Improvements in Mechanical Stokers.
Year: 1895

page_text: Date of Application, 2nd Feb., 1895
Complete Specification Left, 31st Oct., 1895-Accepted, 7th Dec., 1895
Improvements in Mechanical Stokers.
I, THOMAS FORKNALL of Blake Street, Leicester, Engineer, do hereby declare
the nature of this invention to be as follows:-
This invention relates to mechanical stokers for steam boiler furnaces and
consists of improvements having for their object (1) to effect a continuous supply
of fuel to the furnace, and (2) to insure an equal distribution of fuel over the
entire surface of the fire.
The fuel is first placed in a hopper from whence it may pass between spiked
rollers or other crushing devices for complete disintegration in the usual
manner.
According to the present invention the fuel thus prepared either falls on or is
delivered to one or more suitably arranged revolving Archimedean screws or their
equivalents which conduct it into one or more boxes or chambers communicating
therewith and in which are located revolving fans which throw the fuel on to
the fire.
In order to insure the fuel being evenly distributed over the surface of the fire,
the fan boxes i.e. the chambers in which the fans revolve are vibrated in such a
manner as to form a deflector to direct the fuel on to the required part of
the fire.
The vibrating fan box when in its lowest position causes the fuel to fall on that
part of the fire nearest the furnace door and as the said fan box gradually rises it
allows the fans to throw the fuel on to other parts of the fire farther away from the
door until the said fan box commences its return movement when the reverse action
takes place.
Dated this 2nd day of February 1905
BOULT & WADE,
Agents for the Applicant.
I, THOMAS FORKNALL, of Blake Street, Leicester, 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 :-
This invention has reference to apparatus technically termed "Mechanical
Stokers" and embodies improvements particularly applicable to the type in which
fans distribute or forcibly eject the fuel over the surface of the furnace.
The improvements constituting the present invention have for their object (1) to
effect a continuous supply of fuel to the fire and (2) to insure an equal distribution
of fuel over the surface of the fire.
For these purposes the invention consists in the employment, as hereinafter more
fully described, of one or more Archimedean screws, spiral blades or equivalents
DO31

page_text: for conducting or delivering the prepared fuel to the fans, and also of one or more
vibrating fan-boxes which are actuated in such a manner as to allow the fans to
deposit the fuel at one time on parts of the fire at increasingly greater distances
from the door and subsequently vice-versa, i.e. at increasingly shorter distances from
the door as hereinafter fully described.
The invention will be clearly understood from the following further description
in reference to the accompanying drawings wherein
Figure 1, is a view showing the application of my invention to a double-flued
boiler, one of the apparatus being illustrated in section and the other in
elevation.
Figure 2, is a horizontal plan on the line A A of Figure 1, also partly in section
and partly in elevation, and
Figure 3, is a vertical section on the line B B of the same figure.
Figure 4, is a detail view (drawn to a larger scale than the preceding figures)
illustrating the mechanism for vibrating the shaft K and mechanism on the latter
for vibrating the fau boxes.
C represents a plate fixed to the ends of the flues D E and carrying the
operative mechanism of the "stoker"; F, are the hoppers into which the fuel is
placed; G, the porcupines or spiked rollers for reducing or disintegrating the fuel
before being delivered to the usual revolving fans H.
These spiked crushing rollers are mounted on a shaft G' which is driven by a
worm wheel G 3, Figs. 1 and 4, actuated by a worm on the bottom of a spindle
located within the casing G 4 and upon the upper end of which spindle is a worm
wheel G 5 operated by a worm G 6 on the end of the shaft G 7 receiving motion
from speed pulleys G 8 and driving band G 9, all of which mechanism is arranged
and operates substantially in the well known manner.
In order to obtain a continuous supply of fuel to the fans H and thus to the
surnace, employ in connection with each fan, an Archimedean screw or its
equivalent which in its preferred form consists of a spiral blade J, Fig. 1, formed
on a sleeve J¹ passed over the shaft G¹ and located in close proximity to the
crushing rollers G so that as the prepared fuel drops into the chamber J 2 it is
conducted by the revolving spiral blade to an opening J 3, Figs. 1 and 3, in the said
chamber whence it passes through a similar opening H 2, Fig. 3, in the fan box H'
communicating therewith and on to the revolving fan H which projects it on to
the furnace.
By means of the spiral blade J revolving within the chamber J 2 as described,
prepared fuel is being continuously fed to the furnace.
In cases where two fans are employed, as illustrated in the drawings, the spiral
blades are preferably arranged right and left hand as shown.
To insure an even distribution of fuel over the surface of the fire as herein before
mentioned I provide for vibrating the fan boxes, the upper part of the mouth of
each of which forms a deflecting plate whose movement determines the position
upon the furnace that the fuel will be deposited.
H' represents the fan boxes loosely mounted on the fan shaft H 6 and within
which the fans revolve.
The upper part of the mouth of each fan box is directed into the furnace and
forms a deflecting plate H 3, Fig. 3, which, as it is raised from or lowered to the
position indicated by the dotted line gradually enlarges or contracts the orifice or
mouth of the fan box so that the fan projects the coal either upon parts of the fire
farther from the door or nearer to it.
When the deflecting plate is in the lowest position, indicated by the said dotted
lines in Figure 3, the fuel projected against it by the fans, drops on to that part of
the fire nearest the furnace door and as the deflector is gradually raised it allows
the fuel to be spread over other parts of the fire farther away from the furnace
door until the said deflecting plate commences to descend when the action is
reversed.
The lower part H 4 of the fan box is loosely pivotted at H 5 so that its own weight

