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)鋼管埋弧(hu)焊設備(bei)按(an)送(song)絲機構可(ke)分為(wei)等速(su)送(song)絲和(he)均(jun)勻(yun)調節送(song)絲兩大類。

1. 等速送(song)(song)絲（又稱電弧自身調(diao)節送(song)(song)絲）

   等速(su)(su)送絲(si)(si)適(shi)用于細焊絲(si)(si)或高電(dian)(dian)(dian)(dian)流密度(du)的焊接場合，配合管狀導(dao)電(dian)(dian)(dian)(dian)嘴（或稱管狀偏(pian)心導(dao)電(dian)(dian)(dian)(dian)嘴、偏(pian)心導(dao)電(dian)(dian)(dian)(dian)嘴）。焊絲(si)(si)的送進按預(yu)選定(ding)的速(su)(su)度(du)等速(su)(su)進入焊接區，其工作(zuo)原(yuan)理是(shi)采用機械方法（更換變速(su)(su)齒輪(lun)）來調(diao)速(su)(su)。依靠電(dian)(dian)(dian)(dian)弧(hu)的自(zi)身調(diao)節作(zuo)用來維持弧(hu)長(chang)相對穩定(ding)。當(dang)焊接電(dian)(dian)(dian)(dian)弧(hu)受到(dao)外界干擾而弧(hu)長(chang)增加時(shi)，下降外特性電(dian)(dian)(dian)(dian)源供給(gei)的焊接電(dian)(dian)(dian)(dian)流減(jian)小，焊絲(si)(si)熔化速(su)(su)度(du)減(jian)緩(huan)，電(dian)(dian)(dian)(dian)弧(hu)便會(hui)由長(chang)變短(duan)，趨向(xiang)給(gei)定(ding)值。反之，電(dian)(dian)(dian)(dian)弧(hu)變短(duan)時(shi)，焊接電(dian)(dian)(dian)(dian)流增大，焊絲(si)(si)熔化加快，弧(hu)長(chang)又由短(duan)變長(chang)，趨向(xiang)給(gei)定(ding)值。按這個工作(zuo)原(yuan)理制造的等速(su)(su)送絲(si)(si)埋弧(hu)焊設備有MZ1-1000、MZ2-1500和(he)MZ3-500等型號，其焊接電(dian)(dian)(dian)(dian)源可采用交流、直流弧(hu)焊電(dian)(dian)(dian)(dian)源。

2. 均勻調(diao)節送(song)絲(si)（又稱強迫調(diao)節送(song)絲(si)、變速送(song)絲(si)）

   均勻調(diao)節送絲適(shi)用于粗(cu)焊(han)絲或低(di)電流密度的焊(han)接(jie)場合，配合滾輪(lun)式(shi)或夾瓦式(shi)導電嘴。

   焊(han)絲(si)的送(song)(song)進速(su)度(du)(du)按電(dian)(dian)(dian)(dian)弧電(dian)(dian)(dian)(dian)壓的高(gao)低(di)自動均勻調(diao)節(jie)(jie)(jie)，電(dian)(dian)(dian)(dian)弧電(dian)(dian)(dian)(dian)壓調(diao)節(jie)(jie)(jie)原理是利(li)用(yong)電(dian)(dian)(dian)(dian)弧電(dian)(dian)(dian)(dian)壓作為反饋信(xin)號(hao)，經過控制調(diao)節(jie)(jie)(jie)系統改變(bian)(bian)(bian)送(song)(song)絲(si)速(su)度(du)(du)而保持(chi)弧長(chang)相對不變(bian)(bian)(bian)。當電(dian)(dian)(dian)(dian)弧受外界干擾變(bian)(bian)(bian)長(chang)，電(dian)(dian)(dian)(dian)弧電(dian)(dian)(dian)(dian)壓升(sheng)高(gao)時，控制調(diao)節(jie)(jie)(jie)系統接(jie)到電(dian)(dian)(dian)(dian)壓反饋信(xin)號(hao)后送(song)(song)絲(si)速(su)度(du)(du)調(diao)快，弧長(chang)由長(chang)變(bian)(bian)(bian)短，趨向穩定(ding)值。當電(dian)(dian)(dian)(dian)弧長(chang)度(du)(du)變(bian)(bian)(bian)短，電(dian)(dian)(dian)(dian)弧電(dian)(dian)(dian)(dian)壓下降時，將送(song)(song)絲(si)速(su)度(du)(du)調(diao)慢，弧長(chang)增長(chang)趨向給定(ding)值。這種埋弧焊(han)機的控制系統稍復(fu)雜，具體型(xing)號(hao)有MZ-1000、MZ-1-1000和MU1-1000等。其(qi)焊(han)接(jie)電(dian)(dian)(dian)(dian)源可采(cai)用(yong)交流、直(zhi)流弧焊(han)電(dian)(dian)(dian)(dian)源。

   按工作需要，埋弧焊(han)機(ji)(ji)常見的構造形式有：焊(han)車式、懸掛式、機(ji)(ji)床式、門架(jia)式和懸臂式等，如圖4-12所示。