®SIGRABOND

Graphite Specialties

Carbon Fiber-Reinforced CarbonProperties · Uses · Forms supplied

2

Contents

®SIGRABOND carbon fiber-reinforced carbon

The tailor-made composite material for extreme stresses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 3

High-performance products fabricated from ®SIGRABOND for tomorrow’s industries . . . . . . . . . . . . . . Page 4

The most important ®SIGRABOND materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 5

Selected materials from a variety of production processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 6

Production scheme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 7

Properties of ®SIGRABOND

Thermal and mechanical properties of selected ®SIGRABOND materials . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 8

Chemical properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 16

Applications of ®SIGRABOND

Furnace construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 19

Chemical process technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 20

Glass industry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 21

High-tech applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 22

Designing with ®SIGRABOND

Quality assurance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 23

Machining . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 23

Design of components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 24

Forms supplied and dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 29

3

1001

1601

2001

3001

4001

®SIGRABOND is the trade nameused by SGL Carbon for a high-strength composite material con-sisting of a carbon or graphite matrixwith carbon fiber reinforcement.This combination of carbon orgraphite with carbon fibers unitesthe many and varied favorable material properties of fiber com-posites with those of electrographite.

The tailor-made composite material for extreme stresses

• Heat resistance under protectivegas up to temperatures in excess of2000°C

• High specific strength and rigidity

• Low density and open porosity

• Low thermal expansion

• Extremely high resistance tothermal shock

• Electrical conductivity

• Anisotropy: in materials withaligned carbon fibers the flexuraland tensile strength and also theelectrical and thermal conductivityhave different values parallel to thefiber from those perpendicular tothe fiber or layer

• Excellent resistance to alternatingloads, even at relatively high tem-peratures

• Pseudoplastic fracture behavior

• Corrosion resistance andresistance to radiation

• Production of high-purity gradespossible

Characteristic properties

4

High-performance products fabricated from ®SIGRABOND for tomorrow’s industries

High-temperature technology Hollow glassware industry

Chemical industry High-tech applications

5

The most important®SIGRABOND materials

Table 1

* 0° corresponds to the alignment of the warp fibers or the axis of rotation of a winding mandrel

Material Type of fiber Standard fiber Form Preferred use,type reinforcement alignment* industry or product

1001 G Staple fiber fabric 0° / 90° Sheets Furnace construction

1501 G Roving fabrics A: O° / 90° Sheets and High-tech uses1601 G B: O° / ± 45° / 90° complex Glass industry1701 G components Heating conductors

2001 G Wound rovings, A: [(± 20°)2x (± 90°)1x]nx Pipes, axially Molds for hot2302 G reinforced B: [(± 45°)2x (± 90°)1x]nx symmetrical compression molding

C: [(± 75°)2x (± 90°)1x]nx hollow items Heating conductorsHight-tech uses

3001 G Felt Random orientation Sheets, blocks Glass industry

4012 G Chopped fibers Random orientation Sheets Glass industry

6

Selected materials from a variety of production processes

The individual properties of®SIGRABOND are determined byvarious factors, namely the type offiber, fiber content, fiber arrange-ment, matrix materials layer build-up, densification, thermal treatmentand any upgrading. Carbon fiber-reinforced carbon (CC) can thus beadapted to each individual profile ofrequirements or desired componentdesign. Only the most importantclasses of raw material and processsteps are shown in the production scheme opposite.

During the “green“ productionstage liquid binders are applied tothe various textile forms of the carb-on fibers. In this operation the fiberis – if necessary – suitably aligned,the fiber/binder ratio is determinedand the component is shaped. As itremains soft at this stage, the shapedcomponent is then densified andhardened.

The thermal treatment steps involvebaking at around 1000°C andgraphitizing at up to 2700°C.

In the baking operation (also knownas carbonizing) the volatile constitu-ents are driven out of the binders,which are initially liquid until cured.What remains is a porous carbonmatrix, which holds the carbonfibers together. To reduce porosityand increase both the strength andother properties, the baked materialis then reimpregnated and bakedagain, in some cases repeatedly. Thegraphitizing process improves someof the composite material’s prop-erties such as its electrical conduc-tivity, thermal stability and resistanceto both oxidation and corrosion.

