Plasma Cutter

[Pat]

Stimw, Thanks for the water warning. I'll be getting disposable dryers and when I plumb in my new upright compressor I intend to have some long vertical "U" bends with drains at the bottoms. My shop has A/C and I thought about wrapping an A/C duct with tubing to form a heat exchanger to condense water upstream of one of the drains that itself will be upstream of a water absorber. I'm too cheap to buy a freon/compressor type dryer.

My plasma maxes out at 27 amps but the next size up was $600 more, runs on 240VAC only and I don't expect to cut much thick stuff. My 27 amp unit has a switch in the back accessible through a slot to select operating voltage, 120 or 240. That is a handy feature as the unit is portable and I may go where getting 240 is a hassle. It sure slices 3/16 material very well and will chop off 1/2 inch (reallly ugly) and I cut some 3/4 round rod by rotating it (also ugly) I did have to make up an adaptor cord to be able to plug into 240 instead of following the instructions and cutting the molded plug off and replacing with 240 vac plug.

When starting a cut by piercing rather than starting at an edge there is some flying debris in the way of molten metal and slag that will burn the snot out of you if it hits and sticks to your skin (like your face.) So I intend to use a hood but with a large viewing area and use shade 4 or 5 depending on how high I turn it up. Murphy tries to make an example of me so I have to be more careful.

[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]

[MadReferee]

Well, better late than never.

Clean dry air is an absolute requirement if you want to get optimum performance from your plasma cutter. If you live in a climate where there is significant moisture in the air, you must insure that the air from your compressor contains NO moisture by the time it reaches the plasma cutter.

In my case I tripple filtered the compressor air. Once at the compressor with particule and water filters and twice at the plasma cutter. At the cutter I used a reusable filter/regulator followed by a MotorGuard water separator.

If you use anything, use the MotorGuard. While rather expensive ($75-$100) it is probably the best out there for the money spent, and it works. It is highly recommended by most people on the Miller and Hobart welding forums too.

I have attached a picture of my setup. The argon bottle is for my tig unit which shares the cart (which is a Craftsman project cart).

[Pat]

Mad, Thanks for the gift of your experience. I have been running without a water filter but will be getting one soon. I had previously considered a dessicator filter arrangement for the input of the air compressor. Why suck in moist air, condense it and then store it in the "rustable" tank as well as distribute it to all your tools? Why not pre-treat the source (and the output if needed?)

Anyway I will be getting an in-line water stopper thingy for the output of the compressor real soon now. I have never used any "driers" for air lines before. Are any of them user servicable? I thought a granular dessicant product followed by a particle filter to keep any dessicant dust out of the air line would be a good thing. Instead of buying throw away cartridges just empty and refill the canister with new/recharged granules. Recharging some of the dessicants is just a matter of baking them at a prescribed temp for a prescribed time. This works for more than just the silica gel type. Over time there miught be some "shrinkage" of the dessicant from my sloppy handling and small quantities ending up in the particulate filter but except for these losses you should be able to recycle the dessicant as long as you want.

Maybe a piece of fair sized diameter pipe as the filter body and a few fittings to reduce it down to air hose connection size would do the job. If the filter were placed after the compressor but before the tank the filter would not restrict the flow exiting the tank (although it would reduce the CFM ability of the compressor a bit. I'd have to study on this a mite as there might be a requirement for an "intercooler" upstream of the filter to keep the dessicant temp from getting to high.

Food for thought...



[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]

[MadReferee]

You can purchase an air dryer and use it in place of the MotorGuard or any other water filters. I would still use a particle filter at the compressor though. These dryers can be found for $400-$700. Warning - dont' buy a HF or eBay cheapie. Get a good one.

Here is a link to a manufacturer that was recommended on one of the welding forums.

Compressed Air Dryers

[Pat]

Ref, Maybe I'm missing something but do I need a compressor type dryer or would a dessicant type, throwaway or rechargeable be sufficient. Just how low does the relative humidity have to be in the long term for plasma cutting?

[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]

[MadReferee]

If you plasma cut everyday then a standalone dryer is probably more cost effective. If you only plasma cut occasionally (ie. hobby use) then a water separator like the MotorGuard would suffice.

