tecnovist

Forge weld flux

525 posts in this topic

Lou, check the local Ace Hardware, True Value Hardware and Dollar General stores in your area.  Often they carry the 20 Mule Team Borax.

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Better still, check with the local welding supply for a can of powdered . . . Welding flux. The same basic mix is used for torch: brazing, hard soldering, etc. welding: cast iron, stainless steel, aluminum, brass bronze, etc. I picked up a 1lb. can at Aire Liquide once I read the list of ingredients on the can. Borax, boric acid and some proprietary ingredient that turns it blue. I didn't get the high temp version with the powdered iron oxide in it. I use flux to keep the oxides out of my welds, not include them.

Frosty The Lucky.

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Note that Roach Prufe sold at Ace Hardware in the USA is 99% Boric Acid,  So a Box of 20 mule team and a can of roach prufe and I'm set to mix my own.

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dang Thomas....I don't have roaches in my shop, so never would of thougt of that......:unsure:

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I found I could buy a pound of R-P for less than a couple of ounces of USP boric acid at the pharmacy; the steel didn't complain about it not being USP.

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I pick up boric acid, a.k.a. orthoboric acid, at Lowes; "HOTSHOT ROACH KILLING POWDER". It's  $4.25 for 16 ozs. Label states 99% orthoboric acid, as does on-line MSDS,. The MSDS does not state what the remaining 1% is. 

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This may have been said in the 10 years this thread has been up. But what I do is I put borox in between the joints before I fit them together. This way it doesn't foam up and off and instead forms a nice even layer. I see very little sense in trying to force the flux into a tiny crack when it should be there in the first place.

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4 hours ago, Iron Poet said:

This may have been said in the 10 years this thread has been up. But what I do is I put borox in between the joints before I fit them together. This way it doesn't foam up and off and instead forms a nice even layer. I see very little sense in trying to force the flux into a tiny crack when it should be there in the first place.

I believe I've said pretty much just that every one of those 10 years except maybe for a time when my brain wasn't working so well say '09-'12.

Frosty The Lucky.

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That's true, but don't discount the ability of capillary action to pull melted flux into that tiny crack.

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Just quickly, as I guess this has been done to death, is borax from the hardware store, Bunnings here in Western Australia ok for welding flux, or am I best getting it from a Blacksmith Supplier? 

 

cheers 

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Hey, there! Quick pro tip: it's very easy to find what you're looking for if you go to the search engine of your choice, type in "iforgeiron.com" and whatever other keywords are relevant, and hit <enter>. I just did that on Google with "borax" and "Bunnings", and the fourth response speaks directly to your question. Give it a try!

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I use plain borax from a grocery store and mix in some roach powder that is 99% boric acid (generally I use around 3 borax to 1 boric acid)

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What is the advantage of adding boric acid that the straight borax won't do?

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Tends to make it work better on modern alloys---though for high chromium or nickel alloys you may need a still stronger flux than for regular steels.

However: I feel a lot of what flux does is to provide confidence to the smith, much like Dumbo's Magic Feather...

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OK, thanks for the explanation.  I had heard some folks use boric acid in flux but never heard the reason.

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A lot of the lower grade modern steels, like A-36 a common steel in ornamental smithing, may have more tramp elements in them as they are all re-melt steels rather than steels made directly from ore. This can cause problems when forge welding and so every little bit helps. Boric acid melts at a lower temp than borax does and so helps shield the joint from Oxygen sooner.

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Some fluxes (like the Alaska flux  described elsewhere in the forum) also include a carbon source (like powdered charcoal) to scavenge oxygen from inside the joint as it comes up to welding heat.

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22 minutes ago, ThomasPowers said:

A lot of the lower grade modern steels, like A-36 a common steel in ornamental smithing, may have more tramp elements in them as they are all re-melt steels rather than steels made directly from ore. This can cause problems when forge welding and so every little bit helps. Boric acid melts at a lower temp than borax does and so helps shield the joint from Oxygen sooner.

