Tribological Characteristics Test And Mechanism Analysis Of Brake Shoe For Hoist Disc Brake

Brake as a key safety equipment,is an important part of the mechanical system.In the working process of mechanical equipment,the reliable operation of the brake plays a decisive role to improve the equipment control system,the operating system and the reliability of the whole machine.With the production of transport equipment,large-scale,high-speed,high-load development trend,the need for reliable braking of large-scale equipment is very important.It means the more heat the brake friction produces,the higher ofthe brake shoe friction surface temperature,and it requires brake shoes with a high coefficient of friction coefficient of stability,and lower wear rate.Organic Friction Materials Due to the thermal decomposition of the matrix of polymer resin based materials,the friction coefficient is greatly reduced and the wear rate increases sharply,which limits the use of organic friction materials in a wider range of fields.Brake shoe is the working part of the brake system,and it has a direct relationship between thebrake safety and the friction and wear performance,therefore,it hasimportant theoretical and practical significance to carry out the tribological characteristics test and mechanism analysis of brake shoe for hoist disc brake.In this paper,thematerialsof brake shoe for hoist disc brake are used as the object of study,and the parameters of the actual braking conditions are taken as reference.We perform a comprehensive test of tribological properties withthe different brake pressure,sliding speed and friction surface temperature separately,so we getan abundant experimental data.And based on that we analysis of its friction and wear mechanism,finally we get some practical theoretical results.First of all,a comprehensive test of the brake shoe material is performed,and then the data processing and characterization are done for the brake shoe material in the comprehensive test of the friction performance.Based on the analysis of the composition and type of brake friction during braking,the variation law of transient friction coefficient with time under different working conditions is studied.The quantitativediscriminant of the transient friction coefficient mutation is obtained.The changes of the average friction coefficient during the braking pressure,the sliding speed and the friction surface temperature are analyzed.And the mode is divided into constant temperature variable speed and pressure,constant pressure variable speed and temperature,constant speedvariable temperature and pressure,etc.The variation law of the average friction coefficient,the stability coefficient and the degree of dispersion is analyzed,and the change mechanism is obtained.Secondly,the statistical theory is introduced into the analysis of the average friction coefficient,and the theoretical basis of the statistical analysis of the average friction coefficient is established,that is,the three characteristic criteria.The standard deviation of the average coefficient of friction is chosen to study the degree of discretization of the average friction coefficient.Based on the three criteria of the standard deviation of the average friction coefficient,the friction of the brake shoe material is carried out from the statistical point of view Analysis of the mechanism of performance.Considering the important role of PV mechanism diagram in the friction design of brake shoe materials,it put forward the viewpoint of parameter combination parameter investigation,characterization and analysis of theaverage friction coefficient of brake shoe material.And it systematically studied the combination of various parameters.The properties of the curves and the inherent tribological significance are analyzed.Based on the relationship between thecombinational parameters and the average friction coefficient,the advantages and disadvantages of the combinational parameters and the single parameter are obtained,and the different curves are obtained separately in the general trend,the concussion and the mutation.Based on the average friction coefficient curve with single parameter andcombinational parameteras variables,the relationship model of parameter combination variable and average friction coefficient is established.The failure probability space is proposed,the failure probability space is obtained,and the safety model of the condition parameter and friction system is established.The application of the model is illustrated.This is not only the necessary condition for the safe operation of the brake shoe system,but also the boundary condition of the material tribological design,which also can't be neglected for the tribological design and tribological control.At the same time,the research ideas and data processing methods of the safety relationship model of the friction system are applicable to the research of other friction materials.It is of universal significance and even the friction material can be applied.And the curves of the single parameter,double parameter,three parameter and multi-parameter friction coefficient obtained by the brake shoe material test are not only rich in the design theory of the friction material,but also as the measured data can be used to carry out the safety of the material friction check and reliability calculation and serve the industrial production.Thirdly,the wear and tear data obtained from the test specimen in the test are analyzed and processed.The characteristics of the system and the influencing factors of the wear of the brake shoe are briefly introduced.In view of the difference between the thermal decomposition temperature and the wear mechanism before and after the thermal decomposition temperature of the brake shoe material,the variation law and mechanism of the wear of the brake shoe and the change law of wear rate and time curve and its influence on the surface morphology of brake shoe under different friction surface temperature are studied.The influence mechanism of the dynamic pressure and the sliding speed on the wear coefficient and the wear coefficient of the brake shoe are analyzed when the friction surface temperature of the brake shoe is different,and at the same time,the influence mechanism of brake pressure and sliding speed on the wear degree of brake shoe material is analyzed,so a very rich regular rule is obtained.A method of calculating the life of brake shoe based on the wear area is put forward,which is basically consistent with the practice.Finally,the friction mechanism of the brake shoe in the thermal decomposition stage is discussed.Through the friction and wear test of the brake shoe material in the pyrolysis stage,the experimental results show that the average friction coefficient of the brake shoe material changes when the braking pressure and braking speed change.The microstructures of the brake shoe materials after the thermal decomposition stage are analyzed,and the microstructural changes in the thermal decomposition stage are analyzed,and the mechanism of this change is analyzed.The products and the mechanism of the oxide film,air cushion film,transfer film and so on were analyzed respectively in the thermal decomposition stage.The effects of different working conditions on the lubrication of the surface film were analyzed,and the thin film lubrication in the lubrication of the surface film was analyzed,and two design criteria of the friction material were put forward according to the film lubrication mechanism.Based on the assumption that the surface film lubrication conforms to the characteristics of Newtonian fluid,the approximate calculation method of the friction coefficient of the thermal decomposition surface of the brake shoe material is given.