1. Preparations Before Welding
(1) Check whether the wiring is correct. The equipment shell must be grounded. When a welder gets an electric shock, the power supply should be cut off before rescuing.
(2) Wear dry gloves before pushing and pulling the power switch, and it is forbidden to face the switch, so as to avoid arc sparks burning your face.
(3) Welding cables are not allowed to be placed near the welding machine nor on hot metal welds, and collisions and abrasions should also be avoided.
When welding job is done, the power should be cut off in time, and the equipment should be covered when working outdoors.
2. Selection of Welding Materials
The selection principle of welding rod follows the principle of equal strength, principle of equivalence, and principle of equal conditions.
Fox Alloy E6013 can be used for ordinary thin plate welding with easy arc ignition, minimum spatter and less welding fume. It is very friendly to beginners. If you want higher strength weld bead, Fox Alloy E7018 is a good choice with over 550Mpa tensile strength. Its strength, making It a good choice for welding medium and thick low alloy steel. When it comes to pipe welding, Fox Alloy E6010, E6011 cellulose welding electrodes are extremely suitable for this job for strong arc force, deep penetration, and very good vertical down position welding performance.
3. Selection of Welding Current
(1) In the actual production process, welders choose welding current according to the results of trial welding and their own practical experience.
(2) If the current is too small, arc ignition will be difficult and the electrode is easy to stick to the weld piece, the weld bead will be thick with bad fusion on two sides.
(3) If the current is too high, there will be a lot of spatters and fume during welding, the electrode will be burnt red, and the weld bead will be very bright, burning through and undercut can happen sometimes.
(4) When the current is suitable, arc ignition will be easy, stable arc can be observed, the spatter is minimum, and the uniform crackling sound can be heard, the two sides of the weld bead are smoothly transitioned to the base metal, the molten pool ripple is fine, and the slag removal is easy.
4. Selection of Arc Voltage
The arc voltage mainly affects the width of the weld bead. But in the case of electrode arc welding, weld bead width is mainly controlled by the lateral swing of the electrodes, thus the influence of the arc voltage is not great.
When the welding current has been chosen, the longer the arc is, the higher the voltage. But when the arc is too long, the combustion is unstable, there will more spatters, and defects such as undercut and pores are easy to occur; if the arc is too short, electrodes are easy to stick to the weld piece. In normal situation, the arc length should be equal to 1/2 or 1 times of the diameter of the electrode.
5. Selection of Welding Speed and Number of Weld Layers
The welding speed refers to the length of the weld seam completed per unit time. Under the principle of ensuring the required size and shape and good fusion, the welding speed is flexibly controlled by the welder.
When welding thick plates, multi-layer welding or multi-layer multi-pass welding will be applied. The previous weld pass preheats the next weld pass, and the latter weld pass heats the previous weld pass. It is beneficial to improve the plasticity and toughness of the weld metal. The thickness of each layer of weld bead should not be greater than 1.5 times the diameter of the electrode.
6. Welding Rod Travelling Skills
(1) Arc ignitionKnocking method: knock the weldment with the electrodes end tip lightly, lift it up quickly and keep a certain distance, and welding arc will be ignited then;
Scratch method: Scratch the end tip of the electrode on the surface of the weldment to ignite an arc.
(2) Electrodes travelling
When the electrode is burning, it should be swayed slightly and laterally to obtain a uniform weld shape, and effectively control the temperature of the molten pool and prevent burning through. The commonly used methods are linear reciprocation (a) and crescent shape (b) , Inclined circular (c) travelling method. As shown below
The welding seam after welding starts from the tail of the first welding seam. It is required to strike the arc about 10mm before the arc crater. The arc length can be slightly longer, and then move back to the arc crater to lower the arc for normal welding.
(4) Finishing
The normal molten pool temperature should be maintained at the end of the weld. Common methods include drawing a circle to end, repeated arc breaking to end, and back welding to end. The purpose is to fill the arc crater at the end of the weld to avoid defects.
7. Contraindications in Electrodes Travelling
(1) It is difficult for beginners to master the knocking method in arc ignition, as it is easy to cause arc extinguishment or short circuit. This is the reason for not mastering the speed and keeping a certain distance when leaving the weldment.(2) It is easier to master the scraping method of arc ignition. If the electrode is pulled up too fast or too high during operation, the arc cannot be ignited or the arc will only burn for a moment and then go out. Conversely, moving too fast may cause the electrode to stick to the weldment, causing a short circuit in the welding circuit.
(3) If the welding rod sticks to the weldment during arc ignition, the welding clamp should be released immediately. If the short-circuit time is too long, the very high short-circuit current will damage the welding machines.
(4) The travelling speed of the electrode has great influence on the weld quality and welding productivity. If the electrode travels too fast, there will not be enough time for the arc to melt the electrode and the base metal, resulting in incomplete penetration or narrow welds; if the electrode moves too slowly, the temperature of the molten pool will be too high, resulting in burn-through in weld piece and also bring problems like welding lumps, too wide weld bead, metal accumulation, too high weld seam and irregular bead formation. Therefore, it is required that the travelling speed of the electrode must be appropriate to obtain qualified weld bead.
(5) In arc stop, it is necessary to ensure that the gas inside the molten pool is fully discharged, and prevent air intrusion caused by the exposure of the molten pool due to too fast arc stop, resulting in defects such as cold shrinkage holes and internal pores.