1.What happens when scale and surface quality problems occur during hot rolling? How to solve them?
Problem manifestation: When hot rolling large diameter round bars, thick oxide scale is generated on the steel surface at high temperature, which is closely bonded to the matrix after cooling, resulting in deterioration of surface roughness (Ra ≥ 25μm), and may be embedded in the matrix to form "pitting".
Solution: Online descaling: Use high-pressure water jet to spray the surface during hot rolling to break the structure of the oxide scale in the hot state;
Subsequent treatment: After hot rolling, pickling or sandblasting pressure is performed to completely remove the oxide scale.
2.What are the manifestations of cold working plastic deformation difficulties and work hardening? How to deal with it?
Problem manifestation: When cold drawing or cold bending round bars with a diameter of ≥80mm, the large deformation leads to significant work hardening (yield strength increased by 15-20%), and even cracks.
Solution: Segmented processing: Use the "cold drawing + annealing" cycle process, for example, the deformation of each cold drawing is controlled at 10-15%, followed by recrystallization annealing;
Lubrication optimization: Use a phosphating + saponification composite lubrication layer to reduce the friction coefficient between the die and the steel to below 0.05.
3.What are the symptoms of uneven current distribution during electroplating? How to solve it?
Problem manifestation: The large diameter round rod has a large surface area, and the current density in the center is low during electroplating, resulting in uneven coating thickness.
Solution: Anode design optimization: Use "ring anode" to wrap the round rod, or use a combination of soluble zinc anode and insoluble anode to adjust the current distribution;
Pulse plating: Apply pulse current and use the "tip effect" to balance the coating deposition rate.
4.What are the manifestations of zinc liquid flow resistance during hot-dip galvanizing? How to solve it?
Problem manifestation: When a round rod with a diameter of ≥60mm is immersed in zinc liquid, the large cross-section causes a large amount of zinc liquid to adhere to it. When the rod is lifted, the excess zinc liquid flows slowly, which is easy to form "zinc nodules".
Solution: Rod lifting speed control: set the rod lifting speed according to the diameter;
Vibration assistance: apply mechanical vibration during the rod lifting process to destroy the surface tension of the zinc liquid and reduce the formation of zinc nodules.
5.How does tool overheating during high-speed cutting behave?
Problem manifestation: When cutting large diameter round bars, the cutting volume is large, and the temperature of the tool (such as carbide blade) can reach over 600℃, causing the blade to crack.
Solution: Upgrade tool material: Use ceramic tools or CBN tools, which have a heat resistance temperature of over 1200℃ and can increase the cutting speed to 800m/min;
Optimize cooling method: Use high-pressure internal cooling cutting fluid, which is directly sprayed into the cutting area to reduce the tool temperature by more than 30%.