Improvements in the Art of Plating and Colouring Aluminium.
Year: 1899

page_text: Date of Application, 14th June, 1899-Accepted, 29th July, 1899
COMPLETE SPECIFICATION.
Improvements in the Art of Plating and Colouring Aluminium.
I, MICHAEL BARTHOLOMEW RYAN, of 21, Vancouver Road, Catford, in the County
of Kent, Manufacturer, do hereby declare the nature of this invention and in
what manner the same is to be performed, to be particularly described and ascer-
tained in and by the following statements:-
--
This invention relates to the electro-deposition of metals and particularly to
the deposition thereof on the metal aluminium, and its alloys, and has for its
object the perfection of the process of electro-plating aluminium, whereby the
deposition of various metals and alloys of metals, on metal aluminium may be
made permanent and not subject to change after said deposition has been made:
And the invention consists in the process of preparing the surface of aluminium
for the reception of a metallic amalgam, or base, on which the metal is finally
deposited, all as fully described in the following specification and clearly pointed
out in the claims.
Processes have already been invented for depositing metals on aluminium, but
they have been faulty in, that after a certain time salts form between the surface
of the aluminium and the deposited metal, which cause a pitting of the plate and
disintegration of the deposited metal; said salts will force the latter away from
the surface of the plate, causing what is, in appearance, small blisters which are
readily broken and which give to the plated article a rough surface and expose the
surface of the aluminium below, whereby oxidation thereof is rendered possible,
and hence a further separation of the deposited metal from the aluminium plate.
These defects arise from an imperfect cleaning of the surface of the aluminium
to be plated, resulting in an imperfect union of the deposited metal and the sur-
face of the article plated. The known processes of plating aluminium have fol-
lowed the methods usually employed in preparing metallic surfaces to receive a
coating of some other metal, riz.,by gradually building up a thin metallic coat-
ing on said surfaces by the use of what are known as the "striking" solutions
or whiteners," and are familiar to those skilled in the art.
66
The essential feature of this invention, on the contrary lies in the process as
hereinafter fully described for fixing on the surface of the aluminium article to
be plated, a metallic amalgam, whereby a base is provided on which the striking
solution may act with positiveness, the said amalgam base so intimately adhering
to the surface of the aluminium that, after passing through the striking solu-
tions, the metal may be rolled, drawn, or handled in any similar way, without
causing any separation of the deposited metal film from the surface thereof.
And, furthermore, the process to which the aluminium is subjected, as herein set
forth, preparatory to the application of the amalgam to the surface thereof, is
of such a nature as to preclude the formation of metallic salts, at any time after
the plating process has been completed, between the surface of the article and the
metal deposited thereon, whereby a separation of the latter from the former may
be effected.
The aluminium articles to be plated are first put into boiling whale-oil soap

page_text: or so-called "platers compound" for a few moments, and are then rinsed in boil-
ing water, to remove any of the soapy solution adhering to them.
After rinsing in running water, they are dipped in a bath of muriatic acid,
having a gravity of 15 degrees by Baume hydrometer, and remain in this bath
until some evolution of gas takes place. This dip acts more particularly upon
traces of iron and silica lying on the surface of the aluminium, and from this
acid bath the articles are dipped in hot water, to destroy the bubbles left on the
Burface thereof by the action of the acid-bath; otherwise, the metal would, after
plating, show pits in the surface where the bubbles of gas formed on its surface.
After proper rinsing, the articles are then dipped in a cyanide of potassium
solution of about 20 degrees gravity, by Baumé hydrometer and from thence,
after rinsing, into phosphoric acid of 50 degrees gravity Baumé, where it remains
from eight to ten minutes.
This acid being a solvent for aluminium, its attack upon the metal removes the
greasy surface peculiar thereto, and which, (together with traces of other metals
in the aluminium) has been the great obstacle to perfect union between said metal
and metal deposited thereon, which serves ultimately for the base on which the
final coating is deposited.
It can easily be determined, by an experienced man, when this greasy surface
has all been properly cleansed, by the manner in which the solution runs off from
the surface of the metal. As soon as it is in proper condition. it is withdrawn
from the acid bath, rinsed, dipped in the cyanide of potassium bath again, and
finally rinsed, when it is ready for immersion in the amalgamating solution which
is composed of the following ingredients:-
-
To one gallon of rain water, as much sal-ammoniac is added as it will take up-
say practically eight ounces to the quart. To this gallon of solution add one
ounce of bichloride of mercury. Cyanide of mercury may be substituted for the
bichloride, if desired.
The solution should have a gravity of 12 degrees by Baumé hydrometer, and
may be tested by dipping a piece of clean copper wire into it in the usual
manner, and if it whitens the wire it shows it is in working order.
The aluminium article to be plated is now dipped, as a next step, into this
amalgamating solution, and, after rinsing into a boiling solution of caustic
potash, "wood-potash" so called, or any alkaline solution.
The article may be passed through the amalgamating solution and hot alkaline
bath twice, if required, to perfectly coat every part of it.
When the article is properly amalgamated, it has the same appearance a piece
of zinc would have, if first cleansed by acid and then dipped in mercury.
When properly amalgamated, the article may be rinsed off and then passed
through the striking solutions or whiteners, and from thence to the plating solu-
tion, for final coating with whatever metal may be desired.
It will be observed that the process, up to the point of immersing the article
in the whiteners, has been directed to preparing it to receive a very thin coat of
amalgam, and to the application of the latter by dipping in a solution having the
requisite properties.
Tp to this point, the process differs radically from previous processes, in, that
in the latter efforts have been directed to preparing the surface of the aluminium
for the reception of the metal to be deposited thereon, by immersing the articles
in the whiteners and thus building up an electrically deposited base for the
reception of the final coating.
In this invention that base is provided by the flowing of the entire surface of
the article to be plated, with an exceedingly attenuated amalgam, having the
qualities which adapt it to the reception of metals by electro-deposition.
The process which seek to prepare the surface of aluminium by the usual
methods, of subjecting the metal to striking solutions, or whiteners, are faulty,
for there is not a perfect union between the metal deposited, and the surface
receiving it, as demonstrated by the formations, some time after plating, of the

page_text: a phosphoric acid solution having a gravity of substantially 50 degrees Baumé,
(4) in a solution containing bichloride of mercury, and (5) then into an alkaline
solution, (6) passing it through suitable electrically operated striking solutions,
and from thence (7) into the electrically operated solutions for depositing thereon
the final coating of metal, substantially as described.
Claim 3. The process of plating aluminium comprising the following steps-
after suitably cleansing it- (1) dipping in muriatic acid solution having a
gravity of substantially 15 degrees Baumé, (2) dipping in cyanide of potassium
solution having a gravity of substantially 20 degrees Baumé, (3) dipping in a
phosphoric acid solution having a gravity of substantially 50 degrees Baumé, (4)
dipping in a solution comprising one gallon of water, two pounds of either sal-
ammoniac or, muriate of ammonia, and one ounce of bichloride of mercury, then
(5) dipping in an alkaline solution, as caustic potash, (6) and thence through
the electrically connected whitening or striking solutions, and then (7) into the
electrically connected solutions containing the metal to be deposited substantially
as described.
Claim 4. The method of preparing aluminium for deposition of the final metallic
coating thereon consisting in chemically cleaning the surface thereof substantially
as described, applying an amalgam of mercury to said surface, and then, passing
the metal through electrically operated and progressively graded whiteners solu-
tions, whereby it is adapted to receive a final electrically deposited coating of any
suitable metal, substantially as described.
Dated this Thirteenth day of June 1899.