I asked this question a while back in another NG, but nobody could give me an answer. There seems to be a lot more action in this NG. What is the best temperature to dry out silica gel crystals that are in oil filled transformer breathers, and how long to keep in oven? TIA
We used to dry at 150 degrees ish and leave them in the oven till they turn back to a deep blue colour - I know it sounds a bit vague but we used to dry them on a hob in an old saucepan (honest!) HTH, Richard.
120-150C, spread out on a dish no deeper than 2cm, 24 hours.
But they only turn blue if they have indicator added - plain silica gel is just white, regardless of moisture content.
However, they have now discovered that the old indicator is a carcinogen, and a new one is blue when wet, orange when dry. pays to know which one you have got.
Chris
A bit of an over-statement. The old indicator, cobalt chloride, is present in very small quantities in silica gel. Some reports have suggested that cobalt compounds are carcinogenic.
In real terms, the risk from exposure to silica dust is much greater than the risk from exposure to the cobalt.
In article , BIGEYE writes
Where can one get bags of silica gel (the indicator ones) at a reasonable price?
If its any help, we had a simple hot air blower arrangement for drying out indicating silica gel cartridges (~18" tall, ~12" diameter), but ISTR they gave up when they realised it was quicker and probably cheaper just to take the pack apart and replace it :-} (although in some cases the packs are fairly securely sealed with silicone or similar, so the blower is still to hand in the workshop)
The silica gel we got was in rather squat square tins - i`ll see if I can find out who the supplier was for you.
This *was* for tx use btw...
In article , Colin Wilson writes
Thanks, The silica gel packs I have were obtained out of redundant distribution boards, equipment, bins and the smaller ones out of test equipment original packaging.
Unfortunately when I used them to dry out prayer books which got soaked at a funeral the keeper of the books misinterpreted me telling them to keep a hold of them as me offering to let them keep them.
RA (Radio Spares) are a bit dear and one has to buy the minimum quantity (50) of each size of non-indicating one needs or packs of indicating types which are really too small when I'm really after a mix of 50g and
100g bags . I've got rather a lot of stuff in storage I want to keep the damp out of and a small library of books which are smelling a bit musty.I made up silica gel bag holders in a couple of my toolboxes using old filter guards and they have actually done a very good job of keeping hand tools rust-free. I can never tell when they need swapped out but when they are I just put them on top of the radiator (domestic GCH radiator)
Isn't silica gel silica gel, or are there different grades?
(oops, I forgot to check who we use as a supplier :-} )
AFAIK it comes in different sized lumps - the stuff we use generally has a granular appearance and is several mm in diameter.
The kind you`re describing is more of an oval pellet and smaller in size I think :-}
The reason I said this was for TX`s was the subject line - I thought you had that in mind !
This would appear to be who we use at first glance
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