Reasearch On Manufacturing Technique Of PTFE Matrix Composites

In the liquid rocket engine,the turbine pump is working under a high d·n value and a hugh load,and the bearing is work in the cryogenic liquid hydrogen or oxygen medium,which is very hard.Working under this condition,the traditional grease lubrication is no longer applicable in the rolling bearing,due to the ultra-low temperature environment. So the self-lubricating cage must be taken to provide lubricating film.The self-lubricating cages which are made of the PTFE composite materials are used very frequent,and aramid fiber has been used as additives. But the study of the preparation technology of PTFE composite materials is still not perfected, leading to the unstabitily of the PTFE composite material.There are some problems greatly influence the application of the cage, such as insufficient strength,material crack and spot.The the PTFE composite materials using now,is made by the cold-press sintering method,,and this thesis focuses on the researching of the preparation technology,which is in much more detailed.This thesis come up with a More detailed requirements about the choice of PTFE materials,and studied the mechanical properties of the PTFE composite materials made by different aramid fiber which are pretreated by different ways.The results show that the larger size of PTFE particles, the better and more stable the mechanical properties of the composite materials are.And pretreating the aramid fibers in some ways could enhance the PTFE composite materials,which is very helpful for the improvement of the mechanical properties of the PTFE composite materials.This thesis studied the pressing process,and analyzed the stress and the movement of the powder in the suppressing process.Described the curve of pressure and density of powder compacting process,and came to the conclusion that a wide range of sliding in the powders could leading to the cracks on the material.This thesis came up with the solution of changing the mold.Refined the parameters of the mixing process,and studied the relation between the mixing temperature,the stirring rate and the environment humidity.studied the relation between spots and the mixing temperature through a lot of samples.The way of the crystallization of PTFE has been analyzed,which leading to the conclusion that too much heat is the reason of the reunion of the PTFE composite materials.So,limit the mixing temperature below30℃,and control the air humidity to ensure that the PTFE composite materials stable.