Let you know about industrial equipment lubrication

Reducing friction is one of the main purposes of lubricants. In addition, lubricants have other functions, such as 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 toxins in our body, which are carried out of the oil and removed through the filter element; cooling effect, friction between metals generates heat, and lubricating oil flows through the metal surface to take away the heat.

Lubrication is a common problem encountered in equipment maintenance, but what is lubrication? When it comes to lubrication, the scene that appears in our minds may just be applying oil or grease to the mechanical friction surface to reduce friction. Although 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 paste at room temperature). Grease is thicker than lubricating oil because grease uses thickeners on the basis of lubricating oil. The oil used for lubrication can be mineral oil from petroleum, or it can be artificial chemically synthesized oil. Vegetable oil and animal oil can also be used as lubricants. The lubricating oils and greases used now 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 has lubricity, but in order to optimize the overall performance of the base oil, we add some additives. Mineral oil can meet the requirements of ordinary industrial lubrication, so more than 90% of the current oil products are based on mineral oil. Synthetic oil has better performance, and the use of vegetable oil is mainly for environmental protection considerations.

Additives can optimize the performance of base oil, suppress bad properties, enhance favorable properties, and even give base oil some new properties. However, the more additives, the better, because additives are chemical substances, and various additives must be reasonably matched in categories and proportions to achieve the expected effect. In addition, the number of additives must also consider the occasion of use. For example, the lubricating oil (motor oil) of automobile engines requires better cleaning and dispersing effects 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 ability.

The role of lubrication

Three states of lubrication

There are three states of lubrication: full-film lubrication, boundary lubrication, and mixed lubrication. They are three different states, but all rely on lubricating oil to lubricate and resist wear.

Full-film lubrication: Full-film lubrication is divided into two types - hydrodynamic lubrication and elastohydrodynamic lubrication. Hydrodynamic lubrication means that two sliding friction surfaces in relative motion are completely separated by a layer of fluid lubrication film generated by relative speed to prevent them from direct contact and dry friction and wear. Elastic hydrodynamic lubrication is similar to hydrodynamic lubrication, and also relies on a layer of fluid lubrication film to separate the contact surfaces. The difference is that the relative motion between the contact surfaces is rolling, and the pressure formed by the full-film lubrication film is greater than that of hydrodynamic lubrication, and the lubrication separation film produced is thinner than that under hydrodynamic lubrication.

Even metals with high processing precision are not completely flat and smooth. Under a microscope, we can see that the metal surface is actually bumpy. Burrs are protrusions that we can already see with the naked eye, and those higher metal protrusions under the microscope are some peaks, which are difficult to see with the naked eye, but are very important for lubrication. In order to achieve full-film lubrication, the thickness of the lubricating film must exceed the height of these peaks, and they must be completely separated to avoid peak contact between the two contact surfaces. Being able to achieve full-film lubrication is the best lubrication state, and it can achieve the most effective protection for the contact surface of the machine.

Boundary lubrication: Although full-film lubrication is ideal, in some cases, a complete lubrication film may not be formed, such as frequent machine start-stop, impact load, speed, load factors are not enough to form full-film lubrication, etc. 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 film becomes thinner (at high temperature), the critical state before the transition from liquid friction to dry friction (direct contact between friction surfaces) occurs, which is boundary lubrication. Therefore, in combination with the structure and use of the machine, 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 full film lubrication cannot be achieved and boundary lubrication occurs, these additives play a role in protecting the mechanical surface. This type of additive can be adsorbed on the metal surface to form a protective layer to avoid metal wear. When boundary lubrication occurs, the extreme pressure additives are used to protect the metal surface. Compared with full film lubrication, the lubricating film friction generated during boundary lubrication is greater and the heat generated is also greater, but complete dry friction is avoided.

Mixed lubrication (Mixed lubrication): Mixed lubrication state refers to the situation where full film lubrication and boundary lubrication are mixed. As mentioned earlier, if the peak point of the metal surface is higher than the lubricating film, it will contact each other. In mixed lubrication, although most of the area is in full film lubrication, local boundary lubrication occurs when these peak points come into contact.