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Патент USA US2111377

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March 15, 1938. `
F, A, WALES
2,111,377
ART oF GOATING ALUMINUM
Filed Nov. 14, 1935
@L
2 Sheets-Sheet. l
5,
A TTORNEYÖ.
March 15, 1938.
F. AQWALES
2,111,377
ART OF COATING ALUMINUM
Filed Nov. 14, 1935
2 Sheets-Sheet. 2
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"„Iun“u
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INVENITOR.
„ai /Z Mles.
BY
ATTORNEYâ.
2,111,377
Patentedl Mar. 15, 1938
UNITED STATES
PATENT OFFICE
2,111,377
ART, oF ooA'rlNG ALUMINUM
Fred A. Wales, Detroit, Mich.
Application November-14, 1935, >serial No. 49,647
3 Claims.
'I‘he present invention relates to the art of
coating aluminum or aluminum alloys or ar
ticles formed therefrom, and particularly to
improvements in the method of and apparatus for
5 forming such coatings, particularly coatings of
Óthe so-called "oxide” type.
Such coatings on aluminum or aluminum alloys
are commonly recognized as being formed chiefly
of A1203, S03, and H2O, and are formed as a
1n plurality of laminated layers which vary. as to
thickness, hardness and porosity. Such coatings
(Cl. 204-1)
a protective coating on aluminum or aluminum
alloys, or articles formed therefrom, which is
particularly, but not exclusively, adapted to pro-`
duce the improved coatings on. pistons formed
of aluminum or aluminum alloys ~for use in_in- 5
ternal combustion engines or similar purposes.
A `further object of the present invention is '
to provide a process for the production of pro
tective coatings _on aluminum or aluminumalloys,
or articles formed therefrom, in which the cost 10
of operation and of the equipment has been re
duced over similar costs of prior art processes
have been formed by processes heretofore known
. to the art by making the aluminum or aluminum - and equipment, and which, while being more eco
alloy an anode in an electrolytic cell having sul
nomical than processes and equipment of the
15 phuric acid asthe electrolyte. The coatings are prior art, produces coatings which are superior 15
formed upon the passage of direct current elec
to the coatings produced by the prior art.
trical energies through the cell and are formed
It is a further object of the _present invention
on the aluminum or the aluminum alloys which to provide an apparatus for use in forming pro
form the anode in the cell. The direct current tective coatings on aluminum or aluminum al
20 used in such processesI is of the order of twelve
loys, or articles formed therefrom, which is a
20
to eighteen volts and of from six to twenty am
portable self-contained unit.
peres per square foot of material undergoing
Other objects of the present invention will ap
treatment. A cathode,` electrically connected in
the circuit, forms the other contact with the
pear 'in the following description and appended
«- electrical circuit and is placed in the electrolyte.
bodying the present invention is shown by Way
of example Vin the accompanying drawings form
ing a part ofthis speciñcation wherein like ref
erence characters designate corresponding Darts
In certain embodiments, such cathode frequently
was the tank, and the current ñowed between the
cathode and the anode through the electrolyte and
caused the growth of the sor-called “oxide”'coat
30 ing at the anode. In using such processes for
the formation of the oxide coatings on aluminum
or aluminum alloy articles, 'such for example as
pistons for use in internal combustion engines,
I have discovered that the coating formed by the
35 processes of the prior art was not'satisfactory
in such fields due particularly to the large var
iations in ñneness of grain structure, the irregu
larity asto size and distribution of p'ores, the
extreme variations in hardness between the re
¿0 spective layers, and the relatively high` cost of
`processing and of the apparatus for use there
with.
‘
«
claims.
One preferred form of apparatus em-.
in the several views, and in which
,
Fig. 1 is a view in perspective of an apparatus 30
which is adapted to be used in connection with
the present process and embodied in the form
of a self-contained portable unit.
'
Fig. 2 is a front view in elevation of the ap
paratus of Fig. 1 showing the enclosing cover in 35
closed position.
'
Fig. 3 is an end view in elevation of the appa
ratus shown in Fig. 2.
. Fig. 4 is a sectional view taken along the line
4-4 of Fig. 2 in the direction of the arrows.
Before explaining in detail the present inven
40
tion it is to be understood that the invention is
The process and apparatus of the present in- ` not limited in its application to the details of
. vention has as its principal object to provide a
45 coating for aluminum or aluminum alloys, or ar
construction and arrangement of parts illus
trated in the accompanying drawings, since the
invention is capable of other embodiments and of
being practiced or carried out in various Ways.
