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Forming side welding technique of exploration and practice
Abstract: In some of the pressure vessel welding, require full penetration welded joints, but in practice, due to restrictions by the weldment structure, would often undercut and weld phenomenon. This paper elaborates on the side welding forming study the application of this technology, so that the welding problem has been resolved, effectively improve the welding pressure vessel safety factor and reliability.
Keywords: forming side welding technology exploration and practice.
Welding boilers and pressure vessels and other structures often require full penetration welded joints in order to meet the quality and performance requirements of pressure parts. However, due to the size and shape of the restriction member, such as small diameter vessels, piping in which welding can not only be welded to the outer container, if the outer side of a conventional single-sided welding method, which will not weld penetration, undercut, and the presence of weld defects, can not meet the requirements of welding quality. I have ten years of welding technology through learning and practical work in repeated practice, since the use of the right hand sides of welding, welding pieces of the implementation side welding technique, so that pressure vessel weld joints to achieve a complete penetration of Claim. The following describes the specific technical characteristics forming side welding operation of law and the operating points: one, forming side welding operation of law Introduction forming side welding operation method is the use of common electrode, a special method of operation, the slope at the back of the mouth without any auxiliary measures conditions in front of the welding groove, the groove after welding to ensure the positive and negative can be obtained even tidy, forming a good, consistent operation method of welding seam quality requirements. It is SMAW greater difficulty in operating a technology for weld root can not be cleared from the back and re-welding of important weldment. Second, the scope side welding method of forming operations such operation method is mainly applicable to a plate butt joints, tube butt joints, riding pedestal tube plate joints, according to the joint position may be different welding, vertical welding, cross welding and overhead welding positions, such as welding. Third, the technical characteristics of side welding forming side welding operation of law forming welding methods are generally V-shaped groove for butt welding, suitable for container housing a plate butt welding, small-diameter container and pipe girth butt welding container takeover tube sheet welding. Forming side welding on the welding method and the general flat, vertical, horizontal and overhead welding different, but basically the same operating points and requirements, and should not occur within the weld porosity, slag, the roots should be uniform penetration, There should be welded on the back of tumors and depression and so on. Fourth, forming side welding operation points and operation instance operation of law to the thickness of 12 mm below the V-shaped butt-welding, for example, welding method further elaborated side welding forming.
1, the test plate assembly dimensions (Table 1) bevel angle (°) assembly clearance (mm) blunt edge (mm) anti-distortion (°) wrong side (mm) beginning welding weld end end end 3.2 60 4.0 03 ~ 4 ≤1
2, the welding parameters (Table 2) welding layers backing weld filler passes (the first) filled weld (second line) filling welding (the third) capping electrode diameter (mm) 3.2 3.2 4.0 4.0 4.0 welding Current (A) 100 ~ 120 140 ~ 150 195 ~ 200 195 ~ 200 185 ~ 190
3, when the welding point welding, soldering due to the weldment in a top position, as compared with other welding position of the operation easier, it is the basis for a variety of other plate-shaped position, the tubular specimen at various positions of the welding operation. However, the flat welding position backing welding, melting holes difficult to observe and control, under the Arc force of gravity and the molten metal, so easy to produce ultra-high back bead or weld defects. a, weld bead profile five five-sided, as shown in Figure A Figure A bead distribution b, test plate welding position on the horizontal plane, a small gap on the left end.
4, backing weld welding forming single-sided welding, weld welding primer first layer is the key operation at high temperatures and blowing the arc force, beveling the root portion of the metal is melted to form a metal bath, in the pool will have a leading edge groove assembly gap is slightly larger than the hole, called melt holes. Slag and gas melting electrode coating formed by melt holes on the back seam effectively protected.
Meanwhile, the quality of the workpiece is determined by the back bead of melt hole size, shape, movement uniformity. Side welding forming, according to the different operating practices when backing welding first layer can be divided into continuous welding method (also known as the connecting arc method) and intermittent arcing welding method (also known as broken arc welding) two kinds.
