Refractory manufcturing,properties

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Refractory manufacturing Refractory testing

andRefractory properties

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What is refractory ?

Is it a material which should withstand high temperature only ?

The right definition is that it should withstand high temperature,resistance to thermal and thermo chemical load, posses high volume stability, resistant to erosion and abrasion, be tough , and resistant to chemical corrosionetc. Or otherwise it should have high RUL, high PCE, low conductivity , high hot MOR, high creep resistance and optimum CCS etc

Overall it is a compromise with all the above properties.Choice of refractories depend on the operating and mechanicalconditions of the kiln.

There is no refractory material which posses all the above properties 100 %

In general any material which in service > 600 deg C is called refractory



Refractories

Shaped refractories Unshaped refractories ormonolithics

Acid refractories Basic refractories Neutral refractories

Silica basedrefractories, fire clay

bricks

Magnesia, MagnesiaChromium , Magnesia

Alumina , Dolomite

Alumino silicatesAlumina bricks,Zirconia

based refractories, like zirconal, zircon, etc



Fire Clay bricks

refractory clays Kaolins extended with chamotte or non plastic argillacious matter unwetted by water Al2O3 content = 30 to 45 %

High alumina bricks

1)Cyanite,andalusite,and siliminite 2) natural hydrated alumina(hydrargillite,bohemite,and disapore contained in bauxite) 3)Artificial calcined hydrated alumina, and natural and electro fused alumina ( Alpha -alumina or

Class A =45 - 60 % Al2O3 Class B = 60 - 70 % Al2O3

Class C = > 75 % Al2O3Silica bricks Dinas

Magnesia bricks

Magnesit ( MgCO3), Dolomite ( MgCO3.CaCO3), Mg(OH)2,Mgo Obtained from

dolomite,saline water and sea water

Spinel bricks

MgO and Al2O3 together sintered or fused MgO from sea water and alumina from alumina industries ,alpha alumina etc)

Raw materials used for manufacturing of bricks



Acidic Basic

neutral

Raw material user



ZrO2 Cr2O3

CaOSiO2

ZrSZircon silicate

1775 O C

A3S2mullite 1840 O C

Important mineral phases in refractories

M2SForstrite1890 O C

MCrPicro chromite

C2SBredigit 2130 O C

CA6Hibonite

1850 O CMA-spinel

2135 O C

MgOAl2O3

2180 O C



Melting point of pure refractory oxide

1200

1400

1600

2000

2200

2400

3000

2800

2600

SiO2 Al2O3 Cr2O3 CaO ZrO2 MgO

1702

2050

2275

26002700 2800

Deg c



Classification of refractories regarding melting point and alkalinity

1234567891011121314

3000

2750

2500

2250

2000

1750

1500

melting point Deg c

pH value

Cao

MgO

Al2O3

ZrO2

Cr2O3

SiO2

basic neutral acidic



Process flow chart for manufacturing

Comminution

preparation

classification

mixing

shaping

drying

firing



SIC crystals ( Silicon carbide)



ZrSiO4

Zircon crystals ,ZrSiO4



Refractory manufacturing process

Tunnel kiln Tunnel dryer

Tunnel carsFinished product storage

Brick press machines

Coarsecrusher

Fines crusher

Ball mill

storage

elevatorVibrating screen

Storage silosclassifier

Clay crusher

Clay mill

Drying tower / classifier Binder & liquids

Liquid dosage



Refractory manufacturing processSchematic diagram of refractory manufacturing

Roughcrushing

Rawmaterial

middlecrushing distribution

finecrushing

Storage byGrain size

Measuringquantity

mixing mouldingdrying

firing

inspection packing shipping



Refractory clay mine

Opencast mining

Under ground mining



Cone crusher



Hydraulic press



Iso static press machine



Tunnel dryer



Tunnel kiln



Important refractories used in cement industry

Magnesia containing bricks _ mag chrome, mag spinel,dolomite,hercynite, galaxite based, zirconia based

High alumina bricks - 60 - 70 % Al2O3

Fire clay bricks - 30 % Al2O3

Light weight insulating bricks

Unshaped refractories or castables - conventional,low cement castable, ultra low cement castables,insulation castables



