GB2125945A

GB2125945A - Sliding gate valves

Info

Publication number: GB2125945A
Application number: GB08322610A
Authority: GB
Inventors: Dr Karl-Otto Hornung; Otto Kagi
Original assignee: Stopinc AG
Current assignee: Stopinc AG
Priority date: 1982-08-24
Filing date: 1983-08-23
Publication date: 1984-03-14
Also published as: DE3321619A1; LU84977A1; SE454800B; GB8322610D0; FR2536490B1; JPS5950964A; CH659602A5; EG15515A; ZA836274B; NL8302839A; ES282051Y; IL69287A0; CA1239539A; AU1833983A; GB2125945B; SE8304540D0; SE8304540L; DD210224A5; FR2536490A1; ES282051U

Abstract

The two valve members of a sliding gate valve for pouring metal melts are made of abrasion-proof material and material which is relatively subject to abrasion, at least on its sliding surface, respectively. In use, wear grooves or recesses are formed in the sliding surface 9 of the valve member 12, which is subject to abrasion and these grooves are filled with a mixture 20 of abraded particles and metal particles or droplets which form a lasting seal between the sliding surfaces of the two valve members. <IMAGE>

Description

SPECIFICATION Pairs of valve members for sliding gate valves for metallurgical use The invention relates to a pair of valve members adapted to slide in contact with and relative to one another for a sliding gate valve for pouring metal melt in particular a light metal melt and is concerned with the provision or production of a sealing arrangement between these valve members, when in use. The invention further relates to a sliding gate valve incorporating such a pair of valve members.

In sliding gate valves as are primarily used for the casting of steel, the integrity of the seal between the valve members is generally ensured by, amongst other things, precise flat grinding of both valve members, i.e. the fixed and movable valve plates. As is known, the steel melt flowing through the valve causes an intensive erosion both of the bores or flow openings of the plates and also of the sealing surfaces despite the use of particularly high grade refractory materials. For this reason the plates must be replaced for safety reasons after only a few pourings.

DE-AS 2404 881 discloses a sealing arrangement on a rotary sliding gate valve which comprises an annular sealing ring concentric with the axis of rotation. This ring can be arranged at the periphery of the plates or inserted between the plates within a groove in one of the sealing surfaces. This arrangement is intended to prevent the melt flowing outwardly between the sealing surfaces of the plates, i.e. it is intended to act as a security against a break-through of the melt in the case of a serious operational disturbance or damage. This arrangement, however, in no way affects the erosion phenomena referred to above or the service life of the plates which is limited by these phenomena.

However, the proposal in British Patent Specification No. 2982303A attempts to alter the erosion characteristics of a sliding gate valve. In the construction disclosed therein the penetration of melt between the sliding surfaces of the plates is intended to be prevented and the solidification of any penetrated melt inhibited. This effect is achieved by combining valve plates of specific different materials with one another, that is to say a fixed plate of soft, lubricating and poorly wettable material of high thermal conductivity with a movable plate of hard and dense material of low thermal conductivity. It has, however, been found that even with this low wettability there is always a certain adhesion between the plate material and the melt and on actuation of the valve a "sucking in" of small quantities of melt between the sliding surfaces of the plates is inevitable.It is true that a high thermal conductivity of the fixed plate is indeed a suitable feature (in combination with other features) to prevent the solidification of the melt in the region of the flow passage or to ensure the spontaneous discharge of the melt when the valve is opened.

However, at a small distance from the said passage the temperature on the sliding surfaces must of necessity be lower than the solidification temperature of the melt otherwise the integrity of the seal of the valve is rendered doubtful.

It is an object of the present invention so to construct a pair of valve members for a sliding gate valve that the integrity of the seal along the sliding surfaces of the valve may be ensured during a large number of movements of the slidable membertfius enabling extended periods of operation of the valve without replacing the valve members. In this connection it should be mentioned that under certain operational conditions, particularly when casting light metal melts, the wear on the flow passages of the valve members is slight. In such circumstances the condition of the relatively slidable surfaces is in practice determinative of the service life of the valve members.

