Thin Metal Strips Research Articles

Development of Friction-Assisted Extrusion Process for Producing Thin Metal Strips.

A new concept of "friction-assisted extrusion" to produce a thin metal strip is proposed. In the process, a rectangular prismatic workpiece inserted into the container is compressed by a punch against an anvil, and the anvil is forced to move horizontally. A thin strip can be extruded through the gap by the high friction force over the anvil surface. Very thin strips of aluminium and copper up to about 50 μm in thickness could be formed up to the extrusion ratio R = 200 with a considerably low punch pressure ratio p/2k=1∼2(p : punch pressure, k : yield shear stress), which agreed with the theoretical value estimated by the upper bound method.

Equivalent network of transverse dipoles in inset dielectric guide: application to linear arrays

The inset dielectric guide (IDG) is an alternative to the image line, retaining most if its advantages without its main disadvantages. In particular, IDG makes it possible to realize low-cost leaky wave antennas with very pure polarization properties by laying thin metal strips (dipoles) on the air-dielectric interface. The scattering properties of thin metal strips are analyzed by means of a Ritz-Galerkin variational approach, taking into proper account the edge singularities. A variational expression for the equivalent circuit of the radiating dipole is derived, and this information is applied to the design of a tapered linear array by network methods. The array was built and tested, and it showed excellent performance.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Induction heating with transverse flux in strip-metal process lines

Induction heating, with its excellent controllability and response, is unequalled for the heating of metal at very high power density; its application in transverse-flux modes is the key to ultra-rapid prcessing of thin metal strip, utilising electricity efficiently at megawatt power levels and at good load factor.

Magnetic braking: Simple theory and experiment

A simple theory of magnetic braking in a thin metal strip is proposed. The predictions of the model are compared to experiment and good agreement is obtained. The experimental tests were conducted by spinning a thin aluminum disk of large radius between the pole pieces of an electromagnet. A field range of 0 to 150 mT was used.

Fast convergent integral equation solution of strip gratings on dielectric substrate

A fast convergent integral equation solution to the scattering problem of a transverse electric/transverse magnetic (TE/TM) plane wave by a one-dimensional periodic array of thin metal strips on a dielectric substrate is described. The formulation of the integral equation is similar to that derived by Montgomery for a two-dimensional periodic array of thin conductors on a dielectric substrate. However, the basis functions which satisfy the appropriate edge conditions are incorporated here for the unknown current expansion on the strips. Following the standard Galerkin's procedure, one may readily determine the induced currents on the strips and thus the reflected and transmitted fields. Sample numerical results are given and good agreement with previously published data is obtained. It is found that the convergence rate of this method is improved by an order of magnitude. Also it is shown that the dielectric substrate has a strong effect on the scattering from the large spacing strip grating.

Investigation of Turbulators for Fire Tube Boilers

This paper summarizes an experimental study of three popular “turbulator” inserts for fire tube boilers. An electrically heated flow facility was developed to deliver hot air to a water-cooled steel tube instrumented to derive sectional average heat transfer coefficients for four regions of the tube. Reference data for the empty tube are in excellent agreement with the accepted correlation. Two commercial turbulators, consisting of narrow, thin metal strips bent and twisted in zig-zag fashion to allow periodic contact with the tube wall, displayed 135 and 175 percent increases in heat transfer coefficient at a Reynolds number of 10,000. A third commercial turbulator, consisting of a twisted strip with width slightly less than tube diameter, provided a 65 percent increase in heat transfer coefficient. The friction factor increases accompanying these heat transfer coefficient increases were 1110, 1000, and 160 percent, respectively, for the same Reynolds number. These data should be useful in assessing overall performance gains to be expected when turbulators are used in actual boilers.

Strip gratings at a dielectric interface and application of Babinet’s principle

In this paper, we consider the transmission-line model used to calculate the transmittance of thin metallic strip gratings (at wavelengths longer than the grating period) to resolve a conflict of published expressions for the effect of a thick dielectric substrate on the equivalent circuit capacitance of capacitive gratings. By using rigorous diffraction theory we establish the correct expression and derive a modified form of Babinet’s principle for use with strip gratings on dielectric boundaries. It is found that the equivalent circuit capacitance of a strip grating on the boundary between media of refractive indices n1 and n2 is larger than its free-space value by a factor (n12+n22)/2. The result is applicable in general to the capacitive part of the equivalent circuit of grid reflectors, which are widely used at submillimeter wavelengths. A useful set of rigorously calculated transmission curves for strip gratings is presented, and these are used to establish the range of validity of the transmission-line model.

