| Friction lining,serving as the key component of friction hoists,can absorb load from the wire rope and rope terminal and can drive the lifting system by providing the friction force.Therefore,the properties of friction lining directly influence on the working capacity,lifting efficiency,safety and reliability of hoists.Based on the white-box method and using VW9000 high-speed camera,the friction process of K25 friction lining in different loads and speeds was recorded and observed real-timely,micro interface contact morphologies were obtained,and the occurrence and developing processes of all sorts of micro phenomena in the frictional interface were observed.Moreover,the micro contact properties of friction lining were studied and the micro wear mechanism was analyzed.Eventually,works can offer basic reference and gist to study the friction mechanism of friction lining and wire rope.Friction linings K25,G30 and GM-3,widely used by the domestic friction hoists at current,were chosen as research subjects.Frictional experiments were operated under the condition of different dynamic loads.contact situation and micro wear molophogy of friction interface were obtained,and composition changes of lining wear debris were analyzed to reveal wear mechanism of linings.For revealing friction mechanism,the relationship between friction coefficient and viscoelasticity of friction linings,and the characteristic of sliding friction coefficient of friction linings and wine rope was analyzed under dynamic loads.The main results are listed as follow:(1)Sliding test of K25 friction lining in constant load shows that adhesive and hysteresis frictions contribute to the friction coefficient of friction lining with an exponential increase with time.Moreover,the friction coefficient increases with the increase of sliding speeds.Furthermore,the frictional mechanism of friction lining mainly includes adhesive friction under high-pressure and high-speed conditions;whereas it mainly includes hysteresis friction under low-pressure and low-speed conditions.Then the friction mechanism includes adhesive and hysteresis friction as the working conditions changes from high speed and pressure to low speed and pressure.(2)In the loading and unloading stages,three contact states that are adhesive,half adhesive and sliding appear obviously between K25 friction lining interface.Only adhesive and sliding states are existed in the friction interfaces of GM-3 and G30.Besides,the friction mechanism of K25 friction lining in the adhesive stage during loading and unloading process is adhesive friction.Meanwhile,the friction mechanism of lining is the maxed friction mechanism of adhesive and hysteresis friction,while the main friction mechanism of lining in the unloading sliding stage is adhesive friction.The instantaneous friction mechanism of GM-3 friction lining is same as that of G30 friction lining.In the adhesive stage,the friction mechanism is adhesive friction.And in the loading sliding stage the main friction mechanism is the maxed mechanism of adhesive and hysteresis friction.But in the unloading stage,the friction mechanism of friction lining is mainly adhesive friction.(3)Many convex and concave valleys with high directivity could be observed in the friction surface of K25,GM-3 and G30 friction linings.In addition,severe plastic deformation occurred on theconcave valley of K25 friction lining,and scratches occurred on the edge of concave valley,moreover,a large number of agglomerated debris were distributed in the peak position.severe plastic deformation also occurred on theconcave valley of GM-3 friction lining,and the surface produced a large number of peeling pitslike shell,but only a handful of abrasive particles were produced.Plastic deformation was worst,and the part of the surface was blackened,however,no obvious peeling pit and abrasive particle occurred on the wear surface.(4)The wear debris generated on the contact interface of K25 friction lining increased gradually with the increase of dynamic load,which resulted in the occurrence of the formation of compact third body andthe decrease in friction coefficient.Furthermore,micro wear debris morphology showed that wear mechanismwas mainly adhesive wear under dynamic load.With dynamic tensile force up to 2-13 KN,frictional heat,accumulated continuously on the contact surface,softened the surface of friction pad material,which resulted that the hydrogen bonds in the debris were oxidized and broken to form free hydroxyl groups.Consequently,the part of the surface was blackened,the number of wear debris increased significantly,which resulted in obvious thermal adhesive wear.(5)With the increase of the amplitude of dynamic tensile force,adhesive friction leads to the decrease of sliding friction coefficient of k25 friction lining.As the dynamic tensile force increases from 3-5KN to 3-8KN,hysteresis friction leads to the increase of sliding friction coefficient of GM-3 and G30 friction lining.As the dynamic tensile force increases from 3-8KN to 3-10 KN,adhesive friction leads to the decrease of sliding friction coefficient of GM-3 and G30 friction lining.In addition,with the increase of loading speed,hysteresis friction leads to the decrease of sliding friction coefficient of K25 friction lining,adhesive friction leads to increase of sliding friction coefficient of GM-3 friction lining,and adhesive and hysteresisfriction make G30 friction lining increase firstly and then decrease. |
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