Special beamforming by means of a semi-spherical Lüneburg lens

The paper considers a semi-spherical Lüneburg lens with a conductive shield. In certain conditions a lens of such design may form radiation patterns without the side lobe or cosecant-type patterns. Such radiation patterns can be formed by controlling the following parameters: antenna feed angle, conductive shield diameter, dielectric substrate thickness. The paper focuses on particular cases of obtaining special-type radiation patterns.

Study of the rollers geometry effects in rotary tube piercing and wear analyses of mandrel according to the finite element method

The rotary tube piercing (RTP) is the first process of making the seamless tube after producing the desired alloy ingot. There are several approaches to manufacture a seamless tube, but one of the most common types is RTP. This approach covers a wide range of processes that are categorized according to the number and shape of the rollers. On the other hand, each of these types has designed guides in the output and input of the piercing process. In this paper, a new design of the input guide for four types of rollers have been examined and simulated. Thus, four specimens including Diescher and Conical rollers were considered, with the different number of rollers. Results including torque, total force, mandrel wear, temperature distribution, and strain were extracted using FEM simulation. In order to the validation of simulation, the total force and oscillations of applied force within the process have been compared with the experimental results. The results obtained through this simulation, are more in line with the empirical results obtained from previous research. As well as, the FEM simulation confirmed the performance accuracy of the output and input guides of the RTP process. On the other hand, the results indicate that the three-roller Diescher type with 17° feed angle, has the most suitable arrangement for production of seamless tube.

Elaboration of a mathematical model and a computer program for calculation of energy-power parameters of reduction process of continuously casted billets at three-roll screw mills

For production seamless hot-rolled pipes, round continuously casted billets (CCB) are used, the diameter of which is restricted by the limit sizes of CCM moulds. The expansion of billets assortment necessary to provide pipe-rolling lines (PRL) by required diameters is possible through preliminary reduction of CCB, which is made mainly at three-roll screw-rolling mills having powerful drives. If a plant has no such mills, billets reduction can be accomplished at existing three-roll Assel’s mills being comprised by various PRLs. However, the possibilities of such mills are restricted by acceptable current loads for their drives, since they are designed to roll out pierced pipe stock, but not to reduce solid billet. To determine energy-power parameters of the process of pipe billet reduction at three-roll Assel’s mills, a mathematical model was elaborated accounting geometric, temperature, kinematic and deformation peculiarities by determination the volume of accumulated metal at each roll before rolling out, section of forming diameter of reduced pipe billet and temperature variation during the reduction. As a result, the software product “Reduction Motor Load 2020” (RML2020) was elaborated, which includes a computing kernel based on the elaborated mathematical model for determining the power parameters of the reduction process and a module for analyzing the initial data with a system of boundary conditions. The interface of the software product allows displaying the results of calculations and analysis both in numerical form and in the form of graphs. The elaborated software product contains a database of the main steel grades and allows calculating the current loads on the Assel’s mill drives during the reduction of billets made of various steel grades. The software allows also to accomplish analysis of the acceptable values of various initial parameters (diameters of the initial and reduced billets, temperature of the initial billet, feed angle and rotation frequency of rolls) to ensure the operation of the mills in the acceptable range of current loads. There is also a possibility of making a report in the form of an Excel document and collecting statistical data on the actual values of current loads. By application the RML2020 program, acceptable reduction modes of a pipe billet made of 15Х13Н2 steel (AISI 414) with a diameter of 156 mm into a billet with a diameter of 120 mm were calculated for screw Assel’s mills of PTL-1 of JSC VTZ.

Comparative analysis of damage criteria for screw rolling using computer simulation

Two-high screw rolling of billets was carried out using a MISIS-130D rolling mill. AISI 321 steel billets were deformed with feed angles of rolls of 6°, 12°, 18° and 24°. The diameter reduction was 17%, with the initial billets’ diameter being 60 mm. An axial fracture, the so-called Mannesmann effect, of the billets was observed after screw rolling. The experimental rolling was simulated using QForm finite element method software. Initial and boundary conditions were set in concordance with the experimental rolling. Several damage criteria were used for fracture prediction during computer simulation. The results of computer simulation of fracture prediction were compared with the billets fracture after screw rolling for stationary and non-stationary stages. The most effective parameter (in terms of fracture prediction) is triaxiality. The distribution of this parameter showed that the higher the feed angle value is, the lower the fracture risk is. Notably, the risk of fracture is lower at a stationary stage compared with the same risk of fracture at a non-stationary stage; the listed trends agree with experimental rolling results. The Oyane, Ayada, Brozzo, and Cockroft-Latham Normalized criteria are partly effective. These criteria are ineffective for fracture prediction 6 degrees feed angle of rolls because they showed that fracture is most probable at the billet’s surface, which contradicts the experimental rolling results. All these criteria are partly effective when predicting a less fracture risk at a stationary stage compared with the same criteria at a non-stationary stage or when predicting a decrease of fracture with increasing the rolls feed angle.

