Manufacture of Defined Residual Stress Distributions in the Friction-Spinning Process: Investigations and Run-to-Run Predictive Control

Friction-spinning as an innovative incremental forming process enables high degrees of deformation in the field of tube and sheet metal forming due to self-induced heat generation in the forming area. The complex thermomechanical conditions generate non-uniform residual stress distributions. In order to specifically adjust these residual stress distributions, the influence of different process parameters on residual stress distributions in flanges formed by the friction-spinning of tubes is investigated using the design of experiments (DoE) method. The feed rate with an effect of −156 MPa/mm is the dominating control parameter for residual stress depth distribution in steel flange forming, whereas the rotation speed of the workpiece with an effect of 18 MPa/mm dominates the gradient of residual stress generation in the aluminium flange-forming process. A run-to-run predictive control system for the specific adjustment of residual stress distributions is proposed and validated. The predictive model provides an initial solution in the form of a parameter set, and the controlled feedback iteratively approaches the target value with new parameter sets recalculated on the basis of the deviation of the previous run. Residual stress measurements are carried out using the hole-drilling method and X-ray diffraction by the cosα-method.

Centrifugal spinning of viscoelastic nanofibres

The centrifugal spinning method is a recently invented technique to extrude polymer melts/solutions into ultra-fine nanofibres. Here, we present a superior integrated string-based mathematical model, to quantify the nanofibre fabrication performance in the centrifugal spinning process. Our model enables us to analyse the critical flow parameters covering an extensive range, by incorporating the angular momentum equations, the Giesekus viscoelastic constitutive model, the air-to-fibre drag effects and the energy equation into the string model equations. Using the model, we can analyse the dynamic behaviour of polymer melt/solution jets through the dimensionless flow parameters, namely, the Rossby ( $Rb$ ), Reynolds ( $Re$ ), Weissenberg ( $Wi$ ), Weber ( $We$ ), Froude ( $Fr$ ), air Péclet ( $Pe^*$ ) and air Reynolds ( $Re^*$ ) numbers as well as the viscosity ratio ( $\delta _s$ ), corresponding to rotational, inertial, viscous, viscoelastic, surface tension, gravitational, air thermal diffusivity, aerodynamic and viscosity ratio effects. We find that the nonlinear rheology remarkably affects the fibre trajectory, radius and normal stresses. Increasing $Wi$ leads to a thicker fibre, whereas increasing $\delta _s$ shows an opposite trend. In addition, by increasing $Wi$ , the fibre curvature is enhanced, causing the fibre to spiral closer to the rotation centre.

Finite-Element Modelling of Double-Roller Clamping Spinning of Wind Concentrator

In order to improve the unit-power of a wind-driven generator, a wind concentrator with complex shape is installed in front of the impeller, which makes the airflow integrated and accelerated. It is important to manufacture the wind concentrator with high precision. The double-roller clamping spinning (DRCS) is a dieless, flexible spinning process that is very suitable for forming a wind concentrator with complex shape. The profile of a wind concentrator is divided into two parts: the contraction section and the expanding section. The process routes of both the contraction section and the expanding section are determined, and roller path equations are derived. Then the finite element (FE) analysis model that can describe the plastic deformation behavior of the DRCS forming for a wind concentrator is established, and the DRCS process of the flange is simulated. Furthermore, the wall-thickness distribution on the expanding section during the forming process is obtained. Finally, the reliability of the FE model is verified using the experimental results.

Novel TiO2/TPU Composite Fiber-based Smart Textiles for Photocatalytic Applications

Herein, we prepare a novel hollow composite fiber via a wet-spinning process to overcome separation and recovery problems of nanostructured catalysts. The obtained TiO2/TPU fiber showed excellent mechanical and photocatalytic...

Zn22Al4Ag ALLOY MICROWIRES CASTING TO RAPID SOLIDIFICATION PROCESS BY ROTATING DRUM

In this work, the Zn22Al4Ag alloy was synthesized by melting in a muffle furnace.The alloy obtained was characterized by Scanning Electron Microscopy Energy Dispersive Spectroscopy and was analyzed by the X-Ray Diffraction technique, where the crystallinity of the material was verified before and after being processed. Likewise, the Differential Scanning Calorimetry technique was used to obtain the temperatures where phase transformations occurin the alloy. These results were fed to the Termocalc®, software to numerically obtain the phase diagram of the alloy. Subsequently, a section of the ingot was taken to the rapid solidification process by rotating drum. The process variables were manipulated: jet stability, nozzle diameter, distance from the nozzle surface to the cooling medium, the delay time of the molten material in the crucible, speed of the rotating drum and jet angle, until obtaining a microwire with a diameter of ~ 160µm. Finally, it was determined that inadequate control of these parameters can result in powders, flakes or blockage of the crucible outlet. Potentially uses within the micro and nanoworld as an analogy to structural elements and electrical conductors, in addition to its current use as a coating anti-corrosive. Key Words: ZnAlAg alloy, Melt spinning process, Microwire, DSC analysis, Thermodynamic simulation

