U.S. patent application number 09/968923 was filed with the patent office on 2002-04-04 for mgalloy member and its use.
Invention is credited to Fujii, Kazumi, Kato, Tomoya, Obana, Takeshi, Ohashi, Kenya, Shouji, Mitsuyoshi.
Application Number | 20020039528 09/968923 |
Document ID | / |
Family ID | 13364405 |
Filed Date | 2002-04-04 |
United States Patent
Application |
20020039528 |
Kind Code |
A1 |
Kato, Tomoya ; et
al. |
April 4, 2002 |
MGalloy member and its use
Abstract
A Mg alloy member with an anticorrosive coating free from any
environmental load can be produced by using a solution for chemical
conversion treatment for anticorrosive coating, which comprises
0.05 to 1 mol/l of an oxoacid compound of heavy metal selected from
Mo, W and V and has a pH of 2 to 6 adjusted by sulfuric acid or
nitric acid, and is characterized by contacting the surface of Mg
alloy preferably containing 2 to 10% Al with the solution, thereby
forming a specific oxide film and, if necessary further forming a
fluorine-containing organic film on the film, the resulting Mg
alloy member being used in electrically driven blowers, note-type
personal computers, various household electrical appliances,
etc.
Inventors: |
Kato, Tomoya; (Hitachi-shi,
JP) ; Obana, Takeshi; (Hitachi-shi, JP) ;
Shouji, Mitsuyoshi; (Ibaraki-Ken, JP) ; Fujii,
Kazumi; (Hitachi-shi, JP) ; Ohashi, Kenya;
(Hitachinaka-shi, JP) |
Correspondence
Address: |
ANTONELLI TERRY STOUT AND KRAUS
SUITE 1800
1300 NORTH SEVENTEENTH STREET
ARLINGTON
VA
22209
|
Family ID: |
13364405 |
Appl. No.: |
09/968923 |
Filed: |
October 3, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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09968923 |
Oct 3, 2001 |
|
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09261963 |
Mar 3, 1999 |
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Current U.S.
Class: |
415/182.1 |
Current CPC
Class: |
C23C 22/42 20130101;
C23C 22/44 20130101; C23C 22/40 20130101; F05D 2300/512 20130101;
F05D 2230/90 20130101; F05D 2300/125 20130101; Y10T 428/31544
20150401; F04D 29/023 20130101; F05D 2300/17 20130101; A47L 5/22
20130101; Y10T 428/3154 20150401; F05D 2300/611 20130101 |
Class at
Publication: |
415/182.1 |
International
Class: |
F04D 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 18, 1998 |
JP |
10-068114 |
Claims
What is claimed is
1. A solution for chemical conversion treatment for anticorrosive
coating, characterized by comprising 0.05 to 1 M of a heavy metal
oxo acid compound comprising at least one of heavy metal atoms
selected from Mo, W and V in terms of the heavy metal atom and
having a pH of 2 to 4 adjusted by sulfuric acid or nitric acid.
2. A process for producing a Mg alloy member, characterized by
contacting a Mg alloy with an aqueous acidic solution containing a
heavy metal oxo acid compound of at least one of heavy metals
selected from Mo, W and V, thereby forming an oxide film on the
surface of the Mg alloy.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Continuation Application of
application Ser. No. 09/261,963 filed Mar. 3, 1999.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a process for forming a
novel anticorrosive coating on Mg alloy, to an Mg alloy member and
household electrical appliances, audio systems, etc. using
materials with such an anticorrosive coating, and more particularly
to a Mg alloy member having a good corrosion resistance given by an
environmentally harmless chemical conversion treatment, its use, a
solution for chemical conversion treatment and a process for
anticorrosive coating.
[0003] Mg alloy materials have the lightest weight among the
practical metallic materials and also have a large specific
strength and a good castability, and thus their wider application
to cases, structural bodies, various parts, etc. of household
appliances, audio systems, aircrafts, automobiles, etc. has been
desired. Particularly, Al-containing AZ91D (Al:8.3-9.7 wt. %) and
AM60B (Al:5.5-6.5 wt. %) have a good fluidity in die casting and
thixo molding and thus are most desirable alloys.
[0004] However, Mg has the basest normal electrode potential among
the practical metallic materials, resulting in a high corrosion
susceptibility when the metal is brought into contact with other
metals and a considerably poor anticorrosiveness in an aqueous
acidic, neutral or chloride solution. Thus, for its application to
corrosion-excluding positions, e.g. good appearance-maintaining
positions etc., it is necessary to provide an anticorrosive
treatment. Coating is the most popular anticorrosion means, but it
is hard to apply coating to Mg alloy materials per se because of
the disadvantage that the resulting coating film, even if obtained,
has a poor adhesiveness. Sometimes, corrosion may occur under the
coating film, and thus it is the ordinary practice to conduct a
substrate surface treatment in advance of the coating process.
[0005] The substrate surface treatment technology includes, for
example, substrate surface treatments of forming a metal oxide film
or a sparingly soluble salt film by chemical conversion treatment
or anodizing using such heavy metal oxo acid salts as chromates,
permanganates etc., or phosphates so as to improve the corrosion
resistance and the adhesiveness of coating films.
[0006] It is also the ordinary coating practice to use oil paints
and synthetic resin paints which contain lead compounds, zinc
powder and its compounds, chromates, etc. as an anticorrosive
pigment.
[0007] Processes for forming an anticorrosive film on a Mg alloy
are disclosed in JP-A-9-176894 and JP-A-9-228062.
[0008] Surface treatments using specific chemical compounds such as
chromates, permanganates, etc. however have problems relating to
environmental friendliness, such as effluent water pollution
problems and skin allergy problems to operators. The use of such
surface treatments is increasingly subject to strict regulations.
Phosphates are also more or less harmful to the environment, and
the corrosion resistance of resulting phosphate films is not
satisfactory. Substitute processes for such substrate surface
treatments are now under development but still have problems with
respect to corrosion resistance, etc.
[0009] Lead compounds or chromates contained as anticorrosive
pigments in coating technology also have problems relating to the
environmental friendliness. Furthermore, there are occasionally
problems relating to corrosions probably due to diffusion of oxygen
or water generated by corrosion under the coating film or by
coating film.
