Steel industry refractories Archives - Page 2 of 2

RH is vacuum argon blowing recycling degassing equipment for steel liquid refinery, and DH is vacuum degassing refinery equipment. By blowing high speed argon in immersion tube and vacuum chamber upper part, steel liquid in ladle will flow into bottom side of vacuum chamber and be degassed, and then flow back to ladle through the other dipping tube. Through vacuum recycling degassing, harmful gases such as nitrogen, hydrogen in steel liquid can be removed. If oxygen blowing is adopted, carbon content can be decreased to a very low extent. RH and DH refinery equipments are mainly used for low carbon steel, low nitrogen steel and low hydrogen steel. Under those working conditions, furnace lining refractory materials should have good scouring resistance, vacuum resistance and thermal shock resistance.

RH refinery

In concern of cleaning steel production, refractory materials should better contain no carbon, nitrogen and hydrogen. Usually, vacuum chamber can use magnesia chrome bricks, inner side of immersion tube can use magnesia chrome bricks, while the outer side can adopt alumina magnesia spinel castable. The service life of magnesia chrome bricks at vacuum chamber upper part can reach to 2000 times or more, but the lower part is only about 500 times. The service life of immersion tube is about 100 times, varies with working condition and maintenance quality.

RH furnace structure

Magnesia alumina spinel bricks can be a good replacement of magnesia chrome bricks, but the corrosion resistance is not as good as magnesia chrome bricks. Another replacement of magnesia chrome bricks is low carbon magnesia carbon bricks, which has good performance price ratio compared with MgO-Cr2O3 bricks. RH immersion tube can be integrally casted by magnesia alumina spinel castable or magnesia zirconia castable. Through patching, the service life of integrally casted immersion tube can reach to or exceed magnesia chrome bricks lining.

RH Refractory Material Physiochemical Index

Item	Basic mortar	Alumina magnesia castable	Insulating brick	Calcium silicate board	Direct bonded magnesia chrome brick
Application	Masonry of magnesia chrome brick	Immersion tube, vacuum chamber upper part	Vent pipe, vacuum chamber	Vacuum chamber	Vacuum chamber
MgO %	92	>2	/	/	80
Al2O3%	/	>90	51.2	/	/
Fe2O3 %	/	/	1.7	/	/
Cr2O3 %	/	/	/	/	6~13
SiO2 %	/	/	/	/	1.98
Apparent porosity %	/	/	/	/	15
Bulk density g/cm3	/	≥2.90	≤0.9	0.23	3.06
Compression strength Mpa	/	≥40(11o℃)	7.37	≥0.5	59.2
Rupture strength Mpa	/	≥8.4(110℃,24h)	/	0.52	≥6.0(1200℃)
Reheating linear change rate %	/	±0.5(1500℃,3h)	-0.43	1.5 (1500℃,3h)	/
Refractoriness ℃	>1790	>1790	/	Max.1000	/

Item	Magnesia gunning mix	Magnesia chrome gunning mix	Magnesia injection mix	Magnesia carbon brick	Magnesia spinel precast block
Application	Vacuum chamber lower part, immersion tube	Immersion tube, vacuum chamber upper part	Immersion tube, vacuum chamber upper part	Vacuum chamber lower part, immersion tube	Vacuum chamber lower part, immersion tube
MgO %	≥85	≥70	≥70	≥85	80
Al2O3%	/	4	3	F.C≤5	10
Fe2O3 %	/	≤5	≤5	/	/
Cr2O3 %	/	≥5	≥5	/	/
SiO2 %	≤6	≤4	≤5	/	≤2
Apparent porosity %	≤24	≤24	≤24	≤4	≤15
Bulk density g/cm3	≥2.2	≥2.3	≥2.4	≥3.10	3.06
Compression strength Mpa	≥25 (11o℃)	≥20(11o℃)	≥20(1600℃,3h)	≥30 (11o℃)	≥40 (11o℃)

