| 1. |
- Anderberg, Cecilia, et al.
(författare)
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Alternative descriptions of roughness for cylinder liner production
- 2009
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Ingår i: Journal of Materials Processing Technology. - Amsterdam : Elsevier. - 0924-0136 .- 1873-4774. ; 209:4, s. 1936-1942
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Tidskriftsartikel (refereegranskat)abstract
- The roughness of stratified surfaces such as cylinder liners, produced by plateau honing, is functionally important in their tribology but is notoriously difficult to characterise. An issue in manufacturing quality control related to their tribological function is the comparative ability of various roughness characterisation systems. In this paper the Rk family of parameters is compared with the Rq family as regards stability and discrimination. When coefficients of variation of the two parameter families are compared as a measure of stability, CVs of individual parameters vary between 8% and 20% but do not seem to indicate a clear advantage to either family. When the correlation of parameters within and between the two groups is computed as a measure of relative discriminative ability, many parameters are found to be highly correlated, to the point where values of Rpk and Rpq are effectively indistinguishable. The relative robustness of the parameters is also established by simulation of surface or measurement artefacts: outlying peaks and valleys, high-frequency noise, changes in stylus or skid radius, changes in high-pass filter and in assessment length. Outlying peaks cause a large increase in Rpk, while outlying valleys have little effect. The Rq parameters are more sensitive to high-frequency noise than the Rk parameters. Increasing the stylus radius reduced the valley parameters, while adding a 25 mm radius skid increased Rk and Rpq by as much as 15%. Increasing the short-wavelength cut-off from 2.5 m to 8 m reduced most parameters, particularly the peak parameters, while replacing the robust Gaussian filter used throughout by a valley-suppression filter had little effect. Finally reducing the assessment length from 17 mm to 4 mm decreased the values of many parameters by up to 11%. Increasing plateau honing time decreased plateau roughness, while increasing pressure during coarse honing increased valley roughness, but these changes could not be correlated with roughness parameters. This suggests that the optimum parameter set has not yet been found. 2008 Elsevier B.V. All rights reserved.
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| 2. |
- Andersson, P., et al.
(författare)
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Hot rolling tests with steel bars and silicon nitride rolls
- 2009
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Ingår i: Journal of Materials Processing Technology. - : Elsevier BV. - 0924-0136 .- 1873-4774. ; 209:2, s. 884-893
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Tidskriftsartikel (refereegranskat)abstract
- An experimental study was carried out to investigate the possibilities to use rolls made from Si3N4-TiN ceramic composite in hot rolling of steel. The results show that the wear of the ceramic material was lower than the wear of a reference cast iron. The results suggest that the Si3N4-TiN material is beneficial to use in a hot rolling process, on condition that the temperature of the work piece material is held sufficiently high. © 2008 Elsevier B.V. All rights reserved.
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| 3. |
- Andersson, P., et al.
(författare)
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Transfer of surface texture from silicon nitride rolls to stainless steel wire in cold-rolling
- 2006
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Ingår i: Journal of Materials Processing Technology. - : Elsevier BV. - 0924-0136 .- 1873-4774. ; 173:3, s. 394-400
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Tidskriftsartikel (refereegranskat)abstract
- A set of cold-rolling experiments with ceramic rolls was carried out using facilities for the production of profiled steel wire. Based on the experiments, the strength of sintered silicon nitride was found sufficient for allowing cold-rolling of austenitic stainless steel wire. The wear rate of the silicon nitride rolls in the tests was low. Metal was transferred from the wire to the rolling tracks of the ceramic rolls. The surface texture of the rolls was reproduced on the rolled product. © 2006 Elsevier B.V. All rights reserved.
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| 4. |
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| 5. |
- Eriksson, Conny
(författare)
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Working range for sequences and series of two-symmetrical grooves in wire rod rolling
- 2006
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Ingår i: Journal of Materials Processing Technology. - : Elsevier BV. - 0924-0136 .- 1873-4774. ; 174:1-3, s. 250-257
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Tidskriftsartikel (refereegranskat)abstract
- A calculation procedure has been developed to determine the working range for series of grooves including "oval", "round", "false round", "square" and "diamond" shapes. The minimum and maximum roll-gap setting and corresponding bar areas are calculated for all grooves. Flatter ovals increase the flexibility in false round-oval series and low rolling geometry factors reduce the working range. The working range is smaller for pass sequences designed for high reductions. To evaluate the model, laboratory tests for passes in "round"-"oval"-"false round"-"oval" sequences were carried out. Samples from a square-oval series were examined and it was shown that this series was insufficient for stainless steel wire rod rolling. The fitting factors were too high and the square grooves were slightly overfilled. It is shown that "false round"-"oval" series give the largest working range and thus enable the rolling of a wide range of different stainless steel grades.
