Roll Speed Ratio Research Articles

Microstructure and mechanical properties of severely deformed Mg–3%Al–1%Zn alloy via isothermal differential speed rolling at 453 K

The paper reported the microstructure evolution and mechanical properties of the severely deformed Mg–3%Al–1%Zn alloy sample via isothermal differential speed rolling (DSR) at 453K. The present samples were subjected to DSR operations with the height reduction of 30% at the roll speed ratio of 1:3 for the lower and upper rolls, and these results were compared to those deformed by equal speed rolling (ESR). After two-pass of the DSR, most of the grains were refined markedly to ∼3.3μm with a globular shape whose grain size was lower than that via ESR. In addition, Vickers microhardness values of the samples via DSR were higher than those via ESR. The results of tension tests revealed that yield and ultimate tensile strengths of the severely deformed samples via DSR were measured to be ∼198 and ∼228MPa, respectively. It is worth noting that, with increasing numbers of operations, the tensile ductility of the sample deformed by the DSR was restored whilst the elongation of the sample deformed by the ESR was monotonously deteriorated although both of the cases exhibited lower elongation compared to the as-homogenized. Such phenomenon underlying the restoration of the tensile ductility was discussed by taking the role of the conjugated macro-shear deformation into account.

Effect of roll speed ratio on deformation characteristics of IF steel subjected to differential speed rolling

The paper investigates the effect of the roll speed ratio on the deformation characteristics of interstitial free (IF) steel processed by the differential speed rolling (DSR) technique. An intense plastic strain induced by a single DSR with various roll speed ratios ranging from 1:1 to 1:4 for the lower and upper rolls was successfully imparted to the samples, resulting in the formation of fine elongated ferrite grains as the roll speed ratio increased. Observations of the preferred orientation using electron back-scattered diffraction and transmission electron microscopy revealed that the {110} slip was readily activated as the dominant deformation mode in order to accommodate the intense plastic strain imposed by the DSR. In addition, the microhardness values of the IF steel sample deformed via DSR under a roll speed ratio of 1:4 increased, and this is discussed on basis of the frictional force between the roll and the sample during DSR deformation.

Microstructure evolution and mechanical properties of ultrafine grained IF steel via multipass differential speed rolling

The microstructural evolution and mechanical properties of ultrafine grained interstitial free steel fabricated by multipass differential speed rolling (DSR) technique were investigated. A series of DSR operations were performed up to four passes under a roll speed ratio of 1∶4 for lower and upper rolls. Microstructural observations using a transmission electron microscope showed that the deformed microstructure comprised the severely deformed ferrite grains with a mean size of ∼0·7 μm having a relatively high dislocation density. In addition, the nearly equiaxed grains were effectively formed due to the sample rotation of 180° around the transverse axis between each passage where the macroscopic shearing was reversed. Electron backscattered diffraction analysis revealed an increase in the fraction of the high angle grain boundaries in the severely deformed samples with increasing number of DSR operations. The mechanical properties were also examined utilising microhardness and tensile tests, and these were discussed in relation to the shearing and microstructural characteristics.

Theoretical and experimental investigation of superplastic rolling process

Rolling play an increasingly significant role in forming process, very few studies have been devoted to the case of rolling superplastic alloy. This paper presents an investigation of symmetrical and unsymmetrical rolling process, which is of fundamental interest for forming processes. The prediction of the strain rate in the unsymmetrical rolling process is thus a challenging task. This paper has a novel discussion of symmetrical and unsymmetrical rolling of superplastic (lead-tin) eutectic alloy and with different range of rolling speed ratios and percentage reduction in thickness. It was found that the strain rate calculated experimentally was always greater than that calculated from theoretical considerations. Curling of the specimen as it leaves the rolls in the unsymmetrical rolling depends on the percentage reduction in thickness and on roll speed ratio.

Temperature rise during differential speed rolling

Abstract The present work investigated the temperature rise of an interstitial-free steel sample during differential speed rolling as functions of the height reduction and roll speed ratio. The temperature rise increased with increasing either height reduction or roll speed ratio, approaching a maximum value of 100 °C under height reduction of 40% and roll speed ratio of 1:4. In addition, the temperature rise of the sample during deformation was predicted by the concept of the energy-based state equation.

Numerical Simulation for Metal Powder Cross Shear Rolling Compaction

Characteristics of cross shear rolling for metal powder roll compaction were analyzed. The finite deformation elasto-plastic constitutive model and corresponding calculation code were derived based on compressible continuum mechanics. Numerical simulations were performed for the cross shear rolling of metal powder. The rolling force development law under different compaction ratio and rolling speed ratio was studied. It showed that the rolling force decreased apparently as differential velocity ratio increased. Comparisons were done between simulations and experiments from references and the reliability of the mechanical models and calculation code derived in this paper were proved.

