US2991684A

US2991684A - Method of supervising metallurgical and metal melting processes

Info

Publication number: US2991684A
Application number: US601151A
Authority: US
Inventors: Wever Franz; Koch Walter
Original assignee: Max Planck Institut fuer Eisenforschung
Current assignee: Max Planck Institut fuer Eisenforschung
Priority date: 1955-08-02
Filing date: 1956-07-31
Publication date: 1961-07-11
Anticipated expiration: 1978-07-11

Description

July 11, 1961 wEvER AL 2,991,684

METHOD OF SUPERVISING METALLURGICAL AND METAL MELTING PROCESSES Filed July 51, 1956 3 Sheets$heet 1 July 11, 1961 w v ETAL 2,991,684

METHOD OF SUPERVISING METALLURGICAL AND METAL MELTING PROCESSES Filed July 31, 1956 5 Sheets-Shet 2 L r L s; 1 Q i L g l if July 11, 1961 F. WEVER ETAL 2,991,684

METHOD OF SUPERVISING METALLURGICAL AND METAL MELTING PROCESSES Filed July 31, 1956 3 Sheets-Sheet 5 f it tates ate 1 1;

2,991,584 Patented July 11, 1961- many Filed July 31, 1956, Ser. No. 601,151 priority, application Germany Aug. 2, 1955 3 Claims. (CI. 88-14) For supervising the course of metal melting processes, especially steel melting processes, samples are continuously taken and analysed during the course of the melting. The results are the more valuable for following the course of the reaction the more quickly they are obtained. Consequently, automatic spectroscopic analysis apparatus has recently been used for this purpose, and with this apparatus most of the alloying elements can be analysed in a few minutes. A number of elements which are important for appreciating the course of the metallurgical process cannot, however, be quickly analysed spectroscopically. In particular the elements oxygen, hydrogen and nitrogen cannot be detected by the usual spectroscopic apparatus. The determination of these elements by the processes hitherto usual, however, takes up so much time that the samples taken for supervising the course of the reaction in the melting furnace and for determining the result of deoxidation treatment which usually takes place in the ladle can no longer be evaluated.

The usual method of determining the gases oxygen, hydrogen and nitrogen in steel and other metals is by melting the metal in a carbon crucible under a high vacuum i.e. a hot extraction process. The oxygen escapes from the super-heated melt in the vacuum in the form of carbon monoxide and hydrogen and nitrogen escape in elementary form. In addition gases such as S H 8, CO H O, CN nitric oxide, hydrocarbons and other gases are liberated. This evolution of gases from steel melts takes place at a temperature of 1600-1700" C. very quickly depending on the size of the sample, for example, with samples of a few grams in 1-3 minutes. The gases are evolved still more quickly at 1400 C. from copper melts. The gases liberated are usually brought to atmospheric pressure with the aid of a diffusion pump and a following collecting pump and are thereafter examined in a gas analysis apparatus. With the known apparatus, the compression and analysis take a longer time than the extraction, so that in this part of the examination expensive time is lost and consequently the process is unsuitable for the analysis of preliminary samples.

The invention relates to a process for supervising the course of metal melting processes, especially steel melting processes, and according to the invention, the gases, after being liberated at pressures of 001-5 mm. Hg, preferably at pressures between 0.1 and 1 mm. Hg, are caused to glow by a high frequency discharge and the light emission in a characteristic range is measured automatically and without loss of time by a spectroscopic analysis apparatus. In addition, for measurement of the total amount of gas, the pressure is fixed.

Experiments have proved that analysis of the three most important gases, namely carbon monoxide, hydrogen and nitrogen can be carried out side by side, in which case, however, certain corrections must be made which take into account the reaction of the gases with one another in the high frequency field.

The measurements can be carried out in a current of gas which, however, is held at constant pressure in a section in which it is activated by means of two valves.

Claims Under these conditions the reaction of the gases with one another need not be taken into account and also other gases can be included in the mixture.

