Study On The Reliability Of Knotter Tripping Mechanism Based On Rigid And Flex Contact-fatigue Check And Wear Calculation

On the basis of comprehensive analysis of domestic and international research on tripping mechanism of D-type knotter,according to the design requirements of a knotter driven by double toothed discs with same tooth direction,in view of unreasonable space shape of tripping mechanism,difficult adjustment and compensation of wear clearance,the structure of tool arm surface and tripping groove is optimized on the basis of tripping mechanism of the knotter driven by double fluted disc,rigid-flexible coupling dynamics analysis and fatigue life check are carried out.The predictive model for key wear parts is given and verified by test.The main contents of this paper are as follows:(1)Optimization design of the tripping mechanism of the knotter driven by double toothed discs with same tooth direction:According to the spatial position parameter analysis of the baler,the knife arm surface contour is parametrically reconstructed based on the NURBS surface construction method,which provides greater passage space for the rope needle.Using the calculation method of radian change rate,the curvature change rate decreased by 14.8%to 21.1%in the key areas with large contour changes.The maximum radian change rate of the improved knife arm is 2.70,avoiding increasing the radian as much as possible while improving the passability of the rope needle.Considering the serious wear of the tripping notch,a wear gap compensation structure is designed.(2)Dynamic analysis of tripping mechanism based on modal stress:the ADAMS multi-rigid body dynamic model of knoter tripping mechanism is established,and the action sequence and contact load of the two kinds of tripping mechanism are compared.The action timing of the tripping mechanism driving the knotter is consistent with the original tripping mechanism.Compared with the original tripping mechanism,the contact force of the new tripping mechanism is decreased.Based on the modal stress method,the paper obtained the contact force curve of cam-ball roller and the load time course curve and dynamic stress result.Considering the flexible deformation of the knife arm,the extreme value of the load between the parts is significantly reduced.In the case of the contact between the tripping groove and the knotter,the peak load is 75.72%compared with the multirigid body dynamics.After analysis,the kinetic model calculation of rigid and soft contact emulates the actual situation more accurately,and the load time course curve provides a basis for the fatigue calculation.(3)Fatigue calculation based on the load time course curve of rigid and flexible contact dynamics:the S-N curve of 40Cr Mn Mo steel is calculated theoretically by using the empirical formula of fatigue limit and strength relationship.The load time course curve was processed and the load spectrum was compiled.The stress-strain results obtained from finite element statics were fed into FE-safe fatigue analysis software.Based on the von Mises stress and Goodman criteria,the fatigue life calculation was completed.It is concluded that the fatigue life of the tripping mechanism of the same ter is of the same order of magnitude as the original structure,and the fatigue life of the whole knife arm and the large tooth plate except the direct contact parts with the point is more than10~5times,which meets the industry standard and the fatigue check is qualified.(4)Finite element wear analysis of tripping mechanism based on Archard model:.Based on the nonlinear finite element software MSC.Marc MENTAT,the tripping mechanism finite element simulation wear model is constructed.The cloud map of strip and large disc cam is obtained through600 simulations or 6000 working cycles,and the key parts and extension trend are analyzed.The wear of the tripping piece mainly occurs on the tripping working face.The wear of the large disc cam begins at the tripping action drive point,which is consistent with the loading peak-point of the kinetic simulations.Analyzing the numerical table,it is found that at the 532-533 cycle,the wear growth rate of the strip surface is near zero,so it can be estimated that the wear will stop when actually used for about 5300 times.(5)Pull-off performance test and wear test:using self-made knotter fatigue wear test bench.Through the analysis of the data obtained in the test:the success rate of the same tooth to double tooth disc drive knotter debutton mechanism is 100%,which has a reasonable design and meets the use requirements.In the test,the maximum wear of the strip is 0.7334mm,the maximum wear of the disc cam is 0.8964mm,and the wear gap of 5000-6000 is negative to 0,losing the forced tripping function.Through the comparison,the simulation results and the test results have good consistency,including the wear state of the wear surface and the value of the surface wear amount,which are close to the test.The number of available wear of the tripping piece is in the same interval as the test results,indicating that the wear model can be used to predict the wear of the tripping mechanism parts.Heat treatment process recommendations for tripping plate and disc cam are given based on wear times and actual hardness.