US2143982A

US2143982A - Collecting gases from metals

Info

Publication number: US2143982A
Application number: US227334A
Authority: US
Inventors: Weston A Hare; Leland D Peterson; Soler Gilbert
Original assignee: Timken Roller Bearing Co
Current assignee: Timken Co
Priority date: 1938-08-29
Filing date: 1938-08-29
Publication date: 1939-01-17
Anticipated expiration: 1956-01-17

Description

Jan. 17, 1939.

w.AA HARE ET AL COLLECTING GASES FROM METALS Filed Au 29, 1938 FIG. I.

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, /6; ,4 INVENTORS w) Q/d 15PM v M ATTORNEYS.

Patented Jan. 17, 1939 UNITED STATES PATENT OFFME COLLECTING GASES FROM METALS poration of Ohio Application August 29,

12 Claims.

This invention relates to an apparatus for and method of collecting gases evolved from molten metal during its solidification, whereby to obtain information for scientific or other purposes, such as controlling the character and properties of metal in its production.

The invention is applicable generally to the determination of the gas content of molten metals, or of gas evolved in their solidification, but such information is of especial importance in connection with steel making, for which reason the invention will be described with particular reference thereto by way of illustration, but not of limitation.

In the solidification of a molten metal gas may be evolved which was in solution in the melt. Such evolved gas may also arise from another source, namely, gas liberated in reactions occurring in the cooling of the molten metal. The gas evolved in solidification of a molten metal may be of either or both types. Knowledge of the amount and constitution of the gas evolved in solidification of a molten metal may be of considerable importance, particularly in controlling the quality of metallic products and in producing desired characteristics therein.

In the production of high-grade steel, for example, the manufacturer is called upon frequently to control not only the chemical composition of a given product, but also to exercise control over various other factors. In steel manufacture one of the most important of these factors is a knowledge of the degree of oxidation, in term of FeO, of the steel bath during the working and deoxidation stages of a heat. This is important because satisfactory control of grain size, hardenability, abnormality, andsimilar properties is intimatelyconnected with the degree of oxidation of the bath. Heretofore the control of the state of oxidation of a steel bath has generally been quite empirical due to lack of a rapid, simple and dependable means of measuring the percentage of iron oxide in the molten steel. Most analytical procedures and methods of evaluating FeO in steel are inapplicable to control of the steel bath during the making of a heat because they do not give accurate results or because the test data can not be obtained rapidly enough.

Iron oxide dissolved in steel reacts with the carbon in the bath with liberation of carbon monoxide in accordance with the following equation: FeO+C=CO+Fe.

The carbon monoxide thus produced will be evolved substantially completely upon freezing of the metal, and since the carbon monoxide is di- 1938, Serial No. 227,334

rectly proportional to the iron oxide, its determination would afford a means of measuring the degree of oxidation of the steel bath.

Various means have been proposed for collecting for analysis the gases evolved during solidification of molten metals. These have not been applicable to accurate determination of, for exampie, carbon monoxide for control purposes in production, partly because some such apparatus have been cumbersome, not adapted to factory use. or not adapted to the obtaining of results which could be considered reliable in any given instance or in successive operation. Hence, the apparatus previously used for this purpose has not been adapted to control work in steel making.

It is among the objects of the invention to provide a method for the collection of gases evolved during solidification of molten metal which is simple, rapid, adapted to use in control work, does not require highly skilled operators, and provides accurate and reliable results.

A further object of the invention is to provide apparatus for practicing the method of the invention which is light, easily used, relatively inexpensive, and sturdy.

The invention will be described with reference to the drawings, representing the preferred embodiment of apparatus, in which Fig. 1 is a vertical longitudinal section through the apparatus provided by and adapted for practicing the meth- 0d of the invention; Fig. 2 is a fragmentary section, on an enlarged scale, through a test spoon containing a pool of molten metal and showing the lower end of the apparatus of Fig. I inserted therein; and Fig. 3 is a vertical sectional view of the lower end of the tube after making a test.

In accordance with the invention the gases evolved in solidification of molten metal are collected by inserting into a pool of the metal one end of an evacuated tube sealed with a closure which fuses at the temperature of the molten metal to permit a sample thereof to be forced into the end of the tube in consequence of the difference in pressure between the atmosphere and the interior of the evacuated tube when the tube seal is broken. Metal is then frozen about the end of the tube to close it and entrap the sample and the gas which is evolved from the sample during its solidification. Thereafter the gas collected in the tube is withdrawn and subjected to analysis.

