Little_Ghost_again
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RTV Silicone (slow catalyst) any ood for bungs?
Hi
Can anyone tell me if this stuff
http://www.ebay.co.uk/itm/321507937124?_trksid=p2060778.m274...
is any good for making bungs for chemistry? I have the slow catalyst. The cost of the rubber ones is horrific and I have access to this kind of
silicone, I just dont want any strange reactions occurring by using it  .
If it is usable then it will save me a fortune in adapters and rubber bungs, I need some pretty big ones and they are around £15 each!!! I could make
them in silicone a lot cheaper.
Or maybe the food safe silicone is a better option? I dont have this but could get hold of some of that
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blogfast25
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Silicones come in many grades so it's unwise to generalise too much, as properties vary from one grade to another considerably.
Personally I've had only limited success with silicone in my lab. I've used tubing (various grades) and found the stuff to be very prone to
hydrolysis, especially in acid conditions: first the tube loses opacity and becomes milky (SiO<sub>2</sub> formation), then brittle, after
which it fails at some point.
One 'premium' grade silicone tubing gave up the ghost extremely quickly when exposed to hot SnCl<sub>4</sub> fumes.
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Little_Ghost_again
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Quote: Originally posted by blogfast25  | Silicones come in many grades so it's unwise to generalise too much, as properties vary from one grade to another considerably.
Personally I've had only limited success with silicone in my lab. I've used tubing (various grades) and found the stuff to be very prone to
hydrolysis, especially in acid conditions: first the tube loses opacity and becomes milky (SiO<sub>2</sub> formation), then brittle, after
which it fails at some point.
One 'premium' grade silicone tubing gave up the ghost extremely quickly when exposed to hot SnCl<sub>4</sub> fumes.
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That is not what I was hoping to hear!! I might try some food grade stuff for things like steam distillations, my main problem is I have a lot of
quick fit glass that dosnt fit each other! so sometimes I have to add rubber bungs etc to get it all to fit. Making silicone molds would have been a
easy cheap way for me.
I was shocked just how much bungs cost! It kind of puts me off drilling holes in it lol. I might give the A57 stuff I have here a go, its a bit soft
though.
I need to get some rubber tubing as well, It just takes me a lot of time to earn the money! I am not at School much at the moment because of
treatment, so my Led flashing Cube business has been hit hard .
Still we are coming into the winter season and that means a surge in dirty tractors to clean! That should bring some cash in
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arkoma
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Sounds like an opportunity to employ the "scientific method". Make some stoppers and adapters out of the silicone available to you and expose them to
scaled down versions of the reactions you are interested in and supply the rest of us with a little data!
I found out a quick wrap of PTFE plumbers tape on my 24/29 joints works VERY well for that extra bit of seal and keeps them from seizing, with no
grease to worry with.
"We believe the knowledge and cultural heritage of mankind should be accessible to all people around the world, regardless of their wealth, social
status, nationality, citizenship, etc" z-lib
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Little_Ghost_again
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| Quote: Originally posted by arkoma | Sounds like an opportunity to employ the "scientific method". Make some stoppers and adapters out of the silicone available to you and expose them to
scaled down versions of the reactions you are interested in and supply the rest of us with a little data!
I found out a quick wrap of PTFE plumbers tape on my 24/29 joints works VERY well for that extra bit of seal and keeps them from seizing, with no
grease to worry with. |
I am using PTFE tape on my condenser joints with the water pipes. I am using crap tubing so it leaks at the joints. The PTFE works well. But I have a
situation where I need to drop from 29 to 24, or sometimes I use a non quick fit flask with a quickfit condenser etc. Or just everyday use of bungs!
Different size glass tubes etc etc etc. I am more concerned with the silicone leaching something than anything else. It wont do every job but it might
cut down some of the cost. I will report back The first few will be made with
the silicone in the above link, I use the blue (slow cure) catalyst. the data sheets are also on the page if anyone wants/needs them.
Its a medium type silicone, not as soft as many but does have plenty of give in it.
Failing that I might try a food grade but they tend to be softer.
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blogfast25
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'Standard' rubber bungs are usually made of cheap Natural Rubber or SBR rubber and have very limited chemical and thermal resistance to boot, despite
not being cheap. They will resist boiling aqueous solutions (acid or base) fairly well.
Alternatives made from CR rubber, NBR rubber, and others tend to be much better but far more expensive and not easy to get.
I've used Teflon gas tape to protect cheap bungs somewhat by tightly wrapping them in the gas tape. Starting from the top, then wrapping round the
bottom and lightly staggering each wrap until the bug is wholly covered (perhaps even twice) showed a remarkable improvement in chemical resistance
when I was distilling benzene vapour from a sodium benzoate and sodium hydroxide mixture.