According to the present invention there is provided a pair of valve members adapted to slide in contact with and relative to one another for a sliding gate valve for pouring a metal melt, one valve member being subject to abrasion, at least on its sliding surface, and the other valve member being relatively substantially abrasion-resistant whereby, in use, after repeated actuation of the valve grooves extending in the direction of relative movement are formed by abrasion in the sliding surface which is subject to abrasion and a mixture is formed of abraded and metal particles between the valve members which is retained in the said grooves and thereby forms a sealing arrangement between the two valve members.

The invention also embraces a sliding gate valve, e.g. of linear or rotary type including such a pair of valve members which are preferably of plate form.

The invention further embraces such a valve in service connected to a metallurgical vessel, in which, after repeated actuation of the valve whilst contacted by a melt in the metallurgical vessel, grooves extending in the direction of relative movement of the valve members have been formed by abrasion in the sliding surface of the valve member subject to abrasion and a mixture of abraded particles and metal particles has been formed between the valve members which mixture is retained in the said grooves and constitutes a sealing arrangement between the valve members.

The construction of the present invention can ensure the sealing integrity of a sliding gate valve for several thousand up to far in excess of 10,000 separate actuations with the same valve members, and thus new fields of use open up for the sliding gate valves. Thus, for example, a continuous operation on melting, holding or casting furnaces with melt constantly present becomes possible as does the use of such valves for the continued pouring of separate successive metered quantities of melt when casting shaped articles.

It should be recalled that the seal on the sliding surfaces of the valve members, starting from the fixed flow opening, must be ensured not only in all directions towards the edge of the sliding surfaces, but also, when the movable valve member is in the closed position, in the direction of the flow opening in the movable member, that is to say in the direction of movement or in the direction of the "abrasion grooves". Having regard to the second requirement referred to above, it is surprising that the recesses or "grooves" formed, in use, in the present invention by abrasion can constitute part of a reliable sealing arrangement.

Thus a deliberate induction and exploitation of abrasion and wear runs completely counter to the conventional view of "lubrication" which is directed precisely to the avoidance of wear and the reduction of friction (though this naturally does not exclude the possibility that the abradable material can also have favourable lubricating or sliding properties which act on the entire sliding surface to produce low friction).

Thus the invention relies on the recognition that the formation of a mixture of dust abraded from the adradable valve member and metal particles is critical for the production of a long term sealing integrity with continued operation of the valve. It is not possible to make a general and conclusive statement as to which specific pairs of materials lead to the production of the sealing arrangement of the present invention hut on the basis of the present specification such specific compatible pairs can be determined from case to case with relatively simple experiments.

The mode of operation of the said mixture can be considered to be as follows: The presence of the particles produced by abrasion between the valve members prevents the build up of coherent metal bodies between the sliding surfaces which, on solidification into "metal tongues" or "metal plates", inevitably lead to the rapid degradation of the valve members. It has been determined that the mixture has a very low strength but that there is a certain cohesion between the particles which prevents a "washing out" and the grooves or recesses remain constantly filled with the mixture.

Furthermore, the sealing effect is found clearly not to depend on whether the metal particles in the mixture stay molten or (temporarily) solidify.

Thus even if after a series of valve operations the metallurgical vessel is, for instance, emptied and the temperature at the sliding surfaces of the valve sinks considerably below the solidification temperature of the melt the valve can later be operated again without difficulty after re-filling the vessel with melt.

The invention is equality applicable to linear sliding gate valves and to rotary and swivel valves. In rotary valves the rotary movement can be of differing direction (analogously to the linear valve) or always in the same sense. The mounting of the valve on the furnace or other metallurgical vessel can be such that the sliding surfaces are horizontal, inclined or vertical.

