Note: Descriptions are shown in the official language in which they were submitted.
5628
A preheating furnace for elongated material
The invention relates to a preheating furnace for elongated
material, like bars, ingots, billets, and the like of metal,
particularly aluminum or aluminum alloys, comprising a
funace tunnel made of continuous or segmentally joined re-
5 fractory furnace shells, particularly thin-walled furnace
shells, and adapted to be heated by heater elements, like
burners, hot gas nozzles, and ~he like which extend through
the shell walls and are directed toward the material intro--
duced in longitudinal orientation in the furnace tunnel for
10 direct hearing of the same, and further comprising an ex-
haust gas duct disposed in the uppper furnace range.
In a known furnace of this kind (DE-PS 18 07 504) the thin-
walled furnace shells are inserted in the furnace structure
without heat insulation. This causes heat losses especially
15 by radiation from the outside walls of the furnace shells.
The exhaust gas is sucked off into the exhaust gas duct
through a slot in the top of the furnace tunnel. In the
path of the gas between the furnace tunnel and the exhaust
gas duct heat gets lost. For this reason the efficiency of
20 the known furnace is low. Besides, the known structure is
complicated and high because the exhaùst gas duct is arrang-
ed separately above the furnace tunnel.
It is the object of~the invention to design a preheating
furnace of the kind specified initially such that the ener-
25 gy supplied for heating is utilized more effec~ively witha simple and compact structure.
To meet this object it is provided, in accordance with the
invention, in a preheating furnace of the kind specified
initially that the furnace tunnel is integrated in the ex-
30 haust duct which somprises a heat insulation. Preferablythe heat insulation of the exhaust gas duct covers the
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furnace shells of the furnace tunnel from outside at least
in their central range so that the lower areas of the fur-
nace shells remain free for purposes of assembly and main-
tenance n
5 The fact that the invention provides for much better utili-
zation of the energy is due to the circumstance that the
exhaust gas is transferred from the furnace tunnel into the
exhaust gas duct without any heat losses, for instance
through the upper gap bet~een the vertically disposed fur-
10 nace shell halves. By virtue of the design in accordancewith the invention the central and upper portions of the
furnace tunnel are sufficiently well thermally insulated
by the exhaust gas duct itself J i.e. without any additional
measures. Heat insulation of the lower areas of the furnace
lS tunnel has been dispensed with on purpose to provide better
accessibility for assembly work and maintenance. The inven-
tor found out that the losses by heat radiation in the
lower areas of the furnace shells are relatively small.
Leaving out a heat insulation in these lower areas is high-
20 ly advantageous because there remains space for the recep-
tion and accessibility of aggregates, like burners, support-
~ ing frame for the furnace shells, and the conveyor meansfor the material to be preheated.
The insulation members may extend vertically upwardly from
25 the support members or they may adapt to the upper areas
of the furnace shells.
A further development of the invention which is particular-
ly advantageous as regards simple assembly and disassembly,
is characteri~ed in that heat insulation is supported by
30 support members mounted stationarily on a support frame of
the furnace and comprises removable insulation members dis
posed above the same, the lower members thereof affording
lateral support and insulation of the furnace shells.
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According to a preferred embodiment of the invention with
which lower and upper burner rows are provided, distributed
around the circumference of the furnace tunnel, it is pro-
vided that the burners of the upper burner rows extend
5 through removable insulation members, while the burners of
the lower burner rows are located in the lower range of the
furnace shells which is not heat insulated, and that each
insulation member through which burners pass has the same
length as corresponding segments of the furnace shells.
10 If lower burner rows alone are required, another ~urther
development of the -invention provides for all burner rows
to open into the furnace tunnel below the heat insulation,
and the exhaust gas duct to be a removable assembly unit.
This design is especially favorable as regards simple assem-
15 bly, maintenance, or exchange of the furnace shells sincethe exhaust gas duct may be removea as a whole so that the
or individual furnace shells may be replaced easily.
With more modern preheating furnaces of the type described
the hot exhaust gas is passed from the exhaust gas duct in-
20 to a preheating zone of the preheating furnace or anotherfurnace for preheating the material (DE-OS 26 37 646) where-
by especially economic fuel exploitation is guaranteed. In
this context a furnace group is advantageous with which the
exhaust gases of the preheating furnace serve to heat an
25 upstream preheating f~rnace which passes the exhaust gas
through at least one fan to at least one row of slot type
nozzles arranged along the material and directing the ex-
haust gas at the material.
The design according to the invention is particularly ad-
30 vantageous where the furnace space of the preheating fur-
nace is divided into several heating and control zones
which communicate through a common exhaust gas duct. If in-
dividual zones are turned off as the rated temperature is
reached, they are not influenced by the other zones in
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spite of the connection through the exhaust gas duct. The
flue gases simply flow out in longitudinal direction in the
upper part of the common exhaust qas duct, with preference
into a preheating ~one or for preheating the material in
5 an upstream preheating furnace for optimum exploitation of
the heat capacity of the fuel in this manner in a furnace
group consisting of the preheating furnace and further heat-
ing furnaces connected in series downstream thereof.
The invention will be described further, by way of e~ample, -
10 with reference to cross sections of two preheating furnaces
actually constructed.
In the drawings:
Fig. 1 is a cross section along line l-I of fig. 3 through
a first embodiment of a preheating furnace according
to the invention;
Fig. 2 is a cross section at the same location through a
second embodiment;
Fig. 3 is a lateral elevation, partly in section, of a fur-
nace group consisting of a preheating furnace and
an upstream heating furnace in accordance with a mo-
dification of the invention; and
Fig. 4 is a section along line IV-IV of fig. 3 through a
heating furnace of the furnace grol~p connected up-
stream of a preheating furnace according to fig. 1
or 2.
