Investigation of the wear of rolls in asymmetric rolling

In the present work, both symmetric and asymmetric rolling processes were investigated by means of numerical approaches. From the algorithm presented, the values of rolling pressure and sliding velocity in the roll gap were determined. These variables allow the estimation of tribological parameters of a given material. To determine the wear of the rolls and rolled materials the Archard's law has been employed. Results of numerical simulations show that the quantitative characteristics of the wear reveal a slight change for slower roll. Whereas the wear value for the faster roll increases with an increase of roll velocity ratio. It was found that for a given roll velocity ratio, rise of friction coefficient causes insignificant change in the wear value for the slower roll, while this value tends to decrease rapidly for the faster roll.

Vibration Control of Vehicle by Active Suspension with LQG Algorithm

In this paper, the ride performance of a vehicle with active suspension and Linear Quadratic Gaussian (LQG) controller has been studied and is compared to the performances of a traditional passive suspension system. The study includes variables that are related to a passenger’s comfort: vertical position, vertical velocity, pitch angle, pitch velocity, roll angle, and roll velocity. The performances of the two systems are evaluated by maximum values and root mean square (RMS) of the variables when riding on a sinusoidal road profile. The simulation results show that the vehicle with active suspension and LQG controller performs better than passive suspension system where the maximum values decrease by 85.77%, 92.73%, 50.31% 86.83%, 89.41%, 43.28%, and RMS values decrease by 88.59%, 92.36%, 42.99%, 87.61%, 90.85%, and 42.79% for vertical position, vertical velocity, pitch angle, pitch velocity, roll angle, and roll velocity, respectively.

Ring Rolling speed rolls optimization to improve ring quality and reduce production time

In this paper, an analysis of the production time reduction as a function of the Idle and Axial rolls speed law in a Ring Rolling process was examined. Starting from an industrial case study, the authors defined a new milling curve able to produce a better ring quality with lower loads. From this result, the authors tested the effect of the production time reduction till the 40% of the initial one. The Ide roll velocity was varied in a range between 0.71 and 1.13 mm/s while the Axial roll between 0.35 and 1.70 mm/s. Geometrical and load parameters have been taken into account to compare the results achieved. The authors identified in the external ring diameter and in the Idle roll maximum load the most critical parameter to control; in particular, a break-even point was determined in order to select a set of rolls speed laws able to produce a good quality ring with lower production time (about 20%) and lower loads (about 10 %). In this research both experimental and numerical approaches were followed.

Development of Breathable Films from Blends of Low-Density Polyethylene and Thermoplastic Polyester Elastomer

The main drawback of low-density polyethylene (LDPE) film for packaging of fresh fruit or vegetables is low moisture breathability. This study developed breathable films by blending LDPE with thermoplastic polyester elastomer (TPEE). LDPE and TPEE in the weight ratios of 95/5, 90/10, 80/20, 70/30, and 60/40 wt% were melt blended and then extruded into films using a cast film extruder. Clarity of films was characterized by UV-VIS spectroscopy. Tensile properties, tear resistance, the degree of crystallinity, and morphology of blend films were evaluated. Water vapour transmission rate (WVTR) was investigated using a desiccant method. The prepared films were transparent. However, the UV-VIS transmittance was reduced slightly. Blending TPEE of more than 10 wt% reduced the modulus but increased elongation at break. It did not impact on the tensile strength of the blends. Since LDPE and TPEE are immiscible, applied stress during extrusion pulled them apart at the interphase boundaries creating micro-pores. As a result, these micro-pores reduce tear resistance significantly but increase WVTR of the blend films. Using a blend ratio of 90/10 wt%, the effect of chill-roll temperature and nip-roll velocity on film properties were studied. It was found that nip-roll velocity had more influence on WVTR than chill-roll temperature due to elongation of the pores.

Numerical Simulation of the Effect of Process Parameters on Cooling Rate and Secondary Dendrite Arm Spacing in High-Speed Twin Roll Strip Casting of Al–15 wt % Cu Alloy

Twin roll casting is a process used to produce thin strips of metals by continuously pouring melt on to rotating rolls. In order to make the process more productive and economical, high roll speed is recommended. The numerical simulation of high-speed twin roll casting is performed by analyzing fluid flow, heat transfer, and solidification behavior of Al–Cu hypo-eutectic alloy. The flow field, temperature, liquid fraction distribution, and cooling rate are analyzed by solving governing transport equations of continuity, momentum, energy, and turbulence. The low-Re Turbulence model is used to capture turbulence effects in the process and enthalpy-porosity technique used to account for the rise in viscosity due to phase change. The effect of melt pool height and roll velocity on average cooling rate along the strip surface is investigated. It is found that the increase in melt pool height and roll speed increases the average cooling rate along strip surface due to rise in heat transfer up to certain roll velocity but beyond that process fails due to breakout. The average cooling rate of process affects the microstructure and properties of strips. It is found that higher cooling rates result in a decrement of secondary dendrite arm spacing (SDAS) of 1 mm thin strip along strip surface results in the fine and homogeneous microstructure.