The invention will now be described with the aid of the accompanying drawing, in which:

FIG. 1 is a diagram showing the main parts of an apparatus for carrying out the method of the invention;

FIGS. 2, 3 and 4 are curves and diagrams showing the results of the examination.

Referring to the drawings, the reference letter designates an extraction furnace, B a diffusion pump which, however, may be omitted, C an activating vessel having inlet and outlet valves D and B respectively and a coil F for high frequency activation of the gas. The reference letter G designates a pressure measuring apparatus and H a spectroscopic analysis apparatus.

In the vessel C the gas activation can be kept so constant that the relative intensities need not be meas-' ured, as is usual, but analysis by measuring the absolute intensities of the individual components is possible. This considerably simplifies the apparatus and reduces its cost. In addition to maintaining the high frequency field constant and regulating the pressure, Water cooling of the high frequency electrodes is also necessary.

The time required for carrying out the analysis according to the invention is extremely short. Directly after the gases enter the activating vessel C the intensities of the individual spectral lines which are used for the analysis are indicated. The lines which are used for the analysis are in the case of hydrogen the lines H,,, H,,, and H, whereas, for the analysis of carbon monoxide and nitrogen bands in the range of 3000-8000 A. are used, those for CO being preferably around 4510 A., and those for nitrogen being in the region of 7000A.

In all vacuum metallurgical processes the supervising method of the invention is of considerable importance because it is now possible to connect the gas analysis part of the apparatus beginning with the diffusion pump or the gas activating vessel directly to any vacuum metallurgical installation, for example to a high frequency vacuum furnace or to a vacuum casting installation and continuously to analyse the gas given off from the melt.

The method of the invention instead of being carried out in the above-mentioned manner at constant gas pressure can also be carried out in a different manner. Thus, experiments have shown that the light emission of all the gases investigatedwith a constant activation field passes through a maximum at pressures of approximately 10- mm. Hg. This knowledge can now be used for a further simplication of the gas analysis which will now be explained with the aid of FIG. 1.

The gases from the extraction furnace A or the diffusion pump B are first introduced at a pressure of 01 mm. Hg into the vessel C and the pressure is then lowered by evacuation through the valve E to 0.1 mm. Hg. The intensities of the spectral lines, therefore, pass through their maxima. The maximum intensities correspond to the concentration of the mixtures. They are separated, measured photoelectrically and registered. In this case it is no longer neces sary to keep the pressure in the vessel C constant which considerably facilitates the direct analysis process. A measurement of the total gas quantity can also take place here in known manner in the chamber G behind the valve E.

When the apparatus is directly connected to a vacuum metallurgical installation, the escaping gases can be continuously analysed by admitting gas in rhythmic sequence through the valve D, which is automatically controlled, so that the pressure in the chamber C exceeds the maximum pressure of about 0.1 mm. Hg. The gas is continuously then withdrawn through the valve E until the pressure is gases in the gas below the maximumpressure. In this way the emission continuously passes through its maximum at short intervals of time and thus the composition or the gas may be continuously registered and its alterations followed.

This continuous gas analysis can also be used for a series of other gases, for example carbon monoxide, hydrogen, halogens as well as for a large number of compounds of hydrogen with carbon, nitrogen, phosphorus and silicon amongst others as well as with volatile compounds of the halogens. The method can, therefore, be used not only for supervising metallurgical reactions but also for supervising chemical processes. The spectral conditions, especially the resolving power of the spectro scopic apparatus which is used should be adapted to suit the conditions at the time.

Various examples of the use of the new process will now be given to explain how the apparatus is calibrated and how the analysis is carried out both at constant pressure in the activating vessel C, as well as with the fall in intensity maximum with falling pressure. The gas mixtures analysed all contained hydrogen in addition to nitrogen and carbon monoxide.

