電弧在焊劑層下燃燒進行焊接的方法稱為埋(mai)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)焊設備按送絲(si)機構(gou)可(ke)分為(wei)等速送絲(si)和均勻(yun)調節送絲(si)兩大類(lei)。
1. 等速(su)送(song)絲（又(you)稱(cheng)電弧(hu)自身調節送(song)絲）
等(deng)速(su)送絲適用(yong)于細焊(han)(han)(han)絲或(huo)高電流(liu)密度的焊(han)(han)(han)接(jie)(jie)場合，配(pei)合管狀導電嘴(zui)(zui)（或(huo)稱管狀偏心(xin)導電嘴(zui)(zui)、偏心(xin)導電嘴(zui)(zui)）。焊(han)(han)(han)絲的送進按預選定(ding)(ding)的速(su)度等(deng)速(su)進入焊(han)(han)(han)接(jie)(jie)區，其(qi)工作(zuo)原理是(shi)采(cai)用(yong)機械方法（更換變速(su)齒輪）來調速(su)。依靠電弧(hu)(hu)(hu)的自身(shen)調節作(zuo)用(yong)來維持(chi)弧(hu)(hu)(hu)長相(xiang)對穩定(ding)(ding)。當焊(han)(han)(han)接(jie)(jie)電弧(hu)(hu)(hu)受到外界干擾而弧(hu)(hu)(hu)長增加時，下降外特性電源供(gong)給的焊(han)(han)(han)接(jie)(jie)電流(liu)減(jian)小，焊(han)(han)(han)絲熔(rong)化速(su)度減(jian)緩，電弧(hu)(hu)(hu)便會(hui)由長變短，趨(qu)向給定(ding)(ding)值(zhi)(zhi)。反之，電弧(hu)(hu)(hu)變短時，焊(han)(han)(han)接(jie)(jie)電流(liu)增大(da)，焊(han)(han)(han)絲熔(rong)化加快，弧(hu)(hu)(hu)長又由短變長，趨(qu)向給定(ding)(ding)值(zhi)(zhi)。按這個工作(zuo)原理制造的等(deng)速(su)送絲埋(mai)弧(hu)(hu)(hu)焊(han)(han)(han)設備有MZ1-1000、MZ2-1500和MZ3-500等(deng)型號(hao)，其(qi)焊(han)(han)(han)接(jie)(jie)電源可采(cai)用(yong)交(jiao)流(liu)、直流(liu)弧(hu)(hu)(hu)焊(han)(han)(han)電源。
2. 均(jun)勻調(diao)節(jie)(jie)送(song)絲(si)（又稱強迫調(diao)節(jie)(jie)送(song)絲(si)、變速送(song)絲(si)）
均勻調節送絲適用于粗(cu)焊(han)絲或低電流密度的焊(han)接(jie)場合(he)，配合(he)滾(gun)輪式(shi)或夾瓦(wa)式(shi)導電嘴。
焊(han)(han)絲的(de)送進速度按電(dian)(dian)(dian)(dian)(dian)弧(hu)(hu)(hu)(hu)(hu)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)的(de)高(gao)低自動均勻調(diao)(diao)節(jie)，電(dian)(dian)(dian)(dian)(dian)弧(hu)(hu)(hu)(hu)(hu)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)調(diao)(diao)節(jie)原理是(shi)利用電(dian)(dian)(dian)(dian)(dian)弧(hu)(hu)(hu)(hu)(hu)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)作為反饋(kui)(kui)信號(hao)，經(jing)過控(kong)制調(diao)(diao)節(jie)系統改(gai)變(bian)送絲速度而(er)保持弧(hu)(hu)(hu)(hu)(hu)長相對不變(bian)。當電(dian)(dian)(dian)(dian)(dian)弧(hu)(hu)(hu)(hu)(hu)受(shou)外界(jie)干(gan)擾變(bian)長，電(dian)(dian)(dian)(dian)(dian)弧(hu)(hu)(hu)(hu)(hu)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)升高(gao)時，控(kong)制調(diao)(diao)節(jie)系統接到電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)反饋(kui)(kui)信號(hao)后(hou)送絲速度調(diao)(diao)快，弧(hu)(hu)(hu)(hu)(hu)長由長變(bian)短，趨(qu)向穩定值。當電(dian)(dian)(dian)(dian)(dian)弧(hu)(hu)(hu)(hu)(hu)長度變(bian)短，電(dian)(dian)(dian)(dian)(dian)弧(hu)(hu)(hu)(hu)(hu)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)下降時，將送絲速度調(diao)(diao)慢，弧(hu)(hu)(hu)(hu)(hu)長增長趨(qu)向給定值。這種埋弧(hu)(hu)(hu)(hu)(hu)焊(han)(han)機的(de)控(kong)制系統稍復雜，具體型號(hao)有MZ-1000、MZ-1-1000和MU1-1000等(deng)。其(qi)焊(han)(han)接電(dian)(dian)(dian)(dian)(dian)源可采用交流、直流弧(hu)(hu)(hu)(hu)(hu)焊(han)(han)電(dian)(dian)(dian)(dian)(dian)源。
按工作需(xu)要(yao)，埋弧焊機常見的構(gou)造形式有(you)：焊車式、懸掛式、機床式、門架(jia)式和(he)懸臂式等，如圖(tu)4-12所(suo)示。