Annealing behavior of severely deformed IF steel via the differential speed rolling method

The present study was made to demonstrate the annealing behavior of severely deformed interstitial free (IF) steel processed by differential speed rolling (DSR). The initial ferrite grain size of ≈35μm was significantly refined to ≈0.7μm after four DSR operations corresponding to the effective strain of ≈1.7 under the roll speed ratio of 1:4 for lower and upper rolls. Microstructural observations revealed that most of the initial coarse ferrite grains were subdivided with an aid of dislocation activities, resulting in the formation of fine ferrite grains. During post-DSR annealing at 673–773K, the grain size of the fine ferrite grains was observed to remain unchanged, which implied that static recovery was in progress. At 823K, the microstructure exhibited the coarse recrystallized ferrite grains while the grain growth of ferrite grains started to take place above 873K. Mechanical properties were also assessed by taking the annealing characteristics of the ultrafine grained IF steel into consideration.

Friction effect on ball positioning of an automatic balancer in optical disk drives

This study was aimed at evaluating the perfect balancing position of an automatic ball balancer installed in optical disk drives taking into consideration the effects of the rolling friction, speed ratio, and scaling parameter on ball positioning. A mathematical model that is employed to derive the dynamic equations of the ABB system was constructed. Stability of the steady-state solutions was then analyzed. A numerical simulation and an experimental study were conducted to verify the mathematical model. The simulation and experimental results were in good agreement.

Instrumented roll technology for the design space development of roller compaction process

Instrumented roll technology on Alexanderwerk® WP120 roller compactor was developed and utilized successfully for the measurement of normal stress on ribbon during the process. The effects of process parameters such as roll speed (4–12rpm), feed screw speed (19–53rpm), and hydraulic roll pressure (40–70bar) on normal stress and ribbon density were studied using placebo and active pre–blends. The placebo blend consisted of 1:1 ratio of microcrystalline cellulose PH102 and anhydrous lactose with sodium croscarmellose, colloidal silicon dioxide, and magnesium stearate. The active pre-blends were prepared using various combinations of one active ingredient (3–17%, w/w) and lubricant (0.1–0.9%, w/w) levels with remaining excipients same as placebo.Three force transducers (load cells) were installed linearly along the width of the roll, equidistant from each other with one transducer located in the center. Normal stress values recorded by side sensors and were lower than normal stress values recorded by middle sensor and showed greater variability than middle sensor. Normal stress was found to be directly proportional to hydraulic pressure and inversely to screw to roll speed ratio. For active pre-blends, normal stress was also a function of compressibility. For placebo pre-blends, ribbon density increased as normal stress increased. For active pre-blends, in addition to normal stress, ribbon density was also a function of gap.Models developed using placebo were found to predict ribbon densities of active blends with good accuracy and the prediction error decreased as the drug concentration of active blend decreased. Effective angle of internal friction and compressibility properties of active pre blend may be used as key indicators for predicting ribbon densities of active blend using placebo ribbon density model. Feasibility of on-line prediction of ribbon density during roller compaction was demonstrated using porosity–pressure data of pre-blend and normal stress measurements. Effect of vacuum to de-aerate pre blend prior to entering the nip zone was studied. Varying levels of vacuum for de-aeration of placebo pre blend did not affect the normal stress values. However, turning off vacuum completely caused an increase in normal stress with subsequent decrease in gap.Use of instrumented roll demonstrated potential to reduce the number of DOE runs by enhancing fundamental understanding of relationship between normal stress on ribbon and process parameters.

Effect of Pass Thickness Reduction on Microstructure and Formability in AZ31 Magnesium Produced by Differential Speed Rolling

AZ31 magnesium alloy sheets were prepared by multi-pass differential speed rolling (DSR) with small mismatch roll speed ratio. Effect of pass thickness reduction on microstructure, texture and formability at room temperature were investigated. The results showed that the low pass thickness reduction DSR is effective to improve the formability by refining the grain size and weakening the basal texture, which is characterized by the increasing of strain hardening exponent (n value) and elongation as soon as decreasing of yielding ratio and normal anisotropy ratio (r value). With the increasing of pass thickness reduction, more effective grain refinement is achieved due to the forming of deformation bands. While the ability of forming the title basal texture is weakened and the formability is reduced.

