INCREASING THE OUTPUT OF OPEN-HEARTH FURNACES FOR PRODUCING CAST STEEL

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• Sequence Number: 387
• Publication Date: February 25, 1952
• Content Type: REPORT

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CLASSIFICATION CONFIDENTIAL ( VNI-IDENTIAL
SECURITY INFORMAT
CENTRAL INTELLIGENCE AGENCY REPORT
INFORMATION FROM rra
FOREIGN DOCUMENTS OR RADIO BROADCASTS CD 170.
COUNTRY German Democratic Republic
SUBJECT Scientific - Engineering, metallurgy
HOW
PUBLISHED Monthly periodical
WHERE
PUBLISHED Berlin
DATE
PUBLISHED Jun 1951
LANGUAGE German
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01 Txg eano gT??g nl?I. T.g ^uaa IF UReuu ?CT u
/. g. o.. gl ?.e U. u ?OmO. ~? ?MUIi/10. on ?g .pgun0.
01 I? CO.?.? I. ?.T ..uu To .. eue?onlne rum. U .,,no >7 4.. nornoueno. oT Tow ... Ig noael?e.
DATE OF
INFORMATION 1951
DATE DIST. 24"Feb 1952
NO. OF PAGES 10
SUPPLEMENT TO
REPORT NO.
THIS IS UNEVALUATED INFORMATION
SOURCE Metallurgic and Giessereitech..ikVol I, No 6, 1951, pp 174-180.
INCREASING THE OUTPUT OF OPEN-HEARTH FURNACES
FOR PRODUCING CAST STEEL
sables and figures referred to are appended]
In an attempt to fulfill the 1950 plan ahead of schedule, the steel
plants of the German Democratic Republic started a program to reduce the time
required for each individual melt in open-hearth furnaces. This included
better organization of the work of the crews and technical means of acceler-
ating the process, such as adding of molten pig iron and blowing in of oxygen
or compressed air. This program was adopted not only by the large steel mills,
but also by the casting departments operating smaller sized open-hearth fur-
naces . The smelting operations had previously been considered to be of sec-
ondary importance by the casting departments, but it has now been realized that
these furnaces can be used to good advantage for the production of high-grade
steels to be cast as ingots for forging or rolling.
We shall report here on the success achieved along these lines by the
open-hearth department of a central German steel mill. The increase in effi-
ciency depends on three factors, of equal importance: increase of the furnace
output, shortening the periodr luring which the furaacE 1s out of operation,
and increasing the longevi,y of the furnace. We shall discuss only the first
of these points in detail, and touch upon the others only as necessary. First,
we must determine the standard output for a furnace of a definite melt capacity
and corresponding hearth area.
Normal Output of German Cast-Steel Furnaces
The standards were determined by Guthmann, in 1943 (Guthman: Kennzahlen
Deutscher.Siemens-Martin Oefen (Characteristic Data of German Open-Hearth Fur-
Report No 68 of the VDEh, June 1944). Furnaces producing at least 50%
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cast steel are classif+ed as cast-steel furnaces. Their size varies between
3 and 33 tons. The characteristics are shown in Figure 1, which shows the
standard values for hearth area, output per hour, and total melting time.
Two curves are shown for output per hour and for total melting time. The
broken line shows the melting time from the start of the charge to tapping,
while the solid line includes nonoperating periods up to 30 into, especially
the time between tapping and recharging. These data apply to the plant which
is being discussed.
The Steel Mill
The mill has three generator-gas-heated basic open-hearth furnaces,
built in 1939 - 19'+0 (furnaces I and II) and 1944 (furnace III) with a melt
weight of 10 tons. They have standard Siemens heads. In 1947, they were
equipped with Crespi hearths and in 1949 oblique tar-dolomite mixture real
walls were installed. Following are the principal dimensions of furnace
III; the other two furnaces differ only slightly.
Data in Table 1 require some explanation. While the dimensions given
are for a 10-ton furnace, the melt weight has been increased in the course
of time to from 13 to 25 tons, with an average of 18 tons, without any ill
effects on operation. Only the hearth area had to be increased, the depth
of the bath decreased, and the space between bath surface and crown increased,
as shown in the table. No other modifications were carried out. The doors
had been widened from 0.80 to 0.83 m and heightened from 0.80 to 1.05 m as
early as 1948 to make charging easier.
