IMPROVEMENTS IN MECHANICAL STOKING APPARATUS FOR BOILER AND OTHER FURNACES.
Year: 1874

page_text: LETTERS PATENT to James Smith, Engineer to Messieurs Walter
Crum and Company, of Thornliebank, in the County of Renfrew,
North Britain, for the Invention of "IMPROVEMENTS IN MECHANICAL
STOKING APPARATUS FOR BOILER AND OTHER FURNACES.
PROVISIONAL SPECIFICATION left by the said James Smith at the
Office of the Commissioners of Patents, with his Petition, on the
20th June 1874.
I, JAMES SMITH, Engineer to Messieurs Walter Crum and Company,
of Thornliebank, in the County of Renfrew, North Britain, do hereby
declare the nature of the said Invention for "IMPROVEMENTS IN MECHANICAL
STOKING APPARATUS FOR BOILER AND OTHER FURNACES," to be as follows, that
is to say :-
This Invention relates to improvements in mechanical stoking
apparatus for supplying fuel to and moving it forward in boiler and
other furnaces in a continuous and regular manner, the objects being to
simplify the construction and working parts, and to render the apparatus
more efficacious and satisfactory than heretofore, and less liable to get
out of order.

page_text: The Invention consists in substituting for ordinary fire-bars a series
of longitudinally placed screws which are made to rotate continuously
(or it might be at short intervals) by gearing applied to their outer ends
and driven from a steam engine, or other suitable prime mover. A
hopper is constructed over the outer ends of the screw bars, and the
coal or other fuel descending from it upon the screw bars is by their
screwing action gradually carried upon them into the furnace, and
along them to the inner end. At the inner end the ashes or residues
fall over the inner ends of the bars through a space provided for the
purpose into the ash-pit, a damper preventing excess of air from getting
up through such space.
The minor details of the apparatus may be variously arranged, but in
a preferable modification they are as follows:-The bars are made one
half with left-hand screw threads, and the other half with the screw
threads right-handed, and those on the right hand half are made to
turn over to the right, and the remainder the other way. With this
ärrangement the screw threads at the contiguous parts of any two bars
move in opposite directions, except between the two middle bars, and
this prevents any tendency to roll in fuel between them. In the case
of the middle bars the contiguous screw threads move upwards, and if
this causes the fuel to gather towards the sides the action may be
corrected by placing these two bars at a lower level. The screw threads
of each bar enter between the threads of the contiguous bars, but
sufficient clearance is left between to insure perfectly free and inde-
pendent working, and avoid unnecessary friction. The bars are made in
the form of tubes with the screw threads on their outsides, and slots are
formed through the tubes between the screw threads to allow air to
pass up into the furnace in addition to what gets up between the bars.
As the fuel progresses inwards through the furnace and becomes
gradually consumed its bulk becomes correspondingly diminished, it
being however desirable to maintain a certain depth of fuel on the bars.
The diminution in bulk is compensated for by gradually lessening the
progressive motion towards the inner end of the furnace. The pro-
gressive motion, with a stated rate of rotation of the screw bars,
depends on the pitch of their screw threads, and the desired lessening
in the progressive rate is obtained by simply diminishing the pitch
of the threads towards the inner ends of the bars. In addition
to this the bars are made plain for a few inches at their extreme inner
ends.

page_text: It will be. obvious that with the improved apparatus the fire can be
kept always in a practically uniform condition, the best proportion of
air easily ascertained and uniformly admitted, so that the best possible
duty can be got from the fuel, and that without smoke.
The quantity of fuel supplied can be regulated by adjusting a
vertically sliding door, under which the screw bars carry the fuel from
the hopper into the furnace.
SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said James Smith in the Great Seal Patent Office on
the 18th December 1874.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, JAMES
SMITH, Engineer to Messieurs Walter Crum and Company, of Thorn-
liebank, in the County of Renfrew, North Britain, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Twentieth day of June, in the year of
our Lord One thousand eight hundred and seventy-four, in the thirty-
eighth year of Her reign, did, for Herself, Her heirs and successors, give
and grant unto me, the said James Smith, Her special licence that I,
the said James Smith, my executors, administrators, and assigns, or
such others as I, the said James Smith, my executors, administrators,
and assigns, should at any time agree with, and no others, from time to
time and at all times thereafter during the term therein expressed, should
and lawfully might make, use, exercise, and vend, within the United
Kingdom of Great Britain and Ireland, the Channel Islands, and Isle
of Man, an Invention for "IMPROVED MECHANICAL STOKING APPARATUS
FOR BOILER AND OTHER FURNACES," upon the condition (amongst others)
that I, the said James Smith, my executors or administrators, by an
instrument in writing under my, or their, or one of their hands and
seals, should particularly describe and ascertain the nature of the said
Invention, and in what manner the same was to be performed, and
cause the same to be filed in the Great Seal Patent Office within six
calendar months next and immediately after the date of the said Letters
Patent.

