U.S. patent application number 10/872318 was filed with the patent office on 2005-12-22 for method for producing porous metal with micro-holes.
Invention is credited to Kang, Shang Wen, Lee, Ching Man, Tseng, Hsin Chao, Tseng, Shao Chien, Yuan, Te Yu.
Application Number | 20050281699 10/872318 |
Document ID | / |
Family ID | 35480767 |
Filed Date | 2005-12-22 |
United States Patent
Application |
20050281699 |
Kind Code |
A1 |
Kang, Shang Wen ; et
al. |
December 22, 2005 |
Method for producing porous metal with micro-holes
Abstract
A method for producing porous metal with micro-holes comprises
the steps of selecting a base material, sintering or smelting,
removing the filling material, washing, drying and reduction. The
base material is selected from pure metal and alloy powder for
sintering or casting. The filling material is fine powder solvable
in water or in alkaline solvents. The sintering step further
includes steps of mixing and metal powder metallurgy. The casting
utilizes high or low waves to fuse the base material particles. A
selected solvent removes the filling material in the raw metal bulk
produced in the sintering or casting step, and a product of porous
metal with micro-holes is formed.
Inventors: |
Kang, Shang Wen; (Taipei,
TW) ; Tseng, Shao Chien; (Tau Yuan Hsien, TW)
; Tseng, Hsin Chao; (Tau Yuan Hsien, TW) ; Yuan,
Te Yu; (Tau Yuan Hsien, TW) ; Lee, Ching Man;
(Tau Yuan Hsien, TW) |
Correspondence
Address: |
Shang Wen Kang
235 Chung-Ho
Box 8-24
Taipei
TW
|
Family ID: |
35480767 |
Appl. No.: |
10/872318 |
Filed: |
June 18, 2004 |
Current U.S.
Class: |
419/2 |
Current CPC
Class: |
B22F 3/1134
20130101 |
Class at
Publication: |
419/002 |
International
Class: |
B22F 003/11 |
Claims
What is claimed is:
1. A powder metallurgy method for producing porous metal with
micro-holes, comprising the steps of: (a) selecting materials, a
base material being selected from pure metal powder and alloy
powder for sintering; a filling material being fine powder solvable
in water or in alkaline solvents, said filling material having a
melting point higher than that of said base material; (b)
sintering, said sintering further including a mixing step for
mixing said base material and said filling material and in which a
binding material for making the piling of said base and said
filling materials uniform and dense, said mixture being dried and
preheated to remove the water vapor attached to said filling
material, said mixture being heated to sintering temperature to
become a dense metal bulk having micro-hole texture; (c) removing
said filling material by immerging said metal bulk in a washing
tank of a selected solvent and then applying ultrasonic waves for
shaking away said filling material, whereby a porous metal
half-product with micro-holes configured by said sintered base
material is formed; (d) washing away remained solvent between
micro-holes of said porous metal half-product; and (e) drying away
remained water drops between micro-holes of said porous metal
half-product from said washing step; whereby product of porous
metals with micro-holes can be formed.
2. The method for producing porous metal with micro-holes of claim
1 wherein said base material is in powder form and selected from
pure Al metal and alloys of Al and another metal selected from Si,
Mg, Cu and Zn, and wherein said filling material is fine powder
selected from CaCl.sub.2, MnO, NaCl, TiO.sub.2, WO.sub.3,
V.sub.2O.sub.3, ZnO and MgO.
3. The method for producing porous metal with micro-holes of claim
1 wherein said base material is in powder form and selected from
pure Cu metal and alloys of Cu and another metal selected from Zn,
Sn, Al and P, and wherein said filling material is fine powder
selected from MnO, TiO.sub.2, WO.sub.3, V.sub.2O.sub.3, ZnO and
MgO.
4. The method for producing porous metal with micro-holes of claim
1 wherein said base material is pure Fe metal powder, and wherein
said filling material is fine powder selected from MnO, TiO.sub.2,
WO.sub.3, V.sub.2O.sub.3, ZnO and MgO.
5. The method for producing porous metal with micro-holes of claim
1 wherein said base material is in powder form and selected from
pure Pb metal and alloys of Pb and another metal selected from Sn
and Zn, and wherein said filling material is fine powder selected
from CaCl.sub.2, MnO, NaCl, TiO.sub.2, WO.sub.3, V.sub.2O.sub.3,
ZnO and MgO.
6. The method for producing porous metal with micro-holes of claim
1 wherein said base material is in powder form and selected from
pure Mg metal and alloys of Mg and another metal selected from Li,
Al and Cu, and wherein said filling material is fine powder
selected from CaCl.sub.2, MnO, NaCl, TiO.sub.2, WO.sub.3,
V.sub.2O.sub.3, ZnO and MgO.
7. The method for producing porous metal with micro-holes of claim
1 wherein said base material is in powder form and selected from
pure Mn metal and alloys of Mn and another metal selected from Fe
and Ni, and wherein said filling material is fine powder selected
from MnO, TiO.sub.2, WO.sub.3, V.sub.2O.sub.3, ZnO and MgO.
8. The method for producing porous metal with micro-holes of claim
1 wherein said base material is in powder form and selected from
pure Mo metal and alloys of Mo and another metal selected from Fe,
Ni, Co and Cr, and wherein said filling material is fine powder of
MgO.
9. The method for producing porous metal with micro-holes of claim
1 wherein said base material is in powder form and selected from
pure Ni metal and alloys of Ni and another metal selected from Fe,
Cr, Mo and Co, and wherein said filling material is fine powder
selected from MnO, TiO.sub.2, WO.sub.3, V.sub.2O.sub.3, ZnO and
MgO.
10. The method for producing porous metal with micro-holes of claim
1 wherein said base material is in powder form and selected from
pure Ag metal and alloys of Ag and Cu, and wherein said filling
material is fine powder selected from MnO, TiO.sub.2, WO.sub.3,
V.sub.2O.sub.3, ZnO and MgO.
11. The method for producing porous metal with micro-holes of claim
1 wherein said base material is in powder form and selected from
pure Sn metal and alloys of Sn and another metal selected from Pb,
Cu and Bi, and wherein said filling material is fine powder
selected from CaCl.sub.2, MnO, NaCl, TiO.sub.2, WO.sub.3,
V.sub.2O.sub.3, ZnO and MgO.
12. The method for producing porous metal with micro-holes of claim
1 wherein said base material is in powder form and selected from
pure W metal and alloys of W and another metal selected from Ni, Cu
and Ag, wherein pure Ni metal powder is added, and wherein said
filling material is fine powder selected from MnO, TiO.sub.2,
WO.sub.3, V.sub.2O.sub.3, ZnO and MgO.
13. The method for producing porous metal with micro-holes of claim
1 wherein said base material is in powder form and selected from
pure V metal and alloys of V and another metal selected from Mo,
Ni, Co and Ti, and wherein said filling material is fine powder
selected from WO.sub.3, V.sub.2O.sub.3, ZnO and MgO.
14. The method for producing porous metal with micro-holes of claim
1 wherein said base material is in powder form and selected from
pure Ti metal and alloys of Ti and another metal selected from Al,
Ni and Co, and wherein said filling material is fine powder
selected from WO.sub.3, V.sub.2O.sub.3, ZnO and MgO.
15. The method for producing porous metal with micro-holes of claim
1 wherein volume ratio of said filling material to said base
material is larger than 1.
16. The method for producing porous metal with micro-holes of claim
1 wherein said solvent is CH.sub.3CH.sub.2OH when said filling
material is CaCl.sub.2.
17. The method for producing porous metal with micro-holes of claim
16 wherein said solvent is suitable for Al, Pb, Mg and Sn in pure
and alloy forms as said sintering base material.
