US3095283A - Porous wall structure - Google Patents

Description

June 25, 1963 H. WHEELER, JR 3,095,283

' POROUS WALL STRUCTURE Filed June 22, 1959 3 Sheets-Sheet 1 INVENTOR.

HARRY L.WHEELE JR.

ATTORNEY June 25, 1963 H. L. WHEELER, JR

' POROUS WALL STRUCTURE 3 Sheets-Sheet 2 Filed June 22, 1 959 INVENTOR HARRY L. WHEELER JR.

A TTDR NE).

June 25, 1963 H. L. WHEELER, JR

POROUS WALL STRUCTURE '3 Sheets-sheaf 3 Filed June 22, 1959 L J11 J DEVELOPMENT OF HELIX CIRCUMFERENCE or cYL= lit? 13 ff I15 INVENTOR. HARRY L. WHEELER JR.

AT TORNE Y United States Patent 3,095,283 POROUS WALL STRUCTURE Harry L. Wheeler, Jr., Madison Heights, Mich., assignor to The Bendix Corporation, a corporation of Delaware Filed June 22, 1959, Ser. No. 821,953 8 Claims. (Cl. 29191.6)

This invention relates to a porous wall structure and method of making same and more particularly to a porous Wall structure of the wire wound type.

One of the objects of this invention is to provide a wire wound porous wall construction which is radially stronger than other known wire wound constructions.

Another object of this invention is to provide a wire wound porous wall structure and method of making same in which uniform pore spacing and size may be more easily attained than in other comparable structures.

A further object of this invention is to provide a porous wall structure of helically wound wire forming a figure of revolution in which the number of pores and size of pores per unit area is constant and clearly definable regardless of the changing cross section of any figure of revolution.

A still further object of this invention is to provide a porous wall construction in the form of a figure of revolution such as, for example, a cylinder, a cone, or a vem turi shaped nozzle and which may further be reformed from such initial shapes into other asymmetrical forms or cut and reformed into flat sheets.

More specifically, it is an object of this invention to provide a wire wound porous wall structure which is fabricated by simultaneously winding a first wire having a smooth round surface and a second wire having a helicoidal surface about a mandrel in a side by side relationship to form a figure of revolution having alternate convolutions of said first and second wires arranged so that the convolutions of one wire contact only the convolutions of the other wire, and bonding said first and second wires to each other throughout their entire lengths at their points of contact to form uniform interstices therebetween, said points of contact being spaced from each other a distance equal to the pitch of the helices forming the helicoidal surface on the second wire. Examples of wires having a helicoidal surface are stranded wires, the strands of which are twisted to form helically disposed protuberances on the surface thereof, or solid wires having a polygonal cross-section which are axially twisted to form helically disposed protuberances on the surface thereof.

Another object of this invention is to provide a wire wound porous wall structure which can be machined without creating free ends or burrs.

A further object of this invention is to provide a wire wound porous wall structure and method of making same which will permit, on a practical basis, the forming of very large figures of revolution.

A still further object of this invention is to provide a wire wound porous wall structure which may be constructed at very low cost because of the rapid winding rate which may be used during fabrication.

Another object of this invention is to provide a wire wound porous wall structure, made in accordance with this invention, which may be used for (l) fluid filters; (2) sweat or transpiration cooled surfaces such as rocket motors, nozzles, nose cones, turbine blades, afterburners, combustion chambers, and all structures subject to aerodynamic heating; (3) bearings; (4) reactor cores; (5) heat exchangers, and (6) other applications obvious to those skilled in the art.

