Forge weld flux

[Akad]

So in general one should use ash as a flux at higher temps, and borax for lower temps?

[pkrankow]

Wood ash contains Calcium carbonate (CaCO3) which melts (decomposes) at 895C or 1643F, soda ash, or sodium carbonate (Na2CO3) which melts at 851C or 1564F and Pot ash or Potassium Carbonate (K2CO3) which melts (decomposes) at 891C or 1635F. The melting points are higher but in a similar range as borax (Na2B4O7) which melts at 743C or 1369F.

The boiling points are 1600C and 1575C for soda ash and 2912F and 2867F for borax. Pot ash and calcium carbonate decompose instead of properly melting. The boiling points for borax and soda ash are well above the melting point of iron, 1537C or 2800F.

For forge welding, it seems that wood ash would not wet out the surface to aid in removing and prevent formation of scale.

Soda ash, washing soda, Sodium Carbonate (Na2CO3) seems like it would work as a forge welding flux, but the msds reads as rather unpleasant affecting lungs and eyes. Soda ash is not rated significantly more hazardous than borax on the MSDS I have found.

Yes, I had to look all this up, you got me thinking. I have not found a reference to wood ash being used as flux, but Calcium carbonate, sodium carbonate and Potassium Carbonate are all used as ingredients in the flux coatings on some arc welding rods. I have not found a reference for wood ash as a forge welding flux.

Much of my information came from Wikipedia and from various MSDS sheets. If a chemist has better information please post it. I am not a chemist.

http://www.fpl.fs.fed.us/documnts/pdf1993/misra93a.pdf discusses decomposition of wood ash as a function of temperature. This article states that wood ash seems to sinter instead of melting together.

Phil

[De St Uby]

The old blacksmiths here in Alsace ( France ) using quartz sand locally and it works very well, so although the result is really impressive.
Former German blacksmiths also used silica sand, for welding in the forge.

[ThomasPowers]

I have always felt it was the *silica* in wood ash or rice straw ash that was what was fluxing---just like using quartz sand or powdered glass.

Pkrankow---you didn't address the silica aspect at all; could you edit your post to include it as well?

And when I said that wood ash was better at high temps it was not that it was better than other fluxes at high temps but that it didn't work worth a hoot at lower temps but did seem to work some at higher temps. Sorry for the confusion!

[pkrankow]

Thomas,
I didn't address silica because it is nearly non-existent in wood ash. The highest concentrations listed in the attached document are 0.24% by weight of products burned to 600C. Some species did not even contain Si. Wood ash is primarily calcium and potassium compounds. In fact, rereading potash (Na2CO3) was not found according to the linked document, Sodium was less than .06% in most analyzed wood ashes.

Admittedly I only found one set of chemical analysis.

Potash was referenced elsewhere when I was looking, but I did start on Wikipedia.

I did not look for rice ash compounds.

Quartz sand is silica sand. Different names for the same stuff.

Phil

[ThomasPowers]

Silica content differs greatly depending on wood species; if your data does not take that into account it is suspect!

example:
"Data on ash and Silica content of 43 Mexican tropical hardwoods are presented. The highest silica portions were found inPoulsenia armata (1.0–4.7%),Dialium guianense (0.37–1.40%) andDipholis Stevensonii (0.49–0.68%)"

Silica content relatively high, ranging from 0.82 to 2.74 percent of the weight of the oven dry wood. Average silica content of the specimens

Silica content is often directly proportional to how fast a type of wood dulls cutting tools and has a high correlation on how well a fuel wood it is as silica seems to make for a longer burning wood.

[pkrankow]

North American fuel cord woods, such as oak and maple contain minimal quantities of Si, conifer species such as fir and pine contain small portions of Si. Even after high heating the sintered ash will break up and become loose and fluffy.

Wheat and rice straw and many grasses contain high amounts of Si, and when burned form a course hard ash that can melt and wet out metal as a flux.

http://www.trmiles.com/alkali/alkali.htm
I have a few other documents that read similar, but they are not as organized.

Phil

[reefera4m]

I have a soft-spot for anhydrous borax - You can convert 20-Mule Team into it by melting it down, then grinding it up into a powder again. I used to do that when I was a student with lots of time on my hands...


Watch the Borax glass, it's sharp, and use a proper crucible for the melt - even if it looks tough, an enameled steel coffee-cup will last about 10 minutes with that molten acid in it...

All you accomplish by melting it down and regrinding is eliminating the water (H20). Anhydrous borax is chemically(Na2B4O7), while Borax (the Twenty Mule Team Variety) is Na2B4O7·10H2O having ten water molecule per unit of borax. Simply heating the borax in a shallow pan in an oven at over 212 degree F for a half hour or so will accomplish the same thing - evaporate and eliminate the water. This will happen in the forge but the H20 evaporation will contribute some oxidation in the process. It best to dry the borax first. Borax readily re-asborbs water so after drying use it or store it in a sealed, moisture proof container or plan on re-drying it before each use.

[reefera4m]

I ran into a new type of flux a few weeks ago while attending a Hammer-in hosted by a ABS Journeyman bladesmith. He demonstrated making a damascus billet using a number of alternating layers of 1080 & 15N20 stacked 2 -3 inches high. He simply sprayed WD40 between the layers and heated to welding temp and press welded the layers into a 1" billet (30 ton press). His technique produced the cleanest, inclusion free weld possible. According to him the burning/evaporating WD40 eliminates all the oxygen preventing any scale from forming. If seeing is believing then I'm definitely a believer!

He cut a cross-section of the resulting 1" billet and we were all amazed at how clean and solid the interior of the billet was - simply beautiful.

