Study On The Ingredient Design,preparation Process And Performance Of NAO Disc Brake Pads

Friction materials generally have the disadvantages of lower and unstable friction coefficient,prone to thermal recession,higher wear rate and noise level for braking.Developing a new kind of friction materials and preparation process with excellent comprehensive performance and considerable cost so as to ensure the safety performance of the brake system and optimize the safe and efficient production of friction materials,which ultimately improves economic and social benefits are of great significance.Due to have the advantages of stable friction coefficient,resist thermal recession and low wear rate and noise,resin-based composite materials are commonly used type of friction materials,currently.In view of this,this paper designs a low resin-based NAO-type friction material by dry production process.The single factor variable method was used to preliminarily adjust several ingredients in the raw materials（such as Phenolic resin,Zirconium silicate,Antimony sulfide and Electrolytic copper powder）and the Orthogonal test method was used to design the process parameters to explore the effect of different conditions on the performance of friction materials.In order to study and explore the amount of ingredients and the level of process parameters on the friction and wear behaviors of friction materials,the test methods are as follows:using the Rockwell hardness tester to test the surface hardness of the sample,an XD-MSM constant speed tester to test the friction and wear properties with GB 5763-2008 and scanning electron microscope（SEM）to observe the surface morphology of the wear-tested samples.This research provides a reference for the study of formulation of ingredients and optimizing process parameters to explore the friction and wear behavior of friction materials.The conclusions are as shown below:（1）The physical and mechanical properties are well in designing the percentage of Phenolic resin（4.0～6.5%）,such as the average hardness is maintained at 50～80HRS and the density is 2.20～2.33g/cm³.The normal friction coefficient is relatively stable.The fade friction coefficient as a whole increases slowly and then basically maintains a stable trend with the temperature rising.The recovery friction coefficient in the cooling stage can also return to the level before the friction test.In terms of wear rate,as the phenolic resin content increases,the wear rate tends to decrease firstly and then increase.SEM shows that the wear mechanism is the result of the combined action of adhesive wear and abrasive wear.The sample has the best performance with a total preferred Phenolic resin content of 4.5%.（2）In designing the percentage of Zr Si O₄（4.0～6.5%）,the average hardness is maintained at 55～65HRS and the density is 2.22～2.29g/cm³.Increasing the percentage of Zr Si O₄ can properly increase the density of the material.As the temperature rises,the fade friction coefficient gradually increases the thermal fade rate effect of the material with the increase in the percentage of Zr Si O₄.In terms of wear rate,increasing the percentage of Zr Si O₄ can reduce the wear rate of the material and ensure a certain wear resistance.SEM shows that the phenomena of potholes and furrows have decreased with the increase in the percentage of Zr Si O₄ and the friction interface layer has become more stable with the mechanisms such as adhesive wear and fatigue wear.The sample has the best performance with a total preferred Zr Si O₄ content of 6.0%.（3）In designing the percentage of Sb₂S₃（3.5～9.5%）,the average hardness is maintained at 56～63HRS and the density is 2.21～2.25g/cm³.Adding the percentage of Sb₂S₃ can slightly increase the hardness and density of the material.As the temperature rises,the fade friction coefficient tends to increase slowly and then decrease.Adding Sb₂S₃ could increase the high-temperature friction coefficient and decrease the fade rate of the material.In terms of wear rate,Sb₂S₃ can increase the high temperature wear of the material.SEM shows that the wear mechanism is the result of the combined action of adhesive wear and cutting wear.The sample has the best performance with a total preferred Sb₂S₃ content of 5.5%.（4）In designing the percentage of Electrolytic copper powder（2.0～11.0%）,the average hardness is maintained at 56～66HRS and the density is 2.11～2.24g/cm³.The physical and mechanical properties are stable,adding the percentage of Cu powder can slightly increase the density of the material.The more of the copper powder added,the more increase of the fade friction coefficient of the material,but there will also be different degrees of fade rate.In terms of wear rate,the samples has good wear resistance and the percentage of Cu powder has little effect on the wear rate of the material.SEM shows that different degrees of pits,holes and other defects affect the stability of the friction coefficient in the worn surface of the samples.The sample has the best performance with a total preferred Cu powder content of 8.0%.（5）To study the effect of different process parameters on the tribological properties of the material by use of the orthogonal test method,the pressing temperature has a greater influence on the average hardness,thermal fade rate resistance and recovery rate of the material.The performance is best at 150℃.The pressing pressure and holding time have a greater impact on the wear rate of the material.The larger the pressing pressure,the longer the holding time and the better the wear resistance.SEM shows that the choice of process parameters has a significant effect on the friction material interface layer.The wear mechanism is the result of the combined action of adhesive wear,abrasive wear,fatigue wear and cutting wear.In a word,design of raw material composition and selection of preparation process parameters can contribute to obtain friction materials with excellent tribological properties,and have crucial significance in the aspects of designing production process of brake pads.