Other objects and advantages of this invention will become apparent from the following description taken in connection with the accompanying drawings which form a part of this specification and in which:

FIGURE 1 is a perspective view of a porous wall cylinder constructed in accordance with my invention;

FIGURE 1A is a fragmentary enlarged view of the circumscribed portion 1A in FIGURE 1 which shows alternate convolutions of stranded and solid wires;

FIGURE 1B is a sectional view taken substantially along line 1B-1B of FIGURE 1A;

FIGURE 2 is a fragmentary enlarged perspective view of a porous wall having two layers each of which includes three stranded wire and solid Wire arranged and bonded in accordance with my invention;

FIGURE 3 is a fragmentary enlarged perspective view of a porous wall of seven stranded wire and solid wire arranged and bonded in accordance with my invention;

FIGURE 4 is a fragmentary enlarged perspective view of an alternate arrangement and construction of a porous wall having two or more laminations;

FIGURE 5 is a fragmentary enlarged perspective view of a porous wall formed of wire having a smooth round surface and wire having a square cross-section which has been axially twisted;

FIGURE 6 is a view partially in section of a porous wall cylinder constructed in accordance with my invention which has a perforated core therein;

FIGURE 7 is a perspective view of a porous wall cylinder constructed in accordance with my invention which is partially broken away to show the fluted core therein;

FIGURE 8 is a side view of a wire having a square cross-section which has been axially twisted;

FIGURE 9 is a diagram showing the development of a helix;

FIGURE 10 is a diagrammatical view of a cone constructed in accordance with my invention;

FIGURE 11 is a diagrammatical view showing a venturi nozzle and rocket motor combustion chamber constructed in accordance with my invention;

FIGURE 12 illustrates diagrammatically in cross-section a turbine blade constructed in accordance with my invention; and

, FIGURE 13 is a diagrammatical view of an ellipsoid of revolution, minus the ends, constructed in accordance with my invention.

Referring to FIGURE 1, 1A and 1B it will be 'seen that the figure of revolution shown, namely the porous wall cylinder 12 of FIGURE 1, consists entirely of two different types of wires 14 and 16, the first of which is a solid wire having a smooth round surface and the sec 0nd of which is a three stranded wire, the strands of which are helically twisted to form a helicoidal surface. The porous wall cylinder 12 is fabricated by winding under high tension the solid wire 14 and stranded wire 16 side by side about a cylindrical mandrel in such a manner that the convolutions of the solid wire contact only the convolutions of the stranded wire and vice versa.

The wire wound structure may then be placed in a furnace in a neutral or reducing atmosphere and heated to a temperature sufficient to bond the stranded wire and the solid wire to each other throughout their entire lengths at their points of contact to form a coherent porous cylinder having uniform porosity.

The preferred manner of fabricating a porous wall of the type discussed above is to simultaneously wrap the two types of wire at a very low pitch so that all of the wires on a single layer are in intimate side 'by side contact. While it is simplest to wind one solid and oiie stranded wire simultaneously, it is also possible to wind two or more solid and two or more stranded wires disposed alternately so that the end product will have the same appearance as though the wires were wound as a pair, except that the pitch will be higher.

If a wall thicker than that formed by one layer is required, a second layer having a construction identical to that of the first layer may be added by starting at the same end of the mandrel from which the first layer was started. In making multiple layer walls it has been found very desirable to use stranded and solid wires of dilferent effective diameters, so that when the second layer is added a staggered nesting effect is obtained, as shown in FIG- URE 1B. Any number of additional layers may be added, each succeeding layer being wrapped in the same direction and in the same manner as those preceding it. The nesting effect obtained by the use of wires having different effective diameters not only increases the axial strength of the finished structure, but also may be used to control the tortuousity of the pores of interstices which traverse the porous wall. In forming various porous wall structure of the type described, it has been found that where wires having different effective diameters are used, maximum packing densities and axial strength may be achieved by utilizing wires having the following diametrical relationship:

Wherein Ds is the smaller diameter wire and De is the larger diameter wire.

If wires of equal effective diameter are used, the construction shown in FIGURE 4 may be obtained. However, nesting effects, as described with respect to wires of unequal effective diameters, may also be obtained by using stranded and solid wires of equal efi'ective diametens, if the winding process is properly controlled. It should be pointed out that in the FIGURE 4 embodimerit the pores traverse the wall in a somewhat more direct manner than in the embodiment shown in FIG- URES 1B and 2. The actual path followed by each pore of these embodiments is that of a spiral, the axis of which is curved and runs circumferentially about the mandrel. It is important to note that, since a solid wire lies between each stranded wire, the maximum pore opening is clearly and uniformly defined by the stranded wire beaming against the solid wire. The size of this opening will be a function of the diameters of the individual strands of the stranded wire and of the diameter of the solid wire.

