Defects in welding of galvanized steel pipe is mainly: thick edge, zinc, steel leakage defect layer falls off the three.
1, the thick edge
Specifications thick hot rolled plate, strip running speed is low, when the hot-dip galvanized steel strip edges than in the central zinc zinc layer thickness occurs when the thick edge defects. Coiling the strip such defects particularly harmful, edge thickness, after a roll diameter of the tape roll edge will be greater than the central diameter, rim diameter, tensile stress is generated, so that the side portion easily stretched, and then forming wave edge defects. Strip defects formed under high-speed operation for high-speed thick, low defect formed under low-speed thick edge. A high thick edge knife mainly due to the angle adjustment of the gas is poor, resulting in the blowing, and the formation of turbulence generated. Appropriate adjustments to the air knife angle to fix this flaw. Mainly due to the low thickness B-side heat dissipation rate of the low-side portion, and the outward flow loss across the nozzle part, thus reducing the impulse flow edge, resulting in the middle than zinc scraping edge is small, so the formation of low thickness edges. Address this manufacturing defects, can be installed in addition nozzle strip edge to increase the air pressure of the strip edge. Also used on both sides of the strip removable baffle eliminates low thick edge defects.
2, Breakout defects
In order to reduce costs and increase steel strength, typically higher in the steel base is added elemental silicon. Resulting in an excess of silicon surface tension increases, reducing the wetting liquid zinc plate capacity, increasing the possibility of leakage of plating. In addition, silicon is easily oxidized to form SiO2, is not easily removed in acidic and thus easily formed on SiO2 breakout defect gathering region. This problem-free pickling hot-rolled steel strip continuous hot-dip galvanizing process solutions. Pickled hot strip without directly into the reduction furnace, and the strip in the reduction furnace temperature was raised to 650-750 ℃, holding time increased to 120-400s. H2 shielding gas volume fraction increased to 20%. At this time, hot rolled strip volume expansion due to oxidation skin cracks and voids, H2 can enter through these cracks and voids, the oxide of Fe and FeO into a pure form by a porous layer. In the hot-dip galvanizing, the surface to form Fe-Al-Zn alloy layer to improve adhesion of the coating to eliminate defects breakout.
3, the zinc layer off
No oxidation furnace gas heating value due to the low pressure fluctuations and other reasons that appear oxidizing atmosphere, resulting zinc layer off. This can be taken: choice excellent combustion performance of the gas burner; the air, the gas pressure is maintained at a predetermined range; gas heating value fluctuation range is less than ± 5%; flame furnace heating zone above 1000 ℃; without burning mouth preheating furnace above 800 ℃; strip out non-oxidizing furnace temperature below 650 ℃.
Post time: Oct-18-2019