Electrical Deposition of Zinc and Alloys of Zinc, and Apparatus therefor.
Year: 1894

page_text: Date of Application, 16th Mar., 1894
Complete Specification Left. 15th Jan., 1895-Accepted, 15th June, 1895
PROVISIONAL SPECIFICATION.
Electrical Deposition of Zinc and Alloys of Zinc, and Apparatus
therefor.
RICHARD HEATHFIELD of 1 Leadenhall Buildings E.C. Metal Merchant and
WILLIAM STEPNEY RAWSON of 86 York Street Westminster Electrical Engineer
do hereby declare the nature of this invention to be as follows:-
Our invention relates to the electrical deposition of zinc & alloys of zine and is
intended to obtain an adherent, bright & protective coating especially upon articles
of iron and steel. To secure this we may after the usual chemical cleaning,
deposit upon the article a thin coating of mercury by making it the cathode in a
solution of salt of mercury such as the sulphate & using such an E.M.F. as will
cause a free disengagement of hydrogen. Mercury may thus be alloyed with even
iron and steel.
We then deposit a coating of zinc from a salt of zinc such as the ammonio-
chloride and having well washed the article we may again subject it to the action
of the current in a mercury salt so as to give it a bright color and assist to close
the pores.
With the sulphate of mercury we may use lead or carbon plates as anodes.
When we use the ammonio-chloride of zinc we may obtain our solution by
washing with water the residue which forms on the top of an ordinary galvanizing
pot.
The solution will then contain ammonio chloride of zinc & also some of the same
salt of iron.
If an iron anode be used the solution will deposit an alloy of iron and zinc if a
suitable E.M.F. be used.
If however a zinc anode be employed the iron will be thrown down and the
liquid may be freed from it by filtration.
The mixture of iron & zinc known as hard spelter may be used as an anode with
this solution. Ammonia may be added in small quantities from time to time if the
solution becomes too acid. If we use carbon anodes we may supply the zinc
deposited at the cathode by passing the solution continuously over fresh supplies of
material.
In order to allow of a rapid deposit we may mechanically agitate the articles or
we may produce an agitation in the liquid by forming the anodes in such a shape
that by their revolution or other movement they may keep the liquid stirred.
In the case of small articles such as screws & nails the like we may use an
apparatus such as a drum with a centre spindle formed of zinc cast to a suitable
shape forming the anode and an outside perforated envelope which may be metallic
or may be of non conducting material with bars of metal at certain intervals
running the length of the drum & electrically connected to an exterior band
of metal on which contact may be made by a brush above the surface of the
liquid.
The current enters by the spindle & passes out by the external brush.
By rotating the drum mechanically the small articles are continually stirred,
their movement being further promoted by the bars of metal which carry them up
chest wav
than allow them to fall

