| The friction hoist mainly relies on the friction between the friction lining and the wire rope for transmission.The source of the friction is the dynamic viscoelastic contact deformation between the friction lining and the wire rope.The dynamic viscoelasticity of the friction lining is directly related to the lifting capacity,the working efficiency and the reliability of the friction hoist.Based on the arc surface method,this paper uses the in-situ microscopic observation method to study the dynamic viscoelastic friction mechanism and wear behavior between the friction lining and the wire rope of friction hoist.The real-time observation of the viscoelastic friction mechanism under static and dynamic loads was carried out.The mechanism of boundary lubrication under the water-dripping and friction-enhancing conditions was explored.The Effect of the viscoelasticity of the friction lining on the wear behavior of the contact interface was analyzed.The Euler's formula for friction transmission under lifting conditions was modifiled.(1)An arc surface method for measuring the friction coefficient of the friction lining was proposed.By monitoring the relative slip distance and relative slip speed of the friction lining and the wire rope,the friction cycle was divided into 6 stages.The stick-slip determination criterion was proposed:the appearance of the"platform"on the curve was used as the basis for judging the critical point of the dynamic and static friction transition between the friction lining and the wire rope.The friction coefficient between the friction lining and the wire rope tested by the plane method and the arc surface method was compared,and it was found that the friction coefficient measured by the plane method was relatively large.(2)Based on the arc surface method,the viscoelastic friction mechanism between the friction lining and the wire rope under static load conditions was observed in real time.The adhesion friction and hysteresis friction were observed and quantified.The relationship equations between the adhesion friction,hysteresis friction and viscoelasticity was established.equation.The results show that adhesion friction is proportional to the loss modulus.hysteresis friction is proportional to the value of E”/(E'~2).Adhesive friction increases with the pressure,and decreases with the sliding speed.Hysteresis friction decreases first and then increases with increasing pressure and sliding speed.Friction vibration is affect by the combined action of adhesive friction and hysteretic friction.The viscoelasticity of K25 lining is the best,its adhesive friction is the largest and its friction vibration amplitude is the smallest.(3)Based on the arc surface method,the viscoelastic friction mechanism between the friction lining and the wire rope under dynamic load conditions was observed in real time.The full slip critical value of dynamic alternating loads was revealed.It was found that the full slip critical value of K25 and G30 friction linings was 1200N.The full slip critical value of GM-3 friction lining was 900N.At the critical value,the friction force and friction coefficient were the smallest,the adhesive friction contact was the smallest,and the vibration amplitude increased sharply.This is the most dangerous situation for friction systems.The relationship between the alternating load and the frictional vibration was established.The amplitude of the frictional vibration increases with the amplitude of the alternating load,and the vibration amplitude of full slip was 2-3 times that of the vibration without full slip.Increasing the frequency of the alternating load leaded to an increase in full slip,friction and vibration.(4)By testing the friction lining's water absorption,sensitivity to water molecules,and the rheological properties of friction-enhancing grease,the mechanism of boundary lubrication between the friction lining and the wire rope under the water-dripping and friction-enhancing conditions was explored.The results show that the thickness and bearing capacity of the water-absorbing layer affected the viscoelastic contact and the interface friction lubrication.The Effect of water medium on the bearing capacity of K25 lining is the least.So it is safer to use K25 friction lining in mines with severe water penetration.The loss modulus(viscosity)of friction-enhancing grease is proportional to the friction coefficient.The larger the loss modulus of friction-enhancing grease is,the more favorable it is for anti-friction.The more stable the rheology is,the more favorable the smoothness of friction is.This result provides a theoretical basis for improving and developing new friction-enhancing greases.(5)By monitoring the viscoelastic contact,friction,wear,and temperature changes during the friction process,the relationship equations of viscoelasticity,friction coefficient,and wear under frictional thermal conditions were established.It was found that the loss factor has a positive correlation with the friction coefficient,and the amount of wear increases exponentially with the increase of the loss factor.The greater the viscoelasticity of the lining is,the greater the interface friction coefficient and the frictional resistance are.During the friction process,the surface was easy to be damaged to generate cracks.These cracks were easy to cause spalling,and it was easier to wear and tear under the action of reciprocating friction,and to form wear debris.The relationship equations of viscoelasticity,friction coefficient and wear under frictional heat conditions not only guide the practical application of the project,but also provide a theoretical basis for the development of new types of linings with high friction and high wear resistance.(6)The friction coefficient between friction lining and wire rope under different working conditions was tested on a self-developed dynamic micro-slip friction test platform.The relationship between friction coefficient and loss factor,pressure,slip speed,alternating load amplitude and frequency were established.So the Euler formula for friction transmission under dynamic lifting conditions was modified and verified by an example.It was found that the friction coefficient under dynamic load conditions decreased by 27.1%compared to the friction coefficient under static load conditions.The anti-skid safety factor under dynamic load conditions is 55.4%lower than that under static load conditions.The revised Euler formula of friction transmission under dynamic lifting conditions can provide a provide more accurate reference for anti-slip design and safety reserve factor of the friction hoist. |
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