Dec. 06, 2023
Machinery
I have once again learned the hard way; that 1) the importance of dry compressed air CANNOT be overstated in the process of plasma cutting, IMHO of course. 2) the current degree of one’s dry compressed air is usually assumed to be (perhaps falsely) OK; again from experience, it was certainly assumed as such in my case. And last but not least, 3) the expense of attaining dry compressed air is worth it albeit relative to your tolerance of expense.
All that said, the purpose of this paper is to share my experiences with you, the assumed neophyte plasma cutting enthusiast, just as I began as a neophyte attempting to achieve this skill and master this process a couple of years ago. I began by aspiring to build a CNC plasma cutting machine during COVID (what else was there to do?), and with assistance from my good friend Blaise (no pun intended), we accomplished that. It’s been a work in progress, but I believe we’re finally there. We have a reliable, accurate, versatile, portable, and consistent CNC plasma machine that produces seemingly limitless and great results. The most significant aspect of this project I believe was finally observing the true meaning and results of using “Dry Compressed Air”. Thus, we thought it would be nice to share how we not only attained dry compressed air, but also how we realized that we did attain it, including the proof necessary for ongoing maintenance of it.
Nearly everything you read about plasma cutting, from the most reliable sources, most likely mentions “make sure you use dry compressed air...”. But nowhere do I recall reading “this is how you KNOW that you have dry air...”. However, in reading and following various plasma process product and enthusiast blogs and forums, I certainly noticed the pattern where ‘experts’ would reply to a posting, usually of a disastrous plasma torch nozzle mishap or cutting result, with a well-intentioned – “it looks like you don’t have dry air”. So, I had plenty of examples of ‘moist air’, or varying degrees of less than ‘dry air’, and I could compare those experiences with mine at times. This was an ‘Ah Ha!’ moment for us... if torch consumables (nozzle and electrode) are dark and arc pitted, or if cutting results have large, deep striations on the edge, or if consumables don’t last well over 200 pierces, or if proven cut parameters that worked well last week don’t seem to be working well today, or if things happen that just can’t be explained, then you may have moist air. I wish it were more absolute than that, but in the absence of knowing for sure to what degree the compressed air may be dry or not dry, let’s go with these analogues for now.
Summary: The Realization of Attaining Dry Compressed Air
We should assume then...
Summary: This is what it took to attain dry air, by the measures noted above...
I added these improvements for a mere $320 to my existing air compressor system which already included a $60 Harbor Freight desiccant dryer and coalescing filter. And it’s portable and does not take up additional floor space.
Details if interested...
Resuming from the episode before the Summaries... But then comes the downside from the expert recommendations, the advice that “it will cost you between $1,000 and $2,000 to fix that (moist air)”, that is to attain dry air; at least those were the prices of the parts that were invariably recommended to fix the problem. But every now and then, someone would reply that simply adding a condenser to the air compressor system was sufficient to dry the air. I made note of that. I began looking at turnkey air compressor systems that claimed to have 98% or higher ‘dry air’, and citing certain ISO standards. But wait... all of those air compressor systems had seemingly simple tube and fin condensers, see California Air Tools as an example. Now I’m not one to jump on the chance to spend a lot of money, so I began researching air condensers and found them to be quite expensive, to the point that the prices for CalAT air systems were somewhat justified. But I also noticed that the temperatures, pressures, and construction of so called ‘air compressor condensers’ were very similar to specs for oil coolers such as those used for engines and transmissions, and that some enterprising craftsman were using the latter for compressed air moisture condensers, and that the pricing of oil coolers could be an order of magnitude less than that of a sold-for-purpose compressed air moisture condenser. I made note of that also, but after careful consideration, did not act on it because I thought I had dry air. My air storage tank was essentially serving as the condenser in the system, it has a drain and I drain it every day, and after all I had a HF desiccant dryer and coalescing filter after the tank on the air output! What could be better? And besides, I was already “successfully” plasma cutting, or so it seemed, albeit that there were enough failure cuts that I could not always explain. Then came July in North Carolina. Humidity drips from the air when the sun is shining, we call it rain only when it’s cloudy.
