US3123446A - Porous wall construction - Google Patents

Description

March 3, 1964 H. L. WHEELER, JR

POROUS WALL CONSTRUCTION Filed Aug. 25. 1958 mm k AY" "188mm s" "Hmmm vmut`s""` 2710.3 2

United States Patent C) 3,123,446 PGRUS WALL CONSTRUCTIN Harry L. Wheeler, lr., La Canada, Calif., assignor to California institute Research Foundation, Pasadena, Calif., a corporation of California Filed Aug. 2S, 195e, Ser. No. 756,912 9 Clain (fil, 2-9-183) This invention relates to porous wall construction and is a 'continuation-'impart of my copending application Serial No. 335,670, filed February 9, 1953, now abandoned, for Porous Wall Construction ,and Method of Manufacture. included in the objects of my invention First, to provide a porous wall which may be made tubular in form or tapered or which may be reformed from such initial shapes into asymmetrical form or cut and reformed into a sheet.

Second, to provide a porous wall construction wherein the pore spaces may be accurately controlled so that not only is the construction of uniform porosity, but the size, direction and tortuousness of the pore spaces may be accurately predetermined so as to meet specific needs; that is, the pores may be normal to the wall surface, inclined, varying in area, or of a labyrinth nature.

Third, to provide a porous wall construction which may have a controlled variation in porosity to predetermine relative flow of fluids within different areas.

Fourth, to provide a porous wall construction through which a fluid may be introduced to serve as a coolant or a fuel and in either case maintain a protective boundary layer.

Fifth, to provide a porous wall construction which may be made sufficiently thin and large enough in area to permit its use as an aerodynamic surface, to serve, for example, for boundary layer control or removal.

Sixth, 'to provide a porous wall construction which may be arranged to function as an effective filter.

Seventh, to provide a porous wall wherein a plurality of layers or lamin-ations of wires are formed on a mandrel by wrapping wire under tension helically back and forth along a mandrel, whereupon the wire is heated to fuse and bond the wire at cross points, the mandrel being treated to avoid bonding with the wire, and wherein the body formed rby the wire is then removed from the mandrel and pressed between rollers or the like to compress the wires comprising the wall, particularly at and adjacent the cross points, and whereupon the wire body is again heated to effect further fusion and bonding of the Vflli.

With the above and other objects in View' as may appear hereinafter, reference is directed to the accompanying drawings in which:

FIGURE 1 is an enlarged fragmentary plan view showing a pair of laminations of a typical porous wall constructed according to this invention.

FlGURES 2, 3 and 4 are fragmentary sectional views taken tln'ough 2 2, 3--3 and tr- 4, respectively of FlGURE l.

FIGURE 5 is a greatly exaggerated, fragmentary' plan' view showing one form of porous wall constructed according to this invention. j

FlGUE 6 is an idealized, sectional View thereof taken through 6--6 of FIGURE 5 `FEE- EURE 7 is a similar sectional view thereof taken through 7 7 of FIGURE 5.

FGURE 8 is an exaggerated, fragmentary, plan" View taken substantially along the line S-S of FlGURE 9 showing successive layers of another form of the porous wall construction.

FIGURE 9 is a transverse', sectional view thereof through 9--9 of FIGURE 8.

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FIGURE 10 is an exaggerated, sectional view similar to FIGURE 6 by showing a modified form of the porous wall vconstruction in which the porosity varies between the two surfaces of the wall construction.

FIGURE 11 is a fragmentary, sectional View indicating diagram-medically an arrangement of pore spaces tending to induce tangential flow of fluid.

FIGURE 12 is a diagrammatical, sectional `view of the wall construction las it :appears when flat and arranged with the pore spaces sloping relative to the surfaces of the wall construction.

FIGURE 13 is a diagrammatical View showing two layers of wire comprising the wall construction in juxtaposition before heating and bonding.

FIGURE 14 shows these wires as they bond together in the course of heating.

FIGURE l5 is a fragmentary, sectional View similar to FIGURE 14 showing the wires coated or plated.

FIGURE 16y is a similar view showing the coated wires after bonding wherein the coating of adjacent wires is fused together.

ln the exercise of this invention, one or more fine wires 1 are wound under tension on to a mandrel having the shape of the finished object or a shape from which the finished object can be developed. Essentially such a mandrel is a figure of revolution such as a cylinder, cone, or more complex shape such as a venturi throat. By controlling the manner in which the wire is wound on the mandrel and by controlling the cross section of the wire itself, a porous wall may be constructed, the porosity of which may be uniform, or, if desired, non-uniform, or graduated, but in any case the porosity is predictable to a close degree.

