Carbide Central Coolant System, What coolant will work best?

[bigj4]

I have a 8,000 gallon Central Coolant System I use for grinding carbide rods and use a water soluble coolant. The Central System uses four Large sand filters that get back flushed to keep the coolant clean. I was told that you can only use synthetic coolants in the system due to the sand filters, this coolant system is 30 years old and works fine but I want to change to a coolant that is a semi-synthetic so the machines get some lubrication on the metal sliding covers, etc. Was synthetic coolant around thirty years ago? The coolant that I want has to work good on centerless grinding and keep my machines clean and not allow the cobalt to be leached from the carbide and no foaming. Can someone assist me with this problem.

 

[saberblue]

You need to look at fluid selection very carefully!

The first question you need to look at is the question of Co (cobalt) leach- this is when the fluid solublizes the Co binder (the most common WC -tungsten carbide- binder. leaching the Co out will cause the WC to have reduced shock resistance, in creased surface area, rougher finish etc. Additionally, Co in solution may create health safety and disposal issues. If the Co in solution is allowed to build up tho the point that it participated it will form a very hard abrasive residue on you machine tools -- the only effective removal technique is elbow grease because most people don't want to wash down their grinders with ver low pH cleaning compounds for all the obvious reasons.

Co in solution also tends to feed fungus which can cause all sorts of problems -- the Co[sup]++[/sup]will also tend to "strip out" the fungicides most often formulated into WC grinding fluids

the next big issue is that WC diamond grinding wheels particularly resin bond can be easily affected by changes in fluid working pH, oil and surfactant selection etc. etc. Have your wheel supplier give you ranges or test the fluid and the bond. Also remember that you are probably using coated diamond either Cu or Ni and if your new fluid goes after the coating or the bond your "G" ratios will go way down and very rapidly.

If you move to a semi synthetic (one using petroleum oil in particular) as the fluid picks up cat ions the particle size of the fluid will change get larger and you may loose grinding efficacy- moving to a semi may also affect the flux rate of filter.

WC grinding is very hard on work rest blades particularly if they are WC. Co leach again. If work rest blade l life is a problem you should look at fluid cleanliness and application. to have the type of fluid make a substantial difference in blade life you would probably have to go the high concentration soluble oil of even oil. these changes would probably require completely re engineering you process.

As to foaming you need to be very careful about the kind of anti foam used as it may clog up both the regulating and grinding wheels and can affect filtration.

Depending on what you drivers are for looking at this fluid change my first thought is to get a good quality fluid suppler who has been down this path and buy the best quality WC grinding fluid you can get and then manage the "hell" out of it -- control the concentration with in +/- 1% test for the presence of mental in solution and then take appropriate action.

A long time ago in a different era I spent $1,000,000+ a year on diamond wheels and getting control of the fluid saved me 5-6 lost days a year to dermatitis and saved about 5% on wheel purchases.

Do you sell your diamond WC swarf? Do you keep the WC swarf separate from other grinding swarf? You should check with who ever is actually processing the swarf as the fluid used can affect the reclamation process.

The best only way to keep the machines clean is to was them down at the end of every setup and the end of the shift. As make sure that the wash down lines and return lines fo their jobs properly.


As to you more general questions "synthetics have be around since Fredric Taylor did his research late 1800s. WC grinding fluids have been around since the middle 40's - there was a bid change in the market and formulation of these fluid as as H&S rules change -- the elimination of Cr as a corrosion inhibitor and NaN. So there are a relatively few fluid manufactures actively chasing this market.


good luck with this project as I have just scratched the surface of the issues --


A.R. "Andy" Nelson
Engineering Consultant
anelson@arnengineering.com