Lasers, Wood-Cutting And CO2 (possibly nitrogen maybe)

Lasers, Wood-Cutting And CO2 (possibly nitrogen maybe)

Joined: February 2nd, 2017, 2:27 pm

March 24th, 2017, 8:28 pm #1

So we upgraded to a 60 watt laser and word got around that we have it. Been cutting a lot of thin wood for various customers.

Top of the sheet, the laser head has an air-assist. When the beam fires the wood ignites briefly and the air-jet extinguishes it. There is a char-spot where the beam burns through and of course the edges of the cut are singed as well. The air-jet prevents fires and blows out flare-ups... in certain situations though the wood can ignite and you end up with an air-jet fueled fire.

Seems to me better results could be had if I use a stream of Co2 instead of air. The laser has a huge exhaust fan so we'd be pulling the CO2 out of the work area and our workshop has an always-open (even in the winter) window-and-fan because of the fumes we generate doing other stuff. I'm thinking CO2 would prevent even that brief flare/burn at burn-through and it would work better at keeping flare-ups under control. Given that we are effectively directing cool CO2 gas at the burn point we've displaced oxygen and kept the work surface cool at the same time.

Aside from the hazard of overwhelming one's self with CO2 and ending up dead and on the news, am I thinking right here? It seems it would work, there are some safety challenges (interlocks?) that I would have to work through but if it's technically sound I might look into it further.
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Joined: January 1st, 1970, 12:00 am

March 24th, 2017, 8:49 pm #2

Might be a workable idea, and worth a try.

However, a couple things to keep in mind: First, you'll use up a LOT of gas. Depending on how much you cut and what kind of flow rate you set, I could see even a 50-lb tank only lasting a few days, or maybe only as much as a week.

Locally, CO2 is almost $2 a pound, so that's $100 in gas a week, assuming my rough seat-of-my-pants guess is close.

Then of course there's the hassle of having to keep swapping tanks, the requirement you have at least two on hand (one in use, one full backup, which often works out to being three on hand- one in use, one full backup, and an empty waiting to be exchanged) and having to keep moving around heavy tanks.

Second, also depending on flow rates, you can fairly easily "freeze" even a big tank. Sustained draw from the tank can cool it rapidly, potentially even to the point of freezing it solid- meaning little or no tank pressure, meaning little or no blast at the cutting point.

Neither of those things are unworkable, of course, or fatal to your idea. But should be kept in mind.

You can give it a try with a cheap 20-pounder (know anyone with a Kegerator? ) and a relatively inexpensive flowmeter. ($75-$100.) You'll probably want a flowmeter rather than just a regulator- the flowmeter has a reg built in, and does a better job of controlling the rate of gas flow.

A 20-pounder will also give you a better idea if you're going to get "freezing" issues- the smaller tank will freeze up a lot faster than the 50 or 100-pounders. If you don't have a significant problem with the 20, a 50 will work just fine.

And, as added protection, throw an inexpensive CO detector in the cutting room, down low. I'm pretty sure they also detect CO2, and should give you a warning if there's a leak or excess buildup.

Doc.
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Joined: October 28th, 2014, 1:06 am

March 24th, 2017, 10:40 pm #3

I sometimes wet down the wood before I cut it. It seems to reduce the charring a bit. If your laser has a "frequency" setting, (pulses per inch I think is more correct), try reducing that substantially. On my little 30W, most things cut at the max frequency of 5000, but I cut wood at 400.
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Joined: September 16th, 2016, 6:41 pm

March 25th, 2017, 12:03 am #4

So we upgraded to a 60 watt laser and word got around that we have it. Been cutting a lot of thin wood for various customers.

Top of the sheet, the laser head has an air-assist. When the beam fires the wood ignites briefly and the air-jet extinguishes it. There is a char-spot where the beam burns through and of course the edges of the cut are singed as well. The air-jet prevents fires and blows out flare-ups... in certain situations though the wood can ignite and you end up with an air-jet fueled fire.

Seems to me better results could be had if I use a stream of Co2 instead of air. The laser has a huge exhaust fan so we'd be pulling the CO2 out of the work area and our workshop has an always-open (even in the winter) window-and-fan because of the fumes we generate doing other stuff. I'm thinking CO2 would prevent even that brief flare/burn at burn-through and it would work better at keeping flare-ups under control. Given that we are effectively directing cool CO2 gas at the burn point we've displaced oxygen and kept the work surface cool at the same time.

