DE2657116C2 - Monitoring method for metal melting in electric arc furnaces - Google Patents

Description

The invention also relates to electrometallurgy, namely on monitoring meth. · Jen for metal melting in electric arc furnace.

The most effective field of application of the invention is metal production in electric arc furnaces.

When melting metal in an electric arc furnace, it is particularly important to monitor the following operations: Time when the insert melts, when the furnace is switched off because of the reloading, the completed melting of the insert including the slag-forming and alloying materials, Slag work and temperature control in the melt. The monitoring of these operations is crucial for both the performance of the furnace and the quality of the molten metal.

There is a method (A. M. Gaj, USSR copyright! 94124. Kl. C21C05 / 52) known that it allows to grasp the moment when the melting or its individual periods have ended. The method measures the current consumption in ampere-hours during the entire melting period and determines whether a melting period has ended according to the consumption of electricity.

This process has not caught on in industry because of the electricity required to melt the metal depends on the weight and nature of the mission; but these parameters are not constant, but move in quite wide areas. In the event of a short circuit between electrodes and The current is the maximum input material, - on the other hand, the amount of heat given off by it to the metal, because the There is no arc, minimal. The result is that although the calculated ampere-hours have already been consumed the metal in the furnace has not yet melted.

It is also a process (I. M. Korobko, Ju. S. Isgojew, USSR copyright certificate 235785, class C21c, 05/52) for detecting the beginning of the oxidation period in the melting process. The procedure measures the power consumption in ampere-hours and the weight and nature of the application are taken into account, by changing the calculated electricity consumption for melting accordingly. The electricity supply is calculated with the help of a computer. This method suffers from some disadvantages of the previous one Method free, but the number of ampere hours recorded by measurement can be your calculated Number can also be reached at a time when the metal (due to frequent short circuits between electrodes and Charge) has not yet melted down. Due to this fact, this method of surveillance could not be used of electrofusion in the industry.

A monitoring method for the melting of steel in an electric arc furnace has also been proposed (See the USSR copyright certificate 358796 H 05b 7/00 of October 23, 1970). In this process, arc current or arc voltage oscillations by breaking down the electrical signal into harmonic components and comparison of the values obtained or their ratios with normal sizes in different Areas of the vibration spectrum are continuously analyzed. The normal sizes are after evaluation statistically determined from the data of a number of melts.

This process allows the boiling of metal in its intensity, the time of melting of slag forming and alloying materials and poor slag work.

However, it is suitable for recording the state of the melt material not during the melting process and requires a previous statistical evaluation of the Data from a large number of batches to maintain reliable reference values for each individual furnace in advance.

There is also a method for detecting the end of melting for electric arc furnaces with electrode control (see Konissi Tzutomu, Automatic monitoring of the end of melting in electric arc furnaces. "Chitati Cheron", 1966, Volume 48, Issue 2, pp. 266-273).
With this method, the absolute electrode speed is measured from a certain value for all three phases and compared with its normal value.

But this process only allows the end To record the meltdown, like the previous one, has a previous statistical evaluation of the Data from a plurality of batches is a prerequisite for maintaining a reliable comparison value and is against changes to the electrode adjustment system as well as against a different nature of the Items used are very sensitive.

The invention is based on the object of specifying a monitoring method for the melting of metals in electric arc furnaces, in which the changing conditions of the melting process due to the electron emission from the metal used and the slag-forming and alloying materials are taken into account.
This task is done with a monitoring method

for metal melting in electric arc furnaces with Electrode control resulting in an analysis of the electrical values of the arc and a comparison of the Actual values with setpoints provided by a statistical evaluation of the data from a number of batches exists, and a melt management based on it in such a way that the melting process in the sense of compensation the deviations that have occurred in the arc values from the nominal values are influenced, according to the Invention solved in that the arc voltage and arc surge several times within certain periods measured and then the sums of the recorded direct current or direct voltage components for the individual measurement periods are formed, with the duration of each individual measurement period divided by time is determined, during which the electrical quantity in question is practically constant for the measuring period Can achieve value.

This process allows the melting of metals to be accelerated significantly. Analysis of the Direct current and direct voltage components allow the most important work processes to be precisely monitored and thereby the Qüäiiiäi of the. melted metal largely to improve.

In addition, the invention provides much better operating data for the electric arc furnace: The energy consumption for melting is lower, the metal does not overheat, so that the Dephosphorization can go better, and the metal shows less burn-up and fewer gases absorbed.

As a result of the monitoring method according to the invention, the furnace lining lasts much longer.

The measurements are expediently carried out continuously within the individual periods; the The duration of a measurement period can range from one oscillation of the measured variable to the duration of the shortest Be an operation.