18. The method for producing porous metal with micro-holes of claim
1 wherein said solvent is NH.sub.4Cl when said filling material is
MnO.
19. The method for producing porous metal with micro-holes of claim
18 wherein said solvent is suitable for Cu, Fe, Mg, Mn and Ni in
pure and alloy forms as said sintering base material.
20. The method for producing porous metal with micro-holes of claim
1 wherein said solvent is cold or hot water when said filling
material is NaCl.
21. The method for producing porous metal with micro-holes of claim
20 wherein said-solvent is suitable for Al, Pb, Mg and Sn in pure
and alloy forms as said sintering base material.
22. The method for producing porous metal with micro-holes of claim
1 wherein said solvent is selected from NaOH and KOH when said
filling material is TiO.sub.2.
23. The method for producing porous metal with micro-holes of claim
22 wherein said solvent is suitable for Cu, Fe, Mn, Ni and Mg in
pure and alloy forms as said sintering base material.
24. The method for producing porous metal with micro-holes of claim
1 wherein said solvent is selected from NaOH and KOH when said
filling material is WO.sub.3.
25. The method for producing porous metal with micro-holes of claim
24 wherein said solvent is suitable for Cu, Fe, Mn, Ni, Ag, V and
Ti in pure and alloy forms as said sintering base material.
26. The method for producing porous metal with micro-holes of claim
1 wherein said solvent is selected from NaOH and KOH when said
filling material is V.sub.2O.sub.3.
27. The method for producing porous metal with micro-holes of claim
26 wherein said solvent is suitable for Cu, Fe, Mn, Ni, Ag, V and
Ti in pure and alloy forms as said sintering base material.
28. The method for producing porous metal with micro-holes of claim
1 wherein said solvent is selected from NaOH and KOH when said
filling material is ZnO.
29. The method for producing porous metal with micro-holes of claim
28 wherein said solvent is suitable for Cu, Fe, Mn, Ni, Ag, V and
Ti in pure and alloy forms as said sintering base material.
30. The method for producing porous metal with micro-holes of claim
1 wherein said solvent is selected from NH.sub.4OH and NH.sub.4Cl
when said filling material is MgO.
31. The method for producing porous metal with micro-holes of claim
30 wherein said solvent is suitable for Cu, Fe, Mn, Ni, Ag, V, Ti
and Mo in pure and alloy forms as said sintering base material.
32. The method for producing porous metal with micro-holes of claim
1 wherein said preheat temperature for removing water attached to
said filling material is from 500 to 700.degree. C.
33. The method for producing porous metal with micro-holes of claim
1 wherein said sintering temperature is above half of the melting
point of said base material and blow the melting point of said
filling material.
34. The method for producing porous metal with micro-holes of claim
1 wherein said washing step is performed in a tank provided with
ultrasonic waves.
35. The method for producing porous metal with micro-holes of claim
1 wherein said drying step is performed an infrared oven.
36. The method for producing porous metal with micro-holes of claim
1 wherein said drying step is performed in a microwave oven having
a microwave frequency from 100 to 140 GHz and a wavelength from 1
mm to 1 m.
37. The method for producing porous metal with micro-holes of claim
1 further including a step of reduction for removing oxidation
layers (films) when said filling material is an oxide.
38. The method for producing porous metal with micro-holes of claim
37 wherein said step of reduction is placing said porous metal
after drying in a vacuum chamber, filling in hydrogen gas as a
reduction gas for the reduction reaction by which said oxidation
layers (films) between micro-holes of said porous metal are
removed.
39. The method for producing porous metal with micro-holes of claim
37 wherein said step of reduction is performed using a solvent that
dissolves said oxidation layers (films) between micro-holes of said
porous metal.
40. The method for producing porous metal with micro-holes of claim
39 wherein said solvent is selected from NaOH, KOH, NH.sub.4Cl and
NH.sub.4OH.
41. A smelting method for producing porous metal with micro-holes,
comprising the steps of: (a) selecting materials, a base material
being selected from pure metal and alloy of a predetermined melting
point for smelting; a filling material being fine powder solvable
in water or in alkaline solvents, said filling material having a
melting point higher than that of said base material; (b) smelting,
said smelting further including a mixing step for mixing said base
material and said filling material in an oven equipped with high or
low frequency waves for inducing a desired magnetic stirring
effect, said smelted mixture being disposed in a thermo chamber
equipped with ultrasonic waves for uniformly stirring, said mixture
undergoing a fast casting process whereby solid particles of said
filling material can be uniformly distributed between molten
smelting base material, said mixture undergoing being cooled to
form a dense metal bulk having micro-hole texture; (c) removing
said filling material by immerging said metal bulk in a washing
tank of a selected solvent and then applying ultrasonic waves for
shaking away said filling material, whereby a porous metal
half-product with micro-holes configured by said sintered base
material is formed; (d) washing away remained solvent between
micro-holes of said porous metal half-product; and (e) drying away
remained water drops between micro-holes of said porous metal
half-product from said washing step; whereby product of porous
metals with micro-holes can be formed.
42. The method for producing porous metal with micro-holes of claim
41 wherein a high frequency oven is used for said smelting step
when said base material is of high melting point.
43. The method for producing porous metal with micro-holes of claim
41 wherein said base material for high melting-point smelting is
selected from pure Cu metal and alloys of Cu and another metal
selected from Zn, Sn, Al and P, and wherein said filling material
is fine powder selected from MnO, TiO.sub.2, WO.sub.3,
V.sub.2O.sub.3, ZnO and MgO.
44. The method for producing porous metal with micro-holes of claim
41 wherein said base material for high melting-point smelting is
pure Fe metal, and wherein said filling material is fine powder
selected from MnO, TiO.sub.2, WO.sub.3, V.sub.2O.sub.3, ZnO and
MgO.
45. The method for producing porous metal with micro-holes of claim
41 wherein said base material for high melting-point smelting is
selected from pure Mn metal and alloys of Mn and another metal
selected from Fe and Ni, and wherein said filling material is fine
powder selected from MnO, TiO.sub.2, WO.sub.3, V.sub.2O.sub.3, ZnO
and MgO.
46. The method for producing porous metal with micro-holes of claim
41 wherein said base material for high melting-point smelting is
selected from pure Mo metal and alloys of Mo and another metal
selected from Fe, Ni, Co and Cr, and wherein said filling material
is fine powder of MgO.
47. The method for producing porous metal with micro-holes of claim
41 wherein said base material for high melting-point smelting is
selected from pure Ni metal and alloys of Ni and another metal
selected from Fe, Cr, Mo and Co, and wherein said filling material
is fine powder selected from MnO, TiO.sub.2, WO.sub.3,
V.sub.2O.sub.3, ZnO and MgO.
48. The method for producing porous metal with micro-holes of claim
41 wherein said base material for high melting-point smelting is
selected from pure Ag metal and alloys of Ag and Cu, and wherein
said filling material is fine powder selected from MnO, TiO.sub.2,
WO.sub.3, V.sub.2O.sub.3, ZnO and MgO.
49. The method for producing porous metal with micro-holes of claim
41 wherein said base material for high melting-point smelting is
selected from pure W metal and alloys of W and another metal
selected from Ni, Cu and Ag, wherein pure Ni metal powder is added,
and wherein said filling material is fine powder selected from MnO,
TiO.sub.2, WO.sub.3, V.sub.2O.sub.3, ZnO and MgO.
50. The method for producing porous metal with micro-holes of claim
41 wherein said base material for high melting-point smelting is
selected from pure V metal and alloys of V and another metal
selected from Mo, Ni, Co and Ti, and wherein said filling material
is fine powder selected from WO.sub.3, V.sub.2O.sub.3, ZnO and
MgO.
