U.S. patent application number 11/578578 was filed with the patent office on 2007-08-30 for method of manufacturing of a sintered metal fiber medium.
This patent application is currently assigned to NV BEKAERT SA. Invention is credited to Constantina Andreouli, Constantine Stournaras, Zoi Tatoudi, Gerrit Van Betsbrugge, Frank Verschaeve, Carl Vromant.
Application Number | 20070202001 11/578578 |
Document ID | / |
Family ID | 34928956 |
Filed Date | 2007-08-30 |
United States Patent
Application |
20070202001 |
Kind Code |
A1 |
Stournaras; Constantine ; et
al. |
August 30, 2007 |
Method Of Manufacturing Of A Sintered Metal Fiber Medium
Abstract
The invention relates to a method for manufacturing a sintered
metal fiber medium, comprising the steps of: providing metal
fibers; making a slurry comprising the metal fibers and a binding
agent by mixing the metal fibers and the binding agent, possibly
with a solvent; casting a layer of the slurry on a support using an
applicator; solidifying this slurry, providing a foil comprising
the metal fibers and the binding agent; debinding the binding agent
in the foil and sintering the metal fibers.
Inventors: |
Stournaras; Constantine;
(Chalkida, GR) ; Andreouli; Constantina; (Vathi
Avlidos, GR) ; Tatoudi; Zoi; (Chalkida, GR) ;
Verschaeve; Frank; (Otegem, BE) ; Vromant; Carl;
(De Pinte, BE) ; Van Betsbrugge; Gerrit;
(Bellegem, BE) |
Correspondence
Address: |
FOLEY AND LARDNER LLP;SUITE 500
3000 K STREET NW
WASHINGTON
DC
20007
US
|
Assignee: |
NV BEKAERT SA
|
Family ID: |
34928956 |
Appl. No.: |
11/578578 |
Filed: |
March 24, 2005 |
PCT Filed: |
March 24, 2005 |
PCT NO: |
PCT/EP05/51378 |
371 Date: |
October 16, 2006 |
Current U.S.
Class: |
419/9 |
Current CPC
Class: |
B22F 2998/10 20130101;
B01D 39/2044 20130101; B22F 3/002 20130101; B22F 3/22 20130101;
B22F 3/02 20130101; B22F 2998/10 20130101; B22F 3/10 20130101; B22F
7/002 20130101 |
Class at
Publication: |
419/009 |
International
Class: |
B22F 7/04 20060101
B22F007/04 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 15, 2004 |
EP |
04101531.4 |
Claims
1. A method for manufacturing a sintered metal fiber medium,
comprising the steps of: providing metal fibers; making a slurry
comprising said metal fibers and a binding agent by mixing said
metal fibers and said binding agent.; casting a layer of said
slurry on a support using an applicator; solidifying said slurry,
providing a foil comprising said metal fibers and said binding
agent; debinding said binding agent in said foil and sintering said
metal fibers.
2. A method as claimed in claim 1, wherein the concentration of
metal fibers in said slurry is in the range of 2% weight to 40%
weight of said slurry.
3. A method as claimed in claim 1, wherein said slurry comprising a
solvent dissolving said binding agent.
4. A method as claimed in claim 3, wherein said solidifying of said
slurry is done by evaporation of all of said solvent from said
slurry.
5. A method as claimed in claim 3, wherein said solvent is
water.
6. A method as claimed in claim 1, wherein said slurry is provided
by heating said binding agent.
7. A method as claimed in claim 1, wherein said method comprises an
additional step of reducing the thickness of said foil by a
pressing operation.
8. A method as claimed in claim 1, wherein said method comprises an
additional step of reducing the thickness of said sintered metal
fiber medium.
9. A method as claimed in claim 1, wherein said method comprises an
additional step of stacking several foils to each other prior to
said debinding of said binding agent.
