Study On The Process Of Electroless Nickel Plating On High-Speed Railway Bridge Pad

High-speed railway bridge pad is the key structural part which supports the bridge body and transmits the force to the bridge pier.At present,the common surface treatment methods include spherical coating,clad stainless steel plate and chromium plating,but these technologies have some shortcomings.Electroless nickel plating technology has the advantages of uniform and beautiful plating,strong binding force,excellent hardness and corrosion resistance.It is of great significance to apply electroless nickel plating technology to the surface treatment of bridge pad to improve the safety and service life of bridges.However,there are still some problems in the application of this technology in the automatic production line of bridge pad:(1)electroless nickel plating has autocatalytic characteristics,which is easy to deposit on the pipeline and tank wall,causing decomposition of the electroless plating solution.(2)H2 evolution in the reaction process of electroless nickel plating,which can not escape in time,will cause pinholes in the plating and reduce corrosion resistance.(3)The aging of the plating solution in the later period of use will aggravate,which will reduce the plating speed and increase the brittleness of the plating.In view of the above problems,on the basis of the existing process,the bath composition,plating process,substrate surface roughness and plating method were determined by single factor experiment;the corrosion resistance of chlorate passivation was studied,and the corrosion resistance mechanism was discussed;the adjustment and maintenance methods of plating solution with different service cycles were designed to ensure the stability of the bath and plating performance,and the fast plating speed and stable plating solution were finally obtained Electroless nickel plating process with excellent performance.(1)The effects of bath composition and plating process on plating rate and bath stability were studied.With the increase of the concentration of nickel salt,reducing agent and accelerant,plating temperature and pH,the stability of plating solution will decrease and the plating rate will increase;the increase of complexing agent concentration will improve the stability of plating solution and reduce the plating speed;a small amount of stabilizer can significantly improve the stability of the plating solution,but if the concentration is too high,it will cause adverse effects such as bath poisoning and plating peeling.The optimum range of bath composition and plating process was determined.(2)The effects of substrate surface roughness and plating method on plating rate and porosity of 50 ?m plating were studied.It was found that the substrate surface roughness was kept below 1.5?m,the workpiece rotation speed was 8-10min,and the air stirring speed was 0.5?1 L/min in each liter of plating solution.The plating rate could be kept at 10 p,m/h and the porosity of plating could be reduced to less than 2 pieces/dm2.After passivation by chlorate,the corrosion resistance of Electroless Ni-P plating is greatly improved.XPS analysis showed that the plating was composed of NiO and Ni(OH)2,which showed that chlorate passivation could neutralize the residual of the plating surface,produce a dense NiO protective film,produce Ni(OH)2 to fill the pores,thus improving the corrosion resistance of the plating.(3)The change of bath and plating properties with service cycle was studied.Adding nickel salt and reducing agent in specific service cycle can improve plating speed,stabilizer C can improve bath stability,softener saccharin sodium can reduce plating brittleness and improve brightness.With the prolongation of the service life,the bath and plating properties can be kept stable by gradually reducing the bath pH and plating temperature.(4)The improved electroless nickel plating process can keep the plating speed at 10?m/h,the phosphorus content of plating is 7.7%?9.0%,and the hardness of plating is 500?530Hv in 6 MTO.