51. The method for producing porous metal with micro-holes of claim
41 wherein said base material for high melting-point smelting is
selected from pure Ti metal and alloys of Ti and another metal
selected from Al, Ni and Co, and wherein said filling material is
fine powder selected from WO.sub.3, V.sub.2O.sub.3, ZnO and
MgO.
52. The method for producing porous metal with micro-holes of claim
41wherein said solvent is CH.sub.3CH.sub.2OH when said filling
material is CaCl.sub.2.
53. The method for producing porous metal with micro-holes of claim
52 wherein said solvent is suitable for Al, Pb, Mg and Sn in pure
and alloy forms as said base material.
54. The method for producing porous metal with micro-holes of claim
41wherein said solvent is NH.sub.4Cl when said filling material is
MnO.
55. The method for producing porous metal with micro-holes of claim
54 wherein said solvent is suitable for Cu, Fe, Mg, Mn and Ni in
pure and alloy forms as said base material.
56. The method for producing porous metal with micro-holes of claim
41 wherein said solvent is cold or hot water when said filling
material is NaCl.
57. The method for producing porous metal with micro-holes of claim
56 wherein said solvent is suitable for Al, Pb, Mg and Sn in pure
and alloy forms as said base material.
58. The method for producing porous metal with micro-holes of claim
41 wherein said solvent is selected from NaOH and KOH when said
filling material is TiO.sub.2.
59. The method for producing porous metal with micro-holes of claim
58 wherein said solvent is suitable for Cu, Fe, Mn, Ni and Mg in
pure and alloy forms as said base material.
60. The method for producing porous metal with micro-holes of claim
41 wherein said solvent is selected from NaOH and KOH when said
filling material is WO.sub.3.
61. The method for producing porous metal with micro-holes of claim
60 wherein said solvent is suitable for Cu, Fe, Mn, Ni, Ag, V and
Ti in pure and alloy forms as said base material.
62. The method for producing porous metal with micro-holes of claim
41 wherein said solvent is selected from NaOH and KOH when said
filling material is V.sub.2O.sub.3.
63. The method for producing porous metal with micro-holes of claim
62 wherein said solvent is suitable for Cu, Fe, Mn, Ni, Ag, V and
Ti in pure and alloy forms as said base material.
64. The method for producing porous metal with micro-holes of claim
41 wherein said solvent is selected from NaOH and KOH when said
filling material is ZnO.
65. The method for producing porous metal with micro-holes of claim
64 wherein said solvent is suitable for Cu, Fe, Mn, Ni, Ag, V and
Ti in pure and alloy forms as said base material.
66. The method for producing porous metal with micro-holes of claim
41 wherein said solvent is selected from NH.sub.4OH and NH.sub.4Cl
when said filling material is MgO.
67. The method for producing porous metal with micro-holes of claim
66 wherein said solvent is suitable for Cu, Fe, Mn, Ni, Ag, V, Ti
and Mo in pure and alloy forms as said base material.
68. The method for producing porous metal with micro-holes of claim
41 wherein volume ratio of said filling material to said base
material for high or low melting-point smelting is larger than
1.
69. The method for producing porous metal with micro-holes of claim
41 wherein said smelting temperature is above the melting point of
said base material, and blow the melting point of said filling
material.
70. The method for producing porous metal with micro-holes of claim
41 wherein said washing step is performed in a tank provided with
ultrasonic waves.
71. The method for producing porous metal with micro-holes of claim
41 wherein said drying step is performed an infrared oven.
72. The method for producing porous metal with micro-holes of claim
41 wherein said drying step is performed in a microwave oven having
a microwave frequency from 100 to 140 GHz and a wavelength from 1
mm to 1 m.
73. The method for producing porous metal with micro-holes of claim
41 further including a step of reduction for removing oxidation
layers (films) when said filling material is an oxide.
74. The method for producing porous metal with micro-holes of claim
73 wherein said step of reduction is placing said porous metal
after drying in a vacuum chamber, filling in hydrogen gas as a
reduction gas for the reduction reaction by which said oxidation
layers (films) between micro-holes of said porous metal are
removed.
75. The method for producing porous metal with micro-holes of claim
73 wherein said step of reduction is performed using a solvent that
dissolves said oxidation layers (films) between micro-holes of said
porous metal.
76. The method for producing porous metal with micro-holes of claim
75 wherein said solvent is selected from NaOH, KOH, NH.sub.4Cl and
NH.sub.4OH.
77. The method for producing porous metal with micro-holes of claim
41 wherein a low frequency oven is used for said smelting step when
said base material is of low melting point.
78. The method for producing porous metal with micro-holes of claim
41 wherein said base material for low melting-point smelting is
selected from pure Al metal and alloys of Al and another metal
selected from Si, Mg, Cu and Zn, and wherein said filling material
is fine powder selected from CaCl.sub.2, MnO, NaCl, TiO.sub.2,
WO.sub.3, V.sub.2O.sub.3, ZnO and MgO.
79. The method for producing porous metal with micro-holes of claim
41 wherein said base material for low melting-point smelting is
selected from pure Pb metal and alloys of Pb and another metal
selected from Sn and Zn, and wherein said filling material is fine
powder selected from CaCl.sub.2, MnO, NaCl, TiO.sub.2, WO.sub.3,
V.sub.2O.sub.3, ZnO and MgO.
80. The method for producing porous metal with micro-holes of claim
41 wherein said base material for low melting-point smelting is
selected from pure Mg metal and alloys of Mg and another metal
selected from Li, Al and Cu, and wherein said filling material is
fine powder selected from CaCl.sub.2, MnO, NaCl, TiO.sub.2,
WO.sub.3, V.sub.2O.sub.3, ZnO and MgO.
81. The method for producing porous metal with micro-holes of claim
41 wherein said base material for low melting-point smelting is
selected from pure Ag metal and alloys of Ag and Cu, and wherein
said filling material is fine powder selected from MnO, TiO.sub.2,
WO.sub.3, V.sub.2O.sub.3, ZnO and MgO.
82. The method for producing porous metal with micro-holes of claim
41 wherein said base material for low melting-point smelting is
selected from pure Sn metal and alloys of Sn and another metal
selected from Pb, Ni, Cu and Bi, and wherein said filling material
is selected from fine powder of CaCl.sub.2, MnO, NaCl, TiO.sub.2,
WO.sub.3, V.sub.2O.sub.3, ZnO and MgO.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to methods for producing
porous metal with micro-holes, and more particularly to a method
for producing porous metal with micro-holes of micron order
(250-0.1 .mu.m). The method is easy to apply and can control the
distribution density of mutually connected micro-holes, and the
materials thereby produced are of low cost and can be used in
catalysts, filters, and electrodes for batteries. They can be also
used as anti-shock, anti-electromagnetic wave, heat-diffusing and
sound-damping materials.
BACKGROUND OF THE INVENTION
[0002] The so-called porous metal or foam metal in the market
refers to sintered metals of which the ratio of occupancy of the
remnant holes therein exceeds 10%. The holes consist of randomly
distributed inter-connected holes and isolated holes. The method
cannot control the shape, the diameter and the distribution ratio
of the holes it produces.
[0003] The methods for producing porous metal of the prior art
includes:
[0004] (1) powder metallurgy that sinters a plurality of metal or
alloy powder;
[0005] (2) sintering using metallic fibers as a replacement for the
aforesaid metal powder;
[0006] (3) porous casting method that heats and cools a metal
around the phase transition point thereof so as to cause the metal
to expand and contract;
[0007] (4) foam or porous aluminum added into a molted metal;
[0008] (5) reducing the metal compounds in foam iron or foam
titanium.
