Calculation of fits for cylindrical connections with key for reducers in agricultural machinery
2019
Erohin, M., Russian State Agrarian Univ. − Moscow Timiryazev Agricultural Academy (Russian Federation) | Leonov, O., Russian State Agrarian Univ. − Moscow Timiryazev Agricultural Academy (Russian Federation) | Kataev, U., Russian State Agrarian Univ. − Moscow Timiryazev Agricultural Academy (Russian Federation) | Vergazova, U., Russian State Agrarian Univ. − Moscow Timiryazev Agricultural Academy (Russian Federation)
The lack of reliability of cylindrical connections with the key is explained not only by the low quality of the materials of the parts, but also by the inconsistency of the fit. The presence of a gap in these compounds leads to fretting and fretting corrosion due to the ingress of wear products, dust, moisture and soil. Increasing the gap leads to beatings and plastic deformations of surfaces. A method for calculating the fits with interference has been developed for cylindrical connections with a key. The method includes calculation of the pressure from the cantilever and radial forces in order to exclude the opening of the joint at low interference values and the transition to the zone of plastic deformation due to exceeding the maximum pressure at high interference. To ensure possible disassembly and assembly of the connection in the field the operational requirements for limiting the maximum interference were calculated to replace the drive elements, such as chains, sprockets, pulleys, belts, etc. Restrictions on the roughness of the hole and the shaft were introduced to ensure the quality of the contact area in the fit. Geometric parameters of keyways are introduced into calculations. The recommendations for thermal calculation of the dimensions of parts in the landing were improved. The dynamic coefficient, which takes into account the possible overload of connections, is included in the calculation of the minimum interference. As a result of testing the methodology, it was revealed that, when applying the obtained landings, the wear rate of the connection is significantly reduced. As an example of cylindrical connections with the key of reducers “Mosselmash”, the wear rate of the sprocket-shaft connection with the use of the fit 30H7/x6 decreased by 12 times and the wear rate of the connection gear in the fit 40H9/z8 decreased by 3 times.
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