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Author: Subject: Flask cracked
vmelkon
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[*] posted on 11-11-2013 at 10:27
Flask cracked


WTF, I had a nice RBF that I used for distilling water. One day, I come and find that the bottom has a large crack.
It is from united nulear.com

http://unitednuclear.com/index.php?main_page=product_info&am...

I've had it for about 2 years.
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Dariusrussell
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[*] posted on 11-11-2013 at 10:38


Could you provide more information as to the conditions leading up to its cracking?
That sucks, I hate broken glassware. Anyways you probably already know about cracked glass, as its been discussed to death.
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Antiswat
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[*] posted on 11-11-2013 at 10:48


RBF are the ones least prone to cracking of what i know.. 2 years is a good amount of time although..

once found a flask with HNO3 to be having a decent sized crack, very confusing.. dont recall anything that should of made a crack at all.. shit happens (;




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vmelkon
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[*] posted on 11-11-2013 at 11:02


Quote: Originally posted by Dariusrussell  
Could you provide more information as to the conditions leading up to its cracking?
That sucks, I hate broken glassware. Anyways you probably already know about cracked glass, as its been discussed to death.


It was empty. I wrapped it in bubble-wrap like I do for some of my other glassware and it was sitting in a box, lying sideways. There was nothing on top of it! No stress!

It makes no sense.
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bfesser
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[*] posted on 11-11-2013 at 11:55


It makes sense if the glass wasn't properly annealed to begin with. If you buy cheap off-brand glassware, such things are to be expected.



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Funkerman23
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[*] posted on 12-11-2013 at 21:26


Certainly eye opening but without seeing how stressed the remnants are or other analysis( yeah I know; not worth it for a single flask ) Not much can be drawn from this. It's got MY attention as I own some Laboy & Synthware and I don't know it is annealed properly after seeing this( no polariscope to look for stress). Oddly enough I've seen that brand elsewhere and thought it was 'Meh' quality. Looks aren't everything though so what do I really know. on a unrelated note: should this be in reagents & Apparatus or not?



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MichiganMadScientist
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[*] posted on 13-11-2013 at 13:13


I've purchased glassware from UnitedNuclear in the past. While I love that company to death (since they are so one-of-a-kind), the glassware they sent me was all Bomex. While I personally have not had any issues with Bomex, I understand it to have a reputation for being economy-grade glassware.

90% of what I own is Kimax or Pyrex now, and I recommend anyone starting out to simply spend the extra money and buy the good stuff.
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vmelkon
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[*] posted on 15-11-2013 at 09:58


I think it is from Bomex. There is nothing printed on it.
I also bought some flasks and beakers. The beaker's mouth wasn't well done.

Pyrex is extremely expensive. I own a few Pyrex things but they are used.

Anyway, I is sad.
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bfesser
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[*] posted on 15-11-2013 at 10:03


<a href="http://bomexbj.com/e_about.asp" target="_blank">Bomex</a> <img src="../scipics/_ext.png" />, eh? Mystery solved. Perhaps use the remainder for applications not requiring heating.

<strong><a href="viewthread.php?tid=4933">Question about Bomex equipment</a></strong>




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bfesser
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chemrox
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[*] posted on 15-11-2013 at 14:07


I got two boxes of Erlenmeyer flasks from them and both sizes had no mechanical strength. The guy that I got them through is having them replaced. We think they had some annealing problems early on. A broken 3L flask half full of water can be a real drag!



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gravityzero
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smile.gif posted on 15-11-2013 at 16:07


Quote: Originally posted by MichiganMadScientist  
I've purchased glassware from UnitedNuclear in the past. While I love that company to death (since they are so one-of-a-kind), the glassware they sent me was all Bomex. While I personally have not had any issues with Bomex, I understand it to have a reputation for being economy-grade glassware.

90% of what I own is Kimax or Pyrex now, and I recommend anyone starting out to simply spend the extra money and buy the good stuff.



You are correct with that information. When starting out it is easy to get ahead of oneself and purchase cheaper items. That is what I did.
I figured out quickly that most items should be from quality manufacturers: Wilmad, Kontes, Pyrex, Duran, Chemglass.

There are items like graduated cylinders, beakers, and others where it probably does not matter nearly as much. If it is going to be under vacuum or other possible stress, I go for quality.