10. A method as claimed in claim 1, wherein said method comprises
an additional step of adding a porous metal structure, a metal foil
or metal plate to said foil prior to debinding said binding
agent.
11. A method as claimed in claim 1, wherein said method comprises
an additional step of sintering a porous metal structure, a metal
foil or metal plate to said sintered metal fiber medium.
12. A method as claimed in claim 1, wherein the thickness of said
sintered metal fiber medium less than or equal to 0.2 mm.
13. A method as claimed in claim 1, wherein the porosity of said
sintered metal fiber medium is in the range of 40% to 99%.
14. A method as claimed in claim 1, wherein the bubble point
pressure of said sintered metal fiber medium is more than 10000
Pa.
15. A method as claimed in claim 1, wherein the mean flow pore size
of said sintered metal fiber medium is less than 1.5 times said
equivalent fiber diameter D of said metal fibers.
16. A method as claimed in claim 1, wherein the metal fibers have
an UD of less than 110, said L being the average fiber length.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a method of manufacturing
of a sintered metal fiber medium.
BACKGROUND OF THE INVENTION
[0002] Sintered metal fiber media are well known in the art for
numerous applications, such as e.g. liquid or gas filtration.
[0003] A first method for providing sintered metal fiber medium is
to provide a metal fiber web by air lay down, and sintering this
air laid web in appropriate furnaces.
[0004] A disadvantage of this air lay down web, is the fact that
the web is usually relatively inhomogeneous, especially when
relatively thin sintered metal fiber medium are to be provided.
This because the air laid webs can hardly be provided sufficiently
homogeneous, and therefore, to have a sintered metal fiber medium
with homogenous properties over its surface, usually several air
laid webs are stacked (so-called doubled).
[0005] An other method to provide a web, prior to sintering
operation, is to use the so-called wet lay down method or paper
making method, as described in WO98/43756, EP933984A, JP11-131105,
JP61-225400 and JP61-223105. The metal fibers are brought in a
slurry, which slurry is poured on a screen. The water is sucked
from the slurry through the screen. The remaining dewatered slurry
is then sintered. A binding agent may be used to temporarily bind
the metal fibers to each other and so to make the dewatered slurry
transportable. This dewatered slurry is then sintered, possibly
first debinding the binding agent.
[0006] A disadvantage of the wet webbing is that in case that thin
and relatively short fibers are used, some of the shorter fibers
are sucked through the screen, together with the water being
removed from the slurry. In case of thin webs made prior to
sintering, the dewatering step may suck small or larger holes in
the web where few or no fibers are retained for sintering. Also, an
imprint of the supporting net, used to support the wet slurry
during dewatering, is obtained. The net pattern is noticed on the
dewatered web as repetitive thinner spots.
[0007] As a result, the dewatered slurry and thus the sintered
metal fiber medium, may have inhomogeneous zones where less fibers
are present, even when several layers of the freshly dewatered webs
are stacked one to the other prior to sintering.
[0008] Especially in case fibers with small equivalent diameter,
e.g. 2 .mu.m to 6 .mu.m, are used, the phenomena of sucking fibers
with the water during dewatering is noticed. This because usually
the amount of fibers with smaller lengths is larger, the finer the
fibers are. As a result, more fibers with a short length are sucked
with the water during dewatering in case of fibers with small
equivalent diameter.
SUMMARY OF THE INVENTION
[0009] It is an object of the present invention to provide a method
for manufacturing sintered metal fiber media which overcomes the
drawbacks of prior art. It is an object of the present invention to
provide a method of manufacturing a sintered metal fiber medium
with homogeneous properties over its surface. It is also an object
of the present invention to provide a method of manufacturing a
sintered metal fiber medium with homogeneous properties over its
surface comprising relatively short and/or fine metal fibers. It is
further an object of the present invention to provide a method of
manufacturing a sintered metal fiber medium with homogeneous
properties over its surface, which medium has a relatively small
thickness.
