Increase in the Durability of the Refractory in the Melting
Processes in AMM - Continuation
MS Met. Terrazas, Mario
Metallurgy & Process
Engineering
Acerlan Matrix Metals
San Juan del Rio, Qro.
Mexico
mt1m@matrix-sanmargroup.com
76th Technical & Operating Conference of the Steel Founder’s Society of America
Chicago, Illinois
December 8-10, 2022
Abstract. The present paper is the continuation of the paper
presented in the 2021 SFSA T&O, which subject was the
increase of the refractory life in electric arc furnaces at AMM.
The project, started in 2018, brought many side perks like
reduced reoxidation and improved cleanliness of the metallic
bath. Along with the furnace refractory economy, came an
increase in the number of heats, using a balanced ratio of Lime
and Dolomite that promotes a submerged arc process, with
graphite electrodes and power consumption reduction. This
paper also discuss the use of SiC to keep the consistency of
the slag (thicker layer), and includes the results of different
lining trials in IF and ladles using the same principles ; 5 years
of results are summarized in this paper.
Keywords— Electric Arc Furnace (EAF), Induction Furnace
(IF), Tea Pot ladle, Castable refractory, basic refractory bricks,
alumina (Al2O3), magnesite (MgO), Silicium Carbide (SiC) slag
foaming,
I.
INTRODUCTION
“Aceros Lanzagorta (Acer-Lan)” was founded in 1979
with the purpose of entering the steel industry and low-alloy
foundry in the valve sector. Acerlan began with the process
of green molding and acid melting in EAF. Over the years,
they increased their production lines and installed IF with a
high alumina lining according to the variety of alloys
demanded by the valve sector, among others. for many years
Acerlan produced under these new technologies at that time.
As products and customer requirements evolved, Acerlan
now with the name of Acerlan Matrix Metals (AMM) adapted
its technologies and infrastructure to ensure customer
satisfaction. In recent years, Acerlan has been acquired to
high-alloy steels, thus producing nickel-based alloys. For
this, it had to adapt to furan no bake system and shell molding
as well as adapting the chemical composition of its
refractories and develop its metallurgical and melting
practices to achieve quality products according to market
requirements.
consumption per ton of steel produced will result in reduced
spent refractory material landfilled, while improvements to
the efficiency of the steel foundry operation will reduce
emissions during production and during rework of products.
Improved refractory selection with longer campaign life,
fewer tear-outs and relining will reduce the cost of operation
for the plants making them more available and competitive.
Determining the optimum refractory, slag and operating
system to produce clean steel will be very important to
improve the technical viability and environmental
sustainability of the steel foundry industry.[1]
The use of SiC
A significant portion of the arc energy is reflected from the
arc and bath surface to the sidewalls and roof where the
energy is lost in heating (and often melting) refractory rather
than steel, but the addition of a material such as SiC, which
produces exothermic reactions during the oxygen blowing,
does not require any capital investment. Figure 1 illustrates
the advantage of using SiC as a source of chemical energy.
The SiC addition not only decreases the electrical energy
required, but the recovery of the chemical energy is also
better, as a Carbon boil is less violent than arcing, thus
reducing the “power-on” time and eliminating delays due to
an overactive bath. Early estimates showed that the heat
obtained from the oxygen boil using SiC is cheaper than the
heat obtained from electricity. The bath was enriched with
carbon prior to and during oxygen lancing by adding SiC to
the solid charge.[2]
i.ELECTRIC ARC FURNACE
Improved melting and slag practices in combination with
better refractory systems will increase the melting efficiency
in the electric arc furnaces, which will result in decreases in
the electrical energy requirements and graphite electrodes
consumption. Cleaner steel will result in higher casting yields
with less rework (weld repair, machining, repair, grinding,
etc.) and substantial energy savings. Reducing the refractory
Technical & Operating Conference of the Steel Founder’s Society of America
Figure 1. Chemical energy in the steel, slag and above the bath of the EAF.
These practices were part of “Back to basics”, and
“Thinking outside the box” concepts and objectives of the
company to reach the best practices and the continues
improvement of the plant.
As the heat is generated within the liquid steel, the heat
transfer efficiency from the exothermic reactions should be
nearly 100%, higher than the typical 40% efficiency for post
combustion of CO above the bath.[2]
i.ELECTRIC ARC FURNACE
The method used to determine the category of lining is by
the basicity (V) of the slag formed on the metal surface.
