SU710529A3 - Current conducting device of arc oven - Google Patents

Description

one

The invention relates to current-carrying devices for an arc furnace fed by direct current, comprising at least one bar of steel or cast iron, which is housed in a lining material and surrounded by a shell.

For furnaces of this type, the current-carrying device must be durable and must withstand high temperatures.

It is known that current-carrying devices are located below or in the furnace of a furnace in direct-current furnaces, and the electrode takes the form of an elongated tide or rod drawn from a melt to be connected to the positively charged side of the current source.

The proposed current-carrying device is characterized in that in order to increase the power of the furnace, the outer side of the shell is preferably cooled with water using one or more cooling elements, such as water cylinders or coils; the bar thus reaches the melt channel, which communicates with the furnace space.

In a preferred embodiment of the device, the electrode consists of two steel or cast iron bars; the ends of the latter reach the end point of the nozzle in the furnace body or channel, which directly or through another channel communicates with the furnace space and which is filled with melt when the melt is in the furnace; after contact, the melt-bar of the latter melts again in the direction of external contact, and the heat escapes through the lining material at the same time that the reverse melting is prevented by a water-cooled shell and a bar occurs with an equilibrium of the molten and solid parts. The described current-carrying device can be used in high-temperature furnaces, for example, in steel-smelting furnaces, as well as in high-capacity furnaces. FIG. 1 shows the connection of the current supply device with the furnace body; in fig. 2 — device, cross section; in fig. 3 shows an embodiment of the device for direct current furnaces of large dimensions; in fig. 4 is another embodiment.

FIG. I shows the outer shell 1 of the furnace body, the lining layer 2 of the furnace, for example pressed material and (or) brick, the inner side 3 of the lining layer, i.e. the side facing the furnace space. Magnesite can be used as compressed material. A channel 4 with an annular cross section, extending from a point below the melt pool level to the melt channel, which communicates with the electrodes in the current-carrying device, passes through the lining layer.

The current carrying device (see Fig. 2) consists of one, two or several curved steel or cast iron bars 5, which are directly connected to the melt and are surrounded by a lining layer 6. Channel 4 is connected to a forked channel 7, which is bordered by bars 5. One . The end of steel or cast iron bars 5 is in contact with the melt below the level of the bath surface, so that this end is melted again, and a melt channel is formed in the current-carrying device. Heat is lost from the melt channel and from the unmelted part of the bar as a result of heat transfer from the lining material to the cooled outer shell. Thus, the reverse melting of the bar is prevented and such a thermal balance is achieved when the amount of heat obtained by conduction and convection from the melt plus the amount of heat accumulated in the bar and channel as a result of current movement decreases in the external shell of the current-carrying device. Bar 5 is not consumed, since its molten part is located below the level of the bath and does not spill when the furnace is unloaded. Steel or cast iron electrodes are surrounded by a lining layer 6, preferably a cast, e.g. magnesite composition, from which they are cast; The lining layer may also consist of the same compound as the rest of the kiln. The heat transfer through this inner layer to the outer shell 8 of the current-carrying device, cooled by water, causes the steel or cast iron electrodes to partially melt in the direction of their contacting device. M, while the heat escapes through the lining layer; this, however, is counteracted by the cooling effect of the cooled outer shell 8, and a certain part of the bar remains solid, thus creating some balance between the molten and solid parts of the bar. The bars 5 may, for example, reach the branch point, and during the heating period the molten part of the channel will expand in the direction of the contact device, but only to the balance point.

The current lead shown in FIG. 3, curved so that its upper end is open in the level area of the bath. This provides some guarantee against melt exit in the case where the lining

the layer does not completely isolate the bar. The proposed device can also be extended straight along the side or straight down.

Most suitable for large currents (see Figs. 1 and 2). The power supply device has two curved bars 5, a lining layer and external cooling surfaces. A special connecting channel 4 and an expanding space 9 are necessary if the Current-carrying device is located outside the furnace body. If the power supply device is connected through the nozzle opening directly to the bottom or wall of the furnace, then the need for a connecting channel and expanding

jj space can be completely or partially eliminated.

Cooling cylinders or cooling surfaces 10 are cast in a lining layer. Steel bars are equipped with contact devices 11 located at their

 end surfaces, and the positive pole of the direct current source is connected to these contact devices. Contact devices 11 can also be cooled. Slag enters expanding space 9 and passes through channel 4. This slag must be periodically poured or raked. In this case, two steel or cast iron -electrodes are bent LJ-shaped.

It is possible to design a power supply device with only one electrode. It is permissible, without using the connecting channel 4, to connect the steel electrode directly to the nozzle, the opening of which is located at the bottom of the furnace, as in induction channel-type furnaces. In addition, a water-cooled housing can be used to connect the current carrying device and the furnace body, as well as in channel-type induction furnaces. In this way, the furnace lining is prevented from sintering with the coating of the current-carrying device, and the latter can be replaced without destroying the internal coating of the channel or nozzle, as in the inductor of a tunnel-type furnace. In this case, the 0 method used for replaceable channel-type inductors can be used. A non-caking composition can be used in the connecting part between the current-carrying device and the furnace body.

Water-cooled elements 12 (see Fig. 3) neutralize the heat losses from the current-carrying device and prevent its melting; the action of these cooling elements helps to get

a certain balance between the solid electrode and the molten part of the electrode. The cooling elements are also located on the shell on the inner side of the current-carrying device. FIG. Figure 3 also shows the funnel-shaped furnace body 13, temperature measurement points 14 for its regulation in the molten part of the current-carrying device, equilibrium point 15.

