View Full Version : Water filtration for a plasma table.

08-28-2014, 11:39 AM
Instead of hijacking another thread (http://bbs.homeshopmachinist.net/threads/64198-Air-pressure-required-to-lift-water/page5), I thought I would start a new one on building a tank and filtration system for a plasma table.
My general idea for the plasma table once I get my new shop built is a 5' X 10 - 12' table with a water tray and filtration system.
I have not yet decided on whether or not to bring the fluid* up to cover the work piece as of now but I do want the water to flow through the table to carry away the dust created from cutting,
So if I go 5' X 12' table with a 3" deep fluid level, that is about 112 gallons of water to cover the table to that depth. If the pump moves 7gpm at 0psi than it would take about 16 minutes to replace the fluid in the tray.
Having a tank that holds 28 gallons would add another four minutes to that figure, so 20 minutes to completely circulate the fluid in the system.
The first step in the filtration system would be a well about 12" deep at one end of the water tray that the fluid would flow into before going over the top of the stand pipe. This would allow the gross particles to settle out before flowing into the tank. The stand pipe would be a piece 2"BIP cut to length to establish the water level. The well area would be covered with grating to prevent small parts from dropping to the bottom of it.
The stand pipe would than be plumbed to the holding tank or a dedicated magnetic filtration tank.
Inside the tank would be a series of 304 SS baffle plates with neodymium magnets attached to catch the finer dust as the water flows over them.
Than a strainer for good measure to protect the pump from any larger non magnetic particles that would get through the system.
The holding tank and the optional magnetic filtration tank would have bolt on plate tops to prevent an overflow if the bypass was accidentally left on.
The well would have a drain and bypass that would allow the fluid to be pumped to drums for storage or to a drain for disposal.
Fluid level in the tray would be handled by the standpipe.
Having a separate tank to house the magnetic plates would add to the total fluid capacity of the system increasing the time it takes for one change of the fluid.
The tanks could be mounted on a dolly to allow them to be rolled out from under the table for cleaning and maintenance.
FLUID* referred in this thread is water without chemical additives.

08-28-2014, 12:58 PM
Good lord, you have made this complicated!

Just build a generic square tank and let the stuff settle and clean it out with a shop vac every once in a while. A large portion of the crud gathering will be non magnetic so you will have to drain it and shop vac it anyway. The crap in the water will tear up pumps and there is just no need for it. Use an upside down trough pressurized with air to raise and lower the water level.

08-28-2014, 01:11 PM
One thing i was involved with was building a waste removal system for mill scale and torch dross, it was big removing about 25 tons a shift off steel casters where the slabs were cut, it was called a hydrocyclone, like a wet dyson if you will, the test bed was in a lab so small, it elegant and simple, its somthing i was quite proud of te be honest
Look it up on utub

08-28-2014, 02:00 PM
Macona beat me to it.

You can't make a wheel "rounder". Even a filtered water tank is going to have "dead" areas where sludge acumulates. Have you ever tried cleaning iron dust off of neodymium magnets? Dry, it's a pain. Wet, well... lets just say that the masking tape trick won't work. You'd have to cover them with a rubber glove or something to make cleaning easier.

A standard tank will be just as effective at the primary function, and will be EASIER to clean (drain it, scoop out the sludge, hose the rest out). All this extra stuff is silly, seeing as you'll still have to completely drain the tank for cleaning, and you'll still have to clean out the filters, magnet baffles, etc. Where is there ANY benefit?!

08-28-2014, 05:15 PM
You need air to get the **** into suspension, then pump it out

08-28-2014, 06:11 PM
Yea id say just put some air stones in the tray to keep the nasty bacteria at bay (Tank full of iron + water = low oxygen!) and just dump/vacuum/scrape it up every few months, how often are you really going to be using it in a home shop? I bet you'll end up using it as space to put tools/parts most of the time. Its not like the tank has to stay clean, all you need is to keep less then 3" of debris in it. you could just scoop out crap with a strainer when it gets bad and rake down any deposits that get above the water line

If its full of oxygen rich water, all the debris will turn into iron oxide powder :)

No idea why you would want to raise the water level to the work, wouldn't the gas from the plasma cutter spray water everywhere?

08-28-2014, 07:05 PM
The tables I have worked on slightly submerged the plate. This reduces smoke and noise greatly as well as keeps thin plate from warping. No, the torch does not care. In fact my machine to hand an option that replaces the gas cover with water to lower smoke, noise, and UV even more.

Plain ol Bill
08-28-2014, 07:31 PM
I don't know about other machines but Hypertherm does not recommend water over the material for their air plasma units. I have a home built water table and use a Hypertherm 1250 w/ a Duramax machine torch and usually cut with the water about 1/4" below the material. Still captures 99% of the dust and prevents heat warpage from cutting heat. It is nice to cut a part, reach in and retrieve it barehanded. My water table holds approx. 350 gallons and I raise and lower the water into the bottom tank w/ air. Cutting dross and dust (which is metal by the way) is heavy and settles straight down. My table has been in use for about six years and I have very little metal dust that has traveled to the bottom of the sump area and have never cleaned that area out. I drain the table dry (just release the water into the tank) whenever I need to clean the table of dross and waste material. I do use a rust preventative in my water made and distributed by Miller Welding for use in plasma cutting.

08-28-2014, 08:58 PM
I built my table with a low spot in the middle of the bottom, and a drain pipe down there, with a ball valve and a hose connector on it- so when I want to clean it, I hook up a fifty foot hose, run it outside, and just open the valve.
But whats left is not "particles"- its muck, heavy, iron muck. I have to shovel it out, after picking out any metal drops bigger than a golf ball. Nasty stuff, guaranteed to clog any screen you can come up with. And my table, only 4'x4', produces two or three five gallon buckets of the stuff a year- it would overwhelm a magnet in about 2 days.
I know of no other way than drain, and shovel. Dirty work, but necessary.

08-29-2014, 10:36 AM
Macona & Bill, raising the water level with air is would be an option if my insurance did not need proof that anything that holds air pressure has a certification on it.
Boslab, will look for that.
Roy, the magnets would be epoxied into the SS plates so the iron particles could be squeegeed off the surface.
Ries, the bottom of the tray would have a slight slope to the "well" or sump to help the iron particles to move along to the sump, I will do some small scale testing to see what works the best.
I will redo a couple of the parts of my plans to increase the size of my holding tank to allow for the particles to settle out.
The whole idea behind this thread is to get ideas on how to do this before I start building.