cost of welding gas?

Is that 20 cubic feet per MINUTE or per HOUR?

I think that a simple division would suggest that at 20 cfH, it would last for 125/20 hours, or approximately 6 hours (note that also some gas will be left in the tank). You divide the fill cost by 6 (hours) and then by 60 (min/hr) to get the cost per minute.

Say your fill cost is $48.

Cost per minute = 48/(125/20)/60 = 12.8 cents per minute or $7.68 per hour.

i

Ah. I think I'm beginning to see where I was led astray. If it's CFH, and the tank is rated in cubic feet then the math is trivial. Thanks.

GWE

"Grant Erwin" wrote: (clip) I'm running it 20 cubic feet per minute at 20 psi, (clip) ^^^^^^^^^^^^^^ The part I don't get is the "20 psi" part.

It doesn't matter. The psi. All that matters is flow per time. All the pressure does is push the gas out through an orifice. ERS

Actually, it may matter. The flowmeters are calibrated for one gas, at one pressure. If this is a one-piece, non-adjustable TIG regulator, the flowmeter is probably calibrated for Argon or CO2 at the regulator pressure. In the most general case, flowmeters are calibrated at STP, so if the system is at 20 PSI gauge pressure, that is 2.3 Atmospheres, and so the flowmeter will read somewhat low.

But, assuming the flowmeter was calibrated at this pressure, for this gas, then PSI makes no difference in the gas consumption.

Jon

Connect a running time meter to the gas on contactor relay of your mig welder and read it when the bottle runs dry. Divide the cost of the gas cylinder by the number of minutes recorded on the timer.

John

You have to convert the numbers to volume of gas at standard pressure to come up with a valid answer.

John

Is the tank pressure higher that the regulator pressure? If the tank is

100 PSI and the regulator is set for 20 PSI then 1 cf in the tank will be 5 cf after the regulator.

When the tank pressure drops the expansion will also drop. So the calculation is not trivial.

Bill K7NOM

the cubic feet capacity of the tank refers to quantity of uncompressed gas at atmospheric pressure. I have a 300 c.f. tank, but it does not occupy 300 ft of space (equivalent to 10 refrigerators). It only occupies perhaps 5 cf or so.

i

Are you still figuring the bid on that 3'x3' cube project? How did that work out??

The project wasn't actually a 3x3' cube. I just posed that as an ubersimple design that anyone could comprehend with no drawings, to learn how you guys do bidding. I figured it one way, then I figured the number of inches of weld and cost it out the other way, they were within about 2%. I didn't get the job but it wasn't because of my numbers, I couldn't store the customer's jig long-term since my shop is in my house and my shop is too small so it would have to sit outside, and in the town where I live this would result in losing my business license.

I did learn a lot by bidding the job, though.

Grant

Thanks for the correction. After I posted It accured to me that the capacity as I stated would require a large tank.

So I stand corrected (informed).

Bill K7NOM

If this is the usual rotameter (ball in a tapered tube floweter), the accuracy will be affected by downstream pressure, but is relatively insensitive to the regulator setting. In other words, backpressure due to restrictions between the flowmeter and atmosphere will affect accuracy more than the pressure at the inlet to the needle valve, which is upstream from the flowmeter.

Ned Simmons

Take the bottle hire charges, divide by 365x24x60

Prices round here, the gas itself is free 8-(

Its indeed in CFM/H

Gunner, who pays $18USD + $3 for a 135 CF tank of Argon OR C25

"Pax Americana is a philosophy. Hardly an empire. Making sure other people play nice and dont kill each other (and us) off in job lots is hardly empire building, particularly when you give them self determination under "play nice" rules.

Think of it as having your older brother knock the shit out of you for torturing the cat." Gunner