AU610697B2

AU610697B2 - Gas-permeable block for metallurgical operations

Info

Publication number: AU610697B2
Application number: AU30619/89A
Authority: AU
Inventors: Rudolf Handler
Original assignee: Veitscher Magnesitwerke AG
Current assignee: Veitscher Magnesitwerke AG
Priority date: 1988-02-19
Filing date: 1989-02-17
Publication date: 1991-05-23
Anticipated expiration: 2009-02-17
Also published as: HU891288D0; ZA891290B; ES2021894B3; EP0329645A1; WO1989007659A1; IN170797B; KR900700638A; EP0329645B1; EP0356483A1; ATE62937T1; AU3061989A; DE58900091D1

Abstract

A gas-permeable block for metallurgical vessels consists of a shaped refractory body (1) penetrated by flow channels (7). To facilitate purging by melting or blowing of metallic infiltrations following an interruption in blasting, the channels (7) are steeply inclined to the longitudinal axis of the block, at least in the region adjacent to the gas outlet orifices. The angle ( alpha ) between the channels and the face (8) of the block provided with said orifices can vary between 15 DEG and 60 DEG , preferably between 20 DEG and 50 DEG . The flow channels (7) are preferably of spiral, undulating or zigzag construction.

Description

r OPI DATE 06/09/89 IAOJP DATE 05/10/89

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APPLN. ID 30619 89 PCT NUMBER PCT/AT89/000157 ER DIE S (PCT) (51) Internationale Patentklassifikation 4 0(1J.Iternationale Veroffentlichungsnummer: WO 89/ 07659 C21C 7/072, F27D 3/16 Al te to B22 1/0 ~Q~r8 eat uit m. /August 1989 (24.08.89) (21) Internationales Aktenzeichen: PCT/AT89/0OOI5 (81) Bestimmungsstasiten: AT (europaisches Patent), AU, BE (europtiisches Patent), BR, CH (europiiisches Pa- (22) Internationales Anmeldedatumn: tent), DE (europaisches Patent), FR (europaisches Pa- 17. Februar 1989 (17.02.89) tent), GB (europaisches Patent), HU, IT (europdiisches Patent), JP, KR, LU (europtiisches Patent), NL (europtiisches Patent), SE (europdisches Patent), SU, (31) Priorititsaktenzeichen: A 404/88 us.

(32) Priori tatsdatum: 19. Februar 1988 (19.02.88) Vermfentlicht (33) Priorititsland: AT Mit interna tionalem Recherchenbericht.

Vor Ablauf der far .nderungen der Ansprz'iche zugelassenen Frist. Verdffentlichung wird wiederholt falls An- (71) Anmelder (fur alle Bestimmungsstaaten ausser US): derungen eintreffen.

VEITSCHER MAGNESITWERKE-ACTIEN-GE- SELLSCHAFT [AT/AT]; Schubertring 10-12, A-l010 Wien (AT).

(72) Erfinder; und Erfinder/Anmelder (nur far US) HANDLER, Rudolf [AT/All; Hafning 22, A-2620 Neunkirchen (AT).

(74) Anwalt: KLIMENT, Peter; Singerstralle 8/3/8, A-l0l0 Wien (AT), (54) Title: GAS-PERMEABLE BLOCK FOR METALLURGICAL OPERATIONS (54) Bezeichnung: GASSPOLSTEIN (57) Abstr'act A gas-permeable block for metallurgical vessels consists of a shaped refractory body penetrated by flow channels To facilitate purging by melting or blowing of metallic. infiltrations following an interruption in blasting, the channels are steeply inclined to the longitudinal axis of block, at least in the region adjacent to the gas outlet orifices. The angle (a) between the channels and the face of the block provided with said orifices can vary between 15* and 60*, preferably between 200 and 500, The flow channels are preferably of spiral, undulating or zigzag construction, (57) Zusanmnenfassung Ein Gasspillstein filr metallurgische Geffle, enthlllt einen feuerfesten Formk6rper mit. durchgehenden Str6mungskanien Um das Aufschmelzem und Ausblasen, von Metallinf iltrationen nach elner Blasunterbrechung zu erleichtern, sind die Strom ungska niile zumnindest in dem ihren. A!.istrittsl~ffnungcn benachbarten Bereich, stark geneigt gegenober der Rlchtung der ULngsachse des Spillsteines angeordnet, wobei sic einen, Neigungswinkel zwischen 1S* und 600, vorzugsweise zwischen 20' und 500, gegenilber der die Austritts~ffinungen der Str~mungskangle enthaltenden Stirnfliiche des. Spalsteines aufweisen k~5nnen, Vorzugsweise sind die Strbmungskanllle schraubenlinienf6rmig, wellenfdrmig oder zick:zackformig atisgebildet.

