US2957936A - Electric smelting furnace with bottom tapping hole - Google Patents

Description

N. E. BUGGE ELECTRIC SMELTING FURNACE WITH BOTTOM TAPPINGHOLE Filed July 5l, 1958 BYMJMMQ LAAG ATTORNEYS.

Oct. 25, 1960 N.. E. BUGGE 2,957,936

ELECTRIC SMELTING FURNACE. WITH BOTTOM TAPPING HOLE Filed July 31, 1958 3 Sheets-Sheet 2 N km O O N- gi O 1L N f Q 4 x w INVENTOR. NILS EMIL BUGGE BY Xu kamhw A TTORNE YS.

Oct. 25, 1960 N. E. BUGGE 2,957,936

ELECTRIC SMELTING FURNACE WITH BOTTOM TAPPING HOLE .//F'iled July 5l, 1958 3 Sheets-Sheet 3 Unite ELECTRIC SMELTING FURNACE WITH BO'I'IOM TAPPING HOLE Nils Emil Bugge, Oslo, Norway, assignor to Elektrokemisk A/ S, Oslo, Norway, a corporation of Norway This invention relates to electric smelting furnaces particularly of the type in which an electrode penetrates deep down into a charge to be smelted, and has to do both with the construction of the furnaces themselves and with their operation.

Furnaces of this type are invariably tapped through one or more tap holes arranged in a generally horizontal direction running through the furnace wall on the same level as the inside furnace bottom.

The molten material produced in the furnace is tapped into casting machinery or ladles, cars or the like placed outside the furnace. In some cases furnaces of this type are made to rotate (see for example Ellefsen Patent No. 2,300,355) and in such case, where the tap holes move slowly around, cars moving on circular rails around the furnace often are used so that the charge from the furnace may be caused to flow into the tapping cars independent of the position of the tap holes.

The number of tap holes in any given furnace depends on the furnace type as well as the type and quality of the material produced. For example stationary furnaces usually have from 1 to 3 tap holes whereas rotating furnaces have as many as nine tap holes.

In any case it is essential that the tap holes are accessible with the necessary tapping equipment which includes not only the cars or vessels for receiving the product but also the devices for opening and closing the holes. Further it is important to provide space enough for the crew operating this equipment in those areas where the tapping holes may be located. This demands considerable space which may be valuable in a plant.

During the tapping of the furnaces from the usual tap holes the material flows from the high temperature zones of the inner part of the furnace out to the tapping hole in the furnace side wall where the temperature ordinarily is much lower. The resulting cooling of the product may cause difficulty during the tapping as the product may solidify, thereby plugging up the tap holes. In some cases, as for example, in the production of corundum, this cooling problem is so acute that tapping is virtually impossible and such materials have to be produced by block smelting.

The cooling down of the charge and the change in its fluidity may be said to be a function of the distance from the high temperature zone (the smelting zone) to the tapping hole and every change of this distance is of great importance especially for calcium carbide and other high temperature products.

It is further recognized that the effective area of the high temperature zone may vary with the furnace load and this again will create a variable condition in tapping.

In the case of rotating furnaces another factor which will vary the distance from the smelting zone to the tapping hole is the fact that the electrodes are usually arranged in the form of a triangle and remain stationary whereas the tapping holes formed in the rotating part of the furnace will move relative to the electrodes and thus the distance from a given tap hole to an electrode will be rates Patent O continuously varying. It has been found that this variation in distance in rotating furnaces is sufficient to change the rate of ow of material such as carbide and also as a new tapping hole may come into position some time is consumed before it is hot enough for the charge to flow properly. These variations cause intermittent and pulsating production and this has to be taken into consideration in designing the installation.

Another drawback connected with the ordinary tapping hole in rotating furnaces is that the frequent opening and closing of the tap holes (even with continuous tapping) causes wear of the refractory lining around the holes and the ow of the material into the tapping holes may cause corrodng or wear on the inside furnace lining.

In some instances the factors of wear and damage on the tap hole may be great enough so that it has been found necessary to place the tap holes relatively far from the high temperature zone and this again creates diculties as have already been pointed out.