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| 6. |
- Ervasti, Esa, et al.
(författare)
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A quasi-3D method used for increasing the material yield in closed-die forging of a front axle beam
- 2005
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Ingår i: Journal of Materials Processing Technology. - : Elsevier BV. - 0924-0136 .- 1873-4774. ; 160:2, s. 119-122
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Tidskriftsartikel (refereegranskat)abstract
- The aim of the work is to increase the material yield in closed-die forging of a front axle beam meant for heavy trucks. The amount of flash obtained in production constituted 35% of the total workpiece weight, which was equal to 115.4 kg. The strategy for improving the material yield was to modify the initial forging workpiece geometry, keeping the pre- and finishing die geometries constant. Recommending new shapes for certain cross-sections of the reducer-rolled billet did this. The goal was reached by using a quasi-3D analysis. Three critical cross-sections that showed close to plane strain conditions during forging were chosen for the analysis. The FE-code Form2D was used. The losses of material in the sections caused by axial material flow were measured from full-scale experiments and added to the optimised cross-sectional areas established from the FE-analysis. Because of advice front industry the initial cross-sections used in the 2D-forging simulations were chosen to be circular. Also the final results, after compensation for the axial material flow are presented as circular cross-sections. Utilising the results from the quasi-3D approach the theoretical material yield was increased by 2.58-7.59% for the cross-sections. Results from this work have facilitated the development of adequately shaped grooves in the reducer rolling mill so that the flash volume obtained in production has been reduced. The investigation was carried out with data from IMATRA KILSTA AB.
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| 7. |
- Ervasti, Esa, et al.
(författare)
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Void initiation close to a macro-inclusion during single pass reductions in the hot rolling of steel slabs : a numerical study
- 2005
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Ingår i: Journal of Materials Processing Technology. - : Elsevier BV. - 0924-0136 .- 1873-4774. ; 170:1-2, s. 142-150
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Tidskriftsartikel (refereegranskat)abstract
- The work is focussed on the start of void formation close to a hypothetical single macro-inclusion in the hot rolling of steel slabs. The inclusion is chosen to be either three times harder or three times softer than the surrounding matrix. A commercial FE-code LS-Dyna3D has been utilized for the numerical analysis. Process data from the Swedish company "SSAB Tunnpl (a) over circlet AB" are used. The initial inclusion geometry is assumed to be cylindrical with an extension through the entire width of the slab. Different distances from the slab surface, on the vertical symmetry plane in rolling direction, are chosen as locations for the enclosure. Influence of different single pass reductions and roll radii are analysed. The only boundary force used on the matrix/inclusion interface is referred to friction. By treating a very big inclusion and neglecting bonding forces in radial direction, a worst-case scenario means to be studied. Two indices, one describing the deformation of the inclusion and one the surrounding matrix are used to estimate the likelihood for start of void formation. If the matrix index is bigger than that of the inclusion, voids are assumed to be initiated. This hypothesis gives trusty results. Near the hard particle, voids are likely to be formed. It became clear that the risk is smaller when large rolls are used. Furthermore, the threat for start of void formation turned out to be slighter for high reductions and in the vicinity of the slab surface. Soft particles were just elongated and no risk for void formation could be predicted.
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| 8. |
- Gillström, Peter, et al.
(författare)
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Mechanical descaling of wire rod using reverse bending and brushing
- 2006
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Ingår i: Journal of Materials Processing Technology. - Amsterdam : Elsevier. - 0924-0136 .- 1873-4774. ; 172:3, s. 332-340
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Tidskriftsartikel (refereegranskat)abstract
- Wire rods are covered with an oxide layer, which must be removed before wire drawing. This paper presents an investigation of mechanical descaling by reverse bending and brushing as replacement for pickling. Steel grades studied were low carbon steel and silicon chromium steel. Brushing was done with steel brushes and nylon brushes with SiC. The amount of scale remaining after reverse bending of the low carbon steel depended on the roller diameter. After brushing traces of scale remained in valleys on the surface. Surface damage was observed after brushing with steel brushes but not after SiC-nylon brushing. Silicon chromium alloyed steel was not possible to clean by bending and brushing with the roller diameters studied. The electrical energy required for the mechanical descaling of low C steel may be estimated to be 7kWh/tonne with SiC-nylon brushes and 14kWh/tonne with steel brushes. [All rights reserved Elsevier]
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| 9. |
- Gustafsson, Erik, et al.
