SE454800B - SEALING DEVICE FOR A SLIDING CONNECTION AND THE USE OF TWO CONNECTING BODIES FOR THE IMAGE OF A SEALING DEVICE - Google Patents

Description

20 25 30 35 454 800 _ 2 hard and dense material with poor thermal conductivity. However, it has been shown that even with low wetting there is always a certain adhesion between the plate material and the melt and when operating the closure, a "draw-in" of small amounts of melt between the plate sliding surfaces cannot be avoided. Furthermore, a good thermal conductivity of the stationary plate is certainly a suitable means (in connection with other measures) to prevent the solidification of the melt in the area of the through-flow opening or to guarantee spontaneous flow when the closure is opened. Nevertheless, at a distance from the said opening, the temperature of the plate sliding surface must necessarily be lower than the solidification temperature of the melt, otherwise the tightness of the closure would be compromised.

The object of the invention is to ensure tightness along the sliding surfaces during a large number of sliding movements, thereby enabling extended operating periods without changing the closing bodies. In this context, it should be mentioned that under certain operating conditions, especially when casting light metal melts, the wear at the flow openings of the closing plates is small. In such cases, the condition of the sealing surfaces sliding on each other is in practice decisive for the service life of the plates.

This object is achieved according to the invention by means of a sealing device which is formed in the manner specified in claim 1.

Since the invention guarantees a tight closure for several thousand to over 10,000 slide operations with the same closure bodies, new areas of application for the slide closure are opened up. This enables, for example, continuous operation in melting, holding or casting furnaces under standing melt and the use for continued casting of separated, measured amounts of melt in mold casting.

In connection with the invention, it should be noted that the seal along the sliding surfaces of the closure body, starting from the stationary flow opening, must be guaranteed 10 15 20 25 30 35 40 3 454 800 both on all sides against the edge of the sliding surface and also - in the closed position of the movable closure body - against its flow opening, i.e. in the direction of movement or in the direction of the "closure grooves". With regard to the second requirement mentioned above, it is somewhat surprising that, according to the invention, depressions or "grooves" formed by wear are included in the sealing device. Intended exploitation of wear and abrasion also completely contradicts the common notion of "lubrication", which is precisely aimed at avoiding wear and reducing friction (this does not of course exclude the fact that wear-resistant materials can also have favorable sliding properties, which on the total sliding surface result in low friction).

According to the invention, the occurrence of wear residues mixed with metal particles is identified as crucial for lasting tightness during continued operation of the closure.

It is true that it is not possible to state in general and in summary which concrete material pairs lead to the goal, but this can - thanks to the invention - be determined on a case-by-case basis with relatively simple experiments.

The functioning of the aforementioned mixture can be mainly imagined as the presence of abrasive particles preventing the formation of continuous metal bodies between the sliding surfaces, which, when solidified as "metal tongues" or "plates", would lead to rapid destruction of the sealing bodies. The mixture has a very low strength, but there is still a certain cohesion with the particles, as a result of which "rinsing out" is prevented and the groove-shaped depressions remain constantly filled with the mixture. Moreover, the sealing effect is apparently not dependent on whether the metal particles remain molten in the mixture or (temporarily) solidify. Only when, after a series of operations, e.g. the melting vessel is emptied and the temperature at the sealing sliding surfaces drops significantly below the solidification temperature of the melt, can the sealing be continued without any problems later, after the melt has been refilled.

The invention is equally applicable to linear sliding closures as to rotary and pivoting closures. 10 15 120 25 30 45&_8ÛÛ 4 The rotary movement can then be of alternating direction (analogous to the linear closure) or always in the same direction. The closure can also be mounted on the furnace or melting vessel with the sliding surfaces in a horizontal, inclined or vertical position.

