Single Roll Research Articles

Tensile Properties of Austempered Ductile Iron under Thermomechanical Treatment

A new processing method was investigated for improving the strength and elongation of austempered ductile iron (ADI) by grain refinement of parent austenite using thermomechanical treatment. The material was deformed at the austenitization temperature by single and multipass rolling before the austempering treatment. The effects of the amount of deformation, austenitization temperature, austempering temperatures, reaustenitization, and secondary deformation on the tensile properties were studied. The properties obtained using the method were compared with those of the ASTM standards. The effect of deformation on the graphite shape was also studied. Tensile strength/yield strength/elongation values were found to increase with increasing austenite deformation up to 40% and then to start decreasing. Tensile strength/yield strength and elongation values of 1700 MPa/1300 MPa/5% and 1350 MPa/920 MPa/15% can be achieved with this method in the ranges of variables studied.

Resonant interactions in thermosolutal convection

When convection occurs in a finite box, successive modes become unstable as the Rayleigh number is increased, giving rise to branches of nonlinear solutions that are linked by mixed–mode branches emerging from Hopf, transcritical or pitchfork bifurcations. The fundamental mode, in particular, gives rise to resonant interactions. Several specific examples of these generic features have already been described. Here we study resonant interactions in two–dimensional thermosolutal convection (with point symmetry imposed), where behaviour is enriched by the presence of oscillations and of subcritical steady convection. Steady m–roll solutions are obtained numerically and their stability properties are investigated by computing the leading real and complex eigenvalues. We find that the branch of fundamental m = 1 solutions for a box with aspect ratio λ = 1.5 develops loops that touch the m = 3 branch in transcritical bifurcations. As λ is reduced these loops detach themselves from the m = 1 branch and eventually join the stacked m = 2 branch. Increasing λ, on the other hand, leads to complicated triple resonances involving m = 1, m = 3 and m = 5 solutions. These resonant interactions are associated with pattern selection and the transfer of stability from single–roll to multiple–roll solutions in wider boxes.

Ｍｎ‐Ａｌ‐Ｃ合金の磁気特性におよぼす急冷凝固速度の影響

Magnetic properties of Mn-AI-C alloy magnets produced from gas-atomized alloy powders were improved by using the finer particles because the cell size and the segregation of finer particles were very small. So, by using more rapidly solidified powders, the excellent characteristics of Mn-Al-C magnet was expected. In this work, the effect of the rapidly quenched ribbon on the characteristics of Mn-Al-C alloy was investigated, and discussed from the point of rapid solidification. The specimen were prepared by the rapid solidification apparatus with the single roll in the Ar gas atmosphere. Phase analysis of as-quenched and after heat treatment was done by X-ray diffraction analysis. Magnetic properties were estimated on the magnet made from the powder-extrusion process. Tile magnetic properties of Mn-Al-C alloy were improved by using of more rapidly solidified ribbons. Br, iHc, (BH)max and anisotropy of ferromagnetic T-phase were improved to higher level by using thiner thickness ribbons. At extrusion ratio 4, (BH)max value of 57.lkJ/m3 was obtained by the magnet prepared from rapidly solidified ribbons of 12gm average thickness, which was much higher than that by cast process or by gas atomization process. The improvement of magnetic properties of the extruded magnet from rapidly solidified ribbons was found to be caused by the finer microstructure and very small amount of non-magnetic phases such as γ2-phase and β-phase.

Stability Analysis of Chatter on a Tandem Rolling Mill

Accurate prediction of the onset of chatter is difficult in designing and operating a rolling mill. Both the lack of precise rolling process models and analytical methods for the investigation of mill stability have forced designers and users to rely on experience and trial and error, which are time consuming and cost demanding. A comprehensive rolling process model is introduced to form the foundation of chatter analysis that includes a range of possible process variations. Analytical chatter models for both single and multiple-stand rolling mills are constructed that account for interactions between mill structure and rolling process, as well as between adjacent stands. Stability analysis is performed to formulate criteria for rolling mill design and operation. Finally, simulations and experiments are presented to verify some basic components of the rolling process model that constitute the proposed chatter models.

1015 ロールキャスティングによる積層材の作製(GS-4 材料加工)

Clad strip casting was tried using a single roll caster and two types of twin roll casters. The clad strip could be cast directly from melt. The two pieces of strips could be connected easily by very small force, for example, 5N/mm width. Interface between the strips was formed clearly, and two pieces of strips was connected strongly. To cast strongly connected clad strip, connecting surface had to be semi-solid condition. Both of overlay type clad strip and inlay type clad strip could be cast using the twin roll caster in this study. The clad strip was rapidly solidified like a single strip. Size of copper roll was φ250×100 mm. Roll speed was 20 m/min. Al-12%Si and A1050 were used. Width of the strip was 20〜50 mm. Thickness of the clad strip was 1.5〜3mm.