An even arc welding method is even continuous combustion in electric arc welding process, do not go out, take a smaller gap blunt edge groove, use a smaller welding current, and always maintain a continuous short-arc welding. Even arc welder is only required to maintain a smooth and uniform transport section, no major changes in operating practices, easy to grasp. The back of the weld relatively dense, neat, to ensure that the internal weld quality requirements, but if done incorrectly, could easily lead to the back of the weld fusion or incomplete penetration phenomenon.
2, broken off arc welding arc in the welding process, by burning and extinguishing of the arc and alternately control the extinction time, thus controlling the temperature, the shape and position of the bath, in order to obtain good shaping the back surface and internal quality. Bevel land gap taken off the arc welding even slightly larger than, the choice of a wide range of welding current, the arc having a sufficient penetration.
Conducting sheets, small diameter pipe welding and actual changes in the larger gap product assembly conditions, using broken arc welding method has become more flexible and applicable. Because broken arc operating practices vary widely, there are some difficulties to master, requiring more skilled welders operating techniques. When backing weld angle between the electrode and the specimen as shown in Figure B, using a small zigzag lateral oscillation amplitude and slightly sloping sides remain in the mouth, continuous forward welding, arc welding method which uses even bottoming. Figure B-flat position backing welding electrode backing weld angle to note the following: (1) control the position of the arc hit the bottom of the test plate from the left end of the beginning of the welding seam position at the beginning of the arc after arc ignition, a pause preheat, then swing to the right transverse welding, the weld to be positioned on the right side to reach the forefront of the arc when welding under the pressure and pause to form melt holes. (2) controlled pore size melt at high temperatures and blowing force the arc melting test plate groove root formation and breakdown melt holes, as shown in Figure C, you should immediately lift the rod to leave the pool to about 1.5 mm or so, which can be normal right welding. The back in order to get a good shape and high quality welds, welding arc to control the one in Figure C melt hole flat butt-welding seam at 1 ---- 2 --- 3 --- melt puddle welding hole hit bottom shorter, shipped strip should be uniform, not too fast forward speed. Pay attention to the welding arc on the pool cover 2/3, 1/3 of the arc to keep in front of the pool, the slope for melting and breakdown of specimens of root formation of melt holes. Welding process to strictly control the shape of the pool and try to keep the same size. And observe the changes in the molten weld pool and groove root case, welding, if there is a clear melt holes appear, you may want to burn on the back or produce weld. Determine the size of the hole on the back of molten weld width and more than high, if the hole is too small melt, fusion weld root is bad, easy to crack when bent back; if the fuse hole is too large, then the back of the bead both very good-looking high and wide , and easy to burn, melt hole diameter of generally 1 ~ 2mm better than the gap. If it is found during welding melt holes too, can be a little speed up the welding speed and swing frequency, reducing the angle between the electrode and the weldment; if melting hole is too small, you can slow down the pace and swing frequency welding, and welding electrode to increase angle between pieces. Of course, the welding current can also be used to change the way to adjust the size of the melt hole, but this method is not desirable, because the actual production due to the bevel angle, assembly gap and structural changes in the form, is not allowed at any time to adjust the welding current, and adjust the welding current is too much trouble, it must be mastered by changing the welding speed, swing frequency and angle of approach to improve the welding puddle situation, which is what the advantages of manual arc welding. (3) control the flow direction of the molten iron and slag. Always arc welding process in front of the iron, the use of directional arc and medicated skin blowing force generated when melted gas blowing the molten puddle behind, so can guarantee penetration, but also to ensure separation of slag and molten iron, reduce the possibility of slag and porosity. Welding bath to observe the situation, the pool in front of the slightly concave, iron relatively calm, there are darker line emerges from the pool, and gradually concentrated towards the upper part of the bath after, this is the slag, if the melt pool advance, that when the pool behind the arc, it is easy to slag. (4) controls the fusion groove on both sides of the case. Must be observed at all times during welding groove weld surface conditions, must be clearly visible groove surface melted and mixed with the electrode deposited metal forming