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Getting Machine Coolant Where You Need It

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Getting Machine Coolant Where You Need It

In a huge number of cases, maybe the majority, machine coolant is applied improperly.  Often a great amount of machine coolant is used improperly when much better results would be achieved by precisely using much smaller amounts of machine coolant.  See the article on Excessive use of Machine Coolant.

Applying machine coolant properly and consistently is critical to grinding and machining operations.  Some of the benefits of applying machine coolant properly are reducing and preventing scrap work pieces by reducing thermal softening, burning and hardening as well as reducing cycle‑time and tool wear.  Improvements are seen in dimensional accuracy, throughout, part‑to‑part and set‑up to set‑up consistency.  All these mean significant cost reduction.  Refer to our Filtration Index for more articles on reducing cost and improving Quality through a Machine Coolant Management Plan. 

Areas to consider are:

Nozzle placement

Laminar flow 

Nozzle edge condition

Discharge coefficient

Nozzle position

Coherent jet flow

Nozzle wear

Air barriers

Nozzle shape

Air dams

Nozzle angle

Part-to‑part consistency

Machine coolant condition

Set‑up to set‑up consistency

Blockage of nozzles

Machine to machine consistency

 As a grinding wheel or machine tool turns it moves air around the edge.  This creates an air dam.  Pointing the machine coolant stream in the wrong place causes it to blow out.  This physics is just like spitting into the wind, walking through an air door or holding your hand out the window of a moving car.  

Moving air has a lot of force.  It can force a board through a tree.  

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A 4” wheel moving at 2500 rpm has a rim speed of about 30 mph.   If you hold your hand out a car window at 30 mph you can feel the force of the wind. 

When a wheel spins it throws off a little breeze.   You can feel it if you hold a piece of light paper close enough.   

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What most people fail to consider is that there is a layer or coat of air that surrounds the wheel and creates a barrier of moving air at 30 mph that prevents machine coolant from getting to the wheel.

Moving air hitting something makes turbulence which creates an air dam. 

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When you take a freely rotating wheel and bring it into contact with something such as a saw tip then you change the physics of the set up.  Think about what happens when you stick your hand out the car window or wad up a piece of paper and throw it at a fan.  

When you take a hose and point it at something you get a lot of splashing.   If you point the stream at a hole bigger than the stream, then it all goes through with no splashing.  If the hole is smaller than the stream then there is splashing.   

When you grind saw tips there is no hole for the air or the liquid to go through so it wants to splash out and back. 

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Getting machine coolant where you want it is like running a boat on river.   You get in the current when it is going your direction and you stay out of it when you are going the other way.   

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Aim your machine coolant so it gets sucked into the work area instead of aiming it directly into turbulence.

 

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Machine coolant can be applied through manual, flood or mist application.  In manual application an operator uses an oilcan to apply cutting machine coolant.  This is the simplest, cheapest costly method, however; it has limited use in any but the simplest applications and is very inconsistent. In flood cooling, machine coolant is directed under pressure to the work area.  machine coolants can be sprayed onto the work area as a mist. The pressure and direction of the mist stream are also crucial to the success of the application.  Machine coolants are typically stored and distributed a sump in each machine or a central system.

 Testing

1.  Test to see how much of the machine coolant pumped actually goes through the work zone and how the flow rate through the zone compares to the flow rate from the pump.  An increase in the flow rate of the machine coolant pretty well equates to an increase in machine coolant efficiency.

 2.  Test to see what happens to the work as you change delivery considerations.

 Use a test block with sensors such as pressure, temperature, vibration etc. inserted.   Either put them into the test block and drill a hole the rest of the way through or test without the hole.  The tool is positioned over the test block until it just touches the block.

The machine coolant and machine are turned on.  The tool or wheel is traversed back and forth several inches on either side of the hole in the set block to see where the pressure begins to build where it peaks and where it declines and ends. 

As machine coolant passes between the tool and the part it is squeezed and a pressure is developed. This pressure is measured and relates to how properly the machine coolant is being applied.  The more machine coolant that is forced into the same size space between the tool and the part the higher the pressure.  Also compare the pressure through the space with the pressure form the pump.

Test results

The type of nozzle can reduce temperature by 105 F from 280 F to 105 F.  This means the difference between boiling of the machine coolant and consequent part damage and no boiling and no damage.  It also means that higher metal removal rates are possible without damage to the part or tool because of reduced temperature.

Air dams are designed to remove the layer of air, or air barrier, that can surround a grinding wheel or tool especially at high rotational velocities, and thus hinder machine coolant from entering the grinding zone.  An air dam or air scraper placed upstream of a grinding wheel created a 15% improvement in efficiency

Heat transfer out of the work area

A key area for process improvement is heat transfer out of the work area by machine coolant.  Poor cooling means excess heat, which, in turn, means residual stress, work hardening, burn and possible structural change in the material  

High-pressure machine coolants can do a better job of moving heat out of the work area than low-pressure systems.  High pressure can include flow rates up to 600 I/min.  However many high-pressure systems are not nearly as effective as they could be due to poor nozzle design and use.

An air cushion is built up around the tool or wheel, which interferes with the application of machine coolant by deflecting the machine coolant jet.  It is important that the nozzle design and airflow as well as air dams be used to get the machine coolant into the work area. 

Nozzles incorporating flow de‑turbulence zones with a sharp‑edged nozzle opening can create a laminar flow that can be directed at the work area contact zone very precisely.

A stripper can separates the rotating air cushion from the tool. Negative pressure results from the rotation of the wheel in the area of the opening and the enclosing nozzle shoe drags the lubricant into the work zone.

Multiple flow nozzles and nozzles with guide jets can also improve machine coolant delivery.


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