U.S. patent application number 11/364184 was filed with the patent office on 2006-07-06 for short metal fibers.
This patent application is currently assigned to N.V. BEKAERT S.A.. Invention is credited to Lieven Anaf, Ronny Losfeld.
Application Number | 20060143882 11/364184 |
Document ID | / |
Family ID | 8172425 |
Filed Date | 2006-07-06 |
United States Patent
Application |
20060143882 |
Kind Code |
A1 |
Losfeld; Ronny ; et
al. |
July 6, 2006 |
Short metal fibers
Abstract
The present invention relates to short metal fibers. A set of
short metal fibers, with an equivalent diameter ranging from 1 to
150 .mu.m, comprises entangled and curved fibers. At least 10% of
the short metal fibers are entangled, whereas the length of the
curved fibers is distributed according to a gamma-distribution,
having an average length preferably between 10 and 2000 .mu.m.
Inventors: |
Losfeld; Ronny; (Waregem,
BE) ; Anaf; Lieven; (Waregem, BE) |
Correspondence
Address: |
FOLEY AND LARDNER LLP;SUITE 500
3000 K STREET NW
WASHINGTON
DC
20007
US
|
Assignee: |
N.V. BEKAERT S.A.
|
Family ID: |
8172425 |
Appl. No.: |
11/364184 |
Filed: |
March 1, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10450139 |
Jun 12, 2003 |
7045219 |
|
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PCT/EP01/14648 |
Dec 10, 2001 |
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11364184 |
Mar 1, 2006 |
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Current U.S.
Class: |
29/4.53 ;
29/4.55; 442/377 |
Current CPC
Class: |
C04B 2235/96 20130101;
Y10T 428/12431 20150115; Y10T 29/143 20150115; B22F 2009/046
20130101; C04B 2235/9607 20130101; Y10S 165/907 20130101; C04B
35/488 20130101; C22C 47/025 20130101; Y10T 442/654 20150401; F28F
2255/18 20130101; B23P 17/06 20130101; Y10T 428/12424 20150115;
F28F 21/082 20130101; B22F 1/004 20130101; B01J 35/04 20130101;
Y10T 428/2913 20150115; F28D 17/02 20130101; B22F 3/002 20130101;
Y10T 442/60 20150401; Y10T 428/249931 20150401; Y10T 428/249967
20150401; C04B 2235/526 20130101; Y10T 442/655 20150401; Y10T
428/249962 20150401; F28F 7/02 20130101; B01D 39/2044 20130101;
B22F 2998/00 20130101; Y10T 29/147 20150115; Y10T 428/249924
20150401; Y10T 428/249928 20150401; C04B 2235/5264 20130101; C04B
35/76 20130101; C04B 35/80 20130101; C04B 35/803 20130101; B01D
39/2048 20130101; B01J 35/06 20130101; B22F 2998/00 20130101; B22F
5/007 20130101; B22F 2998/00 20130101; C22C 47/025 20130101 |
Class at
Publication: |
029/004.53 ;
029/004.55; 442/377 |
International
Class: |
B23P 17/06 20060101
B23P017/06 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 13, 2000 |
EP |
00 204 497.2 |
Claims
1. A method to provide a set of short metal fibers, comprising the
steps of: individualizing the metal fibers by a carding operation;
providing the set of short metal fibers by cutting or entangling
and sieving the set of short metal fibers.
2. A method to provide a set of short metal fibers as in claim 1,
said providing the set of short metal fibers by cutting or
entangling and sieving the set of short metal fibers is done using
a comminuting machine.
Description
[0001] The present application is a divisional of U.S. application
Ser. No. 10/450,139, filed Jun. 12, 2003, the entire contents of
which is incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The invention relates to short metal fibers and to a
sintered metal fiber product, using such fibers. The invention
further relates to a method to produce short metal fibers and a
sintered metal fiber product, using such fibers.
BACKGROUND OF THE INVENTION
[0003] Metal fibers having a rather flat cross section, with
diameter less than 15 .mu.m and a length of less than 400 .mu.m are
known from U.S. Pat. No. 4,703,898. These fibers have a crescent
shape and have a small, point-like hook at both ends. This document
further provides a method to produce such fibers.
[0004] JP2175803 describes similar short metal fibers, which have a
curved shape.