page_text: The drum may be provided with suitable openings for insertion of the articles
& provision may be made for the easy replacement of the anode when it has been
sufficiently dissolved.
March 16th 1801
RICHARD HEATHFIELD.
W. STEPNEY RAWSON.
Electrical Deposition of Zinc and Alloys of Zinc, and Apparatus
therefor.
We, RICHARD HEATHFIELD, of 1 Leadenhall Buildings, in the City of
London, Metal Merchant, and WILLIAM STEPNEY RAWSON, of 86 York Street,
Westminster, Electrical Engineer, 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:—
Our invention relates to a process and apparatus for electrically depositing
zinc and alloys of zinc, our object being to obtain an adherent and bright and
protective coating especially upon articles of iron and steel.
For this purpose after the usual chemical cleaning we deposit upon the article
a thin coating of mercury by making it the cathode in a solution of a salt of
mercury such as the sulphate and using such an E.M.F. as causes a free disengage-
ment of hydrogen. We then on the coating of mercury deposit a coating of zinc
from a salt of zinc such as the ammonio chloride. When it is desired to protect
the coating and give it brilliance we wash the article thoroughly and again deposit
mercury on it from a nearly neutral solution of a mercury salt. When the salt
employed is sulphate of mercury lead or carbon plates can be used as anodes.
When an iron anode is used for depositing the zinc, the deposit is an alloy of iron
and zinc a suitable E.M.F. being used. When a zinc anode is employed, the iron
is thrown down and the liquid may be freed from it by filtration.
iron and zinc known as hard spelter may be used as an anode.
The mixture of
Ammonia may be added in small quantities from time to time when the solution
becomes too acid.
When carbon anodes are used the zinc deposited at the cathode may be made up
for by passing the solution continuously over fresh supplies of ammonio chloride
of zinc. Instead of the ammonio chloride other salts of zinc may be used such for
instance as zincate of potash.
In order to obtain a rapid and sound deposit we agitate the articles treated or
the liquid in the bath.
In the case of small articles such as screws or nails and the like we employ
apparatus such as we shall describe referring to the accompanying drawings.
Figure 1 is a transverse and Figure 2 is a longitudinal section of a barrel caused
to revolve in the electrolytic bath, and of its electrical connections for depositing
zinc on small articles from a solution of alkaline character such as zincate of
potash.
Figure 3 is a longitudinal section of a modification which is employed when
the solution as for instance ammonio chloride of zinc is such as would corrode an
iron network which forms part of the apparatus shewn in Figures 1 and 2.
In all the figures like reference letters are used as far as possible to denote
like parts.
Referring first to Figures 1 and 2, the barrel may be made (as shewn of poly-
gonal section consisting of wooden staves A having holes through them fixed to
end discs B (of insulating material) by which the barrel is mounted on a central
shaft C, the discs and a tube D connecting the discs and surrounding the shaft being

page_text: insulated from the shaft which extends beyond the ends of the barrel and is
mounted in bearings E provided on the ends of the tank in which the barrel
revolves. At some distance from the central tube D and in electrical connection
therewith is fixed to end discs G G', a cylinder F' of network or perforated plate
of iron or other suitable metal. The disc G is in electrical connection with
an external flange H which revolves in a mercury trough connected to the
+terminal of a dynamo or other source of electricity. The cylinder F being
charged with scraps or fragments of zinc, these being in contact with the network F,
discs G G and tube D constitute with these parts the anode.
Along the staves A extend rods of half-round iron J which are bent upwards
and also sideways as shewn in Figure 14 their upper ends passing through
insulating material into an annular trough K containing a quantity of mercury,
which, as the barrel revolves, lies in the lower part of the annular trough in
contact with the ends of several of the rods J. The side of the annular trough is
in electrical connection with a flange M which dips into mercury contained in a
trough and connected with the negative terminal of the clectric generator.
Thus
those of the iron rods J which have their ends covered by the mercury in K
constitute cathodes, all the others of these rods being inert until they come round
in the course of each revolution of the barrel to the position in which their ends
are again covered by the mercury in K. The cylinder F is preferably protected
by a louvre casing P. The articles to be coated being charged into the barrel by
openings provided with covers, roll over and over as the barrel revolves there
being always some of them in contact with a few of the rods J which are in
connection with the negative terminal, and therefore are in the condition of
cathodes. As only those of the rods J which have articles on them are at any
time connected to the negative terminal, there is no waste of electrical energy in
passing through the parts of the apparatus where there are no articles to be
coated.
When the solution in the bath is such as would corrode the cylinder F, the
anode employed is that shewn in Figure 3, that is to say, a number of zinc plates
or discs Q fixed on the tabe D enclosing the shaft.
In order to prevent short circuiting by the cathode articles touching the discs Q,
we stretch round the edges of the discs bands of caoutchouc q, which owing to
their elasticity take a U form enclosing the edges of the discs.
Although we have described the apparatus as applied to the depositing of zinc,
it may obviously be employed to the depositing of other metals from solutions of
their salts.
Having now particularly described and ascertained the nature of our said
invention and in what manner the same is to be performed we declare that
what we claim is :
1. The herein described process for depositing on iron, steel or other metallic
articles zinc
or its alloy by first electrolytically coating the articles with
mercury and then electrolytically depositing zinc upon the articles thus coated.
2. The apparatus for effecting the process above referred to substantially as
described with reference to Figures 1, 1 and 2.
3. The modified apparatus substantially as described with reference to Figures 1^
and 3.
Dated this 15th day of January 1895.
ABEL & IMRAY,
Agents for the Applicants.