Another method of wrapping which may be used in forming multiple layered porous walls involves the use of a return stroke in applying the even numbered layers during winding. However, if such a method is used, the wires will not nest as shown in FIGURES 1B and 2, and the structure therefore will be weaker, more porous and more permeable.

The stranded wire used in connection with my invention may be composed of two or more strands which are helically twisted to in effect form helically disposed protuberances on the surface of the stranded wire. The effective diameter of the wire will be determined by the size and number of strands used, and will be equal to the diameter of the smallest circle circumscribing all of the strands in the wire. Groupings of three and seven strands are most satisfactory because they produce the highest density packing. Note FIGURE 3 which shows a portion of a porous wall formed of a helically twisted seven stranded wire 18 l and a solid round wire 20.

The pitch with which the wires are twisted may be varied at will. Thus, the shorter the pitch, the greater the number of pores per unit length of wire, and the greater the radial inclination of the pore path.

Instead of using helically twisted stranded wire in the forming of the previously discussed porous structures, it is also possible to get a similar effect by using a solid wire having a polygonal cross-section which has been helically twisted to form a helicoidal surface thereon. Thus, by winding a square wire 22, which has been twisted to form helically disposed protuberances on the surface thereof, as shown in FIGURES 5 and 8, between solid round wires 24 in the manner previously described, predetermined uniform interstices or pores of the same general nature as those formed when using comparable stranded wire will also be formed in this instance. Instead of using solid round wires 24, solid square wires or other polygonal shaped wires might also be used in place thereof. Helically twisted three stranded wire would have a comparable surface to that of a solid wire having a triangular cross-section which has been axially twisted, while helically twisted seven stranded wire would have a comparable surface to that of a solid wire having a hexagonal cross-section which has been axially twisted. The reason for the latter equivalency is that one of the strands of the seven stranded wire is in effect a core around which the other six wires are helically disposed. It should be pointed out, however, that although the pores formed between the solid round wire and the adjacent wire having the helicoidal surface are somewhat the same for equivalent wires, the stranded wires will have lower densities than their solid twisted polygonal equivalents, and will of course be more porous.

The helices formed on the surface of both the twisted stranded wires and the axially twisted polygonal shaped solid wire are true helices, that is, each is a curve generated by a point moving about a cylindrical surface (real or imaginary) at a constant rate in the direction of the cylinders axis. Referring to the diagram of FIGURE 9, it will be seen that the lead of a helix is the distance that it advances in an axial direction, in one complete turn about the cylindrical surface. If one turn of a helical curve were unrolled onto a plane surface, as shown by the diagram, the helix would become a straight line forming the hypotenuse of a right triangle. The length of one side of this triangle would equal the circumference of the cylinder with which the helix coincides, and the length of the other side of the triangle would equal the lead of the helix. The angle A is often referred to as the helix angle and the angle B as the lead angle.

With this in mind, the square cross-section wire, shown in FIGURES 5 and 8, which was axially twisted, could be referred to as a four lead helix, wherein the lead L is equal to four times the pitch P, the pitch being the axial distance from one helix to the next helix. The twisted three strand wire or an axially twisted triangular crosssection wire could be referred to as a three lead helix, wherein the lead is equal to three times the pitch.

After winding the wire having a helicoidal surface and the wire having a smooth round surface to the required wall thickness and in the desired configuration in accordance with my invention, the figure of revolution and mandrel may be placed in a furnace in a neutral or reducing atmosphere and heated to a temperature suificient to fuse or bond the two wires to each other throughout their entire lengths at their points of contact to form uniform interstices therebetween. Thus, bonding will occur at these points of contact, said points being spaced from each other a distance equal to the pitch of the helices formed on the surface of the wire having the helicoidal surface. it should also be noted that where a stranded wire is utilized to form the structure, bonding will also occur between the strands themselves.