[0010] The invention disclosed in said JP-A-9-176894 relates to an
electrolytic treatment. Anodizing requires a power source of high
voltage. An entirely uniform film is also hard to obtain. In the
invention disclosed in said JP-A-9-228062, treatments using an
organometal are highly reactive and thus an entirely uniform film
is likewise hard to obtain.
BRIEF SUMMARY OF THE INVENTION
[0011] An object of the present invention is to provide a Mg alloy
member having a chemical conversion film with a good corrosion
resistance obtained by using an environmentally harmless aqueous
solution, its use, a solution for the chemical conversion treatment
and its process.
[0012] Another object of the present invention is to form a
super-water-repellent film on the chemical conversion film.
[0013] The present invention provides a Mg alloy member comprising
a Mg alloy and formed thereon an oxide film comprising 15 to 35% by
atom of Mg and 5 to 2% by atom of Mo, and, if necessary, 30% by
atom or less of Al or a metallic Al-containing oxide film.
[0014] The present invention also provides a Mg alloy member
comprising a Mg alloy and formed thereon a noble oxide film having
a corrosion potential of -1,500 mV or more in 1 M--Na.sub.2SO.sub.4
and 0.01 M--Na.sub.2B.sub.4O.sub.7 (pH 9.18).
[0015] The present invention further provides a Mg alloy member
comprising a Mg alloy and formed thereon the oxide film mentioned
above or the noble oxide film mentioned above, and formed on the
oxide film a fluorine-containing super-water-repellent organic
film.
[0016] The present invention still further provides use of the Mg
alloy member mentioned above as a blade wheel in an electrically
driven blower, as a casing of a personal computer, as a casing of a
video camera, cases for various electrically driven tools, a
portable telephone case, a television case, automobile sheet parts,
etc.
[0017] The present invention also provides a solution for chemical
conversion treatment for anticorrosive coating, characterized by
comprising 0.05 to 1 M of a heavy metal oxo acid compound
comprising at least one of heavy metal atoms selected from Mo, W
and V in terms of the heavy metal atom and having a pH of 2 to 6
adjusted by sulfuric acid or nitric acid.
[0018] The present invention further provides a process for
producing a Mg alloy member, characterized by contacting a Mg alloy
with an aqueous acidic solution containing a heavy metal oxo acid
compound of at least one of heavy metals selected from Mo, W and V,
thereby forming an oxide film on the surface of the Mg alloy.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a profile showing components in the AES depth
direction of the present chemical conversion film.
[0020] FIG. 2 is a profile showing component in the AES depth
direction of the present chemical conversion film.
[0021] FIG. 3 is a graph showing changes in corrosion potential in
time course of the present chemical conversion film and comparative
film in 0.01 M Na.sub.2B.sub.4O.sub.7 (pH=9.18).
[0022] FIG. 4 is a graph showing changes in corrosion potential in
time course of the present chemical conversion film and comparative
film in 1 M Na.sub.2SO.sub.4.
[0023] FIG. 5 is a plan view and side view of blade wheel made from
Mg alloy AZ91D with anticorrosive coating according to the present
process.
[0024] FIG. 6 is a cross-sectional view of electrically driven
blower using the present blade wheel.
[0025] FIG. 7 is a perspective view of electric cleaner encasing
the electrically driven blower.
[0026] FIG. 8 is a exploded perspective view of the present blade
wheel.
[0027] FIG. 9 is a perspective views of various cases for
notebook-type personal computer made from Mg alloy AZ91D with
anticorrosive coating according to the present invention.
[0028] FIG. 10 is a cross-sectional view of thixomolding
apparatus.
DETAILED DESCRIPTION OF THE INVENTION
[0029] The present invention provides a Mg alloy member,
characterized in that the Mg alloy member has, on the surface, an
oxide film comprising 15 to 35%, preferably 20 to 30%, of Mg by
atom and 5 to 20% of Mo by atom; an Al-containing oxide film
comprising 15 to 35% of Mg by atom, 5 to 20% of Mo by atom and not
more than 30%, preferably 10 to 25%, of Al by atom; an oxide film
comprising 15 to 35% of Mg by atom, 5 to 20% of Mo by atom, 10 to
30% of Al as an oxide and not more than 15%, preferably 4 to 12%,
of metallic Al by atom; a noble oxide film with a corrosion
potential of not less than -1,500 mV, preferably not less than
-1,400 mV, after immersion in an aqueous 0.01 M
Na.sub.2B.sub.4O.sub.7 solution at a pH of 9.18 and 25.degree. C.
for 30 minutes; or a noble oxide film with a corrosion potential of
not less than -1,500 mV, preferably not less than -1,400 mV, after
immersion in an aqueous 1 M Na.sub.2SO.sub.4 solution at 25.degree.
C. for 15 minutes.
[0030] Furthermore, the present invention provides a Mg alloy
member, characterized in that the Mg alloy member has the oxide
film or a specific oxide film and a fluorine-containing
super-water-repellent organic film on the film.
[0031] The fluorine-containing film is preferably a film comprising
a compound of the following general formula (1) and an organic
polymer:
Rf-A-X-B-Y . . . (1)
[0032] wherein Rf is a perfluoropolyoxyalkyl group or a
perfluoroalkyl group; A and B are independently an amido group, an
ester group or an ether group; 1
[0033] and Y represents or 2
[0034] In the definition of Rf, the perfluoro-polyoxyalkyl group is
preferably represented by the formula: (C.sub.nF.sub.2n-O).sub.x-,
wherein n is preferably an integer of 1 to 3; and x is preferably
an integer of 5 to 70, and the perfluoroalkyl group is preferably
represented by the formula: F-C.sub.mF.sub.2m-, wherein m is
preferably an integer of 3 to 12.
[0035] The fluorine-containing film is preferably a film comprising
a compound of the following general formula (2):
Rf-A-R-Si-OC.sub.nH.sub.2n+2).sub.2 . . . (2)
[0036] wherein Rf is a perfluoropolyoxyalkyl group or a
perfluoroalkyl group as defined above; A is an amido group, an
ester group or an ether group, R is an alkylene group; and n is 1
or 2.
