Pair Of Rolls Research Articles

Air‐Water Mist and Homogeneity Degree of Spray Cooling Zones for Improving Quality in Continuous Casting of Steel

AbstractA theoretical investigation used previous experimental works for validation of model predications and for studying the effect of different nozzle designs on the quality of continuously cast steel slabs has been undertaken. This is by optimizing the homogeneity degree of cooling pattern “HDCP” between a pair of rolls. The idea behind this technique is to maximize the solid shell resistance against thermo‐metallurgical and mechanical stresses and therefore minimizes the defects generated in different cooling zones. A 2‐D mathematical model of thermal, solidification, solid shell resistance and cooling conditions has been developed. The model determines the temperature distributions, the different phases associated with the solidification and three phase peritectic reaction L + δ → γ of Fe−0.12%C steel alloy as well as isotherms. The effect of different cooling patterns for various spray cooling systems on the homogeneity degree and solid shell resistance are examined. In additional to traditional water and air‐water (AWM) nozzles, a new design of air‐water mist nozzle has been proposed to improve the homogeneity degree of spray cooling system. The results indicate generally that the increasing in the homogeneity degree of cooling conditions is proportional to the increasing in the solid shell resistance and therefore to the improving of slab quality. Model predications of different effects of different nozzle designs on the surface and inner quality levels are compared and discussed in the mold and secondary spray cooling zones.

Dynamics of mechanisms with kinematic rolling pairs

We consider a number of characteristics of friction mechanisms related to continuously rated drives (variators) in which the motion in some kinematic pairs is transmitted by friction forces. It is shown that dynamic equations include nonholonomic constraints under these conditions, so the solution is carried out within the framework of generalized Lagrange equations.

NUMERICAL EXPERIMENTS ON THE TWO-STEP EMERGENCE OF TWISTED MAGNETIC FLUX TUBES IN THE SUN

We present the new results of the two-dimensional numerical experiments on the cross-sectional evolution of a twisted magnetic flux tube rising from the deeper solar convection zone (-20,000 km) to the corona through the surface. The initial depth is ten times deeper than most of previous calculations focusing on the flux emergence from the uppermost convection zone. We find that the evolution is illustrated by the two-step process described below: the initial tube rises due to its buoyancy, subject to aerodynamic drag due to the external flow. Because of the azimuthal component of the magnetic field, the tube maintains its coherency and does not deform to become a vortex roll pair. When the flux tube approaches the photosphere and expands sufficiently, the plasma on the rising tube accumulates to suppress the tube's emergence. Therefore, the flux decelerates and extends horizontally beneath the surface. This new finding owes to our large scale simulation calculating simultaneously the dynamics within the interior as well as above the surface. As the magnetic pressure gradient increases around the surface, magnetic buoyancy instability is triggered locally and, as a result, the flux rises further into the solar corona. We also find that the deceleration occurs at a higher altitude than in our previous experiment using magnetic flux sheets (Toriumi and Yokoyama). By conducting parametric studies, we investigate the conditions for the two-step emergence of the rising flux tube: field strength > 1.5x10^4 G and the twist > 5.0x10^-4 km^-1 at -20,000 km depth.

Hungarian-Australian collaborations in flour milling and test milling over 120 years

In Australia in the early 1890s, the wheat breeder William Farrer and chemist Frederick Guthrie shared a vision of selecting cross-bred wheats for enhanced grain quality. Guthrie was the newly appointed chemist of the Department of Agriculture of the Colony of New South Wales. Their goal to select lines with good milling quality was difficult because Farrer’s plots produced only ounces of grain for testing. In a day when there was no written background to the task, Guthrie set about devising small-scale milling equipment that could produce flour from the many small samples of grain coming from Farrer’s breeding program. Guthrie used two pairs of small rolls manufactured by the Ganz Company of Budapest. The testing procedure was extremely tedious, requiring 13 successive passes of milling and sieving. Guthrie’s test mill and the results have been described in several publications. In addition, his mill has been reconstructed as a one-quarter-scale model as a result of the efforts of Mr Colin Hopkins, a retired chemical engineer. In contrast to this 120-year-old technology, there is now more advanced technology for test milling very small grain samples (only 5 to 10 grams of grain) with the development of a novel laboratory micro-mill, the FQC-2000, manufactured by Inter-Labor, Hungary. These old and new developments have involved collaborations between Hungary and Australia.