Raw materials for Magnesia bricks are

• Natural magnesite , MgCO3 , Coarse crystalline ,fine crystalline

• Synthetic magnesia,sea water magnesia , salt brine • The principal constituent determining the characteristic

properties of magnesia refractories is periclase

Properties of periclase

0 Melting point = 2800 deg . C0 Thermal conductivity = 3 - 4 w / mk0 Thermal expansion = 1.4 %

Refractory products for the cement kiln



• Magnesia bricks, MgO, > 80 %

• Magnesia spinel bricks, MgO , 80 - 90 %

• Magnesia hercynite bricks, MgO, 80 - 96 %

• Magnesia Zirconia bricks MgO, 85 - 96 %

• Magnesia chromite MgO, 55 - 80 %

• Chromite bricks Cr2 O3=25%MgO = 25 %

• Forsterite MgO and SiO2

• Dolomite MgO = 60 % and CaO=40 %• Magnesia, galaxite bricks Mgo=91% ,and MnO=2.6%

Basic bricks used in the cement industry



Mineral Formula Abbreviation Fusiontemp ,Deg CPericlase MgO M 2800 deg CForsterite 2 MgO.SiO2 M2S 1890

Monticellite CaO.MgO.SiO2 CMS 1495Merwinite 3 CaO.MgO.2SiO2 C3MS2 1575

Dicalcium silicate 2CaO.SiO2 C2S 2130Magnesium ferrite MgO.Fe2O3 MF 1750Dicalcium ferrite 2 CaO.Fe2O3 C2F 1435

Tri calcium silicate 3CaO.SiO2 C3S 1900Brown mellarite 4CaO.Al2O3.Fe2O3 C4AF 1395

Dolomite CaO.MgO CM 2450Andalusite Al2O3.SiO2 AS

Mullite 3Al2O3.2SiO2 1840Siliminite Al2O3.SiO2 AS 1545

Important refractory minerals used in refractories



Andalusite Al2O3.SiO2 ASMullite 3Al2O3.2SiO2 1840

Siliminite Al2O3.SiO2 AS 1545Corundum 2050Hercynite FeO.Al2O3 FA 1760Galaxite Mno.Al2O3 mA

Magnesia aluminaSpinel MgO.Al2O3 MA 2135Gehelinite 2CaO.Al2O3.SiO2 C2AS 1590

Calcium aluminate CaO,Al2O3 CA 1600Anorthite CaO.Al2O3.2SiO2 CAS2 1550

Dicalcium ferrite 2CaO.Fe2O3 C2F 1450Myenite 12CaO.7Al2O3 C12A7 1455

Gehelinite 2CaO.Al2O3.SiO2 C2AS 1590Calcium aluminate CaO,Al2O3 CA 1600

Anorthite CaO.Al2O3.2SiO2 CAS2 1550Dicalcium ferrite 2CaO.Fe2O3 C2F 1450

Myenite 12CaO.7Al2O3 C12A7 1455

Important refractory materials used in refractories



Major refractory bricks used in cement industries

70 % Alumina bricks Cooling zone ,burning zone,transition zone

60 % Alumina bricks transition zone,calcining zone, t.a.duct,calciner, cooler area

40-50 %Alumina bricks calcining zone, t.a.duct,calciner, cooler area

30 % Alumina bricks t.a.duct, ,calciner, cooler area,pre-heater cyclones

Magnesia chrome bricksDolomite bricks Burning zone

Magesia spinel bricks cooling zone,burning zone ,transition zone

Hercynite ,nochromeGalaxite no chrome transition zone

Location where it is usedType of brick



Refractory propertiesPhysical properties

1)Bulk density g / cm3

2)Apparent porosity %3)Cold crushing strength N/ mm2

Thermal properties1)Refractoriness under load (RUL)

OCtate

2) PCE ( pyrometric cone equivalent)SK (Arton cone in ASTM standard)