[0037] The perfluoropolyoxyalkyl group preferably has a chain of
repetition units of oxyalkylene represented by the following
structural formula (3), (4) or (5) alone or in combination:
CF.sub.2-O.paren close-st. . . . (3)
C.sub.2F.sub.4-O.paren close-st. . . . (4)
C.sub.3F.sub.6-O.paren close-st. . . . (5)
[0038] Examples of specific structure of the general formula (1)
include the following structures of (formula 1) to (formula 8):
3
[0039] (wherein m is 14 on average).
[0040] Examples of specific compounds of the general formula (2)
include the following structures of (formula 9) to (formula
14).
F(CF.sub.2--CF.sub.2--CF.sub.2--O.paren
close-st..sub.nCF.sub.2--CF.sub.2C-
ONH--CH.sub.2CH.sub.2CH.sub.2--Si(--OCH.sub.2CH.sub.3).sub.3 . . .
(formula 9)
F(CF.sub.2--CF.sub.2--CF.sub.2--O.paren
close-st..sub.nCF.sub.2--CF.sub.2C-
ONH--CH.sub.2CH.sub.2--NH--CH.sub.2CH.sub.2CH.sub.2--Si(--CH.sub.3)(--OCH.-
sub.3).sub.2 . . . (formula 10)
CF.sub.3--CF.sub.2--CF.sub.2--CF.sub.2--CF.sub.2--CF.sub.2--CF.sub.2CONH---
CH.sub.2CH.sub.2CH.sub.2--Si(--OCH.sub.2CH.sub.3).sub.3 . . .
(formula 11)
F(CF.sub.2--CF.sub.2--CF.sub.2--O.paren
close-st..sub.nCF.sub.2--CF.sub.2C-
H.sub.2--O--CH.sub.2CH.sub.2CH.sub.2--Si(--OCH.sub.3).sub.3 . . .
(formula 12)
F(CF.sub.2--CF.sub.2--CF.sub.2--O.paren
close-st..sub.nCF.sub.2--CF.sub.2C-
OO--CH.sub.2CH.sub.2CH.sub.2--Si(--OCH.sub.3).sub.3 . . . (formula
13)
CF.sub.3--CF.sub.2--CF.sub.2--CF.sub.2--CF.sub.2--CF.sub.2--CF.sub.2--COO--
-CH.sub.2CH.sub.2CH.sub.2--Si(--OCH.sub.3).sub.3 . . . (formula
14)
[0041] (wherein n is 21 on average)
[0042] The present invention provides an electrically driven blower
which comprises a motor encased in a housing a blade wheel fixed to
the rotating shaft of the motor, stationary guide blades provided
against the flow passage end of the blade wheel and a fan casing
housing the blade wheel and the stationary guide blades,
characterized in that the blade wheel is composed of the
above-mentioned Mg alloy member having an oxide film on the
surface.
[0043] Furthermore, the present invention provides an electrically
driven blower which comprises a motor encased in a housing, a blade
wheel fixed to the rotating shaft of the motor, stationary guide
blades provided against the flow passage end of the blade wheel and
a fan casing housing the blade wheel and the stationary guide
blades, characterized in that the blade wheel comprises a front
plate, a back plate counterposed to the front plate and a plurality
of blades provided between the front plate and the back plate, at
least one of the front plate and the back plate being integrated
with the blades, and is composed of a Mg alloy member having an
oxide film on the surface.
[0044] The blade plate is composed of the above-mentioned Mg alloy
member.
[0045] Furthermore, the present invention provides a personal
computer, a video camera, a single-lens reflex camera, a compact
camera, an MD player, an HDD, an automobile, a television, a
portable telephone and an electrically driven tool, characterized
by using a case, etc. composed of a Mg alloy member having the
above-mentioned oxide film on the surface or further a
super-water-repellent, fluorine-containing organic film on the
oxide film.
[0046] The present invention provides a solution for chemical
conversion treatment for anticorrosive coating, characterized by
comprising 0.05 to 1 M (mol/l of a heavy metal oxo acid compound
comprising at least one of heavy metal atoms selected from Mo, W
and V in terms of the heavy metal atom and having a pH of 2 to 6
adjusted by sulfuric acid or nitric acid.
[0047] The present invention provides a process for producing a Mg
alloy member, characterized by contacting a Mg alloy with an
aqueous acidic solution containing a heavy metal oxo acid compound
of at least one of heavy metals selected from Mo, W and V, thereby
forming an oxide film on the surface of the Mg alloy.
[0048] That is, in the present invention, an aqueous solution
containing 0.05 to 1 mol/l of a heavy metal oxo acid compound
comprising at least one of heavy metal atoms selected from Mo, W
and V in terms of heavy metal atom and having a pH of 2 to 6
adjusted by sulfuric acid or nitric acid is brought into contact
with the surface of preferably Al-containing Mg alloy, thereby
conducting a chemical conversion treatment of the Mg alloy,
followed by water washing and drying, to form the above-mentioned
oxide film. It is preferable to form a compound oxide film
containing the above-mentioned heavy metal atom and Al, or a
compound oxide film, where the Al cation fraction is at least three
times as large as the Al content of the substrate, or a compound
oxide film where the heavy metal atom is in a polyvalent state. It
is preferable that the Al-containing alloy contains 2 to 10 wt. %
Al.
[0049] The amount of the heavy metal oxo acid compound in the
solution for chemical conversion treatment is 0.05 to 1 mol/l in
terms of heavy metal atom so as to retain cations of heavy metal
atom in the chemical conversion film. Below 0.05 mol/l the chemical
conversion film will be hardly formed, whereas above 1 mol/l it
will be saturated. A range of 0.2 to 0.5 mol/l that can ensure
formation of a good film is desirable. The pH of the solution for
chemical conversion treatment is preferably in a range of 2 to 6,
so that the Al-containing Mg alloy can be brought into a readily
reactable, active state to form a good film. Below 2 melting of the
substrate will be too vigorous to form a chemical conversion film,
whereas above 6, the reaction rate to form a film, which follows
the melting of substrate, will be lower. To form a better film, a
pH range of 2.5 to 4 is more desirable. Time for chemical
conversion treatment is preferably in a range of 5 to 300 seconds.
Below 5 seconds, a satisfactory film will fail to grow, whereas
above 300 seconds its effect will be saturated. To form a better
film, a range of 30 to 200 seconds is more desirable. Water washing
following the chemical conversion treatment must be continued until
no bubbles generate from the chemical conversion film. An aqueous
solution of a weak base such as Na.sub.2B.sub.4O.sub.7,
Na.sub.2CO.sub.3 or the like may be substituted for water. Drying
can be natural drying, but may be drying in a temperature range of
20.degree. C. to 80.degree. C.