Where: a ratio of less than one is considered acid, more than
one is basic, and approximately one is neutral. which can be
calculated from the formula (1) [4]:
𝑽=
𝐶𝑎𝑂+𝑀𝑔𝑂
𝑆𝑖𝑂2
>1
In the 8t EAF, the standard melting practice with boiling of
35 points by oxygen lancing within a basic lining is used.
Shorter processing and tap-to-tap times, in combination with
the better controlled temperatures and alkaline slag in EAF,
resulted in a reduction of wear areas at and below slag line.
Also, glassy phases are no longer present in proportion
because of the CaO:SiO2 ratio of the basic slag.[4]
(1)
The double slag “oxidized / reduced” practice is now used,
the follow-up of the basic slag practices and the updated
lining procedures are proving beneficial to the refractory,
with more than 260 taps in a refractory campaign. In this
context, one aim of this project was the development of the
slag process through the addition of a mixture of MgO, CaO
+ SiC during steel melting in the EAF, intending to reach the
optimum saturation point of MgO in the slag. While inducing
a beneficial thick, foamy slag, the use of SiC promotes the
submerged arc process. [4]
ii.INDUCTION FURNACE REFRACTORY
Steel foundries have attempted to modify large ladle porous
plug technology to the induction furnace in hope of using
argon gas bubbling to reduce the gas content of the steel.
Notably, these furnaces use a rammed lining that lends itself
to the installation of the nozzle in the bottom of the furnace.[3]
The gas diffuser must be easy to install, operate, able to last
for the life of the induction furnace lining and it must be cost
effective, too. Where possible, a diffuser should be installed
in the center of the furnace base, or as close as possible to the
center.[3] (see Figure 2).
Since the process was introduced, significant benefits
identified include:
➢
➢
➢
➢
➢
Homogenization of bath temperature
composition
Improvement in casting quality
Reduction in Nitrogen content
Cleaner metal
Increase lining life
ii.INDUCTION FURNACE REFRACTORY
In AMM case, a 90% alumina preformed crucible was used
to line a nominal 2t furnace. The crucible was backlined with
a regular high Alumina (Al2O3) and after research and trials
AMM selected high and dry magnesium oxide lining (MgO)
for the induction coil. A typical campaign life before using
high alumina was 80 heats.
With a high Al2O3 (85%) + MgO (15%), the IF lining
campaigns improved because of the better resistance to
erosion of the lining. Also, a porous plug was placed in a
crucible-lined furnace, a full study was part of the company
continuous improvement projects.[3]
and
Homogenizing in temperature (as previously described)
would have a positive effect on the condition of the lining. A
significant number of users now report increases in lining life
since introducing the process.[3]
iii.REFRACTORY IN LADLE
The standard practice for teapot ladles used to be with high
alumina brick and patching with high Al2O3 and Chromite
Cr2O3 plastics, resulting in an expensive practice with a
maximum campaign of 60 Taps. In 2019, a new technology
with low cement concrete was proposed from a supplier to
test in the small 0.5t teapot ladle to compare the durability
easy way of manufacture also supplier trained the refractory
crew to manufacture the ladles in house. The high quality
chamotte-based alumina refractory concrete and its excellent
workability allow it to be used in a myriad of applications
such as refractory maintenance of foundry ladles and
crucibles: runners, necks, furnace delta, spouts, frames,
doors, lintels, supports, etc.
III.
Figure 2. Porous Plug and Injection of Argon Gas Through the Bottom
in Induction Furnaces configuration.
II.
METHOD
A. Silicium Carbide (SiC)
In AMM, we have a particular product mix composition and
we have determined the best proportions of lime and dolomite
in order to satisfy our carbon and stainless clean steels and
furnace lining longevity requirements.
BACKGROUND
In 2018 AMM decided to reorganize its melting area and
deploy new practices in the electric arc melting department.
2
In 2020, the foamy slag was introduced in the process by
using anthracite during melting to create a thicker slag and
submerged arcs in the flat-liquid stage. In 2021 EAF “A”
achieved the 262 taps and in parallel furnace “B” saw its
campaign topped at 230 taps by the end of the year with the
same mix.
In the second stage, the SiC gave the expected Si
contribution to the liquid metal, having the same recovery as
the regular Ferro Silicon, with a cost lower by 40%.
However, the two following additional advantages are
obtained: superior exothermic reaction and a foamy slag on
the metal bath, which reduces the flares on the walls.
Therefore, the advantage of direct savings goes hand in hand
with a technical advantage during the process.
In 2021, SiC was added to the mix to add exothermic energy
to the bath and it was also noticed that SiC in proper quantities
increases the thickness of the slag in comparison to the regular
standard practice.
