Backward Slip Research Articles

Research on the characteristics of forward slip and backward slip in alloyed bar rolling by the round-oval-round pass sequence

For determining the neutral line on the contact zone to distinguish the forward slip zone and backward slip zone on the contact surface between the deformed pieces and the roll, the contact surface was discretized as finite flow line elements to build a novel analytic model to reconstruct the geometry of contact surface. Moreover, the velocity of flow lines on the contact surface along the direction of x-axis was derived by the condition of steady-state incompressible flow, and the function of neutral line was obtained by determining the neutral radius and the neutral angle of the points on the neutral line. In addition, the forward slip coefficient and backward slip coefficient was derived and the relative slip condition of contact surface between the roll and the rolled pieces was determined. Based on these mathematical models the geometry of contact surface and neutral line were drawn up by mathematical software. The validity of the theoretical model was verified by rolling experiments of alloyed bar and the numerical simulation by rigid-plastic FEM software. Compared with the experimental data and simulation results, the prediction error of the mathematical model is acceptable and results from the mathematical model are satisfying.

Theoretical analysis of minimum metal foil thickness achievable by asymmetric rolling with fixed identical roll diameters

A novel approach is proposed for computing the minimum thickness of a metal foil that can be achieved by asymmetric rolling using rolls with identical diameter. This approach is based on simultaneously solving Tselikov equation for the rolling pressure and the modified Hitchcock equation for the roller flattening. To minimize the effect of the elastic deformation on the equal flow per second during the ultrathin foil rolling process, the law of conservation of mass was employed to compute the proportions of the forward slip, backward slip, and the cross shear zones in the contact arc, and then a formula was derived for computing the minimum thickness for asymmetric rolling. Experiment was conducted to find the foil minimum thickness for 304 steel by asymmetric rolling under the asymmetry ratios of 1.05, 1.15 and 1.30. The experimental results are in good agreement with the calculated ones. It was validated that the proposed formula can be used to calculate the foil minimum thickness under the asymmetric rolling condition.

Effect of Cold Rolling Parameters on the Longitudinal Residual Stress Distribution of GH4169 Alloy Sheet

For plastic deformed parts, the dimensional accuracy is significantly affected by residual stresses and so does the performance in service. Therefore, the rolling process of GH4169 alloy sheet at room temperature was investigated by finite element method. The effects of rolling reduction, friction coefficient, rolling velocity and initial stress on the longitudinal residual stress distribution over the thickness of GH4169 alloy sheet were analyzed. The results show that the values of longitudinal residual stress can be slightly reduced by increasing the rolling reduction and velocity. The longitudinal residual stress over the thickness distributes as “V” type or weak “W” type. The initial stress mainly has an effect on the longitudinal stress in the backward slip area. But the friction coefficient has remarkable influence on longitudinal residual stress. With the friction coefficient increasing from 0.1 to 0.5, the value of longitudinal residual stress on the sheet surface is reduced by 282 MPa. Simultaneously, the tensile stress turns into compressive stress with a strong “W” type distribution.

THE INVESTIGATION OF THE MAXIMUM POSITION IN CONTACT NORMAL STRESSES RELATIVE TO THE NEUTRAL PLANE BY THE COLD ROLLING

Ascertained data as to the character of the contact stresses distribution have been obtained thanks to the application of the ascertained solution for the differential equation of longitudinal forces’ balance by the cold rolling. The mentioned solution takes into account the kinematics particularities of a deformation zone. These data have been used to determine the position of the maximum in contact of normal stresses relative to the neutral plane. It has been established that the section of the maximum in contact normal stresses is always situated in the backward slip zone and is substantially behind the neutral plane. This fact corroborates conclusions about the discrepancy of these two sections made earlier by A. Nadai, A.A. Korolyov and A.I. Tselikov. It represents the answer to one of the least studied questions in the up-to-date theory of the thin-sheet (cold) rolling. The qualitative data about the influence of technological parameters of the cold rolling process without tension upon the situation of the maximum for epures of the contact normal stresses relative to the neutral plane have been presented in the paper as well as their analytical treatment.

