IMPROVEMENTS IN THE MEANS AND APPARATUS FOR GALVANISING IRON, OR COATING IT WITH ZINC AND TIN
Year: 1877

page_text: PROVISIONAL SPECIFICATION left by Frederick Braby and Arthur Charles
Moore at the Office of the Commissioners of Patents on the 1st March 1877.
FREDERICK BRABY, of No. 358, Euston Road, in the County of Middlesex,
Galvanised Iron Manufacturer, and ARTHUR CHARLES MOORE, of Ida Wharf, Deptford,
in the County of Kent, Galvanised Iron Manufacturer. "IMPROVEMENTS IN THE
MEANS AND APPARATUS FOR GALVANISING IRON, OR COATING IT WITH ZINC
AND TIN."
In galvanising sheet iron, netting, or other extended iron surfaces, these are
immersed into a bath of molten zinc at one side thereof, and pass out of the bath at
the other side. The zinc bath requires to have a layer of muriate of ammonia or
other deoxidizer upon its surface, in order to prevent the molten zinc from oxidizing
on the surface through contact with the air, and also for the purpose of cleansing
the surface of the iron before it passes into the zinc, and to prevent any zinc oxide
from adhering to the surface of the coated iron as it passes out of the bath. The
muriate of ammonia has itself however an injurious effect upon the coated galvanised
iron as it emerges from the bath in discoloring the coating of zinc thereon.
One part of our present Invention has for its object to avoid this injurious effect,
and it consists in providing, at the delivery or exit side of the bath, a pair of rollers
or cylindrical skimmers that are partially immersed in the molten zinc, and have a
narrow space between them through which the sheet iron or other extended surface
is made to pass as it issues from the bath. By means of these cylindrical skimmers
the surface of that part of the zinc in which they are immersed is kept clear of the
muriate of ammonia, this being confined to the outer sides of the cylindrical skim-
mers, while these at the same time protect the zine from contact with the
atmosphere, and thus insure that the molten zinc through which the sheet iron
emerges from the bath is free from oxide or scum. We term the said rollers
"uniform continuous skimmers" because they continually induce a fresh surface of
clean zinc for the iron to pass through. A rotary motion being imparted to the
cylindrical skimmers in contrary directions from the inner or meeting side to the
outer side, any zinc that may adhere to their surfaces, and thus become oxidized
when carried round that part which is exposed to the air, will become deoxidized
again by contact with the layer of the muriate of ammonia or other deoxidizing

page_text: agent employed through which the surface of the revolving skimmers must pass
before dipping into the zinc again.
In order to economize the muriate of ammonia, it may be confined to the space
immediately at the back of each revolving skimmer by means of metal plates
arranged parallel with the revolving skimmers at a certain distance therefrom, and 5
dipping into the molten zinc, and if desired such plates may have hoods attached
thereto covering in the layers of ammonia so as to enclose the fumes arising there-
from, spouts closed by covers being provided in such hoods through which fresh
muriate of ammonia may be introduced when required, and openings or tubes for
leading away the fumes evaporated therefrom to condensors or elsewhere. The 1
other part of the surface of the zinc bath on the delivery side may be covered with
a layer of spent muriate of ammonia, or with any other suitable material that will
float on the inolten zinc so as to protect it from contact with the atmosphere, and
will at the same time not be acted upon by the molten metal. Thus sheets of
aluminium may answer for this purpose.
According to another modification of our Invention a single revolving skimmer is
employed, the iron plate being made to issue through a narrow slit between it and a
curved, straight or angular surface at the side of the zinc bath; this arrangement would
however not act so efficiently as that previously described, as any zinc that might be
deposited by the plate upon that part of the said fixed surface which is in contact
with the air would if it became oxidized not be removed as in the case of the
revolving skimmers, and in accumulating it might adhere to and deteriorate the one
surface of the galvanised sheet as it issues:
A further modification of our Invention consists in an arrangement to dispense
altogether with the use of muriate of ammonia or other deoxidizer on the delivery
or exit side for some classes of galvanised work by providing fixed or stationary
cylindrical, flat, straight, or angular guide or guides partially immersed in the
molten zinc and tin, and so placed as to have only a narrow space between them
sufficiently wide to allow of a sheet or plate to pass through, and underneath either
of these and immersed in the molten metal may be a pair of rollers or a fixed guide
to guide the sheet (to be emerged) between the said cylindrical, flat, straight, or
angular guide or guides. The wholly immersed rollers or fixed guide underneath
the molten metal are not absolutely necessary, as the sheet of iron could be guided.
to the narrow space between the stationary guide or guides arranged at, or on, or in
the surface of the molten zinc and tin by the workmen with the assistance of a
piece of iron hooked at one end. Neither this nor the previously described arrange-
ment would act as efficiently as the two revolving cylindrical skimmers first
described, and we therefore prefer in all cases to employ these.
Another part of our Invention has for its object to obviate the inconvenience
and loss that now arises from the evaporation of the volatile constituents from the
layer or muriate of ammonia covering the zinc bath on the receiving or entrance
side thereof, such vapours, as also the gaseous products of combustion from the
incandescent coke, coal, or other fuel at the side of the bath, being at present
allowed to escape free into the workshop, occasioning both a loss of material and
considerable inconvenience to the operatives.
According to one modification of our Invention we enclose the receiving side of
the zinc bath by a hood or cover that dips a short distance with a vertical portion
into the molten metal of the bath at or about the middle thereof, thus completely
'separating the receiving from the delivery side thereof, and extends from that point
either to the side of the bath, if it is desired only to confine the vapours thereof, or
to the brickwork enclosure beyond the fuel at the side of the bath, if it be desired
also to confine the gases rising from the fuel. At a short distance above the top of
the bath we provide in the hood a long narrow opening through which the sheet
metal to be galvanized may be inserted, such opening having by preference on the
one edge a strip of elastic or yielding material such as vulcanized caoutchouc, while
the other edge is formed either by a plate so arranged and acted on either by its
own weight or springs or weights connected thereto, that when no sheet metal is