Also, it is to be understood that the phraseology
or terminology employed herein is for the pur
pose of descriptionv and not of limitation, and it 50
is not intended to limit the invention claimed
ticles formed therefrom, the coating being su
perior to coatings previously known and charac
terized by having a very dense ñne grained lami
nated structure. The various layers exhibit sub
50 stantially uniform hardness characteristics and
are permeated with very small and substantially
uniform pores between the particles of the coat _ herein beyond the requirements of the prior art.
The apparatus, shown in the drawings com
'It is a'further object of the present invention `prises a casing I0 which is mounted upon a sup
55 to provide a process and apparatus for producing porting rack Il, which may be provided with a ’
A
2
2,111,377
-plurality of casters I2 to permit moving the en.
tire unit from place to place about a plant. The ‘
casing I0 is divided interiorly to form a rinse
tank I3 anda tank I4, which is provided with a
lead or other non-corrosive lining I5 and is
adapted to contain the electrolytic bath.
Mounted on one end of the framework II is
a bracket I6 on which is mounted an electric
motor I1 which drives a~ fan I 8 of the blower
10 type. An air pump IB, preferably of the pulsat
ing type, is also driven by the motor Il and is
connected by „means of the conduit 2l) with a
A suitable control panel 3l is electrically con
nected with the transformer 3i) and actsto pro
vide the connections through which the current
flows tothe electrolytic bath. Electrical connec
tions are provided between the vtransformer 3i!
through the control panel 3| with bus bars 32
which extend crosswise of the tank M. The ar-'
_ticlers to be treated, such for example as alumi
num or aluminum alloy pistons 33, are provided
with a suitable clamp 34 which is electrically 10
connected with and engages one of the bus bars
.32.110 suspend the article being treated into the
series of perforated pipes 2I yextending across they .electrolyte in the tankV I4. In this manner
bottom of the lead-lined tank I4. Air is sup
articles to be treated 'are connected through
electrolytic bath in a parallel series so that
15 plied to the pipes 2| and is discharged there
through to keep the electrolyte agitated during flow of electricity is through the bus bars 32,
operation of the apparatus.
The fan or blower
I8 is connected by means of a duct 22 with the
hooded upper part of the tank I4 (Fig. 4) and
20 serves to ventilate the apparatus while in op
eration.
‘
the
the
the 15
the
clamps 34, the article 33, through the electrolytic
bath to the article 33, its clamp 34, and the bus
bar 32. This method of connection is contrary
tovconventional >methods ln that the tank or bath
remains neutral, whereas in prior known proc
During the operation of the apparatus, a hood ¿ esses the, bath or tank forms the other connection
or cover 23 is‘placed in the closed position, as with the electrical current and only the article
shown in Fig. 4. 'I'he cover 23 prevents fumes
25 given olf during the carrying out of the process
from escaping into the atmosphere, thus func
tioning as a collection hood from which the' col
lected fumes are drawn through the duct 22l and
are thereafter discharged through a stack (not
30 shown),- which is connected with a discharge
opening 24 on the blower I8.Í
i
'
As shown in Fig. 4, the lead lining I5 forming
the tank I4 is spaced apart from the casing IU
in such a manner as to provide a duct 25 which
35 extends about all sides of the lead lining I5 inside
the casing I0. The duct 25 communicates with
the -interior of the tank I3, into which may
be placed a suitable temperature controlling fluid
mass which will flow through the chamber I3
40 and around the duct 25 surrounding the lead,`
lining I5 -of the tank I4. By varying the teme,
perature of thefluid medium in the tank I3, the
temperatures within the tank I4 may b_e con
trolled within definite predetermined limits.
'I‘he ñuid is fed into the tank I3 through a
45
suitable conduit 26 which is operatively con
nected with the source of ñuid supply and the
level is maintained in the tank I3 by means of a
waste or outlet pipe 21 which acts as an over
50 iiow pipe when the fluid reaches the top thereof.
If water is used as the fluid temperature con
trol medium in the tank I3, and its temperature
is not sufficiently low to control the temperature
of the tank I4, a cake of ice or other refrigerant
may be placed therein and so refrigerate the
iiuid which runs through the tank and around
`the chamber 25. During the operation of the
being treated forms the anode thereof.
