Shattered filtering flasks!

[g_axelsson]

Get a vacuum regulator but use proper filtering flasks. Even with less vacuum how do you know what the safe limit is on a modified Erlenmeyer flask? With proper equipment you know that it can take a full vacuum and not break and still have a proper safety factor.

A vacuum regulator is good for not breaking the filters but you should not rely on it for personal safety.
If you use it to regulate the vacuum to not break flasks then a stuck contact could blow the flasks.

At least, that's my opinion.

Göran

 

[aga]

Yep. Never heard of anyone having a vacuum pump strong enough, or glassware weak enough to smash the glass that way.

... With a new filter paper I keep the vacuum light till it beds in and gets a layer of deposit on the top which then makes it stronger. Then I decrease the pressure further to achieve the flow rate that I want...

Never heard of that before either, but it's seriously Smart and makes absolute sense

That's a Gem to keep for sure. Thanks.

 

[kurtak]

Out of the 7 filtering flasks that I had, 5 of them imploded, 1 was dropped accidentally and now only one remains. Although these flasks were modified erlenmeyer flasks to have a tubulation. I guess that was the cause, or its age(1 year of use). I always check for cracks.

5 out of 7 :shock:

I asked a laboratory glass shop to add a pipe at the side as it originally did not have any.

Been following this - the discussion about vacuum, pressure, regulators, etc. is certainly all good discussion points - but getting to the point of the original question "why are you having a problem with so many filter flasks implode" ?

vacuum, pressure, regulators, etc. are not so much the problem as is the above quotes - as pointed out by some of the other replies

(Nick posted) My advice is buy only the best ones when using a vacuum pump

(Goran posted) Did you use standard erlenmeyer flasks and not the special buchner flasks? Then it was only an accident waiting to happen.

(& again Goran posted) Get a vacuum regulator but use proper filtering flasks.

I am not sure the pic is actually going to show it all that well - but a real filter flask made with a barb (for hooking up the vacuum) is close to if not twice the thickness of a regular flask

autumnwillow - when you had the laboratory glass shop modify your erlenmeyer flasks did you tell them you wanted that modification done so you could hook up a vacuum "for filtering" ?

If so - they should have told you that an erlenmeyer flask is NOT made to withstand a vacuum when filtering

It is one thing when to use a vacuum to scrub fumes during a reaction - it is another thing when using a vacuum for filtering

When scrubbing fumes in a reaction vessel - if set up right - there should be a tube in the (top) stopper that allows air in as the vacuum pulls fumes out through the scrubber - thereby preventing building pressure on the vessel during operation --- on the other hand - when filtering - the more the filter plugs - the less you have air flowing in & the less air in flow you have the more the pressure builds to the point of "max" pressure being applied to the vessel when the filter is "plugged" to a point of drip --- drip ----- drip ------- drip --------- drip ---------------- drip

Hence the reason actual "filter" flasks being made of thicker glass

Though I have broke a few (filter) flasks in the 7 - 8 years of doing this (usually because of handling like dropping while washing with slippery soapy hands) I have "never" broke one during vacuum filtering & I have often pulled vacuums for extended periods of time on totally plugged filters (walked away during the filtering & came back who knows how long after the filter became totally plugged)

Kurt

 

[autumnwillow]

It was a thick walled erlenmeyer flask that was modified to have a tubulation. I also had one 2L filtering flask(no modifications) break on vacuum.

But it could also possibly be because I also use them as reaction vessels and some are cooled after boiling to reduce waiting time by putting them inside a bucket filled with water.

Cuchugold, I meant no offense.

I saw how fast the liquid was passing thru the filter paper before it imploded, and with that speed filtering should be done in 2 minutes. Do you guys filter like that? If I could achieve that speed with my next order of filtering flasks it'll be great! Since a lot of my refining bottlenecks is actually in the filtering. I actually bought a 240mm buchner funnel, but I don't think the 4L filtering flask can support it. I used a PVC bucket which deforms when the vacuum reaches certain pressure. I'm still trying to figure out where to put it.

 

[autumnwillow]

If you use it to regulate the vacuum to not break flasks then a stuck contact could blow the flasks.
Göran

What is a stuck contact?

 

[cuchugold]

No problem willow. Sorry for encroaching your thread. Peace

 

[kurtak]

It was a thick walled erlenmeyer flask that was modified to have a tubulation.

That may be true but a thick walled erlenmeyer is still thinner then an actual "filter" flask

In my first pic the erlenmeyer IS a thick walled flask & it is about (plus/minus) half the thickness of the filter flask

In this pic we have the (thickest) filter flask (on the left) - then on the right is the same thick walled erlenmeyer as in the first pic - the erlenmeyer in the center is a thin walled erlenmeyer which is again about (plus/minus) half the thickness of the thick walled erlenmeyer

Again - I am not sure how well the pic is going to show the difference in the glass thickness but the glass of my filter flasks is definitely thicker then the glass of my "thick" walled erlenmeyer flasks

Probably the reason I only have 1 thin walled erlenmeyer left is that any other thin walled erlenmeyers I "may" have had have all long ago broke & I avoid using the remaining one unless I actually need it

Bottom line - get "actual" filter flasks - they are thicker & will take more vacuum - & it certainly can not hurt to add a regulator that will break the vacuum if you exceed the desired vacuum setting of the regulator

Kurt

 

[g_axelsson]

If you use it to regulate the vacuum to not break flasks then a stuck contact could blow the flasks.
Göran

What is a stuck contact?