The continuity of the measurement makes it possible to terminate the individual operations in the course of the Detecting the melting of metal in the electric arc furnace more precisely.

The chosen division of the process into measuring periods makes the acquisition even a short one Operation possible.

Other objects and advantages of the invention will become apparent from the following detailed description with reference to FIG Drawings that show

Fi g. 1 to 3 the individual stages of the melt rupture in an electric arc furnace schematically,

4 shows the curve of the mean probable values of the equilibrium voltage component of the arc voltage over the melting time,

F i g. 5 shows the circuit of the simplest device for detecting the direct current components of arc voltage and current,

6 shows the connection of the device for detection the DC components of the arc voltage and current to the arc furnace.

As is well known, the arc stiom is primarily caused by the thermal emission, the saturation current I _{n of} which can be calculated using the Richardson-Dushrnan formula.

It is

/, = A ■ S

■ exp \ -y

in it mean:

A = 120.4 A ■ cm- 'degree- ² -, ommerfeld thermal

mission constant, absolute
T temperature of the cathode spot in ⁰ K,
S area of the cathode spot in cm ² ,
b constant proportional to the work force.

Immediately after the meltdown has started, the arc burns between electrode 1 and the cold feed material 2 (Fig. 1). Hence, at the time that the Charge 2 serves as a cathode, the saturation current is weaker and the voltage at the arc is higher than to the half cycle in which the electrode 1, the temperature of which is higher than that of the insert metal Cathode is used. This causes the voltage or current of the arc to be a direct current component has, which is the voltage or current means over the entire period of oscillation.

The particular conditions in which the arc during melting burns (frequent tearing, short-circuiting through the outgoing unt · ■ Einsatzmaieriaisiücke, a:. E can touch the electrode rufaiiig, etc.) are the cause for the fact that the amplitude values and thus the Gleichstromkompo The elements of the arc voltage and current are random quantities. It is therefore not possible to theoretically calculate the curve of the direct voltage or direct current component for the melting process.

However, one can draw the curve of the mean probable values of the direct voltage or direct current component, on which the real direct current component means then come to lie over a certain time at the arc voltage or the arc current.

In Fig. 4 is the ·: curve of the mean probable Values of the direct current component of the arc voltage are plotted for the meltdown time. These Curves show all types of metal to be melted together. During the Oxydacions- and the The DC components of arc voltage and current each have a reduction period a..the course of which depends on the type of metal to be melted.

When the arc is ignited, the electrodes 1 first touch the insert 2, then they go up. When the electrodes 1 are lifted from the insert 2, the arc is created. This is where short circuits occur and arcing are common. In the case of short circuits and arcing breaks, current and Voltage in the electrode insert circle is sinusoidal. their DC components are zero. Throughout becomes üe direct current component of the arc spinning during the time from 0 to ii (Fig. 4) greater than one end of the arc hits the surface of the solid and cold feedstock mosquito. so that the electron emission from around metal is disabled.

The arc discharge generally comes only at

eo a minimum voltage at the electrodes which is sufficient to maintain the gas filling the interelectrode space in the ionized state. The higher the degree of ionization of the gas, the lower the voltage that is needed to maintain the arc. With continued by melting c ^lr \ s 2 1 insert holes are formed below the electrodes in use to the diameter 2. i0 bi "; 60% the Dnr <hmp «pr .-! Pr

Electrode (I ig. 2) exceeds. The molten metal 4 flows down and collects in the furnace hearth. After the layer of material 2 has melted through, the end of the electrode I already occupies the bottom layer, and the arc now burns on the surface of the molten metal 3, surrounded on all sides by the salting material 2. The wiping electrode area (from the face of the electrode to the surface of the melt) now cools less when the supply voltage crosses zero. The recombination and diffusion processes slow down: consequently the arc has better racing conditions The voltage of the arc decrease suddenly (time span from Λ to /> in \ ί Fig . 4).

As the lensate melts down / the metal level rises, the electrodes move upwards, and if the arc is exposed, the direct current components of the arc voltage and current become larger (time span from /. To u in (Fig. 4) The meltdown is complete at time U (FIG. 3).

(. F- "ig 4) which adjusting direct current component i '/>, the l.ichtbogcnspannung is by weight and chemical composition of ^L: insatzin; iterials in 2 => furnace and the metal temperature at the Locate the Einschmelzperiode (the higher the Temperature, the stronger the electron flow from the metal surface according to formula (1), the lower the direct current components are dependent on the arc voltage and current These factors only influence the speed with which the mean values of the direct current components of the arc voltage grow, i.e. determine whether the time interval from (1) is h (FIG. 4) is larger or smaller.

