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发表于 2007-7-26 17:10:15
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< class=MsoNormal><FONT size=3><SPAN><FONT face="Times New Roman">2.2 </FONT></SPAN><SPAN>采用电弧冷焊减小焊接应力的措施:</SPAN></FONT><FONT size=3><SPAN><FONT face="Times New Roman"> <BR></FONT></SPAN><SPAN>选用塑性较好的焊接材料,如用</SPAN><SPAN><FONT face="Times New Roman"> </FONT></SPAN><SPAN>镍</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>铜</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>镍</SPAN><SPAN><FONT face="Times New Roman"> </FONT></SPAN><SPAN>铜</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>高钒钢等作为填充金属,使焊缝金属可通过塑性变形松弛应力,防止裂纹;用细直准焊条,小电流,断续焊,分散焊的方法可减小焊缝处和基本金属的温度差而减小焊接应力;通过锤击焊缝可以消除应力,防止裂纹。</SPAN></FONT><FONT size=3><SPAN><FONT face="Times New Roman"> <BR></FONT></SPAN><SPAN>使焊缝冷却时能补受阻碍底自由收缩,从而避免用力过大而导致裂纹。</SPAN></FONT><FONT size=3><SPAN><FONT face="Times New Roman"> <BR>2.3 </FONT></SPAN><SPAN>采用热焊法并控制好温度</SPAN></FONT><FONT size=3><SPAN><FONT face="Times New Roman">. <BR></FONT></SPAN><SPAN>当温度高于</SPAN><SPAN><FONT face="Times New Roman">600</FONT></SPAN><SPAN>℃时</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>由于产生于一定的塑性变形</SPAN><SPAN><FONT face="Times New Roman">.</FONT></SPAN><SPAN>而使部分内应力得到消除</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>一般在</SPAN><SPAN><FONT face="Times New Roman">600</FONT></SPAN><SPAN>℃以上焊接时就不会产生热应力裂纹</SPAN></FONT><FONT size=3><SPAN><FONT face="Times New Roman">. <BR></FONT></SPAN><SPAN>三</SPAN><SPAN><FONT face="Times New Roman">. </FONT></SPAN><SPAN>灰口铸铁的补焊方法</SPAN></FONT><FONT size=3><SPAN><FONT face="Times New Roman">: <BR></FONT></SPAN><SPAN>灰口铸铁的补焊方法主要采用焊条电弧焊</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>气焊</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>钎焊</SPAN><SPAN><FONT face="Times New Roman">.</FONT></SPAN><SPAN>。</SPAN><SPAN><FONT face="Times New Roman">.</FONT></SPAN><SPAN>按照焊件在焊前是否预热可以把焊条电弧焊分为冷焊</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>半热焊</SPAN><SPAN><FONT face="Times New Roman"> <SPAN>(</SPAN></FONT></SPAN><SPAN>预热温度</SPAN><SPAN><FONT face="Times New Roman">400</FONT></SPAN><SPAN>℃以下</SPAN><SPAN><FONT face="Times New Roman">)</FONT></SPAN><SPAN>和热焊</SPAN><SPAN><FONT face="Times New Roman">(</FONT></SPAN><SPAN>预热温度</SPAN><SPAN><FONT face="Times New Roman">600-700</FONT></SPAN><SPAN>℃</SPAN></FONT><FONT size=3><SPAN><FONT face="Times New Roman">). <BR></FONT></SPAN><SPAN>四</SPAN><SPAN><FONT face="Times New Roman">.</FONT></SPAN><SPAN>灰口铸铁的补焊工艺</SPAN></FONT><FONT size=3><SPAN><FONT face="Times New Roman">. <BR>4.1.1 </FONT></SPAN><SPAN>冷焊法</SPAN><SPAN><FONT face="Times New Roman">. </FONT></SPAN><SPAN>电弧焊冷焊法就是焊件在焊前不预热</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>焊接过程中也不辅助加热</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>因此可以加速焊补生产率</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>降低成本</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>改善劳动条件</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>减少焊件因预热时受热不均匀而产生的变形和焊件已加工面的氧化</SPAN><SPAN><FONT face="Times New Roman">.