Work Roll Wear Research Articles

Spalling Prevention and Wear Improvement of Rolls in Steel Strip Hot-Rolling Process

Rolls are key components in hot strip mill. Roll wear and fatigue are inevitable phenomena during hot-rolling process. Finite element (FE) analysis shows that roll profiles, especially work roll wear profile, have significant effects on contact stress distributions. Long-term effect of huge contact stress peaks in roll sides is the main factor for roll spallings. In order to solve serious roll spallings, a design process of backup roll profile is proposed to homogenize contact stress distributions. FE calculation demonstrates the superiority of the new profile in eliminating stress peaks. Industry application also manifests its good performance in preventing roll spalling and improving roll wear.

ASR Bending Force Mathematical Model for the Same Width Strip Rolling Campaigns in Hot Rolling

According to the requirement and condition of schedule‐free rolling (SFR) for non‐oriented electrical steel production with a large number of the same width strip rolling campaigns, asymmetry self‐compensating work rolls (ASR) bending force mathematical model for different rolling schedules is established. Based on ANSYS software package, a 3D finite element model of roll stacks is established on the consideration of roll wear and thermal contour of work rolls. The effects of the bending force, the strip width, the rolling force, the diameters of backup and work rolls, the work roll shifting stroke on the loaded roll gap crown in rolling process are quantitatively analyzed. The developed ASR bending force mathematical model for different conditions is proved to be reasonable and has been applied to the 1700 hot strip mills.

Development of simple equation for calculating average wear of hot strip mill work rolls

Plastic deformation of the strip, thermal crown of rolls, roll deflection, flattening and roll wear are the main factors that have influence on the surface quality of strip. Roll wear represents complex friction conditions that, after some specific tonnage rolled, become critical. This is because the pressure distribution is not uniform, so the stress between the work and the back-up roll, plus the contact between the strip and the work roll affects the performance of the work rolls. Investigation of the mechanism of the surface deterioration of the work roll is very important for the development of an average wear control system used in real time in hot strip mills. This project has developed a simple equation that considers the Hertzian pressure distribution and mechanical contact between two cylinders with parallel axes in order to calculate the average wear in the work roll.

An investigation of worn work roll materials used in the finishing stands of the hot strip mill for steel rolling

The surface failure characteristics of different work roll materials, i.e. high speed steel, high chromium iron and indefinite chill iron, used in the finishing stands of a hot strip mill have been investigated using stereomicroscopy, three-dimensional optical profilometry, scanning electron microscopy and energy-dispersive X-ray spectroscopy. The results show that the surface failure mechanisms of work rolls for hot rolling are very complex, involving plastic deformation, abrasive wear, adhesive wear, mechanical- and thermal-induced cracking, material transfer and oxidation. Despite the differences in chemical composition and microstructure, the tribological response of the different work roll materials was found to be strongly dependent on second phase constituents such as the size, morphology and distribution of different carbide phases and graphite (in the case of indefinite chill iron), which was found to promote cracking. Cracking and chipping of the work roll surfaces, both having a negative impact on work roll wear, are strongly influenced by the presence of carbides, carbide networks and graphite in the work roll surface. Consequently, the amount of carbide-forming elements as well as the manufacturing process must be controlled in order to obtain an optimised microstructure and a predictable wear rate.

Study on Roll Wear Model for Hot Strip Mill

Roll wear model for Hot Strip Mill (HSM) was researched and the factors affect roll wear are analyzed. The simulation program was compiled by program visual C++ language and work roll wear was calculated according to the rolling schedule. Calculation results shows that roll wear like box shape. Strip width affects roll wear clearly. The strip length is one of the important issues which affect roll wear. Work roll wear of F7 top roll middle get to 280μm after a rolling schedule. Roll wear curve calculated by program were good agreement with the wear curve got by high-precision grinder. The results show that the roll wear model has high accuracy.

Development and Application of Hot Rolling Lubrication Control System Based on Expert System

To integrate a new roll gap lubrication system into an existing hot strip mill is a challenge problem. A lubrication expert system was developed and embedded into finish rolling setup system. The reference value setup by expert system is downloaded to roll bite lubrication PLC via finish mill PLC to open oil spraying valve and regulate the oil concentration. Oil spraying time sequence is an important factor to make good lubrication effect and to keep the rolling process stable. Since online application of the hot rolling lubrication system, rolling force and work roll wear has been reduced dramatically, especially rolling thin strip.