[0005] Short metal fibers are also known from GB889583. These metal
fibers may be undulated or "kinked" over their length. In this
document, these terms mean that the major axis of the fibers change
two or more times over the length of the fiber.
SUMMARY OF THE INVENTION
[0006] Most known short metal fibers are rather difficult to pour
homogeneously in a mould, providing identical properties throughout
the whole mould volume such as density and sizes of open space
between adjacent fibers, although lots of improvements have been
suggested.
[0007] The present invention relates to an alternative set of short
metal fibers, which have an improved pourability. Further, the
invention relates to sintered short metal fiber products and to a
method to provide short metal fibers and sintered short metal fiber
products.
[0008] A set of short metal fibers used to provide the temperature
resistant material as subject of the invention is characterized by
the presence of two different groups of short metal fibers, being
"entangled" fibers and "curved" fibers.
[0009] A set of short metal fibers as subject of the invention
comprises short metal fibers with an equivalent diameter "D"
between 1 and 150 .mu.m preferably between 2 and 100. Most
preferably the equivalent diameter ranges between 2 and 50 .mu.m or
even between 2 and 35 .mu.m such as 2, 4, 6.5, 8, 12 or 22
.mu.m.
[0010] With the term "equivalent diameter" is meant the diameter of
an imaginary circle, which has the same surface as the surface of a
fiber, cut perpendicular to the major axis of the fiber.
[0011] The set of short metal fibers comprises entangled fibers.
The number of entangled fibers in a set of short metal fibers as
subject of the invention ranges from 5 to 35%. Preferably more than
10% of all short metal fibers in the set of short metal fibers are
entangled. These fibers are hereafter referred to as "entangled
fibers". To have a statistically reliable percentage, a sample of
at least 50 fibers, randomly chosen out of the set of short metal
fibers are to be evaluated.
[0012] The percentage of entangled fibers is measured and
calculated as: % entangled fibers=100.times.(#entangled/#total)
wherein #entangled=number of entangled fibers out of the sample;
#total=number of fibers out of the sample.
[0013] The entangled fibers of the set of short metal fibers as
subject of the invention have an average length "Le", which is
considerably longer as the average length of the curved fibers
"Lc". The average length of the entangled fibers is at least 5
times the average length of the curved fibers. Preferably, the
average length of the entangled fibers is more than 10 times the
average length of the curved fibers. Preferably, the average length
of the entangled fibers is larger than 200 .mu.m, or even more than
300 .mu.m, most preferably more than 1000 .mu.m. the entangled
fibers may be entangled with themselves (individually) or may be
entangled together with some other entangled fibers. The entangled
fibers, either individually or together with other entangled
fibers, cannot be individualized as an essentially straight fiber
out of the shape which is defined by the entanglement of the
fibers. The major axis of each fiber changes so often and
unpredictably, that the fiber may be entangled in many different
ways. Some of the fibers are present in a shape, which resembles to
a clew. The effect is comparable to the so-called pilling effect,
well known in the textile industry, and in carpet industry more in
particular. One or more fibers get trapped into a small ball. The
trapped fibers may not be separated from this ball anymore. Other
fibers look more like a pigtail. The are characterized by a major
axis which changes several times in an unpredictable way, so a
relatively chaotic shape may be provided.
[0014] The other short metal fibers out of the set of short metal
fibers are hereafter referred to as "curved" fibers
[0015] The average length "Lc" of the curved fibers of the set of
short metal fibers may range from 10 to 2000 .mu.m, preferably from
30 to 1000 .mu.m such as 100 .mu.m, 200 .mu.m or 300 .mu.m. When a
length distribution is measured from these curved fibers as part of
a set of short metal fibers as subject of the invention, a
gamma-distribution is obtained. This gamma-distribution is
identified by an average length Lc and a shape factor "S".
According to the present invention, the gamma-distribution of the
length of the curved fibers, has a shape factor S ranging between 1
and 10.
[0016] For average lengths Lc larger than 1000 .mu.m, usually a
shape factor S lager than 5 is measured. For average lengths Lc
between 300 .mu.m and 1000 .mu.m, a shape factor S between 2 and 6
is usually measured. For average lengths Lc smaller than 300 .mu.m,
usually a shape factor S smaller than 3 is measured. To have a
statistically reliable distribution, at least 50 curved fibers,
randomly chosen out of the set of short metal fibers are to be
measured.
