What is Varnish?
How clean is your oil? Do you perform routine oil analysis? Is a consistent oil analysis program in place? Is oil analysis by way of free, paid services or a combination of both? These are important questions when faced with oil contamination issues. Traditional oil analysis reports report elements, ISO Code, TAN and water. This may not be enough to detect fluid failure. Varnish potential is not routinely included in many oil analysis offerings. Fluid / oil failure results in trips, sticking valves and bearing failure.
Oil contamination is made up of water, particles, varnish and soluble varnish. Removing all of these contaminants is important to healthy oil conditions.
What is Varnish?
Varnish is a thin, insoluble film deposit that is usually found on bearings, reservoirs, and internal components.
Varnish is a high molecular weight substance that is insoluble in oil. This substance is mostly made up of soft contaminants that are less than 1 micron in size. Traditional ISO 4406:99 testing or ISO cleanliness codes do not detect these particles. Current laser technology can only detect down to 2.5µm.
Insoluble compounds are polar in nature and as time goes on they migrate from the body of the base oil to machine surfaces. Initially, the surfaces start to show a gold or tan color building to darker gum layers that develop into lacquer.
A great analogy is a rain cloud. Just like a rain cloud, oil has the natural ability to hold oxidation-by-products in suspension. Once the “cloud” is full it rains, this “rain” is the point where varnish deposits start forming on internal metal surfaces of the lubrication system.
Another way to look at it is like cholesterol in the blood. Blood can only hold so much cholesterol before it starts to “plate” out on artery walls. Oxidation by products are much the same. This of routine oil analysis like blood lab work to detect a problem before it strikes.
How is Varnish Formed?
Insoluble contamination or varnish creation is due to oxidation, thermal degradation and water contamination. Other factors include cross contamination and micro-dieseling. The most common cause of varnish formation is oxidation. In a nutshell, oxidation is the loss of electrons. It happens when an atom or compound loses one or more electrons. We all know what happens to iron when exposed to oxygen; it produces iron oxide (rust) and breaks the metal down. The same process occurs in lubricating oil and hydraulic fluids.
Oil manufactures include additives in their lubricants to combat this process. These antioxidant additives are sacrificial to protect the oil. However, these antioxidants get “used up” or depleted over time.
Without these antioxidants, free radicals destabilize / oxidize the hydrocarbon molecules. Non-polar free radical molecules bond to non-polar oil molecules. This process repeats until the oil can no longer hold the varnish in suspension. These polar oxidation molecules bond to metal surfaces.
By proper oil analysis and filtration methods, this problem can be prevented or reversed.
In future blog posts, I will be discussing filtration methods and the process of stripping varnish.