Quantitative characterisation of substructural development during warm working of an interstitial free steel

A Ti containing interstitial free steel was warm rolled in the temperature range 500–800°C, using wedge shaped slabs to produce a range of strains in a single rolling test. Some plane strain compression tests, under similar conditions, were carried out to obtain accurate stress–strain data. Variations in substructural features including subgrain sizes, subgrain aspect ratios, and misorientations between subgrains were quantitatively measured by TEM. Close correlation was observed between mechanical behaviour and variations in the substructure at different temperatures. At the lower temperature (500°C), the material showed cold worked characteristics, but as the deformation temperature was increased the effects of recovery became more pronounced, and hot working behaviour was obvious in the flow stress as well as in the substructural observations at 800°C.

1503 急冷凝固 Ti-Pd-Ni 形状記憶合金の物性

Shape memory ally Ti-Pd-Ni films were made by the melt spinning apparatus with a single roll of rapid solidification method. Obtained specimens were ribbon shaped films, 20∿30μm in thickness and 1mm in width. The structures of the surfaces were observed by an optical microscope. The crystal structures at various temperatures were studied by the X-ray diffraction. Preferred crystal orientation was observed in these films. The martensitic and the reverse martensitic transformation temperatures were determined by the temperature changes of X-ray diffraction patterns and a differential scanning calorimeter. These transformation temperatures were lower than that of bulk specimens. After annealing at 800℃, these transformation temperatures did not increase up to that of bulk specimens.

Initial rollover effectiveness evaluation of an alternative seat belt design for agricultural tractors.

A test program was conducted to determine the effectiveness of a seat belt restraint in preventing occupant movement in a rollover accident. A baseline type-2 seat belt (pelvic and torso restraint), and an improved type-2 seat belt restraint, both designed to restrict occupant motion in a rollover accident, were tested in a rollover restraints tester (RRT). Each seat belt was placed on a H-III 50th percentile male dummy and testing conducted at a single roll rate and two D-ring adjustment positions. Each test simulated what was approximately a 260 degrees per second rollover parallel to the longitudinal axis of the tractor with the top of the ROPS impacting the ground after 180 degrees of roll. Forces on the dummy's head and neck were measured, and video was taken to measure the head motion in the x-, y-, and z-axis of the dummy. The average vertical, forward, and lateral head movement in the baseline seat belt was 144, 222, and 184 mm, respectively, when the adjustable D-ring anchorage supporting the shoulder belt was in its lowest position. At the lowest D-ring height, the shoulder belt became ineffective and the seat belt performance became similar to a type-1 restraint (required for tractors with ROPS) resulting in increased vertical, forward, and lateral movement. The improved restraint reduced vertical head movement by as much as 75% without increasing head and neck loads above established injury criteria. Testing seat belts for rollover effectiveness will become increasingly important as seat belt usage on tractors with ROPS increases.

Magnetohydrodynamic convectons

In modelling two-dimensional nonlinear magnetoconvection a fundamental new spatially isolated convective pattern is found. The pattern consists of a single convective roll (a `convecton') that is able to expel practically all magnetic flux from its neighbourhood, whilst the rest of the computational domain contains an almost uniform magnetic field strong enough to suppress convection.

A Systematic Approach to Modeling Nonlinear Multi-DOF Ship Motions in Regular Seas

The modeling and dynamics of nonlinear, large-amplitude motions of vessels in regular beam seas are studied. By using a wave-fixed coordinate system, a three-degree-of-freedom ship model which contains roll, sway, and heave motions is obtained. This model systematically includes various factors that contribute to ship motions. After nondimensionalization and rescaling, it is transformed into a form that is amenable to analysis that takes advantage of various time scales in the problem. This analysis provides a systematic reduction of the full system to a single-degree-of-freedom (DOF) dynamics problem in which roll is dominant. The analysis is based on invariant manifold theory of dynamical systems, and allows one to account for coupling to the quasi-static heave dynamics and the sway velocity. Numerical simulations of a model for a typical fishing vessel are presented and demonstrate that the traditional single DOF roll model represents approximately the dynamics on a special subset—an invariant manifold—of the higher dimensional state space of the full three-DOF model. This work points the way towards a systematic means of modeling general, large-amplitude motions of vessels in a variety of sea states.

