GB1589659A - Refractory plates - Google Patents

Description

(54) IMPROVEMENTS RELATING TO REFRACTORY PLATES (71) We, VYSOKA SKOLA CHEMICKO TECHNOLOGICKA of Praha, Czechoslovakia, a body corporate organised and existing under the laws of the Czechoslovak Socialist Republic, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a refractory plate for slide valve closures of foundry ladles, consisting of two parts bonded together.

As known, steel is cast at present out of foundry ladles provided with stopper rods having stopper plugs. However, such a simple arrangement has many disadvantages; the stopper rod consisting of a plurality of stopper pipes has to be exchanged for a new one after each use, a relatively high consumption of stopper pipes prevents high-grade materials from being used for the manufacture thereof while currently used materials such as fireclay or a fireclaygraphite composition do not offer the full reliability expected from the stopper or plug mechansims; the plug and the stopper pipes get worn out by superficial melting, and the stopper may eventually get burnt off, which all make the casting process defective. Among other disadvantages there can be named laborious preliminary steps before the casting process since the ladle has to be pre-cooled which in turn endangers the oven lining lifetime, or makes it necessary to use a protective cover making the attendance work troublesome.

Foundry ladles equipped with plug or stopper mechanisms may not be heated to highly elevated temperatures since possible dunts or cracks arising thereby in the ceramic material of which the stopper rod is made may cause failures in the casting process.

The developments in modern technological steel making processes such as vacuum degassing and continuous casting, make it necessary to provide, without any delays, new foundry ladle sealing modes. In an endeavour to eliminate disadvantages of plug closures of foundry ladles, there has been developed a valve closure, the plates of which are made of refractory ceramic materials based on corundum, zirconium silicate or, alternatively, magnesite. However such technology is rather demanding since it requires specific plants as well as high firing temperature exceeding 1600 C.

During a single casting cycle, multiple shifts of a movable plate of the valve on a stationary plate thereof occur. Thereby the surface of said valve plate is abraded and roughened, which, eventually, may impair the tightness of the valve closure. Apart from this, the outflow hole in the valve plates gets worn out due to an errosive action of molten steel, which can result in an unctrollable enlargement of said hole and, consequently, in an undesirable casting rate modification.

To cope with the above-mentioned unfavourable influences it has been proposed to manu facture the valve plates from resistive and, consequently, expensive materials, and to fire them at highly elevated temperatures, which process is expensive per se. According to another suggested method, a less resistive basic material has been provided with with a coating of a more resistive material. In this case, however, the damaging of the outflow hole in the valve plate cannot be prevented since such a protective layer protects its upper edge only.

The aim of the invention is to eliminate, or at least mitigate, the drawbacks of prior art as hereinbefore referred to.

The invention provides a refractory plate for slide valve closures of foundry ladles, said plate comprising a first refractory element having a top and a bottom surface and containing a first hole extending between said surfaces, a second refractory element containing a second hole for the flow of molten metal therethrough, the second element being inserted in said first hole and extending the whole length thereof, the melting point of the second element being at least 5 P.C.E. (pyrometric cone equivalent) higher and its softening point at least 150 C higher than those of the first element, a dilation liner being provided between the outer surface of the second element and the inner surface of the first hole.

The second element may be a body of revolution. Preferably, the outer surface of the second element and the inner surface of the first hole are cylindrical or conical.

Unlike the hitherto known arrangements wherein the mating surfaces of the two elements of a refractory plate are parallel with the largest or operative surface of such plate, the first, which means the less refractory element of the plate, is prevented, according to the present invention from getting into contact with molten steel. The latter contacts the second plate element only, which is less voluminous. Thus the first or larger element can be made of a low-grade inexpensive material and can be fired at a lower temperature of about 1400"C, both of which facts are economically advantageous.

One preferred embodiment is hereinafter described with reference to the accompanying somewhat schematic drawings in which: Figure 1 is a sectional view of a comparative plate comprising the two elements bonded together; Figure 2 is a top view of the plate shown in Figure 1; and Figure 3 is a sectional view of an embodiment of the plate according to the invention comprising the two elements and a dilation liner therebetween.

As can be seen in the drawings, the refractory plate consists of a first refractory element 1 and a second refractory element 2 which latter is embodied, in this case, as a cylindrical body of revolution having an annular base. The two elements 1 and 2 have respective mating surfaces 3 and 6 which intersect one largest surface 4 of the first element 1. The largest surface 4 simultaneously consititues an operative surface for engaging stationary members when being displaced across said stationary members (not shown).

As materials with different dilatability (thermal expansion) are used for manufacturing the two elements 1 and 2, a dilation liner 5 is inserted between the mating surfaces of the elements 1 and 2 (see Figure 3), which liner 5 is designed for preventing unfavourable effects resulting from a different dilation of the two elements 1 and 2.

According to the invention the second element 2 has a melting point of at least 5 P.C.E.

higher and a softening point at least 150 OC higher than those of the first element.

WHAT WE CLAIM IS: 1. A refractory plate for slide valve closures of foundry ladles, said plate comprising a first refractory element having a top and a bottom surface and containing a first hole extending between said surfaces, a second refractory element containing a second hole for the flow of molten metal therethrough the second element being inserted in said first hole and extending the whole length thereof, the melting point of the second element being at least 5 P.C.E.

(pyrometric cone equivalent) higher and its sof tening point at least 1 500C higher than those o the first element, a dilation liner being provide between the outer surface of the second eleme and the inner surface of the first hole.

2. A plate according to Claim 1 wherein th second element is a body of revolution having an annular base.

3. A plate according to Claim 1 or 2 where in the outer surface of the second element and the inner surface of the first hole are cylindri cal or conical.

4. A refractory plate for valve closures of foundry ladles, said plate being constructed, arranged and adapted to operate substantially as hereinbefore described with reference to, and as illustrated in, Figure 3 of the accom panying drawings.

5. A valve closure comprising a refractory plate according to any one of the preceding

Claims (1)

1. claims.

   6. A foundry ladle having a valve closure according to Claim 5.