Key Engineering Materials Vol. 572

Abstract: In this study, an optimization methodology is proposed to systematically define head-cutter geometry and machine tool settings to introduce optimal tooth modifications in face-hobbed hypoid gears. The goal of the optimization is to simultaneously minimize tooth contact pressures and angular displacement error of the driven gear, while concurrently confining the loaded contact pattern within the tooth boundaries. The proposed optimization procedure relies heavily on a loaded tooth contact analysis for the prediction of tooth contact pressure distribution and transmission errors. The objective function and the constraints are not available analytically, but they are computable, i.e., they exist numerically through the loaded tooth contact analysis. The core algorithm of the proposed nonlinear programming procedure is based on a direct search method. Effectiveness of this optimization was demonstrated by using a face-hobbed hypoid gear example. Considerable reductions in the maximum tooth contact pressure and in the transmission errors were obtained.

Abstract: This paper studies the conjugated involute profile which are used in internal gear pumps. In this type of gear mechanisms, the internal gear profile is completely conjugate of the external gear profile. A composite line of action curve is obtained because the root fillets also play role in engagement cycle. The perfomance of the mechanism is increased. By applying consequent transformations, firstly the tooth surface of the generated external gear is obtained and secondly the tooth surface of the conjugated involute internal tooth surface is obtained. Also asymmetric tooth is considered. Mathematical models of generating and generated tooth surfaces are given. Based on the given mathematical models, a computer program is developed to obtain generating and generated surface. Conventional and conjugated involute profiles are compared.

Abstract: Involute helical gears are widely used in high-speed and heavy-load transmission systems of automobiles, helicopters, etc. Poor working conditions lead to fatigue crack and other faults of gear key parts such as tooth face and tooth root. To identify the root causes of gear faults, strain monitoring methods are often used to monitor the stress changes of gear key parts so as to work out individualized improvement plans. However, stress of gears in the work process is typically the result of the coupling effect of thermal stress and mechanical stress. The existing strain monitoring methods cannot separate them effectively, and thus it is impractical to quickly find the corresponding improvement measures. To reveal the coupling relationship between thermal stress and mechanical stress during gear meshing and find out the source of gear faults, this paper uses the transient finite element-based analysis method to study the coupling relationship between thermal strain and mechanical strain of a pair of helical gears in the test direction and find the coupling rules of thermal strain and mechanical strain among the strains of gears in the strain test direction that may provide effective guidance for the fault diagnosis of gear meshing.

Abstract: The general trend in the field of machine tools is to increase the speed of feed axes with the aim of reducing manufacturing times, high speed machining is a significant example of such increase. Ball screws have proven their ability to fulfill requirements of workpiece positioning accuracy, nevertheless, the heat generated in the screw-nut interaction increases proportionally with the speed of the axes. As a result, an increase in temperature takes place, which causes thermal expansion of the ball screw, producing positioning errors and decreasing the service life of the ball screws, therefore it is important to have effective methods for predict the temperature.The main objective of the present work is to predict the heat generated in the screw-nut contact based on analytical models in order to estimate the temperature distribution in the nut. For this purpose a heat transfer FE model of a preloaded high speed ball screw nut has been developed. Additionally, experimental heating tests have been performed to validate the FE numerical model. In this way, the temperature predictions obtained at different working conditions have less than 6% of deviation comparing with the experimental results.

Abstract: A multibody formulation is used to accurately describe the relation between the different components in chain drive systems and their full dynamics [1]. All components, including sprockets, are represented by rigid bodies connected to each other by revolute clearance joints [2]. The complete formulation is implemented in a computational simulation tool integrating all relevant dynamic characteristics inherent to chain drives and incorporated in the general-purpose multibody program [3]. Penalty contact force models are considered for modelling the revolute clearance joints, particularly those proposed by Lankarani and Nikravesh to quantify the normal contact force [4]. The friction force is accounted for based on the modified Coulombs friction law [2]. This work draws on the influence of dry contact parameters such as friction coefficient, restitution coefficient and clearance value on the dynamics of chain drives. The effect of a pretension level is also analyzed.

Abstract: Mechanical seal plays a very important role in rotating machinery for space exploration, but it is very difficult to estimate its friction performance by simulative experiment. In this paper, a experimental system for measuring friction properties of mechanical seal materials used in spacecraft is developed. It is able to provide some adjustable parameters in the experiment, such as environment temperature -60°C~60°C, load 100N~300N, rotational speed of 30r/min~110r/min and atmospheric pressure and high vacuum. Friction coefficients of babbitt graphite M120B and hard alloy YG6 are obtained by the test rig and the experimental results testify that the device can conduct simulative experiment effectively.

Abstract: In order to get PTFE(polyfluortetraethylene) composites of good friction and wear properties used in vacuum and low temperature conditions, do the tribological experiments of GF (glass fibre)/PTFE composites under vacuum and low-temperature environment. The results show that: with the increase of the GF size, the friction coefficient increases, with the increase of GF content, the friction coefficient increases.

Abstract: In the automotive industry the goal for engine designers is not purely power output. Stringent environmental regulations demand improvements in power, fuel consumption, reliability and service life of engine components. A significant contributor to all of these improvements is a good understanding of the tribology of bearings including the effect that surface texturing techniques can have on bearing performance. This paper discusses the micro finishing process known as GBQ (Generating Bearing Quality) which optimizes bearing surfaces in terms of profile, geometry and surface finish. GBQ has been applied to the bearing surfaces of high performance and mass produced crank and camshafts to reduce friction and extend service life.

Abstract: Many Factors affect the oil-air lubrication of sliding bearing such as oil supply, air pressure, load, bearing structure and so on. In order to study the effects of bearing structure on oil-air lubrication in sliding bearing, the oil-air lubrication and oil lubrication experiments of grooved sliding bearing have been done by using friction-abrasion testing machine. By means of measuring the temperature rise and the friction coefficient of grooved sliding bearing on oil-air lubrication and oil lubrication with different level of load at the same rotating speed, the results obtained show that the friction coefficient of oil-air lubrication with oil supply 30ml/h, air pressure 0.25MPa is almost the same as oil lubrication with oil supply 1.4L/h. The oil-air lubrication temperature rise is much lower than the oil lubrication in grooved sliding bearing with the same experimental conditions.

Abstract: In this study, the frictional contact with partial slide between two elastic cylinders is considered. According to the Spence’s self-similarity condition, a system of singular integral equations is constructed with respect to the normal pressure and the shear traction in the contacting area. Based on the Goodman’s hypothesis, the preceding system is uncoupled. Based on this, the tangential load in the central sticking zone is possible to be obtained analytically by means of the theory on the singular integral equation. Besides, a nonlinear equation with respect to the ratio of the slip and adhesive zone sizes is derived on the basis of the continuity of the tangential load. The stick zone size can thus be determined by solving the nonlinear equation mention above iteratively. A numerical example is provided to verify and validate the theory proposed in this work.