Improvements in Mechanical Stokers.
Year: 1897

page_text: Improvements in Mechanical Stokers.
We, FRITZ FRANZ MAIER, of IX, Eisengasse, 16, Engineer, and SIGMUND KANITZ,
II, Nordbahustrasse, 44, Merchant, both of Vienna, in the Empire of Austria, do
hereby declare the nature of this invention to be as follows:-
This invention relates to improvements in connection with the well known Dobbs
furnace in which the feeding forward of the fuel, the clearing of the firegrate and
the removal of clinkers and ashes therefrom are effected by means of a movable
sliding grate in conjunction with a fixed step grate provided with cooling means.
These furnaces have many and serious defects which interfere with their good
working and which form disturbing elements generally.
"
The defects consist mainly in that the fixed step grate bars are so constructed
that all the grate openings are closed by the rising of the sliding grate and thus
prevent the entry of air;—that the cooling passages are too far removed from the
surfaces to be cooled and thus through the unfavorable circulation of the cooling
medium, cause a defective system of cooling; further in consequence of the great
quantity of material, required in the construction of the parts forming the "Dobbs
furnace the apparatus is rendered clumsy while at the same time the free surface
of the fire grate is greatly reduced, thereby causing a heat conducting surface which
greatly interferes with the air currents passing through the open spaces of the grate.
The improvements for obviating the above defects and for rendering such furnaces
really smokeless must therefore aim
(a) At an arrangement of step grate and its supporting frame relatively to the
sliding grate in which the air passages between the two remain open in every
position of the latter,
(b) At rendering the action of the cooling medium in the frame most effective;
and
(c) At arranging the cooling passages in the step grate as near as possible to the
surface of combustion.
Improvements have also been introduced for moving the sliding grate and in the
means for supplying and distributing the combustible material evenly over the whole
firegrate and finally for enabling the parts of both the step and the sliding grate to
be easily renewed.
The accompanying drawings illustrate several furnaces provided with the above
improvements: Fig. 1, is a vertical longitudinal section of a furnace constructed
according to this invention.
Figure 2 is a plan of the same.
Figure 3 is a side elevation of the grate, and
Figs. 4 and 5 are two cross sections taken on different vertical planes..
Fig. 6 is a vertical longitudinal section of a modified construction of furnace.
Fig. 7 is a vertical cross section of the same.
Figures 8 and 9 represent one of the sliding bars of the movable grate in two
external views and in two cross sections.

page_text: Figures 10 and 11 show a longitudinal and a cross section respectively of a
furnace built of bricks or masonry.
are the hollow bars of the fixed or step grate. bare the sliding bars of the
movable grate which are arranged between the former in such a manner as to effect
at one and the same time the feeding forward of the fuel as well as the clearing of
the grate and the removal therefrom of the ashes and clinkers.
The main support of the fire grate is in the form of a frame having in both its
longitudinal branches A passages serving as inlet and outlet to the cooling medium,
which latter, may be water, air, or air mixed with atomized water. These two
longitudinal branches are connected together by the hollow step bars a
The latter
are provided with ribs a¹ and with an asbestos packing ring, at each end and are
screwed to the branches A in such manner as to enable each single bar to be taken
out when required for renewal without having to take the whole grate out or even
without having to dismount any other parts whatever.
The hollow step bars a are of comparatively small cross section so as to leave
large openings between them for the passage of air from the ash pit for combustion.
Further these bars are arranged parallel with the slides 6 of the movable grate and
so that said slides, even in their most outward position only reach with their split
ends into the spaces between the hollow bars and thus never block out the air.
This arrangement enables the section of the iron in the grate to be reduced to a
minimum so that the cooling of the same will be more easily effected inasmuch as
by these means a more advantageous proportion exists between the cooling surface
and the mass to be cooled while at the same time it becomes possible to provide cooling
passages a² in the grate bars and thus cool the whole surface where combustion
takes place.
In consequence of this arrangement the sliding bars 6 are now cooled by the cold
air from below as well as by the artificial cooling means of the step bars at the
upper end which latter are also cooled by the air passing through the passages
between them.
