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Machine Coolant Analysis

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Machine Coolant Analysis

Machine Coolant Filtration Case Studies

 

#1  Machine Shop Machine Coolant Analysis

  End mill at 10x and four corners of the end mill at 60-x magnification.

Analysis of a tool that was ground at a machine shop.  The corners were chipped which may have been a result of particles in the coolant hitting it during the grinding process.  For ways to avoid this or for information on a Coolant management Program refer back to the filtration index

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Corners 1, 2 & 3 show the fracture planes that indicate a shearing.  The tool became dull because pieces chipped off rather than through wear.   This can, and usually does, happen when the pressure between the tool and the work piece is concentrated in one small point.  If the tool is trying to cut the aluminum and there is a significant particle in the way the tool will put all its force into that particle.  This force concentration can shear off a significant chunk along a facture plane.  This is the same mechanism used to “cut” diamonds or to chip obsidian into arrowheads with a deer antler.  Corner four looks more like a wear situation.  

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Here we have an end mill that was cutting with one corner when it was removed.  Corners 2 and especially 3 have been chipped off to the point where they do not do full cutting simply because the edge does not stick out far enough any more.  Corner one has the edge slightly retarded and what is left presents a flat surface into the cut instead of an edge.  When you chip one edge then it makes it much more likely that you will chip and / or the edge behind it because the trailing edge hits with much more force.  

When you only have one edge doing the work that four edges are supposed to do then that one edge gets dull very rapidly.

In this case the tool was running more slowly than it would have if it were sharp.  The surface was much less smooth and there was more power draw on the machine.

Two flute drill

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These are pictures of a drill taken at 10-x magnification on the left and at 60-x magnification in the middle and right.  The middle picture shows a chip in the side of the drill and the right picture shows at least three distinct fracture planes where the carbide was sheared off because of force concentration on a particle that got between the drill and the work.  In this case the failure mechanism was chipping rather than dulling from straight wear. 

Chips from a representative sump

"The Surfing Dinosaur" is an aluminum chip welded to bit of carbide.  It is very common in metal working.  As the aluminum and the carbide 'welded' during cutting it damaged both materials.  The total chip is 0.075" high x 0.122" wide.  This is more than large enough to cause pressure fracturing to the tool as the chip gets repeatedly recirculated with the machine coolant into the area between the tool and the material being cut. 

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Chips 10-x magnification with paper clip on upper right

60 x Photos lit from below

This machine coolant was collected coming out of the nozzle so it is representative of the machine coolant being sprayed into the cut.  You can see that these are very big chips.  Nobody would deliberately put a paper clip between the tool and the material being cut but dirty machine coolant is doing the equivalent. 

These chips are from one pint of machine coolant.  The machine coolant was given to us as probably being representative of the machine coolant throughout the plant.  The dull tools were also given to us as probably being representative.  The tools are not necessarily from the same machine as the machine coolant.  Since there are 30 machines in the operation the odds are obviously fairly small. 

Cobalt that leached out of the tungsten carbide / cobalt matrix tools

Cobalt  method 200.7    

 

Unfiltered

Filtered

Milligrams / Liter or parts per million

0.065

0.057

Percent %

0.00065%

0.00057%

This is very, very low.  One common standard is 100 ppm or 1500 times as much as here.  

Chunks of carbide, aluminum, etc. in the machine coolant

Total Suspended Solids Method 160.2

Unfiltered

Filtered

Recommended

Milligrams / Liter or parts per million

1200

150

under 200 ppm

Percent %

0.12%

 0.015%

0.02%

Troy ounces per gallon

0.1536

0.0192

0.0256

40 gallons = 151 Liters

1200 mg / L x 151 Liters = 181,200 mg

181,200 milligrams = 0.37 pounds = 5.9 oz.

Mixing & Operating Specifications 

1.  Refractometer reading  5  for  5 % percent solution

2.  Brix chart & graph      If you use a Brix scale refractometer then the Brix reading is about 1:1 with the concentration.  There is an error of  + / - 10%, which is typically, as good as you are going to get on a plant floor. 

3.  Make-up Make up a solution 1/3 the strength of the original / desired

4.  Lubricity is generally aided by additives to the machine coolant or components in the new machine coolant.  It helps the tool cut easier and more smoothly.  This gets lost as the machine coolant ages or breaks down much as rust preventative gets lost.  In this case it is probably not relevant since machine coolant is contaminated with fines.  It doesn’t matter how slick the machine coolant is if it is cutting through sand.         

5.  pH     8.9 - 9.2 @ 5%

6.  Conductivity of new mixture should be 0.7 millisiemens (700 microsiemens)  / cc with tap water at 90 ppm hardness                                               

7.  Turbidity - a measure of cloudiness. This doesn’t apply with miscible oils since they are designed to form very small droplets that disperse evenly in the machine coolant mix.  In other words they are designed to be cloudy.  Oil globule size is about 0.09 microns in new mixture.  As the mixture ages the globules become larger as the join with tramp oils and trap particles. 


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