Oxidation has earned a reputation for being an enemy of effective lubrication. The most prominent negative reaction lubricants in active service experience, it occurs when base oils in products are exposed to oxygen. A wide range of factors can trigger oxidation, including operating temperatures and contamination that cause lubricants to degrade. As they deteriorate, an extensive list of unwanted consequences arise, which ultimately lead to lubricant failure. If oxidised lubricants are not replaced, it can lead to loss of performance and productivity, as well as equipment damage and mechanical inoperability.
In the following sections, we’ll put lubricant oxidisation under the microscope. We’ll explore the main causes of this chemical reaction and factors that hasten the process. We’ll highlight indicators of oxidation to keep an eye on and examine its unfortunate outcomes.
What are the key causes and accelerators of lubricant oxidation?
Lubricants working under high operating temperatures are susceptible to oxidation. As the intense heat breaks down base oil molecules, the reaction rate doubles at each increase.
Understandably, oxygen exposure is another driver in lubricant oxidation. Open systems see lubricants make direct contact with air, however, mechanical agitation can also create microscopic bubbles to form in lubricating oils. Bubbles are rapidly compressed causing “micro-dieseling”, a form of thermal degradation, and oils are fouled with soot, sludge and varnish deposits.
Chemical degradation is also accelerated by metal particles entering the lubrication cycle. Common metal catalysts include lead, copper and iron. Not all contaminants are solid, however. Acids and water combining with a lubricant can also cause it to degrade. Direct sunlight is another driving factor for deterioration, as UV radiation can cause the base oil’s chemical structure to break down.
Many lubricants include sacrificial additives that safeguard against oxidation over an extended time. As the protection antioxidants provide depletes, base oils become vulnerable to the chemical process and degradation accelerates.
What are the signs of lubricant oxidation?
A physical inspection of lubricants in use and the machinery they maintain can provide operators with insights into oxidation issues. Typically, an oxidised lubricant will have an increased viscosity and slower flow rate. It may have an unpleasant odour and is usually much darker in colour than fresh oil. Checking equipment valves for varnish and sludge deposits can also show oxidation at work.
Proactive maintenance and oil testing is advised as operators who don’t follow a strict regimen often get their first sign of lubricant oxidation when equipment fails. Taking oil samples allows a visual on oil quality and colour, however, sending lubricants for testing is advised where their exact acid number (AN) can be revealed. Oil analysis can also show operators when lubricants still have available active service life to avoid unnecessary changes and reduce running costs.
What are the main outcomes of lubricant oxidation?
On a physical level, oxidation results in lubricants darkening significantly. Also, as lubricants oxidise, they thicken and their ability to flow effectively is impeded. As a result, the oils can’t reach moving parts to lubricate and protect them adequately. This leads to performance loss and increased wear and tear from friction, causing damaged parts that must be repaired or replaced.
Sludge and varnish deposits build up in systems when lubricants degrade through oxidation. Insoluble by-products form and jam filters, clog oil passageways and coat metal surfaces. The contaminated oil is unable to enter blocked filters and carries unwanted deposits into key work areas of machinery, leading to inoperable parts.
Organic acids can also form as oils oxidise. Once in the system, they can eat into crucial metal parts, causing widespread corrosion. Left unchecked, this can cause irreparable damage to expensive machinery at a loss of investment to equipment owners.
Antioxidant additives are used up as oils are subject to oxidation, making the base oil ever more vulnerable to further deterioration. This causes “runaway oxidation”, causing degradation at a rapid rate.
Do you need high-quality lubricant products for your operation?
Today, expert lubricant manufacturers like Millers, Morris, Mobil and Shell include antioxidant additive in formulas for industrial gear oil, grease, hydraulic oil and other products that must operate in the most demanding conditions. At Oil Store, we are proud to stock solutions from these leading brands and many others. Touch base with our team of product experts for further details on a specific lubricant or order from our available lines now.