Item	Magnesia chrome brick	Magnesia chrome brick	Magnesia chrome brick	High alumina castable	Direct bonded magnesia chrome brick
Application	RH vacuum chamber upper part	RH lower part, recycling tube and immersion tube	OB gunning machine for RH	Vacuum chamber	Immersion tube
MgO %	80	76.9	69.9	/	65
Al2O3%	/	/	/	92.8	/
Fe2O3 %	/	/	/	/	/
Cr2O3 %	8.4	10.9	18.67	/	19
SiO2 %	1.6	1.46	1.52	/	≤2
Apparent porosity %	16	15	15	/	15
Bulk density g/cm3	3.05	3.11	3.00	2.79(1500℃,3h)	≥3.12
Compression strength Mpa	60	66	61	≥30(1500℃,3h)	60
Rupture strength Mpa (1480℃)	10	7.6	9.1	≥8.4（110℃）	60
Reheating linear change rate %	/	/	/	-0.27 (1500℃,3h)	-0.27 (1500℃,3h)
Refractoriness under load ℃	>1650	>1700	>1700	/	>1700

Item	RH gunning mix	RH injecting mix	CAS immersion tube castable	KIP spray gun castable
Application	Masonry of magnesia chrome brick	Immersion tube, vacuum chamber upper part	Vent pipe, vacuum chamber	Vacuum chamber
MgO %	/	/	≥4	/
Al2O3%	≥92	≥92	≥87	≥95
Refractoriness ℃	>1790	>1790	/	/
Bulk density g/cm3(110℃,24h)	≥2.90	≥2.60	≥2.95	≥3.00
Compression strength Mpa(1500℃,3h)	≥50	/	≥40	/
Rupture strength Mpa (110℃,24h)	≥4.0	≥4.0	/	≥4.0
Linear change rate %(1500℃,3h)	±1.0	±1.0	/	0~2.0

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Steel industry refractories

Dec 4 2018

Nozzle Refractory For Continuous Casting System

Nozzle Refractory Description

Nozzle series refractory can be divided into long nozzle, metering nozzle, submerged nozzle and separation ring.

Long Nozzle

Long nozzle is the connection part between steel ladle and tundish. Head end of long nozzle connects to steel ladle down nozzle, bottom end embeds into tundish steel liquid. Long nozzle can keep steel liquid from contacting with air during transferring from ladle to tundish, so steel liquid won’t splash, impurity won’t enter into steel liquid. The working condition suggests that long nozzle should not only endure strong thermal shock, steel liquid scouring and corrosion, but also suffer the corrosion of tundish cover flux. With the increasing requirement on steel quality, protecting casting ratio is continuously growing, so long nozzles using ratio is surging.

elongated nozzle

Quartz long nozzle is earliest used, which has very low linear expansion rate or nearly no thermal expansion, excellent thermal shock resistance, but it’s corrosion resistance is weak, especially for the casting of special steel such as high Mn steel, the service life is even shorter. With the developing of continuous casting technique, especially the casting of special steel, quartz long nozzle can also have unfavorable effect on steel quality, so new type of alumina carbon long nozzle is developed. Alumina carbon long nozzle’s service life is significantly longer than quartz long nozzle, but alumina carbon long nozzle’s main components are corundum, mullite, graphite and molten quartz, although mullite and quartz can large scale increase thermal shock resistance, the corrosion resistance to Mn steel and other special steel is not very good.

long nozzle

To solve this problem, composite long nozzle is developed, i.e., slag line magnesia carbon material, zirconia carbon material, main body adopts alumina zirconia carbon material, to meet low carbon steel casting needs, inner layer adopts alumina magnesia and Sialon ceramic carbon free material.

In recent years, unshaped long nozzle is also developed. Casting molding method is used to replace isostatic pressing molding for the production of alumina carbon quartz long nozzle and alumina magnesia long nozzle.

Long Nozzle Physiochemical Index

Item	Alumina carbon long nozzle	Alumina carbon long nozzle		Quartz nozzle	Quartz nozzle	Al2O3-C long nozzle
Item	Alumina carbon long nozzle	Main body	Purging ring	Quartz nozzle	Quartz nozzle	Al2O3-C long nozzle
Al2O3 %	43.81	≥40	≥85	/	/	≥50
F．C %	30.65	≥27	/	/	/	≥25
SiO2 %	/	/	/	≥99	≥99	/
Bulk density g/cm3	2.24	/	/	≥1.82	≥1.84	/
Apparent porosity %	17	≤20	/	≤19	≤18	12~20
Compression strength Mpa	25.2	≥20	/	≥40	≥40	≥15
Rupture strength Mpa	7.82	≥6	/	/	/	≥4
Air flow rate L/min	229	/	100	/	/	/
Thermal shock resistance/times	229	/	100	/	/	/