Aside from the hazard of overwhelming one's self with CO2 and ending up dead and on the news, am I thinking right here? It seems it would work, there are some safety challenges (interlocks?) that I would have to work through but if it's technically sound I might look into it further.
...tie in a secondary CO2 line with a junction and quick action valve that will inject CO2 into the air jet's flow. In case of a fire that the jet can't extinguish a simple push or twist will cut off the normal atmospheric flow and inject CO2 directly onto the fire. Much safer (and cheaper) than continuous flowing CO2 into the area's atmosphere.
Plus, even with an exhaust fan you would need to have a high flow system with a dedicated intake that completely changes the area's atmosphere to prevent CO2's effects on a body. Normal atmospheric CO2 is 0.04%. 3% causes mental confusion, heart and blood pressure problems and 8% unconsciousness. So, anything that increases CO2 in an enclosed area is dangerous. Any safety/insurance inspection noticing such a setup will result in a shutdown of the business until removed/corrected. Usually meaning big bucks. Hope this helps.
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Joined: October 8th, 2014, 2:05 pm

March 25th, 2017, 12:05 am #5

So we upgraded to a 60 watt laser and word got around that we have it. Been cutting a lot of thin wood for various customers.

Top of the sheet, the laser head has an air-assist. When the beam fires the wood ignites briefly and the air-jet extinguishes it. There is a char-spot where the beam burns through and of course the edges of the cut are singed as well. The air-jet prevents fires and blows out flare-ups... in certain situations though the wood can ignite and you end up with an air-jet fueled fire.

Seems to me better results could be had if I use a stream of Co2 instead of air. The laser has a huge exhaust fan so we'd be pulling the CO2 out of the work area and our workshop has an always-open (even in the winter) window-and-fan because of the fumes we generate doing other stuff. I'm thinking CO2 would prevent even that brief flare/burn at burn-through and it would work better at keeping flare-ups under control. Given that we are effectively directing cool CO2 gas at the burn point we've displaced oxygen and kept the work surface cool at the same time.

Aside from the hazard of overwhelming one's self with CO2 and ending up dead and on the news, am I thinking right here? It seems it would work, there are some safety challenges (interlocks?) that I would have to work through but if it's technically sound I might look into it further.
A couple of thoughts come to mind:

1) CO2 absorbs certain infrared wavelengths. You might consider checking your laser's output against CO2's absorption spectrum. It might make your cuts a little fuzzy if they coincide.

2) Are there cheaper gases? If the goal is to displace oxygen, even the product of a gas flame (which is mostly CO2 and N2) might work. Implementation is left as an exercise for the student. (Although Scientific American ran a piece decades ago on how to make low pressure N2 for a homemade UV laser from regular air with a Bunsen burner and some plumbing that would have made Rube Goldberg proud.)

If it ain't broke, I'll fix it!
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Joined: February 2nd, 2017, 2:27 pm

March 25th, 2017, 3:38 am #6

...tie in a secondary CO2 line with a junction and quick action valve that will inject CO2 into the air jet's flow. In case of a fire that the jet can't extinguish a simple push or twist will cut off the normal atmospheric flow and inject CO2 directly onto the fire. Much safer (and cheaper) than continuous flowing CO2 into the area's atmosphere.
Plus, even with an exhaust fan you would need to have a high flow system with a dedicated intake that completely changes the area's atmosphere to prevent CO2's effects on a body. Normal atmospheric CO2 is 0.04%. 3% causes mental confusion, heart and blood pressure problems and 8% unconsciousness. So, anything that increases CO2 in an enclosed area is dangerous. Any safety/insurance inspection noticing such a setup will result in a shutdown of the business until removed/corrected. Usually meaning big bucks. Hope this helps.
I was wondering about using a short burst at startup and in areas prone to burning (high detail areas come to mind)

Short quick bursts plus our running fan plus other considerations would sharply reduce the risk of insurance/safety vultures raising my rates.

