Specialized metallurgical processes – compositions for use therei – Processes – Electrothermic processes
Patent
1986-01-17
1988-09-13
Andrews, Melvyn J.
Specialized metallurgical processes, compositions for use therei
Processes
Electrothermic processes
75 45, 75 68R, C21C 700, C22B 2106
Patent
active
047706996
DESCRIPTION:
BRIEF SUMMARY
This invention relates to processes and apparatus for testing molten metals. More particularly, it relates to testing batches of molten metals (hereinafter described as "metal melts") such as aluminium, ferrous metals such as cast iron and steel, nickel, cobalt, titanium, copper and alloys, by acoustic techniques, to determine the quality, purity etc. of the batch.
It is known to use an ultrasonic technique to investigate the presence of oxides and precipitated phases in melts of aluminium alloys. This is described in a paper by N. D. G. Mountford and R. Calvert, "Journal of the Institute of Metals", 1959-60, Volume 88, pages 121-127. This work demonstrated that the quality of liquid aluminium alloys could be studied and such effects as peritectic reactions could be measured in relation to their equilibrium conditions. A recent technique embodying an improved transducer has been set up, and quantitative measurement electronics have been very successful in registering the efficiency of filters.
A principal difficulty in conducting techniques for studying the quality of molten metals is caused by the solid/liquid interface where a sound-emitting probe enters the melt. At such a location, the sound must be transmitted across a liquid-solid interface. Then, to receive and analyse the sound reflections or echoes, these reflections must be transmitted back across a liquid-solid interface, to a receiver probe, for analysis. In previous work with aluminium metal, it has been common practice to use separate transmitting probes and receiving probes. In other cases, a single probe is used both as transmitter of ultrasound pulses to the melt and as receiver of reflections therefrom. Unless the interference with the sound waves caused by the liquid/solid interfaces can be reduced to a sufficiently low value, the interference is likely to mask any reflections obtained from, say, inhomogeneities, impurity particles, air pockets and cavities in the melt. Analysis of the composition of the melt from the reflected signals is thus made impractical.
To reduce the problem of interference at the interface, it has been suggested that the same base metal as the alloy to be examined should be used for the transmission probe. This provides very similar densities and speed of sound in the liquid and solid media, giving rise to good acoustic impedance matching.
In the case of steel probes used for examining steel melts, in which the speed of sound is 5.8 mm/sec, the density is 7800 kg/m.sup.3, and thus the acoustic impedance (Z.sub.s) is 45.24. For liquid steel, experiments have shown the speed of sound therein to be 5.2 mm/sec and the density approximately 7100 kg/m.sup.3, giving an acoustic impedance of 36.92. From these figures, it can be calculated that only about 1% of the sound is reflected at the interface. The main problem in using a probe with such an interface is the maintenance of the interface itself, in a stable condition. This can be overcome by enclosing the molten end in some form of ceramic sleeve, but then the actual position of the liquid-solid interface within the sleece is determined by the rate at which heat can be abstracted by the probe, and by the thermal conductivity of the steel itself.
It is desirable to use steel for the construction of an ultrasound probe, because of its cheapness and high melting point, especially when testing or treating a ferrous metal melt.
The present invention provides a novel probe for transmission of ultrasound pulses to a molten metal and reception of sound reflection therefrom, in which the ultrasound pathway through very high temperature metal of the probe is reduced to a very small length. This is accomplished by providing the probe with a cooling means near to the melt-penetrating end thereof. The cooling means is effective in use to ensure that reflected sound waves from the melt do not travel for a distance of more than about 50 mm through a metal probe portion having a temperature within 700 C. degrees of the temperature of the melt.
It has been found that, whilst ultraso
REFERENCES:
patent: 3585865 (1971-06-01), Bungart et al.
patent: 4261197 (1981-04-01), Mansfield
patent: 4287755 (1981-09-01), Mansfield
patent: 4373950 (1983-02-01), Shingu et al.
"Acoustic Methods", by V. M. Lantukh et al., 2418 The Soviet Journal of Nondestructive Testing, vol. 15, May 1979, No. 5, New York, pp. 404 through 410.
"Precipitation Effects in Liquid Aluminum Alloys", by N. D. G. Mountford and R. Calvert, Journal of the Institute of Metals, 1959-60, vol. 88, pp. 121 through 127.
Andrews Melvyn J.
The University of Toronto Innovations Foundation
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