Effects of Roll Diameter and Offset on Sectional Shape of Square Steel Pipe Processed by Roll Forming

A square steel pipe is reshaped from a welded round pipe by roll forming. We investigated the effect of the roll diameter on the cross-sectional size of the square steel pipe by experimentation and three-dimensional finite element (FE) simulation. When the diameters of the top and bottom roll pairs are larger than those of the pair of side rolls, the cross section width of the formed pipe is less than the height. To equilibrate them, we perform finish forming at the final stage. Furthermore, the width of corner part of the formed pipe is greater than its height. The difference between these two sizes of width and height of the corner part in the final product is greater than those at upstream stands and increases with the ratio of the diameter of top and bottom roll pairs to that of side roll pairs. Offset the smaller roll pairs upstream makes the pipe square. Such offset is effective for producing pipes with equal width and height at the corner.

Two phenomena: Honji instability, and ringing of offshore structures

Honji instability and ringing of offshore structrures are two different phenomena. Honji instability occurs at a circular cylinder in transverse periodic finite motion in a water tank. It is superposed on the streaming flow induced by the cylinder's boundary layer. Its oscillation period is half of the period of the cylinder oscillation. Finite volume calculations of the filtered Navier-Stokes equations visualize the three-dimensional instability, where fluid particles transported by the circumferencial roll pairs exhibit a periodic mushroom-like pattern. Force is the same with and without the Honji instability. The large eddy simulation calculations for high Reynolds number support a drag coefficient in accordance with the Stokes-Wang solution below separation and conform with experimental measurements of the damping force on a harmonically oscillating cylinder. Ringing of offshore structures are vibrations which appear at natural frequencies and concern fatigue. It is generated by a higher harmonic force oscillating with frequency being 3–4 times the fundamental wave frequency. Together with a strong inertia load in phase with the incoming wave's acceleration, a secondary load cycle appears in strong seas when the wave crest leaves the structure; this occurs about 1/4 wave period after the main force peak, it starts when the wave crest is about one cylinder radius behind the cylinder, lasts for about 15–20 percent of the wave period and has a magnitude up to 11 % of the peak-to-peak total force. It is a gravity effect and appears in strong irregular seas when kA > 0.18 and um/gD>0.4 (k wavenumber, A amplitude, um maximal wave induced velocity, g acceleration of gravity, D cylinder diameter).

Representation of planar motion of complex joints by means of rolling pairs. Application to neck motion

We propose to model planar movements between two human segments by means of rolling-without-slipping kinematic pairs. We compute the path traced by the instantaneous center of rotation (ICR) as seen from the proximal and distal segments, thus obtaining the fixed and moving centrodes, respectively. The joint motion is then represented by the rolling-without-slipping of one centrode on the other. The resulting joint kinematic model is based on the real movement and accounts for nonfixed axes of rotation; therefore it could improve current models based on revolute pairs in those cases where joint movement implies displacement of the ICR. Previous authors have used the ICR to characterize human joint motion, but they only considered the fixed centrode. Such an approach is not adequate for reproducing motion because the fixed centrode by itself does not convey information about body position. The combination of the fixed and moving centrodes gathers the kinematic information needed to reproduce the position and velocities of moving bodies. To illustrate our method, we applied it to the flexion–extension movement of the head relative to the thorax. The model provides a good estimation of motion both for position variables (mean Rpos=0.995) and for velocities (mean Rvel=0.958). This approach is more realistic than other models of neck motion based on revolute pairs, such as the dual-pivot model. The geometry of the centrodes can provide some information about the nature of the movement. For instance, the ascending and descending curves of the fixed centrode suggest a sequential movement of the cervical vertebrae.