the pool, the pool edge to be fused together and face the job on both sides of the groove, the most Fortunately, a little puddle in front of a small pit, but then be filled with molten iron, otherwise a bad fusion, easy to crack when bent back. (5) the weld joint backing weld welded joints can not be avoided, it is necessary to grasp the connector technology. When finished welding electrode is about, you need to replace the rod, the rod back in the opposite direction of the weld about 10 ~ 15mm, as shown in Figure Da, and quickly lift the rod, and gradually lengthen the arc quickly extinguished. This shrinkage of the crater to the bead surface to eliminate or to the next one when the welding rod to melt away. Note flashback time not too long as to make the joints become slope. Db shown in Fig. Crater position a diagram D (a) changing the electrode before (b) the weld joint seam weld joints before, there are two methods: the hot and cold connection connection. Hot Connection: welding puddle before a not yet fully cooled immediately connector. This method is commonly used in production, most suitable, but the joint difficult. The key take a good head has three: a, replace the electrode to be fast, preferably at the beginning of welding, left hand holding the mask to catch a few ready to replace the electrode, welding electrode after ventral root immediately for a good rod, while the melting When the pool is not fully solidified in the bath at 10 ~ 20mm front arc ignition, and immediately the arc back to the joint. b, location to be accurate, the arc back to the original crater at the new estimate after the bath along with the original crater along the tangent to the rod forward immediately to begin continuous welding. As the original crater was covered with slag, can only use their experience to judge the position after the crater edge, so the operation is difficult. If the new bath along the trailing edge of the crater do not coincide, then the joint is the lack of meat is not too high, it must be repeated practice. c, master arc under the pressure of time, when the arc has been moved forward to the forefront of the original arc welding pit, it must be under the pressure of the arc, and then re-creates a gap breakdown melt hole, until the formation of the new melt holes, then aforementioned essentials continue welding. During this time and location is appropriate, determine the quality of the weld bead on the back, and it is difficult to grasp. Cold Connection: before a puddle welding has cooled. Before welding, grinding into the first gentle slope at the crater-shaped arc at about 10mm from the bath after. Electrode do horizontal swing forward welding, arc welding to close at the leading edge, fill the crater, under pressure welding and pause. When you hear the sound of arcing, the formation of new melt holes, gradually lift the rod, the normal welding. 5, before filling welding filler layer welding, weld together before the first slag, spatter clean, will hit the bottom of the weld joint weld polished smooth, then filled welding. Filling layer welding rod angle is shown in Figure E E electrode welding filler layer angle bead welding filler layer takes time to note the following: a, good control of both sides of the weld fusion cases, when filling welding, welding increased swing, groove on both sides of the mouth while longer residence time than some backing weld, must ensure that both sides of the groove has some penetration, and to fill the bead surface slightly concave. b, control the final filling height and location of the weld. Height of weld filler layer should be less than the base material of about 0.5mm ~ 1.5mm, preferably slightly concave, be careful not to melt flute edges on both sides of the groove, easy to be able to see the groove surface layer welding, surface solder layer to lay the foundation. When filling weld bead, electrode layer by layer to increase the swing, but not too much to pay attention, do not let the pool beyond the edge of the top edge bevel edge. c, fitting method shown in Figure F, without pressing down the arc. Additional requirements with backing weld. Arc welding filler layer at Figure F head 6, capping cover surface welding rod angle when, transportation methods and strip joints filled with layers of the same method. But capping layer welding rod swing amplitude than the filling layer large. Note that consistent swing swings, transport speeds uniform. At the same time observe the melting groove on both sides of the case, a pause in the groove on both sides, so that when welding the edges on both sides of the weld fusion is good, avoid biting edges to get the cap weld quality. Electrode swing is determined by the edge of the bath, the bath must be taken to ensure that the surface of the test plate should not exceed the edge of the groove edge 2mm welding, weld otherwise wide. Pay special attention to cover up the joint, otherwise unsightly.
References: "welder Handbook"
单面焊双面成形操作技术的探索与实践
摘要：在焊接某些压力容器时，要求焊接接头完全焊透，但在实际操作中，由于受焊件结构的限制，经常会出现咬边及焊瘤现象。本文通过详细阐述对单面焊双面成形这项技术的研究运用， 使这一焊接难题得到了解决，有效提高了焊接压力容器中的安全系数和可靠性。
关键词：单面焊 双面成形 技术探索 实践.
