Louvered Screen Support Member For Particulate Material

Abstract

Louvered screen support member for particulate material and especially for ceramic catalyst pellets provides increased resistance to bending in one direction by having vanes which define the louver openings torqued from the plane of a metal sheet in such a way that one lip edge of the vane extends above one side of the metal sheet less than the thickness of the sheet and the other lip edge of the vane extends below the opposite side of the metal sheet less than the thickness of the sheet. The vanes are formed by a punching operation so that the lip edge is elliptically curved in the plane of the edge on one side of the sheet so as to prevent the catalyst pellets from becoming uniformly aligned, and straight on the other side so as to define as large an opening between adjacent vanes as possible. Circular segments formed at the ends of the louver openings eliminate localized stress concentrations which could produce fatigue failure under conditions of severe vibration.

Parent Case Text

BACKGROUND OF THE INVENTION

The present invention relates to an improved louvered screen support member for supporting particulate material, and especially, for supporting ceramic, catalyst coated pellets in a catalytic converter, and is a Continuation -in-Part of Ser. No. 126,816, filed Mar. 22, 1971, now abandoned.

It is generally known that a screen member having louver fins or vanes formed integrally with a flat sheet body member provides resistance to bending in the direction along the length of the fins. Screen members incorporating this principle are widely used for ventilation purposes where the fins not only keep out insects and prevent the entry of rain or sunlight but provide a degree of strength which permits very thin material to be used. Prior art examples of such thin, light deflecting and ventilating screens can be found in U.S Pat. Nos. 2,366,224 and 2,430,518 which disclose fins which are struck out of a thin sheet metal body in such a way as to extend outwardly from both sides of the sheet at a substantial angle.

While thin louvered screens are suitable for ventilation, they would be quite useless as a catalyst support surface in a catalytic converter used to reduce the amount of exhaust pollution emanating from an automobile or other device utilizing an internal combustion engine. One general form of catalytic converter contains loose catalytically coated ceramic pellets which are retained on a screen surface. Typically, the screen surface has elongated slotted openings punched out of a flat surface, with the openings being of smaller transverse dimension than the diameter of the pellets. To lend rigidity to such flat screens, even in relatively small sizes, such as those having a diameter of 5 inches, reinforcing ribs have been welded to the side of the screen which does not contact the catalyst. The welded ribs increase the cost, thickness and weight of the screen and reduce its free area. It has been shown that the environment inside a catalytic converter cna be quite brutal to the parts thereof, and particularly to the support screens which contact the catalyst. When the engine misses, or when it is accelerated, it passes a quantity of unburned fuel into the converter. As the converter reacts with this fuel it becomes extremely hot, sometimes upwards of 2,000.degree.F. In this heat range, the material of the screens, typically stainless steel, is less strong than it is at lower temperatures. It is therefore more susceptible to fatigue failure arising from even the slightest stress concentrations such as those in the vicinity of the stiffening rib welds. The possibility of fatigue failure is especially great due to vibrations when the engine is rapidly accelerating or maintained at a high speed. The exhaust stream is always pulsing when it contacts the inlet screen since it is produced by distinct explosions in the cylinders. However, as the engine speed increases and drives more exhaust gases into the catalyst, the back pressure produced by the catalyst bed can increase sufficiently so as to cause the screen to tend to move forward and backward at the same pulsing rate as the incoming gas stream. Obviously, to have any metal screen survive such an environment for a prolonged period requires that the screen be as free of stress concentrations as possible. It would also be desirable for the screen to be easily and economically manufacturable, non-abrasive to the fragile catalyst pellets, as open as possible to permit the free flow of gases through the converter, and shaped so as to minimize blockage of the screen openings by the catalyst pellets.