[0009] The current porous metallic materials are mainly produced by
means of powder metallurgy sintering. The steps of powder
metallurgy is mixing metal power with a binding material,
sufficiently stirring the mixture and filling the mixture in to a
mold, punching the mold as that the mixture takes form, and then
sintering the mixture. In the sintering process, metal powder 9
integrated by a binder 22 will transit from an initial loose state
(FIG. 1(a)), to a state in which metal powder starts to merge (FIG.
1(b)), and then to a state in which merged metal powder increases
gradually (FIG. 1(c)), and finally to a state in which the merged
metal powder forms a solid bulk (FIG. 1(b)).
[0010] In the aforesaid sintering process of powder metallurgy, the
metal powder particles 9a firstly contact with each other at
contact points 91a; between the contact points there form holes
92a, as shown in FIG. 2(a). As the temperature increases, the
contact points 91a extend gradually to form neck portions 91b, as
shown in FIG. 2(b). As the neck portions 91b, 91c, 91d continue to
extend, the bulk of metal powder becomes more and more solid and
the holes 92b, 92c, 92d become smaller and smaller, as shown in
FIG. 2(b), (c) and (d). Thereby, the closeness of metal powder
particles is enhanced, but the hole distribution is poor.
[0011] Therefore, the conventional method of powder metallurgy
enhances the closeness of metal particles but do little about
upgrading the hole distribution.
[0012] Further, the uniformity of the mixture of metal powder and
binding medium is susceptible to the mobility, the size and the
shape of the metal powder particles, as well as the friction
between the particles and the surfaces of the molding machine,
resulting in uneven distribution of stress and strain and low
material density. Take iron powder particles as an example, FIG.
3(a)-(b) shows the density distribution (in units of g/cm.sup.3)
with respect to cylindrical materials made of iron powder under a
variety of pressures, which is rather non-uniform. It can be
further shown in FIG. 4 that the density of iron powder in a
pressurized chamber is rather non-uniform. As shown in FIG.
5(a)-(c) are the pressure distributions in iron powder contained in
a pressurized chamber at a pressure of 7 ton/cm.sup.2. The height
to diameter ration of the pressurized chamber H/D is 0.42 in FIG.
5(a), 0.79 in FIG. 5(b) and 1.66 in FIG. 5(c). Therefore, the
pressure distributions as shown in FIG. 5(a)-(c) are rather
non-uniform.
[0013] Further, depending on manufacturing methods, the shape of
metal powder particles can be spherical, polygonal, slab-shaped,
liquid-drop-shaped. For achieving better shaping, ventilating
property and hole distribution for ordinary metal powder,
gas-cooling spray is utilized to create spherical metal particles.
It is known that there are several ways to fill with spherical
particles, such as cubic, rectangular, square and hexagonal
arrangements. According to experiments, the hole diameter is 41.4%
of the particle diameter when the cubic piling is used. The
formation and scale of hole diameter are shown in FIGS. 6(a) and
(b), wherein
[0014] FIG. 6(a) discloses that D.sub.1=D.sub.0(2/{square root over
( )}3-1)=0.156D.sub.0;
[0015] FIG. 6(a) discloses that D.sub.2=D.sub.0({square root over (
)}2-1)=0.414D.sub.0;
[0016] where D.sub.1 and D.sub.2 are the hole diameters between
metal particles;
[0017] where D.sub.0 is the particle diameter.
[0018] Therefore, it is known theoretically that the hole diameters
between metal particles D.sub.1 and D.sub.2 are 15.6-41.4% of the
particle diameter D.sub.0. However, because of non-uniform particle
diameters, the actual percentage lies between 16-20%. It is a
further effect that, as the particles are oxidized and become wet,
the stress and strain between the particles become uneven,
resulting in deformation and breakdown. Therefore, the hole
diameter deduced by maximum particle diameter or estimated by
probability is 18% of the spherical metal particle diameter.
Accordingly, the hole occupancy ratio of the porous metal sintered
from metal powder using common metal metallurgy methods is less
than 50%. However, it can attain more than 90% using metal fiber
sintering. Therefore, it is a common practice that metal fibers,
bridging materials and foam materials are added to powder-binder
mixture for enhancing hole distribution; the added materials are
then burn away by heating. However, it is still difficult to
control the hole diameter and the hole distribution. At the same
time, burning the bridging materials may produce poisonous gases
and oxidization, accumulating choral substance in the holes, which
is difficult to clean away. This effect causes troubles in
utilizing porous metal materials. For example, the function and
quality of catalyses or battery electrodes made of porous metal
materials thereby produced may be seriously affected.
[0019] Since the holes in conventional porous metals are spacing
between powder particles, fibers and other constitutes, they are
irregular in shape and distribution. Therefore, the hole
distribution is of poor uniformity and therefore low quality.
[0020] Further, there exists a manufacturing method for spongy
metal in which uniform hole shape and diameter and high density can
be attained, which is disclosed by R.O.C. patent numbers 434323 and
491903. Those two methods utilize an organic material of desired
size, shape and particle diameter as the filling material. The
material is then soaked with fire-resistant mud and then goes
through a piling process to attain desired shapes and diameters for
isolated holes and interconnecting holes. However, as the diameter
of the organic particles becomes too small (say, approaching
millimeter scale), the material density is difficult to control.
This is disadvantageous in mass production of materials of fine
isolated holes and interconnecting holes.
[0021] Therefore, if the hole diameter and distribution can be
effectively and stably controlled, the porous metals thereby
produced can be used in catalyst filters, and electrodes for
batteries, anti-shock, anti-electromagnetic wave, heat-diffusing
and sound-damping materials, of which the functions are
significantly enhanced. But a method for producing porous metal
with micro-holes is still absent, therefore motivating the present
invention.
SUMMARY OF THE INVENTION
[0022] Accordingly, the primary objective of the present invention
is to provide an innovative method for producing porous metal with
micro-holes, in contrast to the conventional metal powder
metallurgy.
[0023] The secondary objective of the present invention is to
provide a sintering method for producing porous metal with
micro-holes.
[0024] The method for producing porous metal with micro-holes
according to the present invention has the following
advantages.
[0025] 1. It is easy and cheap to acquire the pure metal or alloy
powder used as the base material for the sintering process or the
casting process. Including metal powder, alloy powder and solvent
fine powder, the suitable material is selected to produce porous
metals of desired distribution of the fine holes.
[0026] 2. Metal powder metallurgy utilizes cold or hot press
forming in the sintering process, thereby the base material and
filling material attain perfect mixing. It is equivalent that high
or low frequency sound waves are used in the sintering process in
which the filling material is mixed uniformly with the molten base
material according to a selected proportion. Therefore, the method
according to the present invention can effectively control the
distribution of the interconnecting holes in the porous metals
produced, further enhancing the density and stability of the fine
holes.
[0027] 3. Ultrasonic waves are used to remove the filling material
distributed uniformly in the metal raw bulk, which is a stable
technology for lowing production cost and fault rate.
[0028] 4. The oxidation layers (films) on the surface of the porous
metals produced is removed by injecting reduction gas in a vacuum
chamber or being dissolved in a solvent. The product therefore has
nice looking out look and is suitable for making catalyst filters,
and electrodes for batteries, anti-shock, anti-electromagnetic
wave, heat-diffusing and sound-damping materials.
[0029] To achieve the object, the present invention provides a
powder metallurgy method for producing porous metal with
micro-holes, comprising the steps of: (a) selecting materials, a
base material being selected from pure metal powder and alloy
powder for sintering; a filling material being fine powder solvable
in water or in alkaline solvents, said filling material having a
melting point higher than that of said base material; (b)
sintering, said sintering further including a mixing step for
mixing said base material and said filling material and in which a
binding material for making the piling of said base and said
filling materials uniform and dense, said mixture being dried and
preheated to remove the water vapor attached to said filling
material, said mixture being heated to sintering temperature to
become a dense metal bulk having micro-hole texture; (c) removing
said filling material by immerging said metal bulk in a washing
tank of a selected solvent and then applying ultrasonic waves for
shaking away said filling material, whereby a porous metal
half-product with micro-holes configured by said sintered base
material is formed; (d) washing away remained solvent between
micro-holes of said porous metal half-product; and (e) drying away
remained water drops between micro-holes of said porous metal
half-product from said washing step. The product of porous metals
with micro-holes can be formed.
