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  1. #1
    Guys, I have built a simple Coalescing type system for removing Tramp Oil from CNC machines. The system consists of a floating suction device that is dropped into the machine tank, a centrifugal pump and a Coalescing Plate-Pack type oil water separator that does a good job of removing most tramp oil from the machine coolant tank in less than an hour.

    Now, I was wondering what other improvements I can make to this system. How about something to remove odor? An inline filter for metal chips perhaps?

    Any other issues you guys face with your machines that you would like to have addressed by such a system?

    Any help/leads would be appreciated.
    Thanks.

    KV

  2. #2
    Quote Originally Posted by kunalv View Post
    does a good job of removing most tramp oil from the machine coolant tank in less than an hour.
    That's ideal for a company that moves the equipment between machines, of you were running a skimmer you'd never see a build up of oil in the first place.
    I use a belt skimmer running 1 hour on, 4 hours off, it uses almost no power and does a great job of keeping my coolant oil free.
    I have a pumped cartridge filter system (which runs for the hour before the skimmer) which keeps my coolant clean.
    In total I have a couple of hundred quid in it and the system has worked nicely for a couple of years.
    You think that's too expensive? You're not a Model Engineer are you? :D

  3. #3
    A quick question or two. Is the tank you are referring to under the machine, combined with the chip conveyor, or do you have a remote tank? Machine sumps are quite shallow and that may affect your choices. Belt and disc skimmers seem to be very effective - where I worked we used belts. Most systems work best when the coolant can be static, and are surprisingly effective.
    I had thought of trying a system like a swimming pool leaf remover, but the tank agitation levels we had would have swamped the system with coolant rather than pulling oil.

    Odor. Almost certainly the coolant has bacteria in it. Once the amount of biocide in the coolant has been consumed then the amount added by topping up coolant will be insufficient. The only cure is then a coolant flush with a special purpose machine cleaner that uses disinfectant and detergents to loosen sludge build up, followed by a mechanical clean. You can top up biocide content in the coolant but only for a very short time. It must be compatible with the coolant chemistry too. Bacteria destroy coolant very quickly.

    To control bacteria you need a pH meter or pH papers that cover the range of pH stated by the manufacturer. Back that up with regular bacteria slide checks. Your thread appears to be from India - I would suggest that monitoring coolant temperature is also advisable. Keep the coolant temperature below 25 degrees if at all possible - 20-22 c would be better. Most coolant temperatures follow ambient temperature conditions unless chillers are used. That would be true with non-ferrous machining. Heavy ferrous machining can add temperature to a tank and that will begin to destroy the coolant. The highest temperature I found was 37 C on one occasion. Needless to say the coolant was replaced.

    Swarf in coolant depends on what you're cutting. If you are cutting ferrous materials or magnetic types of stainless then filtration works well. You need filter mesh or screens for the visible chips and magnetic filters for the 'fines' or re-processed micro-chips. Non-ferrous materials require finer screens and the time for them to pass the volume of coolant you need to filter in down-time between shifts. If the fines build up then the risk is the metallic content will cause binding in taps, in particular fluteless form taps, You can see the 'fines' under a microscope and the level at which trouble may start is surprisingly sparse in quantity. Unless you have scales capable of weighing to three decimal places (of grammes) I wouldn't bother trying to measure it. Your coolant supplier should do it for you as a service.

    One issue that may be part of your problem is the compatibility of the coolant with the tramp oil. Some coolant chemistry is designed to absorb tramp oil, and use it's lubricity to aid machining - others reject tramp oil. That only works if the chemical systems in use are designed with your tramp oil in mind. The chemistry of tramp oil is also coming under the spot light in that tramp oils were often quite crude in comparison to the coolant chemistry, and that is changing.

    Also don't mix coolant at a higher concentration than the maker's recommendations. The balance of the coolant is wrong. If the maker's recommendations aren't working then you have the wrong coolant. Higher concentrations are just a waste of money.

    Good luck

  4. #4
    Quote Originally Posted by Sliding Head View Post
    A quick question or two. Is the tank you are referring to under the machine, combined with the chip conveyor, or do you have a remote tank? Machine sumps are quite shallow and that may affect your choices. Belt and disc skimmers seem to be very effective - where I worked we used belts. Most systems work best when the coolant can be static, and are surprisingly effective.
    I had thought of trying a system like a swimming pool leaf remover, but the tank agitation levels we had would have swamped the system with coolant rather than pulling oil.
    Yes the tank is under the machine. We have a belt skimmer which does not function as well as we would have liked, hence we developed a coalescer in-house.