The function of the overall bonding operation is to produce a porous wall capable of withstanding mechanical and hydraulic forces of itself, to prevent any shifting or gapping of the wires under the influence of vibration or wedge shaped particles activated by hydraulic pressure, and to prevent the entire winding from disintegrating should one of the strands become severed. The bonded porous structure will be completely free of any form of media migration, and will be resistant to potential damage resulting from fatigue or impact. Furthermore, the porous structure may be ground or machined without the creation of any burrs.

Added strength may be gained if the wall is simultaneously bonded to the mandrel, which may be a perforated core 26, as shown in FIGURE 6; or a fluted core 28, as shown in FIGURE 7. Such arrangements, as shown in FIGURES 6 and 7 will permit flow of fluid therethrough and may be used as effective filters.

After heating, the porous cylinder may be removed from the mandrel, if the mandrel is of ceramic or ceramic coated metal, and processed further by placing it between rollers in order to compact the porous structure and reduce the pore size. Such rolling, however, is not mandatory. Where the porous wall is not to be removed from the mandrel, it may still be rolled. In this instance the mandrel will serve as one of the two rollers between which the porous wall is passed. Further bonding and strengthening may be obtained if the porous structure is then given a second heat treatment similar to the first. If desired, the porous figure of revolution may be slit and rolled out into a fiat sheets.

The bonding of the individual wires may be accomplished by one or more of the following means: (1) fusion at high temperature without the presence of a liquid phase or any bonding agent; (2) by coating the wire with a low melting point pure metal or alloy such as tin, silver, copper, gold, tin-lead alloys or copper-silver alloys, which wil melt and fuse or braze the structure into an integrated mass; (3) by spraying or otherwise applying a finely divided form of brazing material (powder) between each layer of wrapping; (4) by spraying or otherwise applying an easily reducible oxide such as, but not restricted to, CuO, CuO or AgO which will reduce to a low melting point metal in a reducing atmosphere furnace; (5) by wrapping in addition to the strand and solid wire a third very fine wire of brazing alloy; (6) by dipping the finished winding in a molten bath of tin, copper, plastic or other bonding material.

The strength of the bonded joint is greatly increased by winding the wire under the highest possible tension so that a very firm contact is established between adjoining convolutions of wire.

The metal comprising the wire will be determined by the use for which the porous wall is intended. Thus, steel, copper, titanium, or molybdenum wires, as well as alloys, to mention only a few, may be employed to meet specific conditions. As a matter of fact my invention may be utilized in connection with plastic wires or wires of any materials which are connectible to each other by fusing, gluing or by some other suitable means.

In the preferred embodiment which utilizes stranded wire and solid wire the porosity or permeability will be controlled, as previously discussed, by the size of the individual strands in the stranded wire, by the number of individual strands in the wire, by the pitch or twist of the strands, by the ratio of the efiective diameter of the stranded wire to the solid wire, and by the amount of rolling on the finished structure.

Some of the advantages of my invention are (1) the low cost of construction due to the rapid winding rate which may be used; (2) the fact that there is virtually no limit to the diameter or length of the porous wall to be formed; (3) the fact that any shape of cylindrical or near cylindrical cross-section can be made, such as the conical form 30 of FIGURE 10, the rocket motor 32 of FIG- URE lil which has a nozzle 34, the ellipsoid of revolution 36 of FIGURE 13 which may be used for torpedo shells, or missile and nose cone skins, and the turbine blade 38 which may be pressed into the desired shape from a cylindrical figure of revolution; (4) the extremely uniform pore distribution which results in the basic construction regardless of changing diameter; and (5) the fact that each wire in the structural wall is bonded to one or more contiguous wires throughout its entire length.

The several practical advantages listed above which flow from my invention are believed to be obvious from the previous description of the invention and other advantages and applications may suggest themselves to those who are familiar with the art to which this invention relates.

Hlavingthus described the various features of my invention, what I claim as new and desire to secure by Letters Patent is: 1

l. A self-supporting porous wall structure capable independently of other extraneous means of withstanding mechanical and hydraulic forces comprising alternate contacting three stranded wires and solid wires arranged so that each of said wires contacts only the other of said wires, said stranded and solid wires being bonded to each :other throughout their entire lengths at their points of contact.

