Development of Next Generation Wiping Air Knifese

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In continuous hot dip galvanizing, a high speed planar air jet, known as an "air knife", is used on each side of the sheet steel substrate to control the thickness of the zinc coating. The impingement of these jets on the moving steel sheet, after its immersion in a bath of molten zinc, causes the excess molten zinc to be wiped back into the zinc bath. To date, only single-slot jets are used in galvanizing industry and other thermal processing applications such as glass tempering, heating of complex surfaces, cooling of turbine blades and for the cooling of electronic devices. The objective of the proposed research work is to develop new air knife geometries consisting of multiple slot jets, which can be designed to produce specific and desired combinations of pressure gradient and shear stress distribution on the steel sheet and thereby facilitate superior coating weight control for a wide range of galvanizing process parameters. The use of multiple slot jets, instead of a single jet, is also expected to reduce pressure fluctuations on the steel strip which improves the coating quality and its weight consistency and reduces the noise generated by the air knives. It is further anticipated that use of the multiple jet technology will allow lower coating weights to be produced than is currently possible with the single jet technology, thereby overcoming this limitation of the current single jet technology. This Engage proposal deals with the first phase of this project and the requested funding will be used to establish a multiple-slot jet facility and measurement techniques. A versatile test facility consisting of a multiple-slot jet impinging on a plate will be designed, manufactured and commissioned. This initial phase will also include intensive use of Laser Doppler Velocimetry and Particle Image Velocimetry as well as pressure transducers and microphones to establish the experimental techniques needed to investigate the jet development stages, pressure and shear stress distributions on the plate, and the velocity and pressure oscillations on the plate. Upon completion of this project, the applicant laboratory will have the necessary facility to initiate a CRD project with ArcelorMittal (Dofasco) to develop the next generation wiping air knifes.