STRUCTURAL INVESTIGATION OF A HIGH-CHROMIUM MATERIAL USED AS AN EXTERNAL, WORKING LAYER OF A BIMETALLIC MILL ROLLER

The bimetallic mill roller has been produced by the method of vertical axis centrifugal casting. The processes, accompanying the formation of the structure of the external (working) layer from high chromium material of the bimetallic roller have been investigated. A mathematical model for the geometry of the working layer was created. By using the MAGMA Soft software package, simulations of the processes of casting and crystallization have been made. A metallographic assessment of the microstructure has been made.

STRUCTURAL INVESTIGATION OF THE INTERMEDIATE LAYER IN A BIMETAL MILL ROLLER PRODUCED BY THE METHOD OF VERTICAL AXIS CENTRIFUGAL CASTING

Subject of the investigation is a bimetallic mill roller with external, working layer from high chromium material and inner, supporting layer from ductile cast iron. The processes, accompanying the formation of a transition layer in bimetallic castings, produced by centrifugal casting have been investigated. Attention has paid to the structural changes in the transition zone, caused by the diffusion processes occurring during the casting and crystallization.

Determination of Rolling Mill Roller Load during Procurement Transportation

The paper shows how to calculate the loads on conveyor rollers at different positions of the conveyed billet. It also contains the diagrams of conveyors with different types of drives and loading diagrams as well.

Internal Cracks and Non-Metallic Inclusions as Root Causes of Casting Failure in Sugar Mill Roller Shafts

The sugar mill roller shaft is one of the critical parts of the sugar industry. It requires careful manufacturing and testing in order to meet the stringent specification when it is used for applications under continuous fatigue and wear environments. For heavy industry, the manufacturing of such heavy parts (>600 mm diameter) is a challenge, owing to ease of occurrence of surface/subsurface cracks and inclusions that lead to the rejection of the final product. Therefore, the identification and continuous reduction of defects are inevitable tasks. If the defect activity is controlled, this offers the possibility to extend the component (sugar mill roller) life cycle and resistance to failure. The current study aims to explore the benefits of using ultrasonic testing (UT) to avoid the rejection of the shaft in heavy industry. This study performed a rigorous evaluation of defects through destructive and nondestructive quality checks in order to detect the causes and effects of rejection. The results gathered in this study depict macro-surface cracks and sub-surface microcracks. The results also found alumina and oxide type non-metallic inclusions, which led to surface/subsurface cracks and ultimately the rejection of the mill roller shaft. A root cause analysis (RCA) approach highlighted the refractory lining, the hot-top of the furnace and the ladle as significant causes of inclusions. The low-quality flux and refractory lining material of the furnace and the hot-top, which were possible causes of rejection, were replaced by standard materials with better quality, applied by their standardized procedure, to prevent this problem in future production. The feedback statistics, evaluated over more than one year, indicated that the rejection rate was reduced for defective production by up to 7.6%.

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.

Failure Analysis and Research Progress of Resurfacing Welding Material of Coal Mill Roller

Failure mode of coal mill roller was comprehensively analyzed and current situation of mill roller repair was elaborated. Process characteristic and application effect of metal cerement and high chromium cast iron building-up materials were expounded in the article. Owing to excellent wear resistant and low cost, high chromium cast iron building-up materials have been applied widely. The current research situation of self-shielded flux-cored wire with high chromium cast iron was summarized and the existing problem and probable solution were pointed. Key word: Coal mill roller, Abrasive wear, Flux-cored wire, Resurfacing welding