第五章埋弧焊报告.ppt

SAW的熔敷率 对于不同直径的焊丝，推荐的电流和熔敷率 kg/m Welding speed in m/h 0,4 0,3 0 0,1 0,2 40 80 60 100 160 140 120 焊剂的消耗 Higher amperage gives deeper penetration Higher voltage gives wider penetration. The arc length gets extended. 焊接电流和电弧电压的影响 Longer stick-out gives higher deposition rate, but also more shallow penetration. Above: Penetration at different stick-out Right: Deposition rate at different stick-outs. A: 25 mm B: 57 mm C: 83 mm 干伸长的影响 Deepest penetration with positive electrode. Normally, the welding machine is equipped with DC positive electrode. At constant amperage, the penetration gets deeper with smaller wire diameter, due to the higher current density. 极性和焊丝直径 Backhand Vertical Forehand The wire angle influences both penetration, the weld convexity, and the tendency to undercutting. Backhand gives high penetration, narrow and high weld convexity, and relatively high risk for undercutting. Vertical welding gives normal values. Forehand gives low penetration, wide and low weld convexity, and relatively slight risk for undercutting. Influence of wire angle Root defect Examples of incorrect weld joints Welding with too high current and / or too slow speed, results in an incorrect cross - section. There is a big risk for cracking. Too high voltage can cause an incomplete penetration * * * * * * * * * * * * * * * * * * * * * 7.6.1 SAW电弧特性及熔滴过渡 通过X光透视得到的电弧电压与电弧弧长的关系，两者之间也有良好的线性关系电弧电压随焊接电流的增大而降低，SAW电弧呈现负阻特性 SAW电弧在气泡（空洞）中燃烧，电弧电压越大、焊接速度越慢，所形成的空洞也就越大，变动也越大。 电弧电压较低或者焊接速度较慢时，在焊丝的前面有未熔化的焊剂，在焊丝的后部形成空洞。埋弧焊是在相当高的电流密度下进行焊接，由于电磁拘束效果的作用，焊丝前端的熔化金属呈细小颗粒过渡。 低速焊接，熔滴多数是沿着前面的熔渣壁产生过渡。焊接速度增大后，熔滴多从后部过渡。由于电流密度低(与GMAW相比)，熔滴的过渡频率达不到喷射过渡程度。电流400A、焊丝接负时每秒约过渡10次。焊丝接正时熔滴过渡的频率是焊丝接负时的数倍。但即使在焊丝接负时，也许是熔滴接触熔渣或电弧气氛的缘故，熔滴的尺寸较小，熔滴的直径大体与电极焊丝的直径相当。 7.6.3 SAW焊丝及母材的熔化特性 DRη表示焊丝电阻热对焊丝熔化速度的增加成分，与电弧热对焊丝的熔化速度DR0相比，DRη数值是很大的，不能忽略。电流密度δ、焊丝干伸长l增加时，焊丝的熔化速度亦增加，其增加量与(δ×l)1.22成比例。有效利用焊丝干伸长上的电阻热，能够提高焊接生产率。干伸长达到300mm时，焊丝熔化速度约为普通情况（50mm）的2倍。 干伸长