Well, I'm gonna get some boric acid and give it a try.  Maybe it will help in my forge welding...aside from needing more practice!!!

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What you want to look for is anhydrous borax, that is borax with the moisture taken out. 

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What I like about adding boric acid is it's lower melting temperature and good wetting properties, it seals the joint surfaces off from air sooner. Laundry borax foams around 212f and doesn't wet as well nor as smoothly as anhydrous borax. 

Teenylittlemetalguy is still tinkering with his Alaska Flux. It hardly takes any charcoal at all to make it work.

I found that the dry powder welding, brazing flux at the welding supply works s well as any of the fluxes made for "forge welding". Read the ingredients on the can, if it has borax and boric acid it'll work a treat and cost you a LOT less than a "real" forge welding flux. I've been using Peterson Blue.

Frosty The Lucky.

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21 hours ago, ede said:

What you want to look for is anhydrous borax, that is borax with the moisture taken out. 

I mistakenly thought the same thing till a chemist corrected me on another forum..     While partially true  there is still water in it.. It has to do with the molecular quantity of water and is what the chemist looks for..

  

The term borax is often used for a number of closely related minerals or chemical compounds that differ in their crystal water content:

  • Anhydrous borax (Na2B4O7)
  • Borax pentahydrate (Na2B4O7·5H2O)
  • Borax decahydrate (Na2B4O7·10H2O)

Borax is generally described as Na2B4O7·10H2O. However, it is better formulated as Na2[B4O5(OH)4]·8H2O, since borax contains the [B4O5(OH)4]2− ion. In this structure, there are two four-coordinate boron atoms (two BO4 tetrahedra) and two three-coordinate boron atoms (two BO3 triangles).

Borax is also easily converted to boric acid and other borates, which have many applications. Its reaction with hydrochloric acid to form boric acid is:

Na2B4O7·10H2O + 2 HCl → 4 H3BO3 + 2 NaCl + 5 H2O

The "decahydrate" is sufficiently stable to find use as a primary standard for acid base titrimetry.[9]

When borax is added to a flame, it produces a yellow green color.[10] Borax is not used for this purpose in fireworks due to the overwhelming yellow color of sodium. Boric acid is used to color methanol flames a transparent green.

 

I personally bought or I should say was given 80lbs back in the 80's..  I still have 1.5 5gallon pails full of the stuff..    I actually boil mine, let it harden and then grind it all back up..  

I prefer this 100% more than 20 mule team or the un boiled stuff I have.. When I boil it it transforms into a smaller quantity.. Takes about 1.25-1 and basically I do this in an iron rich pot..  It actually makes it turn a green color..  Anyhow, It will melt at a slightly lower temperature and it covers extremely well..  Watch the lastest video "How to" on hinge pintel making and I show a picture with the flux being applied..  It covers completely and I started doing this back in the early 90's.. Whether it's voodoo or not I can't say.. 

I can say I will continue as the results I get are better and more in line with what I want.. 

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Anhydrous in this context refers to driving off the "Hygroscopic" moisture and is not molecularly bound. It's in compound like the water in set concrete. Heated above 212f  the moisture boils and the borax foams. Let it cool from 212 and it sets like concrete but isn't glassy as it hasn't melted it actually went into solution. This is why laundry borax isn't quite as good a flux as anhydrous while it foams it doesn't "wet" the steel so it doesn't form an airproof barrier till it gets much hotter.

Heat laundry borax to 230f. and the hygroscopic moisture is driven off leaving no moisture in "Compound" with the borax. Molecular H2O is still present, our forges don't get nearly hot enough to break the borax molecules apart.

Anhydrous borax has no moisture to boil so it doesn't foam and when heated enough melts. Molten borax is VERY sticky fluid but also both thick and a strong penetrant. I don't recall the term but in a liquid state it spreads till it coats everything in a layer of even thickness, seeping into the smallest voids. Capillarity acts very strongly on molten borax or dusting it on the outside of a billet wouldn't penetrate to the center. 