As for the angle of the gas and air conduits, about half of the intersect-
ing square formed by lengthening the gas and air intakes lies on the surface
of the bath and the distance of the center of the square from the mouths of
the conduits is about 28 percent of the hearth length. The cross section of
one rising gas shaft is adequate, while the two air shafts should be increased
to an area of 0.50 to 0.54 sq m. The content and checkerwork space of the
gas and air checker chambers are more than adequate, and correspond to the
dimensions of a 13-too furnace. The cross sections of the shaft openings of
the Forter valve and of the air reversal valve are very narrow, and would have
to be expanded by 40 to 50 percent to be considered satigf story.
The chimney dimensions originally were poorly adapted to the furnace
dimensions. Draft was greatly dependent on air temperature and direction
and force of wind. The height of the chimneys has been increased from 36 to
41 m, and these effects have thereby been eliminated, so that an even draft
of about 22 mro water column is now main.ained.
Each furnace head is cooled by two water pipes of about 1 1/4 in,
arranged in a semicircle around the gas conduit. Water-cooled door frames
are to be installed as soon as continuous water supply can be guaranteed.
The longevity of the furnace heads from the first to the third quarter
of 1950 was about 165 melts, that of the crown, 320 melts. Repairs are
regularly carried out over the week end and, since 1948, it has therefore
not been necessary to carry out special repairs during the regular work week.
This greatly increased output and quality.
The gas-generator plant, installed in 1947, originally consisted of
two rotary grates with a masonry-shaft diameter of 2.2 in and a rotary grate
with a shaft 2.6 m in diame'ir. Brown-coal briquettes with an addition of
open-burning coal were used to produce the gas. The installation, as a rule,
was operated in such a way that the 2.2-m gas generators jointly supplied
one furnace, while the 2.6-m generator supplied one furnace by itself. The
throughput of the 2.2-m generators was 96 kg/sq m hr each, that of the 2.2 m
gas generator, 120 kg/sq m hr.
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It was often tried to use each of the 2.2-m generators for just one fur-
nace but the required increased throughput of 160-18U kg/sq m hr caused con-
siderable operational and metallurgical difficulties. Therefore, since 1947,
the throughput in continuous operation has not exceeded 100-130 kg/sq m hr.
In the third quarter of 1950, another 2.6-m gas generator was installed,
Lnd three-furnace installation replaced the old two-furnace system. Local
conditions made it impossible to install a joint gas line to the furnaces. The
gas is piped to the furnace from each of the 2.6-m generators, and from the
pair of 2.2-m generators in subterranean, noninsulated conduits, 15-17 m long
and with a 0.5 sq m cross section. The conduits are cleaned on Sundays.
Un'il March 1948; One 5-ton bridge crane was available for charging with
scrap end pig iron ac, for moving the charge to the charging box. Then, an
additional 5-tot rane was installed. In 1950, the number of scrap cranes was
increased to three. From the charging boxes, the charge is placed into the
furnace with a 1-ton charging crane. Installation of a second charging crane
is planned.
The production program includes mainly carbon steels for castings and
forging and rolling ingots; but small quantities of alloy steel are also made.
In general, the scrap pig-iron method, with a pig-iron charge of about 18-22
percent, is used. During times of pig-iron shortages, the scrap-coal method
had to be used occasionally during the past years, with less than 10% pig-iron
charge, and a resulting drop of 10-15% in production.
Furnace Output
Operations at the plant were resumed toward the end of 1949, after a
stoppage of nearly 1 1/2 years. The difficulties caused by the postwar condi-
tions were not overcome until the fourth quarter of 1947, when an hourlyoptput
of 1.59 tons, including the time for patching the tap hole, was reached with
10- to 11-ton melts. In the second quarter of 1948, it increased to 1.79 t/hr
and in the fourth quarter of 1949, it reached 2.14 t/hr. This means a 34.7
percrzt increase in hourly output. and an increase in the production of molten
steel of 76.7.percent.
In October 1949, operation with higher melt weights was started. Due to
the fact that the crane capacity in the casting department was inadequate, this
was a gradual process which did not show any effects until the first quarter
of 1950, at which time an hourly output of 2.32 t/hr with a mean melt weight
of 16.6 tons was reached. According to Guthmann's standards, this corresponds
to a hearth surface output of 213 kg/sq m and to the normal output of a 40-ton
furnace with double gas operat:on (coke oven gas plus generator gas) and a
molten charge.
As the crane installations are capable of pouring no more than 11 tons of
steel, tapping into two ladles had to be carried out with larger melts. The
cascade method with two ladles turned out to be very suitable, especially
since the tapping temperature of 1,570-1,6000 C (uncorrected) was too high.
This method is still in use. Experiments were made on individual 25-ton melts
with a tilting double trough and three ladles. This method, however, required
tedious preparatory work, and impaired the quality of the steel because it
formed vortices at the fork in the trough. The Steinheisser trough, although
definitely superior, has not yet been tried, because major modifications on
the casting cranes would be required to allow its use.
