referring to fig1 and 2 , rails 1 and 2 , the members to be welded , are placed so that a suitable gap is set between the ends of these two rails . a backing 3 is pressed against the back of the rail base and co - operates with a copper plate 4 in the forming of a root bead . a pair of copper molds 5 and 6 are mounted on the upper surface of the rail base at both sides of the rails 1 and 2 , respectively , to enclose the welding groove defined by the rail edges and thereby prevent molten metal from flowing out of the groove . copper shoes 7 and 8 for welding the rail web and head are mounted on the top surfaces of the copper molds 5 and 6 and can be slidably moved , as welding proceeds , in the directions of the arrows 9 and 10 by a driving means ( not shown ) such as a motor , a hydraulic drive mechanism , or the like . a guide tube 12 guides a filler wire 11 into the groove and feeds power from a welding transformer to the filler wire 11 . the guide tube 12 is held by a horizontal travelling member 14 and a fixture 16 through a holder 17 and a connecting plate 18 . the horizontal travelling member 14 travels along a horizontal axis as shown by an arrow 13 , and the fixture 16 moves vertically as shown by an arrow 15 . a guide rail 19 guides the fixture 16 . welding proceeds is such a way that the tip of the filler wire 11 runs along a trace 20 as shown in fig2 . when and after the tip enters the rail web region , i . e ., passes a point &# 34 ; a &# 34 ; of the trace 20 , the copper shoes 7 and 8 are positioned as shown by 7a and 8a , respectively . referring to fig3 to 5 , a process according to the present invention will be described in more detail together with the welding sequence . fig3 schematically shows a root welding at the rail base . numeral 21 denotes a fused - type flux , 22 a solidified root bead , and 23 a slag covering the bead 22 . welding proceeds as the guide tube 12 moves from a position 12a to the right in the figure . the flux 21 is scattered within the copper molds 5 and 6 so that it covers the groove to protect the welding arc against air and to be partially melted to form a slag which covers a molten pool and the vicinity thereof . as welding proceeds , the backing 3 is also partially melted to cover the back side of the bead 22 with a thin layer of slag and form a smooth bead . in the submerged arc welding for welding of the root run , fused - type flux is suitably used to ensure a stable welding during the subsequent electroslag welding of the sequent runs even when a molten slag bath is shallow and also most suitably a backing 3 of laminated glass tapes with a backup support of copper plate 4 is used to prevent an excess reinforcement of the root bead at the base side even when the groove has an &# 34 ; i &# 34 ;- shape and a relatively large root gap of 12 to 20 mm . fig4 is a schematic view of the welding of the second and the subsequent runs at the rail base . welding is performed by electroslag welding . fig4 depicts a stage of the welding sequence near completion when welding of the rail base has proceeded to the fifth run . fig4 includes beads 24 of the second and the subsequent runs a slag bath 25 , and copper shoes 7b and 8b used for welding the rail web and head , respectively . welding of the second run is performed after the welding of the root run described above by moving the guide tube in the reverse direction without interrupting welding . in the welding of the second run , if the guide tube 12 travels at the same speed as used during the welding of the root run , a solidified slag 23 cannot be remelted , which causes an unstable welding arc and , in turn , welding per se . to avoid this problem , the guide tube 12 travels at a speed 30 to 70 % lower than that used for welding of the root run , with the result that the solidified slag 23 is remelted and the non - molten part of the flux 21 scattered during welding of the root run is also melted to form a slag , which both lead to the formation of a slag for electroslag welding . welding of the rail base is thus shifted from the submerged arc welding to the electroslag welding when welding of the second run starts , and welding proceeds to weld the subsequent runs by a repeated , reciprocal travelling of the guide tube 12 . the stroke of the horizontal travel of the guide tube 12 is preferably stepped down at each half of one reciprocation cycle to prevent a formation of an excess reinforcement of the weld and reduce the welding finishing work . the copper shoes 7 and 8 are brought close to the rail web step by step