A Method for Repairing the Rotating gear ring of an excavator

During the operation of the excavator, the rotating gear ring bears a large impact load. When the excavator tilts, the force state is even more unfavorable. When a general excavator has been in operation for about 350,000 hours, the teeth of the rotating gear ring may be crushed or broken. The wear and breakage of the tooth profile at the junction of the two halves of the gear ring are particularly severe. Practical experience has shown that using insert welding to repair the rotary gear ring is not only simple and fast but also ensures the overall performance of the machine.

1. Pre-welding preparation

(1) Based on the damage condition of the gear ring, determine the position of the fixed hole and the damaged section that needs to be replaced, and then cut off the section of teeth to be replaced with gas cutting.

(2) According to the part of the gear ring that needs to be repaired, process and fabricate the insert, or from the corresponding part of another old gear ring, under the condition of ensuring the pitch, cut out a relatively intact section of the gear teeth, and gas cut out the bevel shape at the connection.

(3) Determine the position of the fixing holes for the inserts, drill holes to fix them at the corresponding parts of the gear ring, and pay attention to ensuring the accuracy of the fixing hole positions.

(4) To ensure that the weld seam has high strength and can withstand significant impact and vibration, a 507 electrode with a diameter of Φ 4mm is selected. Before use, the electrode should be baked at a temperature of 250 to 350 ℃ for 1 hour.

(5) The AX3500 DC arc welding machine is used for DC reverse connection welding, with A current of 130 to 140 A.

2 Welding process

(1) Preheat before welding. Use two large gas welding torches to heat the welding surface to about 200 ℃.

(2) By using the tempering weld bead method, the subsequent weld seam can temper the previous one, which is conducive to eliminating the hardened structure produced in the previous weld seam.

(3) Due to the large bevel, when welding the first weld seam, it should be welded slightly thinner to reduce the weld width and decrease the carbon content of the steel. When welding, tilt the electrode forward by about 15° and move it in a straight line. When ending the arc, make sure to fill the arc pit to avoid arc pit cracks. After welding, quickly strike the weld seam and both sides with a pointed small hammer to relieve the stress until the weld seam is densely covered with pockmarks. Continue welding when the weld seam cools down to about 200 ℃.

(4) The welding method for each subsequent weld seam is the same as that for the first one. The electrode can be slightly swung, but to avoid porosity, it should not be swung too much.

(5) After welding, to eliminate hardened structures and stresses, heat the weld seam and both sides to approximately 600 to 650 degrees Celsius with an oxygen-acetylene flame, hold for 20 minutes, and then cover the weld seam with asbestos, slaked lime powder or dry sand to allow it to cool slowly to room temperature.

(6) Use a polishing grinding wheel to smooth and polish the weld seam. At this point, the repair of the gear ring is completed.

3 Conclusion

The segmented insert block process is used to repair the gear ring. The process is simple, the technical requirements are low, the repair time is short, and the quality of gear ring repair is high. The service life of the gear ring repaired with old inserts is about one third of that of the new gear ring. The service life of the gear ring repaired with newly processed inserts is comparable to that of the new gear ring. This method can be adopted to repeatedly insert blocks into the gear ring, with significant economic benefits.