Suds Thief

OK people, who's syphoning off my suds ?

I have been playing with my newly rebuilt CNC mill, cutting aluminium and generally enjoying myself when suddenly I find that the soluble oil coolant in the (20 litre) reservoir has started to foam and has disappeared, or at least halved.

What's going on ? I expected it to last months, but within a few hours of use it has lost probably 5 litres.

There are no puddles of coolant on the floor and no evidence of condensation or a damp workshop. But the logic is it's evaporating at a heck of a rate.

Is this normal ??

Help, Will B

Hi Will,
Have you checked that is not finding its way into some cavity in the machine ? Assuming it is water based coolant it would take about 3.14 KWH to vaporise 5 litres of water. (Based on Latent heat of vaporization of water is 2260 Kj/Kg 2260 x 5 = 11300 KJ divide by 3600 to convert to KWH = 3.14) If it is a big machine then I suppose that much heat could be generated in cutting. It would equate to about 4 HP being converted into heat for 1 hour so unless it is a very big machine (20 HP) then the cutting procces is very inefficient.

Les.

Do you have a de-humidifier running? mine seems to take loads out of the suds tanks.

The only evidence I have for that statement is that when the de-humidifier is off I don't lose any coolant.

Have you created a lot of swarf? If you read the PM forum you can see swarf carry off is a major problem for commercial operators who may wash and centrifuge after basic draining.

I don't have a dehumidier but I do keep the workshop warmish, i suppose about 18 to 20 degs around the clock but only heated by a 600w oil filled radiator.

I didn't think about the loss like that Les and no, the mill is running off a single 240v plug so it's not taking that much energy - I'm able to play again today so I will measure exactly what happens.

Cheers - Will

Hi Bazle - about half a bucket load of fine chips over the last month. All pretty dry now, but yes it was probably wettish when I cleared it.

My suds evaporate, just add a bit more water. Question is, does this loss of water manifest itself as rust on your work tools? My workshop is all wood and we live in a less damp region so it doesn't cause me a problem.

Good idea to put an open container of suds mix out to get some idea of the natural rate of water evaporation. Ratio of surface area and top area to volume needs to be similar to the mill tank for best results. Then you have a good estimate of how much water to add to compensated for evaporation so mix ratio stays pretty constant.

Ex kitchen measurment jug looks to be a good way to go. SWMBO probably won't complain if she gets a nice new one out of the deal.

Cutting / swarf loss can be assumesd to be at mix ratio.

Clive

I reckon most of your loss is sprayed into the air as a very fine mist. Colin

Colin

Sorry I have to disagree. Any significant coolant loss as a very fine mist will make the atmosphere very unpleasant indeed and produce considerable carry-over mess onto other surfaces.

I use a Bjur Spraymist system on my Bridgeport. Never really worked out what my consumption per hour is but rather more than 50 hours run time per litre feels somewhere near. Which I'm sure is more than book consumption but the beast won't self start at less. Most of that goes on the tool, work and machine too. Wipe off area to avoid sticky residues is larger than one might expect too.

Clive

Edited By Clive Foster on 20/12/2014 23:12:13

I feel I should contribute a little to the actual performance of water based suds. Some theoretical work posted above has talked of the energy input not being sufficient to account for the evaporation of the water content.

Water- based fluids should normally be supplied to the tool/metal working point in a concentration range of oil concentrate 5-8% and should be mixed to form a stable emulsion. (There is some debate whether an oil in water emulsion or water in oil is formed.)

Having done some years work on water-based suds I had opportunities to investigate this problem, the temperatures at the cut are very high, much above the boiling point of the oil-water mix, the heat being carried away by the water component and the aerosol formed. The oil serves mainly as a lubricant as well as a film former inhibiting the instantaneous corrosion of the hot metal.

Of course the heating also occurs where non-water based coolants are employed but the physics are significantly different. The droplets are significantly larger and are also more stable and tend to recombine more easily thus re-converting from aerosol to liquid.

This is offered as a possible line of investigation, but I have found that it is quite involved needing a lot more data before coming to any meaningful conclusions.

Most of us will have our own thoughts and experiences and I am reminded of 'Horses for Courses'.

Jerry

And let us not forget that the boiling point of a mixture of two imiscible liquids (i.e. an emulsion like suds) is below the boiling point of both liquids!

**LINK**

Neil