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Thread: Building a cooling mist system

  1. #1
    Join Date
    Jul 2009
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    SF bay area, CA
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    Default Building a cooling mist system

    Right now, the system consists of separate air and coolant lines, which converge pretty much right at the nozzle. Ideally, I'd want a system that shoots a narrow solid cone of air, with a slight stream of coolant in the middle. That way, the air has some spread to blow away chips, while the coolant is more directly aimed at the tool bit.

    I made a concentric nozzle, where the air nozzle is just the usual loc line nozzle with 1/8" opening, and about 1/4" inside of this is a small nozzle for the coolant. There are separate valves for air and coolant.
    The main issue is how can I determine whether the coolant is coming out as micro-sized droplets, or as a completely atomized mist? I've read that the latter is bad since it tends to fog up the shop and you end up breathing it.

    Based on some reading, it seems that what makes this difference is the configuration of the junction (something about meeting at right angles and particular sizes of the air and coolant junction, as based on posts trying to replicate the Bijur spray mist system) and also something about the coolant being pressurized vs getting sucked out by the Venturi effect. The latter reason makes no sense to me because the valve is downstream from the pressurized coolant, and if you try to use that to regulate flow, then it will take all the pressure drop, and the coolant at the nozzle tip gets "sucked out" anyway.

    Short version of my questions:
    What's a good nozzle design to achieve the effect I want?
    How can I tell if the mist is overly atomized?

    Thanks

  2. #2
    Join Date
    Jan 2005
    Posts
    141

    Default I have the Trico MD-1200.

    The tank is pressurized.
    The air goes into the Loc-line.
    The coolant is in a tube connected to the end of the Loc-line.
    The coolant nozzle is tapered at the end, it's a hex shaped to allow the air to flow around it, converging on the nozzle.

    The coolant comes out from the center of the nozzle and the air carries it to the tool.

    Hope that helps.

    Jimno

  3. #3
    Join Date
    Aug 2006
    Location
    Beaverton, OR
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    Default

    If your shop starts filling up with mist you know youre getting mist!

    As long as you keep your pressure low ~25psi you should not get mist. The nozzle for a bijur mister has a real small hole. Something like .010". The tank the air goes into has a pressure regulator, reservoir tank, water separator and a solenoid. The regulator supplies pressure to the nozzle and to pressurize the coolant.

    For the price of a NOS bijur tank on ebay you cant hardly make one.

  4. #4
    Join Date
    Jan 2005
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    141

    Default I run A LOT higher psi.

    When I'm running the RZ at 30k rpms I blast with about 90 psi, virtually no coolant and have never gotten fog.

    I could only imagine how bad the fog would be...eeesh.


    Jimno

  5. #5
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    the sub-tropical island of Anglesey, North Wales
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    Default Health warning

    Whilst oil mist cooling/lubrication is ideal for metalworking, it is not suitable for humans.

    It can lead to-
    - irritation of the skin or dermatitis[1]; and
    - occupational asthma[2], bronchitis, irritation of the upper respiratory tract, breathing difficulties or, rarely, a more serious lung disease called extrinsic allergic alveolitis (EAA), which can cause increasingly severe breathing difficulties in recurrent episodes, following repeated exposure.

    Fine particulates of oil enter the lung & cover the surface preventing oxygen from entering the bloodstream. Few face masks will prevent the most dangerous particulates (.5 -3.5um)

    If the machine is totally enclosed make sure it has an effective negative air pressure filtration system.
    If the machine is open, use an proper air feed mask (expensive setup but cheaper than a lung transplant), or better still dont use a mist system.

  6. #6
    Join Date
    Sep 2005
    Location
    Twin Cities, MN
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    243

    Default

    I believe you are trying to build a system similar to the Trico micro-drop system. I have been very interested in also building such a system and just today brought home from work a small discarded gas cylinder to use as the coolant supply tank and some old flow control valves. From what I have read such systems pressurize the coolant, contain a pulse type timer for coolant supply metering, and separate coolant and air supply lines. I also picked up a HF air brush thinking that it could be modified in some way for a nozzle.

    Clippard and Bosch are two suppliers of pneumatic controls and valves which could also be used. Bosch has a pneumatic pulse generator which looks interesting.

    Robert
    Last edited by RTPBurnsville; 09-16-2009 at 05:48 PM.

  7. #7
    Join Date
    Mar 2006
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    1,182

    Default

    Right now, the system consists of separate air and coolant lines, which converge pretty much right at the nozzle. Ideally, I'd want a system that shoots a narrow solid cone of air, with a slight stream of coolant in the middle. That way, the air has some spread to blow away chips, while the coolant is more directly aimed at the tool bit.
    Yeah that's exactly how the Fogbuster system works. http://www.fogbuster.com/Frame.htm
    I have a fogbuster system and it works really well!

    http://www.fogbuster.com/Frame.htm

    But it's pretty expensive so many have made their own systems based on the fogbuster nozzle. I think if you do a search over at www.cnczone.com a few guys posted how they built their homebrew fogbuster systems.
    Steve

  8. #8
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    Default

    According to this post on a mist system based off of a patent:

    http://www.cnczone.com/forums/showth...highlight=mist

    the coolant opening is .04". This is a really big opening, and I think you are basically relying on the valve to prevent coolant from gushing out. It seems more like Venturi effect, and not pressurized coolant. On the other hand, a .01" opening sounds a bit more reasonable.

    I also wonder about the really long nozzle (6"). Is the coolant and air supposed to be mixed that far back? If the mixture travels down a long tube, does it atomize more or condense?

  9. #9
    Join Date
    Aug 2006
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    Taylorsville Ky
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    Default

    I experimented making my own and then went to Little Machine Shop and bought one of theirs. It works just fine and it was cheap compared to others.
    It's only ink and paper

  10. #10
    Join Date
    Jan 2005
    Posts
    141

    Default Jugs, we appreciate the concern.

    I use Tricool MD-7. Here's what it says on Trico's website.

    APPLICATIONS:

    MD-7 is a pure synthetic based lubricant designed for use in various metal cutting operations. With the use of a Micro-Dispensing system, more effective machining productivity and saving in fluid costs can be achieved, while waste and disposal problems are reduced. MD-7 is non-toxic, non-flammable, non-corrosive, and will not become rancid.

    FEATURES:

    * Zero toxicity - contains no petroleum or chlorinated derivatives.
    * Reduces heat and friction.
    * Works in a wide-range of micro-dispensing systems.

    I'm sure the guys who are using the mist system are familiar with the safety precautions necessary.

    Regards,
    Jimno

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