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(she)備按送(song)絲機構(gou)可分為(wei)等速送(song)絲和均勻調(diao)節送(song)絲兩大類。
1. 等速送絲（又(you)稱(cheng)電弧自(zi)身(shen)調節送絲）
等速(su)送絲適用于細焊(han)(han)絲或高電(dian)(dian)(dian)流密(mi)度的(de)焊(han)(han)接場合，配合管狀(zhuang)導(dao)電(dian)(dian)(dian)嘴（或稱(cheng)管狀(zhuang)偏心導(dao)電(dian)(dian)(dian)嘴、偏心導(dao)電(dian)(dian)(dian)嘴）。焊(han)(han)絲的(de)送進按(an)預選定的(de)速(su)度等速(su)進入焊(han)(han)接區，其(qi)工作原理是采用機(ji)械方法（更換(huan)變(bian)速(su)齒(chi)輪）來(lai)調(diao)速(su)。依靠電(dian)(dian)(dian)弧(hu)(hu)的(de)自身調(diao)節作用來(lai)維持弧(hu)(hu)長(chang)相對(dui)穩定。當焊(han)(han)接電(dian)(dian)(dian)弧(hu)(hu)受到(dao)外(wai)界(jie)干擾而弧(hu)(hu)長(chang)增加時(shi)，下降外(wai)特性(xing)電(dian)(dian)(dian)源(yuan)供給的(de)焊(han)(han)接電(dian)(dian)(dian)流減小，焊(han)(han)絲熔化速(su)度減緩，電(dian)(dian)(dian)弧(hu)(hu)便會由長(chang)變(bian)短，趨向給定值(zhi)。反之，電(dian)(dian)(dian)弧(hu)(hu)變(bian)短時(shi)，焊(han)(han)接電(dian)(dian)(dian)流增大，焊(han)(han)絲熔化加快，弧(hu)(hu)長(chang)又由短變(bian)長(chang)，趨向給定值(zhi)。按(an)這個工作原理制造(zao)的(de)等速(su)送絲埋弧(hu)(hu)焊(han)(han)設備有MZ1-1000、MZ2-1500和MZ3-500等型號，其(qi)焊(han)(han)接電(dian)(dian)(dian)源(yuan)可采用交流、直流弧(hu)(hu)焊(han)(han)電(dian)(dian)(dian)源(yuan)。
2. 均勻調節(jie)送絲（又稱強迫調節(jie)送絲、變速送絲）
均勻調(diao)節(jie)送(song)絲適用于粗焊(han)絲或低電(dian)流(liu)密度(du)的(de)焊(han)接(jie)場(chang)合，配合滾輪(lun)式(shi)或夾瓦式(shi)導電(dian)嘴。
焊(han)絲(si)(si)的(de)(de)送(song)進速度(du)按電(dian)(dian)弧(hu)(hu)電(dian)(dian)壓(ya)的(de)(de)高低自動均勻調(diao)節(jie)，電(dian)(dian)弧(hu)(hu)電(dian)(dian)壓(ya)調(diao)節(jie)原理是利(li)用(yong)(yong)電(dian)(dian)弧(hu)(hu)電(dian)(dian)壓(ya)作為反饋(kui)信(xin)號，經(jing)過控(kong)制調(diao)節(jie)系(xi)統(tong)改變(bian)送(song)絲(si)(si)速度(du)而保持(chi)弧(hu)(hu)長(chang)(chang)相(xiang)對不變(bian)。當(dang)電(dian)(dian)弧(hu)(hu)受外界干(gan)擾變(bian)長(chang)(chang)，電(dian)(dian)弧(hu)(hu)電(dian)(dian)壓(ya)升高時，控(kong)制調(diao)節(jie)系(xi)統(tong)接(jie)到(dao)電(dian)(dian)壓(ya)反饋(kui)信(xin)號后(hou)送(song)絲(si)(si)速度(du)調(diao)快，弧(hu)(hu)長(chang)(chang)由長(chang)(chang)變(bian)短(duan)(duan)，趨(qu)向穩定(ding)值(zhi)。當(dang)電(dian)(dian)弧(hu)(hu)長(chang)(chang)度(du)變(bian)短(duan)(duan)，電(dian)(dian)弧(hu)(hu)電(dian)(dian)壓(ya)下降時，將送(song)絲(si)(si)速度(du)調(diao)慢，弧(hu)(hu)長(chang)(chang)增長(chang)(chang)趨(qu)向給定(ding)值(zhi)。這(zhe)種埋弧(hu)(hu)焊(han)機的(de)(de)控(kong)制系(xi)統(tong)稍復(fu)雜，具(ju)體型(xing)號有MZ-1000、MZ-1-1000和MU1-1000等。其焊(han)接(jie)電(dian)(dian)源可采用(yong)(yong)交流、直(zhi)流弧(hu)(hu)焊(han)電(dian)(dian)源。
按(an)工作需(xu)要，埋弧焊機常見的(de)構造形(xing)式有(you)：焊車式、懸(xuan)掛式、機床式、門架式和懸(xuan)臂式等，如圖4-12所(suo)示。