SUMMARY

The preceding problems are quite effectively solved by the catalyst or other particulate material support screen of the present invention which comprises a relatively thick sheet of metal, preferably stainless steel, which has a plurality of elongated openings formed by bending portions of its surface. The openings are formed by shearing the metal in short segments along a series of parallel lines and simultaneously twisting or torqueing the metal segments defined by each succeeding adjacent pair of cut lines so as to produce a series of parallel vanes which, at their centers, are located at about a 30.degree. angle to the plane of the metal sheet. By the use of appropriate cutting and forming members, the edge portions of the vanes which extend outward from the plane of the sheet to form the catalyst pellet engaging side of the screen are formed so as to have an elongated, elliptically curved edge profile in the plane of the edge while the edge portions of the vanes which extend outward from the opposite side of the screen have an elongated, straight edge profile in the plane of the edge. The provision of a curved profile at one edge of the vanes and a straight profile at the other edge is, for several reasons, of substantial significance in achieving a support screen which will perform effectively for an extended period. The elliptically curved edges provide a constantly changing opening dimension which prevents the catalyst pellets from assuming a uniform state of repose against the louver opening, thus providing for optimum passage of gases around the pellets and thence through the louver opening. By having a straight edge profile defining one side of a louver opening and a curved edge profile defining the other side, a large opening area can be achieved, for the same vane angle, than if both edge profiles were curved.

In forming the louver screen, the tools used to cut and form the louver openings start cutting at the center of the opening and then cut progressively toward the ends. This method of gradual generation of the openings insures that localized stress zones at each end of the lanced openings will be minimal as compared to the situation where the cutters are acting along the entire length of the opening at one time. Furthermore, the cutters coact so as to produce smooth, slightly rounded burr-free edges on the catalyst contacting curved profile side of the screen. The burr-free edges are of course quite desirable since they prevent damage to the fragile ceramic pellet which contact the screen and which are vibrated against it by road shocks as well as by the continual pulsing of the exhaust gases. The burr-free edges also eliminate the necessity of deburring the edges, an operation which would not only be expensive but which could introduce tiny points of localized stress concentration which could result in premature fatigue failure of the screen.

In a modification of the invention, the louver openings are formed so as to include a circular segment at each end. The circular segments improve the resistance of the support screen to fatigue failure by eliminating the very small stress concentrations which naturally exist at the ends of the openings despite the progressive forming operation and the minimal torqueing applied to the vanes at their ends.

It is not intended to limit the louvered, particulate matter supporting screen to a specific type of construction material inasmuch as such screens may be formed from various types of deformable metals such as steel, aluminum, brass, copper, galvanized sheet metal, and the like. When the particulate matter to be supported is to be subjected to a high temperature oxidizing environment, as would be the case with catalyst pellets in a catalytic converter, the screen material would obviously have to be able to withstand the temperature.

Since the torqued vanes extend outwardly from each side of the plane of the metal sheet, each vane assumes the nature of an angularly positioned rib or beam structure with outer edge portions spaced from its neutral axis to thereby provide an increase in moment of inertia, or radius of gyration, thus increasing the resistance of the sheet to bending in the direction of the length of the louver openings and greatly increasing its ability to carry a given loading in a rectangular configuration which has its longest sides parallel to the openings.

As previously mentioned, it is extremely important when the screen is to be used in an environment subject to vibration that stress concentrations be reduced. The degree of torqueing of the vanes relative to the plane of the sheet material is, accordingly, preferably limited to an angle of about 30.degree.-35.degree.. This rather small angle minimizes the formation of stress concentrations in the metal and forms a cradle-like support for the supported pellets or other particulate matter which prevents them from passing through the louver openings of being abraded by sharp corner portions of the vane edges. To provide maximum strength and protection for particulate material supported by the screen, the louvered screen should have a thickness no greater than about three times the thickness of the screen material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a plan view of the non-particulate matter supporting side of a louvered screen support member having torqued vane members defining the louvered openings;

FIGS. 2, 3, and 4 are sectional views through the support member of FIG. 1 taken on lines 2--2, 3--3 and 4--4 of FIG. 1 and 4--4 of FIG. 3;

FIGS. 5 and 6 indicate diagrammatically the edge configuration of the torqued vane members and the louver openings defined thereby, as viewed angularly in accordance with lines 5--5 and 6--6 in FIG. 3;