Characteristic and formation mechanism of matt surface of double-rolled copper foil

Copper foils for flexible printed circuit boards were prepared by double rolling, and the matt surface of double-rolled copper foil was characterized by atomic force microscope, scanning electron microscope, 3D optical interferometer, optical microscope and surface profiler. The morphology characteristics of matt surface were studied, and the formation mechanism of matt surface was discussed. The results showed that the matt surface of the double-rolled copper foil presented rough and relatively homogeneous morphology, and the morphologies of upper and lower matt surfaces were practically coincident. As the copper strips just entered into the deforming zone, the roughening of laminated surface occurred, but the roughness was relatively small. When the copper strips passed through the neutral plane, the roughness of the laminated surface increased significantly. In the backward slip zone, the initial micro-dimples between the two laminated surfaces were connected in the rolling direction, which led to the formation of larger and airtight dimples; when the copper strips moved toward the neutral plane and entered into the forward slip zone, the pressure of fluid in the airtight dimples increased rapidly, which enhanced the depths of the dimples; meanwhile, the depression corrugations with certain depth and larger width were formed on the laminated surface because of the dimple connection in the width direction. The copper foils with thickness of 36–54μm were fabricated by double rolling, and the Rz value of their matt surfaces was 1.0–1.3μm, which meet the requirements for directly using as adhesive surface of resin substrate, and therefore multiple roughening treatments during the traditional production process of flexible printed circuit board might be omitted. The formation mechanism of the matt surface of double-rolled copper foil proposed on the basis of the metal flow and deformation mechanics theory could explain the representative characteristics of the length direction of corrugations on matt surface being perpendicular to the rolling direction, several corrugations within a grain on the matt surface and the coincident morphologies of the upper and lower matt surfaces.

Modeling and Analysis of Interstand Tension Control in 6-high Tandem Cold Rolling Mill

The interstand tension control is one of the most important ways to meet tight tolerances for strip product quality during tandem cold rolling process. Using coordinate analysis and parabolic approximation for the mass flow balance principle, the strip velocities eliminating the use of forward slips and backward slips were calculated. In order to reduce the effect of roll eccentricity on the tension measurement, a filter based on bilinear transformation was designed. Applying a first-order Taylor series approximation, the transfer function matrix model of interstand tension stress was derived. The actual measurements on-site and the final calculation results showed that the established model had high calculation accuracy and was beneficial for interstand tension control of tandem cold rolling process.

Burrowing behavior in mud and sand of morphologically divergent polychaete species (Annelida: Orbiniidae).

Muddy and sandy sediments have different physical properties. Muds are cohesive elastic solids, whereas granular beach sands are non-cohesive porous media. Infaunal organisms such as worms that burrow through sediments therefore face different mechanical challenges that potentially lead to a variety of burrowing strategies and morphologies. In this study we compared three morphologically distinct polychaete species representing different clades in the family Orbiniidae and related differences in their burrowing behaviors and morphologies to their natural environments (mud or sand). Worms burrowed in transparent analogs for muds and sands, and kinematic analysis showed differences both among species and between materials. Leitoscoloplos pugettensis lives in mud and burrows by fracture, using its pointed head to concentrate stress at the tip of the burrow. Naineris dendritica lives in sand and uses its broader head that fluctuates in width over a burrowing cycle to decrease backward slipping in sand, potentially preventing burrow collapse. Orbinia johnsoni lives in sand and uses internal body expansions to pack sand grains, another mechanism to prevent burrow collapse. By combining data from species and materials to obtain a broad range of burrowing velocities, we show that burrowing worms control their velocity by increasing or decreasing their burrowing frequency rather than by altering cycle distance as shown previously for crawling earthworms. This study demonstrates how fairly small evolutionary divergences in morphologies and behaviors facilitate locomotion in environments with different physical constraints.

Forward Slip and Backward Slip in Radial Ring Rolling Process

During the process of radial ring rolling, relative slip or relative slip tendency occurs on the interface between the ring and the rolls. Research on the relative slip or relative slip tendency plays an important role on reducing friction to ensure the ring rolling smoothly. In this paper, the reason of relative slip or relative slip tendency is investigated that there is speed difference between tangential component of the ring and linear velocity of the rolls. According to speed difference, slip types of the interface are classified. Forward slip coefficient and backward slip coefficient are defined and derived and relations between them are studied. Comparison between the new method and the previous one is conducted via case study, which proves the rationality and effectiveness.

Degenerative retrolisthesis

We investigated the spinopelvic morphology and global sagittal balance of patients with a degenerative retrolisthesis or anterolisthesis. A total of 269 consecutive patients with a degenerative spondylolisthesis were included in this study. There were 95 men and 174 women with a mean age of 64.3 years (sd 10.5; 40 to 88). A total of 106 patients had a pure retrolisthesis (R group), 130 had a pure anterolisthesis (A group), and 33 had both (R+A group). A backward slip was found in the upper lumbar levels (mostly L2 or L3) with an almost equal gender distribution in both the R and R+A groups. The pelvic incidence and sacral slope of the R group were significantly lower than those of the A (both p < 0.001) and R+A groups (both p < 0.001). The lumbar lordosis of the R+A group was significantly greater than that of the R (p = 0.025) and A groups (p = 0.014). The C7 plumb line of the R group was located more posteriorly than that of the A group (p = 0.023), but was no different from than that of the R+A group (p = 0.422). The location of C7 plumb line did not differ between the three groups (p = 0.068). The spinosacral angle of the R group was significantly smaller than that of the A group (p < 0.001) and R+A group (p < 0.001). Our findings imply that there are two types of degenerative retrolisthesis: one occurs primarily as a result of degeneration in patients with low pelvic incidence, and the other occurs secondarily as a compensatory mechanism in patients with an anterolisthesis and high pelvic incidence.