</FONT></SPAN><SPAN>目前冷焊法正在推广</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>并迅速发展</SPAN><SPAN><FONT face="Times New Roman">.</FONT></SPAN><SPAN>但是冷焊法在焊接后因焊缝及热影响区的冷却速度很大</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>极易形成白口组织</SPAN><SPAN><FONT face="Times New Roman">.</FONT></SPAN><SPAN>此外因焊件受热不均匀</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>常形成极大的内应力</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>会造成裂纹</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>在冷焊时应注意以下几点</SPAN></FONT><FONT size=3><SPAN><FONT face="Times New Roman">: <BR></FONT></SPAN><SPAN>①</SPAN><SPAN><FONT face="Times New Roman"> </FONT></SPAN><SPAN>焊前应彻底清理油污</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>裂纹两端要打上裂孔</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>加工的坡口形状要保证便于焊补及减少焊件的熔化量</SPAN></FONT><FONT size=3><SPAN><FONT face="Times New Roman">. <BR></FONT></SPAN><SPAN>②</SPAN><SPAN><FONT face="Times New Roman"> </FONT></SPAN><SPAN>采用钢芯或铸铁芯的以外的焊条</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>小直径焊条应尽量用小的焊接电流</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>以减少内应力和热影响区的宽度</SPAN></FONT><FONT size=3><SPAN><FONT face="Times New Roman">. <BR></FONT></SPAN><SPAN>③</SPAN><SPAN><FONT face="Times New Roman"> </FONT></SPAN><SPAN>采用短焊道焊接法</SPAN><SPAN><FONT face="Times New Roman">.</FONT></SPAN><SPAN>一般每次焊</SPAN><SPAN><FONT face="Times New Roman">10-40mm,</FONT></SPAN><SPAN>待其充分冷却后再焊</SPAN></FONT><FONT size=3><SPAN><FONT face="Times New Roman">. <BR></FONT></SPAN><SPAN>④</SPAN><SPAN><FONT face="Times New Roman"> </FONT></SPAN><SPAN>采用分段倒退焊</SPAN><SPAN><FONT face="Times New Roman">.</FONT></SPAN><SPAN>这样可以降低拉应力</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>对防裂有好处</SPAN></FONT><FONT size=3><SPAN><FONT face="Times New Roman">. <BR></FONT></SPAN><SPAN>⑤每项焊一短焊道后</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>用圆头锤沿焊逢向外锤击</SPAN></FONT><FONT size=3><SPAN><FONT face="Times New Roman">. <BR></FONT></SPAN><SPAN>冷焊焊条按焊后焊缝的可加工性分为两大类</SPAN><SPAN><FONT face="Times New Roman">:</FONT></SPAN><SPAN>一类用于焊后不需要机械加工的铸件</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>如钢芯铸铁焊条</SPAN><SPAN><FONT face="Times New Roman">(EZCQ)</FONT></SPAN><SPAN>,只适用小型薄壁铸件刚度不大部位的缺陷焊补;另一类用于焊后需要机械加工的铸件,如纯镍焊条(</SPAN><SPAN><FONT face="Times New Roman">EZNi-1</FONT></SPAN><SPAN>)镍铁铸铁焊条(</SPAN><SPAN><FONT face="Times New Roman"> <SPAN>EZNiFe-1</SPAN></FONT></SPAN><SPAN>)镍铜铸铁焊条(</SPAN><SPAN><FONT face="Times New Roman">ENiCu-1</FONT></SPAN><SPAN>)等。</SPAN></FONT><FONT size=3><SPAN><FONT face="Times New Roman"> <BR>4.1.2 </FONT></SPAN><SPAN>热焊法</SPAN></FONT><FONT size=3><SPAN><FONT face="Times New Roman"> <BR></FONT></SPAN><SPAN>热焊法是在焊接前将焊件全部或局部加热到</SPAN><SPAN><FONT face="Times New Roman">600-700</FONT></SPAN><SPAN>℃,并在焊接过程中保持一定温度,焊后在炉中缓冷的焊接方法。