25 Pounder info needed.

[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!

[Private_collector]

It took me a week, but I've just had the opportunity to discuss my welding requirements with the pro welder neighbour. He has been away in western Queensland for the past 8 days. I figured he was away. Hadn't seen his vehicle all week, and have been chomping at the bit to get his thoughts on my sight carrier repair patches. The outcome is encouraging. It would appear that the original section is indeed magnesium alloy. Potentially problematic to weld, but he is confident, and fully appreciates the peculiarities & unique properties of working with such an unusual metal. The welding should get done through the coming week, and I expect to have the finished product back with me by next weekend. There's nothing like having professional assistance with a tricky job like this!

All going well, I hope to be applying the minimal amount of filler needed to entirely disguise the grafted in repair section. Should have filing, filling, sanding, and priming done during, or ideally by next Sunday. If still enough daylight left after all that, I may even get color on. If so, reassembly may commence by Monday evening. That will be exciting, and will give me the first opportunity to see the parts working together again as one unit.

David, i understand your point. that has been worrying me as well. I'm afraid having the two metals in contact with each other is unavoidable, but I can assure you the finished product will have a far more sheltered life that it has enjoyed in past 70 to 80 years. I've been visiting my 'local' 25Pr for past 3-4 years, slowly taking measurements and photographs. In that time I've literally watched and (unwittingly) documented the guns slow, but inevitable, deterioration. Because I am only now rebuilding a sight carrier assembly of my own, my attention to the extent of same damage on their assembly was only drawn in past few months or so. I had to look back through some much older photos I had taken, to fully realise how badly (and quickly) the exposure to weather is breaking their weapon apart! It is both sad, and largely avoidable. My piece won't be seeing anywhere near such destructive elements. Once the entire sight carrier assembly is complete, including the horizontal adjustment parts I am yet to acquire (or make), the very next thing will be to create a suitable canvas cover for it. It's mostly needed to keep dust and airborne contaminants from settling on the surfaces. Water is an obvious peril, but i acknowledge humidity combined with surface debris is more subtle and just as dangerous, long term. With that in mind, my gun will live indoors, and ideally shouldn't see any rain. it's bound to at some stage though, and that's why the canvas cover will have a lining or waterproof vinyl on inside of the canvas cover itself. I know I can sew canvas reasonably successfully, although I am now banned from using my Wifes domestic sewing machine......(..apparently!) Sewing vinyl or similar waterproof material, and sewing it inside of canvas, is something of an unknown quantity. Or should that be unknown quality? Either way, we'll find out soon. It is also my plan to coat all bare internal surfaces with a lanolin compound, attempting to further reduce time related deterioration. I need to be careful there, because some internal parts will require grease and ablilty to move freely. Typical rust proofing products thicken over time and may gum up the internal workings/gears.

[David Dunlop]

Good news, indeed, on the welding project, Tony.

Not sure how humid, and for how long, that condition can last in your neck of the woods, but if you decide on the fully waterproof type of cover for your 25-PDR, give some thought to keeping some desiccant bags tucked under it to help keep things dry. Out this way when it is humid, when the air temp drops overnight, you can get condensation forming under plastic tarps.

Larger versions of the ones you often find inside NOS Military part packages is what I am thinking about.

Enjoy your weekend!

David

[Private_collector]

Now that's a good idea, David! Didn't think of that. Our humidity gets extreme here at times. I hate it. I swear, every summer is getting worse. I can forsee a geographical change in my future.

We use a product called Closet Camel in our walk through wardrobe, which does that exact job of removing moisture, but on a larger scale. It would be maybe 10-12cm long, 10cm wide, and about same depth. Wouldn't take much to adapt those to suit, and they even come 8n their own plastic case. I'll buy an extra one next shopping trip, and play around with how to suspend beneath the planned cover.

Now, i haven't checked this myself, but I have ben told that the blue (the ones I've seen) gel kitty litter/odour remover works in same way as the dearer moisture removers. That might be worth looking into as well. I could make my own container for it, and tailor it to my exact needs. I'll look into that type too, for curiosity if nothing else.

[Private_collector]

Look what I've got!
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It's not finished yet. My welder mate had extreme difficulty with the welding, and as a result of the porous original magnesium and new repair of aluminium being different metals with different cooling rates, he wants me to add additional strength holding both together. He suggested I fill the inside of the repair with fibreglass, and overlap beyond the line of weld. We think about an inch and half would be plenty. He also suggested I buy Liquid Aluminium to fill welding imperfections. I'm having a look for that online now. If I can locate something suitable locally, I'll get into that job tomorrow afternoon.

My fellow had a hard time working this piece, and he's a professional welder who owned a large engineering works. If it gave him grey hairs, imagine what it would have done to me! I'm ever so grateful for what he has achieved. The next step is up to me now.

[rnixartillery]

Sweet Victory !! Well done.

Rob................rnixartillery.