When checking the corrosion cracks on the welds of the boom side plate of the excavator, the paint layer and corrosion on the weld surface need to be scraped off or polished. During observation, tap the weld with a small hammer and observe with a magnifying glass if necessary.
1. Causes of cracks on boom side plate
Including bubbles, slag inclusion and micro cracks in the original weld. When the excavator is overloaded, small cracks will appear at the original weld and expand slowly. When welding, the performance of the electrode is inconsistent with that of the plate, resulting in cracks. Due to the large volume of the excavator boom, it is difficult to adopt reliable and effective heating and thermal insulation measures, and the hardened area of the base metal around the weld can not be completely removed after welding, resulting in the decrease of weld strength. During the operation of excavator, the vibration and impact are large, and the stress at the weld is uneven, which makes the weld crack.
2. Repair method
Clean the oil stain, paint, rust, etc. at the crack of the original weld with a hand grinding wheel. Cut off the weld crack with an air planer to the body of the side plate, and remove the hardened area of the previously welded base metal. After planing, grind the notch with an angle grinding wheel, and grind the inner interface to a V-shaped groove. After cleaning and inspection, confirm that all cracks have been found and removed.
According to the existing maintenance conditions, select the corresponding type of welding rod, bake it at 350 ℃ for 2h, and then keep it warm at 100 ℃ to prevent the welding rod from absorbing moisture. Take it as you use it. Welding current 190 ~ 230A. Due to the large thickness of the side plate of the excavator, the welded part shall be preheated to 150 ~ 250 ℃ before welding. In the welding process, segmented, symmetrical and backward welding methods can be used. During the cooling process of the weld, the weld metal shall be knocked with a hand hammer continuously to eliminate the stress. When welding at the corner of the side plate, in order to avoid and arc defects, continuous welding should be carried out to improve the stress condition of the connection.
After welding, the spatter, welding slag and overlap shall be completely removed, and the weld reinforcement shall not be greater than 2.5 mm. Magnetic particle flaw detection shall be conducted for welds, and cracks and other defects are not allowed.
3. Anti weld corrosion measures
The welds shall be thoroughly polished, derusted and coated with antirust paint. In the excavation construction site, for the existing corroded welds, manual derusting can be selected according to the actual situation. The disadvantage is that the labor intensity of workers is large and the labor cost is high. Acid pickling can also be used to remove rust, that is, taking organic acid as the main base, combined with corrosion inhibitor, surface active agent, rust remover, rust inhibitor and film-forming agent to prepare an acid pickling solution with the functions of rust removal, rust prevention and primer, so as to achieve the purpose of rust removal and rust prevention through cleaning.
In addition, in the process of use, attention should also be paid to keep the excavator in a clean and dry environment, maintain good ventilation and eliminate corrosive gas and moisture in time.