Item	Alumina carbon quartz long nozzle	Alumina magnesia carbon long nozzle		Alumina zirconia carbon long nozzle	Alumina carbon long nozzle
Item	Alumina carbon quartz long nozzle	Main body	Slag line	Alumina zirconia carbon long nozzle	Main body	Purging part
Material	Alumina carbon	Alumina carbon	Magnesia carbon	Alumina zirconia carbon	Alumina carbon compound	Alumina carbon compound
Al2O3 %	50	≥40	MgO, 74	≥40	50	90
F．C %	30	≥27	25	≥27	31	/
SiO2 %	14	/	/	/	/	/
ZrO2 %	/	/	/	6~10	/	/
Bulk density g/cm3	2.50	2.38	2.40	≥2.50	2.25	/
Apparent porosity %	14	≤20	16	≤18	17	/
Compression strength Mpa	/	≥20	/	≥20	24.4	/
Rupture strength Mpa	/	≥6	/	≥6	/	/
Air flow rate L/min(0.1Mpa)	/	/	/	/	/	210
Thermal shock resistance/times	/	≥5	/	≥5	5	/

Metering Nozzle

Metering nozzle is mainly used for the continuous casting of small billet. It is installed at the bottom of tundish. Metering nozzle should not have diameter enlargement or erosion under the strong scouring and corrosion of steel liquid. Inserting metering nozzle’s inner layer is made from zirconia ceramic refractory, which has excellent performance, outer layer is made from high alumina refractory. Inserting metering nozzle’s performance cost ratio is very high, so is popularly used. Integral metering nozzle is made by single type of refractory material, but performance cost ratio is not so high as inserting type metering nozzle. Worthy to be mentioned is that, a lot of steel mills insert pocket bricks and metering nozzles together and form a whole body, which is convenient for construction and safer for production.

metering nozzle

To prolong metering nozzle’s service life, zirconia content and zirconia ceramic’s density should be improved. The content of zirconia is raised from 65% to 94%, the density is increased from 3.4g/cm3 to 5.0g/cm3. To improve thermal shock resistance, semi stable zirconia is usually adopted, CaO is used as stabilizer.

zirconia metering nozzle

Metering Nozzle Physiochemical Index

Item	DJ-65	DJ-70	DJ-75	DJ-80	Zirconia metering nozzle	Zirconia metering nozzle	WG-70	WG-80
Position	Whole body and inner core						Outer layer and pocket block
ZrO2%≥	65	70	75	80	90	94	/	/
Al2O3 %	/	/	/	/	/	/	≥70	≥80
Apparent porosity% ≤	20	21	21	22	22	23	19	19
Bulk densityg/cm3≥	3.70	3.75	3.90	4.10	4.30	4.50	2.60	2.80

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Dec 3 2018

LF-VD Furnace Refractory Material

LV-VD furnace is steel liquid refinery equipment, which’s working condition is very harsh, should endure all kinds of high temperature corrosion, chemical corrosion, mechanical stress and thermal stress. So high quality refractory products should be adopted in according parts of LF-VD furnaces.
Magnesia carbon bricks are mainly used at furnace bottom and working lining. Corundum precast block which has high mechanical strength is mainly used at furnace bottom impacting zone. Magnesia chrome ramming mass is mainly used at furnace wall corner. Magnesia chrome mortar can be used for the masonry of magnesia chrome bricks.

LF-VD Furnace Refractory Material Physiochemical Index

Name	Magnesia carbon brick	Corundum precast block	Magnesia mortar	Magnesia chrome ramming mass	Magnesia carbon brick
Application	Bottom, wall working lining	Bottom impacting zone	Steel ladle working lining	Wall corner	Below slag line, free surface working lining
MgO %	92.5	/	96	52	92.5
CaO %	2.5	/	2.2	Cr2O3,19	2.5
Fe2O3 %	4	/	0.3	19	4
SiO2 %	/	/	1	0.5	0.6
Al2O3 %≥	/	97	/	6	/
F.C % ≥	5	/	/	/	10
Apparent porosity %	≤7	/	/	/	<7
Bulk density g/cm3 ≥	3.07	2.98	/	/	2.98
Compression strength Mpa	>.40	80	/	25(110℃)	>30

