Measuring and testing – Gas content of a liquid or a solid – Of metal
Reexamination Certificate
1998-12-16
2001-04-17
Larkin, Daniel S. (Department: 2856)
Measuring and testing
Gas content of a liquid or a solid
Of metal
C073SDIG009
Reexamination Certificate
active
06216526
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a probe for use in apparatus and a method for measurement of gas concentrations in molten metal. More particularly, the invention relates to such a probe suitable for determination of dissolved hydrogen, oxygen, and/or nitrogen content in molten metals, such as steel.
BACKGROUND OF THE INVENTION
Various devices have been developed heretofore to measure the content of dissolved gases such as hydrogen in molten metals, such as molten aluminum or molten steel. An early device is described in U.S. Pat. No. 2,861,450 issued to Ransley et al. The device shown therein is referred to as the Telegas device. This device is included in an immersion head of generally a bell-shaped configuration and entails discharging or debouching a carrier gas into the molten metal and recapturing bubbles by the probe head. These devices entailed the recirculation of the gases through a closed loop until equilibrium is reached. The nitrogen reached an equilibrium with the dissolved hydrogen, which thus enables monitoring and measurement of the dissolved hydrogen content in the metal. These devices, as well as subsequent variations thereof, uses a membrane which is permeable to the gas, usually hydrogen, whose concentration is to be determined, but which is stated to be impermeable to molten metal. A need continues to exist for such probes which offer testing of increased speed and accuracy.
SUMMARY OF THE INVENTION
It is a principal object of the invention to provide a new and improved probe and processes for determination of dissolved gas contents in molten metals. The invention has important application to the determination of the concentrations of hydrogen, oxygen, and nitrogen dissolved in molten steel, but can be used also to determine concentrations of other dissolved gases in molten steel and in other molten metals. The invention, thus, has applicability to determination of dissolved gas concentrations in most other molten metals such as copper, aluminum, tin, or lead. The invention provides such devices and methods which enable simultaneous determination of the concentration of several gases by means of a single test procedure. In a preferred embodiment using a mass spectrometer, the dissolved gases are absolutely characterized by their molecular weights, as well.
An important aspect of the invention relates to providing of an immersion probe which eliminates the use of and need for a membrane which is impermeable to molten metal. A related aspect entails use of a porous material which, instead of being impermeable to molten metal, is of a type used as a strainer for removing solid impurities from a molten metal. The new probes, by eliminating the impermeable member and substituting a porous metal-permeable material enables more rapid determinations of gas contents than heretofore possible, and, the simultaneous determination by means of a single test procedure of the concentration of a number of gases including hydrogen, oxygen, and nitrogen.
Another aspect of the invention relates to the introduction of streams of inert gases which contain known concentrations of the gas or gases being measured, at least one of these gas streams having a known concentration higher than that of the gas in the metal being tested and another one of the gas streams having a concentration less than that of the gas in the metal being tested. The true amount of the gas being characterized in the metal is then computed to a high degree of accuracy.
Briefly, the invention provides an immersion probe for determination of the concentration of a gas dissolved in molten metal which includes a probe body in the form of an elongated housing. The probe body is formed of a gas and molten metal impervious material of sufficient thermal resistance to withstand immersion in molten metal for the analysis time and is connected to a gas conduit for inflow of an inert gas. The immersible end of the probe body has a porous member which, unlike previous devices, may be, in a preferred embodiment, permeable to both gas and liquid molten metal. The porous member is loosely fitted and unsealed in the probe head and serves to support a layer of loose insulation material, and acts as a heat and splash shield.
An inert carrier gas, such as nitrogen or argon, is used in practice of the process of this invention. After immersion, the probe of this embodiment is preferably purged with pure inert dry gas having a known concentration of hydrogen gas for about fifteen-thirty seconds, and then a negative pressure is drawn through a thermal conductivity device (TCD) such as a katharometer using a pump, a step which is continuous and reaches equilibrium within less than about forty-five seconds. Dissolved gas concentration is then rapidly determined by a connected analysis device.
The method for determining gas contents in molten metal in accordance with the invention includes the steps of providing a probe as defined above, the probe being connected by a gas flow conduit to a gas analysis device. The probe is immersed in the molten metal and then preferably purged and standardized with a pure inert carrier gas stream until an equilibrium is reached and recorded. Then, in accord with a preferred procedure, a stream of pure carrier gas is introduced through the probe which contains predetermined known concentrations of gases to be analyzed, usually hydrogen, oxygen, and/or nitrogen gas which are greater than those contained in the molten metal until equilibrium is recorded. The gases are recovered by the submerged hollow or bell-shaped submerged probe end as it bubbles through the metal bath. The analysis device is then used to determine the content of hydrogen, oxygen, and/or nitrogen contained in the gas flowing out of the metal. Subsequently, there is introduced into the molten metal, through the probe, a second gas stream of an inert carrier gas which contain second predetermined concentrations of hydrogen, oxygen, and/or nitrogen gas which are less than those contained in the molten metal. The second gas is also recovered and analyzed as it bubbles out of the metal to determine its content of hydrogen, oxygen, and/or nitrogen. The gas content determinations are then compared and used to accurately and absolutely compute the content of gases dissolved in the metal. If a mass analyzer, such as a quadrupole mass gas analyzer, is used as the gas analysis device, determinations of hydrogen, oxygen, and nitrogen contents may be effected with high accuracy using a single test procedure.
Other aspects and advantages of the invention will be apparent from the following detailed description, claims, and accompanying drawings.
REFERENCES:
patent: 2861450 (1958-11-01), Ransley
patent: 3820380 (1974-06-01), Miller et al.
patent: 4170139 (1979-10-01), Narita et al.
patent: 4454748 (1984-06-01), Terai et al.
patent: 4624128 (1986-11-01), Pelton
patent: 4731732 (1988-03-01), Warchol et al.
patent: 4757707 (1988-07-01), Harvey et al.
patent: 4879005 (1989-11-01), Fray et al.
patent: 4918974 (1990-04-01), Hachey et al.
patent: 4998432 (1991-03-01), Plessers et al.
patent: 5591894 (1997-01-01), Falk et al.
Falk Richard A
Junker Thomas W
Larkin Daniel S.
Midwest Instrument Co., Inc.
Ryan Kromholz & Manion S.C.
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