Critical Rolling Speed Research Articles

A numerical study on the impact of lubricant rheology and surface topography on heavily loaded non-conformal contacts

The increasing requirement of high-power density (power throughput/ weight) in modern day machines lead to thin film lubrication condition in various machine components (rolling element bearings, gears, cams, etc,) due to severe loading conditions. Surface roughness features and lubricant rheology plays a vital role in thin film lubrication, and significantly affects the lubrication performance and lifetime of machine components. The present work demonstrates surface topography and lubricant rheology effects on the traction coefficient for heavily loaded non-conformal contacts. The load-sharing concept considering elastic-plastic deformation of asperities, and Carreau shear-thinning rheological model is employed to describe the dry rough contacts and non-Newtonian behavior of lubricant. An influence of surface topography parameters such as roughness, skewness, kurtosis, and pattern ratio on the traction coefficient is discussed. From results, it is found that among different surface topographies, negatively skewed surfaces having isotropic surface pattern exhibit minimum traction coefficient. The load share function and the critical rolling speed are determined for various surface topographies which provides further insights into the surface topography effect on traction coefficient. The findings of present study are noteworthy as they provide a theoretical basis for an assessment of the lubrication performance of heavily loaded non-conformal contacts.

Study on Defect Evolution of Steel Strip under High-speed Cold Rolling

In this paper the strain rate effect of the material was quantitatively tested by INSTRON tensile testing machine and Zwick/Roell HTM5020 high-speed tensile testing machine. The dimple size of the fracture surface of the tensile specimen was determined and analyzed by using the scanning electron microscope. Based on the Cowper-Symonds constitutive model, the parameters in the dynamic constitutive model and the true stress-strain curve under quasi-static condition were obtained by combining the results of quasi-static and dynamic tensile tests and the finite element numerical analyses. Considering the strain rate effect of the material the effects of cold rolling speed on the evolution of different types of defects were analyzed by the ANSYS/LS-DYNA dynamics code. The results show that with the increasing of crack length and decreasing of crack width, the critical rolling speed decreases. But if the crack length is less than 5 mm and the aspect ratio of crack length to crack width is larger than 5, the critical rolling speed of crack growth can be much large.

Dynamics-based optimization of rolling schedule aiming at dual goals of chatter suppression and speed increase for a 5-stand cold tandem rolling mill

In the process of cold tandem rolling, chatter instability leads to serious impacts on enhancing rolling speed, improving product quality, reducing production cost and realizing intellectualization. Chatter occurs with the rolling speed up to a certain threshold value, but the critical speed is determined by both product specifications and rolling schedules. A 5-stand cold tandem rolling mill whose first three stands and subsequent two stands, respectively, have four and six rolls was investigated by formulating its dynamic equations with the corresponding structure–process coupling. By applying the stability-based calculation model about the critical rolling speed in each stand, the system dynamic responses around the critical rolling speed were simulated, and the system eigenvalues which represent instability and characteristic frequencies were figured out. Thereafter, via combining the critical rolling speeds with the system dynamic behavior, a dynamics-based optimization model of rolling schedule for the 5-stand cold tandem system was proposed for the purposes of both the chatter suppression and rolling speed increase. In the optimization model, eight rolling technique parameters (four strip thicknesses and four tensions between the upstream and downstream stands) were taken as design variables, and the constraint conditions were set as no chatter instability in all five stands, and the optimization goal was to maximize the outlet speed of the final stand. The pattern search method was introduced to solve the optimization model. By applying such a dynamics-based optimization model for the 5-stand cold tandem rolling process, the chatter instability was suppressed effectively and the rolling efficiency was improved considerably; therefore, such an optimization model is expected to be valuable for intelligent manufacturing of rolling process.

Dynamic analysis of vibration stability in tandem cold rolling mill

Tandem cold rolling mills are comprehensive dynamic systems coupling with structure and rolling technology. A frequent problem is mill chatter, often occurring when rolling hard, thin materials at high speed and affecting the quality of the strip. In this paper, a dynamic increment model for chatter in a Universal Crown Control mill (UCM mill) is proposed with the considering of strip hardening, elastic deformation of the work roll, non-linear friction, transfer delay of the strip, and dynamic coupling effect of tension between adjacent stands. Mathematically, this model is based on the Taylor series expansion of the Bland-Ford-Hill rolling force equation. The comparative results of both simulation and experimental data show that this chatter model has a high accuracy. A novel, time-varying stability criterion is proposed to evaluate mill stability. Further study is provided on the optimal friction coefficient and reduction ratio required to increase the critical rolling speed and vibration stability in a tandem cold rolling mill. This mathematical criterion is validated by comparing the actual rolling speed with the calculated critical rolling speed. The present work provides a more accurate prediction of mill chatter and a basis for optimal design of rolling conditions.