Experimental study on wear and friction of work roll material with 4% Cr and added Ti in cold rolling

Abstract Cold rolling is one of the most essential elements in the manufacture of flat products of metals. Work roll wear is always a topic of interest to many researchers. In this paper, the disc-to-disc tests of the material with 4% Cr and that with 4% Cr + Ti were carried out respectively under the conditions of dry contact and emulsion lubricant of 3.9% Quakerol N680-2-DPD. The wear and friction patterns were discussed by correlating the disc surface morphologies and the microstructures of both materials. The surface roughness of the disk of the material with 4% Cr + Ti deteriorates much slower than that with 4% Cr under the condition of lubrication. The material with 4% Cr + Ti is characterised as carbonitrades precipitated in a fine tempered martensite matrix while coarse carbides (M 7 C 3 ) exist in the material with 4% Cr. The disk of the material with 4% Cr + Ti wears differently to that with 4% Cr. Delamination may become an important wear mechanism earlier in the case of 4% Cr than that of 4% Cr + Ti. Micro spalling and pitting occur after 120 min of wear in the case of 4% Cr, but not in the case of 4% Cr + Ti until 330 min. Detached carbides are responsible for the abrasive wear on both discs at the late stage. Ti alters the friction pattern due to surface regeneration that resulted from the abrasive effect of carbonitrades. Generally, the wear-resistance of roll material may be improved by 175% by introducing added Ti. The outcome is beneficial for developing new materials for prolonging the service life of the cold work roll.

ASR work roll shifting strategy for schedule-free rolling in hot wide strip mills

In order to meet the requirement of schedule-free rolling (SFR) for wide non-oriented electrical steel production with a large number of the same width strip rolling campaigns, ASR (asymmetry self-compensating work rolls) shifting strategies for different rolling schedules are studied. According to the actual rolling process, the work roll wear prediction mathematical model for non-oriented electrical steel sheets and a 3D finite element model for roll stacks are established. The effects of the shifting step and the shifting rhythm on the ASR wear contour and the loaded roll gap profile within the entire rolling campaign are analyzed. The reasonable ASR shifting strategies for different rolling schedules are developed. In comparison with the conventional work roll contour of K-WRS mill, the self-maintenances of roll contours for ASR reach to more than 88%, the rate of the measured strip crown less than 45 μm increased from 41.8% to 94.9%, and the rate of the measured strip crown larger than 52 μm decreased from 32.6% to 2.0% by industrial test on the production of the same strip-width for wide non-oriented electrical steel sheets in the 1700 mm hot strip mill of WISCO. The ASR technology has applied to the production successfully.

Research and Application of Flat Roll Technology in the Downstream Stands for CSP

CVC mills are generally used in the whole stands of CSP (Compact Strip Product). Their special “s” curve of work roll contour and shifting strategy aimed at controlling strip shape, and the characteristics of continuous casting and rolling production, which make the work roll wear in downstream stands seriously uneven, and easily form abnormal transverse profile at the rolling end. As a result, CVC mill configuration in the downstream stands can not meet the profile and flatness control requirement for schedule free rolling, and bring some difficulties in profile and flatness control for the subsequent cold rolling. Based on the characteristics of the shape control system of CSP production line, and combined with the theory of flat roll technology, a kind of technology solution of using flat roll in the downsteam stands for CSP hot strip mills was proposed. At last, industrial test was carried out in the last stand of Masteel CSP, and good results were obtained.

VCR and ASR technology for profile and flatness control in hot strip mills

The roll contour pattern and variety of work and backup rolls in service and its effect on profile and flatness control performance in 1 700 mm hot strip mill at Wuhan Iron and Steel (Group) Corporation were tested and analyzed by the developed finite element models of different typical roll contours configurations. A rather smooth local work roll contour near strip edges and an increase in rolled length can be obtained by application of long stroke work roll shifting system with conventional work roll contours that is incapable of the crown control. In comparison with the conventional backup and work roll contours configuration, the crown control range by the roll bending force enhances by 12.79% and the roll gap stiffness increases by 25.26% with the developed asymmetry self-compensating work rolls(ASR) and varying contact backup rolls(VCR). A better strip profile and flatness quality, an increase in coil numbers within the rolling campaign and a significant alleviated effect of severe work roll wear contours on performance of edge drop control are achieved by the application of ASR with crown control and wear control ability in downstream stand F5 and VCR in all stands of 1 700 mm hot strip mill.

