IMPROVEMENTS IN MEANS AND APPARATUS FOR DIMINISHING THE LIABILITY TO CORROSION OF SCREW PROPELLER BLADES
Year: 1882

page_text: LETTERS PATENT to David Johnston, of Govan, in the County of Renfrew,
North Britain, Superintendent Engineer to the Allan Line of Steamers, for
an invention of IMPROVEMENTS IN MEANS AND APPARATUS FOR DIMINISHING
THE LIABILITY TO CORROSION OF SCREW PROPELLER BLADES
PROVISIONAL SPECIFICATION left by the said David Johnston at the
Office of the Commissioners of Patents on the 28th April 1882.
DAVID JOHNSTON, of Govan, in the County of Renfrew, North Britain Super-
intendent Engineer to the Allan Line of Steamers "IMPROVEMENTS IN MEANS
AND APPARATUS FOR DIMINISHING THE LIABILITY TO CORROSION OF SCREW-
PROPELLER BLADES
"
This Invention has for its object to diminish the liability to corrosion of screw-
propeller blades; and it consists in coating, the parts of the blades on which
experience has shown that corrosion ordinarily acts, with tin or other suitable
metal or alloy applied in a novel manner and with the aid of improved apparatus.
The Invention is specially applicable to blades of steel or iron, and in practically
carrying it out the surface to be coated with tin, and which will in most cases be
the outer part of the back of the blade, is first prepared by being ground so as to
be quite clean and bright and free from oxide. An emery wheel is used for the
preparatory operation and is mounted and driven in a manner to admit of its
being easily made to act on the curved surface of the blade. The emery wheel is
fixed on a horizontal spindle which has also fast on it a pulley for a driving rope,
and it is carried in a small frame attached to a long lever which extends hori-
zontally or nearly so from a double centre or universal joint allowing the lever
to be moved angularly in any direction. The lever extends beyond the frame
carrying the pulley, its end serving as a handle by means of which a workman
moves it so as to apply the emery wheel to the surface of the blade, the blade
being placed in a suitable position with the surface to be acted on as nearly

page_text: horizontal as conveniently possible. The loop of the driving rope the bottom of
which passes round the pulley of the emery wheel passes up between a pair of
overhead guide pulleys from above which the two parts of it proceed horizontally
in opposite directions, one part going to a pulley from which the driving power is
derived and returning horizontally from that pulley, whilst the other part passes
round a horizontally movable pulley and returning, joins the other part. The
movable pulley which may be carried by a bar sliding in horizontal guides is
drawn outwards by a rope or chain passing over a guide pulley to a counterweight
and this counterweight not only keeps the driving rope tight but also counter-
balances as much as may be desired of the weight of the emery wheel and of the
lever carrying and guiding it. The lever has a screw thread formed on it to work
in an internally scrowed bush held in the bearings at the centre, and this bush has
fixed to it a handwheel by turning which the emery wheel may be shifted nearer
to or further from the centre of the lever so as to act on different parts of the
blade.
After the blade has been prepared by means of the emery wheel it is placed
with its bright side uppermost over a fire and is heated sufficiently_to_allow_of_the_
tin or other metal adhering to it like solder when applied by means of an instru-
¨¯ment analogous to a soldering bolt. It is preferred to use tin as the coating metal
and to apply a thickness of at least inches but lead or an alloy like solder
might be used; or the blade prepared by means of the emery wheel as herein-
before described might be first galvanised and afterwards tinned.

