Talk:Flux (metallurgy)

Steel welding
what about steel welding? &mdash;The preceding unsigned comment was added by 66.69.253.41 (talk &bull; contribs).

"Flux" referring to a solvent for corundum
The term "flux" also refers to cryolite used to dissolve corundum for aluminum smelting and growth of synthetic ruby and sapphire. The books I'd seen have suggested that the term is used this way outside of aluminum smelting, but didn't quote any references for that. While this is touched on in the existing text, it would be nice if a Chemical or Metallurgical Engineer with appropriate specialities could expand on it. --Christopher Thomas 05:42, 1 December 2005 (UTC)


 * Here's a link that discusses the flux-growth method for synthetic gemstones (from ; it appears to be course notes for a chemistry course). Googling for "flux growth" gives about 10 million links to papers and pages discussing use of the technique.


 * I'll write a section about this in the article eventually (still nominally on sabbatical), and I'll dig up my old encyclopedia of gemstones as a proper book reference when I do get around to it (it gave an overview of several popular techniques for crystal growth, of which flux growth was one). --Christopher Thomas 22:42, 1 April 2006 (UTC)

First two sentences
"In metaland borax, for brazing.

I had a problem with the grammar and changed it to:

"In metallurgy, flux is a substats chemical action facilitates soldering or brazing of metals. Some common fluxes are ammonium chloride or rosin, for soldering tin; hydrochloric acid and zinc chloride for galvanized iron and other zinc surfaces; ::Fair enough. I've ammended my edit and left out the mention of melting point. The rest if the article also makes for difficult reading and, in my view, is not technically correct. I'll change it with references given time. --Tatty 10:02, 16 February 2006 (UTC)


 * it now reads "In metallurgy, flux is a substance which facilitates soldering, brazing, and welding by chemically cleaning the metals to be joined."  But this to me is not technically correct.  In my opinion, the use of the word "cleaning" is the standard jargon, but I think it reveals a lack of understanding of the actual process.

A flux lowers melting points. See Ceramic flux where the same process going on. A lower melting point is caused by a eutectic substance (i.e. the flux plus that upon which the flux is used has a lower melting point than either the flux or the substance would have separately. See Eutectic point.  Because there is a lower melting point, certain oxides and or in the case of ceramics/glass (certain crystalline structures - partially true with steel too) do not form and/or by process of diffusion impurities are removed (I think usually vaporized).  I think this is where the "cleaning" idea comes from: the idea that oxides are being removed -- but the process, I think is really the creation of eutectic substances hence we say that the coating of oxides, that would otherwise prevent or inhibit complete melting at temperatures commonly used in brazing, welding and soldering, are "dissolved".

My experience is that mostly only those who understand the chemistry involved in ceramics and glass understand actually what is happening chemically with flux in brazing, welding, soldering. So you get terms like "cleaning".

Of course, I could be wrong. 70.22.66.212 (talk) 17:00, 14 March 2008 (UTC)

Brazing links
I noticed that the external links (to jm-metaljoining.com) in the references on "Brazing" had become quite difficult to follow -- the content is in a small frame, poorly organized (imho) and difficult to follow. I left one of the two original links (hopefully the more useful one) and added two others which might provide more useful information. Feel free to change stuff back if the wording changes introduced errors; I'm a chemist but not a fluxing expert. /Jaeger5432 15:47, 28 August 2006 (UTC)

Introduction -> wetting ?
Iepeulas changed the introduction from:

''In high-temperature metal joining processes (welding, brazing and soldering), the primary purpose of flux is to prevent oxidation of the base and filler materials. Tin-lead solder (e.g.) attaches very well to copper, but poorly to the various oxides of copper, which form quickly at soldering temperatures. Flux is a substance which is nearly inert at room temperature, but which becomes strongly reducing at elevated temperatures, preventing the formation of metal oxides. Secondarily, flux acts as a wetting agent in soldering and brazing processes.''

to

''In high-temperature metal joining processes (welding, brazing and soldering), the primary purpose of flux is to remove oxides from the metal surface and prevent oxidation of the base and filler materials. Tin-lead solder (e.g.) easily wets copper, but does not wet oxides of copper, which form quickly at soldering temperatures. Fluxes dissolve metal oxides and often provide a reducing atmosphere at elevated temperatures, preventing the further oxidation of the base material. The clean, activated metal surface is easily wetted by the molten solder or brazing alloy.''

