GB2254029A

GB2254029A - Plate for a slide closure ans process for producing it

Info

Publication number: GB2254029A
Application number: GB9206269A
Authority: GB
Inventors: Lorenz Doetsch
Original assignee: Radex Heraklith Industriebeteiligungs AG
Current assignee: RHI AG
Priority date: 1991-03-23
Filing date: 1992-03-23
Publication date: 1992-09-30
Anticipated expiration: 2012-03-23
Also published as: GB9206269D0; GB2254029B; ATA52592A; FR2674155B1; ITMI920649A0; DE4109659C2; AT402034B; DE4109659A1; FR2674155A1; ITMI920649A1; IT1254682B; BE1006770A5

Description

2254029 ---1 - t Plate for a slide closure and process for producing it

The invention relates to a plate for a slide closure on the nozzle of a metallurgical melting crucible. Slide closures of this type are known especially as linear or rotary slides. They consist of two or three plates which are each designed with at least one throughflow orifice. As a result of a linear displacement or a rotation of the plates relative to one another,, the orifices are either brought into coincidence, to allow molten metal to flow out, or else offset relative to one another, in order to prevent the flow of the molten metal.

For slide plates of this type, it is also known to assemble them in a circumferentially arranged tensioning band. For this, conventionally an endless tensioning band made of steel is heated (thereby expanding) and, whilst cooling (thereby contracting again), is shrunk onto the circumferential surface of the plate.

During the shrinking-on operation, it is necessary to ensure that the compressive stress transmitted from the tensioning band to the plate body does not become so great that cracks occur in the plate body or the plate body is destroyed.

There is consequently used a tensioning band, the length, thickness and material of which are so selected or in which the heating and cooling curve during the attachment of the tensioning band is so selected that, after the shrinking-on operation, the tensioning band transmits at most such compressive stresses to the plate that the plate itself remains crack-free and undestroyed.

But it is necessary, at the same time, to ensure that the tensioning band is not shrunk too loosely onto the circumferential surface of the plate, with the result that it comes loose from the plate again later during the use of the plate in a slide closure when the hot molten metal passes through the passage orifice of the plate and tensile stresses are induced in the plate.

Although these theoretical principles are familiar to an average person skilled in the art, there are still always problems in correctly coordinating the tensioning band and plate with one another in this way.

It was therefore proposed in DE 31304,938 C2 to arrange between the circumferential surface of the plate and the tensipning ring a layer of mortar which is partially squeezed out upwards and downwards during the shrinking-on of the tensioning ring. The mortar layer is intended to ensure that, after the shrinking-on operation and the cooling, no or only slight pressure forces are transmitted to the plate.

In this process, a mortar has always to be prepared separately and introduced between the plate and tensioning band and squeezed-out mortar subsequently removed again.

Apart from these additional process steps, there is not always a guarantee that, during casting, the tensile stresses induced in the slide plate by the hot molten metal will not become so great that the tensioning band comes loose again from the plate or the mortar layer.

To that extent, the object on which the invention is based is to provide a plate for a slide closure on the nozzle of a metallurgical melting crucible and an associated production process, which lead as a result to a plate which is assembled in a metal tensioning band attached to the circumferential surface of the plate by being shrunk on, but in which the pressure forces transmitted to the plate by the tensioning band are at all events limited to such a degree that the plate is not destroyed, but at the same time there is also the guarantee that the tensioning ring will not come loose from the plate under thermal shock -stress on the plate (for example, during casting).

The invention is based on the knowledge that this object can be achieved if a stress compensation is afforded for the tensioning band.

This stress compensation is to be obtained by means of one or more depressions on the circumferential surface of the plate. The invention starts, at the same time, from the consideration that the tensioning band, which itself likewise has corresponding indentations,, when being shrunk onto the circumferential surface of the plate, follows.the path of least resistance and, after it rests on the circumferential surface of the plate, also in the region of the indentations, during a further contraction stretches more or less "smooth" in the region of the indentations and excessive compressive forces on the plate are thus prevented. Ideally, therefore, after complete cooling, the tensioning band bears on the inner face of the indentations with at most low compressive stress. But if the contraction of the tensioning band is not yet concluded at this moment because the plate is "too large" or the tensioning band "too small", the result of this further contraction is that the tensioning band "loosens" again from the indentations and is completely or partially stretched smooth. An increase in the compressive stress from the tensioning band to the plate is reliably prevented at the same time, because some "overlength" of the tensioning band is utilised.