An Accurate Determination of Dielectric Loss Effect in Monolithic Microwave Integrated Circuits Including Microstrip and Coupled Microstrip Lines

For the first time, by a rigorous analysis, the performance of MIC planar transmission lines with Iossy substrates can be studied accurately. The generaf structural shape chosen for the analysis includes infinitely thin metallic strips embedded within the layers of homogeneous dielectric substrates. The rigor of the analysis was guaranteed by the assumption of the propagation of an electromagnetic hybrid wave (i.e., TE+TM) along tbe planar transmission lines. An efficient computation was, however, achieved by implementing the spectral domain approach as the basis for the analysis. To test the analysis, phase constants, characteristic impedances, and attenuations, due to dielectric losses, were computed for microstrip and coupled microstrip lines. The results obtained were compared with those given previously by the spectral domain analysis in which dielectric losses were not included directly [1]. The comparison showed an excellent agreement between the two theories for low-loss substrates. However, for Iossy substrates the present method is more accurate.

The origins of failure instability in metal-working processes

The development of pinholes in thin metal strip, the failure of aluminium compressed between opposed parallel platens and the spiral markings on hard-drawn copper tubing are discussed in relation to the cause of failure instability in technological processes. It is suggested that surface features caused initially by slip bands and at large deformations by shear bands resulting from strain concentrations dictated by the gross geometry of deformation (e.g. the geometry which is likely to be found at the edge of a tool) may initiate instability rather than “structural softening” within the shear bands, although the path of failure follows shear bands. The planes at 35° to the median plane are planes of shear instability and failure in incompressible isotropic non-work-hardening material which yields in plane stress according to the von Mises criterion, so it is not necessary to consider the orientation resulting from the mechanism of microscopic deformation to explain the direction of shear bands in rolled material.

Noise-reducing support for friction linings of braking devices

The invention relates to a noise-reducing support for the friction lining of a braking member in which said lining is fixed to said support and is adapted to be clamped against a friction track by the effect of a force applied to said support, this friction track being incorporated for example in a disc or a ring or alternatively in a wheel-drum, especially of an automobile vehicle. According to the invention said support comprises a stack of a plurality of thin metallic sheets or strips, contiguous to each other over their whole surface and all assembled together by glueing, welding in zones, riveting insetting in a rim or flange, etc.

A spectral domain approach for computing the radiation characteristics of a leaky-wave antenna for millimeter waves

A new method for evaluating the complex propagation constant \beta in a leaky-wave structure comprising thin metallic rectangular strips etched on a dielectric rod of rectangular cross section is described. The radiation pattern of the leaky-wave antenna can be determined once \beta is known, since Re( \beta ) governs the direction of the main beam and Im( \beta ) accounts for the beamwidth and aperture efficiency. In addition the knowledge of the dependence of \beta on frequency allows one to design the antenna for frequency-scanning applications. The method employed in this communication is based on the spectral domain approach that formulates the eigenvalue problem in the Fourier transform domain. Computed results are shown to be in very good agreement with experimental measurements.

New method for measuring thermal properties of transparent solids

A non-steady-state method for measuring the thermal conductivity and thermal diffusivity of transparent solids is described. A thin metal strip is pressed between two plane pieces of the material to be tested and, through electrical heating, works as a continuous plane heat source. The temperature distribution is monitored with uncollimated-beam interference, the experimental conditions of which are discussed in some detail. The method is tested on fused quartz and the accuracy and the internal consistency of the measurements are demonstrated.

Further studies of the ignition of gases by transiently heated surfaces

Earlier work at SMRE on the ignition of methane-air mixtures by rapidly heated surfaces has been supplemented by a study of the ignition characteristics of propane-air and ethylene-air mixtures. A capacitor discharge through a thin metal strip was used to produce transient heating in experiments to find the most readily ignitable compositions and their induction times. The ignition of propane-air by means of a frictional impact between tungsten carbide tipped steel and sandstone was also investigated for comparison.

On the Influence of Hardening and Anisotropy on the Plane-Strain Compression of Thin Metal Strip

This paper presents a theoretical investigation into the continued quasi-static compression of a thin metal strip between two rigid, parallel rough dies. Three different constitutive postulates for the strip material are considered: (a) rigid isotropic hardening, (b) rigid-perfectly plastic with an anisotropic yield criterion, and (c) rigid-kinematic (anisotropic) hardening. An initially homogeneous such strip develops inhomogeneities through its thickness as it is compressed. This is due to the dependence of the yield locus on the rigid-body spin for an anisotropic material and on the strain-history for a hardening material. The length of the dies is supposed to be much greater than the current strip thickness. The solution is hence effectively independent of position along the length of the strip and can be found by integrating an ordinary differential equation.