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Causes of Higher Efficie2CY
The activist movement led to the organizing of competitions between 1 il-
vidual shifts in an attempt to cut down the time required to produce one melt
without lowering its quality. Table 2 shows the results of these competitions.
The melting time given is the time from the beginning of the charging operation
to the removal of the first preliminary sample from the furnace. The time
required for patching the tap hole is not included. These melts were used
mainly for wheel disks and castings.
The processing of the melt is shown by the data in Table 3. The melts
produced no waste due to inferior quality. Fears that the boiling time of
1.5 hr would be too short turned out to be groundless. This has been proved
repeatedly since then.
In February 1950, the operations were definitely converted to melts
above 11 tons. Melts of 11 tons are run only occasionally, for special
orders, e.g., for alloyed steels.
The average hearth surface output of 318 kg/sq m/hr leads us to state
that literature contains no data which indicate that such high efficiency has
ever been achieved before under similar operating conditions.
The technical measures taken to achieve this performance were chiefly
the following:
1. Proper preparation and mixing of the charge, so that charging time
can be kept low and the correct analysis maintained.
2. Melting with high flame, i.e., a maximum gas supply and correspond-
ing volume of air, to achieve high bath temperature at the start of the boil-
ing process and to permit violent start of the metallurgical reactions.
Concerning point 1, the effect of charging time on melting time, boil-
ing time, and thus on the total melting time, was investigated on a large
scale. Figure 2 shows the results plotted for a 1-ton melt, with melting
time, boiling time, and total melting time as function of the charging time.
It is obvious that this effect is a very pronounced one and that all measures
improving the preparing of the scrap and the charging technique are definitely
worth the trouble.
. These measures included the maximum development and maintenance of the
scrap cranes and charging cranes, installation of a sufficient number of
charging boxes, and educating the charging personnel to'prOper'utilizatioa of
charging box space. Some success has beed achieved in this.respec^t: for. more
than 50 percent of all melts, the charging time was less than 5.8 min/t,
although the scrap was not in good condition. However; full success will have
been achieved only when this time has been cut down to a maximum of 4 min per
ton, despite the unwieldiness of the scrap
The dependence of the boiling time on the charging time should be noted.
Well-prepared and quickly charged melts have the lowest boiling times. Charg-
ing times of 6-13 min/t do'not affect it, while longer charging times may pro-
long the boiling time. In that case, the melt is usually too soft, and requires
the addition of carbon, which causes considerable loss of time.
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Concerning point 2, Figure 3 shows the operating condition of a furnace
during the melting process, with the tables giving the temperature, draft, and
pressure at the points indicated. The furnace represented here is furnace I,
heated by the 2.6-m gas generator IV which was built in 1950. The hourly out-
put of the two melts on which the measureme.it was made was 3.57 and 3.35 t/hr,
which is fairly high. Despite the high melt weights, the tapping temperatures
were at the upper limit.
The furnaces are supplied with combustion air by a 3,000 cu m/hr blower
which is fully utilized. The gas generator, in the case under discussion, was
operated on a 1:1 mixture of lignite briquettes and open-burning coal. The
throughput of practically dust-free mixture was 118 kg/sq m/hr; 2.83 cu m of
gas were generated per kilogram of mixture with 1.95 cu m/kg of combustion air.
The temperature of the steam-air mixture was maintained at 550 C. The
fuel consumption Is 200 kg of standard coal per ton of liquid steel (the mix-
ture coal converted into standard coal with a lover limit of the thera~l value
of 7,000 kcal/kg). This is an extraordinarily low consumption figure. The
consumption of the entire installation, in November 1950, was 240 kg of stand-
ard coal per ton of steel, including the periods during which the furnaces
were empty and kept heated. Each gas generator is equipped with instruments
measuring and recording forced draft, gas pressure, steam-air mixture tempera-
ture, and the gas temperature in the exhaust stack. The furnace is equipped
with devices indicating the temperature of the gas chambers at the top of the
checkerwork, the exhaust temperature, the pressure and draft in the reversal
conduits, and the chimney draft. All these measuring and recording devices
are again being manufactured with adequately exact indication and sufficiently
high safety factors.