[0010] A method for manufacturing a sintered metal fiber medium as
subject of the invention comprises the steps as described in claim
1.
[0011] Preferably, the slurry used for casting using an applicator,
or so-called tape casting, comprises an amount of metal fibers in
the range of 2% weight to 40% weight of the slurry, more preferred
between 5% weight and 15% weight of the slurry. Apparently, such
concentration combined with the tape casting action to provide
substantially flat layers of slurry, causes metal fibers to be
distributed more homogeneously, so providing sintered metal fiber
medium having more homogeneous properties over its surface and in
depth of the medium.
[0012] Too much metal fibers in the slurry may cause conglomeration
of the fibers, causing on its turn inhomogeneous metal fiber
distribution throughout the sintered metal fiber medium.
[0013] Too little metal fibers in the slurry may cause problems
during debinding, where too much debinding causes disturbing of the
sintering of the metal fibers. Further, such production of sintered
metal fiber medium becomes uneconomic, as too much energy is to
consumed for debinding the binding agent, and a large volume of
binding material is to be removed. In each cast layer, the metal
fiber distribution over the surface may become irregular.
[0014] In a further preferred method, the slurry comprises a
solvent for dissolving the binding agent, and during solidification
of the slurry, all solvent is removed by evaporation. This has a
further advantageous effect on the metal fiber distribution
homogeneity over the surface and in depth of the sintered metal
fiber medium which results from the further process.
[0015] Considering now the method to provide a sintered metal fiber
medium as subject of the invention in more detail.
[0016] In a first step, metal fibers are to be provided. Any type
of metal or metal alloy may be used to provide the metal
fibers.
[0017] The metal fibers are for example made of steel such as
stainless steel. Preferred stainless steel alloys are AISI 300 or
AISI 400-serie alloys, such as AISI 316L or AISI 347, or alloys
comprising Fe, Al and Cr, stainless steel comprising Chromium,
Aluminum and/or Nickel and 0.05 to 0.3% by weight of Yttrium,
Cerium, Lanthanum, Hafnium or Titanium, such as e.g. DIN 1.4767
alloys or Fecralloy.RTM., are used. Also Cupper or Copper-alloys,
or Titanium or Titanium alloys may be used.
[0018] The metal fibers can also be made of Nickel or a Nickel
alloy. Metal fibers may be made by any presently known metal fiber
production method, e.g. by bundle drawing operation, by coil
shaving operation as described in JP3083144, by wire shaving
operations (such as steel wool) or by a method providing metal
fibers from a bath of molten metal alloy.
[0019] In order to provide the metal fibers with their average
length, the metal fibers may be cut using the method as described
in WO02/057035, or by using the method to provide metal fiber
grains such as described in U.S. Pat. No. 4,664,971.
[0020] The metal fibers used to provide the sintered metal fiber
medium are characterized in having an equivalent diameter D and an
average fiber length L.
[0021] With equivalent diameter of a metal fiber is meant the
diameter of an imaginary circle having the same surface as the
surface of a radial cross section of the fiber.
[0022] Preferably the equivalent diameter D of the metal fibers is
less than 100 .mu.m such as less than 65 .mu.m, more preferably
less than 36 .mu.m such as 35 .mu.m, 22 .mu.m or 17 .mu.. Possibly
the equivalent diameter of the metal fibers is less than 15 .mu.m,
such as 14 .mu.m, 12 .mu.m or 11 .mu.m, or even more preferred less
than 9 .mu.m such as e.g. 8 .mu.m. Most preferably the equivalent
diameter D of the metal fibers is less than 7.mu.m or less than 6
.mu.m, e.g. less than 5.mu.m, such as 1 .mu.m, 1.5 .mu.m, 2 .mu.m,
3.mu.m, 3.5 .mu.m, or 4 .mu.m.