So, I’m cutting a large plasma job one day in July; 24”x32” 10ga. mild steel, a business logo for a friend of mine, the design has 84 pierces and 22 meters of cut length, he wants 12 units. I discovered a few things on that job, the least of which were:
See photos for consumable results under both minor and severe air moisture conditions. In the case of those consumables in the yellow boxes, this was an extreme case of moist air, and a fairly obvious one at that. It still took at least 2 welded nozzles to diagnose the problem, and 2 more welded nozzles plus numerous ruined ones that didn’t weld, to get the job done.
The yellow box are the same 4 sets, just different angles, these are the nozzles and electrodes that arc welded due to moisture accumulation during cutting.
The red and green boxes are nozzles well used before and after the condenser was installed, I do not recall which are which. The photos below are the same sets of red and green boxes from different angles. So, if your nozzles and electrodes look like this, you likely have some degree of moist air, but nonetheless you are plasma cutting with some success. But believe me, plasma cutting process gets much better with absolutely dry air.
It was at this point that I saw the value of a tube and fin condenser on my air supply system. So, I added one between the compressor and the storage tank, along with a fan and drain tube. WOW! I had a distilled water plant now. An even better alternative to this type of condenser is a refrigerated condenser, but those start at $600 (at HF of course), and up to $1,800 (name brand) for 10 SCFM and require about 5 to 10 sq.ft. of floor space and more power, none of which I had at the time. I added my tube and fin condenser to the vertical tank air system for $150 in parts (I had some parts on hand, else it would have cost $220); and its portable with the air system since its attached to it. Immediately the continuous-run warm moist air problem was solved, the storage tank hasn’t been warm since and has resumed its secondary job of now being the secondary condenser in the system, I still drain it after daily use but not with nearly as much water, rather most of the moisture is being trapped in the tube and fin condenser and drain trap. I also still see the need to change the 1/3 cup desiccant dryer beads about every 10 minutes of compressor run time. However, my torch electrodes and interior of the nozzles are still looking dark stained, and arc pitted, but much less than pre-condenser cutting, and I’m assuming this is now the new normal and believe I have dry air. But not so fast.
Net net, the tube&fin condenser allowed me to use my plasma cutter for long lengths of time during humid months. Great. Other than that, the condition of the consumables did not seem to have changed much but given the amount of water I was trapping now, but I sure felt good about improving the process, and it seemed like a huge leap. The temperature of the output port of the compressor runs up to and stabilizes at about 250F deg during runtime, however that heat and air temperature is dissipated to room temperature by the 5th to 7th tube passing through the condenser. Even during periods of constant compressor runtime, the tube and air higher temperature does not propagate below the 7th tube from the top. This is key because it allows the tank to act as a secondary condenser. Thus, I added an easy to reach and operate drain to the tank.
BTW- I should also mention that after adding the tube&fin condenser, I had to purposefully purge the water that condensed and collected in my 50 ft. air hose sitting on a hose winder (hey, another condenser) by using compressed air and gravity, and do the same with my 25 ft of torch lead, and re-tap the M5 threaded electrode plunger in the PTM60 torch. I now use an 8 ft. hose from my air supply to the plasma cutter, another standard recommendation I chose to ignore earlier, believing I had dry air of course.
So now 6 months later, December, nice cold, crisp, dry atmospheric air in North Carolina. I’m using my afore referenced but now named (in part) Tri-CAM CNC (Routing, Laser, Plasma Process) in laser process mode, with compressed air assist which is common. The air flow is 1/10th that of plasma cutting, so about 0.5 SCFM. Yet I notice after a few compressor cycles over a period of a couple of hours, the equivalent of maybe 10 minutes of compressor runtime, I still have to change the 1/3 cup desiccant dryer, the beads have changed over from blue to pink! How can this be? I’m not trapping nearly the amount of water in the tube&fin condenser and tank as I was in July, which makes sense since the atmospheric air is so dry now, yet the desiccant dryer is choked with moisture at the same compressor runtime interval as in July. So, it occurred to me that perhaps the RATIO of desiccant bead volume –TO-- air flow volume had something to do with this process of attaining ‘dry air’. Perhaps this explains why even after the tube&fin condenser was added, I still had dark stained electrodes and pitted nozzles, I had what must have been the markings of moist air and I didn’t trust it, perhaps didn’t want to believe it.
