Anyone who operates an excavator knows that the bucket tooth is an accessory of the excavator. During excavator operations, the bucket tooth is relatively easy to break. Once a large stone is dug, the bucket tooth will probably break accidentally. Therefore, the first step must be to find a way to repair it, usually by re welding the bucket tooth to the bucket body. Welding bucket teeth is not a simple task. Here is also a test of the welding skills of the repairman. Here is how to correctly weld the bucket teeth firmly, so that welding the bucket teeth of the excavator can be done for more than a year without any problems!
1. The welding site must be cleaned before welding.
"It means removing the original cracked solder joint and grinding it with an alternating phase polishing machine or using carbon arc air gouging if conditions permit, but after gouging, the iron oxide must be polished clean"
2. Before welding, certain preheating should be carried out.
If possible, it is also necessary to preheat the welding position by 100 degrees. Then use a 3.2J507 welding rod to weld. After a while, stop welding and tap the weld and its edges with a hammer. After complete welding, continue to tap with a hammer until the weld is basically cooled. The purpose is to release welding stress, as it is not possible to perform heat treatment after welding.
3. Suitable welding materials must be selected for welding.
The type of welding rod is important. "If you want to understand what material is, you need to take some iron foam for testing. Once tested, it will come out, and then match electrodes according to their composition.".
4. Welding between bucket body and bucket tooth of excavator must ensure full penetration
During welding, it is necessary to ensure full penetration. If the gap between the weld positions is large, a back plate can be added inside.
2、 Excavator Bucket Materials and Their Weldability
The bucket material of wY25 excavator is Q345, which has good weldability. The bucket tooth material is ZGMn13 (high manganese steel), which exhibits a single-phase austenitic structure at high temperatures and has good toughness. Under impact load, it has high wear resistance due to work hardening of the surface layer. However, this kind of steel has poor weldability: Firstly, carbide precipitation in the welding heat affected zone causes material embrittlement; The second is that the weld produces thermal cracks, especially liquefaction cracks in the vicinity of the weld.
1. Embrittlement caused by carbide precipitation in the heat affected zone
When ZGMn13 high manganese steel is reheated at more than 250 ℃, carbide may precipitate along the grain boundary, greatly reducing the toughness of the material, and seriously damaging the excellent properties of high manganese steel. According to analysis, when the high manganese steel is reheated and cooled quickly, the carbide first precipitates at the grain boundary. With the extension of residence time, the grain boundary carbide will change from a discontinuous particle state to a network distribution, and its brittleness will significantly increase. Therefore, when high manganese steel is reheated after welding repair or welding, carbides will precipitate to varying degrees in a section of the welding heat affected zone and may transform into martensite, not only making the material brittle, but also reducing its wear resistance and impact toughness. Moreover, the longer the residence time within the temperature range (around 650 ℃) where carbide is easily precipitated in the heat affected zone, the more carbide precipitates.
In order to reduce the precipitation of carbide and prevent the material from losing its toughness and becoming brittle, measures should be taken to accelerate its cooling rate, that is, shorten the residence time at high temperatures. Therefore, when welding the bucket body and bucket teeth of an excavator, short welding, intermittent welding, and water immersion welding should be used.
2. Welding hot cracks
The way to prevent thermal cracking is to reduce the content of S and P in the base metal or welding material; Measures can also be taken from the welding process to minimize welding stress, such as using short section welding, intermittent welding, scattered welding, and post weld hammering. When surfacing high manganese steel on the bucket body, a layer of Cr-ni, Cr-ni-Mn, or Cr-Mn austenitic steel can be welded as an isolation weld bead to prevent cracks.
3、 Welding process for bucket body and bucket tooth of excavator
1. Preparation before welding
First, cut off the worn bucket teeth from the bucket body, and then use an angle grinder to polish the installation bucket teeth clean, free of dirt and rust. Carefully check for defects such as cracks; Use carbon arc air gouging to make a groove at the position of the bucket tooth to be welded, and clean it with an angle grinder.
2. Welding
① Firstly, use GBE309-15 welding rod for surfacing welding on the bucket body (the joint with the bucket tooth). Before welding, the welding rod should be dried at 350 ℃ for 15 hours. The welding current should be relatively high and the welding speed should be slightly slow to ensure that the nickel content in the fusion zone is 5% to 6%, preventing the formation of martensite sensitive to cracks.
② Perform tack welding. After the bucket teeth are assembled in place, use a D266 electrode with a diameter of 32MM to perform symmetrical tack welding on both sides, with a weld length not exceeding 30MM. Immediately after welding, water cool and hammer.
③ Backing welding. Use a D266 electrode with a diameter of 32MM for backing welding. Use small current, DC reverse polarity, intermittent welding, short section welding. Each time welding is stopped, water cooling should be carried out in a timely manner, and the interlayer temperature should be controlled below 50 ℃.
④ Perform a fill weld. After the bottom welding is completed, use a D266 welding rod with a diameter of 4MM for intermittent welding. The welding current is 160A. One welding rod is welded in 3 to 4 times. When stopping welding each time, it is still necessary to cool the weld bead to below 50 ℃ with water in a timely manner, and hammer it to eliminate stress and prevent carbide precipitation; After each two layers of welding are completed, rotate the left and right welds to ensure the symmetry of the welding until the weld leg reaches 16MM. After each welding pass, use a magnifying glass to inspect the cracks. If there are cracks, use carbon arc gouging to eliminate them before welding.
After welding the bucket teeth of the excavator through the above steps, the welds are still intact after more than a year of use. This method of repairing the bucket teeth has high efficiency, low cost, and good results. Not only can the repairman be familiar with it, but also it is worth learning from the excavator drivers to prevent unexpected needs and ensure the normal operation of the work.