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Admanfrd

A chemical composition and heating values for common fluxes

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       Compiled by Adam Ford

 

COMPARISON

BORAX

followed by

BORIC ACID

FORMULA

Na2B4O7·10H2O

H3BO3

MOLAR MASS

381.37 g/mol

61.83 g/mol

MELTING POINT

1,369°F (743°C)

339.6°F (170.9°C)

BOILING POINT

2,867°F (1,575°C)

572°F (300°C)

DENSITY

1.73 g/cm³

1.44 g/cm³

SOLUBILITY

Water

Water

IUPAC  ID

Sodium tetraborate decahydrate

(so-dee-um tet-ra-bo-rate dec-a-hi-drate)

 

Trihydroxidoboron, Boric acid

(tri-hy-drox-ide-o-bo-ron)

 

 

DIFFERENCES

BORAX

followed by

BORIC ACID

Differences

 

FORMULA                                                                      Na2B4O7·10H2O

H3BO3

BORAX much more complex

MOLAR MASS

381.37 g/mol

61.83 g/mol

Difference

319.54 g/mol

MELTING POINT

1,369°F (743°C)

339.6°F (170.9°C)

Difference

1029.4°F (554.111°C)

BOILING POINT

2,867°F (1,575°C)

572°F (300°C)

Difference

2295°F (1257.222°C)

DENSITY

1.73 g/cm³

1.44 g/cm³

Difference

0.29 g/cm³

 

In the end, You will have to heat the metal a lot less to be able to get the metal fluxed with Boric acid.

This is JUST A REFERANCE SHEET

I am NOT ADVOCATING FOR ONE OR THE OTHER, THAT IS YOUR CHOICE

This sheet may be used as you want. Redistribution is fine by me

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Wax will melt even lower; but doesn't flux as well.  More to it than melting point.

 

Now one recipe for flux: Hrisoulas' "Metal Glue"  has a number of different items in it to deal with the various different temp actions

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I'm sure that there is another point, but i just thought someone would find this interesting. That last bit was just a conclusive statement

thanks for reading

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What we need is a guide to how active various fluxing compounds are at various temperatures---sounds like a thesis topic!  (And the arguments about how to measure "activity"...)

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Metallurgists need to contribute something here because I dont know how to measure activity other than it's chemical potential to store heat.

(which i dont know how to measure)

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Admanfrd, based on what I've seen smiths in Egypt, Syria, Kuwait & UAE use sand, the UK no flux and USA borax and borax mixtures and a couple  That are also now fluxless. :) I think it's try something by all means but if you have something that works use it. I have tried all the above and I have managed all except the sand and believe me I've tried!

ian

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Sand and glass were traditional wrought iron fluxes (along with rice straw ash...)  Real wrought iron is prettymuch self fluxing anyway.  If you get the metal hot enough to melt the scale then flux is not so important.  The problem is that high carbon modern steels have trouble getting that how without burning and so fluxes really help prevent cottage cheesing or burning of such steels by over heating.

 

IIRC: Practical Blacksmithing, Richardson, a collection of articles from a smithing journal from 1889, 1890, 1891; has a discussion of how the "modern" steels (Bessemer, Open Hearth, etc) required different fluxing and welding than the familiar wrought iron and wrought iron derrived steels.

 

I was thinking on "activity" and if you could take standard samples oxidized to a standard level and then weigh them and immerse them in the flux at various standard temps for a set time and then clean them and re-weigh them to see how much oxidation was removed might be a possible method; but rather a pain to do.  This is a rather armchair gedanken experiment though.

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I recon you might be shy on gedanke on this site should you be in the mood to try Thomas :D

 

Ian

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One thing you left out of your consideration for the flux temps.   I do add Boric acid to my fluix mix beause of its low melting temp, but you did not show what it is doing at the actual welding temps. If it used alone one needs to know that as well.

 

Example of a test some one did is a borax test I saw where a person was "proving" borax is useless as flux.  His testing showed it does not effect scale and added that it is not good to have the moisture on the steels.  He forget that borax behaves differently at welding temps. His testing was done at room tempratures.   At  near welding temps its liquid, the water hgas evaporated, and its Ph is 2.2 which of course is very active on steel.   So his room temp testing was of no value to a smith, except for hand washing.  

 

Context matters.

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Exactly!  So a mix that would provide an O2 barrier at temps from below scaling temp to approaching welding temp and an active aggressive flux at welding temps might be a good thing.  (I think the "steel glue" flux was designed that way) and then there are the recalcitrant oxides like chrome where toxic fluorine is used....

 

So from an old post on this forum:

"Steel Glue:
Flux mix is as follows:
 
5 parts anhydrous borax
2 parts powdered boric acid
1 part powdered iron oxide (the real STUFF NOT the concrete dyes)
1/2 part Flourspar
1/4 part sal ammoniac
 
This stuff sticks most anything together"
 
Warning
Use proper respirator with this mix

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I have less shop time than I used to....When I do forge I am less intersted in trying new things or methods..I grab wot I keep on hand, for flux it is either twenty mule team or the same with a bit of boric acid in it..

.And I have used JPH's flux,,wonderful stuff.

New folks may find the data a starting point to delve into how things work and why...I just like that they do workl.

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Boiling at 572, wouldn't boric acid used alone be gone by the time you reached welding temps?

 

mark

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