[0023] The metal fibers all have an individual fiber length. As
some distribution on these fiber lengths may occur, due to the
method of manufacturing the metal fibers, the metal fibers, used to
provide a sintered metal fiber medium as subject of the invention,
have an average fiber length L. This length is determined by
measuring a significant number of fibers, according to appropriate
statistical standards. The average fiber length of the metal fibers
is smaller than 10 mm, e.g. smaller than 6 mm, preferably smaller
than 1 mm, such as smaller than 0.8 mm or even smaller than 0.6 mm
such as smaller than 0.2 mm. As according to the present invention,
substantially all fibers used during the method of manufacturing
the sintered metal fiber medium will occur in the sintered metal
fiber medium, the average fiber length L can be measured in a
similar way on the sintered metal fiber medium.
[0024] The metal fibers in the sintered metal fiber medium thus may
have a ratio of average fiber length over diameter (UD) being
preferably less than 110, more preferred less than 100, but usually
more than 30. An UD of about 30 to 70 is preferred for metal fibers
with equivalent diameter in the range up to 6 .mu.m, in case the
metal fibers are obtained by the process as described in
WO02/057035, hereby incorporated by reference.
[0025] In the second step of the method as subject of the
invention, a slurry is to be provided. Although not to be
understood as limiting, preferably the slurry, comprising metal
fiber, a solvent and a binding agent, has a metal fiber
concentration in the range of 2% weight to 40% weight of the
slurry. Preferably 5% weight to 15% weight of the slurry is
provided by metal fibers. It was found that the smaller the
equivalent diameter of the metal fibers, the lower the
concentration of metal fibers is kept. Alternatively, the slurry
comprises a polymer binding agent and metal fibers, which polymer
binding agent is heated to reduce its viscosity.
[0026] A binding agent for the purpose of the invention is to be
understood as a product for thickening the slurry. Preferably a
water soluble binding agent is used, e.g. polyvinyl alcohols,
methyl cellulose ethers, hydroxypropylmethylcellulose, polyethers
from ethyleneoxide, acrylic acid polymers or acrylic copolymers.
The binding agent is added to the solvent, in a concentration of
preferably between 0.5% weight and 30% weight of the slurry. Most
preferred, a binding agent is chosen which requires a concentration
of less than 20% weight or even less than 15% weight or even less
than 10% weight of the slurry, in order to provide the required
viscosity. A viscosity range between 1000 cPs and 20000 cPs is
preferably used for the slurry. The components of the slurry are
blended using appropriate mixing equipment. In case foaming of the
slurry occurs, small amounts of a defoaming component is added.
[0027] In a third step, the slurry is tape cast using an
applicator, such as a doctor blade, on a preferably substantially
flat surface. The clearance of the applicator is kept relatively
small, this is preferably between 0.2 mm and 6 mm, more preferred
between 0.2 mm and 3 mm. The speed of movement of the applicator is
chosen according to the viscosity of the slurry and the composition
of the slurry.
[0028] The clearance and thus the thickness of the layer of the
slurry is chosen in function of the amount of metal fibers in the
slurry, the required weight per surface unit of the sintered metal
fiber medium, and the required density of the sintered metal fiber
medium.
[0029] In a next step, the cast slurry is solidified, forming a
foil which comprises the binding agent and the metal fibers. This
is preferably done by evaporating the solvent. A solvent may be
used which evaporates easily at ambient temperature. Alternatively,
the evaporation may be executed as a drying step in case water was
used as solvent. The drying or evaporating may be executed or
assisted by air-drying or may be forced by heating the cast slurry,
e.g. by forcing heated air over the surface of the cast slurry, or
by radiating, e.g. microwave- or IR-radiating. It is understood
that only the solvent, e.g. water is removed, which solvent was not
chemically bound to the binding agent. It is understood that, in
case solvent is evaporated, the thickness of the cast slurry is
reduced up to some extent, as the volume of the cast slurry is
reduced to provide the volume of the foil. Alternatively, the
binding agent is solidified by cooling the cast slurry, in case the
binding agent was heated to reduce its viscosity.
