Development of a bench-scale liquid metal wiping pilot system for understanding and optimizing the jet wiping process during hot dip galvanizing

在热镀锌的情况下，在连续运动的钢带上涂上一层薄薄的锌，以防止氧化。保护金属在其液态下，通过将基材浸入涂层浴液中来施加。然而，在普通的带钢速度下，由移动的纸幅拖曳的液体层太厚且不均匀，不适合所考虑的应用。因此，最终的涂层厚度由气刀控制，气刀将二维高速气体射流冲击到液层上。气刀射流在液体中施加的力导致向下形成向下到熔池的Runback流，从而在基材上留下更均匀和恒定的涂层厚度。尽管如此，操作限制和工艺参数变化仍可能导致显著的涂层不均匀和过量锌消耗。这项研究计划将专注于开发一种试验台规模的镀锌试验台，其中将使用低熔点液态金属作为锌的模拟物，并将旋转皮带布置与气刀相结合，以更详细地可视化喷射擦拭过程。在申请人的实验室开发的最先进的成像技术将用于可视化擦拭过程，涂层波纹度和解决策略将被提出，以优化擦拭系统的工艺参数和气刀设计。热镀锌生产线存在的问题较多，难以满足市场需求。该项目的成果有望帮助像AM Dofasco这样的镀锌带钢生产商确定和控制最佳的涂层性能，使他们能够获得最高的生产率，同时获得高质量的带钢和所需的产品质量。正确理解喷射擦拭工艺及其对镀锌产品质量的影响，对热镀锌的商业化有着深远的影响。根据目前对这一工艺优化和生产率提高(由AM Dofasco热镀锌线表示)的兴趣，这项研究的结果预计每年可产生600万美元的经济影响，在该项目完成后的五年内可转化为3000万美元

In the case of hot-dip galvanizing, a continuously-moving steel strip is coated with a thin layer of zinc in orderto resist to oxidization. The protective metal is applied in its liquid state, by dipping the substrate into a bath ofcoating. However, at common strip speeds, the liquid layer dragged by the moving web is far too thick anduneven for the applications considered. The final coating thickness is therefore controlled by an air knife,which impinges a two-dimensional high-speed gas jet on the liquid layer. The forces imposed in the liquid bythe air knife jet results in the formation of a runback flow down to the bath, leaving a more uniform andconstant coating thickness dowsntream on the substrate. Nevertheless, operational constraints and processparameter variation can still result in significant coating non-uniformity and excess zinc consumption. Thisresearch program will focus on developing a bench scale galvanizing pilot where a low melting point liquidmetal will be used as an analogue to zinc and a rotating belt arrangement will be combined with an air knife tovisualize the jet wiping process in more detail. State of the art imaging techniques developed at the applicant'slaboratory will be used to visualize the wiping process, coating waviness and solution strategies will beproposed for optimizing the wiping system in terms of process parameters and air knife design. With manyexisting problems at the hot dip galvanizing lines it is difficult to meet the market demands. The results of thisproject are expected to help galvanized strip producers like AM Dofasco to determine, and control theoptimum coating properties that will allow them obtaining the highest productivity and simultaneously achievehigh quality strips with desired product quality. Proper understanding of the jet wiping process and itsinfluence on galvanized product quality has profound impacts on the commercial aspects of hot dipgalvanizing. Based on the current interests in this process optimization, and enhanced productivity (expressedby AM Dofasco hot dip galvanizing lines), an economic impact of $6 million /year is expected from the resultsof this research, which translates to $30 million within five years after completion of this project