用热焊法时,焊件冷却缓慢,温度分布均匀,有利于消除白口组织,减少应力,防止产生裂纹。但热焊法成本高,工艺复杂,生产周期长,焊接时劳动条件差,因此应尽量少用。</SPAN></FONT><FONT size=3><SPAN><FONT face="Times New Roman"> <BR>4.2</FONT></SPAN><SPAN>气焊焊补灰口铸铁的补焊工艺:</SPAN></FONT><FONT size=3><SPAN><FONT face="Times New Roman"> <BR></FONT></SPAN><SPAN>气焊火焰温度比电弧温度低得多,因而焊件的加热和冷却比较缓慢,这对防止灰口铸铁在焊接时产生的白口组织和裂纹都很有利。所以用气焊焊补的铸件质量一般比较好,因气焊成为补焊铸铁的常用方法。但气焊与焊条电弧焊相比,焊工的劳动强度高,焊件变形较大,焊补大型铸件时难以焊透。但由于气焊铸件的质量较好,易切削加工,使许多工厂中的中小型灰口铸件,还是较多用气焊焊补。</SPAN></FONT><FONT size=3><SPAN><FONT face="Times New Roman"> <BR>4.2.1 </FONT></SPAN><SPAN>焊前准备</SPAN></FONT><FONT size=3><SPAN><FONT face="Times New Roman"> <BR></FONT></SPAN><SPAN>①</SPAN><SPAN><FONT face="Times New Roman"> </FONT></SPAN><SPAN>在焊件清除完毕后</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>检查缺陷</SPAN><SPAN><FONT face="Times New Roman">.</FONT></SPAN><SPAN>焊件上的缺陷可起码接观察</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>也可用</SPAN><SPAN><FONT face="Times New Roman">10-20</FONT></SPAN><SPAN>倍的放大镜查找</SPAN></FONT><FONT size=3><SPAN><FONT face="Times New Roman">. <BR></FONT></SPAN><SPAN>②</SPAN><SPAN><FONT face="Times New Roman"> </FONT></SPAN><SPAN>裂纹找出后</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>在裂纹的两端钻直径φ</SPAN><SPAN><FONT face="Times New Roman">4-6mm</FONT></SPAN><SPAN>的</SPAN><SPAN><FONT face="Times New Roman"> </FONT></SPAN><SPAN>裂孔</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>以防止裂纹扩展</SPAN><SPAN><FONT face="Times New Roman">.</FONT></SPAN><SPAN>焊接灰口铸铁时可选用铸铁焊丝</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>丝</SPAN><SPAN><FONT face="Times New Roman">401A</FONT></SPAN><SPAN>或丝</SPAN><SPAN><FONT face="Times New Roman">401B. </FONT></SPAN><SPAN>焊接时气焊熔剂选用气剂</SPAN><SPAN><FONT face="Times New Roman">201,</FONT></SPAN><SPAN>铸铁气焊熔剂熔点为</SPAN><SPAN><FONT face="Times New Roman">650</FONT></SPAN><SPAN>℃成碱性</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>能将铸铁气焊时产生的二氧化硅</SPAN><SPAN><FONT face="Times New Roman">(</FONT></SPAN><SPAN>熔点为</SPAN><SPAN><FONT face="Times New Roman">1350</FONT></SPAN><SPAN>℃</SPAN><SPAN><FONT face="Times New Roman">)</FONT></SPAN><SPAN>变为易熔的盐类</SPAN><SPAN><FONT face="Times New Roman">.</FONT></SPAN><SPAN>铸铁用气焊熔剂进行灰口铸铁补焊时</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>应选择较大号的焊炬</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>以提高焊接头焰效率</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>有利于气孔夹渣等缺陷</SPAN><SPAN><FONT face="Times New Roman">.</FONT></SPAN><SPAN>焊嘴孔径可根据焊补处的壁厚确定。</SPAN></FONT><FONT size=3><SPAN><FONT face="Times New Roman">. <BR>4.2.5 </FONT></SPAN><SPAN>操作技术</SPAN></FONT><FONT size=3><SPAN><FONT face="Times New Roman">: <BR></FONT></SPAN><SPAN>在气焊过程中</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>必须选用中性焰或弱碳化焰</SPAN><SPAN><FONT face="Times New Roman">;</FONT></SPAN><SPAN>在焊接结束时可用碳化焰使焊缝缓冷</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>这样可以减少碳和硅的烧损</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>消除过厚的氧化膜</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>防止白口冷硬现象</SPAN><SPAN><FONT face="Times New Roman">;</FONT></SPAN><SPAN>当消除缺陷的底部或开坡口时可用氧化焰</SPAN><SPAN><FONT face="Times New Roman">.