Name	Magnesia carbon brick	Magnesia chrome brick	Magnesia chrome mortar	Magnesia castable (ramming mass)	Chrome silica ladle filler sand
Application	Slag line working lining	Slag line permanent lining	Magnesia chrome brick	Ladle nozzle	Tapping hole
MgO %	96	60	52	91	6~12
CaO %	2.3	Cr2O3, 18	Cr2O3, 19	2.0	Cr2O3 >30
Fe2O3 %	0.3	14	19	5.8	20
SiO2 %	1.2	0.5	0.5	0.5	30
Al2O3 %≥	/	6	6	0.3	5~10
F.C % ≥	10	/	/	/	/
Apparent porosity %	≤7	<15	/	/	/
Bulk density g/cm3 ≥	3.00	3.26	/	/	/
Compression strength Mpa	>30	>30	/	30(110℃)	/

Name	Corundum block	Magnesia block	Corundum brick	Magnesia brick	Corundum mullite brick
Application	Purging plug, sleeve brick, pocket block	Purging plug, sleeve brick, pocket block	Purging plug, sleeve brick, pocket block	Dispersive type Purging plug	Purging plug core plate
MgO %	/	97	/	97	/
CaO %	1.8	1.7	2.4	1.9	/
Fe2O3 %	/	/	/	/	/
SiO2 %	0.1	0.6	0.1	0.5	9
Al2O3 %≥	88	/	97	/	90
F.C % ≥	/	/	/	/	/
Apparent porosity %	/	<25	/	26	/
Bulk density g/cm3 ≥	3.22	2.75	3.00	2.60	2.95
Compression strength Mpa	>60	>30	>50	>30	>60
Thermal conductivity w.(m.K)^-1(1000℃)	/	3.0	2.8	3.0	/

Name	Alumina magnesia castable	Alumina chrome castable	Corundum castable	Magnesia chrome castable	Alumina chrome chamotte
Application	Purging brick surrounding	Purging brick surrounding	Purging brick surrounding	Lower Dispersive purging brick	Purging brick
MgO %	8	/	/	77	/
CaO %	1	1.8	2.4	/	/
Cr2O3 %	/	10	/	12	2.0
SiO2 %	0.1	/	0.1	/	7
Al2O3 %≥	88	88	97	/	84
F.C % ≥	/	/	/	/	/
Apparent porosity %	/	/	/	26	/
Bulk density g/cm3 ≥	3.00	3.22	3.00	2.60	/
Compression strength Mpa	>60	>60	>50	>30	/
Rupture strength Mpa(1400℃)	12	15	8	/	/

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Nov 28 2018

VOD Furnace Refractory Material

VOD Furnace Introduction

VOD is the acronym of vacuum oxygen de-carbonization, i.e., steel liquid vacuum degassing, oxygen blowing de-carbonization treatment can be carried out in VOD refinery furnace. Oxygen blowing VOD furnace’s temperature can be higher than 1700℃, desulfurization and reduction reaction are also carried out in VOD furnace, slag alkalinity will change greatly, high smelting temperature and vacuum atmosphere will also do huge damage to furnace lining refractory material. Therefore, VOD furnace should adopt high grade refractory material.

VOD Furnace Refractory Materials

VOD slag line: Slag line zone usually adopts re-bonding magnesia chrome bricks or pre-reaction magnesia chrome bricks. Ladle wall can use low grade magnesia chrome bricks. Although magnesia chrome bricks can prolong VOD furnace’s service life, but the production cost is high. So in Europe, where dolomite refractory is abundant, VOD furnace slag line zone mainly adopts ultra high temperature sintered magnesia dolomite bricks. Furnace wall can choose lower grade sintered magnesia dolomite bricks or pitch binding unburned magnesia dolomite bricks. Magnesia dolomite refractory lining’s service life is slightly shorter than magnesia chrome refractory lining, but steel smelting cost is significantly decreased, it can bring in good economic benefits.

Below slag line: With the development of magnesia carbon bricks, for furnace body, below slag line, low carbon content magnesia carbon bricks or magnesia dolomite carbon bricks become a reasonable choice, VOD molten bath’s service life can reach to 40 times or more. After proper maintenance or patching, molten bath’s service life can be higher than 60 times. Another developing trend of molten bath refractory material is alumina magnesia castable or precast block, it can ultimately eliminate carbon in furnace lining caused adverse effect.