Influence of asymmetric structure parameters on rolling mill stability

Considering the asymmetric structure of a rolling mill system, a chatter model is established by coupling a rolling process model and structure model to describe the asymmetric vibration characteristics. According to this mathematical model, the critical rolling speed is determined by calculating eigenvalues of the characteristic matrix. Model correctness and validity are confirmed by an experimental observation of a 2030 cold rolling mill. On this basis, the effects of asymmetric structure parameters on the rolling mill stability are investigated with the help of the numerical approach. It is found that the influence of the asymmetric structure parameters on stability and critical conditions is significant. An optimal stiffness ratio and optimal mass ratio is determined, in order to ensure the best stability for the considered system. As the asymmetry in terms of the stiffness and mass becomes considerable, a modal conversion phenomenon occurs. This study serves as a contribution both for the mill vibration suppressing, and for mill optimization design.

NOISE AS AN INDIRECT CRITERION FOR EVALUATING THE CRITICAL SPEED OF VEHICLE TIRE AT HYDROPLANING

An alternative method for determining the critical rolling speed of automobile tires with various tread patterns during hydroplaning is considered. The critical speed of the car at which the hydroplaning process takes place is determined. This method is based on recording the tire noise emission when driving on a wet road pavement

On models and methods of mechanics of pneumatic tires and rubber-cord shells. Development of the ideas due to Professor V. L. Biderman

A survey of work of Professor V. L. Biderman’s scientific school concerned with the mechanics of tires and rubber-cord shells is presented. Analytical models of diagonal and radial tires aimed at analyzing their stress-strain state, calculating the critical rolling speed, and determining their operating characteristics are discussed. The theory of pneumatic lattice shells is presented in detail, and its new technical applications are considered. The equations of lattice shells of revolution are generalized to the case of nonsymmetric cord placement.

Research on Critical Rolling Speed of Self-excited Vibration in the Tandem Rolling Process of Thin Strip

Research on Critical Rolling Speed of Self-excited Vibration in the Tandem Rolling Process of Thin Strip

Multiple-Modal-Coupling Modeling and Stability Analysis of Cold Rolling Mill Vibration

An effective dynamic model is the basis for studying rolling mill vibration. Through analyzing characteristics of different types of vibration, a coupling vibration structure model is established, in which vertical vibration, horizontal vibration, and torsional vibration can be well indicated. In addition, based on the Bland-Ford-Hill rolling force model, a dynamic rolling process model is formulated. On this basis, the rolling mill vertical-torsional-horizontal coupled dynamic model is constructed by coupling the rolling process model and the mill structure model. According to this mathematical model, the critical rolling speed is determined and the accuracy of calculated results is verified by experimental data. Then, the interactions between different subsystems are demonstrated by dynamic responses in both time and frequency domains. Finally, the influences of process parameters and structure parameters on system stability are analyzed. And a series of experiments are conducted to verify the correctness of these analysis conclusions. The results show that the vertical-torsional-horizontal coupled model can reasonably characterize the coupling relationship between the mill structure and the rolling process. These studies are helpful for formulating a reasonable technological procedure of the rolling process and determining a feasible dynamic modification strategy of the structure as well.

Thin lubricating films behaviour at very high contact pressure

Thin film colorimetric interferometry has been used to examine the behaviour of thin elastohydrodynamic (EHD) lubricant films under very high contact pressures of the order of 0.5–3 GPa. It has been shown that at moderate pressures, the variation of film thickness with speed follows the Hamrock and Dowson prediction down to one nanometer. As the load is increased, however, thin films behave differently from the prediction of the conventional EHD theory. For a certain lubricant and operational conditions, there is a critical rolling speed below which a reduction of film thickness is observed. This behaviour is very similar to that previously predicted computationally by Zhu.

