Oxygen Assist

[Axeman]

I've seen a bit of confusion or misinformation about oxygen and what not on here so I wanted to post some clarification.

Oxygen is only 1 piece of the 3 piece fire triangle, it breathes 'life' into the fire, but it is not the fuel. If you take oxygen and give it fire, the oxygen itself does not burn. It simply makes whatever fuel it is burning, burn that much faster. Hydrogen is a flammable gas, oxygen is not. That's where the term "oxidizing" comes from. Safe materials for oxygen handling are silicone, brass, and aluminum.

For an example on how oxygen makes fire work, find some oxygen, put a match or cigarette in front of it and let the gas out. The fire will flare up and the match stick/cigarette will almost instantly disappear but will not 'chase' the oxygen source.

Much like an engine, you have fuel + air + electricity = fire

So, if you have oxygen being pumped down through your air assist, it will make whatever your cutting MUCH hotter, but it will not have a 'ball of fire' crawl up into your lens or into your tubing unless your cutting something that produces a flammable gas that could go into other places.

Oxygen + heat is very dangerous and you should be prepared for how dangerous it can be. I've been in the oxygen industry 10+ years, so I thought it might help you guys out some to know the what's what.

[hardshoe]

It's an air assist mate not oxygen. I use a small compressor working at 15psi stops acrylic deforming at the edges while cutting.
Ger

[Axeman]

I was referring to specifically adding/using oxygen.

Not 'air assist'. I know what that is...I have 30 and 40 psi compressors in the shop for the vacuum table & air assist on my equipment.

I'm referring to Marco mentioning he wanted to try cutting 1mm steel on a 130W RECI + O2 assist. So, I wanted to clear up the misconceptions.

[Tech_Marco]

Correct me if I'm wrong. The laster head that used for steel cutting is different than a regular laser head. There is air-assisted and oxygen injection tube. For the air-assisted, it looks the same as a regular laser head with air injected to the chamber. Doing so, it 'clean' smoke from the lens and it blow out dust or somok from the object to be cut. But, the oxygen tube must be installed outside of the laser head. It is because that oxygen will boost the temperature very high when heated. The laser beam can reach 1000'C so with help from oxygen, it could boosted up to 1500'C or up. If we pump pure oxygen inside the laser head as usual, the champer may be over-heated and it may explose in rare case. Therefore, the oxygen must be feed in through an extra tube and it must be installed outside from the laser head. Or, it could be a double chamber but without beam pass through.


Marco

[Axeman]

Ah! Good point Marco. That makes sense.

One could inject air down off the side at a 45 degree angle + the air assist...though I don't know much about steel cutting heads. I just wanted to clear up the concept that oxygen itself was flammable...

[medicdude]

The idea is to increase the oxygen available to chemically react (oxidize) with the metal. You can do this by increasing the pressure OR concentration of oxygen at the reaction site. Concentration is increased by introducing additional O2 or pure O2 to the air stream. Pressure is increased by increasing the supply pressure of the stream. Pressure drop from the nozzle to the reaction site is minimized by bringing the nozzle as close to the work material as possible, using the smallest opening possible for the nozzle, cutting shallow (thinner stock or engraving vice cutting), and cutting narrow (thinner stock or tighter beam). If the nozzle is TOO close (especially before a new cut has penetrated) you might have an issue where you get a 'pressure bubble' at the nozzle, due to the thermal expansion of the gas from the heat of the cut, exceeding the air assist supply pressure and impeding the supply. A ceramic nozzle is probably required so it doesn't melt from the radiated and convected heat from the cut.

[baccus61]

I have tried to cut 0.2 - 0.4 mm (I can't remember how thin it was) stainless steel with just the air assist and I can pierce holes ok but it won't cut with the 100 watt RECI tube. The thin plate warped a lot eliminating the focus of the beam. With O2 you could probably cut ok but you would have to do it fast or get an auto focusing head assembly to ride the "wave".
With the O2 passing through the lens assembly I should think it would cool the head and not let it heat too much and the reflected heat from the job wouldn't be enough to melt the thing as it's also moving about a lot passing air over it and cooling it somewhat anyway. The O2 is expanding from the bottle which cools the gas as well.
I would use as small a hole as is practicable in the lens to intensify the "velocity" of the O2 which would also aid in blowing the dross out of the cut as the metal oxidises due to the O2 concentration.
I wish I had a full bottle of O2 here at home to try it out. I have a bottle but I don't have much gas in it and need it for my home renovations so it can't be used for this.
Richard.