Grinding coolant VS Milling coolant

Ok guys, time to settle another debate. I say that coolant intended for milling/turning/conventional machining should not be used for surface grinding operations. The grinding coolants that I have had experience with is basically water with ethylene glycol to cool and prevent the materials from rusting/corroding. Conversely, fluids intended for "cutting" applications, although they may be water based, have additional additives to lubricate the tools and work.

I have issues with:
The additives "clogging" the pores of the grinding wheel, thus making it cut less effectively, possibly making it run "hot"...creating a possible dangerous condition.
With the filtration systems (bed filters and/or hurricane style, or even centrifuge systems), will the additives plug the filters?

And, by the same token, based on my experience, because grinding fluids do not have the same lubricity, they do not make a good choice for use in a milling center.

Please chime in...

Mark

Hi M. Roberts:
I got a bucket of Fuchs grinding concentrate once by mistake, so I used it on the grinder.
I thought it worked better than the mill and lathe coolant I used before, so that's what I've been buying ever since.
I can't grind to a better finish and I can't grind more accurately, but there's another really good reason I made the switch.

My main complaint with mill coolant on the grinder is that it gets really nasty, seemingly much faster than the proper stuff.
Grinding swarf holds it stagnant like a big sloppy sponge and anaerobic stink bugs just LOVE a stagnant environment with no oxygen around.
I used to pop a piece of copper into the tank to try to minimize this bacterial overgrowth, but now I had stinky green instead of stinky cream coloured slime water.
The Fuchs seems to be much more resistant to this...I don't know why but it does so I don't question it.

Rotten coolant has a unique smell we're all familiar with; I just can't stand the stink of it on my hands so it's the Fuchs for the grinder and a vegetable oil MQL system for the mill and straight cutting oil for the lathe.
I'm a much happier man than I used to be and my shop doesn't stink at all.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

We use different coolant for chip making and grinding. Along the same reasons you mentioned. Clear blue less sticky for grinding, milky white for chip making. Can't recall brand names off the top of my head.


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O.P.: Sometimes the coolants for different operations are completely different, and sometimes a single coolant can be used for different types of operation simply by changing concentration. It's generally best to follow manufacturers' guidelines. If they're worth a shit they have generally tested their products until they're blue in the face, and know whether they are suited for a certain purpose way better than you or I on a lark.

This is a free internet book that has a chapter on coolant types and delivery:
Principles of Modern Grinding Technology | W. Brian Rowe (Auth.) | download
See Chapter 8, pages 124 through 156 It is a 21 MB PDF.

He has a earlier book "Machining with Grinding Wheels" with Co authors Ioan Marinescu, Mike Hitchiner, Eckart Uhlmann, and Ichiro Inaski. which is more useful but is not a free download.

The quick answer is that the lubricants in grinding fluids reduce wheel wear, reduce wheel loading, improve surface finish, and reduce the energy required per cubic inch of material removed. The trade off is that the lubricants are not as efficient as water in removing heat. In very demanding applications such as creep feed grinding the coolant is a low viscosity oil. The advantages listed above take priority over the efficient heat transfer requirement.

Oil coolants are also required in many CBN and diamond grinding applications due to the greatly increased grinding wheel life compared to grinding with water based coolants.

The additives in a water based grinding fluid may be different than in a water based cutting fluid. For example, a anti-mist compound may be needed for grinding.. Grinding wheel speeds are in the 5,000 FPM range for conventional abrasives and wheel construction. Cutting speeds are 1/10 that or less.

The coolant will also be exposed to much higher temperatures at the wheel to work piece interface. The additives should not degrade at the higher operating temperatures. However, sulfur and phosphorus high pressure lubricants require high temperatures to be effective.

The viscosity requirements for grinding coolants are also more demanding. There is a optimum viscosity for a given wheel speed and abrasive grain size. If the viscosity is too high the wheel will hydroplane at the grinding interface. If it is too low there will be insufficient lubrication.

