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(xiu)鋼(gang)管埋弧(hu)焊(han)設備按(an)送絲機(ji)構可分為等速送絲和均(jun)勻調節送絲兩大類。
1. 等速送絲（又稱電弧(hu)自身調(diao)節送絲）
等(deng)(deng)(deng)速(su)送絲(si)適用(yong)于細(xi)焊(han)(han)(han)(han)(han)(han)絲(si)或(huo)高(gao)電(dian)(dian)(dian)(dian)流(liu)(liu)密度的焊(han)(han)(han)(han)(han)(han)接場合，配合管狀(zhuang)導(dao)(dao)電(dian)(dian)(dian)(dian)嘴(zui)（或(huo)稱管狀(zhuang)偏(pian)心(xin)導(dao)(dao)電(dian)(dian)(dian)(dian)嘴(zui)、偏(pian)心(xin)導(dao)(dao)電(dian)(dian)(dian)(dian)嘴(zui)）。焊(han)(han)(han)(han)(han)(han)絲(si)的送進(jin)按預(yu)選定(ding)的速(su)度等(deng)(deng)(deng)速(su)進(jin)入焊(han)(han)(han)(han)(han)(han)接區，其工(gong)作(zuo)原理(li)是采用(yong)機械(xie)方(fang)法(fa)（更換變(bian)速(su)齒輪(lun)）來調(diao)速(su)。依(yi)靠電(dian)(dian)(dian)(dian)弧的自身調(diao)節作(zuo)用(yong)來維持弧長相對穩定(ding)。當焊(han)(han)(han)(han)(han)(han)接電(dian)(dian)(dian)(dian)弧受到外(wai)界(jie)干擾而(er)弧長增加時(shi)，下降外(wai)特性電(dian)(dian)(dian)(dian)源(yuan)(yuan)供給(gei)的焊(han)(han)(han)(han)(han)(han)接電(dian)(dian)(dian)(dian)流(liu)(liu)減(jian)小(xiao)，焊(han)(han)(han)(han)(han)(han)絲(si)熔化(hua)速(su)度減(jian)緩，電(dian)(dian)(dian)(dian)弧便(bian)會(hui)由(you)長變(bian)短(duan)(duan)，趨向(xiang)給(gei)定(ding)值。反之，電(dian)(dian)(dian)(dian)弧變(bian)短(duan)(duan)時(shi)，焊(han)(han)(han)(han)(han)(han)接電(dian)(dian)(dian)(dian)流(liu)(liu)增大(da)，焊(han)(han)(han)(han)(han)(han)絲(si)熔化(hua)加快(kuai)，弧長又由(you)短(duan)(duan)變(bian)長，趨向(xiang)給(gei)定(ding)值。按這個工(gong)作(zuo)原理(li)制造的等(deng)(deng)(deng)速(su)送絲(si)埋弧焊(han)(han)(han)(han)(han)(han)設備(bei)有MZ1-1000、MZ2-1500和(he)MZ3-500等(deng)(deng)(deng)型號，其焊(han)(han)(han)(han)(han)(han)接電(dian)(dian)(dian)(dian)源(yuan)(yuan)可采用(yong)交流(liu)(liu)、直流(liu)(liu)弧焊(han)(han)(han)(han)(han)(han)電(dian)(dian)(dian)(dian)源(yuan)(yuan)。
2. 均(jun)勻調節送絲(si)（又(you)稱(cheng)強迫調節送絲(si)、變速送絲(si)）
均(jun)勻調節送絲適用于粗焊(han)絲或(huo)低電(dian)流密度的焊(han)接場合，配合滾輪(lun)式(shi)或(huo)夾瓦式(shi)導(dao)電(dian)嘴。
焊(han)絲的送(song)(song)進速度(du)按電(dian)(dian)(dian)弧(hu)電(dian)(dian)(dian)壓(ya)的高(gao)低自(zi)動均勻調(diao)節(jie)，電(dian)(dian)(dian)弧(hu)電(dian)(dian)(dian)壓(ya)調(diao)節(jie)原(yuan)理(li)是利用電(dian)(dian)(dian)弧(hu)電(dian)(dian)(dian)壓(ya)作為反(fan)饋信號，經(jing)過控制調(diao)節(jie)系(xi)統(tong)改變(bian)送(song)(song)絲速度(du)而保(bao)持弧(hu)長(chang)相對不變(bian)。當電(dian)(dian)(dian)弧(hu)受外界(jie)干(gan)擾變(bian)長(chang)，電(dian)(dian)(dian)弧(hu)電(dian)(dian)(dian)壓(ya)升高(gao)時，控制調(diao)節(jie)系(xi)統(tong)接(jie)到電(dian)(dian)(dian)壓(ya)反(fan)饋信號后送(song)(song)絲速度(du)調(diao)快，弧(hu)長(chang)由長(chang)變(bian)短，趨向穩定值(zhi)。當電(dian)(dian)(dian)弧(hu)長(chang)度(du)變(bian)短，電(dian)(dian)(dian)弧(hu)電(dian)(dian)(dian)壓(ya)下降時，將送(song)(song)絲速度(du)調(diao)慢，弧(hu)長(chang)增長(chang)趨向給(gei)定值(zhi)。這種埋弧(hu)焊(han)機的控制系(xi)統(tong)稍(shao)復(fu)雜，具體型號有MZ-1000、MZ-1-1000和MU1-1000等(deng)。其焊(han)接(jie)電(dian)(dian)(dian)源可采用交流、直流弧(hu)焊(han)電(dian)(dian)(dian)源。
按工作(zuo)需要，埋(mai)弧焊機常見(jian)的構造(zao)形式(shi)有：焊車式(shi)、懸掛式(shi)、機床式(shi)、門架式(shi)和懸臂式(shi)等，如圖4-12所(suo)示。
