US3437457A - Reinforced metal fiber composites - Google Patents

Description

April 8, 1969 J. 1. FISHER REINFORCED METAL FIBER COMPOSITES Filed April 13. 1965 FIGS INVENTOR.

JAMES I. FISHER 3,437,457 REINFORCED METAL FIBER COMPOSITES James I. Fisher, Orange, Conn., assignor to Huyck Corporation, Stamford, Conn., a corporation of New York Filed Apr. 13, 1965, Ser. No. 447,718 Int. Cl. B22f 7/02 U.S. Cl. 29-1821 12 Claims ABSTRACT OF THE DISCLOSURE U.S. Patent 3,127,668 describes a process for forming metal fiber bodies and products produced thereby. In that patent, metal fibers are individually suspended in a fluid medium to form a slurry and the metal fibers are felted from the slurry. In felting, the metal fibers are dispersed to form a felted body of randomly disposed, intersecting metal fibers. The felted body is then sintered, causing the randomly disposed fibers to interdilfuse and bond together at the points where the fibers intersect or touch each other. The body thus formed is substantially uniform in bulk density and porousness, the pores in the body being interconnected and joined and being substantially uniformly distributed throughout the felted, sintered body.

Metal fiber bodies or mats produced in accordance with the aforementioned patent have a wide variety of uses, such as for filters, diffusing membranes, sound absorbers, and many other uses. In some of the many uses, the metal fiber body member may be felted and sintered in the configuration in which such member may be used. In other uses, it may be desirable to initially form the body in a flat sheet or slab and, later, shape the sheet or slab into the desired configuration, as by bending or roll forming. In many instances, where the sheet or slab of metal fibers is to be shaped or formed difficulties are often encountered in maintaining the integrity and continuity of the metal fiber mat, particularly where the sheet or slab is being formed into a configuration having sharp turns and curvatures of relatively small radius.

In some cases, fiber metal bodies are of use where very low bulk density, high porosity, is required. The strength of such bodies is normally a disproportionally small percentage of the strength of the solid metal, and application of such bodies is therefore inhibited. In other cases, because many of the fiber ends at or near the surface of the sheet or slab are not terminated in sinter bonds, the unbonded ends can be bent outward from the mat surface. The nap which results from the bent or outwardly projecting fiber ends is undersirable in many applications, posing an obstacle to smooth air flow over the surface of the sheet, for example.

Under the instant invention reinforced bodies of metal fibers are formed 'by suspending metal fibers in a fluid suspension medium and forming the fibers into a felted body of randomly disposed fibers. Either as the fibers are felted or after felting a pervious metal sheet, which may be woven, expanded or perforated, is placed over one or both faces of the felted body. The felted body and the sheet, or sheets, are then compressed and, while compressed, the' temperature of the felted body and the sheet is raised to the diffusion temperature of the metal, or metals, in the felted body and the sheet. At the diffusion temperature, the metal, or metals, of the metal fibers in nited States Patent the felted body and the sheet sinter, forming diffusion bonds between the fibers in the felted body and between the fibers at, or near, the surface of the mat and in contact with the metal sheet. The reinforced body thus formed is a felted mass of randomly disposed, bonded metal fibers reinforced on one or both sides, depending on whether woven, expanded or perforated sheets are employed on one or both faces, by a metal sheet, the sheet, or sheets, being imbedded in the surface of the felted body.

One of the objects of the instant invention is to form improved fiber metal bodies.

A further object of the invention is to form such bodies which are reinforced and can be formed or shaped after formation without disrupting or affecting the integrity and continuity of the body.

A further object is to form such a body without appreciable damage to or substantial decrease in the porosity of such body.

A still further object is to form such bodies whose strentgh is enhanced at low bulk density.

Still a further object is to provide such a body in which the fiber ends at or near the surface of the mat are locked into the mat surface thereby preventing napping.

These, and other objects, will be more apparent from the following description and attached drawings in which:

FIG. 1 is a perspective view of a metal fiber mat;

FIG. 2 is an exploded view, in perspective, of the fiber metal mat of the instant invention; and

FIG. 3 is a diagrammatical illustration of the sintering principle employed.

In carrying out the instant invention, a metal fiber mat in accordance with U.S. Patent 3,127,668 is formed. Metal fibers are suspended in a fluid medium and felted from the fluid medium into a felted mass of randomly disposed fibers. A woven, expanded or perforated metal sheet or screen is placed over one or both faces of the felted fiber mass. While holding the felted mass and metal sheet together under a light load suflicient to maintain contact between the felted metal fibers with each other and with the metal sheet, the felted mass and metal sheet are sintered together at the appropriate sintering temperature.

The metal fibers may be felted first and then placed on the woven, expanded or perforated metal reinforcing sheet or screen or may be felted directly onto the reinforcing sheet. Where reinforcing sheets are to be used on both surfaces, the top reinforcing sheet is, of course, placed over the felted mass after felting.

Both the fibers and the reinforcing sheet may be selected from a wide variety of metals and alloys, depending on the properties desired and the use to which the end article is to be put. The metals and alloys must, of course, be cosinterable.

Woven, expanded and perforated metal sheets are available in a wide variety of thicknesses and with a wide variety of opening sizes. Preferably, in carrying out the instant invention, the thickness and opening sizes are selected to impart the desired reinforcement without impairing porosity or other properties desired in the reinforced article. By selecting a material with openings several times larger than the openings or pores in the felted mat, the reinforcing material whether applied to one or both faces of the mat, does not interfere with the porosity of the mat.