Surface electromagnetic wave coupling efficiencies for several excitation techniques

The excitation efficiencies for coupling surface electromagnetic waves onto aluminum at a microwave frequency (f = 8.445 GHz, lambda = 3.55 cm) were studied experimentally for several different standard microwave techniques as well as two optical techniques (prism and grating) applied to the microwave frequency region and two new techniques (hump and valley). The peak measured efficiencies found were: for the standard rectangular waveguide, 92%; for the horn antenna, 73%; for the right angle prism properly gapped above the metal, 60%; for the hump of 10-wavelength radius of curvature, 35%; for the thin grating strips on polystyrene coated metal, 30%; for the grating bars gapped (1/2) wavelength above the metal, 26%; and, for the valley of 10-wavelength radius, 12%. The measurement of the excitation efficiencies for prism and grating coupling techniques sometimes required that the prism or grating be in the near field of the antenna. In addition to measuring peak efficiencies, the efficiencies were measured as functions of the gap heights, the angular orientations, the different diffraction modes, the shapes, and the materials of the grating bars. The coupling efficiencies for both prism and grating couplers show a strong dependence on gap height above the metal. Dielectric grating bars were found to be inefficient compared to solid or hollow metallic bars, or thin metallic strips. The distance between the target point of the center line of the microwave horn antenna and the corner of the prism was found to be about 1 wavelength for maximum prism coupling efficiency.

Diffraction radiation from a modulated electron beam moving near a thin metal strip

Diffraction radiation from a modulated electron beam moving near a thin metal strip

Quantitative measurements of the mass distribution in thin films during electrotransport experiments

A method is described which allows a thin metallic film strip to be scanned transversally with an electron beam. Thus a strip 780μm long is divided into about 390 individual parts. The mass of each of these “slices” can be evaluated electronically. Such a series of individual determinations, made with a modified scanning electron microscope, gives the mass distribution along the strip. Experiments were done on Al films in the temperature range 230°–510°C. The temperature dependence of the ion migration velocity gives an activation energy of ion migration of 0.7 eV which confirms that electromigration in these films (grain size 1 μm) takes place via grain boundaries in the whole temperature range.

Diffraction of a plane wave by an infinite strip grating in the short-wavelength case

A MATHEMATICALLY valid method of investigating the problem of the diffraction of a plane electromagnetic wave by a periodic grating consisting of ideally conducting infinitely thin metallic strips, situated in one plane, is presented. The method enables the behaviour of the diffracted field in the short-wavelength case to be described with any degree of accuracy.

Transient Behavior during Electrodeposition onto a Metal Strip of High Ohmic Resistance

Electrochemical deposition onto a thin metal strip of high resistance can result in a deposit of varying thickness along the strip if the electrode resistance is sufficiently large to cause a nonuniform reaction rate distribution. As deposition proceeds, the ohmic resistance of the strip decreases and thus transient behavior is observed. The transient thickening process is modeled by a one‐dimensional pseudo steady‐state method. The results illustrate how transient behavior during deposit growth depends upon the mass transfer, charge transfer, ohmic resistance, and geometric characteristics of the system. Conditions are discussed under which nonuniform deposits may be anticipated.

Low-Pass Quasi-Optical Filters for Oversized or Focused-Beam Waveguide Applications

A form of Iow-pass quasi-optical filter for millimeter-wave and possibly infrared applications is described which consists of thin layers of dielectric interspersed with arrays of thin metallic strips in a manner similar to an artificial dielectric. Equivalent circuits for filter half-sections of the type used were developed, and formulas and graphs are presented from which image parameters for such half-sections can be obtained. A design procedure is given from which multisection fiters of this type can be designed from low-pass lumped-element prototypes in order to give prescribed transmission characteristics. Some trial designs were worked out and fabricated for use in oversized waveguide, and their responses were computed in detail with a digital computer. Except for some higher order mode effects believed to be due to the standard-size to oversize waveguide tapers which were used, the measured responses were in good agreement with the theory. Stopband edge ratios between 3:1 and 4:1 are possible. Filter structures of this type are amenable to fabrication by techniques similar to those used in integrated circuit technology.