Well just like the title says. I would like to start experimenting with doing simple welds and what not as I learn more about forging but also dont want to destroy my forge. It is a propane tank home built guy lined with wool, satanite and itc100.

I have scene the Zweld stuff that you can get from blacksmithdepot which is suppose to be good for gas forges but it is expensive. Compared to regular welding borax. I have also heard but not sure that it isnt so much the borax that is bad for the forges but the moisture that is in it.

Still a newb and a search didnt really yield the answers I was looking for.

Thanks all.

Naw, it's the borax that eats common refractories. Any silicate based refractory is vulnerable to caustics and molten borax is darned caustic. The ITC 100 is really helps protect the liner though, it's zirconia flour and kaolin. Kaolin (porcelain) is a high alumina refractory and caustic resistant.

The flux I use in my gas forge is 1pt boric acid (roach pruf) to 4 pts borax. It's a little more aggressive than plain borax and works well enough for me.

Frosty The Lucky.

I'm no expert, but I think it might be helpful to take a step back and think about what you use flux for.

As I understand it, an important property of flux is its ability to dissolve the metal oxides that would otherwise contaminate the weld, and transport them away from the weld in solution.

Because the refractories used in most gas forges are made from metal oxides, any effective flux will give them a very hard time.

I think (but I don't know for sure) that the biggest problem with the insulating refractories is the low density and large surface area, which combine to make them dissolve very fast. From my limited experience, both Alumina blanket and Zirconia blanket dissolve very quickly in contact with hot borax. Type 23 IFBs are slower and dense fire bricks are slower still.

A hard refractory coating applied to the surface should give the advantage of slow attack, combined with good insulation.

The water content of the Borax is inconsequential in terms of how it reacts with the lining, because all the water has boiled off by the time it's molten.

Where the water content makes a difference is in how easy it is to keep it on the work.

Borax comes as Decahydrate, Pentahydrate and Anhydrous types. Decahydrate has 10 molecules of water associated with each borax molecule, Pentahydrate has 5 and Anhydrous has none. When you apply the borax, the water boils off as the borax melts. As it boils off, the water makes the borax froth and some will inevitably fall off.

Ideally, you'd use Anhydrous borax. Next best is Pentahydrate, with the frothiest being the Decahydrate.

The most common is the Decahydrate (mule team, etc). This can fairly easily be cooked in a domestic oven to drive off some of the water and get it to the Pentahydrate. To really finish the job and make it anhydrous needs bringing it up to melting, letting it cool and pulverizing the glassy mass that results.

The Pentahydrate is easy. Anhydrous is more hassle and not without risk.

Thanks Timgunn thats alot of good info. Now I am curious why they say the Zweld is so much better to use in gas forges. The sodium tetraborhate which is I thought another name for borax (not sure of the difference will have to look it up) that makes up 99% of whatever is in it. So essentially they are just different forms of borax.

Ill have to do some more research. Thanks guys.

You are right; Borax is just the common name for Sodium Tetraborate.

One of your interest seems to be protecting your forge along with forge welding. There are posts on IFI about using kerosene. I tried it, it works at least for black iron, don’t know about any other types of metal. I usually clean the metal in muriatic acid, then wash the metal with water, then dry it and soak in kerosene. It is necessary to keep the pieces stable as it tends to slip more than when using borax. At least that is my limited experience.

Thanks Timgunn thats alot of good info. Now I am curious why they say the Zweld is so much better to use in gas forges. The sodium tetraborhate which is I thought another name for borax (not sure of the difference will have to look it up) that makes up 99% of whatever is in it. So essentially they are just different forms of borax.

Ill have to do some more research. Thanks guys.

they WHO? if you traced it down I bet THEY = the people trying to sell it to you... cant imagine why they would do that :rolleyes:

There are lots of different flux compositions, but I can't find anything on "zweld" online.

A flux that's primarily anhydrous Borax would obviously give the advantages of anhydrous borax, so would probably be noticeably "better" to use than either the pentahydrate or the readily available decahydrate. I'd certainly expect anyone comparing it to 20-Mule Team borax (the decahydrate) to notice a difference.

Anhydrous doesn't foam when it reaches 212f and is only a problem if you aren't afixing small pieces before taking a heat. On the occasions I actually need foam free flux I just melt some borax in a small iron ladle I have and dip a bit.

Frosty The Lucky.

So anhydrous is a problem when you are not affixing smaller pieces? I had some trouble with anhydrous on a lap weld recently. It clumped and did not spread, and the metal wasted away without sticking. The 20 mule foamed and spread well. Strange, others seem to do fine with it.

What about the Iron Mountain Flux? From what I've seen on youtube that stuff seems to be the cats whiskers of flux's

Why not just make a little metal pan to shield the bottom of the forge?