Improvements in Means for Diminishing the Liability to Corrosion of Screw Propellers.
Year: 1888

page_text: PROVISIONAL SPECIFICATION.
Improvements in Means for Diminishing the Liability to Corrosion
of Screw Propellers.
We, WILLIAM CARLILE WALLACE, of Louing Cardross, in the County of
Dumbarton, North Britain, Engineer, and ROBERT DANIEL SMILLIE, of Risk Street,
Dumbarton, in the same County, Electrician, do hereby declare the nature of this
Invention to be as follows, that is to say :-
Our said Invention has for its object to diminish the liability to corrosion of screw
propellers; and it consists in coating such propellers with copper in the manner
hereinafter particularly described.
If the blades and boss
In carrying out our Invention we employ electro-plating processes to deposit on the
surface of the propeller or on its blades an adherent and firm coating of copper of a
considerable thickness, say for large propellers about a quarter of an inch-sufficient
for withstanding a considerable amount of attrition or wear.
of the propeller are in one piece we coat the whole with copper; but if the blades are
may also
in separate pieces it may be sufficient to coat them only, although the boss
be similarly coated although in a separate piece.. When the blades only are coated
care must be taken to entirely cover with copper every part of each blade piece to
which the water can have access, the copper coating being made to extend under the
bolt nuts which should be cap nuts and be themselves coated with copper if of steel
or iron; and at the joint line between the blade and the boss the copper coating must
be made to itself form a close joint at the outer surface to prevent access of water at
copper tho
the joint to the steel or iron of the blade piece. If the boss is coated with
same precautions must be adopted to prevent access of water at the junction with
the shaft or at any other point.
When proceeding to apply the coating the propeller or blade of steel or iron is first
very carefully cleaned. The surface may be made smooth by grinding, but in any
case the propeller or blade is pickled in a bath of hydrochloric or sulphuric acid of
sufficient strength to remove scale, oxide, or adherent sand. The propeller or blade is
next carefully scrubbed with sharp sand and water; and particles of slag picked and

page_text: holes scraped. It should then be rinsed with water and placed for a short time in a
bath composed of a hot solution of caustic alkali to remove all traces of greasy
matters, next rinsed again and immediately put into a first coppering bath. This
first coppering bath must be alkaline in order to. have a very adherent film of copper
deposited in the first instance. When the depositing electric current has been at
work for a little time the propeller or blade must be carefully examined, and if any
parts are found uncolored by deposited copper such parts must be carefully cleaned,
and the propeller or blade must be returned to the alkaline bath until the coppering is
complete and perfect on every part. When finally removed from the alkaline
coppering bath the propeller or blade is rinsed with water and immediately put into
an acid coppering bath, and is allowed to remain there with the electric current
working until the deposited copper attains the desired thickness. It is advantageous
to keep the liquid of the bath in circulation by means of agitators; but the deposition
of the copper should take place with comparative slowness in order that the copper
may be dense and durable.
When a thick coating is formed we prefer to fix strips of copper or other suitable
metal to the edges of the blade in order that the coating may extend out far enough
to allow of a sharp edge being formed on it.
Various kinds of alkaline and acid baths are known to electro-platers and any of
these which is found suitable and convenient may be used.
Instead of pure copper, brass or other suitable alloy of copper which can be
electrolytically deposited may be used. After an adherent coating of copper has
been obtained by means of an alkalino bath, tin or lead or suitable metal may be
deposited as an outer coating on such copper coating instead of copper or an alloy of
copper.
Dated this Tenth day of March 1888.
EDMUND HUNT,
Applicants' Agent.

