Note: Descriptions are shown in the official language in which they were submitted.
" ~06438~
This invention relates to a burner.
Although the burner of the present invention is
suitable for use in a number of different furnaces, it
will be described for illustrative purposes embodied in
a launder, such as one used to convey molten brass from
a melting furnace to a holding furnace and automatic
casting machine.
Known launders conventionally use a plurality of
gun type burners which shoot a high velocity flame onto
the surface of the flowing molten metal. These burners
not only consume relatively large quantities of fuel, but
also, because of the direct impingement of the flame upon
the surface of the molten metal, cause the latter to oxidiæe
and/or constituents of an alloy to be burned out. Further-
more, this direct impingement causes erosion of the
refractory lining, which results in pockets being formed
therein in which pools of molten metal collect at the end
of a run, the metal in these pools being further oxidized
and/or burned by the flames so that they contaminate the
next run. In addition, most launders are so constructed
that they must be run twenty-four hours a day because it
would take too long to bring them up to temperature at the
beginning of a day.
According to the present invention there is provided
a burner including housing means de~ining an enalosure
having an open ~ace, wall means closing the open face and
defining a plenum in the housing means. Inlet means is
provided for placing the plenum in communication with a
supply of gaseous fuel with means defining an elongated
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106~384
slot through the wall means. An elongated strip of
porous refractory is disposed in the slot, the strip
being of sufficient porosity to permit fuel to pass
from the plenum through the strip. The strip has an
elongated hot face and an oppositely disposed elongated
cold face, both the faces being narrower than the thick-
ness of the strip in the direction of the fuel flow
therethrough.
The burner of the present invention has as its
~ 10 object overcoming the above-described disadvantages of
- known burners, in launders as well as other furnaces
which suffer from the same problems. By utilizing a
relatively narrow strip of porous refractory material
which breaks the flame up into a large number of
relatively small low-velocity flames which are spread
over a strip of finite width which extends for sub-
stantially the full extent of the combustion chamber in
at least one direction, the heat is very evently dis-
tributed. Because of the reduced velocity there is no
undesirable
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in~pinGemcnt of thc fl~rmc dtrcctly on the molten mctal, ~nd furthcrmorc
the heat of combustion is retaincd in the furnacc for a longcr timc than
with high velocity ~un type burners (which forcc a great deal of heat up
the stack), thus perml~ting the heated material to absorb more of the
- 5 heat generatcd by a unit of fuel, whercby thermal efficiency is
increased and fuel consumption reduced. The present invention has as
a further object the provision of an improved launder construction, and
one which can be turned off at night, thus reducing fuel consumption,
fire hazard, insurance rates and the like. ~
Another object of the present invention resides in the provi~ion
of an improved burner which itself receives maximized cooling, by
having a ininimum of surface area exposed to the radiant and convective
heat in the combustion chamber, thus improving reliability and life.
A related object concerns the provision of æuch a burner which has a
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15 relatively large dimension in the direction of fuel flow, whereby flash
backs are prevented and thorough fuel/air mixing is insured.
Another object of the ,~resent invention resides in the provision
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of an improved porous refractory type burner which does not require
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special surface treatment to increase the reflectivity and reduce the
20 heat absorption qualities thereof, thus facilitating cooling and reducing
the production of infra red radlation.
Another object of the present invention resides in the provision
of a furnace having a minimum surface area in the combustion chamber,
whereby the degree of heating by convection is increased and amount of
~5 radiation is reduced, whereby thermal efficiency is improved.
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~64384
Anothcr objcct of thc prcscnt inventlon residcs In the provislon
of a furnace which docs not require the use of cxcess air for solely
cooling purposes.
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BRIEF DESCRIPrION OF THE DR~,VINGS
Figure 1 is a transverse scctional vicw through a launder
embodying the principles of the present invention; and
Figure 2 is a fragmentary sectional view taken along line `
2 - 2 in Figure 1.
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DETAILED DESCRIPTION OF THE PREFE~RED EMBODIMENT
Although the burner in the furnace of the present invention
;; may be adapted for use in a number of different furnace environments, ` .
~; it iB shown herein for illustrative purposes in the form of a launder
of the type used for conveying molten metal from a melting furnace
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to a holding furnace and/or casting machine. Generally speaking, the
launder is of elongated construction consisting, in simplest terms,
~-~ merely of a heated trough for conveying the molten metal between the
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desired stations. Since launders are convesitionally of substantially .