The wire Iis wound on a mandrel capable of withstanding the bonding temperature of the material comprising the wire' l. Thus the mandrel may be formed of ceramic material lor formed off metal and Ycoated with a ceramic material or otherwise treated so that its surface will not bond with the wire 1. After the wire has been wound to `form a plurality of 'laminations the mandrel with the wire thereon, is subjected to bonding temperatures lcausing the contacting surfaces of the laminations of Wire to' zfuse together under the influence of pressure resulting from tension.

While the wire may have a wide Variety of cross sectional conligurations such as circular, rectangular, or ellipsoifdal' cross section, it has been found that a relatively flat wire is advantageous; for example, a wire flattened to ya thickness-to-width ratio of two to one or more. This may be accomplished by running the wire between rollers either prior to winding or in the course of the winding the wire on the mandrel. The flat configuration provides a maximum area over which the successive laminations of wire are in pressure Contact and thus insures an adequate area to be bonded when heated.

The cross sectional area of the wire l varies with the intended use and size of the mandrel on which it is wound. The larger the' mandrel the more coarse the wire which may be used. However, in any case extremely fine wire may be used. For example, wire flattened to one thousandth in thickness has been used with success.

It has been found feasible first to provide an initial bond, between the wires, by heating the wires while on the mandrel, then remove the mandrel, thenv subject the porous wall formed by the wire to mechanical pressure, and then reheat and complete the bond. Also, the wire may be' wound' in cylindricalform then pre-bonded, then removed ,from the mandrel and slit lengthwise, then flattened into a sheet, and then passed between rollers, and then againv heated to increase the bond.

Inasmu'ch as the wire is wound under highy tension, high radial pressure is exerted between the wires at the points of crossing and is maintained in the completely wound structure while it is still on the mandrel. The initial bonding is accomplished by heating the wound wire while still on the mandrel and the pressure exerted by wire tension provides the required pressure for eecting a secure bond at the temperatures employed. After the structure is removed from the mandrel and compressed to a finer dimension, the portions of the wires adjacent the initial bond are deformed and the area of contact between the wires is extended or increased. Since the wire is plastically deformed and by reason of such deformation pressure exists between the wire surfaces at the extended areas of contact and the final heating results in fusing the wires, by heat and the then existing pressure, to provide the required bond. During the compression of the porous wall after removal from the mandrel, the wires of the laminations are forced closer together, thus producing passages of even smaller dimension than existed at the start of the rolling and permits construction of porous walls with extremely fine passageways therethrough and permits accurate control of the uniformity and porosity of the product.

Thus, the porosity is not only controlled by the initial spacing and dimension of the wires as wound but also by the degree of compression. if relatively light rolling pressure is exerted by the rollers, maximum porosity for a given initial wire spacing is obtained; whereas if a heavy rolling pressure is exerted the porosity is correspondingly reduced.

While the major rolling pressure is preferably applied after removal from the mandrel, an initial rolling operation may be performed after the porous wall structure is sintered but while the porous wall structure is still on the mandrel. This operation tends to loosen the porous wall structure from the mandrel. lf a thin ceramic coating is utilized on the mandrel as a parting agent, it may be crushed by such initial rolling and thus further facilitate removal of' the porous wall structure.

As has been indicated hereinbefore, the spacing between individual convolutions of wire and the relative position of the wires comprising succeeding convolutions makes possible the construction of a porous wall havhig precisely the selected porosity and resistance to fiow; that is, with a given porosity the resistance to flow may be increased or decreased depending on the relation between succeeding laminations of the wire.

Whether a single wire or a multiplicity of wires are used, the winding pitch is such that the wires of succeeding layers cross at a substantial angle With a result that the resulting wall structure, will have favorable strength longitudinally as well as circumferentially.

lf a single wire is used, it follows that many traverses of the wire are required before the spaces between the initial convolutions of the wire may be filled. This, of course, results in crossing of the wires at periodic points along the figure of revolution as shown in FIGURES 1 through 6. Any increase in thickness at these points is eliminated after the initial heating and bonding of the wires by pressing or running the wall structure between rollers.

More specifically, in the course of filling in or completing one lamination designated 2 in FIGURES 1 through 4 by repeated traverses of the wire, a second lamination designated 3 is also completed, due to the fact that for each forward traverse of the wire there is a return traverse. Each lamination corresponds to a row of wires as shown in these figures, that is, the first lamination 2, corresponds to the bottom row in these figures and the second lamination 3 corresponds to the second row.