Cr Free Refractory Bricks for VOD Furnace

Cr2O3 in magnesia chrome bricks will finally be oxidized into Cr6⁺, which has great environment pollution, so magnesia chrome bricks’ application is constrained. Ultra high temperature sintered high purity magnesia dolomite brick is a good replacement of slag line magnesia chrome bricks. Molten bath can adopt low carbon magnesia carbon bricks or low carbon magnesia dolomite carbon bricks.

VOD Furnace Refractories Physiochemical Index

Item	High alumina spinel castable	High alumina castable	Direct binding dolomite brick	Direct binding magnesia dolomite brick	Resin binding dolomite carbon brick	Resin binding magnesia dolomite carbon brick
Application	Ladle cover	Vacuum cover	Molten bath	Molten bath, slag line	Slag line, molten bath	Slag line, molten bath
Al2O3%	92	70	/	/	/	/
SiO2 %	/	22	/	/	/	/
TiO2 %	/	2.8	/	/	/	/
MgO %	5	/	41	59	43	65
CaO %	2	3	57	39	55	33
C %	/	/	/	/	<3	<5
Bulk density g/cm3	3.0	2.80	2.82	3.00	2.94	2.92
Apparent porosity %	/	/	<17	<13	<5	<5
Compression strength Mpa	/	/	65	60	>60	>60

Item	Alumina chrome precast block	Corundum precast block	Magnesia chrome brick	Magnesia chrome brick	Unburned corundum spinel brick	Magnesia chrome joint material
Application	Ladle cover	Ladle cover	Slag line, molten bath	Molten bath, slag line	Molten bath	Magnesia chrome bricks lining
Al2O3%	92	94	<6	<6	>90	<7
Cr2O3 %	>3	/	18~23	12~18	/	18~23
Fe2O3%	/	/	<12	<12	/	<12
SiO2 %	/	/	<1.5	<1.5	/	<1.5
MgO %	/	/	>60	>65	6~12	>55
CaO %	2	2	/	/	/	/
Bulk density g/cm3	3.0	3.0	>3.15	>3.10	>3.05	>2.80
Apparent porosity %	<15	<15	<17	<17	<15	/
Compression strength Mpa	>30	>40	>35	>40	>40	>20

Item	Magnesia spinel bricks	Alumina magnesia castable	Alumina magnesia precast block	Low carbon magnesia carbon brick	Magnesia chrome gunning mix	Magnesia chrome gunning mix
Application	Molten bath	Molten bath	Molten bath	Molten bath, slag line	Molten bath, slag line	Molten bath, slag line
Al2O3%	8~12	>90	>90	/	<8	<8
Cr2O3 %	/	/	/	/	18~23	12~18
Fe2O3%	/	/	/	/	<12	<12
SiO2 %	/	/	/	/	<3	<3
MgO %	>80	4~8	4~8	>90	>55	>55
CaO %	/	<2	<2	/	/	/
C %	/	/	/	<5	/	/
Bulk density g/cm3	>2.90	>3.00	>3.00	>3.05	>2.50	>2.40
Apparent porosity %	<15	<15	<15	<5	/	/
Compression strength Mpa	>60	>30	>30	>80	>10	>10

Item	Magnesia calcia gunning mix	Dolomite gunning mix	Magnesia gunning mix	Magnesia calcia joint material
Application	Magnesia calcia lining	Magnesia calcia lining	Magnesia calcia and magnesia chrome lining	Magnesia calcia brick lining
MgO %	40	65	>92	43
CaO %	50	25	/	55
SiO2 %	<3	<3	<3	<3
C %	/	/	/	<5
Bulk density g/cm3	>2.40	>2.40	>2.40	>2.80
Compression strength Mpa	>20	>25	>25	>30

Methods for Prolonging VOD Furnace Lining Service Life

Apart from choosing high grade furnace lining refractory material, the following methods can be taken to prolong VOD furnace’s service life.

Improve smelting condition. Dolomite slag making method and properly decreases smelting temperature are effective measures to prolong furnace lining service life. Speeding up turnover speed and enhancing heat preservation can also significantly prolong furnace lining service life.

2. Enhancing furnace protection and furnace patching. Usually, gunning mix which has same composition with lining bricks are adopted for furnace lining patching. For example, magnesia chrome bricks lining should be patched by magnesia chrome gunning mix, magnesia dolomite bricks lining should be patched by magnesia calcia gunning mix.

