Coolant foaming is a common issue faced by metalworking fluid users and can be caused by various factors. In this blog, Pennine Lubricants will go into detail about why coolant foaming takes place and what steps to take to avoid it.
So, why is my coolant foaming? The main reason coolant foaming takes place is that the machine and the coolant in use are not being maintained correctly. Examples include blocked sump filters that restrict the flow of the coolant or running the coolant at too high a percentage mix.
Keep reading to find out more about coolant foaming, including how to stop coolant from foaming and what the negatives of coolant foaming are.
As manufacturers of lubricants and machine coolants, we receive many technical queries relating to why coolant foaming takes place. There are multiple factors that contribute to coolant foaming; therefore, we have detailed them below to help you identify why your coolant could be foaming.
Running the coolant percentage too high is a common cause for coolant foaming. Most products will have an operational band determined by the manufacturer, which takes into account a number of factors for optimal performance, including defoaming performance. Running your coolant at a concentration significantly higher than the range specified can increase the risk of foaming due to the higher volume of oil, emulsifiers, detergency additives and other chemicals within the coolant formulation.
The operational band will be unique to each product, but as an example, Ultrasol X-777 is a popular coolant, as it has exceptionally low foaming properties. The data sheet for Ultrasol X777 details a typical dilution range (min – max) of 4% – 10%. It is important to gain technical advice on your application and coolant; our technical team can advise on the correct dilution range for your application. Get in touch with our technical team easily here.
To find a datasheet for your coolant, click here, and you will be taken to our helpful technical information page, where you can search for your specific product’s datasheet. Alternatively, if you are seeking some more specific advice, be sure to get in touch with us today.
If the volume of coolant in the machine’s sump is low, this will significantly increase the risk of foaming occurring due to air entrainment. If the fluid level is approaching or below the pickup point for the coolant pump, then there is a high risk of air being sucked up, which will cause the coolant to foam excessively. This will have a detrimental impact on tool life, surface finish and swarf washing, as air has poor cooling, lubricating and flushing properties.
Most machines will have different types of filters in the sumps, including simple lift-out gauze plates, filter cartridges and bag-type filters. These are in place to protect the pumps and remove impurities which, if circulated, would have a detrimental impact on tool life and surface finish. As filters start to blind or block, this can restrict coolant flow, leading to air entrainment, which will cause excessive coolant foaming.
Certain coolants are produced with specific antifoam additives within the formulation. However, it is possible that systems employing fine micron/mesh filter paper can physically strip the antifoam from the emulsion as it passes through. This then leads to blinding of the filter paper, which may cause flooding along with an increased risk of coolant foaming.
Not all coolants are designed for use in high-pressure coolant systems. This does not mean it is a “bad” coolant; it is just not suitable for high-pressure applications. Older technology products, or products designed for low-speed applications, are less likely to contain low-foam additives. If you use the same coolant today as you did 20 years ago, it’s unlikely to contain additives suited to modern CNC machines and high-pressure coolant systems.
Although soft water is excellent for making long-lasting, stable emulsions with low corrosion potential, you are much more likely to experience coolant foaming issues when using soft make-up water or pure demineralised water. Some products are not manufactured for use in soft water, too, and using a coolant produced for medium- to hard-water make-up will also increase the risk of coolant foaming.
Hard water soaps are formed in areas with high levels of insoluble calcium in the makeup water. As the coolant ages, the calcium levels build up as the water evaporates and can create greasy, slimy calcium soaps in the coolant tank and even inside the machine. In severe cases, the soap can form a blanket on the coolant surface (almost like tramp oil), which will support foam as it prevents air from being released from the fluid.
Ultrasol X-NT products are a new range of boron-free metalworking fluids and are suitable for both soft and hard make-up water and are low foaming. For more information on this new range and whether it would suit your application, get in touch with our technical team today.
Fluid displacement caused by heavy swarf contamination in sumps is another cause of coolant foaming. If a significant proportion of the fluid volume is reduced by built-up swarf, this reduces the ability of the coolant to dissipate air effectively. As the reduced volume of coolant is being pumped around the system, the air bubbles build up to a point where the coolant may become a mass of creamy foam.
