The pin sleeve at the connection between boom and stick was cracked due to the long-term use of crushing hammer in a tire hydraulic excavator. This leads to cracks in the steel plate at the lower part of the pin sleeve. If the crack is welded directly, small welding cracks will occur at the stress concentration part. Therefore, we summarized a method in practice, which can effectively prevent cracks, for reference only.
The weld shall be treated, stiffeners shall be set, electrodes and welding machines shall be reasonably selected, and necessary welding quality assurance measures shall be taken in the welding process.
1. Weld treatment
Firstly, clean the oil, paint and rust at the original weld cracks with diesel, find all the cracks, and correct the deformed parts. Secondly, the hardened area of the weld and the parts of small divergent cracks shall be cut off with an oxygen acetylene flame cutter to expose the pin sleeve and steel plate material. Finally, polish the weld with an angular grinder, and grind the weld into a single-sided V-shaped groove.
2. Set stiffeners
The thickness of the steel plate at the connection between the boom and the pin sleeve is 10mm. In order to firmly connect the steel plate and the pin sleeve, stiffeners are added at the connection between the two. Cut 3 pieces with the size of 50mm with the oxyacetylene flame cutter × 30mm × 10mm steel plate, and then polish its edge with a grinder as a stiffener plate for standby.
3. Select welding rod and electric welding machine
Select carbon steel electrode of specific model to meet the requirements of welding strength. Before use, the welding rod shall be baked at 350 ℃ for 2h, insulated at 100 ℃ and taken at any time. In order to reduce air holes and spatter, the reverse connection method of DC welding machine is selected. Set the welding current to 125 ~ 140A.
4. Welding method
First, extend the piston rod of the stick cylinder to the longest position, and then place the excavator stick on the ground to reduce the stress on the pin sleeve during welding. Then preheat the welding part to 150 ~ 250 ℃ with oxygen acetylene flame torch. Secondly, weld the weld between the pin sleeve and the boom. If the weld is higher than the boom plane, grind the higher part with an angular grinder. Thirdly, spot weld three stiffener plates on one side of the pin sleeve with a spacing of 30 °. The stiffener plate is closely attached to the boom steel plate, and the distance from the pin sleeve is 10mm. All welds shall then be welded. Sectional, symmetrical and backward welding method shall be adopted. In order to avoid pits and slag inclusion in the weld, continuous welding shall be carried out. The weld between pin sleeve and boom steel plate shall not be less than 3 layers, and the weld height shall be 15mm. Then weld the weld at the connection between the stiffener plate and the pin shaft sleeve. Finally, remove welding slag, welding spatter and weld bead. Grind the protruding welds with weld reinforcement greater than 2.5mm with an angular grinder, and grind all welds smooth. Then check the weld to confirm that there are no cracks, pores, slag inclusion and other defects in the weld.
5. Deformation and crack control
In order to prevent welding deformation, each time the welding is stopped, the weld bead shall be cooled to below 50 ℃ with water, and the weld shall be hammered with a small hammer to eliminate the welding thermal stress. During the use of the excavator, the operator shall add grease to the pin sleeve to make the pin sleeve and the pin shaft run in quickly, so as to improve the service life of the pin shaft and the pin sleeve and prevent the pin sleeve from tearing again.