The cooling medium which may be water or air, or air mixed with atomized water,
is conducted through a pipe c into the rear and lowest end of one of the longitudinal
branches A of the frame. These hollow longitudinal branches are provided with
cross partitions d, so as to cause the cooling medium to pass from the one
longitudinal branch through the passage a² of one of the step-bars (or if desired
through several bars) into the opposite longitudinal branch A, from here again
through the next following group of step bars back into the first longitudinal branch
and thus pass in the same zigzag current through the whole frame and out through
the pipe c¹ back into the reservoir from which it had been drawn off.
The cooling medium is caused to flow in the opposite direction to the draught
in the furnace, and thus the coolest portion of it is brought into contact with the
hottest part of the grate which it naturally cools more or less according to the
difference in temperature in the two.
With the absorption of heat and consequent dilatation of the cooling medium the
rising tendency of the latter is increased which causes a rapid passage of the cooling
medium from the reservoir through all the parts of the fire grate and thereby cools
effectually even the less heated front bars of the grate.
The inclined sliding bars f of the moveable grate are guided between guide bars
on the longitudinal branches A and are supported by quadrants mounted on
shafts 2 and provided at their sides with toothed sectors f3 adapted to engage
with the teeth of bars f and thus cause the sliding of the grate b. A counter-
weight fis employed whereby but little power is required to move the sliding bars.
The hollow longitudinal branches A of the frame are adapted to fit the circular
form of furnace walls where such exist as shown at Figures 4 and 7. For boilers
with vertical furnace walls, see Figures 10 and 11, the longitudinal branches A are
of rectangular section.
In 'corrugated furnace tubes Figs. 4 and.7 the spaces between the corrugated

page_text: walls and the branches A require to be filled in so as not to interfere with the work-
ing of the furnace. These spaces are closed by side flanges which may be
arranged on a level with the upper surface of the longitudinal branches A
Figs. 1 and 4.
It is however more advantageous to arrange these flanges at an incline and so as
to cause them to be above the upper edges of the step bars a and of the sliding
bars as shown in Fig. 7.
These flanges may as shown at Figs. 6 and 7 be provided with rectangular open-
ings so as to cause an even combustion over the whole of the grate.
The step bars a in the arrangements represented at Figs. 1 to 7 are connected
to the side branches A by two screw bolts & see Figs. 6 and 7 whilst only one such
screw bolt s¹ is required in the arrangement represented at Figs. 10 and 11.
These screws are easily removed when required for the purpose of removing and
renewing one of the step bars.
The quadrant pieces flat the front and rear or in some instances those at the front
only are rounded at the front part f5 (Figs. 9 and 10) so as to enable them to be
moved from the position shown in full lines to that shown in dotted lines and thus
enabling the sliding bars to be removed and also the screws s to be loosened by a
suitable spanner.
The sliding bars b of the moveable grate in the furnace shown at Figs. and 2
are provided with rectangular openings as well as with slots at the front edge. In
some instances however they may only have the first mentioned openings and the
edges surrounding these openings be extended laterally so as to prevent the sliding
bars from becoming warped by the heat.
The fuel is supplied to the furnace from a hopper g arranged in front of the boiler
and provided with an inclined bottom plate g¹. This bottom plate is adjustable by
means of a weighted arm g². A balanced vertical plate at the rear of the hopper
together with the plate g¹ enables the supply of combustible material to be regulated
according to the advancing movement of the same on the furnace grate.
manner of adjustment enables all sorts of solid fuel to be employed such as wood
shavings, wood-dust and cuttings, coal in its different forms, viz. dust, rubble,
nuts, and cobbles as well as coke and peat.
The
The ashes and clinkers are removed and thrown into the ashpit by means of a
sliding plate adapted to be moved by a lever 12 against the inclined edge h¹ at the
lower part of the fire bridge where the accumulated ashes are caused to fall down
into the pit by simply sliding the plate h inward.
· Dated this 24th day of Mar 1807
HARRIS & MILLS,
23, Southampton Buildings, London, W.C., Agents.