Specification below:
➢
➢
➢
➢
➢
➢
➢
SiC: 85% Min
Si: 60%
C: 25%
Free C: 4% Max
SiO2: 4% Max
Size:0-10 mm
Moisture: 1% Max
B.
Induction furnace refractory
Figure 3. Foamy slag in EAF
The present operation uses a 2t IF with a porous plug, and
a method for preparing and using the crucible in a way to
promote the purity of molten metal and crucible life.
The validation for the installation of porous plug and the
change of the refractory composition from high alumina to
high Al2O3 (85%) + MgO (15%) was for one campaign, which
lasted approx. 120 heats. Since the results came out very
favorable, it was decided to install the porous plug in all
induction furnaces at AMM.
IV.
This new melting practice of basic/reduced slag was
satisfactory in terms of consistency and procedures for the
maintenance of the lining. By the end of 2021, AMM was
able to achieve 250+ heats per campaign in both its EAFs,
See below EAF campaigns trend from year 2018 to 2022 in
Figure 4.
RESULTS
EAF Refractory
The project gained traction in 2019 when a basic slag was
sought in such a way for the refractory to be less attacked and
its useful life extended. With the usage of Dolomite lime
(MgO) in the charge of the EAF, in the first trial campaign
144 heats were made in total in one furnace in 2020. The
useful life of the refractories was initially forecasted to be 120
heats, so an increase of 20% was immediately obtained. In
2021 a record of 262 heats was obtained in furnace B.
During the las 3 years, X-ray fluorescence spectrometry
(XRF) was used to get a fast, reliable, and repeatable solution
for measuring slag, see average results of the Basicity (V) in
Table 1:
%SiO2
16
%Al2O3
14
%CaO
32
%MgO
22
Figure 4. Refractory life in furnace EAF from 2018 to 2022.
V
3.37
The theory tells us that if the equation results in a value
greater than 1, the slag is alkaline, which is consistent with
the practical results of > 3 for an over saturated slag of
basicity, increasing the useful life of the refractory by 200%.
In 2021, AMM decided to continue working with the
consistency of the slag, this time with the use of SiC,
anthracite and Dolomite.
The initial boiling stage with anthracite and SiC released
more heat than expected, also contributing to the formation
of a thick foamy slag beneficial to the metal bath protection.
Figure 5. Graphite Electrode Consumption in EAF from 2018 to 2022.
3
Since the creation of a foamy slag, an increase of
submerged arc process time was obtained, as well as a
reduction in electrodes consumption. See below graphite
electrodes consumption trend from 2018 to 2022 in Figure 5.
for the combined improvements, culminating in a 40%
increase of the lining life for the three IFs.
Beyond the brick and graphite savings, there is a
significant reduction in energy consumption, after the
implementation of a foamy slag with SiC. In Figure 6, the
trend of kWh/t from 2018 to 2022, reducing 100 kWh/t
average.
Figure 7. Refractory life in IF from 2018 to 2022.
Refractory in ladle
A 2t teapot ladle was manufactured with concrete known as
castable material.
Bill of Material:
➢ Castable material
o Al2O3 - 85%
o SiO2 - 10%
o Fe2O3 - 1.5%
➢ Density 2.8 Kg/m3
➢ Stainless Steel fibril 3%
➢ Water 3-4%
Figure 6. Power Consumption in EAF from 2018 to 2022.
The consumption recorded before this project was 580
kWh/t. After this project, the average power consumption is
450 kWh/t.
Induction furnace refractory
In 2020 AMM was looking for sustainability in all melting
processes and the implementation of porous plug with a high
Al2O3 and MgO furnaces was a new development in AMM
and the combination of both technologies resulted in great
metal quality and improvements in mechanical properties. The
test material is inexpensive and promised to increase the life
of the furnaces. The test was carried out in the small induction
furnace as a trial, exclusive refractory material for the 350 Kg
induction furnace.
Preparation in the paddle mixer:
a) Load of 100 kgs of concrete
b) 3% of SS fibril
c) 4-8% water needed to strain / vibrate (depending on
the mixing conditions: external temperature, type of
mixer, etc.).
d) 3 minutes mixing time
e) Ceramic paper (between ladle shell and concrete)
Vibration:
f) start vibration from the first stroke, and leave on
until filling
g) completely fill the pot until the bubbles come out of
the concrete
h) keep for 15 minutes after filling
Bill of Material:
➢ Former for oven 350 kg: 1 pc
➢ 1 porous plug
➢ Lining (Al2O3+MgO): 70% of furnace capacity
➢ Top lining: 30%
➢ 0.3 mm Micanite: 3 meters
The ladle must be clean and smooth, patching material must
be used to flatten the ladle walls (before tap) to avoid the
metal to stick (after pouring). The most important aspect of
the drying/sintering process is to follow the instructions of the
castable material supplier.
