MXPA98000908A - Plastic valve resistant silver unit for a valve, sliding gate that is used with metal fund - Google Patents

Abstract

The present invention relates to a cracking resistant valve plate for controlling a flow of molten metal in a sliding composite valve, comprising: a refractory valve plate having a shaft, and a hole for conducting molten metal which is placed along the axis, and corners truncated to focus a clamping force towards the axis in the vicinity of the hole, in order to avoid the formation and dispersion of cracks in the same, where each of the truncated corners is orthogonal in a line that extends between a point tangent to the hole, through the axis, and through an intersection of lines that are drawn parallel to the convergent plate edges that are separated from the edges by a distance equal to half of an orific width

Description

SILVER UNIT VALVES RESISTANT TO CRACKING, FOR A SLIDING GATE VALVE THAT IS USED WITH FUSED METAL BACKGROUND OF THE INVENTION This invention relates in general to valve plates that are used in slide gate valves to control the flow of molten metal, and in particular it relates to a valve plate unit that is resistant to cracks caused by thermal tensions. Sliding gate valves are typically used to control a flow of mental melt in steelmaking and other metallurgical processes. These valves comprise a support frame, an upper stationary valve plate having a hole in coincidence with a trough nozzle or spoon for conducting a flow of molten metal, and a construction plate which likewise has a metal conduit orifice. that can move slidably below the stationary valve plate. In the slide gate valves that are used in conjunction with continuous casting molds, a lower stationary valve plate is provided below the movable constriction plate, which PlO ^ -nß MX. similar has a conductive flow orifice that is substantially aligned with the orifice of the upper stationary plate. The flow velocity of the molten metal depends on the degree of overlap of the orifice of the sliding regulator plate with the hole of the upper stationary plate. The movable regulating plate is usually longer than the stationary regulating plates in order to give it the ability to regulate the flow of molten metal, both from the front edge and from the rear edge of its own hole, as well as the ability to close the flow in a manner joint by putting your hole completely out of overlap with the holes in the stationary plate. Normally, the regulating plate is manipulated in a sliding manner between the stationary plates by means of a hydraulic linkage. The regulating plate and the stationary plates of these sliding gate valves are formed from refractory materials resistant to heat and erosion, for example aluminum oxide, alumina-carbon, zirconium oxide. However, despite the resistance to heat and erosion that these refractory materials present, the severe thermal stresses to which they are subjected eventually cause a certain degree of cracking. For example, in steelmaking, each valve plate is subjected to temperatures of approximately 2900 ° P1075-98 MX in the area immediately surrounding the conductive flow orifice, while its outer edges experience only ambient temperatures. The large thermal gradients resulting from the above create large amounts of mechanical stresses as the area of each plate immediately surrounding its orifice expands at a rate substantially greater than the plate's balance. The stresses cause cracks that form radiated outward from the hole in the plate. If nothing is done to contain the dispersion of these cracks, they may extend until they reach the outer edges of the plate, causing it to break. In order to avoid the dispersion of the cracks and the consequent breaking of the valve plates, several clamping mechanisms have been developed in the prior art. The purpose of these mechanisms is to apply sufficient pressure around the perimeter of the plate so that cracks emanating from the hole do not disperse towards the edges of the plate. In one of these mechanisms, the steel band is stretched around the perimeter of each of the valve plates. Unfortunately, applicants have observed that there are at least three disadvantages associated with the use of these band-type fastening mechanisms. First, because the steel that forms these bands is a thermal conductor ii superior to the air that otherwise surrounds the edge of the plates, the use of the steel strip actually increases the thermal gradient across the entire length and width of the plate axes, thus encouraging cracking to occur. Secondly, as the steel band is heated as a result of being in the vicinity of the molten metal, these expand much faster than the refractory material that forms the valve plates, which in turn causes the forces of the metal to relax. compression that need to be applied around the plate in order not to encourage the dispersion of cracks. Thirdly, if the corners of the plate are not rounded, these fastening bands can apply localized mechanical stresses on the corners of the plates, which in turn can cause unwanted cracking in these areas. To solve these and other problems, the fastening systems have been developed so as to comprise a frame having flanges operated by screws that engage the corners of the plate and that have been truncated at an angle that is complementary to the angle of the screws. eyelashes or wedges. While this frame and these wedge-type clamping mechanisms constitute an obvious advantage over the simple use of steel bands around the perimeter of the plates, the inventors have further noted that at least two problems arise.

