Aluminum Slab Research Articles

Numerical simulation of the temperature field in the electromagnetic semi-continuous casting of slab

Electromagnetic casting of aluminum is a semi-continuous casting process and the corresponding mathematical model is a non-steady non-homogeneous heat-transfer equation. This paper indicates and testifies that the dynamic temperature field can be calculated with a three-dimensional non-steady homogeneous heat-transfer equation. The software program has universal use. Further, a casting process of 1860 × 510 mm aluminum slab is simulated, the results agreeing well with those reported in the literature.

Comparison of adult and paediatric spine and whole body software for the Lunar dual energy X-ray absorptiometer.

Simple phantoms were devised to compare the performance of adult (software 3.64) and paediatric (software 3.8 g) spine and whole body software developed for the Lunar dual energy X-ray absorptiometer. Rectangular slabs of aluminium with high (1.18 g cm-2) and low (0.57 g cm-2) density were used to represent bone mineral. For spine measurements, the phantoms were scanned in water at depths of 5-20 cm. For whole body measurements, the phantoms were scanned with known amounts of oil and water to represent fat and lean tissue. This simulated tissue depths of 5.5-19.7 cm and body composition ranging from 14-29% fat. There were systematic differences in spine and whole body bone mineral content (BMC), bone area (BA) and bone mineral density (BMD) measurements and also between adult and paediatric software versions. The magnitude and direction of these differences were dependent on BMD of the phantom and tissue depth. Similar systematic differences were observed in vivo when volunteers were scanned using adult and paediatric software. Paediatric software enabled measurements to be made at low tissue depths. The weights of fat, lean and total soft tissue measured by the adult and paediatric whole body software were similar to the values calculated from the known composition of the phantom. Precision estimates for all softwares were excellent. In conclusion, paediatric software should improve bone mineral measurements of children but the discrepancies between adult and paediatric softwares may cause problems in longitudinal studies of skeletal growth and when compiling reference data from infancy through to adulthood.

A numerical method for simulation of thermal stresses during casting of aluminium slabs

We present a numerical study of a quasistatic evolution problem for a system of partial differential equations modelling the thermomechanical behaviour of a direct chill (DC) or electromagnetic (EMC) casting of aluminium. It is a quasistatic evolution problem of a three-dimensional elastic-viscoplastic solid with contact. This model can be used to predict and assess the most fundamental variables in the casting process: casting speed, alloy composition, cooling conditions, mould shape, ... To solve the discrete problem at each time step, we propose a discretization by a tetrahedral finite element method and an iterative algorithm. At each iteration, one must solve a linear elasticity problem. To validate the proposed algorithm it has been applied to some test examples with known analytical solutions. Finally, we present the results of calculations corresponding to a real industrial casting process.

Observation of excited level populations of Li-like aluminium ions in a recombining plasma: role of atomic processes involving doubly excited levels of Be-like ions

An aluminium slab target was irradiated by multiple pulses of Nd:glass laser light with the irradiance of . After the laser irradiation, a laser-produced aluminium plasma was observed in its recombining phase using a spectrometer whose relative sensitivity was calibrated. We measured relative intensities of the resonance series lines and the lines of the - and - series of the Li-like aluminium ions and derived the excited level populations of the upper levels. From the slope of the population distribution of the high-lying excited levels and the transition from the series lines to the continuum, the electron temperature and the electron density were estimated to be 8 eV and 3-. A comparison of the experimental population distribution with a collisional-radiative (CR) model calculation indicates that recombination of the excited Li-like ions through doubly excited levels of the Be-like ions plays an important role in the population kinetics of the Li-like ions.

Substructure Characteristics of Grain Boundary Regions and Nucleation of Recrystallisation at Grain Boundaries in High Purity Aluminium

Boundaries existing prior to deformation are well known nucleation sites for recrystallisation. Several mechanisms have been suggested, e.g. strain induced boundary migration (SIBM) and ordinary nucleation of recrystallisation by growth of highly misoriented subgrains. The objective of the present work was to give some insight on the formation and characteristics of such boundary zones Substructure evolution nearby pre-exsisting grain boundaries was studied as a function of orientation differences or Taylor factor differences between neighbouring grains and of pre-deformation grain size, i.e., amount of shear deformation (grain boundary sliding) occuring in grain boundary areas. Slabs of high purity aluminium with different initial grain sizes were cold rolled to strains of 0.5, 1 0 and 2.0. The substructure, i.e., subgrain size and sub-boundary misorientation, were measured along grain boundaries with different orientation relationships and in the interior of the neighbouring grains. It was observed that the misorientations between subgrains were larger in the grain boundary regions than in the interior of the grains The high misorientations and high stored energy in the grain boundary regions makes them preferential as nucleation sites for recrystallised grains This was also shown indirectly by the fact that smaller initial grain size leads to smaller recrystallised grains in samples deformed to identical deformation strains.

