25 Pounder info needed.

[David Dunlop]

Tony. It is hard to tell from your photos, but is the corrosion damage on your potentially magnesium part on a load bearing surface for the part or other fittings?

If the piece in question just 'sits there', could you perhaps build up the missing bit with body filler, epoxy paste, or similar, and then carve/sand to the correct profile for painting?

David

[Private_collector]

No David, not load bearing, but whatever I graft on will need to be 100% fixed permanently in place, or cracks will eventually show around the edges. I did consider doing that, but using fibreglass. This morning I made all the sections to repair the hole once and for all.......hopefully!

I'm almost sure this thing isn't aluminium now. Seems lighter than aluminium, and it files differently. My welder friend isn't home today, so I never got the definitive diagnosis. Will watch for him tomorrow.
20170122_103213-resized-1024.jpg
20170122_152105-resized-1024.jpg
I didn't set anything on fire while cutting the rot away, and was VERY careful I did not put too much heat in one place. When all corrosion was cut away, I was left with quite a hole.
20170122_120227-resized-1024.jpg
20170122_143126-resized-1024.jpg
There are 6 separate pieces making the repair patch.
I taped them all together to see what the profile will look like. While it's not exactly original, it will do.
20170122_142242-resized-1024.jpg
More details in the next posting....

[Private_collector]

Once all the aluminium repair sections are welded together, I will attach the entire thing as one piece. I'm not sure of method to keep this in place, but am considering construction glue and having a plate welded against inside of the repair patch, overlapping the inside edge of the original by at least 1". The metal of both items is thick enough for me to drill and tap the few holes for better fixing. I will need to be careful not to go too high with anything on the inside, because there is a gear toothed sector that adjusts up & down in there. If done carefully, I should be OK.
20170122_144649-resized-1024.jpg
20170122_143136-resized-1024.jpg
The new pieces sit better than they look in my photos. They're only held in reasonable proximity, with a few bits of masking tape.
20170122_144625-resized-1024.jpg
The below photo shows the only piece that won't be seen, but it's important. This piece needs to help secure the large cover panel you can see sitting above it, and one hole will be required for a fixing bolt to keep the cover in place. That bolt will also help keep my repair in place. I should have no problem keeping the new bit in place, once all methods of fixing are used.
20170122_151545-resized-1024.jpg
All these bits go together to fix one rust out!
20170122_152408-resized-1024~2.jpg

[David Dunlop]

Nice work with shaping up the patch pieces, Tony.

Not sure if you looked into it on the web, but I poked about a bit and discovered one can tig weld magnesium, and even weld aluminum and magnesium bits together. Lots of sites about it and lots of videos.

Didn't know it could be done.

David

[Mrs Vampire]

Not mag alloy .. when this baby was made we had just mastered smelting al al over at silver water . There is a table of reactive elements and aluminum . Brass is not the culprit but steel is . In this case long term exposure to salt laden mist.

Moisture gathering on edges and low points . Use of al al to reduce weight . Made to British spec but weldable . A basic All

[Richard Farrant]

It sounds like this casting is of magnesium content. The guy in the workshop next to me was salvaging parts from a Ferguson TE20 gearbox and said that when he used a disc cutter to split the box (don't ask), it was like fireworks. I told him the casting were Elektron, which is a magnesium alloy. It was first used in the 1930's in the UK, a German development but a company in UK was producing it. The gun mantlet on the late 30's Vickers Light Tank Mk6a was Elektron and when one was being restored over here, I was doing some work on it and the welder fabricator had to build up corroded areas of it. This he done with TIG and used an Elektron rocker cover from a racing car to cut up and weld in, finished job was very good, but he said he had to do it in small bits in order not to have it catch alight. An old neighbour of mine worked for Dunlop during the war, machining aircraft wheels, he said you learnt quickly on not to take large cuts on the lathe otherwise the swarf would catch alight and cleaning up a lathe after it has been covered with sand is something you did not want to repeat.
Electron is lighter than aluminium but also stronger.

regards, Richard

[Private_collector]

I say, this is getting REALLY interesting for me! Metallurgy and welding are two subjects i know very little about, so i do appreciate all your input, folks. Today is my day off, and it's when i take Mother shopping, but I will be banging on my friends door as soon as i return home again, presenting him with all the pieces and a nice chunk waste material for him to toast with his oxy.

The information about TIG welding the two metals sounds very encouraging! God forbid there should be a simple solution to all this. It sure goes against everything my Father taught me, to glue something like this together. Once all the repair sections are welded together (away/off the ? Mg stuff), it doesnt really require a lot of welding to properly the two metals/pieces together. If TIG welding is the way to do it, my guy can do that easily! His work is fantastic.

I'll let you know what we have discovered, later on today.

[Richard Farrant]

Originally Posted by Gina Vampire

Not mag alloy .. when this baby was made we had just mastered smelting al al over at silver water . There is a table of reactive elements and aluminum . Brass is not the culprit but steel is . In this case long term exposure to salt laden mist.

Moisture gathering on edges and low points . Use of al al to reduce weight . Made to British spec but weldable . A basic All

Hi Gina,
I understand BHP had a plant in Newcastle producing magnesium by 1941 and Elektron was then produced in Australia for war work.

regards, Richard

[david moore]

Tony
You might want to insulate the al repair from the Mg - or else you will have the old problem over again! Even a good paint layer will do - at least for quite a few years!
Galvanic corrosion affects all dissimilar metals in contact - and magnesium is about the most reactive (and therefore protective - used as sacrificial anodes on metal boat hulls, props etc. ) Mg will dissolve in contact with Al ( or steel or copper) ; Al will dissolve in contact with steel etc. - there is a galvanic table.
Stop the electrical ("galvanic") contact and no problem even when moisture (or worse - salt) is present.
Though Mg has been around for more than 80 years in transportation, and we all know the Beetle engine block, it is still widely used - the instrument panel support in your car is almost certainly a Mg casting!