We, FRITZ FRANZ MAIER, of IX, Eisengasse, 16, Engineer, and SIGMUND KANITZ,
of II, Nordbahnstrasse, 44, Merchant, both of Vienna, in the Empire of Austria, 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 improvements in connection with the well known Dobbs
furnace in which the feeding forward of the fuel, the clearing of the firegrate and
the removal of the clinkers and ashes therefrom are effected by means of a movable
sliding grate in conjunction with as fixed step-grate provided with cooling means,

page_text: These furnaces have many and serious defects which interfere with their good.
working and which form disturbing elements generally.
The defects consist mainly in that the fixed step grate bars are so constructed
that all the grate openings are closed by the rising of the sliding grate and thus
prevent the entry of air; that the cooling passages are too far removed from the
surfaces to be cooled and thus through the unfavorable circulation of the cooling
medium, cause a defective system of cooling; further in consequence of the great
quantity of material required in the construction of the parts forming the Dobbs
furnace the apparatus is rendered clumsy whilst at the same time the total area of
openings of the fire grate is uselessly reduced, and the increased heat conducting
surface greatly interferes with the air currents passing through the open spaces
of the grate.
The improvements for obviating the above defects and for rendering such furnaces
really smokeless must therefore aim, (a) at an arrangement of step grate and its
supporting frame relatively to the sliding grate, in which the air passages between
the bars of the step-grate possess in every position of the sliding grate, a relatively
larger cross sectional area; (b) at rendering the action of the cooling medium in
the frame most effective; and (c) at arranging the cooling passages in the step
grate as near as possible to the surface of combustion.
Improvements have also been introduced in the device for moving the sliding
grate in the feeding device and in the means for obtaining a uniform combustion
of the fuel throughout the entire width of the firegrate and finally for enabling the
parts of both the step and the sliding grates to be easily renewed and exchanged.
The drawings accompanying my Provisional Specification and the accompanying
drawing illustrate several furnaces provided with the above improvements, Fig. 1
is a vertical longitudinal section of a furnace constructed according to this invention
and provided with the improved charging device, Fig. 1 is a modification of the
charging device, Fig. 2 is a plan of the furnace, Fig. 3 is a side elevation of the
grate, and Figs. 4 and 5 are two cross sections taken on different vertical planes,
Fig. 6 is a vertical longitudinal section of a modified construction of furnace, Fig.
is a vertical cross section of the same, Figs. 8 and 9 represent one of the sliding bars
of the movable grate in two external views and in two cross sections.
Figures 10 and 11 show a longitudinal and a cross section respectively of a
furnace built of bricks or masonry.
a are the hollow bars of the fixed or step grate, b are the sliding bars of the
movable grate which are arranged between the former in such a manner as to effect
at one and the same time the feeding forward of the fuel as well as the clearing of
the grate and the removal therefrom of the ashes and clinkers.
The main support of the fire grate possesses the form of a frame having in both its
longitudinal branches A passages serving as inlet and outlet to the cooling medium,
which latter may be water, air, or air mixed with atomized water. These two
longitudinal branches are connected together by the hollow step bars a. The latter
are provided with ribs a¹ and with an asbestos packing ring, at each end and are
screwed to the branches A in such manner as to enable each single bar to be taken
out when required for renewal without having to take the whole grate out or even
without having to dismount any other parts whatever.
The hollow step bars a are of comparatively small cross section so as to leave
large openings between them for the passage of air from the ash pit for combustion.
Further these bars are arranged parallel with the bars or slides of the movable
grate and so that said slides, even in their most outward position only reach with
their recessed portions into the spaces between the hollow bars and thus never block
out the air.
This arrangement enables the section of the iron in the grate to be reduced to a
minimum so that the cooling of the same will be more easily effected inasmuch as
at a constant combustion surface a favorable relation between the cooling area and
the iron mass to be cooled is realized while at the same time it becomes possible to
provide cooling passages a² in the grate bars and therefore nearer to the fire.

