Underwater Plasma ?

[Barry_ward]

Does anyone here have their torch tip underwater?

I just spoke to an old friend and he said that years ago he used to run his table with the part under an inch of water.

He said that the tip life was greatly improved.
He also said that he added a dye which absorbed the UV.

Having all the smoke and scrid contained under water sounds very cool to me.


Any comments or experience?

best regards,

Barry

[Mike@Torchmate]

We have cut under water before, however the tip consumable life was reduced rather then increased.

The water level on the table should never reach higher then the top of the material, it's just not necessary. The water being at the bottom of the plate, or even slightly below that, will still consume nearly all the smoke and dust associated with the plasma cutting process.

[xt300301nut]

Underwater cutting: 1) remember that you reduce your cutting capacity due to the cooling action of the water. 2) Pierce capacity is greatly reduced. 3) not recommended if you do not have an automated height control. Nearly impossible to set cut height by eye when everything is under water. 4) Koal Industries (847-956-7920) sells a product called Kaol Quench to add to your water table to reduce fungus growth and color the water.

[JL Fabrication]

Will cutting with water just touching the bottom of the material help reduce warpage. There are numerous time when cutting 10 gauge ss and thinner into long narrower parts that I experience warpage as well as the material sometimes trying to crawl around the table. I have thought to try a water table to help solve this?????

[Mike@Torchmate]

The water does help in cooling the material, because even at the bottom of the material, water splashes across the bottom and top from the air blowing/bubbling. We never cut thinner then 10 gauge on our watertable so I'm not sure if it helps alot or not. We only usually cut larger plate sizes. I can tell you that the cooling is obvious and very noticeable to the parts.

[Richard Honey]

Mike,

The concept of a water table is attractive in that it captures dust and smoke and reduces material warpage.

The downside as I understand it is the rusting of the support slats, the retrieval of small cut parts that may fall in, the removal of sludge from the tank and the disposal of the rusty, dirty water.

Also the weight of the water is something to consider. It makes moving the table when filled very problematic and means that heavy support structures are required for the tank.

Has anyone contemplated a smoke hood under the table attached to the moving gantry? I understand that to effectively remove smoke from under the plasma table requires a VERY big fan.

My idea is to have an inverted smoke hood the width of the table and say 2 foot long slung under the table and attached to the gantry. The extraction source would be attached via a flexible tube say 8 inches in diameter. The tube control could be similar to the cable carrier concept on the rest of the table.

X movement of the gantry would be mirrored by the attached hood and the y movement of the torch accommodated because the hood extends across the full width of the table underneath.

The idea is that the maximum dust extraction vacuum would be directly under the torch and not spread all over the table. I know that the extra weight if the hood would impact on the inertia and acceleration of the gantry however with the big servo kits available from CandCNC this shouldn't be a problem.

Also the hood could be constructed of thin galvanised sheet hence it wouldn't weigh much. The biggest friction/weight issue may be the flexible extraction hose.

[Mike@Torchmate]

Originally Posted by Richard Honey Mike, The concept of a water table is attractive in that it captures dust and smoke and reduces material warpage. The downside as I understand it is the rusting of the support slats, the retrieval of small cut parts that may fall in, the removal of sludge from the tank and the disposal of the rusty, dirty water.

Yes, I am well aware of what the water table is actually for, I was simply pointing out the cooling effects of the water.

The downsides are accurate, however I feel the benefits far outweigh the downsides. There are benefits to downdraft designs as well though so it may be personal preference.

[massajamesb]

I am actually looking at building my water table, and in it I am using a Ph control solution that will allow me to keep everything from rusting. Generally An application of rubberized undercoating or Por15 before hand to the tank walls and base would aid as well.

As far as the parts falling to the bottom, I have devised a metal mesh screen (expanded metal) that clips in place directly below the cutting slats. If the part falls out, it doesn't fall far. A finer, metal mesh screen similar to that on some doors would allow for cleaning out the fallen material easier. Drain the water some, and shop-vac out the screened slag and metal.

[Perp]

Originally Posted by massajamesb I am actually looking at building my water table, and in it I am using a Ph control solution that will allow me to keep everything from rusting.

Could you eloborate on the rust inhibitor solution you plan to use? Is it the cost that prevents the use of stainless steel for the frame/water tray (not the consumable slats) or is it something else I should know about before I start. Thanks

[massajamesb]

Originally Posted by Perp Could you eloborate on the rust inhibitor solution you plan to use? Is it the cost that prevents the use of stainless steel for the frame/water tray (not the consumable slats) or is it something else I should know about before I start. Thanks

I have some chemicals at hand that are not available "over the counter" for most people for my Ph control. I will be using a 50% caustic soda solution. I would suggest going to a pool supply shop, and see what they recommend to make the water in your machine more alkyli. What you are trying to do is to basically put a calcium buildup on your metal, which will prevent the normal rust you see. A undercoating or paint covering will be helpful beneath that layer of buildup.

If caustic does not suffice, I will be using a quicklime slurry.

When I say calcium buildup, I don't mean you want to pour a jug of milk in your table, nor should your cutting water be white.

Stainless is a nice option, if you can afford it. I priced a 4x8 sheet of 18 ga brushed stainless the other day at 275 dollars.
I priced out the materials in mild steel to build my water table for my new 5x10 cut area table I am working on, and I am looking about 150 bucks. To do it in stainless would cost me about 500 easily.

[grinder_gary]

Originally Posted by Richard Honey Mike, Also the hood could be constructed of thin galvanised sheet hence it wouldn't weigh much. The biggest friction/weight issue may be the flexible extraction hose.

I don't think I would want all that slag falling into the thin galvinized hood. It would eventually become heavier and heavier with all that slag sticking to your hood. I had that problem when somebody forgot to take a large piece out from under the table and now it is covered with slag.

Great idea, just worried about build up of slag

Gary

[Torchhead]

1: You don't have to worry about changing dirty water. It will evaporate fast enough you can add fresh.

2: Cleaning out the tank if you make the slats removable is a function sorta like panning for gold but it's panning for steel (:-). After removing the bigger pieces by hand (fun!) I use a big dust pan and just scoop the bottom for the slag and let the water run back in.

3: Most cleaning solutions are alkiline in nature. I dump half a bottle of cheap dishwashing liquid in the water to prevent mold. Plus the air blowing inot the water makes really pretty bubbles.

4. Rusty slats don't effect cuts (just look bad)

5. Finding drop-out parts can be a challenge. A shallow tank makes it easier. A keen sense of feel lets you sort through the debris and "find" a shape that has fallen through. Besides, it gives you something to do that is better than chipping off slag! A catch grid would be okay but you still have to sort through all of the parts you DON'T want (most of what falls through) anyway.

The tank does not need to be but 3 or 4 inches deep. You do need some way to empty it if you have a roll-around table but in 5 years of cutting I have used the drop-down wheels on my table twice. My drains are 1" pipe and are close to worthless. You have to completely clean the tank BEFORE you drain it or it just clogs the valve with the steel "gravel" in the tank.

TOM CAUDLE
www.CandCNC.com