as the stroke of the guide tube 12 is stepped down and are positioned at the vicinity of the rail base , as shown by 7b and 8b in fig4 when welding of the rail base is almost completed , to stand by for a quick shift of the welding from the rail base to the rail web . welding of the rail web and head will be described with reference to fig5 . fig5 shows a guide tube position 12b and a molten slag bath 26 during welding of the rail web , as well as guide tube positions 12c and 12d and a molten slag bath 27 during welding of the rail head . welding of the rail head is performed by a repeated , reciprocal travelling of the guide tube within the region between the positions 12c and 12d , as shown in the figure . the copper shoes 7 and 8 are pressed against the rail and are in close contact therewith to prevent a flow out of the slag 26 or 27 and adjust the bead shape . after the electroslag welding of the rail base a described with reference to fig4 the horizontal travel of the guide tube 12 is stopped midway in the rail width and then the electroslag welding of the rail web is performed by moving the guide tube 12 only upward . when the welding of the rail web is completed and the guide tube 12 enters the rail head region , the reciprocal , horizontal travel of the guide tube 12 is restarted and the stroke of the reciprocal , horizontal travel is gradually substantially increased up to the entire width of the rail head , with the result that welding is performed by a reciprocal , horizontal travel of the guide tube between the positions 12c and 12d . as the electroslag welding proceeds from the rail base to the rail head , flux is fed to make up for the decrease of the slag bath depth . in the present invention , the following welding conditions for the filler wire size , the welding transformer , the flux type , etc ., are suitable from the viewpoints of welding workability and weld performance . a filler - wire is suitable to shift welding continuously from the submerged arc welding to the electroslag welding without changing the flux and removal of the slag , since such wires are easily melted even when the slag bath depth is small , such as during the welding of the rail base . the optimum filler wire diameter ranges from 1 . 2 to 2 . 0 mm . a wire diameter less than 1 . 2 mm results in a poor arc force and a small arc spread and , therefore , cannot provide a preferable root bead . a wire having a diameter exceeding 2 . 0 mm is not easily melted in a shallow slag bath . a dc welding transformer having constant potential characteristics is suitably used with a constant wire feed rate to successfully perform the submerged arc welding and the electroslag welding with a filler wire . fused - type flux is suitable for providing a good workability in both the submerged arc welding and the electroslag welding . the present inventors have found that the fused - type flux preferably contains , as main components , at least caf 2 and tio 2 . when a fused - type flux containing these components as main components is used , the amount of caf 2 and the amount of tio 2 in the flux is suitably within the ranges of from 15 to 45 % and from 15 to 35 %, respectively , the total amount of caf 2 and tio 2 being 50 % or more . an amount of caf 2 less than 15 % results in an unsuccessful welding shift from the submerged arc welding to the electroslag welding . an amount of caf 2 of more than 45 % causes a pollution of the work environment due to the emission of fluoride gases . the component tio 2 is used in combination with the component caf 2 to ensure that the electric conductivity of the slag is at a suitable value during the electroslag welding . an amount of tio 2 of less than 15 % cannot provide this effect . an amount of tio 2 of more than 35 % results in an elevation of the melting point of the slag and welding cannot be successfully shifted from the submerged arc welding to the electroslag welding . the total amount of caf 2 and tio 2 contained as main components in the flux is suitably 50 % or more , to ensure a successful welding shift from the submerged arc welding to the electroslag welding and a good welding workability . examples according to the present invention , and comparative examples , will be described below . a 132 lb - rail for railroad used was butt - welded in the constitution and process sequence according to the present invention . welding transformer : constant potential characteristics , dc transformer with 500 a rated current . a 132 lb - rail for railroad use was butt - welded in the constitution