[0017] The L/D ratio of a set of short metal fibers as subject of
the invention has an L/D-ratio of more than 5, preferably more than
10, wherein L is the average length of all fibers, present in a
representative sample of fibers from the set of short metal fibers.
As described above, this sample comprises at least 50 fibers out of
the set of short metal fibers. Preferably, but not necessarily, the
curved fibers out of a set of short metal fibers as subject of the
invention has an Lc/D-ratio of more than 5, preferably more than
10.
[0018] Further, a majority of these curved fibers have a major
axis, which changes over an angle of at least 90.degree.. This
angle is the largest angle, which can be measured between two
tangents of this major axis. Preferably, 40% of the curved fibers
has a major axis, changing more than 90.degree., e.g. more than
45%, or preferably more than 50%. To measure these curves of the
major axis, a microscopic image with appropriate enlargement is
taken from several short metal fibers. Using a computer imaging
system, the tangents of the major axis and the largest angle
between them is calculated. To have a statistically reliable
sample, at least 50 curved fibers, randomly chosen out of the set
of short metal fibers are to be measured.
[0019] Such a set of short metal fibers has several advantages. A
set of short metal fibers as subject of the invention has good
pouring behavior.
[0020] Further, when short metal fibers as subject of the invention
are poured, e.g. in a specific three-dimensional mould or on a flat
surface, numerous contact points can be noticed between the short
metal fibers. They are, so to say, ready to be sintered without a
major force which is normally to be applied before sintering. The
amount of contact points is present without requiring a force,
which is not the case when the diameter of the short metal fibers
extends beyond 150 .mu.m. One understands that, if necessary to
increase even more the number of contact points, or to decrease the
pore volume and/or size, such forces may be applied before or
during further processing.
[0021] Once poured, a set of short metal fibers as subject of the
invention has an apparent density in the range of 10 to 40%,
according to ISO 787-11. The pores between the short metal fibers
are very small, but the number of pores is sufficiently large to
provide an apparent density which is typically between 10 and 40%.
A porosity, calculated as indicated below, ranges between 60 and
90%. Porosity (%)=100%-apparent density (%)
[0022] The volumes between the fibers are similar throughout the
poured volume, so providing an isotropic volume.
[0023] Short metal fibers as subject of the invention may be
obtained by a method comprising the following steps: [0024]
individualizing the metal fibers by a carding operation; [0025]
providing the set of short metal fibers by cutting or entangling
and sieving the set of short metal fibers, preferably by using a
comminuting machine.
[0026] First, metal fibers, being present in a bundle of fibers, in
a yarn or a textile structure, or even as staple fibers, are
individualized to some extend by a carding operation.
[0027] These more or less individualized fibers are brought into a
comminuting device. In this device, each fiber is cut into short
metal fibers by fast rotating knifes. The blade of these knifes,
having a certain blade thickness, encounter or `hit` the fibers
usually in radial direction. The fibers are mechanically
plastically deformed and entangled or possibly broken into a
smaller length. Due to the centrifugal force, the so provided short
metal fibers (curved or entangled) are blown outwardly against the
external wall of the comminuting device. This external wall
comprises a sieve with well-defined openings. According to these
openings, short metal fibers with a certain length may pass through
the sieve, whereas too long short metal fibers will stay in the
comminuting device and possibly be hit once again, until the
lengths are sufficiently small to pass the sieve, or until they are
entangled enough to allow passage through the sieve.
[0028] The alloy of the metal fibers is to be chosen in order to
provide required properties such as temperature resistance or
electrical conductivity. Stainless steel fibers out of AISI
300-type alloys, e.g. AISI 316L or fibers based on
INCONEL.RTM.-type alloys such as INCONEL.RTM.601 or
NICROFER.RTM.-type alloys such as NICROFER.RTM. 5923 (hMo Alloy 59)
and NICROFER 6023, or fibers based on Fe--Cr--Al alloys may be
used. Also Ni-fibers, Ti-fibers, Al-fibers, Cu-fibers or fibers out
of Cu-alloy or other alloys may be used.
