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talbot
United Kingdom
718 Posts |
 Posted - 17/12/2012 : 20:36:28
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On my M Type I secured the two aluminium covered plywood platforms that the bonnet catches are fitted to with two domed coach bolts. These pass through the aluminium, plywood and the steel chassis. I didn't have any chromium plated ones so used some bright galvanised ones. I've just had to remove them and the threaded sections, where they pass through the chassis, are badly corroded - even though they are only a year or so old. Is this electrochemical corrosion between the aluminium and zinc or perhaps some chemical in the plywood? I will replace them with some spare stainless ones which I bought at Silverstone to make the buttons for the bonnet tops but am intrigued by the ammount of corrosion.
Jan T |
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John Reid
United Kingdom
704 Posts |
Posted - 18/12/2012 : 09:17:27
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Jan,
In the aviation world, especially where the construction involves wood/metal contact and metal/metal contact, a jointing compound is used to prevent the type of galvanic corrosion you have experienced. Duralac and JC5A are two such chromate jointing compounds. Bolts are coated with this material before assembly.
Duralac is cheaper than JC5A, but the latter has the advantage of remaining flexible. More details in the LAS Aerospace website, http://www.lasaero.com/site/products/category?id=H02UPOL0J
John R |
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spitfire
United Kingdom
371 Posts |
Posted - 18/12/2012 : 10:12:55
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Stripped down some aluminium, some years back. It was behind ply trim. In contact with steel.
The ally sheet had almost become a white dust/paste.
Even stainless steel has adverse reactions unless Copperease or the like is used.
I wonder the fate of those buried Myanmar/Burmese Spitfires?
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Colin Butchers
United Kingdom
1487 Posts |
Posted - 18/12/2012 : 10:32:01
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Spit,
I believe that the Burmese Spitfires were all greased and wrapped in waterproof covering before they were buried. Whoever did it, was sure tha they would be needed again one day.
Colin B. |
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spitfire
United Kingdom
371 Posts |
Posted - 18/12/2012 : 17:52:09
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Admittedly Colin. American Harley 45ci motorbikes have been exhumed over the years. After being buried in WW2. We are many years on. South East Asian soil can be very powdery and dense. Any disturbed land could well create fissures that water could have entered. I watched a programm where an American car of/in the 1950s was entombed in a concrete cast chamber with many artefacts of that year. This was in a city central plaza. Due to be opened year 2000.
It had sweated under the concrete. Sat in a metre of water. Useless. |
Edited by - spitfire on 18/12/2012 23:16:19 |
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talbot
United Kingdom
718 Posts |
Posted - 18/12/2012 : 18:46:53
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Photo of a "zinc plated" bolt, six months old, securing an aluminium clad piece of plywood. Bolt was waxoiled before insertion. Is there a difference between "zinc plated" and "galvanised". I suspect there is and it's related to health and safety. It looks like the plywood caused the corrosion!
Jan T
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John Reid
United Kingdom
704 Posts |
Posted - 18/12/2012 : 19:06:46
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Jan,
This can be prevented by assembling with either Duralac or JC5A jointing compound.
Bolts we recently removed after several years from a Dragon Rapide for inspection were in perfect condition. They are in contact with spruce and cadmium plated steel fittings.
John R |
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John Reid
United Kingdom
704 Posts |
Posted - 18/12/2012 : 19:50:16
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Colin,
The problem with old Spitfires, however well preserved, is that they probably still have magnesium rivets, thousands of them - notorious for exfoliation corrosion starting around the end grain of the rivet hole. Spitfires flying today have been totally dismantled and rebuilt with appropriate grade aluminium rivets. Not a straightforward job since it is a stressed skin aluminium structure and needs to be done on a jig - serious money.
John R |
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Oz34
United Kingdom
2534 Posts |
Posted - 18/12/2012 : 23:37:03
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Nevertheless John, there seems to be no lack of wealthy enthusiasm to rebuild any that come along. Long may it be so, although the rebuilding of somewhat rarer machines would be more exciting. Anyone know of the remains of a de Havilland Hornet? That would be VERY exciting!!
Dave |
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Cymber
United Kingdom
966 Posts |
Posted - 19/12/2012 : 20:27:19
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Have you seen the films of a recently rebuilt De Haviland Mosquito in New Zealand?
Maurice Blakey. |
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Oz34
United Kingdom
2534 Posts |
Posted - 19/12/2012 : 23:36:09
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No, but I've read of it in Aeroplane mag. Beautiful (but not QUITE like a Hornet!)
Dave |
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Oz34
United Kingdom
2534 Posts |
Posted - 19/07/2013 : 14:14:46
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Revisiting this thread for other reasons I saw again Maurice's post about the New Zealand Mossie, whose American owners BTW have now put their whole museum up for sale; anyone fancy a Mossie?
If you're dithering over that question, maybe this will make up your mind!
http://www.youtube.com/watch?v=rGfQQWOsoB8
Happy viewing.
Dave |
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