[Gligor]

Since I started welding, it was never logical to me the way gas flow was set for TIG welding. I was hearing the popular rule "Cup size x2 = required gas flow rate in CFh". For example 5 cup = 10 CFh; 6 cup = 12 CFh; 7 cup = 14 CFh; etc.
The diameter of cup 5 is half of the diameter of cup 10, but it's not nearly the half cup area. So by that logic, if cup 5 uses 10CFh of argon, cup 10 should use way more than 20CFh.

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So I have taken Furick Fupa 12 cup. The flow rate for fupa 12 is 25-35 CFH. As a referent point I used 35 CFH (the maximum) for 12 cup, and I assumed that the flow of 35CFh will achieve the best laminar flow (in reality it will not, lower CFH will give better results, but I wanted to use the maximum). After that I did some basic fluid dynamic calculations, and came up with this. All the calculations are made in metric because it's easier for me, but the end results (flow rates) are converted in imperial (I'm far away from USA, but I wish that one day I'll get there ).

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What do you think about my calculations? I think that they are way better than the popular "flow rate = cup size x2"
Thnak you for your time.

[Spartan]

For stainless I run my #10s at right about 20CFH. They have a diffuser screen which I think helps out a bit. I'll run the #12s about 25CFH. Both get bumped up a bit when I need more stickout.

Works well enough for me. I also use x2.2 for the "rule of thumb" you had mentioned. That gets it a bit closer to your calculations.

[Gligor]

For stainless I run my #10s at right about 20CFH. They have a diffuser screen which I think helps out a bit. I'll run the #12s about 25CFH. Both get bumped up a bit when I need more stickout.

Works well enough for me. I also use x2.2 for the "rule of thumb" you had mentioned. That gets it a bit closer to your calculations.

Yes, my calculations are for gas lens setup and diffuser screens. And I know it works, I've been using the popular rule of thumb since I started welding. But in those calculations I'm getting the maximum required CFh for laminar flow. I'm also going to do calculations based on the minimal required gas flow for 12 cup (25CFh), and I'll get the minimal required gas flow for all the other cups, and I think that those number will be way smaller (I assume that the sweet spot will be somewhere in the middle between those numbers). I know that Amps, stickout and electrode diameter play a role in the gas flow settings, but that's another topic.
My point here is getting the best laminar flow and best gas coverage, but also saving some argon and some money .
Best regards

[Oscar]

The calculations are fine, but un-necessary to a certain extent, due to the fact that you decided to use 0.06 as a constant in the calculations. Since area can be shown to be proportional to diameter², the round-off errors of actually calculating the area using π can be eliminated entirely. Since you used 35 CFH as the baseline for Q, all the calculations can be generalized and simplified by using the difference in areas by way of ratios between the square of the diameters, without even needing to do metric↔imperial conversions:




Basically what I'm saying is I removed a lot of the "fluff" via algebraic manipulation and those are the resulting operations that actually generate the values seeked.

[Gligor]

The calculations are fine, but un-necessary to a certain extent, due to the fact that you decided to use 0.06 as a constant in the calculations. Since area can be shown to be proportional to diameter², the round-off errors of actually calculating the area using π can be eliminated entirely. Since you used 35 CFH as the baseline for Q, all the calculations can be generalized and simplified by using the difference in areas by way of ratios between the square of the diameters, without even needing to do metric↔imperial conversions:




Basically what I'm saying is I removed a lot of the "fluff" via algebraic manipulation and those are the resulting operations that actually generate the values seeked.

Thank you sir. I was aware that I can make the calculations way easier than I did and get similar results, but I wanted to point out some basic things that affect the fluid dynamics like the fluid density, velocity, dynamic pressure etc. If I made the calculations basic using only numbers and not pointing out what is what, I think that some people will find hard to understand what those numbers are representing, and how I got the results, especially the beginners.

[BugHunter]

A fun math exercise I'm sure but for the most part I let the weld tell me with the flow should be.

(I'm far away from USA, but I wish that one day I'll get there ).

You may have waited too long. The USA as we knew it doesn't exist anymore.

[Spartan]

A fun math exercise I'm sure but for the most part I let the weld tell me with the flow should be.

(I'm far away from USA, but I wish that one day I'll get there ).

You may have waited too long. The USA as we knew it doesn't exist anymore.