Roll compaction/dry granulation: Comparison between roll mill and oscillating granulator in dry granulation

Different experimental factorial designs were employed to evaluate granule properties obtained from oscillating granulator and roll mill. Four oscillating-granulator parameters were varied, i.e. rotor speed, oscillating angle, aperture of mesh screen and rotor type. Six roll-mill parameters that were throughput, speed ratio in both first and second stages, gap between roll pair in both stages and roll-surface texture were also investigated. Afterwards, the granule properties obtained from two milling types with similar median particle size were compared. All milling parameters in both milling types affected significantly the median particle size, size distribution and amount of fine particles (P < 0.05), except the rotor types of oscillating granulator on fines. Only three milling parameters influenced significantly the flowability (P < 0.05). These were the throughput and the gap size in the first stage of roll mill and the sieve size of oscillating granulator. In comparison between milling types, the differences of granule properties were not practically relevant. However, the roll mill had much higher capacity than the oscillating granulator about seven times, resulting in improving energy savings per unit of product. Consequently, the roll mill can be applied instead of oscillating granulator for roll compaction/dry granulation technique.

Characteristics of solute segregation in continuous casting bloom with dynamic soft reduction and determination of soft reduction zone

A mathematical model accounting for the discharge of solute enriched liquid from the mushy zone with soft reduction by one pair of pinch rolls was established, and the ratio of solute concentration in the mushy zone before and after soft reduction, named as solute segregation ratio, is proposed to describe the characteristics of solute segregation. The theoretical analysis of solute segregation ratio at different soft reduction positions shows that the start point of the soft reduction zone should not be greater than the minimum optimum soft reduction position and the end point of the soft reduction zone should not be less than the maximum optimum soft reduction position corresponding to minimum solute segregation ratio. The soft reduction industrial practices of steel YQ450NQR1 and steel 37Mn2 were carried out with the soft reduction parameters determined by the model, and results showed that the inner quality was improved.

A new design method for single DOF mechanical presses with variable speeds and length-adjustable driving links

This paper proposes a new design method for obtaining or improving the desired output motion characteristics of single-degree-of-freedom mechanical presses by appropriate design of the speed trajectory and length of the adjustable driving links. This approach adds a ternary link to the original mechanism. The ternary link is adjacent to the driving link, roller link, and connecting link, making use of a sliding pair, revolute pair, and a second revolute pair, respectively. The roller link is adjacent to the ternary link and fixed link by a revolute pair and a rolling pair. It is guided by a specially designed slot in the fixed link while the driving link is driven by a servomotor with a specific speed trajectory. A Bezier curve is used to design the input speed trajectory and the contour of the slot. Examples are given to demonstrate the feasibility of this work.

Representation of motion of human joints by means of rolling pairs. Application to neck motion

Representation of motion of human joints by means of rolling pairs. Application to neck motion

A Design Method for Four-bar Mechanisms with Variable Speeds and Length-adjustable Driving Links

This paper proposes a design method to improve or obtain the desired output motion characteristics of single degree-of-freedom (DOF) Four-bar mechanisms by varying the speed trajectory and the length of the input link. This approach adds a ternary link to the original mechanism. The ternary link is adjacent to the input link, roller link, and connecting link, and makes use of a sliding pair, revolute pair, and revolute pair, respectively. The roller link, which is adjacent to the ternary link and fixed link by a revolute pair and a rolling pair, is guided by a designed slot embedded in the fixed link while the input link is driven by a servomotor with a specific speed trajectory. A Bezier curve is applied to determine the input speed trajectory and contour of the guiding slot. Examples are given to verify the feasibility and effectiveness of this work.

