Single-use disposable molten metal inclusion sensor

Details Single-use disposable molten metal inclusion sensor Single-use disposable molten metal inclusion sensor

1991-10-28

1993-03-30

Harvey, Jack B.

Electricity: measuring and testing

Determining nonelectric properties by measuring electric...

324 714, 266 99, 164 41, G01N 2702

Patent

active

051987490

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 zoner 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 broad 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 Nov., 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) is the 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 for use with molten metal comprises a hollow inner first electrode made from an electrically-conducting, heat-resistant material, this inner electrode being supported inside a quartz tube and connected to an electrode rod through a graphite reinforcing member. An orifice is provided in a portion of the quartz tube near to its lower end, while a cylindrical layer which protects against slag is disposed around a central portion of the outside surface of the quartz tube. The tube is mounted on a water-cooled support apparatus through a coupler which is equipped with an O-ring to seal the joint between the tube and the coupler. 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

REFERENCES:
patent: 3259841 (1966-07-01), Proctor et al.
patent: 3395343 (1968-07-01), Morgan et al.
patent: 3963984 (1976-06-01), Coulter
patent: 4413810 (1983-11-01), Tenberg et al.
patent: 4555662 (1985-11-01), Doutre et al.
patent: 4600880 (1986-07-01), Doutre et al.
patent: 4763065 (1988-08-01), Hachey
Ono, A., "Development of Direct Analysis Method for Molten Steel," pp. 51-57 (1989).
van der Plaats, G. et al., "Size Determination of Conductive Particles with a Coulter Counter," Particle Size Analysis 1981, pp. 208-215.

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