In the machining operation theworkpieces are machined to thedesired dimensions. A number ofupgrading measures can also becarried out. In certain cases theseconsiderably improve the utilityvalue. Most ®SIGRABOND com-ponents are of monolithic design.Larger components, e. g. those forhigh-temperature furnaces, are heldtogether by CC screws or bolts.Other jointing techniques can alsobe used.

7

Carbon fibers

Basis: PAN, cellulose or pitch;various textile forms such asrovings, chopped fibers, yarns,felts, nonwovens, warp cloths,tapes, woven fabrics

Resins / pitches

Phenolic and furan resins; pitcheswith different softening points forvarious uses

Combined processing

of fiber products and binders, e.g. into

• Prepregs and laminates• Impregnated felts• Molding compounds• Wound components

Shaping

Densification and hardening

Baking

Impregnation and rebaking

Graphitizing

Machining

Upgrading measures

e.g. • Application of anti-oxidation finish• Coating with silicon carbide• Post-purification to a very low ash content

Production scheme

Raw

mat

eria

ls“G

reen

“ pr

oduc

tion

Ther

mal

fin

ishin

g sta

ges

Fina

l tre

atm

ent

8

Thermal and mechanical properties of selected ®SIGRABOND materials

As the range of CC material variantsthat can be produced is very exten-sive, the data given in the followingare only those for the most impor-tant applications and are confined to our ®SIGRABOND standardmaterials. Data relating to specialmechanical characteristics, surfaceproperties or stability are given for afew ®SIGRABOND grades by wayof example.

In most high-temperature applica-tions, use is made of CC materialstreated at 2000°C whose propertiesappear in Table 2.

Dependence of properties onthe number of impregnations

The change in the properties of themost important ®SIGRABONDgrades as a function of the numberof impregnation and rebaking oper-ations is shown in Figure 1, exem-plified by material grade 1601. Thefinal stage is identical to that forstandard grade 1601 G. As a generalrule the material is found to improvein line with the number of densifi-cation (impregnation and baking)stages. A number of characteristicvalues such as interlaminar shearstrength, flexural and tensilestrength, bulk density, pore volumeand Young´s modulus, are given byway of example. This improvementalso extends to many other prop-erties, including electrical and thermalconductivity, compressive strengthand resistance to alternating loads.An increase in the number of densi-fication stages, however, pushes upproduction costs.

Figure 1

Overall improvement in properties with the number of densification stages

®SIGRABOND 1601densification

GS1x

GH2x

G3x

Densityg/cm3

1.60

1.50

1.40

≈

GS1x

GH2x

G3x

Flexural strengthMPa

200

150

100

≈

GS1x

GH2x

G3x

Flexural modulus of elasticityGPa

80

70

60

≈

GS1x

GH2x

G3x

Interlaminar shear strengthMPa

12

10

8

≈

9

Typical values for the properties of graphitized ®SIGRABOND

Material type 1001 G 1501 G 1601 G 1701 G 2001 G1) 2) 3001 G 4012 G3)

Property* 2302 G

Heat treatment °C 2000 2000 2000 2000 2000 2000 2000

Bulk density g/cm3 1.38 – 1.48 1.45 – 1.55 1.36 – 1.52 1.28 – 1.44 1.20 – 1.40 ≈ 1.00 1.4 – 1.5

Porosity, open % 18 – 25 10 – 12 11 – 15 n. d. n. d. n. d. n. d.

Flexural strength, D MPa 110 – 130 240 – 300 150 – 220 140 – 180 30 – 70 ≈ 30 35 – 40

Flexural modulus of elasticity, II GPa 28 – 33 70 – 85 60 – 80 60 – 70 15 – 25 ≈ 10 20 – 25

Tensile strength, II MPa 55 – 65 320 – 400 300 – 350 280 – 350 n.d. compressive compressivestrength D strength D

