Methodology of completing the parts of the “Shaft seal” connections during repair

The reliability of modern sealing units of agricultural machinery is insufficient. Due to surface wear of the shaft and the seal during operation, the tightness in the movable joint decreases. This condition leads to the onset of leaks and the assembly failure. Leaks of technical fluids in units account for 20 to 30% of the total number of failures; during the overhaul period, seal failures occur 1.5 times more often than in new equipment. The method of completing the parts of shaft connections with seals will be useful for assigning rational repair dimensions of the shafts and selecting suitable seals. For its development, the authors considered the main ways to ensure the operational reliability of shaft connections, including advanced methods for restoring the shaft surface. When developing the method, 100 worn input shafts of the YaMZ‑239 engine gearbox and 100 new seals 1.2‑52´72‑8 were studied. Measurements were taken of the worn surface of the shaft under the seal and the inner diameters of the seal holes. The wear of the shaft surface under the seals reached 0.5 mm, and the probability of the shafts with wear exceeding the allowable 51.7 mm was 33%. When assembling worn shafts with new seals, the spread of interference ranged from 1.7 to 3 mm. At the same time, the limit of the least tightness, equal to 2 mm, was violated in 15% of the connections. In the connections of new seals with shafts machined to a repair size of 51.4 mm, the spread of interference ranged between 1.6 mm and 3 mm, while the limit of the least interference was violated in 20% of the connections. According to the criterion of maintaining the least tightness in the connection, the method of completing the parts of the “shaft-seal” connection was tested, including the calculation of the number of groups, the assignment of shaft repair dimensions and the selection of seal diameters. As a result, the probability of appearing connections with a guaranteed tightness of at least 2 microns was 88%, therefore, the proposed method of selecting shafts and seals makes it possible to make the durability of shaft-seal connections comparable to the new ones.

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