[0029] Metal fibers may e.g. be bundle drawn or shaved, or provided
by any other process as known in the art.
[0030] The short metal fibers as subject of the invention may be
used to provide a sintered product. The method of manufacturing a
sintered product comprises the steps of: [0031] providing a set of
short metal fibers; [0032] pouring said set of short metal fibers
into a three-dimensional mould or on an essentially plane surface;
[0033] sintering said set of short metal fibers to form a sintered
product.
[0034] Possibly, before the sintering, the short metal fibers are
pressed together to improve the coherency and/or to change the
density.
[0035] Alternatively, the short metal fibers are brought in a
suspension, using an appropriate agent or a mixture of appropriate
agents.
[0036] The suspension is brought into a mould or poured onto an
essentially plane surface. In a subsequent step the suspension
liquid is removed, e.g. evaporated or sucked out. The mould,
comprising the short fibers is then subjected to a sintering
process in which all non-metal fiber elements are removed and in
which a sintering between the metal fibers is obtained.
[0037] The sintering conditions are dependent upon the alloy and
the properties required by the short metal fibers and the final
sintered metal fiber product.
[0038] A great advantage of the method of the present invention is
that the set of short metal fibers can easily be poured
homogeneously; resulting in isotropic properties over the whole
volume of the sinter metal fibers product. For example the density
and the sizes of the pores are homogeneous over the whole volume of
the product.
[0039] Another advantage of sintered products according to the
present invention is their high porosity.
[0040] As indicated above, the short metal fibers will arrange
themselves providing a three dimensional fiber structure, with
numerous small pores and numerous contact points. The pores are
characterized by a relatively small size.
[0041] Applying forces on the short metal fibers during sintering
may decrease pore size and porosity.
[0042] The porosity of a sintered product according to the
invention is equal to the porosity of the poured fibers, as
described above. The fibers do not have to be put under pressure to
form a coherently sintered volume. This means that the porosity
ranges generally between 60 and 90%. The porosity is for example
70, 80 or 85%.
[0043] However, dependent on the type and level of pressure, the
porosity may be lowered to 49% if necessary, for example by cold
isostatic pressing.
[0044] According to the specific use of the short metal fibers or
the sintered metal fiber product, different metals and/or alloys
may be used to provide the short metal fibers or the sintered metal
fiber product.
[0045] Sintered short metal fiber products may have different
shapes, according to the specific requirements of their
application. Short metal fibers may be sintered into flat plates,
rings, cylindrical or tube like shapes. Also more complex shapes
such as monolithic structures may be obtained.
[0046] Sintered products may be used for different
applications.
[0047] They may be used as a filtering device, for example a
filtering device to filter gases or liquids.
[0048] The alloy of the metal fibers may be chosen in order to
provide the filtering device the required properties such as
temperature resistance and chemical resistance. Consequently, the
filtering device may be used for high temperature applications, for
example for the filtration of hot gases or for the filtration of
corrosive gases or liquids.
[0049] The filtering device may have any shape. Preferred shapes
are flat plates, rings, or cylindrical or tube like shapes.
[0050] When a sintered product as subject of the invention is used
as a filtering devices, especially after being isostatically
pressed, such filtering device may have an absolute filter rating
of 0.5 .mu.m up to 20 .mu.m. Usually, the absolute filter rating
may range between 1/3 and 1/2 of the equivalent diameter of the
short metal fibers used.
[0051] A filtering device according to the present invention can
thus be used for microfiltration applications, for example for the
filtration of air in clean labs or in product rooms of electronic
components.
[0052] A sintered product according to the present invention is in
particular suitable to filter diesel exhaust gases.
[0053] A product as subject of the present invention may also be
used as a carrier for catalysts. Therefore, commercially available
catalyst can be applied on a sintered product.
[0054] A sintered product on which a catalyst is applied,
hereinafter referred to as the catalyst, can be used to treat
exhaust gases such as exhaust gases from incinerators or diesel
engines, thereby removing harmful substances, such as NO.sub.x,
NH.sub.3, CO, dioxins, O.sub.3.
[0055] The catalyst is characterised by a porous open structure and
a high specific surface. At the same time it is characterised by a
high strength. Since the sintered product may withstand high
temperatures, the catalyst can be used at high operating
temperatures.