FIGS. 7 through 10 indicate diagrammatically, and in a step wise manner, a method which may be utilized for forming the torqued vane members and the resulting louvered sheet wherein the edge or lip portions of the torqued vanes have one lip edge portion extending above one side of the sheet and a second lip edge portion extending below the other side of the sheet;

FIG. 11 is a perspective view of a modified form of louvered sheet shown in contact with representative rows of catalyst pellets;

FIG. 12 is an enlarged sectional view taken on line 12--12 of FIG. 11; and FIG. 13 is an enlarged sectional view taken on line 13--13 of FIG. 11.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now particularly to FIGS. 1 through 4, there is indicated a louvered sheet of material 1, as an article of manufacture, which has a plurality of louvers or openings 2 that are in turn formed by spaced twisted or torqued vanes or louver pieces 3. As best shown in FIG. 2, 3 and 4, it will be observed that each fin or louver piece 3 has an edge or lip portion 3' which is raised above the face of one side of the sheet material 1 while, at the same time, an opposing edge or lip portion 3" will be twisted in a manner to extend beyond the face of the opposite side of the sheet material. It will also be noted in both FIGS. 2 and 4 that a major portion of the lips or edges 3' will have a relatively straight edge alignment parallel with the sheet material 1 while with respect to edges or lips 3" there is a continuous curve providing a maximum distance of the lip portion from the sheet material 1 at the zone opposite the center of each louver opening 2.

In view of the differing edges or lips provided for the fins or louvered pieces 3, it will be noticed that in FIG. 5 or the drawing there is a substantially flat leading edge portion 3' in turn leading into the opening 2 for the louvered sheet 1. At the same time, as shown by FIG. 6, upon viewing the louvered sheet 1 from the opposing face, the curved edge of lip portion 3" provides for a curved inlet portion to each of the plurality of louver openings 2.

With respect to forming the improved louvered sheet with the torqued form of fins between louvers, there may, of course, be varying methods for forming the louvered sheet as an article of manufacture. For example, as noted hereinbefore, where the sheet material is of plastic or other moldable composition, the twisting or torqueing of the fin members 3 may be accomplished by the molding operation or optionally by a cutting and thermosetting operation. On the other hand, where the louvered screen material is to be supplied from a deformable material, such as of sheet metal, then the method of forming may be in accordance with the diagrammatic procedure illustrated in FIGS. 7 through 10. Specifically, there is shown diagrammatically in FIGS. 7 and 8 the initial relative positions of material 1' and an upper cutter member 4 and a lower torqueing and forming member 5. Also, as best shown in FIG. 8, there may be utilized holding members 4' on each side of cutter means 4 which move with cutter means 4 and additional spring biased holding means 5' on each side of forming means 5 which can move relative to the forming means 5 whereby the sheet material 1' can be held in place as the cutter means 4 and forming means 5 continue their operations. In FIG. 9 of the drawing, there are indicated further movements for both the cutter means 4 and forming means 5, with the cutter means 4 having passed through and initially lanced the material 1' prior to the forming means 5 passing beyond the face of the material 1'. At the same time, it can be seen that the sloping faces of cutter means 4 and forming meand 5 will provide for forming each fin member 6 as provided by adjacent cuts in the sheet 1'. In a subsequent movement, forming member 5 will be pushed toward an opposing cutter member 4 to complete the twisting and forming of fin member 6 into a desired position. Specifically, as best shown in FIG. 10 there is shown tne completed passage of forming means 5 through the depth of sheet material 1' and after cutter members 4 have made the initial lancings into the sheet material 1', whereby each of the fins or louver pieces 3a will be caused to be twisted and torqued into the desired angular positions.

Typically, there will be a plurality of louver openings in any one group, or in any one row on a sheet, and as a result, there is the utilization of a plurality of adjacent cutter members 4 and a plurality of opposing forming members 5 as illustrated in part in FIG. 10 of the drawing. Also typically, as indicated in FIG. 10, there will be an additional cutter member required at every group of louvers as compared to the number of forming members 5. In other words, where four louvers are to be provided in any one group through a sheet material, there will be five cutter members 4 and four forming members 5, with the latter being in alignment with four of the cutter members.