[0030] In the preferred situation, where all solvent is removed by
evaporation or where the binding agent is solidified by cooling, no
fibers are lost due to the mechanically removal of the solvent.
This has a further advantageous effect on the metal fiber
distribution homogeneity over the surface and in depth of the
sintered metal fiber medium which results from the further process.
As no fibers are removed, in this way the L/D ratio of the fibers
in the sintered metal fiber medium is identical to the UD of the
metal fibers used to make the slurry.
[0031] Possibly the foil, which can be handled as the binding agent
interconnects the metal fibers sufficiently, may be subjected to a
pressing action to further reduce the thickness of the foil.
[0032] In a final step, the foil comprising the metal fibers and
the binding agent is subjected to thermal treatment, for debinding
of the binding agent, and consecutively to sinter the metal fibers
to each other. Such debinding and sintering may be done in one
thermal operation, or may be executed as two consecutive
operations, not necessarily being done immediately one after the
other.
[0033] After sintering, the sintered metal fiber medium may further
be subjected to a compression, e.g. rolling or calendaring, in
order to further reduce the thickness of the sintered metal fiber
medium, or to smoothen the surface of the sintered metal fiber
medium.
[0034] Possibly, several layers of foil may be stacked to form a
layered medium. The different foils are not to comprise identical
metal fibers, nor should they be of an identical metal fiber
content per surface unit or volume. The different foils may differ
from each other in metal fibers, metal fiber content, thickness,
weight and other properties. Possibly, other porous metal
structures may be stacked to one or more foils. As an example, a
metal wire mesh, an expanded metal sheet or one or more layers of
air laid web, wet laid web or a layer of metal powder may be added
to the foils comprising metal fibers and a binding agent.
[0035] Possibly, a metal foil or a metal plate is added to the
stack.
[0036] Alternatively, such porous metal structure or metal foil or
plate may be added to the sintered metal fiber medium as subject of
the invention, e.g. by sintering such porous metal structure or
metal foil or plate to the sintered metal fiber medium as subject
of the invention in a second sintering operation.
[0037] Surprisingly it was found that a metal fiber medium obtained
by using a method as subject of the invention, has an improved
homogeneity of its physical properties such as air permeability,
filtration efficiency, pore size, bubble point pressure and pore
distribution.
[0038] The thickness of the sintered metal fiber medium may vary
over a large range, but relatively thin sintered metal fiber medium
may be obtained, e.g. sintered metal fiber medium with thickness
less than or equal to 0.2 mm or even less than or equal to 0.1 mm.
Even more surprising, it was found that sintered metal fiber media
having such thickness less than 0.2 mm or less than 0.1 mm, a
bubble point pressure of more than 10000 Pa may be obtained. It was
also notices that a high filtration efficiency may be obtained when
such sintered metal fiber media having a thickness less than 0.2 mm
or less than 0.1 mm are used as a liquid filter.
[0039] The bubble point pressure is measured using according to the
ISO 4003 testing method.
[0040] The weight of the sintered metal fiber medium as subject of
the invention is preferably less than 500 g/m.sup.2, more preferred
less than 400 g/m.sup.2 or even less than 300 g/m.sup.2, such as
less than 100 g/m.sup.2 such as about 3Og/m.sup.2.
[0041] The porosity of the sintered metal fiber medium may vary
over a large range, but it was found that such sintered metal fiber
medium may have 55% to 80%, such as in the range of 55% to 70%.
Without applying a rolling or pressing operation to the foil or
sintered metal fiber medium, porosities of 80 to 99% may be
obtained. Lower porosities may be obtained by applying a rolling or
pressing operation to either the foil and/or the sintered metal
fiber medium.