The cohelical sets of wires comprising, respectively, the sum of the forward traverses and the sum of the return traverses are not identical with the first and second laminations 2 and 3, particularly after the wall structure thus formed is compressed; that is, the portions of the wires comprising the forward cohelical set of wires overlie the return cohelical set of wires and are thus pressed into the second lamination, and similarly portions of the return cohelical set of wires are pressed into the first lamination. The depressing operation deforms each wire where it shifts from one to the other lamination as indicated by d, resulting in increased bond adjacent at these spaced points after the final heating and bonding step. As the winding of the wire is continued, additional pairs of laminations are formed.

As mentioned hereinbefore, the wire may be wound on itself to produce a wide Variety of porous conditions. Perhaps the simplest form involves winding the wire at a uniform rate back and forth over a rotating cylinder. By controlling the relative rate of rotation and feed, the succeeding laminations of the wire may be stacked in such a way that vertical pores may be formed. Thus, as shown in FIGURES 5, 6 and 7, the wire 1 may be wound to form channels or passages 5 parallel to each other and to the surfaces of the wall thus formed. If the wires are laid uniformly they may define ports 6 which extend normal to and uninterrupted between the two surfaces of the resulting cylinder or other figure of revolution. The porosity is controlled by the closeness with which the wires are wound, as well as lateral fiattening as may occur when the wall is compressed.

The manner in which the wire may be fed on to the rotating mandrel may be so regulated that succeeding layers do not place the ports in alignment. Thus, as shown in FIGURE 8 if the succeeding layers are staggered, the ports 6 are not connected except through the channels 5. The result is that a multiplicity of labyrinth passages are formed, which, however, may be uniformly spaced and quite predictable in character. This type of construction is particularly suitable for porous walls to be used as filters. v

It is sometimes desirable that the porosity of the resulting structure vary from one side to the other. This may be accomplished by altering the cross sectional configuration of the Wire as succeeding laminations are wound on the mandrel. This may be done as the wire is wound by gradually or intermittently changing the adjustment of the flattening rollers through which the wire passes. rlhus, the first laminations of the wire may be fiat as indicated by 7 in FIGURE 10 and succeeding layers rendered less flat until the final layer may be square or round as indicated by 8 in FIGURE 10.

It is, of course, not necessary in order to have relatively straight pore spaces that these pore spaces be normal to the surfaces of the finished wall. By proper control of the rate of the feed the succeeding laminations of wire may be displaced slightly so that the resulting pore space is essentially tangential as indicated by 9 in FlG- URES 11 and 12. In this regard, it will be observed that in forming a cylinder the axes of the pore spaces may be tangential as well as provided with a slope directed toward one end or the other of the cylinder.

As indicated hereinbefore, the mandrel on which the porous wall is formed may take the shape of the finished object providing such object is a figure of revolution or an approximation thereof such as an ellipse or polygon.

Due to the initial bond between the wires it is possible to cut a porous wall cylinder or cone after sintering so as to form a flat sheet. Such sheet may then be reformed as desired. It is not necessary, however, to cut the cylinder or other generated shape. Instead such member may be pressed into the desired final asymmetrical shape.

The metal comprising the wire is determined by the use for which the porous' wall is intended. Thus, steel, copper, titanium, molybdenum wires, as well as alloys, to mention only a few, may be employed to meet specific conditions. Still further as shown in FIGURES 15 and 16, the wire may be plated or otherwise coated as indicated by 10. In this case, the bonding temperature need only be high enough to fuse the coating material.

For example, a copper plated steel wire would thus be capable of being bonded or fused at a lower temperature than unplated steel wire.

It, of course, follows that in winding the wire back and forth across the mandrel, the pitch must change to Zero and reverse at each end with the result that there is a build-up at the extremities of the ligure of revolution. If the resulting decrease in porosity in these end regions is objectionable in the final production, these portions may be trimmed off after sintering. However, in many cases, these ends will be welded or otherwise secured to other members, and the lack of porosity and correspondingly increased density and strength is advantageous.

It is necessary, of course, that the ends of the porous wall figure wound on the mandrel remain in place and not shift axially. If the winding pitch angle is less than the frictional contact between the wire and the mandrel is sufficient to prevent axial shifting of the wire.

However, in winding the wire at pitch angles greater than 20 it is necessary to pass the wire as a chord across the end of the mandrel. The location of the chord path is such that the angle formed by the subtended arc has a value equal to twice the pitch angle. By so winding the ends of the gure forming the porous wall, the pitch angle may be 60 or, if desired, even more. A 45 pitch angle will give the resulting porous wall figure equal strength in a longitudinal and a circumferential direction. If greater than 45 pitch angle is used, the strength in a longitudinal direction is made greater than in a circumferential direction. Thus the strength characteristics of the porous wall may be adjusted to meet particular needs'.