[0056] All these features result in a catalyst having a high
efficiency of catalytic conversion.
[0057] Furthermore, a sintered product according to the present
invention may be used as a catalytic filter which combines particle
and/or dust retention and catalytic conversion of harmful
components.
[0058] A sintered product may also be used as heat exchanging
device. e.g. in Stirling engines, where a sintered product may be
mounted in the passage of the working fluid or gas. Such device is
also referred to as heat recuperator. The sintered product is
heated when the working fluid or gas passes from the hot to the
cold chamber of the Stirling engine. Afterwards, the heat, captured
in the sintered product is regenerated when the cold working fluid
or gas passes again through the sintered product, while it flows
back to the hot chamber of the Stirling engine.
[0059] A three-dimensional sintered product according to the
present invention can also be used a porous mould, for example as a
mould to form glass products such as windshield glass.
[0060] Surprisingly, another use of a set of short metal fibers as
subject of the invention is found by blending a set of short metal
fibers with a ceramic matrix or ceramic or high-temperature
resistant glue. A blend of short metal fibers and ceramic matrix or
ceramic or high temperature resistant glue, up to 15% or even 20%
by weight of short metal fibers, seems to resist thermal expansions
to a larger extend, compared to the pure ceramic or high
temperature resistant glue, once the glue or matrix comprising
short metal fibers are cured. A higher resistance to thermal cracks
in the glue was obtained. Preferably, the set of short metal fibers
represents at least 0.5% of weight of temperature resistant
material. Positive results were obtained especially when a set of
short metal fibers is used which comprises entangled and curved
fibers of which more than 10% of the set of short metal fibers are
individually entangled fibers.
[0061] Surprisingly, only a relatively small change in electrical
conductivity was noticed when the amount of the set of short metal
fibers is kept lower than 10% by weight of the temperature
resistant material, e.g. in the range of 1% to 9.5%, in the mean
time providing sufficient resistance to thermal shocks and cracks.
Higher percentages by weight of a set of short metal fibers may be
used, e.g. more than 15% or even more than 20% or 30%, however such
percentages of weight are not absolutely necessary to obtain a
sufficient resistance to thermal shocks.
[0062] This effect is not restricted to short metal fibers as
subject of the invention, but was also noticed using other short
metal fibers. However the presence of entangled fibers plays an
important role for the improvement of the thermal shock resistance.
On the other hand, the presence of the curved fibers provides
better pourablity and mixing behavior into the ceramic matrix or
glue.
[0063] Preferably, ceramic matrices or ceramic glues based on
SiO.sub.2, Al.sub.2O.sub.3, ZrO.sub.2 and/or MgO are used.
BRIEF DESCRIPTION OF THE DRAWINGS
[0064] The invention will now be described into more detail with
reference to the accompanying drawings wherein
[0065] FIGS. 1A, 1B, 1C, ID, 1E and 1F are images of short metal
fibers, all being part of a set of short metal fibers as subject of
the invention.
[0066] FIG. 2 shows a curved fiber being part of a set of short
metal fibers as subject of the invention.
[0067] FIG. 3 shows a graph of the length distribution of a set of
short metal fibers as subject of the invention.
[0068] FIG. 4 shows a graph of the curvature distribution of the
curved fibers out of a set of short metal fibers as subject of the
invention.
[0069] FIG. 5 shows a sintered metal fiber product as subject of
the invention.
[0070] FIGS. 6a and 6b show a sintered product having a monolithic
structure.
DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
[0071] A preferred embodiment of a set of short metal fibers as
subject of the invention is shown in FIGS. 1A, 1B, 1C, 1D, 1E and
1F, which all show short metal fibers out of the same set of short
metal fibers as subject of the invention. The short metal fibers,
having an equivalent diameter of 22 .mu.m, are obtained by
providing a bundle of AISI 316L bundle drawn fibers of a carding
device and further to a comminuting device. As may be seen from
FIG. 1A to 1F, the shape of the short metal fibers may be very
different. Some short metal fibers are clearly entangled fibers,
such as fibers 11, 12 and 13. Fibers 12 are more curled
irregularly, providing a non-defined shape. Fibers 13 are
individually entangled to a non-defined shape. Fibers 11, 12 and 13
are to be understood as "entangled fibers". Other fibers 14 are
clearly curved, although the curling angles are unpredictably. Some
fibers, such as fiber 15, may have a limited curvature. An example
of such a curved fiber is shown schematically in FIG. 2. A curved
fiber has two ends, being a first end 21 and a second end 22. A
major axis 23 connects the center of the transversal cuts over the
whole length of the fiber. The direction of the major axis 23
changes over an angle .alpha.. Angle .alpha. is absolute value of
the largest angle which can be measured between two vectors 24
having a direction equal to the tangent of the major axis, starting
point being a point of the major axis, and a sense pointing from
first end 21 to second end 22.