It sometimes happens during the meltdown. that the charge melted at the bottom a Forms a stable bridge from unmelted solid pieces of material for some time. Then it falls Bridge on (time f j in FIG. 4). and as at the beginning of the melt, the electrode has a solid, proportionate one cold feed in front of you. Therefore, the DC component of the arc voltage increases very much at this moment, but then goes back again, as the dashed line in FIG. 4 shows.

The higher the base rate of the slag (ratio of its percentage contents of CaO and SiOj), the lower the work function of the electrons is known to be from the slag surface. In the case of basic slag formation (adding lime to the surface of the liquid metal), the direct current constants of the arc voltage -current are significantly smaller (2 to 3 times as small as U " _t ).

Changes in the slag composition and the addition of alloys influence the chemical-physical properties of the melt and thus the size of the work function of the electrons from its surface. The result is that the mean values of the direct current components of the arc voltage and current also change accordingly.

By capturing the DC components of The arc voltage and current can be used to indirectly monitor the melting of metal in arc furnaces.

The target values for the direct current components of the arc voltage and current are obtained from the results of a statistical evaluation of the data from several batches with one and the same type of metal.

For the measurement of the voltage and current of the arc one needs the standard voltage and ammeters. The electrical current components of arc voltage and current are also measured with series devices. In Fig. 5 shows the circuit of the simplest device for detecting the direct current components of the electric arc voltage and current. This device is a double smoothing filter. The direct current component of the arc voltage or the arc current is picked up at points α and / 1.

This filter has a 10-to-1 arc furnace for example the following data:

Γ, 160 V.

Γ _: - 0.01 V at C, - (\ - 60, 1

Τ ~ ^ 0.6.

The connection of the device for detecting the DC components of arc voltage and The electric motor 4 is connected to the device 5 for detection the direct current components of the electric arc voltage are electrically connected. The latter the registration devices (a voltage recorder or a potentiometer) are connected downstream.

The in F i g. The circuit shown in FIG. 6 works as follows: The voltage to ground tapped at the electrode holder 4 is applied to the input of the device 5 (terminals i_ /, in FIG . 5). The direct current component of the arc voltage is taken from points ab (Fig. 5) and fed to the recording device 6 (a voltage recorder or a potentiometer).

The analysis of the electronic components of the Arc voltage and current allow:

1. determine exactly when the electrodes through crafted have when so the furnace transformer to a different voltage level, ie, the power to the furnace to a higher or lower voltage (time f g in F i 4?.) Is to be switched:

2. to record the exact point in time at which the furnace is to be switched off because of the reloading (if the input material has a low density)

3. to register the exact moment at which the insert is practically completely melted down (except for the remains on the slopes in the furnace) and the furnace transformer is to be switched to a lower voltage level (time U in FIG. 4);

4. the point in time for the timely treatment of the difficult-to-melt masses of the insert by blowing with oxygen (the curve U _n (O in FIG. 4 would then retain its minimum value for a longer period, ie the time interval from ti to U would be greater) determine;

5. To avoid overheating of metal (U " _t falls with increasing metal temperature ):

6. Indirectly monitoring the composition of the slag, because if the slag is correctly composed, LJ _{Sj is} close to zero or changes its sign, for example in basic, 10-tonne furnaces.

7 8

Taking into account the mentioned factors melting of metal in electric arc furnace applied

makes it possible to melt metal in an electric arc, showed that in this method the energicver-

ovens to speed up largely. The need for melting down is 9 to 10% less.

The experiments with a 10-t electric arc furnace, in which the furnace lining lasts on average 4 to 5% longer and

which the new monitoring method does 3% more for the ί of the furnace.

For this purpose 2 sheets of drawings

Claims (2)

Patent claims: 1. Monitoring method for the melting of metal in an electric arc furnace with electrode control, which consists in an analysis of the electrical values of the arc and a comparison of the actual values with nominal values provided by a statistical evaluation of the data of a number of batches, and melting control based on this in such a way that the melting process is influenced in the sense of compensating for the deviations that have occurred in the arc values from the setpoint values, characterized in that arc voltage and arc current are measured several times within certain periods and the sums are formed from the recorded direct current or direct voltage components for the individual measuring periods, with the duration each individual measuring period is determined by the time _t while the relevant electrical quantity can reach a value that is practically constant for the measuring period. 2. The method according to claim I _1, characterized in that the measurements are carried out continuously within the individual periods and the duration of a measuring period is selected from the range of duration of an oscillation period of the electrical measured variables up to the duration of the shortest operation.