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Nov 28 2018

Factors Affecting VOD Furnace Refractories Serving Life

AOD furnace smelting temperature is very high, acid slag and basic slag are formed in different smelting period, meanwhile, fierce gas fluxing is occurred during oxygen blowing. Under synthesized action of various smelting conditions, AOD furnace lining refractories will be damaged gradually.

Factors Affect AOD Furnace Lining Refractories Service Life

Rebinding magnesia chrome bricks is easier to be corroded with the increasement of slag alkalinity. Service life is longest when slag alkalinity is between 1.2~1.5.
The higher MgO, Cr2O3 and Al2O3 ratio is in slag, the slower magnesia chrome bricks corrosion rate will be.
Reductant is apt to react with Cr2O3 and FeOn in magnesia chrome bricks, thus bricks’ structure is destroyed and brick grains will be scoured by steel liquid. Cr content in steel liquid is also hard to be controlled.
During smelting Al/Si killed steel, Al killed steel will have lower refractory material corrosion rate than Si killed steel. Because Si and Mn in alloy steel will increase corrosion rate of refractory lining.
Between 1600℃~1750℃, per increasement of 100℃, magnesia chrome refractory material’s dissolving rate will increase 4~5 times, while magnesia calcia refractory will increase 2~3 times.
Magnesia chrome bricks will suffer smelting atmosphere influence, Cr and Fe in magnesia chrome bricks will have valance alternation and generate large volume change effect, brick’s structure is destroyed.
Fluorite in slag and Al2O3 will react with magnesia calcia brick and form low viscosity, low melting point eutectics, so corrosion rate is accelerated.
Magnesia calcia material has better low basicity slag corrosion resistance than magnesia material, while MgO refractory has better high Al2O3 slag or high iron slag corrosion resistance than magnesia calcia refractory.
Air blowing angle will have great influence on corrosion rate, generally, back angle of inclination is between 5°~7°.
For low alkalinity slag, magnesia chrome bricks have better corrosion resistance than magnesia calcia bricks, for high alkalinity slag, magnesia calcia bricks have better corrosion resistance than magnesia chrome bricks.
The dissolution rate of magnesia chrome refractory and magnesia calcia refractory in acid slag is in proportion to the 0.7 power of rotation speed.
When slag alkalinity is less than 1.3, high temperature solid phase magnesia chrome refractory’s slag corrosion resistance ability is Cr2O3>MgO-Cr2O3>MgO>MA>Al2O3.
The lower porosity rate is, the better slag corrosion resistance ability is.
In magnesia calcia bricks, slag permeation resistance and spalling resistance is increased with the increase of MgO content.
The denser raw material is, the evener composition distribution is, the better slag corrosion resistance is.
Rebinding magnesia chrome bricks has poor spalling resistance than direct binding magnesia chrome bricks.
The decrease of Cr2O3 in firebricks will weaken its permeation resistance, crack resistance and corrosion resistance.
The higher sintering temperature is, the slower corrosion rate is.

Measures to Prolong AOD Furnace Lining’s Service Life

Increase MgO and Al2O3 content in slag, when their contents approach saturation state, magnesia chrome brick lining can have a longer service life. Increase MgO and CaO content (dolomite slag making) in slag to a saturation state, magnesia calcia brick lining’s serving life can be prolonged.
Properly decrease smelting temperature is beneficial for prolonging service life.
Speed up smelting tempo, shorten smelting time can contribute to prolonging service life.
Enhancing furnace heat preservation, reducing temperature fluctuation are very important for reducing furnace lining spalling.
Choose high density, high strength and highly direct bonded magnesia chrome bricks and magnesia calcia bricks.
According to operation condition, especially slag alkalinity and interval time to choose corresponding Magnesia chrome bricks and magnesia calcia bricks.

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Nov 27 2018

AOD Furnace Refinery Refractories

With the development of steel smelting technique, there is higher and higher demand on high quality steel. To meet market requirement and clean steel development trend, out-furnace refinery ratio is continuously increasing. Therefore, refractory materials for out-furnace refinery application is developing rapidly.

