Water removal in non-miscible cutting oil

steve-l · May 18, 2021

I use normal cutting oil on my L&S lathe, not water soluble. Water soluble oil does not work for me on big lathes. In my experience it makes a mess, causes corrosion issues and gums everything up over time. So I have very successfully used normal high sulfur cutting oil. It works perfectly for me, but it is expensive to use at 4.99 Euro a Liter. My tank is 70 liters. Over time though the oil picks up moisture through condensation. The moisture causes oil gelling and foam. My question is; Does anyone know of a way to periodically purge or polish my cutting oil in order to separate the water?

Gordon Heaton · May 18, 2021

If its in suspension and won't settle out, one way is to heat the oil above the boiling point of water and let it evaporate. You could probably do the heating at a single point and repeatedly circulate the oil through that point, but if you have the ability to heat the entire tank that might be less trouble.

Another possibility is to apply a vacuum to the oil for a period of time which will accomplish the same thing. Perhaps a combination of the two at milder temps would be even better.

Mark Rand · May 18, 2021

I once removed the water from 60 litres of cutting oil. I used a large, high sided pan (Ikea) and an induction hob (Lidl/Aldi) and heated the oil 15litres at a time. If you are doing this it is very important to agitate/stir the oil. If it is still, steam will be generated at the bottom of the pan and hot oil will explode all over the place. I used a paint/plaster stirring paddle on a battery powered drill. This had the added advantage that the violent movement of the oil increased the surface area and allowed the water to evaporate more easily. 2kW of heat makes wuite a lot of steam.

.

There are probably more professional ways to do this, but heat, stirring and surface area are the important things.

I think the high sulfur oils tend to emulsify quite easily. In power stations, the steam turbine oil is a straight oil with a low viscosity, the condensate separates out to the bottom of the (large) oil tanks quite simply.

Joe Gwinn · May 18, 2021

One can buy commercial oil dehydrators intended to solve exactly this problem, and they work by boiling the water out of the oil, either by heating the oil or by pulling a vacuum on the oil so that the water boils at room temperature.

Here is a US example; I'd expect that there are German examples as well.

Water Removing Oil Dehydrator Systems - Schroeder Industries

I would guess that if one is cobbling a solution together, vacuum might be the easier (and safer) approach.

Or find a used commercial unit in a barn somewhere.

Rickyb · May 18, 2021

Regarding vacuum dewatering. Water boils at about 70°F in a vacuum which is why it can work. Storage tanks can implode/buckle from an internal vacuum. Choose your container wisely.

Ziggy2 · May 18, 2021

Gordon Heaton said:
If its in suspension and won't settle out, one way is to heat the oil above the boiling point of water and let it evaporate. You could probably do the heating at a single point and repeatedly circulate the oil through that point, but if you have the ability to heat the entire tank that might be less trouble.

Another possibility is to apply a vacuum to the oil for a period of time which will accomplish the same thing. Perhaps a combination of the two at milder temps would be even better.

On transmission test stands, we heat the oil to around 135F to 155F depending on the particular oil under 29in. of vacuum. Water comes out very quickly.

steve-l · May 19, 2021

Thank you all for those tips. It is a shame nothing appears available on the market for a reasonable price to do this. I am quite certain I am not the only person suffering this problem. To change the oil in my L&S cost almost $700. If a device should exist it would have to include a vacuum tank, temperature and vacuum controls and built in agitation.

DDoug · May 19, 2021

I think I would switch to a different cutting oil.

Is there some kind of desiccant pack that you could put in the sump ?

Joe Gwinn · May 19, 2021

steve-l said:
Thank you all for those tips. It is a shame nothing appears available on the market for a reasonable price to do this. I am quite certain I am not the only person suffering this problem. To change the oil in my L&S cost almost $700. If a device should exist it would have to include a vacuum tank, temperature and vacuum controls and built in agitation.

I don't think it needs to be that complicated. You do not need to handle all 70 liters at once, and if boiling at low temperature in a reasonable size vacuum tank, even abrupt boil-over isn't going to cause a disaster. Just don't fill the tank too full at any time.

I don't know if boiling beads work with oil, but they are widely used in distilling of alcohol, and it's easy enough to just try:

Ceramic Boil Enhancers (Still Spirits)

DDoug · May 19, 2021

Have you tried a stick on heater to the underside of the pan ?
Not to boiling, just heated.

Maybe a centrifugal separator ? DeLaval comes to mind.

steve-l · May 19, 2021

digger doug said:
Have you tried a stick on heater to the underside of the pan ?
Not to boiling, just heated.

Maybe a centrifugal separator ? DeLaval comes to mind.

Doug, I like the idea of a heater. It would be a lot less expensive than a vacuum setup. How do they attach to the bottom of the tank/bed and couple the heat efficiently? Perhaps an immersion heater? If so, how many watts? The tank is empty now. I'm waiting for my new oil to be delivered. As far as a centrifuge, I have only seen ones for diesel not for oil as viscous as cutting oil, but I did look.

DDoug · May 19, 2021

steve-l said:
Doug, I like the idea of a heater. It would be a lot less expensive than a vacuum setup. How do they attach to the bottom of the tank/bed and couple the heat efficiently? Perhaps an immersion heater? If so, how many watts? The tank is empty now. I'm waiting for my new oil to be delivered. As far as a centrifuge, I have only seen ones for diesel not for oil as viscous as cutting oil, but I did look.

I was thinking of these magnetic ones:
magnetic oil pan heater at DuckDuckGo

Joe Gwinn · May 19, 2021

The oil pan heater suggestion gives me an idea:

Have a pan with a heater at the bottom fed by a pump in the machine's cutting oil tank. The oil spreads out in the pan, is heated, and the water is driven off and vented to the outside. Oil then drains from heated pan back to the cutting oil tank somewhere far from the intake pump. This is done at atmospheric pressure, so the pan will operate above the boiling point of water.

To economize on heater power, one can implement a simple counter-current heat exchanger:

There are two copper pipes or tubes, soft-soldered to one another lengthwise. Pressurized oil from the pump goes through one pipe towards that heated pan, and dehydrated and partly cooled oil runs in the opposite direction, from pan back to the tank, in the other pipe. If the soldered section is long enough, nearly 100% heat transfer will be achieved, and the heater power will be a fraction of what would otherwise be needed.

This gadget can be run periodically, and for as long as needed to achieve and maintain reasonable de-watering.

steve-l · May 20, 2021

Thank you all again. I'm going to go with Gordon's idea of heating the tank. I also seriously considered Mark's warning about exploding steam bubbles, but as the tank is fully enclosed with the grate only on one end and relatively small I don't think it will be an issue. I will use a removable heating element for tank cleaning reasons and then we will see how it works. I am prepared to change my plan as required, but this will be the first step. I will also monitor tank temperature, heating time and effectiveness and get back here to let you guys know how it works.

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