VOD furnace structure
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

ItemHigh alumina spinel castableHigh alumina castableDirect binding dolomite brickDirect binding magnesia dolomite brickResin binding dolomite carbon brickResin binding magnesia dolomite carbon brick
ApplicationLadle coverVacuum coverMolten bathMolten bath, slag lineSlag line, molten bathSlag line, molten bath
Al2O3%9270////
SiO2 %/22////
TiO2 %/2.8////
MgO %5/41594365
CaO %2357395533
C %////<3<5
Bulk density g/cm33.02.802.823.002.942.92
Apparent porosity %//<17<13<5<5
Compression strength Mpa//6560>60>60

     

ItemAlumina chrome precast blockCorundum precast blockMagnesia chrome brickMagnesia chrome brickUnburned corundum spinel brickMagnesia chrome joint material
ApplicationLadle coverLadle coverSlag line, molten bathMolten bath, slag lineMolten bathMagnesia chrome bricks lining
Al2O3%9294<6<6>90<7
Cr2O3 %>3/18~2312~18/18~23
Fe2O3%//<12<12/<12
SiO2 %//<1.5<1.5/<1.5
MgO %//>60>656~12>55
CaO %22////
Bulk density g/cm33.03.0>3.15>3.10>3.05>2.80
Apparent porosity %<15<15<17<17<15/
Compression strength Mpa>30>40>35>40>40>20
ItemMagnesia spinel bricksAlumina magnesia castableAlumina magnesia precast blockLow carbon magnesia carbon brickMagnesia chrome gunning mixMagnesia chrome gunning mix
ApplicationMolten bathMolten bathMolten bathMolten bath, slag lineMolten bath, slag lineMolten bath, slag line
Al2O3%8~12>90>90/<8<8
Cr2O3 %////18~2312~18
Fe2O3%////<12<12
SiO2 %////<3<3
MgO %>804~84~8>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
ItemMagnesia calcia gunning mixDolomite gunning mixMagnesia gunning mixMagnesia calcia joint material
ApplicationMagnesia calcia liningMagnesia calcia liningMagnesia calcia and magnesia chrome liningMagnesia calcia brick lining
MgO %4065>9243
CaO %5025/55
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.

  1. 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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    AOD furnace
    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

    1. 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.
    2. The higher MgO, Cr2O3 and Al2O3 ratio is in slag, the slower magnesia chrome bricks corrosion rate will be.
    3. 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.
    4. 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.
    5. 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.
    6. 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.
    7. Fluorite in slag and Al2O3 will react with magnesia calcia brick and form low viscosity, low melting point eutectics, so corrosion rate is accelerated.
    8. 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.
    9. Air blowing angle will have great influence on corrosion rate, generally, back angle of inclination is between 5°~7°.
    10. 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.
    11. 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.
    12. 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.
    13. The lower porosity rate is, the better slag corrosion resistance ability is.
    14. In magnesia calcia bricks, slag permeation resistance and spalling resistance is increased with the increase of MgO content.
    15. The denser raw material is, the evener composition distribution is, the better slag corrosion resistance is.
    16. Rebinding magnesia chrome bricks has poor spalling resistance than direct binding magnesia chrome bricks.
    17. The decrease of Cr2O3 in firebricks will weaken its permeation resistance, crack resistance and corrosion resistance.
    18. The higher sintering temperature is, the slower corrosion rate is.

    Measures to Prolong AOD Furnace Lining’s Service Life

    1. 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.
    2. Properly decrease smelting temperature is beneficial for prolonging service life.
    3. Speed up smelting tempo, shorten smelting time can contribute to prolonging service life.
    4. Enhancing furnace heat preservation, reducing temperature fluctuation are very important for reducing furnace lining spalling.
    5. Choose high density, high strength and highly direct bonded magnesia chrome bricks and magnesia calcia bricks.
    6. According to operation condition, especially slag alkalinity and interval time to choose corresponding Magnesia chrome bricks and magnesia calcia bricks.

