AN IMPROVED METHOD OF CONSTRUCTING PISTONS OR SIMILAR DISC BODIES
Year: 1876

page_text: LETTERS PATENT to William Clark and James Clark, of Low Elswick, in the
Borough and County of Newcastle-upon-Tyne, Marine Engineers and Iron-
founders, for the Invention of "AN IMPROVED METHOD OF CONSTRUCTING
PISTONS OR SIMILAR DISC BODIES."
Scaled the 9th September 1876, and dated the 24th May 1870.
PROVISIONAL SPECIFICATION left by the said William Clark and James
Clark at the Office of the Commissioners of Patents on the 24th May 1876.
WILLIAM CLARK and JAMES CLARK, of Low Elswick, in the Borough and County
"AN IMPROVED
of Newcastle-upon-Tyne, Marine Engineers and Tron-founders.
METHOD OF CONSTRUCTING PISTONS OR SIMILAR DISC BODIES."
Our Invention has reference more particularly to those large pistons provided in
low pressure engines.
To obviate the difficulty in casting soundly a large disc of metal, due to the
contraction of the same when cooling, which leaves the casting in a strainer and
weakened state is the object of our Invention, for which purpose we cast the piston
in the first instance, say to three-fifths the diameter of the cylinder for which it is
intended. This size will insure a sound casting, the periphery of which is formed to
receive an annular casting that will constitute that portion of the piston to which
the junk ring or other approved method of packing is secured.
When the diameter of the cylinder is very large, more than one annular portion of
the piston may be formed and bolted one upon the other. In this way a piston
could be increased in diameter to any moderate extent.
Although in some cases we divide the piston into a number of segments and
bolt these segments to each other, which would in a measure insure sound work,
we prefer however the above method of constructing pistons of large diameter,
which is equally suitable to the construction of large disc bodies of a similar nature.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said William Clark and James Clark in the Great Seal Patent Office on
the 24th November 1876.
WILLIAM CLARK and JAMES CLARK, of Low Elswick, in the Borough and County
of Newcastle-upon-Tyne, Marine Engineers and Iron-founders. "AN IMPROVED
METHOD OF CONSTRUCTING PISTONS OR SIMILAR DISC BODIES."
Our Invention has reference more particularly to those large pistons provided in
low-pressure engines.
To obviate the difficulty of casting soundly a large disc of metal, due principally
to the contraction of the same while in the act of cooling, and which leaves the
said casting in a strained and weakened condition is the object of our Invention,
and is effected as follows, taking a large low-pressure piston as an example.
The piston is cast in the first instance to, say, three-fifths the diameter of the
cylinder for which it is intended, care being taken of course that the parts are of
sufficient strength to carry the supplementary portion that is afterwards added.
This dimension will insure a sound casting, the periphery of which is formed to
receive and havo bolted thereto an annular casting to which the junk ring may be
secured.
When the cylinder is of an unusually large diameter two or more of these annular
castings, each being concentric with the other and of a suitably increasing diameter,
may be added. The piston may thus be built outward from the centre to any
reasonable extent, and finally turned up true to its finished dimension.
Although in some cases we construct the piston of a number of sectors or seg-
ments, which would in a measure insure sound work, we prefer, however, as being
cheaper and more efficient, the method above described.
We will now proceed to describe our Invention more fully by aid of the accom-
panying Drawing, reference being had to the letters and figures marked thereon.
Figure 1 is an elevation of a large piston constructed according to our method
first described. Half of this Figure is a section on line C*, D*, (Figure 2). Figure 2
is a plan of the same, also partly in section on line A*, B*, (Figure 1).
In these Figures A, A, is the nucleus, which should be of a diameter no larger
than would insure a sound casting. The periphery of this nucleus is formed as
shown in section at a, a, (Figure 1), or it may be formed in any other suitable
manner to receive the annular casting B, and to be bolted thereto by screwed
bolts c, c, a box spanner being employed for the purpose. B is the annular casting
aforesaid, the inner circumference of which is formed to accurately fit the nucleus A.
Before the union is made between the two castings the surfaces about to come in
contact are cach truly turned and covered with red lead or other suitable material
to render the joint firm and steam tight.
The outer circumference of the casting B may be formed similar to the outer
circumference of the said nucleus in order to enable it to receive a second ring. In
this way a piston could be built outward from the nucleus to any reasonable extent,
and finally turned up true to its finished dimension. The width of the rings should
in all cases be such as would not endanger the soundness of the casting by excessive
contraction in cooling.
D, D, is the junk ring secured by screwed bolts e, c, or other approved method,
to the ring or annular casting last added. The introduction of the usual packing
ring and springs completes the piston, to which the piston rod E may be secured in
the usual way. The webs and gare for the purpose of stability, and may be
omitted when not required; h, h, are nuts made of brass as is customary the case
to prevent the screwed bolts rusting within the female screw, and thus delay the
removal of the same when at any time the packing of the piston is required to be
readjusted.
Having now described and particularly ascertained the nature of our said Inven-
tion, and explained the manner of carrying the saine into effect, we wish it to be

page_text: understood that under the above in part recited Letters Patent we claim, the method
of constructing pistons or similar disc bodies as above described and illustrated on
the accompanying Drawing, or any mere modifications thereof.
In witness whereof, I, the said James Clark, have hereunto set my hand and
seal, this Twenty-third day of November, in the year of our Lord One
thousand eight hundred and seventy-six.
JAMES CLARK. (L.S.)