Enhancement of the 15.4 nm Line of the Lithiumlike Aluminum Recombining Plasma Laser using a Half Cavity

A 30-mm long aluminum slab target was irradiated by a line-focused Nd; glass laser light. The relative intensity of the 3d2D–4f2F laser line (15.4 nm) of the lithiumlike aluminum ions was measured. In this experiment, we put a Mo/Si multilayer mirror on the opposite side of the spectrometer to construct a half cavity. With the use of this mirror, the intensity of the 15.4 nm line became 1.8 times larger than the case without the mirror.

Observation of amplified spontaneous emission in the soft-x-ray region from a recombining lithiumlike aluminum plasma pumped by multipulse irradiation

An aluminum slab target was irradiated by 1.5×1012 W/cm2 glass-laser light. The irradiating laser light consisted of 16 pulses, each was 80 ps wide (FWHM), and the pulses were separated by 100 ps. Amplification of soft-x-ray light in the lithiumlike aluminum recombining plasma was observed, and gain–length products of 4.2 for the 15.4-nm line and 4.5 for the 10.5-nm line were obtained for a 3.0-cm-long target. The beam divergence was ∼10 mrad for a 2.5 cm-long target. The experimental result was compared with a hydrodynamics simulation coupled with a collisional–radiative model.

Monte Carlo based phase-space evolution for electron dose calculation.

A system of computer codes based on phase-space evolution is developed and applied to low energy therapeutic electron beams. Monte Carlo (EGS4) is used to pre-calculate the electron transport and dose deposition in a 0.5 cm width cubic voxel. Dose calculations at larger scales are computed from the pre-calculated data using phase-space evolution. This approach has the theoretical accuracy of Monte Carlo with potentially significant speed gains resulting from the pre-calculation. This study demonstrates the accuracy of this technique while providing a preliminary assessment of the calculation time. For a 4.3 MeV electron beam in water with a 0.5 cm thick slab of either water (homogeneous), air, or aluminum at 1 cm depth, we observe differences relative to Monte Carlo of less than 3% along the central axis for a pencil-beam. For a 3.5 cm x 3.5 cm field we observe a maximum difference on the central axis of 4% in the build-up region and less than 0.1 cm in the fall-off region for all three phantoms. Calculation times are disappointing; however, there is high potential for their reduction to values comparable to or better than condensed history Monte Carlo while retaining clinically acceptable accuracy.

アルミニウム連続鋳造スラブの鋳塊底部形状に及ぼす鋳造条件の影響

アルミニウム連続鋳造スラブの鋳塊底部形状に及ぼす鋳造条件の影響

An investigation into the control of thermal camber by spray cooling when hot rolling aluminium

Of major concern to the producers of aluminium sheet is the variation in the thickness of the sheet across its width. Profile is the result of the interactions of a number of factors. Of prime importance is the thermal camber of the work rolls. This paper demonstrates how thermal camber can be controlled using cooling sprays, set to suitable patterns. To determine the patterns an optimization program was developed. This program incorporates a finite difference thermal camber model, the spray patterns being the independent variables. The case of a single stand reversing mill, used to break down slabs of aluminium is studied.

The application of correlated sampling to the computation of electron beam dose distributions in heterogeneous phantoms using the Monte Carlo method

Although the Monte Carlo method is capable of computing the dose distribution in heterogeneous phantoms directly, there are some advantages to computing a heterogeneity correction factor. If this approach is adopted there are savings in time using correlated sampling. This technique forces histories to have the same energy, position, direction and random number seed as incident on both the heterogeneous and homogeneous water phantom. This ensures that a history that has, by chance, travelled through only water in the heterogeneous phantom will have the same path as it would have through the homogeneous phantom, resulting in a reduced variance when a ratio of heterogeneous dose to homogeneous dose is formed. Metrics to describe the distributions of uncertainty, efficiency, and degree of correlation are defined. EGS4 Monte Carlo calculation of the dose distribution from a 20 MeV electron beam on water phantoms containing aluminium or air slab heterogeneities illustrate that this technique is the most efficient when the heterogeneity is deep within the phantom, but that improved efficiency can be realized even when the heterogeneity is at or near the surface. This is because some correlation between the two histories is retained despite passage through the heterogeneity.

