Machinery Lubrication

Machinery Lubrication May June 2015

Machinery Lubrication magazine published by Noria Corporation

Issue link: http://www.e-digitaleditions.com/i/520842

Contents of this Issue

Navigation

Page 44 of 71

40 | May- June 2015 | www.machinerylubrication.com O i l O x i d a t i o n ubricants age and alter chemically by a process called oxidation. In fact, oxidation is the primary way a lubri- cant degrades over time from normal service. It typically results in impaired chemical and physical properties of the base oil and additives. Understanding why a lubricant oxidizes is essential to prevent, delay and monitor the process. As oil is used in a machine over time, the oxidation process occurs, typically starting with the degradation of antioxidant additives. If the driving conditions that stress the oil remain unchanged, these addi- tives will deplete at a near linear rate. This is sometimes called the induction period. When the oxidation inhibitors are largely depleted, the breakpoint of the lubricant is reached, at which time the base oil has lost its fi rst line of defense against oxidation. Some base oils are extremely robust and resist oxidation naturally. Examples include most synthetics. However, if exposures to pro-oxidants such as high temperature, moisture, metal parti- cles, agitation and oxygen are severe enough, even the most robust synthetics will give way to oxidize. This oxidation process has the potential to begin almost spontaneously for even oil sitting dormant in a storage container. However, the rate of additive depletion and base oil oxidation generally correlates to the intensity of pro-oxi- dants existing within the oil. Ultimately, the consequences of this chemical process will include increased oil viscosity and organic acids; the formation of sludge, varnish and deposits; additive depletion (including anti-wear additives, dispersants, corrosion inhibitors, etc.); and the loss of other vital base oil performance properties. Once these undesirable lubricant conditions exist, the machine no longer will be protected effectively against friction, wear and corrosion. Oxidation Overview Oxidation is a complex series of chain reactions. To better understand the process, follow the chart on page 42 as each element is explained. The oxidation process consists of three key stages: initiation, propagation and termination. Initiation describes the mechanisms by which a lubricant's components can chemically combine with one or more catalysts to produce a free radical. (Free radicals are highly reactive molecules that attempt to fi nd other molecules to combine with and create new products.) Propagation refers to the complexity of additional reactions of various types of free radicals and catalysts that result in the production of more free radicals and oxygenated compounds. Termination involves the eventual end of the oxidation process, either negatively or positively. If it is negative, the antioxidants typically have been depleted and the oxidation process will continue. If it is positive, an antioxidant likely has stunted the oxidation's progression. Keep in mind that antioxidants are sacri- fi cial, which means they become depleted as they do their job. Therefore, the positive effects of antioxidants will expire, while the overall oxidation process will not. Oxidation Stages The lubricant (a), which is a formulation of hydrocarbon base oil and additives, is subjected at some point to various catalysts and conditions that allow the initiation of oxidation to occur. Both BENNE T T FI T CH | NORI A CORPOR AT ION LESSONS IN LUBRICATION IDENTIFYING the Stages of OIL OXIDATION L Key Takeaway: For your lubricants to last longer and your machines to run longer, you must understand why oxidation occurs.

Articles in this issue

Links on this page

Archives of this issue

view archives of Machinery Lubrication - Machinery Lubrication May June 2015