The Causes And Control Of Punching Cracks In Galvanized Sheets

The production process of the galvanizing line is: chilled coil → degreasing → continuous annealing → galvanizing → smoothing → drawing straightening → roller coating → induction heating → air cooling → quality inspection → oiling, weighing and packaging. Stamping and cracking defects are easy to appear in its production, which affects the production of users. Analysis of its causes are:

1. Annealing temperature

Annealing temperature is an important process parameter in the galvanizing process, and the annealing temperature has a greater impact on the yield strength of the product. When the annealing temperature is low, the annealing is not sufficient, the grains are fine, the strength is high, and the elongation is low; if the annealing temperature is too high, the grains are easy to be abnormally coarse, and the yield strength decreases while the tensile strength decreases more severely. It is easy to break directly during the stamping and stretching process.

2. Processing lubrication

The surface roughness of the material will affect the oil storage capacity of its surface. The appropriate surface roughness of the steel coil is also very important for the stamping performance of the material. At the same time, the choice of the amount of oil is very important. If the amount of oil is too small, the material will not be sufficiently lubricated during the stamping process, which will cause the material to crack; if the amount of oil is too much, the slitting and forming process will easily slip, which will affect Production rhythm.

3. The material thickness is matched with the mold clearance

During the stamping process of the material, the match between the die gap and the material thickness is also an important factor leading to material cracking

4. Control of defects such as inclusions

Defects such as inclusions and foreign bodies are very unfavorable to the stamping forming of stamping products. Due to the insufficient local elongation of the inclusions, stamping and tensile cracking are easy to occur. According to the above analysis, the following measures can be taken to avoid stamping cracks of the galvanized sheet :

• Set a reasonable annealing temperature for galvanizing, the target value is controlled at about 850℃, and the stability of temperature control needs to be ensured;
• Choose the correct stamping anti-rust oil and give a reasonable amount of oil;
• The rolling force of the finish mill should be controlled above 1200kN;
• The steelmaking process should control inclusions to ensure the cleanliness of molten steel;
• Fully understand the conditions of the molds used to ensure the matching of mold gaps, material deformation capabilities, and material thicknesses.

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