Why is the hydraulic oil pollution of cement machinery? harm? Control?
November 12, 2022
Various hydraulic systems are used in cement machinery, such as the roller pressurization system of vertical mill and roller press, the hydrostatic lubrication hydraulic system of ball mill, the blocking wheel hydraulic system of rotary kiln, etc. The main function of hydraulic oil in the hydraulic system is to transmit power, and it also lubricates and protects the mechanical moving parts in the hydraulic system. The reliability of the hydraulic system and the service life of the hydraulic components largely depend on the cleanliness of the hydraulic oil, which mainly depends on the degree of contamination of the hydraulic oil in the hydraulic system. According to statistics, 70% of the hydraulic system failures are caused by the contamination of hydraulic oil. Therefore, it is of great significance to analyze the causes and hazards of hydraulic oil pollution and seek effective control measures to ensure the normal operation of the hydraulic system, improve its working reliability and improve the service life of components.
01 Causes of hydraulic oil pollution There are three kinds of hydraulic oil pollution: solid particle pollution, water pollution and air pollution. Sources of solid particle pollutants The hydraulic system itself contains a certain amount of residual impurities. The new oil contains impurities. During the working process of the system, it is inevitable that various particles will be immersed in the hydraulic system. When changing the oil, the filling tool has not been cleaned, and the pollutants enter the system together with the hydraulic oil. Abrasion particles of metal and sealing materials, particles or fibers falling off filter materials, paint and slag flakes peeling off oil tank, etc. constantly generated during use. Sources of water pollutants Water vapor in the atmosphere. Water immersion during storage, transportation, pumping and use. Sources of air pollutants The sealing of the system is poor, and the oil is in direct contact with the air. The oil level of the oil tank is not within the specified height, the oil suction pipe and filter are exposed to the oil level, and the hydraulic pump absorbs air when it is running.
02 Hazards of hydraulic oil pollution
Harm of solid particle pollution
1) Sticking and blocking the filter eyelet and various gaps and channels make the hydraulic pump difficult to operate and generate noise. 2) Destroy the lubricating oil film and increase the friction and wear of machinery. The solid particles will destroy the lubricating oil film whose thickness is less than 0.6 times of its size and become invalid, so that the friction force and wear of the machine will increase significantly. 3) Accelerate the wear of sealing materials and increase the leakage. The external leakage pollutes the working environment around the equipment. If the external leakage is serious, the oil in the oil tank will be insufficient, and the hydraulic pump will be emptied (the oil sucked in by the hydraulic pump is mixed with air), which is easy to produce cavitation and increase the noise. 4) Some or all of the pores of the hydraulic components are blocked, causing the control components to malfunction and affecting the working performance. 5) The metal and metal compound particles in the solid particles will play a catalytic role in the oxidation and deterioration of the hydraulic oil, and the oxidation of the oil will deteriorate the oil quality and reduce the oil performance. Harm of water pollution The hydraulic oil contains water, which will not only have a great impact on the physical and chemical properties of the oil itself, but also affect the normal operation of the entire hydraulic system. 1) The water in the hydraulic oil can generate an emulsion that is extremely difficult to destroy. When there are surface active substances (additives and oxidation products of hydrocarbons), the stability of the emulsion is enhanced. The existence of oil-water emulsion in the hydraulic system will cause various faults of the system. Viscous organics are adsorbed on the surface of tiny water droplets, and the emulsion generates oil dirt, which blocks the oil filter, oil pump and regulating element, affecting the working performance of the system. 2) The water in the hydraulic oil can greatly accelerate the oxidation process and corrosion process. When the water and inorganic pollutants (metal particles, which are oxidation catalysts) act together, the hydrocarbon oxidation of the working fluid will be greatly enhanced. 