1 GAS PERMEABLE BLOCK The invention relates to a permeable element to be used in metallurgical vessels, the element comprising a refractory shaped body with flow channels therethrough.

It is common practice to introduce various kinds of gases through the refractory lining of vessels into the molten metal. This is done in converters for steel refining, in casting ladles, in tundishes for continuous steel casting and in other types of metallurgical furnaces and vessels. Gas bubbling has either a stirring effect in the metal melt or can also give rise to various metallurgical reactions. For this purpose, refractory elements which are permeable to gas are inserted into the refractory lining, most frequently in the bottoms, of furnaces and vessels. They are commonly described as permeable elements.

Permeable elements may either comprise a refractory brick body of high porosity, with the gas flowing through the open pores between tile refractory grains, or they may comprise a refractory brick body of low or no porosity, the brick being provided with slots or channels which allow for the passage of gases, the latter type being referred to as permeable elements with aligned S 20 porosity.

•e According to Austrian patent AT-B-248 936, refractory shaped bodies r provided with narrow channels for the introduction of gas into a metal melt *0@S may be prepared by arranging and securing cores or pins for forming the S channels in a casting mould for the shaped body. A fluid refractory mass is cast into the mould and consolidated. The shaped body so prepared is removed from the mould and dried. The cores or pins used to form the channels can be metal tubes which remain in the finished shaped body; they can also be wire rods which are withdrawn from the shaped body; this is facilitated if the wire rods are covered with a suitable shell. The cores or pins can also consist of 30 a fusible or evaporating material, for example a synthetic material, which is melted out or evaporated during the drying operation. In this connection, the preparation of shaped bodies with curved channels has also been considered S without making any statements as to the purpose or the kind of such curved channels.

In actual operation, gas bubbling through permeable elements is required at specific times only, e.g. during the refining process. In the intermediate periods, e.g. during sampling, tapping or charging, the gas supply could be stopped. However, if this is done, molten metal can enter the gas channels or L. brick pores and harden there, thus blocking the gas passage. When bubbling is

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*OSSo~ resumed, the metal inside the channels is only partly re-melted and removed. For preventing molten metal from entering into the channels, gas bubbling through the permeable element, e.g. with inert gas, is continued also during the intermediate periods. This method requires a continuous gas feed to the furnace or vessel and can therefore be employed with stationary equipment only.

Permanent gas supply cannot be maintained in movable vessels such as casting ladles which are moved by a crane within the casting bay. As a result, the bubbling effect will be gradually decreased by metal which has hardened and settled inside the channels and which cannot be re-melted. For this reason, the actual bubbling efficiency of permeable elements with aligned porosity is 15 between 40 and 85 percent, and that of porous plugs between approximately 60 and 95 percent of the theoretical value. This means that the permeable elements cannot be operated over their full theoretical life time but have to be renewed earlier in proportion to the above percentages.

It is the object of this invention to design a permeable element which allows a high degree of re-melting and removing of metal infiltrations after every interruption in gas bubbling.

The present invention, therefore, consists in a gas permeable element for metallurgical vessels for introducing a bubbling gas having a stirring effect in the metal melt, comprising a refractory shaped body with flow channels therethrough, characterized in that the flow channels are considerably inclined against the longitudinal axis of the gas permeable element at least in the area adjacent to their exit openings, the angle of inclination between the flow channels and the face of the gas permeable element, which contains the exit openings of the flow channels being between 150 and 60 The angle of inclination between the flow channels and the

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2a face of the element containing the exit openings of the flow channels is preferably between 200 and 500.

In conventional permeable elements with gas channels extending through the refractory shaped body, such channels are usually vertical, i.e. they are arranged parallel to the longitudinal axis of the permeable element. In permeable elements having the shape of truncated cones or truncated pyramids, some of the flow channels which are closer to the outer surface may be slightly inclined towards the longitudinal axis of the permeable element in correspondence to its shape (e.g.

Austrian patent AT-B-384 623).