Fatigue-induced surface failure of rolling-pair members under conditions of active lubricating medium

The work presents the results of experimental investigation of pitting in rolling pairs. The role of the microgeometry of friction surfaces and active components of the lubricating medium containing wear debris is shown in the formation of microcracks leading to fatigue failure of materials. A criterion for estimating resistance to pitting depending on the working surface quality of the parts is proposed.

Characterization of fluid flow patterns and heat transfer in horizontal channel mixed convection

Two mechanisms of roll initiation are highlighted in a horizontal channel flow, uniformly heated from below, at constant heat flux (Γ = 10, Pr = 7, 50 ≤ Re ≤ 100, 0 ≤ Ra ≤ 106). The first mechanism is the classical one, it occurs for low Rayleigh numbers and is initiated by the lateral wall effect. The second occurs for higher Rayleigh numbers and combines the previous effect with a supercritical vertical temperature gradient in the lower boundary layer, which simultaneously triggers pairs of rolls in the whole zone in between the two lateral rolls. We have found that in the present configuration, the transition between the two roll initiation mechanisms occurs for Ra/Re2 ≈ 18. Consequently, the heat transfer is significantly enhanced compared to the pure forced convection case owing to the flow pattern responsible of the continuous flooding the heated wall with cold fluid.

이중 곡률을 가지는 선박용 외판 성형을 위한 점진적 롤 성형 공정의 적용에 관한 실험적 연구

In order to manufacture a doubly curved sheet metal, the incremental roll forming process which adopts advantages such as the flexibility of the incremental forming process and continuous bending deformation of the roll forming process has been experimentally investigated. An experimental equipment was developed which was named as unit roll set (URS) consisting of two pairs of support rolls and an upper center roll. The upper roll equipped with the servo control unit is motor-driven and can be positioned in the vertical direction according to the user's commands. Four support rolls are idle, and they freely rotate only along the axis so as to transfer the plate more stably in the tangential direction of the rotation of the driving roll. In the process, the plate is deformed incrementally as deformation proceeds simultaneously in longitudinal and transverse directions. Through the experiments using URS, information regarding to forming schedules is found out to fabricate curved hull plates. This study demonstrates the further application of the incremental roll forming process in shipbuilding industries.

Modification of the Atmospheric Boundary Layer by a Small Island: Observations from Nauru

Abstract Nauru, a small island in the tropical Pacific, generates cloud plumes that may grow to over 100-km lengths. This study uses observations to examine the mesoscale disturbance of the marine atmospheric boundary layer by the island that produces these cloud plumes. Observations of the surface layer were made from two ships in the vicinity of Nauru and from instruments on the island. The structure of the atmospheric boundary layer over the island was investigated using aircraft flights. Cloud production over Nauru was examined using remote sensing instruments. The diurnal cycles of surface meteorology and radiation are characterized at a point near the west (downwind) coast of Nauru. The spatial variation of surface meteorology and radiation are also examined using surface and aircraft measurements. During the day, the island surface layer is warmer than the marine surface layer and wind speed is lower than over the ocean. Surface heating forces the growth of a thermal internal boundary layer, within which a plume of cumulus clouds forms. Cloud production begins early in the morning over the ocean near the island’s lee shore; as heating intensifies during the day, cloud production moves upwind over Nauru. These clouds form a plume that may extend over 100 km downwind of Nauru. Aircraft observations showed that a plume of warm, dry air develops over the island that extends 15–20 km downwind before dissipating. Limited observations suggest that the cloud plume may be sustained farther downwind of Nauru by a pair of convective rolls. Suggestions for further investigation of the cloud plume are made.

Traveling-wave convection with Eckhaus instability modulation in a binary fluid mixture

For Rayleigh-Bénard convection in a binary fluid mixture, we obtained a traveling-wave state with periodic modulation of spatiotemporal dislocation defects in a rectangular cell by the numerical simulation of full hydrodynamic equations. The investigations show that the creation of pairs of convective rolls triggered by Eckhaus instability leading to this modulation. Because the generating frequencies of rolls at the left wall smaller than the annihilating frequencies of rolls at the right wall, the system soon move out of the stable region, in this way the system oscillates back and forth between the stable and unstable Echkaus wave number band. The properties of heat transfer and fluid mixing also studied too.

