Have you ever wondered if your coolant has low lubrication? It's a valid concern, as lubricity is crucial for optimal coolant performance, especially under high pressure. In this article, we’re going to cover what lubrication is, what the difference is between high-lubricity and low-lubricity coolants, and why you should care about it.
What does lubrication mean?
Lubrication is the term commonly used to measure lubrication performance on a coolant. It is tested using a torque test (which involves putting coolant in a hole and tapping the hole with a thread) to measure the amount of force required to do the machining operation. The lower the force required, the higher the lubricity of the coolant. Another option is the Reichert Wear Test, which measures the wear area size (again, the less wear, the higher the lubrication).
You’ll find lubrication performance is often harder to measure when it’s being used (rather than being tested in a lab). That’s because unless you’re accurately measuring tool life, you won’t have any idea about how effective your coolant is at reducing friction and extending the life of the cutting tool. For instance, in some cases by changing the coolant you are able to dramatically improve the tool life due to the lubricating benefits. Rather than getting 200 parts per insert, the insert an last up to 1000 parts.
The other thing to consider is that in most cases, where the coolant is being used with softer metals such as aluminium and brass, the tool is less likely to wear out as fast, meaning that there is no real way of accurately measuring the performance of lubrication.
What makes a coolant high in lubrication?
If you're curious about what the difference is between high and low-lubricity coolants, it primarily comes down to the extreme pressure additives. Extreme pressure additives are the components of the coolant that remain at high temperatures.
When using soluble coolants in cutting, milling, or machining applications, they must be mixed with water. However, due to the high heat generated at the cutting tip from friction, the water and other additives in the coolant evaporate quickly. This leaves only the extreme pressure additives present in the workpiece. In general, the EP additives are activated by high heat or remain on the cutting tool during high heat, providing the best lubrication. Some coolants available in the market claim to have EP additives and are labelled as 'soluble coolant EP'. However, it is important to note that all premium coolants already contain EP additives even if it is not stated on the packaging, like the Excision range. On the other hand, cheaper coolants are less likely to contain EP additives, meaning that their lubrication at high heat is not guaranteed. Chlorine is an example of a cheap EP additive that is used by companies looking for performance – however, in high concentrations it can be harmful, meaning premium coolants do not contain it.
What about synthetic coolants?
How fully-synthetic (or neo-synthetic) coolants achieve lubrication differs from a standard semi-synthetic or soluble. The lubrication is achieved through a polymer, rather than being provided through oils or traditional methods. Most of the details around these polymers are protected because it is a new technology, but the way these polymers work is they are activated at high temperatures, providing excellent lubrication at high heat. This is where the benefits of a fully synthetic (such as Excision's XDP3800) truly come through, especially in a difficult application.
How do I fix lubrication problems?
This is a tough answer because it is really difficult to adjust lubricity once it is in the sump. That’s because the lubrication of coolant is determined by the coolant itself – there are no additives that can increase the lubricity of the coolant that is currently in your machine.
That said, if you’re finding that your tool life is not what you want it to be, you do have the option to increase your concentration.
Essentially, you increase the amount of coolant in the emulsion and decrease the water. This is a trade-off between the cooling power and lubricating power of the coolant because the reduction in water means it has a lesser ability to cool, which can also increase tool life. You don’t want to go too far over the top so you’re not cooling the tools down.
Most coolants have a concentration range (e.g. between 5-12%) where they should be operated that you can adjust to get the optimum lubricating-cooling balance. For example, if you’re machining stainless steel and finding tool life is not where you want it to be, the best way for you to improve it would be to increase the concentration from 7% to 9%.
Why should I care?
Taking notice of the lubrication of your coolant means taking notice of your tool life. If your goal is to improve your tool life, chances are you're going to need to assess how the lubricity of your coolant, and what effect it's having. It's not a hard-and-fast rule that you need to change what coolant you use if you're not getting the lubrication performance you want, but it's important to consider. In addition, a tool that lasts longer provides better value for your money. This means that if your cutting tip is not under as much stress, you won't have to replace it as frequently, resulting in a tangible positive impact on your business.
The best way to start is to begin consistently tracking your tool life, especially if you decide to change coolant or increase the concentration, as it's the only way to objectively determine the lubricity of your coolant. As you delve deeper into the importance of lubrication in your operations, you'll likely realize it has the potential to impact your business in a very positive way.