3)Thermal expansion ,lin % (PLC) at 4000c

8000c12000c



4)Thermal shock resistance (TSR)at 9500 c in airor

Water quenching cycles

5) Thermal conductivity at3000c7000c

10000c Chemical analysisMgOAl2O3Cr2O3Fe2O3CaOSiO2ZrO2 MnO2 etc



1. Bulk density

Density of all refractories is an indirect measure of their capacity to store heat .2. Apparent porosity

The porosity of a refractory is a measure of % pores to the( summation of open and closed pores)total weight of a brick. This property is significant to decideupon its resistance to penetration by slags and fluxes ,itspermeability to gases and its thermal conductivity

Porosity is controlled by the following1) by controlling the texture of the bricks2) by controlling the size of the particles3) by method of making4) by controlling the firing temperature

Physical properties



Porosity affects

• the strength of thebrick

• porous bricks are mechanically weak

• lower porosity givesbetter resistance to slag attack

• thermal conductivitypc

po

po

po

po

po

Po –open poresPc –closed pores

po

pc

Pc



3. Cold crushing strength ( CCS )

Cold crushing strength of a refractory material represents itsstrength .In other words it tells us how much load it can bearin cold condition

The mechanical strength (CCS) of refractory brick is governed largely by the amount and the character of the matrix material between the larger grains. Good tool to provide for evaluatingthe degree of bond formation during production. It indicates theability of the brick to withstand abrasion and impact in lowtemperature application.



CCS testing machine



Cold crushing equipment and CCS valuesBrick grade CCS ( N / mm2)Silica 15 -20Fire clay 12 - 70Corundum 35 - 80Magnesia 50 - 110Magnesia chromite 30 - 70Magnesia spinel > 40 Insulating Brick 3 - 20



Density Coefficient of thermalconductivity

Thermal shock

resistance

Cold crushingstrength

Porosity

Correlation between the physical properties



Thermal properties1.Refractoriness( fusion temperature or softening temp)

Transition of a solid material into the liquid form underthe influence of heat. A true melting point is temperatureat which the solid and liquid phase of the compositionco-exist in equilibrium.

It is the ability of a refractory to remain rigid at a giventemperature. It is an indirect indication of the amountand the viscosity of any liquid which it may contain.

The reference samples are called seger cones in DIN standards and Norton cones in ASTM standards.

Or PCE (pyrometric cone equivalent)



Test sampleStandard samples

12 3

45

PCE test(pyro-metric cone equivalent)

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Seger cones before and after firing



Seger cone and reference temperature



Determination of the softening behaviour under temperature and load

The three methods evolved are

• Determination of the refractoriness under load

• Determination of the refractoriness load ( diifferential)

• Determination of the thermal expansion under load ( creep)



Determination of refractoriness under load (RUL)

Characteristic temperatures are Brick grade t a / O c

t a : 0.3 mm compression from the Fire clay 1300 -1550temperature the temperature of Corundum 1600 - 1750highest expansion Silica > 1660( 0.6 % compression of test sample) Magnesia chromite > 1550

t e : 10 mm compression from the Magnesia-hercynite 1600temperature of highest expansion Dolomite 1700(20 % compression of test sample) Magnesia spinel > 1700

t b : temperature of breaking sample: Carbon brick non-softening



Curve example of refractoriness under load

Determination of the refractoriness under load (differential)



Determination of the thermal expansion underload ( creep)

Curve example of Creep under load



Creep test equipments



Refractoriness under loadThis is a measure of the resistance of a refractory bodyto the combined effects of heats of load.This test helpsto study the behavior of a refractory product when

subjected to a constant load under conditions of progressively rising temperature.The ground mass / matrix helps to bond the entire mass of a refractory brick strongly together. The amount and the strength of the glass is fixed by the alumina - silica ratio, fluxing oxide content and the temperature of firing.

It is an important parameter to decide upon the safer limit of service temperature in a given situation.Contributing factors to the increased resistance to the pressure are

a) More thorough distribution of liquid throughout the brickb) The growth of crystals through the influence of heatc) Crystallization of a portion of the liquid during cooling.



High temperature creepIn a brick held at constant temperature and pressure,

gradual solution of solid material up to the limits of itssolubility in the liquid may cause some increase in theviscosity of the liquid. This increase is dependent onthe nature of ground mass, glass content. Higher glass content will result higher deformation in thissituation. This property of refractoriness is called hightemperature creep. Lower deformation will ensurerigidity under the service condition.

