Hot Bar Research Articles

Influence of Different Arranges of Vortex Generators on Heat Transfer

In this paper, effects of flat plate obstacles and rectangular and triangular decorated bars on cooling of a hot bar were investigated experimentally and numerically. The experiments were performed in a wind tunnel with transient heat transfer through the hot bar. Results showed that in case of staggered tube banks and Reynolds range of 350–2100, heat transfer increased from 10 to 30 % while pressure decreased from 55 to 34 % and in case of in-line tube banks and the same range of Reynolds, heat transfer encountered a rise from 10 to 20 % and the pressure reduced from 15 to 8 %. Moreover our study indicates the Nusselt increased when Reynolds number enhances, furthermore, the Nusselt variation corresponding to the rectangular flat obstacles was compared to other modes.

Anisotropic Fatigue & Fracture Behaviour in Hot-Rolled and Cold-Drawn Pearlitic Steel Wires

This paper analyses the role of cold drawing in the fatigue and fracture behaviour of pearlitic steels with distinct drawing degree (a hot rolled bar and a commercial prestressing steel wire). Fatigue crack growth develops globally in mode I and locally in mixed mode in both steels, the micro-crack deflection angle depending on the drawing degree. With regard to fracture behaviour, it takes place in mode I in the hot-rolled bar and in mixed mode (with a strong component of mode II) in the case of the cold-drawn wire, so that strength anisotropy appears in the drawn steel and a sort of directional toughness can be defined.

Experimental and numerical evaluation of different vortex generators on heat transfer

Effect of Sinusoidal (Sin), Wave and Broken obstacles followed by rectangular and triangular decorated bars on cooling of a hot bar was investigated experimentally and numerically in the present investigation. Experiments were performed in a wind tunnel in which transient heat transfer were considered on the hot bar. The obtained results revealed that the heat transfer corresponding to the Sin obstacles followed by rectangular arrange of bars was more compared to other modes.

Demonstration of a Periodic Passband Filter Based on Coupled Microfiber Knots

In this letter, a periodical passband filter based microfiber structure is proposed. The structure is made of successive microfiber knot resonators. The periodical spectral filtering is a result of superposition of the uncoupled modes that belong to the individual microfiber knots and coupling induced resonant wavelength shift. This letter demonstrates the experimental investigation of the thermal effect on the spectral modulation of the structure. The proposed resonator consists of two knots with radii 460.01 and $230~\mu \text{m}$ , which are knitted successively, in a column. This results in a periodic spectrum with 720-pm passband, 425-pm stopband, and a suppression ratio of 5.2 dB. Increasing the optical path, using a hot metal bar with a temperature of 30° close to the big knot, the periodic passband filter switches to all pass filter with a free spectral range of 1150 pm and quality factor 6000. This letter as well demonstrates experimentally how to enhance passband and stopband widths through decreasing the knot’s radii as well as increasing the number of knots. Compatibility of this structure with single-mode fiber systems makes it easy to be used as noise filtering in telecommunication and fiber lasers.

Evaluation of the Microstructure and Charpy Impact Toughness of Hot Worked Powder Ti-6Al-4V

Ti-6Al-4V powder, produced by the hydride-dehydride (HDH) process, was hot isostatically pressed (HIP) into three bars. The 10 cm (4 in) diameter bars were hot worked (HW) to three different diameters: 5.1 cm (2 in) (75% reduction in area), 3.8 cm (1.5 in) (86% reduction in area), and 2.5 cm (1 in) (94% reduction in area). Three samples were machined out of each bar along the end, middle and transverse orientations. These samples were ground, polished, and etched. The microstructure of the samples was evaluated at 100X and 200X magnifications. The objective of this experiment was to examine the effect of deformation on the microstructure and properties of hot rolled titanium alloy bar product. Charpy impact samples were also machined out of each of the various diameter bars. Impact testing was used to quantify toughness by correlating the microstructure to the energy absorbed. The tensile properties of the hot bars were determined as well as the crystallographic texture. Scanning electron microscopy (SEM) was performed on the fractured surface of the Charpy impact samples.

Fatigue cracking in high-strength cold-drawn pearlitic steel wires for anchorage in rocks

This paper analyzes the fatigue crack path in two pearlitic steels with very different microstructural arrangement: a hot rolled pearlitic steel bar and a commercial high-strength cold drawn prestressing steel wire frequently used for anchorage in rocks. In both materials, fatigue cracks are mostly transcollonial and tend to fracture pearlitic lamellae, so that many different micro-phenomena appear such as non-uniform crack opening displacement, micro-discontinuities, branchings, bifurcations and frequent local deflections, all of them creating a sort of microstructural roughness with regard to the fatigue crack path which is different in hot rolled bar and in the cold drawn wire.