P1U75-JH with this design, avoiding that the real cracking delay is achieved. In all the variations of this design known to the applicant, the angle of each of the corners truncated with respect to any of the longitudinal or transverse edges of the plate is the same, regardless of the position of the hole along the line longitudinal center of the plate. Consequently, in plates where the hole is offset along the longitudinal centerline of the plate (which includes virtually all valve plates), the clamping forces can not be focused uniformly where the maximum is presented. amount of cracking, that is, in the vicinity of the hole where most of the thermal stresses are present. Furthermore, even in cases where the hole is centrally located in the valve plate, applicants have observed that the angular orientation of the corners truncated in those plates does not optimally prevent the dispersion of the cracks, as previously thought. . These results are not optimal from the point of view that the formation of cracks is not evenly distributed 360 ° around the orifice, but rather occurs in angled form along the longitudinal centerline of all the valve plates, regardless of that are stationary or mobile. This asymmetric distribution of cracks around the P1075-PH MX.

Plate holes are believed to occur as a result of the longitudinal sliding action of the regulator plate across the faces of the stationary plates. Still other problems associated with the prior art fastening mechanisms are their use, in some cases, of less than 20 ° angle with respect to the longitudinal edges of the plate. In addition to providing inadequate clamping forces to close the cracks along the transverse axis of the plate, the use of reduced angles generates large localized stresses due to the large amount of compression that the clamping wedges apply to the truncated corners. These localized stresses can result in cracking and cracking of the corner regions of the valve plates, which is directly contrary to the overall purposes of the clamping mechanism. A final problem associated with the valve plates is, in general, their lack of optimization in the length of the truncated corners, or in the sections of the width of the plate with respect to the diameter of their orifice. While the length of the corners must be of a defined minimum size in order to avoid the production of undesired localized mechanical stresses in these regions of the plate, it must also be considered that they should not be extremely large. Obviously, there is a need for a valve plate whose corners are truncated at the corners and which optimally focus to the clamping forces in the areas most prone to cracking of the plate, in order to take as long as possible the shift of any crack . Ideally, the corners should be of sufficient length to avoid the production of undesired localized mechanical stresses at the corners.

SUMMARY OF THE INVENTION In general, the invention is a crack resistant valve plate unit which is used in a sliding gate valve which overcomes the advantages associated with the prior art or at least exceeds them to a certain degree. The unit comprises a refractory valve plate having a hole for conducting molten metal that is placed along a center line of the plate, and truncated corners to focus a clamping force towards the center line in the vicinity of the hole, so as to to avoid the formation and dispersion of cracks therein, wherein the angular orientation of each of the truncated corners varies with the position of the hole along the center line. The unit further comprises a clamping frame for applying the required clamping force to each of the truncated corners. P1 7S-9H MX.