There remains the guarantee that the tensioning band will continue to bear with some compressive stress against the circumferential surface of the plate (outside the indentations), in order, among other things, to guarantee a secure assembly of the slide plate even under a thermal shock stress such as occurs during casting.

The indentations thus serve as stress compensation during the shrinkingon of the tensioning band.

Preferably, a plurality of indentations are provided and are so arranged that they are distributed symmetrically in relation to the plate body. At all events, the actual arrangement of the indentations will be such that stress peaks of the band on the plate are prevented as far as possible. The transition from the 4 indentations to the remaining circumferential surface will therefore also be as "smooth" as possible.

A plate for a linear slide is, for example, of oval shape. In this case, on each of the two regions of curvature of the plate there could be one or two indentations (then at a distance from one another),, these in turn being arranged mirror-symmetrically relative to one another.

The indentations themselves can have various shapes. It is preferable to design the indentations so that their cross- section has approximately the shape of a semicircle or half-oval with curved transitions to the further circumferential surface.

Of course, it is also possible, in this plate or in the process for producing it, to provide a mortar layer between the circumferential surface of the plate and the tensioning band, as described in the introduction. But this measure constitutes only an alternative possibility of assembly. If only for reasons of simpler production, it is directly possible to do without this mortar layer.

The length, thickness and material of the tensioning band and the heating and cooling curve for the tensioning band are preferably selected so that, after the shrinking-on and complete cooling, the tensioning band rests in the region of the indentations against the surfaces of these with, at most, a low compressive stress. In other words, the tensioning band is so coordinated with the plate that in the extreme (ideal) situation it also covers the surface of the indentations in the same way as the remaining circumferential surface. But, after complete cooling, it will often project only partially into the indentations, so that a space remains between the tensioning band and the surface of the indentations.

The advantage of the process described is that, during the shrinking of the tensioning band onto the circumferential surface of the plate, tolerances always t present no longer have to be taken into account from the outset to the extent necessary in the state of the art. on the contrary, they are compensated by the indentations.

The process is easy to put into practice. The plate thus produced affords maximum safety.

The tensioning band will preferably be a steel band, a steel.grade with a low ageing tendency being preferred. The circumferential surface of the plate should be as smooth as possible,, in order to prevent stress peaks.

Preferably, the tensionng band is placed onto the circumferential surface of the plate in such a way that a short distance from the topside and underside of the plate remains in order to ensure the movement of the plate in the slide closure. The tensioning band is preferably arranged at the same distance from the topside and underside of the plate.

Further features of the invention are the subject of the subclaims and of the other application documents. The invention is explained in more detail below by means of an exemplary embodiment.

In the highly diagrammatically represented drawing:

Figure 1 shows a top view of a plate according to the invention for a slide closure, in which the tensioning band rests completely on the circum ferential surface, Figure 2 shows a top view of the place according to Figure 1, in which the tensioning band extends only partially into the indentations.

The plate made of refractory ceramic material is designated by the reference symbol 10. As seen in the top view. it has approximately an oval shape with two flat sides 10a, 10b and two curved sides 10c,, 10d and is designedbentrally with two passage orifices 12a. b at a distance from one another.

On its circumferential surface 14, the plate 10 is i designed with a total of two indentations 16,, 18 which, as can be taken from the top view, each have a semicircular shape in cross-section. The indentations 16, 18 extend continuously from the topside 22 to the underside of the plate 10.

A tensioning band 24 consisting of steel bears with low compressive stress against the circumferential surface 14 of the plate 10. The tensioning band extends at a short distance from the topside 22 and is at a short distance from the underside of the plate 10, that is to say is arranged centrally on the circumferential surface 14 of the plate 10.

is The distance, shown in the Figures, between the tensioning band 24 and circumferential surface 14 actually does not exist and serves here merely for clearer representation.