In connection with the present drawing, attention is particularly directed to FIG. 8 wherein there is the illustration of a curved leading 4" for the cutter member 4 as compared with a straight edge portion 5" on forming member 5 whereby there will be resulting different formations to opposing edge portions of a vane and varying inlets to the louver openings 2 as best shown by the configurations illustrated with respect to FIGS. 5 and 6. It can be readily seen that the cutter member 4 will initially contact the metal member 1 at a point, rather than along a line, thus progressively cutting and forming the metal from the center of the opening towards the ends.

Referring to FIG. 11, a modification of the louver screen shown in FIG. 1 can be seen with the curved or catalyst supporting side uppermost. The louvered screen member 10 includes a plurality of louvered openings 12 defined by vanes 13 having curved upper end edges 13" and straight lower end edges 13'. The ends 12' of each louver opening 12 are formed in a semi-circular shape, preferably by punching holes in the member 10 prior to torqueing the metal to produce the vanes 12. The openings in the ends 12' serve to prevent stress concentrations from arising at the ends of the openings 12 due to the slitting and bending of the louver vanes 12 relative to the louver sheet material.

Referring to FIGS. 11 though 13, it will be evident that the curved vane edges 13" which extend up from the support sheet 10 will cooperate with adjacent vane side portions 13'" and catalyst pellets 15 resting on the sheet to cradle and support a row a of pellets resting at the inlet to opening 12. The side portions 13'" also support a row of pellets b which is spaced from the opening 12 by the row of pellets a so that the pellets in row b will lie on a curved line. The non-uniform state of repose assumed by the row b pellets permits better flow of exhaust gases through the openings 12 than if the rows of pellets were parallel as they would be if they rested on the opposite side of the screen 10.

The pellets 15 are shown in FIG. 12 as having a diameter approximately 50 percent of the pitch distance or spacing between adjacent vane segments 13. This size pellet has proved to be quite satisfactory although, pellets may range in size from about 35 percent to 75 percent of the vane pitch and still retain a tangential contact with both the surfaces 13". Dotted pellets 15' and 15" illustrate the contact geometry of smaller and larger particles. Although the pellets are illustrated as uniform spheres, they are actually of slightly obloid shape and of somewhat varying dimensions.

Claims

I claim as my invention:

1. A louvered screen support member for retaining particulate material having a plurality of adjacent, elongated louver type openings therein, said openings being defined by the elongated edges of torqued vane members which are integrally attached at their ends to the support member and rotationally torqued about an axis in the plane of the support member so as to have a longitudinal vane edge extending outwardly from each side of the plane of the support member, the vane edges on one side of the plane of the support member being continuously curved away from the plane of the sheet and projecting outwardly therefrom and the vane edges on the other side of the plane of the support member being substantially linear throughout their extent and projecting outwardly from the plane of the sheet.

2. A louvered screen support member in accordance with claim 1 wherein said vane members are torqued to a position relative to the plane of the screen support member by an amount no greater than that which would cause any portion of the vane member to be displaced from the plane of the screen support member by a distance equal to the thickness of the screen support member.

3. A louvered screen support member in accordance with claim 2 wherein said vane members are torqued to an angle relative to the plane of the screen support member which is no greater than 34.degree..

4. A louvered screen support member in accordance with claim 1 wherein said vane members are spaced from each other by a predetermined pitch, said vane members being sufficiently thick and of such an angle relative to the plane of the support member so as to be capable of supporting particulate matter on its first side in a range of diameters between about 35-75 percent of said pitch so that any of such particulate matter which is supported by a pair of vanes so as to bridge one of said openings will be in contact with a flat planar side surface of one vane of said pair of vanes and with a flat planar edge portion of the other vane of said pair of vanes.

5. A louvered screen support member in accordance with claim 1 wherein said support member includes a semi-circular opening defining the end of each of said louver openings.

6. A louvered screen support member in accordance with claim 1 wherein the maximum width of the louver openings is less than twice the thickness of the vane members.

7. A louvered screen support member in accordance with claim 1 wherein the maximum width of the louver openings is less than the thickness of the vane members.