電弧在焊劑層下燃燒進行焊接的方法稱為埋(mai)弧焊(han)（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。
不銹鋼管埋弧焊(han)設備按送絲(si)機構可分為等速送絲(si)和均勻調(diao)節送絲(si)兩大類(lei)。
1. 等速送絲（又稱電弧(hu)自(zi)身調節送絲）
等(deng)速(su)(su)送(song)絲適用(yong)于細焊(han)(han)(han)(han)絲或高(gao)電(dian)(dian)(dian)流(liu)密度(du)的焊(han)(han)(han)(han)接(jie)場合，配合管(guan)狀導(dao)電(dian)(dian)(dian)嘴（或稱管(guan)狀偏心導(dao)電(dian)(dian)(dian)嘴、偏心導(dao)電(dian)(dian)(dian)嘴）。焊(han)(han)(han)(han)絲的送(song)進按預選(xuan)定(ding)的速(su)(su)度(du)等(deng)速(su)(su)進入焊(han)(han)(han)(han)接(jie)區，其工(gong)作原(yuan)理(li)是采用(yong)機(ji)械方(fang)法(fa)（更(geng)換變速(su)(su)齒輪）來調速(su)(su)。依(yi)靠電(dian)(dian)(dian)弧(hu)(hu)(hu)的自身調節作用(yong)來維(wei)持弧(hu)(hu)(hu)長(chang)(chang)相對穩定(ding)。當焊(han)(han)(han)(han)接(jie)電(dian)(dian)(dian)弧(hu)(hu)(hu)受到外界(jie)干擾(rao)而弧(hu)(hu)(hu)長(chang)(chang)增加時，下降外特性電(dian)(dian)(dian)源(yuan)供(gong)給的焊(han)(han)(han)(han)接(jie)電(dian)(dian)(dian)流(liu)減(jian)小，焊(han)(han)(han)(han)絲熔化速(su)(su)度(du)減(jian)緩，電(dian)(dian)(dian)弧(hu)(hu)(hu)便會由(you)長(chang)(chang)變短，趨向(xiang)給定(ding)值。反(fan)之(zhi)，電(dian)(dian)(dian)弧(hu)(hu)(hu)變短時，焊(han)(han)(han)(han)接(jie)電(dian)(dian)(dian)流(liu)增大，焊(han)(han)(han)(han)絲熔化加快，弧(hu)(hu)(hu)長(chang)(chang)又由(you)短變長(chang)(chang)，趨向(xiang)給定(ding)值。按這個工(gong)作原(yuan)理(li)制造(zao)的等(deng)速(su)(su)送(song)絲埋弧(hu)(hu)(hu)焊(han)(han)(han)(han)設備有MZ1-1000、MZ2-1500和MZ3-500等(deng)型(xing)號，其焊(han)(han)(han)(han)接(jie)電(dian)(dian)(dian)源(yuan)可采用(yong)交流(liu)、直流(liu)弧(hu)(hu)(hu)焊(han)(han)(han)(han)電(dian)(dian)(dian)源(yuan)。
2. 均勻調(diao)(diao)節送絲(si)（又稱強迫調(diao)(diao)節送絲(si)、變速送絲(si)）
均勻調(diao)節送絲(si)適用于粗焊絲(si)或低電(dian)流密度的焊接場合(he)(he)，配(pei)合(he)(he)滾輪式或夾瓦式導(dao)電(dian)嘴(zui)。
焊絲(si)的送(song)(song)進速(su)(su)度(du)(du)按電(dian)(dian)(dian)(dian)弧(hu)電(dian)(dian)(dian)(dian)壓(ya)的高低自動均(jun)勻調(diao)節(jie)，電(dian)(dian)(dian)(dian)弧(hu)電(dian)(dian)(dian)(dian)壓(ya)調(diao)節(jie)原理是利用(yong)(yong)電(dian)(dian)(dian)(dian)弧(hu)電(dian)(dian)(dian)(dian)壓(ya)作為反(fan)饋信(xin)號(hao)，經(jing)過控制調(diao)節(jie)系(xi)統(tong)改變(bian)送(song)(song)絲(si)速(su)(su)度(du)(du)而保持弧(hu)長相對不變(bian)。當電(dian)(dian)(dian)(dian)弧(hu)受(shou)外界干(gan)擾變(bian)長，電(dian)(dian)(dian)(dian)弧(hu)電(dian)(dian)(dian)(dian)壓(ya)升高時，控制調(diao)節(jie)系(xi)統(tong)接到電(dian)(dian)(dian)(dian)壓(ya)反(fan)饋信(xin)號(hao)后送(song)(song)絲(si)速(su)(su)度(du)(du)調(diao)快，弧(hu)長由長變(bian)短，趨向穩(wen)定(ding)值。當電(dian)(dian)(dian)(dian)弧(hu)長度(du)(du)變(bian)短，電(dian)(dian)(dian)(dian)弧(hu)電(dian)(dian)(dian)(dian)壓(ya)下降時，將送(song)(song)絲(si)速(su)(su)度(du)(du)調(diao)慢，弧(hu)長增長趨向給定(ding)值。這(zhe)種埋弧(hu)焊機(ji)的控制系(xi)統(tong)稍復雜，具體型(xing)號(hao)有(you)MZ-1000、MZ-1-1000和(he)MU1-1000等(deng)。其焊接電(dian)(dian)(dian)(dian)源(yuan)可采用(yong)(yong)交(jiao)流(liu)、直(zhi)流(liu)弧(hu)焊電(dian)(dian)(dian)(dian)源(yuan)。
按工作需(xu)要，埋弧焊機(ji)常見(jian)的(de)構造形式(shi)有：焊車式(shi)、懸(xuan)掛式(shi)、機(ji)床式(shi)、門架(jia)式(shi)和(he)懸(xuan)臂式(shi)等，如圖4-12所示(shi)。
