After 9 years of use of the QT16 tower crane, the tower body could not be turned over during the construction process. When the speed reducer was disassembled, it was found that there were many cracks, wear and falling on the second stage cycloidal pin wheel of the reducer. Due to the lack of spare parts, it was decided to repair by welding.
1. Solderability analysis
The cycloidal needle wheel is made of GCr15, which has high carbon content, large hardening tendency, easy cracking and S and P segregation, high thermal cracking sensitivity and poor weldability.
2. Repair welding measures
(l) Elimination of cracks According to the crack shape, depth and length, the grinder is used to eliminate shallow and short cracks, and then to eliminate deep cracks. The grinding sequence starts from the crack tip until the crack is removed to prevent the crack from spreading while grinding the groove. For unsplit cracks, the bottom of the groove is smoothly transitioned to reduce stress concentration; for cracking cracks, a single V-shaped groove is opened.
(2) The repair welding process corrects the cracking crack so that the surface is in a plane and spot welding is fixed. The repair welding sequence is to weld short and shallow cracks first, then weld cracks and cracks, and finally weld the defect to the original shape.
When repairing short and shallow cracks, pay attention to the arc from the tail of the crack to prevent cracks during the welding process, weld by spot, and observe while welding. Through the first crack repair welding observation, no crack phenomenon occurred, and no new crack appeared, which proved that the welding process was feasible.
When repairing cracks and cracks, the sand must be thoroughly cleaned before the back welding to reveal the metallic luster.
For wear and defect parts, oil and rust should be removed first and then repaired.
(3) Welding specification parameters Because the parts require good wear resistance and high precision, but the weldability is poor, stainless steel welding rods with good crack resistance, wear resistance and machinability are selected as filling materials. Its grade is A307, the specification is ¢3.22mm, it is baked to 350°C for 2h, the welding current is 90-100A, the welding voltage is 20-22V, and the welding line energy is 8-12kJ/cm. The welder is AX-320, reverse connection.
(4) Post-weld treatment The whole part is heated and cooled slowly after welding. After cooling to room temperature, the upper lathe is machined on two planes, and the excess surfacing metal at the edge is trimmed with a file until the cycloidal needle wheel returns to its original geometry.
3. Effect
The cycloidal pin wheel has been used since its repair for more than 5 years, and its performance is good. It fully meets the requirements for use and saves maintenance costs.
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