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(an)送(song)(song)絲機(ji)構可分為等速送(song)(song)絲和均勻調(diao)節送(song)(song)絲兩大(da)類。
1. 等(deng)速送絲（又稱電弧自身調節送絲）
等(deng)速送絲(si)(si)適用于細焊(han)(han)(han)(han)絲(si)(si)或高電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)密度(du)的焊(han)(han)(han)(han)接場合(he)，配(pei)合(he)管(guan)狀(zhuang)導(dao)電(dian)(dian)(dian)(dian)(dian)(dian)嘴（或稱管(guan)狀(zhuang)偏(pian)心導(dao)電(dian)(dian)(dian)(dian)(dian)(dian)嘴、偏(pian)心導(dao)電(dian)(dian)(dian)(dian)(dian)(dian)嘴）。焊(han)(han)(han)(han)絲(si)(si)的送進(jin)按預選定的速度(du)等(deng)速進(jin)入焊(han)(han)(han)(han)接區(qu)，其工(gong)作(zuo)(zuo)原(yuan)(yuan)理(li)是采(cai)用機械方法（更(geng)換(huan)變(bian)速齒輪）來(lai)(lai)調速。依(yi)靠電(dian)(dian)(dian)(dian)(dian)(dian)弧(hu)的自(zi)身調節作(zuo)(zuo)用來(lai)(lai)維持弧(hu)長(chang)(chang)相(xiang)對穩定。當(dang)焊(han)(han)(han)(han)接電(dian)(dian)(dian)(dian)(dian)(dian)弧(hu)受到外(wai)界干擾(rao)而弧(hu)長(chang)(chang)增加(jia)時，下降外(wai)特性電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)供給的焊(han)(han)(han)(han)接電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)減(jian)小，焊(han)(han)(han)(han)絲(si)(si)熔(rong)(rong)化速度(du)減(jian)緩，電(dian)(dian)(dian)(dian)(dian)(dian)弧(hu)便(bian)會(hui)由長(chang)(chang)變(bian)短(duan)，趨向給定值。反之，電(dian)(dian)(dian)(dian)(dian)(dian)弧(hu)變(bian)短(duan)時，焊(han)(han)(han)(han)接電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)增大，焊(han)(han)(han)(han)絲(si)(si)熔(rong)(rong)化加(jia)快，弧(hu)長(chang)(chang)又由短(duan)變(bian)長(chang)(chang)，趨向給定值。按這個工(gong)作(zuo)(zuo)原(yuan)(yuan)理(li)制(zhi)造的等(deng)速送絲(si)(si)埋弧(hu)焊(han)(han)(han)(han)設備有(you)MZ1-1000、MZ2-1500和MZ3-500等(deng)型(xing)號，其焊(han)(han)(han)(han)接電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)可(ke)采(cai)用交流(liu)、直流(liu)弧(hu)焊(han)(han)(han)(han)電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)。
2. 均勻調(diao)節送(song)絲(si)（又(you)稱強迫調(diao)節送(song)絲(si)、變速送(song)絲(si)）
均勻調節送絲適用于粗(cu)焊絲或(huo)低電流密度的焊接場合(he)(he)，配合(he)(he)滾輪式或(huo)夾瓦(wa)式導(dao)電嘴。
焊絲的(de)送(song)(song)進速度按電(dian)弧電(dian)壓(ya)(ya)的(de)高低(di)自動均勻調(diao)(diao)節(jie)(jie)，電(dian)弧電(dian)壓(ya)(ya)調(diao)(diao)節(jie)(jie)原理是利用電(dian)弧電(dian)壓(ya)(ya)作為反饋信(xin)號，經(jing)過控(kong)制調(diao)(diao)節(jie)(jie)系統改變(bian)(bian)送(song)(song)絲速度而保持(chi)弧長(chang)(chang)相對(dui)不(bu)變(bian)(bian)。當電(dian)弧受外(wai)界干擾(rao)變(bian)(bian)長(chang)(chang)，電(dian)弧電(dian)壓(ya)(ya)升高時，控(kong)制調(diao)(diao)節(jie)(jie)系統接(jie)到電(dian)壓(ya)(ya)反饋信(xin)號后送(song)(song)絲速度調(diao)(diao)快，弧長(chang)(chang)由長(chang)(chang)變(bian)(bian)短，趨向穩(wen)定(ding)值。當電(dian)弧長(chang)(chang)度變(bian)(bian)短，電(dian)弧電(dian)壓(ya)(ya)下降時，將送(song)(song)絲速度調(diao)(diao)慢，弧長(chang)(chang)增長(chang)(chang)趨向給定(ding)值。這種埋弧焊機的(de)控(kong)制系統稍(shao)復雜，具體型號有MZ-1000、MZ-1-1000和MU1-1000等。其焊接(jie)電(dian)源(yuan)可采用交(jiao)流(liu)、直(zhi)流(liu)弧焊電(dian)源(yuan)。
按工作需要，埋弧焊(han)機常見的(de)構造形式(shi)(shi)有：焊(han)車式(shi)(shi)、懸掛式(shi)(shi)、機床式(shi)(shi)、門架式(shi)(shi)和(he)懸臂(bei)式(shi)(shi)等，如圖4-12所示。
