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焊接基础知识系列-焊接缺陷及防控之焊接气孔
更新时间:2018-08-28 17:27:39 字号:T|T
焊缝中的气孔是焊接缺陷之一,会降低焊接接头的严密性和塑性,减少焊缝有效截面而使焊接接头的机械性能下降,根部气孔和垂直气孔可能造成应力集中,成为裂纹源,甚至造成脆性破坏
焊缝中的气孔是焊接缺陷之一,会降低焊接接头的严密性和塑性,减少焊缝有效截面而使焊接接头的机械性能下降,根部气孔和垂直气孔可能造成应力集中,成为裂纹源,甚至造成脆性破坏,影响产品质量。实际生产中,尤其是焊接大型工件,几米甚至十几米或更长的焊缝中,气孔是不可避免的,可能因气孔问题返修次数超标而使设备报废。所以了解气孔的产生原因及防控,从中总结经验,尽可能的减少气孔的发生具有重要意义。
一、焊接气孔的分类
气孔的形成贯穿着金属熔化的全过程,即焊接的热过程、化学冶金过程。气孔形成的条件: Ve≤R(Ve—气泡浮出速度;R—焊缝凝固速度)。常见气孔可按如下4种方式进行分类:
1)按形态可分为单个气孔、成串气孔、有针状气孔、蜂窝状气孔、圆形气孔、椭圆形气孔;
2)按气孔所在位置可分为表面气孔、内部气孔、贯穿性气孔;
3)按颜色可分为乌黑气孔、白亮气孔;
4)按气孔形成原因可分为氮气孔、氢气孔、一氧化碳气孔。其中①析出型——溶解度突变的气体N2、H2;②反应型——熔池反应生成溶解度极低的气体CO。
1、CO气孔
焊接材料中脱氧元素(Mn/Si)含量不足,焊接过程中就会有较多的FeO熔于熔池金属中。随后在熔池冷凝时,熔池中的FeO和C发生化学反应:[FeO]+[C]=(FeO)+CO↑
当熔池金属冷凝过快时,生成的CO气体来不及完全从熔池内部逸出,从而成为气孔。通常这类气孔出现在焊缝根部与表面,且呈“条虫状”,为贯穿性气孔或表面气孔。


2、氮气孔
熔池冷凝时,随着温度降低,氮的溶解度降低,结晶过程更甚,导致氮不能及时逸出,在焊缝表面出现蜂窝状气孔,或者以弥散形式的微气孔分布于焊缝金属中。这些气孔呈“针尖”状。往往在抛光后检验或水压试验时才能发现。

3、氢气孔
氢气孔的出现,多由于焊缝金属溶解了过量的氢,如:焊接时焊丝或焊件表面有铁锈油污与水分、焊条/焊剂未烘干、CO2气保焊所用气体中含有水分、环境湿度过大、电弧高温作用下某些物质分解产生的氢等。熔池金属冷凝结晶时,氢的溶解度急剧下降而来不及逸出,引起焊缝金属产生氢气孔。氢气孔呈喇叭口形。

二、不同焊接方法气孔成因及防控
1、手工电弧焊
发生原因及气孔类型:
1.焊条烘干不充分或从烘箱中取出时间过长。(H2↑)
2.焊件有水分、油污、绣;手套潮湿、有油,更换焊条时油和水粘在焊条药皮上。(H2↑/CO↑)
3.焊接速度太快,空气侵入熔池,横焊比立焊更容易出现气孔。(N2↑)
4.电流太强,Si、Mn过量烧损,导致熔池中C的脱氧反应增多,生成CO。(CO↑)
5.电弧长度不合适。(N2↑)
6.焊件厚度大,金属冷却过速。(H2↑/CO↑)
7.碱性低氢型焊条焊接时,如果采用断弧收尾法,会造成电弧区渣气保护不良,空气侵入。(N2↑)
防控措施:
1.选用适当的焊条并注意烘干;
2.焊接前清洁被焊部分;
3.适当降低焊接速度,使内部气体容易逸出;
4.使用厂商建议的适当电流;
5.采用合适的电弧长度;
6.对焊件进行适当的预热。
2、CO2气体保护焊
发生原因及气孔类型:
1.母材未清洁;(H2↑/CO↑)
2.焊丝有锈或焊药潮湿;(H2↑/CO↑)
3.点焊不良,焊丝选择不当;(N2↑)
4.干伸长度太长,CO2气体保护不周密;(H2↑/CO↑)
5.风速较大,无挡风装置;(N2↑)
6.焊速过快,冷却速度过快;(N2↑/H2↑/CO↑)
7.喷嘴粘着火花飞溅,造成气体乱流;(N2↑)
8.气体纯度不良,含杂物多(如水分)(N2↑/H2↑/CO↑)
防控措施:
1.焊接前注意清洁被焊部位;
2.选用适当的焊丝并注意保持干燥;
3.点焊焊道不得有缺陷,且清洁干净,使用焊丝尺寸要适当;
4.减小干伸长度,调整适当的气体流量。
5.加装挡风设备;
6.降低焊速,使内部气体逸出;
7.注意清除喷嘴处焊渣,并涂以飞溅附着防止剂,以延长喷嘴寿命。
8.CO2纯度≥99.98%,水分≤0.005%。
3、埋弧焊
发生原因及气孔类型:
1.焊材或母材不清洁,焊剂烘干不彻底,使熔池氢含量增高而产生气孔;(H2↑)
2.钢材轧制或热冲压、卷板过程中,形成或脱落的氧化皮;定位焊渣壳、碳弧气刨飞渣等夹入焊剂,使焊缝产生气孔;焊剂堆高不够;(H2↑/CO↑)
3.焊剂颗粒太小气体不易逸出,或颗粒太粗空气侵入电弧区;(N2↑/H2↑/CO↑)
4.磁偏吹造成气孔;(N2↑/H2↑)
防控措施:
1.①清理焊丝,坡口表面及领近区域的油、锈、水分②焊剂充分烘干(潮湿天气,取出烘箱到使用时间不宜过长,******在50度左右保温待用)回收焊剂避免水、尘土等污染;焊剂颗粒度适当,保证一定的透气性;
2.焊接前确定无杂质混入焊剂,焊剂堆高不宜过高或过低;
3.选用颗粒适宜的焊剂;
4.合理安排地线位置,或直流换为交流。
 
参考文章:
崔岩《谈焊接气孔的成因、危害和防止》•装甲兵技术学校•长春•
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