I think this new explanation is not clear at all. When I read it, I do not really understand what flux does. This is mainly because the term 'wetting' is used, although it is not at all clear what this is. The introduction should be relatively easy to understand and use as little jargon as possible. Therefore, I suggest going back to the original explanation. —The preceding unsigned comment was added by Rabarberski (talk • contribs) 11:03, 17 January 2007 (UTC).

As a layman here I strongly agree. In addition, it sounds to me as though "wetting" has some specific definition or aspect that differs from just "making wet."

Gruber76 02:55, 16 March 2007 (UTC)

I'd guess wetting agent means the same in this context as it does when dealing with water: A wetting agent in a detergent seeks to reduce surface tension of water so that it will encapsulate dirt particles--In metallurgical context a wetting agent in flux serves to prevent the solder from beading on the working piece rather than flowing into the joint as one wants. Same fundamental idea, just sounds odd when we're talking about liquid metal.-MalkavianX 17:21, 2 September 2007 (UTC)

I agree completely with the comment above. When solder "wets" a metal surface is it obvious to anyone who observes the phenomenon that the term is perfectly appropriate. The angle of contact increases dramatically, and the visual effect is exactly like that which occurs when water wets a hydrophylic surface. Conversely, when solder "beads" on a surface is is clear that a proper soldered joint has not been achieved. This is commonly termed a "dry joint", and is electrically and mechanically unsound. The terms "wet" and "dry" and "bead" in this context are examples of the delightful tendency of engineers to recruit common words and incorporate them appropriately into their specialist jargon (c.f. "nut", "nipple", "male" and "female" parts, etc). In this respect they stand at the opposite pole from the medical profession, which systematically replaces common words with incomprehensible ones so as to exclude the layman.

List
A list of fluxes would surely be useful. True that such lists can be a bit open ended, but there are only so many in use.


 * beeswax
 * tallow
 * paraffin
 * palm oil
 * zinc chloride (aka killed spirits)
 * zinc chloride & sal ammoniac
 * olive oil & sal ammoniac, 50/50, for iron
 * rosin, tallow, olive oil, zinc chloride: for aluminium
 * cryolite
 * cryolite & phosphoric acid
 * phosphoric acid & alchohol
 * cryolite & barium chloride
 * oleic acid
 * MgCl, NaCl, KCl.

well, its a start. Tabby (talk) 04:55, 28 December 2007 (UTC)

Flux as a heat ttransfer medium
The sixth paragraph contains the following statement: "In some applications molten flux also serves as a heat transfer medium, facilitating heating of the joint by the soldering tool or molten solder". I may be looking at this from just an electronics soldering point of view, but the fluxes we use are mostly alcohol with organic flux solids both of which have poor thermal conductivity. It may appear that it transfers heat because it has removed the oxides which were preventing good heat transfer. In truth, the alcohol flases off almost instantly, and the remaining flux solids are not much better than the oxides for thermal conductivity. The molten solder between the soldering iron tip and the items being soldered (heat bridge/solder bridge) greatly increases the surface contact area allow for faster heat transfer. — Preceding unsigned comment added by 69.73.17.2 (talk) 18:32, 12 September 2011 (UTC)

Halide activator content
In the section on J-STD-004, it says

"Halide content <0.05% 0 (yes) - 1 (No)"

But this is ambiguous. Does it mean "0" does contain halides, or not?

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Carbonate of Soda
I hope this is the right place to discuss this, since my edit was reverted. I think that „carbonate of Soda“ is 1. redundant (Soda is already sodium carbonate) and 2. not fitting of modern American English. I changed it to „sodium carbonate“ which was reverted, reasoning that words such as potash and borax indicate that IUPAC names such as sodium carbonate are not appropriate. I am not a metalworker so I can’t say if they use the phrase „carbonate of Soda“ in their professional vocabulary. I doubt they do.

As a compromise I would simply write „Soda“ — Preceding unsigned comment added by Kjfalf (talk • contribs) 09:37, 4 December 2020 (UTC)

List of fluxes
This part of article has multiple problems and its contents are much more thoroughly described in the section above. I suggest that we either remove this section or move it to an upper position in the article as an overview for readers who don't want to spend too much time learning about all the specific usages of fluxes. Pygos (talk) 09:48, 14 May 2024 (UTC)