page_text: In consequence of this arrangement the sliding bars b are now protected against
excessive heating by being cooled from below by the cold air and at the upper parts
by the artificial cooling means of the step bars, which latter are also efficaciously
cooled by the air passing unhindered through the recesses of the sliding bars b.
The cooling medium which may be water or air, or air mixed with atomized water,
is conducted through a pipe c into the rear and lowest end of one of the longitudinal
branches A of the frame. These hollow longitudinal branches are provided with
cross partitions d, so as to cause the cooling medium to pass from the one
longitudinal branch through the passage a² of one of the step bars (or if desired
through several bars) into the opposite longitudinal branch A, from here again
through the next following group of step bars back into the first longitudinal branch
and thus pass in the same zigzag current through the whole frame and out through.
the pipe c back into the reservoir from which it had been drawn off.
The cooling medium is caused to flow in a direction opposite to the draught
in the furnace, and thus the coolest portion of it is brought into contact with the
hottest part of the grate which it naturally cools more or less according to the
difference in temperature in the two.
With the absorption of heat and consequent dilatation of the cooling medium the
rising tendency of the latter is increased which causes a rapid passage of the cooling
medium from the reservoir through all the parts of the fire grate and thereby cools
effectually even the less heated front bars of the grate.
The supporting bars f of the movable grate having a to and fro sliding motion
and at the same time an up and down motion are guided between guide bars on the
longitudinal branches A. and are supported by quadrants f¹ mounted on shaft f³
and provided at their peripheries with toothed sectors f³ adapted to engage with
the teeth of the bars f and thus cause the motion of the grate b. When the sliding
grate is in its lowest position it will be balanced by a counter-weight f* whereby,
but little power is required to move the sliding bars.
The hollow longitudinal branches A of the frame are adapted to fit with their
exterior walls the circular form of the furnace walls where such exist as shown
at Figures 4 and 7.
For boilers with vertical furnace walls, see Figures 10 and 11, the longitudinal
branches A are of rectangular section.
In corrugated furnace tubes Figures 4 and 7 the spaces between the corrugated
walls and the branches A require to be filled in, so as not to impair the effectual
working of the furnace.
These spaces are closed by side flanges a* which are entirely of solid material and
may be arranged on a level with the upper surface of the longitudinal branches A,
Figures 1 and 4.
It is however more advantageous to arrange these flanges at an incline and so as
to surpass in height the upper edges of the step bars a and of the sliding bars b
as shown in Fig. 7.
These flanges may as shown at Figures 6 and 7 be provided with openings so as
to cause an even combustion over the whole width of the grate.
The step bars a in the arrangements represented at Figures 1 to 7 are connected
to the side branches A by two screw bolts s¹, see Figures 6 and 7, whilst only one
such screw bolt s¹ is required in the arrangement represented at Figures 10 and 11.
These screws are easily removed when required for the purpose of removing and
renewing one of the step bars.
The quadrant pieces f¹ at the front and rear or in some instances those at the front
only are rounded at the front part f5 (Figs. 6 and 10) so as to enable them to be
moved from the position shown in full lines to that shown in dotted lines and thus
enabling the sliding bars to be removed and also the screws s¹ to be loosened by a
suitable spanner.
The sliding bars 6 of the movable grate in the furnace shown at Figures 1 and 2
are provided with rectangular openings as well as with recesses at the front edge.

page_text: In some instances however they may only have the first mentioned openings and the
edges surrounding these openings be of an increased height, in comparison with the
bottom parts of these bars (see Figs. 6 and 9) so as to prevent the sliding, bars from
becoming warped by the heat.
.
540
The fuel is supplied to the furnace by a hopper g arranged in front of the boiler
above the grate. According to the arrangement shown in Fig. 1, this hopper is
provided with bottom gl inclined towards the rear..
3..
!!.
5. This bottom is adjustable by means of a weighted bell crank lever g² the short
arm of which is connected to said bottom. A balanced vertical plate 93 at the
rear of the hopper together with the bottom g¹ enables the supply of combustible
material to be. regulated according to the advancing movement of the same on the
furnace grate.