The present invention aims to overcome these difficulties by so constructing the furnace and by providing special mechanism so that the furnace can be tapped from the bottom of the pot in an area near the center of the furnace. In such case the heat developed underneath the furnace will be very great so that it is virtually impossible for workmen to stay there to control the tapping and it is necessary to provide special equipment for opening the furnace tap and closing it again and for handling the charge as it comes from the furnace.

This invention can readily be understood from the illustrative example shown in the accompanying drawings in which:

Fig. 1 is a cross section through a furnace embodying my invention.

Fig, 2 is a plan View on line 2-2 of Fig. 1.

Fig. 3 is a view similar to Fig. 2 with the parts in different position; and

Fig. 4 shows certain permissible modications.

In these drawings the actual furnace pot is indicated by Ithe numeral 10 and this pot is carried on circular eye-beams 12 and radial supporting beams 14. The radial eye-beams 14 do not run all the way to the center but connect with circular eye-beams 16 and at their ends carry a circular shield 18. This shield should be either-of heat resistant material or be uid cooled as Idescribed later in connection with Fig. 4. This shield not only protects the metal sup-port beams from the heat of `the molten material during tapping, but it also Vserves to maintain a cushion of hot reducing gases around the tap-hole. This will prevent the charge from being chilled as it first leaves the furnace and reduces oxidation of the material around the tap-hole.

In this example the pot is constructed so that it will rotate and is mounted on wheels 20 which run on a crcular track 22. The electrodes for smelting the charge are indicated at 24. The furnace is caused to rotate by a motor 26 which drives a shaft 28 and gearing 30.

At approximately the center of rotation the pot 10 is provided with a tap-hole 32 and preferably at the bottom of the tap-hole there is formed a removable block 34 of ceramic material which is held in place by bars 36 which pass through the circular eye-beam 16 and the shield 18. This block is provided so that it can be readily replaced in the event of wear.

When the furnace is discharging the molten material ows into a movable chute and may be discharged into any kind of receptacle such as, for example, the endless transport conveyor 40. The chute 3S can be moved out from under the tap-hole by means of the cylinder 42 which is fluid operated preferably by air supplied by the pipes 44. It may be noted that the air supplied by the pipes 44 is controlled by a valve 45 located at the side of the pot so that the movement of the chute 38 can be controlled from that point. Preferably a tapping ladle 46 is provided below the chute to catch any of the molten product or slag that may not be caught by the chute 3S.

To control the tapping `and blocking of the tap hole a mechanism is supplied carried on the fixed shaft 48 adjacent the periphery of the under part of the pot. A bar 50 rotates on this shaft which extends to an operating handle 52. The inner end of this bar :is supported by an inclined support member 54. Carried by the inner end of the bar 50 is a cylinder 56 controlling the movement of a piston 58. By moving the handle 52 the piston 58 can be swung directly beneath the tap-hole 32 as shown in Fig. 3 or it may be swung out towards the edge of the furnace where it is accessible to the workmen as indicated in Fig. 2. The upper end lof the piston 58 is made pointed and is provided with a removable plate 60. When it is desired to block the furnace the handle 52 is swung around and the plate 60 is put on the piston 58 and the blocking compound indicated at 62 is put on the plate 60. The piston is then forced upward by fluid pressure admitted through the lower of the pipes 64 which may, for example, be supplied with compressed air through the pipe 66. A flexible connection is supplied as indicated at 68 to permit the pipes to be rotated with the cylinder 56. This will force the blocking cornpound 62 into the bottom of the tap-hole 32 to close the tap-hole.

When it is desired to open the tap-hole the handle 52 is swung around so that access can be had to the pis-ton 58. The plate 60 is then removed and when the piston 58 is forced upward it will pierce the tapping compound and open the tap-hole 32. To assist the action of the piston 58 it preferably is connected into the electrical circuit so that it will serve as a ltapping electrode. For this purpose I supply a flexible connection 7G connected to a bus bar 72 controlled by ya switch not shown. Current is allowed lto flow through the connection 70 and piston 58 when it is desired to use the piston 58 for opening the tap-hole. A graphite block indicated at 74 is preferably supplied to protect the cylinder 56 and pipe 64 from any hot metal that may drop out of the tap-hole during the blocking or unblocking operations. If desired any convenient means may be employed to cause ya current of cool -air to flow under the pot to prevent undue heat from developing.

