134,764 research outputs found
Some problems in hot rolling of al-alloys solved by the finite element method
No full textThis thesis is focused on employing the finite element method (FEM) to simulate hot flat rolling process. The relevant work involves selecting a suitable constitutive
equation, predicting the rolling load and roll torque, computing temperature changes and lateral deformation, simulating the evolution of substructure, modelling static recrystallisation and designing the rolling pass schedule.
A practical pass schedule supplied by an aluminium company and containing reliable measured data of roll load and torque is analysed by a commercial 3-D thermornechanical coupled FEM program FORGE3 V5.3. The inverse analysis method is adopted to obtain the friction coefficient and heat transfer coefficient. The distribution of pressure, equivalent strain, the stress and damage in the roll gap in breakdown rolling are discussed. The changes of temperature and lateral profile under both laboratory and industrial rolling conditions are computed and compared with experimental measurements, the differences are then investigated. Through applying the Taguchi experimental design method, the influence of each rolling parameter on the spread, i. e. the ratio of width to thickness, the roll radius to thickness, the thickness reduction, and the deformation temperature, the relative contribution of each control parameter is quantitatively estimated and expressed as a percentage. A new spread formula is built up based on a large amount of FE analyses. The new formula is able to deal with both laboratory and industrial rolling conditions with high accuracy. Critical reviews are presented for the previous work in the modelling of subgrain size and static recrystallisation. Both empirical and physical models are applied to investigate the evolution of subgrain size, dislocation density, misorientation and the flow stress in the roll gap. The predicted subgrain size agrees very well with the experimental measurement. The difference between the use of two models are illustrated and analysed. Studies on modelling of static recrystallisation are carried out by incorporating the plastomechanical parameters, i. e. strain, strain rate and temperature, into empirical model. Various approaches are proposed to reduce the predicted volume fraction recrystallised at the surface and are verified by the comparison with measurement. Simulation results show that some of the previous work reported in the literature are erroneous. Further work in the modelling of static recrystallisation and texture evolution is detailed. The Taguchi experimental method is also applied to study the influence of the rolling parameters on the fraction recrystallised (Xv ). The study shows that rolling temperature has the greatest influence on the Xv, followed by the parameter H. 1L. The roll temperature and roll speed have little influence on the Xv. Designing a rational rolling pass schedule is critical for the control of strip profile and product quality. In the present thesis, the procedure of designing a rolling pass schedule is illustrated. The formulae used in scheduling are listed and explained. The scheduling program is then performed to check with two existing industrial schedules. The comparison shows that the rolling load, temperature and power model is reliable and shows high accuracy. A multipass simulation by the use of finite element method is also carried out and the results are compared with various
model predictions. The problems in the simulation are illustrated and explained
Rolling mill roll design
No full textIn this thesis, some previously published experimental and theoretical studies of hot rolling are reviewed. A thorough understanding of the available roll design methods, and conditions of their application is extremely important in order to achieve the objective of producing high quality rolled products. Successful hot roll design is dominated by the calculations of some important parameters, which describe two-dimensional (2D) or three-dimensional (3D) deformation in the workpiece. These parameters, such as roll separation force, torque, elongation, spread and draft, are discussed in detail. The method or formula for the calculation of each parameter is different for each set of different application conditions. A thorough study of these methods in different application cases will lead to the optimised design of hot rolled products. Finite Element (EE) is an important method which has been employed in the study of hot rolling. Design theory, commercial software and application cases have been described. 2-D and 3-D Finite Element Methods (FEM) for hot rolling simulation have also been discussed within the work. The current techniques and the problems of using the Finite Element system in hot roll design have been presented briefly. Possible solutions to these problems have also been discussed and there need to be considered in order to successfully apply Finite Element theory in hot roll design. An important alternative approach for hot roll design has been introduced in this thesis. A Matrix-based roll design system has been developed. It includes a Matrix-based system for flat and section roll designs. The realisation of the Matrix-based system is discussed. All the methods and formulae considered previously can be integrated in the proposed roll design system. The approach emphasizes the need for teamwork. The design procedure allows both less experienced designers and senior designers to benefit from participation. It is suggested that high quality rolled products could be achieved from optimised designs produced using this systematised the approach compared to the ad-hoc use of existing techniques, formulae and methods
Rolling contact fatigue of silicon nitride.
