An Improvement in Screw Propeller Blades.
Year: 1897

page_text: Date of Application, 3rd May, 1897-Accepted, 12th June, 1897
COMPLETE SPECIFICATION.
An Improvement in Screw Propeller Blades.
We, CHARLES FLEMING, of Balmain, Sydney, New South Wales, Foreman
Moulder, and JAMES RICHARD THOMSON, of Woolwich, Sydney aforesaid, Consulting
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:-
The object of this invention is to make iron and steel marine propellers proof
against pitting and corrosion on the backs and tips of the blades.
Heretofore various devices have been adopted for minimising and checking the
extreme tendency to corrosion in the parts named. These devices have taken the
form of sheathing of brass, aluminium or other incorrodible metal applied by pinning:
on or casting on. To a limited extent such devices have been successful in such
constructions, but the union between the metals is not perfect or permanent and
water gains entrance to the joints and sets up local galvanic action.
Pitting or corrosion does not occur to an appreciable extent when the propeller
blades are made wholly of a non-corrodible metal; but the cost of such blades is.
very great. The present invention aims at obtaining at a moderate cost the
immunity from corrosion and pitting which is at present secured by making the
blades wholly of an incorrodible metal; and it consists in making the body of
the blade of iron or steel and the outer end or tip, in which corrosion is liable to
occur, of an incorrodible metal. It is not obvious how such a two-metal blade may
be made and it has been necessary to invent a method of uniting the metals.
"
In carrying out the invention the iron or steel body of the blade is cast first;
then the tip is cast; and finally, the tip is "burnt on to the body. In applying
the invention to complete or existing propellers or blades the tips are broken off
and non corrosive tips attached in the same way. The tip may be cast
separately, the body brought into place in the mould, and the burning on then
effected.
Referring to the annexed sheet of explanatory drawings, Fig. 1. is a longitudinal
section of the blade and mould prepared for the burning on process, and Fig. 2 a plan..
It is preferred to cast the whole blade (in the case of a solid propeller all the blades
are cast with the boss at the one time) in iron or steel as the first step, and to break
off the tip in order to obtain a clean joint. It is preferred to break the blade by
drilling a row of holes through it and then cracking it ander the hammer. The tips.
may be of any incorrodible metal which will burn on to iron or steel such as brass,.
bronze, or gun metal. The body of the blade may be cast alone and the edge cleaned
by planing, filing, chipping, or in any other way.
A mould for the tip is made and the end of the body of the blade inserted in it as
shewn. It is preferred to use the unbroken blade as the pattern in order that true-
pitch will be obtained. After making the mould the tip of the blade is broken and
the body replaced as shewn in the drawings. The tip is then cast in si u. This.
done, the sand A is worked down near the joint B so as just to cover the joint or
overlap it a little. A baulk C is set in place and the body of the blade D heated to.
incandescence or nearly so. Hot metal in quantity is then poured through tho
gutter E until the body melts at the joint B, a pricker being used to determine this.

page_text: fact. When the end of the body fuses the tip metal will also be fused; at this stage
the two metals unite perfectly. When cool, the whole blade so made is lifted out and
cleaned off and finished in the usual way.
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. A marine propeller blade having an iron or steel body and a solid tip of an
incorrodible metal united to the body, substantially as described.
2. The method herein described of making a two metal marine propeller blade
consisting in "burning on ",the tip to the body, substantially as described.
D
CL1007
JENSEN & SON,
77, Chancery Lane, London, W.C., Patent Agents.