2. A self-supporting porous wall structure capable independently of other extraneous means of withstanding mechanical and hydraulic forces comprising a layer of alternate contacting first and second wires arranged so that each of said wires contacts only the other of said wires, one of said wires being a seven stranded wire the strands of which are helically twisted to form helically disposed protuberances on the surface thereof, said first and second wires being bonded to each other throughout their entire lengths at predetermined points along said helically disposed protuberances to form non-variable interstices therebetween.

3. A self-supporting porous wall structure forming a figure of revolution capable independently of other extraneous means of withstanding mechanical and hydraulic forces comprising a layer of [alternate contacting convolutions of first and second wires arranged so that the convolutions of said first wire contact only the convolutions of said second wire, one of said wires being a three stranded wire the strands of which are helically twisted to form helically disposed protuberances on the surface thereof, said first and second wires being bonded to each other throughout their entire lengths at predetermined points along said helically disposed protuberances to form uniform non-variable interstices between said points.

4. A self-supporting porous .wall structure forming a figure of revolution capable independently of other extraneous means of withstanding mechanical and hydraulic forces comprising a layer of alternate side by side contacting convolutions of a first round wire and a second seven stranded Wire having a helicoidal surface arranged so that the convolutions of said first wire contact only the convolutions of said second wire and the convolutions of said second wire con-tact only the convolutions of said first wire, said first and second wires being bonded to each other throughout their entire lengths at their points of contact to form uniform non-variable interstices therebe tween, said points of contact being spaced from each other a distance equal to the pitch of the strands forming the helicoidal surface of said second wire.

5. A self-supporting porous wall structure capable independently of other extraneous means of withstanding mechanical and hydraulic forces comprising a plurality of laminations each of which includes alternate contacting three standed wires and solid wires arranged so that each of said wires contacts only the other of said wires, said stranded and solid wires being bonded to each other throughout their entire lengths at their points of contact; said laminations being bonded to each other at their points of contact to form a coherent porous laminar structure.

6. A porous wall structure as defined in claim 5 wherein the stranded wires of each of the laminations contact the solid Wires of the next adjacent laminations while the solid Wires of each of said laminations contact the stranded wires of said next adjacent laminations.

7. A porous wall structure as defined in claim 5 wherein the stranded wires of each of the laminations contact the stranded wires of the next adjacent laminations while the solid wires of each of said laminations contact the solid wires of said next adjacent laminations.

8. A self-supporting porous wall structure forming a figure of revolution capable independently of other extraneous means of withstanding mechanical and hydnaulic forces comprising a plurality of laminations each of which includes alternate convolutions of contacting seven stranded Wires and solid wires arranged so that each of said Wires contacts only the other of said wires, one of said wires having a greater effective diameter than the other of said wires, said stranded and solid wires being bonded to each other throughout their entire lengths at their points of contact; said laminations being arranged so that the stranded wires of each of the laminations contact the solid wires of the next adjacent laminations while the solid wires of each of said laminations contact the stranded wires of said next adjacent laminations, said contacting wires being bonded to each other throughout their entire lengths at said points of contact to form a coherent laminar structure.

References Cited in the file of this patent UNITED STATES PATENTS Hurrel] Apr. 25, Liddell June 2, Johnson July 7, Kinnear Mar. 23, Tursky Jan. 4, Layte Oct. 6, Specht July 13, Fernandez Mar. 19, Wheeler Oct. 28,

FOREIGN PATENTS Germany Aug. 12,

Claims (1)

1. A SELF-SUPPORTING POROUS WALL STRUCTURE CAPABLE INDEPENDENTLY OF OTHER EXTRANEOUS MEANS OF WITHSTANDING MECHANICAL AND HYDRAULIC FORCES COMPRISING ALTERNATE CONTACTING THREE STRANDED WIRES AND SOLID WIRES ARRANGED SO THAT EACH OF SAID WIRES CONTACTS ONLY THE OTHER OF SAID

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