Assuming that metal droplets enter an equally long way into conventional flow channels and into inclined flow 15 channels as described by the present invention, the depth •"of entrance as measured along the longitudinal axis of the permeable element is smaller in channels as described by this invention than in conventional channels. Due to the temperature gradient along the longitudinal axis of the permeable element, re-melting of metal infiltrations is possible in the vicinity of the hot face of the element only; the chances of re-melting and removing metal infiltrations after interruptions in gas '5 k S S L 1 i bubbling are th..efore higher with gas channels shaped according to the invention than wlth conventional gas channels.

As permeable elEments wear down during operation, refractory areas which had originally been inside the permeable elements will after some time of service become the hot end surface of the permeable element. For facilitating the re-melting of steel infiltrations according to the invention also in such cases, the flow channels should preferably be inclined not only in the vicinity of the hot face but also in lower lying areas of the element. In order to allow for incorporating inclined flow channels even in permeable elements of limited width, one embodiment of this invention suggests giving the flow channels a helical, undulated or zigzag shape.

As a rule, permeable elements are replaced when they have worn by about two thirds of their original height. Therefore, according to the present invention, the flow channels can also be given the inclined, preferably helical, undulated or zigzag shape along two thirds of the element height only, as seen from the face of the element which contains the exit openings of the flow channels.

With conventional permeable elements where the gas leaves in substantially vertical direction, i.e. in the direction of the longitudinal axis of the 20 element, a gas bubble accumulates in the metal melt directly above the element face which contains the exit openings. Due to the pulsating movemrnt of the o gas bubble, the molten metal continuously hits back on the hot face of the permeable element. By this phenomenon, known as "back attack", the wear of the permeable element is accelerated.

In permeable elements according to this invention where the flow channels and their openings are inclined, the leaving gas stream is given a twist; this decreases the above mentioned back attack and reduces its wearing effect.

Twist formation can further be enhanced if the flow channels have the same angle of inclination in a dynamically balanced arrangement in each cross section of the permeable element.

Permeable elements of the present invention can be prepared according to an established method described at the beginning, whereby the flow channels are formed by embedding cores into a shaped body made from a refractory casting mass. These cores can for example consist of combustible, fusible or 35 volatile materials such as synthetics, or of wire rods covered for example with synthetic material, or of thin-walled metal tubes from copper or steel.

The dimensions of the cores are chosen such as to result in flow channels with I an inner diameter of 1 mm or less.

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Suitable casting masses are mainly materials based on high alumina or alumina, or so-called "low cement castables", i.e. casting masses which contain approximately 5 percent by weight of cement. The base materials of such casting masses are predominantly sintered alumina, corundum, mullite, mullite clinker containing 50 to 72 percent by weight of A1 2 0 3 bauxite, sintered bauxite or andalusite. Suitable additives to these materials are chromium oxide Cr 2 0 3 zircon (zirconium silicate), zirconium oxide, clay and calcined alumina. The casting masses can either be hydraulically bonded, e.g. with aluminous cement, or chemically bonded, e.g. with a phosphate binder. Magnesia-based casting masses as described in Austrian patent AT-B-248 936 can also be employed.

Figures 1 to 3 show the diagrams of three examples of permeable elements according to the present invention, partially in section. Figure 4 is the longitudinal section of a detail of the permeable element shown in Figure 2.

The permeable element according to Fig. 1 comprises a refractory shaped body 1 made from a refractory casting mass, a metal case 2 and a bottom plate 3 welded to the metal case 2; attached to the centre of the bottom plate is a gas feed pipe 4. The gas pipe 4 opens into a gas distribution chamber filled with a plate 5 of porous refractory material which is permeable to gas.

20 This plate 5 can for example consist of a porous refractory material prepared according to the method described in Austrian patent AT-B-374 164. The permeable element is surrounded by a well block 6. For better illustration, only one quarter of the well block is shown in the drawing.

The refractory shaped body 1 is provided with flow channels 7 which have a helical shape in the example of Fig. 1. The permeable element as shown includes 17 flow channels 7 which are evenly distributed across its circular cross section. For better illustration, only one flow channel 7 is shown in the drawing, and a few further channels are outlined. The flow channels extend from the gas distribution chamber which is filled with the gas permeable refractory plate 5 at the cold end of the permeable element to its hot end face 8 where the flow channels 7 have their exit openings.

The permeable element can beneficially be prepared as follows: Metal case 2, bottom plate 3 and gas feed pipe 4 are assembled by welding. The resulting hollow space is filled with the gas permeable plate 5; the cores for forming the flow channels 7 are inserted and secured in their position.

