[wilmayo]

I am a homeowner and I have found that when I need to repair something or make something with steel, I can usually get the job done with a brazing rod and MAPP torch. Most of my work is light duty with thin material and flux coated bronze rods (like those from Bernzomatic) usually do the job. Occasionally, I run into a situation where the MAPP torch is not quite hot enough to melt the bronze. In those cases, I have used a high silver content filler like 45% or 56%. I would like to find a good balance between cost and strength and I'm wondering if going to a 25% or 30% silver content would sacrifice much strength. Also, I read that 25% and 30% do not flow as readily and are better for "less than perfect" fitting joints. This would suit my needs well. I would appreciate any suggestions/recommendations. I have thought about and considered a small oxy/acetylene system and just can't justify the cost for what I do.
Thanks

[LtBadd]

Look HERE and download the Guide to Brazing and Soldering, and Filler Metal Selection Guide. These are located on the right hand side under Common Resources

[wilmayo]

LtBadd, Thanks for the link. i have seen that information. My problem is it doesn't address the relative strength of the various alloys. I can only find that a silver brazed joint may withstand between 40 and 70,000 psi and that more silver content means more strength. So, my question is, am I sacrificing significant strength going to a lower silver content to save some money? BTW, I note that the chart you linked doesn't show any info for a silver content of 25% or 30%. I have also noted in search for sources that those two alloys are hard to find, particularly in small quantities.

[LtBadd]

My understanding is, in a brazed joint the strength comes from the design of the joint, not sure that more filler = strength because you really need very a tight fit up to achieve the strongest joint.

Harris has a tech support line you can call and talk with someone who could better answer your specific question, I would encourage you to do that.

[wilmayo]

OK. Thanks.

[Poland308]

You will have a hard time getting any silver braze rod below 45% to work reliably on steel. 45% also works well for SS.

[Arno]

My understanding is, in a brazed joint the strength comes from the design of the joint, not sure that more filler = strength because you really need very a tight fit up to achieve the strongest joint.

Yup.. Like bonded/glue joints a brazed connection, esp. with a silver based braze works best when you can design/use connections that maximise the surface area between the materials. Eg. overlap sheet material and use the overlap area itself to connect them. Butt-joints tend to not work very well strength-wise when brazing as the surface/contact area connecting the two parts is very small.

A tight fitup between surfaces will allow the braze (with the proper flux) to wick between the surfaces and as a result spread the load across a bigger surface area resulting in a very strong bond. Something that you'd need something like friction-welding to replicate with a welding process in many cases.

Also, like glued/bonded connections, braze joints can be affected by failure because of 'peeling' where the load is put on a 90-degree or more angle to the joint and as the name implies it start to pull open the connection like peeling away a sticker. Try to avoid that in designs or add some form of mechanical fastener (rivet, bolt, etc.) to stop the peeling effect from starting.

Bye, Arno.

[wilmayo]

Poland308, Thanks. I have noted that there are few sources available on the net for silver content below 45. I will just stick to that and try to find the best buy I can as I need it.
Arno, Good info. Thanks. Most of what I do doesn't require a huge amount of strength. But, I'll certainly do my best to make the tightest fit I can. I did a lap joint with two pieces of 1/8" using 45%. It gets a shear load and is holding so far.