and process sequence according to the present invention . flux : fused - type flux , caf 2 31 %-- tio 2 28 %-- cao 17 %-- sio 2 22 %-- mgo 2 %, welding transformer : constant potential characteristics , dc transformer with 500 a rated current . a 132 lb - rail for railroad used was butt - welded in the constitution and process sequence according to the present invention . flux : fused - type flux , caf 2 40 %-- tio 2 20 % - cao 15 %-- sio 2 19 %-- al 2 o 3 6 %, welding transformer : constant potential characteristics , dc transformer with 500 a rated current . a 132 lb - rail for railroad use was butt - welded in the constitution and process sequence according to the present invention . flux : fused - type flux , caf 2 25 %-- tio 2 25 %-- cao 18 %-- sio 2 20 %-- mgo 5 %-- zro 2 7 %, welding tranformer : constant potential characteristics , dc transformer with 600 a rated current . in the examples 1 to 4 according to the present invention , welding took about 14 min except for the necessary preparation and after - treatment and a high work efficiency was achieved without weld defects . a 132 lb - rail for railroad use was butt - welded in the constitution below . flux : fused - type flux , caf 2 25 %-- tio 2 27 %-- cao 16 %-- sio 2 28 %-- mgo 45 , welding transformer : constant potential characteristics , dc transformer with 600 a rated current . welding after the second run of the rail base could not be performed , because the filler diameter exceeded the specified range of the present invention , with the result that a good electroslag welding was not maintained . a 132 lb - rail for railroad use was butt - welded in the constitution below . flux : bond type flux , caf 2 14 %-- tio 2 20 %-- cao 5 %-- sio 2 25 %-- al 2 o 3 36 %, welding transformer : constant potential characteristics , dc transformer with 500 a rated current . welding after the second run could not be performed , because the flux type used was unsuitable with the result that welding was not successfully shifted from the submerged arc welding to the electroslag welding . table 1______________________________________ welding speedwelding welding ( cm / min ) current voltage upward horizontalposition ( a ) ( v ) movement travel______________________________________baseroot 450 47 -- 30run2nd to 400 40 -- 205th runweb 380 36 6 . 0 -- head 380 36 1 . 5 120______________________________________ ( root gap = 17 mm ) table 2______________________________________ welding speedwelding welding ( cm / min ) current voltage upward horizontalposition ( a ) ( v ) movement travel______________________________________baseroot 450 48 -- 20run2nd run 400 38 -- 83rd to 380 36 -- 207th runweb 380 36 6 . 0 -- head 380 36 1 . 5 24______________________________________ ( root gap = 17 mm ) table 3______________________________________ welding speedwelding welding ( cm / min ) current voltage upward horizontalposition ( a ) ( v ) movement travel______________________________________baseroot 400 45 -- 17run2nd run 350 35 -- 53rd to 350 35 -- 156th runweb 350 35 4 . 0 -- head 350 35 1 . 0 30______________________________________ ( root gap = 17 mm ) table 4______________________________________ welding speedwelding welding ( cm / min ) current voltage upward horizontalposition ( a ) ( v ) movement travel______________________________________baseroot 520 50 -- 25run2nd run 450 42 -- 103rd to 420 40 -- 255th runweb 420 40 7 . 0 -- head 420 40 2 . 0 25______________________________________ ( root gap = 17 mm ) table 5______________________________________ welding speedwelding welding ( cm / min ) current voltage upward horizontalposition ( a ) ( v ) movement travel______________________________________baseroot 500 45 -- 30run2nd run 450 40 -- 123rd run further welding impossibleweb -- head -- ______________________________________ ( root gap = 17 mm ) table 6______________________________________ welding speedwelding welding ( cm / min ) current voltage upward horizontalposition ( a ) ( v ) movement travel______________________________________baseroot 450 47 -- 30run2nd run 400 40 -- 203rd run further welding impossibleweb -- head -- ______________________________________ ( root gap = 17 mm ) as described hereinabove , the present invention realized an automatic fusion welding of rails , particularly in field welding , at a high efficiency through a combination of submerged arc welding and electroslag welding for welding the rail base through the rail head without a complicated shift in the welding transformer operation and without changing the welding materials .