1.
:
The movable and adjustable bottom g₁ of the hopper 9 can also be arranged
horizontally, as shown in Fig. 1. In this case, instead of the weighted lever an
oscillating slitted: lever g is provided, connected on one side, with the bottom gland
on the other side with the adjusting lever 95. Any motion given to the lever.95
results in a movement of the bottom g¹, whereby the feeding aperture and. conse-
quently also the supply of the fuel is regulated to any desired extent. . I H
The described manner of adjustment of the feeding aperture within very large
limits enables all sorts of solid fuel to be employed such as wood shavings, wood
dust and cuttings, coal in its different forms viz:: dust, rubble; nuts and cobbles as
well as coke and peat.
!
The ashes and clinkers are removed and thrown into the ashpit by means of a
sliding plate h.adapted to be moved by a lever he against the inclined edge. hat.the
lower part of the fire bridge where the accumulated ashes are, caused to fall down
into the pit by simply sliding the plate h inward......
'
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. In furnaces comprising a fixed step-grate and a movable sliding grate the
arrangement of the hollow bars a of the step grate, each of the said bars being com-
posed of a tube a provided with ribs a and being in all. parts parallel to the
slides b. movably arranged between the same, whereby the possibility is afforded
to give the said steps or bars of the fixed grate the smallest possible cross section
whilst the slides of the movable grate can receive the greatest possible cross section,
and in every position of the latter a uniform quantity of air is allowed to pass
between the steps, substantially as and for the purpose set forth.
2. In furnaces comprising a fixed step grate and a movable sliding grate, a grate
support composed of two longitudinal tubes A divided into compartments by the
partitions d and of the grate-steps a, said grate support receiving the cooling medium
which is introduced into the support at that end of the same which is submitted to
the highest degree of heat, whence the cooling medium is caused to flow in a
direction opposite to that of the draught of the fire in the furnace, alternately from
one longitudinal branch A through a system of cooling passages: a of the step-
bars a into the other longitudinal branch,, and to circulate in a rapid and vigorous
manner, substantially as and for the purpose set forth.
.7
3. In furnaces comprising a fixed step-grate and a movable sliding grate the
arrangement of cooling passages a² in the step-bars a as close as possible to the
fire, for the purpose of obtaining a vigorous cooling of the step-bars themselves as
also of the slides b from above, so that the air which is producing the cooling of the
latter is enabled besides to produce also a cooling action upon the recesses of the
step-bars a, substantially as and for the purpose set forth. :
4. In furnaces comprising a fixed step-grate and a movable sliding grate, a device
for, imparting motion to the sliding grate, said device consisting of quadrants f¹,
arranged to rotate simultaneously with the toothed sectors f, the supporting bars f

page_text: with the slides b resting upon said quadrants f¹ and being kept in suspension by a
counter-weight, substantially as and for the purpose set forth.
5. In furnaces comprising a fixed step-grate and a movable sliding grate, a feeding
arrangement consisting of a charging hopper g, provided with a movable and
adjustable bottom gl and with a rear plate g³ capable of being raised and lowered,
substantially as and for the purpose set forth.
6. In furnaces comprising a fixed step-grate and a movable sliding grate an
arrangement having for its purpose to obtain a uniform combustion of the fuel
throughout the whole width of the fire-grate, this arrangement being characterized
by side flanges a* provided with openings s and arranged laterally of the
longitudinal supporting branches A, the latter being adapted to fit in their shape
the walls of the furnace, substantially as and for the purpose set forth.
7. In furnaces comprising a fixed step-grate and a inovable sliding grate, for the
purpose of obtaining an easy removal and exchange of the separate grate-slides
and grate-steps, the arrangement of the quadrant pieces f¹ provided with rounded
off ends f, said quadrant pieces, when tilted back, permitting the free removal of
the grate-slides b and the unscrewing of the screws a¹ at the grate-steps a, sub-
stantially as and for the purpose set forth.
1-
0 73 1
1000
HARRIS & MILLS,
23, Southampton Buildings, Chancery Lane, London, W.C., Agents.