The apparatus provided by the invention comprises an elongate refractory tube closed at one end and provided at the other end with a closure adapted to fuse rapidly when inserted in a pool of the metal being subjected to analysis. The term refractory is used in its broadest sense to refer to material adapted to withstand the temperatures to which it is exposed. For most cases metal tubes, most suitably of steel, are best adapted to the purposes of the invention. The tube is provided with means, such as a vacuum-tight valved outlet, for connecting it to an evacuating system and to gas analysis apparatus.

The fusible closure is one adapted to melt at the temperature of the molten metal being tested. To this end it may be of lower melting metal, or it may be made of the metal being tested but in a section so thin as to melt rapidly when immersed in the metallic bath. It is essential, of course, that this closure be capable of with standing the pressure created when the tube is evacuated. The other end of the tube is prefer ably closed by a gas-tight removable closure.

Most suitably the tube is of relatively narrow diameter and relatively great length, thus providing a high ratio of length to diameter. Experience has shown that with short tubes, particularly of relatively large diameter, the volume may be insufficient to accommodate the gas evolved from the sample, and droplets of metal which are projected from the sample in its solidification may seal oif the opening to the evacuating and gas-sampling line. Preferably, therefore, the tubes are of relatively great length to provide considerable gas-receiving volume and also to permit cutting off the sampling end after test, so that the tube may be used for further tests.

To insure adequate volume for collection of the gas, particularly as the volume of the tube bu comes less as it is shortened through removal of sections at its lower end after successive tests, the apparatus preferably includes a gas reservoir connected to the tube and carrying the vacuum-tight valved evacuating gas-withdrawing outlet. The total volume of the system should be such that after the metal sample has frozen the pressure in the system is considerably below atmospheric, to insure maximum removal of gas from the metal under test. The connection between the reservoir and the tube is preferably located adjacent the upper end of the tube to minimize the possibility of its being closed off by droplets of metal, and to permit removal of a substantial length from the lower end of the tube so that it may be used repeatedly.

The parts of the apparatus are associated so that the entire apparatus is capable of holding vacuum, i. e., it is gas tight.

Having reference now to the drawing, the apparatus shown in Fig. 1 comprises an elongate steel tube provided at its upper end with a closure cap 2. In the embodiment shown this cap 2 is made by brazing or welding a plug 3 into one end of a length of tubing of larger diameter than tube I so that the cap member acts also as a trap for metal splashed during sampling. Although cap 2 must be associated with tube 1 to provide a gas-tight closure, it is preferably removable, and to this end it may be silver soldered to the tube at 4.

The lower end of the tube is provided with a fusible closure member as described above. For most purposes it is preferred to use a thin disc 5 of metal disposed in a recess machined in the end of the tube, as seen in Fig. 1. For use in sampling steel this disc may comprise thin sheet copper. The thickness of the disc will depend upon its area and the degree of evacuation of the tube. The disc may be silver soldered in place to provide a gas-tight seal.

The apparatus shown includes also a gas reservoir member R made, for instance, by welding plates 6 in the ends of a length of tubing 7. One plate is provided with a vacuum-tight valve 8 and with an opening for receiving a conduit 9, suitably of copper tubing, connecting the reservoir to tube i. As shown in Fig. 1, conduit 9 is preferably connected to the tube adjacent cap 3. The reservoir may be supported by a clamp IE3 carried on tube In the practice of the invention the apparatus must be gas tight and capable of retaining a relatively high vacuum. This is best accomplished by making the connections by welding, brazing, silver soldering, or the like.

In the use of the apparatus in practicing the method provided by the invention the elements of the apparatus are assembled and tested for leaks, suitably by introducing air under substantial pressure, say 30 to 50 pounds, and immersing the apparatus in a tank of water, whereby leaks will be revealed by bubbles. After the apparatus has been found to be gas tight it is dried and then evacuated by connecting valve 8 to a vacuum pump provided with a manometer. In general the best results are obtained through the use of a high vacuum, such as that produced by a Megavac pump. After evacuation valve 3 is closed and the apparatus allowed to stand for a period of time, say an hour, after which the vacuum is tested by opening the valve connected to the evacuated manometer system. If no leaks exist the tube is weighed and is then ready for use. For most purposes it suffices to use a balance capable of weighing with an accuracy of 1 gram. The length of tube l is also recorded for use in subsequently calculating the gas volume.