[0050] Furthermore, the present invention provides further coating
of the chemical conversion film to improve the corrosion resistance
or to form a fluorine-containing, super-water-repellent film on the
chemical conversion film after the substrate surface treatment.
[0051] The fluorine-containing film preferably comprises a film of
the thermosetting silicone resin, etc. as the major component and a
layer of a fluorine-based compound of the foregoing general formula
(1) or (2) formed on the surface of the film or a single film of
the fluorine-based component of the general formula (2) without the
organic polymer film. Three specific procedures for coating the
fluorine-containing film will be given below:
[0052] (I) An organic polymer material and a fluorine-based
compound of the general formula (1) are dissolved into an organic
solvent to prepare a coating material. The chemical conversion film
surface is immersed into the coating material and then picked up,
followed by heating to the polymer heat curing temperature. By the
treatment, the perfluoropolyoxyalkyl group or perfluoroalkyl group
of the general formula (1) is fixed to the polymer surface
layer.
[0053] (II) An organic polymer material is dissolved into an
organic solvent to prepare a coating material. The chemical
conversion film surface is immersed into the coating material and
then picked up, followed by heating to the polymer heat curing
temperature to form a polymer film on the surface. Then, the
polymer film-formed surface is immersed into a solution containing
a fluorine-based compound of the general formula (2) as dissolved
therein, and then picked up, followed by heating at 150.degree. C.
for 10 minutes. By the treatment, the fluorine-based compound of
the general formula (2) is fixed to the polymer surface by chemical
reaction.
[0054] (III) To prepare a fluorine-containing single film composed
of a fluorine-based compound of the general formula (2) without the
organic polymer film, the chemical conversion film surface is
washed to remove the oil and fat matters therefrom, immersed into a
solution containing a fluorine-based compound of the general
formula (2), which chemically reacts with the substrate surface and
is fixed thereto.
[0055] Examples of specific structural formulae of the general
formula (1) are those given by (formula 1) to (formula 8).
[0056] Examples of specific structural formulae of the general
formula (2) are those given by (formula 9) to (formula 14).
[0057] Organic polymers for use in the present invention are those
which can be used as a coating material to form a coating film
having the required mechanical strength. For example, epoxy resin,
phenol resin, polyimide resin, silicone resin, etc. are desirable
as thermosetting polymers.
[0058] According to the present invention, a metallic material can
be coated with a film having a distinguished corrosion resistance
without using environmental harmful materials. Furthermore, a
material with a large area can be coated at relatively low
temperatures.
[0059] Its principle and process will be described in detail
below.
[0060] Usually, the anticorrosive coating to metallic materials has
micron-size defects or sometimes may be damaged due to external
factors, etc. Corrosion proceeds due to such defects. When an oxide
film, such as a chromate film containing both hexavalent and
trivalent Cr ions, is formed and exists, an anodic reaction to
dissolve the substrate metal through the micron-size defects takes
place and also a cathodic reaction to reduce the hexavalent Cr ions
to the trivalent Cr ions in the surrounding oxide film takes place
at the same time.
[0061] M.fwdarw.M.sup.n+ne:anodic reaction
[0062] Cr.sup.6++3e.fwdarw.Cr.sup.3+:cathodic reaction
[0063] By these reactions a Cr.sub.2O.sub.3 film having new
M.sup.7+filled in the film defects is formed, so that the resulting
chromate film show a distinguished corrosion resistance with a
defect-remedying action.
[0064] MoO.sub.4.sup.2-, WO.sub.4.sup.2 -,VO.sub.4.sup.3 -and
VO.sub.3 .sup.-can be also used as a passivating agent or an anodic
inhibitor and can suppress corrosion of metallic materials, when
put into the corrosive circumstances in a small amount. Its
mechanism is shifting the corrosion potential to a nobler level by
a few hundred mV and facilitation to form an oxide film showing a
high corrosion resistance so called "passivation film" on the
substrate surface. That is, the passivating agent has a specific
property of being rapidly reduced by a cathode current and thus can
be preferentially adsorbed onto the metallic substrate surface.
[0065] Inclusion of two kinds of valency such as MoO.sub.3 and
MoO.sub.2, etc. has the same effect as that of the chromate
film.
[0066] A film of oxide and/or hydroxide and/or oxyhydroxide
containing metal ions having a plurality of valencies can be formed
by providing a metallic material with an aqueous H.sub.2O.sub.2
solution prepared by dissolving metal and/or metal carbonate
composed of at least one of Mo, W and V and removing excess
H.sub.2O.sub.2 therefrom by decomposition, followed by heat
treatment at a temperature of not more than 80.degree. C. to effect
dehydration and stabilization.
[0067] Alternatively, a film of oxide and/or hydroxide and/or
oxyhydroxide containing metal ions having a plurality of valencies
can be formed according to a process for immersing a metallic
material into a solution containing at least one of
MoO.sub.4.sup.2-, WO.sub.4 .sup.2-, VO.sub.4.sup.3- and VO.sub.3
.sup.- and/or according to a process for electrochemically
anodizing a metallic material in a solution containing at least one
of MoO.sub.4.sup.2-, WO.sub.4.sup.2-, VO.sub.4.sup.3-and VO.sub.3-,
and the film is heat treated at a temperature of not more than
80.degree. C. to effect dehydration and stabilization, and then a
fluorine-containing film is formed on the surface.
[0068] Alternatively, a film of oxide and/or hydroxide and/or
oxyhydroxide containing metal ions having a plurality of valencies
can be formed according to a reactive sputtering process, and a
fluorine-containing film is formed on the film.
[0069] Alternatively, a film of oxide and/or hydroxide and/or
oxyhydroxide containing metal ions having a plurality of valencies
can be formed by providing a metallic material with an aqueous
H.sub.2O.sub.2 therefrom by decomposition, followed by heat
treatment at a temperature of not more than 80.degree. C. to effect
dehydration and stabilization, and a fluorine-containing film is
formed on the surface in the same manner as above.
[0070] According to the present invention, it is preferable to form
the above-mentioned oxide film as an undercoat and further form a
coat having the ordinary corrosion resistance or various color
tones showing a proper appearance on the surface of the film.