[0030] Moreover, the present invention provide a smelting method
for producing porous metal with micro-holes. The method comprises
the steps of: (a) selecting materials, a base material being
selected from pure metal and alloy of a predetermined melting point
for smelting; a filling material being fine powder solvable in
water or in alkaline solvents, said filling material having a
melting point higher than that of said base material; (b) smelting,
said smelting further including a mixing step for mixing said base
material and said filling material in an oven equipped with high or
low frequency waves for inducing a desired magnetic stirring
effect, said smelted mixture being disposed in a thermo chamber
equipped with ultrasonic waves for uniformly stirring, said mixture
undergoing a fast casting process whereby solid particles of said
filling material can be uniformly distributed between molten
smelting base material, said mixture undergoing being cooled to
form a dense metal bulk having micro-hole texture; (c) removing
said filling material by immerging said metal bulk in a washing
tank of a selected solvent and then applying ultrasonic waves for
shaking away said filling material, whereby a porous metal
half-product with micro-holes configured by said sintered base
material is formed; (d) washing away remained solvent between
micro-holes of said porous metal half-product; and (e) drying away
remained water drops between micro-holes of said porous metal
half-product from said washing step. The product of porous metals
with micro-holes can be formed.
[0031] The various objects and advantages of the present invention
will be more readily understood from the following detailed
description when read in conjunction with the appended
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] FIG. 1(a) shows the loosely distributed metal powder
particles, connected by a binding material, before the conventional
process of metal powder metallurgy.
[0033] FIG. 1(b) shows that the metal powder particles in the raw
material start to fuse with each other in an initial phase of the
conventional process of metal powder metallurgy.
[0034] FIG. 1(c) shows that the metal powder particles in the raw
material become denser in a medium phase of the conventional
process of metal powder metallurgy.
[0035] FIG. 1(d) shows that the metal powder particles in the raw
material become solidly sintered after the conventional process of
metal powder metallurgy.
[0036] FIG. 2(a) shows the contact points of and the holes between
metal powder particles in an initial phase of metal powder
metallurgy.
[0037] FIG. 2(b) shows the contact points in FIG. 2(a) extend to
form contact faces and neck-like portions.
[0038] FIG. 2(c) shows that the neck-like portions in FIG. 2(b)
continue to enlarge and the volume of holes shrinks gradually.
[0039] FIG. 2(d) shows that the neck-like portions in FIG. 2(c)
maximize and the volume of holes shrinks to minimum.
[0040] FIG. 3(a) shows the unevenness in density of a cylindrical
object formed by iron powder under a pressure of 10 ton per
centimeter squared.
[0041] FIG. 3(b) shows the unevenness in density of a cylindrical
object formed by iron powder under a pressure of 15 ton per
centimeter squared.
[0042] FIG. 3(c) shows the unevenness in density of a cylindrical
object formed by iron powder under a pressure of 20 ton per
centimeter squared.
[0043] FIG. 3(d) shows the unevenness in density of a cylindrical
object formed by iron powder under a pressure of 25 ton per
centimeter squared.
[0044] FIG. 4 shows the unevenness in density of iron powder in a
pressurized chamber from measurement.
[0045] FIG. 5(a) shows the unevenness in pressure distribution of
iron powder disposed in an H/D=0.42 pressurized chamber having a
pressure of 7 tons per centimeter squared.
[0046] FIG. 5(b) shows the unevenness in pressure distribution of
iron powder disposed in an H/D=0.79 pressurized chamber having a
pressure of 7 tons per centimeter squared.
[0047] FIG. 5(c) shows the unevenness in pressure distribution of
iron powder disposed in an H/D=1.66 pressurized chamber having a
pressure of 7 tons per centimeter squared.
[0048] FIG. 6(a) shows spherical particles expressing metal powder
and filling material in rhomb piling.
[0049] FIG. 6(b) shows spherical particles expressing metal powder
and filling material in cubic piling.
[0050] FIG. 7 is the flow chart illustrating the method of metal
powder metallurgy of the present invention.
[0051] FIG. 8 is the flow chart illustrating the method of
sintering of the present invention.
[0052] FIG. 9 is a local enlarged view of the base material for
sintering stuffed uniformly within filling material.
[0053] FIG. 10 is a local enlarged view of the texture of the metal
raw bulk.
[0054] FIG. 11 is a local perspective enlarged view of the texture
of the metal raw bulk.
[0055] FIG. 12 shows the relation between filling material particle
diameter D and the neck portion diameter X.
[0056] FIG. 13 is a local perspective enlarged view of the texture
of a porous metal thereby produced.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0057] The method for producing porous metal with micro-holes may
have at least two preferred embodiments; one is a powder metallurgy
method, and the other is a smelting method.
[0058] The powder metallurgy method comprises the steps of material
mixing 1, sintering fusing process 2, filling material removing 3,
washing 4, drying 5 and reduction 6. The sintering step 2 further
comprises steps of mixing and stirring 21, form fixing 25,
preheating 26 and sintering 27, as shown in FIG. 7.
[0059] The smelting method comprises the steps of material mixing
10, smelting fusing process 7, filling material removing 30,
washing 40, drying 50 and reduction 60. The smelting fusing process
7 is bifurcated into two paths, one using high frequency oven and
the other using low frequency oven. There is then a process of
casting for form fixing, as shown in FIG. 8.
[0060] The first step of the above two methods are all material
mixing 1, 10.
[0061] For the material mixing 1 of the powder metallurgy method, a
pure metal or alloy powder must be selected as a sintering base
material 11. And a filling material 12 that is solvable in water or
alkaline solvents and having a melting point higher than that of
the sintering base material 11 must be provided, so that the
filling material 12 will not be sintered during the sintering
process.
[0062] For the material mixing 10 of the smelting method, a pure
metal or alloy powder must be selected as a smelting base material
13. And a filling material 12 in fine powder form that is solvable
in water or alkaline solvents and having a melting point higher
than that of the smelting base material 13 must be provided, so
that the filling material 12 will not be sintered when the mixture
is disposed in a high frequency or low frequency oven for
smelting.
[0063] The sintering base material 11 and the smelting base
material 13 can be pure Al metal or alloys of Al and another metal
selected from Si, Mg, Cu and Zn. The sintering base material 11 and
the smelting base material 13 can also be pure Cu metal or alloys
of Cu and another metal selected from Zn, Sn, Al and P. They can
also be pure Fe metal powder or pure Pb metal or alloys of Pb and
another metal selected from Sn and Zn. They can be pure Mg metal or
alloys of Mg and another metal selected from Li, Al and Cu. They
can be pure Mn metal or alloys of Mn and another metal selected
from Fe and Ni. They can be pure Mo metal or alloys of Mo and
another metal selected from Fe, Ni, Co and Cr. They can be pure Ni
metal or alloys of Ni and another metal selected from Fe, Cr, Mo
and Co. They can be pure Ag metal or alloys of Ag and Cu. They can
be pure Sn metal or alloys of Sn and another metal selected from
Pb, Cu and Bi. They can be pure W metal and alloys of W and another
metal selected from Ni, Cu and Ag. They can be pure V metal or
alloys of V and another metal selected from Mo, Ni, Co and Ti. They
can be pure Ti metal or alloys of Ti and another metal selected
from Al, Ni and Co. These materials are listed in Table 1.
