Study Of Reinforced Polyamide6Based Multiphase Friction Material And Its Tribological Characteristics

Abstract:With the development of science and technology, the need for high-performance polymer grows day by day. PA6, which is widely used as a friction material, has the advantages of high specific strength, self-lubrication, corrosion resistance, easy processing and forming. However, the study about high performance PA6is quite scarce, which is how to ensure the mechanical properties of PA6as well as improve the friction performance. Meanwhile, the anti-friction and anti-wear mechanism especially synergy effect of fillers lacks deep study. With the purpose of developing high performance PA6:firstly, the PA6was reinforced with glass fiber (GF) or nanometer titanium dioxide (nano-TiO2) to improve the mechanical properties and wear resistance; then the reinforced PA6was modified with single or combined solid lubricant, in order to futher improve the friction property. The influences of solid lubricants type, content and ratio, as well as applied load and velocity on the tribological properties were systematically investigated; and the synergy effect between fillers as well as the wear mechanism of the composites was studied; meanwhile the static and dynamic mechanical properties and melt crystallization behavior were also studied.(1) The effects of single filler on the tribological and mechanical properties of PA6were systematically investigated. The results revealed that the mechanical properties of PA6were significantly increased and its wear resistance was appropriately improved at the same time by GF and nano-TiO2.While the friction coefficient was greatly reduced by PTFE, but the wear rate was increased by adding the commonly used several kinds of solid lubricant.(2) The glass fiber reinforced PA6(PA6/GF) was modified with solid lubricant. The study found that, under40N and200rpm, while single solid lubricant used as modifiers, PTFE and GF showed synergism effect. PTFE could formate a transfer film rapidly, and GF strengthened the matrix and could support the stress, the two together improved the tribological properties of PA6/GF. Combined solid lubricants PTFE/UHMWPE, Gr/PTFE, Gr/UHMWPE and PTFE/UHMWPE/Gr were also used to improve the tribological performance of PA6/GF, the results revealed that under40N and200rpm, all the combined solid lubricants except Gr/UHMWPE showed synergism effect and could enhance the tribological behavior of PA6/GF significantly in proper ratio. The wear mechanisms and tribological properties of single or combined solid lubricants filled PA6/GF were related to the components as well as applied load and velocity, when the worn surface was characterized by a large number of fiber breakage, the composite may have poor tribological performance; Except for graphite, single and combined solid lubricants all improved the performance of PA6/GF at high speed conditions. The temperature of the worn surface were controlled by the lowest melting point material, while the temperature of the worn surface achieved the lowest melting point, it will no longer rise, and the materials which have higher melting point protected the subsurface, then the friction and wear of the composite reduced. Solid lubricants all had less influence to the mechanical properties of PA6/GF. Except for PTFE/UHMWPE/Gr, all the solid lubricants could improve the storage modulus of PA6/GF. Simultaneously the solid lubricants all reduced the crystallinity of PA6in the composites.(3) The modifying effects of PTFE, UHMWPE, MoS2and their combinations on nano-TiO2reinforced PA6(PA6/TiO2) were studied. The results revealed that, under40N and200rpm, PTFE and UHMWPE showed synergism with nano-TiO2. PTFE and UHMWPE could formate a transfer film or lubricant film rapidly, while nano-TiO2might pin them on the worn surfaces and act as stress support point itself, which could prevent the surface asperities inserting the worn surface and avoid deformation of matrix, solid lubricants and nano-TiO2synergy to improve the tribological properties. Under different load and velocity, PTFE have the best modify effect, the main wear mechanisms were adhesive wear and abrasive wear. Combined solid lubricants UHMWPE/PTFE、UHMWPE/MoS2、 PTFE/MoS2and UHMWPE/PTFE/MoS2all could improve the tribological properties of PA6/TiO2significantly, different combined solid lubricant showed synergism effect.Under40N and200rpm, the best tribological properties among combined solid lubricant modified composites were achieved by PA6/TiO2+5%PTFE+5%UHMWPE+5%MoS2. The presence of UHMWPE and PTFE helps in some ways in promoting the formation of FeSO4, and Fe2(SO4)3, which increases the adhesion between the transfer film and the counterface, therefore the friction coefficient and wear rate reduced, the main wear mechanism were adhesive wear and abrasive wear. Under100N,200rpm and40N,200rpm, the best modify triblogical properties were achieved by UHMWPE/MoS2(7.5/7.5) and UHMWPE/PTFE (7.5/7.5) filled composites, respectively. Adhesive wear was the main wear mechanism. The impact strength of PA6/TiO2was improved obviously by single and combined solid lubricants except for MoS2and UHMWPE/MoS2. The storage modulus of PA6/TiO2were increased by MoS2, PTFE/MoS2and PE/MoS2, but decreased by other solid lubricants. Except for PTFE, all solid lubricants reduced the crystallinity of PA6in PA6/TiO2composites.(4) Based on the research results, the PA6based wear-resisting material was successfully developed which has excellent compressive properties and applied to belt conveyor roller.The roller has good use effect and remarkable economic and social benefits may be produced.