How Do I Mix My Coolant?

Do you ever get rust spots on the machine and workpiece, or bacteria growth in your cutting fluid?

When issues occur with cutting fluid, it usually comes back to issues with mixing.

It may be surprising, but there is a ‘wrong’ way to mix your coolant. The way you mix your coolant can have a significant impact on its sump life and performance.

With this in mind, let’s unpack exactly how you should be mixing your metal working fluid.

Should I put the coolant or water in first?

This might seem obvious, but it’s too often done wrong and misunderstood.

When mixing metalworking fluids always add the concentrate to the water. Never the other way around.

Always add the coolant concentrate to the water.

To make it clear – add the coolant to the water, not the water to the coolant.

Why is this important?

This is critical as a chemical reaction called ‘reverse emulsification’ occurs if done wrong.

In laymen’s terms, the concentration will be the minor part of the solution that will not be able to mix with all the water. It is critical that the coolant's emulsifiers 'join’ or ‘connect’ to the water molecules.

If the mix is done the wrong way around then you can get water molecules without coolant. Essentially, the fluid will be partially separated with small globs of coolant and water. This can can cause rust and cater to bacteria.

Remember – always add the oil to the water.

How do I mix my coolant?

We would always recommend mixing in a separate drum or tank before adding it to the sump. Don’t try and mix it in the sump.

Agitation and movement is best. Get the water moving and then add the concentrate slowly until it is completely mixed and stable.

Synthetic Fluids

Synthetic and semi-synthetic fluids mix easily – you shouldn’t have any problems here.

Mineral Fluids

However, a mineral soluble fluid often requires more mixing to get all the oil to mix through. Often you can get small clumps of unmixed oil on the surface – don’t panic, as this is normal. Keep mixing until you get a consistent white milky colour.

Cold water can also cause issue. If you're having issues, it might be a good idea to add some hot water to increase the temperature to help it mix better.

What ratio should I mix at?

Ratios of concentrate to water is very important and is often the biggest cause of issues in coolant.

Unless specified by the manufacturer, all coolants need at least 5% concentrate. Why? Most coolant manufacturers work off 5% as a benchmark. This means that they’ve calibrated the levels of bactericide, rust inhibitors and other additives to make the coolant stable at 5% concentration.

If your concentration level is below 5% then you may get rust issues and bacteria growth.

It can vary depending on application

The ratio also depends on the type of cutting fluid you have and what your application is. Some coolants need higher concentration to get a suitable amount of lubricity. This depends on the severity of your application and the metals you are machining.

For example, when doing grinding you can have a low concentration, around 5%. If you're broaching (very severe) you’d increase your concentration, potentially up to 10-12%. If you’re not sure, check the manufacturers Technical Data Sheet (TDS) for more information.

How do I top up my machine?

1. Check your concentration
2. Use the concentration calculator to determine quantities needed
3. Premix your coolant
4. Add to the tank

Why do I need to top up?

When topping up your machine, you need to understand what is happening to the coolant.

Tanks lose volume from two things. Evaporation and a technical terms called ‘Drag-Out’.

Drag-Out

‘Drag out’ is a technical term referring to the coolant removed with a workpiece during the machining process.

Say you’re machining a piece of steel on a CNC machine. Coolant flows over the tool and into the cut. The fluid then flows off the workpiece and into the sump, except for a residual layer of oil that adheres to the workpiece. When you remove the workpiece you also remove the residual coolant. This lowers the concentration of the tank bit by bit. Over a period of 6 months, this can have a surprising impact.

Evaporation

Evaporation is big thing in Australia, and affects our coolants more than we may realise.

Evaporation affects our coolant by doing one thing – removing water from the tank. Essentially, there is less water in the tank but the same amount of cutting fluid, meaning that the concentration percentage has increased.

Topping Up

1. Check your concentration

Although you should check your concentration on a weekly basis, it's first step in topping up your coolant. The concentration will often be higher than when you first filled the tank.

Depending on the severity of the application, it shouldn’t get much higher than 12%. Check the details on the label of your coolant or on the TDS if you’re unsure what concentration it should be.

2. Work out the quantities you need

Once you know your concentration, then you need to work out what ratio of water to cutting fluid you need.

We’ve got a handy concentration calculator you can use to work out what you need - no maths or formulas! (You will need to know the current concentration).

It will give tell you how much concentrate and water you need to get it to the correct concentration.

Often, you’re going to be trying to lower the concentration of your coolant, so you won’t need as much cutting fluid.

3. Premix your coolant

Do not make the mistake of thinking you can add water to your existing tank to ‘dilute’ your coolant a little bit. If you are trying to dilute your coolant, add a premix at a very low percentage - but don't add only water.

This will ‘reverse emulsify’ the coolant in your entire tank. It can lead to significant problems down the track with rusting and bacteria attacks.

Instead, premix your coolant in a separate drum. Remember to add the water first, and the coolant second.

4. Add the premixed coolant to your tank

How do I use a refractometer?

Every company that mixes coolant should have a refractometer.

Refractometers (digital or manual) are key to getting good performance and sump life from your coolant. That's because they’re the easiest way to work out a coolant’s concentration.

If you want to learn more about how to use a refractometer, check out this article.

Do I need an emulsion mixer?

Emulsion mixers are used to assist in mixing coolant, although you do not strictly need one.

They act like a venturi system and use water pressure to mix the coolant in with the water. While these mixers can be very handy by making life easier for filling coolant tanks they can cause issues.

Often, the ratios are not set correctly. We recommend to pump a small amount through the mixer first then check the real ratio using a refractometer. Adjust accordingly until you get the desired percentage. We recommend doing this more than once while filling the tank as some mixers can change ratios depending on the water pressure.

In short? Get it right

Mixing coolant up is often seen as a messy job and is left to the apprentice or an inexperienced member in the team.

However, in our view, it is the most important step to getting long sump life and preventing common issues with coolant. You can guarantee to save yourself money and hassles by mixing your coolant correctly to begin with.