20 - 25 100 – 140

Resistivity at 20°C, II Ωµm 29 – 34 22 – 26 22 – 26 22 – 26 n.d. 25 – 30 –

Coefficient ofpermeability cm2/s 7 · 10-2 5 · 10-2 0.3 – n.d. n.d. –

Interlaminarshear strength MPa 11 – 15 11 – 15 8 – 12 7 – 10 5 – 7 – –

* ®SIGRABOND with standard laminate build-up or standard wind-up pattern1) Layer build-up 2001 G: 0°C / ± 45° / 90°; build-up 2302 G, wound: roving and inner prepreg layer2) Direction-dependent values: 0°; 90° values not shown3) Trial product in the course of development

D Measured perpendicularly to the plane of the laminateII Measured parallel to the plane of the laminaten. d. = no data available

Table 2

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Thermal and mechanicalproperties of selected ®SIGRABOND materials

Fracture behavior

When placed under load, compo-nents made from fiber compositesdo not fracture suddenly but neitherdo they exhibit the plastic behaviorof metals when these are stressedbeyond the creep limit. Stressesimposed on CC cause only a fewfiber strands to fracture at first, andonly after repeated stretching doesfurther failure occur. This type offracture is known as quasi-plastic.Readers are also referred to details ofeffective bearing strength on page 27.

Because of its quasi-plastic behaviorand porosity, CC can be secured bynails.

Figure 2 shows a typical stress-straingraph for CC materials, in this caseSIGRABOND 1501 G. The maxi-mum permitted load is achieved atan extension of around 0.3 %. Theelongation of the material at fractureis between 0.7 and 1.0 %.

®SIGRABOND’s transverse con-traction number, like all its otherproperties, depends on the fibercontent and alignment. Typical

values are given in the followingtable.

Figure 2

Typical failure behavior of abending specimen of®SIGRABOND1501 G material

Table 3Material type Fiber Direction of Typical

alignment measurement transversecontraction number

1001 G 0° / 90° 0°; 90° 0.15

1501 G 0° / 90° 0°; 90° 0.0145° 0.65

1601 G 0° / 90° 0°; 90° 0.10

2001 G 0° / 90° 0°; 90° 0.010° / ±45° / 90° 0° 0.30

Stre

ss

Strain

Region wherefiber fracturesbegin

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Properties at high temperatures

The thermal treatment of®SIGRABOND materials has thegreatest influence on the physicalproperties of CC. It is even greaterthan that of other governing factorssuch as fiber content, fiber alignmentand nature of the matrix.

Hot bending strength

Unlike all other ceramic or metallichigh-temperature materials, carbon-fiber materials increase in strengthwith a rise in temperature. At high

temperatures the materials are in alargely stress-free state. As they cool,the materials undergo a continuousbuild-up of internal stresses whichare additional to any stresses imposedfrom outside. This results in lowstrength at room temperature buthigh strength at 1000°C or 2000°C,for example (Table 4).

It should be noted in regard to Table4 that the rates of increase instrength from room temperature toelevated temperatures are lower forCC than for graphite. Comparedwith graphite, however, CC is 10 to 20 times stronger.

Specific electrical resistance

The characteristic paths of the curvesfor various grades of material areshown in Figure 3. The curves areunaltered by repeated heating. Thehighly graphitized material grade1501 Z has the lowest specific elec-trical resistance.

Tubes with different wind-up pat-terns have very different specificelectrical resistance values even ifother production parameters areidentical, e.g. number of densifi-cation processes and treatment tem-perature. The less the fibers arealigned with the axis of the pipe, thehigher is the resistivity.

• Example from Figure 5 for RT and pipes with ± 20° winding: 24 Ωµm• Example for RT and pipes with ± 75° winding: approx. 100 Ωµm• Tubes with wind-up pattern [(± 20°) 2x (± 90°)1x]nx

Table 4Typical percentage changes in the hot bending strength valuesof selected carbons

Material 20°C 1000°C 2000°C

®SIGRABOND 1001 G 100 % + 20 % + 40 %

®SIGRABOND 1501 G 100 % + 15 % + 30 %

Electrographites 100 % + 40 % + 85 %

Temperature [OC]

0

5

10

15

20

25

0 400 600 800 1000200 1200 1400 1600 1800 2000

30

35

1001 G1501 G 2001G 1001 Y2001Y1501 Z

Resis

tivity

[Ωµm

]

