Reducing friction is one of the main purposes of lubricating oil. In addition, lubricating oil also has other functions. For example, the lubricating oil film can prevent rust; prevent metal from being corroded; lubricating oil can also play a cleaning role. Impurities inside the equipment are like The same toxins in our body are carried from the oil and removed through the filter element; cooling effect, friction between metals generates heat, and the lubricating oil flows through the metal surface to take away the heat.

Lubrication is a problem often encountered in equipment maintenance, but what exactly is lubrication? When it comes to lubrication, the scene that appears in our minds may be just applying oil or grease to the mechanical friction surface to reduce friction. While this concept is correct, it is only one aspect of lubrication.

Many substances can be used for lubrication. The most common ones are lubricating oil (liquid oil) and grease (usually in paste form at room temperature). Grease is thicker than lubricating oil because grease is used on the basis of lubricating oil. Thickener. The oil used for lubrication can be mineral oil derived from petroleum, or artificial chemically synthesized oil. Vegetable oils and animal oils can also be used as lubricating oils. The lubricating oils and greases used today are mainly derived from petroleum or synthetic oils. The oil before additives and thickeners are added is called base oil, which is the main component of lubricating oil. The base oil itself already has lubricity, but in order to optimize the overall performance of the base oil, we add some additives. Mineral oil can meet ordinary industrial lubrication requirements. Therefore, more than 90% of current oil products are based on mineral oil. Synthetic oil has better performance. Vegetable oil is mainly used for environmental reasons.

Additives can optimize the performance of the base oil, suppress bad properties, enhance favorable properties, and even give the base oil some new properties. However, the more additives, the better. Because additives are chemical substances, various additives must be properly matched in category and proportion to achieve the desired effect. In addition, the amount of additives should also consider the situation in which it is used. For example, the lubricating oil (motor oil) of a car engine needs to have a better cleaning and dispersing effect to remove carbon deposits and soot in the engine. The lubricating oil used in heavy-duty machinery may be added with Extreme pressure additives to increase anti-wear capabilities.

The role of lubrication

Reducing friction is one of the main purposes of lubricating oil, but in addition to reducing friction, lubricating oil also has other functions. For example, the lubricating oil film can prevent rust and prevent metal from being corroded. Lubricating oil can also play a cleaning role. The impurities inside the equipment are like toxins in our bodies. They are carried through the filter element and removed from the oil. Cooling effect: Friction between metals generates heat, and lubricating oil flows through the metal surface to take away the heat.

Three states of lubrication

There are three states of lubrication: full film lubrication, boundary lubrication, and mixed lubrication. They are in three different states, but they all rely on lubricating oil for lubrication and anti-wear.

Full-film lubrication Full film lubrication is divided into two types – hydrodynamic lubrication and elastohydrodynamic lubrication. Hydrodynamic lubrication refers to two sliding friction surfaces that move relative to each other. A layer of fluid lubricating film generated by relative speed completely separates the two friction surfaces to prevent them from direct contact and causing dry friction and wear. Elastomeric hydrodynamic lubrication is similar to hydrodynamic lubrication. It also relies on a layer of fluid lubricating film to separate the contact surfaces. The difference is that the relative motion between the contact surfaces is rolling, and the pressure of the formed full-film lubricating film is greater than that of the hydrodynamic force. Lubrication produces a lubricating separation film that is thinner than that under hydrodynamic lubrication.

Even metals that are processed with high precision are not flat and smooth on the surface. Looking under a microscope, we can see that the metal surface is actually pitted. The burrs are protrusions that can be seen with the naked eye, and those higher metals under the microscope The raised parts are peaks that are difficult to see with the naked eye, but are important for lubrication. In order to achieve full film lubrication, the thickness of the lubricating film must exceed the height of these peak points and completely separate them to avoid peak point contact between the two contact surfaces. It can achieve full film lubrication, which is the best lubrication state and can achieve the most effective protection of the mechanical contact surface.

Boundary lubrication Although full film lubrication is ideal, it may not be able to form a complete lubricating film in some situations, such as frequent starts and stops of the machine, impact loads, speed, and load factors that are insufficient to form full film lubrication. These situations will cause boundary lubrication. . It is good to be able to form a complete lubricating film, but when the conditions are not enough, a complete lubricating film cannot be formed or the lubricating oil film becomes thin (at high temperature), the critical point before the transition from liquid friction to dry friction (direct contact between friction surfaces) occurs. The state is boundary lubrication. Therefore, based on the structure and use of the machinery, some equipment requires the use of extreme pressure lubricants, which contain extreme-pressure additives (EP: extreme-pressure additives) or anti-wear additives (AW: anti-wear additives). When this is not possible Full film lubrication is achieved. When boundary lubrication occurs, these additives play a role in protecting the mechanical surface. This type of additive can be adsorbed on the metal surface and form a protective layer to prevent metal wear. When boundary lubrication occurs, extreme pressure additives are relied upon to protect the metal surface. Compared with full film lubrication, the lubricating film friction generated during boundary lubrication is greater and more heat is generated, but complete dry friction is avoided.

Mixed lubrication The mixed lubrication state refers to a mixture of full film lubrication and boundary lubrication. As we mentioned earlier, if the peak points of the metal surfaces are higher and higher than the lubricating oil film, they will contact each other. In mixed lubrication, although most areas are in full film lubrication, when these peak points contact, local boundary lubrication will occur.

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