Study Of Micro-Dimensional Dynamic Cross Behavior Mechanism Of Four-High Mill And Its Control Method

The four-high mill is the most commonly used type for production of foil and extremely thin strip, even heavy and medium plate. The length of its production is tremendous, and maybe a few hundred circles of earth or moon. The modern four-high mill has a tendency to become more precise and have a higher speed. Especially for aluminium foil mill, the high production speed is the only one. At present, the thin strip cold rolling four-high mill with 2000m/min speed is developed in Japan. The 2200mm aluminium foil four-high mill with 2000~1800m/min speed, which is developed by English Davy company, is now inputting test run. One of these, which have 1800m/min rolling speed, is used in domestic. But the double rows angular contact end thrust bearing of work roll happens longevity-shortening and burning accidents frequently. It is force to run at half design speed to maintain production. The mill is only used half production ability. This is the bottleneck of the mill to realize high speed rolling. According to mechanics, mill design and rolling theory, the rolls of four-high mill with high speed will keep parallel because of offsetting and the axial force should be small. More than ten doctor dissertations about axial force only give an axial model derived from pre-displacement, which has a bad practicability. The model cannot answer the end thrust bearing longevity-shortening problem, and reduces it a random phenomenon. This paper focus on 2200mm aluminium foil four-high mill end thrust bearing longevity-shortening and burning problem. After a serious experiments being carried out and numerical analysis being taken, the micro dimensional dynamic cross phenomenon of four-high mill is found at last. The theory of gyroscopic precession and thermal expansion opposite dynamic cross is set up. And a new method that can prevent the end thrust bearing longevity-shortening and burning accidents is given out, so the bottleneck of the mill high speed rolling can be removed. The paper has 7 chapters. The first chapter is introduction of problem of four-high mill high-speed technology reform. In the second chapter, the development of the on site test device of four-high mill axial force is introduction. In the third chapter, the data of 9 experiments is shown and the effect that the cross-angle and rolling speed applies on the axial force is analysis. In the fourth chapter, the mechanism of gyroscopic precession micro dimensional dynamic cross behavior is explained. The fifth chapter focus on the effect resulted by thermal deformation. In the sixth chapter, a new fit equation about axial force, which has the speed factor, is given out. In the seventh chapter, the method that has ability to prevent dynamic cross and its main structure is given out. The found of gyroscopic precession and thermal expansion micro dimensional dynamic opposite cross behavior and discussion of its mechanism will renew the theory of offsetting force restraint and random phenomenon of four-high mill and push forward the high speed technology reform process of every kind four-high mill certainly. These researches have important guidance for creation of new type four-high mill with ability to prevent dynamic opposite cross, and also large economic value.