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      AOD furnace refractory
      Nov 27 2018
      AOD Furnace Refinery Refractories

      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

      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 FeOn 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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        kiln furniture
        Nov 27 2018
        Kiln Furniture

        Kiln Furniture Description

        Kiln furniture is ceramics kiln functional refractory products, which’s main function is separation, support and protection of ceramic wares green body during high temperature sintering in ceramic kiln. By materials compositions, kiln furniture can be divided into different categories. Clay kiln furniture made by chamotte and clinker (waste saggers, waste clay) can  be used at about 1300℃. High alumina kiln furniture, which’s Al2O3 content is higher than 46%, can be used at temperature under 1450℃. Mullite kiln furniture, which’s main crystalline phase is mullite(10 % kaolin, 90% synthesized mullite), has good mechanical strength and can be used between 1400~1500℃. Cordierite mullite kiln furniture, which’s principle crystalline phase is cordierite and mullite, can be used below 1310℃. Silicon carbide kiln furniture and re-crystallized silicon carbide kiln furniture have extraordinary good thermal shock resistance and high strength, can be used below 1400℃. Re-crystallized silicon carbide kiln furniture’s short term max. working temperature can reach to 1650 ℃. Long term max. working temperature of silicon nitride binding silicon carbide kin furniture can reach to 1550℃.

        cordierite kiln furniture

        By function, kiln furniture can be classified into tiles kiln furniture, bricks kiln furniture, solid shed board, hollow shed board, batts, props, plate sagger, profile setters, sintering trays and so on.

        cordierite hollow shed board

        Kiln Furniture Characteristics

        Good thermal shock resistance, room temperature and high temperature mechanical strength.

        Excellent thermal conductivity and air permeation ability.

        High refractoriness and refractoriness under load(RUL), RUL temperature should be 50~100 ℃ higher than ceramics sintering temperature.

        Lightweight, low specific heat capacity, accurate size and nice regularity.

        cordierite mullite kiln furniture

        Kiln furniture max. Working Temperature

        ItemClay kiln furnitureHigh alumina kiln furnitureMullite kiln furnitureCordierite mullite kiln furnitureSilicon carbide kiln furniture
        MaterialClay, saggerBauxiteMullite, bauxiteCordierite, mulliteSilicon carbide
        Al2O3 % ≥/46///
        Max. working temperature ℃130014501400~150013101400

        cordierite shed board

        Kiln Furniture Application

        Ceramics industry kiln furniture pieces should endure harsh conditions, repeated heating and cool cycles, the main damages are cracking, bending, dirt accumulation and surface glazing due to oxidation and other chemical reaction. So, for service temperatures up to 1300°C, cordierite mullite furniture which has very small thermal expansion and  excellent thermal shock resistance is popularly used.

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          bottom air supply brick
          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.

          bottom air supply brick

          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.

          steel ladle purging plug

          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

          ItemConverter air supply componentUHP air supply componentPurging ramming mass
          MgO %768175
          C %1414/
          CaO %/1.0920
          Al2O3 %/3.0/
          Fe2O3 %/0.893.5
          Apparent porosity %4.02.93/
          Bulk density Mpa/56/
          Rupture strength Mpa/23/
          High temperature rupture strength Mpa(1400℃)10.012.6 
          Air flow rate m3.h-120//

          steel ladle purging brick

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            zirconia metering nozzle
            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.

            zircon metering nozzle

            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.

            metering nozzle

            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

            ItemX-75X-80X-85X-93X-95Z-65Z-75Z-95
            ZrO2%758085939567.376.295.6
            SiO2%31.121.5
            CaO%3.03.03.0
            MgO%2.4
            Apparent porosity%22212224182020.512.5
            Bulk density g/cm33.94.04.14.34.73.753.944.95
            Compression strength MPa609560
            Thermal shock resistance times>5>5
            Continuous casting time/h578815//20

             zirconia metering nozzle

            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

            ItemMaterialChemical composition (w%)Bulk density g/cm3Apparent porosity %Compression strength Mpa
            SiO2ZrO2Al2O3MgO
            ZrO2 coreZrO21.195.0/2.64.9213.0/
            Outer jacketCorundum castable//98.0/3.1016.535.0
            Tundish pocket blockSintered high alumina15.0/83.0/2.6721.0/

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