Usually a vacuum regulator cuts the power to a pump when a certain vacuum is reached and turns it on again when the vacuum is too bad.
If it breaks down without breaking the power to the pump then it is stuck in the on position.

I guess the proper English word would have been a "stuck vacuum switch"... or am I still using the wrong words?
Sorry if my Swedish heritage shines through... :wink:

In any way, the failure modes for a vacuum regulator is either on or off, the vacuum increases (can be bad) or the vacuum dies off (only a problem for filtering).
Whenever assessing risks, take into concern the probability that something fails in every way possible and the consequence if it does so. The probability and consequence points out where the risks in an operation lies.

We had to use this method and document it well on my old job whenever we did human biological experiments. Connecting electrodes and electrical equipment to humans can be tricky sometimes.

Göran

 

[g_axelsson]

Thick walled flasks doesn't like strong heating or cooling, that may shatter a flask too. Glass is such a bad conductor of heat so a thick walled flask would have contraction on the cold side and expansion on the hot side, too much and the stresses will break it.

There is a reason there is so thin glass in coffee pots. Thin glass can also flex easier than thick so the stress never becomes as great as in a thick walled container.

Göran

 

[4metals]

In all my years doing this I have never seen a vacuum receiver implode, and I've seen a few liters filtered! That includes pulling vacuum into and filtering into 4 liter erlenmeyer filter flasks, 19 liter filtering jugs, 10 liter filtering jugs, and 45 liter filtering jugs. (which aren't practical because you cannot lift them to empty them)

I have broken a few, but from banging them or dropping when cleaning them but no implosions. I do not think the right flask will ever see enough vacuum to break it so I have to ask one question. You said you had these flasks modified. Did the glassblower anneal the glass? If not, or if not done properly (i.e. too fast), not annealing or faulty annealing after fusing on a vacuum stub will weaken the glass.......substantially.

 

[autumnwillow]

To sum it all up the probable causes should only be improper modification of the flask or deterioration by heat.

I had the bleeder valve on when I was filtering so I don't think it was too much vacuum pressure.

Just for the record, I'll list how my filtering flasks broke:
1) Too much vacuum and heat, worker forgot to use the proper stopper with a hole. It only cracked, it didn't implode.
2) Me - vacuum and heat drying of potassium gold cyanide, cracked only, and slight leak.
3) Me - filtering of spent washing liquid of gold, cracked but only the bottom plate of the filtering flask fell off.
4) Worker filtering spent washing liquid of gold, imploded.
5) Worker and me, filtering AR solution, imploded.

In the previous filtering tasks that we did, it was always the filter paper that broke first. It is only maybe it is stronger now because I actually use three of goldsilverpro's wick trick instead of one, they are stacked together in a triangular form because they keep on shrinking due to heat.

Thank you guys for all the help! Filtering flasks will be arriving tomorrow and we can continue with our refining jobs. I only bought the 2L flask this time, a vacuum gauge and cling wrap! I will test how far these flasks can go in terms of vacuum pressure before I go for the 6 pack 4L flasks. If anyone could suggests a better way to filter as I am willing to spend $1000 on the 6 pack filtering flasks then please let me know. Hopefully no more shattered flasks this time!

Edit to add: We were able to recover 25g of gold out of the AR solution that went everywhere, we used tissue and cloth to capture it. Dumped it all in a bucket with liquid, precipitated with SMB without removing the cloth and tissue, washed, pyrolized then incinerated after that we smelted with soda ash and borax.

 

[autumnwillow]

Filtering Flasks came in today.
Compared with what I had, they are way much thicker than the remaining 4L filtering flasks.
I guess I was ripped off by the laboratory supply who sold me the brand new pyrex claimed "filtering" flasks.
They probably used an erlenmeyer then modified it with tubulation.
The first four I bought was brand new from them.
Even the previous 2L filtering flasks that I bought from them were thin!

 

[4metals]

Good you were able to get to the bottom of this issue and realize the real culprit was the glass you had wasn’t what it was claimed to be.

On the bright side you learned a valuable lesson in cleaning up spills and recovering the values from them. That is a skill that is always hard learned but a good one to have. If anyone who has been refining seriously for some time hasn’t had a spill to clean up they’re likely not telling the truth. Spills happen, things break, and recovering the values from those spills is a valuable skill to have.

 

[autumnwillow]

We are approximately 25grams short!

Does anyone know how to remove the AR liquid from paint? They are in wood and cement paint.