screen that wont restrict flow? 1

[reploglejj]

Our stainless steel mill has a ESAB plasma table for cutting down stainless plates to spec for customers. The table was poorly engineered in many people's opinions. The table has a false bottom with a "bladder" beneath it. When the operator begins cutting and the system calls for water to flood the table, high air pressure is pushed into the bladder to displace the water onto the cutting area.

The problem is with the slag/sludge. Where the water flows in is along one of the length sides of the table and after the system calls for the water level to decrease, there's nothing stopping the by-product of cutting the plate from getting into that cavity. Over time it takes more and more pressure to get that water out because the flow becomes more and more restricted. The table is completely emptied out and cleaned every three weeks, but table was not constructed to be able to access the cavity beneath the false bottom. As the amount of slag increases in that cavity and the gate area along the wall, and the pressure needed increases, we see the tank itself begin busting welds more and more frequently.

This is the second tank and is relatively new. But we are already seeing the same signs of what occurred last time at a faster rate. My question is if anyone knows of a screen or material that we can design to create removable trays along the side of the tank to catch the slag. The trick is it has to able to catch the slag particles that are almost "sand-like" in structure, but not restrict the flow. I don't have numbers or figures currently on the flow rate, I'm just looking for a place to start. By the way if I seem like I'm leaving a lot out or my terminology is lacking it's because I'm a co-op (still learning). Any pointers would be greatly appreciated!

 

[EdStainless]

You do know that there is no such thing.
You will need a screen with opening sizes that are smaller than the particles that you are trying to catch.
There will be significant flow restriction. You just need to figure out if you can live with it.
There are SS screens that have been sintered and rolled. This makes them very strong and smooth, better than just a woven wire screen.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[btrueblood]

You might look at re-arranging the flow pattern, so that clean water comes in from one side of the table, and dirty water is drained off from the opposite side, into a sump. The sump would allow the particulate to settle out, and/or be filtered, prior to returning the water back to the "clean water" tank.

 

[reploglejj]

edstainless, you're right that was my mistake on wording. There will be restriction on anything being added to the path of the water flow. I'll look into the screens you spoke of, thanks for the tip.

btrueblood, that sounds like a really good idea for when we're purchasing the next plasma table (which if we don't fix this will be sooner than later) but the mill isn't looking to re-design the tank to that extent. Too much down time. Just like everywhere else, time is money, even if its an idea that will save them money in the long run they see the lose they would take now and not the loss they're going to take if the take breaks completely again. I'm doing my best to look into "non-evasive" ways to at least make the tank last them longer if not solve the problem.

 

[1gibson]

Put some magnets in the tray (or underneath the tray, if the wall is thin enough) to try to attract the particles, then periodically clean off the magnets. Might buy you some time between cleanings.

Could you fit long rails with magnets every few inches, that sat just outside/above the tray areas? Or maybe your screen idea, with large openings and magnets mounted to the screen.

Am I wrong in thinking that the slag will be mostly ferromagnetic?

 

[reploglejj]

I'm still learning about the different material properties but as far as I know the majority of the stainless plates we work with are not magnetic. I know some grades in the 400 series are but we run a lot of 300 series that's not. But, do the properties of the steel change after being cut-away by the plasma machine? Obviously the physical characteristics are different but I have no knowledge on if the slag would be magnetic.

 

[1gibson]

A lot of it has to do with the crystalline structure of the metal, once you plasma cut it that is out the window. You're left with small blobs that contain iron, that have been rapidly cooled/quenched by the water bath. Grab a magnet next time you clean it out, I'm honestly not sure, but guessing it will stick.

 

[reploglejj]

Wouldn't hurt to try haha. I'll see if I can find a magnet. Thanks for the advice, if it is magnetic that would be a great idea.