The creep is the measurement of deformation of arefractory product as a function of time when it issubjected to a constant load and heated at a specifiedtemperature.



RUL measuring equipment

Carbon or mullite rod

insulating brick lining

Corundum, magnesiteor mullite tube

Steel casing

Metal electrode

Coarse amorphouscarbon

Test specimen

View point



RUL testing machine and creep test machine



Creep curves



Softening under load

0 200 400 600 800 1000 1200 1400 1600 1800

P res

sur e

/ e x

ten s

ion

(%)

- 2

- 1

0

1

2

3

Temperature o C

magnesia zirconia

magnesia spinel

Magnesia chromate

dolomite



Creep measurement of various high alumina refractories under 25 psi load at 2600 O F for 0 - 100 hours

L in e

a r s

u bs i

d en c

e-p e

rce n

t

54

32

1

0-1

-2-3-4

-5-6

-7

-8-9

-100 10 20 30 40 50 60 70 80 90 100

Time(hrs)

60 % alumina - low alkali

70 % alumina

50 % alumina

85 % alumina



Linear expansion (Permanent linear change)High temperature reheat test maybe used to reveal

1) if a brick has been fired long enoughor at a high temperature

2) whether a brick has adequaterefractoriness and volume stabilityIt is expressed as a percentage , preferably by the ratio of the length of the test piece after heating andthe original value of the length

Equipments used to determine

Thermal expansion



20 deg c

1000 deg c

2000 deg c

L= 1000 mm

L= 1013 mm

L = 1026 mm

Magnesia : Thermal expansion = + 1.3 % at 1000 degc

Alumina oxide : Thermal expansion = + 0.8 % at 1000 degc

Fire clay Thermal expansion = + 0.5 % at 1000 degc

Thermal expansion or refractory materials



Thermal expansion curves



Thermal expansion is important in service , as the effect of expansion hasto be taken into account during refractory installation and construction oflarge installations ( expansion joints). The expansion curves of most of refractories is more or less linear with increasing temperature or reversible.



Thermal shock resistance( spalling resistance)

Thermal spalling results from stresses caused byunequal rates of expansion and contraction in different parts of brick and usually associated with rapid changes of temperature.

In cement rotary kiln the brick lining needs to bespalling resistant as the lining is subjected tocontinuation variation of temperature because of rotary motion of kiln.

TSR ( thermal shock resistance ) is given in cycles.Quenching is done by air or water



Equipments for thermalshock resistance test



Thermal conductivityThe coefficient of thermal conductivity is defined as the quantity ofheat that flows across unit area in unit time if the temperature gradient across this area is unity.

Thermal conductivity K is given ask ( T1 - T2 ) At Kcal / hr - m - O C or BTU / hr -sq.ft - O F

Q = d Q = amount of heat

T1 = hot face temperatureT2 = cold face temperatureA = area cross sectiont = timed = thickness

Thermal conductivity of a refractory decreases with increase in porosity.Increase and decrease of thermal conductivity at elevated temperature also depends on amount of glass, liquid and crystallinity of the material.



12

346

578

9 10

11

12

13 14

200 400 600 800 1000 1200 deg c

2

4

6

8

10(w

/ k

m)

Thermal conductivity offired refractory bricks

1. Insulating refractory bricks2. Zirconia3. Dry- pressed fire clay4. Fused silica5. Forsterite6. Chromite7.Corundum 90 %8. Magnesia- chrome9.Zircon silicate.10. Corundum 99 %11. Carbon12.Silicon carbide 40%13. Magnesia14. Silicon carbide



Thermal conductivity depends on temperature , chemical and mineralogical, composition of the brick , porosity, pore size and brick firing temperatureMaterial Thermal conductivity

at 1000 O C (W/(m.K)

Magnesia 4.4Magnesia chromite 2.5Magnesia –spinel 2.8Magnesia hercynite 2.6Alumina 3.0Insulating brick 0.6Iron 28.0

Thermal conductivity



The bending strength can be calculated by means of the equationσ bending = 3.F.l / (2.b.h2)l = distance between bladesb = width of sampleh= height of sample

In order to determine the magnitude of the rupture stress ofrefractoies , the resistance to deformation under bending load is measured.

