Preparation Of Flux Strips For Ultra-narrow Gap Welding And Its Research On The Butt Joint Of Rail And Frog

The method of Ultra-narrow Gap Welding with constrained arc by Flux Strips has the advantages of high welding efficiency,low residual stress and excellent joint performance.In the welding process,the Flux Strips is affected by the arc,the root melts to form slag and gas,protects the arc and molten pool,and forms the heat shrinkage effect on the arc,However,the Flux Strips which is not burned at the upper end controls the heating area of the arc,which has a wall binding effect on the root arc,effectively prevents the arc from climbing,and ensures the fusion of the side wall,especially the root of the side wall.But,the preparation of welding tape has not met the requirements of industrial production,which has hindered the application of the Flux Strips confined arc Ultra-narrow Gap Welding in industry for a long time.In order to solve this problem,this paper presents the preparation of the Flux Strips for Ultra-narrow Gap Welding.The main results are as follows(stage 1):(1)A new structure of Flux Strips,glass fiber mesh supporting flux sheet,was designed.The structure of the Flux Strips can make the flux sheet under the elastic force of the glass fiber net,and ensure that the flux sheet is closely connected with the side wall at the bottom of the groove,Improve the stability of Ultra-narrow Gap Welding process.(2)A set of stable and reliable device for automatic preparation of Flux Strips has been developed.The device is composed of Brushing device for penetrant of glass fiber mesh weft,a weft heating device,Glass fiber mesh rolling device,The binder Brushing device of glass fiber mesh Rough longitude line and Flux Strips belt conveying and collecting device.This device greatly improves the quality and efficiency of the production of Flux Strips,and makes full preparation for the industrialization of flux strip confined arc Ultra-narrow Gap Welding.By redesigning and fabricating the structure of Flux Strips welded with Ultra-narrow Gap,In this paper,the welding process of the groove rail and the wear-resistant alloy steel frog is tested by using the welding method of Flux Strips confined arc Ultra-narrow Gap,On the one hand,verify whether the Flux Strips can meet the welding requirements,On the other hand,the welding process specification for the super narrow gap between the rail and the frog is given,welding angle deformation,cold crack tendency,microstructure and mechanical properties of the welded joint are systematically studied,The main results achieved are(stages 2):(1)The welding test device of the Ultra-narrow Gap between the groove rail and the frog is designed,According to the characteristics of welding deformation,the reverse deformation base which can realize the groove size setting is designed,According to the cross-section characteristics of rail and frog,the constraint arc shaping block and clamp are developed to extend the weld bead and ensure the flatness of the weld bead,Combined with the Groove Width of the Ultra-narrow Gap and the height of the rail frog,the ultra-narrow gap welding gun is designed.(2)By using the method of Ultra-narrow Gap Welding with constrained arc by Flux Strips,and 4.5mm Groove Width completed by 60 passes,59R2 Grooved Rails is docked with Abrasion resistant steel Frogs.The relationship between the Root width of sidewall,Welding Parameters and Groove Width is analyzed,and the matching of welding voltage and welding current suited to the groove width is given.When the Groove Width is 4mm,the appropriate welding voltage is 23-23.5V,and the welding current is 215-228 A.The angular distortion is measured during welding,and the largest angular distortion occurs when the thickness of the fourth welding layer is about 13 mm.When the thickness of welding layer is about 128 mm,there is no more obvious angular distortion;Furthermore,The preset anti deformation angle about1.6 °? 1.7° before welding can ensure the glancing flatness of the work after welding.The tendency of welding crack in the ultra-narrow gap welding between rail and frog is studied,The welding test is carried out by three different methods of preheating before welding and slow cooling after welding,Finally,it is found that the crack can be avoided only when the preheating temperature is raised above 350 ?.(3)Research on the Microstructure of the welding in the ultra-narrow gap welding between rail and frog,It is found that the weld zone of dissimilar steel welded joint is composed of massive ferrite and a small amount of pearlite,and its hardness can reach 258 HV,The heat affected zone on one side of Q235 is mainly composed of pearlite,widmanstatten and acicular ferrite,and its hardness can reach235 HV,The heat affected zone on one side of nm400 is mainly composed of acicular ferrite,granular bainite and pearlite,and its hardness can reach 545 HV.(4)Tensile test of the welding in the ultra-narrow gap welding between rail and frog,The test results show that The same kind of steel sample breaks at the weld,All specimens of dissimilar steel fracture at Q235 base metal,and Both joints are guaranteed in strength.And impact test at-20 ?,The macro impact fracture of nm400 side and Q235 side of dissimilar steel welded joint is ductile fracture,The heat affected zone of the welded joint with ultra-narrow gap has good impact toughness,but the toughness of the weld zone is low.