The 2p-subshell photoabsorption spectrum of Al+ in a laser-produced plasma

The authors have recorded the time-resolved photoabsorption spectra of aluminium plasmas in the 50-200 AA wavelength range using the dual laser produced plasma technique (DLPP). Absorbing plasmas were generated by focusing the output from a pulsed dye or a Q-switched ruby laser onto an aluminium slab target. The continuum backlight was provided by irradiating a tantalum rod with the output from a time-synchronized Q-switched Nd-YAG laser. Some of the spectra were recorded with the aid of a toroidal mirror. By combining time and space resolution the authors have been able to isolate almost exclusively Al+ and record its photoabsorption spectrum. They provide an analysis of 2p to nd, (n+1)s Rydbergs in Al+ based on multiconfiguration ab initio atomic structure calculations and quantum defects for the higher members of each series. They have also observed and tentatively classified a number of members of the 2p63s2 to 2p53s3p2 doubly excited transition array.

Scaling laws for pressure, temperature, and ionization with two-temperature equation-of-state effects in laser-produced plasmas

A two-temperature equation of state (EOS) for a plasma medium was developed. The cold-electron temperature is taken from semiempirical calculations, while the thermal contribution of the electrons is calculated from the Thomas–Fermi–Dirac model. The ion EOS is obtained by the Gruneisen–Debye solid–gas interpolation method. These EOS are well behaved and are smoothed over the whole temperature and density regions, so that the thermodynamical derivatives are also well behaved. Moreover, these EOS were used to calculate the average ionization 〈Z〉 and 〈Z2〉 of the plasma medium. Furthermore, the thermal conductivities have been calculated with the use of an extrapolation between the conductivities in the solid and plasma (Spitzer) states. The two-temperature EOS, the average ionization 〈Z〉 and 〈Z2〉, and the thermal conductivities for electrons and ions were introduced into a two-fluid hydrodynamic code to calculate the laser-plasma interaction in carbon, aluminum, copper, and gold slab targets. It was found that the two EOS are important mainly from the ablation surface outward (toward the laser). In particular, the creation of cavitons in the distribution of the electrons is predicted here, especially for light materials such as aluminum. These studies enable us also to establish that the commonly used exponential scaling laws of the type Pa = A[I/(1014 W/cm2)]α for the ablation pressure and similar laws for the temperature are valid only for absorbed laser intensities in the range 3 × 1012-3 × 1014 W/cm2, while the degree of ionization (at the corona) follows a quite different scaling law. We also found that the parameters A and α. in the above expression are dependent on material, laser wavelength, and pulse shape. Thus we determined for the ablation pressure, using a trapezoidal Nd laser pulse, that α varies between 0.78 and 0.84 and that A varies between 14 and 8 Mbar for 6 ≤ Z ≤ 79. Beyond the range of validity the scaling laws may give values at least twice as large as those obtained by the simulation.

Laplace’s equation in freshman physics

Heat-sensitive liquid crystal sheets are used to observe quantitatively the temperature contours on the surface of an aluminum slab subjected to constant-valued boundary conditions. The experiment is then modeled numerically using spreadsheet techniques. The theoretically derived power series solution to the Laplace equation is given and students use the spreadsheet to numerically investigate its convergence. In a single laboratory session, the introductory physics student studies the Laplace equation from experimental, numerical, and theoretical perspectives.

Synthetic lubricants in cold strip rolling

AbstractThe embedded‐pin technique is used to monitor the variation of the interfacial forces during cold rolling of aluminium slabs. The results confirm earlier conclusions, indicating that the frictional coefficient is a strong function of the process and material parameters. Coefficient of friction values deduced from forward slip measurements are close to the present data, confirming that in spite of several drawbacks of the experimental technique, it can yield very useful results. Lubricants are shown to reduce the loads on the rolling mills in a significant manner.

10‐MV x‐ray primary and scatter dose calculation using convolutions

Three-dimensional (3-D) forward and backward primary dose spread functions in water were developed for 10-MV x rays. Three-dimensional forward and backward primary dose spread functions in a heterogeneous medium were constructed from the ones in water using the density scaling theorem. Each of the forward and backward primary dose components were calculated using a method of convolving the primary water collision kerma distribution with the forward or backward primary dose spread function. Scatter dose was separated into forward and backward components. Each scatter dose component was calculated using a differential scatter method, a kind of convolution method, where the primary water collision kerma distribution was convolved with a differential scatter-maximum ratio or differential backscatter factor equation. From the dose calculation and measurement results obtained for water phantoms containing a cork or aluminum slab, it was found that the 3-D forward and backward primary dose functions were effective especially in regions where there was a loss of longitudinal and/or lateral electronic equilibrium.