F Pressure load

Tensile load

Determination of modulus of rupture

sample



Determination of hot modulus of rupture (HMOR)

Structural configuration of the refractory material as well as the amount and properties of occurring melts characterize the HMOR

HMOR (N /mm2)

Testing temperature (deg C) 1200 1400 1500

Magnesia , low iron content > 14 11 8

Magnesia , high iron content > 12 5 1

Magnesia – Chromite > 10 5 3

High alumina > 25 18 7

Zirconia > 25 > 25 > 18



Modulus of rupture

MOR test

The resistance to bending stress of refractory products provideinformation on their deformation behavior at high temperature.



Hot MOR Test



Principle of wedge splitting test



Wedge splittingmachine

Groovedsplit

The specific feature ofthis method of testing is thedetermination of fracture mechanical parameters athigher temperatures , up to

1200 deg C



Influence of of the aggregates on the secondaryload bearing capacity of the softening behavior



Chemical composition

By quantifying all the constituents present in refractory, it ispossible to assess the chemical properties and melting behaviorof a given refractory.As it is important to know the % Al2O3 inhigh alumina brick, % MgO in magnesite brick , and % SiO2 in silica brick etc.,the determination of minor constituents hasalso been recognized as controlling factors in the performanceof many refractories. The chemical composition is of greatimportance with respect to attack by slag , glass melts , flue dusts and vapors. In general the principle applies that a brick ismore resistant the lower the rate of chemical reaction gradientbetween the slag and brick is. Therefore, where the acid slagis expected , acid bricks are preferably used , and basic brickswhere basic slag is expected.



According to the behavior during contact reaction ,the following groups of bricks can be differentiated.

Acid group - fused (99% SiO2), Silicon carbide bricks,Zircon crystobalite . Zircon silicate

Basic group - dolomite, magnesia, magnesia chrome, chrome magnesia ,forsterite

Inert or neutral - carbon , high alumina chromite group



Cup corrosion test

Alkali test of a high alumina brickwith K2CO3

Alkali test of a sic containing high alumina brick with K2CO3



Mineralogical investigations by X-ray diffractionDetermination of the mineral phases composition of material

X-ray diffraction diagram of a used magnesia –spinel brick grade ,salt infiltrated



Microscopically techniques ( micrologies)

• Light micoscopy ( transmitted light and reflected light microscopy

• Microprobe analysis ( WDS, EDS)

• Scanning electron microscopy

Advantages of these micrlogies opposite other investigationmethods

• Diagnosis of mineral phases composition in raw materials , refractory products etc and their configuration

( textural/ structural criterions, pore shape and size etc



Mineralogical investigationsReflected light microscopy

Pictures of magnesia - spinel brick grades with different raw material composition



Microprobe Analysis

Chemical – mineralogical composition in m mBoundary between slag and corundum brick

Polished section image (reflected light microscope)

Back scattered electron image(microprobe)



Mineralogical investigationsScanning electron microscopy (SEM)

Hydration of Magnesia .crack formation ,caused byformation of brucite(Mg(OH)2



Minerological investigations



Cont...

Refractory Bricks PropertiesChem. Comp. Bulk

DensityApp.

porosity CCS PCE Therm exp.

Therm. Condct. TSR (air)

(%) (gm/cm3) (%) (N/mm2)ta

(°C) tb

(°C) s.cat 1200

OC %

(W/mK)at 1000

OC

(cycles at 950

OC)

Ankral S 65-(Mg

chrome)

M = 77- 80Cr = 7 - 9 Al = 2 - 4 F= 7 - 10C= 1 - 2 S= 0.4 - 1

3.00 < 21 35 >1650 >1700 > 42 1.04 2.1 > 150

Perilex - 83 (Mg chrome)

M=80 - 85Cr = 3 - 5 A= 1 - 3F= 7 - 9C =2.5S = 1.5

2.9 - 3.05 17 - 19 55 1600 >1700 42 1.7 2.8 80

Bazal Z extra (Mg

chrome)

M = 77 Cr = 8A= 3 F= 9.5 C =1.6 S = 0.6

3 19 55 1720 1.6 2.4 100

Rexal S extra

(Spinel bricks)

M = 87 Cr = 0 A= 11 F < 0.5C < 1 S < 0.3

2.93 17 50 >1740 1.7 2.9 >120

RUL



Cont...