Hereinafter, various embodiments of the invention are described in more detail in connection with the drawing. There, Fig. 1 shows essential parts of a linear sliding closure mounted on a melting vessel in longitudinal section, Fig. 2 a view of the sliding surface of the stationary closure plate (partially broken away) of the closure according to Fig. 1, Fig. 3 a corresponding view of the stationary closure plate of a rotary casting closure, §¿g¿_g a section along the line IV-IV in Fig. 2 through a portion of the stationary and the movable closure plate in a greatly enlarged view, Fig. 5 a microscopic grinding image photograph of the mixture of wear and metal particles in a section along the line V-V in Fig. 3, i.e. perpendicular to the direction of movement (magnification approx. 150 times linear), and Lig¿_§ a similar grinding image photograph in a section along the line VI-VI in Fig. 3, i.e. in the direction of movement (magnification approx. 165 times linear). ' In the embodiment according to: Fig. 1, only the two closure bodies - here in the form of two flat plates 12 and 14 - are drawn with solid lines, while further parts of the sliding closure 10 as well as parts of the melting vessel, on which the closure 10 is mounted, are only indicated in dashed lines. The melting vessel 1 contains a metal melt 3, for example an aluminum melt, and has a casting opening 2, which leads to the sliding closure 10. The stationary bottom plate 12 of the closure is fixed in a base plate 16 attached to the melting vessel 1 and has a flow-through opening 13 continuing the vessel opening 2. The movable slide plate 14 of the closure is in sliding contact with the bottom plate 12 or with its sliding surface 9, i.e. The slide plate, together with the slide 18 which receives it, can be moved back and forth in the direction of the arrow P along the sliding surface 9. The flow opening 15 of the slide plate is then brought in a known manner either to overlap the flow opening 13 of the base plate 12 (opening position of the closure) or, as shown, offset towards it (closing position). A casting sleeve 17 inserted in the slide 18 can connect to the flow opening 15 in a known manner.

It is not necessary to show in detail the further construction of the closure according to Fig. 1, since this is not required for understanding the invention. For the sake of completeness, reference is made to Swiss patent application 3255/81-5 or German patent application P 32 08 101.4, Swiss patent specification 523 730 and German patent specification 19 51 447 as examples for linear sliding closures and to European published patent application 0 040 692 or German Offenlegungsschrift 30 13 975 as examples for rotary sliding closures. It should nevertheless be emphasized that the sealing device according to the invention can not only be used with plate-shaped closure bodies with a flat sliding surface such as, for example, according to Fig. 1, but in principle also with closure bodies of other designs with, for example, cylindrical, conical or spherical sealing surfaces.

The tightness of the closure 10 is ensured during its commissioning in a known manner by the sliding surfaces of the two plates 12, 14 being precisely flat and by the plates being permanently clamped together perpendicular to the sliding surfaces. In order to guarantee tightness not only for a few operations but according to the invention also during continued operation with thousands of operations, one of the closure bodies, in this case the stationary base plate 12, is made of a wear-resistant material at least along its sliding surface 9, while the other closure body, here the displaceable plate 14, consists of a wear-resistant material. The wearability of the material is evident in the wear results at the sliding surface 9 of the plate 12, which are shown in more detail in Figs. 2 and 4 and are explained below.

When the closure with new plates 12, 14 and during filling with melt 3 according to Fig. 1 is continued to be operated, i.e. the sliding plate is displaced back and forth in relation to the bottom plate in the direction of arrow P, a "wear pattern" very soon arises at the sliding surface 9 of the wear plate 12, as can be seen in Fig. 2. In a surface area extending from the flow bore 13 outwards by approximately the stroke length to both sides (the bore 15 in the closed position is indicated in Fig. 2), more or less randomly arranged and shaped groove-shaped depressions 19 are formed, which mainly run in the sliding direction. The width of the said surface area corresponds approximately to the diameter of the bore 13 (even when this is, for example, larger than that of the bore 15), and it can also, according to Fig. 2, extend slightly beyond this diameter. Fig. 4 shows this typical wear pattern in cross-section in a greatly enlarged manner. As can be seen from the figure, the said depressions or "wear grooves" 19 are not empty, but are initially filled with a material mixture 20, which arises during the closing operation between the plates 12 and 14 and is deposited in the depressions 19. This is a mixture of wear particles from the wear plate 12 and small particles, for example drops of the melt 3, which are drawn between the plates during the sliding movement. As can be seen from Fig. 4, the sliding surface of the wear-resistant plate 14 remains, as expected, practically flat or without wear.

The results and processes described above have the effect that the closure remains operationally and reliably tight over a very large number of operations. Thus, at the beginning of operation, by operating the closure while filling with melt in the manner described, a sealing arrangement is formed between the closure bodies 12 and 14. It has been found that the wear or depth of the grooves 19 does not increase continuously, but remains practically constant after possibly a few hundred operations. The groove depth observed ranges from a few tenths of a millimeter to over a millimeter. Even with the reverse arrangement of the closure bodies - wear-resistant body stationary and wear-resistant body displaceable - the formation of the described sealing arrangement is in principle possible in a similar way. This may, however, have certain disadvantages in other respects, e.g. when bi' 10 15 20 25 30 35 40 454 800 the wearable sliding surface is in contact with the standing melt 3 for a long time.