Impact of Spasticity on Balance Control during Quiet Standing in Persons after Stroke

Background. Balance impairments, falls, and spasticity are common after stroke, but the effect of spasticity on balance control after stroke is not well understood.Methods. In this cross-sectional study, twenty-seven participants with stroke were divided into two groups, based on ankle plantar flexor spasticity level. Fifteen individuals with high spasticity (Modified Ashworth Scale (MAS) score of ≥2) and 12 individuals with low spasticity (MAS score <2) completed quiet standing trials with eyes open and closed conditions. Balance control measures included centre of pressure (COP) root mean square (RMS), COP velocity, and COP mean power frequency (MPF) in anterior-posterior and mediolateral (ML) directions. Trunk sway was estimated using a wearable inertial measurement unit to measure trunk angle, trunk velocity, and trunk velocity frequency amplitude in pitch and roll directions.Results. The high spasticity group demonstrated greater ML COP velocity, trunk roll velocity, trunk roll velocity frequency amplitude at 3.7 Hz, and trunk roll velocity frequency amplitude at 4.9 Hz, particularly in the eyes closed condition (spasticitybyvisioninteraction). ML COP MPF was greater in the high spasticity group.Conclusion. Individuals with high spasticity after stroke demonstrated greater impairment of balance control in the frontal plane, which was exacerbated when vision was removed.

Sensory Interactions for Head and Trunk Control in Space in Young and Older Adults During Normal and Narrow-Base Walking

Fifteen young (20–30 years old) and 15 older (>65 years old) healthy participants were recruited to investigate age-related differences in head and trunk control under suboptimal vestibular conditions (galvanic vestibular stimulation, or GVS) and vision conditions during normal and narrow-based walking. Head-roll velocity decreased in the blurred-vision condition and marginally increased with GVS in older but not in young participants. Head pitch increased, whereas head-roll velocity decreased in narrow-base walking. Trunk pitch, trunk-pitch velocity, and gait speed increased with GVS, whereas trunk-pitch velocity and gait speed decreased in narrow-base walking. Marginally increased head-roll velocity in the older participants possibly suggests decreased integrative ability of the central nervous system in elderly people. The changes in head control during narrow-base walking may be an attempt to simplify the interpretation of the vestibular signal and increase otolith sensitivity. The complexity of controlling the trunk in the mediolateral direction was suggested by different strategies used for trunk control in different conditions.

Analysis of Flexible Roller Parameters Influences on Roll Forming of Three-Dimensional Parts

Roll forming is a well known bending process and sheet metals can only be machined into two-dimensional surfaces in traditional roll forming. While with more and more personalized demands, three-dimensional surfaces are widely required. Thus, flexible rollers are used to achieve three-dimensional surfaces. And in order to optimize experimental parameters and to predict experimental results, finite element method (FEM) is developed. In this paper the set-up of flexible roll-forming is described and the process of roll forming is simulated. Then the influences of forming parameters, such as the thickness and the roll velocity, on forming quality of the sheet metal in roll forming process are discussed. The results show that the analysis of flexible roller parameters is practical for the continuous and efficient forming of three-dimensional surfaces.

Ribbing Instability Analysis of Forward Roll Coating

The ribbing instability of forward roll coating is analyzed numerically by linear stability theory. The velocity ratio of two rolls is fixed to be 1/4 for practical surface coating processes. The base flows through the gap between two rolls are solved by use of powerful CFD-RC software package. A numerical program is developed to solve the ribbing instability for the package is not capable of solving the eigenvalue problem of ribbing instability. The effects of the gap between two rolls, flow viscosity, surface tension and average roll velocity on ribbing are investigated. The criterion of ribbing instability is measured in terms of critical capillary number and critical wave number. The results show that the surface coating becomes stable as the gap increases or as the flow viscosity decreases and that the surface coating is more stable to the ribbing of a higher wave number than to the ribbing of a lower wave number. The effect of average roll velocity is not determinant to the ribbing instability. There are optimum and dangerous velocities for each setup of rolling process.