Lube-Tech


When it comes to oil condition management in 2019, varnish is a hot buzzword. But what is varnish? Can this one word really be an accurate description for every sludge-like material that develops in your hydraulic or lubricating system? Varnish is a good generalisation for the conglomeration of sediment products that can build up after extended degradation of the base oil; it effectively describes that yellow/ brown sludge that you may have noticed in tanks or on used filter elements.


What causes the formation of varnish? Oil degradation describes the fracturing of oil molecules and the constituent additives; these broken molecules can ultimately stick to each other, as well as other contaminants present, to form varnish. But what is the cause of oil degradation in the first place? The process is called oxidation, which essentially describes the reaction of the base oil with oxygen.


There are many factors that can act as catalysts to this process, the first major contributor being contamination of various types. An obvious contaminant is solid particulates; whether it’s environmental residue that’s entered the system or wear metals, any form of solid material will aid the


22 LUBE MAGAZINE NO.151 JUNE 2019


PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE


No.122 page 1 Varnish Identification


Measuring oxidation products through temperature manipulation when particle counting


Sam Keating, Laboratory Manager, Fluid Care Division, Hydac Technology Ltd.


varnish formation process. Oxidation products also stick to these contaminants to increase the quantity of sludge. A wide range of filtration is available, with the ability to assist in the removal of these harmful particulates.


Water is another common contaminant. Even dissolved water can heavily contribute to the oxidation process, we would recommend a maximum water saturation of 50% for your mineral-based oils in hydraulic and lubrication applications.


Finally, an often lesser-considered contaminant is air. The introduction of more oxygen containing materials will assist the unwanted oxidation process. Methods of water and gas removal are available, including a range of equipment based on the principle of vacuum dewatering; this enables the separation of water and gases from hydraulic and lubrication fluids.


As well as contamination, another factor can be excessively stressful system parameters. Pressures and temperatures that are beyond the fluid’s capability can quickly cause the deterioration of the fluid. For example, excess temperatures can mean thermal degradation; it’s important to remember that for every 10°C increase, the rate of reaction is doubled.


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