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POL 5. Part 1. Slide 1. Welcome to the Principles of Lubrication, module 5, an introduction to lubricant additives. In the previous module we learned about base oils with a basic overview of the different types and groups. Slide 2. In this module, we will cover the following areas. What is an additive? Focusing on Performance Modifiers, Surface Modifiers, Lubricant Protectors & Other Additives used in the manufacture of lubricants. Slide 3. So, what is a lubricant additive? An additive is simply any substance added to a base oil in order to enhance its properties. These can be categorised into different groups. There are performance modifiers, to alter the lubricants performance under certain conditions or to meet specific criteria. These are typically.  Pour point depressants.  Viscosity Index improvers.  Seal swell agents. There are Surface Protectors, to protect the surface of the material under certain operating conditions. These are typically.  Anti-corrosion.  Detergents / Dispersants.  Extreme pressure and Anti-wear.  Friction modifiers. There are Lubricant Protectors, to protect the lubricant and extend its overall effective lifetime. These are typically:  Anti-oxidants.  Metal deactivators.  Anti-foam. Then of course there are many Other Additives that can be used in the manufacture of a lubricating oil or grease. These can be:  Tacky / adhesive additives.  Solid lubricants.  Fillers.  Thickeners. Slide 4. Pour point depressants. These performance modifying additives Prevent build up of wax crystals at low temperatures. At low temperatures many mineral based lubricants will cease to flow, and the viscosity will in effect thicken up because of the formation of wax crystals. These additives Stop the joining of wax crystals from forming a lattice type structure which stops the flow of oil. They reduce the size of the wax crystals and how they interact with each other, resulting in a lubricant that will flow much more easily at lower temperatures. Slide 5. Viscosity Index Improvers. These performance modifying additives act in a way to subdue, or reduce any reduction in viscosity as the temperature of the lubricant rises. They use what is called a Polymeric additive – like polymethyl methacrylate (PMMA) or Poly isobutylene (PIB). They produce long chain polymers, that are tightly bound at low temperatures and open up as temperature increases. The increase in mass raises the internal friction of the fluid causing an increase in viscosity, thus slowing down the rate at which the lubricants viscosity would normally reduce at. For example at 60oC the viscosity of a lubricant with no V I improvers could be, let’s say, 100 centistokes, and the viscosity of a lubricant containing V I improvers would be higher, say for example, 120 centistokes. Therefore, able to maintain a higher level of required lubrication at that temperature compared to the non V I lubricant. Slide 6. Seal swell additives. These performance modifying additives act to maintain the integrity of the seal material. They prevent shrinkage and hardening or brittleness of the seal material. And in turn, they help to prevent oil leaks and contamination ingress. It is important to know what type of seal material is being used in your machinery, to avoid any compatibility issues with certain lubricant types. Slide 7. Anti-corrosion. These surface protecting additives help to prevent surface corrosion of the materials being lubricated. There are two types of corrosion. Electrochemical and chemical. As you can see from the illustration, a hydrophobic barrier of polar corrosion inhibitors is built on the metal surface, which in turn prevents any moisture from attacking the surface and causing corrosion. Inhibitors can reduce or eliminate rust and corrosion – they can neutralise acids and repel moisture. Corrosion can weaken the surface structures and initiate fatigue, which can lead to component failure. Slide 8. Detergents and dispersants. These surface protecting additives, clean and disperse contaminants. Detergents have two primary functions for the protection of metal surfaces: They Clean deposits, and Neutralise acid build up in the lubricant. Dispersants then, clear away any soot / dirt particles created by the detergents. They form what is known as micelles, or colloidal particles by encasing the soot deposits, and flush them away through to the filters etc. These types of additives are found mainly in engine oils, but also in industrial applications such as hydraulic and gear lubricants. Slide 9. Extreme pressure additives. These surface protecting additives are used to protect the metal surfaces and reduce wear. The illustration shows a magnified cross-section of two metal surfaces, with a very thin layer of lubricant between. Frictional heat and pressure cause the Extreme-pressure the Extreme-pressure additive to react chemically with the peaks of the bare metal surfaces, producing a sacrificial protective lubricant slurry. Over time the additives are used up, so it is important to regularly change the lubricant to help maintain the surfaces. This type of additive is typically reactive sulphur, phosphorus, or molybdenum. Sulphur can be corrosive to yellow metals, so a non-reactive sulphur-phosphorus can be substituted for lubricants intended for gearboxes that contain yellow metals. Slide 10. Anti-wear additives. These surface protecting additives are used with EP additives to protect the metal surfaces and reduce wear. The additives react with the metal surfaces to give boundary lubrication, as seen in the illustration. They are activated by moderate temperature or load. Zinc-dialkyl di thiophosphate or what is known as ZDDP is commonly used and produces a semi-solid or hard phosphate glass-like protective layer. ZDDP can also be problematic. They can cause the formation of ash deposits which can be corrosive to certain metals. In car engines the formation of the glass-like structure can damage and block catalytic converters. They are also deemed non-biodegradable.