[0072] FIG. 3 shows the angle distribution of the change of major
axis of the curved fibers of the set of short metal fibers from
FIGS. 1A to 1F. A sample to 316 fibers, randomly chosen out of the
total set of short metal fibers was taken. Each bar 33 in the graph
represents the number of fibers (to be read at the left ordinate
34), having a major axis changing with an angle .alpha., .alpha.
being smaller than the angle value underneath the bar, which is
related to that bar, but larger than the angle, related to the bar
at its left side. E.g. the bar related to 90.degree., indicates the
number of curved fibers, having an angle .alpha. smaller than
90.degree., but larger than 80.degree..
[0073] Related numbers are summarized in Table I TABLE-US-00001
TABLE I % curved with % curved with angle angle .alpha. or angle
.alpha. of number in .alpha./total curved entangled/total fibers
sample fibers fibers 0 0 0.00 0.00 10 2 0.65 0.55 20 3 0.97 0.83 30
10 3.24 2.77 40 16 5.18 4.43 50 16 5.18 4.43 60 19 6.15 5.26 70 22
7.12 6.09 80 21 6.80 5.82 90 18 5.83 4.99 100 17 5.50 4.71 110 10
3.24 2.77 120 14 4.53 3.88 130 14 4.53 3.88 140 15 4.85 4.16 150 28
9.06 7.76 160 18 5.83 4.99 170 31 10.03 8.59 180 35 11.33 9.70
entangled 52 -- 14.40 total 52 entangled total curved 309 total
361
[0074] Line 31 indicates the cumulative curve of the number of
curved fibers having an angle .alpha., less than the angle value in
abscissa. This number is expresses, as indicated on the right
ordinate 35, in percentage compared to the total number of curved
fibers in the sample. More than 50% of the curved fibers have a
major axis direction changing more than 90%.
[0075] As also indicated in FIG. 3, more than 10% of all short
metal fibers out of the set of short metal fibers are entangled
fibers. This is indicated by the dots 32, which represent the
percentage of fibers, also to be read on the right ordinate 35,
comprised in the related bar 33, compared to the total number of
short metal fibers out of the sample taken from the set of short
metal fibers.
[0076] FIG. 4 shows the length distribution of the curved fibers of
two sets of short metal fibers as subject of the invention.
[0077] A first length distribution 41, indicated with black bars,
is a length distribution of the curved fibers of a set of short
metal fibers, having an equivalent diameter of 8 .mu.m. The set of
short metal fibers was provided using bundle drawn stainless steel
fibers, alloy AISI 3O2. A representative and randomly chosen sample
of 227 fibers was taken. An average length Lc of 420 .mu.m was
found. The length distribution is a gamma-distribution 42, being
characterized with a shape factor S being 3.05. The bars of
distribution 41 is to be understood as the percentage of curved
fibers out of the sample (read in ordinate 43), which has a length
(expressed in .mu.m and indicated in abscissa 44) in the range with
upper limit as indicated underneath the bar, and lower limit being
the length indicated under the adjacent bar left if it. In the same
way, the gamma-distribution reads the percentage of fibers in
ordinate 43 in the range indicated on the abscissa 44 as explained
above.
[0078] Another length distribution 45 is shown in FIG. 4, indicated
with white bars, which is a length distribution of the curved
fibers of a set of short metal fibers, having an equivalent
diameter of 12 .mu.m. The set of short metal fibers was provided
using bundle drawn stainless steel fibers, alloy AISI 316L. A
representative and randomly chosen sample of 242 fibers was taken.
This length distribution accords to a gamma-distribution 46, which
is characterized with a shape factor S being 3.72. An average
length Lc of the curved fibers of 572 .mu.m was measured.
