Research On Local Stiffness And Bearing Characteristics Of The Pressure Nut

The pressure screw-pairs are one of important parts of modern high intensity mill to adjust roll gap and need rapid, large stroke, frequent adjustment of roll gap. However, The pressure nut is expensive and easily damaged, and both ends are subjected to a pressure load at working. The peak load of the screw teeth was U- shaped, and the two ends of the screw teeth were prone to failure due to excessive stress.On the basis of elastic mechanics and thermo elastic mechanics, finite element software ANSYS is used to establish the three-dimensional model of pressure screw-pairs which carried on the finite element calculation and the improvement of structure. The main research contents of this paper are as follows:(1) The finite element calculation was carried out for the three dimensional model of the ordinary pressure screw-pairs. The distribution of equivalent stress along the root of the screw teeth was extracted, the correctness of the finite element model was verified, and the load bearing characteristics of the ordinary pressure nut were analyzed.(2) Composite pressure nut structure is proposed. The radial strain of the lower end of the pressure nut was suppressed by the installation of the steel sleeve, and some load was transferred to the screw tooth in the middle of the pressure nut, and the upper end of the pressure nut is cut in order to reduce its stiffness. The stress peak value of the root of the screw teeth at both ends of the composite pressure nut was reduced. The effect of the geometric parameters of the composite pressure nut on the strength of the root of screw teeth was analyzed, and the variance analysis was carried out at the significant level of ? ?0.05.(3)On the basis of the ordinary nut and the composite pressure nut, the structure of the improved pressure nut is proposed,and its three dimensions model was established and was calculated in finite element. The distribution of equivalent stress of the root of three kinds of pressure nut along the axial direction was compared. The effect of the geometric parameters of the improved pressure nut on the load distrib ution was studied(4) On the basis of the elastic mechanics of thermal structure coupling, the load bearing characteristics of three kinds of pressure nut are simulated at the temperature of 60?and100?. The effect of temperature on root strength and the effect of contact pressure on the working face of the pressure nut were analyzed.(5)The resistance strain gauge method was used for load bearing test of ordinary pressure nut. The experimental results a nd the finite element results are compared to verify directly the reliability of the finite element model and results of calculation of ordinary pressure nut, to verify indirectly the reliability of the finite element calculation of both composite nut and improved nut.The research results show that structure of both the composite pressure nut and the improved pressure nut are based on the change of local stiffness of the ordinary nut, which equivalent stress peak value of the root of the teeth can be reduced to 60% and 30%. The finite element results of the thermal structure coupling show that composite nut and the improved nut that equivalent stress of the root of the teeth and the contact pressure of the screw surface are greatly reduced. By changing the local stiffness of the pressure nut to achieve the purpose of reducing the stress peak value of the root of the screw teeth at its both ends...