2 Welding process Before welding, use two large-scale gas cutting guns to preheat the flange and valve body parts. Use the model HY-302A electric shock thermometer to test the flange surface temperature, preheat to 350 ~ 400C, and when welding. Ensure that the temperature between the layers is greater than 350C. After the welding, post-heat treatment of the welding site is performed to more than 400°C. The entire valve body is tightly wrapped with asbestos cloth and fire-resistant rock wool to make it cool.
During welding, a symmetrical welding sequence is used in the circumferential direction to control the welding deformation. In the case of partial welding, the meat is first fluted on both sides of the groove, and welding is performed from the two sides to the middle portion to prevent welding cracks and peeling of the welding meat.
The welding rod must not oscillate when welding. When the flesh on each side of the groove is long, the layers are welded and then pushed to the middle. Between the layers must be cleaned with an angle grinder. If slag, air holes, cracks, and other defects are found, they must be removed before welding to avoid affecting the welding quality.
When installing on site, apply a layer of oil leaching on the flange sealing surface and the asbestos mat (mixing lacquer with talcum powder) to ensure that no welding cracks on the flange sealing surface are bonded and sealed.
3 post-weld inspection inspection weld surface quality, no slag inclusions, pores, cracks and other defects. Check the flatness of the flange sealing surface to meet the structural requirements. Remove the copper rod and check that the inner wall of the bolt hole is continuous and smooth.
4 Conclusion After the cast iron valve was repaired, it has been installed for two years and no flange cracking and leakage have been found. This process can replace the traditional full penetration and eliminate the full cracking process requirements in special circumstances, while reducing the welder's labor intensity, improve the economic efficiency, meet the project quality requirements and gain valuable time.
(2004 01 12): Xu Shixiong was born in 1969, a welding engineer.
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