There are markets where good used items can be found. This is always a gamble, but can also be very rewarding.
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Dr.Bob
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[*] posted on 15-11-2013 at 19:46


With most glassware, I have found that most cracks occur during handling, but might not be seen until later, especially star cracks. I have not seen glassware crack often, but I see star cracks form on flasks where they were allowed to roll loose in a drawer or were washed in a dish washer. And while cheap glass might be thinner or poorly made, it is rare that it would just crack in storage without some shock or reason. But sticking to better quality glass will almost always pay off, as it is usually just better made, joints that don't leak, better stopcocks, thicker walls (these will crack easier if heated too quickly, however), and better markings. I have some grad cylinders where the ink has all washed off-that is just poor manufacturing, I have Pyrex ones that are 20 years old and still easily read.
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Natures Natrium
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[*] posted on 16-11-2013 at 06:16


Regarding laboy glass, I have purchased some in the past. I checked it with a home made polariscope, and found that the glass was reasonably well annealed. Stress rainbows were pretty much non-existent.

As a counter example, a pyrex brand store bought measuring cup lit up with more rainbows than a leprechaun convention.

A homemade polariscope is very easy, assuming you have an LCD monitor. The light coming off of them is already polarized. A pair of polarized sun glasses can act as the rotatable lens.




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Dr.Bob
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[*] posted on 16-11-2013 at 08:01


Quote: Originally posted by Natures Natrium  

As a counter example, a pyrex brand store bought measuring cup lit up with more rainbows than a leprechaun convention.


That is partly due to the fact that Pyrex brand CONSUMER items are not only not made of Pyrex glass, since a number of years ago, but also not made by Pyrex, being made of soda lime glass, made in low quality factories. Pyrex sold their consumer items branch and branding to another company, who does not make the same quality as almost any lab glass company does.
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watson.fawkes
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[*] posted on 16-11-2013 at 09:58


Quote: Originally posted by Natures Natrium  
As a counter example, a pyrex brand store bought measuring cup lit up with more rainbows than a leprechaun convention.
Many consumer glass products such as these are manufactured "tempered", which means that they're cooled rapidly. The outer shell hardens slightly larger that it would otherwise. The result is that the outer surface is under compression and the inner body is under tension, improving ordinary strength against breakage. For this class of ware, tempered glass is of higher quality than non-tempered.
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Natures Natrium
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[*] posted on 16-11-2013 at 15:48


Interesting, kind of like Prince Rupert's drops.

http://www.youtube.com/watch?v=xe-f4gokRBs

That would explain the stories of Pyrex cooking dishes exploding into a million bits inside cabinets, hours or days after they had last been touched.




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BobD1001
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[*] posted on 16-11-2013 at 21:32


Quote: Originally posted by Natures Natrium  
Interesting, kind of like Prince Rupert's drops.

http://www.youtube.com/watch?v=xe-f4gokRBs

That would explain the stories of Pyrex cooking dishes exploding into a million bits inside cabinets, hours or days after they had last been touched.


Awesome find! By far the best video of prince ruperts drops I have ever seen. I still remember my 8th grade science teacher making these for us, and demonstrating their properties (in a ziplock bag to contain the fragments). He also showed us the incredible properties of them by polarizing the light from an overhead projector and placing the drop on it so the internal stresses would be visible. Ill have to make these sometime soon!
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watson.fawkes
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[*] posted on 17-11-2013 at 07:28


Quote: Originally posted by Natures Natrium  
That would explain the stories of Pyrex cooking dishes exploding into a million bits inside cabinets, hours or days after they had last been touched.
It's happened to me once, long enough ago that I don't recall exactly what it was that broke. But I was in the next room when it happened. There was a big muffled crash inside a cabinet. No one was in the kitchen at the time.

My best guess is that what happens here is very slow crack propagation from the surface inward that stems from thermal cycling. At the outset, the crack tip is under very low force because it's in a region which is under compression. After a time, it penetrates past the outer layer. Once it gets to a point where the crack tip is now under tension, the rate of crack growth changes by orders of magnitude. Once the first break happen, they cascade, because now you've got areas on the surface that are now under tension.
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[*] posted on 19-11-2013 at 07:27


BTW,

Here is a nice guide to glassblowing and glass working. Perhaps someone could put it into the library. I found it while looking for some other info on glassware breakage.

http://www.public.asu.edu/~aomdw/GLASS/book.pdf
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