Lorentz force infiltration of fibrous preforms

A new process for the production of metal matrix composites, whereby molten metal is forced into the interstices of a fibrous preform using electromagnetic body forces, is presented. These forces are created by subjecting the molten matrix to a concentrated transient magnetic field which, in turn, induces intense eddy currents in the melt. This gives rise to Lorentz forces which propel the metal into the preform. Equations governing the mechanics of Lorentz force infiltration of an axisymmetric preform surrounded by molten metal are solved numerically. A finite difference algorithm is applied to solve Maxwell's equation of electromagnetic field propagation and to determine the flux density as a function of radial position. The resulting Lorentz force is then calculated and balanced with the inertial, fluid friction and capillary forces, taking preform compression into account, to predict infiltration velocity and cumulative infiltration distance. Apparatuses were designed and constructed to infiltrate cylindrical preforms of 24 vol pct 3-μm-diameter chopped alumina fiber preforms with commercial purity aluminum. Two capacitor banks were charged from 1 to 4 kV and rapidly discharged to produce magnetic pulses of up to 4 tesla peak, at frequencies of 2 to 3 kHz in the infiltrating furnace. A commercial MAGNEFORM unit was also used to produce fields of up to 5 tesla at 5.6 kHz.-Sound composite samples were produced, to a depth of 1.8 mm into the preforms, with little or no breakage of fibers. Good agreement between theoretical model predictions and experimentally measured infiltration depths was demonstrated. Primary process variables for a given matrix-preform system, were the number of discharges, the magnetic pulse intensity and frequency, and the melt ring thickness. The model predicts a pulse frequency below which infiltration does not occur and an optimum frequency for maximum infiltration depth. Successive pulses are predicted to produce only slightly decreasing increments in infiltration depth with the parameters explored, indicating that the process allows greater infiltration depths than were attained with preforms and apparatuses used in this work.     

Investigation of Lorentz Force Velocimetry Using Electromagnets

The present work is an analysis on the ElectroMagnetic Lorentz Force Velocimetry(EM-LFV).This noncontact flow measurement technique is based on evaluating the Lorentz force generated by the interactions of an electrically conducting fluid with a localized magnetic field that is produced by electromagnets.Analytical and numerical calculations were carried out as a continuation of a previous work published by Thess et al.The objective is to establish the behavior of the Lorentz force as a function of the main geometric parameters considered in the studied geometry.Thus we present here the evolution of the Lorentz force induced in a translating cylindrical solid body and the coefficient of sensitivity of the flowmeter thanks to numerical simulations in respect with the main geometrical parameters of the problem.     

An Online Contactless Investigation of the Meniscus Velocity in a Continuous Casting Mold Using Lorentz Force Velocimetry

Metallurgical and Materials Transactions B - Monitoring the meniscus velocities of molten steel in continuous casting molds is critical for revealing the velocity field in the whole mold and...     

Rotor Lorentz force as a parameter for the estimation of vortex flows in a DC electric arc furnace with different bottom electrode positions

This article is devoted to researching a simple parameter which can predict the electrovortex flow in a liquid conductor under a Lorentz force. This is provided by a numerical simulation of the electrovortex and convection flows in a DC electric arc furnace with the bottom electrode in different positions. The electromagnetic, temperature and hydrodynamic distribution parameters are given. It is shown that lifting the bottom electrode above the fettle surface by the electrode radius leads to the decrease of shear stress on the fettle area by 30%, while putting the bottom electrode lower than the fettle surface by a distance equal to the electrode radius and its expansion by the same distance reduces stress by 10%. A good correlation between the shear stress on the fettle area and a rotor Lorentz force provide possibility to use rotor Lorentz force as a simple electromagnetic parameter for the estimation of the vortex flow influence on the increased wearing of the fettle.     

Lorentz Force Sigmometry

The present communication reports a new technique for the contactless measurement of the specific electrical conductivity of a solid conductor or an electrically conducting fluid.We tenn the techniqueLorentz Force Sigmometrywhere the neologismSigmometryis derived fiom the Greek letter sigma,often used to denote the electrical conductivity.Lorentz force sigmometry(abbreviated LoFoS)is based on similar principles as the traditional eddy current testing but allows a larger penetration depth and is less sensitive to variations in the distance between the sensor and the sample.Here we formulate the theory of LoFoS and numerically compute the calibration function which is necessary for determining the unknown electrical conductivity from the measurement of a Lorentz force.