Bronze brazing?

[Brass_Machine]

Anyone have experience with Bronze brazing? I know some shops make chopper & bicycle frames using it. I was told (or read somewhere) that you can bronze braze with mapp gas.

Anyone want to write a how to?

Eric

[PTsideshow]

Don't  know what they are referring to as "Bronze Brazing". As with "Silver Soldering" It is often a common misuse of the terms.  As it is more a temperature dependent procedure. Since brazing rods are mostly a naval bronze/ silicone bronze/phosphorous bronze alloys.
If what you are talking about is the Brass/yellow/gold looking brazing filler metal  whether it is on steel or other.

Soldering takes place below 840'F (450'C) filler metal meting temperature.

Brazing is above 840'F (450'C) filler metal melting temperature.

Both of the processes, depend on the use of fluxes and non ferrous filler metals to wet the metals surface. For the increased ability for capillary flow, which draws the filler metal into the joint.

There is a process that is called braze welding, which doesn't depend on capillary action, but the use of filler metal to fill in  joints designed like those for Oxy/Act welding. It is used for mostly cast iron cracked or broken parts.

It is welding without melting the base metal, lower temperature and therefore less distortion of the part.

The short answer is that other fuel gases,instead of "Acetylene" Natural-gas, Methlacetylene-propradane stabilized (MPS MAPP gas) Propane, Hydrogen, and the proprietary gas mixtures that some supplier sell.

They all can be used for soldering, brazing, pre heating and cutting(oxygen). It will depend on the type of torch tip design. and whether it is air/fuel and oxygen/fuel. But that's another whole can of worms and misinformation

http://madmodder.net/index.php?topic=2679.0 here is info on silver brazing. Is more info on silver brazing

Just a side note, the reason you can not ferrous weld with any other fuel gas/oxygen mix is that only Acetylene/Oxygen mix can truly achieve the neutral flame so the weld/filler molten pool isn't contaminated. And end up with a substandard weld.

If you are looking for a color match to the base bronze you may have to try a number of brazing filler metal alloys.
Crown 125 or 125FC is a general purpose
Royal 130FC-P
Crown Sil-Cop 0 Close to Harris 0 ) leaves sort of copper color needs Crown 45 flux(brass and Bronze) The favorite of heating and cooling copper/copper
Crown Sil-Cop 5 Crown 45 flux
Crown Sil-Cop 15 Crown 45 flux
There are others and other brands, the flux is a branded generic type flux temperature range is 1,000'F to 1,600'F #45white   the #45black is a higher temp flux.

Hope this helps I will try to answer an more questions you have.

[Jasonb]

I would think that MAPP gas would only work on small parts as the brazing rods have a melting point around 900 deg C and you need to get the base metal upto this temp for a good bond.

My Uncle was a cycle frame builder, I have one of his fillet brazed mountain bike frames. This method of brazing with a bronze based filler and usually oxy-acet gas is often used on cycle frames where a large fillet of the bronze is built up and then filed/sanded into smooth contours, it also helps spread the stresses over a larger area of teh tube than welding and can be used for any frame geometry without relying on available lugs.

Jason

[PTsideshow]

Something that I forgot to clarify, The Letters FC are Flux coated rod. Generally it is better and easier to control the amount of flux if you put it on the joint. The Flux coated rods are covered and deposit way to much glass like slag on the join that requires clean or removal.

Since some recommend scraping some of the flux off the rod before use. I prefer to use the un coated or bare rod.

Also since this a capillary action process, the size of the pieces being put together make little difference. as long as the area can be heated to the flow or liquidus point. For the capillary action to take place.

I would think that MAPP gas would only work on small parts as the brazing rods have a melting point around 900 deg C and you need to get the base metal upto this temp for a good bond.