No full textSilicon Nitride has traditionally been used as rolling contact bearing material owing to its superior performance compared to bearing steels. Its successful application as a bearing element has led to the development of Silicon Nitride in other rolling contact applications in the automotive industry and the power industry. However, a major limitation of its wider application is its high material and machining cost, especially the cost associated with the finishing process. In the present study, a low cost sintered and reaction-bonded Silicon Nitride is used to study the surface machining effects on its rolling contact fatigue performance. Studies have been carried out to link the surface strengths of Silicon Nitride derived from half-rod and C-Sphere flexure strength specimens to the rolling contact lives of Silicon Nitride rod and ball specimens. The rolling contact fatigue tests were carried out on ball-on-rod and modified four-ball machines. Three types of surface with coarse, fine and RCF-conventional finishing conditions were examined. Flexure strength tests on half-rod and C-Sphere showed an increasing surface strength from specimens with coarse, fine to RCF-conventionally machined conditions. During rolling contact fatigue tests of as-machined specimens, no failures were observed on either ball-on-rod or four-ball tests after 100 million stress cycles. However, a trend of decreasing wear volumes was measured on the contact path of rods and balls with coarse, fine and RCF-conventional conditions. In four-ball tests, spall failures were observed on pre-cracked specimens. There was a trend of increasing rolling contact fatigue lifetime from pre-cracked specimens with coarse, fine to RCF-conventional machining conditions. The study of Silicon Nitride machining was also carried out using an eccentric lapping machine to investigate the effect of eccentricity on the finishing rate of hot isostatically-pressed and sintered and reaction-bonded Silicon Nitride. The eccentricity had no significant impact on finishing rate as concluded in this study. The effect of lubricant viscosity and chemistry on the rolling contact fatigue performance of Silicon Nitride was also studied. The result is inconclusive
Residual stress field of HIPed silicon nitride rolling elements
No full textThe residual stress field of HIPed Si3N4 rolling elements were studied. Two kinds of HIPed Si3N4 ball blanks self-finished at different nominal lapping loads ranging from 1.3 to 10.87 kgf/ball and four kinds of commercially finished 1/2 in (12.7 mm) HIPed Si3N4 balls before, during and after RCF tests were investigated. The experimental results showed that in the finishing process of HIPed Si3N4 rolling elements. the surface and subsurface compressive residual stress induced is proportional to the lapping load applied. There was initially a high compressive residual stress layer on the HIPed Si3N4 ball blanks and this layer is mostly removed during the finishing process. During the rolling contact fatigue process of HIPed Si3N4 rolling elements, the residual stresses on the rolling track will change dramatically as RCF proceeds
Comparison of 4-ball and 5-ball rolling contact fatigue tests on lubricated Si3N4/steel contact
No full textAccelerated four-ball and five-ball rolling tests were performed on HIPed Si3N4 ball samples (rough lapped with surface
roughness value Ra0.08 μm and Rq0.118 μm) in fully lubricated condition. The contact load and the stress cycles per minute
for four-ball rolling and five-ball rolling tests were maintained the same. The rolling track appearances of five-ball tests reveal
severe sliding occurred. In one case, the opposite arc cracks were generated all over the two sides of the rolling track, and this
could not be explained by simplified kinematics model. The failure mechanisms were discussed, which suggest the sliding on the
two sides of the track was in the opposite direction
Re-scheduling in railways: the rolling stock balancing problem
No full textThis paper addresses the Rolling Stock Balancing Problem (RSBP). This problem arises at a passenger railway operator when the rolling stock has to be re-scheduled due to changing circumstances. These problems arise both in the planning process and during operations. The RSBP has as input a timetable and a rolling stock schedule where the allocation of the rolling stock among the stations does not fit to the allocation before and after the planning period. The problem is then to correct these off-balances, leading to a modified schedule that can be implemented in practice.For practical usage of solution approaches for the RSBP, it is important to solve the problem quickly. Therefore, the focus is on heuristic approaches. In this paper, we describe two heuristics and compare them with each other on some (variants of) real-life instances of NS, the main Dutch passenger railway operator. Finally, to get some insight in the quality of the proposed heuristics, we also compare their outcomes with optimal solutions obtained by solving existing rolling stock circulation models.heuristics;railway planning;integer linear programming;rolling stock re-scheduling
Influences of surface quality on the rolling contact fatique behaviour of ceramics
No full textA novel eccentric lapping machine was designed by the author and manufactured in-house, to serve as a test bench to investigate the finishing process parameters in relation to surface quality, as well as the feasibility of accelerating the finishing process of HIPed silicon nitride balls. The kinematics of the eccentric lapping were