page_text: constantly maintains it in the position shown, thereby enabling the vibration of the
fan box to vary the position of the deflecting plate relatively thereto and thus
increase or decrease the area of the orifice as and for the purpose named.
In some cases however I may make the lower part H4 of the fan box integral
with the latter and movable therewith.
The upper and lower parts H3 and H 4 respectively of the mouth of the fan box
in such case would always occupy the same positions relatively to each other and the
angle of the mouth of the fan box in relation to the surface of the furnace would
determine the position upon the fire that the fuel would be placed.
For example, as the mouth of the fan box rises the fuel will be thrown by the
fans on to parts of the furnace farther and farther away from the door until the
limit of movement is reached, at which time the more nearly the mouth of the fan
box approaches the horizontal position and parallel to the surface of the fire the
further into the fire will the fuel be thrown.
Upon the descent of the mouth of the fan box the faus will throw the fuel upon
the fire in the reverse direction i.e. upon parts thereof gradually nearer the door
until the lowest point is reached, when the more obtuse the angle of the mouth of
the fan box is relatively to the surface of the fire the nearer the furnace door will
the coal be deposited.
Convenient mechanism for vibrating the fan boxes in the manner hereinbefore
described may consist of a shaft K carried in bearings K' attached to the plate C.
This shaft has a rocking or vibrating motion imparted to it by means of a
connecting rod L, Figs. 1, 2 and 4, one end of which is attached to a pin L'
eccentric on the face of the worm wheel G³, the other end being pivotted
between the bifurcated end of a link plate M secured on the shaft by a set
Screw M¹
.
To vibrate the fan boxes a second link plate N, Figures 2, 3 and 4, is fixed by a
set screw on the vibrating shaft K and a connecting rod N¹ is attached between the
forked end of the said link plate and also by a pivot N 2 to the side of one of the fan
boxes, the adjacent fan box being made to partake of the same vibrating motion by
being suitably connected thereto, which, as most clearly illustrated in Figures 1
and 2, may be effected by a sleeve O passed over the fan shaft H 6 intermediate of
the two fan boxes and connected to the latter by screws O' passing through a
flange O2 on each end of the said sleeve.
The speed of the shaft on which the spiral blades are mounted may be regulated
by the speed pulleys H 7 G 8 and driving band G 9.
The invention is not limited to the particular mechanism shown in the drawings
and hereinbefore described for revolving the spiral blades or vibrating the fan boxes
as it is obvious that the said mechanism may be readily altered or varied within the
skill of the mechanic for the purpose named.
The invention is also applicable to mechanical stokers in which other than
revolving fans are employed for throwing fuel on to the furnace and in which fuel
crushing devices other than spiked rollers are used.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed I declare that what
I claim is :-
1. In a mechanical stoker the use or employment of one or more revolving spiral
blades such as J or equivalent for supplying fuel to the fans which feed the said
fuel to the furnace.
2. In a mechanical stoker the combination of fuel crushing devices, one or more
revolving spiral blades or equivalent and fans for projecting the fuel on to the
furnace substantially as described.
3. In a mechanical stoker the combination with fuel crushing devices, and a fan
for throwing fuel on to the fire, of a vibrating fan box for the purpose described.
4. In a mechanical stoker the combination with a fuel crushing device and a fan
for throwing fuel on to the furnace, of a vibrating fan box arranged in such a

page_text: manner that as the. fan box is being raised or. lowered respectively the fan is
thereby enabled to project the fuel upon parts of the fire either increasingly farther
from or increasingly nearer to the furnace door substantially as described.
5. In a mechanical stoker the combination with a fuel crushing device, and fan
for throwing fuel ou to the fire, of a vibrating fan box, the mouth of which may be
alternately enlarged and contracted by the raising or lowering thereof substantially
as and for the purpose described.
6. In a mechanical stoker the combination with a fan for throwing fuel on to the
furnace, of a vibrating fan box the mouth of which consists of a lower part, and an
upper part forming a deflector and movable with the fan box and relatively to the
said lower part substantially as and for the purpose described.
7. In a mechanical stoker the combination of a fuel crushing device, spiral blade,
a fan for throwing fuel on to the furnace and a vibrating fan box substantially as
and for the purpose described.
8. The improved mechanical stoker consisting of the parts constructed, arranged
and operating substantially in the manner and for the purpose described and
illustrated in the accompanying drawings.
Dated this 26th day of Ontahan 1005
Witness―
E. N. LEWIS,
Berridge Street Chambers,
Leicester.
THOMAS FORKNALL.
Boult & Wade,
Agents for the Applicant.