1TABLE 1 The sintering and smelting base materials used in the
present invention and their properties. Sintering and Melting
Boiling Solvable solvents Insolvable smelting Specific point point
Cold Hot Other solvents Names materials weight .degree. C. .degree.
C. water water solvents Solvents Al and Al, 2.7 660(low) 2056 No No
In HCl, CH.sub.3CH.sub.2OH Al alloys Al-Si, Mg,Cu,Zn .congruent.2.7
<660(low) <2056 NaOH, KOH (alcohol), glycerine Cu and Cu,
8.92 1083(high) 2300 No No In HNO.sub.3 NH.sub.4Cl, NaOH, Cu alloys
Cu-Zn, Sn, Al, P .congruent.8.92 <1083(high) <2300 hot
H.sub.2SO.sub.4 KOH, NH.sub.4OH Fe and Fe 7.86 1535(high) 3000 No
No In H.sub.2SO.sub.4, NH.sub.4Cl, NaOH, Fe alloys 7.6 .about. 7.8
1575(high) <3000 HNO.sub.3, HCl KOH, NH.sub.4OH Pb and Pb 11.34
327.5(low) 1620 No No In HNO.sub.3 CH.sub.3CH.sub.2OH Pb alloys
Pb-Sn, Zn <11.34 <327(low) <1620 (alcohol), glycerine Mg
and Mg 1.74 651(low) 1110 No Yes, In H.sub.2SO.sub.4,
CH.sub.3CH.sub.2OH(al- Mg alloys Mg-Li, Al, Cu .congruent.1.74
<651(low ) <1110 mildly HNO.sub.3,dilute cohol), H.sub.4Cl,
HCl glycerine, NaOH, KOH Mn and Mn 7.2 1260(high) 1900 Yes No In
NH.sub.4Cl, NaOH, Mn alloys Mn-Fe, Ni .congruent.7.2 <1260(high)
<1900 dilute H.sub.2SO.sub.4, KOH, NH.sub.4OH Dilute HNO.sub.3,
dilute HCl Mo and Mo 10.2 2620(high) 3700 No No In hot and
NH.sub.4OH, Mo alloys Mo-Fe,Ni, Co,Cr .gtoreq.10.2 <2620(high)
<3700 thick H.sub.2SO.sub.4 NH.sub.4Cl Ni and Ni 8.90 1452(high)
2900 No No In dilute NH.sub.4Cl, NaOH, Ni alloys Ni-Fe,Cr,Mo,Co
.gtoreq.8.90 <1452(high) <2900 HNO.sub.3 KOH, NH.sub.4OH Ag
and Ag 10.5 960.5(low) 1950 No No In HNO.sub.3, NaOH, KOH, Ag
alloys Ag-Cu .gtoreq.10.5 <960.5(low) <1950 hot
H.sub.2SO.sub.4 NH.sub.4OH, NH.sub.4Cl Sn and Sn 7.31 232(low) 2260
No No In HCl, CH.sub.3CH.sub.2OH Sn alloys Sn-Pb, Cu, Bi
.congruent.7.31 <232(low) <2260 H.sub.2SO.sub.4, (alcohol),
dilute HNO.sub.3 glycerine W and W 19.3 3370(high) 5900 No No In
hot and NH.sub.4Cl, NaOH, W alloys W-Ni, Cu, Ag <19.3
<3370(high) <5900 thick KOH KOH, NH.sub.4OH, NH.sub.4OH PS:
To lower the sintering temperature of W and W alloys to below
1500.degree. C., Ni powder is added. The filling material is
selected to be solvable in alkaline solvents. The filling material
should have a melting point higher than 1600.degree. C., such as
MnO, TiO.sub.2, V.sub.2O.sub.3, ZnO, MgO, and ZrO.sub.2 V and V
5.96 1710(high) 3000 No No In HNO.sub.3, NaOH, KOH, V alloys V-Mo,
Ni, Co,Ti .gtoreq.5.96 .gtoreq.1710(high) <3000 H.sub.2SO.sub.4
NH.sub.4OH, NH.sub.4Cl Ti and Ti 4.5 1800(high) >3000 No Yes In
HCl, HNO.sub.3, NaOH, KOH, Ti alloys Ti-Al, Ni, Co .gtoreq.4.5
.gtoreq.1800(high) .gtoreq.3000 H.sub.2SO.sub.4 NH.sub.4OH,
NH.sub.4Cl
[0064] The filling material 12 can be selected from CaCl.sub.2,
MnO, NaCl, TiO.sub.2, WO.sub.3, V.sub.2O.sub.3, ZnO and MgO, which
are fine powder solvable in water or alkaline solvents, as listed
in Table 2.
2TABLE 2 The filling materials of the present invention. Melting
Boiling Solvable solvents Corresponding Chemical Specific point
point Cold Hot sintering of smelting Names formula weight .degree.
C. .degree. C. water water Other solvents base materials Calcium
CaCl.sub.2 2.15 772 >1600 Partially Partially In
CH.sub.3CH.sub.2OH For Al, Pb, Mg, chloride (alcohol) Sn and their
alloys Manganese MnO 5.18 1650 >1600 No No in NH.sub.4Cl For Cu,
Fe, Mg, monoxide Mn, Ni and their alloys Salt NaCl 2.163 801 1413
Yes Yes In glycerine For Al, Pb, Mg, Sn and their alloys Titanium
TiO.sub.2 4.26 1640 <3000 No No in NaOH, KOH For Cu, Fe, Mn,
dioxide Ni, Mg and their alloys Tungsten WO.sub.3 7.16 2130
<3000 No No in NaOH, KOH For Cu, Fe, Mn, trioxide Ni, Ag, V, Ti
and their alloys Vanadium V.sub.2O.sub.3 4.87 1970 <3000 Yes,
Yes in NaOH, KOH For Cu, Fe, Mn, trioxide mildly Ni, Ag, V, Ti and
their alloys Zinc ZnO 5.61 1800 <3000 Lightly No in Na0OH, KOH
For Cu, Fe, Mn, monoxide Ni, Ag, V, Ti and their alloys Magnesium
MgO 3.65 2800 3600 Lightly No in NH.sub.4OH, For Cu, Fe, Mn,
monoxide NH.sub.4Cl Ni, Ag, V, Ti, Mo and their alloys
[0065] The present invention utilizes the above-mentioned sintering
base material 11 and filling material 12, and the process of the
powder metallurgy method is described as follows and shown in FIG.
7.
[0066] In the material mixing step 1, the sintering base material
11 is selected to be Al metal or alloys of Al and another element
selected from Al, Si, Mg, Cu and Zn, in powder form. Since the
melting point of the base material is less than 660.degree. C., the
filling material 12 is chosen to be of higher melting point.
According to Table, available filling materials 12 are fine powder
of CaCl.sub.2, MnO, NaCl, TiO.sub.2, WO.sub.3, V.sub.2O.sub.3, ZnO
and MgO.
[0067] In another case, when Cu metal or alloys of Cu with another
element selected from Zn, Sn, Al and P in powder form is selected a
sintering base material 11, the preferred filling materials 12
listed in Table 2 are MnO, TiO.sub.2, WO.sub.3, V.sub.2O.sub.3, ZnO
and MgO, since the melting point of the base material is less than
1083.degree. C.
[0068] According to the principle just described, other sintering
base materials 11 listed in Table 1 can form the following
combinations with the filling materials listed in Table 2.
