Study On Technology And Tribological Behavior Of Cathodic Electrodeposition Coatings With PTFE

As a new superficial protection technology, cathodic electrodeposition (CED) finishing has receivedwidely attention due to its advantages such as easy operation, automation to paint, uniform thickness ofcoating film, high efficiency of coating utilization, less pollution to environment, and has been widelyapplied in auto, machine, building materials, hardware and electric appliance. With the expansion of CEDapplication, the requirements of CED coatings become rigorous. They should perform the functions as notonly the primer with high corrosion resistance but also the finishing with good wear resistance. Therefore,the development of new functional CED attracts unremitting efforts in coating industry.Improvement of tribological properties specifically is one of important research areas of developingCED coatings. In this thesis, aimed at improving performance of CED coatings, we prepared two kinds ofCED coatings, including acrylic-CED coating and epoxy-CED coating, by synthesizing two kinds of CEDresins and optimizing CED process conditions. For the purpose of further improvement of anti-frictionproperty of the film, we prepared PTFE modified epoxy CED coating. Based on a lot of friction and wearperformance tests of CED coating, the effects of PTFE content on friction and wear resistance of CEDcoating were analysed. A kind of CED coating with good combination property and correspondingapplication technology was developed in this thesis.The main contents and conclusions from this thesis are listed as follows:(1) Based on studying the tribological behavior of classic CED coatings, two kinds of resins,including cationic epoxy resin and cationic acrylic resin were synthesized, and their CED coatings wereprepared.(2) Electrodeposition (ED) pretreatment and ED technology factors which have influence on theproperties of film were investigated, the former including grease-removing, rust-removing, pre-dip,phosphating and water scrubbing, and the latter including voltage, time, temperature, nonvolatile andcuring process and so on. The suitable CED technology conditions are optimized finally.(3) The tribological behavior of acrylic-CED coating/steel GCr15) and epoxy-CED coating/steel (GCr15) rubbing pairs were measured under the condition of dry friction by the ring-block tester. Theresults show that anti-friction and anti-wear performance of epoxy-CED coating was better thanacrylic-CED coating.(4) PTFE emulsion was added to CED coatings in different concentration to prepare a new style ofCED coating. PTFE and epoxy resin particle co-depositing on the substrate was revealed by metallic phasemicroscope, surface topography and thermal gravity(TG) analysis. The results show that, with the increaseof the PTFE concentration, the complex elctrocoating became thinner, the adhesion ability has nosignificant change, and the water contact angle increased. The rigidity decreased and the surface roughnesswas risen sharply when the PTFE content exceed 20%, hence the PTFE content should be controlled, nottoo large or too small.(5) The effect of PTFE concentration on the sliding tribological behavior of PTFE modified CED filmunder the condition of dry friction was studied by the ring-block tester. The results show that both frictioncoefficient and linear wear were increased first and then decreased as the PTFE concentration increased,and composite CED film with 20% PTFE has the best anti-friction and anti-wear performance.(6) The PTFE-epoxy resin complex electrocoating's fretting wear behaviors were studied under thecondition of dry friction and boundary lubrication respectively by the short runs reciprocate testing. Theresults show that, the epoxy-CED coating's anti-friction and anti-wear performance was meliorated notablyby PTFE under the condition of dry friction, and the optimal PTFE concentration is 20%. But the oilplayed a main role in improving anti-friction performance under the condition of boundary lubrication, andthe PTFE's contribution was weaken.(7) The carrying capacity of the best PTFE-epoxy resin complex electrocoating and epoxy-CEDcoating were measured by the ring-block tester. The results show that the carrying capacity of the complexelectrocoating was 2.25 times better than that of the epoxy-CED coating.