settle an argument

Date 05-06-2009 17:51

The textbook answer is 20% co2 is the limit. However, I had a boss once that made the same argument as your boss with me. The difference was that we were running solid wire though. I finally had to admit that he had a pseudo-spray process. It was pretty close to a straight argon process, but we had to push the machine to the extreme limits of voltage and amperage to do it. There were just a few little globs once in awhile, but for the most part, you could see the pinch cone at the tip of the wire and little droplets going off. But, any globs at all, no matter how few, might force the textbook answer to be 20% co2.

By ctacker (****)

Date 05-06-2009 18:48

you can get a "spray like" transfer with 75/25.
here's an example : http://products.esabna.com/EN/home/filler_metals_catalog/filler_metals_product_detail/q/display_id.id4367f2a9627493.86933304/category_id.729/path.filler_metals_cored_wire_carbon_low_alloy_steel_low_alloy_gasshielded_flux_core_dual_shield_ii_110_111t1k3

By Lawrence (*****)

Date 05-06-2009 18:55 Edited 05-06-2009 18:57

Most of the data listing spray charcateristics for spray vs globular vs short circuiting transfer modes are based on trials with solid wire.

80% argon is commonly the number used for solid wire... Spray can be achieved with 0.045 soid wire and 75/25 but the voltage required is over 32 and not condusive to production. Cant be done at all with 0.035

Gas shielded FCAW can indeed spray...

Spray transfer is defined by an open arc and droplets smaller than the diameter of the filler...

Some Gas Shielded FCAW wire can do this with both 75/25 and 100% CO2, This is because the agents in the flux in conjunction with the shield gas are producing an atmosphere and arc plasma condusive to spray.

Performance of Gas Shielded FCAW wires can vary from vendor to vendor... But all you really need to do is watch the arc..... If it sprays droplets smaller than the wire... it's spray transfer.... Usually the manufacturers suggested arc voltages are such that the arc lenght is very tight (as it should be to avoid undercut) so it may be difficult to see a pinch effect... But you can always turn up the voltage a bit on a piece of scrap just to have a look.

By Metarinka (****)

Date 05-06-2009 23:27

It was my understanding that a several factors affect transfer mechanism in wire fed processes:

Shielding gas composition
Filler metal composition
current density
electrode stick out and feed rate
welding power source inductance (the pinch affect)

By far the most obvious factor is Shielding gas composition: As it was explained to me the arc will create plasma around the electrode. The disassociation of CO2 into it's elements will create a plasma force that acts opposite to the direction of metal deposition. Thus this force counter acts gravity and the ark force and prevents the droplet from breaking off cleanly and instead forming heavy globs. I can't remember the technical explination but welding atmosphere also affects liquid metal surface tension I believe due to molecule properties at the boundary between the liquid and the atmosphere. This surface tension affect is independent of gas properties that cause cause more liquid or sluggish weld pools. I can't find a reference on this right now, anyone care to elaborate or refute this?

However other factors play rolls in transfer mechanism

Filler metal composition also affects surface tension of the droplets, and inductance. For steel alloys this mainly comes in the form of deoxidizer and alloying elements. This is most obvious as Stainless steel filler material is generally considered to act much more "sluggish" than carbon steels and I believe additional carbon content has the same affect?

Current density is perhaps the most relavent here, because of the tubular nature of FCAW wire the current density will be much higher than solid wire GMAW, This also helps affect a generally lower arc voltage which may reduce some of the negative aspects of CO2 plasma by reducing it's intensity (but I'm not sure if that's correct). To my knowledge FCAW is ALWAYS considered to be spray transfer regardless of gas composition given that the correct gas is used as specified by the manufacturer and proper settings are in place. Such as the 100% CO2 fcaw wires which most definitely can run in spray transfer

electrode stickout and feed rate play a small role in spray transfer as this determines the degree to which the wire is preheated before reaching the arc. Anyone who has welded GMAW or FCAW can attest that varying stickout while welding can drastically affect weld quality and sound. stickout is a significant issue in robotic welding applications at high travel speeds and wire feed rates.

Finally the inductance of a welding machine has an affect on arc properties and transfer mechanism (slightly) http://www.esabna.com/EUWeb/MIG_handbook/592mig3_7.htm and while inductance is primarily considered a property of short circuit transfer, it is still present in spray and globular transfer. The reason this is a notable is that some power sources do not allow for the adjustment of inductance and instead have an ingrained inductance curve that varies with amperage. This means that at varying amperages you could have a desired (or not) amount of inductance

Basically my point is that spray mechanism is determined by more than just filler metal composition. To my knowledge FCAW is ALWAYS considered spray unless otherwise noted and more so it definately is not bound to the 80% CO2 "rule" which is really more of a guideline as you can achieve spray transfer with 75/25 using 0.035 GMAW wire given a high enough current density I believe around 36-42v would be the transition voltage, but these settings are far from practical or generally considered usable with 0.035 wire.

Please someone correct me if I'm wrong on any of this information this was all off the top of my head as I sit here in between studying for finals

By 357max

Date 05-08-2009 14:11

Good thread; ...how about the SMAW process - XX10 spray or globular transfer? XX18 spray or globular? What is the shielding gas?

By DaveBoyer (*****)

Date 05-10-2009 04:43

If I remember right, lime in the electrode coating makes CO2 when it gets hot for shielding, at least in some electrode types.

By strother (***)

Date 05-10-2009 04:26

you can make make anything spray w/ enough volt. But if you are running E71-t you are defeating the purpose . just my opinion