GB2085126A

GB2085126A - Valve plates for a sliding gate valve

Info

Publication number: GB2085126A
Application number: GB8128596A
Authority: GB
Original assignee: Stopinc AG
Current assignee: Stopinc AG
Priority date: 1980-09-24
Filing date: 1981-09-22
Publication date: 1982-04-21
Also published as: FR2490767B1; IT1142825B; BE890313A; ES267850Y; CA1187696A; DE3131819A1; ES267850U; CH649610A5; BR8106004A; JPS5781951A; FR2490767A1; GB2085126B; ZA816655B; IT8149327A0

Abstract

A pair of valve plates 1, 2 for a rotary or linearly sliding gate valve, particularly for use in controlling the flow of molten metal, each have a sliding surface 4 which, in use, slide relative to one another and a discharge aperture which passes through the plate and opens onto the sliding surface. Each aperture is defined by two wall sections 21 which extend perpendicular to the intended direction of relative displacement of the sliding surfaces and two wall sections 22 which extend parallel to the said direction of displacement. <IMAGE>

Description

SPECIFICATION Valve plates for a sliding gate valve The invention relates to a pair of valve plates for a sliding gate valve and to a sliding gate valve incorporating such plates. Such plates have a sliding surface which, in use, slides relative to the sliding surface of the other plate and are used to control the flow of molten metals.

It is known that, during the regulated discharge metals, especially steel, the plates of sliding gate valves are subjected to severe wear despite the use of high-grade refractory materials. The apertures in the plates and the attached refractory parts undergo continuous widening of their cross-sectional area caused by the melt flowing out. What is much more serious, however, is that in the intermediate positions of the gate valve, that is to say during opening and closing of the valve and during throttled pouring, parts of the edges of the apertures and adjoining regions of the sliding surfaces are exposed to the flowing melt and are particularly severely attacked because the discharge channel narrows there. This situation has been known for a long time, and is described in e.g.Swiss Patent No. 528942, Figures 2 and 3, and as a rule determines the number of pourings which can be carried out with one set of plates because the continuing erosion of the sliding surfaces in the said regions finally renders a sealed closure impossible, whereupon the plates must be replaced. Inspection of the installed plates after each casting to determine whether the degree of wear will permit further reliable use is not very easy because of the restricted view of the sliding surfaces and requires a certain experience.

In order to reduce the wear on the edges referred to above a stepped widening of at least one of the discharge apertures towards the sliding surface has been proposed in German Offenlogungsschrift No.

2014331. However, for a given bore diameter this implies a considerable lengthening ofthe path between the open and closed positions and a reduced overlap of the plates at right angles to the direction of relative displacement path. Therefore, this proposal can only be put into practice with a relative increase in the size of the plate surfaces and thus of the whole valve.

It has been further proposed in German Offenlegungsschrift No. 1937742 that the sliding plate be provided with a special liner made from heatproof metallic hard material, e.g. a metal ceramic solid solution, along the discharge aperture and on the sliding surface in order to protect the points which are subject to wear. However, the varying coefficients of thermal expansion of the liner material and the backing material lead to problems, and the production of such plates is naturally substantially more expensive.

By contrast, an object of the present invention is the reduction and better control of the wear occurring on the valve plates, or the effects thereof, without having to accept the considerable disadvantages attached to the known proposals.

According to the present invention there is provided a pair of valve plates for a sliding gate valve, each plate having a sliding surface adapted, in use, to contact and slide relative to the sliding surface of the other plate and a discharge aperture passing through the plate and opening onto the sliding surface, each discharge aperture being defined, at least at the region where it opens onto the associated sliding surface, by two first wall sections which are substantially straight and intersect the intended direction of relative displacement of the sliding surfaces at substantially the same angle and by two second wall sections which connect the ends of the first wall sections and extend substantially parallel to the said direction of relative displacement.

Valve plates according to the invention can be produced in a simple manner but without a significant increase in cost by comparison with conventional plates having circular discharge apertures.

