焊接时防止变形的方法.doc

Distortion - Prevention by fabrication techniques 制造技术防止变形 Distortion caused by welding a plate at the centre of a thin plate before welding into a bridge girder section. Courtesy John Allen 焊接桥梁部分前由在薄板中央焊接钢板时产生的变形. Courtesy John Allen Assembly techniques 组装技术 In general, the welder has little influence on the choice of welding procedure but assembly techniques can often be crucial in minimising distortion. The principal assembly techniques are: tack welding back-to-back assembly stiffening 通常,焊工在选择焊接工艺时没有什么影响但关键的是在组装技术上控制最小变形.主要安装技术是: 点焊 重叠组装 加强板 Tack welding 点焊 Tack welds are ideal for setting and maintaining the joint gap but can also be used to resist transverse shrinkage. To be effective, thought should be given to the number of tack welds, their length and the distance between them. With too few, there is the risk of the joint progressively closing up as welding proceeds. In a long seam, using MMA or MIG, the joint edges may even overlap. It should be noted that when using the submerged arc process, the joint might open up if not adequately tacked. 点焊能很好的定位和保证连接间隙但不能防止横向收缩.为了起到好的效果,应考虑点焊数量,长度以及他们之间的距离.太少,导致焊接时接头缝隙逐渐靠拢.对于长焊缝,使用MMA 或MIG,接头边可能重叠.注意当使用埋狐焊时,如果没有足够的定位接头可能外露. The tack welding sequence is important to maintain a uniform root gap along the length of the joint. Three alternative tack welding sequences are shown in Fig 1: tack weld straight through to the end of the joint (Fig 1a). It is necessary to clamp the plates or to use wedges to maintain the joint gap during tacking tack weld one end and then use a back stepping technique for tacking the rest of the joint (Fig 1b) tack weld the centre and complete the tack welding by back stepping (Fig 1c). 为了在接头长度方向保证一致的根部间隙,点焊的顺序很重要.图1中有三个可供选择的点焊顺序. 点焊直到接头端部(图1a).必须夹住金属板或在点焊过程中用楔保证接头间隙. 点焊一端然后用反手技术点焊接头剩余部分(图1b) 点焊中心然后反手完成点焊(图1c) a) tack weld straight through to end of joint 点焊直到接头端部  b) tack weld one end and then use a back stepping technique for tacking the rest of the joint 点焊一端然后用反手技术点焊接头