[0071] The present invention is illustrated by way of the following
Examples.
Example 1, Comparative Example 1-3
[0072] Table 1 shows the composition of aqueous solutions for
forming an oxide film on the surfaces of Mg alloys used in Run Nos.
1 to 6 of the present invention and Comparative Examples 1 to 3 and
conditions for chemical conversion treatment.
1TABLE 1 Run No. 1 1M-Na.sub.2MoO.sub.4 (with H.sub.2SO.sub.4 to
make pH = 3.0) 60.degree. C., 180 sec. Run No. 2
0.5M-Na.sub.2MoO.sub.4 (with H.sub.2SO.sub.4 to make pH = 3.0)
60.degree. C., 180 sec. Run No. 3 0.1M-Na.sub.2MoO.sub.4 (with
H.sub.2SO.sub.4 to make pH = 3.0) 60.degree. C., 180 sec. Run No. 4
1M-Na.sub.2MoO.sub.4-0.5M-NaF (with H.sub.2SO.sub.4 to make pH =
3.0) 60.degree. C., 180 sec. Run No. 5
0.5M-Na.sub.2MoO.sub.4-0.5M-NaF (with H.sub.2SO.sub.4 to make pH =
3.0) 60.degree. C., 180 sec. Run No. 6 0.1M-Na.sub.2MoO.sub.4-0.-
5M-NaF (with H.sub.2SO.sub.4 to make pH = 3.0) 60.degree. C., 180
sec. Comp. Ex. 1 Na.sub.2Cr.sub.2O.sub.7180 g/1, HNO.sub.3(60 wt
%)260 ml/1, 30.degree. C., 120 sec. (chromate: one species) Comp.
Ex. 2 Na.sub.2Cr.sub.2O.sub.7180 g/1, HNO.sub.3(6O wt %)84 ml/1,
F15 g/1, Al.sub.2(SO.sub.4).sub.310 g/1, 20.degree. C., 180 sec.
Comp. Ex. 3 0.05M-Na.sub.2MoO.sub.4-0.15M-H.sub.3PO.sub.4 (to make
pH = 2.0) 60.degree. C., 180 sec.
[0073] In Run Nos. 1-6 and Comparative Examples, AZ91D (Mg alloy
diecasting material containing 9 wt. % Al and 1 wt. % Zn,
10.times.10.times.50 mm) was used as test pieces.
[0074] In this Example, oxide films were formed by immersion into
solution for chemical conversion treatment of Table 1. As a
pretreatment, the test pieces were polished to #2,000 with SiC
paper and then defatted in acetone by ultrasonic washing. The test
pieces were subjected to chemical conversion treatment under
conditions given in Table 1 and then immediately washed with water
and dried in air. In the table, M means a molar concentration,
temperature (.degree. C.) is a temperature of solution for chemical
conversion treatment, and time (sec.) is an immersion time.
[0075] By immersing the Mg alloy into solutions for chemical
conversion treatment, the surface of the alloy is colored.
Thickness of the film can be anticipated from the degree of
coloring. By immersion for 3 minutes, light brown turns to dark
brown and further to blackish.
[0076] FIG. 1 and FIG. 2 are profile in AES depth direction of
films on the alloy after chemical conversion treatment in 1 M (Run
No. 1) and 0.1 M (Run No. 3) of Na.sub.2MoO.sub.4 (with
H.sub.2SO.sub.4 to make pH=3.0), respectively. In both cases, it
can be seen that Al contained in the substrate is enriched on the
surface and Mo is incorporated into the oxide film from the
solution.
[0077] As shown in FIG. 1, at a thickness ranging from 0 to 3 .mu.m
(from 0 to 3,000 nm) the oxide film has 25-30 at. % Mg (27 at. % on
average), 15-22 at. % Al as an oxide (20 at. % on average), 9-12
at. % Mo (10 at. % on average), 0-17 at. % Al as metal (6 at. % on
average), 30-42 at. % O (37 at. % on average), where the
concentration of Al as metal increases with film thickness and the
concentrations of O, Al as oxide and Mo gradually decrease with
film thickness. The concentration of oxygen decreases in the depth
direction at an average rate of 3.4 at. % per 1 .mu.m of oxide film
thickness. The concentration of Al as metal gradually increases in
the depth direction.
[0078] Also as shown in FIG. 2, at a thickness ranging from 0 to
0.5 .mu.m (from 0 to 500 nm) the oxide film has, on average
concentrations, 15 at. % Mo, 15 at. % Al as oxide, 20 at. % Mg and
41 at. % O, where the concentration of Al as metal gradually
increases with increasing depth and has 9 at. % on average, and the
concentration of oxygen decreases in depth direction at an average
rate of 35 at. % per 1 .mu.m of oxide film thickness.
[0079] FIG. 3 and FIG. 4 show changes in time course of corrosion
potential at 25.degree. C. in 0.01 M Na.sub.2B.sub.4O.sub.7
(pH=9.18) and in 1 M Na.sub.2SO.sub.4, respectively. Both molybdate
conversion films have a higher corrosion potential than those of
untreated AZ91D and chromate conversion film and have an equivalent
or superior effect of anticorrosive coating to that of the chromate
conversion film.
[0080] As shown in FIG. 3, the chromate conversion films resulting
from the treatment for 30 minutes have base corrosion potentials of
not more than -1,500 mV, whereas the present conversion films have
a noble corrosion potentials of not less than -1,500 mV,
specifically not less than -1,350 mV. By increasing the
concentration of the solution for chemical conversion treatment a
much nobler corrosion potential can be evidently obtained.
[0081] As shown in FIG. 4, the chromate conversion films resulting
from the treatment for 15 minutes have base corrosion potentials of
not more than -1,500 mV, whereas the present conversion films have
noble corrosion potentials of not less than -1,500 mV, specifically
not less than -1,450 mV. By making the concentration of the
solution for chemical conversion treatment higher from 0.5 M to 1 M
a much nobler corrosion potential can be evidently obtained.
EXAMPLE 2
[0082] In this Example, fluorine-containing, super-water-repellent
organic films of the following (1) to (4) were formed as an
anticorrosive coat after the chemical conversion treatment of Run
No. 1 in Example 1. Test pieces were the same as used in Example 1.
