Research On Controlled Cooling Performance Of Large Bar

The rapid development of manufacturing industry in our country, leads to the growing demand for the large bar. The bar with a diameter of 50 mm or more is usually referred to the large bar, while below 50 mm is called the wire. Due to large volume and thermal capacity, the temperature change of bar is difficult to be controlled, so cooling control technology has become the mainly limited factor of large bar production. Currently, the Stelmor cooling process is widely used in the world. Developing the temperature control technology, mastering the temperature variation and evolution process of material property during the steel bar rolling process, and enhancing the independent design and innovation capacity is essential for designers.The flow resistance and heat transfer characteristic of the water-cooled jet equipment is the basis of controlled cooling technology of big bar and the basis of cooling system design. In this paper, the physical and mathematic model of flow and heat transfer of in the spray cooling water tank for large bar is established, and the corresponding numerical solution is carried out. Based on a series of working conditions, the flow resistance and heat transfer characteristics of spray cooling water tank is systematically analyzed, also, the influence of nozzle size(diameter and angle) on flow resistance and heat transfer of device as well as the influence of flow rate, pressure,diameter and velocity of bar is investigated. The optimized nozzle parameters are obtained according to the simulation results. The results show that the flow resistance and heat transfer characteristics of cooling water tank in the nozzle section are the key factor to determine cooling capacity. Then, cooling performance test bench is designed and built, and resistance and heat transfer characteristics of cooling water tank in different structures and working conditions is tested. The fitted empirical formula of resistance and heat transfer performance of the spray cooling is modified, which lays the foundation of transient temperature prediction in the cooling process of large bar.Finally, the transient temperature change model in the cooling process of large bar is established, which considers the axial heat conduction in the governed equation. The finite difference method is employed to calculate the transient temperature numerically, and the influence of the correction term on the simulation results is also analyzed. The results show that the ratio of radial and axial diffusion intensity is the criterion of ignoring the axial heat conduction.