Abstract: Oil seal is an important sealing component in agricultural machinery. Oil seal leakage not only wastes engine oil and pollutes the environment, but also accelerates the wear of parts, affecting the service life of machinery. Therefore, the causes of oil leakage in agricultural machinery oil seals were analyzed, and preventive measures were proposed.

Keywords: agricultural machinery; Oil seal; Oil leakage; preventive measure

Oil seals are used to seal shaft components and achieve liquid lubrication. They ensure that the liquid lubricating oil does not leak by contacting the rotating shaft with a certain pressure through the extremely narrow sealing contact surface of their lips. Oil seals, as mechanical components for sealing, are widely used in agricultural machinery. Various oil seals are installed on agricultural machinery such as combine harvesters and tractors, which can effectively prevent the leakage of lubricating oil and hydraulic oil, and prevent dust and dirt from entering the interior of the machine. The common fault of oil seals is oil leakage, which leads to a decrease in the amount of lubricating oil and directly affects the reliability of various agricultural machinery and equipment. This article mainly analyzes the causes and preventive measures of oil seal leakage.

1. Reasons for oil leakage in oil seals

(1) Improper installation of oil seal. The oil seal is compressed and deformed during installation; Oil encapsulation reverse; When installing the oil seal onto the shaft, if it passes through the threaded spline of the shaft head, it may scratch the lip or cause the spring to fall off; Reducing the length of the spiral self tightening spring arbitrarily can lead to oil seal leakage or early leakage. (2) The shaft itself has defects. After long-term use, shaft components such as crankshafts and rear axle shafts experience bending fatigue deformation, with radial and end face runout tolerances exceeding the specified standards (the radial runout tolerance of the rear axle shaft is not greater than 0.04mm. The end face runout tolerance of the rear axle shaft and the radial runout tolerance of the journal surface where the large bevel gear is installed are not greater than 0.05mm, and the straightness tolerance is not greater than 0.1mm). When the tractor is running, there is significant radial and end face runout on the shaft, which reduces the viscoelastic "following" performance of the oil seal blade on the shaft neck surface, leading to leakage. (3) At the contact point between the shaft neck surface and the oil seal edge, there are defects such as circular grooves, ripples, and oxide scales on the surface, which cause gaps in the fit between the two. In addition, the shaft components were not ground or replaced during major repairs, so during the trial operation phase, the oil seal blade would quickly wear and break, leading to early failure. According to data and usage, more than 50% of the damage to the rotating shaft seal occurs at the contact between the shaft neck and the oil seal lip, resulting in surface wear and leakage. (4) Improper installation of the oil deflector (taking the rear axle oil deflector as an example) Install the oil baffle in reverse. When replacing the rear axle oil baffle, turn the open end of the oil baffle towards the small end of the inner ring of the tapered roller bearing, which hinders the flow of gear oil into the annular oil chamber (after the oil seal is installed in the inner hole of the tapered roller bearing seat, it forms a 13mm wide annular oil chamber together with the rear axle journal and tapered roller bearing), or the gear oil in the annular oil chamber is too little, causing dry friction between the rear axle journal and the oil seal lip, burning out the oil seal blade. Therefore, when installing the oil baffle on the shaft, make sure that the open end faces the oil seal open end (with a spring end) The oil baffle is loose or not installed in place. After installing the oil seal into the inner hole of the tapered roller bearing seat, the end face of the oil seal opening should be flush with the inner end face of the tapered roller bearing seat. After installing the oil baffle on the rear axle shaft neck, there should be a gap of 2-2.4mm between the end face of the oil baffle opening and the end face of the oil seal opening. However, due to loose fit (or axial sliding) or improper installation of the oil blocking plate with the rear axle shaft neck, the end face of the oil blocking plate at the opening end of the oil seal blocks the end face of the oil seal, making it difficult for gear oil to enter the contact area between the rear axle shaft neck and the oil seal lip, resulting in dry friction between the rear axle shaft neck and the oil seal lip, causing the oil seal lip to overheat, harden or burn out. Therefore, when installing the oil deflector on the rear axle shaft, it is necessary to ensure an interference fit of 0.147-0.377mm. (5) Not following the tractor technical maintenance procedures Excessive or insufficient filling of gear oil can cause oil seal leakage. The gear oil of the central transmission and gearbox is connected and shared. The oil level can be checked by unscrewing the oil filler plug (along with the dipstick). The oil level should reach the upper line of the dipstick. If it is insufficient, it should be added. If it is excessive, it can be released through the small inspection plug on the left side of the oil filler Regularly replace the lubricating oil and gear oil in the gearbox and central transmission gear compartment. Some operators believe that completely replacing the lubricating oil is a waste, only adding new oil and rarely replacing the gear oil in the central transmission and gearbox. In this way, the accumulation of impurities in the lubricating oil will cause abrasive wear of the shaft, bearing parts, and oil seal, accelerating the early failure of the oil seal. It is also necessary to change the gear oil according to the season, otherwise using winter gear oil in summer or summer gear oil in winter will cause oil seal leakage. (6) The gear oil is not clean. ① Some transmission boxes and rear axle housings of agricultural machinery are castings, and there may still be sand, sticky sand, residue or metal shavings left inside after sand cleaning. It is difficult to clean these impurities during repair, and these impurities will enter the gear oil, causing oil seal wear During the overhaul of a tractor, if the gears, shafts, bearings, and other parts are not cleaned thoroughly, it can cause unclean gear oil Improper storage, transportation, and use of lubricating oil can also lead to the invasion of impurities. (7) Poor quality of oil seal. Poor manufacturing quality of oil seals, or improper transportation and storage, resulting in aging of the oil seal lip, loss of gloss on the surface, and decreased elasticity; Oil seal deformation or lip cracking; Insufficient elasticity of the spiral spring or rusting or damage to the spring can cause early failure of the oil seal. Therefore, the appearance quality and specifications of the oil seal should be carefully inspected during installation. Oil seals are vulnerable parts that need to be replaced regularly. It is recommended to replace them during tractor major repairs, and the use of used oil seals is prohibited.

2. Preventive measures

Oil seal leakage is a common fault, and preventive measures should be taken. (1) For components that generate abnormal heat, timely troubleshooting should be carried out to avoid overspeed and overload operation, and to prevent rubber aging and rapid wear caused by the temperature rise of the oil seal lip. (2) Regularly check the oil level and quality of the lubricating oil. If the oil level is too low or there are too many impurities, thoroughly replace the oil with a new one. The brand and quality of the replaced oil should meet the requirements of the season. (3) During the break in period and initial use of the tractor after major repairs, it is necessary to regularly inspect the oil seal for any oil leakage. If the rear axle shaft oil seal is used, the left and right screw plugs at the "grease injection" position on the rear wall of the rear axle box should be unscrewed, and carefully observed with the help of light, work light, or flashlight to see if there is gear oil leaking out from the lip of the oil seal along the tapered roller bearing seat. During normal work, attention should be paid not to let the gear oil in the central transmission large and small bevel gear chambers and the transmission device housing leak into the steering clutch and brake chambers. To check for this phenomenon, it is necessary to unscrew the oil drain plug under the rear axle compartment (between the partition and the steering clutch compartment) and any bolt that fastens the brake band limiter to drain the accumulated oil.

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