Where’s this rust come from ?

[Neil WyattModerator @neilwyatt]

I can vouch for the effect of PVA. Used a new screw to seal my diluted PVA bottle yesterday (for 3D printer adhesion coating).

It's showing rust already despite appearing to be stainless, and the old screw had almost rusted away.

Neil

[Rod RenshawParticipant @rodrenshaw28584]

I accept that PVA glue as supplied may be chemically neutral and safe for children but that is not the end of the story!

PVA is a water based glue. The manufacturer adds water to the mix to make the glue fluid enough to be used.

When the glue is used 2 separate things happen. The water in the glue evaporates – and rusts anything nearby!

And the glue "sets", a chemical reaction which releases acetic acid, hence the smell of vinegar. Acetic acid is what a chemist would call a "weak" acid, as distinct from "strong" acids like nitric or hydrochloric, and it is not dangerous – but it will also rust anything nearby! (weak and strong in this context has nothing to do with concentration)

So if you use PVA, and it is cheap and effective, it is best to allow it to dry thoroughly and ventilate the job well before trusting it not to affect your tools.

Rod

[old martParticipant @oldmart]

I would empty the box take the drawers out and put everything in an airing cupboard if you have one, or for a week or two in a dry place. Its a shame we are into October, or a couple of weeks in the attick would dry everything out.

PVA glues are water based which explains why sticking a nail in the top results in rust. There is no acetic acid associated with PVA glues, that is the common type of silicone sealant, although there are silicone sealants which are acetic acid free.

[not done it yetParticipant @notdoneityet]

Posted by Steviegtr on 01/10/2020 16:26:43:

Also maybe consider buying some packets of Silica gel. Maybe 1 in each drawer.

It is the time of year for me to start thinking about damp. I have a dehumidifier in the main garage but not in the workshop. I have a tubular greenhouse heater on the wall near the mill , which will stay on over winter. I think they are 60watts per foot. So 120 watts all winter should not break the bank.

Steve.

A silica gel packet will soon require regenerating. Not much good unless it is the ‘tell-tale’ type with cobalt chloride, or similar chemical, that changes colour between dry and exhausted gel.

120 watts 24/7 could cost as much as ninety quid (perhaps more if one is on a really poor tariff) over 6 months. It may not break the bank but that money (or some of it) would buy insulation and/or draught excluders that will still be working in following years – or even for decades. It needs a thermostat, at least, and needs to be low down, close to floor level (heat rises🙂 ). Our machines are worth looking after, mind!

My draught-proof (and well insulated) workshop only requires 750Wh/day, except when the weather is particularly inclement, to keep it dry and condensation-free (but not necessarily at a ‘working’ temperature). Could be as low as £15 but usually a fair bit more. On one tariff (5p/unit) it could cost only half of my dehumidifier running costs.

Well worth thinking of climate change, these days – not for us but for our children and grandchildren, etc – rather than thoughtlessly increasing global warming. I hate wasting resources.

[Rod RenshawParticipant @rodrenshaw28584]

I don't want to labour a point but PVA does produce acetic acid, see " cameo.mfa.org/wiki/Polyvinyl_ acetate" and to quote from "Collection Risks" – "May release acetic acid on curing, ageing and deterioration."

I am not much of a chemist, and I had to look this up, but I understand that PVA was originally made by a German chemist, Fritz Katte, in 1912 by reacting acetic acid with ethylene in the presence of mercury. I don't know the precise reaction for the release of the acid but I imagine the PVA is partially decomposing as it cures. The aging and deterioration will be very slow so I don't think any acid release will be troubling after the initial cure.

Rod

[Frances IoMParticipant @francesiom58905]

Old Mart – it certainly ate the stainless steel that I used to plug the spout after I noticed the previous plain steel went within a few days – think it was somewhat stronger than plain water- the SS lasted a little longer tho – the PVA was from Axminster so may it have been improved?.

Edited By Frances IoM on 01/10/2020 23:12:55

[Bob WildParticipant @bobwild67557]

Thanks chaps for all your divers comments. I should have mentioned that it was a new product and my workshop is pretty dry without the need for de-humidifiers.. I'm inclined to the opinion that it was caused by some reaction with the felt or glue. I'm puzzled as to why I should have the problem when other purchasers of this tool box have not.

Anyway, I've reported the problem to the supplier and asked for my money back. Watch this space (slowly).

Bob

[JasonBModerator @jasonb]

Frances, find yourself an old golf tee if you need to plug the spout, that will resist the somewhat acidic ph value of 4 that PVA adhesives can go down to.

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, just to say A2 stainless steel isn't very resistant to acids, whereas A4 is.

Regards Nick.

[Neil WyattModerator @neilwyatt]

Posted by Nicholas Farr on 02/10/2020 09:50:49:

Hi, just to say A2 stainless steel isn't very resistant to acids, whereas A4 is.

Regards Nick.

There you have it.

Only on the Model Engineer Forum can you find the correct specification of stainless steel for plugging your bottle of PVA glue.

Neil

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