Speaking of which... how's the weather over there in Macedonia??

[bap_]

Just going to throw this out there.

I think that its rad that you took the time to question the 2x rule and calculate it to verify for yourself. Tig gas flow is as easy as turning it up or down if its not giving you results, but still a good exercise to come to your own conclusions. Well done.

[Gligor]

A fun math exercise I'm sure but for the most part I let the weld tell me with the flow should be.

(I'm far away from USA, but I wish that one day I'll get there ).

You may have waited too long. The USA as we knew it doesn't exist anymore.

Speaking of which... how's the weather over there in Macedonia??

The weather is cold, bad, and unstable, just like everything else in my country. I'm mechanical engineer, and I was a pretty good student when I was studying. I was studying with understanding and practical jobs, not just by the books.
Long story short, when I asked for a job in one big factory, I was offered job as an engineer (CAD/CAM, construction projections, analysis etc.), and job as a MIG welder (no certifications or experience needed) . The salary as a welder was 40% higher than the salary as mechanical engineer. But I refused those offers, and decided to open my own workshop (I'm still working on it) , and also get a master degree.
Best regards.

[eelman308]

After looking at all those equations.......I'm liking the 2.2 rule.

My brain started to hurt. I just want to weld

[cj737]

I'm with Buggy... turn the knob until the weld tells you what it wants. There is no mathematical formula that can dictate conditions accurately enough to determine flow requirements.

Differing ambient temperature, cylinder pressures, regulator quality, joint configuration, etc.. all play an integral part of "flow". And I doubt you could financially calculate in a manual welding workshop the difference in cost of gas between 14 and 15cfh. Or 14.3 and 16.1 for that matter.

I do appreciate the engineering approach to your exercise though.

[Gligor]

I'm with Buggy... turn the knob until the weld tells you what it wants. There is no mathematical formula that can dictate conditions accurately enough to determine flow requirements.

Differing ambient temperature, cylinder pressures, regulator quality, joint configuration, etc.. all play an integral part of "flow". And I doubt you could financially calculate in a manual welding workshop the difference in cost of gas between 14 and 15cfh. Or 14.3 and 16.1 for that matter.

I do appreciate the engineering approach to your exercise though.

You are absolutely right. There are many variables to accurately calculate the adequate gas flow. Joint configuration, weld position, torch angle, electrode diameter, welding current, humidity, electrode stickot, base material, torch height, difuser type etc.
My equations are very basic assuming there are none variables (ideal environment), but because I calculated the maximum recommended gas flow for each cup I think that the results are in the ballpark. The differences in gas flow for larger cups are not that drastic, but for smaller cups, the difference is big. For example cup 5 requires around 6 CFh, and with the rule od 2.2 we get 11 (almost double).
Experienced welders know exactly what works for them.
In don't consider myself very experienced welder, but I can lay down some beads.
But a person who picks up a torch for a first time in its life, should know where to set the gas flow and don't worry about it, because in the beginning everything is a reason for a bad weld. Ask me how I know.
I'm going to calculate the minimum gas flow requred, and I'm going to make a chart, that hopefully will help someone.

[cj737]

For example cup 5 requires around 6 CFh, and with the rule od 2.2 we get 11 (almost double).
Experienced welders know exactly what works for them.

This is a perfect example of where math doesn't compute

Using a gas lens below a #6 cup is essentially ineffective at reducing the turbulence. So mostly collet bodies should be used with <#6 cups and experience tells me that a collet body does not react well with 2x cup size gas flow. In fact, welding with #5 on inside corner joints, I use less than 7cfh because of turbulence created when the flow is too high.

There's value to your pursuit, especially since you are obviously someone who learns better when you understand the technical side; me too. It allows us to make informed changes to understand the results we yield. self-diagnosis basically. But I would encourage you to not become too obsessed with technical variables and instead focus on technique, technique, technique.

I know enough folks who can set it and forget it and weld like a robot every day, all day. I aspire to be more like them.

[Gligor]

Using a gas lens below a #6 cup is essentially ineffective at reducing the turbulence. So mostly collet bodies should be used with <#6 cups and experience tells me that a collet body does not react well with 2x cup size gas flow. In fact, welding with #5 on inside corner joints, I use less than 7cfh because of turbulence created when the flow is too high.