page_text: be performed, to be particularly described and ascertained in and by the
following statement in writing, reference being had to the accompanying
Drawings, that is to say :-
My said Invention relates to improvements in mechanical stoking
apparatus for supplying fuel to and moving it forward in boiler and
other furnaces in a continuous and regular manner, my object being to
simplify the construction and working parts to render the apparatus
more efficacious and satisfactory than heretofore, and less liable to get
out of order.
My Invention consists in substituting for ordinary fire-bars a series of
longitudinally placed screws which are made to rotate continuously
(or it might be intermittently or at short intervals) by gearing applied
to their outer ends, and driven from a steam engine, or other suitable
prime mover. A hopper is constructed over the outer ends of the screw
bars, and the coal or other fuel descending from it down upon the screw
bars is by their screwing action gradually carried upon them into the
furnace, and along them to the inner end. At the inner end the ashes
or residues fall over a plate at the inner ends of the bars, through a
space provided for the purpose, into the ash-pit, a damper preventing
excess of air from getting up through such space. The bars are made
in the form of tubes with the screw threads on their outsides, and slots
may be formed through the sides of the tubes between the screw threads
to allow air to pass from the ash-pit up into the furnace in addition to
what gets up between the bars, the object of this construction being to
keep the bars comparatively cool whilst admitting the requisite air. I
however now prefer to have the bars kept cool by means of water
passing inside of them, as herein-after more particularly described, the
air admitted from the ash-pit passing up only between the bars and
through certain apertures at the sides of the furnace.
.
And in order that my said Invention and the manner of performing
the same may be properly understood, I hereunto append a Sheet of
explanatory Drawings to be herein-after referred to, and representing a
boiler furnace as fitted with my improved apparatus. In these Drawings
the same reference numerals are used to mark the same or like parts
wherever they are repeated.
Figure 1 of the Drawings is a sectional front elevation, and Figure 2
is a longitudinal vertical section of a boiler fitted with my improved

page_text: furnace; whilst Figure 3 is a plan of the fire-bars. The boiler 1 is of
a well-known type consisting of a horizontal cylindrical shell with two
large flues 2, at the front end of each of which a furnace is situated.
In place of the ordinary fire-bars there are in each furnace six cast-iron
tubes 3 which are formed with screw-shaped or helical flanges 4 on their
outsides, and which are disposed longitudinally and with a slight
inclination downwards towards their inner ends. These sorew bars are
supported on transverse bearers 5, 6, at their outer and inner ends, but
in such a way as to be free to turn, being formed with journals which
occupy half-round bearings in the pieces 5, 6, and which are covered by
bars having half-round recesses on their under sides. The front ends of
the screw bars 3 are formed with projecting necks 7, on which are fixed
worm wheels 8, gearing with screw worms on a transverse horizontal
shaft 9 which is carried in bearings on brackets 10, and has fast on its
outer end a pulley 11 to receive a driving belt from an overhead shaft.
The three screw bars 3 occupying one half of each furnace are made
with right-hand screw threads or flanges, and the three occupying the
other half with left-hand threads. The three right-hand bars revolve in
one direction, and the three left-hand bars in the opposite one, the parts
of the transverse worm shaft 9, which act on the respective sets of bars,
being formed with right-hand and left-hand worms accordingly. The
screw threads 4 on each of the bars 3 work between the screw threads
of the bars on each side, but the spaces between the threads are made
sufficiently large for some air to pass up between the bars from the
ash-pit 12. Narrow plates or bars 13 are fixed between the extreme
screw bars 3 and the sides of the furnace, and a number of notches are
formed in these plates or bars for the passage of air. A hopper 14 is
constructed just outside of each furnace and above the level of the fire-
bars, and the fuel being supplied to this hopper descends in it down.
upon the outer ends of the screw bars 3, and is by them carried forward
into the furnace under a door 15 fitted to slide vertically in guides at the
inner side of the hopper, and hung by chains from a shaft 16 above.
Each shaft 16 is fitted with a hand wheel 17 and with a ratchet
wheel 18 which has a pawl or catch in connection with it. Each
door 15 can thus be raised or lowered to any position, and be held where
required by means of the catch and ratchet wheel, and as the depth of
fuel on the bars will obviously depend on the extent to which each
door 15 is raised or opened the rate of feed can easily be regulated at
any time by suitably adjusting the doors. The rate of rotation of the

