The Triumph Dolomite Club - Discussion Forum

The Number One Club for owners of Triumph's range of small saloons from the 1960s and 1970s.
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PostPosted: Fri Sep 09, 2016 9:17 pm 
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... I found a copy of the 1951 "Motor manual " on bodywork repairs. It was quite interesting as it was advocating brazing in new sections of metal to bodywork. I can see this won't be as strong as welding for chassis repairs but would seem to have advantages for non-structural repairs as the filler metal is a brass alloy and the working temperature is a lot lower than welding. Why don't we use it these days ?
Ta,
Tony.


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PostPosted: Fri Sep 09, 2016 11:59 pm 
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In the 70s and 80s I worked for a specialist welding materials manufacturer as a tech sales eng. Our main products were the more exotic materials used in the nuclear, chemical, and specialist fabrication and repair. We also produced brazing and silver solders and at that time I did a lot of business with all types of garages from back street to main dealers with various brazing products. They were used extensively on car body repairs, the main thing to be aware of was to remove the flux as this was corrosive, so counter productive.

Done correctly a braze joint can be stronger and more ductile than a weld, and the ultimate tensile strength of the vast majority of the higher quality products is higher than mild steel. In fact one product we did that had a small amount of silver added was the strongest material available at 56 tons per sq inch. This was used by f1 teams to braze chassis and turbo exhaust systems rather than welding for the higher strength and ductility of the joint.

There was however one advantage to some but definite disadvantage for others in that you cannot weld rust, the metal has to be clean for the weld to be made. However you can braze rust so many unscrupulous or unskilled, or of not enough knowledge would not clean off the rust sufficiently to produce a sound safe joint. It then became illegal and an mot failure if brazed joints were found so the practice stopped. Recently however I was informed that brazing is now allowed in certain circumstances, but because I now have nothing to do with the industry I have not looked into this so do not know if this is in factual.


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PostPosted: Sat Sep 10, 2016 4:58 am 
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Lead loading is a great way of filling certain places. I bought a kempi MIG welder about ten years ago that you can MIG braze with. I asked the chap and he informed me that as there's different types of metal being used on car bodies these days that it could be used to join an alloy wing to the main steel panel. The MIG cost £1300 back then but I was able to slip it through the business.
Yes flux can be highly corrosive and also lead to paint bubbling after a few months of being applied. Similar to electrical soldering where soldered joints can actually break after a year!


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PostPosted: Sat Sep 10, 2016 1:51 pm 
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We supplied the wires that could be used in "mig. brazing". They were Cu. Ni. alloys normally used in the petro chemical, nuclear industries for welding "exotic" metals. A weld melts the parent metal being joined and fills in with molten metal from the filler wire or rod. During brazing the parent metal does not melt only the filler wire and a surface alloying takes place. If during brazing the parent metal melts or the brazing rod gets too hot the joint will be much weaker and zinc will boil out of the brazing rod, and this is very unhealthy for the operator, can causes metal fume fever, and can put you in hospital. The danger with mig. brazing is that the parent metal can easily melt so pointless. The amps need to be kept as low as possible to get a good joint. Zinc boiling off however is not a problem with the mig. wires as it should not have any in. We hardly sold any wire for mig brazing, the best use would be for galvanised steel. Being zinc coated any welding of it causes the zinc to boil off so its considered very dangerous and bad practice. (Galvanised products should be welded first then galvanised). By mig. brazing at the lowest poss. amps a joint can be made with minimum heat input so reduced zinc boil off. The added advantage is the joint is non rusting however the transition area will rust between the joint and the coating. When welding galvanised steel all rust protection is lost in the joint and for a fair amount both sides, so a bit pointless doing it.

I would question the brazing of "alloy" to steel if the alloy is aluminium or an aluminium alloy, you cannot use a welding or brazing wire for steel or non ferrous metals on aluminium or its alloys, nor the wires that would be used in mig. Neither would an aluminium mig wire work on steel. You can braze aluminium and some aluminium alloys, we were specialists at that, but that's a different story. If he meant alloy steels or stainless steels to mild steel yes, but better wires especially designed to weld these dissimilar steels are readily available and a far better solution.


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