[0042] The term "porosity" P is to be understood as
[0043] P=100*(1-d)
[0044] wherein
[0045] d=(weight of 1 m.sup.3 sintered metal fiber medium)/(SF)
[0046] wherein
[0047] SF=specific weight per m3 of alloy out of which the metal
fibers of the sintered metal fiber medium are provided.
[0048] As the sintered metal fiber medium may be used for surface
filtration in solid-liquid filtration.
[0049] A sintered metal fiber medium as subject of the invention
may have a mean flow pore size of less than 2 times the equivalent
diameter D.
[0050] Preferably it was found that the sintered metal fiber medium
has a mean flow pore size of less than 1.5 times said equivalent
diameter D. More preferred, the mean flow pore size of the sintered
metal fiber media is equal or less than the equivalent diameter D
of the metal fibers of the sintered metal fiber medium, increased
by one .mu.m.
[0051] The mean flow pore size is measured using a "Coulter
Porometer II" testing equipment, which performs measurements of the
mean flow pore size according to ASTM F-316-80.
[0052] In the preferred case, when the mean flow pore size of less
than 2 times the equivalent diameter D and when the metal fibers in
the sintered metal fiber medium have a ratio of average fiber
length over diameter (UD) which is preferably less than 110, more
preferred less than 100, but usually more than 30, surprisingly it
was found that such sintered metal fiber media can be cleaned
repetitively, e.g. by back flush, back flush or back pulse, with
high efficiency and apparently with a restricted or even no
particles retained after cleaning. Especially when the method is
used in which all the solvent is removed by evaporation.
[0053] An L/D of about 30 to 70 is preferred for metal fibers with
equivalent diameter in the range up to 6 .mu.m, in case the metal
fibers are obtained by the process as described in WO02/057035,
hereby incorporated by reference.
[0054] Advantageously the outer surface of the sintered metal fiber
medium, to be used as inflow side of the medium when used for
solid-liquid surface filtration, has a substantially flat surface.
With substantially flat is meant that the Ra value measured over a
statistically relevant length less than three times the equivalent
diameter D of the metal fibers of the sintered metal fiber medium.
More preferred, Ra value of the first outer surface of the sintered
metal fiber medium is less then the equivalent diameter D, for
example less than 0.5 times the equivalent diameter D.
[0055] Ra value is defined as the arithmetic mean deviation of the
surface height from the mean line through the measured profile from
the measured length. The mean line is defined so that equal areas
of the profile lie above and below the line.
[0056] A sintered metal fiber medium obtained by the method as
subject of the invention may advantageously be used as filter
medium, for filtration of particulates from fluids, either gas or
liquid, e.g. by surface filtration. As an example, the sintered
metal fiber medium may be used for soot filtration, or for
filtration of beverages, such as beer, wine, or for filtration of
oils or coolants. The sintered metal fiber medium may also be used
in fuel cells.
BRIEF DESCRIPTION OF THE DRAWINGS
[0057] The invention will now be described into more detail with
reference to the accompanying drawings wherein
[0058] FIGS. 1, 2, 3, 4 and 5 show schematically the steps of
methods as subject of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
[0059] An embodiment of the present invention is described
hereinafter.
[0060] In a method as shown in FIG. 1, in the first step 110 of the
method as subject of the invention, metal fibers 111 are
provided.
[0061] In a next step 120, a slurry 121 was made from metal fibers,
a binding agent and a solvent preferably water.
[0062] This slurry was blend, using a blending means 122, for
several minutes in order to form a substantially stable slurry.
[0063] In step 130, the slurry 121 was provided to an applicator
131, being doctor blade and tape cast on a substantially flat and
water repellant surface 132. A cast slurry 1 33 was provided.
[0064] In the next step 140, the cast slurry 133 was dried and
transformed into a foil 141, as an example in ambient
temperature.
[0065] In a next step 150, a thermal treatment was executed in two
steps. During the first part, in order to debind the binding agent,
the foil 141 was subjected to a thermal treatment under ambient
atmosphere. Consecutively, the debound material was sintered using
a sintering process.