[0069] As the sintering base material is pure Fe metal powder, the
filling material is fine powder selected from MnO, TiO.sub.2,
WO.sub.3, V.sub.2O.sub.3, ZnO and MgO. As the sintering base
material is pure Pb metal or an alloy of Pb and another metal
selected from Sn and Zn, the filling material is fine powder
selected from CaCl.sub.2, MnO, NaCl, TiO.sub.2, WO.sub.3,
V.sub.2O.sub.3, ZnO and MgO. As the sintering base material is pure
Mg metal or an alloy of Mg and another metal selected from Li, Al
and Cu, the filling material is fine powder selected from
CaCl.sub.2, MnO, NaCl, TiO.sub.2, WO.sub.3, V.sub.2O.sub.3, ZnO and
MgO. As the sintering base material is pure Mn metal or an alloy of
Mn and another metal selected from Fe and Ni, and wherein said
filling material is fine powder selected from MnO, TiO.sub.2,
WO.sub.3, V.sub.2O.sub.3, ZnO and MgO. As the sintering base
material is pure Mo metal or an alloy of Mo and another metal
selected from Fe, Ni, Co and Cr, the filling material is fine
powder of MgO. As the sintering base material is pure Ni metal or
an alloy of Ni and another metal selected from Fe, Cr, Mo and Co,
the filling material is fine powder selected from MnO, TiO.sub.2,
WO.sub.3, V.sub.2O.sub.3, ZnO and MgO. As the. sintering base
material is pure Ag metal or an alloy of Ag and Cu, the filling
material is fine powder selected from MnO, TiO.sub.2, WO.sub.3,
V.sub.2O.sub.3, ZnO and MgO. As the sintering base material is pure
Sn metal or an alloy of Sn and another metal selected from Pb, Cu
and Bi, the filling material is fine powder selected from
CaCl.sub.2, MnO, NaCl, TiO.sub.2, WO.sub.3, V.sub.2O.sub.3, ZnO and
MgO. As the sintering base material is pure W metal or an alloy of
W and another metal selected from Ni, Cu and Ag, the filling
material is fine powder selected from MnO, TiO.sub.2, WO.sub.3,
V.sub.2O.sub.3, ZnO and MgO. As the sintering base material is pure
V metal or an alloy of V and another metal selected from Mo, Ni, Co
and Ti, the filling material is fine powder selected from WO.sub.3,
V.sub.2O.sub.3, ZnO and MgO. As the sintering base material is pure
Ti metal or an alloy of Ti and another metal selected from Al, Ni
and Co, the filling material is fine powder selected from WO.sub.3,
V.sub.2O.sub.3, ZnO and MgO.
[0070] When choosing the above materials, the sintering base
material 11 of pure metal or alloy in powder form and the filling
materials 12 in powder form can be acquired at low prices in the
market, the diameter of which ranging from 250 to 0.1 micron. And
the shape of the particles has already attained spherical, suitable
for dense piling up.
[0071] Further, in addition to the diameter of the particles, when
choosing the above mixing materials, the smaller the angle of
repose of the particles, the better the mobility of the particles
during stirring is. And the friction between particles is
smaller.
[0072] As an even further consideration, the occupied volume of the
filling material 12 should exceed 50%, namely the volume ratio of
the filling material to the sintering base material must be greater
than 1. The mixing and stirring 21 is then performed, producing a
porous metal with hole ratio greater than 50%.
[0073] In the step of mixing and stirring 21, as shown in FIG. 7,
the selected sintering base material 11 and filling material 12 are
disposed in a stirring container and added with binder 22 and
plasticizer 23, so that the base material 11 and filling material
12 can be uniformly mixed, as shown in FIG. 9.
[0074] Binder 22 provides a sintering base material 11, in form of
pure metal or alloy powder, and a filling material 12 with binding
force and flexibility in the step of dry molding 25. In the later
step of sintering 27, the binder 22 will be removed from the
mixture through high temperature oxidation. The binder 22 can be
selected form polyvinyl alcohol, wax, cellulose, dextrin,
thermosetting plastic, calcium chloride compounds, algae gel,
lignin, rubber, starch, flour, gelatin, protein, asphalt, acrylic,
polystyrene, paraffin wax and beeswax.
[0075] If polyvinyl alcohol is chosen to be the binder 22, the
polymerization number as defined in the molecular formula
[--CH.sub.2--CH--].sub.n is preferably, around 1500-1700. However,
polyvinyl alcohol is not suitable to be used with alkaline oxides,
such as MgO, CaO, BaO, ZnO, borate and phosphate.
[0076] On the other hand, if polyvinyl acetate is chosen to be the
binder 22, the polymerization number as defined in the molecular
formula: 1
[0077] n is preferably around 400-600. It can also used with
alkaline oxides. However, polyvinyl acetate is solvable only in
organic solvents such as alcohol, benzene and methylbenzene.
[0078] Paraffin wax and beeswax can be also chosen as the binder
22, which have good fluidity when heated. They can damp a sintering
base material 11 rather effectively, but the heating temperature
should not exceed 130.degree. C., or they will be oxidized
quickly.
[0079] The plasticizer 23 enhances mobility between a sintering
base material 11 and a filling material 12, lessening the problem
of high viscosity induced by the binder 22. It can enhance the
mixing uniformity in the step of mixing and stirring 21. The
plasticizer 23 can be selected from glycol, glycerin, sulfuric
acid, stearin acid, oleic acid, wood oil and other vegetable
oils.
[0080] If glycerin is chosen to be the plasticizer 23, it can
provide an additional effect of moisture absorption. If oleic acid
is used as the plasticizer 23, it can provide an additional effect
of lubricating and activating the surfaces of powder particles. If
wood oil and other vegetable oils are chosen, they can lubricate,
emulsify and bind powder particles.
[0081] After the step of mixing and stirring 21, the next step is
dry molding 25, as shown in FIG. 7. In this step, a base material
11 and a filling material 12 are heated to 250.degree. C. so that
they become dry. Since they are bound by the binder 22, the uniform
distribution and compact stacking are preserved. The filling
material 12 acts as bridging material between particles of the base
material 11.
[0082] After the step of dry molding 25, the molded filling
material 12 is preheated at a temperature between 500 and
700.degree. C. in a step of preheating 26, for removing water from
the filling material 12 and therefore facilitating the subsequent
step of sintering 27, as shown in FIG. 7.
[0083] In the step of sintering 27, the mixture of a base material
11 and a filling material 12 is cast into a dense raw metal bulk 28
by means of cold isostatic pressing or hot isostatic pressing. The
sintering temperature is controlled above 50% of the melting point
of the metal and below the melting point of the filling material
12. If the base material 11 is alloy powder, the sintering
temperature is generally lower.
[0084] To prevent oxidation of the raw metal bulk 28 in the step of
sintering 27, the process is performed in a reduction gas.
[0085] Under the above conditions for sintering, the filling
material 12 and the base material 11 originally contacted at points
(FIG. 9) become a structure in which the melted base material 11
fills the space between the particles of the filling material 12,
as shown in FIG. 10. A multiple of neck portions 120 are formed
between particles of the filling material 12a and between the
filling material 12a and its surrounding base material 11a. The raw
metal bulk 28 after cooling possesses internal granular textures.
This powder metallurgy method particularly suits for making high
melting point metal or alloy parts with a complex shape under 500
grams.
[0086] The neck portions 120 become channels between the
micro-holes after the filling material 12a is removed. The
distribution ratio of the holes can be obtained by X/D (FIG. 12),
where D is the powder particle diameter of the filling material 12
and X is the diameter of the cross-section of the neck portions
120. The neck diameter is controlled by sintering temperature, time
and mixing ratio of the base material 11 and the filling material
12. Therefore, the hole distribution ration can be determined
before the step of sintering.
[0087] Further, the second embodiment of the present invention as a
smelting method for producing porous metal is described below, as
shown in FIG. 8.
