Correct Method for mixing metal working coolants

[GeorgeCLS]

One of the most non common-sense procedures, yet *most* important for the proper performance of a water soluble metal working coolant is, simply, Oil In Last or OIL. Common sense says "put the quart of coolant concentrate in a 5 gallon pail first, then fill the pail up with water to get a better mix, solution" Wrong.. By adding the water TO the coolant, it is most likely that a significant portion of the mix will be an invert emulsion as opposed to a regular emulsion, which is what we want/need! An invert emulsion occurs when the coolant is overwhelmed by too much water; water is a very agressive solvent and if enough is present can completely surround the oil molecule, creating an 'invert' emulsion. The problem with an invert emulsion is that it can cause corrosion, greatly reduce the effectiveness of the coolant and create the possibility of mocrobial growth and its side affects. So, the procedure is: take a five gallon pail and fill it with water to the 5 gallon level, then add the appropriate amount of coolant, slowly, stirring as it is added. Then you will have the perfect emulsion and the maximum performance from your metal working coolant.
George Morrison

 

[Neil Womack]

Sound just like the way you get an oil emulsion in the kitchen.

 

[SteveD2]

At our shop we have "auto mixing" of coolant for our lathes and mills. The coolant is contained in a 55 gallon drum and de-ionized water is pumped thru a mixing chamber and blended with the appropriate amount of coolant as it is dispensed via pvc pipe directly into the coolant tank of the machine. I really have no way of knowing if this "mixing" is taking place "oil in last" or not. Bill T.

 

[GeorgeCLS]

The method you described is as close to perfect as one can get; the turbulence provided by the mixer blends the coolant in superbly. About as good as it can get...
George

 

[cc rider]

George is right on target. Anyone who suffered through a Chemistry Lab should remember you always add the 'stuff' to the water, not the other way 'round. The mixing chambers Bill describes are probably the 'least bad' way of mixing coolants, but what usually happens is someone takes the correct orifice out of the mixer (if there ever was one in there at all) and throws it away. My experience was most of the mixers tended to clog up at the orifice, since the emulsion was trying to mix but instead made a sort of paste. Then the coolant would start coming out weak, so the operator would go fiddle with the mixer, which would screw up the whole balance and you'd end up with too strong or too weak coolant or whatever. Plus, you really need to have two different ratios set up, one for filling up an empty sump, and one for make-up filling. This is because the coolant in the sump tends to get slightly more concentrated as the water evaporates, so if you add makeup coolant at the regular strength you start getting more concentrated coolant. Realistically this effect is pretty minor, but you could notice some reduced heat-carrying capacity if you had a really heat-critical machining operation going on. The way I always tested coolant concentration was with a refractometer, which your coolant supplier should be happy to sell you and show you how to use. It just takes putting a few drops of coolant under a lens and reading the refraction off a scale. But I think coolant concentration is less critical than maintaining the quality of the coolant itself, by keeping tramp oil skimmed out, keeping coolant circulating, etc.

For awhile TRIM used to advertise you could use straight undiluted coolant as a way and gear lube, which eliminated tramp oil contamination since there was no tramp oil per se. I'm not totally sold on the idea, but I suspect you could do it if you really needed to for some reason.

Once again I'm foaming at the keyboard. Sorry for the long-windedness...

c.

 

[Kestas]

Where could I get a refractometer?... or are they simple enough so somebody can make one? How much do they cost?

 

[tom slick]

if there is a local machine shop/industrial supply shop they'll have them. also if there is a homebrew (beer) or home winemaking shop or even a farm supply local they will carry them too.
they are amazingly easy to use and accurate, but you cannot make one yourself.
if you send me a priviate message i can tell you where to buy them online.