Arc Characteristic And The Development Of Flux Bands In Ultra-narrow Gap Welding

Ultra-Narrow Gap welding has high production efficiency,excellent performance in welded joint and important application value to material in need of low welding heat input.UNGW with flux strips/bands,using production processes of flux strips/bands and torch specially developed to meet basic requirements of this welding method, makes it available to achieve a stable welding process and a good formation of weld. Preliminary studies showed that flux position is a vital factor in UNGW with flux strips/bands.However,flux bands are not conducive to industrial applications due to the difficulty in slag remove after welding and possibility of weld defects of slag inclusion,UNGW with flux strips has a poor stability of the process,neither of them can get precise control to the degree of constrained arc.Besides,characteristics of the constrained arc needs a further study.Therefore,the main research contents of this paper are developing new suitable methods to UNGW with flux strips/bands and study characteristics of the constrained arc though analysing voltage and current waveforms.Based on the merits and demerits of the flux strips/bands,after a series of making up experiments,new methods that flux materials are put into arc zone are put forward. Two kinds of pre-set flux bands respectively using metal holder and using iron gauze are made.Both of them are verified through welding test.The results shows that pre-set flux bands using iron gauze could achieve a high positioning accuracy and precise control to the degree of constrained arc.Metal arc welding tests were also carried out on I groove deposited with the flux by pre-set flux bands using iron gauze,change welding voltage and the height of lower sidewalls uncovered by flux bands respectively.Results show that,welding voltage has affects on arc length and functional range of the arc during short circuit and impacts to the mode of metal transfer.When the voltage is very small,the arc length is low,the arc only heats the groove's bottom,in voltage waveforms the voltage is high as arc reignites,and then quickly decreases,at the same time short-circuit peak current is high;When the welding voltage-increases,the arc length is longer as the arc reignites, the heating range of the arc expends from the groove's bottom to the sidewalls. Therefore,the voltage slowly decreases afer arc reigniting,even doesn't decrease.the probability of instantaneous short current increases;While voltage further increased, the mode of metal transfer changes from short-circuit to non-short-circuit.The height of lower sidewalls uncovered by flux bands controls the degree of constrained arc and functional range of constrained arc in ultra-narrow gap.When the height of lower sidewalls uncovered by flux bands is very small,the arc only heats the groove's bottom,the arc length is longer while short circuit ends and the arc reignites, and gradually become shorter as molten drop grows up.Therefore,the voltage is higher as arc reignites,and then rapidly decreases.In this case,due to low frequency of short circuit,the current peak of short circuit is larger.When the height of lower sidewalls uncovered by flux bands increases,the heating range of the arc expends from the groove's bottom to the sidewalls,the arc length is shorter as the arc reignites. Therefore,the voltage is lower as arc reignites,and then slowly decreases,even doesn't decrease.And that,frequency of short circuit increases,the current peak of short circuit lowers,and the probability of instantaneous short current increases.