Temperature distribution and its influence on microstructure of alloy AZ31 during semisolid rheo-rolling process

In the backward slip zone, the buckling direction of the isothermal lines near the surface of the alloy was toward the exit of the roll gap, the buckling direction of the isothermal lines at the centre was toward the entrance of the roll gap and semisolid metal deformation happened. In the forward slip zone, the buckling direction of the isothermal lines was toward the exit of the gap, the bending degree increased from the neutral flow plane to the exit of the roll gap and solid metal deformation took place. The microstructure of the strip became more refined with the decrease in casting temperature. When the casting temperature was between 670 and 690°C and the rolling speed was 0·167 m s−1, the alloy AZ31 strip with cross-section size of 4×160 mm was prepared. The mechanical properties of the product were higher than that of conventional roll casting.

Biomechanical characteristics of slipping during unconstrained walking, turning, gait initiation and termination

Slipping biomechanics was investigated on both non-contaminated and oil-contaminated surfaces during unconstrained straight-line walking (‘walking’), turning, gait initiation and termination. In walking, backward slipping was more frequent, whereas forward slipping was more frequent when turning. Stopping and gait initiation engendered only forward and backward slipping, respectively. Based on slip distance and sliding velocity, severity of forward slipping was least in walking than for the other gait tasks, whereas the tasks had similar effects on backward slipping. Relative to the dry surface, heel and foot contact angles reduced and heel contact (HC) velocity increased for all gait tasks on the contaminated surface. Ground reaction forces were generally lower on the contaminated surface, suggesting kinetic adaptation immediately following HC. Required coefficient of friction (RCoF) did not correlate with slip distance suggesting that RCoF may not be a useful kinetic parameter for assessing slipping risk on contaminated surfaces. Practitioner Summary: Slipping is hazardous in everyday locomotion and occupational settings. This study investigated foot control kinematics and kinetics across various gait tasks on both a non-contaminated and an oil-contaminated walking surface. Turning, gait termination and gait initiation were associated with a greater risk of slip-related falls than unconstrained walking.

Mathematic model of rolling pressure during a semisolid shearing-rolling process

A mathematic model of rolling pressure during a novel semisolid shearing-rolling process was established. The rolling pressure in this process is higher than that in the conventional rolling. The increment of rolling pressure in the backward slip zone is higher than that in the forward slip zone, and the neutral plane moves toward to the roll gap entrance. The maximum and the average rolling pressures increase with the decrease of strip thickness, and the effects of strip thickness on the rolling pressure is more obvious in the forward slip zone than in the backward slip zone. Meanwhile, the neutral plane moves toward the roll gap exit with the decrease of strip thickness. The maximum and average rolling pressures increase with the decrease of strip width, and the strip width affects the pressure more obviously in the backward slip zone than in the forward slip zone. At the same time, the neutral plane moves toward the roll gap entrance with the decrease of strip width. The maximum and average rolling pressures increase with increasing roll radius, and the neutral plane moves toward the roll gap exit.

Numerical Simulation of Crack Tip Behavior under Fatigue Loading

Fatigue damage is a localized phenomenon controlled by the near-tip crack behavior. This paper presents an application of a dislocation distribution technique to the simulation of crack tip behavior under fatigue loading. A centre-cracked tension specimen under uni-axial fatigue loading is used in the study. Crack opening and plastic deformation around the crack tip are simulated by distributions of dislocation dipoles in crack plane and four inclined planes ahead of the crack tip. Climb dislocation dipole is used to model the opening and closing of the crack while glide dislocation dipole is used to simulate the backward and forward slip in the inclined planes during loading and unloading of the fatigue cycle. Stress field around the crack tip is obtained by the superposition of the contributions of the applied external load and the distributed dislocation dipoles. Correct boundary conditions of the model are achieved by employing a quadratic programming technique to minimize a properly constructed non-negative object function. It is found that the simulated crack closure variations under the constant amplitude fatigue load agree well with the result of a previously developed modified strip yield model with an appropriate constraint factor.

