Brazing Questions

[macdad-]

Hey everyone,

I'm still relatively new to robotics, and have already built several wooden bases for my first(Yet to be completed line-follower). But I have gotten into metal working and specifically Brazing. I've already gotten a propane torch and some bare metal(Zinc Plated Steel, and some Aluminum Sheeting) and about to actually get started on doing the basics. I have some Acid Core Solder, would that work for the filler metal or would I have to get some legit Brazing Wire?

Thanks

[waltr]

You can solder with a propane torch but to braze you will need a much hotter flame.

Do some googling on soldering and brazing for background info. They are a bit different as to the materials and temperatures used.

[macdad-]

Thanks for the notice, I checked around and fortunately my torch does achieve temps. for brazing. As for the filler metal, would Acid Core Solder work or do I have to get some brazing rods?

[Soeren]

Hi,

You don't say what kind of metal is outside the acid core and that would say a lot on how well it would hold up, as there are numerous types of solder material.
For aluminum, you'll need special solder (and flux) though.

I have done my fair share of brazing with a propane torch, with both silver and bronze material and you can't really compare it to solder, although, with the right solder and the right technique, you can make very solid work.

Brazing is still much stronger and for a robot that will rumble around, you need that strength, unless you combine solder and other means, like rivets, bolts or similar.

[macdad-]

The acid core solder is Silver bearing(not Rosin Core), does that sound about right?

[vinito]

There are tons of different solders out there. Much more than even the varieties you can choose from for electrical work.

Technically, true "silver soldering" is actually brazing because of the temperature it takes. From there, things can be added to make it stronger or melt lower. Some structural (as opposed to electrical) lead solders add silver to make it somewhat stronger but will still melt low enough to use propane. Typically "brazing" is done with brass filler rod and it takes a pretty high temp to do it, so you need acetylene. Silver is a bit less but acetylene still works much better. Once you get into blends of silver & lead, it could be almost anything. If what you have was sold to be "silver-bearing" and work with propane, it will be some stronger than typical plumbing solder. Actually they sell silver-bearing solder for plumbing too.

Anyway, without knowing the exact type of solder you have, advice is difficult to give.

I can tell you that zinc-plated steel will be almost impossible to braze to aluminum. You would need some kind of special type of rod for that to work, and it may exist but prolly be a little hard to find.
Also, if you have "zinc-plated" steel, are you talking about galvanized? If so, DO NOT attempt to solder it - galvanized coatings will burn off and give a very noxious gas that can and will make you very sick. At best, you will smell it in your nose for a week.

If you want to do some brazing or silver soldering or whatever you want to call it, practice with something else and see what you can do. Just use the silver-bearing stuff you have and figure out its particular mojo. Maybe use some "wire hanger" wire, nuts, bolts & washers (NON galvanized), silverware, the wife's jewelry - whatever. Twist a little something together, like a stick figure or something, then solder the joints together to get a feel for it. Once you get a little bit of chops (and it doesn't take all that long) you'll be able to do some functional soldering pretty quickly.

[Soeren]

Hi,

Here is some data on temperatures (Acetylene vs. propane) when oxygen is added.

[vinito]

I did know that a lot of big operations use propane rather than acetylene for cutting because (they say) it's more economical. I did not know that propane/oxygen was that hot. Good to know.

Of course the story is different with plain ambient air and in that case the hotter flame in acetylene is pretty obvious with standard equipment. But the torch type can make a difference and there are some which claim temperatures that are only 500 degrees difference or less (propane/air).
Here's another temperature chart I lifted from a site listing temps when mixed with oxygen:
    * 2200°C = 3992°F, for Propane/Oxygen
    * 2927°C = 5300°F, for MAPP Gas/Oxygen
    * 2700°C = 4892°F, for Acetylene/Oxygen
    * 3200°C = 5792°F, for Hydrogen/Oxygen

All of them overlap somewhat, so I guess the equipment you have can make a big difference.

One thing you can glean from this is if you decide to tease your hair with a couple live ferrets, dig out the mad scientist goggles, dive into the iron pile and get into torch cutting, propane is a pretty good way to go. The tanks are much cheaper and propane is safer than Acetylene in some ways. Though either is capable of major damage to property and flesh in the case of an accident, so be careful no matter what you do.
I guess that's true of the humble soldering iron too.

edit: because I realized that it wasn't showing temperature ranges, but C to F conversions. Doh!

[macdad-]

This is the kind of 'Acid Core Solder' I have, it is designed for metal working:
http://www.homedepot.com/Building-Materials-Plumbing-Torches-Soldering-Irons/BernzOmatic/h_d1/N-5yc1vZ1xg1Zark2Z2cz/R-100494076/h_d2/ProductDisplay?langId=-1&storeId=10051&catalogId=10053

I tested this with my torch and it did melt.

Thank you both for the head ups about this, it helps to know that propane can be used for cutting.
So long, Hack Saw

[MikeK]

I have the same solder and I've used it to braze together two pieces of steel.  Didn't try hammering them apart, but pliers on each piece and all my strength couldn't separate them.  Definitely use flux.

[Brandon121233]

Brazing Aluminum is quite difficult for several reasons. It melts at a relatively low temperature, any kind of brazing rod you get for it is going to melt at a temp rather close to that of the aluminum you plan on brazing, and there is no good way of telling how hot the aluminum is getting since it doesnt really glow at different colors based on its temp. Finally unless you know an insane amount about heat treating AL and have a basement full of precise annealing kilns, you will never achieve the same strength that the aluminum had before you heated it up for brazing. In summary there are many more ways I would join two pieces of aluminum waaayyyyy before I would braze them, or just use a different kind of material all together.

[macdad-]

Thanks for the heads up, yea I'll more or less stick with zinc plated steel for my metalllic robot bases/etc. Aluminum is not worth it.