This can be done, for example, by pressing a corresponding die or core around in the same operation in which the plates are given their rough shape. The principal advantage of the invention is that by comparison with round discharge apertures smaller and better formed wear surfaces are produce on the sliding surfaces of the plates, as will be described in greater detail below. In addition the edge portions, which are exposed to the flow of the melt in the intermediate positions of the gate valve, are always the same size and on average shorter than with a round discharge aperture.

Although in the past valve plates have, in practice, been used exclusively with circular discharge apertures, there have been isolated proposals for noncircular aperture cross-sections, e.g. in German Offenlegungsschrift No. 1910247 and German Auslegeschrift No. 2006523. The main object of these was to achieve a particular regulating characteristic (aperture cross-section as a function of the displacement path), whilst the problem of the wear on the edges, which underlies the present invention, still remained.

The first and second wall sections preferably all touch an imaginary inscribed circle, but in a modified construction the first wall sections lie outside this circle. The cross-section ofthe apertures may be constant over the thickness of the plates or it may change overthethickness of the plates so as to be, e.g., circular on the sides of the plates remote from the sliding surfaces.

The invention also embraces a sliding gate valve incorporating such a pair of plates. It will be appreciated that for a rotary valve the discharge apertures will be part-annular, that is to say their shape is that of a sector of an annulus, and for a linearvalvetheir shape is a parallelogram and may be a square or rectangle.

Further features and details of the invention be apparent from the following description of certain known constructions and of certain constructions in accordance with the present invention which is given by way of example only with reference to the accompanying drawings in which: Figures 1 and 2 are a schematic vertical section through a pair of valve plates for a rotary and linear sliding gate valve, respectively, showing theirgen- eral construction; Figure 3 is a diagrammatic scrap plan view showing the constructional proportions in a rotary gate valve of known construction with circular discharge apertures; Figure 4 is a view similar to Figure 3 showing a pair of valve plates according to a first embodiment of the invention; Figure 5 is a scrap perspective view of the plates of Figure 4 in the throttled position;; Figure 6 shows a preferred geometric form of the aperture cross-section in the plates of Figures 4 and 5; Figure 7 is a plan view of a further embodiment of a pair ofvalve plates intended for use in a linear sliding gate valve; and Figures 8 and 9 show further variants of aperture cross-sections in a pair of valve plates according to the invention for a linear sliding gate valve.

Figure 1 shows the two valve plates of a rotary sliding gate valve comprising an upper stationary base plate 1 and a sliding plate 2, which is rotatable about the central axis 3 as indicated by the arrow 10.

Each plate is provided with at least one discharge 5, 6; the sliding plate 2 can, as is known, have several discharge apertures with the same or different cross-sections. The valve plates are made from high-grade refractory material and come into contact with each other on their sliding surface 4, along which they move relative to each other when the valve is operated. The plates may be in the open position, in which the discharge apertures are aligned with each other, the throttled position, in which the apertures are partially offset and the closed position, in which the apertures are completely offset. The generally sleeve-like refractory parts 7 and 8, which are connected to the valve plates at the top and bottom and together with the discharge apertures form a pouring channel, are indicated by chain dotted lines.

Figure 2 shows the corresponding situation in a linear sliding gate valve with a stationary base plate 11 and a movable sliding plate 12. The latter is movable along the sliding surfaces 14 in the direction of the arrow 13 in order to bring the discharge apertures 15, 16 out of the illustrated closed position into the open position or a throttled position. As in the case of the rotary valve the sliding plate can be provided in a known manner with several discharge apertures offset in the sliding direction. The refractory casings 17 and 18 which are connected to the plates at the top and bottom are again indicated by chain dotted lines.

The general constructions described with reference to Figures 1 and 2 apply both to known pairs of plates for rotary or linear sliding gate valves and to plates in accordance with the present invention. Figure 3 shows the situation as regards the wear on the plates 1,2 in a rotary sliding gate valve of known construction, namely with discharge apertures 5 and 6 of circular cross-section. The two plates are shown in the closed position, in which the aperture 6 of the sliding plate is offset relative to the aperture 5 in the base plate by a distance which ensures a tight seal.