Comparative study of superelastic Ti–Zr–Nb and commercial VT6 alloy billets by QForm simulation

A comparative simulation of hot radial shear rolling (RSR) of billets made of a superelastic Ti–Zr–Nb and a commercial VT6 alloy was performed using the QForm finite element modeling program. Rolling in 48 modes with a variable feed angle and elongation ratio at 4 levels and initial rolling temperature at 3 levels was investigated for each alloy. The Ti–Zr–Nb alloy rheology during hot deformation was determined experimentally by hot upset forging and imported into the QForm program. The presence of maxima on the flow curves at the initial stage of deformation, which are absent in the VT6 alloy, is revealed. Simulation results are presented in the form of fields of the stiffness coefficient, strain rate intensity, cumulative strain degree in the maximum reduction section depending on the rolling mode. General regularities of the Ti–Zr–Nb and VT6 behavior in RSR are similar. The gradient of the fields studied decreases, and the roll pressure and torque increase with an increase in the feed angle and elongation ratio. The initial rolling temperature does not significantly affect the deformation pattern, but it significantly affects the roll pressure and torque. At the same time, the experimental alloy demonstrated the greater tendency to localize deforming forces in the near-contact zone and to increase the gradient of stress-strain state parameters over the billet section. The study of the tightening shape and depth of rolled billet ends showed that the Ti–Zr–Nb alloy has a 3.5–9.6 % greater tightening depth. It is shown that experimental alloy rolling requires 1.6–2.4 times higher roll pressure and torque as compared to the commercial alloy.

Reverse correction parameters during helical reduction

The technology of helical reduction with reverse correction is presented. The key difference of the technology is the change in the feed angle during the reduction process to the region of negative values, which allows reverse correction (reduction in the region of small feed angles) and remove the workpiece from the roll gap. This technology can be used to obtain axisymmetric billets of variable profile. The main parameters that determine the reverse correction process are the rotation speed of the rolls, the rate of change of the feed angle, as well as the dimensions of the rolls and the workpiece. When the feed angle changes (in particular during correction), the workpiece continues to move in the axial direction, which makes it necessary to evaluate the magnitude of this movement. In this work, an accurate calculation of the length of the reduced part of the workpiece with a change in the feed angle is carried out.

Influence of construction parameters on heating process in air tuyere blast channel of the blast furnace

Ansys Fluent 18.2 software was used to simulate PAO NLMK air tuyere functioning. It was established that 5 degrees hot air feed angle and 22 mm inner nipple diameter for natural gas feeding are rational. It was recom-mended to increase coal dust fuel feed angle till 20 degrees, to decrease dis-tance between natural gas nipple and flange till 30 mm.

Computer-Simulation of the Billet Shape Change during Helical Piercing

In this paper the task of the study of the deformation during helical piercing of the metal was set and solved with the use of the DEFORM-3D software. Methodology, that allows to calculate the length of helix lead along the deformation zone, as well as determine for each lead absolute and relative reduction, the width of the contact area and the metal strain refinement indicator was developed. Based on the developed methodology application the following variation regularities were established: helix lead length (li), quotient reduction (Δr/r0), ratio of the billet radius to the width of the contact area (r0/b), as well as the length of the billet contact surface (l0) with the roll in dependence of the feed angle (β), the roll number of revolutions (N) and the plug nose advancement over the gorge (Cg).

Research on Wall Thickness Uniformity of Hollow Axles by Three-Roll Skew Rolling

The paper describes wall thickness non-uniformity of hollow axles by three-roll skew rolling and the proposed improved measure. According to the characteristics of the three-roll skew rolling process, a simulation model of hollow axles by three-roll skew rolling was established. In order to study the influence of different process parameters on wall thickness uniformity, five main process parameters (feed angle, rolling angle, length of forming zone, axial feed speed, temperature) were selected and imported into the simulation model for simulation analysis. The results show that the optimum process parameters are feed angle 7°, rolling angle 30°, length of forming zone 5mm, axial feed speed 20–30 mm/s and temperature 1050°C with the same conditions, and the maximum deviation of the wall thickness is 0.7mm. The uneven wall thickness of the axle body is caused by the metal reflow, which can be solved by compensating for the radial feed of the roller or by secondary machining. Reasonable selection of process parameters can significantly improve wall thickness uniformity of hollow axles by three-roll skew rolling.

SCREW ROLLING OF PIPES IN A FOUR-HIGH ROLLING MILL

A model of four-high screw rolling mill was developed and manufactured with the help of additive technologies. The work rolls are installed: the main ones – by cup-shaped scheme and auxiliary – by mushroom scheme with an angle of rolling of ±7 degrees, with an unregulated feed angle of 15 degrees. The main and auxiliary rolls have a barrel length of 70 mm. Diameter of the main rolls in pinching is 50 mm, of auxiliary rolls – 36 mm. At the exit in cross section of the tube outlet from the rolls, their diameters are almost the same and are 72 mm. Each of the four rolls is driven by an individual drive with a 100 W motor-reducer and a rotational speed of 60 rpm by a mushroom scheme and of 83 rpm by a cup-shaped one, which minimizes the divergence of peripheral speeds in the deformation zone at different roll diameters. On the developed model of four-high rolling mill, rolling of liners from plasticine with a diameter of 25 mm with a wall thickness of 7.5 was carried out; 5.5 and 3.5 mm, corresponding to the ratio of diameter to wall thickness 3; 5 and 8. Pipe rolling was carried out on floating mandrels with diameters of 9, 13 and 17 mm. After rolling, measurements of the diameter and wall thickness of the pipes were carried out in 5 cross sections that were equally spaced from each other. In each cross section, the diameter was measured at 5, and the wall thickness at 10 points. The finite element method has been used to simulate the process of rolling these pipes in the QForm program. Assessment of the model adequacy was carried out by comparing the size of pipes and their accuracy after rolling with the results of computer simulation. When rolling at a four-high rolling mill, the wall thickness is significantly reduced.