Research And Application Of Heavy-duty Anticorrosive Coatings In Railway Steel Bridges

At present, a large number of railway steel bridges are building, and steel corrosion and protection have always been a subject of intensive investigation.In order to improve service life of the railway steel bridge, the best approach of protection based on understanding the mechanism of metal corrosion to control the steel corrosion rate has been explored.In this paper, the properties of zinc rich epoxy primer,epoxy mica iron medium coating and tetrafluoro-type fluorocarbon topcoat were investigated,and the coatings used in railway steel bridges with excellent weatherability,good moisture and heat resistance and salt-fog resistance were prepared.Their performances like salt-fog resistance,thick coating performance,weatherability,moisture and heat resistance, dispersion and conventional mechanical property were explored.The optimun collocation and coating thickness were obtained through massive application tests. The structure and performances of coatings were characterized by IR, DSC,advanced microscope,SEM and TG.The results showed that:The epoxy zinc-rich paint has the optimal mechanical properties and salt-fog resistance when the PVC content of the zinc rich epoxy primer film is 42% and the zinc powder content of the dry paint film is 82%.The time of the salt-fog resistance is 1518 h.The dry film thickness in medium coat is up to 150 micron without sagging when resin and thixotropic agent were matched according to a certain proportion.Compared to ordinary polyamide curing agent, using cashew nut oil modified amine curing agent as the curing agent of medium coating at 5℃,the ring-opening rate of epoxy group could be improved from 28% to 84% and the drying property of coatings was greatly enhanced.The coatings showed good mechanical properties and preferable sanding ability when the content of PVC of epoxy medium coating was 39%.The accelerated aging resistance of fluorocarbon coatings is up to 4000h,and the gloss retention rate of the paint film is up to 90% after outdoor exposure for 30 months when using tetrafluoro-type fluorocarbon resin, trimer-isocyanate curing agent,coated rutile titanium dioxide,ultraviolet absorbent and light stabilizer.The paint film have the optimum when the mole reation of-NCO groups of curing agent and-OH groups of fluorocarbon resin is 1.3:1.Polyurea dispersant was employed to form a stable dispersion of fluorocarbon coatings,and no flooding and floating phenomenon at the surface of films were observed.The coatings showed good flooding and floating resistance after stored for 12 months under the room temperature.By compare with different coating systems,the paint film has the optimal properties when the coating system consisted of zinc rich epoxy primer, epoxy mica iron medium coating and tetrafluoro-type fluorocarbon topcoat,and the total thickness is a ranges of 300～350μm.The time of moisture and heast resistance is 1560 h, and the time of the salt-fog resistance ranges from 2016 to 2088h, the adhesion for pulling ranges from 7.6 to 9.8 Mpa.they are the optimal system and thickness for painting construction of the steel railway bridges.The study solved some critical issues such as the optimization of anticorrosion coating system and the dispersion stability of fluorocarbon topcoat.The formula and process of heavy-duty anticorrosive coatings with the optimal performance used in railway steel bridges were formed.