Aluminium corrosion ?

I guess it is the old electrolytic reaction of the steel frame and the aluminium, the door bottoms just rot.

I was angry when I discovered the last owner of my pride and joys solution to this, but now I realise that to reconstruct the bottom with fibreglass is not a bad idea.

What about a "sacrificial electrode" method ?

Steve

Is the ride really that bad he made a plastic buttock sheild?

Ah I get it... to keep out the damp!

;-)

Lee D

I teach the principal, but have'nt a clue how to apply it in practice. The idea is to set up an electrical current so as to cause the Zinc used to corrode first (being more reactive than steel/ iron). I have never had the courage to use it as I am not sure if it would work and to what extent the surrounding area of the zinc block would be affected. The real problem is that Aluminium is a very reactive metal and is only used because it has been tamed due to the layer of oxygen on it's surface that is resistant to further attack. Once breached the aluminium underneath reacts very quickly. what is needed is some method of halting the reaction and then re-sealing the breach, but how ?

Yes it does, but it should react with oxygen instanneously to form aluminium oxides again - so summat is keeping the channel open. It's road salt of course that keeps conditions sufficiently conductive that the film is broken down electrolytically.

No, I haven't tried the electrolytic method on a vehicle, but it works well enough on ships ( protects the propellers) and pipelines.

Like you say, its hard to see just how to implement it. I have just enquired in sci.engr.metallurgy.

Steve

Their products are bound to be available in the UK as they say they were tested by a UK university.

John,

Over many years I sought such an inhibitor. _Found_ it about ten years ago !! There's _nothing_ like it. It _works_ !! :)

Check out a product called "Penetrol" .

Best wishes,

... frodo

The first requirement for the sacrificial electrode method is to have the entire structure permanently immersed in an electrolyte. (It only works on ships and marine structures below the water line.) As I assume you have no plans for submarine operations, this counts it out for protecting the whole structure. As far as local protection goes, you already have a sacrificial anode - its the aluminium skin! To prevent it corroding sacrificially relative to the steel door frame, there are two solutions; ensure that there is no electrolyte (e.g.water) in contact with both the steel and the alloy, or ensure there is no electrical contact between the two metals. As both are difficult to achieve with complete reliability except during design and manufacture (not even then, really), you should probably do the best you can with both. And a good start here is the Penetrol suggested, or a similar product, which has very low surface tension on metal surfaces, and will penetrate the nooks and crannies that hold water, and then dries. As it is an insulator, it helps to insulate the metals, and the film will prevent the water from coming in contact with the metals.

Hope this helps JD

Have you got a website for them as I can't find one.

Andrew

On or around Mon, 18 Oct 2004 17:35:15 GMT, "Hirsty's" enlightened us thusly:

take the door skin off the frame and re-attach it with some suitable (electrical) insulation in the joint.

G'day Andrew,

Just had a look in 'Google"... there're a swag of 'em there. Take your pick!

Note that 'Penetrol' is added to paint to 'make it stick' ...... And this it does admirably. I painted my old 4wd with paving paint 'enriched' with Penetrol and I reckon you'd have trouble _sandblasting_ it off :))) ... Even diesel spill around the filler has no effect!!!

But 'Penetrol' is _also used 'neat' on new metal surfaces as a _primer_, especially on marine metal surfaces. Maybe it's low surface tension enables some superficial intergranular penetration , but it will sure get into _every_ surface of metals and then dry as an almost unremovable skin. .... and this will act as an 'insulation' to prevent the electrolytic destruction of the aluminium that is the subject of this thread.

It can be bought in pressure pack spray but this is an expensive way to buy it. Here in Oz many paint stores sell it ( as the paint additive referred to). A 4lt tin costs around Oz$55. ( I bought one only a few weeks ago to spray in the inside of _my_ doors !!. The old stuff from a few years ago is still there but I like to keep 'topped up'... and _no_ rust.....e.g. My 27 year old HJ45 has never been garaged and the only signs of rust are those that ensued _before_ I 'found' Penetrol some ten years ago or so..! My '97 Defender has _no_ metal breakdown , anywhere... Penetrol since new!!)

.... frodo.

Get a large zinc anode (available from any chandler's), attach to the chassis with a good electrical contact, and immerse the entire vehicle up to the waistline in salt water. Make sure the anode is submerged, and remember to replace it every year. Works on boats.

:-)

Rich

"Lee_D" wrote

Or in.

On or around Tue, 19 Oct 2004 20:03:15 +1000, snipped-for-privacy@wherever.inOz (frodo) enlightened us thusly:

so d'you reckon it'll stop corrosion once it's well established?

"frodo" wrote about "Penetrol"

Still can't find anything in the UK though, all either US or Oz.

likewise

Insulating it may not stop the bimetallic corrosion. Have a look at the first paragraph in Section 4.0 of the bimetallic corrosion guide from the boffins over at NPL:

Corrosion control is not simple!

Pittsburgh Pete (usually found over at sci.engr.metallurgy)

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By the way, I forgot to add that Flood's Penetrol is also called Owatrol Oil. Geedon used to distribute it in the UK, but now it's coming via Igoe.

Pittsburgh Pete