Molten borax is also pretty caustic which aids iron reduction, helps break down rust into iron and O2. Being caustic is also what allows it to dissolve silicates like fire brick and refractories like Kaowool.

Before anybody starts quoting me I have to fess. I hardly know any chemistry so I can't tell anybody WHY molten borax helps reduce iron. Nor do I understand the various types of borax, how and why they differ. Borax is a salt or so I've been told so mixing a strong base like borax with boric ACID for some reason I don't understand doesn't make another salt.

What I do have a handle on are: hydrous, hydrophillic, hydrophobic, anhydrous, hygroscopic, and such. I had to learn what they are and properties to perform the soils tests we did in the materials lab.

Here's a simple trick that makes keeping your welding flux prime without having to buy anhydrous borax. Keep some borax in a steel or iron ladle or cup by the forge, when you want to weld put it in the fire and melt it, use something like a honey dipper thingy, to dip it and apply it to the weld. Be aware the first time you melt it it's going to foam like crazy till it's anhydrous. Once it's melted it won't foam again when you melt it again. It'll cool like a piece of glass forget trying to chip or crush a little and use it that way. 

And those are your how Frosty does it tips for this afternoon. :huh:

Frosty The Lucky.

 

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43 minutes ago, Frosty said:

Anhydrous in this context refers to driving off the "Hygroscopic" moisture and is not molecularly bound. It's in compound like the water in set concrete. Heated above 212f  the moisture boils and the borax foams. Let it cool from 212 and it sets like concrete but isn't glassy as it hasn't melted it actually went into solution. This is why laundry borax isn't quite as good a flux as anhydrous while it foams it doesn't "wet" the steel so it doesn't form an airproof barrier till it gets much hotter.

Heat laundry borax to 230f. and the hygroscopic moisture is driven off leaving no moisture in "Compound" with the borax. Molecular H2O is still present, our forges don't get nearly hot enough to break the borax molecules apart.

Anhydrous borax has no moisture to boil so it doesn't foam and when heated enough melts. Molten borax is VERY sticky fluid but also both thick and a strong penetrant. I don't recall the term but in a liquid state it spreads till it coats everything in a layer of even thickness, seeping into the smallest voids. Capillarity acts very strongly on molten borax or dusting it on the outside of a billet wouldn't penetrate to the center. 

Molten borax is also pretty caustic which aids iron reduction, helps break down rust into iron and O2. Being caustic is also what allows it to dissolve silicates like fire brick and refractories like Kaowool.

Before anybody starts quoting me I have to fess. I hardly know any chemistry so I can't tell anybody WHY molten borax helps reduce iron. Nor do I understand the various types of borax, how and why they differ. Borax is a salt or so I've been told so mixing a strong base like borax with boric ACID for some reason I don't understand doesn't make another salt.

 

Frosty The Lucky.

 

I got my butt chewed for this same argument..      Wow, if you need to melt the borax everytime you have to use it..   I just let it cool in the pan, bang the back. The flakes come off, and I have a special crusher i use to crush it all back up.. Works mint.. 

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1 hour ago, jlpservicesinc said:

I got my butt chewed for this same argument..      Wow, if you need to melt the borax everytime you have to use it..   I just let it cool in the pan, bang the back. The flakes come off, and I have a special crusher i use to crush it all back up.. Works mint.. 

Uh huh. I picked up a $5.00 hobby rock tumbler at a yard sale, melted the borax and boric acid in a silicone cake pan so it breaks into manageable size pieces easy when it cools. Toss it in the tumbler with a handful of ball bearings and forget it for a while, 

I gave the tumbler to Tristan, AKA Teenylittlemetalguy to do a proper job of milling his Alaska Flux.

The keep some melted and handy was an old experiment that worked surprisingly well and is budget friendly. :)

Frosty The Lucky.

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