The lower end of the tube I is warmed to insure freedom from moisture and is then immersed in a pool of molten metal. Preferably this is done by inserting it in a sample ll of the molten metal held in a sampling spoon l2. In testing steel a spoon holding 6 to 8 pounds of metal suffices. If slag is present on the surface of the metal it should be carefully scraped away, and the end of the tube should not project into slag which may be beneath the metal. When immersing the tube it should be held at an angle describing an inverted cone by such movement,

to cause a gob or ball IQ of the metal to form and seal the end air tight. The tube is then removed from the spoon and the gob of steel hammered to assure a perfect seal. In steel testing it is desir able to throw a few chips of aluminum into the metal pool before gob It has been completely frozen, which assures the formation of a nonporous seal.

If the tubes have been properly evacuated there is substantially no danger of splashing or spitting of steel during sampling. However, if much air is present within the tube its expansion when the molten steel is drawn in may blow the steel back out of the tube with considerable force.

v and relatively inexpensive.

To eliminate the danger of injury to the operator from such a result the tube may be provided with a safety shield iii in the form of a cone of heavy wire screen of relatively fine mesh which may be removably mounted upon the tube by a clamp member 56 of any conventional form so that it may be moved upwardly as the lower end of the tube is cut off.

After the tube and its sample have cooled the tube is again weighed to obtain the weight of the sample, but the actual weight must be corrected for that of the gob l4 which has not supplied any of the gas in the tube. The gas evolved from the sample it is then Withdrawn through valve 8 for analysis. Ihe analytical procedures will, of course, depend upon the particular constituents of the gas, but such procedures are well known and in use in the art. A procedure adapted to the testing of steel for determination of its FeO content, and the calculations involved, is reported in detail in a paper by the applicants appearing in the Transactions of the American Society for Metals for September, 1937.

After the gas has been withdrawn the lower end of tube l containing the solidified metal is removed and a new closure 5 is connected thereto, to prepare the apparatus for further use. If need be cap 2 is removed for cleaning the bore of the tube if any considerable amount of metal has been sprayed thereon during sampling.

The exact dimensions and proportioning of the parts will depend, of course, upon the metal being tested and the purpose for which the data are intended. However, to exemplify the invention further reference will be made to an apparatus constructed as shown and described that has been used extensively in connection with steel. It comprises a steel tube l seven feet long having an inside diameter of i inch and a wall thickness of e inch. This is suited for steel of relatively low FeO content. Where the FeO content of the steel is high, or the steel relatively cold, the tube is preferably of somewhat larger diameter, say inch. The tube is machined at its lower end to a depth of inch to receive a '78 inch diameter disc 5 of copper of about 0.005 to 0.007 inch thickness. At its upper end the exterior wall of the tube is machined to a diameter of 1 inch to receive cap 2 which is ten inches in length, inch inside diameter, and 1 inches outside diameter. The reservoir is made from a steel tube 30 inches long, 1% inches inside diameter, and having a wall thickness of inch, and it is connected to tube 5 about 4 inches below its upper end. About 4 inches is out from the end of tube 5 after each test, and it may be re-used until it has been cut back to a length of about 5 feet.

Extended use of the apparatus and method provided by the invention has shown that it is well adapted to the collection of gas evolved in solidification of molten metal. The apparatus is light enough to be handled readily, it is sturdy so that it is adapted to plant operations, and it is simple The reservoir, valve and cap member last indefinitely and may be assembled with new tubes. The application of the invention to steel practice has shown that it affords a means for rapidly and effectively controlling the steel during its production, not only because the collection of the gassample and the determination of critical constituents, such as carbon monoxide, occupies but a short time, so that the steel bath can be altered in accordance with the indication of the analysis, but also because of the reliability of the results. The invention also isof value as a tool in working out the best practice for a given specification of steel, and for other related purposes.

According to the provisions of the patent statutes, we have explained the principle and mode of operation of our invention and have illustrated and described what we now consider to represent its best embodiment. However, we desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

We claim:

1. Apparatus for collecting for analysis gases evolved during the solidification of molten metal, comprising an elongate refractory tube closed at one end and provided at the other end with a gastight closure of metal fusible at the temperature of said molten metal, and valved means associated with said tube for connecting it to evacuating means.

2. Apparatus for collecting for analysis gases evolved during the solidification of molten metal, comprising an elongate metallic tube provided at one end with a removable gas-tight closure member, and at the other end with a gas-tight closure of metal fusible at the temperature of said molten metal, and valved means associated with said tube for connecting it to evacuating means.