***Normal atmospheric CO2 is 0.04%. 3% causes mental confusion, heart and blood pressure problems***

So old age is caused by CO2? Dagnabit...!
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Joined: September 16th, 2016, 6:41 pm

March 25th, 2017, 4:28 am #7

A couple of thoughts come to mind:

1) CO2 absorbs certain infrared wavelengths. You might consider checking your laser's output against CO2's absorption spectrum. It might make your cuts a little fuzzy if they coincide.

2) Are there cheaper gases? If the goal is to displace oxygen, even the product of a gas flame (which is mostly CO2 and N2) might work. Implementation is left as an exercise for the student. (Although Scientific American ran a piece decades ago on how to make low pressure N2 for a homemade UV laser from regular air with a Bunsen burner and some plumbing that would have made Rube Goldberg proud.)
Besides that costs incurred using either CO2 or N2 as a possible fire suppressant, you also run into the physical dangers using gasses in such a manner.
Nitrogen in amounts higher than atmospheric normal (78%) can cause mental confusion, unconsciousness and death as it displaces Oxygen in the bloodstream. We used N2 to purge electronic assemblies to prevent condensation and our safety procedures required high flow ventilation even though very little N2 was released into the atmosphere of the shop. An "uncontrolled" release such as you suggested would require either a ventilation system capable of completely replacing the entire volume of air in a shop within a minute or evacuation of the area until safe. Even when purging in an aircraft hanger we were required to use large, high-capacity fans to prevent high concentrations in the area.
Since we repaired electronic assemblies as well as mechanical, we used three types of fire extinguishers in our shop: dry chemical, CO2 and Halon. ANY discharge of CO2 or Halon REQUIRED immediate evacuation of the shop until cleared by the fire department. A dry chemical discharge only required using a face mask until it was cleaned up.
Any gas continuously released into an enclosed area, even well ventilated, can cause adverse effects to the human body in seemingly insignificant concentrations. CO2, N2 and Halon will quickly asphyxiate somebody by simply preventing Oxygen from entering the bloodstream. In a small enclosed room as described by Lord Redacted, any continuous release, however small, would quickly raise gas levels to dangerous concentrations. Add to that the costs of using compressed gases (tanks, transportation, hookup, etc.) could quickly result in uneconomic final pricing. And an inspection (safety, business and insurance) would fail unless an aforementioned atmospheric or enclosed worksite evacuation system was installed at high costs. Either way, while seemingly simple and easy, the uncontrolled usage of gases for possible fire suppression is too dangerous and costly to be considered for a small business.
NOTE: As a volunteer firefighter, entering this workshop while the gas is being released would be considered as a "hazardous atmosphere enclosed area situation" that would require the use of SCBA (Self-Contained Breathing Apparatus) and an atmospheric monitor. SCBA wouldn't be removed until gas levels returned to normal and levels continuously monitored until the call was completed.
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Joined: September 16th, 2016, 6:41 pm

March 25th, 2017, 5:22 am #8

I was wondering about using a short burst at startup and in areas prone to burning (high detail areas come to mind)

Short quick bursts plus our running fan plus other considerations would sharply reduce the risk of insurance/safety vultures raising my rates.

***Normal atmospheric CO2 is 0.04%. 3% causes mental confusion, heart and blood pressure problems***

So old age is caused by CO2? Dagnabit...!
The easiest and cheapest way to use CO2 as a fire ssuppressor would be a small (< 5 pound) extinguisher) wall mount unit about waist high, five to ten feet away near the power supply to the machine. If a fire starts that the airjet fails to extinguish you cut power to the laser AND airjet, a three to five second burst from the extinguisher (more if needed), start a high-flow exhaust fan and leave the room. Pros: Cheap (cost of extinguisher), simple and easy to use. Cons: Multiple steps/locations, relocating power supply/exhaust fan switches.
Or set up a "Panic Button" that when pressed: cuts power to laser and airjet, releases a three-five second burst from a permanently mounted, small (20 pound) CO2 tank and starts a separate high-flow exhaust fan to clear smoke/CO2 from the room. Have it near the door if you have to press it again it the first burst doesn't extinguish any flame. Have a small container of water nearby in case the wood reignites even after multiple uses of the extinguisher. Use only as a last resort as water plus electronics is NOT recommended!
Panic button Pros: one-step, easy to do under stress, you don't have to refill extinguisher after using (yes, recommended after any usage however small!) and while you're heading out the room! Cons: Costs, electrical and mechanical hookups. However, it would be a one time fixed cost that has the added advantage of possibly reducing your insurance rate. The rate reducement might even pay off the initial costs within a couple of years.