Effect of pass schedule and groove design on the metal deformation of 38MnVS6 in the initial passes of hot rolling

The deformation behaviour of a hot rolled micro-alloyed steel bar of grade 38MnVS6 was examined using an FEM model during the initial passes in a blooming mill, as a function of three different pass schedules, roll groove depth, collar taper angle and corner radius. The simulations predicted the effective strain penetration, load, torque, fish tail billet end shapes, and metal flow behaviour at a chosen temperature, mill rpm and draft. The model predictions were validated for typical groove geometry and a typical pass schedule. Lower collar taper angle, lower corner radius and higher depth of groove in hot rolling enabled achievement of higher strain penetration, higher mill load and lower fish tail formation. The present study establishes the capability of the model to improve the internal quality of the rolled billet as measured by effective strain which was corroborated to the rolled bar macrostructure and microstructure. The model enables yield improvement by the choice of draft to minimise fish tail losses. The surface quality is improved by the ability to avoid fin formation that occurs at certain conditions of rolling. Thus, the groove geometry, roll pass schedule and rolling mill parameters and temperature can be optimised for best product quality and yield.

Study on Mechanical Properties and Components of HRB400 Steel for High-strength Building

The study took five samples of screw-thread steel III, i.e. HRB400 steel bar of different diameters: 10mm, 12mm, 16mm, 20mm and 25mm; and conducted contrast experiments of their mechanical properties and components. The 600 sets of data collected from the experiments were processed by multivariate regression analysis of mechanical properties and components by diameter with MATLAB. The result showed that differentHRB400 screw-thread steel bars have different components with the mechanical properties meeting the standard of GB1499.2-2007 [1] part 2 steel for reinforced concrete hot rolled ribbed steel bar, which has a guidance function to scientific research in universities and production in enterprises.

CONCEPTUAL DESIGN OF HELICAL COILING MECHANISM FOR THE INTEGRATION OF ROLLING MILL

Circular bar of range of diameters is one of the significant products of rolling mill used for civil construction purpose. The reinforcement of construction work consists of longitudinal and transverse members. Transverse member is called as stirrup. According to the need of civil structure various shapes and sizes of stirrups are used for constructing the beams and columns. The stirrups are made manually or using semiautomatic machines at construction site or separate units are set up with automatic computer control machines. It is proposed to make stirrups at the last stand of rolling mill in the form of helical continuous coil instead of existing practices of stirrup making. Stirrups are cut from helical coil at construction site or continuous coil can be employed as a helical reinforcement. Existing engineering standards recommend use of continuous helical coil for the better strength. The work is aimed on conceptualizing a device, can be called as helical coiling mechanism, and integrating it with hot rolling mill. The efforts are made to access different alternative mechanisms which would be capable to work with the outlet conditions of bar of rolling mill. The bar coming out from the rolling mill is fed to the proposed mechanism for forming the helical coil. The suitable alternatives are discussed. The evaluation is done on the basis of merits and demerits for the selection of best suitable mechanism for the purpose. It is concluded that triple dowel mechanism out of six identified mechanisms would be best suited for the conceptual helical coil machine. The stirrup made by proposed technique achieves competitive advantages over existing stirrup making practices like the reduced handling of bar, hot rolled bars are bent into required sizes with less power along with good metallurgical and mechanical properties.

Analysis of Fatigue Crack Paths in Cold Drawn Pearlitic Steel.

In this paper, a fracto-metallographic analysis was performed on the cracked specimens of cold drawn pearlitic steel subjected to fatigue tests. Fatigue cracks are transcollonial and exhibit a preference for fracturing pearlitic lamellae, with non-uniform crack opening displacement values, micro-discontinuities, branchings, bifurcations and frequent local deflections that create microstructural roughness. At the micro-level, the cold drawn pearlitic steel exhibits higher micro-roughness than the hot rolled bar (this is a consequence of the manufacturing process by cold drawing), so that the actual fractured surface in the cold drawn wire is greater than that in the hot rolled bar, due to the fact that the crack deflection events are more frequent and with higher angle in the former (the heavily drawn prestressing steel wire). These findings show the relevant role on the manufacturing process by cold drawing in the fatigue crack propagation in pearlitic steel.

