焊接电弧的结构及温度分布如何,何谓正接反接

Major contents of this course: Ignition process of welding arcs; structure and surface characteristics of welding arcs; polarity and applications of welding power and stability of electric arcs; welding arc blow; pre-heating, post-heating, post-welding thermal treatment and the methods of improving manual production of welding arcs; droplet transfer of welding arcs; types of welding joints and welding seams; arc striking and related methods; starting, ending and connection of welding seams; welding process parameters; microstructure of welding seam solidification and welding joints; causes for, preventive measures against and handling of air pores in welding seams and cracks in welding.

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1、电弧具有两个特性,即它能发出强烈的光和大量的热.电弧发出的光和热被广泛地应用于工业上,如电弧是所有电弧焊接方法的能源.到目前为止,电弧焊在焊接方法中其所有仍然占据着主要地位,一个重要的原因就是因为电弧能有效地把电能转换成熔化焊接过程所需要的热能和机械能.
2、由焊接电源供给的,具有一定电压的两极间或电极与焊件之间,在气体介质中产生的强烈而持久的发电现象,称为焊接电弧.

把要焊接的金属作为一极,焊条作为另一极,两极接近时产生电弧,使金属和焊条熔化的焊接方法叫做电弧焊接.通称电焊.保护电弧以避免空气渗入

电弧长度指的是焊接过程中焊材(焊条、焊丝等）的燃烧点与母材的距离 ,选B

电弧的长短指的是焊接时焊枪或焊条离焊道的远近,离得远电弧就长.离得近电弧就短.电弧越短受热面积越小,焊道越窄.电弧越长受热面积越大,焊道越宽.

电弧的长度 跟电压有关系,不是说你说的那样,那么一般情况是根据你焊接的材料,焊接的工件类型选择.

电弧的引燃
将焊条末端与焊件接触形成短路,在触点上产生很大短路电流形成大量电阻热,使金属温度急剧升高而熔化,然后迅速将焊条提起一段距离,在电场力作用下被加热的阴极有电子高速飞出,撞击空气中的分子和原子,使空气电离成阳离子,阴离子和自由电子.阳离子奔向阴极,阴离子奔向阳极,在它们运动途中和到达两极时,不断碰撞和复合,产生大量的热和光,形成电弧.
当焊接电流一定时,阴极区的产热功率取决于UK与Uw的差值；阳极区的产热量取决于Uw.在细丝熔化极气体保护电弧焊、使用含有CaF2焊剂的埋弧焊或使用碱性焊条电弧焊等情况下,当采用同样大小的焊接电流焊接同一种材料时,焊丝作为阴极时的产热功率比作为阳极时的产热功率多,在散热条件相同时,焊丝作阴极比作阳极时熔化速度快.

实质就是电极与工件间的空气在电压下被电离而导电.
直流电弧焊或电弧切割时,电源输出端有固定的正极和负极.焊件接电源正极、电极接电源负极的接线法,叫正接；焊件接电源负极、电极接电源正极的接线法,称为反接.
正接和反接时,焊接电弧的形状不一样.显然,只有采用直流焊接电源时,才有正接和反接两种接线法,交流焊接电源由于正、负极在不断地交替,所以不存在极性问题.
焊件极性的选择原则：
1、焊条电弧焊使用碱性低氢焊条时,一律采用反接.若采用正接,则电弧燃烧不稳定电弧声音很暴燥,发出强烈的嘶嘶声飞溅很大,并且极容易产生气孔.使用酸性焊条时,极性对电弧的稳定燃烧影响不大.
同样道理,埋弧焊若使用直流电源施焊时,一般也采用反接.
2、钨极氩弧焊焊接钢、黄铜时,一律采用正接.因为阴极的发热量远小于阳极,所以用直流正接电源时,钨极接负极,发热量小,不易过热,钨极寿命长,同样直径的钨极可以采用较大的焊接电流.同时正接时,焊件为阳极发热量大,因此熔深大,生产率高.

To analyze tungsten electrode argon arc welding (GTAW) arc welding arc under the effect of applied longitudinal magnetic field behavior,based on the dc tungsten electrode argon arc welding arc as the research object,according to the theory of magnetohydrodynamics is established based on free burning GTAW arc welding under the effect of applied longitudinal magnetic field of the fluid flow and heat transfer process of the three-dimensional transient numerical model,all programs are written in FORTRAN language.
首先,分析外加纵向磁场的分布规律,建立励磁线圈磁感应强度计算数学模型,并对基本方程中的瑕点进行处理,在数值计算时采用稳定性好,计算精度高,误差容易控制的龙贝格积分法.
First of all,analysis of the applied longitudinal magnetic field distribution,excitation coil magnetic induction strength calculation mathematical model is established,and the imperfections in the basic equations,the numerical calculation with good stability,high calculation precision,the error is easy to control the dragon berg integral method.
该数学模型和数值计算方法具有模型简单,计算精度高和计算速度快等特点.
The mathematical model and numerical calculation method is simple,high calculation precision and calculation speed,etc.
在外加纵向磁场分析和计算的基础上,建立了电弧空间内带电粒子运动速度和位移的三维数学模型.
In the applied longitudinal magnetic field on the basis of analysis and calculation,established the arc space charged particle movement speed and displacement of three dimensional mathematical model.
根据牛顿运动定律,麦克斯韦方程给出了控制方程组和边界条件,模拟了GTAW焊接过程中外加纵向磁场作用条件下电弧空间内带电粒子运动行为动态变化过程.
According to Newton's laws of motion,maxwell equations governing equations and boundary conditions are given,GTAW welding process was simulated with longitudinal magnetic field effect under the condition of arc space charged particle motion behavior dynamic change process.
为深入研究外加纵向磁场作用下GTAW焊电弧动态行为数值模拟提供了前提和基础.
For further research and longitudinal magnetic field under the action of GTAW welding arc dynamic behavior simulation provides the premise and foundation.
根据质量守恒定律、动量守恒定律、能量守恒定律以及麦克斯韦方程,建立了描述外加磁场作用下GTAW焊接电弧传热传质过程的控制微分方程组,并给出了相应的边界条件和初始条件.
According to the law of mass conservation,momentum conservation law,the law of conservation of energy and maxwell's equations,established the description and magnetic field under the action of heat and mass transfer process of GTAW welding arc control system of differential equations,and gives the corresponding boundary conditions and initial conditions.
采用分离变量法成功地处理了电场、磁场、流场和热场的耦合问题.
Using the separation variable method successfully deal with the electric field,magnetic field,flow field and thermal field coupling problems.
利用所建立的数值模型,对外加纵向磁场下镁合金GTAW焊电弧的动态行为进行了数值分析.
Using the established numerical model of magnesium alloy under the applied longitudinal magnetic field GTAW welding arc dynamic behavior to carry on the numerical analysis.
以无外加磁场作用下电弧形态为参考,研究了外加纵向磁场及主要焊接参数对电弧电场、电流密度、温度分布、电弧电压及等离子流速分布的影响.
With no additional magnetic field under the action of arc shape for reference,studies the applied longitudinal magnetic field and the main welding parameters on arc electric field and current density,temperature distribution,the influence of arc voltage and the plasma velocity distribution.
得到了外加纵向磁场作用下GTAW焊电弧动态行为的变化规律.
Got the applied longitudinal magnetic field under the action of GTAW welding arc dynamic change rules of behavior.