Certain specific embodiments of the invention will now be described below in more detail by way of example only with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic sectional elevation of the essential parts of a linear sliding gate valve mounted on a metallurgical vessel; Figure 2 is a diagrammatic plan view of the sliding surface of the fixed valve plate (partly broken away) of the valve of Figure 1; Figure 3 is a view similar to Figure 2 of the fixed valve plate of a rotary sliding gate valve; Figure 4 is a substantially enlarged scrap sectional elevation on the line IV--IV in Figure 2 showing part of the fixed and of the movable plates;; Figure 5 is a photomicrograph of a polished section of the mixture of abraded and metal particles on the line V-V in Figure 3, i.e. perpendicular to the direction of movement (magnification ca. 1 50 times linear); and Figure 6 is a similar photomicrograph of a polished section on the line VI--VI in Figure 3, i.e.

parallel to the direction of movement (magnification ca. 1 65 times linear).

In the embodiment of Figure 1 the two valve members, which are in the form of two flat plates 12 and 14, are shown in solid lines, whilst the remaining parts of the sliding gate valve 10 and parts of the metallurgical vessel on which the valve 10 is mounted are shown only in chaindotted lines. The metallurgical vessel 1 contains a metal melt 3, for instance an aluminium melt, and has a pouring opening 2 which leads to the sliding gate valve 10. The fixed base plate 12 of the valve is held in a ground plate 1 6 secured to the metallurgical vessel 1 and has a flow opening 1 3 which forms a continuation of the pouring opening 2.

The movable slider plate 14 of the valve is in sliding contact with the base plate 12, that is to say with its sliding surface 9, i.e. the slider plate is displaceable back and forth together with the slider 1 8 accommodating it in the direction of the arrow P along the sliding surface 9. The flow opening 1 5 of the sliding plate 14 is movable in a known manner between the open position of the valve with the flow opening 1 3 of the base plate 1 2 directly above it and the illustrated closed position in which it is obscured by the base plate 12. A discharge sleeve 1 7 may be carried by the slider 18 in communication with the flow opening 1 5 in a known manner.

It is thought unnecessary to describe or illustrate the remaining constructional features of the valve of Figure 1 in detail since this is not necessary for an understanding of the present invention. Merely 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 1951 447 as examples of iinear sliding gate valves and to European published patent application 0 040 692 or German Offenlegungsschrift 30 1 3 975 as examples of rotary sliding gate valves.It is however emphasised that the sealing arrangement of the present invention can be realised not only on plate-shaped valve members with a flat sliding surface as e.g. in Figure 1, but also on valve members of other shape with e.g. a cylindrical, conical or spherical sealing surface.

The sealing integrity of the valve 1 0 when it is put into operation is provided in known manner in that the sliding surfaces of both plates 1 2 and 14 are exactly flat and the plates are permanently biased together perpendicular to the sliding surfaces. However, in order to ensure the sealing integrity not only for a few operations but also, in the sense of the present invention, in extended service with thousands of sequential operations, one valve member, in the present case the fixed base plate 12, is manufactured at least over its sliding surface 9 from material which is subject to abrasion whilst the other valve member, in this case the slidable plate 14, comprises relatively abrasion-resistant material.The susceptibility to abrasion of the material is evidenced by wear phenomena on the sliding surface 9 of the plate 12 which are illustrated in more detail in Figures 2 and 4 and will be described below: When the valve with new plates 12 and 14 and whilst acted on by, i.e. contacted by, the melt 3, as shown in Figure 1, is repeatedly actuated, i.e.

