Water Table rust update

[WereWoof]

Howdy all.

Just a general status update regarding our plasma cutter water table and the anti rust chemicals that I use in it.

Since we have set up our cnc plasma cutter, it has been a full year now. In that period of time, we have done a lot of cutting.

First observation and opinion.. I totally love our water table. There is absolutely NO way that I would ever accept a dry cutter now. The water absorbs virtually all the smoke and dust that the plasma cutter produces, and allows us to cut in the shop, without having to worry about a dedicated ventilation system for the plasma machine. That saves us having to heat make up air in the winter.

Having the water table also makes it very nice in removing cut parts. Even though we normally set the water level at just under the bottom surface of the metal, the splash up of the water, from the plasma air jet instantly cools the part, which allows it to be picked up by hand immediately. This instant cooling also tends to greatly reduce warping of thin section parts, particularly of stainless steel, due to the heat of cutting.

After a year of cutting, we have not changed the water until just the other day. We finally drained the system and removed the cutting grates to allow us to muck out the bottom of the table. There was approximately 1 inch of "mud" in the bottom of the table, which consisted mostly of fine metal dust. I believe that some "smoke" compounds were a component of the "mud" as well, as we cut lots of material with vinyl protective "laserguard" film on it. Once the grates were lifted out of the way, and the water level drained to its lowest, it was a simple matter to shovel out the "mud" into buckets for disposal.

Second observation and opinion, regarding anti rust chemicals.

Our water table is made from 304 stainless steel, but the cutting slats I constructed of 14 gauge carbon steel... cold rolled mostly. At the initial filling of the table with water, I added approximately 4 pounds of sodium nitrite and 3 pounds of 20 mule team borax to the 190 gallons of water that our table/reservoir holds.
In that year, there has been NO observable rusting of any of the carbon steel slats or any of the cutting drops that were found in the bottom of the table at mucking out. The steel slats have been exposed to water levels that normally left the top 1/8 inch or so above water level, and the rest submerged, with periods of a day or so where I had the water level down lower, exposing most of the slats to air. It is my opinion that the sodium nitrite and borax did a very fine job of preventing corrosion of the metals exposed to the table water.

One thing I do note though is that when galvanized steel is exposed to the treated water for an extended period of time, it WILL be affected by the chemicals involved, or possibly a galvanic reaction with the chemically treated water as an electrolyte. I added a few galvanized cutting slats and found that they reacted strongly with the water and perhaps the stainless steel table.

When cutting galvanized, I simply make the cuts and then remove the cut parts in a more or less timely manner from the table and dry them off, and there are no adverse reactions.

We use a Hypertherm 1250 plasma cutter with a machine torch, and I could not be happier with it. Normally I used fine cut consumables since we cut mostly 3/16s or less in thickness, either carbon steel or stainless steel. While I normally run the torch above water level, I have at times cut with the torch tip fully submerged and that seems to work fine as well. I dont leave the torch standing in water, since water would tend to infiltrate into the torch tip and around the electrode, which is not a good idea. Though its a probably a point for another thread, I have made a simple modification to our hypertherm plasma cutter, which allows it to have a slow trickle of air at low pressure into the torch, even when the torch is off. This keeps the water out of the torch when it is not cutting but the tip is submerged, with a slow bubbling of air from the torch tip, but I cut with the tip submerged so infrequently that I normally dont turn this feature on. If I ever set our machine up to cut on nitrogen and fully submerged for stainless steel, I will begin using this trickle flow on a regular basis.

Sorry for the long post, but it might be of use to someone out there.

Best Wishes and happy cutting!

[WSS]

Read every word. Thanks for posting

WSS

[slammedxonair]

nice info. makes me want a water table more now lol.

[plain ol Bill]

As some of you know I built my table with a built in water table also. I agree w/ Werewoof in that I would not want to ever have a plasma table without using a water table. I had purchased some Plasma Quench for my table (5 gallons) and that was not enough. So rather than go through the hassle of TRYING to purchase some more (and that stuff is not cheap - especially w/ shipping) I bought some sodium nitrite off Ebay and added that to get a good mix. I have not seen any rust and the water has been in the table 6-7 months now.

[WSS]

OK, what does this anti-rust mix do, how does it compare to plasma quench? How much was the plasma quench w/shipping? Is sodium nitrate and borax mix safe for my girly hands? How about passing employees getting splashed (on accident)?

I have heard to many pros and few cons for the water table. The exhaust type seems to be just the opposite. We don't worry about "heat" during the winter but we do worry about it in the summer (As I type it is 106f) here in so cal.