Effect of reinforcement strength on seismic behavior of concrete moment frames

The effect of reinforcing concrete members with high strength steel bars with yield strength up to 600 MPa on the overall seismic behavior of concrete moment frames was studied experimentally and numerically. Three geometrically identical plane frame models with two bays and two stories, where one frame model was reinforced with hot rolled bars (HRB) with a nominal yield strength of 335 MPa and the other two by high strength steel bars with a nominal yield strength of 600 MPa, were tested under simulated earthquake action considering different axial load ratios to investigate the hysteretic behavior, ductility, strength and stiffness degradation, energy dissipation and plastic deformation characteristics. Test results indicate that utilizing high strength reinforcement can improve the structural resilience, reduce residual deformation and achieve favorable distribution pattern of plastic hinges on beams and columns. The frame models reinforced with normal and high strength steel bars have comparable overall deformation capacity. Compared with the frame model subjected to a low axial load ratio, the ones under a higher axial load ratio exhibit more plump hysteretic loops. The proved reliable finite element analysis software DIANA was used for the numerical simulation of the tests. The analytical results agree well with the experimental results.

Investigation of thermal effects in a resonance condition of microfibre double‐knot resonators as high‐order filter

Theoretical and experimental investigations are conducted into the thermal effect on resonance conditions of microfibre double-knot resonators. A double-knot microfibre resonator which utilises heat for optical path correction is introduced to increase the finesse. The proposed resonator consists of two knots with radii of 357.66 and 357.73 µm which are placed in series. Each individual knot has a finesse of 5 and an extinction ratio of 6 dB. When placed in series, the extinction ratio of the comb spectrum varies from 3.5 to 15 dB by controlling the resonance wavelength of both knots through optical correction. Optical path correction is implemented by placing a hot metal bar with a temperature of 30°C close to the smallest knot. This path resulted in a flat comb spectrum with a high extinction ration of 15 dB. The produced resonance has an unchanged free spectral range of 715 pm, a quality factor of 20 000, FWHD of 85 pm and a finesse of 9.5.

Computational Fluid Dynamics Simulation of Steel Bars Cooling by Free Convection and Thermal Radiation

In this article, the pilling process of hot steel bars is analyzed. During the loading three bars are placed over a wood surface, after those other three are placed over the previous for two times with 5 minutes intervals between them.They are all subject to a slow cooling by thermal radiation and free convection.A Computational Fluid Dynamics (CFD) model to predict the temperature profile of them is developed. Comparison between the CFD simulation results and experimental data yielded an average difference in the bars temperature between -0.3oC and 3.5oC.

Diameter control of copper rod in hot rolling processes

This paper aims to address the issue of fluctuations of copper rod diameter during the process of hot rolling. In addition, it proposes a solution to control the diameter of the copper rod in order to improve the quality of the hot rolling mill products. The change of copper rod diameter during the process of hot rolling results from disturbance effects (such as temperature, torque loading, and plant ageing) which leads to the deterioration of product quality. To overcome changes in the copper rod diameter, a proportional-integral-derivative (PID) based on a particle swarm optimization, auto tuning diameter controller was designed to reduce the fluctuations in the rod diameter and different control techniques with variable structure PID controllers were proposed, evaluated, and compared by extensive simulation tests. The PID diameter controller was designed based on the experimental data that showed that the speed of the rolls leads to sensible differences in the copper rod diameter. It was also designed to guarantee that the synchronization between the stands of the rolling mill is maintained so that the metal flow rates from the first stand to the last one is kept constant. Moreover, it was designed in a way which assures that the tension of the cast bar will remain unchanged and does not conflict with the tension controller. The design of the diameter controller, modeling, validation, verification and simulation of the rolling mill process is presented, which involves the reduction of the copper rod diameter by passing the hot cast bar through a preset roll gap between two work rolls that are driven by a DC motor. A proposed combined-control of motor speed and rod diameter controller reduces fluctuations in the rod diameter.

Application of a Composite Hot Shearing Tool Manufactured by Co-Spray Forming

In modern manufacture, like in automotive industry, high quality products and high output rates as well as low costs are achieved by highly efficient processes. Optimized tool design represents a key factor for such processes, leading to long tool life and hence to low tooling costs. Early in the industrial manufacturing chain of roller bearings for example, hot bars are sheared into billets, which are subsequently transported automatically to the first forming stage of a press. The shear blades should have a high wear resistance at high temperatures. In this study the first bi-metal composite shear blade made by spray-forming has been developed and tested in industrial environment. The composite tool has been deposited in a co-spray forming process to directly combine a hard-facing alloy layer with a hot working steel body in order to take advantage of the high microstructural homogeneity and the low segregation generated in spray forming. After machining, heat treating and quality inspection of the new material composite, the hot working tool was used in manufacture to prove its wear resistance and durability. The results show that the interface properties of the composite are of high quality and the material has a lower vulnerability to cracks after use in production than the conventional tool, respectively material. Only the porous zone near the interface leads to fissures which are partially going deep into the tool. Hence the parameters of the co-spray forming process need to be improved.

