When rail oil meets cutting fluid, stay away!

Unfortunately, although the above-mentioned additives are important, many of their components are oil-based and quite temperamental—some are incompatible with each other, while others don’t dissolve in water. Meanwhile, the newly purchased cutting fluid is a concentrated solution that must be diluted with water before use.

Therefore, we’d like to specially introduce the following additive, which is essential—without it, emulsion-type concentrates would struggle to blend evenly with water and form a stable cutting fluid. In fact, without this additive, all the cutting fluid’s performance would quickly fade away, leaving nothing but fleeting illusions. This crucial ingredient is called an "emulsifier." The role of the emulsifier is to enable ingredients that are normally immiscible—or difficult to dissolve—in each other or in water to come together seamlessly, much like how milk achieves its smooth, creamy texture. As a result, various additives can be uniformly and stably dispersed throughout the cutting fluid, creating the versatile, easily dilutable product we need.

Now let’s talk about machine tool guide rail oil. Like all lubricants, it needs to deliver excellent lubrication performance, as well as rust-prevention and anti-wear properties—specifically, the ability to maintain a robust oil film under heavy loads without being squeezed or ruptured. Another crucial feature is its excellent emulsion-breaking performance. As we know, cutting fluids often contain emulsifiers that help fully disperse their various components into a stable emulsion.

The question we’re exploring today is this: one side demands emulsification, while the other seeks anti-emulsification. When cutting fluid comes into contact with guide rail oil, the active components in the guide rail oil get emulsified by the emulsifiers present in the cutting fluid. As a result, your guideways are left in a "three-nothing" state—no protection, no lubrication, and no rust prevention. So, what do you do? By the way, the emulsifiers in cutting fluids don’t just affect guide rail oil—they also have adverse effects on other machine oils, such as hydraulic fluids, and even on painted surfaces. In fact, many cases of machine tool wear, corrosion, loss of precision, or even equipment failure can be traced back to the presence of these emulsifiers.

If the operating environment of your machine tool guideways is enclosed, you no longer need to read further. However, 99% of machine tools cannot completely seal their guideways.

In modern machining workshops, the selection of guide rail oil is crucial. Guide rail oil can influence the precision of mechanical processing and the service life of metalworking fluids, directly impacting the production efficiency of machine tools. Ideally, guide rail oil not only needs to exhibit exceptional friction control but also must be compatible with the metalworking fluids commonly used during machining processes. Water-soluble cutting fluid It maintains excellent separability. If the selected guide rail oil and cutting fluid fail to fully separate, the guide rail oil will emulsify, or the cutting fluid's performance will deteriorate—both of which are major factors leading to rusting of modern machine tool guideways and poor lubrication effectiveness.

For machining, when rail oil meets cutting fluid, their sole mission is to keep them "apart"!

Therefore, when selecting guide rail oil and cutting fluid, it is essential to conduct an effective evaluation and inspection of their separability. Properly assessing and measuring the two substances is crucial. Separability , it can help avoid losses during the actual machining process, which undoubtedly plays a crucial role in ensuring the precise operation of machining equipment.

The editor specially introduces six simple and practical methods: one trick to identify, two steps to verify, and three tips for maintenance—these can help you easily tackle the separation issue of guide rail oil and cutting fluid!

One trick to spot it: Symptoms caused by poor separation performance

If the guide rail oil becomes emulsified and fails, your machine tool may experience the following issues:

　　 ·Reduced lubrication effect, increased friction

　　·May lead to higher energy consumption

　　· Wear appears on the material surface or coating in contact with the rail

　　·Machinery and components suffer from corrosion

　　Or perhaps your cutting fluid has been contaminated by way of guide rail oil, leading to certain issues, such as:

　　·When the concentration of the cutting fluid changes, its performance becomes difficult to control.

　　· Lubrication performance deteriorates, leading to severe tool wear and a decline in the surface quality of machined parts.

　　·The risk of bacterial growth increases, leading to unpleasant odors.

　　·Lowering the pH value of the cutting fluid may cause corrosion.

　　·Excessive foam in the cutting fluid

Two methods for verification: Quickly determining the separability of guide rail oil from cutting fluid

Lubricant-contaminated cutting fluids are costly to treat. Therefore, rather than reacting after problems arise, it’s better to prevent them from happening in the first place. Machining companies can quickly determine the separability of rail oils and cutting fluids under consideration by simply conducting two straightforward standard tests.

