The Right Way to Top-Up Metalworking Fluids

Why do you need to calculate Top-Up emulsion concentration?

Let’s start with the basics: During the initial fill-up, it’s simple. You know the volume of your tank (e.g., 1000 liters or 264.17 gallons) and the recommended concentration for your coolant (e.g., 8% as stated in the product documentation).

For example: 8% of 1000 liters (264.17 gallons) = 1000L × 0.08 = 80L (21.13 gallons) of concentrate required for the initial fill.

In this case, you don’t need to worry about the concentration in every bucket when mixing manually or checking the mixer output. You just control the liquid level in your concentrate drum or IBC container.

But what happens next?

Why Is Maintaining Concentration So Complex?

Coolant volume decreases over time due to several factors:

1. Water evaporation in the cutting zone due to high temperatures.
2. Natural evaporation in the tank, influenced by ambient temperature.
3. Loss with chips removed from the machine.
4. Loss with finished parts , especially in automated processes
5. Airborne mist loses when the machine doors are open without mist collector usage.

As a result, the volume of coolant in the tank decreases. But here’s the key question: Can you always top up with just 8% coolant?

The answer is no .

Why Not Always Top-Up with 8%?

Coolant is a mix of concentrate (oil) and water. Evaporation primarily affects water, not the concentrate . Over time, this causes the concentration to increase as the tank’s emulsion volume decreases .

Example: Calculating a Top-Up

• Suppose you have a 1000-liter (264.17 gallons) tank. After a week of operation:
• Tank volume decreases by 300 liters (79.25 gallons) = Sensor shows 700 liters (184.62 gallons) of coolant remains in the tank.
• Measured concentration (using an optical refractometer) has increased to 10%.

Therefore your task is to:

• Top-up 300 liters (79.25 gallons) of liquid.
• Bring the concentration back to 8%.

If you add coolant with an 8% concentration:

• Remaining concentrate: 700L (184.92 gallons) × 10% = 70L (18.49 gallons)
• Concentrate added with top-up: 300L (79.25 gallons) × 8% = 24L (6.34 gallons)
• Total concentrate after top-up: 70L + 24L = 94L (24.82 gallons)
• Final concentration: 94L / 1000L = 9.4%

Clearly, adding coolant at 8% won’t reduce the concentration to the desired 8%.

How to Calculate the Correct Top-Up?

To achieve the target concentration:

• Calculate the existing concentrate : 700L of remaining emulsion at 10% = 70L (18.49 gallons)
• Calculate the concentrate needed for an 8% full tank : 8% × 1000L = 80L (21.13  gallons)
• Subtract the existing concentrate from the target: 80L - 70L = 10L (2.64 gallons)

To mix the emulsion correctly for given example, your top-up should consist of: 290 liters of water and 10 liters of concentrate we calculated above. This gives a top-up concentration of 3.3% .

Simplify the Process with our TOP-UP Coolant Calculator

Manual calculations can be tedious and error-prone, especially when factoring in refractometer correction coefficients.

Our Coolant Top-Up Calculator eliminates the hassle by:

• Calculating optimal top-ups for any tank size or water miscable coolant type
• Supporting liters and gallons
• Working seamlessly on mobile devices

Desktop:

Mobile:

Stay efficient and protect your CNC machines—try our calculator now: CNC Coolant Calculator