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(guan)埋(mai)弧焊設備按送(song)絲(si)機構可分為等(deng)速送(song)絲(si)和均(jun)勻(yun)調節送(song)絲(si)兩大類。
1. 等(deng)速(su)送絲(si)（又稱電弧(hu)自身調節(jie)送絲(si)）
等(deng)(deng)速送絲(si)適用(yong)于細焊(han)絲(si)或高電(dian)(dian)(dian)流(liu)密度的(de)(de)焊(han)接(jie)場合，配合管狀導電(dian)(dian)(dian)嘴(zui)（或稱管狀偏(pian)(pian)心(xin)導電(dian)(dian)(dian)嘴(zui)、偏(pian)(pian)心(xin)導電(dian)(dian)(dian)嘴(zui)）。焊(han)絲(si)的(de)(de)送進按(an)預選(xuan)定(ding)的(de)(de)速度等(deng)(deng)速進入焊(han)接(jie)區(qu)，其工作(zuo)(zuo)原理(li)是采(cai)用(yong)機械方法（更換變(bian)(bian)速齒輪）來(lai)調速。依靠(kao)電(dian)(dian)(dian)弧的(de)(de)自身(shen)調節(jie)作(zuo)(zuo)用(yong)來(lai)維(wei)持(chi)弧長(chang)相對穩(wen)定(ding)。當焊(han)接(jie)電(dian)(dian)(dian)弧受到外界干擾而(er)弧長(chang)增(zeng)加時，下降外特性電(dian)(dian)(dian)源(yuan)供給(gei)的(de)(de)焊(han)接(jie)電(dian)(dian)(dian)流(liu)減小，焊(han)絲(si)熔化(hua)速度減緩，電(dian)(dian)(dian)弧便會由(you)(you)長(chang)變(bian)(bian)短(duan)(duan)，趨向(xiang)給(gei)定(ding)值。反之，電(dian)(dian)(dian)弧變(bian)(bian)短(duan)(duan)時，焊(han)接(jie)電(dian)(dian)(dian)流(liu)增(zeng)大，焊(han)絲(si)熔化(hua)加快，弧長(chang)又由(you)(you)短(duan)(duan)變(bian)(bian)長(chang)，趨向(xiang)給(gei)定(ding)值。按(an)這個工作(zuo)(zuo)原理(li)制造的(de)(de)等(deng)(deng)速送絲(si)埋弧焊(han)設備有MZ1-1000、MZ2-1500和(he)MZ3-500等(deng)(deng)型號，其焊(han)接(jie)電(dian)(dian)(dian)源(yuan)可采(cai)用(yong)交流(liu)、直(zhi)流(liu)弧焊(han)電(dian)(dian)(dian)源(yuan)。
2. 均勻(yun)調節(jie)送(song)絲（又稱強(qiang)迫調節(jie)送(song)絲、變速送(song)絲）
均勻調節送絲適用(yong)于(yu)粗焊絲或低電(dian)流密度的焊接場合，配(pei)合滾輪式或夾瓦式導電(dian)嘴。
焊(han)絲(si)的(de)送進(jin)速度按電(dian)(dian)(dian)弧(hu)(hu)電(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)的(de)高低(di)自(zi)動均(jun)勻調(diao)(diao)(diao)節(jie)(jie)，電(dian)(dian)(dian)弧(hu)(hu)電(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)調(diao)(diao)(diao)節(jie)(jie)原理是利用電(dian)(dian)(dian)弧(hu)(hu)電(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)作為反(fan)饋(kui)信號(hao)，經過控(kong)制(zhi)調(diao)(diao)(diao)節(jie)(jie)系(xi)(xi)統(tong)改變送絲(si)速度而保(bao)持弧(hu)(hu)長(chang)(chang)相(xiang)對不變。當(dang)電(dian)(dian)(dian)弧(hu)(hu)受外界干擾變長(chang)(chang)，電(dian)(dian)(dian)弧(hu)(hu)電(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)升高時，控(kong)制(zhi)調(diao)(diao)(diao)節(jie)(jie)系(xi)(xi)統(tong)接到電(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)反(fan)饋(kui)信號(hao)后送絲(si)速度調(diao)(diao)(diao)快，弧(hu)(hu)長(chang)(chang)由長(chang)(chang)變短，趨向(xiang)穩(wen)定(ding)值(zhi)。當(dang)電(dian)(dian)(dian)弧(hu)(hu)長(chang)(chang)度變短，電(dian)(dian)(dian)弧(hu)(hu)電(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)下降時，將(jiang)送絲(si)速度調(diao)(diao)(diao)慢，弧(hu)(hu)長(chang)(chang)增長(chang)(chang)趨向(xiang)給定(ding)值(zhi)。這種埋(mai)弧(hu)(hu)焊(han)機(ji)的(de)控(kong)制(zhi)系(xi)(xi)統(tong)稍復雜，具體(ti)型(xing)號(hao)有MZ-1000、MZ-1-1000和MU1-1000等。其焊(han)接電(dian)(dian)(dian)源可采用交流、直(zhi)流弧(hu)(hu)焊(han)電(dian)(dian)(dian)源。
按工作需(xu)要，埋弧焊機(ji)(ji)常(chang)見(jian)的(de)構造形式(shi)有：焊車式(shi)、懸掛式(shi)、機(ji)(ji)床式(shi)、門架式(shi)和(he)懸臂(bei)式(shi)等，如圖4-12所示。