When the metal sheet, either woven, expanded, or perforated, is placed over one or both faces of the felted metal fiber body, and the sheet and body are placed under a light load and compressed, the metal sheet is imbedded in the surface and bonded to the fibers on or near the surface of the body. Thus, the reinforcing sheet forms a layer at the surface of the reinforced body, bonded to the felted body, which is both continuous and planar. This continuous and planar layer resists stresses which, otherwise, might cause failure at the surface where the felted fibers, although continuously metallic, are random with respect to direction. The continuous layer provided by the metal sheet also decreases the possibility of free fiber ends on the surface. Such free ends, where the felted body is not reinforced, may nap or turn upward and outward of the felted surface. These outwardly projecting fibers, when they occur, form protuberances, make handling difiicult and, in many instances, impair use of the felted body.

Referring now to the drawings, mat 2 of FIG. 1 is a felted, sintered mat produced in accordance With US. Patent 3,127,668. Mat 2 is formed from a slurry of fluid suspended metal fibers and the fibers are felted from the.

slurry. The metal fibers may be felted onto a woven, expanded, or perforated metal sheet and, where such a sheet is to be used on both faces, the metal sheet may be placed on the opposite surface after felting. The fibers may also be felted and positioned on the metal sheet after felting.

For purposes of illustration, in FIG. 2 reinforcing sheets 4, 6 are placed on the opposite faces of the mat and felted mat 2 is then lightly compressed with reinforcing sheets 4, 6 and, while compressed, the sheets and mat are heated to the diffusion temperature of the metal. As reinforcing sheets 4, 6 and mat 2 are compressed, sheets 4, 6 are imbedded in the opposite faces of mat 2 and the fibers are brought into and held in contact with the reinforcing sheet and into and held in contact with each other. While the sheets and mat are heated, diffusion bonds form between the metal fibers of the mat and the sheets and between the points of contact of the metal fibers with each other. As best shown in FIG. 4, sheets 4, 6 are imbedded in the opposite faces of mat 2.

As an example of the instant invention, stainless steel fibers of Type 302 stainless steel having a fiber size of microns were suspended in a fluid medium and felted. Two felted mats were formed. On one mat 18 by 18 Type 316 stainless steel screens, woven from 0.009 inch wire, were placed on the opposite faces of the mat. There was no screen or other reinforcing metal member used on the other.

Both mats were compressed and sintered, one with the screens and the other without reinforcing screens or other reinforcing members. Both mats, after sintering, had a density of 30% and a thickness of 0.100 inch.

The sintered m-ats were tested for tensile strength. The unreinforced mat had a tensile strength of 3300 p.s.i. while the mat, reinforced on both sides, had a tensile strength of 4525 psi.

It has also been found that the radius over which fiber metal mats can be bent or roll formed is substantially improved by reinforcement. The degree of improvement, however, decreases as the bulk density of the fiber metal mat increases, that is, as the bulk density approaches the density of solid metal. A typical improvement with a mat of 20% density of Type 302 stainless steel 15 micron fibers is a factor of 5. Thus, such unreinforced mats can be bent, or roll formed, over a radius of 50 times the mat thickness while a reinforced mat can be bent, or roll formed, over a radius of 10 times the mat thickness.

The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed,

What is claimed is:

1. A reinforced mat comprising metal fibers randomly disposed in a felted body of intersecting fibers, said fibers being metal diffusion bonded to each other, and a pervious metal reinforcing sheet imbedded in at least one surface of said mat, metal fibers at said one surface contacting said perivous metal sheet and being metal diffusion bonded to said sheet.

2. A reinforced mat as recited in claim 1 in which said pervious metal sheet is woven wire.

3. A reinforced mat as recited in claim 1 in which said pervious metal sheet is an expanded metal sheet.

4. A reinforced mat as recited in claim 1 in which said pervious metal sheet is a perforated metal sheet.

5. A reinforced mat comprising metal fibers randomly disposed in a felted body of intersecting fibers, and said fibers being metal diffusion bonded to each other, and pervious metal sheets on opposite surfaces of said mat, each of said pervious metal sheets being metal diffusion bonded to one surface of said mat and imbedded therein.

6. A reinforced mat as recited in claim 5 in which said pervious metal sheets are woven wire.

7. A reinforced mat as recited in claim 5 in which said pervious metal sheets are expanded metal sheets.

8. A reinforced mat as recited in claim 5 in which said pervious metal sheets are perforated metal sheets.

9. A reinforced, compressed mat comprising a body of randomly disposed, intersecting metal fibers which are metal diffusion bonded to each other, and pervious metal sheets at opposite surfaces of said mat, said mat being between said pervious metal sheets with said pervious metal sheets imbedded in said opposite surfaces in contact with, and metal diffusion bonded to, said pervious metal sheets.

10. A reinforced mat as recited in claim 9 in which said pervious metal sheets are woven wire.

11. A reinforced mat as recited in claim 9 in which said pervious metal sheets are expanded metal sheets.

12. A reinforced mat as recited in claim 9 in which said pervious metal sheets are perforated metal sheets.

References Cited UNITED STATES PATENTS 2,819,962 11/ 1958 Salauze. 2,833,847 5/1958 Salauze. 2,903,787 9/1959 Brennan. 3,102,329 9/1963 Horn 29182.3 3,127,668 4/1964 Troy 214 X 3,149,253 9/ 1964 Luebke. 3,165,826 1/1965 Bentov. 3,178,280 4/1965 McGee 75200 3,186,871 6/1965 Donohue 75208 X 3,266,936 8/ 1966 Krebs. 3,278,279 10/ 1966 Kraft.

FOREIGN PATENTS 933,825 8/1963 Great Britain.

OTHER REFERENCES Chem. & Engr. News, vol. 46, No. 6, Feb. 11, 1963, p. 49. REUBEN EPSTEIN, Primary Examiner.

A. J. STEINER, Assistant Examiner.

US. Cl. X.R. 29182.3; 75208

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