| With the extension of mine exploitation and the requirements for safe and efficient production of large mines,the large friction hoist system will generate violent and complex dynamic tension and vibration during the lifting operation.This typical dynamic friction transmission state will affect the transmission reliability and safe production of the hoist system in coal mines.In this paper,according to the dynamic friction drive transmission of flexible steel wire rope,the transverse-longitudinal dynamics,the dynamic friction contact between rope and lining,the control of transmission stability,and the coupling characteristics of rope dynamics and friction transmission are studied.The calculation models of dynamic rope tension and the dynamic contact and creep between the rope and lining are established by Simulink.The results show that the mean value of the dynamic rope tension is 7%higher than the static average value.The fluctuation of dynamic tension can reach 44.8%of the static average.The maximum contact stress of the lining is 1.9MPa in the acceleration stage.The maximum variation range of creep velocity and creep quantity of the rope relative to the lining are-7.6 to 12.8mm/s and 0 to 209mm,respectively.Larger container weights,high quality lining,appropriate load configuration and optimized operating parameters can reduce the creep.An experimental platform for friction transmission of flexible wire rope is developed and the accuracy of the calculation results of the dynamic tension and creep of is verified.The theory of using dynamic friction angle as the design safety reserve of friction hoist system design is put forward.Based on the dynamic contact stress of lining,the wrap angle is divided and the concept of mixed angle is proposed.The results show that the total creep of the rope relative to the lining under different parameters is between 4-6 mm.The friction angle is minimum when the initial acceleration time is 1.4s.The range of each region of the wrap angle—minimum static angle(0~10.6°),mixed angle(10.6°~125.5°)and minimum friction angle(125.5°~195°).The tension and transverse longitudinal vibration of the wire rope are obtained in the normal lifting process through the experimental platform.A friction hoist system simulation model is established based on Adams/Cable.The transverse and longitudinal real-time dynamic response at each point of the rope and the contact friction characteristics between the rope and friction pulley are obtained.The results show that the transverse vibration intensifies with the increase of lifting speed.The longitudinal vibration is characterized by random disturbance.The rope tension is divided into dynamic tension zone and inertial tension zone according to the distribution characteristics.The transverse rope vibration becomes violent when it approaches the friction pulley,and the vibration causes the rope to shift away from the friction pulley.The"skidding"phenomenon of the rope is obtained by simulation when the friction coefficient of the lining is less than 0.25.The increase of friction coefficient will widen the dynamic tension zone,and the rope vibration will be detrimental to the effectiveness of the friction pair.The tension and vibration of the rope under the condition of friction pulley emergency braking,container jamming and periodic excitation are obtained through the experimental platform.The results show that the vibration has several abrupt peaks at the same interval after the braking.The transverse peak is 280m/s~2,the longitudinal peak is 40m/s~2.The shock stress wave generated by braking will conduct and reflect along the rope.After the container is stuck,the transverse vibration is stronger than longitudinal.The transverse vibration under periodic excitation appears as forced vibration dominated by the excitation frequency.The discovery of sub-order transverse vibrations elucidates the characteristics of multi-stage natural frequencies of the wire rope.The time-frequency ridge distribution of transverse and longitudinal vibration have a certain degree of coincidence,which reveals the coupling characteristics of transverse-longitudinal vibration of the rope.Taking the operation stability of the system as the research objective,the effects of different acceleration curves and different lifting parameters on the rope dynamics are discussed through the simulink model and the experimental platform.The initial acceleration time is optimized by the application of the impact restriction theory.The results show that the increase of lifting speed will aggravate the transverse and longitudinal vibration,and the change of acceleration and load has the opposite effect on the transverse and longitudinal vibration.The inertia tension zone widens with the increase of lifting speed,and the dynamic tension zone narrows with the increase of acceleration.The peak value and fluctuation of the dynamic rope tension under trapezoidal acceleration curve is minimal.When the initial acceleration time is 1 times the vibration period of the fundamental wave,the most stable tension and transverse vibration state of the rope can be obtained.The field vibration test of a practical mine friction hoist system is carried out.The global dynamic model of the friction hoist system is established based on Adams/Cable.The model unifies the rope dynamics(lifting side and lowering side)and the interaction between the rope and pulleys(friction pulley and guide pulley)as a whole.The dynamic rope tension at any position,the vibration in three directions,and the frictional contact mechanical response between the rope and pulleys are obtained.The results show that at the initial stage of acceleration and at the end of deceleration,the rope appears a dynamic instability vibration with a spindle shape in the short side direction of the cage and is the most violent of the three vibration directions.The global model has obtained very similar results.The tension fluctuation at the midpoint of the string between the friction pulley and guide pulley is the most intense.and the tension fluctuation in each position increase with the lifting speed increase.In the vicinity of the friction pulley,the dynamic instability characteristics and the vibration caused by the proximity of the friction pulley are intensified cross-linked to form a long-term large-scale vibration.Vibrations in the z(short side),y(vertical)direction at the rope string location present“beat”features.After the rope rotates 180 degrees on the friction pulley,the contact force is significantly increased due to the dominant role of string tension.The most of the friction force of the hoist is provided by relatively small regions(1/5 to 1/2 wrap angle).The maximum average contact force between the rope and friction pulley is 177.5N/mm,and the maximum average slip velocity is 26.2mm/s. |
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