[0066] As shown in FIG. 2, in an additional step 210, several foils
141 may be stacked to each other prior to debinding the binding
agent.
[0067] As shown in FIG. 3, an additional step of compressing, e.g.
rolling the sintered metal fiber medium 311 in step 310 may be
executed. All other steps are identical to the steps as described
and shown in FIG. 1 and FIG. 2.
[0068] As shown in FIG. 4, in a next step after sintering of the
metal fibers in the thermal treatment step 150, and possibly after
compression step 310, a porous metal structure 411, e.g. a mash, a
metal foil or a metal plate may be added to the sintered metal
fiber medium 311 and sintered in a second sintering operation to
the sintered metal fiber medium.
[0069] As shown in FIG. 5, an additional step of compressing, e.g.
rolling the foil prior to debinding in step 510 may be executed.
All other steps are identical to the steps as described and shown
in FIG. 1.
[0070] It is understood that this compression step 510 may as well
be combined with all other steps as shown in FIGS. 1, 2, 3 and
4.
[0071] Possibly, the sintered metal fiber medium was layered with a
metal wire mesh and sintered a second time to attach the mesh to
the sintered metal fiber medium.
[0072] As an example, a sintered metal fiber medium was provided
using the method as shown in FIG. 4.
[0073] In a first step, metal fibers with equivalent diameter of 2
.mu.m, made by means of bundle drawing processes, are provided. The
endless metal fibers are cut into metal fibers having an average
length of 109 .mu.m, using the method of WO02/057035. The metal
fibers were provided out of AISI 316L alloy.
[0074] Hereafter, a slurry was made using following
composition:
[0075] 9.09% weight of the slurry being metal fibers, 1.36% weight
of the slurry being methyl cellulose ether (being binding agent)
89.55% weight of the slurry being water (being the solvent).
[0076] The slurry was tape cast using a doctor blade having a
clearance of 1.5 mm.
[0077] Such cast slurry was solidified by drying to the air for
about 24 h. Alternatively, IR-radiation may be used to heat the
cast slurry and assist the drying operation. A foil was obtained
comprising the binding agent with chemically bound water and metal
fibers. A non-sintered metal fiber medium was obtained having a
thickness of 251 .mu.m and having a weight of 127 g/m.sup.2. The
non-sintered metal fiber medium comprised 13% weight of binding
agent, and 87% weight of metal fibers.
[0078] Several foils were stacked to provide a layered foil of
about 400 g/m.sup.2.
[0079] This stack of foils is subjected for about 30 minutes to a
temperature of 400.degree. C. under ambient atmosphere for
debinding the binding agent. Consecutively, the debound material
was sintered at 1100 C for about 30 minutes under H2. The metal
fibers of all layers of foil are sintered to each other.
[0080] The sintered metal fiber medium obtained was rolled to a
porosity of 65%, having a weight of about 369 g/m.sup.2. The
sintered metal fiber medium has a bubble point pressure of 9470 Pa
and a mean flow pore size of 2.9 .mu.m. An Ra of 0.99 .mu.m was
obtained.
[0081] A metal wire mesh is added to the sintered metal fiber
product, and again subjected to a sintering operation under high
vacuum atmosphere at about 1050.degree. C. for 60 minutes.
Alternatively a metal foil or plate is sintered to the sintered
metal fiber medium. The mesh may as well be added to the stack of
foils made prior to the first sintering operation.
[0082] Using similar steps, a sintered metal fiber product may be
obtained, when using metal fibers of 1.5 .mu.m diameter, having a
substantially similar UD. The obtained sintered metal fiber medium
have a weight of about 333 g/m.sup.2 and a porosity of 65%. The
sintered metal fiber medium has a bubble point pressure of 13609 Pa
and a mean flow pore size of 2.4 .mu.m.
* * * * *