Increase of Output by Charging With Premolten Pig Iron
The advantages of the use of molten pig iron in the scrap pig-iron
method, especially in cutting down the melting time, are used mostly where
the pig iron can be transported directly from the blast furnace to the open-
hearth furnace. In the steel mills of the German Democrc.tic Republic, this
is not possible as yet. It is important to determine, however, what increase
.in output can be achieved by charging with steel pig shippea in in the si.lid
state and then molted, or by the use of steel pig artificially made from steel
and casting scrap in a cupola furnace. This method has been known for a long
time, and according to areport by Herzog in Stahl and Eisen. Vol 46, 1926, proved
to be entirely satisi.actory. It is thus surprising, that the use of premelted
pig iron has never been adopted by German steel mills.
Table 4 gives the results of two experimental series of melts which were
made by this process. They were conducted in November 1950, each comprising
five melts. The steel pig was first melted in a 2.5-ton Fiat electric-arc
furnace and poured into the open-hearth furnace through a trough in the rear.
Unfortunately, the measuring instrument failed and the charging temperature
mould not be determined. The two series also differ in that the furnace was
operated only with a 2.2-m gas generator during series I. because the second
gas generator was being .-epaired at the time, while two 2.2-m generators were
used for the second series. The steel pig was poured into the furnace no
later than 45 min after charging the furnace with scrap; thus there were still
piles of scrap in the furnace at the time.
The melts of the first series showed an 18.7-percent increase in output
over the normal output with a solid steel pig charge, while the second series,
carried out with a more adequate gas supply, showed an increase of 33.0 per-
cedt. In practice, premelting of the steel pig will have to be carried out in
a cupola furnace, and the lower tapping and charging temperature will not
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shorten the open-hearth melting time as much as the use of an arc furnace will.
The arc furnace, however, was used only experimentally, but above tests prove
that tbebuilding of a pre-melting installation would be justified by the
results achieved with it. The economy of such a method will be guaranteed
only -- under the conditions prevailing at present -- when sufficient steel
pig can be made in a cupola furnace by means of an "economy mixture." At
present, work is progreL31ng on this question, and some very promising results
'already have been obtained.
It was also attempted to duplicate the output obtained with a molten
steel pig charge by using solid steel pig. Figure 4 shove the result for 79
successive melts of 13 to 25 tons weight, with the melt weight as the ordinate
and the hearth area output and the hourly output as the abscissae. The highest
output in each weight group is marked. The outputs for the various weight
groups, obtained between June and October 1950 and considered as normal, are
plotted for cormarison. The graph shows, first of all, that individual melts
with solid steel pig showed even higher output than obtained in the other test
series with molten steel pig, while the average output of the furnace was
increased over the previous months.
Tables and figures follow
Up to Mar
Since Mar
1950
1950
Melting space
Length of hearth at level of fore plate
5.20.m
5.70.m
Width of hearth at level of fore plate
2.10.m
2.10.m
Hearth surface at level of fore plate
10.90.sq m
11.80 sq m
Calculated mean depth of bath
157 mm
145 ma
Maximum depth of bath
450 mm
415 mm
Distance between surface of bath and crown
1.25 m
1.40 m
Gas and air conduits
Number of oblique gas conduits
1
Height at mouth
0.30 m
Width at mouth
0.50 m
Cross section at mouth
0.15 sq m
Angle
140
Number of oblique air conduits
1
Height at mouth
0.30
Width at mouth
1.20 m
Cross section at mouth
0.36 sq m
Angle
250
Air conduit width/gas conduit width = 1.20/0.50 *
2.4
Rising gas and air shafts per furnace side
Cross section of one gas shaft 0.50!0.50 =
0.25 sq m
Cross section of one air shaft 0.40.0.45 =
0.18 aq m
Cross section of both air shafts
0.36 eq m
Gas and Air Chambers
One gas checkar chamber
Gas chamber content
19.83 cu m
Width of checkerwork
2.55 m
Depth of checkerwork
2.10 m
Height of checkerwork
2.70 m
Checkerwork space
14.47 cu m
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1 air checker chambe~
Content
Width -if checkervork
Depth of checkervork
Height of checkervork
Chockerwork space
Both checker chamber pairs
Gas chamber content
A}r chamber content
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Up tc Mar
1950
2.19.83 =
2.23.67 =
Total
Gas chamber checkervork space
Air chamber checkervork space
Since Mar
1950
23.67 cu m
2.10 a
3.20 m
2.70 m
18.14 Cu a
39.66 cu a
47.34 .cum
7.00 cu a
2+l4.47 - 28.94 cu m
2.18.14 - 6.28 cu m
Total 65.22 cu m
Reversal ducts
Cross section of gas reversal duct
Cross section of air reversal duct
Valves
Gas valve (Forter type)
One chamber shaft valve
0.45
?0.60 =
One chimney shaft valve
0.45
?O.60 =
Fresh gas nozzle 0.60 din
Air valve (reversal valve)
One chamber shaft valve
0.60
10.6o =
One chimney shaft valve
0.60
0.60 =
Air nozzle 0.60 din
Chimney flues
Chimney flue behind air valve
Chimney flue behind gas valve
main chimney flue (joint vaste gas flue)
Chimney
Height above floor of mill
Height above bath level
Cross section at base
Cross section at mouth
0.50 sq m
0.65 aq m
0.27 sq m
0.27 sq a
0.28 eq a
0.36 sq m
0.36 sq is
0.28 sq a
0.72 sq m
0.90 sq m
0.90 eq m
36 m
30 m
2.54 sq m
1.13 aq m
.Lble 2, Melts With Exceptionally High Output
(10.8 sq m furnace)
Unit
1.
