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View Full Version : Coolant filtering,micron sizes and filtering??



wierdscience
06-14-2006, 10:13 PM
Here is the situation-

Tub grinder at work needs the coolant filtered to remove metal particles and diamonds.Reason being occasionaly a diamond will get picked back up by the intake and imbed in the grinding wheel part way,it sticks there and degrades the ground finish by "witnessing" a series of tiny scratches into the surface.The result of this is the finished parts aren't as sharp as they could be because of all the errant scratches.Keep in mind I'm not talking visable to the naked eye,a 3x loupe is needed to see the effect.

I'm running a 30 gallon coolant tank with a 12 gpm pump which is capable of 15-20psi.I'm going to install a skimmer to get rid of the oil and sudge first,then an inline spin on filter head similar to an automotive oil filter.

I can get the filters down to 5 micron easy enough,one question is thou will that be fine enough?The wheel grit I use is 120-150 grit so I am thinking the 5 micron filter should catch the diamonds,but I'm not sure and I would hate to spend all that time installing and plumbing it,only to tear it all out and start over.

My other question is,I would like to filter the return to the tank,but I still need a fast return rate so the tank doesn't empty out waiting on the return flow.Also the return is strickly gravity fed and I absolutley can't have the return flow backing up in the tub ,if it does the coolant will top the shaft shield and run down into the 90vdc slip rings going to the magnet.

I was thinking some type of a filter material streched over a steel frame tilted on a slight angle off of horizonal,kind of like one of those gold screening troughs.Maybe use a piece of perforated metal over the top so the flow can spread out and cover more ground.

Any ideas?

Oh,I'm also looking for a cheap source for a 1/4hp 3~ in 3~ out vfd,chasis mount with a remote speed pot.

thistle
06-14-2006, 10:29 PM
can you make up a series of pvc pipes that act like the cyclone on a wood dust extraction system as the coolant enters the system fromthe machine to
tryand get the sediment settled ?

CCWKen
06-14-2006, 10:39 PM
Without pressure, I don't think you'll get much flow through a spin-on with gravity feed. No where near 12gpm anyway. You might think about multi-filtering too since a spin-on will free-flow when it gets clogged and the valve opens. Have you looked into "whole house" water filter systems? Most are 5 micron but you can get filters down to .6 micron. These too have to be run under pressure but it's another source for materials.

wierdscience
06-14-2006, 11:09 PM
Thistle,There isn't enough velocity in the system to make a cyclone work,I did thing about a centrifuge type,but that's too much experimention.

Ken,spin-on would be on the pump outlet before the coolant plumbing on the machine where I have 15-20psi.I was thinking of a Baldwin hydraulic filter with no bypass valve,since it's a centrifugal pump all it it will do is quit pumping when the filter clogs.

Herm Williams
06-15-2006, 12:51 AM
There are centrifuge type filters used to keep the oil clean in trucks that may meet your needs. google lists hundreds.
my two cents worth

Alan in Oz
06-15-2006, 03:03 AM
Weird,
For my cylindrical grinder (non diamond wheel, grit size 40-80) I'm using a 4 micron stainless steel mesh in a large funnel for intial filtering, this works well. Take the screen out and just wash backwards. Then onto a flat piece of felt about 10 by 10 inches slightly angled so as the speed of the fluid across it is slow to try and catch the rest including oil from the spindle. This gets most of it before going into a baffeled (2 compartment) settling tank, which usually ends up with an oil sheen on top, this being easily soaked up at the end of the day with several pieces of paper towel. On the pump output side use an inline filter from a Kartcher pressure washer to catch any last minute stuff. Don't know the micron size of this one, probably around 2-4. Mostly home made and not used often or far any extended periods. Surface finish definately better now than when I just had a settling tank only (Jones and Shipman unit) with no filtering.

wierdscience
06-15-2006, 08:24 AM
Thanks for that Alan,I like the filter screen idea and your resulting finish improvements confirms I am on the right track filtering the coolant

greywynd
06-15-2006, 08:45 AM
I know most of the grinders at work (with coolant) have a tray across the top of the tank with an expanded metal bottom. On top of the tray is a filter material, makes me think of the material used in coffee filters. The return line flows out onto this and catches the fine grit and like that are in the coolant. Most of these are set up with the material on rolls, when it gets dirty, just turn the rolls a little, and fresh paper across it. I don't know how fine of particles it will trap though, nor a source for the material. Just food for thought.

Mark

ulav8r
06-15-2006, 09:02 AM
http://www.sefar.com/cms/en.nsf/vPageID/usa_f_home http://www.barnesintl.com/filtration/applicationguide/index.htm

Am not familiar with the brand of filter fabric in the first link but it was the first found. It should give a representation of what is available. The Barnes filter units are what we use on 9 centerless grinders in our shop. The Barnes unit has three stages of filtration. It uses a combination of settling, magnetic separation, and fabric filtering. The fabric is supported on a chain belt that gives a large area for filtering, typically exposing a 36" x 36" area of fabric. The fabric is moving at a few inches per hour to continuously expose fresh surface.

Maybe you could make a similar arrangement without the magnetic drum. Also note that the Barnes units have a large coolant capacity, about 200 gallons on our units. The greater coolant capacity allows warf to settle out better becouse of the lower % flow rates. You are recirculating your entire capacity in 2 1/2 minutes. If you could increase that to 20 - 30 minutes your settling rate would increase by quite a bit.