In the
present apparatus, with the use of alternating 25
current, the articles 33 alternately form the
anode and the cathode of the current flow and on
the 11i) volt, 60 cycle, line this alternation oc
curs sixty times each second, but will vary; how
ever, with variations in the cycles of the a1ter-,
nating current.
A valve _35 is provided in the casing I El and
communicates with the duct 25 to permit with
drawal of fluid temperature control mediums
therefrom.
'
rThe foregoing described apparatuswhile be
35
ing particularly adapted to the process of the
present invention, is also adaptable (with slight
changes, particularly as to its electrical circuit)
' for -use in conventional processes known to the
art, and as such, by reason of the temperature
control provided in the electrolytic bath and in
the portability of the unit, produces results which
-are desirable and which are superior to the ap
paratus previously known to the art, although lt 45
is my belief that using such apparatus with con
ventional processes will not produce the satisfac
tory results produced by the practice of my im
proved process therein.
'I'he improved process of the present invention
proceeds in part upon my discovery that a su
perior type of coating may be formed either on
aluminum or aluminum alloys or articles formed
therefrom, and can be provided by using the
aluminum or aluminum alloy or article formed
therefrom as both the anode and the cathode of
the electrical circuit flowing through the elec
trolytic bath. The change from anode to cath-,
apparatus, the tank I3 functions also as a rinse
tank and the aluminum or aluminum alloys or
60 other articles which have been treated in the
treating tank may be rinsed in the tank I3 after
ode is preferably a successively occurring change
which will be brought about in relatively rapidly
the coating has been formed thereon.
Electrical energy is supplied to the tank I3 by
ceeds upon my discovery that such successively
and rapidly alternating electrical changes in the
' means of a transformer 3D which is suitably
65 mounted on the framework II, preferably at a
character of the aluminum or aluminum alloy
alternating sequence.
The process also pro
during the coating operation can best be effected 65
point adjacentthe bottom of the tank I3. The by utilizing various voltages of 60 cycle alternat
transformer operates on alternating electrical “ihg current, beginning at approximately 12.5
` ~ current and in a preferred-embodiment has a
volts and increasing'the voltage of the electrical
rated capacity of 200 amperes and 24 volts. The flow düring the coating operation to 24 volts at
70 transformer is of a conventional design adapted a time when the temperature of the bath is defl 70
for use either on 110 volts or 220 volts, and is nitely controlled between limits of approximately
- provided with a series of taps through which the
current may be drawn to be passed to the bath,
such current to have controlled and varying
75 voltages up to 24 volts.
69° to '74° F.
'
In carrying. out the present process, I pro
vide an electrolytic bath in the tank by using com
mercial grades of sulphuric acid in concentrations 75
3
2,111,877
of 13% by weight in aqueous solution. At least
y two pieces of the aluminum or aluminum alloy
or article formed therefrom are electrically con
nected, one with each side of the line supplying
the electric current .to the electrolytic bath and
from the anode and cathode respectively of the
cell resulting from the immersion of the articles
formed by means of the process herein disclosed
than that of processes utilizing a ilow of direct
current electrical energy. In a typical example,
the coating formed by the process herein described
is approximately twice as thick as the coating $1
formed by the conventional direct current proc
esses treated for like periods of time.
I believe
this is due to the fact that the metal is not de
The operation is started at a voltage of the composed and changed to the sulphate as is the
10
lower order, preferably from 9 to 121/2 volts, which case in all prior operations.
A particular field in which the present inven
is increased as the operationprcceeds, to the
higher range `of voltages, preferably from 20 to 24 tion has great utility is in the iield of formed pro
volts. The temperature of the bath is /preferably tective and oil bearing coatings onaluminum or
maintained from approximately 69° F. to approxi- ' aluminum alloy pistons for use in internal combustion engines. In this field the coatings of the
mately 73° F. by the use of a suitable circulat
ing temperature control medium surrounding the present invention are -superiorto coatings formed
tank in which the _operation is being carried on. by prior methods in that the coating is very much
more closely knit, being formed of very much
The treatment and processing is complete With
in time intervals of about 20 to 40 minutes, the smaller particles than the coatings resulting from
operation being carried on'approximately three-- the direct current process. The result is that the
pores of the coating are very much smaller and
quarters of the time at the higher range of volt
much more uniformly distributed than in the prior
ages, i. e. voltages in excessÍ of- 12.5 volts.