3) The presence of water can aggravate the corrosion of hydraulic oil to metals, including non-ferrous metals (copper, lead). When water exists, oxidation increases, increasing the acidity of the oil. 4) When water containing hydraulic oil encounters air, it will generate stable foam. This phenomenon will reduce the lubricating performance of hydraulic oil, leading to increased wear; At the same time, the contact surface between hydraulic oil and air oxygen increases, and the corrosion of metal parts intensifies. The foam will also make the oil supply of the hydraulic pump drop sharply, which will worsen the stability of the hydraulic system. Hazards of air pollution 1) Produce noise and cavitation, and damage system components. There are three forms of air in the hydraulic system: first, it exists at the high point of the system in the form of free holes; Second, it is suspended in the liquid in the form of small bubbles; Third, it is dissolved in liquid. As the solubility of air in the liquid is proportional to the pressure of the liquid and inversely proportional to the temperature of the liquid, when the oil flows from the high-pressure area to the low-pressure area or the temperature rises, the air dissolved in the liquid will be separated, forming free bubbles, making the hydraulic oil in the pipeline or components become discontinuous, which is what we usually call cavitation. After the cavitation is formed, if the oil flows through the high-pressure area again, the bubble will break rapidly, and the liquid particles surrounding the bubble will impact the center of the bubble, causing local high temperature and pressure, as well as noise and vibration. At the same time, the impact force generated by the bubble explosion can cause the metal material surface to peel off, damage the hydraulic components, and reduce the service life of the components. 2) The increase of liquid gas content will lead to the decrease of the volumetric efficiency of the hydraulic pump and the increase of energy loss, making the hydraulic system unable to play its due role. 3) Accelerate the oxidation and deterioration of oil to change its viscosity.
03 Control of hydraulic oil pollution Control of solid particle pollution The solid particle pollution of hydraulic oil has existed in the production and manufacturing of equipment, which needs to be carefully cleaned when changing oil after initial running in. For example, the main oil inlet pipe should be pickled, and then it should be cleaned with warm water; The rubber hose shall be cleaned with cleaning liquid under high pressure, and then all pipelines, joints, hydraulic components, etc. shall be blown clean with dry compressed air. Do not wipe the parts with cloth, cotton yarn, or other fibers. After the system equipment operates normally, the following matters shall be noted: 1) Ensure that the hydraulic system equipment is clean and free of impurities such as oil sludge, iron filings, metal filings and fibers; 2) When replenishing or filling new oil, filter it according to the grade of system oil, keep containers, pipes, oil filling ports and tools clean, and avoid secondary pollution during filling and oil changing; 3) If there are parts that need to be welded and ground during maintenance, they should be carefully handled, and welding slag and grinding powder should not be mixed into the system; 4) Observe whether the oil cooler works normally to ensure that the temperature of hydraulic oil is not too high. Control of water pollution 1) As the hydraulic system of cement machinery operates under relatively bad conditions, rainwater may enter the oil tank through the vent hole and filler hole of the oil tank. Therefore, in the use, it is necessary to control the oil filling. Especially in rainy weather, measures must be taken to block and cover the oil filler to absolutely prevent rainwater from entering the oil tank. In addition, after the hydraulic components are repaired, each part must be dried with dry compressed air during assembly to avoid moisture. 2) Regularly check the cooling coil in the oil tank for corrosion or leakage to prevent water from entering the hydraulic oil tank directly. 3) Strengthen the management of hydraulic oil. In the process of storage, transportation, pumping and use, the operating procedures shall be strictly followed to prevent water from being immersed in the oil. Air pollution control Check and eliminate possible air leakage points. The oil level of the oil tank shall be within the specified height to prevent the oil suction pipe and filter from intermittently absorbing air when the oil level is exposed instantaneously. All joints of the system shall be well sealed. If necessary, they shall be tightened and checked for tightness. If they are damaged, they shall be replaced in time. The accumulator shall be checked frequently for gas flow and leakage, and the pipe joints shall be checked frequently to prevent looseness and damage to the seals. Clean the filter and radiator regularly to avoid local vacuum of the system due to poor oil suction and high oil temperature of the hydraulic pump. In addition to the above measures to control hydraulic oil pollution, appropriate oil quality detection instruments can also be equipped to conduct real-time detection of the quality indicators of the hydraulic oil in use in the hydraulic system, and implement on-demand detection and oil change according to quality. When the oil quality fails to meet the standard, clean the hydraulic system in time, filter the oil to the standard or replace it with new oil.