To achieve the objective of force approach mentioned above, each of the truncated corners is orthogonal to a line that falls within an angle whose vertex is defined by a point tangent to the diameter of the hole. One side of the angle is defined by a line extending from the tangent point across the center line and through a point where the converging edges of the plate would intersect but for the presence of the truncated corner. The other side of the angle is defined by a line extending from the tangent point across the center line and through an intersection of lines drawn parallel to the converging plate edges that are separated from those edges by an equal distance to the diameter of the hole. In the preferred embodiment, each of the truncated corners is orthogonal to a line extending between the tangent point toward an orifice having the maximum diameter with which the plate can operate, through the center line and through an intersection of lines drawn parallel to the converging plate edges which are spaced apart from the edges by a distance equal to half a maximum orifice diameter. When the plate is rectangular in shape, each of the corners is truncated along a line that is orthogonal to the aforementioned line and that is P1U7 - »n MX extends through an intersection of one of the parallel lines and the longitudinal edge of the plate. The plate unit may be moved along an axis within the slide gate valve which is coincident with its longitudinal center line, or may be stationary relative to the slide gate valve. In either case, the plate includes a hole along one of its center lines, and truncated corners cut according to the same geometric formula as previously described, in relation to the first valve plate. In any case, a clamping frame is provided to apply the required clamping force on the truncated corners. In order to provide a movable valve plate unit with all the desired capacities of a closing stroke, and front and rear adjustment strokes, which are formed from a minimum amount of ceramic material, the plate of the movable unit of Preferably it is rectangular in shape and has a length between about 5.5 and 5.75 hole diameters, and a width between about 2.9 and 3.1 hole diameters. In the preferred embodiment the length and width of the movable plate are 5.66 and 3.0 hole diameters, respectively. In order to provide a stationary valve plate unit that cooperates with a P1075-9tl MX movable valve plate to provide a closing capacity, and regulating strokes of the front and rear side, the plate of the stationary unit is also configured in rectangular shape, with a length between approximately 4.5 and 4.75 hole diameters and a width of between about 2.9 and 3.1 hole diameters. In the preferred embodiment, the length and width of the stationary valve plate are 4.66 and 3.0 hole diameters, respectively. Regardless of whether it is movable or stationary, the valve plate unit of the invention provides a crack-resistant valve plate having closing and front and rear adjustment capabilities with a minimum amount of wasted ceramic material.

BRIEF DESCRIPTION OF THE DIFFERENT FIGURES Figure 1 is a cross-sectional and schematic side view of a sliding gate valve installed in a trough utilizing the valve plate unit of the invention; Figure 2 is a top plan view of the regulator plate unit of the invention; Figure 3 is a top plan view of the lower stationary plate unit of the invention; Figures 4 to 10 are views on the lower floor P1075-9T MX of the plate used in the lower stationary plate unit of the invention, illustrating a preferred method for providing this plate and the manner in which the corners of the truncated corners are determined, Figures 11, 12 and 13 are top plan views of the plates using the regulator plate unit, illustrating a preferred method for providing this plate and the manner in which the angles of these truncated corners are determined; Figure 14 is a top plan view of the upper stationary plate superimposed on the regulator plate in a closed position; and Figure 15 is the same top plan view of the plates illustrated in Figure 14, wherein the regulating plate has slid longitudinally to a rearward regulating position with respect to the stationary top plate.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES Referring now to Figure 1, wherein the reference numerals used for the components are retained in all the drawings, the invention includes a movable and stationary valve plate unit 1 which is used in a sliding gate valve 2 of the type used to regulate the flow of a molten steel or of P107r, -Q8 M? another metal from a tundish 3. The sliding gate valve l is secured on a mounting plate 5 which in turn is connected to the shell 7 of the trough by means of a mounting structure not illustrated. The valve includes a nozzle 9 formed from a ceramic material having a hole or funnel-shaped perforation 10, to direct a cylindrical flow of the molten metal out of the tundish 3. The nozzle 9 is mechanically mounted the bottom wall of the tundish 3 by means of a thermally resistant particle packing 11. The main purpose of the valve plate unit 1 of the invention is to modulate the flow of the molten