In'coatings which are formed on the aluminum processes. This, in turn, increases the capillary
in the electrolyte.
'
or aluminum alloy, or the articles formed there
25 from, I have _found that »there is relatively no
value of the coating so as to give a better oil ab
sorption of the coating than when the coating is
formed by the prior processes. It is a known
bath such as occurs in forming coatings by means phenomenon that capillary elevations and depres
of conventional processes utilizing direct current sions, other circumstances being equal, are con-v
electricity. This feature of the present process versely proportional to the diameters of the ca
30 permits the use of the electrolytic bath for a very pillary tubes so that, considering the pores of the 30
coating as capillary tubes having an añinity for
much longer period of time, for once the acid con
centration of- the bath has-been normalized it the oil or other ñuid medium, it will be seen -that
the smaller size of the pores and the greater uni
appears to continue at the normalized acidcon
formity of placement of the pores in the coat
centration during the entire operation for a con
„
,Y , ` ing resulting from the present invention, will ac
35 siderable period of time.
precipitation of the metal into the electrolytic
Utilizing direct current, the metal decomposes
yand reacts with the bath to form sulphates.
When the bathl contains 20 grams per litre, the
count for the greatly increased capillary values of
such coating.
,
Excellent oxide coatings are produced under the
bath must be completely changed because 4of -the
resultant decrease in electrical conductivity of
the bath. The present process is characterized
by the fact that little or none of the metal-is
decomposed by the electrolyte and put into the
bath in the form of va, sulphate. This is due to
the use of the relatively dilute bath which is possi
ble by the use of the alternating current electrical
following conditions on pistons produced from a
energy in the' process.
connected to each electrode„.and the .12..volt alter
nating current is‘ impressed'bn the "cell for a
period ofV 3 minutes. The voltage is then in
_creased to 24 volts and the treatment is con
tinued for an additional 20 minutes, While main
taining the bath temperature at between ap
This particular feature is
»one of theoutstax'iding defects of the- direct cur
rent method now being used, as this sulphate is
50 insoluble in the bath and readily affects the con
ductivity of the bath, and when it reaches the
concentration of 20 grams per litre of electrolyte,
the bath must be changed. V 'I'he efliciency of such
low-aluminum high-silicon alloy which contains
approximately 12% of silicon. An equal number
40
of pistons are placed in the electrolyte and act"4 as
the electrodes. The electrolyte is composed of ap
proximately 13% by weight of commercial sul
phuric acid in aqueous solution. A l2 volt alter 45
nating current` is used, one side of the line being
proximately 70° to 74° F.
processes of the‘art is progressively lessened by
Using this particular alloy, the thickness of
the rapidly diminishing conductivity value in this
the coating will be not less than .0004 inch in 55
bath up to the ultimate point of 20 grams per
thickness and the abrasimeter values will read
litre.
30 or more.
-_
The coatings formed . by the process of the
present invention as above described, will be found.
60 to have a substantially increased uniformity of
‘ hardness throughout the successive layers, which,
` f
'
l
For purposes of comparison, it is interesting
-to note that similar coatings formeduby con
yentional methods utilizing direct current and 60
a stronger electrolyte, where the article is treated '
when investigated by means of photomicrographs,
for the same length of time, produces coatings
will be shown to possess a very ñne grained crys
. talline structure and very small and uniformly
having an average thickness of .000327 inch
as against the average thickness of the coatings
distributed pores extending therethrough. -In an
average'4 case, the variation between the softest-
produced by the use of the alternating` current
of .000746 inch; land the abrasimeter values
layer and the hardest layer is inthe neighborhood
of approximately 20%, Whereas in a characteristic
coating formed by the processes of the prior art,
will be less than 30.
70 utilizing direct current electrical energy and baths
of the speciñed concentrations of acid, there is a
variation of from 140 microcharacter to approxi
mately 5,000 microcharacter between the hardest
- layer and the softest layer formed.
Also, there is a considerably thicker coating
y
In treating the aluminum o_r aluminum alloy
articles by the4 present process, I ñnd that it is
possible to dispense with ~the preliminary clean 70
ing and Washing processes which are common to
the prior art, itbeing sufficient with the improved
process of the present invention to merely dip
thealuminum or 'aluminum alloy article in a
hot water bath. This is possible, in my opinion, 75
4
2,111,377
because of the use of the alternating current in
the present process which, in conjunction with
the electrolyte, reacts in such a way as to in
eii’ect clean the articles more completely and
Cl thoroughly than it would be possible to do by
previously suggested methods.