Polygonal Wear of Work Rolls in a Hot Leveler of Steel Making Machine (4th Report, Experimental Verification of a Countermeasure by Using Dynamic Absorbers)

In this paper, a countermeasure of pattern formation phenomena by using dynamic absorbers is investigated experimentally. An experimental equipment of a single degree-of-freedom pattern formation system with a pair of contact rotating rolls and a dynamic absorber are made. The experimental results are compared with the analytical results using approximated characteristic roots. According to the results of the experiments without a dynamic absorber, it is confirmed that the relation among the natural frequency of the system, the polygonal number and the rotating speed agree with the analytical results qualitatively. According to the results of the experiments using a damped dynamic absorber, the delaying effect of pattern formation is confirmed. Also, a good quantitative agreement between the experimental and analytical results is confirmed. According to the results of the experiments using an undamped dynamic absorber, it is confirmed that damping of a dynamic absorber is necessary to delay pattern formation phenomena.

Contact mechanics and work roll wear in cold rolling of thin strip

Simulation of cold rolling of thin strip with work roll edge contact was performed using a developed modified influence function method. Surface roughness of the rolled strip on a cold rolling mill was characterized by a surface profilometer. Roll edge contact and related surface roughness transfer are discussed. The focus of this work on cold rolling of thin strip was to justify the roll bite contact mechanics and to analyse the friction in the roll bite and the effect of the friction on the strip profile and the surface finish. The work roll wear and its value are also discussed. The work roll edge contact affects the work roll edge wear significantly. The strip surface finish becomes better after rolling, and the calculated rolling forces are in good agreement with the measured values.

Modelling the Work Roll Wear Contour in a Four‐high Mill

A method for modelling the wear contour work rolls in a four‐high mill has been developed. The modelling is build up with statistical methods. The bases for the statistics are simulations of different rolling cases and measurements from the production of heavy plates in Oxelösund. These calibrations gave a well‐working model.

Polygonal Wear of Work Rolls in a Hot Leveler of Steel Making Machine (4th Report, Experimental Verification of a Countermeasure by Using Dynamic Absorbers)

In this paper, a countermeasure of pattern formation phenomena by using dynamic absorbers is investigated experimentally. An experimental equipment of a single degree-of-freedom pattern formation system with a pair of contact rotating rolls and a dynamic absorber are made. The experimental results are compared with the analytical results using approximated characteristic roots. According to the results of the experiments without a dynamic absorber, it is confirmed that the relation among the natural frequency of the system, the polygonal number and the rotating speed agree with the analytical results qualitatively. According to the results of the experiments using a damped dynamic absorber, the delaying effect of pattern formation is confirmed. Also, a good quantitative agreement between the experimental and analytical results is confirmed. According to the results of the experiments using an undamped dynamic absorber, it is confirmed that damping of a dynamic absorber is necessary to delay pattern formation phenomena.

Simulation of thermal fatigue in hot strip mill work rolls

The surface deterioration of work rolls constitutes a significant constraint on the operation of hot mills, as the duration of rolling campaigns are greatly restricted by the surface condition of the rolls. Work roll changes account for a large proportion of downtime in the operation of hot strip mills, resulting in financial penalties for the mill operators in terms of lost production and roll maintenance.It is generally accepted that thermal fatigue represents one of the main factors influencing work roll wear in the finishing stands of a hot strip mill. In order to assess the thermal fatigue behaviour of typical work roll alloy grades, a series of tests were performed on high‐speed steel (HSS) and high‐carbon high‐chromium steel samples using a stand alone twin‐disc simulation machine under conditions that are comparable to those of hot rolling of steel. The progressive changes in surface condition of the roll samples were monitored and analysed by means of stylus profilometry, optical and scanning electron microscopy. The experimental results were compared with fragments of scrapped work rolls taken from the mill. Tests performed on the HSS samples did not result in appreciable surface degradation of the test sample. On the other hand, examination of the high‐carbon high‐chromium samples after testing revealed thermal crack morphologies and surface defects comparable to those observed in mill roll samples.