metal leaving the performation 10 of the nozzle 9. For this purpose, the invention includes upper and lower stationary plate units 13 and 17, with a sliding plate unit 23 moving in a sliding manner, sandwiched between them. The upper stationary plate unit 13 includes a stationary plate 14 of ceramic material having a circular hole 15 for conducting a flow of molten metal from the perforation 10. The lower stationary plate unit 17 also has a stationary plate 18 of refractory material with a hole 19 that is the same size as the hole of the upper stationary plate 14 and is aligned P1075-98 MX concentrically with it. Preferably, the upper and lower stationary plates, 14 and 18, have the same width length. On the lower surface of the lower stationary plate 18 is mounted a tube adapter 20 which can be used, for example, to direct a flow of molten steel towards a continuous casting mold. The tube adapter 20 includes a tube mounting plate 21 which is integrally connected to a tube skirt 22. A mounting unit (not shown) secures the plate 21 of the tube adapter 20 in the position illustrated in Figure 1. The tube adapter 20 isolates the modulated flow of the liquid metal leaving the valve plate system 1, from the ambient air, in order to prevent the ambient oxygen from reacting with the molten mental. The regulator plate unit 23 is slidably mounted between the upper and lower stationary plate unit 13 and 17. The regulator plate unit 23 in turn includes a plate 24 formed of a ceramic material having a hole 25, which may be circular and the same diameter as the orifice 15 of the upper stationary plates 14. The hole 18 of the lower stationary plate 18 is larger than the holes 25 and 15 in order to prevent entrapment of the steel in the regulating plate 24 during the operation of closing. However, in order to make the valve plate system 1 have the capacity H07r.- "" MX regulator on the rear edge as well as a front and closing edge regulating capacity, the regulating plate 23 is longer than the upper and lower stationary plates 13 and 17. During the operation of the sliding gate valve 2, the regulating plate 24 moves in a sliding and reciprocating manner by means of a hydraulic linkage (not shown) along an axis A corresponding to the longitudinal centerlines of the plates 13, 17, and 24. In relation to Figure 2, the corners truncated 30a-d are provided in the regulator plate 24 with a generally rectangular shape, in order to focus the clamping forces near the hole 25 along the longitudinal center line 92 (which is collinear with the A axis shown in Figure 1) . A steel band hook 31 is provided in tension around the perimeter of the regulating plate 24 in order to improve the integrity of the plate 24. Both the plate 24 and the band 31 are surrounded by a holding frame 33 which applies forces of considerable compression clamping in the aforementioned truncated corners 30a-d. For this purpose, the holding frame 30 has a stationary holding member 35 with opposite clamping legs 37a, b and is aligned at the same angle with respect to the truncated corners 30a, b on the left side of the plate 34 for P1075-98 MX. avoid generating localized stresses. The holding frame 33 further includes a pair of parallel, spaced frame legs 39 to which a movable holding unit 41 is attached. The unit 41 includes a movable holding member 43 which in the same manner has opposing clamping legs 45a , b which are positioned at the same angle as the truncated corners 30c, d present on the straight side of the plate 24. A clamping screw 49 extending through a performation (not shown) in the clamping support member 47, threadedly engages another bore (not shown) in the movable holding member 43, so that when the screw 49 is rotated, the holding legs 45a, b of the movable holding member 43 engage the truncated corners 30c, d on the right side of the plate 34. This operation in turn causes the holding legs 37a, b of the stationary holding member 35 to apply clamping pressure on the truncated corners 30a, b on the left side of the plate 24. Since the two upper and lower stationary plate units 13 and 17 are essentially identical in the salient aspects, only the lower stationary plate unit 17 will be described in order to avoid repetitions. In relation to Figure 3, the plate unit P1075- '~ > "Lower MX 17 includes a lower stationary plate 18 having a hole 19, which can be circular and identical in diameter to the hole 25 of the regulator plate 24. Like the regulator plate 24, the stationary plate 18 has truncated corners 54a- d for focusing a clamping force along the longitudinal center line 70 of the plate near the vicinity of the hole 19. The lower stationary plate unit 17 further includes a clamping frame 58 for applying clamping forces on the truncated corners 54a-d. For this purpose, the clamping frame 58 includes a rectangular frame unit 59 (illustrated in dashed lines) containing, at its left end, a stationary clamping member 60 having clamping legs 62a, b working in the Same shape as the legs 37a, b described in relation to the holding member 35. The frame unit 59 further contains, on its right side, a movable holding member 64. The holding member 64 