This is a U.S. national stage of Application No. PCT/DE2009/001137, filed on Aug. 7, 2009, which claims priority to German Application No: 10 2008 045 054.5, filed: Aug. 26, 2008, the contents of which are incorporated herein by reference.
1. Field of the Invention
The invention is directed to a method for controlling foamed slag in a stainless melt in an electric arc furnace.
2. Related Art
The advantages of a favorably foaming slag in the electric arc furnace (EAF) are well known. WO 2007/087979 A1 can be referenced in this regard.
In electric arc furnace operation, the charge, i.e., primarily scrap and alloys, are melted by the arcs of electrodes while simultaneously forming a slag. Apart from its primary function, i.e., the removal of unwanted constituents from the melt, the slag performs a protective function when brought to a foaming state. In this state, the slag blankets the space between the electrode tips and the surface of the metal and, owing to its poor thermal conductivity, protects the refractory lining of the furnace against the radiant energy of the electric arc.
The foamed slag sharply reduces the intensive radiation of the arc with respect to the wall of the electric furnace and therefore facilitates the input of energy into the metal melt. This substantially prolongs the life of the refractory material of the furnace.
To achieve these benefits, the foamed slag must always be at a predetermined level in the furnace.
EP 637 634 A1 discloses a method for producing a metal melt in which the level of the foamed slag is determined acoustically, namely by detecting a frequency range characteristic of slag foaming. Comparison of the measured sound level with a reference sound level yields reference points for controlling the addition of foaming agents.
WO 2007/009924 A1 also addresses the determination of the level of the foamed slag in an electric arc furnace. In this case, the determination of structure-borne sound is used as measuring technique.
It is an object of the invention to provide an improved method for controlling foamed slag.
According to one embodiment of the invention, the slag level in the electric arc furnace is continuously detected thermographically as a function of time and slag level, and the addition of foaming material is controlled depending on the temperature and temperature gradient.
Accordingly, one embodiment of the invention is directed to a method for controlling foamed slag in a stainless melt in an electric arc furnace with the addition of a foaming material based on a thermographic system. The addition is controlled based on optimal formation of the foamed slag measured by its level. The level of the slag causes a change in temperature in a thermal element. The thermal element is installed in the wall of the electric arc furnace and has an extremely high thermal conductivity. This also affords the possibility of measuring the temperature gradient.
Therefore, the slag level is detected on the basis of a continuous temperature measurement by the thermal element. The rapid change in temperature caused by the different slag level is received by a receiver in the control stand via wireless infrared signal transmission. The addition of foaming material is controlled in accordance with the temperature curve.
The invention will be described more fully in the following with reference to the drawings.
In the drawings:
The electric arc furnace, which will not be described in more detail, is designated by 1 in
The foamed slag develops quasi-exponentially based on its natural composition as can be seen from
The slag level is identified by the measuring system through a temperature development at the thermal element 5. The temperature of the thermal element 5 is a function of time and slag level as is represented by equations 1 and 2.
The measuring system provides:
a temperature signal as a time function: T=f(t)=f′(h) (1)
a temperature gradient as a time function: dT=df′(h) (2)
The thermal element 5 is installed in the wall of the electric arc furnace 1 and is characterized by an extremely high thermal conductivity. In this way, the temperature gradient can be determined (see equation 3).
The control system supplies: dT/dt=g(h,t)=df′(h)/dt (3)
Therefore:
the addition rate dm/dt (in kg/min) is provided by equations 4 and 5—
dm/dt=v at T>Tmin and dT/dt≧0 (4)
dm/dt=0 at T=Topt and dT/dt<0 (5)
and a duration of the addition t (in minutes) can be determined from equations 6 and 7
Δt=t, provided dT/dt≧0 (6)
Δt=O, provided dT/dt<0 (7)
Since thermography is a non-contact measuring process, distant objects can also be mapped. The IR signals of the camera are received in the control console as radio signals and are converted into the control signals based on equations 4 to 7.
Provided that the mathematical sign of the gradient is positive, which indicates an upward trend in temperature but, at the same time, also an uncovered condition of the electrodes, the addition of material is carried out at a constant rate. On the other hand, the control can also be based on a different practice-oriented function in this case. When the temperature gradient is zero or negative, the addition of material is completely stopped or proceeds at a decreased rate according to another practice-oriented function.
Thus, while there have shown and described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.
Number | Date | Country | Kind |
---|---|---|---|
10 2008 045 054 | Aug 2008 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/DE2009/001137 | 8/7/2009 | WO | 00 | 2/25/2011 |
Publishing Document | Publishing Date | Country | Kind |
---|---|---|---|
WO2010/022703 | 3/4/2010 | WO | A |
Number | Name | Date | Kind |
---|---|---|---|
5611838 | Fritz et al. | Mar 1997 | A |
6793708 | Jones et al. | Sep 2004 | B1 |
20030212502 | Paredes et al. | Nov 2003 | A1 |
20070133651 | Gerhan et al. | Jun 2007 | A1 |
Number | Date | Country |
---|---|---|
200 17 930 | Jan 2001 | DE |
0 637 634 | Feb 1995 | EP |
07 166222 | Jun 1995 | JP |
WO 0172090 | Sep 2001 | WO |
WO 2007009924 | Jan 2007 | WO |
WO 2007087979 | Aug 2007 | WO |
Number | Date | Country | |
---|---|---|---|
20110146447 A1 | Jun 2011 | US |