焊接锅炉及压力容器等结构时，经常要求焊接接头完全焊透，以满足受压部件的质量和性能要求。但由于构件尺寸和形状的限制，如小直径容器，管道在里面无法施焊，只能在容器外侧进行焊接，如果在外侧采用常规的单面焊法，里面会焊不透，存在咬边和焊瘤等缺陷，不能满足焊接质量的要求。 本人通过十多年对焊接技术的学习并在实际工作中反复实践，利用左右手两面起焊，对焊件实施单面焊双面成形操作技术，使受压容器的焊接实现了接头完全焊透的要求。以下具体阐述单面焊双面成形操作法的技术特点及操作要点： 一、单面焊双面成形操作法简介单面焊双面成形操作法是采用普通焊条，以特殊的操作方法，在坡口背面没有任何辅助措施的条件下，在坡口的正面进行焊接，焊后保证坡口的正、反面都能得到均匀整齐、成形良 好，符合质量要求的焊缝的焊接操作方法。它是手工电弧焊中 难度较大的一种操作技术，适用于无法从背面清除焊根并重新进行焊接的重要焊件。 二、单面焊双面成形操作法的适用范围 这种操作法主要适用于有板状对接接头、管状对接接头、 骑座式管板接头，按接头位置不同可进行平焊、立焊、横焊和 仰焊等位置焊接。 三、单面焊双面成形操作法的技术特点单面焊双面成形焊接方法一般用于 V 形坡口对接焊， 适用于容器壳体板状对接焊，小直径容器环缝及管道对接焊，容器 接管的管板焊接。单面焊双面成形在焊接方法上与一般的平、 立、横、仰焊有所不同，但操作要点和要求基本一致，焊缝内 不应出现气孔、夹渣、根部应均匀焊透，背面不应有焊瘤和凹 陷等。 四、单面焊双面成形操作法的操作要点和操作实例 下面以板厚 12 mm 的 V 形坡口对接平焊为例，进一步阐 述单面焊双面成形的焊接方法。
1、 试板装配尺寸（表 1） 坡口角度（°） 装配间隙（mm） 钝边（mm） 反变形（°） 错边量（mm） 始焊端 3.2 60 终焊端 4.0 0 3~4 ≤1
2、焊接工艺参数（表 2） 焊接层数 打底焊 填充焊（第一道） 填充焊（第二道） 填充焊（第三道） 盖面焊 焊条直径（mm） 3.2 3.2 4.0 4.0 4.0 焊接电流（A） 100~120 140~150 195~200 195~200 185~190
3、焊接要点 平焊时，由于焊件处在俯焊位置，与其它焊接位置相比操 作较容易，它是板状其它各种位置、管状试件各种位置焊接操 作的基础。但是，平焊位置打底焊时，熔孔不易观察和控制， 在电弧吹力和熔化金属的重力作用下，使焊道背面易产生超高 或焊瘤等缺陷。 a、焊道分布单面焊五层五道，如图 A 所示 图 A 焊道分布 b、焊接位置 试板放在水平面上，间隙小的一端放在左侧。
4、打底焊 进行单面焊双面成形焊接时，第一层打底焊道焊接是操作 的关键，在电弧高温和吹力作用下，坡口根部部分金属被熔化 形成金属熔池，在熔池前沿会产生一个略大于坡口装配间隙的 孔洞，称为熔孔。焊条药皮熔化时所形成的熔渣和气体可以通 过熔孔对焊缝背面有效保护。
同时，工件背面焊道的质量由熔 孔尺寸大小、形状、移动均匀程度决定。 单面焊双面成形，按照第一层打底焊时的操作手法不同， 可分为连续施焊法（又称连弧焊法）和间断灭弧施焊法（又称 断弧焊法）两种。