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uniform cross-section only a single transverse cross-section i5 illustrated
in the drawings. ` ~:
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With reference to ~igure 1, the launder comprises a stcel
casing 10 having side walls 12 and a bottom wall 14. Disposed within
the open mouth of casing 10 is a launder liner 16 defining an upwardly
open trough 18 which is normally longitudinally inclined to convey the
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moltcn liquid metal, indicated in phantom at 20, longitudlnally from
one end to thc other. Liner 16 is formed of a conventional materlal,
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~0643~34
8uch a9 a rclat~vely dcnse rcfractory mntcrinl te.g. in the order ot 180
pounds per cubic foot). Dlsposcd betwcen liner 16 and casing 101~
in9ulation material 17, such as a relativcly light weight refractory
in9ulation (e. g. in the order of ninety pounds per cubic foot), which
5 serves to thermally insulate the liner from the atmosphere.
Longitudinally extending reinforcing and framing elements 22 may be
provided. Casing 10 may be provided along one side with longitudinally
spaced transversely e~tending projections 24 having openings 26 therein
which serve as lifting lugs, and on the opposite side a plurality of
10 spaced projections 28 having pivotal elements 30 which serve to
pivotally support the laun~er cover, indicated generally at 32. - -
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Cover 32 comprises longitudinally extending side structural
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elements 34, which may be in the form of channel irons as shown,
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between which is positioned a body 36 of relatively dense refractory
15 material, similar to that of liner 16. Body 36 Is provided with a
centrally disposed ~ngitudinally exter.ding slot deffned by upwardly
cbnverging surfaces 38 which define at the upper surface of the cover
an elongated longitudinally extending slot 40. The upper surface of the
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launder liner is complementary to the lower surface of the cover so
20 that when the cover is in place, a9 illustrated in Figure 1, the combu9-
tion chamber i9 defined by ~urface9 38 and the walls of trough 18.
Cover 32 is also provided on one side with a plurality of longitudinally
8pnced projections 42 having openings 44 therein which serve as lifting
lUg8, and on the opposite side with a plurality of projections 46 having
25 lifting lug openings 48 and hinge openings 50 cooperatable with element9
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10643~
30 to providc a hinglng action for opening thc launder cover.
~ ffixed to the top of cover 32 i9 the burner asserr~ly of the
present invention, indicated generally at 52. Burner assembly 52
comprises longitudinally extending side casing elements or members
5 54, which may be channel elements as shown, to which are affixed a
plurality of longitudinally spaced transversely extending ribs 56 which
are attached by means of structural elements 58 to a pair of corres-
ponding elements 60 extending longitudinally along the upper edges of
- cover 32, as by means of threaded fasteners 62. If dcsired, suitable
10 s~acers 64 may be disposed therebetween. D~sposed along the top of
casing members 54 is a top plate 66 which is sealed with respect to
members 54 by means of an insulating gasket 68. Conventional threaded
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fasteners 70 may be used to hold the assembly together.
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~ Disposed between members 54 is a body 72 of relatively light
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15 weight insulating meterial, such as insulation 17, having a longitudinally
extending vertical slot 74 therethrough. The upper surface of body 72
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, i8 spaced from top plate 70 to .. efine a plenum chamber 76 into which
a gaseous fuel/air mixture is forced in the conventional manner by mean~
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of a supply pipe 78. Natural gas, manufactured gas, or the like, may be
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20 used as fuels and are mixed with the proper amount Or air in the usual
manner prior to reaching supply pipe 7û. The lower surface of body
72 is substantially nush with members 54 and compressively engages
a sealing and irisulating gasket 80 which is sealingly disposed between
the burner and launder cover. Gasket 80 may be formed of a fiberous
25 material such as diatomacious silica, and is provided therethrough
,~ with a longitudinally extendin~ slot 82 so positioncd as to placc the
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lowcr end of slot 7~ in communicat~on with slot ~0 and the combustion
chamber. ~ '
The burner itself, indicated at 84. i9 in the form of an
elongated strip of .substantially uniform cross-section and is disposed
S within and extends for the full longitudinal extent of slot 74. Burner
- 84 is tapered in cross-section as carl be scen in Figure 1, in order to
prevent itq dropping into the furnace in the event of shrinkage at high
heats. Because of its tapered shape it not only is prevented from
dropping out of place but is also maintained always in sealing engage-
ment with body 72. As can be seen in Figure 2, although slot 74
- extends substantially the full longitudinal extent of the launder, there
may be interruptions therein, as at 86, in order to provide sufficient
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strength. In any case, each o the burners should extend for the full ;;
longitudinal and transverse e~ tent of each of the slots in which it i9
1~ disposed. As can be visuali~ed, the fuel will burn in a large number
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of relatively low-velocity flames extendin~ downwardly from the
bottom face of burner 84. ' . ;;
The ourner may be formed of any appropriate porous refractory
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`, material, of which a number are well known, the improvement residing
,; 20 more in the shape of the burner. These materials may comprise fire-
- clay and sawdust with the latter burned out, coarse grains Or refractory
cemented together, sintered or fused refractory materials, or the like.