Microstructure evolution and mechanical properties of severely deformed Al alloy processed by differential speed rolling

A study was made to investigate the microstructure evolution and mechanical properties of Al alloy samples deformed by differential speed rolling (DSR) method as functions of the roll speed ratio as well as the number of operation. After a single DSR operation yielding an effective strain of ∼0.8, the microstructure comprised the most of the lamellar bands parallel to the deformation flow direction. After a second DSR deformation, the width of the lamellar bands became thinner and their distribution was also observed to be uniformed as the roll speed ratio increased. In addition, the present TEM observation exhibited that fine grains having an average grain size of ∼0.5μm were detected inside the lamellae when the roll speed ratio was 1:4. Based on the microhardness maps of the deformed samples, the microhardness values of the sample deformed via DSR at the roll speed ratio of 1:4 was twice higher than that of initial counterpart.

Ultrafine grained titanium sheets with high strength and high corrosion resistance

► UFG microstructure was produced in Ti by differential speed rolling. ► The processed Ti exhibited high strength as well as high corrosion resistance. ► The pure Ti with the smallest grain size revealed the lowest corrosion rate. ► The corrosion rate decreased with decrease in grain size. The pure titanium sheets with ultrafine grained (UFG) microstructures were produced by high-ratio differential speed rolling (HRDSR) at different roll speed ratios and different roll temperatures. Significant strengthening was achieved after HRDSR and the sample processed at a higher speed ratio or a lower processing temperature yielded a higher strength. The strengthening mechanism in the HRDSR processed Ti was examined in terms of the models based on the critical stress for activating the Frank–Read source and the grain-size strengthening. The UFG Ti exhibited high corrosion resistance in H 2 SO 4 and HCl solutions. The corrosion rate decreased linearly with the inverse square root of the grain size. The Ti with the smallest grain size, which was HRDSR processed at room temperature, revealed the best combination of high strength and high corrosion rate.

Effect of the speed ratio on grain refinement and texture development in pure Ti during differential speed rolling

The effect of the roll speed ratio (SR) on the microstructure, texture and mechanical properties of commercially pure Ti during differential speed rolling was examined at 673 K in a wide range of SRs between 1 and 5 to produce Ti sheets with an ultrafine-grained microstructure exhibiting high strength. At an SR of 5, a defect-free sheet with shear bands and ultrafine grains homogeneously distributed over the entire thickness of the sheet could be fabricated through a single rolling pass.

DYNAMIC SIMULATION OF THE TAILING PROCESS IN HOT FINISHING MILL

In this paper an explicit dynamic finite element method model has been developed to investigate the strip deformation behavior between two adjacent stands in hot finishing mill. The effect of the roll speed ratio of second stand to first stand on tension and the tailing behavior of the strip has been discussed in details. It has been found that the strip accumulation occurs if the roll speed ratio is small. The tensile stress increases with the roll speed ratio. During the tailing process the accumulated strip caused by the small roll speed ratios knocks onto the roll, while the swing of the strip tail occurs for the large roll speed ratios and it strikes the roll as well. Both tailing phenomena will result in the strip tail pincher or roll damage in the real operation.

Multiscales modeling of microstructure evolution during asymmetric cold rolling process

A micromechanical ductile fracture model extended to take into account thermal heating due to mechanical dissipation within the metal is used to study a 3D-asymmetric cold rolling operation. The void coalescence mechanism by internal necking is also considered by using a modified Thomason’s criteria. The described formulation is implemented into ABAQUS/Explicit finite element package using the Aravas’s schemes. The presented model is applied to simulate the microstructure evolution of a A1050P aluminum with the variation of roll radius and roll speed ratios. The confrontation with available experimental results shows the capability of the constitutive law to predict the rolling force variation for different reductions. The results show also that optimums parameters could be found in order to reduce the rolling force and that rolling parameters exert an influence on the final microstructure of the rolled metal.

Improvement of formability of Mg–Al–Zn alloy sheet at low temperatures using differential speed rolling

The differential speed rolling (DSR) with a roll speed ratio of 1.167 was carried out on an AZ31B magnesium alloy in order to investigate its effects on the formability. Compared with the normal rolled sheet exhibiting approximately the same average grain size, the Erichsen values of the DSR processed sheet with an inclination of basal pole in the rolling direction significantly increased by about 1.5 and 1.9 times at room temperature and at 423 K, respectively. The deep-drawing temperature limit for a drawing ratio of 1.5 was also lowered from 443 K to 423 K. The improvement of the press formability at low temperatures can be attributed to the texture modifications, which led to a lower 0.2% proof stress, a larger uniform elongation, a smaller Lankford value and a larger strain hardening exponent.