    Quote Originally Posted by Sliding Head View Post
    Odor. Almost certainly the coolant has bacteria in it. Once the amount of biocide in the coolant has been consumed then the amount added by topping up coolant will be insufficient. The only cure is then a coolant flush with a special purpose machine cleaner that uses disinfectant and detergents to loosen sludge build up, followed by a mechanical clean. You can top up biocide content in the coolant but only for a very short time. It must be compatible with the coolant chemistry too. Bacteria destroy coolant very quickly.
    Agreed. But I do not want to add any Biocide chemicals as my coolant supplier has advised against it. What are the ways to kill bacteria present in the tank? Ozone is too expensive. UV Light? Not sure about the life of these UV Electrodes. Aeration? How long do you need to 'oxygenate' the coolant in order to introduce adequate oxygen?

  5. #5
    Hi,
    We used Abanaki belt skimmers with the separator system. We did try poly belts and steel belts. You may find that the effectiveness depends on the coolant chemistry and the type of Tramp oil. It isn't an exact science, and we made a few mistakes.
    How deep do you have the lower portion of the belt? Too shallow and you don't pick up enough oil and too deep you will wash off some of what you pick up. The oil wiper should be close enough to wipe oil from the belt but not to cause drag on the belt. We did have steel belts and had more than a few break.

    Are you allowing the tank to settle - so there is zero agitation at the point of pickup? I realise this will need the machine to stop between shifts. We had non-stop operation and found a lot of oil that was picked up was partially emulsified and needed to settle before separation. It meant we lost a lot of coolant this way.

    I am surprised your supplier has advised against adding a biocide. I wonder what they are advising you to do in this situation. Your problem is quite common. Don't forget bacteria can be aerobic and anaerobic so Oxygenation may not help. I didn't try UV light but I think it would work if you can light to travel through the fluid, not just the surface.

    Is it possible to stop the machine long enough to take the sump from the machine and remove all traces of sludge? If you replace the coolant without cleaning the machine you will find the bacteria problems return. It was possible to lose a 1,000 litre sump in 1-2 days without cleaning. We found dead spots in the conveyor which needed scraping and pressure washing to get rid of the sludge. That sludge is soap, emulsified with oil and coolant emulsion - bacterial heaven. Also we found dead spots of swarf and coolant, like nests, under some of the machine covers. These also act as hot spots for bacteria. Our dip slide tests for bacteria were always taken in subsurface coolant - it depends on the depth of your tank/sump but you must be below the surface.
    Our best results were from a 'mechanical' clean, meaning the scraping of sludge from surfaces, the brushing of all sheet metalwork, and wiping with a suitable oil and disinfectant ( a dedicated machine cleaner). Prior to a mechanical clean we always used a cleaning additive to flush the machine while in use. Machining performance was not affected but was in the machine for a day prior to removal and coolant disposal. We always lost a complete shift for this process.

    Biocides and other additives (like Abanaki Coolant Mints) are a temporary solution.

    If you need some information about what can go wrong with coolant and the consequences to people have a look on the HSE (Health and Safety Executive in the UK) website for a copy of the Longbridge Report. It was nearly 20 years ago that over 100 people were made ill by the poor maintenance of coolant in just one factory.

    Also we are at an advantage in the UK with regard to water quality. All UK mains water is drinkable, therefore bacteria free. If your water isn't of that quality you have dimension to your problem that we don't have. You may have to start solving your problem in a different way.

    The UK coolant market has been altered of late, mostly by the consequences of Longbridge. Larger coolant supply companies now offer integrated coolant maintenance contracts as part of the deal. In a small company you have to learn how to deal with your situation as you find it - it is difficult to be accurate with help as your situation is unique. In my view your supplier isn't doing enough to help you - you might be able to find one that does know how to help. In my old company we changed suppliers twice before we found someone who offered real help on an on-going basis. It was better commercially in the longer term as well.

    Good Luck

  6. #6
    Hi,
    A quick addition to my earlier post. I mis-understood your comment about oxygenation. Yes, you can use aeration beneficially - shop air is enough, no need for oxygen alone! We placed a pipe attached to the shop air supply with a regulated low pressure. Start at 1 to 1.5 bar and go upwards if necessary. Use 1 to 1.5 mm holes and increase as required. The effect is like putting air into a fish aquarium. Don't let the bubbles rise too quickly.
    Two things happen. One is that the bubbles can break up the surface if there is an oil film present. The other is that the anaerobic bacteria will be affected by the air, and, you are correct, by the oxygen. However bear in mind that this is more effective while the coolant is stagnant. Once in motion, through pumps, nozzles, and cutting action you will find there is plenty of air getting entrained in the coolant.

    Also, do not forget the bacteria once killed, by biocides or aeration or disinfectants, do NOT disappear. Those bug 'bodies' add to the biological mix that is forming, and it isn't healthy. There is no such thing as Good Bacteria and Bad Bacteria - just bacteria. There is nothing you can add that will eat up the bugs you don't want, and cause no problems themselves.

    I have a link you might find helpful. It's more than twenty years old but was something I read while trying to learn what I know now - which is not enough.
    https://www.ctemag.com/news/articles/coolant-care

    Good luck,

  7. #7
    One question about coolant, - How do you dispose of it? I am only talking about a couple of gallons.

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