Effect of the casting temperature on temperature field and microstructure of A2017 alloy during an innovative continuous semisolid rolling process with a vibrating sloping plate device

In this paper, the effect of temperature field on microstructure of A2017 alloy during an innovative continuous semisolid rolling process with a vibrating sloping plate device was studied. The results show that the alloy temperature decreases gradually from the entrance to the exit of the roll gap. In the backward slip zone, the isothermal lines have twice buckling. In the forward slip zone, the isothermal lines have once buckling. Semisolid region moves forward from the filling mouth to the exit of the roll gap with the increment of casting temperature, and the solid fraction increases from the entrance to the exit of the roll gap. The average grain size of the product increases with the increment of casting temperature, and the plastic deformation along the rolling direction happened obviously. According to the simulation and experiment, the proper casting temperature between 650 and 680 °C is suggested. A2017 alloy strip with good surface quality was obtained. The microstructure of the product is mainly composed of fine spherical or rosette grains which were elongated along rolling direction.

Calculation of Rolling Force of 3700mm Cylindrical Shell Rolling Mill

Rolling force is an important technological parameter in designing of the 3700mm cylindrical shell rolling mill. Due to the characteristics of double driving rolls and asynchronous rolling of 3700 mm cylindrical shell rolling mill, the force analysis of the deformation zone is complex. In this study, an analytic method was used to calculate the rolling force. The deformation zone was divided into the forward slip area, the backward slip area and the rub rolling area on the basis of metal flow velocity. The stress equilibrium equations of each area were built. Then the rolling force model of the 3700mm cylindrical shell rolling mill was built and solved, according to the boundary conditions. At the same time, in order to verify the validity of the analysis, the calculated values were compared with the measured in the spot. They have a good agreement, which indicates the calculation accuracy of the model could meet the industry requirements.

Research of Virtual Test of the Combine Harvester Cleaning Component

According to the purpose and requirements of a virtual test, the complex mechanism of the combine harvester was abstracted and simplified to some extent during modeling, but in order to guarantee the closeness between simulation result and the reality, attention was paid to keeping the total mass of all components close to the actual mass of the combine harvester and reducing workload during modeling. The vibration test of the cleaning operation includes horizontal vibration and vertical vibration. The test conditions are that: the combine harvester is still and has no load and only the engine runs, or the engine and the cleaning component run simultaneously. To guarantee the extractions are thrown out of the machine in the rear end of the screen, the backward slip of the extractions is greater than forward slip. The simulation result satisfactorily reflects the real situation and is same as theoretical analysis. The result indicates the virtual test and the real test are consistent.

Research of Virtual Test of the Combine Harvester and its Key Components

According to the purpose and requirements of a virtual test, the complex mechanism of the combine harvester was abstracted and simplified to some extent during modeling, but in order to guarantee the closeness between simulation result and the reality, attention was paid to keeping the total mass of all components close to the actual mass of the combine harvester and reducing workload during modeling. The vibration test of the cleaning operation includes horizontal vibration and vertical vibration. The test conditions are that: the combine harvester is still and has no load and only the engine runs, or the engine and the cleaning component run simultaneously. To guarantee the extractions are thrown out of the machine in the rear end of the screen, the backward slip of the extractions is greater than forward slip. The simulation result satisfactorily reflects the real situation and is same as theoretical analysis. The result indicates the virtual test and the real test are consistent.

Through-Thickness Shear Strain in Silicon Steel under Asymmetric Rolling

Through-thickness shear strain variation with speed/radius/friction ratio in cold rolled silicon steel under different asymmetric rolling modes was analyzed by finite element method (FEM). Cold rolling textures were also investigated quantitatively to correlate with the calculated shear strain. With increasing speed/radius/friction ratio, shear strain distribution under differential-speed and differential-radius rolling exhibits similar characteristic in contrast to differential-friction rolling. Unidirectional shear strain develops through sheet thickness when asymmetric speed and radius ratio exceeds 1.125, whereas it does not appear even at friction ratio of 1.5. Shear strain distribution dependent on asymmetric rolling modes can be well understood by forward and backward slip zones as well as roll pressure as a function of speed/radius/friction ratio.

EFFECT OF PROCESS PARAMETERS ON MECHANICAL BEHAVIOR IN HOT-SLAB ROLLING

This paper studies hot rolling process of typical low carbon steel by using rigid-plastic finite element&nbsp;also found that rolling force remains unchanged when initial slab temperature reaches certain value. The friction and effective stress distribution in the slab are obtained for the steady-state rolling process. The positive friction in backward slip zone is found to be greater than the negative friction in forward slip zone along rolling direction, indicating that friction acts as the driving force in the rolling process.http://dx.doi.org/10.5755/j01.mech.17.5.722

Study on New Model of Tension Process in Continuous Rolling

It is proved that a tension peak occurred in the beginning of tension process between two stands by the continuous rolling test. Based on the speed difference, motor rigidity and coefficient of forward and backward slip, the steady equation of the kinematical mechanics is built. The simulation results of the tension formula accorded with the experimental data. The calculation of shock peak provides an important reference for the technology of continuous rolling.