My Uncle was a cycle frame builder, I have one of his fillet brazed mountain bike frames. This method of brazing with a bronze based filler and usually oxy-acet gas is often used on cycle frames where a large fillet of the bronze is built up and then filed/sanded into smooth contours, it also helps spread the stresses over a larger area of teh tube than welding and can be used for any frame geometry without relying on available lugs.

Jason

What you are describing is Braze welding  a different process that uses the higher temps to build up the fillet at the joints and doesn't relies, on capillary action to bond the parts together. Braze welding doesn't melt the base metals there fore it has less distortion.
Also due to the lower temperatures involved and the fact that only a small section of the part is brought up to brazing temperature. Instead of the whole thing at once.

You also can have the filler metal/fluxes preformed in any shape as a ring washer or gasket. then it can be brazed by any number of processes. There is Dip brazing, Furnace, brazing,Induction brazing, Infrared brazing, Resistance brazing.

Of course the 2 biggest drawbacks to it are the often times lack of a color match. And it isn't as strong as fusion welding.

Here is the spec's for Bernz-o-matic MAPP
MG9 - 16.92 oz. Fat Boy Max Power Propylene Fuel Cylinder  (MG9)

    * Ideal for medium to heavy soldering and brazing
    * Flame temperature in air = 3600 F
    * 20% more fuel (than standard 14.1 oz cylinders)
    * Recyclable
    * Lower profile

Flame temps in air for the fuel gas no oxygen other than natural occurring:
Butane     3,200'F
Propane    3,450'F
MAPP        3,650'F
Acetylene  4,350'F

Now these are close to the actual temps as equipment and sources can agree on, as ten books with give 10 different temps or vary by 5 to 50'f.

brazing rod selection here is the brazing rods specs and selections

They are available for feeling touchy at your local Home Despot or Highes here in the states

[Jasonb]

What you are describing is Braze welding  a different process that uses the higher temps to build up the fillet at the joints and doesn't relies, on capillary action to bond the parts together.

This is the process used on bike & cycle frames that Brass machine is asking about, usually refered to as fillet brazing. This is not the silver solder (silverbraze) that is used on lugged frames where the filler is drawn into the joint by capillary acton but a process of building up a large fillet.



I've made the mistake of picking up a brazing rod and not been able to melt it with propane so thats why MAPP is unlikely to work on all but the smallest bits of metal as the heat sink effect will be too high. I don't have oxy-acet but use these higher temp rods with a carbon arc setup on a stick welder which gives a temp of 6500F

Jason

[Bernd]

Wow Jason, those are very nice fillets. Lots of work in them.

Bernd

[PTsideshow]

Yes that is a text book picture of  Braze weld on the frame you have shown after finishing. Whether it is a lugless frame or any other item. The layering or build up of the filler metal and then smoothing it down.
There are a number of torches that can Braze weld that use an AIR/Fuel gas mixture. and yes it is easy or at least faster to use oxy/fuel torches. But with the new torches, Like the ones on the web site, I linked to or others that are being sold currently.

[Darren]

Very nice work there Jason, was that yours?

[Brass_Machine]

Thanks Glen & Jason!

Appreciate all the info. Was thinking of making a tricycle for the kid

Eric

[Jasonb]

No Not my work, but the main "castings" on the hit & miss in my Avitar were all fabricated like that, the bronze filler is easily smoothed out to look like the internal fillets you find on castings.

Brassmachine, if you put "fillet brazing" into google you should get some info. Also have a look at this thread on one of the woodworking forums I use, one of the guys went on a course to learn how to build a frame, build starts on teh second page.

Jason

[tel]

I don't think MAPP gas would be up to it - and even if it could do it there would be nothing in hand. Far better to go for O/A from the outset. And, yes - plain rods, warmed and dipped in the container of flux powder as needed.

For the process to work properly you need to get the temp up to the point where the surface of the parent metal is almost at the point of becoming molten, then dabble your rod into the hot spot and work yur way around with torch and rod, re-dipping in the flux as needed. Takes a little practise, but quite easy once you get the hang of it.