Humm... Recall those turnkey air compressor systems like CalAT that I referenced earlier. Those systems not only have tube&fin condensers, but they also have large capacity, serviceable, desiccant or custom cartridge dryers. So, I bit the bullet and dropped $150 on a much larger desiccant dryer, after all I made a few bucks on the 12 units of 24”x32” business logo signs the previous summer, so what the heck, reinvest in the business. The new dryer is a well-reviewed and popular 1 quart capacity desiccant dryer, that is a whopping 12x the capacity of what I previously had in service. I did some plasma cutting, and holy cow!, the world might as well have spun backwards!
Photos of the torch consumables... after 50 pierces and cuts, they look nearly brand new! Not only is the 1.1mm orifice clearly intact, you can even see the beveled or stepped lead out, and the arc pitting is almost nonexistent, and the electrode dark staining is gone also, there is only a hint of swirl tracks on the electrode. This is plasma cutting process with dry air, hands down!
I put the HF 1/3 cup desiccant dryer on the back of the plasma cutter, to act as an indicator of moisture, which is about all that it is good for at 5 SCFM flow rate.
After several plasma cutting jobs since, the results are fabulous! I’m actually re-adjusting my cut parameters as I move through the different mild steel sheet gauges in various jobs. I’m much closer to the PW Cut60 book recommendations than previously. I can change a parameter and get a predictable result. Amazing. Consumables are lasting 2x longer at least, and I don’t have to clean them 2 or 3 times to extend their life, I’m changing them before they actually look worn out. This is night and day difference.
The air is so dry, I’ve had 2 regulators fail from seemingly remnant rust debris on and around the valve and spring seal, I took both of them apart to confirm, and in one case, I just changed the spring valve after cleaning out the rust debris and it’s working fine again. When I say rust, it’s a fine dusting of rust colored film, typical of what may have been microscopic in the moisture of the air flow previously, and there being just enough moisture to keep the seal ‘lubricated’. I’m guessing here, but it’s odd 2 different brands of regulators would fail, one in the plasma cutter, one on the air supply system, shortly after the last improvement for dry air.
I hope this helps a newbie or anyone understand the importance of dry air in the plasma cutting process, including how to achieve it economically and how to know that you have achieved it. I truly feel great about this progress and experience, and wanted to share it.
Parts list:
The Importance of Dry Air for Plasma Cutting
By bLouChip.Consulting@gmail.com
My CNC is a MillRight Mega V XL, built with a custom Open Frame Bed, running Tri-CAM processes of Routing/Milling, Laser, and Plasma. Plasma source is PrimeWeld Cut60 w Tecmo PTM60 Torch.
Router: Makita RT0701C, Laser: Neje A40640
Software: LightBurn, SheetCAM, Aspire V11, UGS, and sometimes [con]Fusion360
Unique side note: I store the CNC on the ceiling of my shop while converting my plasma table into a welding table.
Photo gallery: www.drive.google.com/drive/folders/1Kqt8RInPSwdsv4s-5aUB3uAAHuvQLFic
CNC Build blog: https://millrightcnc.proboards.com/thread/3563/plasma-router-custom-build-frame
YouTube channel: www.youtube.com/channel/UCdUAmFDK3Tw_ihA8WcPkb8g bLouChip.Consulting@gmail.com
Article Written by: bLouChip Consulting
I run the HF refrigerated dryer and it’s fantastic for the money. Down stream I have a 1 quart desiccant dryer and then a Motorguard right before the Plasma. My desiccant does pick up a little moisture that slips past the refrigerated dryer but not much and only on really humid days. I don’t anticipate having to change out the beads more than once a year. You could probably get away with a smaller one.
You’ll want a .01 micron filter between the desiccant and plasma. The Motorguard is .01 or there are other options online but they cost just as much or more. .01 will remove oil mist if you’re running a oiled pump. And having the filter downstream of the desiccant will prevent bits of the blue beads from getting into your torch and consumables. And it does happen, there are a few blue specs on my Motorguard filter here and there.
The Motorguard will also catch moisture but being a sealed unit it has no way to get rid of that moisture. If you live in a humid environment and rely on the Motorguard to remove moisture, you’ll end up with a soggy filter that looks like a wet roll of toilet paper every couple weeks and needs to be replaced or dried out.
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