WSS

[DanOSB]

im currious what cons have you heard about water table.. my cnc has water table and one day i was cutting with my cnc while the water level was really low (3 inch below the material) and i couldnt beleive how much smoke there was (after having it aprox 1/2 to 1/4 inch below the material.. its really working awesome preventing all smoke/dust

[WSS]

DanOSB,
Not comparing it to an exhaust system, it could be expensive if you use stainless, however if rust is not a problem then thats one con crossed off. another is a wet work area. I imagine that has to do with design. So yet another con gone. So let's see? hummm.....Anyone else with a reason not to? I will go the water table route as distortion is an issue for us. It is hard to image but everyone who has one is more than pleased as far as I have read.

plain ol bill, I am still perusing your build thread! The only drawback is it is adding to my build time. Great info.

WSS

[Superman]

Sorry guys, but I'm a noob in this area

But for those experiencing rusting in some way or another

Would having a Zinc blocks added act as sacrificial rust points also assist those having rust problems ???
similar to how ships and oil-rigs would use them

[jimcolt]

Issues with water tables:

In my shop in NH....which is a hobby shop and is not heated when I am not in it....the water will easily freeze in winter. my shop temperature has been as low as -10 F! I suppose you could put a rather large stock tanke heater (as used for cattle feeders in cold climates)....although that would likely consume a fair amount of power to keep the water above freezing.

Other issues...if the plate being cut is in contact with the water (which provides the best of fume control) the cut edge will have a higher propensity for dross.....as the molten metal resolidifies more quickly. Further....plasma cut edges that have water in contact with them during the cut will have a rougher edge finish due to the breakdown of water into oxygen and hydrogen (disassociation and electrolysis processes from the heat and the electrical action)....the hydrogen creates small explosions (you can actually hear little popping sounds from plasma when cutting in water) and these pops actually push the arc a bit, creating striations or pronounced lag lines in the cut face.

Also be aware....most entry level air plasma systems are not recomended for submerged cutting...although they will work. Modern air plasma torches use moving parts inside the torch to create a short circuit spark for starting the ionization process....over time, dirty water from a water table can cause the moving parts to stick and or short...which will cause damage to the torch head. Industrial high frequency start torches are better suited to water table applications as they use a gas preflow that blows any water out of the torch before firing...and they do not have moving parts.

The good things about water tables:

- best way to minimize fumes without wasting building heat (by blowing fumes outside)
-submerged cutting on stainless...using nitrogen...will provide an oxide-free cut face as ambient air is not present.
-Water table sludge is relatively easy to clean out as compared to dry tables...can be shoveled or scooped...as opposed to chipped.

Jim Colt Hypertherm

[Dustin407]

Im sure it is possible to talk to a chemical engineer/chemist about what to add in the water to stop rust and aslo electrolyses. This is not a hard task im sure everything in this world has an opposite chemical/nuetralizer..... But is it going to be lung healthy when cutting all day that is the new problem.

[plain ol Bill]

WSS sorry about adding to your build time (not really - grin). Glad to hear you think enough of some of some of my brain farts to maybe use them. I looked at a lot of builds, checked out a lot of the already built commercial units then just did it my way! So far I have no complaints about the table other than I wish I had been more of an electronics person. The electronics gave me more problems than anything else and the CandCNC packages are a lot easier to use than most others I looked at. If I had bought individual electronic parts I don't think I would have ever been able to get it going. But it is running and I love it.
My table is just A36 steel for the water table and I have seen NO rust at all. Using stainless would be way overkill in my opinion and a lot more $$.

Inccidentally folks if you do not have a water table and are getting plasma dust in your shop while cutting I really hope you are wearing a respirator. That dust is NOT good for your lungs.

[WSS]

Originally Posted by jimcolt Issues with water tables: Other issues...if the plate being cut is in contact with the water (which provides the best of fume control) the cut edge will have a higher propensity for dross.....as the molten metal resolidifies more quickly. Further....plasma cut edges that have water in contact with them during the cut will have a rougher edge finish due to the breakdown of water into oxygen and hydrogen (disassociation and electrolysis processes from the heat and the electrical action)....the hydrogen creates small explosions (you can actually hear little popping sounds from plasma when cutting in water) and these pops actually push the arc a bit, creating striations or pronounced lag lines in the cut face. Jim Colt Hypertherm

I am assuming we are talking about submersion? does the same apply if we just hit the bottom or a .25" below? I don't think I will submerge. Our table can handle up to 3" and I will only have skirts 1" above the slats. Is this enough? I will use oxy as much as the plasma, any thoughts with oxy?

plain ol bill, I like the idea of using air. Air is already handy and sounds like it works fast (hey, weren't we talking about this on another thread?).


The idea of the zinc may have some merit, it is usually used in saltwater but may have some benefit in a plasma table tank. I use them in housings for cameras underwater, both inside and out. I can get them with a 1/4-20 thread and replace them every season or so. I would imagine the block idea would be better if you could get them in big pieces. Anyone else with ideas on the zinc blocks?

Cool thread!
(no pun intended)
WSS