| Porous polyimide(PI)has excellent properties of both porous structure and polyimide material.It can meet long-term lubrication through continuous release of lubricating oil stored in PI when facing severe operating conditions such as dry running and starved lubrication of friction pair part for a long time,and the service life and reliability of mechanical equipment can be improved greatly,so it is very widely used in aerospace and other fields.However,the current molding technology of porous PI is mainly cold pressing and then sintering.The complex structure and comprehensive performance of the porous PI material are mutually restricted,which makes it difficult to produce objects with a complicated shape while retaining good properties in service conditions,resulting in becoming one of the main challenges to limit the application of the porous PI material.Based on it,in this thesis,for meeting the forming requirements of complex porous PI self-lubricating devices,3D printing technology was combined with template method,so as to provide a new idea and opportunity for self-lubricating devices to design and control the friction and wear life.Poly(methyl methacrylate)(PMMA)microspheres were used as rheological modifier and pore-forming agent,and mixed with poly(amide acid)(PAA)precursor solution to form printable PAA ink.Porous PI selflubricating devices were successfully fabricated by direct writing(DIW)3D printing.The composition of PAA ink and the 3D printing preparation process of porous PI were deeply investigated.Self-lubricating property and lubricating mechanism of the porous PI oilcontaining material were discussed.The main conclusions are listed as follows:(1)The optimal ratio of PAA solution and pore-forming agent in PAA ink and the effects of 3D printing parameters on the dimensional stability of the printed parts were investigated.It is found that the addition of the pore-forming agent can greatly improve the rheological properties of PAA ink,and there is an optimal composition ratio of the pore-forming agent and PAA solution,which makes the PAA ink to fulfill the requirements of 3D printing.Based on this,the stable shape and accurate size of the printed parts are obtained by adjusting the printing process parameters.(2)Porous PI parts were prepared by DIW and postprocess.The effects of the pore-forming agent and the printing process parameters on the properties of porous PI were studied.The results show that the porous PI parts with small size shrinkage,good microstructure,excellent mechanical properties and thermal stability are prepared by optimizing the content of the poreforming agent and the specific printing process parameters.(3)Porous PI oil-containing materials and porous PI self-lubricating devices with complex structures were fabricated.The tribological properties and lubrication mechanism of porous PI oil-containing material were investigated.It is found that the friction coefficient of porous PI impregnated with PAO lubricating oil is about 0.06 and the wear life is more than 2 hours under the condition of load of 5N and frequency of 1Hz.However,the friction coefficient of porous PI without lubricant oil used as a reference in this study is unstable and shows a value over 0.4under the same condition,and the wear is serious.Therefore,porous PI self-lubricating devices with complex structures in this paper are expected to expand the application range of porous PI oil-containing materials,especially in the special operating conditions. |
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