Number of melts
2.
Weight of melt
tons
3.
Charging time
hr
4.
Melting time
hr
5.
Boiling time
hr
6.
Total melting time
hr
7.
Furnace output
tons/hr
8.
Hearth surface output
kg/sq m hr
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Nov Oct Feb
1948 1949 1220-
26 10 16
10,200 11,D00 18,750
1:04 1:00 1:42
2:34 2:27 3:41
1:30 1:21 1:46
4:04 3:48 5:27
2.51 2.90 3.44
232 268 318
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Table 3. Metallurgical Characteristics of Melts With Exceptionally Riga output
unit Nov8 Oct Feb
1. Weight of melt tone 10,200 11,000 18,750
2. Level of C-content of
preliminary ample above
that of final sample " % 0.48 0.51 0.50
3. Average decarbonization rate '% C/hr 0.32 0.33 0.29
4. Slag content % 12?- 15 13 13
5. Tapping temperature (not
corrected) ?
6. Pouring temperature (not ,585 1,590 1585/]7O*
corrected)
1st ladle (start/end) 0 C 1,490/1,440 1,480/1,430 1,480/1,430
2d ladle (start/end) o C -- - 1,465/1,425
? Tapping temperature of first and second ladles with use of cascade method.
Table 4. Improvement of Furnace Output by Use of Premolten Steel Pig
(average values)
No
of
Melts
Series I
1 gas
generator
of 2.2 m 5
Series II
2 gas
generator
of 2.2 m 5
Molten
Normal Output
Melt
Steel Melting
Hourly
With Solid Steel Increase
Wt
Charge Time
Output
Pig Chai s
Obtained
tone
(?)
(hr)
tom hr
t ns hr
,
18.500
16.2
6:04
3.05
2.57
ld.7
18.550
17.0
5:25
3.42
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I:
N/Ili~ tl^
i
T Trer
, ~IIY
M
wJ
Or
y ' Yrw ,rj
r M.trll tree
Figure 1. Relationships Between Hearth Area,
Melt Weight, Hourly Output, and
Melting Time in Steel Furnaces
Gas q n t poor.
(SS- / r ....mn wind pr.arureJ
llU
M
ft~
Figure 3. Pesults of Temperature, Draft, and Pressure. easurementa on Open-
Hearth Furnace I, With Tables Shoving Results of Melts and Tapping
and Pouring Temperatures (Measured on 1 November 1950)
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,Measuring
point
1
Temperature ? C
570
Daft, m vater
Pressure,"
+32
C02 CnBa
02
5.0% 0.2?
0
Tapping and Pouring Temperatures, Not Corrected
Tapping Temp Pouring Temp (? C)
(0 C Ladle No Start End
Results of Melts
Melting
Melt Wt Charging Time Boiling Total Melting Hourly
Melt Na tone Time (hr) (hr) Time (hrj .Time (hr) output (t/hr)
7,862 24.75 1:50 4:35 2:10 6:55 3.57
7,864 21.45 1:45 4:45 1:50 6:25 5.35
Melt No
7862
1,600
2 3 4 5 6 7 8 9 10 11 12 13 14 15
360 -- -- 1,040 1,780 -- -- 1,120 -- -- 440 380 -- --
-12 -13 16 -17 1,8 -7 -8
+13410 +9 +8 +1 41 +2
Gas Analysis and Thermal Value
CO H2 CH4 N2 Hu
28.0% 15.6% 2.3% 48.9% 1,484 kcal/N cu m
I 1,500
II 1,480
1,550
1,490
1,450
1,430
1,440
1,430
Ai
?
M.// ".;qA!
Figure 4. Improvement of Hourly Output and Hearth Area
Output of Open-Hearth Furnace I in November
1950 (evaluation of 79 melts with solid steel
pig charge)
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