AOD Furnace Description

AOD furnace is mainly used for stainless steel production. At the beginning, oxygen is blown for oxidized de-carbonization. During oxidization period, slag’s oxidization ability is increasing and temperature can reach to more than 1700℃. Next comes to reduction period, silicon, iron or aluminum is added to reduce chrome in slag, at this period, slag alkalinity is still low. Finally, lime is added to remove sulfur, as desulfurization needs high alkalinity. In the whole smelting process, slag will transform from acid to basic, atmosphere will also change from oxidization to reduction. Because of non-continuous operation, furnace lining temperature is high and has large fluctuation. So AOD furnace lining’s service life is very low, only 30 times or so, by improving smelting condition and gunning patching maintenance, the service life can reach to 70 times or more.

$AOD furnace refractory$

For AOD furnace, earlier, magnesia chrome bricks are widely used. But magnesia chrome bricks requires complicated production craft and ultra high sintering temperature, energy consumption is huge, cost is high, what’s more, magnesia chrome refractory has severe environmental contamination problem, so are gradually replaced by magnesia calcia bricks.

AOD Furnace Lining Damage Reason

The main damage reasons of AOD furnace lining are: 1) permeation and dissolution corrosion caused by high smelting temperature and long acid slag action time. 2) thermal spalling and structural spalling caused by temperature fluctuation. 3) Fierce gas-slag-steel liquid scouring and erosion. 4) Under changing AOD furnace atmosphere, Cr2O3 and FeO_n in magnesia chrome bricks can have oxidization and reduction reaction, which will destroy firebrick’s structure and volume stability.

Tuyere part main damage is thermal spalling and structural spalling, tuyere ambient place mainly suffers eddy and low alkalinity slag corrosion. Slag line’s main damage is high basicity slag permeation caused structural spalling. Furnace bottom’s main damage is high alkalinity slag corrosion and permeation. So, AOD furnace firebricks should have low porosity, high temperature strength, high thermal shock resistance and high slag permeation resistance.

AOD Furnace Lining Refractories

Magnesia calcia bricks have gradually replaced magnesia chrome bricks and are more and more popularly used in AOD furnace linings. Magnesia calcia bricks can be divided into sintered dolomite bricks, pitch binding dolomite bricks, resin binding dolomite bricks and so on. Different grades of dolomite refractory bricks can be used for different parts of AOD furnaces. When smelting temperature is very high, carbon containing refractories will have oxidation and reduction reaction and is not suitable for using. Except for dolomite bricks, magnesia calica lining joint material, magnesia calcia lining gunning mix, magnesia calcia chamotte and so on.

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Nov 26 2018

Purging Plug Bricks

Purging Plug Bricks Description

Gas supply component, also called purging plug bricks is used to blow noble gases into steel smelting vessels for steel liquid stirring. Gas blowing is an important method of modern metal smelting, is a key step of out-furnace refinery. Purging plug’s main function is strengthening smelting speed, speeding reaction process, shortening smelting time, homogenizing steel liquid temperature and ingredients. Meanwhile, non metal impurities in steel liquid can float to surface and be removed, steel liquid is purified and steel quality is improved. Purging plug bricks are widely used in converter steel making, electric furnace steel smelting and refinery ladles. Air supply bricks have a trend to be used in whole smelting process, including tundish, tornado tank and so on.

As air supply component is important functional refractory material of steel smelting, different materials and structures of air supply bricks can be used for different smelting vessels and operation conditions. There are mainly two kinds of purging plug bricks now: one is converter and electric furnace purging plug, the other is steel ladle purging plug brick. They are significantly different in working condition, using requirements, so the materials, structure and manufacturing crafts of them are different.

Converter And Electric Furnace Purging Plug

Converter bottom blowing gas supply component is important refractory material for top and bottom combined blowing craft, it plays an important role in smelting process. Top and bottom combined blowing converter’s gas supply component is magnesia carbon purging plug, which is installed at converter bottom. Currently, mainly used converter purging plug is isostatic pressing molded magnesia carbon air supply brick. This kind of purging plug brick has small expansion coefficient, good spalling resistance and long service life.

Electric furnace bottom blowing air supply components can be divided into two types. One is direct stirring system air supply bricks, which is similar to converter magnesia carbon containing, high pressure formed, sectionally combined air supply bricks. The other is indirect stirring system air supply components. Purging plug won’t contact with steel liquid directly, and air is supplied by surface air permeable ramming mass. Compared with direct stirring air supply component, indirect stirring air supply component’s service life is longer, and requires large flow rate purging plug bricks.