With this material we achieved a 10-months campaign,
between 2019 and 2020, with a total of approximately 80 taps.
After this results AMM decided to implement this material in
a 2t IF. The 2t IF ran well up to 120 heats with spinel bond
Dry high Al2O3 and MgO. These lining materials cost savings
vs the previous practice amount to $1,125 per furnace
campaign.
The installation of porous plugs and the improved lining
practices positively impacted the process temperature stability
and refractory life for all furnaces, as shown in Figure 7. The
next graphic also describes the change in behavior of the high
alumina lining from 2018, with 2020 seeing the learning curve
Figure 8. Tea pot Ladle manufactured with castable material.
4
The patching must be applied to flatten the ladle walls
before tap and the ladle must be clean to avoid metal/slag
sticking on the concrete after pouring. The patching material
has a chemistry like that of the ladle. To avoid early wasting
of the ladle, patch every 30 heats. See Figure 9.
4.
Since Ar stirring improves the homogenization in
the liquid metal temperature, the lining experienced
a 40% life increase. In absolute, the lining life
increased from 80 heats to average 110 heats for all
type of furnaces.
5. The current Al2O3 + MgO lining resulted an
economical material to build furnaces.
Teapot Ladles
6. The concrete castable material for lining, the steel
needles reinforcement and the proper sintering
process led to results that exceeded the expectations.
The various campaigns contributed to increase the
capabilities of our refractory crew, with ideas of
extending applications to tapholes, deltas, protection
stones for induction furnaces and spouts, among
others.
Figure 9. Foamy slag in EAF
The improved sustainability in melting is part of the efforts
to improve our teamwork, our foundry processes, people
knowledge and development, customer satisfaction and the
continuous improvement of AMM.
AMM started using this material in a 2t teapot ladles in
January 2020; we expected to achieve 150 heats in 6-8
months. Instead, it has achieved >650 taps over 23 months.
Incredibly, the durability of this one particular ladle made out
of refractory concrete was two years long.
V.
ACKNOWLEDGMENT
The author would like to express his gratitude to the melting
staff and melting supervisors E. Chavez and F. Cruz. Without
their experience and skills this project would not have been
carried out.
CONCLUSIONS
Campaigning for better slag and lining practices brought
many side perks like reduced reoxidation and improved
cleanliness of the metallic bath. As for the refractories,
furnace, and ladle consumables:
Their guidance and support of the melting and metallurgical
team over the years is very much appreciated.
Many thanks to Paul Lapointe Sr. VP –Technical at MM
Global, for his comments and review of this paper and Edgar
Palma for the illustrations of this paper.
Improved slag and lining practices increased the
number of heats per campaign in both EAF furnaces
by >200% (260 taps).
2. SiC contributes with exothermic reaction and gives
stability to the bath, managing to reduce electrical
energy consumption by > 100 kWh/t.
3. Consistent foamy slag with the use of SiC:
a. Promotes stable temperature.
b. Covers brick walls reducing in refractory bricks
consumption.
c. Protects the metal bath.
d. Increases the thickness of the slag, rendering it
suitable for a submerged arc process with reduced
electrical and graphite electrodes consumption.
1.
REFERENCES
[1] D. Smith, D. Peaslee “Steel Foundry Electric Arc Furnace Refractory
Lining Survey”, Department of Ceramic Engineering, Department of
Metallurgical Engineering, University of Missouri-Rolla, p1, 1999.
[2] K. Peaslee, V. Richards, “Melting Efficiency Improvement” Missouri
University of Science and Technology, Office of Sponsored Programs,
MO, p14-15, 2012.
[3] M. Terrazas “Installation of Porous Plug and Injection of Argon Gas
Through the Bottom in Induction Furnaces at Matrix Metals – Acerlan
Foundry”, 74th Technical & Operating Conference of the Steel
Founder’s Society of America, Chicago, Il, p1, 2020
[4] M. Terrazas “Increase in the Durability of the Refractory in the Melting
Processes in AMM”, 75th Technical & Operating Conference of the
Steel Founder’s Society of America, Chicago, Il, p1. 2021.
In IF
The combined improvements - i.e., high alumina +
magnesium oxide lining and the installation of porous plug delivered the following benefits:
Mario S. Terrazas C. Metallurgy & Process Engineering Manager,
Acerlan Matrix Metals S.A. de C.V. Mexico. Contact e-mail:
mt1m@matrix-sanmargroup.com
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