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Dos and Donts of Emulsifying Coolant


Dos and Donts of Emulsifying Coolant

Topping up a cars engine oil is easy. Topping up a reservoir of emulsifiable metalworking oil? Thats tricky, declared Alan Cross. Machine operators armed with science and the right tools can learn to achieve the stable oil-in-water emulsion they want, batch after batch, day after day. But impatience and improper mixing will get you a sumpful of frustration.

Poorly formed metalworking coolant can go wrong in a multitude of ways, the senior project engineer at Houghton International warned. The entire batch can destabilize. The wrong oil droplet size can form, leading to tool breakage. You may get sludge or hard-water soap formation, and foam can run amok. Needed additives may be stripped out by the filtration system. Residue and corrosion can get a foothold, and chips may float instead of settling out. In short, a nightmare.

Users can avoid these dangers by understanding their fluids two primary components-oil and water-and taking steps to dilute and mix them correctly, especially when making up system volumes lost every day to evaporation, leaks or normal usage, Cross told a recent industry meeting in Minneapolis. Of course, oil and water dont truly mix, but oil droplets can be coaxed with chemicals (emulsifiers) to stay neatly suspended in the water phase as tiny emulsion particles, just 2 or 3 microns in diameter.

Proper dilution and mixing are the secret sauce in this balancing act, he emphasized. Product should always be added to water, not the other way around. Adding water to product can form an inverted emulsion, where a layer of oil floats atop a watery, less-robust coolant.

End users typically will deal with three families of coolant concentrates. Emulsifiable oil, also called soluble oil, is a concentrate that contains 50 percent to 85 percent oil (petroleum or vegetable). After blending with water, it usually looks milky or opaque. A semi-synthetic concentrate contains 5 to 50 percent oil, and may be opaque or translucent in blended form. And a true synthetic, he explained, is a craft cocktail of chemicals alone, with no oil at all.

All three types are fortified with emulsifiers, corrosion inhibitors, antifoaming agents, dyes and other useful components, and are ready to mix right out of the drum at water-to-concentrate ratios ranging from 4-to-1 on up to 20-to-1, depending on the application.

Water is the most important material, after the concentrate, Cross said in his instructive presentation to the Society of Tribologists and Lubrication Engineers in May. Some 80 to 97 percent of the working fluid is going to be water, so water quality is very important, beginning with hardness.

Hard water contains high amounts of dissolved minerals like calcium (Ca) and magnesium (Mg) that combine with materials in the coolant to form soap and residue. These soaps do provide lubricity, but the hardness ions also interact with emulsifiers and reduce the products ability to emulsify and stay there long-term.

Instead, use purified water, urged Cross, who is based in Norristown, Pennsylvania. Its easier to mix, and youll get smaller particle sizes and better wetting and penetration. Other advantages of purified water include greater resistance to bacteria and fungi; less corrosion; reduced concentrate use; less mist; and better overall stability.

That said, he cautioned that users need to be aware of a potential downside to purified water: In certain operations it may shorten tool life (as shown in tapping tool test data he presented at a previous STLE meeting with his colleague, John Burke) and increase foam generation. The right formulation can help sidestep these drawbacks, Cross indicated.

Another consideration is that when you have evaporative losses of your coolant, only the water is evaporating. All the material in the water stays in. So if you make up using only water, youll increase the hardness at each step. He showed how an emulsions hardness can be magnified through repeated cycles of evaporation and plain-water top-offs: One premium emulsified oil started at 120 milligrams of hardness ions per liter, but with water-only additions quickly grew to have 10 times that hardness, splitting the pricey emulsion.

Operators also need to heed the starting temperature of their fluids-concentrate and make-up water alike-when mixing up an emulsion, Cross reminded. Higher temperatures will make emulsification easier and faster, while frigid fluids will need more mixing time to form an emulsion. This is sharply evident in winter, when intake water can be icy-cold and/or drums may be stored in uninsulated spaces. Let them warm up a bit first. If you use warm water and warm product, it helps you get good emulsions, he said. Around 10 to 15 degrees Celsius (50 Fahrenheit) is a good starting point; 23 C (74 F) is even better.

Once the water and concentrate variables are understood, the next steps are dosing and mixing. Dosing can be performed through an array of techniques and equipment. One popular option is a siphon proportioner, which uses Venturi effects to draw the product up a moving water stream. Siphon proportioners are relatively low cost and easy to use, Cross said, but can give uneven results.

A more precise dosing option, at around $1,000 and up, is a positive displacement proportioner. This device, Cross said, uses a water-driven piston to draw product from the drum and inject it at a steady rate into the water stream. Advantages include very consistent dilution, but it does require higher capital investment than a siphon proportioner. Users should research the various units available, keeping in mind their own needs, flow rate, product viscosities and dilution ratios, and inquire about chemical compatibility, as well.

Finally, theres manual addition, which is as simple as it sounds, he continued. The product is physically dumped into the working coolant. On the plus side, this takes no capital investment. The cons are that its very inconsistent, it requires workers to handle heavy drums and totes of product, and most dump zones lack the shearing energy to quickly mix the emulsion.

He added emphatically, Dosing is not mixing! After dosing, the product and water still need to be fully mixed to get a stable emulsion. Whatever kind of mixing agitation you use, the idea is to do it soon as youre done dosing.

Many operators find success by pre-mixing the concentrate in a small vessel or tank of water and ceaselessly agitating it with a propeller or other mixer; then the pre-mix can be pumped to the main tank to reach the desired final concentration. This works well if done correctly, Cross said, but if theres no mixing in the pre-mix, you can create a very poor emulsion or an invert and soap formation. Inattention to this crucial step may be punished with a thick blanket of suds, or an invert oil layer that rests stubbornly on top of the water phase.

Operators can employ a variety of mixing strategies to emulsify products.

In-line Mixer. If using an in-line mixer, install it on the discharge side of the dosing device, Cross advised. This will apply high shearing, similar to a homogenizer or stator.

Machine Pumps and Filters. Centrifugal pumps can help to mix and emulsify products during the pumping process. The diluted coolant should be fed into the suction side of the machines pump. You also want to be sure to feed the concentrate into the clean side of the system, downstream of the filters, to reduce component loss in the filters, he counseled.

Static Mixer. Many shops also utilize static mixers with varied results, he said. This is a series of baffles that fit within a pipe or tube, creating turbulence as the fluid flows through. Static mixers usually are installed immediately after the proportioner, and baffles are available in a variety of profiles-ribbon, corkscrew, helical, criss-cross, etc. Static mixers can generate enough turbulence for mixing synthetic coolants, Cross said, but may be less effective for emulsions with a high percentage of oil.

Reiterating one of the most critical rules, Cross said, Product should always be added to water-not to coolant. Youll find that the concentration will be very high until 100 percent of the fluid is made up. But if you add product to the coolant, it requires far more time to mix and get to an emulsion.

Takeaways for Mixing Coolant

Keep your cool when mixing up coolant by following these tips from Alan Cross of Houghton International:

Always add coolant concentrate to water-not the other way around.

If you add concentrate to made-up coolant, be prepared to spend more time mixing for an emulsion to fully form.

Improper proportioning of concentrate can lead to potential instability. If your budget allows, use a positive displacement proportioner for dosing.

Dosing isnt mixing! Poor mixing after dosing can lead to poor emulsification.

Water quality strongly affects long-term coolant stability. Use good quality make-up water!

Fluid temperature can adversely affect proportioning devices and mixing times. Avoid blending very cold product and very cold water. Warmer ingredients (50 degrees F and higher) will mix better, faster.

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