A refractory casting mass is cast in, consolidated and then dried by heating.

If the cores consist of a material which is consumed by heat (combustible, fusible or evaporating) such as a synthetic material, or of wires covered with such materials, the flow channels 7 will be formed during drying.

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0 *S S S If wires are used, these may be left in the permeable element; the gas can pass through the open space which results when the covering synthetic material disappears.

The permeable element shown in Fig. 2 is identical with that of Fig. 1 except for the fact that the flow channels 7' have an undular or zigzag shape and that the gas distribution chamber is left empty. The permeable element according to Fig. 2 can be prepared in the same way as described for the element shown in Fig. 1; however, the gas distribution chamber is not filled with the gas permeable plate 5, but with a suitably dimensioned body of a consumable material such as styropor which disappears from the gas distribution chamber when the casting mass is dried.

For better illustration, only one flow channel 7' is shown in Fig. 4. It can be seen that the flow channels are inclined at an angle of o. against the element face 8 which contains the exit openings of the flow channels. For comparison, a vertical flow channel is shown in dotted lines in the right half of Fig. 4. Assuming that molten metal enters the channel along a distance x when gas bubbling is interrupted, it can be seen that in the flow channel of the present invention the depth of entrance measured as the vertical distance from the hot face 8 is only x.sincc. This is less than the depth of entrance x 20 in the conventional vertical flow channel. When the hot face 8 is again exposed to heat and gas bubbling is resumed the metal infiltrations are more readily re-melted and removed from the flow channels of this invention than from conventional flow channels.

In its embodiment shown in Fig. 3 the permeable element is provided with a gas distribution chamber which extends up to approximately one third of the element height, for example 80 to 100 mm. The chamber has the shape of a truncated cone and is filled with a gas permeable body 5' of porous refractory material. This is an optical indicator for the residual thickness of the permeable element and for the point of time when it needs replacing, as the 30 refractory body 5' becomes visible at the hot face when the permeable element has worn down so far.

In the embodiment of Fig. 3, the flow channels 7 are arranged helically around supporting bodies 10 which are embedded into the refractory shaped body 1. Beneficially, these supporting bodies have the shape of truncated cones and may consist of the same porous refractory material which is used for the gas distributing body 5' and which is prepared according to the process described in Austrian patent AT-B-374 164. If the supporting bodies 10 are permeable to gas they will provide an additional possibility for gas passage.

r!: II The helical or spiral flow channels 7 extend across the full height of the supporting bodies 10; for better illustration only the upper part is shown in the drawing.

If thin-walled metal tubes are used for forming the flow channels 7, 7', the gas distribution chamber 9 may be sealed off against the refractory shaped body 1 by means of a metal case to which the metal tubes are connected by gas tight welding. This prevents the bubbling gas from entering the refractory shaped body 1.

It is understood that the above described versions of flow channels and alternatives of gas distribution can be matched in any desired combination.

The helical and spiral flow channels may also be interlaced with each other.

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Claims

2. Gas permeable element according to claim 1 characterized in that the angle of inclination is between 200 and 500
3. Gas permeable element according to claim 1 or 2, S.characterized in that the flow channels have a helical, fe •undular or zigzag shape.
4. Gas permeable element according to any one of 5 claims 1 to 3, characterized in that the inclined, Spreferably helical, undulated or zigzag shape of the flow "channels extends across approximately two thirds of the element height as seen from the element face which contains the exit openings of the flow channels. Gas permeable element according to any one of claims 1 to 4, characterized in that the flow channels have the *S same angle of inclination in a dynamically balanced arrangement in each cross section of the gas permeable element.
6. Gas permeable element according to any one of claims 1 to 5, characterized in that the flow channels are arranged helically around supporting bodies, such gee supporting bodies preferably consisting of gas permeable refractory material and being embedded in the refractory shaped body. Kt I Irrairu 8
7. Gas permeable element according to any one of claims 1 to 6, characterized in that flow channels extend from a gas distribution chamber situated at the cold end of the refractory shaped body, the gas distribution chamber being filled with a gas permeable body consisting of porous refractory material.
8. A gas permeable element for metallurgical vessels substantially as hereinbefore described with reference to the accompanying drawings. DATED this 25 day of February 1991 VIETSCHER MAGNESITWERKE- ACTIEN-GESELLSCHAFT Patent Attorneys for the Applicant: F.B. RICE CO. we* 0 .000