[0088] The first thing to do before the step of mixing 10 is to
know the melting point temperature of the smelting base material
13, a pure metal or an alloy. Then we can execute the step of
smelting 7.
[0089] The smelting base materials 13, pure metals or their
associated alloys, must be divided into two categories, those of
low melting points and those of high melting points. The smelting
base materials 13 listed in Table 1 having a melting point
temperature of 1000.degree. C. or above includes:
[0090] Cu (or alloys of Cu with Zn, Sn, Al or P);
[0091] Fe;
[0092] Mn (or alloys of Mn with Fe or Ni);
[0093] Mo (or alloys of Mo with Fe, Ni, Co or Cr);
[0094] Ni (or alloys of Ni with Fe, Cr, Mo or Co);
[0095] Ag (or alloys of Ag with Cu);
[0096] W (or alloys of W with Ni, Cu or Ag);
[0097] V (or alloys of V with Mo, Ni, Co or Ti);
[0098] Ti (or alloys of Ti with Al, Ni or Co).smallcircle.
[0099] The smelting base materials 13 listed in Table 1 having a
melting point temperature below 1000.degree. C. includes:
[0100] Al (or alloys of Al with Si, Mg, Cu or Zn);
[0101] Pb (or alloys of Pb with Sn or Zn);
[0102] Mg (or alloys of Mg with Li, Al or Cu);
[0103] Sn (or alloys of Sn with Pb, Cu or Bi ).smallcircle.
[0104] The principle of choosing a filling material 12 for a
particular smelting base materials 13 is the same as in the
sintering method. That is, the melting point of the filling
material 12 must be higher than that of the smelting base materials
13, so that the filling material 12 will not melt in the later
smelting process.
[0105] To effectively execute the smelting process, the step of
smelting 7 is divided into two independent paths, one using a high
frequency oven 71 and the other using a low frequency oven 72, as
shown in FIG. 8. The above smelting base materials 13 of high
melting points are processed in the high frequency oven 71, and the
above smelting base materials 13 of low melting points are
processed in the low frequency oven 72.
[0106] When using the high frequency oven 71 or the low frequency
oven 72 for smelting, the two ovens can respectively induce a
periodic magnetic force to urge the desired stirring. Thereby, the
smelting base materials 13 and its filling material 12 can mix
uniformly.
[0107] To achieve an even better stirring effect, two thermos
chambers 710 and 720 are respectively provided in front of the high
frequency oven 71 and the low frequency oven 72. The filling
material 12 is further exposed to ultrasonic waves so that it can
even more uniformly distributed in the liquid of the smelting base
material 13. In a later step of vacuum molding 74, the granular
filling material 12 can quickly and uniformly distributed in the
smelting base materials 13, forming a raw metal bulk 78 having an
internal granular structure.
[0108] The raw metal bulk 78, of a low or high melting point, has
the same structure of neck portions 120 as in the case of
sintering, as shown in FIG. 10 and 11. Therefore, the hole
distribution ratio can also be controlled. This method particularly
suits making raw metal bulks 78 of high or low melting point and
simple outlook, such as a slab or a plate.
[0109] The following steps are common to the sintering and the
smelting methods. As shown in FIG. 7 and 8, the step of removing
filling material 3 or 30 applies the property that the filling
material 12 in a raw metal bulk 28 or 78 can dissolve in water or
alkaline solvents. Therefore, we can choose a solvent 31 that is
harmless to the smelting base materials 13 and then put the raw
metal bulk 28 or 78 in a washing tank equipped with ultrasonic
waves. The cavitation effect induced by the ultrasonic waves cleans
the filling material 12a in the raw metal bulk 28 or 78, as shown
in FIG. 11. After the washing, we have a half-product of porous
metal in which either a sintering base material 11a or a smelting
base material 13a exhibit a micro-hole structure.
[0110] When the filling material 12 is CaCl.sub.2, the
corresponding solvent 31 is CH.sub.3CH.sub.2OH (alcohol), as shown
in Table 2. The CH.sub.3CH.sub.2OH (alcohol) is suitable for using
with smelting base materials 13 of Al, Pb, Mg and Sn metals and
their associated alloys, as shown in Table 1.
[0111] When the filling material 12 is MnO, the corresponding
solvent 31 is NH.sub.4Cl, as shown in Table 2. The solvent 31 is
suitable for using with smelting base materials 13 of Cu, Fe, Mg,
Mn and Ni metals and their associated alloys, as shown in Table
1.
[0112] When the filling material 12 is NaCl, the corresponding
solvent 31 is cold or hot water, as shown in Table 2. The solvent
31 is suitable for using with smelting base materials 13 of Al, Pb,
Mg and Sn metals and their associated alloys, as shown in Table
1.
[0113] When the filling material 12 is TiO.sub.2, the corresponding
solvents 31 are NaOH and KOH, as shown in Table 2. The solvent 31
is suitable for using with smelting base materials 13 of Cu, Fe,
Mg, Mn and Ni metals and their associated alloys, as shown in Table
1.
[0114] When the filling material 12 is WO.sub.3, the corresponding
solvents 31 are NaOH and KOH, as shown in Table 2. The solvent 31
is suitable for using with smelting base materials 13 of Cu, Fe,
Mg, Mn, Ni, Ag, V and Ti metals and their associated alloys, as
shown in Table 1.
[0115] When the filling material 12 is V.sub.2O.sub.3, the
corresponding solvents 31 are NaOH and KOH, as shown in Table 2.
The solvent 31 is suitable for using with smelting base materials
13 of Cu, Fe, Mg, Mn, Ni, Ag, V and Ti metals and their associated
alloys, as shown in Table 1.
[0116] When the filling material 12 is ZnO, the corresponding
solvents 31 are NaOH and KOH, as shown in Table 2. The solvent 31
is suitable for using with smelting base materials 13 of Cu, Fe,
Mg, Mn, Ni, Ag, V and Ti metals and their associated alloys, as
shown in Table 1.
[0117] When the filling material 12 is MnO, the corresponding
solvents 31 are NH.sub.4OH or NH.sub.4Cl, as shown in Table 2. The
solvent 31 is suitable for using with smelting base materials 13 of
Cu, Fe, Mg, Mn, Ni, Ag, V, Ti and Mo metals and their associated
alloys, as shown in Table 1.
[0118] The porous half-product 32 produced after the step of
removing the filling material, 3 or 30, must undergo a step of
water cleaning, 4 or 40, since the alkaline solvent 31 attached to
the half-product 32 must be cleared. The step 4 or 40 is executed
in a water tank equipped with ultrasonic waves.
[0119] The porous half-product 32 must go through a step of drying
by heat, 5 or 50. This is done in an infrared or microwave ovens.
The microwave frequency used in the step of microwave drying is
between 100-140 GHz, and the wavelength is between 1 mm-1 m. After
this step, a porous metal 8 having micro-holes 80 is formed.
[0120] Further, if the filling material 12 used is an oxide, a
further step of reduction, 6 or 60, is necessary.
[0121] To execute the step of reduction, 6 or 60, the dried porous
metal 8 is disposed in a vacuum chamber filled with a reduction gas
(hydrogen gas, for example), whereby the oxidation layers or films
between micro-holes 80 can be removed.
[0122] An alternative reduction method for the step 6 or 60 is
using a solvent for dissolving the oxidation layers and films. The
solvent can be NaOH, KOH, NH.sub.4Cl and NH.sub.4OH. This is done
in a tank equipped with ultrasonic waves.
[0123] The present invention is thus described, and it will be
obvious that the same may be varied in many ways. Such variations
are not to be regarded as a departure from the spirit and scope of
the present invention, and all such modifications as would be
obvious to one skilled in the art are intended to be included
within the scope of the following claims.
* * * * *