the sliding plate is slid back and forth with respect to the base plate in the direction of the arrow P, a "wear picture" or "wear profile" soon results on the sliding surface 9 of the abradable plate 12, as may be seen in Figure 2. More or less randomly arranged and shaped groove-shaped recesses 1 9 which extend substantially in the sliding direction are formed in a surface region which extends from the flow passage 1 3 on both sides for about the stroke length, i.e. the distance by which the sliding plate is moved, (the passage 1 5 is shown in Figure 2 in the closed position). The breadth of the surface region referred to corresponds approximately to the diameter of the passage 1 3 (even if this is, for instance, larger than that of the bore 15) but it may extend somewhat beyond this diameter as shown in Figure 2.Figure 4 shows this typical wear picture in cross-section on a greatly enlarged scale. As may be seen, the recesses or "wear grooves" 1 9 referred to above are not empty but are substantially from the beginning of operation filled with a material mixture 20 which is produced between the plates 12 and 14 when the valve is actuated and embeds itself in the recesses 1 9. This is a mixture of particles abraded from the abradable plate 12 and small particles or droplets of the melt 3 which are drawn in between the plates when the sliding movement occurs. As is apparent from Figure 4, the sliding surface of the abrasion-resistant plate 14 remains, as expected, practically flat and without wear.

The phenomena and occurrences described above have the consequence that the valve remains operational and reliabiy sealed over a large number of valve actuations. Thus in the initial stage of the valve operation a sealing arrangement is produced between the valve members 12 and 14 by actuation of the valve whilst being contacted by melt in the manner described. It has been found that the wear or the depth of the grooves 1 9 does not constantly increase but after perhaps a few hundred actuations remains practically constant. The observed groove depth varies from a few tenths of a millimetre to over a miilimetre.

The production of the described sealing arrangement is basically also possible in the same manner with the reverse arrangement of the valve members, i.e. with the abrasion-resistant member fixed and the abradable member slidable. This can however have certain disadvantages in another respect, e.g. because the abradable sliding surface is continuously in contact with the melt 3.

It is worthy of note that the "wear picture" described above with the associated material mixture embedded in the grooves in the abradable sliding surface appears only in the surface region referred to above and shown in Figure 2 and not in the surrounding regions of the sliding surface 9.

This means (as is shown also by the composition of the mixture 20) that the process is associated with the presence of melt. It is presumed that when relative sliding of the valve members occurs small quantities of melt are drawn in between the sliding surfaces and then, possibly after their solidification, cause the abrasion; the phenomenon was observed with precisely those materials which are inherently only slightly wetted by the melt (e.g. different sorts of graphite). Although the processes in the interior of the "wear grooves" 1 9 are not capable of direct observation, it is presumed that the local composition of the mixture 20 constantly changes with continued actuation of the valve. The particles of the mixture certainly have a certain cohesion, at any event in the cooled state.When, after long operation, the valve is taken out of service and the valve plates are separated the mixture remains lightly adhering preferentially to the surface of the wear-resistant plate 14.

It is naturally not necessary that the one valve member comprises material which is subject to abrasion throughout and it is sufficient when this property is present only on its sliding surface.

The valve member in question, i.e. the valve plate 12 in Figure 1, can be composed, e.g. over its thickness of two or more layers of different material. In this manner valve members may be manufactured which, in addition to the necessary susceptibility to abrasion on their sliding surface, have predetermined advantageous combinations of material properties, for instance as regards thermal conductivity, bending strength, hardness and the like.

In contrast to Figure 2, Figure 3 is a plan view of the abradable sliding surface of the fixed valve plate 22 of a rotary sliding gate valve. Its eccentrically disposed flow opening is designated 23 and the flow opening of the movable, abrasion-resistant valve plate (not illustrated) is shown in its closed position at 25 in a chain dotted line. After continued actuation of this valve by rotation of the movable valve plate in the direction of the arrow R the "wear picture" seen in Figure 3 is produced, i.e. substantially circular, concentric, grooves or recesses 19' are produced in the abradable sliding surface of the valve plate 22.If the rotary valve were, on the other hand, opened and closed in a manner which is also known by partial rotations with alternating direction of rotation then the recesses 19' would extend only over a corresponding arc of limited length. In other respects the comments made above in relation to Figures 1, 2 and 4 about the production and properties of the sealing arrangement and, in particular, the material mixture embedded in the wear-grooves apply also to the specific embodiment in Figure 3.