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Joined: October 28th, 2014, 1:06 am

March 25th, 2017, 5:54 am #9

Besides that costs incurred using either CO2 or N2 as a possible fire suppressant, you also run into the physical dangers using gasses in such a manner.
Nitrogen in amounts higher than atmospheric normal (78%) can cause mental confusion, unconsciousness and death as it displaces Oxygen in the bloodstream. We used N2 to purge electronic assemblies to prevent condensation and our safety procedures required high flow ventilation even though very little N2 was released into the atmosphere of the shop. An "uncontrolled" release such as you suggested would require either a ventilation system capable of completely replacing the entire volume of air in a shop within a minute or evacuation of the area until safe. Even when purging in an aircraft hanger we were required to use large, high-capacity fans to prevent high concentrations in the area.
Since we repaired electronic assemblies as well as mechanical, we used three types of fire extinguishers in our shop: dry chemical, CO2 and Halon. ANY discharge of CO2 or Halon REQUIRED immediate evacuation of the shop until cleared by the fire department. A dry chemical discharge only required using a face mask until it was cleaned up.
Any gas continuously released into an enclosed area, even well ventilated, can cause adverse effects to the human body in seemingly insignificant concentrations. CO2, N2 and Halon will quickly asphyxiate somebody by simply preventing Oxygen from entering the bloodstream. In a small enclosed room as described by Lord Redacted, any continuous release, however small, would quickly raise gas levels to dangerous concentrations. Add to that the costs of using compressed gases (tanks, transportation, hookup, etc.) could quickly result in uneconomic final pricing. And an inspection (safety, business and insurance) would fail unless an aforementioned atmospheric or enclosed worksite evacuation system was installed at high costs. Either way, while seemingly simple and easy, the uncontrolled usage of gases for possible fire suppression is too dangerous and costly to be considered for a small business.
NOTE: As a volunteer firefighter, entering this workshop while the gas is being released would be considered as a "hazardous atmosphere enclosed area situation" that would require the use of SCBA (Self-Contained Breathing Apparatus) and an atmospheric monitor. SCBA wouldn't be removed until gas levels returned to normal and levels continuously monitored until the call was completed.
Besides my little desk top laser, my work also has a 2000W steel cutting laser. We used to use CO2 and N2 for assist gas all the time. As Doc pointed out, it gets expensive, but the amount of gas actually released is tiny in comparison to the volume of the shop. The nozzle is just slightly only about .06" dia. It's a lot when you're paying for it, but tiny when you're breathing it. We still keep the gasses in stock for when we need them, but 99% of what we cut is 304 stainless steel, and it cut's adequately with compressed air, so we mostly use that now. Look up "laser assist gas" and you'll see how common those are with big lasers, and I've never heard of any sort of asphyxiation issues.

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Joined: November 19th, 2014, 12:50 pm

March 25th, 2017, 7:31 am #10

So we upgraded to a 60 watt laser and word got around that we have it. Been cutting a lot of thin wood for various customers.

Top of the sheet, the laser head has an air-assist. When the beam fires the wood ignites briefly and the air-jet extinguishes it. There is a char-spot where the beam burns through and of course the edges of the cut are singed as well. The air-jet prevents fires and blows out flare-ups... in certain situations though the wood can ignite and you end up with an air-jet fueled fire.

Seems to me better results could be had if I use a stream of Co2 instead of air. The laser has a huge exhaust fan so we'd be pulling the CO2 out of the work area and our workshop has an always-open (even in the winter) window-and-fan because of the fumes we generate doing other stuff. I'm thinking CO2 would prevent even that brief flare/burn at burn-through and it would work better at keeping flare-ups under control. Given that we are effectively directing cool CO2 gas at the burn point we've displaced oxygen and kept the work surface cool at the same time.

Aside from the hazard of overwhelming one's self with CO2 and ending up dead and on the news, am I thinking right here? It seems it would work, there are some safety challenges (interlocks?) that I would have to work through but if it's technically sound I might look into it further.
We used to use n2 in this capacity for cutting plywood flatbed dies.
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