The current lead can sometimes contribute to the occurrence of so-called bottom melt boiling. Bottom boiling is undesirable, mainly when the current-carrying device is located below the slag level in the furnace, since in this case the boiling pushes the slag back and makes it difficult for it to discharge from the furnace in the region of this level. Boiling over time may cause abrasion of the liner coating. The reason for the origin of boiling is that part of the steel bar that is in contact with the melt is too cold. One of the ways to eliminate this phenomenon is to create another lining layer in the appropriate place of the current-carrying device, which leads to a decrease in heat loss.

In another embodiment where water cooling is used, the part of the bar facing the melt and has a smaller cross-sectional area than the opposite part. When reducing the cross-sectional area of a steel or cast iron bar near the melt, this part is subjected to a greater load when current passes and therefore heats up more strongly due to the loss of resistance in this area. Thus, it is possible to avoid bottom boiling in this part of the current supply device.

In a preferred embodiment of the apparatus, the bar is placed in the channel in the lining material, the core portion of the bar melts from contact with the contents of the furnace and has a smaller cross-sectional area than the peripheral portion. The ratio of the smallest area of the channel in which the bar is placed to the largest area of the steel bar should be 1: 2 (respectively). According to this variant (see FIG. 4), a magnesite compound can be used as a lining or compressed material. In the lining layer 6 there is a channel, in the deeper part 16 of which the melted part of the current-carrying device is located. Digit 17 shows the transition zone between the molten and solid phases; 18 is the solid part of the current-carrying device. The inner end of the electrode is in contact with the melt below the surface of the bath 19; this end is then melted and a melt channel is formed in the current-carrying device. From this channel, heat escapes as a result of conduction through the lining material to the outer shell, which can be cooled with water or in some other way. This prevents the bars from re-melting and achieves a position of such a heat balance when the amount of heat produced as a result of conduction and convection from the melt plus the amount of heat accumulated in the bar and channel as a result of current flow decreases at the outer shell of the current-carrying device. The bar is not consumed because

, j The molten part is located below the level of the bath and does not overflow when the furnace is unloaded. For the lining layer, any material, for example cast, can be selected or it can consist of the same material that is used in the rest

20 parts of the furnace. The heat conduction through this layer to the outer shell of the current-carrying device causes the steel or cast-iron electrodes to partially melt in the direction of their contact devices,

5 while heat escapes through the lining layer. However, this process is neutralized by the cooling effect of the cooled outer shell, and a certain part of the bar remains solid, which leads to some equilibrium between the molten and solid parts of the bar.

It is permissible for the bar area in the electrode to increase from its core part near the melt to its peripheral part located near the contact devices.

5 11- It is also permissible, for example, to part. The bar at the core part had a constant area, which continuously or stepwise increased in the direction of the contact device P. The melted part of the bar may also have a smaller area than the outer part, and the ratio between the core part of the unmelted bar or the cross-sectional area of the bar channel and the cross-sectional area of the contact device

5 II can be 1: 2-1: 3.

A bar with a constant area of 12,500 mm2, which conducts a current of 12.5 kA, is tested; load current 1 A / mm. For comparison, indicate that a channel-type induction furnace with a capacity of 500 kV and has a channel area of 14,600 mm, loaded with a current of 52 kA, i.e. 3.5 A / mm. In this way, the steel bar in the bath electrode can be subjected to a higher current load, and its acceptable value is about 2 A / m m, which provides the required heating and prevents bottom boiling. This is achieved by the fact that the part of the bar facing the melt, regardless of whether this part is melted or not, is smaller than the cross-sectional area of the contact device II. It is desirable that the transition from a small to a larger area be gradual and take place 500 mm from the end of the conductive device and from the end of the channel for the bar near the melt. At the moment of passage of the current, the connecting end 2 remains cold in this place as a result of the low resistance in this part of the bar, and the losses for the current supply device will be generally low. The heat loss will be higher at that end of the current-carrying device, which is kept warm, while the outer connection end 20 remains cold and has low losses.

Claims (8)

1. A current supply device for a direct current arc furnace, comprising metallic electrodes located in a furnace lining enclosed in a housing and connected on one side to a current source and on the other side to a furnace melting space in its lower part, In order to increase the power of the furnace, refrigerators are installed in the electrode placement area. fO // 2. A device according to claim I, characterized in that the refrigerators are located on the outer side of the furnace body. 3. The device according to claim 1, characterized in that the refrigerators are housed in a lining layer. 4. The device according to claim 1, characterized in that the electrodes are made curved and are connected by a hollow channel with the correct space of the furnace. 5. Device on PP. 1-4, characterized in that the electrode and the hollow channel are made with a variable section. 6. The device according to paragraphs. 1-5, characterized in that the cross-sectional area of the channel at the interface with the electrode refers to the cross-sectional area of the outer part of the electrode as 1 / 2-1 / 3. 7. The device according to paragraphs. 1.4 and 6, characterized in that the part of the channel adjacent to the electrode is made with a constant cross section. 8. Device on PP. 1, 4 and 7, characterized in that the electrodes are made in the form of U-shaped curved rods. Priority points: 06/19/74 - by paragraphs 1-4 12/19/74 - on PP. 5-8 Sources of information taken into account during the examination 1. Patent of Sweden No. 382828, cl. C 21 C 5/52, 1974. // ten ten / 7 ten 18 G6