[Jack Ryan]

What is the function of iron oxide in MMA flux?

AWS examples are 6019, 6020, 6027 and 7027 but I don't think I have come across them before.

ISO 2560 does not list iron oxide.

Thanks
Jack

[Gdarc21]

The iron powder not only melts in the heat of the arc to increase deposition rate but also enables the electrode to carry a higher welding current than a 'standard' electrode. The iron powder is electrically conducting, so allowing some of the welding current to pass through the coating.


A quote from twi global

[Gdarc21]

Whats the interest for, if I may ask if not just curious. Are you planning a task where this is critical?

[Jack Ryan]

The iron powder not only melts in the heat of the arc to increase deposition rate but also enables the electrode to carry a higher welding current than a 'standard' electrode. The iron powder is electrically conducting, so allowing some of the welding current to pass through the coating.


A quote from twi global

Thanks, but that is iron powder, not iron oxide.

I have done more research and found some answers.

The question was asked regarding MMA but the same applies to flux core wire - both gas shielded and self-shielded.


Increasing Deposition Rate

The purpose of the iron is to increase the deposition rate (a function now served by iron powder) but the question remained, why iron oxide and not iron powder? As is often the case, there is not a single answer.


Additional Oxygen

Where argon rich shielding gases are used, the additional oxygen in iron oxide increases the reactive component of the shielding gas. The reactive gas increases penetration and the removal of impurities through oxidation.

tubular wires are optimised for particular ranges of shielding gas and those designed to use high argon mixtures may need iron oxide additions to the core to restore the desired oxygen balance.
Tubular Wire Welding by D. Widgery, p44


Hydrogen Control

Resistance to hydrogen (water) absorption.

The extruded electrodes with rutile, iron oxide and silicate coatings do not pick up so much moisture from the atmosphere and function quite well with a small absorbed content.

Improved penetration (depth of fusion) with the addition of reactive oxygen.

In manual metal-arc welding the flux coating to give deep penetration characteristics would contain
(a) iron oxide
(b) manganese
(c) cellulose
(d) calcium carbonate.

The Science and Practice of Welding Volume 2 10th Ed - The Practice of Welding, p12& p510

Iron Oxide as a Slag Producer

Similarly, if we use iron oxide (Fe2O3) and silicon dioxide (SiO2) in the covering of the electrode, in the heat of the arc they will combine chemically to form iron silicate, which floats to the top of the molten pool as a slag, protects the hot metal from further atmospheric oxidation and slows down the cooling rate of the weld.
iron oxide + silicon dioxide = iron silicate
Fe2O3 + 3SiO2 = Fe2(SiO3)3

The Science and Practice of Welding Volume 1 10th Ed - Welding Science and Technology, p58

There are other combinations as well such as Exx20 with a high iron oxide coating bonded with sodium silicate. It looks like iron oxide is firmly in the past now as ISO 2560 does not even list it as an option.

Thanks again,
Jack

[Jack Ryan]

Whats the interest for, if I may ask if not just curious. Are you planning a task where this is critical?

Just curious. Sorry, I can't help it.

Jack

[tweake]

thats interesting info. thx for posting that

[Gdarc21]

I have to ask, what do you think is the difference in the way they using the terms.
One is iron powder the other is iron and oxygen, which also occurs when burning iron powder.
I wonder if you didnt create question to just do an info dump. It is still widely used and to the best of my knowledge, Engineers are the very few people who care about ISO, Everyone else refers to AS/NZ STDS, WTIA notes and AWS in practise.

[Jack Ryan]

I have to ask, what do you think is the difference in the way they using the terms.
One is iron powder the other is iron and oxygen, which also occurs when burning iron powder.
I wonder if you didnt create question to just do an info dump. It is still widely used and to the best of my knowledge, Engineers are the very few people who care about ISO, Everyone else refers to AS/NZ STDS, WTIA notes and AWS in practise.

Well, iron powder is just that, iron oxide is an oxide. Iron powder is used to increase the deposition rate, it is not burnt.

Who are you to make such accusations? If you are overwhelmed, move to the next post.

Widely used? Where?

A disappointing post I have to say.

Jack

[Gdarc21]

If you are overwhelmed, move to the next post.

Widely used? Where?

A disappointing post I have to say.

Jack

Ah whatever

[tweake]

It is still widely used and to the best of my knowledge,

i've never seen iron oxide rods. they certainly not widely used downunder.
in fact most listing of rod spec have no mention of iron oxide. i suspect its old tech thats been superseded a long time ago.

iron powder and iron oxide are two completely different things.