The polished section photomicrographs of Figures 5 and 6 give an idea of the structure of the mixture 20 which is retained in the wear grooves. After sealing arrangement had been produced in the manner described on a rotary valve as shown in Figure 3 and the valve had been in operation for a long period of time, the valve was taken out of operation and disassembled.

When separating the rotatable valve plate from the fixed plate the major proportion of the mixture embedded in the recesses 19' remained adhering to the sliding surface of the rotatable plate. This sliding surface of the rotatable plate forms the lower edge in Figures 5 and 6 and is there designated 14'. The surface 14' with the mixture then has a hardening liquid resin (G in Figures 5 and 6) poured over it and after the setting thereof the preparation was cut on firstly along the line V-V and secondly along the line VI--VI in Figure 3, that is to say in one case transverse to the direction of movement and in the other case tangentially to a predetermined wear groove 1 9', i.e. at the relevant point of contact of the section line in the direction of the actuation movement.

The sections of Figures 5 and 6 were then photographed at the relevant points. In both photographs the embedded metal particles M are visible as bright, practically white flecks. The abraded particles A mixed with the metal particles appear grey. The dark, almost black flecks H indicate hollow spaces in the mixture or irregularities in the plane of the cut which occurred during the production of the samples.

In contrast to Figure 5, Figure 6 permits the direction of movement when the valve is actuated to be clearly seen. Both Figures show a relatively unhomogeneous mixture but is considered to be of importance that no large "metal clumps" form and that ihstead the metal particles are frequently interspersed with abraded particles. A few specific materials or pairs of materials for valve members which have been used with success in the production of the described sealing arrangement will now be given as examples. It will be understood that this information cannot be complete and that it is not possible to give a complete list of suitable pairs of materials. The choice must be made from case to case from materials which are sufficiently resistant to the melt in question at the given temperature.The important consideration for suitability is whether the described abrasion phenomena and the mixture are produced in initial selection experiments which are conducted in the presence of melt which render possible the production, in use, of the sealing arrangement and thus a reliable extended service life of the valve. Early measurements and experiments confirm that above all graphite or material mixtures with a high graphite content or other materials with.a similar characteristic "platelet structure" are suitable for use as the material subject to abrasion.

Example 1 A valve plate of electrographite (99% graphite content, 1 8 Vol.% open porosity) was used as the abradable fixed plate in conjunction with an abrasion-resistant sliding plate of zirconium oxide (95% ZrO2) in a linear sliding gate valve mounted on a pouring spout. Metered quantities of an aluminium casting alloy (G-AlSi9Mg in accordance with DIN 1725, with 9% Si and 0.3% Mg) were poured at a temperature of about 7500C by repeated actuation of the valve. The sealing arrangement referred to above was produced in the manner described. After about 3000 actuations, which were performed without disruption and with a perfect sealing integrity of the valve, the pouring operation was terminated and the valve plates were disassembled in order to examine the sealing arrangement.It was found that the plates would have been further usable without risk.

Example 2 A rotary sliding gate valve was fitted with an abradable fixed valve plate of hot pressed boron nitride (BN) with a hexagonal lattice structure and a rotatable plate of ZrO2, i.e. the same material as in Example 1. A pure aluminium melt (99.5% Al) at 7500C was poured in an experimental device by repeated opening and closing of the valve.

After 965 disturbance-free actuations, i.e.

rotations, during the course of which the described sealing arrangement had been produced, the experiment was terminated.

