Category: Technical and practical guide | Author: Kimiya Sanat Savalan Research and Development (R&D) Unit
Estimating metalworking-fluid concentration by eye is a costly mistake in machining shops, CNC operations and rolling lines. Too little or too much concentrate can lead to poor tool performance, corrosion, damaged cutting inserts and unnecessary fluid consumption.
The most efficient and fastest tool for measuring the concentration of water-miscible metalworking fluid in the workshop Optical refractometer device (Refractometer) is But what is the correct way to use this tool and why is the percentage read on the device usually different from the actual concentration of the emulsion?
1. Why is coolant concentration control so important?
The performance of the metalworking fluid is completely dependent on its mixing percentage with water. Deviation from the standard concentration creates two dangerous scenarios:
a) Consequences of very low concentration (less than 3%:
- Fast rusting and corrosion: Reducing the dose of corrosion and rust inhibitors on the part and rail of the machine.
- Reduced tool life: Severe wear of the chipping tool due to insufficient supply of lubricating film.
- Rapid growth of bacteria: Weakening of the concentration of biocides and premature spoilage of the liquid.
b) Consequences of very high concentration (above 8% to 10%:
- Huge financial loss: Excessive and unnecessary consumption of oil.
- Reduction of cooling properties: Due to the high concentration of oil and the lowering of the heat capacity of the liquid.
- Creating annoying foam and adhesion: Remaining adhesive layers on the piece and making the tool hot.
- Skin Irritation: Cause dermatitis and skin allergies for the device operator.
2. How does a refractometer work?
A manual refractometer is an instrument based on Law of refraction of light (Refraction) works by measuring changes in light refraction through the fluid. The refractive index varies with the fluid’s composition and concentration. The instrument displays a reading, usually in Brix) is displayed.
3. Understanding the refractometer correction factor
The biggest workshop error is that the number read on the refractometer eyepiece (eg 4) is assumed directly as “concentration percentage of 4%”!
Technical Insight: degree A Brix reading reflects the fluid’s refractive index; it is not a direct measurement of the oil percentage. Mineral, semi-synthetic, synthetic and vegetable-oil formulations each require their own Correction factor (Multiplying Factor) they say.
Calculation formula of actual concentration:
Actual concentration (%) = Refractometer reading (Brix) × Fluid correction factor
Practical example:
Suppose from the product SVL FLUID E100 You use a correction factor equal to 1.01.01.0 is If refractometer no Show 4, your concentration exactly It is 4% (4×1.0=4%).
But if from a semi-synthetic product or special base with a correction factor 1.51.51.5 Use and refractometer number 4 show, your actual concentration is equal 6%6\%6% will be (4×1.5=6%)! Ignoring this coefficient will make you misdiagnose the concentration of the liquid.
4. Step-by-step instructions for calibration and measurement in the workshop
Follow the steps below daily or weekly to get an accurate number:
- Clean the Prism: Wipe the glass prism and the clear cover of the refractometer with a soft, lint-free cloth.
- Calibration with distilled water (zero point): Put 1-2 drops of distilled water or pure water on the prism, close the cap and look in front of the light. The blue/white dividing line should be exactly on the number 000 be Otherwise, turn the adjustment screw on the top of the device to calibrate to zero.
- Correct sampling: Take the sample directly from the spray nozzle (in operation), not from the stagnant surface of the tank where suspended oils float.
- Read the Scale: Pour 1 or 2 drops of the emulsion on the prism and read the border line number.
- Apply the Refractometer Factor: Multiply the number read by the factor listed on the TDS sheet of the product.
5. Suggested concentration table for all types of machining operations
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| Type of operation | Suggested actual concentration range (%) | Technical considerations |
|---|---|---|
| Grinding and Light Machining | 2.5%−4.0% | The need for maximum cooling and chip washing |
| General Turning and Milling | 4.0%−6.0% | Balance between lubrication and cooling |
| Tapping, Deep-Hole Drilling and Heavy Machining | 6.0%−9.0% | The need for strength of the lubricating film and high pressure resistance |
| Cold Rolling of Tubes and Profiles | 3.0%−5.0% | Stability in high flow circulation and stain control |
conclusion
Refractometer is a simple but very powerful tool for quality control of metalworking fluid. By allocating only 3 minutes a day to monitor the concentration and multiply the number Standard correction coefficient of Savalan lubricants, You can dramatically increase the life of your emulsion and tools and reduce production line operating costs.
Technical support team Kimiya Sanat Savalan, Provides accurate correction factor for all SVL series grades in Technical Data Sheets (TDS) and is ready to calibrate and train measuring instruments at your factory site.
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