page_text: being passed through it is pressed against the other edge of the said opening, which
will thus be more or less perfectly closed against the escape of any vapour or gases
through it. The inner surface of the hood is made of any suitable material that will
not be quickly destroyed by the muriate of ammonia fumes and other gases, and
the former may either be allowed to condense inside the hood and fall back on to
the bath, or the fumes and gases may be conducted from the hood through a pipe
and led either into a condenser or be otherwise disposed of.
The gases arising from the burning fuel being mainly carbonic anhydride, carbonic
oxide, and nitrogen, will not seriously injure the inuriate of ammonia or the iron or
zinc, and the heat thereof will tend to dry the metal sheets (which are wet from the
pickling bath), and also warm them before they pass into the zinc bath, the steam
thus generated mixing with the other gases, and being conducted away with them.
The closed end surfaces of the hood may be provided with doors opposite each other
closing more or less air tight, through which when required the spent muriate of
ammonia on the zinc bath may be removed and replaced by fresh material, and
spouts provided with covers may be provided at the front of the hood, for the
introduction of the muriate of ammonia. The hood may be provided with one or
more safety valves, which may consist merely of weighted flaps covering openings,
for allowing the escape of gases, should the pressure thereof rise unduly, and similar
valves or flaps may be provided in the escape pipes before mentioned, such valves
being by preference rather more lightly loaded than those on the hood.
For the purpose of guiding the sheet iron in the proper direction as it enters the
bath, three rollers may be provided, two being either above the layer of flux, or by
preference partially immersed in the bath with a space between them covered with
muriate of ammonia through which the sheet metal enters, and the thirbeing
situated below the other two, in order to guide the sheet in the direction towards
the delivery side of the bath. Or in place of the third roller a fixed guide may
be used.
According to another modification we also enclose the delivery or exit side of the
bath with a hood in a similar manner to the receiving side, whereby the further
advantage is gained that the galvanised plates in issuing from the bath into the
heated atmosphere of the hood will not be subject to deterioration by sudden
cooling as is at present the case. In this case the sheet metal may either issue
between revolving skimmers as first above described, or, if the vapours or gases
confined in the hood are not such as would act upon the zinc, the layer of muriate
of ammonia might either be greatly diminished or even entirely dispensed with, and
in the latter case the arrangement of revolving skimmers might also be dispensed
with, the sheet iron being made to issue through a narrow opening in the hood
arranged in a similar manner to that described with reference to the receiving side.
If both the receiving and the delivery side of the bath are enclosed, a partition is by
preference provided in the hood extending down so as to dip into the zinc so as to
effectually separate the two parts.
By entirely enclosing the one or both sides of the bath as above described, the
further advantage is gained that the said fumes and gases in occupying the enclosed
space at a pressure equal to or above that of the atmosphere, will more or less
entirely prevent the ingress of atmospheric air, and consequently also the injurious
contact of the oxygen thereof with the surface of the molten metal.