1、连弧焊 连弧焊法是在焊接过程中电弧连续燃烧，不熄灭，采取较 小的坡口钝边间隙，选用较小的焊接电流，始终保持短弧连续 施焊。连弧焊仅要求焊工保持平稳和均匀的运条，操作手法没 有较大变化，容易掌握。焊缝背面成形比较细密、整齐，能够 保证焊缝内部质量要求，但如果操作不当，焊缝背面易造成未 焊透或未熔合现象。
2、断弧焊 断弧焊法在焊接过程中，通过电弧反复交替燃烧与熄灭并 控制熄弧时间，从而控制熔池的温度、形状和位置，以获得良 好的背面成形和内部质量。断弧焊采取的坡口钝边间隙比连弧 焊稍大，选用的焊接电流范围也较宽，使电弧具有足够的穿透 能力。
在进行薄板、小直径管焊接和实际产品装配间隙变化较 大的条件下，采用断弧焊法施焊更显得灵活和适用。由于断弧 焊操作手法变化较大，掌握起来有一定难度，要求焊工具有较 熟练的操作技术。 打底焊时焊条与试件之间的角度如图 B 所示，采用小幅度 锯齿形横向摆动，并在坡口两侧稍停留，连续向前焊接，即采 用连弧焊法打底。 图 B 平位打底焊焊条角度 打底焊要注意以下几点： （1）控制引弧位置 打底层从试板左端定位焊缝的始焊处开始引弧，电弧引燃 后，稍作停顿预热，然后横向摆动向右施焊，待电弧到达定位 焊缝右侧前沿时，将焊条下压并稍作停顿，以便形成熔孔。 （2）控制熔孔的大小 在电弧的高温和吹力作用下，试板坡口根部熔化并击穿形 成熔孔，如图 C 所示，此时应立即将焊条提起至离开熔池约 1.5mm 左右,即可以向右正常施焊。 1 图C 平板对接平焊时的熔孔 1----焊缝 2---熔池 3---熔孔 打底层焊接时为保证得到良好的背面成形和优质焊缝，焊 接电弧要控制短些，运条要均匀，前进的速度不宜过快。要注 意将焊接电弧的 2/3 覆盖在熔池上，电弧的 1/3 保持在熔池前， 用来熔化和击穿试件的坡口根部形成熔孔。施焊过程中要严格 控制熔池的形状，尽量保持大小一致。并观察熔池的变化及坡 口根部的熔化情况，焊接时，如果有明显的熔孔出现，则背面 可能要烧穿或产生焊瘤。 熔孔的大小决定背面焊缝的宽度和余高，若熔孔太小，焊 根熔合不好，背弯时易裂开；若熔孔太大，则背面焊道既高又 宽很不好看，而且容易烧穿，通常熔孔直径比间隙大 1~2mm 较好。 焊接过程中若发现熔孔太大，可稍加快焊接速度和摆动频 率，减少焊条与焊件间的夹角；若熔孔太小，则可减慢焊接速 度和摆动频率，加大焊条与焊件间夹角。 当然还可以用改变焊接电流的办法来调节熔孔的大小，但 这种方法是不可取的，因为实际生产中由于坡口角度、装配间 隙和结构形式的变化，不允许随时调整焊接电流，而且调整焊 接电流也比较麻烦，因此必须掌握用改变焊接速度、摆动频率 和焊条夹角的办法来改善熔池状况，这正是手工电弧焊的优 点。 （3）控制铁水和熔渣的流动方向。 焊接过程中电弧永远要在铁水的前面，利用电弧和药皮熔 化时产生的气体的定向吹力，将铁水吹向熔池后方，这样既能 保证熔深，又能保证熔渣与铁水分离，减少夹渣和产生气孔的 可能性。焊接时要注意观察熔池的情况，熔池前方稍下凹，铁 水比较平静，有颜色较深的线条从熔池中浮出，并逐渐向熔池 后上部集中，这就是熔渣，如果熔池超前，即电弧在熔池后方 时，很容易夹渣。 （4）控制坡口两侧的熔合情况。 焊接过程中随时都要观察坡口面的熔合情况，必须清楚地 看见坡口面熔化并与焊条熔敷金属混合形成熔池，熔池边缘要 与两侧坡口面熔合在一起才行，最好在熔池前方稍有个小坑， 但随即能被铁水填满，否则熔合不好，背弯时易产生裂纹。 （5）焊缝接头 打底焊道无法避免焊接接头，因此必须掌握好接头技术。 当焊条即将焊完，需要更换焊条时，将焊条向焊接的反方 向拉回约 10~15mm，如图 Da 所示，并迅速抬起焊条，使电弧 逐渐拉长很快熄灭。这样可把收弧缩孔消除或带到焊道表面， 以便在下一根焊条焊接时将其溶化掉。注意回烧时间不能太长 尽量使接头处成为斜面。如图 Db 所示。 a 图 D（a）换焊条前的收弧位置 （b）焊缝接头前的焊道 焊缝接头有两种方法：即热接法和冷接法。 热接法：前一根焊条的熔池还没有完全冷却就立即接头。 这是生产中常用的方法，也最适用，但接头难度大。接好头的 关键有三个： a、更换焊条要快，最好在开始焊接时，持面罩的左手中就 抓几根准备更换的焊条，前根焊条焊完后，立即换好焊条，趁 熔池还未完全凝固时，在熔池前方 10~20mm 处引燃电弧，并 立即将电弧后退到接头处。 b、位置要准，电弧后退到原先的弧坑处，估计新熔池的 后沿与原先的弧坑后沿相切时立即将焊条前移，开始连续焊 接。 由于原来的弧坑已被熔渣覆盖着，只能凭经验判断弧坑后 沿的位置，因此操作难度大。如果新熔池的后沿与弧坑后沿不 重合，则接头不是太高就是缺肉，因此必须反复练习。 c、掌握好电弧下压时间，当电弧已向前运动，焊至原弧坑 的前沿时，必须再下压电弧，重新击穿间隙再生成一个熔孔， 待新熔孔形成后，再按前述要领继续焊接。这段时间和位置是 否合适，决定焊缝背面焊道的质量，也是较难掌握的。 冷接法：前一根焊条的熔池已冷却。施焊前，先将收弧处 打磨成缓坡形，在离熔池后约 10mm 处引弧。焊条做横向摆动 向前施焊，焊至收弧处前沿时，填满弧坑，焊条下压并稍作停 顿。当听到电弧击穿声，形成新的熔孔后，逐渐将焊条抬起， 进行正常施焊。 5、填充焊 填充层施焊前，先将前一道焊缝的熔渣、飞溅清理干净， 将打底层焊缝接头的焊瘤打磨平整，然后进行填充焊。填充层 焊接时的焊条角度如图 E 所示 图E 填充层焊时的焊条角度 焊填充层焊道时需注意以下几点： a、 控制好焊道两侧的熔合情况， 填充焊时， 焊条摆幅加大， 在坡口两侧停留时间可比打底焊时稍长些，必须保证坡口两侧 有一定的熔深，并使填充焊道表面稍向下凹。 b、控制好最后一道填充焊缝的高度和位置。 填充层焊缝的高度应低于母材约 0.5mm~1.5mm， 最好略呈 凹形，要注意不能熔化坡口两侧的楞边，便于表面层焊接时能 够看清坡口，为表面层的焊接打好基础。 焊填充焊道时， 焊条的摆幅逐层加大， 但要注意不能太大， 千万不能让熔池边缘超出坡口上方的棱边。 c、接头方法如图 F 所示，不需向下压电弧了。其它要求 同打底焊。 引弧处 图 F 填充层焊接头 6、盖面焊 盖面层施焊时的焊条角度、运条方法及接头方法与填充层 相同。但盖面层施焊时焊条摆动的幅度要比填充层大。摆动时 要注意摆动幅度一致，运条速度均匀。同时注意观察坡口两侧 的熔化情况、施焊时在坡口两侧稍作停顿，以便使焊缝两侧边 缘熔合良好，避免产生咬边，以得到优质的盖面焊缝。 焊条的摆幅由熔池的边沿确定，焊接时必须注意保证熔池 边沿不得超过试板表面坡口棱边 2mm，否则焊缝超宽。 盖面接头要特别注意，否则不美观。
参考文献： 《焊工手册》
