The Refractometer is the Most Common,
and Most Effective, Concentration Control Instrument in Metalworking

An optical refractometer measures the light bending characteristics of fluids. For water-based fluids,
higher concentrations increase the angle that light is bent as it passes through the fluid. But the
refractometer reading is not the actual concentration of the fluid, only a reading by which the
concentration can be determined using a conversion table (available from Acculube).

By measuring the bending of light through the refractometer (in degrees Brix),
you can determine fluid concentrations.

By monitoring the concentration of a fluid system with a refractometer, the correct dilution can be maintained,
thereby promoting best-possible product performance. Proper concentration control measures can extend
fluid life and help fluids perform more efficiently, and for longer periods.  

There are numerous advantages to using a refractometer:

• Very portable - A hand-held refractometer is easily carried.
• Inexpensive - Low initial cost and low levels of maintenance.
• Easy to operate - Simply read the instructions that accompany the refractometer.
• Instant results - Readings are done "on the spot;" no need to wait for lab results.
• Versatile - A refractometer can be used on most water-based metalworking fluids.

However, since it is an indirect test method, some drawbacks exist when using a refractometer.

A refractometer measures the refractive index of a total solution. It does not measure the concentration
of any specific components present in the fluid. Therefore, refractometer readings can be inaccurate
when the system uses hard water with a high mineral content or when tramp oil is present. It is important
to frequently recalibrate the refractometer using deionized water.

A refractometer is most effective when used under these circumstances:

• Recently charged systems
• Stable fluids
• Well-maintained, clean-running systems
• Uncontaminated fluids
• Solutions that are maintained with quality water

If a refractometer is used as the only concentration control device on a dirty, oily or contaminated system,
this method of retrieving cutting fluid to test is suggested:

• Use a clean, paper or Styrofoam cup to collect a sample.
• Take a sample directly from the fluid nozzle.
• Mark the cup with the date, time and system name.
• Let the cup sit undisturbed for several minutes.
• Poke a hole in the middle of the cup and use this portion as the sample for the test.

It is a good practice to record the refractometer readings from any central system or sump operation.
Readings should occasionally be checked against lab tests to verify the accuracy of the refractometer,
as the system ages and contaminants accumulate. Acculube has concentration control charts which
list acceptable ranges for refractometer readings by product.

The refractometer is a good tool, but it is important to remember that it measures the refractive
index of the total solution, not the cutting fluid concentrate.

For a recommendation on the best value refractometer on the market,
see this new page in the Acculube Lubricant Store.

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