Broken tap removal

I wonder if anyone knows of a firm within reach of Peterborough who could remove a broken 7BA tap in a copper boiler using spark erosion.

Bernard

Bernard,

Can you rust it out?

Neil

Neil,

This is an entirely new concept for me. Can you give more information of what's involved?

Bernard

Hi Bernard,

Sulphuric acid wont atack copper but will teadilly disolve steel so you can remove the tap with that.

Peter.

Hi Bernard Use Ferric Chloride solution it munches steel faster than it munches copper

Regds

Dick

Bernard,

I would recommend that you do NOT use ferric chloride on copper. Ferric chloride is used for etching the copper tracks on printed circuit boards. Richard Parsons is right that it will attack the steel faster, but it will still attack your copper.

I have seen various website posts re the use of Alum to remove steel taps from non-ferrous metals and which appears to be fairly non-aggressive - try googling for that.

Regards Tom

I broke a tap in my boiler, and removed it using Alum. It took quite a long time, but it leaves the copper and brass /bronze completely undamaged. It works quicker if it's stong and hot, but in my case it was on the backhead bush, and I had to mould a litttle plasticene container round it to hold the Alum, it wasn't possible to keep it hot.

Phil, I'm curious - can you quantify that "took a long time". Just order-of-magnitude of course .... an hour? ..... a day? ..... a week?

Yes Ferric Chloride does dissolve copper. But here we have a combination of copper and steel is a little galvanic cell . Galvanic corrosion occurs with the steel acting as the ‘Wasting anode’

Rdgs

Dick

It should be possible to remove the steel chemically leaving the copper untouched.

(the factors are similar to those discussed in the recent pickle thread)

Diluted acid: sulphuric or phosphoric or citric are possible choices (after cleaning of any cutting oil or grease) . Copper sulphate, somewhat acidified is best, will also remove the steel by replacing it wth copper - which will be powdery in nature and crumble away. Some hours/days of treatment may be needed periodic agitation with a nylon fine paint brush will also help.

Hydrchoric acid best avoided due to general rust promotion .

Ferric choride will dissolve the copper: I think the concept of the setting up of a anode/cathode cell in the mechanical circumstances that exist are small. For effective action a circuit needs completing possibly also with a small applied DC voltage. The tap I guess would need to protrude by 1 or 2 mm to make this possible.

I would stick by the above soak and wait strategies!

John

I would go with the alum, I removed three broken 8ba taps from some bronze cylinders, placed the cylinders in a pan of saturated alum solution on the stove and simmered, add a spot of water as the solution evaporates.

Two hours and they were gone.

Alum is cheap and leaves the copper/bronze untouched.

Keith W

Alum was what I had in mind. The hard part is getting hold of some!

Neil

Neil, go to the garden shop, you might have to buy a Kg of it, but it won't cost a great amount. A few years back I needed some to get some rusted screws out of a brass casting, so I went to the chemist, he was able to get some in a few days later. Awee while later I found that mum had a bag of it in her gardening chemicals cupboard, its been there a good many years, and cost less than a dollar for a 2Kg bag. Ian S C

In the UK try 'oneclickpharmacy' where I had 500g of crystals. They were a little slow in delivering however. Also for smaller amounts (200g) try 'kitchen-chemistry' on ebay.

Just searching for alum on ebay gives a number of suppliers.

Les.

Sid,

Re "it took a long time". If I remember right, it took about 3 weeks, but I had plenty of other things to do while I waited. Keiths post was interesting, I didn't realise it could be done as quickly as that. But I couldn't boil it like he did, I only had a few CCs in a plasticene cup. I also used a saturated solution, but is that the best strength? Maybe the chemists among us would know.

Think you'll find it in the supper market, in amoung the spices,and other cooking bits and pieces. Ian S C

Phil,

As a very rough rule-of-thumb, a chemical reaction will double in speed with every 10 degree (C) rise in temperature, so from 20 degrees to boiling (100) it should be about 250 times faster. (Please don't regard this as a precise measure, there are many exceptions!)

David

It would be lovely if someone could answer my original question?

Bernard