includes a holding leg 66a, b which can be engaged by compression against the truncated corners 54c, d of the plate 18, by rotating the clamping screw 68 operating in the same manner as the previously described screw 49. In all cases, the corners of the truncated corners 54a- d and the clamping legs 62a, b and 68a, b are the same so that a contact is made in a wide area between P1075-98 MX these components, thus avoiding localized stresses that would otherwise cause unwanted cracks in the plate 18 at the corner locations. Figure 4 illustrates how the longitudinal and transverse dimensions of the preferred embodiments of each of the stationary plates 14 and 18 are determined as a function of the maximum diameter D of the hole 19 with which the plates can operate (as a practical matter). In order to adjust the closing position with respect to the regulating plate 18, the length of the upper half of the plate 18 from the center point of the hole 19 must be able to adjust the closing stroke Ss of at least 1.5 hole diameters. Although theoretically it is possible for a closing stroke to be only slightly larger than a single hole diameter, this dimensioning scheme would not take into account the substantial elongation that occurs in the hole 19 along the longitudinal centerline 70 of the Plate 18, due to erosion. Therefore, as a practical matter, the closing stroke must be at least 1.5 hole. This stroke would place the orifice 25 of the regulator plate 24 in the position illustrated in dotted lines at the top of the plate 18. In order to have a sufficient amount of the plate in the longitudinal direction to support the developing plate P1075-98 MX 24, when this has reached the closing position illustrated in dashed lines, it is necessary to have an additional length D of the stationary plate beyond the center point of the hole 25, causing the total length of the plate 18 to from the center of the hole 19 is 1.5D + ID = 2.5 D. In determining the remaining length of the stationary plate 18 from the center of the hole 19, it is necessary to consider only a rear regulating position between the hole 19 in the stationary plate and the orifice 25 'of the regulating plate 24, since it is not necessary for the plate 18 to fit two separate closing strokes. Accordingly, the bottom bottom length of the plate 18 is .66D (which allows the orifice of the regulating plate 25 'to reach the maximum rear throttle position illustrated in Figure 4), plus an additional plate length. equal to 1.5 hole diameters, so that the stationary plate 18 provides sufficient support for the regulator plate 24 within the structure of the slide gate valve 2. Therefore, the bottom half of the plate must be of a total of 0.66D + 1.5D = 2.16D. When combining the two halves of the plate, the total length of the stationary plate 18 (as well as the upper stationary plate 14) should be 2.16D + 2.5D = 4.66D. In order that the P1075-98 MX stationary plate 18 has a sufficient width within the sliding gate valve 2 to have sufficient structural strength to withstand the mechanical forces applied to it, from a stream of molten steel, and to provide the suitable surface for A pipe plate or a well nozzle, the plate width 18 should be 1.5 hole diameters on both sides starting from the center line of the hole 19, making a total width of 1.5D + 1.5D = 3.0D. While the lengths and widths of the plates have been expressed in terms of maximum orifice diameter, the same methodology can be employed to express these dimensions in terms of the maximum orifice width in the cases where the orifices are not circular. Turning now to Figures 5, 6 and 7, and referring to the description of the method that is used to determine the angles of the truncated corners 54a-d, the first step of the method for determining the angle is to provide construction lines as length of the internal perimeter of the plate 18, which are parallel but are separated from the outer edges of this plate by a distance to the middle of an orifice, or 0.5D. These construction lines are illustrated in Figure 5 as lines 72a-d .. These lines intersect at the corners P1075-98 MX 74a-d as shown. Figure 6 illustrates the next step of the method for determining the angle. Here, the lines 78a-d are drawn between the corners 74a-d of the construction lines and the tangent points 76a-d with a hole 19 of maximum diameter, wherein each of the lines 78a-d crosses the longitudinal centerline 70. The next step of the method determines not only the angle but the length of the truncated corners. In this step, the lines 80a-d are drawn to be perpendicular to the tangent lines 78a-d and intersect the horizontal construction lines 72b, d. These lines 80a-d are used as guides for a corner cutting operation of the rectangular refractory plate 18 to reach the truncated corners 54a-d. Figure 6 also illustrates a more generalized method wherein the angle of the truncated corners 54a-d can be determined. In this generalized method, the construction segments 82a, b (each of which is an orifice diameter D in length, regardless of whether or not the orifice used in the plate is the maximum diameter) are drawn at right angles to each other. the