analysed and discussed. Taguchi Methods were used to optimise the finishing parameters to achieve maximum material removal rate in lapping and to achieve minimum surface roughness value Ra in polishing. Two kinds of HIPed silicon nitride ball blanks were finished by this machine. A finishing rate of 68 µm/hour was achieved which is 15 times higher than the conventional concentric lapping (normally 3'-4µm/hour). The surface roughness and roundness of the polished ball were above grade 5, close to grade 3 precision bearing ball specification. The upper limits of
lapping load and lapping speed were determined by aggressive lapping tests. The effects of various finishing parameters on the surface quality generated were studied
by detailed surface analysis, including X-ray diffraction residual stress measurement. As a result, the relationship between the finishing process and surface quality has
been established. Accelerated rolling contact fatigue tests were performed both under a standard 4-ball and a modified 5-ball rolling configuration, with a ceramic ball as the upper ball and steel balls as lower balls. The tests were conducted at high speed and lubricated conditions under different loads and were run for up to 135-200 million
stress cycles. Tests were conducted on commercially finished balls with different surface roughness and with different surface integrity (heterogeneous porosity, star
defect, grinding defect and C-cracks). Tests were also conducted on self-finished balls with different finishing parameters and with different surface roughness. After
tests, the rolling tracks and failure areas were examined by detailed surface analysis. The residual stresses on the rolling tracks were measured. Finite Element Approaches
were also employed to describe the contact stress status. Failure modes in relation to surface quality were discussed. The research has provided an understanding of the finishing process, surface quality and rolling contact fatigue behaviour of HIPed silicon nitride balls
Rolling contact fatigue performance of HIPed Si3N4 with different surface roughness
No full textAccelerated rolling contact fatigue four-ball tests were performed on hot isostatically pressed (HIPed) silicon nitride/steel contacts under lubricated condition using a PLINT TE92/HS microprocessor controlled rotary tribometer at a maximum compressive stress of 6.58 GPa and at a speed of 10,000 rpm for 135-200 million stress cycles. Rolling track surfaces were examined by optical microscopy, SEM, 3-D surface analysis, atomic force microscopy and interference profilometry. Experimental results show that with an initial roughness value R-a from 0.016 to 0.094 mum, the surfaces became smoother during testing and surface pitting (10-20 mum) occurred. For the surfaces with a roughness value R-a from 0.002 to 0.008 mum, the surfaces became rougher and lubricant oil residues were deposited at the edges of rolling track. Some small and shallow surface pitting 2-3 mum in size was also observed. Some scratch marks left on the surface by the previous lapping process were further extended during testing. R-a and R-q are still most important roughness parameters in relation to rolling contact behaviour. The effects of other surface roughness parameters, such as the shape of the valley. R-sk and R-ku are not obvious in this study
A review of rolling system design optimisation
No full textRapid product development and efficient use of existing resources are key competitive drivers in the steel industry and it is imperative that solution strategies are capable of delivering high quality solutions at low cost. However, traditional search techniques for Rolling System Design (RSD) are ad hoc and users of them find it very difficult in satisfying the required commercial imperatives. This paper presents a comprehensive review of approaches for dealing with RSD problems over the years in terms of modelling and optimisation of both quantitative and qualitative aspects of the process. It critically analyses how such strategies contribute to developing timely low cost optimal solutions for the steel industry. The paper also explores the soft computing based technique as an emerging technology for a more structured RSD optimisation. The study has identified challenges posed by RSD for an algorithmic optimisation approach, especially for evolutionary computing based techniques
The influence of heterogenous porosity on silicon nitride/steel wear in lubricated rolling contact
No full textHeterogeneous porosity is detected on the surface and subsurface of hot isostatically pressed (HIPed) silicon nitride spherical rolling elements. The extent of the localised porosity accounts for an area of 6% of the rolling element surface and 4% of the material volume. An experimental investigation using a rotary tribometer is described to compare the lubricated rolling wear mechanisms and performance of HIPed silicon nitride with heterogeneous porosity defect in contact with steel. A brief review of previous investigations is presented. Localised porosity detection using white and violet light microscopy with post-test evaluation is described. Discussions, micro-hardness measurements and scanning electron microscopy illustrations are presented. Critical localised porosity size is evaluated from experimental results
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