Chem. Comp.Bulk

Density

App. porosity CCS PCE T herm

exp.Therm. Condct. TSR (air)

(%) (gm/cm3) (%) (N/mm2)ta

(°C)ta

(°C) s.cat

1200 OC %

(W/mK)at 1000

OC

(cycles at 950

OC)

Al mag - 85

(Spinel bricks)

M = 85 - 89Cr = 0A= 9 - 12F < 0.5C < 1S < 0.5

2.85 - 3 16 - 18 50 >1700 >1700 > 42 1.4 2.8 >100

Al mag - 85 SLC

(magnesia fused spinel bricks)

M = 85 - 90 C r = 0 A= 9 - 12 F < 0.5 C < 1.4 S < 0.9

0.9 17 55 >1700 >1700 42 1.4 2.7 100

Ankral R - 19

(Spinel bricks)

M = 94Cr = 0A= 5 F = 0.2C = 0.9 S = 0.2

3 16 40 >1700 >1750 42 1.5 3 >101

Ankral R - 17

(Spinel bricks)

M = 86 Cr = 0A= 12F = 0.5C = 0.7S = 0.2

2.95 16 >40 >1700 >1750 >42 1.49 2.6 >100

RUL



Cont...

Chem. Comp. Bulk Density

App. porosity CCS PCE Therm


(%) (gm/cm3) (%) (N/mm2)ta

(° C ) tb (° C ) s.cat

1200 OC %

(W/mK)at 1000

OC

(cycles at 950

OC)

AS - 90 (Spinel bricks)

M = 91- 94Cr = 0 A= 5 - 7F = 0.5 C = 0.8S = 0.2

2.9 17 >40 1700 2.9 >100

Mag Pure - 93

(Spinel bricks)

M = 89-93A= 5 - 8 Cr= 0F = 0.5C = 2S = 1

2.9 16 - 18 50 >1700 >1700 >42 1.5 2.9 100

Mag Pure - 95

(Spinel bricks)

M = 93-96A= 3 - 5Cr= 0F =0.5C = 1S < 0.7

2.9 17 - 18 50 >1700 >1700 >42 1.6 3 100

Refra Mag -85 (Spinel bricks)

M =84-89A= 9 -12 Cr= 0F =0.8C = 1.4S =0.9

2.9 17 -19 45 >1700 >1700 >42 1.4 2.7 100

RUL



Chem. Comp.

Bulk Density

App. porosity CCS PCE Therm


(%) (gm/cm3) (%) (N/mm2)ta

(° C)tb

(° C) s.c at 1200 OC %

(W/mK)at 1000

OC

(cycles at 950

OC) Ferro Mag

-90 (Magnesia- hercynite)

(Spinel bricks)

M =87 - 92A= 4- 6Cr= 0F =3-5C = 1.5S =0.5

2.9 18 - 20 50 1600 >1600 42 1.5 2.6 100

R -63 (Magnesia- hercynite)

(Spinel bricks)

M =86A= 2.5Cr= 0F =8.2C = 1.8 S =0.9

3.1 17 > 50 >1600 >1700 42 1.5 2.7 > 100

Ankral X2 (Magnesia-galaxite)

M =91A= 3.5Cr= 0F =0.7C = 0 MnO =2.6

2.98 15 90 > 1700 2.7 > 100

VRW-70 A = 70 % Fe2O3 = 3.5 2.65 23 > 55 1460 37 2 1.9 30

VRW- Lofal 70

A = 70 % Fe2O3 = 2.5 2.65 23 > 55 1500 36 2.5 1.9 30

RUL



Thank you for your

Kind attention



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Refractory manufcturing,properties