Example 3 W A rotary sliding gate valve was subjected to a duration test in the same experimental device as in Example 2 and with the same melt. The valve was similar to that used in Example 2 but equipped with different plates, in this case a fixed plate of carbon with a high proportion of graphite (above 92% electrographite) and an abrasionresistant rotatable plate of highly aluminous material (90% Al203, 8% SiO2). The series of experiments comprised not less than 10550 actuations, i.e. pourings separated by varying periods of time which were associated with cooling of the valve plates. The subsequent examination shows that the plates would have been capable of continued operation.

Example 4 A rotary sliding gate valve was mounted as a tapping valve on a melting and holding furnace for pure aluminium (ca. 7500C). The valve was equipped with a fixed plate of electrographite (99% graphite, 14 Vol.% open porosity) and a rotatable plate of aluminium titanate Al2TiO5 and the operation of the valve was characterised by frequent tappings of relatively small quantities of melt. Over about three and a half days about 800 valve actuations were performed with a complete sealing integrity. The subsequent examination showed that the plates were still capable of operation. In a rotary sliding gate valve mounted on an experimental device with valve plates of the same materials as many as about 6400 actuations were achieved without disturbance.

Claims

1. A pair of valve members adapted to slide in contact with and relative to one another for a sliding gate valve for pouring a metal melt, one valve member being subject to abrasion, at least on its sliding surface, and the other valve member being relatively substantially abrasion-resistant whereby, in use, after repeated actuation of the valve grooves extending in the direction of relative movement are formed by abrasion in the sliding surface which is subject to abrasion and a mixture is formed of abraded and metal particles between the valve members which is retained in the said grooves and thereby forms a sealing arrangement between the two valve members.

2. A pair of valve members as claimed in Claim 1 in which the valve member subject to abrasion predominantly comprises graphite.

3. A pair of valve members as claimed in Claim 1 in which the valve member subject to abrasion predominantly comprises boron nitride with a hexagonal lattice structure.

4. A pair of valve members as claimed in Claim 1 in which the abrasion-resistant valve member comprises a highly aluminous material.

5. A pair of valve members as claimed in any one of Claims 1 to 3 in which the abrasionresistant valve member predominantly comprises zirconium oxide.

6. A pair of valve members as claimed in any one of Claims 1 to 3 in which the abrasionresistant valve member predominantly comprises aluminium titanate.

7. A pair of valve members as claimed in any one of the preceding claims which are constructed substantially in the form of plates with planar sliding surfaces.

8. A sliding gate valve for pouring a metal melt incorporating a pair of valve members as claimed in any one of the preceding claims.

9. A valve as claimed in Claim 8 in which the valve member subject to abrasion is fixed and the abrasion-resistant valve member is movable.

10. A valve as claimed in Claim 8 or Claim 9 which is a linear sliding gate valve and in which the grooves formed, in use, are substantially linear.

11. A valve as claimed in Claim 8 or Claim 9 which is a rotarysliding gate valve and in which the grooves formed, in use, are substantially circular or arcuate.

12. A sliding gate valve substantially as specifically herein described with reference to any one of the accompanying examples.

13. A valve as claimed in any one of Claims 8 to 12 in service connected to a metallurgical vessel, in which, after repeated actuation of the valve whilst contacted by a melt in the metallurgical vessel, grooves extending in the direction of relative movement of the valve members have been formed by abrasion in the sliding surface of the valve member subject to abrasion and a mixture of abraded particles and metal particles has been formed between the valve members which mixture is retained in the said grooves and constitutes a sealing arrangement between the valve members.

14. A method of producing a sealing arrangement between the valve members of a sliding gate valve for pouring a metal melt, one valve member being subject to abrasion, at least on its sliding surface, the other valve member being relatively substantially abrasion-resistant, the method comprising repeatedly sliding one valve member relative to the other valve member with the sliding surfaces of the two valve members in contact, forming grooves by abrasion in the sliding surface of the valve member subject to abrasion, which grooves extend in the direction of relative movement of the valve members, forming a mixture of abraded particles and particles of the melt between the valve members and retaining the said mixture in the said grooves.