Nóż gazowy jest kluczowym komponentem do kontroli grubości i równomierności powłoki cynkowej. Nowy nóż powietrzny wykorzystuje regulowaną integralną konstrukcję ramy, która może niezawodnie i precyzyjnie wyregulować szczelinę i kąt pomiędzy nożem gazowym a taśmą stalową i wyregulować odległość między nożem gazowym a garnka cynku. Szczelina krawędzi noża może być automatycznie kontrolowana, aby zapewnić stopień jednorodności i jednorodności warstwy powłoki cynkowej.

http://pl.supereal-enterprise.com/galvanized-steel/galvanize...
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Review on Wiping: A Key Process Limiting CGL Productivity Frank E. Goodwin International Zinc Assn., USA Michel Dubois CMI Metallurgy, Belgium ABSTRACT Gas wiping is used to control the thickness of sheet steel galvanized by the hot dip process. After a brief review of the theoretical basis of gas wiping , the weaknesses of the process are reviewed and also the problems of coating uniformity, limited efficiency at high line speed, specific defects generated at low line speed, film instabilities, edge control, noise level and skimming generation. The question of the nozzle design is then addressed including fluid distribution along the nozzle opening, the effect of the internal and external shape on the gas flow and thermal and mechanical stresses that may lead to in line variation of the slot. Finally, new developments including magnetic wiping and multi nozzle designs are described. Directions for future work are proposed

Key words: wiping, nozzle, coating, nozzle design, air knife



A GLOBAL APPROACH OF WIPING The coating thickness evolution is at any point the result of the various forces applied on the liquid film. The viscous entrainment of zinc by the moving sheet as it emerges from the zinc bath is a dominant effect. The higher the line speed or the liquid viscosity, the higher is the amount of liquid entrained. Therefore, to counteract this inherent entrainment, external forces must be applied on the liquid film. They can be either magnetic as it would be with a specific electrical device, or mechanic as in the case of squeegee rolls, aerodynamic as in case a gas knife is used or finally of a friction type such as in wire galvanizing that uses charcoal wiping. Gravity plays a very limited effect due to its relative weak value compared to the other forces. It is only playing a role when the level of the external forces applied is low that is to say in the case of heavy coating, low line speed and eventually liquid with very low viscosity. The total film profile under an air knife as well as the final thickness can be predicted by solving the Navier-Stokes equations (Figure 1). It turns out that it is not the peak pressure of the gas hitting the sheet that generates the wiping force but the maximum pressure gradient and the shear stresses developed on the entrained liquid film. Various physical wiping models have been proposed in literature. They can be used for in-line closed loop control of the coating thickness, although they suffer from some weakness due to simplifications, such as the ignoring the intermetallic layer formed on the sheet, the cooling and oxidation of the liquid between the bath exit and the nozzles, the exact gas profile at the exit of the nozzle for a defined nozzle design, or the inaccuracy of some process data, for example the exact nozzle to strip distance. Neural network models have also been proposed but they suffer from the fact that because the inherent concept of the black box the model may lead to predictions quite far from the physical laws.

(17) (PDF) Review on wiping: A key process limiting CGL productivity. Available from: https://www.researchgate.net/publication/290100511_Review_on... [accessed Apr 09 2020].

https://www.researchgate.net/publication/290100511_Review_on...