Study On Friction And Wear Properties Of Polyimide Reinforced Phenolic Resin Composites

The smooth operation of transportation vehicles and other mechanical brake transmission systems depends on friction materials with excellent comprehensive properties.With the continuous development of friction materials,people put forward higher requirements for thermal stability,reliability,durability and comfort of friction materials.Polyimide is a kind of high performance polymer containing imide rings in molecular structure.It is a kind of polymer material with high strength and high modulus,low density,impact resistance,corrosion resistance,self-lubrication and high and low temperature resistance.It has been applied in many fields such as electronic and electrical appliances,aerospace,separation film,flame retardant fabric,friction material and so on.The product with floccule microfiber structure obtained by fibrination process is called pulp.Pulp has the advantages of large surface area and more adhesion points when it is combined with matrix.It was introduced into friction materials in order to obtain composites with excellent friction and wear properties.Firstly,the effects of polyimide content and morphology on the tribological properties of the composites were studied.It is found that the addition of polyimide can reduce the friction coefficient,friction fluctuation coefficient and specific wear rate on the whole.With the same mass fraction,the friction coefficient of slurry polyimide reinforced composites is smaller than that of powder polyimide reinforced composites.When the pulp content is 60%,the friction coefficient of the composite reaches the minimum value of 0.247,which is 59.5%lower than that of phenolic resin.When the mass of polyimide was 10%,the fluctuation coefficient of friction and specific wear rate of the material were 0.051 and 8.76×10-6 mm3/N·m,respectively,which decreased by 85.8%and 63.5%compared with phenolic resin.When the mass fraction is greater than 10%,polyimide pulp is easy to be stripped and drawn because phenolic resin is difficult to bond to polyimide pulp completely.As a result,the fluctuation coefficient of friction and specific wear rate increase,but it is still smaller than phenolic resin.Similar to serous polyimide,the fluctuation coefficient of friction and specific wear rate also increase when the content of powdered polyimide is too high.Then the effects of testing conditions on the tribological properties of polyimide slurry reinforced composites were studied.The friction coefficient of polyimide slurry reinforced composites decreased with the increase of load.With the increase of rotational speed,the friction coefficient of the material decreases,and the increase of the friction coefficient of the composite material with pulp content greater than 20%is caused by the increase of the contact area and the acceleration of the friction film consumption.With the increase of temperature,the friction coefficient of the composite increases slightly at first and then decreases rapidly.Finally,nano SiO2 was prepared on the surface of polyimide pulp by sol-gel method,and composite materials were prepared by modified polyimide pulp.Compared with the modified composite,the friction coefficient and the friction coefficient fluctuation of the modified composite are increased by 18.5%and 5.4%,respectively.Meanwhile,the specific wear rate of the composite is significantly reduced by 46.6%.With the increase of load and rotation speed,the friction coefficient decreases,and the friction fluctuation coefficient and wear rate increase.With the increase of temperature,the friction coefficient and wear of the composites first increase and then decrease.