for the HXTAL is a bit more difficult to come by online but here is a site of it:

http://www.glasscolor.com/files/HXTAL-NYL.pdf

I recently had a ground-glass jointed bottle (Pyrex) that I use for solvents - which had dried up. The stopper was frozen :-( Freezing the stopper and heating the bottle may have helped along with several applications of other polar and non polar solvents. Finally tried gently prying with a screw driver - bad. The stopper came loose but a blind crack opened and ran down from the lip to 3/4 down.

[img][/img]

Applied Epotek 301-2 from the outside with a toothpick and it capillaried pretty well into the crack.


You can see some very small voids if you look carefully. Curing was done at ~ 50° for 5 hrs.


Excess epoxy was cut away with a scalpel after curing.

Both the Epoteks and HXTAL are quite unforgiving if improperly measured/mixed.

I would think this would be fine for use on a cracked take-off under moderate vacuum, but I would not want to try it on a star-crack on an RBF with boiling H2SO4.






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binaryclock
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[*] posted on 22-5-2013 at 18:19


Which glassware from China? It wasn't laboy/synthware was it?



Current Project: Playing with my new Laboy advanced distillery kit!
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