Obviously during the time that the tap-hole is being either blocked or opened the movable chute 38 is drawn of to oneY side so that the piston 58 can function `as has been described.

In operating a furnace such as has been described ordinarily one of two methods of operation will be employed. In one case the tap-hole is made small enough so that in ordinary operation continuous tapping takes place and the tapping `and blocking mechanism is only used under special occasions. In the other case when the furnace is tapped, it will be allowed to drain until virtually all of the desired product and slag has been discharged and then it will be reblocked and a new charge smelted in the furnace.

In Fig. 4 I show some permissible alternatives. In this case the bottom of the furnace 11 is slanted toward the center and a central well 13 is formed in the bottom of the pot. Obviously with this arrangement, as metal is smelted from the ore and becomes fluid, it will flow toward the center of the furnace pot and be collected in the well 13, thus having a continuous supply of liquid material available for tapping. This is of particular importance when continuous tapping is used. In place of the removable block 34 I supply a mouthpiece 35 which may be fluid cooled as, for example, with a silicone oil or other cooling media. Water may be employed but ordinarily water is considered dangerous in connection with the heated parts of a furnace. Here also :the shield 19 is cooled with the same type of fluid used in the mouthpiece 35. In this case instead of a blocking and unblocking mechanism a fluid cooled block 63 is supplied oarried on a shaft 59 which will be operated by a cylinder similar to the cylinder 56 and which may be rotated `out from under the tapping hole in the same way las the cylinder 56 `is rotated.

I-t is understood that the example given is intended only by way of illustration and that the same may be modified in any particular without departing from the spirit of my invention.

What I claim is:

1. An electric smelting furnace for electrothermic reduction of the charge which includes ya pot having an outer metal shell that supports a lining of refractory material therein, electrodes positioned within said pot, means for supporting the pot so that access may be had to the underside thereof, a tap hole running down through the bottom of the pot the mouth of which terminates adjacent the said outer metal shell, an annular flange the walls of which are held in substantially vertical position against the bottom of the said pot to surround the mouth of the tap hole, said flange being spaced ia substantial distance away from the mouth of the tap hole to project down below the level thereof whereby when the furnace is tapped a cushion of hot reducing gases will collect within the rannular flange to surround the mouth of the tap hole.

2. A structure as specified in claim 1 in which the furnace pot is adapted to rotate on its support means, a chute member underneath the pot adapted to receive molten material discharged -through said tap hole and means for conducting such mol-ten material out from under the po-t said means for conducting the molten m-aterial out from under the pot being adapted to withdraw such molten material substantially continuously so that lthe furnace may be operated with continuous tapping while the furnace is rotated.

3. A structure as specified in claim l, which further includes mechanism whereby said chu-te may be moved horizontally out from under the tap-hole and means whereby such mechanism may be operated from a position yat the side of the pot.

4. A structure as specified in claim 1, which further includes means for closing the tap hole by inserting a plug into the tap hole vand means operable from the side of the pot whereby the tap-hole may be opened.

5. A structure as specified in claim 1, in which the bottom of the pot is formed with a centrally located well out of which the tap-hole runs and in which the bottom part of the tap-hole is formed in the shape of an inverted funnel and which further includes a member adapted to fit into said inverted funnel to close the tap hole.

6. A structure as specified in claim 4 in which the mechanism for opening the tap-hole may also be used for replugging the tap-hole.

References Cited in the ille of this patent UNITED STATES PATENTS Re. 22,479 Dobscha May 16, 1944 284,005 I-Iainsworth Aug. 28, 1883 343,954 Follett lune 15, 1886 977,271 Callaghan Nov. 29, 1910 1,286,632 Hodge Dec. 3, 1918 1,360,520 Gray Nov. 30, 1920 2,045,073 Eldridge June 23, 1936 2,085,450 Rohn .inne 29, 1937 l i l L

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