The preheating furnaces shown comprise a steel structure
support frame 10.
In the lower furnace space there is a double strand con-
veyor chain 13 to which carrier devices 12 are attached
30 for the material to be preheated, like bars or billets and
which advances the material intermittently through the cy-
lindrical furnace tunnel 15 formed by semicylindrical fur-
nace shell halves 14. In their lower range the furnace
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shells 14 are supported pivotably on carrier rails 16 and
held in position from above by spacers 17.
With the embodiment shown in fig. 1 only one burner row in-
cluding premixture burners 18 disposed in longitudinal rows
5 vertically of the plane of the drawing is provided per row
of furnace shells 14. The burners 18 have burner nozzles 20
which project through openings 21 in the furnace shells in-
to the cylindrical furnace tunnel 15 acting directly on the
material. The burners 18 are so arranged that when preheat-
10 ing material 1 of different diameters, ~he surface is
utilized well for heat transfer and the temperature is dis-
tributed in rotational symmetry across the cross section
of the material. The burner nozzl~s 20 are adjusted to per-
form such that the desired temperature distribution is ob-
15 tained.
Instead of burners 18 hot gas nozzles may be provided for
heating, acting on the material 1 for instance by hot air
which can be heated electrically in known manner
The exhaust gases leave the furnace space 15 in upwàrd di-
20 rection through a longitudinal slot 30 defined by the fur
nace shell halves 14 at the spacers 17 and then reach an
exhaust gas duct 32 directly through a vertical channel ~. x
From the exhaust gas duct the exhaust gas is delivered into
a preheating zone, not shown, for the material 1 and located
25 upstream of the preheating furnace, for example by being
sucked by means of fans, not shown. The exhaust gas duct
includes a heat insulation, the lower insulation members 54
of which extend throughout the furnace length, leaving a
gap for the furnace tunnel 15, and abutting from outside
30 against the central areas of the furnace shells 14. The
lower insulat~nmembers 54 are supported by carrier beams
52 which are mounted stationarily on the support frame 10.
The principal or top portion of the exhaust gas duct 32 is
defined by two ver~ical insulation members 5~ and an upper
35 insulation member 58 integral with them.
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With the embodiment according to fig. 1 the insulation mem-
bers-56, 58 of the upper part also extend throughout the
furnace lengthO Thus the main portion 56, 58 may be removed
as a whole. The furnace shells 14 continue to be held la-
5 terally by the lower insulation members 54, yet upon remo-
val of the spacers 17 they may be removed individually for
replacement by easy inward pivoting about the respective
fulcrum at the carrier rails 16.
The heat insulation comprises two layers for example, the
10 inner one consisting of ceramic fibers which are good heat
insulators but bad for storing heat, while the outer one
located in an area of lower temperatures is made of mineral
fibers.
The embodiment shown in fig. 2 differs from the Gne accord-
15 ing to fig. 1 only in that in addition to the lower burner
row 18 an upper burner row 19 is provided per furnace shell
row. An adjustable throttle valve 24 is arranged in the
fuel supply line 23 for adjustment of the upper burners
with respect to the lower burners.
20 The additional upper burner rows necessitate the position-
ing of vertical insulation members 59, divided into segments
in correspondence with the furnace shells 14, between the
lower insulation members 54 extending throughout the furnace
length and the principal or top portion of the exhaust gas
25 duct 32 whose insulation members 60, 62, 64 again form a
united piece which is removable uniformly as a whole. For
exchange of furnace shells, the piece 60, 62, 64 must be
lifked off. Then the corresponding insulation members 59
must be removed so that upon removal of the spacers l? the
30 associated furnace shells 14 can be exchanged, as with the
embodiment shown in fig. 1. The somewhat more complicated
structuxe as compared to fig. 1 is the price for the bet-
ter uniformity of soaklng - of the material achieved.
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The right half of fig. 3 shows a lateral elevation of a pre-
heating furnace according to fig. l or 2, here designated
9~, whereas the left half shows an upstream preheating
furnace which is heated by the exhaust gases from said pre-
5 heating furnace. To this end the exhaust gas duct 32 opensby an aperture 33 in the right end surface 34, as seen in
fig. 3, of the preheating furnace designated, in general,
by reference numeral 40 and illustrated in greater detail
in fig. 4. In the furnace space 41 which communicates with
lO the exhaust gas duct 32 through the aperture 33 and is pro- -
tected by a heat insulation 42 similar to that of the pre-
heating furnace 90 there are se~eral circulation zones one
behind the other, for example two circulation zones 471 48
each including a fan 43 sucking the exhaust gas in the di-
l5 rection of the arrows F in fig. 3 out of the exhaust gasduct 32 into the furnace space 41 and then directing it
through two rows of slot type nozzles 44 on to the material
l, the nozzles being arranged at both sides so as to con-
verge toward the material l. The material l is fed in con-
20 veying direction T through treatment spaces 45 of each cir-
culation zone47~4~by means of the double strand conveyor
chain 13 which passes through both furnaces 40, 90. Subse-
~ quently the exhaust gas is sucked out of the treatmentspaces 45 by means of the fans 43 and recirculated or dis-
25 charged through an outlet 46.
In the circulation zones 47, 48 succeeding each other fromright to left in fig. 3 temperatures are established which
decrease in a direction opposite to the conveying direc-
tion T. Controllable admission in each circulation zone re-
sults from this cascade-like exhaust gas guidance, and the
heat capaeity of the exhaust gas is utilized in optimum
fashion. Thus the furnace group aeeording to figs. 3 and 4
is characterized by particular economy, i.e. especially low
fuel consumption.
47,48