The TOYODA test simulates the phenomenon of guide rail oil contaminating cutting fluid. In the experiment, 90 milliliters of cutting fluid and 10 milliliters of guide rail oil are poured into a container, then vertically stirred for 15 seconds. After 16 hours, the condition of the liquid inside the container is observed, and the volumes (in milliliters) of the three layers—separated guide rail oil at the top, the "mixed" layer in the middle, and the separated cutting fluid at the bottom—are measured.

As the recorded test result is 90/0/10 (90 mL of cutting fluid, 0 mL of mixture, 10 mL of guide rail oil), this indicates that the oil and cutting fluid have achieved "complete separation"; however, if the result is 98/2/0 (98 mL of cutting fluid, 2 mL of mixture, 0 mL of guide rail oil), it means Emulsification reaction An incident occurred where the cutting fluid and guide rail oil were not properly separated.

This experiment simulates the phenomenon of water-soluble cutting fluid contaminating guide rail oil. In an 80/20 ratio, guide rail oil is mixed separately with various conventional cutting fluids—specifically, 8 milliliters of guide rail oil combined with 2 milliliters of cutting fluid. The mixture is then stirred at 1500 rpm for 1 minute, after which its condition is visually inspected at 1 hour, 1 day, and 7 days post-mixing. Based on the following criteria, the mixture’s state is rated on a scale of 1 to 6:

　　1=Complete separation

　　2=Partial Separation

　　3=Oil + Middle Mixture

　　4=Oil + Intermediate Mixture (+ Cutting Fluid)

　　5=Intermediate mixture + Cutting fluid

　　6=All are intermediate mixtures

Experiments have shown that using cutting fluid and guide rail lubricant sourced from the same supplier helps achieve better separation between the two. For instance, when testing with actual products—specifically by mixing Mobil Vactra™ Digital Series guide rail and slide-way lubricants at oil-to-cutting-fluid ratios of 80/20 and 10/90, respectively—with Mobil’s water-soluble cutting fluid, the Mobil Kutter™ series—the results clearly demonstrated: the Mobil Vactra™ Digital Series could be easily separated from the cutting fluid, while a thin layer of lubricant remained on top of the Mobil Kutter™ cutting fluid. Notably, removing the oil was remarkably straightforward, and only trace amounts of the mixture were observed.

Illustration: Mobil Vactra™ Digital Series rail and slide lubricants demonstrably exhibit superior emulsion separation properties, producing only minimal amounts of mixture. [(Top image) 80/20 oil/cutting fluid ratio; (Bottom image) 10/90 oil/cutting fluid ratio]

Three Maintenance Tips: The Key to Ensuring Efficient Operation of Your Production Workshop

Of course, confirming the separability of guide rail oil and cutting fluid doesn’t mean the problem is completely solved. During equipment operation, numerous uncontrollable factors can still affect the performance of both the guide rail oil and cutting fluid—and these must not be overlooked either. Moreover, routine maintenance and upkeep are essential components in ensuring the workshop runs efficiently.

Proper maintenance: In addition to rail oil, other machine tool lubricants—such as hydraulic oil and gear oil—can also cause contamination. Therefore, regular maintenance is essential to prevent contamination arising from coolant coming into contact with various machine tool oils, inhibit the growth of anaerobic bacteria within the coolant, thereby preserving its excellent performance, extending its service life, and reducing the occurrence of unpleasant odors.

Cutting Fluid Performance Monitoring: Usage Refractometer Regularly monitor the concentration of the cutting fluid—under normal conditions, a sharp, distinct line will appear on the refractometer. However, if the cutting fluid contains a higher amount of emulsified way oil, the line on the refractometer will become blurred, indicating a relatively high level of floating oil. Alternatively, you can measure the cutting fluid’s concentration using titration and then compare the result with that of fresh cutting fluid, which will also reveal the degree of oil emulsification.

Remove Floating Oil: Many modern machine tools are already equipped with automatic oil skimmers, or oil separators can be added separately to existing equipment. In larger systems, filters and centrifuges are typically used to remove floating oil and other contaminants. Additionally, manual removal of floating oil can also be accomplished using tools such as industrial vacuum cleaners.