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What is the demulsibility of lubricants? Demulsibility, in the context of lubrication management, is the ability of a lubricant to separate from water. In other words, when you mix a lubricant and water together, will the lubricant eventually dissolve in the water or will it resist dissolving and stay suspended in the water? This is an important characteristic for any lubricant to have, as it dictates how easily you can remove the lubricant from machinery and systems after use. Poor demulsibility can lead to fouling of machine parts and equipment, so it’s important to select a lubricant with good demulsibility characteristics.

Why Should You Monitor Demulsibility of Lubricants?

When selecting a lubricant for a specific application, it is critical to select one that will meet the needs of that application. In industries where water and oil are present, such as in hydraulic systems or gearboxes, it is important to use a lubricant that has good demulsibility to minimize the formation of emulsions. Basically, you should monitor lubricant demulsibility in any humid environment or machinery that uses water for processing. Emulsions can result in poor performance and shortened component life. This is because water depletes additives and increases the risk of other contaminants collecting in your lubricant, including dust, dirt, and wear debris. Your lubricant will have a shorter useful life as water increases the oxidation rate and wear rate.

What Exactly is it?

A lubricant’s demulsibility is what determines how easily water separates from the oil. Thus, it measures the lubricant’s resistance to emulsion. Lubricants with high demulsibility ratings will resist forming an emulsion with water, while lubricants with low demulsibility ratings won’t. A system with poor demulsibility will typically perform less efficiently. The demulsibility of your lubricant will decrease when there are large amounts of water contamination or certain polar contaminants. Furthermore, adding additives to your lubricant will decrease its demulsibility rating. Adding anti-rust additives, for example, decreases demulsibility and prevents water from settling and breaking the anti-rust film.

Liquid lubricants contain two kinds of water: dissolved water and free water. Dissolved water is molecular water that evenly distributes throughout the lubricant. Typically, free water collects at the bottom of the reservoir because it is not dissolving in the lubricant. You can avoid water contamination if your lubricant has a high demulsibility. It is notable, however, that dissolved water is harder to remove, which is what causes poor demulsibility in the first place.

How Does Demulsibility Affect Other Lubricant Qualities?

Rust inhibitors, antiwear, and lubricity additives can be depleted from oils due to poor demulsibility. Additionally, viscosity issues, acid formation, and varnish problems can be caused by it. The polarity of additive molecules in contact with oil is defined as their natural attraction to other polar materials. Polar materials include water, sponges, glass, dirt, metal surfaces, wood pulp, and sponges. Essentially, additives travel on particles or droplets of water, which is why poor demulsibility depletes additives.

Furthermore, lubricants can be thickened or thinned by contamination, which can change their viscosity. A lubricant’s viscosity is its most important physical property. When viscosity changes, equipment reliability is directly affected. In the presence of water contamination, emulsions become stable, and viscosity increases. In addition, film strength will be reduced, which is necessary for keeping surfaces apart.

Lubricant Testing

Your lab most likely tests for demulsibility as part of your lubricant analysis program, if you have one. In this test, equal amounts of water and lubricant are blended at a temperature comparable to your sump’s operating temperature. Following that, you check the mixture at 5-minute intervals as it separates. At each of these intervals, you measure how much lubricant, water, and emulsion there is to determine the demulsibility.

What is a Good Demulsibility Goal?

Tests like these are crucial for equipment that may be at risk from contamination by water. As a result of improper lubrication, fluid degradation, corrosion, and failure of components can occur when lubricants cannot separate from water.

A good demulsibility goal is:

  • The emulsion should be no more than 3 mL (milliliter) after 30 minutes for lubricants less than 90 cSt (centistokes).
  • If the lubricant has a viscosity over 90 cSt after 60 minutes, the emulsion should be less than 3 ML.

The best way to determine a benchmark for your test is to perform it with a new lubricant and water first. Afterward, test an aged lubricant sample. If the oil and water separate over 20% longer than with your aged lubricant, send a sample to a lab for analysis. A lubricant analysis program is an essential component of the continuous improvement of your lubrication management.

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