Example 1 For calibrating the apparatus difie-rent mixtures of pure gases were made and after being thoroughly mixed were conducted through the apparatus. The inlet and outlet valves were regulated in such a way that there was a constant pressure of 0.3 mm. Hg in the activating vessel C. After this the intensities of the spectral lines used for analysis in the spectrum of the activated gases were measured a number of times at short intervals and registered.

For calibrating purposes, the nitrogen bands at 3943/98 A. and the carbon monoxide bands at 4510 A. were used. FIG. 2 shows by Way of examp e the individual intensities measured for the nitrogen bands with different nitrogen contents, namely 10, 20, 30, and 40% N FIG. 3 shows the nitrogen calibration curve resulting therefrom. The apparatus was also calibrated in a similar manner for carbon monoxide and for hydrogen.

In the analysis of unknown gas mixtures originating from any gas apparatus the contents determined in the usual manner were compared with those obtained by spectroscopic analysis. The following is a comparative example of the results obtained:

N2, percent 00, percent chemical spectroscopic chemical spectroscopic Example 2 tered and FIG. 5 shows the corresponding calibration curve. Since the measurement made in this way is independent of the pressure, the variations are smaller than when measuring with constant pressure. The following table gives comparative results for chemical and spectroscopic analysis:

N2, percent 00, percent chemical spectroscopic chemical spectroscopic We claim:

1. A method of testing a metallurgical process by taking samples of a melt, melting said samples in a vacuum and determining the oxygen, hydrogen and nitrogen gases contained therein and extracted by said vacuum melting, which comprises energizing said vacuumextracted and thus liberated gases so as to cause them to glow by activating them in a gas discharge vessel at a pressure of 0.01 to 5 mm. Hg by a constant highfrequency field and analyzing the light emission spectroscopical-ly.

2. A method of testing a metallurgical process by taking samples of 'a melt, melting said samples in a vacuum and determining the mixture of oxygen, hydrogen and nitrogen gas contained therein and extracted by said vacuum melting, which comprises energizing said vacuum-extracted and thus liberated gas and causing it to glow by activating it in a gas discharge vessel at a pressure of 0.01 to 5 Hg by a constant highf-requency field, lowering the pressure in said vessel from a value above that at which the light emission of the gas is at a maximum to a value below that at which the light emission is at a maximum and determining the composition of the gas mixture from the maximum intensities of its spectroscopically measured light emission.

3. A method of testing chemical reactions, which comprises removing gases evolved during said reactions therefrom, causing them to glow by application of a. constant high frequency field in a discharge vessel, maintaining the pressure therein above that pressure at which the light emission of said gases is at a maximum, followed by lowering that pressure below the maximum light emission, and determining the composition or said gases spectroscopically from the maximum intensities of their light emission, replacing the gases by a fresh supply of gases and repeating the process.

References Cited in the file of this patent UNITED STATES PATENTS 2,339,754 Brace Jan. 25, 1944 2,393,650 Metcalf Ian. 29, 1946 2,544,078 Glassbrook Mar. 6, 1951 2,670,649 Robinson Mar. 2, 1954 2,708,387 Broida et a1 May 17, 1955 2,795,132 Boehme et al. June 11, 1957 FOREIGN PATENTS 329,111 Great Britain May 15, 1930 706,535 Great Britain Mar. 31, 1954

Claims

1. A METHOD OF TESTING A METALLURGICAL PROCESS BY TAKING SAMPLES OF A MELT, MELTING SAID SAMPLES IN A VACUUM AND DETERMINING THE OXYGEN, HYDROGEN AND NITROGEN GASES CONTAINED THEREIN AND EXTRACTED BY SAID VACUUM MELTING, WHICH COMPRISES ENERGIZING SAID VACUUMEXTRACTED AND THUS LIBERATED GASES SO AS TO CAUSE THEM TO GLOW BY ACTIVATING THEM IN A GAS DISCHARGE VESSEL AT A PRESSURE OF 0.01 TO 5 MM. HG BY A CONSTANT HIGHFREQUENCY FIELD AND ANALYZING THE LIGHT EMISSION SPECTROSCOPICALLY.