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(hu)焊(han)設備按送(song)絲(si)(si)機構可分為(wei)等速送(song)絲(si)(si)和(he)均勻調節送(song)絲(si)(si)兩大類(lei)。
1. 等速送(song)(song)絲（又稱電弧自身調節送(song)(song)絲）
等速送(song)絲(si)(si)適用于(yu)細(xi)焊(han)(han)(han)絲(si)(si)或高電(dian)(dian)(dian)流(liu)(liu)密度的(de)(de)焊(han)(han)(han)接(jie)場(chang)合(he)，配合(he)管(guan)狀導電(dian)(dian)(dian)嘴（或稱(cheng)管(guan)狀偏(pian)心(xin)導電(dian)(dian)(dian)嘴、偏(pian)心(xin)導電(dian)(dian)(dian)嘴）。焊(han)(han)(han)絲(si)(si)的(de)(de)送(song)進按預選定的(de)(de)速度等速進入(ru)焊(han)(han)(han)接(jie)區，其工作原理(li)是采(cai)用機械(xie)方法（更(geng)換變(bian)速齒輪）來調(diao)速。依靠電(dian)(dian)(dian)弧(hu)(hu)的(de)(de)自身調(diao)節作用來維持(chi)弧(hu)(hu)長相對(dui)穩定。當焊(han)(han)(han)接(jie)電(dian)(dian)(dian)弧(hu)(hu)受(shou)到外(wai)界干擾(rao)而弧(hu)(hu)長增(zeng)(zeng)加(jia)時，下降(jiang)外(wai)特性電(dian)(dian)(dian)源(yuan)供給的(de)(de)焊(han)(han)(han)接(jie)電(dian)(dian)(dian)流(liu)(liu)減小，焊(han)(han)(han)絲(si)(si)熔化速度減緩，電(dian)(dian)(dian)弧(hu)(hu)便會由(you)長變(bian)短(duan)，趨(qu)向給定值(zhi)。反(fan)之，電(dian)(dian)(dian)弧(hu)(hu)變(bian)短(duan)時，焊(han)(han)(han)接(jie)電(dian)(dian)(dian)流(liu)(liu)增(zeng)(zeng)大，焊(han)(han)(han)絲(si)(si)熔化加(jia)快，弧(hu)(hu)長又由(you)短(duan)變(bian)長，趨(qu)向給定值(zhi)。按這(zhe)個工作原理(li)制造(zao)的(de)(de)等速送(song)絲(si)(si)埋弧(hu)(hu)焊(han)(han)(han)設備有MZ1-1000、MZ2-1500和MZ3-500等型號，其焊(han)(han)(han)接(jie)電(dian)(dian)(dian)源(yuan)可采(cai)用交流(liu)(liu)、直(zhi)流(liu)(liu)弧(hu)(hu)焊(han)(han)(han)電(dian)(dian)(dian)源(yuan)。
2. 均勻調節送絲（又稱強(qiang)迫調節送絲、變速(su)送絲）
均勻調節送絲適用于粗焊絲或(huo)低電流密度的焊接(jie)場合，配合滾輪式或(huo)夾瓦式導電嘴。
焊(han)絲(si)的送(song)進速(su)度按(an)電(dian)(dian)(dian)(dian)(dian)(dian)弧(hu)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)的高低自(zi)動均勻調(diao)(diao)(diao)節，電(dian)(dian)(dian)(dian)(dian)(dian)弧(hu)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)調(diao)(diao)(diao)節原理是利用(yong)電(dian)(dian)(dian)(dian)(dian)(dian)弧(hu)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)作為反(fan)饋信號，經過控制調(diao)(diao)(diao)節系統改(gai)變送(song)絲(si)速(su)度而保(bao)持(chi)弧(hu)長(chang)(chang)(chang)相對不變。當(dang)電(dian)(dian)(dian)(dian)(dian)(dian)弧(hu)受外界干擾變長(chang)(chang)(chang)，電(dian)(dian)(dian)(dian)(dian)(dian)弧(hu)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)升高時(shi)，控制調(diao)(diao)(diao)節系統接到電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)反(fan)饋信號后(hou)送(song)絲(si)速(su)度調(diao)(diao)(diao)快，弧(hu)長(chang)(chang)(chang)由長(chang)(chang)(chang)變短(duan)，趨向(xiang)穩定(ding)值(zhi)。當(dang)電(dian)(dian)(dian)(dian)(dian)(dian)弧(hu)長(chang)(chang)(chang)度變短(duan)，電(dian)(dian)(dian)(dian)(dian)(dian)弧(hu)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)下(xia)降時(shi)，將送(song)絲(si)速(su)度調(diao)(diao)(diao)慢，弧(hu)長(chang)(chang)(chang)增長(chang)(chang)(chang)趨向(xiang)給定(ding)值(zhi)。這種埋弧(hu)焊(han)機的控制系統稍復雜，具體(ti)型(xing)號有MZ-1000、MZ-1-1000和MU1-1000等(deng)。其焊(han)接電(dian)(dian)(dian)(dian)(dian)(dian)源可采(cai)用(yong)交(jiao)流、直(zhi)流弧(hu)焊(han)電(dian)(dian)(dian)(dian)(dian)(dian)源。
按工作需要，埋弧焊(han)機(ji)常見的構造形式有：焊(han)車式、懸掛式、機(ji)床式、門架式和懸臂式等(deng)，如(ru)圖4-12所示。