(1) Process using Glass Resine:
[0083] 50 g of Glass Resine GR650 (commercially available from
Showa Denko K.K.) and 5 g of fluorine-based compound of (formula 4)
were dissolved into 475 g of 2-butanone and 25 g of ethylene glycol
mono-m-butyl ether acetate to prepare a coating agent. A chemical
conversion film surface was immersed into the coating agent and
then picked up, followed by heating at 160.degree. C. for 3 hours.
(2) Process using epoxy resin:
[0084] 5 g of epoxy resin (ED1004) commercially available from
Yuka-Shell Epoxy K.K., 3 g of Maruk a Lyncur M (phenol resin
commercially available from Maruzen Petrochemical K.K.), 0.05 g of
triethylaminetetraphenyl borate TEA-K (trademark of curing promoter
commercially available from Hokko Kagaku K.K.) and 5 g of
fluorine-based compound of (formula 5) were dissolved into a
solvent mixture consisting 100 g of 2-butanone and 5 g of ethylene
glycol mono-n-butyl ether acetate to prepare a coating agent. A
chemical conversion film surface was immersed into the coating
agent and then picked up, followed by heating at 180.degree. C. for
one hour. (3) Process using epoxy resin and phenol resin:
[0085] 5 g of epoxy resin (EP1004) commercially available from
Yuka-Shell Epoxy K.K., 3 g of Maruka Lyncur M (phenol resin
commercially available from Maruzen Petrochemical K.K.) and 0.05 g
of triethylaminetetraphenyl borate TEA-K (trademark of curing
promoter commercially available from Hokko Kagaku K.K.) were
dissolved into a solvent mixture consisting of 100 g of 2-butanone
and 5 g of ethylene glycol mono-n-butyl ether acetate to prepare a
coating agent. A chemical conversion film surface was immersed into
the coating agent and then picked up, followed by heating at
180.degree. C. for one hour. After cooling; the resulting coat was
immersed into a solution containing 1 g of a fluorine-based
compound of (formula 9) in 100 g of perfluorohexane FC-72
(commercially available from Sumitomo-3M K.K.) for 24 hours and
then picked up, followed by heating at 150.degree. C. for 10
minutes. (4) Process using fluorine-based compound:
[0086] A chemical conversion film surface was washed to remove oil
and fat matters, then dipped into a solution containing 1 g of
fluorine-based compound of (formula 9) in 100 g of perfluorohexane
FC-72 (commercially available from Sumitomo-3M K.K.) and then
picked up, followed by heating at 150.degree. C. for 10
minutes.
[0087] The members having a fluorine-containing organic film
according to the present invention all had maximum contact angles
to water of 120.degree. to 130.degree. and also a high water
repellency. The fluorine-containing films obtained according to the
above (1) and (2) had a better durability than that of those
obtained according to the above (3) and (4).
EXAMPLE 3
[0088] FIG. 5 is a plan view and a side view of a blade wheel made
from AZ91D by die casting and thixomolding, the blade wheel being
provided with an anticorrosive coating according to the present
process.
[0089] In FIG. 5, numeral 51 shows a front plate having a suction
inlet, 52 a back plate counterposed to and below the front plate
51, and 53 blades provided and caught between the front plate 51
and the back plate. The blades 53 are provided as curved along the
surfaces of front plate 51 and back plate 52, as shown in FIG. 5.
The front plate 51, the back plate 52 and the blades form a
plurality of air discharge outlets 55. Air is sucked through a
suction inlet 53 by rotation of the blade wheel and discharged
through the air discharge outlets 55. As will be described later, a
fear of corrosion of AZ91D was overcome by applying thereto the
same anticorrosion coating according to the present invention as
the foregoing Examples 1 and 2.
[0090] FIG. 6 is a schematic view of an electrically driven blower
using the blade wheel of FIG. 5. Electrically driven blower 601
comprises a motor 617 and a blower 618. Motor 617 comprises a
housing 602, a stator 603 fixed to the housing 602, a rotating
shaft 605 supported by bearings 604 and 619 provided on the housing
602, a rotor 606 fixed to the rotating shaft 605, a commutator 607
fixed to the rotating shaft 605, a brush conducting an electrical
connection to the commutator 607, and a holder 609 for holding and
fixing the brush 608 to the housing 602.
[0091] Commutator 607 has commutator bars on its peripheral surface
and each of the commutator bars is connected to a coil in the rotor
606.
[0092] Brush 608 is encased in the holder 609 and pushed against
the commutator 607 by a spring 610, thereby attaining a sliding
contact with the commutator 607. Numeral 611 shows a lead wire,
which is electrically connected to the brush 608 to connect the
brush 608 to an external electrode, and is connected to a terminal
(not shown in the drawing) provided on the holder 609. Housing 602
is provided with an end bracket 620, which connects the motor 617
to the blower 618. On the end bracket 620, an air inlet 616 is
formed for introducing air from the blower 618 to the motor 617.
Furthermore, the end bracket 620 is provided with stationary guide
blades 614, and on its upstream side a blade wheel 612 is fixed to
the rotating shaft 605 by a nut 613. A suction inlet 621 is formed
at the center of a fan casing fixed to the outer periphery of end
bracket 620 by pressure insertion.
[0093] When the motor 617 starts to rotate, the rotor 606 rotates
and also the blade wheel 612 coaxially provided on the rotor 606
rotates. By rotation of blade wheel 612 air flows in through the
suction inlet 621 of fan casing 615, passes through the blade wheel
612 and the stationary guide blades 614 and discharged through the
air inlet 616 towards the motor 617.
[0094] FIG. 7 is a perspective view of appearance of an electric
cleaner incasing the electrically driven blower of FIG. 6.
[0095] In FIG. 7, numeral 71 shows a cleaner body encasing a
control circuit, an electrically driven blower, etc., 72 a hose
connected to the suction inlet of cleaner body 71, 73 a hose grip
part, 74 an extension tube connected to the tip end C hose grip
part) of hose 72, 75 a suction inlet body connected to the
extension tube 74, 76 a switch-manipulating part provided at the
hose grip part 73, 77 a first infrared emission part provided at
the hose grip part 73, 78 a second infrared emission part provided
at the hose grip part 73, and 79 an infrared receptor provided on
the upper surface of cleaner body.
[0096] The blade wheel for use in the present invention will be
described in detail below.