In operation, the circular edges of the apertures in the region of the sealing surfaces are subjected to the greatest wear on those parts of both apertures which are directed towards one another because these edge parts are exposed to the flowing melt from the very beginning when the valve is opened to the very end when it is closed. Experience has shown that this severe wear at the edges occurs over about half the circumference of the hole. In addition the adjoining regions of the sliding surfaces on both plates are increasingly attacked by the melt. As a result melt can be drawn in between the two valve plates during the closure movement and these small quantities of melt tend to solidify rapidly. Recent observations and tests have confirmed in fact that "metal lumps" of the approximate shape of the cross-hatched area 26 in Figure 3 are formed between the plates.Naturally, such "metal lumps" or "wedges" constitute a considerable obstacle betweLn the plates on the next opening movement as they cannot be pushed aside between the sliding surfaces, nor can they be pushed into the aperture 6 of the sliding plate due to their shape. The process is repeated and intensified with every operation of the valve and the increasing damage to the sliding surfaces makes an ever increasing overlap of the plates necessary until finally the plates are unusable.

This strong material abrasion caused by metal solidified between the plates can in many cases end the useful life of the plates much earlier than the erosion resulting from the flowing melt. The invention counteracts this tendency by the particular configuration of the cross-section of the apertures in both valve plates.

Figures 4 and 5 show a first embodiment of a pair of valve plates according to the invention for use in a rotary sliding gate valve. The plates 1 and 2 have identical discharge apertures 5' and 6' respectively.

Each of the apertures is defined by two straight wall sections 21 which intersectthe direction of relative displacement, indicated by the arc 10, at right angles, and by two further wall sections 22 which connect the ends of the wall sections 21 and extend in the direction of displacement. In a rotary valve the direction of displacement at any point is tangential, so that a wall section extending "in the direction of displacement" constitutes a part-cylindrical surface and a wall section "intersecting the direction of displacement at right angles" constitutes a radially extending planar surface. The aperture cross-section in valve plates for a rotary valve thus corresponds to a sector of an annulus. In accordance with the invention, this aperture cross-section must occur in the region where this discharge aperture opens onto the sliding surface 4. As can be seen in Figure 5, the cross-section can retain the same shape over the whole thickness ofthe plate or, alternatively may change towards the opposite side of the plate, for example into a circular shape.

The advantages of the cross-sectional shape of the discharge apertures 5' and 6' according to the invention may be seen in Figures 4 and 5 by comparison with Figure 3. When pouring in the throttled position (Figure 5), only the straight working edges of the opposed radial wall sections 21 and the adjoining surface regions 25 of the sliding surfaces 4 (Figure 5) are exposed to the melt, whilst all other edge regions, i.e. approximately three-quarters of the periphery are always covered. The adjoining eroded regions 25 of the sliding surfaces 4 are therefore much smallerthan the corresponding surfaces 26 in the case of the known round discharge openings (Figure 3).What is even more important is that in the closed position (Figure 4) the solidified "metal parts" or "tongues" formed in the region 25 have such a shape that when the valve is next opened they do not jam between the plates but are easily pushed out into the flow channel without causing damage. For the purpose of proper comparison of the surface regions 25 and 26, Figures 3 and 4 are based on aperture cross-sections of the same size and situated on the same mean radius with the same minimum distance of overlap. Figure 5 also shows that, when pouring is completed, the extent of the wear along the working edges and the adjacent surface regions can be very easily observed from the outside (in an intermediate position of the apertures roughly as shown in Figure 5), which is not so easy with round apertures.

Figure 6shows the preferred geometrical relationship of the various walls of the aperture crosssection. A balanced ratio between the width (in the radial direction) and length (in the direction of displacement) of the aperture cross-section 5', or 6', is produced when all the wall sections touch an imaginary inscribed circle 24, as shown in Figure 6. It is, however, also possible to deviate from this rule of "inscribed circle contact" in the choice of the aperture length.Thus, for example, the apertures of the base plate and the sliding plate can have a greater but equal length or the sliding plate can have several apertures with differing lengths; advantageously, however the width of the co-operating apertures in the base plate and the sliding plate are always chosen the same and naturally on the same radius so that the edges of the wall sections 22 are never directly exposed to the melt.