The most important criteria in determining the shape of theburner strip
; is its capacity to be maintained sufficiently cool that the fucl passing
25 theretllrough will not be heated to its flash point.
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10~438~ .
The shapc oî thc burncr of thc prcsent invcntion is arrived at
by strilcing a balancc betwcen a numbcr of parameters. Firstly, the-
burner should extend for substantially the full length of the combu~tion
chambcr in order to provide even heat throughout the longitudinal
5 extent thereof. Secondly, the burner should be of the smallest possible
transverse width capable of passing the quantity of fuel required for
operation of the furnace, which is established by known criteria. If
the burner is made too wide, insufficient cooling ~vill result because
it is the fuel/air mixture ~which is cold relative to the temperature of
10 the interior of the furnace) which provides the primary cooling function,
Thus, if the burner was unnecessarily wide the amount of gas passing
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through each unit area would be less than that necessary for the ;`
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cooling desired. Thirdly, the burner should be sufficiently thick in
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the direction of gas flow to prevent flame flash back and to provide a `
15 thorough miæing of the fuel and air, the latter being accomplished by
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the relatively long, tortuous path through which each fuel and alr
molecule must flow as they traverse through the interior of the porous
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refractory constituting the-burner. The porous refractory is also
preferably of uniform density and porosity throughout its thickness.
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20 It has been found in practice that the burner should be at least 3-1/2
inches thick in the direction Or ~as flow. Fourthly, the total effective
area of the passageways through the porous refractory of the burner
should be at least as great a~ the cross-sectional area of the gas supply
pipe' and preferably in the ordcr of 150% thcreof. If the area of the
25 burner openings i9 less than the area of the ~upply pipe than the Inlet
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i()~4384
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eas will tend to stagnate, causing a substantial rcduction ln the cooling
effcct crcated thereby, e~pecially along the top of the burner. On the
other hand, if the area of the burner i9 too large (i. e. substantially
greater than 150~o of that of the supply pipe~ then there will be insufficient
5 gas flow to provide the necessary cooling.
The shape of the combustion chamber and the positioning of the
burner also contribute to the cooling of the latter. Note that the burner
is disposed wholly outside of the furnace, i. e. above the top of the rover
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in the case of a launder, as far away from the intense heat in the
10 combustion chamber as is possible without actually enlarging the
combustion chamber. Furthermore, the hot face of the burner, i. e.
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the lower surface as seen in Figure 1, is exposed to the combustion
chamber solely through the slots 40 and 82 which are only slightly
wider than the hot face of the burner itself, thus exposing a minimum
15 amount of the burner to the intense heat within the combustion chamber.
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~-- Tapered surfaces 38 contribute greatly to accomplish this. Mounting
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the burnerwholly outside of the furnace permits ambient air to circulate
all around it to assist in cooling. ln extreme cases, if desired, a
water jacket may also be provided around the steel casing for the
20 burner in order to further cool the same to insure that the fuel passing
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, therethrough does not reach it9 flash po~nt, i. e. the poiltt at which it
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breaks up into its constituents and no longer acts as a fuel.
By way of example, the present invention has been embodied in
a launder for conveying molten brass from a melting furnace to a
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25 casting n~achine. The launder had a cross-sectional confi~uration
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106438~
substantial~y thc ~ame as that shown In Figurc 1 nnd was in the order
of six feet long. Each of the burners 84 was approximately 3/4 of an
inch wide at the hot face, one inch wide at the upper face and was
approximately one foot long, three such burners being arranged in
5 end-to-end equally spaced re~ationship for substantially the full length
of the launder. The hot face of the burner was therefore approximately
27 square inches in total area. The radius of trough 18 of the launder
was approximately two inches and the scale substantially that of Figure
1. It has been found that any type of "grog" can be used to form the
10 p-rous reîractory for the burner,providing the flnes are sifted out and
; the coarser grains are crushed to pass through a seive of suitable size;
In the example actually constructed the grog used was "Hyal" insulating
refractory material manufactured by Quigley Company, New York, New
York, which had a composition as follows~
Alumina (Al203)62. 58%
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Silica (Si02) 30. 75 , :
Iron Oxide (Fez03) . 8
: Calcium Oxide (CaO) 3.92
Magnesium Oxide (MgO) . l9
Titanium Oxide (Ti02) . 75
Impurities 1. 01
This material was crushed until it would pass through a seive of 6-mesh
having 0. 035 wire. The material that pa~sed through this scive was then
passed ovcr a 16-mesh screen having 0. 018 wir~. to sift out the fines and
25 flour. The remaining graded granular material was then covcred with
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106438~ ` ,
hot water, which permeated the particles, and was then drained off.
