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The geometric characteristic of tooth surface is the key factor to its performance. In this paper, a geometric generation method of point contact gear pair was proposed. By given a tooth surface, a smooth contact trace was determined according to the transmission demand, and the conjugated contact trace can be obtained. A new tooth surface of mating gear was derived by sweeping along the conjugated contact trace. The calculation of sliding coefficient of this type of gear pair was studied. The internal gear pair was taken as an example by taking involute gear as known gear and gear with quadratic curve profile as the mating gear. The gear pair was manufactured and performance experiment was carried out. The results show that the gear pair maintains point contact during the whole meshing process, and the contact point moves along the contact trace. The variation range of the sliding coefficient mainly depends on the involute parameter values at the meshing-in and meshing-out point. The actual contact trace of gear pair is consistent with the theoretical contact trace, and the efficiency is stable in 97.3% ~ 98.4%.

The paper presents the design and operating characteristics of a model of reversible axial fan with only one impeller, whose reversibility is achieved by changing the direction of rotation. The fan is designed for the purpose of providing alternating air circulation in wood dryers in order to reduce the consumption of electricity for the fan and increase energy efficiency of the entire dryer. To satisfy the reversibility of flow, the shape of the blade profile is symmetrical along the longitudinal and transversal axes of the profile. The fan is designed with equal specific work of all elementary stages, using the method of lift forces. The impeller blades have straight mean line profiles. The shape of the blade profile was adopted after the numerical simulations were carried out and high efficiency was achieved. Based on the calculation and conducted numerical simulations, a physical model of the fan was created and tested on a standard test rig, with air loading at the suction side of the fan. The operating characteristics are shown for different blade angles. The obtained maximum efficiency was around 0.65, which represents a rather high value for axial fans with straight profile blades. [ABSTRACT FROM AUTHOR]