Buoyancy driven vortex flow and its stability in mixed convection of air through a blocked horizontal flat duct heated from below

Experimental flow visualization combined with transient temperature measurement are carried out here to explore the possible stabilization of the buoyancy drive vortex flow in mixed convection of air in a bottom heated horizontal flat duct by placing a rectangular solid block on the duct bottom. Two acrylic blocks having dimensions 40 × 20 × 5 mm 3 (block A) and 40 × 20 × 10 mm 3 (block B) are tested. The blocks are placed on the longitudinal centerline of the duct bottom at selected locations. How the location and orientation of the rectangular block affect the stability of the regular vortex flow is investigated in detail. Experiments are conducted for the Reynolds number varying from 3 to 30 and Rayleigh number from 3000 to 6000, covering a wide range of the buoyancy-to-inertia ratio. For longitudinal vortex flow, the presence of either block near the duct entry causes the onset points of the longitudinal rolls to move significantly upstream especially for the roll pair directly behind the block. Besides, the longitudinal vortex flow in the exit portion of the duct is destabilized by the block. The transverse vortex flow is found to be only slightly affected by the block when it is placed in the exit half of the duct. Significant deformation of the transverse rolls is noted as they pass over the block. However, they restore to their regular shape in a short distance. Substantial decay in the transient flow oscillation results in the region right behind the block. Elsewhere the flow oscillates at nearly the same frequency and amplitude as that in the unblocked duct. When the block is placed near the duct entry, stabilization of the vortex flow behind the block is more pronounced. This flow stabilization is more prominent for block B with its height being twice of block A. Placing the block with its long sides normal to the forced flow direction can also enhance the flow stabilization. For the mixed longitudinal and transverse vortex flow, placing the block near the duct inlet causes the transverse rolls to change to regular or deformed longitudinal rolls in the duct depending on the buoyancy-to-inertia ratio and orientation of the block. The flow stabilization by the block is substantial. Again the stabilization of the mixed vortex flow can be enhanced by increasing the block height and length and by placing the block with its long sides normal to the forced flow direction.

309 ねじり機構を付加したフレキシブルロール成形装置の開発(塑性加工)

A new flexible roll bending system that can bend a plate into various shapes with curved and torsional surfaces was developed. It consists two pair of feeding rolls and a pair of forming rolls. The effects of relative position and the angle of the forming rolls on the shape of deformed specimen were examined. As a result of the experiments, the position and angle affected the feeding direction curvature and the torsion rate of the shape of specimen respectively. Therefore, it is necessary to control those two parameters simultaneously in order to form products that have various curvature and torsion.

A Method of Stock Roll Selection and Order Assignment by Analysis of Flaw Feature for A Rectangular Cutting Stock Problem Against Flawed and Selectable Stock Rolls

The target of this research is a rectangular cutting stock problem against flawed stock that orders are assigned to the stock rolls avoiding flaws and connecting the stock rolls for efficient assignment. The problem has the feature that total area of all stock rolls is larger than one of orders, so that, first the stock rolls used for assignment are selected from all stock rolls. In order to effectively use the “cumbersome stock rolls, whose assignment evaluation tends to be small, in this research, two methods are proposed; a method of formulizing of a cumbersome stock roll, and a method to connect divided stock rolls effectively. In the former method, the is expressed from two factors, namely rate of flaws' area and complexity of flaws, and the parameter is added to a total evaluation. In the latter, “improvement degree of a pair of divided stock rolls is introduced, and the pair whose improvement is high, is connected. The proposed method has been applied to real cutting stock problems. It is confirmed that the method can generate the solutions as same level as expert's solutions.