[0079] A sintered metal fiber product as subject of the invention
may be provided as shown in FIG. 5. The short metal fibers used
have a diameter of 22 .mu.m. The thickness 51 of the medium is
approximately 40 mm. The sintered metal fiber product has a
porosity of 81%. The short metal fibers were stainless steel bundle
drawn fibers, Fecralloy.RTM. type alloy. Such ring-like shape may
be used as heat regenerating device in a Stirling engine. An
alternative sintered metal fiber product, as subject of the
invention is obtainable by sintering short metal fibers as subject
of the invention to a flat shape, plate-like product. E.g. short
metal fibers of alloy AISI 444, having an average length of 1000
.mu.m and an equivalent diameter of 65 .mu.m, obtained by a shaping
process as explained in WO9704152, are sintered to a flat volume
with thickness of 2.35 mm and a weight of 5226 g/m.sup.2. A
porosity of 72% and an absolute filter rating of 92 .mu.m was
obtained. When a similar product, using short metal fibers as
subject of the invention, being bundle drawn fibers of an
equivalent diameter of 12 .mu.m and an average length L of 800
.mu.m, isostatically pressed using 800 Bar, a porosity of 70% was
obtained, and an absolute filter rating of 5.3 .mu.m.
[0080] One understand that other shapes, such as flat plates, or
tube-like or cylindrical shapes may be obtained. Even monolithic
structures, e.g. to be used in a diesel exhaust filter, filtering
soot from the exhaust gas, may be obtained.
[0081] FIG. 6a shows a monolithic structure 600 comprising a set of
short metal fibers. FIG. 6b shows a cross-section along line
A-A'.
[0082] The monolithic structure shown in FIG. 6 is in particular
suitable to filter exhaust gases.
[0083] The gas to be filtered enters the monolithic structure at
inlet side 602 and exits the monolithic structure at outlet side
604.
[0084] The monolithic structure has a number of cells 606. Each
cell has a first end adjacent the inlet of the monolithic structure
and a second end adjacent the outlet of the monolithic
structure.
[0085] At least part of the cells is blocked at the second ends of
the cell by a barrier 607. The barrier comprises a material that
does not allow the passage of the gaseous stream.
[0086] In the preferred embodiment of FIG. 6 a cell is either
blocked at its inlet side as for example cell 608; or at its outlet
side as for example cell 610.
[0087] Thus, the exhaust stream can not pass freely through the
cells, but is obliged to pass through the walls to a neighbouring
cell having an open outlet side.
[0088] For example exhaust gas entering cell 610 passes through the
wall surrounding cell 610, as indicated by the arrows 612, for
example to cell 608 through which it can leave the monolithic
structure at the outlet side.
[0089] Possibly, the cell walls are coated with a catalyst or
alternatively a catalyst is applied into the porous structure of
the monolithic structure.
[0090] A three-dimensional sintered product according to the
present invention can also be used a porous mould, for example as a
mould to form glass products such as windshield glass.
[0091] A set of short metal fibers as of FIG. 3, was used to
improve the resistance to thermal cracking and thermal shocks of a
ZrO.sub.2--MgO based ceramic glue.
[0092] A ceramic material, being a ceramic past, which may be used
as ceramic glue, was prepared using 77 gram ZrO.sub.2--MgO based
compound and 10 gram of water. An amount of a set of short metal
fibers having an average equivalent diameter of 22 .mu.m, of which
the length distribution is provided as indicated with 45 in FIG. 4,
is mixed in this ceramic paste, as indicated in Table I.
[0093] The ceramic paste was heated to a temperature of 600.degree.
C., and this temperature was kept for 90 sec. after which it was
cooled to ambient in 60 sec. The number of cracks on an equal
surface was counted, and is resumed in Table II. TABLE-US-00002
TABLE II Temperature resistant matrix Set of short % of weight of
(ceramic matrix) metal fibers of short metal Number of (gram) 12
.mu.m (gram) fibers (%) cracks (--) 77 0 0 20 77 2 2.5 16 77 4 4.9
8 77 8 (sample I) 9.4 0 77 8 (sample II) 9.4 2
[0094] An identical result was obtained using a set of short metal
fibers of 22 .mu.m equivalent diameter.
* * * * *