length and width of the plate to form a square like the one shown. In this step of the more generalized method, the angle of the truncated corners 54a-d in any line that falls within the angle B defined in its vertices by the tangent point P1075-98 MX 76c, and on one of its sides by a line extending through the intersection 84 of the aforementioned segments 82a, b and on its other side by the intersection 86 of the converging longitudinal and transverse edges of the plate 18, before the truncation. Any of the lines within angle B can be used to create a truncation angle by constructing a line at right angles to any of these line families. Each of these at a right angle should extend through the intersection of the horizontal construction lines 72b, d so that the length of the truncated corners can be determined as well as the angle. Figure 8 illustrates a plate 18 whose corners 54a-d have been truncated according to the most specific embodiment of the method, wherein the lines at right angles to the tangent lines 78a-d are used to determine the specific truncation angles. After the corners have been truncated in this way, they are preferably curved at their ends, as illustrated in number 90 of Figure 9. This rounding off of the corners helps to avoid the generation of localized stresses in the corner regions. of the plate 18. Figure 10 illustrates the final product of the method of proportioning and truncation of the corner of the invention. In particular, it should be observed as a width P1075-98 MX of 3.0D of the plate 18 allows to accommodate the tube adapter 20, with a mounting plate 21 which is of 2.5 hole diameters in both length and width. Figures 11 to 13 illustrate a method that can be used to determine both the length and width proportions of the regulator plate 24 relative to a maximum orifice diameter D, as well as the angle at which the corners 30a-d should be truncated. In relation to the upper half of the regulating plate 24, the closing stroke requires, as in the case of the stationary plate 18, at least 1.5D maximum orifice diameters or 1.5D. Another 1.50D of refractory plate should be added beyond the center of the position of the hole 19 of the stationary plate 18 in the closed position to provide sufficient plate length for coupling and manipulating the hydraulic linkage. Accordingly, the length of the upper half of the regulator plate 24 should be 1.5D + 1.5D = 3.0D. Returning now to the lower half of the plate 24, in order to adjust a rear regulating position, at least two thirds of an orifice diameter or 0.66D are required. In addition, at least 2 diameters of length are required beyond the rear regulating position, both for a suitable support and for a suitable seal surface to prevent unwanted suction between the plates. By P1075-98 MX therefore, the total length of the lower half of the regulating plate must be 0.66D + 2.0D for a total of 2.66D. Addition of the upper and lower halves of the regulator plate 24 together makes the total length to be 3. OD + 2.66D = 5.66D. The width of the plate is determined in the same manner as for the stationary plate 18 in relation to ease and manufacturing compatibility. Accordingly, the width of the regulator plate 24 is 1.5D + 1.5D = 3.0D. Turning now to Figure 13, the angle of the truncated corner 30a-d of the regulating plate 24 is determined precisely with the same methodology described in relation to the stationary plate 18 (and in particular to Figure 6). Consequently, there is no need to repeat the details of this stage of the method. It should be noted that, in addition to the specific method in relation to Figure 6, wherein the angle of the truncated corners is determined by the lines constructed at right angles to the tangent lines described above 78a-d, the generalized method step described with relationship to the upper right corner of plate 18 in Figure 6, can also be applied to the corners of the regulator plate 24. While the invention has been described within the context of a single preferred embodiment, it will be evident P1075-98 MX for those with experience in this field that can be made various modifications, additions and variations. All these modifications, additions and variations are intended to be within the scope of the present invention, which is limited only by the appended claims.

P1075-98 MX

Claims (15)

1. NOVELTY OF THE INVENTION Having described the present invention, it is considered as a novelty and, therefore, property is claimed as contained in the following CLAIMS I 1. A cracked valve plate to control a flow of molten metal in a sliding gate valve, comprising: a refractory valve plate having a shaft, and a hole for driving molten metal which is positioned along the axis, and truncated corners to focus a clamping force towards the shaft in the vicinity of the hole, in order to prevent the formation and dispersion of cracks in it; where each of the truncated corners is orthogonal in a line extending between a point tangent to the hole, through the axis, and through an intersection of lines that are drawn parallel to the converging plate edges that separate of the edges at a distance equal to half of a hole width.