Polygonal Wear of Work Rolls in a Hot Leveler of Steel Making Machine (3rd Report, A Countermeasure by Using Dynamic Absorbers)

This paper deals with a countermeasure by using dynamic absorbers for polygonal wear of work rolls in a hot leveler. First, the authors discuss the optimal design of dynamic absorber mounted on a single degree-of-freedom system where the polygonal wear phenomena are generated. We obtain the characteristic root approximately, and apply the optimal design procedure of dynamic absorber for forced vibration of a single degree-of-freedom system to this self-excited vibration system. As the result, we obtain a design in which the system is stabilized perfectly. Secondly, the result is applied to a hot leveler as a two degree-of-freedom system through the modal analysis. As the result of numerical analysis, the hot leveler is changed into a perfectly stable system by two dynamic absorbers for the first and second vibration modes, and the polygonal wear phenomena are not generated at all.

Growth Rate and Phase Composition of Oxide Scales during Hot Rolling of Low Carbon Steel

The rate of scale growth on low carbon steel in air over the temperature range 600-1200°C and the phase composition changes that occur between 750-1 200°C were investigated. The low carbon steel was oxidized with the air velocity of 4.2 cm/s in order to approximate the formation of secondary and tertiary scales in hot rolling. In addition, some experiments were performed with a lower air velocity of 0.14cm/s. Above 1 000°C, with the air velocity of 4.2 cm/s, a transition from a parabolic rate of oxidation to a linear rate of oxidation was observed as the temperature increased. This transition in oxidizing mechanisms was related to the porosity of the oxide scale. The phase composition of the oxide scales changed with temperature and time. For the initial 30s of oxidation, wustite was the predominant phase in the temperature range 800-1 200°C and as oxidation proceeded, the percentages of magnetite and hematite increased. The homogeneity of the oxide decreased as the oxidation temperature increased. At 850°C, with the air velocity of 4.2 cm/s, the oxide was homogeneous, and for the first 120s of oxidation, the oxide had a high percentage of wustite and a low percentage of hematite. This indicates that 850°C is the ideal temperature for the finishing strip mill in order to reduce work roll wear and surface defects.

Characterisation of multicomponent scales by electron back scattered diffraction (EBSD)

Exposure of metals and alloys to high temperatures leads to the formation of oxide scales. Characterizing the nature of the scale is of considerable importance to the steel manufacturers, who are under continual pressure to improve surface finish. Scale properties are also of interest because of the effect on friction and heat transfer during hot working operations, and the resultant wear of tooling or work rolls. Oxidation of pure iron is well documented and has lead to the classical three layer scale characterization. Hot working operations break up the classical three layer scale and make characterization of the individual components of the scale difficult. Identification of the individual components simply by their layer position is no longer reliable since the layers have been disrupted by the hot working process. Scale microstructures become further complicated on cooling as the wuestite decomposes to magnetite at temperatures below 570 C. The resultant scale microstructures are therefore complex on a sub-micron scale. These secondary and tertiary scales must be removed before subsequent processing, such as cold rolling or wire drawing and the mechanical properties of the scale layers are important factors when considering descalability. For example, hematite is much harder than magnetite and wuestite,more » thus magnetite scales are more brittle and therefore easier to remove than scales containing wuestite.with this in mind it is necessary to develop a reliable technique for the characterization of these scales and their microstructures with respect to developing an ideal scale for easy removal, without sacrificing the mechanical properties of the product. Furthermore a reliable method of characterizing the scale development along the rolling mill would be useful in charting the scale growth and re-growth behavior between passes and may lead to the development of an ideal rolling schedule for the formation of an easily removed scale. This paper discusses the characterization of these scales by electron back scattered diffraction.« less

Polygonal Wear of Work Rolls in a Hot Leveler of Steel Making Machine.

This paper deals with the polygonal deformation phenomena of rolls in a reversible hot plate leveler of the steel making machine experimentally and analytically. The plates leveled by rolls with polygonal deformation become so called defective products because the profile of deformed roll is transferred to the surface of plate. From the measurements of deformed rolls, two kinds of polygonal wear were found. Then, from the vibration measurement of a hot leveler in actual operation, natural frequencies of the hot leveler were determined and the process of the polygonization of rolls was observed. Finally, the authors analyzed a simple model theoretically, regarding the polygonal deformation phenomena as unstable vibration of the hot leveler system caused by time retardation accompanied by wear on the surfaces of rolls. A good agreement between experimental and theoretical results was also confirmed.

冷問圧延におけるワークロール摩耗メカニズムの検討

冷問圧延におけるワークロール摩耗メカニズムの検討