12th International Conference on Zinc & Zinc Alloy Coated Steel Sheet - GALVATECH 2021

The realisation of economic and ecological aims led to a development of improved structural materials. Third generation Advanced High-Strength-Steels and their application in automotive bodies in white are one example of this trend. Those steels are often processed as thin strips in combined continuous annealing and galvanizing lines and require new heat treatment possibilities to acquire their beneficial mechanical properties with price efficient alloying concepts. Disregarding higher soaking temperatures those heat treatments have high demands on the cooling strategy. Enhanced cooling rates with ideal uniformities over the length and width of the strip are required as well as a good flatness. Most commonly jet impingement gas cooling is used in these lines. The jets are formed using arrays of round or slot nozzles or combinations of both. In this study we present the development of an advanced cooling section in collaboration of a university research institute and an industrial plant manufacturer. A fundamental, experimental study was conducted to find an efficient nozzle design for the application. Efficiency in nozzle design means to reach high heat transfer coefficients per needed fluid power. The experimental set-up enables the measurement of local and integral heat transfer coefficient distributions in near industrial sized nozzle fields. Further the flow properties are continuously monitored allowing both, determination of the design efficiency and the influence of typical nozzle array parameters. Based on the previous investigation a prototype is designed and manufactured. The prototype is then analysed regarding the process limitation strip stability. Strip stability is investigated measuring the strip vibration in a cooling section model. The stability quality is quantified by means of the peak-to-peak value, the minimum and maximum strip displacement within a thirty second interval for a certain flow state. After the successful start-up of the industrial cooling section the experimental results are compared to in-plant measurements to validate the accuracy of the estimations.