Texture and Microstructure Control of Al-Mg-Si Alloy Sheet by Differential Speed Rolling

It is known that well developed <111>//ND texture increases Lankford value (r-value) of not only bcc metals but also fcc metals and alloys. However, <111>//ND texture cannot be formed in fcc metals by conventional rolling and annealing processes. The <111>//ND orientation is one of the major components of shear texture. Accordingly, this orientation develops in aluminum sheet when shear deformation is introduced. Al-Mg-Si alloy 6016 sheet was processed by two-pass differential speed rolling at room temperature under a high friction conditions. The rolling direction of the second pass was so selected that the direction of shear deformation introduced in the second pass was either similar (unidirectional shear rolling) to or opposite (reverse shear rolling) to that in the first pass. The roll speed ratio was 2.0. Large shear strain was successfully introduced through the thickness uniformly by the differential speed rolling. The shear texture with major components of {001}<110> and {111}<110> were developed throughout the thickness. Though large reduction in thickness of 75% was applied to the sheets by the rolling, conventional rolling texture such as {112}<111> or {123}<643> orientation was not detected in any part of the thickness. By solution treatment after the rolling, intensity of shear texture weakened and grain size decreased. It has been found that r-value is improved by the differential speed rolling subsequently followed by solution treatment.

Recrystallization Textures of Al-Mg-Si Alloy Sheets Produced by Symmetric and Asymmetric Combination Rolling

In order to improve deep drawability of 6000 series aluminum alloys for automotive body panels, texture control for increasing r-value of the sheets was attempted by combination of symmetric and asymmetric rolling. Asymmetric warm rolling at relatively low reduction after symmetric rolling made it possible to form TD-rotated β-fiber texture including {111} components. Recrystallization textures of the T4-treated materials varied significantly depending on roll speed ratio and reduction in asymmetric warm rolling. On appropriate rolling conditions, {111}<110> orientation with high r-value was formed as a main component of recrystallization texture. On the other hand, two-stage heat treatment consisting of low temperature annealing and subsequent T4-treatment led to a significant change in recrystallization texture. In the sample annealed for long time at a low temperature, TD-rotated β-fiber rolling texture was retained even after solution treatment at a much higher temperature, because recovery or recrystallization took place to some extent during low temperature annealing.

An experimental investigation of transient traction characteristics in rolling–sliding wheel/rail contacts under dry–wet conditions

This paper focuses on the effect of the boundary lubrication of water on the transient traction characteristics of two rollers contact. The traction coefficient was measured under wet condition using a twin-disc-type of rolling–sliding frictional machine, which can simulate the actual wheel/rail contact condition under a low slip ratio and low rolling speed. The experimental results of the transient traction coefficient curve against the sliding distance or running time under the wet condition are compared with the results under the dry condition in the previous paper [K.-S. Baek, K. Kyogoku, T. Nakahara, An experimental study of transient adhesion characteristics between rail and wheel under low slip and low velocity, Proceedings of the 7th Int. Conf. on Contact Mechanics and Wear of Rail/Wheel Systems (CM2006), Brisbane, Australia, 2006, pp. 341–349] for various parameters such as rolling speed, contact pressure, and slip ratio. The roughness and hardness of the contact surface are also measured at several sliding distances under the wet condition and the results show less variation in the roughness and hardness than those under the dry condition reported in the previous paper [1]. In addition, the difference between the new and worn test surfaces was investigated with an interruption in the test in order to observe the traction coefficient curve at the initial stage.

Effects of Manganese on Microstructure and Mechanical Properties of AZ31 Magnesium Alloy Processed by Differential Speed Rolling

A DSR processing with a roll speed ratio of 1.08 was carried out on an AZ31 alloys with Mn additions of 0, 0.2, 0.4 and 0.6 wt.% for investigating the effects of Mn on the microstructural evolution and mechanical properties. The amount of the Al-Mn compounds increased with increasing the Mn content. Compare with the DSR processed sheet without Mn addition with a homogeneous grain size, those with Mn additions exhibited an inhomogeneous microstructure due to the appearance of the shear bands comprising the small grains around 5 μm. The Mn addition exhibited a significant effect in grain refinement even for a low content of 0.2 wt.%, which reduced the average grain size from about 25 μm to 10 μm. The Mn addition resulted in the significant increases in the tensile strength and the 0.2% proof stress by about 25 MPa and 40 MPa, respectively.