[0097] FIG. 8 is an exploded perspective view of a blade wheel
according to one embodiment of the present invention.
[0098] In FIG. 8, a front plate 101 and blades 103 are integrally
formed.
[0099] In this Example, the front plate 101 and the blades 103 are
integrally formed by an injection molding process. The injection
molding process comprises kneading and half-melting a light metal
raw material in a pellet state directly in an injection molding
machine at a temperature permitting liquid phase and solid phase of
alloy to coexist therein without using any melting furnace, etc.,
followed by injection into a mold to obtain a molding article, as
in the resin injection molding process. The process is the same as
in the following Example 4. Mg alloy used in this Example is in a
granular crystal state without any dendrite structure.
[0100] According to the foregoing process, the front plate 101 and
blades 103 can be integrally formed, as shown in FIG. 8. In the
present Example, no projections for fastening to fix the blades 103
exist on the upper surface of front plate 101 by integral formation
of front plate 101 and blades 103, resulting in reduction in the
air resistance over the front plate 101.
[0101] In this Example, the integrally formed front plate 101 and
blades 103 are made from the above-mentioned Mg alloy, e.g. AZ91D
alloy, which is a high purity alloy comprising 8.3-9.7 wt. %
aluminum, 0.35-1.0 wt. % zinc, and 0.15-0.50 wt. % manganese with
suppressed contents of copper, nickel and iron, and a with a good
moldability.
[0102] In this Example, the integrally formed front plate 101 and
blades 103 is made from AZ91D magnesium alloy, but an AM60B
magnesium alloy comprising 5.5-6.5 wt. % aluminum, 0.23 wt. % zinc
and 0.24-0.6 wt. % manganese according to us ASTM code can be
used.
[0103] Magnesium alloy has a specific gravity (g/cm.sup.3) of about
1.8 and thus can make the weight lighter by about 2/3than aluminum
alloy having a specific gravity of 2.7.
[0104] A process for bonding the back plate 102 to the blades 103
integrally formed with the front plate will be described in detail
below.
[0105] Back plate 102 is made from an aluminum alloy of Al--Mg
series according to JIS-A5052 and is provided with a solder metal
layer on the bonding surface in advance. In this Example, zinc is
used for the solder metal layer.
[0106] In this Example, the Zn layer for soldering is formed on the
back plate 102 by electrolytic plating. The electrolytic plating
usually comprises ordinary steps, i.e. steps of defecting, water
washing, electrolysis, water washing and drying. Solder zinc layer
is formed on the bonding surface of back plate 102 by electrolytic
plating in a desired electrolytic solution at desired current
density and solution temperature for a desired plating time.
[0107] Then, the blades 103 integrally formed with the front plate
101 are concentrically counterposed to the back plate 102 having
the solder layer, and the blades 103 are bounded to the back plate
102 by soldering the solder layer as a soldering material formed on
the back plate 102 at a desired temperature of not more than the
melting start temperature of blades 103 and back plate 102 for a
desired heating time under no load or while applying thereto such a
small pressure as not to substantially cause deformation.
[0108] The solder layer melts into the blades 103 and the back
plate 102 at the desired temperature for the desired heating time
to form a reaction layer, thereby strongly bonding the blades 103
to the back plate 102.
[0109] In this Example, the blades 103 and the back plate 102 are
fixed to each other by soldering, and thus no projections for
fastening to fix the blades 103 exist on the lower surface of the
back plate 102, and thus air resistance under the lower surface of
the back plate 102 can be reduced as well as on over the upper
surface of front plate 101.
[0110] The solder layer onto the back plate 102 is formed by
electrolytic plating in this Example, but any or a combination of
physical and chemical vapor deposition, ion plating and thermal
spraying may also be used.
[0111] Furthermore, zinc is used for the solder metal layer in this
Example, but low melting metal elements such as tin and lead and
low melting alloys containing these elements as the main component
may be also used.
[0112] Desirable low melting alloys for this purpose include, for
example, alloys of zinc-tin series, zinc-lead series, tin-lead
series, zinc-magnesium series and zinc-aluminum series.
[0113] In this Example, an aluminum alloy according to JIS-A-5052
is used for the back plate 102, but any of alloys of Al--Mn series
(3000 series), alloys of Al--Si series (4000 series), alloys of
Al--Cu--Mg series (2000 series), alloys of Al--Mg--Si series (6000
series), alloys of Al--Zu--Mg series (7000 series) according to JIS
code may be used.
[0114] Furthermore, in the blade wheel 712 of this Example a
magnesium alloy is used for the front blade 101 and the blades 103
and an aluminum alloy having a larger specific gravity than that of
the magnesium alloy is used for the back plate 102. The back plate
102 is made to take the nearer position to the motor, thereby
making vibration of rotating shaft due to the unbalanced rotation
of the motor rotating shaft smaller, reducing the generating noise
and carbon bruck wear-out and increasing the electrically driven
blower life.
[0115] In this Example, an aluminum alloy is used for the back
plate 102, but the same magnesium alloy as used for the front plate
101 and the blades 103 can be also used for the back plate 102.
[0116] After the foregoing bonding, the entire blade wheel is
heated to the temperature of a solution for chemical conversion
treatment and immersed into the solution for chemical conversion
treatment to form an oxide film on the parts made from Mg alloy as
in Example 1. The parts made from the Al alloy undergo chemical
conversion by the treatment for the same time but by elevating the
chemical conversion treatment temperature to 90.degree. C.
EXAMPLE 4
[0117] FIG. 9 shows examples of various cases made from
anticorrosion film coated AZ91D for a notebook type personal
computer, where the display cover and the case are cases for
protecting and fixing the display, respectively, the palm rest is a
case for keyboard and the bottom case is a case at the bottom.
Process and apparatus for producing these various cases will be
described in detail below.
[0118] FIG. 10 is a cross-sectional view of a reciprocal motion
screw injecting molding machine suitable for use in the process for
producing cases of the present invention. Steps of molding process
in a reciprocal motion screw injection molding machine with a
liquid pressure clamp is as follows:
[0119] 1. Feed Mg alloy crushed to a chip state to a hopper 31.
