Improvements in Mechanical Chain Grate Stokers for Steam Boiler o other Furnaces.
Year: 1899

page_text: Date of Application, 29th Sept., 1899-Accepted, 2nd Dec.,
1899
COMPLETE SPECIFICATION.
Improvements in Mechanical Chain Grate Stokers for Steam Boiler o
other Furnaces.
We, BABCOCK & WILCOX, LIMITED, of 147, Queen Victoria Street, in the City
of London. Steam Boiler Manufacturers, and GEORGE WILLIAM THODE, Engineer
with said Company, 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:―
This invention relates to mechanical stokers of the kind described in the
Specifications of Letters Patent Nos. 21005 of 1890, and 27420 of 1898, and it has
for its object to render such stokers more efficient in action by improving the
construction and arrangement of various parts as hereinafter set forth.
In the accompanying drawings which illustrate the invention, Fig. 1 is a
longitudinal vertical section of a water tube boiler of the Babcock & Wilcox type
shewing the improved chain grate stoker applied thereto; Fig. 2 is a front
elevation partly in section, and Fig. 3 a horizontal section of the same. Figs. 4
and 5 are respectively front and side views of a portion of the chain grate actuating
mechanism to a larger scale.
Fig. 6 is a longitudinal vertical section, and Fig. 7 an end elevation of part of
a boiler shewing an arrangement for actuating the chain grate when under-
driven eccentrics are employed, it being obviously equally adapted for connection
to over-driven eccentrics, and Figs. 8 and 9 are respectively side and end views
of a detail of this arrangement to a larger scale shewing the method of altering
the extent of the feed.
As shewn by Figs. 1 to 5 of these drawings, the improved chain grate stoker
is composed of the usual wheel frame carrying upon sprocket wheels ca re-
volving endless chain composed of stoker links b supported on rollers, as shewn
at Fig. 1, which are more closely spaced at the rear than at the front of the
furnace to better regulate the admission of air through the chain grate, less air
being required at the rear owing to the fuel resting on that part of the grate
being partially consumed and the fire being thinner.
The chain grate 6 is slowly revolved by the rotation of the shaft & carrying the
sprocket wheels c the said shaft having keyed on it a worm wheel with which
gears a worm on a spindle i which may be turned by a hand crank j, but which
is also fitted with a ratchet wheel & shewn particularly at Figs. 4 and 5, keyed
upon said spindle i, and operated as shewn particularly at Figs. 4 and 5, by a pawl e
carried at one end of a bell crank lever f centred loosely on the spindle. The
other end of the hell crank lever f has a link attached to it which has its upper
end secured in a slot in a pivoted arm m reciprocated by the connecting rod n
of a rotating eccentric, the link being adjustable along the slot in the arm m
nearer or further from the centre of rotation of said arm m to give a longer or
shorter travel to the pawl e. The end of the link connected to the pivoted
arm m is centred in a block capable of being clamped in any position in the slot
by means of the clamping lever o so that whilst the throw of the eccentric is
constant the feed motion may be readily varied at will.

page_text: The fuel hopper p instead of forming part of or being secured on the movable
wheel frame a of the stoker as is usual, is secured to the boiler or furnace front
or to a projecting part 9 thereof, as shewn at Figs. 1 and 2, so that leakage of air
between the hopper and boiler front is obviated whilst the fuel in the hopper
resting on the chain grate b closes off ingress of air above the fire. The chain
grate with its driving gear is thus self contained and independent of the hopper
as indicated at Fig. 2.
The arched furnace roof r extending through the boiler front is fitted with a
lifting doors for adjusting the depth of the fuel on the grate. This door is
raised or lowered by means of a screw-threaded spindle furnished with a hand
wheel which is turned to raise or lower the door s. This door also serves to
keep the fuel from kindling outside, and it can be turned upon its hinges like an
ordinary furnace door, as shewn at Fig. 3, and is thus also suitable for hand
firing.
The side framing composed of the plates sunk into the brickwork w forms
part of the furnace instead of being formed on the wheel frame, and thus a close
fit is ensured between the framing and sides a of the chain stoker to exclude
air, the setting of the side framing or brickwork w being recessed to prevent
clinker adhering to the brickwork.
Vi
A dumping plate or plates y is or are fitted at rear of the stoker and each rests
at its lower edge on a cross bar y or brickwork support, whilst its forward edge
almost touches the chain grate links b so as to exclude ingress of air but allowing
fine ash to pass underneath into the pit below. Large and hard clinker passes
over the dumping plate y and into the space v¹. A door u, shewn at Fig. 1, is
provided at the lower end of this space which normally prevents the ingress of
air between the dumping plate y and the bridge t, but is adapted to be turned
on its pivot s to periodically discharge clinker into the pit w, the turning of
the door being effected by means of a worm 1 on a horizontal shaft q¹ extend-
ing from this point to the front of the boiler where it is actuated by a crank p²,
the worm gearing with a segment of a worm wheel o¹ on the pivot s¹ of the
door u. The dumping plate y is free to tilt or lift upwards to allow of hard
clinker passing under it should it tend to jam, the plate immediately dropping
to its normal position after the passage of such clinker.
The method by which the extent of feed of the underdriven chain grate
actuating mechanism shown in Figs. 6 and 7 can be varied, is shown in detail at
Figs. 8 and 9 and consists in centering loosely on the worm spindle i a slotted
segment carrying a shield m¹ which partially covers the teeth of the ratchet
wheel and which when the segment is moved may be made to cover a greater
or less number of teeth in the path of movement of the pawl e so that whilst the
throw of the eccentric is constant the ratchet wheel is unacted on during a greater
or less portion of the travel of the pawl. The segment may be fixed in any
desired position by means of a clamping nut and stud carried in a fixed
bracket j¹.
Having now particularly described and ascertained the nature of our said
invention, and in what manner the same is to be performed, we declare that what
we claim is :-
1. The combination of parts constituting the improved chain grate stoker, sub-
stantially as described with reference to the drawing annexed.
2. The combination with a chain grate stoker of a lifting door operated by a
screwed spindle and hand wheel to adjust the depth of fuel on the grate, said
lifting door being capable of being turned outwards like an ordinary fire door,
substantially as described.
3. The combination with a chain grate stoker of a feed regulating device con-
sisting of a worm (h) gearing with a worm-wheel (g) on a sprocket wheel shaft (d)
a ratchet wheel (k) keyed on the worm spindle (i) and actuated by a pawl (e)
carried on a bell crank lever (f); a link (1) connected to said bell crank lever (f)

page_text: and a pivoted arm (m) to a slot in which the other end of the link (1) is adjustably
connected to regulate the extent of travel of the pawl (e), substantially as
described.
.
4. The combination with a chain grate stoker of a feed regulating device con-
sisting of a worm (h) gearing with a worm wheel (g) on the sprocket wheel
shaft (d) a ratchet wheel (k) keyed on the worm spindle (i) and actuated by a
pawl (e) carried on a bell crank lever (f), a slotted segment (¹) centred loosely
on the worm spindle (i) and carrying a shield (m) adapted to cover a greater or
less number of teeth in the path of travel of the pawl (e), substantially as
described.
5. The combination with a chain grate stoker of a pivoted door situated over
the ash pit and adapted to normally prevent ingress of air behind the stoker and
to be periodically opened to discharge clinker and ash into the pit below, sub-
stantially as described.
บ
WALLACE FAIRWEATHER,
Of the Firm of Cruikshank & Fairweather, Chartered Patent Agents,
62, Saint Vincent Street, Glasgow, Agent for the Applicants.