page_text: COMPLETE SPECIFICATION.
Improvements in Means for Diminishing the Liability to Corrosion
of Screw Propellers.
We, WILLIAM CARLILE WALLACE, of Louing Cardross, in the County of
Dumbarton, North Britain, Engineer, and ROBERT DANIEL SMILLIE, of Risk Street,
Dumbarton, in the same County, Electrician, do hereby declare the nature of this
invention and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement, that is to say :-
Our said Invention has for its object to diminish the liability to corrosion of screw
propellers; and it consists in coating such propellers with copper in the manner
hereinafter particularly described.
In carrying out our Invention we employ electro-plating processes to deposit on the
surface of the propeller or on its blades an adherent and firm coating of copper of a
considerable thickness, say for large propellers, about a quarter of an inch sufficient
for withstanding a considerable amount of attrition or wear. If the blades and boss
of the propeller are in one piece we coat the whole with copper; but if the blades are
in separate pieces it may be sufficient to coat them only, the boss may, however, also
be similarly coated although in a separate piece. When the blades only are coated
care must be taken to entirely cover with copper every part of each blade piece to
which the water can have access, the copper coating being made to extend under the
bolt nuts which should be cap nuts and be themselves coated with copper, if of steel
or iron; and at the joint line between the blade and the boss the copper coating must
be made to itself form a close joint at the outer surface to prevent access of water at
the joint to the steel or iron of the blade piece. If the boss is coated with copper the
same precautions must be adopted to prevent access of water at the junction with tho
shaft or at any other point.
When proceeding to apply the coating the propeller or blade of steel or iron is
first very carefully cleaned. The surface may be made smooth by grinding, but in
any case the propeller or blade is pickled in a bath of hydrochloric or sulphuric acid
of sufficient strength to remove scale, oxide, or adherent sand. The propeller or
blade is next carefully scrubbed with sharp sand and water; and particles of slag
picked out and holes scraped. It should then be rinsed with water and placed for a
short time in a bath composed of a hot solution of caustic alkali to remove all traces
of greasy matters, next rinsed again and immediately put into a first coppering bath.
This first coppering bath must be alkaline in order to have a very adherent film of
copper deposited in the first instance. When the depositing electric current has been
at work for a little time the propeller or blade must be carefully examined, and if any
parts are found uncolored by deposited copper such parts must be carefully cleaned,
and the propeller or blade must be returned to the alkaline bath until the coppering
is complete and perfect on every part. Any desired thickness of copper may be
deposited by means of the alkaline bath; we however prefer to complete the coating

page_text: by means of an acid bath, in which case the propeller or blade on being removed from
the alkaline coppering bath is rinsed with water and immediately put into an acid
coppering bath, and is allowed to remain there with the electric current working until
the deposited copper attains the desired thickness. It is advantageous to keep the
liquid of the bath in circulation by means of agitators; but the deposition of
the copper should take place with comparativo slowness in order that the copper may
be dense and durable.
When a thick coating is to be formed we prefer to fix strips of copper or other
suitable metal to the edges of the blade in order that the coating may extend out far
enough to allow of a sharp edge being formed on it.
Various kinds of alkaline and acid baths are known to electro-platers and any of
these which is found suitable and convenient may be used. Thus for the alkaline (or
so-called alkaline) bath we can satisfactorily employ a solution of cyanide of potassium
in which are suspended copper plates or castings forming anodes. When the anodes
have been placed the propeller or blade is immersed in the solution and connected to
the conductor and the electric current caused to pass. Or we may use a bath made
with 20 parts by weight acetate of copper, 20 parts soda crystals and 200 parts water
to which after thorough intermixture there are added 20 parts bisulphate of soda
dissolved in 200 parts water. At this stage the bath will have a yellow color, and
there are to be added to it 20 parts of cyanide of potassium dissolved in 600 parts
water, or sufficient cyanide of potassium to render the bath colorless or nearly so.
Both the baths work most satisfactorily at a temperature of 130 degrees Fahrenheit.
Copper is repeatedly added to keep up the strength of the solution. The acid (or
so-called acid bath may consist of 3 volumes of a saturated solution of sulphate of
copper and volume of a 10 per cent. solution of sulphuric acid. This bath is
worked cold.
Instead of pure copper; brass or other suitable alloy of copper which can be
electrolytically deposited may be used. After an adherent coating of copper has been
obtained by means of an alkaline bath, tin or lead or other suitable metal may be
deposited as an outer coating on such copper coating instead of copper or an alloy of
copper.
Having now particularly described and ascertained the nature of our said Inven-
tion and in what manner the same is to be performed, we declare that what we
claim is :-
1. Diminishing the liability to corrosion of screw propellers by coating such
propellers or their blades by electrically applying to them a double coating of copper
or an alloy of copper in the improved manner and with precautions substantially as
hereinbefore described.
2. Electrically coating screw propeliers or their blades with copper or an alloy of
copper by means of an alkaline bath and with or without an outer coating of tin or
lead or other suitable metal, substantially as hereinbefore described.
3. In electrically coating screw propellers or their blades with copper or an alloy of
copper, causing the coating to extend into joints or cavities so as to prevent access
of water to uncoated parts substantially as herein before described.
Dated this Eighth day of December 1888.
EDMUND HUNT,
Applicants' Agent.