It is surprising that the described "wear pattern" with embedded material mixture at the wearable sliding surface only occurs in the aforementioned surface area shown in Fig. 2, and not in the surrounding areas of the sliding surface 9. This means (as also shown by the composition of the mixture 20) that the process is linked to the presence of melt. It is assumed that during the relative displacement of the closure bodies, small amounts of melt are drawn in between the sliding surfaces and then, possibly after their solidification, cause the wear. The phenomenon could also be observed with materials that are only slightly wetted by the melt (e.g. different types of graphite). Although the processes in the interior of the "wear grooves" 19 are not available for direct observation, it is assumed that the local composition of the mixture 20 is constantly changing during continued operation of the closure. It is true that the particles of the mixture, at least in the cooled state, exhibit a certain cohesion. When the closure is stopped after a longer period of operation and the closure plates are removed from each other, the mixture suitably remains slightly adherent to the surface of the wear-resistant plate 14.

Of course, it is not necessary that one of the closure bodies consist entirely of wear-resistant material, but it is sufficient if this property is present at least at its sliding surface. The closure body in question or the closure plate 12 can, for example, be composed of two or more layers of different materials in thickness. In this way, closure bodies can be produced which, in addition to the required wear resistance at the sliding surface, exhibit certain advantageous combinations of material properties, for example with regard to thermal conductivity, bending stiffness, hardness, etc.

Fig. 3 shows, in contrast to Fig. 2, the view of the wearable sliding surface of the stationary closing plate 22 of a rotary slide closure. Its eccentrically arranged flow opening is designated by 23 and the position of the flow opening of the (not shown) movable, wear-resistant closing plate in its closed position is indicated by dash-dotted lines at 25. After continued operation of this closure by 10 15 20 25 _30 35 40 454 800 8 rotation of the movable closing plate in the direction of the arrow R, the "wear pattern" shown in Fig. 3 is produced, i.e. essentially circular, concentric, groove-shaped depressions 19' arise in the wearable sliding surface of the closing plate 22. If, on the other hand, the rotary closure, which is also known, is opened and closed by partial rotations with alternating direction of rotation, the recesses 19' would only extend over a corresponding circular arc of limited length. In addition, the above embodiments according to Figs. 1, 2 and 4 for the formation and properties of the sealing device and in particular the material mixture deposited in the wear grooves apply in the same way to the embodiment according to Fig. 3.

The microscopic wear images according to Figs. 5 and 6 give an idea of the structure of the mixture 20 forming a component of the sealing device (Fig. 4).

After the sealing device has been formed in the manner described in a rotary closure according to the example of Fig. 3 and the closure has been in operation for a longer period of time, the closure would be stopped and dismantled. When the rotary closure plate is separated from the stationary closure plate, the greater part of the mixture stored in the recesses 19' would adhere to the sliding surface of the rotary plate.

This sliding surface of the rotatable plate forms the lower edge in Fig. 5 and 6 and is there designated by 14'. The surface 14' with the mixture was then overcast with a hardening casting resin (G in Fig. 5 and 6), and after hardening of this the preparation was cut partly along the line V-V and partly along the line VI-VI in Fig. 3, i.e. in the one case transversely to the direction of movement and in the other case tangentially with a defined wear groove 19', i.e. at the actual point of contact of the cutting line in the direction of actuation movement.

At the relevant locations, the grinding images were then taken according to Fig. 5 and Fig. 6. In both images, the embedded metal particles M are visible as light, practically white spots. The wear particles A mixed with metal particles appear gray. The more or less large dark to black spots H, on the other hand, are to be interpreted as cavities in the mixture or as irregularities in the grinding plane, which arose during the preparation of the specimen. 'ü p.

