Is phosphor bronze adversely affected by phosphoric acid?
Got some large screws stuck in bronze nuts and need to remove the rust 'below' the nut so I don't do too much damage to the nut as I unscrew it (which will take heat). Access is a tad difficult but I can get a plastic tub of phosphoric acid so the screw is immersed in it but will it dissolve the bronze nut?
AWEM
In article , Andrew Mawson writes
Andrew,
I don't know the answer for certain, but genuine bronzes (Cu/Sn alloys) should not be affected by non-oxidising mineral acids, or at least not at an appreciable rate. However, if it contains Zn, this may well be dissolved and you may suffer "de-zincification", as happens to steam boilers if you use brass fittings in them. Your problem is that you have no easy way of knowing the precise composition. Can you scrape a bit off and test it?
If all you want to do is removed rust, it may not need a strong (or strong-ish - phosphoric acid is only what I would call medium strong) acid; a weak organic acid such as citric might well work. With a chelating agent such as EDTA it might work even better. With your experience in water you probably know about this.
David
According to this
Andrew
I don't know if you have good enough access, but electrolytic rust removal might be a good solution. Certainly won't hurt the phosphor bronze.
Mike
What he said - or use citric acid.
Phosphoric acid might leave a layer of insoluble ferric phosphate which might make the threads a little bigger, and thus harder to remove, and phosphoric acid probably wouldn't be too kind to bronze/brass, though this depends on type.
Note, citric acid will dissolve bronze/brass - eventually - if there is air about, but most likely less fast than phosphoric acid will (depends on the exact bras/bronze)
I'm assuming the bronze nuts are more valuable than the steel screws.
-- Peter Fairbrother
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..sadly not! The screws are about 6 foot long by 1.5" acme and the 'nuts' are carved out of a block of bronze about 2.5" square by 6" long so replacing either is to be avoided if possible!
AWEM
Sucess following advice from the group!
I left one of the four 'screws' with bronze nut upright in a pail of citric acid overnight. Before I could unscrew half a turn using a wacking great spanner when heated with an oxy-acetylene torch. This morning it would unscrew 3/4 turn cold so I left it soaking. Just now
8 hours later I've fully unscrewed it with minimal force. Only 3 more screws to go and perhaps I can get this press dismantled for sand blasting and re-painting! It's been a 'back burner' project for too long.Citric acid definately works!
AWEM
unscrew
In article , Andrew Mawson writes
Andrew,
Glad to hear it - and thanks for letting us know.
David
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