[0120] 2. Mg alloy is supplied to screw 10 from the hopper 31 by
rotation of screw 10 and sheared Mg alloy is heated by a heater 5
while passing through the injection molding machine. Heating
temperature can be attained also by the heat of friction by screw
10 and Mg alloy can be maintained at a temperature permitting
coexistence of liquid phase and solid phase. By rotation of screw
10 at that temperature .alpha. primary crystals are formed, but the
alloy following the injection molding is in a granular crystal
state without any dendrite structure. Particularly, the .alpha.
primary crystals of AZ91D alloy have a particle size of 50 to 100
.mu.m on average. The resulting structure is a dispersion of
supersalturated solid solution .alpha. and intermetallic compound
.beta. having a grain size of not more than 20 .mu.m in the
matrix.
[0121] That is, the thixomolding process of this Example comprises
(a) feeding magnesium or magnesium alloy having a dendrite crystal
structure to the screw extruder, followed by heating at a
temperature of not less than the solidus line and not more than the
liquidus line of magnesium or magnesium alloy, and (b) subjecting
the heated metal or alloy to a shearing action enough to break at
least a portion of the dendrite crystal structure of the metal or
the alloy by the screw extruder, thereby forming a metal or alloy
composition of liquid-solid.
[0122] 3. With the tip end of screw 10 being made to serve as a
meter 3, the feed rate to mold 40 is metered, and the Mg alloy in a
semimolten state, where the solid and the liquid are stirred, is
injected from extruder 12 all at once. In FIG. 10, numeral 2 shows
a cylinder, 3 a nozzle, 16 a back flow arrester, 20 a driving
means, 33 a raw material feeder, 41 a movable mold and 42 a
stationary mold.
[0123] The Mg alloy of this Example is subjected, as in the cast
state, to any of a solution treatment or the solution treatment
followed by an artificial aging, and then a chemical conversion
oxide film and a super-water-repellent organic film of Examples 1
and 2 are formed thereon, successively. It is preferable to conduct
the solution treatment at a temperature of 400.degree. to
500.degree. C. and the artificial aging at a temperature of
130.degree. to 260.degree. C.
[0124] According to the present invention, weight can be made
lighter and the thickness can be made smaller by using
anticorrosion film-coated AZA91D.
EXAMPLE 5
[0125] The following various products were produced according to
the thixomolding process as in Example 4, using alloys selected
from Mg alloys shown in the following Table 2 (wt. %) and then
further subjected to the above-mentioned solution treatment and
artificial aging, when required, and then to blasting to remove
oxide scales from the surfaces, followed by defatting and chemical
conversion treatment as in the Example. In this Example, highly
anticorrosive films were obtained as in the foregoing Example 1. As
a result of formation of various super-water-repellent organic
films as shown in Example 2 after the application of the present
chemical conversion treatment, a higher durability could be
obtained. In Table 2, Run Nos. 1 to 7 are used mainly as plastic
molding materials as alloy plates, alloy bars, extrusion molding
materials, whereas Run Nos. 8 to 14 are suitable to casting.
[0126] Other uses of the Mg alloy member of the present invention
are listed below.
[0127] (1) Digital video camera case,
[0128] (2) Upper cover for single-lens reflex camera,
[0129] (3) Upper, lower and back covers for compact camera,
[0130] (4) Case for MD player,
[0131] (5) Head arm for hard disc drive (HDD),
[0132] (6) Automobile sheet parts, steering wheel, piston
parts,
[0133] (7) Television case,
[0134] (8) Portable telephone case, and
[0135] (9) Cases for various electrically driven tools.
2TABLE 2 Run No. Al Zn Zr Mn Fe Si Cu Ni Ca Others Mg 1 2.5-3.5
0.5-1.5 -- 0.15 0.010 0.10 0.10 0.006 0.04 -- Balance or more or
less or less or less or less or less 2 5.5-7.2 0.5-1.5 -- 0.15-0.40
0.010 0.10 0.10 0.006 -- -- Balance or less or less or less or less
3 7.5-8.7 0.2-1.0 -- 0.10-0.40 0.010 0.10 0.05 0.006 -- -- Balance
or less or less or less or less 4 -- 0.8-1.5 0.40-0.8 -- -- -- 0.03
0.006 -- -- Balance or less or less 5 -- 2.5-4.0 0.40-0.8 -- -- --
0.03 0.006 -- -- Balance or less or less 6 -- 4.8-6.2 0.45-0.8 --
-- -- 0.03 0.006 -- -- Balance or less or less 7 1.5-2.4 0.50-1.5
-- 0.05 0.010 0.10 0.10 0.006 -- -- Balance or more or less or less
or less or less 8 5.3-6.1 2.5-3.5 -- 0.15-0.6 -- 0.30 0.10 0.01 --
-- Balance or less or less or less 9 8.1-9.3 0.40-1.0 -- 0.13-0.5
-- 0.30 0.10 0.01 -- -- Balance or less or less or less 10 8.3-9.7
1.6-2.4 -- 0.10-0.5 -- 0.30 0.10 0.01 -- -- Balance or less or less
or less 11 9.3-10.7 0.30 -- 0.10-0.5 -- 0.30 0.10 0.01 -- --
Balance or less or less or less or less 12 -- 3.6-5.5 0.50-1.0 --
-- -- 0.10 0.01 -- -- Balance or less or less 13 -- 5.5-6.5
0.60-1.0 -- -- -- 0.10 0.01 -- -- Balance or less or less 14 --
2.0-3.1 0.50-1.0 -- -- -- 0.10 0.01 -- RE 2.5-4.0 Balance or less
or less
[0136] According to the present invention, an oxide film containing
heavy metal ions having a plurality of valencies and enriched
particularly in Al originating from the substrate can be formed on
the surface of Al-containing Mg alloy by chemical conversion
treatment in the solution, thereby providing a coated substrate
having a distinguished corrosion resistance. Such an oxide film can
be formed without using environmentally harmful substances.
[0137] By further applying the ordinary anticorrosive coating or
super-water-repellent coating to the oxide film, the film can be
given a more distinguished anticorrosive coating.
[0138] Furthermore, when Mg alloy is used in various products such
as the blade wheel of an electrically driven blower, cases for
notebook-type, personal computers, televisions and audio systems of
household electrical appliances, etc., automobile parts, etc.,
their weights can be made lower by forming the present
anticorrosive film thereon and its further coating, and their
corrosion resistance can be made higher thereby.
* * * * *