(författare)
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Residual stresses in a stress lattice : experiments and finite element simulations
- 2009
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Ingår i: Journal of Materials Processing Technology. - : Elsevier. - 0924-0136 .- 1873-4774. ; 209:9, s. 4320-4328
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Tidskriftsartikel (refereegranskat)abstract
- In this work residual stresses in a stress lattice are studied. The residual stresses are both measured and simulated. The stress lattice is casted of low alloyed grey cast iron. In fact, nine similar lattices are casted and measured. The geometry of the lattice consists of three sections in parallel. The diameter of the two outer sections are thinner than the section in the middle. When the stress lattice cools down, this difference in geometry yields that the outer sections start to solidify and contract before the section in the middle. Finally, an equilibrium state, with tensile stresses in the middle and compressive stresses in the outer sections, is reached. The thermo-mechanical simulation of the experiments is performed by using Abaqus. The thermo-mechanical solidification is assumed to be uncoupled. First a thermal analysis, where the lattice is cooled down to room temperature, is performed. Latent heat is included in the analysis by letting the fraction of solid be a linear function of the temperature in the mushy zone. After the thermal analysis a quasi-static mechanical analysis is performed where the temperature history is considered to be the external force. A rate independent J2-plasticity model with isotropic hardening is considered, where the material data depend on the temperature. Tensile tests are performed at room temperature, 200°C, 400°C, 600°C and 800°C in order to evaluate the Young´s modulus, the yield strength and the hardening accurate. In addition, the thermal expansion coefficient is evaluated for temperatures between room temperature and 1000°C. The state of residual stresses is measured by cutting the mid section or the outer section. The corresponding elastic spring-back reveals the state of residual stresses. The measured stresses are compared to the numerical simulations. The simulations show good agreement with the results from the experiments.
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| 10. |
- Han, Han
(författare)
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Determination of mean flow stress and friction coefficient by the modified two-specimen method in cold rolling
- 2005
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Ingår i: Journal of Materials Processing Technology. - : Elsevier BV. - 0924-0136 .- 1873-4774. ; 159:3, s. 401-408
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Tidskriftsartikel (refereegranskat)abstract
- The aim of the study is to investigate the possibility of determining the on-line accurate mean value of both friction coefficient and flow stress for anisotropic materials during cold rolling. For this purpose, the rolling process was carried out by FE-simulations instead of by experiments. In the FEM, elastic flattening of work-rolls and material anisotropy have been taken into account. Based on the rolling data obtained from the FE-simulations, the influence of elastic flattening on estimation of the friction coefficient has been verified by forward slip method. Also the best combination of rolling force models together with equations describing the radius of flattened work-rolls has been selected by means of the modified two-specimen method (MTSM). The work material is low carbon steel provided by SSAB. The strain rate sensitivity of the material was tested in plane strain compression tests at three different strain rates. And its anisotropy was tested in different orientations in cylinder upsetting and plane strain compression tests. Results show that the flow stress determined by off-line methods under low strain rate conditions cannot adequately describe its plastic behavior in rolling process if the rolling speed is extremely fast. Results also show that if the elastic flattening of work-rolls is not taken into account, the friction coefficient can be overestimated by up to 35% based on the forward slip method, meaning that the influence of elastic flattening on determination of the friction coefficient do exist. Comparing different combinations of the rolling force models and the equations describing the radius of flattened work-rolls, results identify that the Ekelund's model combined with the Hitchcock equation modified by Roberts gives the best result. Meanwhile, results demonstrate that the influence of anisotropy on determination of the friction coefficient can be negligible when MTSM is utilized. Finally, it is concluded that MTSM can be an efficient method to determine the on-line mean value of both friction coefficient and flow stress in the rolling process, even if materials possess anisotropy.
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