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。

 不銹鋼管埋弧(hu)焊(han)設備(bei)按(an)送(song)絲機(ji)構可(ke)分為等速送(song)絲和均勻調(diao)節送(song)絲兩大類。

1. 等速送絲（又稱電弧自身調節送絲）

   等(deng)(deng)速送絲(si)適用(yong)(yong)于細焊(han)(han)(han)絲(si)或高電(dian)(dian)流(liu)密度(du)的(de)(de)焊(han)(han)(han)接(jie)(jie)(jie)場合，配合管狀導電(dian)(dian)嘴(zui)(zui)（或稱管狀偏心導電(dian)(dian)嘴(zui)(zui)、偏心導電(dian)(dian)嘴(zui)(zui)）。焊(han)(han)(han)絲(si)的(de)(de)送進按(an)預選定(ding)的(de)(de)速度(du)等(deng)(deng)速進入(ru)焊(han)(han)(han)接(jie)(jie)(jie)區，其工(gong)作原(yuan)理是采(cai)用(yong)(yong)機(ji)械(xie)方法（更換(huan)變速齒輪）來調速。依靠電(dian)(dian)弧的(de)(de)自身(shen)調節作用(yong)(yong)來維持(chi)弧長(chang)相對穩定(ding)。當焊(han)(han)(han)接(jie)(jie)(jie)電(dian)(dian)弧受到外界(jie)干擾而(er)弧長(chang)增加(jia)時，下降外特性電(dian)(dian)源(yuan)供給的(de)(de)焊(han)(han)(han)接(jie)(jie)(jie)電(dian)(dian)流(liu)減小，焊(han)(han)(han)絲(si)熔化速度(du)減緩，電(dian)(dian)弧便會由(you)(you)長(chang)變短，趨向給定(ding)值。反之(zhi)，電(dian)(dian)弧變短時，焊(han)(han)(han)接(jie)(jie)(jie)電(dian)(dian)流(liu)增大，焊(han)(han)(han)絲(si)熔化加(jia)快，弧長(chang)又由(you)(you)短變長(chang)，趨向給定(ding)值。按(an)這個工(gong)作原(yuan)理制造的(de)(de)等(deng)(deng)速送絲(si)埋弧焊(han)(han)(han)設備有MZ1-1000、MZ2-1500和MZ3-500等(deng)(deng)型號，其焊(han)(han)(han)接(jie)(jie)(jie)電(dian)(dian)源(yuan)可(ke)采(cai)用(yong)(yong)交(jiao)流(liu)、直流(liu)弧焊(han)(han)(han)電(dian)(dian)源(yuan)。

2. 均勻調節(jie)送(song)(song)絲（又稱強(qiang)迫(po)調節(jie)送(song)(song)絲、變速(su)送(song)(song)絲）

   均勻調節(jie)送絲(si)適用(yong)于粗(cu)焊絲(si)或(huo)低電(dian)流(liu)密度(du)的焊接場(chang)合，配合滾輪式(shi)或(huo)夾瓦式(shi)導電(dian)嘴。

   焊絲(si)的(de)送進速度(du)按電(dian)(dian)弧(hu)(hu)電(dian)(dian)壓(ya)(ya)(ya)的(de)高低自動(dong)均勻調(diao)(diao)節，電(dian)(dian)弧(hu)(hu)電(dian)(dian)壓(ya)(ya)(ya)調(diao)(diao)節原(yuan)理(li)是利用電(dian)(dian)弧(hu)(hu)電(dian)(dian)壓(ya)(ya)(ya)作為反饋(kui)信號，經(jing)過控(kong)制(zhi)調(diao)(diao)節系(xi)(xi)統(tong)改(gai)變送絲(si)速度(du)而保持弧(hu)(hu)長(chang)(chang)(chang)(chang)相對(dui)不變。當電(dian)(dian)弧(hu)(hu)受外界干擾變長(chang)(chang)(chang)(chang)，電(dian)(dian)弧(hu)(hu)電(dian)(dian)壓(ya)(ya)(ya)升(sheng)高時(shi)，控(kong)制(zhi)調(diao)(diao)節系(xi)(xi)統(tong)接(jie)到電(dian)(dian)壓(ya)(ya)(ya)反饋(kui)信號后送絲(si)速度(du)調(diao)(diao)快，弧(hu)(hu)長(chang)(chang)(chang)(chang)由長(chang)(chang)(chang)(chang)變短，趨向(xiang)(xiang)穩定值。當電(dian)(dian)弧(hu)(hu)長(chang)(chang)(chang)(chang)度(du)變短，電(dian)(dian)弧(hu)(hu)電(dian)(dian)壓(ya)(ya)(ya)下降(jiang)時(shi)，將送絲(si)速度(du)調(diao)(diao)慢，弧(hu)(hu)長(chang)(chang)(chang)(chang)增長(chang)(chang)(chang)(chang)趨向(xiang)(xiang)給(gei)定值。這種埋弧(hu)(hu)焊機的(de)控(kong)制(zhi)系(xi)(xi)統(tong)稍復雜，具(ju)體(ti)型號有(you)MZ-1000、MZ-1-1000和(he)MU1-1000等。其焊接(jie)電(dian)(dian)源可采用交流、直流弧(hu)(hu)焊電(dian)(dian)源。

   按工作(zuo)需要，埋弧焊機(ji)常見的構造形(xing)式(shi)(shi)有：焊車式(shi)(shi)、懸(xuan)掛式(shi)(shi)、機(ji)床式(shi)(shi)、門架式(shi)(shi)和懸(xuan)臂式(shi)(shi)等，如(ru)圖(tu)4-12所(suo)示(shi)。