page_text: screw bars 3 may also be varied, but with bars of the proportions shown
in the Drawings a speed of one revolution per minute is found in
practice to be suitable and convenient. As the fuel travels inwards by
the screwing action of the bars 3 it becomes gradually exhausted, and
by the time each increment of it reaches the inner ends of the bars it is
reduced to ashes, which pass over a plate 19, and finally drop over the
inner edge of such plate down an opening 20 between it and the
bridge 21 into the inner end of the ash-pit 12, from which they are
removed periodically. A damper 22 is fitted in the ash-pit to prevent
an excess of air from getting, up through the opening 20. The screw
bars 3 are cooled or prevented from becoming overheated by water, for
which purpose the necks 7 at their front ends are entered through
stuffing boxes into a water box 23 fixed on the brackets 10. The water
is supplied by a transverse main pipe 24, to which a branch tube 25 is
fixed for each bar 3, such branch tube 25 passing in each case along
the interior of the bar nearly to its inner end. The water issues from
the inner end of each branch tube 25, and returns outwards along the
fire-bar 3, passing from the outer end of the neck 7 into the box 23,
from which last it is led away by a pipe. As with the arrangements
described the water is kept quite clean and free from dust, it may.
used for feeding the boiler so as to utilise the heat it takes up from the
fire-bars 3.
be
The minor details of my improved apparatus may be variously
arranged in different cases.
In the modification herein-before described the screw threads 4 at the
contiguous parts of any two bars move in opposite directions, except
between the two middle bars, and this prevents any tendency to roll in
fuel between them. In the case of the middle bars the contiguous
screw threads move upwards, and if this should in any case cause the
fuel to gather towards the sides the action may be corrected by placing
these two bars at a lower level. In the Drawings the screw threads 4
of the bars 3 are shown as of uniform pitch from end to end so as to
tend to impart a uniform progressive motion to the fuel throughout, but
if preferred the pitch may be diminished towards the inner end with the
view of making the progressive motion less. as the bulk of the fuel
becomes reduced.
In cases in which a very vigorous combustion is maintained not only
at the inner end but towards the front end of the furnace, and when the

page_text: fuel or coal employed has a tendency to cake, a short propeller screw
may be fitted in the bottom of the hopper just over the centre line of
the furnace, to push the fuel into the furnace and to overcome the
resistance due to the caking tendency, such screw being placed with its
axis longitudinal, and being driven in any convenient way.
It will be obvious that with my improved apparatus the fire can be
kept always in a practically uniform condition, the best proportion of
air easily ascertained and uniformly admitted, so that the best possible
duty can be got from the fuel, and that without smoke.
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 the herein-before in part recited Letters Patent is,―
1. The arranging or combining together of parts to form mechanical
stoking apparatus for boiler and other furnaces, substantially in the
improved manner herein described and delineated.
2. The application and use of revolving screw bars for carrying and
progressively moving the fuel in boiler and other furnaces, as herein-
before described.
In witness whereof, I, the said James Smith, have hereunto set my
hand and seal, this Sixteenth day of December, in the year of
our Lord One thousand eight hundred and seventy-four. ·
25 Witness,
EDMUND HUNT,
Patent Agent,
Glasgow.
JAMES SMITH. (L.S.)