Wear and Tear Resistance of Coupling Fits with Clearance Restored by Porous Epoxy Polyamide coatings
Authors:   State Agrarian University of Moldova, Tapu Veaceslav , Gorobet Vladimir ,   State Agrarian University of Moldova
Published: April 2021

The using of polymeric materials as coatings for the restoration of worn–out machine parts has found application in the industry of repairment. Their wider use is hampered because of poor adhesion strength, shrinkage, ageing, low wetting ability and other properties of polymeric materials. To improve the physical and mechanical properties of polyamide P12, it is advisable to add to the composition of various substances that help to reduce shrinkage, ageing, increase wear resistance. It is proposed to increase the oil absorption of the surface layers of polymer composite coatings by introducing 5...10% of sodium chloride (NaCl) into the composition. The obtained porous coatings were further subjected to wear tests under various lubrication conditions. The wear rate of the composite material under different lubrication conditions is different, so after 240 hours of testing, friction wear without lubrication was 18.8 ±2 μm, when using water – 16.8 ±2 μm, and when using LITOL 24 grease – 10±1 μm ... When using LITOL 24, a positive gradient of interfacial resistance of molecular bonds and surface layers is provided. Abrasion of the latter, as a rule, is not abrasive, but frictional and manifests itself in the separation of different, configurations of particles from the surface layer. Also, the lubricant is in the friction zone for longer because it is retained in the artificially formed pores of the surface layer of the coating. The presence of grease in the friction zone reduces the wear rate of the metal counter body. In those cases when there was no lubrication or there was water, the wear rate of the metal counter body was higher and practically had the same character. So, after 240 hours of testing, the following results were obtained: with friction and without lubrication In.l.=14 ±1 µm; friction in the presence of running water Iwater=13±1 µm; friction when using Litol 24, I=9±1 μm. Based on the results obtained, it can be stated that for a metal–porous polymer composite sliding friction pair, the types of lubricants affect the intensity of their wear. It should be noted that during the first hundred hours of testing, the evolution of the wear of the friction pair with different types of lubricant is practically the same and has a tendency to increase smoothly. This type of wear can be explained by the transfer of the composite material to the metal counter body. After removing this layer from the metal counter body, the process of its wear is different and depends on the type of lubricant. Metal counter bodies practically do not change the nature of wear when using water as a lubricant, as well as when friction without lubrication, but when using LITOL 24 lubricant, the wear rate is much less. The durability of friction pairs largely depends on the size of the gap. Thus, for the friction pairs studied with friction without lubrication, the linear intensity of the change in the gap value for 240 hours of testing will be 6.03 ∙ 10–8, for the condition of friction in running water and with Litol 24 lubricant, respectively 5.5 ∙ 10–8 and 3.6 • 10–8. In other words, we can say that in the studied area of 240 hours, the gap in friction pairs with friction without lubrication increased by 60 μm per 1 km of the distance travelled, when using water at 55 μm/km and 36 μm/km when using Litol 24 lubricant. It was found that the intensity of the increase in the gap in the friction pair when using a porous polymer coating based on a polyamide epoxy composition as a counter body in a metal–polymer friction pair, under lubrication conditions with Litol, is 1.64 times less than when using such coatings without pores. The obtained porous coatings showed higher wear resistance when using water as a lubricant (1.1 times less than that of the base one). The results obtained confirm that the creation of a porous surface layer in the coating of the polymer composition will contribute to an increase in the service life of the recovered friction pairs by replacing the usual metal–metal pair with a metal–polymer one.