Buoyancy and electrically driven convection models in thin-layer electrodeposition

Recent work demonstrates the inevitable role of convection during the growth of patterns in thin-layer electrochemical deposition. Convection is driven mainly by Coulombic forces due to local charges and by buoyant forces due to concentration gradients that lead to density gradients. Here we study by theoretical and numerical modeling the limiting regimes under which electroconvection or gravitoconvection prevail. The model describes the diffusive, migratory, and convective motion of ions in a fluid subject to an electric field. The equations are written in terms of dimensionless quantities, in particular, the gravity Grashof and the electrical Grashof numbers. The simulations reveal that gravitoconvection becomes increasingly important as the gravity Grashof number increases, while electroconvection becomes increasingly important as the electrical Grashof number increases. For both regimes the model predicts concentration, electric potential, and velocity patterns that are in qualitative agreement with typical electrodeposition experiments. In gravitoconvection, the model predicts the evolution, before collision, of the convection rolls near each electrode growing first as ${t}^{4/5}$ and then slowing down to ${t}^{1/2};$ the same scaling behavior was observed in experiments. After collision, the cathodic and anodic rolls merge into a single roll. In electroconvection, the model predicts the existence of vortex pairs formed by the electrical force on space charge accumulating near the growing filament tip. Such vortex rolls and pairs have been observed in experiments.

Thermoconvective instability in a rotating magnetic field

The effect of a rotating magnetic field (RMF) on the stability of a fluid contained in a cylindrical column and heated from below is investigated. The RMF increases the critical Rayleigh number for asymmetric flow modes but does not affect the onset of instability for axisymmetric modes. The critical Rayleigh number is dependent upon the relative penetration of the magnetic field into the cylinder and the Prandtl number of the fluid. Instability first develops in the form of a single asymmetric meridional roll rotating around the axis of the cylinder, driven by the azimuthal component of the magnetic field.

Effect of Oxide Shape on Magnetic Properties of Semiprocessed Nonoriented Electrical Steel Sheets.

The effect of oxide shape on magnetic properties of semiprocessed nonoriented electrical steel sheets produced by single reduction cold rolling process was studied. When oxides in steel sheets were elongated inclusions which were prescribed as B type by JIS, the oxides inhibited grain growth during consumer annealing and average grain size became small. As a result, core loss was bad. When oxides were spherical inclusions which were prescribed as C type by JIS, the oxides did not inhibit grain growth and average grain size became large. As a result, core loss was good. Oxide composition affected the shape remarkably. The degree of elongation of oxides had much to do with the viscosity during hot rolling. The viscosity of oxides containing less MnO and much SiO2 was high, and the degree of elongation was small. Consequently, these oxides became spherical C type inclusions.

Effect of preroll quenching and post-roll quenching on production and properties of ultrafine ferrite in steel

The production of ultrafine (1–2 μm) ferrite grains by single pass rolling of steel has led to the development of two modified rolling processes. The preroll quenching technique aims to produce a homogeneous distribution of ultrafine ferrite grains through the strip thickness, while at the same time relaxing some of the processing constraints associated with the production of these types of microstructure. By quenching the strip directly before rolling, the technique successfully produced a uniform distribution of ultrafine grains in a low carbon microalloyed grade. The post-roll quenching technique involved quenching the strip directly after rolling to control the microstructure of the centre of the strip and produce layered composite structures in both plain and microalloyed low carbon grades. These microstructures displayed novel combinations of very high strength and good ductility. These techniques present further opportunities for microstructural manipulation and the production of strip steels with high performance mechanical behaviour.

Simulation of Particle Flow in Rotating Horizontal Cylinder Using Distinct Element Method Improved by Rolling Friction.

Distinct element method (DEM) proposed by Cundal and Strack is useful for simulating behavior of particle beds. However, the results of the simulation differ from the experiment in general Although the rolling friction should be taken into account, it is usually ignored in the existing DFM, so that for instance, a single particle rolling on a horizontal plate keeps unreally constant velocity without deceleration. This paper proposes to take account of the rolling friction generated by the elastic hysteresis of particles in the existing DEM. A particle bed in a rotating horizontal cylinder is chosen as a testing model for the numerical simulation to examine the DEM improved in this paper by introducing the rolling friction. The present DEM can explain the rolling, cascading and cataracting flow modes of the particle bed, while the existing DEM cannot do except the rolling mode.

超微細結晶粒材料の作成と物性 単ロール急冷法により作製したＡｌ‐Ｃｒ‐Ｓｉ合金のＡＦＭによる準結晶の観察

The influence of composition and mechanically grinding (MG) on the heat characteristic and the quasicrystalline size in rapidly solidified Al-Cr-Si alloy is investigated. The size of quasicrystal is quantitatively measured with Atomic Force Microscope (AFM). Al74Cr20Si6, Al77Cr13Si10 and Al90Cr6Si4 alloy ribbons are prepared by single roll quenching. Al74Cr20Si6 alloy consists of quasicrystalline single phase, and others consist of Al phase and quasicrystalline phase. The crystallization temperature of the quasicrystal becomes lower with increasing Al content in alloy. The size of quasicrystal in Al74Cr20Si6 ribbon is larger than 500nm, and the average sizes of quasicrystal in Al77Cr13Si10 ribbon and Al90Cr6Si4 ribbon are 177 and 89nm, respectively. The reduction in the crystallization temperature relates to the size of quasicrystal. By mechanically grinding the crystallization temperature and the size of quasicrystal become lower and smaller. The average size of quasicrystal in mechanically ground Al90Cr6Si4 for 1800s is 76nm. The crystallization temperature decreases because of breaking the quasicrystal in MG.