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To this hot, moist, gravelly matter there was then added caleium-
aluminate cement, 25% by volume. After a thorough mising the
mixture was placed in a steel mold the shape of the desired burner
5 and then cured for 24 hours at 100F. It was then placed in a firing
kiln where the block was brought up to a temperature of about 2000F.
to complete curing. It was then assembled to the burner assembly by
simply setting it in position and then pouring the surrounding refractory,
indicated at 72, around it. This burner and launder was found to give
10 very satisfactory results with molten brass (2250-2350F. ) using 25~
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cubic feet per hour of natural gas and 2500 cubic feet per hour of air mixed
r
together and supplied at standard pressure through a two-inch supply pipe.
. Insulation 17 permits liner 16 to retain a substantial degree of ` -
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the heat which it soaks up during operatior~ of the launder, as a eonsequenee
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15 of which it has been found feasible to turn the burner off at night. It has
been diseovered that after an overnight shut-down the launder can be
- brought baelc up to temperature in less than an hour. This is, of course, -
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very beneficial from the standpoint of reducing the cost of fuel, insurance,
and the like. 5; ' '";, ' `, '~ ''`,'' ' ' . `,' _ .
~ Bécause heating by eonveetion is more effieient than heating ;~ `
by mere radiatio~i, sueh a9 the infra red radiatlon utilizod in eonveetlon
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luminous wall type furnaees, it is desired that in furnaees embodying
the-present invention the surfaee area of the eombustion be redueed to
a minimum. This effeetively reduees the amount of radiat~on and
.s
~ 25 inereases thermal effieieney. The furnaee of the present invention i8
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~0643~4
al90 distingui3habtc from a convcntional luminous wall furnace~ (3uch
as those illustrated in U. S. patent Nos. 2, 828. 813 and 1, 225, 381)
because the present furnace does not require extra air solely for
cooling, which i9 not only c~pensive but which also oxidizes the hot
5 metal being heated in the furnace. Furthermore, a~ noted, the burner
of the present invention is relatively narrow and preferably is of a
minimum width, which is exactly the opposite of that sought in luminous
wall furnaces where heating on all walls and maximum size combustion
chambers are sought in order to increase radiation. Furthermore,
10 the present furnace does not require any special reflective surfaces .:
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on the burner walls in order to reduce heat absorption and increase ~ ~-
reflectivity and radiation. In addition, the present burner does not
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require numerous relatively large holes extending from the outslde
~urface of the porous refractory to adjacent the hot surface ir. order
15 to get proper fuel flow. As can thus be seen, the burner and furnace
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o$ the presert invention utilize an elongated relatively narrow strip
consisting of a myriad of small flames of relatively low velocity, with
the result that there is no direct impingement of the flames upon the
molten metal being heated, and an even distribution of heat is obtained
20 throughout the length of the furnace with a relatively long dwell time of
the heated combustion products in the furnace to facilitate the maximum
o~ heat transmission t~ the metsl being heated per unit of fuel consumed
and thereby increase efficiency, If the prescnt invention i8 embodied
in a crucible melting furnace then the same general principle~ apply,
25 In such a furnace, in which the combustlon chamber is normally
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dlsposed extcriorly of thc cruciblc, the burncr would consist of a
relativcly narrow annular strip of porous refractory extending
around thc circumference of the outside furnace wall, the shape of
such burner being deterrnined in the same manner a~ with respect to
5 the launder herein described. In both cases the burner extends for
substantially the full extent of the combustion chamber in at least
one direction. Furthermore, the porous refractory of which the burner
is composed may be formed in a number of different manners. For
example, it may be formed by casting a ceramic material around a
10 large number of small rod-like ele nents which would thereafter be
removed from the refractory to create a plurality of corresponding
openings, or in some cases a large number of very small holes could
be drilled in a refractory material to give the same result.
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Thus, there is disclosed in the above description and the
15 drawing an embodiment of the invention which fully and
effectively accomplishes the objects thereof. Howevér, it will
be apparent that other variations in the details of the construction
; may be indulged in without departing from the scope of the invention
herein described or 'he sco7e o~ the appellded claims.
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