I would not use a dessicant type separator since I don't think it would be as effective in removing moisture in a high pressure application. The MotorGuard uses replacable paper-like elements that look almost like a roll of toilet paper. In fact people have used rolls of TP in an emergency until the right filter could be obtained.

If you have good moisture removal in your air supply then humidity should have no effect, although a higher air humidity will cause you to replace the water separator filter more often. The trick to good plasma cutting is to remove all moisture from the air before it gets to the cutting tip. Tips will last longer and the cut will be better.

Shop around for a MotorGuard as prices vary considerabily. You want a model M-26.

[egon]

Pat:

Know zip about plasma cutting but haveing seen some air dryers [ all downstream or intercooler ] in operation a comment will be made.

As you have already noted find the limits of moisture allowable for the plasma cutter.

Then use mechanical seperators followed by a regenerating desicant dryer. Continuous operation systems will have several desicant dryers. One on line and the other recharging?. They may switch on a straight timer or by moisture sensing of the outlet air.

From my little world what we termed [" Instrument air "] desicant types were always used.

I'd suggest two smaller cartridge desicant types set up in parallel. When one is used up manually switch and set up the other for heating and drying.

A little water in instrument air lines at -20c makes for a long hard cold day dragging steam hozes around and manually ajusting valves and other such goodies. It's even more fun when the vales are 24 inch under high pressure with old packing in them. Snipes that don't fly are a welcome sight.

Egon [img]/forums/images/icons/grin.gif[/img]

[Pat]

Ref, Thanks again for the inside dope. I don't think I got my question across very good last time. The driers are used to lower the relative humidity of the air passing through the plasma torch. IF the ambient air is dry enough, additional drying would not be required (think Sahara desert.) So my question is: how low does the RH of the air delivered to the tip need to be?

It is unlikely that my ambient air would meet spec much of the time. Oh, and I don't think pressure is a problem for dessicants but high flow rates would put demands on the design.

Addendum I

I went to a couple sites and read about the motorguard filter. It takes out condensed water, i.e. drops and does little or nothing for RH. It is still a very good thing to have because it also gets the oil, rust, dirt etc. I will probably get one or something liike it fairly soon.

I'm thiinking a larger WHOLE SYSTEM filter might be a good idea. Put it on the outlet of the compressor's tank to prevent stuff from getting in the lines to start with. Of course delicate air consuming items would still be better off with a filter just upstream of them for just in case but the majority of the task could be centralized.

As my shop has A/C I thought of putting a finned heat exchanger in the line to help condense water vapors and have a small water collection vessel immediately down stream of it. A sight glass would be nice with a drain petcock under the collection vessel. I know this would not be as effective as a freon compressor type dryer but it would help extend the life of any dryers downstream of it.

I don't weld or cut every day but I have put in a lot of hours welding recently as I have desigbed and am cnstructing a set of 11 security guards for covering windows in a storage bld of a new neighbor whose husband is an electrician. I'm up to about 60 hrs on the project and have used the plasma a few times on it. I tack with the little MIG but use 6011 and 6013 stick to finish welding the 5/8 round bars into the 11/16 holes drilled in the 1 1/2 inch by 1/4 inch flat bar.

Interestingly enough the 5/8 bars will not fit in holes drilled with 5/8 bit. Same size bits work with bolts but not round bar! Had to upsize to 11/16 since didn't see a 21/32 on the shelf. If I wasn't so rusty doing stick I might have used 7018 but that requires just a little actual welding skill of which I am nearly devoid.

Looking forward to her husband getting home from his projects in Hawaii so I can get help with fininshing my electrical.

[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]

[egon]

Desicants stand up to higher pressures and flow rates with no problems.

Egon [img]/forums/images/icons/grin.gif[/img]

[MadReferee]

</font><blockquote><font class="small">In reply to:</font><hr />
Desicants stand up to higher pressures and flow rates with no problems.

[/ QUOTE ]

Assuming you get the right one [img]/forums/images/icons/smile.gif[/img] . Like everything else not all are made the same. This link has a good one. Size it to your needs. They don't list prices so you are on your own.

Super-Dry Desiccant