About design and use of powder plain bearings

Purpose. Optimization of methods of design, calculation and use of slip bearings; elaboration of recommendations on the use of powder materials and lubricants for the production of slip bearings. Research methods. Analysis of existing calculations of slip bearings, of efficiency of the bearing under conditions of self-lubrication and features of using hydrodynamic lubrication theory for calculations of slip bearings in the presence of liquid lubrication. Results. The area of predominant application of slip bearings, their main elements are clarified and described; recommendations on the sizes of structural elements of bearings are given. The main types of slipping friction and their relationship with the bearing design and operating conditions are analyzed. The possible composition of powder materials for slip bearings, the interdependence of bearing porosity and the viscosity of the oil used to ensure the of its longevity is analyzed. Recommendations for the design of bearings in conditions of liquid friction are given. Generalized methodology for calculating the efficiency of slip bearings is proposed. Based on the theory of hydrodynamic lubrication, a method for calculating slip bearings for liquid lubrication conditions, which provides optimal operating conditions is proposed. Scientific novelty. Optimized selection of powder material and structure to improve lubrication conditions is proposed. The analysis of the influence of the chemical composition of the oil to ensure maximum adhesion of this oil with a bearing surface is resulted; the analysis of the influence of the chemical composition of the oil to ensure maximum adhesion of this oil with a bearing surface, as well as mathematical dependencies that make it possible to adjust the composition of the oil by adding specially selected microadditives is resulted. Generalized approaches to the method of calculation of powder slip bearings, which operating under different friction conditions are proposed. Practical value. Practical methods of designing and calculating slip bearings from powder materials are offered.

Dynamic analysis of double-helical gear system considering effect of oil film among meshing teeth

The oil film among meshing teeth is just like a spring-damping element, and it can dominate the friction and meshing characteristics of the gear pair and influence its dynamic performances further. Thus, this article focuses on a double-helical gear system and makes efforts to consider the effect of the oil film among meshing teeth more deeply, which can enhance the precision of dynamic analysis for the gear system. First, based on the elasto-hydrodynamic lubrication theory and “microtomy” method, the models of friction and meshing characteristics are developed including the friction state and spring-damping effect of the oil film among meshing teeth; then, the dynamic models of the double-helical gear system with the effect of the oil film among meshing teeth are established, and finally, the experiments are carried out to verify the value of the models developed in this article. According to the theoretical and experimental analyses, it can be seen that the dynamic model considering the effect of the oil film among the meshing teeth is more precise and practical, and the effect of the oil film should be considered in the dynamic analysis of the gear system, especially at the condition with heavy load or high speed.

Evaluation standard and improvement method for multi-column envelope profile in single screw compressors

Multi-column envelope profile is the newly proposed engagement pair’s profile for single screw compressors. Based on hydrodynamic lubrication theory, a calculation model of the oil film moments for star wheel teeth with multi-column envelope profile was established. In order to balance the total oil film moments of the teeth, a profile evaluation standard and improvement method for the multi-column envelope profile were proposed. Then, the profile for a single screw compressor was optimized. The meshing pair with optimized profile is loaded into a prototype to carry out the running test. Results show that the optimization method improves the wear resistance of the star wheel teeth, especially the teeth’s front side, and enhances the running stability of the compressor.

Analysis and Optimum Structure of Deformation Coordination of Crankshaft-Bearing System

Aiming at realizing the coordination deformation of crankshaft-bearing system for engine, the equation of coordination deformation for crankshaft-bearing system was derived based on the theory of elasticity. According to the hydrodynamic lubrication theory, the mathematical model was established to analyze the bearing characteristics; the displacement of each bearing in the vertical direction was calculated by combined solution of the two parts above. The sum of squared differences of displacements was evaluated as evaluation standard of coordination deformation for crankshaft-bearing system. Then bearing clearances were chosen as optimized variables of crankshaft coordination deformation for the optimization. The crankshaft-bearing system of one type of engine was optimized for the coordination deformation. The results indicate that the optimization scheme of crankshaft-bearing system can make a significant improvement to coordination deformation and provide reference for the design of the engine.

Analysis of vibration characteristic for helical gear under hydrodynamic conditions

Based on the elasto-hydrodynamic lubrication theory, a 2-degree-of-freedom nonlinear dynamic model of helical gears with double-sided film is proposed, in which the minimum film thickness behaves as a function of load parameters, lubricant parameters, and the geometry of the contact. Then, the comparison of the hysteresis loops in different gear models shows the soundness of the presented model. Using numerical method, the time evolution of lubricant normal force, minimum film thickness, and lubricant stiffness is obtained in order to demonstrate the influence of the driving torque and pinion’s velocity. The results obtained in this article can contribute to the root cause for the gear vibration and show that the hydrodynamic flank friction has almost no influence on the gear system.

MAGNETIC LIQUID IN HYDRODYNAMIC LUBRICATION MODE OF SPHERICAL SURFACES

From the position of the hydrodynamic lubrication theory are considered the peculiarities of magnetoliquid lubrication in a point contact determined with a complicated character of the interaction of hydrodynamic and magnetic forces in a lubrication layer. The pressure distribution in a lubrication layer of magnetic liquid is considered as a superposition of the augend and addend pr and pm induced with hydrodynamic and magnetic forces. The contribution of the constituent pr is described by Reynolds equation in accordance with the classic hydrodynamic theory. At the saturation of magnetic liquid the constituent pm is presented as a function of the magnetic field strength, saturation magnetization of magnetic liquid and its viscosity and also velocity of rolling. As a result of the solution of a hydrodynamic problem through a numerical method there are defined conditions under which a lubrication layer loses its stability that is followed with the loss of carrying capacity in areas with negative pressure. The dependences of resistance to rolling forces, and sliding ones in a contact of spherical surfaces.

Propeller Excitation of Longitudinal Vibration Characteristics of Marine Propulsion Shafting System

The submarine experiences longitudinal vibration in the propulsion shafting system throughout most of run. A transfer matrix model of the propulsion shafting system, in which the dynamic characteristics of oil film within thrust bearing are considered, is established to describe the dynamic behavior. Using hydrodynamic lubrication theory and small perturbation method, the axial stiffness and damping of oil film are deduced in great detail, followed by numerical estimation of the foundation stiffness with finite element method. Based upon these values of dynamic parameters, the Campbell diagram describing natural frequencies in terms of shafting rotating speeds is available, and the effect on the 1st natural frequency of considerable variations in thrust bearing stiffness is next investigated. The results indicate that the amplitude of variation of the 1st natural frequency in range of low rotating speeds is great. To reduce off-resonance response without drastic changes in propulsion shafting system architecture, the measure of moving thrust bearing backward is examined. The longitudinal vibration transmission through propulsion shafting system results in subsequent axial excitation of hull; the thrust load acting on hull is particularly concerned. It is observed that the measures of structural modification are of little benefit to minimize thrust load transmitted to hull.