3. Apparatus for collecting for analysis gases evolved during solidification of molten metal, comprising an elongate metallic tube, a gastight closure member associated with the upper end of said tube, a thin disc of metal fusible at the temperature of said molten metal associated with the other end of the tube to make a gastight closure therefor, a gas reservoir provided with a vacuum-tight valve, and a gas-tight connection between said reservoir and said tube adjacent the upper end of the tube.

4. Apparatus for collecting for analysis gases evolved during solidification of molten metal, comprising an elongate metallic tube of high ratio of length to diameter, a gas-tight closure member removably associated with the upper end of said tube, a thin disc of metal fusible at the temperature of said molten metal associated with the other end of the tube to make a gas-tight closure therefor, a gas reservoir provided with a vacumn-tight valve, and a connection between said reservoir and said tube adjacent the upper end of the tube, the volume of said tube and reservoir being such that gas evolved from a sample of said molten metal in the previously evacuated tube remains therein under sub-atmospheric pressure.

5. Apparatus for collecting for analysis gases evolved during solidification of molten metal, comprising an elongate metallic tube of high ratio of length to diameter, a gas-tight closure member removably asosciated with the upper end of said tube, a thin disc of metal fusible at the temperature of said molten metal associated with the other end of the tube to make a gas-tight closure therefor, a metallic reservoir tube of greater diameter and less length than said sampling tube closed at both ends and provided with a vacuumtight valve, and a connection between said reservoir and said tube adjacent the upper end of the tube.

6. Apparatus for collecting for analysis gases evolved during solidification of molten steel, comprising an elongate steel tube, a gas-tight closure member remo-vably associated with the upper end of said tube, a thin disc of copper associated with the other end of the tube to make a gas-tight closure therefor, a gas reservoir provided with a vacuum-tight valve, and a connection between said reservoir and said tube adjacent the upper end of the tube.

'7. That method of collecting for analysis gases evolved in solidification of molten metal which comprises causing a sample of said metal to enter one end of a refractory tube, and freezing an amount of said molten metal about said end to close it and entrap in the tube said sample and gas evolved therefrom in its solidification.

8. That method of collecting for analysis gases evolved in solidification of molten metal, which comprises inserting in. a pool of said metal one end of an evacuated elongate refractory tube and provided at said end with a closure rapidly fusible at the temperature of said molten metal, and after said closure has fused to permit a sample of said molten metal to enter the tube freezing an amount of said molten metal about said end to close it and entrap in the tube said sample and gas evolved therefrom in its solidification.

9. That method of collecting for analysis gases evolved in solidification of molten metal, which comprises inserting in a pool of said metal one end of an evacuated refractory tube having a high ratio of length to diameter and provided at said end with a closure rapidly fusible at the temperature of said molten metal, and after said closure has fused to permit a sample of said molten metal to enter the tube freezing an amount of said molten metal about said end to close it and entrap in the tube said sample and gas evolved therefrom in its solidification.

10. That method of collecting for analysis gases evolved in solidification of molten metal, which comprises inserting in a pool of said metal one end of an evacuated elongate refractory tube provided at said end with a closure rapidly fusible at the temperature of said molten metal, said tube being connected to a gas reservoir of such capacity that the gas liberated from the metal is contained at sub-atmospheric pressure, and after said closure has fused to permit a sample of said molten metal to enter the tube freezing an amount of said molten metal about said end to close it and entrap in the tube said sample and gas evolved therefrom in its solidification.

11. That method of collecting for analysis gases evolved in solidification of molten metal which comprises evacuating an elongate refractory tube provided at one end with a closure readily fusible at the temperature of said metal, then inserting said end into a pool of said molten metal to fuse said closure and permit a sample of the molten metal to enter the tube, freezing an amount of said molten metal about said end of the tube to close it and entrap in the tube said sample and gas evolved therefrom in its solidification, and withdrawing and analyzing the gas from said tube.

12. That method of collecting for analysis gases evolved in solidification of molten metal which comprises evacuating an elongate refractory tube provided at its lower end with a closure readily fusible at the temperature of said metal, and provided adjacent its other closed end with a connection to a gas reservoir, then inserting said lower end into a pool of said molten metal to fuse said closure and permit a sample of the molten metal to enter the tube, freezing an amount of said molten metal about the lower end of the tube to close it and entrap in the tube said sample and gas evolved therefrom in its solidification, and withdrawing and analyzing the gases from said tube and reservoir.

WESTON A. HARE. LELAND D. PETERSON. GILBERT SOLER.