The Benz web site has a chart for selecting the coolant viscosity.

Oil Based Lubricants | Grinding Oil | Straight Grinding Oil

Filtration will not be a problem if a settling tank with baffles is used, The coolant can be depleted of additives if the filter paper roll method is used. I do not have a reference for this. The concern is that the paper filter will retain the oil additives in a semi synthetic coolant.

Robert R said:

...
Oil coolants are also required in many CBN and diamond grinding applications due to the greatly increased grinding wheel life compared to grinding with water based coolants.
.

Click to expand...

Coolants are application specific. In the case of carbide grinding with diamond wheels I'd have to highly disagree here.
Oil is used for many reasons in carbide grinding but performance or wheel life is not one. Same with CBN in HSS.
Stock removal time and wheel performance is way different.
Here is the but. Many of these high end tool grinding machines will not like water based due to design.
Have never seen a oil coolant run better or equal to a water based in this application.
Knowing this speed advantage a little company called Sandvik tried it. In 6 months the $500,000 machine died.
Bob

The influence of coolant composition on CBN wheel life will vary depending on the material being ground. Brian Rowe gives an example of 50 times longer wheel life with oil based coolants when using plated CBN wheels to grind nickel based alloys.

For M2 tool steel he shows 5 times the wheel life. (See page 98 , page 107, page 206, and page 368, Machining With Grinding Wheels 2007)

The explanation is that the improved lubrication reduces wear on the cutting edge of the CBN grain, the use of oil reduces the thermal shock on the CBN grain, and that, at high temperatures, CBN will oxidize when exposed to water. It is also reactive with alkali oxides that may be present in water based coolants.

There is less information on the use of oil based coolants when using diamond wheels. The three factors listed above would still be relevant. For example, the use of oil may reduce the chemical degradation of diamond when exposed to iron, cobalt, or nickel.

The main point is that lubrication should be considered when selecting grinding fluids.

This feels a bit like a chicken and egg debate...

First and foremost there is the question of chemistry... hard water, soft water, DI water, Distilled water... initial concentration and how well both the pH and concentration were maintained. Then comes cleanliness, the bane of every machinist's existence. This leads me to the question of how much swarf is getting to the wheel and what exactly is loading the wheel?

I appreciate these are just the basics of coolant prep and maintenance, but there is always more to the story when the sump is stinky... maybe there were no grinding jobs for a few weeks maybe the mold spores in the air dropped off into the tank...

Nearly every coolant I have looked at was for multi-purpose, even the Fuch mentioned above. As eKretz mentioned it comes down to concentrations, specific to application. All the other stuff I mentioned is just worth banging your head against the desk over.

Jarrod,

I had overlooked the chemistry aspect of the coolant; I do recall talking to one coolant manufacturer, and them asking about our water source...I believe it was Cim-Cool. Funny; some may find this funny, and some may find this infuriating...we were setting up a manufacturing shop in VT, and I was responsible for supplies. I send a barrel of both milling coolant, and one of coolant for the grinders; well, they ended up putting the milling coolant into the grinder (I did not mention that we are a "copy exact" company)...this didn't come to be common knowledge until later, when we had to re-work some of their parts, and it was discovered the difference in the coolants...WE had to drain and re-fill our grinder with the milling coolant.

Again, from what I have experienced with the types of coolant that we use, and the concentrations (and another issue with that***) is that the milling coolant is "slippy"; and I wonder how much of the lubricant gets stuck in the pores of the wheel and potentially reduces the cutting efficiency? IDK....

idle ramblings prior to the coffee kicking in...Mark

***bought a coolant mixer to go in the 55gallon drum to make life easier....they still dump the coolant from the barrel into the tank, then add water....refractometer?? WTH is that??? We don't need that POS....

Dear Mark,

LMAO!

I still need to get a refractometer and was debating about a mixing head, but I'm only mixing in the pail volume, not barrel volume.