By way of comparison Figure 6 shows a circular cross-section 5 with the same area as that of the aperture shaped in accordance with the invention. It will be seen that the displacement path S' between the open and closed position for the plates according to the invention is shorter than the corresponding displacement path S for plates with apertures of circular cross-section. In addition the radial width of the area 5' according to the invention is smaller than that of the area 5 of the same cross-sectional area which makes it possible for the apertures in the plates of the present invention to be positioned so as to have a greater mean radius.

Figures 7 to 9 show embodimens of valve plates for a linear sliding gate valve in accordance with the invention. Figure 7 shows a pair of valve plates 11, 12 intheclosed position and having a discharge aperture 15' or 16', respectively arranged on the central axis which extends parallel to the direction of displacement 13. Each of the discharge apertures is defined by two wall sections 31 intersecting the direction of displacement at right angles and two further wall sections 32 which extend in the direction of displacement and connect the two ends of the wall sections 31. In the preferred embodiment shown in Figure 7 the aperture cross-section is a square, i.e. all the wall sections contact an imaginary inscribed circle and the length of the aperture is equal to its width.

All the statements made above in connection with Figures 3 to 6 in relation to the proportions in the rotary gate valve, and in particular the operation of the construction shown in Figures 4 and 5 in comparison with valve plates with circular discharge apertures, also apply by analogy to valve plates for a linear sliding gate valve. This results from the fact that a rotary movement with an infinitely large notional rotational radius is in fact a linear movement.

Figure 8 shows a modified construction in which the wall sections 33 intersect the direction of displacement not at right angles but at an obtuse angle, although still at the same angle. In the case of a linear gate valve the wall sections 32 and 33 then form an obtuse angled parallelogram (rhombus and rhomboid). This construction is also applicable by analogy to the discharge apertures in valve plates for a rotary sliding gate valve.

Finally, Figure 9 shows a construction in which the wall sections 31 are connected by two longer wall sections 34 extending in the direction of displacement. The rectangular cross-section thus formed corresponds to the construction in which the apertures constitute a sector of an annulus with a greater length relative to the construction in which the walls contact an inscribed circle, as already described in connection with the rotary sliding gate valve.

Claims

1. A pair of valve plates for a sliding gate valve, each plate having a sliding surface adapted, in use, to contact and slide relative to the sliding surface of the other plate and a discharge aperture passing through the plate and opening onto the sliding surface, each discharge aperture being defined, at least at the region where it opens onto the associated sliding surface, by two first wall sections which are substantially straight and intersect the intended direction of relative displacement of the sliding surfaces at substantially the same angle and by two second wall sections which connect the ends of the first wall sections and extend substantially parallel to the said direction of relative displacement.

2. A pair of valve plates as claimed in Claim 1 in which the two first wall sections extend at right angles to the said direction of relative displacement.

3. A pair of valve plates as claimed in Claim 1 or Claim 2 in which the two first wall sections and the two second wall sections each tough an imaginary inscribed circle.

4. A pair of valve plates as claimed in Claim 1 or Claim 2 in which the two second wall section each touch an imaginary inscribed circle and the two first wall sections each lie outside the said imaginary circle.

5. A pair of valve plates as claimed in any one of Claims 1 to 4 in which the cross-section of the discharge apertures is the same over the whole thickness of the plates.

6. A pair of valve plates as claimed in any one of the preceding claims in which the cross-section of the discharge apertures changes over the thickness ofthe plates.

7. A pair of valve plates for a sliding gate valve substantially as specifically herein described with reference to Figures 1,4, 5 and 6 or Figure 2 in combination with one of Figures 7 to 9 of the accompanying drawings.

8. A rotary sliding gate valve incorporating a pair of valve plates as claimed in any one of Claims 1 to 6 in which the cross-section of the discharge apertures is part-annular, at least in the regions where they open onto the associated sliding surface.

9. A linear sliding gate valve incorporating a pair of valve plates as claimed in any one of Claims 1 to 6 in which the cross-section of the discharge apertures is a parallelogram, at least on the regions where they open onto the associated sliding surface.