Rolling Regime Research Articles

Nature of roll to spiral-defect-chaos transition

We investigate the nature of the parallel-roll to spiral-defect-chaos (SDC) transition in Rayleigh-Benard convection, based on the generalized Swift-Hohenberg model. We carry out extensive, systematic numerical studies by, on one branch, increasing the control parameter gradually from the parallel roll regime to the SDC regime and, on the other branch, decreasing it in the opposite manner. We find that the data of several time-averaged global quantities all form hysteretic loops from the two branches. We also discuss several possible scenarios for the transition and analyze our data for SDC accordingly. We conclude that the roll-to-SDC transition is first-order in character and that the correlation length diverges at the conduction to convection onset. We further postulate that this transition can be understood somewhat similar to the hexagon-to-roll transition in non-Boussinesq fluids. Finally we comment on the differences between our conclusion and those in two experiments.

Effects of geometry on the characteristics of the motion of a particle rolling down a rough surface

The different dynamic regimes of a sphere rolling on a rough inclined surface have been studied experimentally, with special attention to the effects of energy dissipation and geometry. A controlled roughness of the surface is obtained by gluing glass beads or sand onto a plane. Three different types of rolling spheres (steel, glass and plastic) have been used on two kinds of rough surface (glass beads and sand). The different regimes can be presented in a phase diagram whose control parameters are θ, the inclination angle of the plane, and R, the radius of the rolling sphere (in fact, we use Φ, the surface smoothness, which is the ratio of R and r, the radius of the glued beads). A comparative analysis is done, showing that the behaviour is qualitatively not dependent on the system, and a ‘universal’ dynamical threshold line is obtained for all the particle-surface systems studied. We also confirm that the motion is characterized by a viscous friction force, strongly dependent on the smoothness.

The modelling of the mechanics of deformation in flat rolling

Numerous mathematical models have been developed at Port Kembla Laboratories, BHP Research, to study the flat rolling processes. This paper discusses those models developed for the examination of the plastic deformation of the workpiece in the roll bite. Depending on the rolling regime, models of different complexities are required to predict accurately the strip and roll deformation in the roll gap. This paper covers models ranging from hot rolling to skin pass rolling, from very high reduction to extremely low reduction. Validation and applications of the models are also illustrated.

On the mechanism of cold rolling thin foil

The deformation mechanism of cold rolling thin foil is investigated with the aid of the slab method in conjunction with an incremental analysis. The interaction between the rolls and foil is explored thoroughly. The effects of initial thickness and yield stress of foil materials are discussed in detail. Extensive numerical studies show that the pressure and shearing force profiles in the rolling bite vary significantly with the increment of reduction ratio. The distribution of slip and no-slip zones is much more complex than that predicted previously. In the regime of rolling extremely thin foils with a constant reduction ratio, the rolling load increases and the rolling torque decreases monotonically with decreasing inlet foil thickness. It is found, however, that the change of the central elastic/plastic no-slip zones has very little effect on the resultant rolling forces.

Combined simulation and knowledge-based control of a stainless steel rolling mill

Abstract A combined Expert System/Simulation approach is outlined which provides consistent reduction schedules for the cold rolling of stainless steel strip. The system combines the heuristic knowledge of the expert operators with deeper physical models of the rolling mill and associated processes. The initial goal of the system is to predict mill setup conditions and provide an appropriate rolling regime (schedule) for the steel strip. The subsequent status of the mill and material being rolled is identified via simulation in a network of component models to detect triggering conditions for various corrective actions. Reactive rescheduling uses information accrued from the on-line real time process data to generate a more suited schedule for subsequent processing of the material.

Improved teeming of steel for drill-pipe production

The open-hearth shop at the Taganrog Metallurgical Plant is undertaking a comprehensive program to improve the technology employed for teeming steel from 150-ton ladles equipped with slide gates. The ladles were designed by the All-Union Scientific Research, Planning, and Design Institute of Metallurgical Machinery. The metal is bottom-poured into unlubricated through-type big-end-down ingot molds. Inserts made of kaolin wool are placed in the top part of the mold. The surface of the molten metal is protected by an ash-graphite mixture. A 140-160-ram-high region where the inserts are located is filled more slowly than the rest of the moldo Here, the stream is narrowed by partially closing the gate for I 1.5 rain. A specially designed gauge is used to objectively monitor the rate at which the mold is filled. Thermal insulation of the top part of the ingots with the inserts and the ash--graphite mixture has significantly improved the macrostructure of the metal. The ingots have a smooth surface free of ripples, and almost no ingots are rejected for cracks and scabs (steel 32G2). A distinguishing feature of drill-pipe production at the plant is the rolling regime. It is known that scab formation on tubes is reduced by reducing the deformation which occurs during piercing of the ingot. To reduce deformation during piercing, we use ingots of smaller diameter than normal. A redistribution of the strains between the piercing and Pilger mills (a reduction in the elongation factor during piercing from 1.74-2.07 to 1.58-1.62 and an increase in the elongation factor on the Pilger mill from 9.7-10.5 to 11-13.4) and a decrease in the diameter of Pilgermill rolls from 198 to 178 mm made it possible to reduce the proportion of tubes rejected for scabs and increase the output of 12-m drill pipe from 42.35-49.43 to 73.35-75.70%~

Ways of improving the quality of automobile steels

If steel has to have good stampability, it must have low yield strength; this is attained by lengthy annealing in bell furnaces. By heat treatment in high-speed continous installations (CI) it is impossible to attain the level of mechanical properties required by GOST 9045-80. The necessity of reducing the time for heat treatment of steel strip entails more stringent requirements concerning its chemical composition (Table I), methods of reduction and pouring of the steel, the regimes of hot and cold rolling, heat treatment and dressing [i].

On the secondary instability in inclined air layers

The heat transfer across an inclined air layer in the longitudinal roll regime often falls below expected values. A companion paper (Ruth et al. 1980) presents the heat transfer measurement and flow visualization observations; the present paper discusses the mechanisms which are thought to be responsible for this anomalous behaviour and formulates a simple model which correlates the results of our previous study and that of Hart (1971). The observed suppression of heat transfer below values expected for pure longitudinal roll motion is explained in terms of a shear instability. A stabilizing mechansim, which would restore the longitudinal rolls at higher Rayleigh numbers, is described; the return of the heat transfer to expected levels at higher Rayleigh numbers is ascribed to this mechanism. Comparisons are made between the results of the present model and the analyses of Clever & Busse (1977).

On the transition to transverse rolls in an infinite vertical fluid layer—A power series solution

The criteria governing the transition from the conduction regime to the transverse roll regime in a vertical infinite fluid layer are found by means of a power series method. The calculated values are shown to be in agreement with previously published results. Findings concerning the variation of the Gr c and α c with Pr are presented. An anomalous behaviour was found at Pr ⋍ 1.75.

Pressure Distribution on a Thin Viscoelastic Strip Rolling between Two Rigid Cylinders

A simplified theoretical analysis has been used to examine the rolling of a thin viscoelastic strip between rigid rolls. For a material, thin in relation to the nip contact length and having the behaviour of a standard linear solid, rolling regimes of practical interest are defined in terms of a parameter τV, where τ is the relaxation time of the material and V is the rolling speed. Simple pressure distributions are derived for each rolling regime. These were interpreted on the basis of the forward skewing of the pressure distribution (the shift of the peak nip pressure to a point between the ingoing contact point and the mid-nip), to establish the conditions for importance of viscoelastic effects. Practical criteria, expressed in terms of τV and length dimensions associated with the nip contact zone, were established to determine when the effect of viscoelasticity was negligible, when it was small, and when it passed through a maximum.