Control of speed modes of heavy-plate mills rolling.

Control of speed modes on heavy-plate mills is one of the factors that determine the efficiency of the rolling process. The choice of speed controls influences the mill productivity, geometric dimensions of the rolled product (longitudinal thickness variations) and compliance with the set temperature mode which determine the mechanical properties of the rolled product, etc. The article considers the limitations in the choice of speed controls which can be divided into two groups: limitations of the capabilities of rolling engines and technological limitations. The first group is determined by the allowable engine under the conditions of reliable current switching on the collector and the maximum allowable engine speed. Technological limitations of speed controls are considered in the paper as well. The speed of grasp is limited to the maximum un-der the condition of metal grasp without skew, blows and dynamic torque overloads in spindles and maintenance of constant grasp without slipping, as well as the possibility of prevention of emergencies. Steady (maximum) rolling speed can be limited to the maximum by the conditions of rolling stability and prevention of sticking of metal to the rolls. The rate of metal release from the rolls is usually chosen in the way so that the pause stipulated by the braking of the sheet on the roller conveyor and its subsequent return to the rolling mill would not exceed the operating time of the pressure mechanism. In some cases, the release rate can be determined by other technological operations. The maximum acceleration of the main drive of the horizontal mill is limited by the conditions of slipping of the working roll towards the sup-port roll. The paper also considers rational speed graphs of rolling on heavy-plate mills. They are the most common type of high-speed rolling graphs on heavy-plate mills. The listed above solutions for the control of high-speed rolling modes can be used in the development of APCS of heavy-plate mills rolling.

The Effects of Reduction and Thermal Treatment on the Recrystallization and Crystallographic Texture Evolution of 5182 Aluminum Alloy

During forming, thickness reduction and thermal treatment affect the recrystallization and evolution of the crystallographic texture of metallic materials. The present study focuses on the consequences of rolling reduction of a widespread aluminum alloy with numerous automotive, marine and general-purpose applications, namely Al 5182. Emphasis is laid on the crystallographic texture and mechanical properties on both hot and cold-rolled semi-final products. In particular, a 2.8 mm-thick hot-rolled product was examined in the as-received condition, while two cold-rolled sheets, one 1.33 mm and the other 0.214 mm thick, both originating from the 2.8 mm material, were examined in both as-received and annealed (350 °C for 1 h) conditions. Electron back-scatter diffraction indicated the presence of a large percentage of random texture as well as a weak recrystallization texture for the hot-rolled product, whereas in the case of cold rolling the evolution of β-fiber texture was noted. In addition, tensile tests showed that both the anisotropy as well as the mechanical properties of the cold-rolled properties improved after annealing, being comparable to hot-rolled ones.

Elaboration of a mathematical model of parameters calculation for section bars leveling at a roller leveling machine

During rolling and cooling at cooling beds, section bars get general and local curvatures, to correct which, leveling at roller leveling machines (RLM) is used. Calculation of leveling parameters of section bars at RLM is based on hypothesis of isotropy and homogeneity of the deformed metal. Besides the calculation is based also on assumptions of a linear distribution of penetration coefficient of plastic deformation along the rolled product thickness at alternating bending, point character of roller and rolled product surface contact, vertical direction of leveling force for all rollers of RLM. Application of those hypothesizes considerably deteriorates the accuracy of technological parameters calculation for rolling and leveling operations. A mathematical model presented for leveling parameters of section bars at RLM calculation. The novelty of the model is an accurate determination of the border between elastic and plastic zone Z0, which is accomplished by an iterative method. The information about exact value of Z0 is necessary for calculation of stress distribution along the piece section, as well as sag and curvature calculation after the leveling. In traditional models the Z0 value is determined approximately and does not meet the today’s requirements. Stress distribution diagrams along the rolled product section at bending under RLM rollers presented for rectangular, square, channel, Z-section profiles of rolled products, as well as for I-beam and rail, necessary for calculation of residual stresses. The comparison was done of P65 rail sag in the plane of maximum rigidity at the six-roller RLM of Kuznetsk steel-works and their value, obtained by the mathematical model application. The discrepancy between actual and calculated data is only 4.5%, which speaks about conformity of the elaborated mathematical model.

Effect of the Production Conditions of Continuously Cast Steels on the Degree of Hot Rolled Product Downgrading

Nowadays, quality development is a growing challenge, which places a heavy burden on economic operators, especially on smaller companies. ISD Dunaferr Zrt is the largest steel company in Hungary with its annual steel production of about 2 million tons, but it is small on a global scale. Taking advantage of the opportunities, locating the hidden problems, qualitative development and productivity enhancement can be realized without major investment. This study points out the steel production and casting parameters that have the greatest impact on the quality of the hot rolled product (sheet and coil) and touches upon the effect of rolled product final thickness on the ratio of downgrading. As a result the examination of overheating shows correlation with the ratio of downgrading, but the age of the mould does not. Regarding the thickness of the rolled product, it can be stated that in the case of thicker products (above 9 mm) the ratio of downgrading increases.

Transformation of cross cracks of continuously casted billet in rolled product

Increased requirements to the surface quality of hot-rolled products used in automobiles manufacturing and endeavor to decrease t rejections of the metal with surface defects, stipulate the necessity to increase the quality of the initial continuously casted billet (CCB). Cracks, formed in the process of crystallization, which are transformed into surface defects of rolled products during hot deformation are attributed to the surface defects of CCB. Classification of defects presented, reasons of cross cracks on CCB and their locations considered. In the course of the experiment the samples, cut from two CCBs in the place, where cross cracks were visually revealed after shot blasting and hot etching in the 50% solution of chloric acid. The cross cracks on the surface of a sample were revealed in the zone of the big side, and the other – on a rib. The longitudinal polished sections were cut from the place of cross cracks location. At the study of the polished sections multiple cracks were discovered. The width of cracks opening was different – from 0.01 up to 0.3 mm, depth in the section of the study – up to 10 mm. The locations of the cross cracks on the billets were marked by notches from two sides (method of “marked” defects). After that the billets were rolled at a one-stand reversible mill 850 for the diameter of 100 mm. At the visual inspection of the rolled product surface, obtained from the defect CCB, surface defects in the form of discontinuity flaws were discovered. The discontinuity flaws looked as metal ruptures of longitudinal and cross orientation and sometimes having a form of tongue. The degree of defects development depends on the depth and the crack location on the initial CCB. The defects which location corresponds to the CCB side have less opening, and defects which location corresponds to the initial billet rib looked as a rough fissure. Cross samples were cut in the places of defects locations on the surface of rolled product for metal science study. At the cross polished sections the defect cavity have several branches, the cavity walls are twisting, around the cavity branches and next to them, aggregation of small globular oxides and massive decarburization were observed. The defects of rolled products surface were classified as rolled-out cracks (cross orientation). The cracks depth in the section under study was 0.6–3.5 mm. Based on the results of the study the surface defects of rolled products were properly classified and reasons of their arising revealed, that will allow avoiding their formation in the future. Based on the proper classification and avoiding of the surface defects reasons, the rolled products rejects by surface defects will be considerably decreased.