Preparation And Properties Research Of PI/Graphite Wear-resisting Coating

The outer wall of piston would have friction with the cylinder wall inevitably, when the engine piston is in the process of continual rapid motion, the friction between metal and metal will cause serious wear and tear on the piston and the cylinder, consequently the life of the piston and its surrounding parts would be reduced greatly; the application of wear-resistant coating can greatly reduce the friction power, extent the engine parts’ service life, the sliding film coating formed on the metal surface of the piston wall can even avoid the friction between metal and metal in the extreme bearer. But in terms of the domestic market, the industrial production and application of wear-resistant coating most dependent on import, although in the laboratory our research of wear-resistant coating have achieved initial success, the process is so complicated and the cost is so high that it can not be industrialized and commercialized.In this paper, by changing process parameters and coating formulations, we test the adhesion and abrasive resistance of coating, to determine the optimum process parameters and optimal formulation under the optimum process parameters. Thermoplastic aromatic polyimide is the key film forming material, fillers are mainly graphite, carbon fiber and SiC powders. Conclusion is as followed:Using simple and flexible physical methods(ball milling) to prepare coating in this paper, the solid lubricating wear-resistant coating on the aluminum alloy matrix is formed by screen printing. Throughout the process, it is easy to control and short time is needed that wholly meets for the condition of large-scale industrial production.With graphite as the filler, the optimum process parameters was explored at first. The higher the coating solids content is, the higher value of viscosity the paint has. When the milling time is increasing, the higher of temperature generated in the system of the ball mill pot, then polymer would more likely to dissociate or other chemical changes, so the high solid content and long milling time are unfavourable to screen printing process and the control of coating comprehensive performance. The best process parameters finally determined is:coating mixing time is 15 min, PI: filler= 40:7. In the case, the filler is distributed evenly in the coating, viscosity is 32240 mPa· s; the bond strength between coating and metal substrate is still intact after ultrasonic bath; the frictional coefficient is under 0.14, the curve is smooth and the wear is least after the same time friction.Based on the optimal preparation process, when carbon fiber adding in the system of PI/graphite coating, through the experiment, PI:carbon fiber:graphite= 40:1.4:5.6, the coating obtained in the system had relative superior comprehensive performance. In particular, when the carbon fiber content was too high, the friction process was clearly divided into two stages from the friction coefficient(the friction coefficient curve appeared "double platform"); when SiC was added in the system, PI:SiC:graphite=40:2:5, the coating had relative superior comprehensive performance.Under the optimum preparation conditions, changing the paint filler for three-component(graphite, carbon fiber, silicon carbide), the experimental results show that:carbon fiber, SiC and graphite have great synergistic effect on bonding strength and friction wear performance; when PI:SiC:carbon fiber:graphite= 40:0.9: 1.22:4.88, the viscosity of coating is 28550 mPa·s, friction coefficient is 0.13, coefficient curve fluctuated less and abrasion loss is smaller.