In the plate according to Figure 1, the tension ing band 24 extends completely into the indentations 16, 18 and bears ovei its entire length with low compressive stress against the circumferential surface 14 of the plate 10 (also on the inner faces of the indentations 16, 18).

The tensioning band 24 was attached to the circumferential surface 14 of the plate 10 by the follow ing process:

The tensioning band 24 originally had a shape approximate to the circumferential surface of the plate 10,, that is to say likewise two indentations on the curved portions. It was then heated by inductive heatingi, thereby expanding, specifically to such an extent that the inside diameters of the tensioning band 24 were slightly larger than the outside diameters of the plate 10. The tensioning band 24 was thereafter slipped in the heated state over the plate 10 and cooled.

During the cooling, the tensioning band 24 contracted again, specifically in such a way that, after 4 a particular cooling rate, it lay on the circumferential surface 14 of the plate 10, including the region of the indentations 16, 18. At this moment, the tensioning band 24 was under slight stress against the circumferential 5 surface 14.

The length, thickness,, choice of material and heating and cooling curve for the tensioning band were previously set, so that the abovementioned state was reached.

The compressive stress is such that the plate 10 is assembled securely by the tensioning band 24, but it is also limited to such an extent that no excessively high compressive stresses are transmitted to the plate 10 and a cracking or destruction of the plate 10 is prevented.

In the exemplary embodiment according to Figure 2, in the region of the indentations 16, 18 the tensioning band 24 is at a short distance from the inner faces of these. This configuration results from the fact that here, during the cooling, the tensioning band 24 has "stretched smooth 11 again due to further contraction and has come loose from bearing contact against the inner faces of the indentations 16, 18, but without the pressure forces on the plate body being increased. 25 The situation as shown in Figure 2 occurs, for example, when a tensioning band 24 of somewhat smaller diameter than in Figure 1 is selected. The foregoing parameters for the tensioning band must always be selected so that the tensioning band 24 is guided out of the indentations 16, 18 again at most so far that it extends with acontinuous curvature over and beyond the indentations 16, 18.

Conversely, the length of the tensioning band 24 is selected at most so that, in the shrunk-on state, it also covers the region of the surfaces of the. indentations 16, 18 with slight compressive stress. The foregoing particulars apply accordingly to the dimensioning of the plate 10.

1 An average person skilled in the art will usually proceed by ranging between these two extreme situations, with the result that an assembly of the tensioning band 24, as shown in Figure 2, is then obtained. This ensures maximum safety even in the event that, during casting onto the plate received in a slide closure, tensile stresses occur in the plate. No detachment of the tensioning band 24 occurs even then.

1

Claims

Patent Claims is 1 Plate for a slide closure on the nozzle of a

metallurgical melting crucible, having at least one indentation on its circumferential surface and assembled in a -metal tensioning band attached to the circumferen tial surface of the plate by being shrunk on.
2. Plate 4ccording to Claim 1, wherein the indentations have a crosssectional shape approximate to a semicircle or half-oval.
3. Plate according to Claim 1 or 2, wherein the indentations extend over the entire thickness (height) of the plate.
4. Plate according to one of Claims 1 to 3, wherein the indentations are distributed on the circumferential surface in such a way that there is as uniform a compressive-stress distribution as possible between the tensioning band and plate.
5. Plate according to one of Claims 1 to 4, wherein the tensioning band extends partially into the indenta- tions.
Process for producing a plate according to one of Claims 1 to 5, wherein the plate, made of refractory ceramic material and having at least one indentation on its circumferential surface, is surrounded by a metal tensioning band previously heated and expanded as a result of direct or indirect heat treatment and having corresponding indentations, and the tensioning band is subsequently shrunk onto the circumferential surface of the plate by cooling, in such a way that, in the region of the indentation or indentations, the tensioning band extends at least partially into this or these.
7. Process according to Claim 6, with the condition that the length, thickness and material of the tensioning band and the heating and cooling curve for the tensioning band are selected so that,, after the shrinking-on and complete cooling, the tensioning band extends over and beyond the region of the indentation or indentations.

- 10
8. A plate substantially as described herein with reference to the accompanying drawings.
9. A process substantially as described herein with reference to the accompanying drawings.

1 i.