1. For shrinkage and crack defects around the shaft hole
For defects such as shrinkage and cracks around the shaft hole, adjust the position of the riser and extend the length of the neck of the riser. After casting, timely add heating agent to the top of the riser. Reduce the probability of casting defects occurring at the main load-bearing positions of the front support steel castings. After rough machining of the shaft hole and end face, each piece is subjected to ultrasonic testing to detect internal defects in important parts of the front support steel casting, and magnetic particle testing to detect surface defects and microcracks in the inner hole.
2. For coarse grains and Weinstein structure
For coarse grain size and Weinstein structure, the normalizing insulation time has been changed from 2 hours to 3 hours calculated based on the normalizing economic insulation coefficient. Considering the thick wall at the fault location, the production process of steel castings has been adjusted to include molding, melting, casting, unpacking, sand cleaning, rough machining of holes and end faces, heat treatment (normalizing), inspection. The initial machining of the shaft holes is followed by heat treatment to reduce the wall thickness at the holes, significantly improve the surrounding structure of the shaft holes, and refine the grains. At the same time, strengthen the quality monitoring of the heat treatment process to ensure the consistency of product quality.
3. Improvement effect
After improvement, the chemical composition, mechanical properties, and metallographic structure of the sample body of the front support steel casting were inspected, and the test results all met the technical requirements of the boom front support steel casting. After tracking the batch installation market, there was no feedback of fracture failure during the 8000 hour working time of the excavator.