Preparation of Hollow Fiber Membranes Based On Poly(4-methyl-1-pentene) for Gas Separation

New hollow fiber gas separation membranes with a non-porous selective layer based on poly(4-methyl-1-pentene) (PMP) granules have been obtained using the solution-free melt spinning process. The influence of the preparation conditions on the geometry of the obtained samples was studied. It was found that a spin head temperature of 280 °C and a specific mass throughput of 103 g mm−2 h−1 are optimal to obtain defect-free, thin-walled hollow fibers in a stable melt spinning process, using the given spinneret geometry and a winding speed of 25 m/min. The gas permeability and separation properties of new fibers were studied using CO2/N2 and CO2/CH4 mixtures, and it was found that the level of gas selectivity characteristic of homogeneous polymer films can be achieved. The features of the gas mixture components permeability below and above the PMP glass transition temperature have been experimentally studied in the range of CO2 concentrations from 10 to 90% vol. The temperature dependences of the permeability of the CO2/CH4/N2 mixture through the obtained HF based on PMP have been investigated, and the values of the apparent activation energies of the permeability have been calculated, which make it possible to predict the properties of membrane modules based on the obtained membranes in a wide temperature range.

Improved Release of a Drug with Poor Water Solubility by Using Electrospun Water-Soluble Polymers as Carriers

In an attempt to improve the solubility of valsartan, a BCS II drug, fibers containing the drug were prepared from three water-soluble polymers, hydroxypropyl-methyl-cellulose (HPMC), polyvinyl-pyrrolidone (PVP), and polyvinyl-alcohol (PVA). Fiber spinning technology was optimized for each polymer separately. The polymers contained 20 wt% of the active component. The drug was homogenously distributed within the fibers in the amorphous form. The presence of the drug interfered with the spinning process only slightly, the diameters of the fibers were in the same range as without the drug for the HPMC and the PVA fibers, while it doubled in PVP. The incorporation of the drug into the fibers increased its solubility in all cases compared to that of the neat drug. The solubility of the drug itself depends very much on pH and this sensitivity remained the same in the HPMC and PVP fibers; the release of the drug is dominated by the dissolution behavior of valsartan itself. On the other hand, solubility and the rate of release were practically independent of pH in the PVA fibers. The different behavior is explained by the rate of the dissolution of the respective polymer, which is larger for HPMC and PVP, and smaller for PVA than the dissolution rate of the drug. The larger extent of release compared to neat valsartan can be explained by the lack of crystallinity of the drug, its better dispersion, and the larger surface area of the fibers. Considering all facts, the preparation of electrospun devices from valsartan and water-soluble polymers is beneficial, and the use of PVA is more advantageous than that of the other two polymers.

RESEARCH OF THE SYSTEM OF AUTOMATIC CONTROL OF THE THREAD TENSION SPEED IN THE SPINNING PROCESS

The paper deals with the creation of a mathematical model of the process of stretching the tape, taking into account the tension of the thread. For this purpose, the relationship between the thread tension and the speed of expression of the electric drives is determined. The proposed mathematical model of the process allows one to synthesize highly efficient control systems for spinning equipment.

Modeling the airflow field of vortex spinning

Vortex spinning technology adopts a high-speed swirling airflow to rotate the fibers with open-ends to form yarn with real twists. The airflow behavior within the nozzle has a great effect on the yarn-formation process. In this study, a three-dimensional calculation nozzle model and corresponding three-dimensional airflow region model were established to enable the numerical calculation; airflow behavior—pressure, velocity, and the turbulent airflow field, and the streamline of airflow—was investigated in the presence of fiber bundles within the vortex spinning nozzle. Hybrid hexahedral/tetrahedral control volumes were utilized to mesh the grids in the calculation region. To consider airflow diffusion and convection in the nozzle, the Realizable k- ε turbulence model with wall function was adopted to conduct the calculation. Dynamic and static pressure values were obtained by numerical analysis to predict the action of the inner surface of nozzle and the wall resistance on the high-speed swirling airflow. The numerical simulation of dynamic airflow behavior can generate great insight into the details of airflow behavior and its distribution characteristics, and is helpful for understanding the spinning mechanism and promoting optimization of the spinning process.