STUDYING THE INFLUENCE OF MECHANICAL AND ELASTIC PROPERTIES OF DEADWOOD BEARINGS ON RIGIDITY COEFFICIENT NUMERICAL VALUE

The article studies the influence of a rigidity coefficient of the elastic supports and a foundation, which simulate deadwood bearings in the design models, on the stress-strain state of the ship shaft line. The importance of a rigidity coefficient in designing the ship shaft line and its elements has been specified. In the analysis the rigidity coefficient is taken as a constant value. Elastic characteristics of the stern bearing bushings may greatly affect the parameters of the designed shaft lines. Generally, the stern bearings are made of caprolon, pockwood, babbit and rubber. There has been presented a design model of the ship shaft line on elastic point support. It has been stated that the value of the rigidity coefficient is specified in many works when calculating the ship shaft line, but there is no reference to the sources and methods of receiving it. The overall view of the deformed contact of the shaft with stern bearing has been illustrated. The technique of determining the rigidity coefficient has been offered, subject to mechanical and geometrical parameters of the ship shaft line and its deadwood bearings. The equation of defining the stern bearing rigidity coefficient has been produced, which helps to account the elastic parameters of the bushings and geometry of contact of the ship shaft line with the bushing. For reliability of the offered technique a number of pilot studies on the hydropress П-125 were conducted, for which there were manufactured special devices and a mandrel. The essence of method of determining a rigidity module, according to GOST 9550-81, is in measuring the ratio of stress increment to a corresponding increment of relative deformation of compression. It was proved that the divergence of the values of rigidity coefficient received by the experimental and theoretical ways does not exceed 8%.

Investigation of the fluctuation of the static axial rigidity for double-nut preloaded ball screws

This article aims to investigate the fluctuation of the static rigidity for preloaded ball screws. Based on the correlation between preload and friction torque, a new model to calculate the contact rigidity by friction torque is proposed. Meanwhile, a novel test bench is constructed to measure the static stiffness at different positions. The experimental results agree well with the theoretical values, which proves the validity of the model. Furthermore, it is found that the screw shaft rigidity has the greatest influence on the system stiffness fluctuation, compared to the bearing rigidity, and the torsional rigidity. For the feed system, increasing the bearing rigidity, which is the lowest stiffness of the whole system, is an effective method to increase the system stiffness. The study provides an accurate method to obtain the stiffness fluctuation in the effective travel of ball screws, which is significant for improving the positioning accuracy of ball screws and computer numerical control machine tools.