Author Topic: Aluminium brazing rod  (Read 253 times)

Online Greybeard

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Aluminium brazing rod
« on: 10.10. 2018 23:07 »
I went looking for information about Lumiweld and came across this video. I think this stuff is the same as Lumiweld. Looks pretty amazing for ally repairs.

https://youtu.be/aj0NjwBqsSg

Offline berger

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Re: Aluminium brazing rod
« Reply #1 on: 11.10. 2018 00:01 »
I am not a real welder, but I notice its all very clean, I tried several times to repair an old weathered grime infested ally mudguard with lumy magic stuff weld. After cleaning it best I could I got no result apart from it trying to take until it found another bit of hidden contamination so I gave up *cry*

Online Greybeard

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Re: Aluminium brazing rod
« Reply #2 on: 11.10. 2018 00:18 »
I am not a real welder,
I know a joke about that.

Offline berger

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Re: Aluminium brazing rod
« Reply #3 on: 11.10. 2018 00:50 »
haha I put in brackets I knew a joke about real welder but then deleted it because it may not be for some of our readers *shh* *whistle*

Offline Swarfcut

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Re: Aluminium brazing rod
« Reply #4 on: 11.10. 2018 09:46 »
  Hi GB.    As the Lumiweld ads used to say, its not welding and it's not brazing. Here is a bit of theory. Strictly defined, welding is "fusion welding" where the parent metal is melted along with the welding rod to produce a homogeneous weld pool of molten metal which then  freezes to give the joint. Brazing  uses a joining metal of lower melting point. The parent metal is unchanged. Brazing and soldering are similar in this respect. Because the braze does not melt the parent metal this is the usual choice for thin sheet repairs such as mudguards etc.  For the inexperienced brazing is easier to master and can be done with cheaper equipment.
  Lumiweld is a halfway house.  You heat the parent metal and melt the Lumiweld rod, which amalgamates itself to your nice clean damaged casting. Perfect...well not exactly.  Look what happened to berger in a cold sober moment.

  It is not a fusion weld as such, since the parent metal does not melt. Neither is it brazing, because it is absorbed  into the parent metal rather than sitting on top as  in a brazed joint.

  So now we come to the tragic bit.  It will only work faultlessly on good uncontaminated clean metal, which we don't have. You have done everything to produce a good joint on your 60 year old oil contaminated unknown alloy precision die casting, and failed. In the end you take it to be welded by someone who knows. "Whats all this"  You sheepishly explain what you have done. Alas, you have introduced another contaminant into your casting, the welder won't waste time on it because his weld will not be sound. You have a in a word, bollockska'd it. To have any chance of success the Lumiweld impregnated metal will have to be cut away, back to uncontaminated alloy.

   So, only use Lumiweld on clean, new uncontaminated metal. It will work just fine. On a valuable casting, leave it to those that know what they are doing. In the right setting it produced amazing results, but your chances of producing a good sound repair to an old crankcase are zilch.

    How do I know this?  Yes, I am yet another who tried and failed.

    Keep Spannering. Swarfy

Online Greybeard

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Re: Aluminium brazing rod
« Reply #5 on: 11.10. 2018 09:59 »
There is video of a chap repairing a camshaft bearing. I guess that part is a modern die-casting so cleaner and denser than our old castings.
Good point about burning your bridges if you have to take the job to a professional.

Online RichardL

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Re: Aluminium brazing rod
« Reply #6 on: 11.10. 2018 11:45 »
It looked good to me and useful in its place. Not that expensive, so ordered some. Planned to practice on scrap before doing anythng critical. Despite high hopes, I'm going to take Swarfcut's timely advice and forego the critical.  What's so critical, you ask? One of my sump plate thread bumps on the barn find is broken out. I had hoped to build it up and, as Swarfcut predicts, seek professional help afterward, if necessary. I am duly admonished, and appreciative, for the advice. That would be a bad place for failure, being above the screen.

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Offline bikerbob

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Re: Aluminium brazing rod
« Reply #7 on: 11.10. 2018 14:47 »
 Swarfcut is correct about welding and brazing as I have done all kinds welding and brazing when I was working but with regard to that Lumiweld I have used it on 2 casings the inner primary on my A7 and the outer primary on my A65 which when I bought it sometime in the past it had been dropped and the footrest dented and cracked the casing I heated the casing up knocked the dent out and after cleaning it up used Lumiweld on the inside and outside it did a good job the only downside is the colour is slightly different from the original casting but when polished up you do not notice it because the footrest hides it. You do have to follow the instructions that come with it no grinding or brushing with a mild steel wire brush as both leave contaminants behind wich stop the Lumiweld from working.

Offline kiwipom

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Re: Aluminium brazing rod
« Reply #8 on: 11.10. 2018 21:43 »
hi guys,i agree with all comments and so if its not `welding `or `brazing`it is probably `soldering` (soddering) for our American members. ( You do have to follow the instructions that come with it no grinding or brushing with a mild steel wire brush as both leave contaminants behind which stop the Lumiweld from working) It is possible to improve the finished job by using Flux, cheers   
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