[jason0012]

I have welded with table salt before, if its a stand in flux you need. I found it flows at a much higher temp than borax so the welds have to be hotter. I have also welded without flux( the parts must be hot enough for the scale to be liquid) . The weirdest welding flux I have used was clinker! ( that was on a dare)

[billd]

This has come up in other posts and I thought instead of hijacking another post I would start this. I can't believe that with all the interest in Japanese smiths, swords, wood working tools etc. there isn't someone out there that knows what the flux is that they use for forge welding tool steel to wrought iron. I have seen it in more than one video. It is a large grained powder. It is put either on the cold tool steel or the hot iron. The two are put together (bare handed) and seem to stick together. Then the item is brought to welding temp and welded. What is the flux?

Bill

[Ben Hartley]

I want to know too after seeing that video where they welded a face onto a hammer. Maybe it has clay in it? I'm not sure if the clay would help or hinder the flux though.

[pkrankow]

One method I am aware of is using straw ash, rice straw has a rather high level of silica and produces a sand-like ash when burned. It is hard gritty ash that will melt at forge temperatures.

Another method I am aware of is use of common wood ash. I am not aware of using water here to make a slurry that sticks, but that is possible. This is enclosed in a packet of paper and clay. At forge temperatures the wood ash decomposes, and displaces the oxygen out of the packet. The packet disintegrates in the first few hammer blows.

I have not tried either method, but other people here on IFI have used one or both.

Phil

[Mitsuwa]

The general formula is a mixture of 2 parts boric acid one part borax and one part iron oxide. The wrought iron is still glowing red
and melts the borax causing the thin tool steeel to stick to the iron.

[Richard Furrer]

The general formula is a mixture of 2 parts boric acid one part borax and one part iron oxide. The wrought iron is still glowing red
and melts the borax causing the thin tool steeel to stick to the iron.

Bill Fiorini uses a mix like that (boric acid and borax) and he has done quite a bit of cross cultural study with smiths in Japan. I have seen a few Japanese smith demonstrations in the US and they have used borax.
I did some experiments almost 18-20 years ago now where I use straw ash...it worked, but the welding temps were very high.

Ric

[Alec.S]

" laffite plate" ......that is one thing that can be used...
I don't know where to get it though...(i read it in a book)... does anyone know where to get it????

my 2 cents



alec :D

[Mitsuwa]

" laffite plate" ......that is one thing that can be used...
I don't know where to get it though...(i read it in a book)... does anyone know where to get it????

Considering Lafitte plate was something available for industrial use 105 years ago, it might not be sold today, seeing how
most big chains and other fabrications are welded electrically these days. Does not seem it was ever intended for small stuff like laminating blades.

[ofafeather]

Hi, All. I have never forge welded before and have a couple of questions. First, can you use straight borax for a flux on mild steel? Second, if you successfully complete a weld and bring the stock up to welding temperature again does (should)that first weld hold? i.e. welding a series of smaller pieces onto a larger piece.

Thanks.

Eric

[ThomasPowers]

Yes and Yes. In fact the more a piece is worked at welding temp the stronger the weld should get! It's not like soldering or brazing where the material between the pieces can re-melt and let them slide. The two (or more) pieces are now *one*!

[CurlyGeorge]

Also, when you first start learning to forge weld, make sure that you TAP the weld together. DO NOT HIT IT!!. If you hit it too hard, you will blow out all of the molten metal and it won't take. When I first learned to forge weld, I had an old timer tell me to use the smallest hammer that I had. That way it's easier to just tap it lightly. Like Thomas said, if it is brought to weld heat more than once, it should just make your weld stronger by making sure that it is bonded well. All that I use for flux is plain ole 20 Mule Team Borax. :D

[ofafeather]

Yes and Yes. In fact the more a piece is worked at welding temp the stronger the weld should get! It's not like soldering or brazing where the material between the pieces can re-melt and let them slide. The two (or more) pieces are now *one*!

Thanks. That's what I thought.

In general is my understanding of forge welding correct (below)?

When preparing to weld you heat the pieces to be welded, brush them to remove scale, put the flux on and heat to welding temperature. Remove the pieces when they are at temp, do a quick brush to remove excess flux then mate the pieces starting with light to medium blows getting heavier as the stock cools.

If I am uses separate pieces of stock, say mounting a hook to a piece of flat stock, would I have enough time to use a hold down on the larger piece? Do I need to heat the anvil a bit in order to give myself more time to position the stock? Is there some other way of holding the items to be joined?

[ofafeather]

Also, when you first start learning to forge weld, make sure that you TAP the weld together. DO NOT HIT IT!!. If you hit it too hard, you will blow out all of the molten metal and it won't take. When I first learned to forge weld, I had an old timer tell me to use the smallest hammer that I had. That way it's easier to just tap it lightly. Like Thomas said, if it is brought to weld heat more than once, it should just make your weld stronger by making sure that it is bonded well. All that I use for flux is plain ole 20 Mule Team Borax.

Thanks, George. Just saw your post when I was replying to Thomas's. I think I will practice some forge welding soon so I'm happy for the input.

[ThomasPowers]

I don't remove "excess" flux, some people do.

Generally there is not enough time to rig a hold down and it's time to borrow help if you would need one.

Of course if your flat piece is 12" thick then there probably is enough time! (or to put it otherwise "it depends")

Preheating the tooling seems to help particularly in the winter

[chrisfrick]

One thing worth mentioning about the preheating of tooling: DO NOT heat excessively!! You could possibly ruin the tempering/hardness of an anvil, etc. (basically don't get it too hot to touch).

[Pat Roy]

Thanks guys, I like it when someone asks a question I need to know the answer to.