I! 10 15 20 25 30 35 40 454 800 In comparison with Fig. 5, the direction of movement during the closing operation is clearly visible from Fig. 6. Both figures show a rather irregular mixture, whereby it is nevertheless essential that no larger "metal lumps" are formed, but that the metal parts are always separated by intermediately stored wear parts. Below are given as examples some concrete materials or material pairs for closing bodies, such as those which are advantageously used in the production of the described sealing device. It is understood that these indications cannot be complete. The selection must be made from case to case from materials which, in relation to the relevant melt at the given temperature, are sufficiently resistant. The decisive point of view for suitability is then whether in the selection tests in the presence of melt the described wear results and the mixture can be obtained, which then enables the formation of the sealing device and thus the excellent long-term operation of the closure. Previous findings and tests confirm that graphite or material mixtures with a high graphite content or other materials with a similar, characteristic "disk structure" are particularly suitable as wear materials.

Example 1: A closing plate made of electrographite (99% graphite content, 18% open porosity by volume) was used as a wear-resistant, stationary plate in connection with a wear-resistant sliding plate made of zirconium oxide (95% ZrO2) in a linear sliding closure fixed to a casting chute. By continuing to operate the closure, measured quantities of an aluminum casting alloy (G-AlSi9Mg according to DIN 1725, with 9% Si and 0.3% Mg) were cast at a temperature of approximately 750°C.

The sealing device was then formed in the described manner.

After approximately 3000 operating strokes without any problems and with the closure being leak-proof, the casting operation was interrupted and the closure plates were removed to examine the sealing device. It was found that the plates were safe to use.

Example 2: A rotary slide closure was provided with a wear-resistant, stationary closure plate made of hot-pressed boron nitride BN with a hexagonal lattice structure and a rotatable plate made of ZrO2 (same material as example 1). In an experimental device, a pure aluminum melt (99.5% Al) was cast 10' 15 20 ZS 30 454 as 10 at 750°C while the closure was continuously opened and closed. After 965 trouble-free operations (rotations), during which the described sealing device was obtained, the experiment was interrupted.

Example 3: The same closure as in Example Z was mounted under the same experimental device and with the same melt, but with a different plate assembly in a long-term test. In this case, a stationary plate made of carbon with a high graphite content (over 92% electrographite) was combined with a wear-resistant rotating plate made of material with a high aluminum content (90% Al2O3, 8% SiO2). The test series included no less than 10,550 operations, i.e. castings with shorter and longer interruptions and the associated cooling of the closure plates. The subsequent examination showed that the plates or the sealing device were still functional.

Example 4: A rotary slide closure was installed as a drain closure on a melting and holding furnace for pure aluminum (approx. 750°C). The closure was equipped with a stationary plate of electrographite (99% graphite, 14% open porosity by volume) and a rotatable plate of aluminum titanate (Al2TiO5) and the operation was characterized by frequent drains of relatively small melt quantities. In this way, approximately 800 closure operations were achieved with complete tightness over a period of approximately three and a half days. The subsequent examination showed that the plates or their sealing device were still operational. With closure plates of the same material, a rotary slide closure mounted on a test device achieved up to approximately 6400 operations without malfunction. i .1 :I III

Claims (7)

fJ 10 15 20 25 30 1, 454 800 Beisnikrax Sliding closure light metal melts, with two preferably flat ones characterized in that the sealing body (14, 14 ') which can be cast for casting metal, especially sealingly against each other, is durable against the other closing body (12, 22). at least at its sliding surface (9) is relatively wearable in such a way that between the closing bodies (12, 22; 14, 14 ') during sliding contact movement between the closing bodies (12, 22; 14, 14') and during supply with the molten metal it is formed a sealing amount (20) of wear particles (A) and metal particles (M). Sliding closure n a d according to claim 1, characterized in that the wearable closure body (12, 22) is fixed and the wear-resistant closure crepe (14) is displaceable. Sliding closure characterized in that according to claim 1 or 2, the wearable closure body (12, 22) has a predominantly bead of graphite. The sliding closure of a den according to claim 1 or 2, characterized in that the sealing body (12, 22) consists predominantly of boron nitride having a hexagonal lattice structure. 5. Sliding closure t e c k n a d that the 14 ') has a high aluminum content. 6. Sliding closure t e c k n a d 14 ') predominantly consists of Sliding closure characterized in that it consists in that it 14 ') predominantly consists according to claim 1 or 2, has the most durable closure body (14, according to claim 1 or 2), has - wear-resistant closure body (14, zirconia) according to claim 1 or 2, feel - alite fixed body (14, aluminum titanate.