Electricity: measuring and testing – Determining nonelectric properties by measuring electric...
Patent
1991-10-28
1993-08-31
Wieder, Kennth A.
Electricity: measuring and testing
Determining nonelectric properties by measuring electric...
324 714, 324717, 324724, 266 99, 164 41, G01N 2707, G01R 2722
Patent
active
052412628
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to an apparatus for detecting the content of inclusions in molten metal, such as precipitated secondary phase particles, drops of slag, and/or air bubbles, during refining thereof, all of which cause a discontinuity in the flow of current in the sensing zone and can therefore be sensed by measurement of this discontinuity. Hereinbelow, for convenience, all of these will be collectively referred to as "inclusions".
In general all such inclusions have a more or less deleterious effect upon the required technical properties of the metal, and it has become more and more essential to have accurate information as to their number and sizes, in order to confirm that the metal is sufficiently "clean" for its intended purpose, and also to show whether the processes employed are producing sufficiently "clean" metal.
INDUSTRIAL APPLICABILITY
The range of molten metals to which the present invention can be applied is board and includes molten metals subjected to refining in steel manufacture, aluminium refining, copper refining, titanium refining, magnesium refining, alloys of these metals, and the like. However, in the following description, molten steel in steel manufacture will be used primarily as an example.
BACKGROUND ART
One prior art invention which relates to the present invention is described in U.S. Pat. No. 4,555,662, issued November, 1985, this patent disclosing a quantitative measurement method for inclusions, the method now being generally referred to as Liquid Metal Cleanliness Analysis (LiMCA for short). The LiMCA method and apparatus were originally developed for detecting nonmetallic inclusions during aluminium refining, but its application to iron and steel refining has also been investigated.
The LiMCA method is sometimes also referred to as the Electric Sensing Zone method (ESZ for short), the principle of the method being that when such an inclusion entrained in an electrically conductive fluid passes through an electrically-insulated orifice the electrical resistance of the fluid which is flowing through the orifice changes in proportion to the volume of the particle. The instantaneous change in the resistance is detected as a pulse in electrical potential between two electrodes on opposite sides of the orifice, and the number and size of the particles can be directly measured in the following manner.
First, if the particles are assumed to be spherical and of diameter d and the orifice is assumed to be cylindrical of diameter D, then the change R in the electrical resistance when a particle passes through the orifice is given by the following equation:
In actual practice, Equation (1) must be corrected by a correction factor F(d/D), which is given by the following equation: 3) electric potential when a particle of diameter d passes through the orifice is given by the following equation:
A previously-disclosed inclusion sensor probe which applies the above-described principles and intended for "continuous" use with molten metal (e.g. for periods as long as about 30-40 minutes) comprises an inner first electrode supported inside a quartz tube and connected to a water-cooled support. An orifice is provided in a portion of the quartz tube near to its lower end. The tube is mounted on the water-cooled support using a gasket to seal the joint between them. The necessary outer second electrode consists of a rod separate from the probe and extending close to the orifice.
When a measurement is to be performed the inside of the hollow electrode, which serves as a chamber to receive the molten metal, is evacuated and the molten metal is sucked inside through the orifice. At this time, the change in electric resistance between the inner and outer electrodes is measured and amplified by conventional means, and the sizes and number of inclusions are determined. When the tube is sufficiently full the negative pressure is replace by a positive pressure until the tube is empty and the cycle is repeated as many times as possible until the tube must be replaced.
The ab
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Kuyucak et al., On-line Inclusion Detection And Measurement In A Tranformer Steel, 2nd symp. on the effects and control of inclusion and residual in steels, Aug. 1986, pp. I44-I61.
Kuyucak et al, On The Measurement Of Inclusions In Copper-Based Melts, Canadian Metallurgical Quarterly, vol. 28, No. 1, pp. 41-48, Dec. 1989.
Ono, A., "Development of Direct Analysis Method for Molten Steel," pp. 51-57 (1989) Dec., Abstract only.
van der Plaats, G. et al., "Size Determination of Conductive Particles with a Coulter Count," Particle Size Analysis 1981, pp. 208-215, Dec.
Guthrie Roderick I. L.
Nakajima Hidemasa
Brown Glenn W.
R. Guthrie Research Associates Inc.
Sumito Metal Industries Inc.
Wieder Kennth A.
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