Thank you sir about the advice. That makes sense, and really I've never tried welding with cup 5 gas lens. I only use the 5 standard collet body for aluminum.
See, when I bought my welding machine, I bought some tools, a foot control, all the kinds and thicknesses of filler rods that were available, a lot of consumables, large cylinder of argon, and at the end of the day I was so broke that I couldn't buy argon flowmeter. Instead of that I used 40 years old CO2 regulator from my grandfather with outlet pressure gauge instead of flowmeter. So I was setting the flow by feel (lick the finger above your nail and slowly move your finger towards the torch. The torch should be in horizontal position. When the argon comes in contact with your finger, you'll feel instant cold on the licked area. I assumed that that's the distance that argon is reaching.). I did that because I was so exhausted to do the math and convert the outlet pressure to fluid flow, I just wanted to test the machine. And It worked pretty well, with minor adjustments. There are many ways to skin a cat. I just want to experiment and do some calculations when I'm free, just to clear my doubts. For example these days I'm into experiment welding thin outside corner joints.
The first is without filler.
The second and the third are dabbing.
The fourth is lay wire 2 pulses per second, 20% on time, 20% background current and larger stickot.
These welds are made with the worst foot pedal in the world. I'm building new pedal at the moment.

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[Spartan]

So I was setting the flow by feel (lick the finger above your nail and slowly move your finger towards the torch. The torch should be in horizontal position. When the argon comes in contact with your finger, you'll feel instant cold on the licked area.

When I'm feeling too lazy to walk over to the bottle (often), I "verify" that the gas is where I need it by holding the torch up to my tongue. Turns out my tongue has a decent calibration. Not joking.

[Gligor]

When I'm feeling too lazy to walk over to the bottle (often), I "verify" that the gas is where I need it by holding the torch up to my tongue. Turns out my tongue has a decent calibration. Not joking.

I've tried that as well But instead of pressing the gas test button, I pressed the pedal. I have 1 sec pre flow, but that wasn't enough. Turns out that my tongue has decent grounding for the high frequency, rather than the calibration..

[BugHunter]

[Oscar]

pretty good TIG welding of those thin blades

[Gligor]

pretty good TIG welding of those thin blades

Thank you. Welding these things have special place in my heart. For a beginner, welding box cutter blades shows exactly what a decent weld needs. But I'm getting off topic here.
I did a quick calculations and made a chart about the gas flow. The numbers in the chart are not exact. The deviation is the closest bigger number with 0.5 precision.

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Note: I haven't tested the minimum required gas flow yet, but I think it will need short tungsten stickout.

[Oscar]

I think the numbers are fine for relatively short stick-out's. Such as say 3-4mm past the cup. More than that, for the non-diffuser type set-up's, and you'd need about 50% more flow. That is one thing that is skewing the numbers. The Fupa has a mesh screen diffuser, which minimizes the necessary flowrate due to the laminar flowing argon 'reaching out further'. So techically this would be a chart that I think is more related to what is commonly known as "gas lens" set-up's.

[Spartan]

Definitely interesting data points, and as others have mentioned, I appreciate both the exercise and the attention to detail.

However, such settings, IMO, are only pertinent for mechanized and/or high-production welding. For hobbyist or job-shop work, the economies are often skewed to a point where it can cost more for a welder to have to stop welding and change a reg setting each time than it is to just weld with the gas a bit higher for the duration of that assembly.

[Gligor]

So techically this would be a chart that I think is more related to what is commonly known as "gas lens" set-up's.

Yes sir, I think I've mentioned that before. This chart is specificity about gas lens setup, (cup sizes that are most commonly used). The standard collet body cups will create more or less turbulent flow no matter what. But for aluminum, I don't know why, standard collet body serup gives an extra "punch".

However, such settings, IMO, are only pertinent for mechanized and/or high-production welding. For hobbyist or job-shop work, the economies are often skewed to a point where it can cost more for a welder to have to stop welding and change a reg setting each time than it is to just weld with the gas a bit higher for the duration of that assembly.

That's a good point sir. But anyway, the next week I'm going to do some testing with the numbers from the chart,and compare the results (In going to post photos here). I'm going to use minimum gas flow for inside corners, average flow for flat butt welds, and maximum flow for outside corners and tubes with smaller diameter.
Best regards.