Marangoni convection in binary mixtures with Soret effect

Marangoni convection in a differentially heated binary mixture is studied numerically by continuation. The fluid is subject to the Soret effect and is contained in a two-dimensional small-aspect-ratio rectangular cavity with one undeformable free surface. Either or both of the temperature and concentration gradients may be destabilizing; all three possibilities are considered. A spectral-element time-stepping code is adapted to calculate bifurcation points and solution branches via Newton's method. Linear thresholds are compared to those obtained for a pure fluid. It is found that for large enough Soret coefficient, convection is initiated predominantly by solutal effects and leads to a single large roll. Computed bifurcation diagrams show a marked transition from a weakly convective Soret regime to a strongly convective Marangoni regime when the threshold for pure fluid thermal convection is passed. The presence of many secondary bifurcations means that the mode of convection at the onset of instability is often observed only over a small range of Marangoni number. In particular, two-roll states with up-flow at the centre succeed one-roll states via a well-defined sequence of bifurcations. When convection is oscillatory at onset, the limit cycle is quickly destroyed by a global (infinite-period) bifurcation leading to subcritical steady convection.

VIBRATION TRANSMISSION THROUGH SELF-ALIGNING (SPHERICAL) ROLLING ELEMENT BEARINGS: THEORY AND EXPERIMENT

Interest in vibration control in systems employing rolling element bearings, ranging from rotor systems used in energy conversion/transmission to high-precision, multi-degree-of-freedom optical positioning systems, has focused attention on the modelling of bearing dynamic stiffness properties. While modelling a rolling element bearing either as an ideal boundary condition for a shaft or as a simple translational element may suffice in understanding basic rotor system dynamics, such simple models are inadequate in explaining how vibratory energy may be transmitted from, for example, transverse shaft vibrations to perpendicular, out-of-plane casing vibrations. Recently, researchers have begun to address this issue for conventional single row ball or cylindrical rolling element bearings which exhibit a strong moment–coupling stiffness. The study reported in this article focuses on double row spherical (self-aligning) rolling element bearings where moment stiffnesses are negligible, but translational cross-coupling stiffnesses between axial and radial bearing directions are present. A new theoretical model for the direct and cross-coupling stiffness coefficients of spherical rolling element bearings is developed and partially validated using new experimental techniques. It is shown that the coefficient values are complicated functions dependent on radial and axial preloads. While cross-coupling stiffness coefficients are negligible with simple radialoraxial preloads, under the combined radialplusaxial preload condition, the cross-coupling stiffness coefficient between the axial direction and the direction of the radial preload becomes significant.

Laminar natural convection in a laterally heated and upper cooled vertical cylindrical enclosure

Numerical simulation of laminar natural convection in a vertical cylinder is proposed. The cylinder is insulated at the bottom, laterally heated at a uniform heat flux density and cooled at the same flux at the top surface. The influence of the characteristic parameters of the problem on the steady-state solution is analysed (10 2⩽ Ra ⩽ 10 6; 0.7⩽ Pr ⩽ 92.5; 1/5 ⩽ Al⩽2). The fluid transient behaviour is also investigated. It is found that the stationary convective heat transfer is more important at the top surface for 1/5 ⩽ Al⩽ 1/2 and is explicitly independent'of the Prandtl number. The steady-state flow presents a single roll pattern in all cases. On the other hand, in the transient phase a time-limited two-roll flow is predicted when Al⩽ 1/3.

Hot rolling and superplastic forming response of net shape processed Ti-6AI-4V produced by centrifugal spray deposition

The hot rolling and superplastic forming response of Ti-6Al-4 V deposits, produced using a unique low pressure centrifugal spray deposition (LPCSD) facility, have been examined. Fundamental information has been generated relating to the parameters which govern microstructural development (porosity distribution, grain size, and α/β phase volume fraction) both during the deposition process and following post-spray thermomechanical processing. As sprayed deposits were characterised by relatively coarse transformed β microstructures, with α lath and prior β grain sizes varying from about 0.6 to 1.1 μm and from 70 to 400 μm respectively, depending on the spray forming environment (Ar or vacuum) and the position within the preform. Despite these coarse microstructural features, and relatively high levels of porosity, single and multipass hot rolling reductions of up to 80% were successfully achieved, yielding microstructures and strain rate sensitivity factors (m values) compatible with superplasticforming grade sheet specifications.