page_text: SPECIFICATION in pursuance of the conditions of the Letters -Patent filed
by the said David Johnston in the Great Seal Patent Office on the
25th October 1882.
DAVID JOHNSTON, of Govan, in the County of Renfrew, North Britain,
Superintendent Engineer to the Allan Line of Steamers "IMPROVEMENTS IN
MEANS AND APPARATUS FOR DIMINISHING THE LIABILITY TO CORROSION OF
SCREW-PROPELLER BLADES
"
My said Invention has for its object to diminish the liability to corrosion of
screw-propeller blades; and it consists in coating the parts of the blades on which
experience has shown that corrosion ordinarily acts, with tin or other suitable
metal or alloy applied in a novel manner and with the aid of improved apparatus.
My Invention is specially applicable to blades of steel or iron, and in practically
carrying it out the surface to be coated with tin, and which will in most cases be
the outer part of the back of the blade, is first prepared by being ground so as to
be rendered quite clean and bright and free from oxide. An emery wheel is used
for the preparatory grinding operation, and is mounted and driven in a manner
to admit of its being easily made to act on the curved surface of the blade.
The apparatus used in applying the emery wheel is shown on two sheets of
explanatory drawings, which are hereunto appended and will be hereinafter referred
to, the reference numerals in these drawings being used to mark the same or like
parts wherever they are repeated.
Figuro 1, of the accompanying drawings is a back clevation figure 2, is a
sectional plan and figure, 3, is a side elevation. In figure, 2, a screw-propeller
blade, 4, is shown as being operated upon being placed on a truck, 5, and a dotted
line, 6, indicates the part of the blade intended to be coated with tin or the like
The emery wheel, 7, is fixed on a horizontal spindle, 8, which has also fast on it
a pulley, 9, for a driving rope, 10, and it is carried in a small frame, 11, attached
to a long lever, 12, which extends horizontally or nearly so from a double centre
or universal joint, 13, allowing the lever, 12, to be moved angularly in any direction.
The frame, 11, has fixed to its outer part a bar, 14, forming a prolongation of the
lever, 12, and made with a cross handle, 15, at its end by means of which a
workman moves it so as to apply the emery wheel 7, to the surface of the blade, 4,
the blade being placed in a suitable position with the surface to be acted on as
nearly horizontal as conveniently possible. The loop of the driving rope, 10, the
bottom of which passes round the pulley, 9, of the emery wheel, 7, passes up
between a pair of guide pulleys, 16, suspended overhead, from above which pulleys
the two parts of the rope, 10, proceed horizontally in opposite directions, one part
going to and round a pulley, 17, from which the driving power is derived and
returning horizontally from that pulley, whilst the other part passes round a
horizontally movable pulley, 18, and returning joins the other part. The movable
pulley, 18, which is carried by a bar, 19, sliding horizontally in guides, 20, is
drawn outwards by a chain, 21, passing over a guide pulley, 22, to a counter-
weight, 23, and this counterweight not only keeps the driving rope, 10, tight but
also counterbalances as much as may be desired of the weight of the emery wheel 7,
and of the parts for carrying and guiding it. The lever, 12, has a screw thread, 24,
formed on it to work in an internally screwed tube or bush, 25, held in the bearings
at the centre, 13, and this tube or bush, 25, has fixed to it a handwheel, 20, by
turning which the emery wheel, 7, may be shifted nearer to or further from the
centre, 13, so as to act on different parts of the screw-propeller blade, 4. As
represented in the drawing the support of the lever, 12, consists of a vertically

page_text: swivelling pin, 27, set in a bearing in a ring, 28, fixed to a column, 29, the top of
the pin, 27, being attached by a horizontal joint or hinge to the bearing of the
tube, 25; but any equivalent arrangement may be adopted that will allow of the
lever being moved angularly in an direction.
After the blade, 4, has been prepared by means of the emery wheel, 7, it is
placed with its bright side uppermost over a fire and is heated sufficiently to allow
of the tin or other metal adhering to it like solder when applied by means of an
instrument analogous to a soldering bolt. I prefer to use tin as the coating metal
and to apply a thickness of at least inches; but any other suitable metal or
alloy may be used; or the blade prepared by means of the emery wheel as herein-
before described might be first galvanised and afterwards tinned.
Having thus particularly described my said Invention and the manner of
performing the same I have to state that I do not restrict myself to the precise
details herein described or delineated but that what I believe to be novel and
original and claim as the Invention secured to me by and in terms of the herein-
-before-in-part.recited Letters Patent is
--
1- The process of diminishing the liability of iron or steel screw-propeller-bla-les-
to corrosion by coating the blades where necessary with tin or other suitable metal
or alloy, the surfaces to be coated being first cleaned by grinding and then heated
sufficiently to cause the coating metal to adhere substantially as hereinbefore
described.
2. The arrangement-of-the-emery-wheel and the parts for carrying driving and
applying it substantially in the manner bereinbefore described.
In Witness whercof I the said David Johnston, have hereunto set my hand
-and-seal-this-twenty-fourth-day of October in the year of our Lord
One thousand eight hundred and eighty-two.
Witness
EDMUND HUNT
Patent Agent
Glasgow
DAVID JOHNSTON. (L.S.)