電弧在焊劑層下燃燒進行焊接的方法稱為埋弧(hu)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)機構可分為等速送(song)絲(si)和均勻調節送(song)絲(si)兩大類。
1. 等速送(song)(song)絲（又稱電弧自身調節(jie)送(song)(song)絲）
等速送絲(si)適用(yong)于細(xi)焊(han)(han)絲(si)或(huo)高電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)密(mi)度(du)的(de)焊(han)(han)接場(chang)合，配合管狀導電(dian)(dian)(dian)(dian)(dian)嘴（或(huo)稱(cheng)管狀偏(pian)心(xin)導電(dian)(dian)(dian)(dian)(dian)嘴、偏(pian)心(xin)導電(dian)(dian)(dian)(dian)(dian)嘴）。焊(han)(han)絲(si)的(de)送進按(an)預選定(ding)的(de)速度(du)等速進入(ru)焊(han)(han)接區(qu)，其(qi)工作原理是采(cai)用(yong)機械方法（更換(huan)變(bian)(bian)速齒輪）來調速。依(yi)靠電(dian)(dian)(dian)(dian)(dian)弧(hu)的(de)自身調節作用(yong)來維持(chi)弧(hu)長(chang)相對(dui)穩定(ding)。當焊(han)(han)接電(dian)(dian)(dian)(dian)(dian)弧(hu)受到外界干擾而弧(hu)長(chang)增加時(shi)，下降外特性電(dian)(dian)(dian)(dian)(dian)源(yuan)供給的(de)焊(han)(han)接電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)減(jian)小，焊(han)(han)絲(si)熔(rong)化速度(du)減(jian)緩，電(dian)(dian)(dian)(dian)(dian)弧(hu)便會由長(chang)變(bian)(bian)短，趨向給定(ding)值。反之，電(dian)(dian)(dian)(dian)(dian)弧(hu)變(bian)(bian)短時(shi)，焊(han)(han)接電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)增大，焊(han)(han)絲(si)熔(rong)化加快，弧(hu)長(chang)又由短變(bian)(bian)長(chang)，趨向給定(ding)值。按(an)這個工作原理制(zhi)造的(de)等速送絲(si)埋(mai)弧(hu)焊(han)(han)設備有(you)MZ1-1000、MZ2-1500和MZ3-500等型號(hao)，其(qi)焊(han)(han)接電(dian)(dian)(dian)(dian)(dian)源(yuan)可采(cai)用(yong)交(jiao)流(liu)(liu)、直(zhi)流(liu)(liu)弧(hu)焊(han)(han)電(dian)(dian)(dian)(dian)(dian)源(yuan)。
2. 均(jun)勻調(diao)(diao)節(jie)送絲(si)(si)(si)（又(you)稱強迫調(diao)(diao)節(jie)送絲(si)(si)(si)、變(bian)速送絲(si)(si)(si)）
均勻(yun)調(diao)節送(song)絲(si)適用于粗焊(han)絲(si)或低(di)電流密(mi)度(du)的焊(han)接場(chang)合(he)，配(pei)合(he)滾輪式或夾(jia)瓦式導電嘴。
焊(han)絲(si)的(de)(de)送進速度按電(dian)弧(hu)(hu)(hu)(hu)(hu)(hu)電(dian)壓的(de)(de)高低自(zi)動(dong)均勻(yun)調(diao)節，電(dian)弧(hu)(hu)(hu)(hu)(hu)(hu)電(dian)壓調(diao)節原理是(shi)利用(yong)(yong)電(dian)弧(hu)(hu)(hu)(hu)(hu)(hu)電(dian)壓作為反饋(kui)信號，經過控制(zhi)調(diao)節系統(tong)改變(bian)送絲(si)速度而保持(chi)弧(hu)(hu)(hu)(hu)(hu)(hu)長(chang)(chang)相對不變(bian)。當電(dian)弧(hu)(hu)(hu)(hu)(hu)(hu)受外界干擾變(bian)長(chang)(chang)，電(dian)弧(hu)(hu)(hu)(hu)(hu)(hu)電(dian)壓升高時，控制(zhi)調(diao)節系統(tong)接(jie)到電(dian)壓反饋(kui)信號后送絲(si)速度調(diao)快(kuai)，弧(hu)(hu)(hu)(hu)(hu)(hu)長(chang)(chang)由長(chang)(chang)變(bian)短(duan)，趨向穩定值。當電(dian)弧(hu)(hu)(hu)(hu)(hu)(hu)長(chang)(chang)度變(bian)短(duan)，電(dian)弧(hu)(hu)(hu)(hu)(hu)(hu)電(dian)壓下降(jiang)時，將送絲(si)速度調(diao)慢，弧(hu)(hu)(hu)(hu)(hu)(hu)長(chang)(chang)增長(chang)(chang)趨向給定值。這種埋弧(hu)(hu)(hu)(hu)(hu)(hu)焊(han)機的(de)(de)控制(zhi)系統(tong)稍復雜(za)，具體型(xing)號有MZ-1000、MZ-1-1000和MU1-1000等。其焊(han)接(jie)電(dian)源(yuan)可采用(yong)(yong)交(jiao)流、直流弧(hu)(hu)(hu)(hu)(hu)(hu)焊(han)電(dian)源(yuan)。
按工作需要，埋弧焊機(ji)常(chang)見的構造形式有：焊車式、懸掛式、機(ji)床式、門架(jia)式和(he)懸臂(bei)式等，如圖4-12所示(shi)。
