How to find Plasma Cutting Gas Flow Rate?

[Gregorydas]

Dear all,

please help me in here. This is for estimation purpose.
we need to cut 22mm thick SS304L plates using plasma.

1. Which gases should we consider for Plasma cutting (Start gas/Cut gas & Shield gas) ?
2. If it is Oxygen & Air (or whatever), how to find the consumption of the gases (flow rate)? In the manufacturers manual, This flow rate is given as below; (for CS cutting 3/4" thick)



PLASMA GAS:Oxygen @ 125 PSI
START GAS:Nitrogen @ 125 PSI
SHIELD GAS:AIR @ 80 PSI
FEED RATE:74 ipm
KERF WIDTH:.185 inch
STANDOFF:145
INITIAL HEIGHT:76
START GAS FLOW: 28.6 (4.4 flow)
CUT GAS FLOW: 60.0 (5.1 flow/50 PSI cutting)
START SHIELD GAS: 45 (7.5 PSI while cutting)
SHIELD GAS:45 (7.5 PSI while cutting)[highlight #FCE94F][/highlight]
REMOTE CURRENT:250
PLASMA RISE ON PIERCE:.3
PLASMA PIERCE TIME:.2
PLASMA TRAVEL DELAY:.1

Please see the texts in red. There they have mentioned the flow rate. But No unit. what is this 26.6 ? and what is 4.4?
in the cut gas flow, what is referred to as "60.0 (5.1 flow/50 PSI cutting)"??


Please explain this. Anybody have oxygen flow rate per minute or per meter?

Thank You,

Gregorydas

 

[racookpe1978]

Plasma cutting 3/4 inch thick carbon steel plate is fairly easy, and should be routine for any of your shop journey men welder/fitters.
Oxy-acetylene cutting (burning) of 3/4 inch thick carbon steel is fairly easy, and should be routine for any of your shop journey men welders/fitters.

See this link for pro's and con's of the different gas systems.

http://www.centricut.com/New_Lessons/lessons_9.html

I use air for that thin of carbon steel with my plasma cutter.

I do not believe the start-gas/burning-gas question or concern is important: There is so little improvement between using oxygen or using air as a burning gas that making up a rig and lines and valves and creating a process to enable the changeover is going to give you enough of a benefit to pay for the extra complexity. That is, if you decide to use oxygen for cutting carbon steel, stick with O2 for starting and burning. If air, use air for both.

 

[Gregorydas]

Thank you for the comment. I will seriously think about it. But here my question is mainly about the gas flow unit. What are the numbers for?. My ultimate aim in simple words is that, I want to calculate the number of O2 cylinders to be used to cut 100 Running metres of CS or SS Plates.

Thanks in advance.

 

[racookpe1978]

What are the numbers for?

??

If flow rates, they tell what you have to set the oxygen regulator to maintain the flow at or above that flow rate
If pressures, they tell you what to set the regulators at to verify that pressure at that flow rate at the plasma cutting tip.

 

[Gregorydas]

thank you

 

[chicopee]

I can not tell you which method is better and what were the flow rates but when our heavy structural steel company involved in manufacturing steel such as tub girders for bridges, it used plasma cutting equipment to cut the flat plates that were over 3/4" thick. So from past experience plasma cutting seems to be a preferred method for heavy stock.