Converter And Electric Furnace Purging Bricks Index

Item	Converter air supply component	UHP air supply component	Purging ramming mass
MgO %	76	81	75
C %	14	14	/
CaO %	/	1.09	20
Al2O3 %	/	3.0	/
Fe2O3 %	/	0.89	3.5
Apparent porosity %	4.0	2.93	/
Bulk density Mpa	/	56	/
Rupture strength Mpa	/	23	/
High temperature rupture strength Mpa(1400℃)	10.0	12.6
Air flow rate m3.h^-1	20	/	/

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Nov 26 2018

Metering Nozzle

Metering nozzle Description

Metering nozzle is functional refractory material for controlling steel liquid flow rate during the process of continuous casting billet making. Through fixed caliber of metering nozzle, steel liquid can flow from tundish to casting mold with a constant speed. The size of nozzle hole depends on billet dimension and drawing speed of continuous casting machine, usually between 12~20mm. During the whole continuous casting process, nozzle hole’s diameter should be constant to ensure stable steel liquid flow rate, thus metering nozzle is key functional refractory component for continuous casting billets making, its quality will affect the whole continuous casting process. Metering nozzle should not only be safe and stable, but also should have characteristics such as no blockage, no spalling, no cracking and small diameter enlarging speed. To meet these requirements, nozzle materials should have excellent scouring resistance, corrosion resistance, erosion resistance and thermal shock resistance.

Metering Nozzle Types

Currently, universally used metering nozzle material is zirconia containing refractory. The content and grade of zirconia can directly affect nozzle hole enlarging speed and service life. The enlargement rate of 95% zirconia nozzle hole is about 0.03mm/h. According to structure, there are 3 types of metering nozzles, homogeneous nozzle, direct compound nozzle and inserting nozzle. Homogeneous metering nozzle are those which’s main composition is zircon or those contain relatively low ratio of zirconia. It is suitable for applications which have shorter continuous casting time. Direct compound metering nozzle main body is zircon based, only nozzle hole part is compounded with high zirconia containing layer. Direct compound metering nozzle has advantages such as longer service life than zircon based nozzle, low production cost. But due to different expansion coefficient , compound nozzle has large cracking possibility during using, composite layer’s zirconia content should not be much high, generally between 70%~80%. Inserting type metering nozzle is divided into outer coating and inner core, they are produced separately and then are bound together by refractory chamotte. Outer coating is sintered high alumina refractory, inserted inner core is zirconia refractory. Inserting metering nozzles have low production cost, good thermal shock resistance and various ZrO2 content, are the main structure adopted in production.

The inner core materials of zirconia metering nozzle are partial stable fused zirconia and zircon. Sintering temperature correlates with zirconia content, the sintering temperature of zircon nozzle is between 1630℃~170℃. Stable fused zirconia nozzle inner core’s sintering temperature is between 1750℃~1800℃.

Zirconia Metering Nozzle Core Refractory Physiochemical Index

Item	X-75	X-80	X-85	X-93	X-95	Z-65	Z-75	Z-95
ZrO2%	75	80	85	93	95	67.3	76.2	95.6
SiO2%						31.1	21.5
CaO%				3.0	3.0	3.0
MgO%								2.4
Apparent porosity%	22	21	22	24	18	20	20.5	12.5
Bulk density g/cm3	3.9	4.0	4.1	4.3	4.7	3.75	3.94	4.95
Compression strength MPa					60	95	60
Thermal shock resistance times				>5	>5
Continuous casting time/h	5	7	8	8	15	/	/	20

Quick Changing Nozzle

Metering nozzle may happen cracking accident or nozzle core enlargement during production. To solve these problems and prolong metering nozzles’ service life, non stop quick changing technique is developed. Through online quick changing of metering nozzle, unit ladle continuous casting time is large scale increased, max. time can reach to 70h.

Quick Changing Nozzle Refractory Physiochemical Index

Item	Material	Chemical composition (w%)				Bulk density g/cm3	Apparent porosity %	Compression strength Mpa
Item	Material	SiO2	ZrO2	Al2O3	MgO	Bulk density g/cm3	Apparent porosity %	Compression strength Mpa
ZrO2 core	ZrO2	1.1	95.0	/	2.6	4.92	13.0	/
Outer jacket	Corundum castable	/	/	98.0	/	3.10	16.5	35.0
Tundish pocket block	Sintered high alumina	15.0	/	83.0	/	2.67	21.0	/

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