This, I believe.,
is due to some extent at least to the action oi’
the alternating current in expelling the adhered
surface oxygen.
10, A characteristic of the coating produced is that
it is very smooth on the exterior surface so as
to make possible the use of the article without
using a buiiing machine for the purpose of re
moving the chalk-like soft coating which is formed
by the treatment of aluminum or its -alloys by
The soft outer coating
formed by conventional processes is a coating
which consists, to a large extent, of the mate-~
rial which is precipitated into the bath as the
20 sulphate which has heretofore been described.
The coating formed by the present process has
no such soft outer coating and tests to date in
_
conventional processes.
dicate that there is not more than approxi~
mately 20% variation in the microcharacter val»
ues from the outside skin of the coating to its
base where it forms on the aluminum or the
aluminum alloy.
Due to the action of the alternating- current,
less metal is taken away from the material un
30 dergoing treatment and thus the coating is oi
greater strength than coatings produced by prior
methods wherein more of the metal is taken
away during the processing operation.
While particular uses have been mentioned in
the foregoing discussion of the apparatus and
process of the present invention, it is to be un
derstood that both the apparatus and the process
are adapted to other uses than those herein par
ticularly mentioned and'may be used success~
40 fully to form protective coatings on articles which
may >bejformed of some material other than
aluminum or aluminum alloy but which may be
coated with aluminum or aluminum alloy by such
processes as calorizing, metal spraying, etc.
I claim: '
'
1_. A process of producing _a protective coat
ing having a thickness ln excess of approxi-_
mately .0004 inch and a hardness in excess of
approximately'30 grams’abraslmeter value, on an
50 alux'ninum-'silicon‘alloy which contains approxi
the immersed articles in parallel with 'a source
of alternating current electrical> energy and. uti
lizing the immersed articles as both the anode
and cathode of the circuit, and subjecting said
articles to a flow of alternating current electrical energy in successive stages beginning at
approximately 9 to 12.5 volts intensity for a
period of approximately 3 minutes duration and
increasing through successive stages to approxi-r
mately 24 volts for a period of approximately7 20
minutes duration at the conclusion of the process.
2. A process of producing a protective coatingv
on an aluminum-silicon alloy containing ap
proximately 12% silicon having substantially
increased uniformity of hardness throughout the
successive layers, which comprises immersing the
aluminum alloy in an electrolytic bath contain
ing 13% by weight of sulphuric acid in aqueom
solution, electrically- connecting the immersed
alloy in parallel with a source of alternating cur
alloy as both the anode and cathode of the cir
cuit through the bath, and subjecting the said
alloy to a flow of alternating current electrical
energy- in successive stages beginning at ap
proximately‘9 lto 12.5 'volts for a period of ap
proximately 3 minutes and thereafter increasing“
to approximately 20 to 24 volts for a period of
approximately 20 minutes while agitating the
bath to maintain a substantially constant circu-l
lation thereof and maintaining a substantially
constant temperature of the bath between ap
proximately 70° and 74° Fahrenheit.
. 3. A process for forming a ñnished and smooth
unbuffed protective coating having a thickness 35
in excess of .0004 inch and a, hardness inl excess ,
of approximately 30 grams abrasimeter value
on an aluminum-silicon alloy containing ap
proximately 12% silicon having substantially 1n
creased uniformity of hardness throughout the
successive layers, which comprises immersing said
alloy in an-oxidizing bath containing 13% by
weight of sulphuric acid in an aqueous solution
and passing an electrical current therethrough
for a period of approximately 3 minutes dura 45
tion at a potential of approximately 9 to 12.5
volts and thereafter for a period of approxi
mately 20 minutes duration at a potential of ap
proximately 24 volts, utilizing the said alloy in ,
the bath as both the anode and cathode of the 50
mately 12% of lsilicon having substantially in
creased uniformity of hardness throughout the
successive layers, which comprises immersing
-stant temperature of between approximately 70°
the farticles'formed of vsaid alloy in an electro
a'ndf'l‘ì" Fahrenheit.
lytic bath 'containing 13% by weight of sulphuric
'acid in aqueous solution, electrically connecting
20
rent electrical energy and utilizing the immersed
circuit through the bath, while agitating the bath
and maintaining therein a substantially con
'
FRED A. WALES.
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