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(bu)銹鋼(gang)管埋弧焊設備按送(song)絲機(ji)構可分為等(deng)速送(song)絲和均勻調節送(song)絲兩大(da)類。
1. 等速送(song)絲（又稱電弧自身調節送(song)絲）
等(deng)速(su)送(song)絲(si)適用(yong)于細焊(han)(han)(han)(han)(han)(han)絲(si)或高電(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)密(mi)度的(de)焊(han)(han)(han)(han)(han)(han)接場合，配合管(guan)狀導電(dian)(dian)(dian)(dian)嘴(zui)（或稱管(guan)狀偏心(xin)導電(dian)(dian)(dian)(dian)嘴(zui)、偏心(xin)導電(dian)(dian)(dian)(dian)嘴(zui)）。焊(han)(han)(han)(han)(han)(han)絲(si)的(de)送(song)進按預選定的(de)速(su)度等(deng)速(su)進入焊(han)(han)(han)(han)(han)(han)接區(qu)，其工作原(yuan)理是采(cai)用(yong)機械方法（更換(huan)變(bian)速(su)齒輪）來調速(su)。依靠電(dian)(dian)(dian)(dian)弧(hu)的(de)自身調節作用(yong)來維持(chi)弧(hu)長相對穩(wen)定。當焊(han)(han)(han)(han)(han)(han)接電(dian)(dian)(dian)(dian)弧(hu)受到外界干擾(rao)而(er)弧(hu)長增(zeng)加時，下降外特性電(dian)(dian)(dian)(dian)源(yuan)供給(gei)的(de)焊(han)(han)(han)(han)(han)(han)接電(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)減(jian)小，焊(han)(han)(han)(han)(han)(han)絲(si)熔化(hua)速(su)度減(jian)緩，電(dian)(dian)(dian)(dian)弧(hu)便會由長變(bian)短(duan)，趨向給(gei)定值。反之，電(dian)(dian)(dian)(dian)弧(hu)變(bian)短(duan)時，焊(han)(han)(han)(han)(han)(han)接電(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)增(zeng)大，焊(han)(han)(han)(han)(han)(han)絲(si)熔化(hua)加快(kuai)，弧(hu)長又由短(duan)變(bian)長，趨向給(gei)定值。按這個工作原(yuan)理制造的(de)等(deng)速(su)送(song)絲(si)埋弧(hu)焊(han)(han)(han)(han)(han)(han)設備(bei)有MZ1-1000、MZ2-1500和(he)MZ3-500等(deng)型號，其焊(han)(han)(han)(han)(han)(han)接電(dian)(dian)(dian)(dian)源(yuan)可采(cai)用(yong)交(jiao)流(liu)(liu)(liu)(liu)、直流(liu)(liu)(liu)(liu)弧(hu)焊(han)(han)(han)(han)(han)(han)電(dian)(dian)(dian)(dian)源(yuan)。
2. 均(jun)勻(yun)調(diao)節送絲（又稱(cheng)強(qiang)迫調(diao)節送絲、變速送絲）
均勻(yun)調節送絲(si)適用(yong)于粗焊絲(si)或低電流密度(du)的焊接(jie)場合(he)，配合(he)滾輪式(shi)或夾瓦式(shi)導電嘴。
焊絲(si)(si)的送(song)進速(su)度(du)按電(dian)(dian)(dian)弧(hu)(hu)電(dian)(dian)(dian)壓的高低自動均(jun)勻調(diao)(diao)節(jie)，電(dian)(dian)(dian)弧(hu)(hu)電(dian)(dian)(dian)壓調(diao)(diao)節(jie)原理是利(li)用(yong)電(dian)(dian)(dian)弧(hu)(hu)電(dian)(dian)(dian)壓作(zuo)為反饋(kui)信號，經過控(kong)制(zhi)(zhi)調(diao)(diao)節(jie)系統(tong)改變送(song)絲(si)(si)速(su)度(du)而(er)保持(chi)弧(hu)(hu)長(chang)相對不變。當電(dian)(dian)(dian)弧(hu)(hu)受外界(jie)干擾變長(chang)，電(dian)(dian)(dian)弧(hu)(hu)電(dian)(dian)(dian)壓升(sheng)高時，控(kong)制(zhi)(zhi)調(diao)(diao)節(jie)系統(tong)接(jie)到(dao)電(dian)(dian)(dian)壓反饋(kui)信號后(hou)送(song)絲(si)(si)速(su)度(du)調(diao)(diao)快，弧(hu)(hu)長(chang)由長(chang)變短，趨向(xiang)穩定值。當電(dian)(dian)(dian)弧(hu)(hu)長(chang)度(du)變短，電(dian)(dian)(dian)弧(hu)(hu)電(dian)(dian)(dian)壓下降(jiang)時，將(jiang)送(song)絲(si)(si)速(su)度(du)調(diao)(diao)慢，弧(hu)(hu)長(chang)增長(chang)趨向(xiang)給定值。這種(zhong)埋弧(hu)(hu)焊機的控(kong)制(zhi)(zhi)系統(tong)稍復雜(za)，具(ju)體型號有MZ-1000、MZ-1-1000和MU1-1000等(deng)。其(qi)焊接(jie)電(dian)(dian)(dian)源可采用(yong)交流、直(zhi)流弧(hu)(hu)焊電(dian)(dian)(dian)源。
按工作需要(yao)，埋弧焊機常(chang)見的構(gou)造形式(shi)(shi)有：焊車式(shi)(shi)、懸(xuan)掛(gua)式(shi)(shi)、機床式(shi)(shi)、門架式(shi)(shi)和懸(xuan)臂式(shi)(shi)等，如圖4-12所示。