There are several ways you can help prevent your coolant from foaming. Read our helpful checklist below to find out how you can avoid the problems caused by coolant foaming:
It is quick and easy to check the dilution rate of your coolant with a refractometer. A refractometer is a handheld instrument used to determine the concentration of water-soluble fluids, such as machine tool coolants. By adjusting and maintaining the coolant within the manufacturer’s dilution range, this will help to reduce the risk of the coolant foaming.
To see an example of a form of testing involving a refractometer that can help avoid coolant foaming, be sure to click and watch our informative video below.
The job of coolant is to cool, so if your sump volume is only half full, the coolant will be pumped around the machine too quickly. This means the coolant will have little time to dissipate the heat from the cutting area before it’s circulated back around the system, trying to cool it again. By ensuring that the sump level of your coolant is more than 75% of the sump volume, your coolant will be able to do its job effectively, avoiding coolant foaming, which is a common problem caused by low sump levels.
If you’re running a high-pressure coolant system, your coolant needs to be able to cope with this. High-pressure coolants contain low-foam additives, which help to reduce the risk of coolant foaming during use. Our technical team can help identify the correct coolant for your application and machine.
f your machine uses a paper filtration system, it is important to use a coolant suited to paper band filtration systems. Your coolant provider should be able to identify the correct coolant for your system.
Using a coolant that isn’t suitable for the make-up water can have a huge impact on coolant foaming. Find out what water type area you are in and seek advice from your lubricant manufacturer on the right product for your application; our technical team can help you with this. Our popular product, Ultrasol X-777 is very low foaming in soft water, whereas Pencool Ultra S102 is suitable for hard water areas, as it prevents the formation of insoluble soaps, which cause foaming.
If the machine sump is heavily contaminated with swarf or tramp oil, use a filtration system like a Freddy coolant vacuum or a Tramp Oil Separator to remove contaminants that cause bacterial growth. Your coolant will then be able to dissipate heat effectively, and your coolant is less likely to foam.
| Disadvantage | Explanation |
| Poor tool life & surface finish | Air has much lower cooling and lubrication properties compared to a soluble coolant. Foam will therefore be detrimental to tool life and surface finish. |
| Increased drag out | When coolant foams, it creates a thick, creamy substance which will cling to components and swarf. It will also sit on swarf conveyors. These three factors all lead to increased “drag out” of the coolant and thus increased coolant consumption and costs. |
We’ve been helping metalworking fluid users get optimum performance from their coolant, which results in increased fluid life, improved product performance and manufacturing quality, as well as assisting with HSE recommendations. If you are experiencing coolant foaming and would like some advice from our technical team, get in touch with us today.
Coolant foaming occurs when air becomes trapped in the fluid. The main causes include:
For more information on dilution rates for our machine coolants, you can visit our technical library, which contains detailed information on concentrations for all of our products. You can also find guidance on the safe use of metalworking fluids in the HSE metalworking fluids good practice guide.
Foaming can usually be prevented with good maintenance and the correct coolant selection:
To learn more about this topic, you might want to check out our blog post, What Are the Main Machine Coolant Hazards?
Yes. Water quality plays a major role in foam formation in two different ways:
1 – Soft water can increase foaming because it stabilises bubbles.
2 – Hard water can form insoluble calcium soaps that trap air and worsen foaming.
There are further considerations for high-pressure CNC systems, which require low-foam coolants with anti-foam additives. For instance:
Choosing a coolant formulated for your water hardness helps reduce these issues. If you’d like to learn more about the hardness of your local water supply, then you’ll find the answers you’re looking for over at the Drinking Water Inspectorate website. They’ve even published a helpful map showing water hardness by region.
Persistent coolant foaming has several negative effects, which can have a serious impact on performance, operating costs and product quality. Here’s an overview of what you can expect to happen should excessive foaming go unchecked:
For more advice on what to do if you notice coolant foaming, get in touch with our team.