2. 2. The crack-resistant valve plate according to claim 1, wherein each of the corners is truncated along a line that is orthogonal to the line and extends through an intersection of one of P1075-98 MX the parallel lines and one edge of the plate.
3. 3. A cracking resistant valve plate unit for controlling a flow of molten metal in a slide gate valve, comprising: a generally rectangular valve plate having a longitudinal center line, the plate includes a circular hole having a center placed on the longitudinal center line, to conduct a flow of molten metal, and truncated corners to focus a clamping force towards the center line in the vicinity of the hole to avoid the formation and dispersion of cracks in it, in where the angular orientation of each of the corners truncated in relation to the center line varies with the position of the hole along the center line.
4. 4. The crack-resistant valve plate unit according to claim 3, further comprising a clamping frame means for applying the clamping force to each of the truncated corners.
5. The crack-resistant valve plate unit according to claim 4, wherein each of the truncated corners is orthogonal to a line that lies within an angle whose apex is defined by a point tangent to the hole, and one of which sides is defined by a line that extends from the tangent point, through the center line, and through a point where P1075-98 MX the longitudinal and transverse edges of the plate would intersect if not for the presence of the truncated corner, and the other side of the angle is defined by a line extending from the tangent point, through the center line and through an intersection of lines drawn parallel to the longitudinal and transverse edges that are separated from the edges by a distance of a hole diameter.
6. The crack-resistant valve plate unit according to claim 5, wherein each of the truncated corners is orthogonal to a line extending from the tangent point, through the center line and through an intersection of lines which are drawn parallel to the longitudinal and transverse edges which are separated from the edges by a distance equal to half of a hole diameter.
7. The crack-resistant valve plate system according to claim 6, wherein each of the corners is truncated along a line that is orthogonal to the line and extends through an intersection of one of the lines parallel and a longitudinal edge of the plate.
8. The crack-resistant valve plate unit according to claim 3, wherein the valve plate unit can be moved within the valve as P1075-98 MX long of the center line and has a length of 5.66 hole diameters ± 0.1 hole diameter.
9. 9. The crack-resistant valve plate unit according to claim 8, where the valve plate has a width of 3.0 hole diameters ± 0.1 hole diameter.
10. The crack resistant valve plate unit according to claim 3, wherein the valve plate unit is stationary within the valve and the length of the refractory plate is 4.66 hole diameters ± 0.10 hole diameter.
11. The crack-resistant valve plate unit according to claim 10, wherein the width of the refractory plate is 3.0 hole diameters ± 0.10 hole diameter.
12. 12. A cracking resistant valve plate unit for controlling a flow of molten metal in a gate valve, comprising: a refractory valve plate having a shaft and a hole for driving molten metal that is placed along the axis, and corners truncated to focus a clamping force towards the center line in the vicinity of the hole to prevent the formation and dispersion of cracks in it; where the angular orientation of each of P1075-98 MX the corners truncated in relation to the center line varies with the position of the hole along the axis. The crack-resistant valve plate unit according to claim 12, further comprising a clamping frame means for applying the clamping forces to each of the truncated corners. The crack-resistant valve plate unit according to claim 12, wherein the hole is also positioned along a center line of the plate, and the truncated corners focus the force toward the center line in the vicinity of the hole . The crack-resistant valve plate unit according to claim 12, wherein each of the truncated corners is orthogonal to a line that lies within an angle whose apex is defined by a point tangent to the hole, and one of which sides is defined by a line extending from the tangent point, through the axis, and through a point where the converging edges of the plate would intersect but for the presence of the truncated corner, and the other side of the angle is defined by a line extending from the tangent point, through the axis and through an intersection of lines drawn parallel to the converging plate edges that are separated from the edges by a distance equal to one hole width . P1075-98 MX