Calculation of three‐dimensional photon primary absorbed dose using forward and backward spread dose‐distribution functions

This paper describes a method of calculating three-dimensional (3-D) photon primary absorbed dose in a homogeneous or heterogeneous medium. The method is based on a technique of convolving a pair of forward and backward spread dose-distribution functions with the primary water collision kerma distribution. Both spread dose-distribution functions can be constructed by analyzing the zero-area tissue-maximum ratio, the primary absorbed dose near the beam exit surface, and the laterally spread dose distribution. Primary absorbed dose calculations are performed along the beam axis for 10-MV x rays. The characteristic patterns of primary dose in heterogeneous phantoms containing an aluminum or lunglike material slab can be obtained.

Review of Scattering Corrections for Calibration of Neutron Instruments

In this paper we consider scattering corrections that must be made when neutron personnel instruments are calibrated with a point source of neutrons near the centre of a calibration room. We consider three basic types of scatter: (1) scattering from a plane slab, (2) scattering from walls of an enclosed room, and (3) air scatter. In each case we proceed from an idealised situation, where the correction can be predicted analytically, to an actual calibration room, where predictions must be checked by Monte Carlo calculations or experiment. Calculations show that the postulation of an image source provides a good model for predicting the fluence of neutrons scattered from aluminium and concrete slabs. Calculations also show how the fluence of neutrons scattered from the walls of an enclosed room relates to the case of neutron fluence in a spherical cavity and how the neutron fluence is increased by scattering in the air around source and detector. Finally, calculations are compared with experiments on the response of a neutron dose equivalent monitor.

A platform for vibration damping, leveling, and height control of high-resolution superconducting magnets

Three years ago, we designed and constructed a platform that provides good vibration isolation, level control, and height control for a high-resolution superconducting magnet. This platform was installed under the magnet of a 200 MHz (‘H frequency) spectrometer, as part of our efforts to develop ultrahigh resolution (I-12). Recently, we have observed that a perfectly vertical magnet significantly improves the resolution for a spinning sample in a 500 MHz spectrometer (13). Also, we have received several inquiries from users of 500 MHz spectrometers who are encountering problems caused by mechanical instabilities. Therefore, we have decided to share the design of our platform. It requires a constant source of compressed air, at a pressure dependent on the load (see below). It provides (i) a high degree of vibration isolation, (ii) the ability to adjust the level ofthe platform, and (iii) an invariant vertical position independent of load. The last feature may be important for maintaining homogeneity of magnets located above concrete floors which contain embedded steel rods. The “rubber tire” vibration isolators provided as extra-cost accessories by some instrument manufacturers obviously yield a gradual change in vertical position as the weight of liquid nitrogen ( 1.76 lb/liter) changes. Figure 1 shows the components of the system and how they are connected together with air hoses. Figure 2 is a top view of the aluminum platform; the dashed lines show the location of the components of Fig. 1, sandwiched between the aluminum platform (which holds the magnet) and two rectangular aluminum slabs on the floor. The platform is 1 inch thick and 40 X 40 inches in size. For a Bruker AM-500 system, it is probably necessary to increase the length to about 50 inches, and to drill holes for attaching an adapter for an automatic sample changer. The floor slabs are $ inch thick and 11 X 44 inches. Figure 3 shows a frontal view, and Fig. 4 gives a cross section of one of the four vibration-isolation components (labeled S in Figs. l-3). Details are presented below. The four items labeled S in Figs. l-3 are 1 S3-0 11 Super-Cushion Air Springs from Goodyear Tire & Rubber Co., Greensburg, Ohio, each designed for a load of 60370 lb. Our magnet weighs about 500 lb when full of liquid nitrogen. The required compressed air pressure for a 125 lb (per device) load is about 35 psi. The pressure gauge shown in Fig. 1 acts as a load monitor; it shows the effect of load change as a result of liquid nitrogen evaporation. The much larger weight of a magnet of a 500 MHz instrument (about 1200 lb fully loaded) will require a pressure of about 80 psi;

A tracking rangefinder for muons from kaon decay

A muon rangefinder with tracking capabilities has been constructed as part of a search for the rare decay K/sub L/ degrees to mu e in experiment 791 at the Brookhaven National Laboratory Alternating Gradient Synchrotron. The rangefinder consisted of two identical arms, symmetric about the beamline, and was the final detector element in a spectrometer system. Each side of the rangefinder was comprised of 75 slabs of marble and 25 slabs of aluminum, each 7.62-cm thick, covering an acceptance area 225 cm wide by 301 cm high, with a total mass of 160 tons. There were 13 pairs of x- and y-measuring proportional tube planes, providing a nominal +or-10% accuracy measurement of muon momentum. During 850 hours of data collection, efficiency averaged 94%, with 160-ns drift time at 1.5- mu A threshold. For well-identified muon tracks, rangefinder muon identification was 99% efficient when penetration to at least 60% of the depth expected from spectrometer-derived momentum was required. >