</FONT></SPAN><SPAN>焊接时</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>在要基本金属熔化后再加入焊丝</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>以防止熔合不良</SPAN><SPAN><FONT face="Times New Roman">;</FONT></SPAN><SPAN>发现熔池中有小气孔和白亮点夹杂物时</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>可以往熔池中加入少量气焊熔剂</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>有助于消除平渣</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>但气焊熔剂不宜加入过多</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>否则反而容易产生夹渣</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>气孔</SPAN><SPAN><FONT face="Times New Roman">;</FONT></SPAN><SPAN>适当加大火焰的功率</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>提高熔池铁水温度</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>有利于气体及杂质浮起</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>因而能减少气孔</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>夹渣</SPAN><SPAN><FONT face="Times New Roman">;</FONT></SPAN><SPAN>操作时应注意火焰始终盖住熔池</SPAN><SPAN><FONT face="Times New Roman">;</FONT></SPAN><SPAN>加入焊丝时</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>经常用焊丝轻轻搅动熔池</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>促使气体</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>熔渣浮出</SPAN><SPAN><FONT face="Times New Roman">;</FONT></SPAN><SPAN>焊补将完毕时应使焊缝稍高于焊件表面</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>并用焊丝刮去杂质较多的表层面</SPAN><SPAN><FONT face="Times New Roman">.</FONT></SPAN><SPAN>由于表层内含杂质较多</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>冷却后硬度较高</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>所以</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>刮去表面层可提高焊缝的切削性能</SPAN></FONT><FONT size=3><SPAN><FONT face="Times New Roman">. <BR></FONT></SPAN><SPAN>当补焊被焊区刚性较大或补焊石积较大</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>以及材质较差</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>组织疏松的铸件时</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>可采用热焊</SPAN><SPAN><FONT face="Times New Roman">.</FONT></SPAN><SPAN>焊后用石棉布或炭灰将铸件盖好</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>使焊缝缓慢冷却</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>以防止产生裂纹和白口组织</SPAN></FONT><FONT size=3><SPAN><FONT face="Times New Roman">. <BR></FONT></SPAN><SPAN>五</SPAN><SPAN><FONT face="Times New Roman"> </FONT></SPAN><SPAN>结论</SPAN></FONT><FONT size=3><SPAN><FONT face="Times New Roman"> <BR></FONT></SPAN><SPAN>灰口铸铁采取合理的焊补工艺</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>可使焊件获得较好的切削性和致密性</SPAN><SPAN><FONT face="Times New Roman">.</FONT></SPAN><SPAN>所以灰口铸铁焊补只要焊补工艺得当</SPAN><SPAN><FONT face="Times New Roman">,</FONT></SPAN><SPAN>可避免白口组织和裂纹的产生</SPAN><SPAN><FONT face="Times New Roman">.</FONT></SPAN></FONT></P> |
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