[Edited on 23-9-2014 by blogfast25]
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aga
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Cheap tubing is, er, Cheap ?
Use it once or twice then use some new Cheap tubing ?
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Little_Ghost_again
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Thank you this makes me feel better! I have used different sized plastic tubing fitted inside each other then wrapped PTFE tape around to make up the
difference.
By plumbers tape do you mean the PTFE stuff? The silicone I use dosnt use the platinum catalyst so isnt as bad chemically as some.
At the moment apart from sodium hydroxide (and that isnt going near my quickfit joints!!), I am not using anything too bad, No nitric acid etc just
mainly solvents. Temperatures are not that high and the silicone should handle upto 240C, so far I have only gone to around 180C so temp is ok.
I like the idea of wrapping in plumbers tape, if only to kind of isolate it from whatever. I have some large (20 Litre) carboy type things with taps.
The hole at the tops are huge, I have several smaller ones (10 litre and down) That aso have wide openings.
These are mainly going to be used to store distilled and RO water, also a couple to make and then store Ethanol. So silicone might be ideal for this.
The silicone we use isnt cheap but its pretty strong, and it would be cheaper than buying bungs. The other thing with casting my own bungs means I can
do several of the same size but with different hole sizes in the tops that exactly fit different quickfit parts like still heads.
If it works out well I will post details as its hard to describe some of what I want to do. Once I make the master molds for them out of herculite2 (
a kind of plaster mainly used for gift ware!), I can turn out fair numbers of bungs. If they work out cheap enough I am more than willing to sell
these 'standard size' ones at cost price to any member here if they want them.
I also found some packs of pipe lagging on sale in a shop! there was two different inside diameter sizes, 6 in a pack just over a meter long, these I
got for 99p a pack! So I grabbed a couple .
Not related but I will ask anyway....... I have found a mineral UV lamp machine with 254/366NM UV tubes inside, I would like to use it for TLC as it
would save me using and contaminating isolated material with Iodine. But I dont know what glasses or glass to use to protect my eyes from the UV. The
unit is open so I need to shield it and either use a window with glasses or a window and suitable glass filter.
Searching has just thrown up sunglasses with UV protection! I doubt they are good enough. So any ideas what colour of glass or what kind of eye
protection I need?
My dad taught me to weld a couple of years ago, I got a bad flash from the Arc welder. I am in no rush to experience that again! Despite my illness I
have never been in so much pain as I was that day lol.
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blogfast25
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Silicone tubing isn't generally cheap and it does work splendidly in many applications but poorly in others.
Someone should look up the chem resistance of various silicone rubber types in function of backbone and crosslink types. The RTV types are likely to
the least resistant. Saint Gobain's Silmedic, a peroxide cured type, is likely at the high end of chemical/thermal resistance.
Little Ghost: yes, PFTE (Teflon) plumber tape.
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Little_Ghost_again
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| Quote: Originally posted by blogfast25 |
Silicone tubing isn't generally cheap and it does work splendidly in many applications but poorly in others.
Someone should look up the chem resistance of various silicone rubber types in function of backbone and crosslink types. The RTV types are likely to
the least resistant. Saint Gobain's Silmedic, a peroxide cured type, is likely at the high end of chemical/thermal resistance.
Little Ghost: yes, PFTE (Teflon) plumber tape. |
Thanks for clarifying, I asked because in our shed is a tin (from around 1950!) that has plumbers tape on the label! I opened the tin and there is a
kind of fibir like material (looks like hemp thread) coated in a brown gunk!!
If I can find a decent silicone that dosnt need to special equipment then I can make decent bungs. I have the means to degas silicone and mold making
stuff. The hard part is finding the right silicone.
The are harder more viscous RTV silicone that I can get and use, and also the platinum cure types. The main one we have and I am going to try is
classed as medium strength. To me it feels far more flexible than rubber bungs but it is hard to tear. This is used in most the molds mum and I make,
its actually overkill for our needs but it means we get alot of use out of each mold.
I have also used some fairly hard type silicone, I prefer slow cure catalyst with these as it can take 3-4 mins to completely degas. The temperature
limit of the silicone I have is 240C there are higher temp ones though. Anyway if anyone wants to look into it and can find a decent silicone for the
job, I dont mind making bungs etc.
Regards
LG
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Little_Ghost_again
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I did manage to find this
http://www.reinhardoil.dk/PDB/Momentive%20PDB%20OG%20SDB/Che...
it gives a list of chemicals and how well RTV stands up to them, a couple of surprises for me in there. No idea how accurate of good the list is but
its a start point
Anyone want a 24 to 29 enlarger , thats going to be my first one as it causes
me the most problems lol
[Edited on 24-9-2014 by Little_Ghost_again]
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