電弧在焊劑層下燃燒進行焊接的方法稱為埋弧焊（submerged arc welding，SAW）。焊接電弧在焊絲與焊件之間燃燒，焊絲沿著待焊軌跡均勻不斷地送往電弧區，電弧熱將焊絲端部及電弧附近的母材金屬和焊劑熔化，電弧移開后熔池金屬凝固成焊縫，熔化的焊劑（未滲入焊縫金屬中的那部分）則凝固成渣殼覆蓋于焊縫表面。埋弧焊分機械操作（自動）和手工操作（半自動）兩種方法。
不銹鋼管埋弧焊設備按送(song)絲(si)機構(gou)可(ke)分為(wei)等速送(song)絲(si)和均勻調(diao)節(jie)送(song)絲(si)兩大類。
1. 等速(su)送絲(si)（又(you)稱電弧自身(shen)調節送絲(si)）
等(deng)(deng)速(su)送(song)(song)絲適用(yong)(yong)于(yu)細(xi)焊(han)(han)(han)絲或高(gao)電(dian)(dian)(dian)(dian)流(liu)密度(du)(du)的(de)焊(han)(han)(han)接場合，配合管狀(zhuang)導電(dian)(dian)(dian)(dian)嘴（或稱(cheng)管狀(zhuang)偏(pian)心導電(dian)(dian)(dian)(dian)嘴、偏(pian)心導電(dian)(dian)(dian)(dian)嘴）。焊(han)(han)(han)絲的(de)送(song)(song)進按預選定的(de)速(su)度(du)(du)等(deng)(deng)速(su)進入焊(han)(han)(han)接區(qu)，其(qi)工作原(yuan)理是采用(yong)(yong)機(ji)械方法（更換(huan)變(bian)速(su)齒輪(lun)）來調速(su)。依(yi)靠電(dian)(dian)(dian)(dian)弧(hu)(hu)(hu)的(de)自(zi)身調節(jie)作用(yong)(yong)來維持弧(hu)(hu)(hu)長相(xiang)對(dui)穩定。當焊(han)(han)(han)接電(dian)(dian)(dian)(dian)弧(hu)(hu)(hu)受到外界干擾而弧(hu)(hu)(hu)長增加時(shi)，下降外特性電(dian)(dian)(dian)(dian)源(yuan)供給(gei)的(de)焊(han)(han)(han)接電(dian)(dian)(dian)(dian)流(liu)減(jian)小，焊(han)(han)(han)絲熔(rong)化速(su)度(du)(du)減(jian)緩，電(dian)(dian)(dian)(dian)弧(hu)(hu)(hu)便會(hui)由長變(bian)短(duan)，趨(qu)向給(gei)定值(zhi)。反之，電(dian)(dian)(dian)(dian)弧(hu)(hu)(hu)變(bian)短(duan)時(shi)，焊(han)(han)(han)接電(dian)(dian)(dian)(dian)流(liu)增大，焊(han)(han)(han)絲熔(rong)化加快，弧(hu)(hu)(hu)長又由短(duan)變(bian)長，趨(qu)向給(gei)定值(zhi)。按這個工作原(yuan)理制造的(de)等(deng)(deng)速(su)送(song)(song)絲埋弧(hu)(hu)(hu)焊(han)(han)(han)設備有MZ1-1000、MZ2-1500和(he)MZ3-500等(deng)(deng)型號(hao)，其(qi)焊(han)(han)(han)接電(dian)(dian)(dian)(dian)源(yuan)可采用(yong)(yong)交流(liu)、直(zhi)流(liu)弧(hu)(hu)(hu)焊(han)(han)(han)電(dian)(dian)(dian)(dian)源(yuan)。
2. 均勻調節送(song)絲(si)（又稱(cheng)強迫調節送(song)絲(si)、變速送(song)絲(si)）
均勻調節送絲適(shi)用于粗焊絲或低(di)電流密度的(de)焊接場(chang)合，配合滾輪式或夾瓦式導電嘴。
焊(han)(han)絲的送進(jin)速(su)度(du)按(an)電(dian)(dian)(dian)(dian)弧(hu)(hu)(hu)電(dian)(dian)(dian)(dian)壓的高低自動(dong)均勻調節(jie)，電(dian)(dian)(dian)(dian)弧(hu)(hu)(hu)電(dian)(dian)(dian)(dian)壓調節(jie)原理(li)是(shi)利用(yong)電(dian)(dian)(dian)(dian)弧(hu)(hu)(hu)電(dian)(dian)(dian)(dian)壓作為反(fan)饋信號(hao)(hao)，經過控制(zhi)調節(jie)系統改(gai)變(bian)送絲速(su)度(du)而保(bao)持弧(hu)(hu)(hu)長(chang)相對不變(bian)。當(dang)電(dian)(dian)(dian)(dian)弧(hu)(hu)(hu)受(shou)外(wai)界干擾變(bian)長(chang)，電(dian)(dian)(dian)(dian)弧(hu)(hu)(hu)電(dian)(dian)(dian)(dian)壓升高時，控制(zhi)調節(jie)系統接到(dao)電(dian)(dian)(dian)(dian)壓反(fan)饋信號(hao)(hao)后(hou)送絲速(su)度(du)調快，弧(hu)(hu)(hu)長(chang)由長(chang)變(bian)短(duan)，趨向穩定(ding)(ding)值。當(dang)電(dian)(dian)(dian)(dian)弧(hu)(hu)(hu)長(chang)度(du)變(bian)短(duan)，電(dian)(dian)(dian)(dian)弧(hu)(hu)(hu)電(dian)(dian)(dian)(dian)壓下降時，將送絲速(su)度(du)調慢，弧(hu)(hu)(hu)長(chang)增長(chang)趨向給定(ding)(ding)值。這種埋弧(hu)(hu)(hu)焊(han)(han)機的控制(zhi)系統稍復雜，具體型(xing)號(hao)(hao)有MZ-1000、MZ-1-1000和(he)MU1-1000等。其焊(han)(han)接電(dian)(dian)(dian)(dian)源可采用(yong)交(jiao)流(liu)、直流(liu)弧(hu)(hu)(hu)焊(han)(han)電(dian)(dian)(dian)(dian)源。
按工作需要，埋弧(hu)焊機常(chang)見的構造形式有：焊車式、懸掛式、機床式、門(men)架式和懸臂(bei)式等(deng)，如圖(tu)4-12所示。
