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Principle and use method of carbon arc gouging 1. Principle Carbon arc gouging is a processing technology method that uses the high-temperature current generated between the carbon electrode and the metal to locally heat the metal to a molten state, and at the same time uses the high-speed airflow of compressed air to blow away the molten metal, thereby achieving planing and cutting of the metal base material, as shown below: Figure 1 Schematic diagram of carbon arc gouging 2. Application scope 1. Weld root picking work. 2. Use carbon arc gouging to create bevels, especially U-shaped bevels. 3. When reworking the weldment, carbon arc gouging can be used to eliminate welding defects (dig out). 4. Remove burrs, spurs, risers on the surface of the casting and defects in the casting. 5. Cut stainless steel medium and thin plates. 6. Drill holes in the plate workpiece. 7. Plane the reinforcement on the weld surface. 3. Process parameters of carbon arc gouging (main) 1. Carbon rod specifications and applicable current (Table 1) Current has a great influence on the size of the gouging. When the current increases, the width of the gouging increases and the depth increases even more. Using a large current can increase the gouging speed and obtain a smoother gouging. However, when the current is too large, the carbon rod head will easily turn red and the copper plating layer will easily fall off. Under normal current, the red length of the carbon rod is 25mm. If the current is small, carbon inclusion will easily occur. In actual production, you can refer to Table 1 to select the current. Table 1 Carbon rod specifications and applicable current cross-sectional shape specifications (mm) Applicable current (A) Cross-sectional shape specifications (mm) Applicable current (A) Round φ3×355φ4×355φ5×355φ6×355φ7×355φ8×355φ10×35 5φ12×355150—180150—200150—250180—300200—350250—400400—550450—6 00 flat 3×12×3555×10×3555×12×3555×15×3555×18×3555×20×3555×25×3556× 20×355200—300300—400350—450400—500450—550500—600550—600550—600 2. Planing speed Planing speed has a certain impact on the groove size and surface quality. If the speed is too fast, the carbon rod will collide with the metal, causing the carbon to stick to the top of the groove, forming a "carbon pinch" defect. On the contrary, if the speed is too slow, the problem of "slag sticking" may occur. Usually the planing speed is 0.5-1.2m/min is more suitable. 3. Arc length When gouging, the arc length will cause arc instability and even cause arc interruption. Generally, short arc should be used for operation to improve production efficiency and carbon rod utilization. Generally, the arc length is 1-2mm. 4. Carbon rod protrusion length. The length of the carbon rod from the jaw to the arc end is the protrusion length (as shown in Figure 1). The longer the protrusion length, the farther the jaw is from the arc. The blowing force of the compressed air into the molten pool is insufficient, and the molten metal cannot be blown away smoothly. ； On the other hand, the longer the extension length, the greater the resistance of the carbon rod and the faster it burns. During operation, the appropriate extension length of the carbon rod is 80-100 mm. When the burnt length reaches 20-30 mm, it must be adjusted. 5. Carbon rod inclination angle The angle between the carbon rod and the workpiece along the groove direction is called the carbon rod inclination angle, and the depth of the groove is related to the inclination angle. The inclination angle increases and the groove depth increases ； On the contrary, as the inclination angle decreases, the groove depth decreases. The inclination angle of the carbon rod is generally 25°--45° 4. Basic operations 1. Before preparing the workpiece for planing, check whether the polarity of the power supply is correct (generally, the planing gun is connected to the positive pole and the workpiece is connected to the negative pole). Check whether the cables and air pipes are connected properly. And select the carbon rod diameter and adjust the current according to the thickness of the workpiece and the width of the groove. Adjust the carbon rod extension length to 80-100mm. Check the compressed air line and adjust the pressure, adjust the air outlet and align it with the gouge. 2. When igniting the arc, you should first slowly open the gas valve and then ignite the arc, otherwise it is easy to cause "carbon inclusion" and the carbon rod to burn red. At the moment when the arc ignites, it should not be pulled too long to avoid extinguishing. 3. Planing ① Because the temperature of the steel plate is low when starting to plan, it cannot melt quickly. When the arc ignites, the planing speed should be slower at this time. ； Otherwise, carbon inclusion will easily occur. When the steel plate melts and is blown away by the compressed air, the planing speed can be appropriately accelerated. ② During the planing process, the carbon rod should not swing laterally or move back and forth, but can only move linearly along the planing direction. ③ The inclination angle of the carbon rod depends on the groove depth requirements, and the inclination angle can be 25°--45°. ④ When planing, the hand movement should be steady and the alignment should be correct. The center line of the carbon rod should coincide with the center line of the planing groove. Otherwise, it is easy to cause the groove shape to be asymmetrical. ⑤ When gouging in a vertical position, it should be moved from top to bottom to allow the welding slag to flow out. ⑥ Maintain an even planing speed. When planing, a uniform and crisp "hiss, hiss" sound indicates that the arc is stable and smooth and uniform grooves can be obtained. When each section of gouging is connected, the arc should be struck on the arc crater to prevent it from touching the gouge or causing serious dents. ⑦ At the end of planing, the arc should be cut off first, and then the air valve should be closed after a few seconds to allow the carbon rod to cool. ⑧ After gouging, the iron slag, burrs and oxide scale on the gouge and its edges should be removed, and the carbon dust and "copper spots" in the gouge should be removed with a wire brush. And check whether the root of the weld is completely gouged and whether the defects are completely removed according to the gouging requirements. 4. Gouging defects during weld repair. After flaw detection of the weld, if any defects exceeding the standard are found, carbon arc gouging can be used to remove them. Planing is carried out according to the mark of the defect position made by the inspector on the welding joint. During the planing process, attention should be paid to planing layer by layer, and each layer should not be too thick. When a defect is found, gently plan down one or two layers until the defect is completely removed. As shown in Figure 2 Figure 2 The groove shape after removing the weld seam