Crack tip fields and mixed mode fracture behaviour of progressively drawn pearlitic steel

This paper deals with the influence of the cold drawing process on the fracture behaviour of pearlitic steels. To this end, fracture tests under axial loading were performed on steel wires with different drawing degree (from a hot rolled bar to a commercial prestressing steel wire), transversely pre-cracked by fatigue, analyzing in detail the changes in fracture micromechanisms. The deflection angles of the fracture path were measured by longitudinal metallographic sections and the characteristic parameters of the loaddisplacement plot were related to different fracture events. Results allowed a calculation of critical stress intensity factors for different fracture angles and drawing degrees, thus evaluating the strength anisotropy and obtaining a sort of directional toughness.

Modeling and experimental analysis of squeeze flow of sealant during hot bar sealing and methods of preventing squeeze-out

Excessive pressure and temperature during hot bar sealing of flexible packaging films can result in seal failure due to squeezing out of the sealant from the seal area. A model is developed that shows the amount of squeeze-out increases with increasing seal bar pressure, seal temperature (by lowering the viscosity of the sealant), sealing dwell time, film thickness, and decreasing seal bar width. Validation experiments qualitatively agree with the model predictions. Both the model and experimental results show that the rheology of the sealant plays a significant role in preventing squeeze-out; high viscosity at low shear rates favor less squeeze-out. The work shows that under normal sealing conditions, squeeze-out is not substantial. Avoiding excessive temperature or pressure is critical to minimizing squeeze out to ensure good sealing performance.

Effect of Specimen Size on the Resistance to Thermal Shock of Refractory Castables Containing Eutectic Aggregates

Thermal shock is one of the most severe conditions to which a refractory lining can be subjected to during its industrial application. Thus, there are several methods available for testing thermal shock damage resistance of refractories. Among them, a very common method is the quench test, which consists of quenching a hot refractory bar into water. After that a retained mechanical property is determined. Considering this, the aim of the work herein is to compare the thermal shock damage resistance between two specimen sizes among several materials. The dimensions 150 mm × 25 mm × 25 mm and 160 mm × 40 mm × 40 mm were used. The small bars are generally used for mechanical characterization in the refractory field (recommended by ASTM C1171-05). The large bars, on the other hand, are a requirement of DIN 196-1, which regards procedures for testing cement materials. Experimental results have indicated that the thermal shock damage is bigger for the large bars, as predicted by theoretical aspects. Although the size difference between the specimens was not so big, it was possible to observe the size effect using a statistical treatment. Five different castable formulations, of which three contained eutectic aggregates, were tested. The highest variation found in thermal shock damage resistance because of the size was about 15%.

Network Carbide Inheritance during Heat Treatment Process of Large Shield Machine Bearing Steel GCr15SiMn

Network carbide inheritance during heat treatment process of large shield machine bearing steel GCr15SiMn was investigated by heat treatment experiments and quantitative metallographic. Samples with the proeutectoid cementite network thickness in the range of 0.19~0.54 μm were obtained by changing austenitizing temperature and soaking time of pearlite transformation. The results show that the network in hot rolled bar can be improved when the pre-heat treatment temperature is 950 °C. When the network thickness is above 0.40 μm, the undissolved cementite networks present in microstructures after quenching and tempering. In a Chinese standard, the network grades are 1.5 and 3.0 degree when the networks thickness are 0.40 μm and 0.54 μm, respectively. The critical network thickness that can be eliminated by heat treatment is 0.29 μm.

Experimental Study on the Seismic Behaviors of HRBF400 RC Columns

Abstract In order to investigate the seismic behaviors of RC columns reinforced with HRBF400 steel bar (HRBF-high strength hot rolled bars of fine grains), four rectangle cross-section HRBF400 RC columns' bending low-cycle reversed loading experiments were made. Influences of reinforcement ratio, axial compression ratio, and stirrup ratio on the seismic behaviors of HRBF400 RC columns were analyzed. Characteristic of hysteretic curve and skeleton curve are studied, and characteristic value and displacement ductility of each specimen was calculated. The results show HRBF400 RC columns have good seismic behavior. Yield load, peak load, and ductility improve with the increasing of reinforcement ratio. Columns of high compression ratio have high peak load and yield load, but their skeleton curves decrease quickly after peak load and have low ductility. Columns of low compression ratio have low peak load and yield load, but decrease gentlly after peak load and also have good ductility. Seismic behaviors and ductility of RC columns improve with the increasing of stirrup ratio.