While it is not necessary to wind over the end of the mandrel or over a shoulder thereon if the pitch angle is less than 20, it has been found that the uniformity is improved if this is done, particularly in the winding of large diameter figures.

Having thus described certain embodiments and applications of my invention, I do not desire to be limited thereto, but intend to claim all novelty inherent in the appended claims.

Iclaim:

1. A porous wall structure having opposed faces and comprising: a multiplicity of similar pairs of laminations of parallel spaced flattened wires, each lamination being the thickness of a single wire and wires of adjacent laminations being in angular relation and extending across' the common sides of a plurality of wires of adjacent laminations, the flat surfaces of adjacent laminations being bonded together at said cross points, the spaces between wires in each of the internal laminations forming channels parallel to but between the opposed faces of said wall structure and the intersections of said channels forming ports extending between and through the said faces of said wall structure.

2. A porous wall structure as set forth in claim 1, wherein: said ports are relatively straight and continuous from face-to-face of said Wall structure.

3. A porous wall structure as set forth in claim 1, wherein: the wires of successive laminations are staggered and said ports form with said channels labyrinth passages through said wall structure.

4. A porous wall structure as set forth in claim 1, wherein: the ratio of wire width and channel width in said successive laminations varies from one side of said wall structure to the other.

5. A porous wall structure having opposed faces, cornprising: a multiplicity of pairs of laminations, each lamination being formed 0f a series of flattened wires disposed in predetermined spaced, parallel relation to each other and to the faces of the wall structure, said wires defining therebetween a multiplicity of passages which are also parallel to each other and to the faces of said wall structure; the Wires and passages of each lamination being disposed transversely to the wires and channels of adjacent laminations, with the flat sides of superimposed crossing wires in abutment, said wires being bonded together at said abutting flat sides; those areas wherein the passages of one lamination crossl the passages of an adjacent lamination dening ports communicating with said passages and extending between and intersecting the opposed faces of said wall structure.

6. A porous wall structure, comprising: a multiplicity of pairsl of laminations, each lamination including a multiplicity of parallel wires forming continuous channels therebetween and defining a common surface, the wires of one lamination of each pair disposed in a transverse relation with those of the other lamination, each pair of laminations defining at the cross portions of said channels a multiplicity of uniformly spaced ports extending through said pair of laminations; said pairs of laminations being stacked to form compositely a wall structure wherein said channels are parallel to and within the external surfaces of said wall structure and said ports extend between the external surfaces thereof.

7. A porous wall structure as set forth in claim 6, wherein: said ports of adjacent pairs of laminations are in alignment thereby to form continuous ports extending between the external surfaces of said wall.

8. A porous wall structure as set forth in claim 6, wherein: said ports of adjacent pairs of laminations are in staggered relation thereby to form labyrinth passages incorporating both said ports and channels and communieating between the external surfaces of said wall.

9. A porous wall structure as set forth in claim 6 wherein: the ratio of channel width to wire width of said pairs of laminations varies between the external surfaces of Said wall.

References Cited in the file of this patent UNITED STATES PATENTS 1,071,822 Storey Sept. 2, 1913 2,082,513 Roberts June l, 1932 2,271,662 Rubissow Feb. 3, 1942 2,327,184 Goodloe Aug. 17, 1943 2,485,827 Hartzell Oct. 25, 1949 2,711,828 Webb June 28, 1955 2,925,650 Pall Feb. 23, 1960 FOREIGN PATENTS 324,924 Great Britain Feb. 3, 1930 OTHER REFERENCES NACA Research Memorandum, Wire Cloth as Porous Material for Transportation Cooled Wall, Nov. 13, 1951, by E. G. Eckert, National Advisory Committee for Aeronautics, NACA RM E 51H23, pages y1l-22.

Claims (1)

1. A POROUS WALL STRUCTURE HAVING OPPOSED FACES AND COMPRISING: A MULTIPLICITY OF SIMILAR PAIRS OF LAMINATIONS OF PARALLEL SPACED FLATTENED WIRES, EACH LAMINATION BEING THE THICKNESS OF A SINGLE WIRE AND WIRES OF ADJACENT LAMINATIONS BEING IN ANGULAR RELATION AND EXTENDING ACROSS THE COMMON SIDES OF A PLURALITY OF WIRES OF ADJACENT LAMINATIONS, THE FLAT SURFACES OF ADJACENT LAMINATIONS BEING BONDED TOGETHER AT SAID CROSS POINTS, THE SPACES BETWEEN WIRES IN EACH OF THE INTERNAL LAMINATIONS FORMING CHANNELS PARALLEL TO BUT BETWEEN THE OPPOSED FACES OF

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