Effect of gripping conditions and strip oscillations on vibrations originating at cold rolling

The process of continuous rolling is subjected to non-stationarity, accompanied by oscillations of not only basic technological and power parameters, but also parameters in the hearth of deformation. Non-stationarity at the rolling accounting high dynamic of the process results in origination of negative vibration effects. To prevent the vibrations originations the rolling speed is decreased, which prevents the reaching of the designing parameters of rolling mills operation. The study of influence of non-stationarity of the rolling technological process on gripping conditions and origination of dangerous oscillations was carried out. Characteristics of rolling mode of strip of 2.0–0.45 × 970 mm dimension, accompanied by vibration was presented, as well as graphs of the strip oscillations in the process of stationary rolling and under conditions of vibrations origination presented. An assumption made, that during vibrations origination the gripping conditions of the strip by rollers are disturbed. It means that provision of the grip stationarity will decrease the risk of the vibrations originating at the rolling. The assumption was confirmed by the studies of the cold rolling at five-stand mill 1700 of Cherepovets steel-works. The calculations of the hearth of deformation parameters were made by application of an elaborated dynamic model of the rolling process. The higher probability of vibrations originating at the rolling of strips of smaller thickness explained. It was shown, that due to the strip length, the rolling of the thinner metal is accomplished at higher speeds, comparing with the rolling of thicker metal. In addition, it was shown that the friction coefficient value at that would promote increase of risk of non-stationary rolling mode originating. The support of stable friction conditions in the hearth of deformation is promoted by usage of chrome-plated working rollers and asymmetrical rolling.

Working out of design procedure of sheet metal straightening parameters on roller-type straightening machine in rollers of different diameter

It is installed that non-uniform deviations from planeness of sheet different in magnitude, and also having negative and positive curvature at straightening on the traditional roller-type straightening machine, as rule, are not corrected, as the car has equal diameters of all working rollers which affects on planeness defect of sheet with equal curvature of rollers barrels. Dependences for calculation of roller radius and return bend angle are presented. It is shown that if the return bend angle is equal to initial bend angle of sheet at counter-camber the sheet is completely detected; if the return bend angle is less than initial bend angle of sheet return bend occurs partially, the sheet also is detected partially; if the return bend angle is more than initial bend angle of sheet the sheet is bent towards return bend. Dependences for calculation of powers of the editing spent for alternating bending of sheet, the power spent for friction of rolling motion of rollers on surface of sheet, the power spent for overcoming of frictional force on necks of carrying rollers in roller-type straightening machine with rollers of different diameters. Calculation of power consumption of the main drive electric motor at straightening of sheets from low-alloy steel for 5 —7-roller straightening machines with different diameters of rollers is presented. Difference between calculation results and the experiment data showed, difference makes 10...20 % that testifi es to adequacy of model and about possibility of its practical use for calculations of straightening parameters of sheet products on roller-type straightening machine with different diameters of rollers.

Perfection of a modelling method of cold rolling mill rollers profiling to increase accuracy of rolled strip cross profile forming

Profiling of rollers, apart from the means of inter-rollers gap control, determines the accuracy of rolled strip cross profile forming and their flatness. A number of articles is devoted to the items of rollers profiling modelling. Based on their study a task of development of strip mill rollers profiling modelling methodology formulated. The methodology based on working rollers generating lines building by geometric summarizing of grinding curves, curves of thermal profile and wear profile curves with elastic deformation curves and further elaboration of a perfected profiling of the 2100 mill roller system to provide the quality world level, characterized by δhпоп index. The elastic deformation curves defined by the finite elements method. Results of modelling of convexconcave CVC profiling of cold rolling mill working rollers quoted. The elaborated and adopted to implementation at the 4-high 2100 mill perfected CVC profiling of working rollers presented, which provides increase of accuracy of rolled strips cross profile forming. The solution based on the mathematical description of quarto roller system loading and deformation, accounting the convex-concave CVC rollers profiling and axes shifting of working rollers. Simulation of loads and elastic deformation of the PAO “Severstal” 4- high cold mill roller system accomplished by application of SIMULIA Abaqus program complex. Accounting symmetry of the task, only one roller half-set considered – the upper working and bearing rollers with CVC profiling. The barrel edge slope taken into consideration in the bearing roller model. Application of the new working rollers profiling will increase the efficiency of their axes shifting and hydro-bending during rolling of 900–1300 mm wide strips, which account the main share of the rolled metal at the mill, with the guaranteed provision of the strip cross crown, not exceeding 2% of the nominal thickness.

Temperature Field and Solidification Structure of a Ductile-Cast-Iron Roller

The quality of the working rollers from ductile-cast-iron used for rolling rails is determined by the chemical and structural composition of the material of the rollers and the production technology. The requirements of the quality cannot be ensured without perfect knowledge of the course of solidification, cooling and heat treatment of the cast rollers as well as the kinetics of the temperature field of the casting and mould. An original application of ANSYS simulated the forming of the temperature field of the entire system comprising the casting, the mold and ambient. In the experimental investigation of temperature field, an original methodology for the measurement of the distribution of temperatures and heat flows in the roller-mould system had been developed and verified in the operation. The kinetics of the solidification has a measurable and non-negligible influence on the chemical and structural heterogeneity of the investigated type of ductile-cast-iron. Tying on to the results of the model of the temperature field of the cast rollers, an original methodology was developed for the measurement of chemical microheterogeneity. The chemical and structural heterogeneity of the cast roller is therefore a significant function of the method of melting, modification and inoculation and the successive procedures of risering, casting and crystallization after cooling.