On the Characteristics and Mechanism of Rolling Instability and Chatter

A nonlinear model describing the dynamical interaction between work rolls and metal sheets and the initiation of fifth octave rolling chatter is presented. The model, which comprises a work roll sub-model and a metal sheet roll-bite sub-model, enables the instability of strip rolling to be qualitatively and quantitatively studied as a function of rollstack stiffness, rolling speed, inter-stand tension, roll-bite entry and exit thickness, and the sheet force resulted from the interactive action of the work roll with the plastic deformation of the rolled strip. It is concluded that, even though the governing dynamics is highly nonlinear, rolling chatter instability is none other than mode excitation or beating, and thus linear. Analyzed results correspond well with what have been observed in physical rolling mills. Specifically, the natural frequency predicted for a 4-H rolling stand fits the fifth octave chatter at 550∼650 Hz and there is a critical rolling speed (2.54 m/sec for the material and sheet configurations considered in the paper) beyond which rolling instability will occur. This research establishes the fundamental knowledge base required for the understanding of chatter characteristics and mechanism, and thus provides the essential bases for effective control of rolling instability and chatter-free roll mill design.

Vibration Instability in Rolling Mills: Modeling and Experimental Results

Abstract Models for the occurrence of the vibrational instability during rolling known as third octave chatter are presented and discussed. An analysis of rolling mill chatter was performed for the purpose of identifying characteristics of the vibrations and to determine any dependency on the rolling schedule. In particular, a stability criterion for the critical rolling speed is used to predict the maximum rolling speed without chatter instability on schedules from a 5 stand tandem mill rolling thin steel product. The results correlate well with measurements of critical speed occurring on the mill using a vibration monitor. This research provides significant insights into the chatter phenomena and has been used to investigate control methods for suppression of the instability.

The Role of Surface Tension and Disjoining Pressure in Starved and Parched Lubrication

The starvation of a rolling, elastohydrodynamic contact has been examined both experimentally and theoretically. It has been shown that starvation occurs at a critical rolling speed which is determined by the rate of flowback of lubricant into the out-of-contact track due to oil/air surface tension forces. Above this speed, however, complete collapse of the oil film in the contact does not occur. Instead a film of approximately 10–20 nm thickness persists even to very high speeds. It has been shown that this behaviour can be explained by considering the flowback into the out-of-contact track due to solid/liquid van der Waals forces. Thus a combination of oil/air and oil/solid surface forces can fully explain the phenomena of starved and parched elastohydrodynamic lubrication.

EHD Film Formation and Starvation of Oil-in-Water Emulsions

The elastohydrodynamic film-forming properties of oil-in-water emulsions in rolling point contacts have been investigated using a combination of ultrathin film interferomelry and short duration TV microscopy. It has been shown that at slow rolling speeds, all the o/w emulsions tested formed EHD films comparable to those of their water-free components. Above a certain critical rolling speed, which, depended upon the emulsion composition, the film thickness started to decrease. This was due to EHD starvation, and the film thickness/inlet oil meniscus relationships developed for starved oil systems were found to apply to emulsion starvation. At high rolling speeds, the EHD film thickness did not collapse to zero, but instead leveled off at a low value, typically 10 to 30 nm, which persisted to the highest rolling speeds attained. Presented as a Society of Tribologists and Lubrication Engineers paper at the ASME/STLE Tribology Conference in San Diego, California, October 19–21, 1992

On the dynamic response of rolling tires according to thin shell approximations

The response of the rolling tire is formulated in terms of the natural modes and frequencies of the non-contacting tire for contact loading due to rolling, braking, accelerating or cornering. The tire is viewed as an equivalent thin shell. Formulation is by way of the three-dimensional dynamic Green function of this shell. As the application example, the response of the tire during pure rolling is evaluated. The critical rolling speed at which the tire develops its first large amplitude standing waves is calculated in a novel fashion, showing the relationship between the standing wave phenomenon and natural tire modes and frequencies. Findings underline the need for measuring or calculating higher order tire modes than those considered in what seems to be the present standard practice.

Influence of air on the rolling of powders

1. The air stream produced in the focus of deformation during the rolling of powders differs in magnitude and direction over the width of the hopper; the edges of the strip are formed under the preferential action of the transverse constituent of the gas flow. 2. In addition to leakage of the powder, the strip width may be reduced because some of the powder particles are carried off by the transverse constituent of the air stream. 3. The maximum critical rolling speed may depend on the hopper width.