12

Thermal and mechanicalproperties of selected®SIGRABOND materials

Figure 4

Linear coefficient of thermalexpansion (a) of various®SIGRABONDsheet materials

Figure 5

Linear axial coefficient of thermal expansion (a) of®SIGRABONDpipes with variousfiber alignments

Coefficient of thermal expansion

The carbon fiber’s anisotropy isreflected in the characteristic thermaldata of composite sheets reinforcedwith 2D fabric. The high thermalconductivity determined in the fiberaxis results in l values between

50 and 180 W/m·K within the plane(II). The values reached perpendicu-larly to the plane (D) are between 5 and 30 W/m·K. Fabric-reinforced®SIGRABOND materials with 260 W/m·K and unidirectionallyreinforced materials with up to 500 W/m·K (at RT) have beendeveloped for a nuclear fusion plantby modifying the production pro-cess for these materials. A crucialfactor in these production processesis the formation of well-defined gra-phitic structures.

The characteristic paths of the curvesfor various material grades are givenin Figure 4. If the coefficients ofthermal expansion of a standardsheet are measured in the plane ofthe sheet but at an angle to the warpfiber direction rising from 0° to 90°,the values alter only slightly.

-2

0

2

4

6

8

10

0 800 1200 1600 2000400

-2

0

2

4

6

8

10

0 800 1200 1600 2000400Temperature OC Temperature OC

a =

x ·

10-6/K

a =

x ·

10-6/K

1001 G 1501 G

⊥

⊥

II II

-3

0

3

6

9

12

15

0 800 1200 1600 2000400

-1

0

1

2

3

4

5

0 800 1200 1600 2000400Temperature OCTemperature OC

a =

x ·

10-6/K

a =

x ·

10-6/K

1502 ZV 22 4012 GV

⊥

⊥

II

II

-1

0

1

2

3

4

5

0 800 1200 1600 2000400

a =

x ·

10-6/K

Temperature OC

[(± 75O)2x (± 90O)1x]nx

[(± 45O)2x (± 90O)1x]nx

[(± 20O)2x

(± 90O)1x]nx

2001 G

13

Figure 6

Thermal conductivity of various®SIGRABONDgrades

The axial coefficients of thermalexpansion of ®SIGRABOND pipeswith the three standard wind-up patterns are shown in Figure 5.

Thermal conductivity

The thermal conductivity values ofmaterial grades with bidirectionallyaligned fibers (woven fabrics) areusually between 5 and 150 W/m·K atroom temperature (see Figure 6).®SIGRABOND materials with ther-mal conductivity up to 500 W/m·Kat room temperature have beendeveloped for a nuclear fusion plantby using ultra-high treatment tempe-ratures and a matrix with a verywell-formed graphite structure (see Figure 6/2002 ZV). Figure 7

Axial thermalconductivity of®SIGRABONDpipes

0

50

100

150

200

0 400 600 800 1000200

0

5

10

15

20

25

35

0 800 1200 1600 2000400

30

Temperature OC Temperature OC

W/m

· K

W/m

· K

1001 Z 1501 G, 1601 G

⊥

II⊥

II

-0

50

100

150

200

250

300

0 800 1200 1600 2000400

0

10

20

30

40

50

0 800 1200 1600 2000400

0

100

200

300

500

0 800 1200 1600 2000400

400

Temperature OC Temperature OC Temperature OC

W/m

· K

W/m

· K

W/m

· K

1502 ZV 22 2001 G 2602 ZV

⊥

II

⊥

II

0

5

10

15

20

0 800 1200 1600 2000400Temperature OC

W/m

· K

4012 G

14

Thermal and mechanicalproperties of selected®SIGRABOND materials

Figure 8

Fatigue in®SIGRABOND1501 G due toalternating load(plot of meanvalues)

Dynamic strength

One special strong point of®SIGRABOND is its dynamicstrength at high service temper-atures. After 106 to 107 load alter-nations the initial strength is foundto have declined by only some 5 %(Figure 8).

0

100 101 102 103 104 105 106 107

50

100

150

200

250

300

Three-point flexure on samples 3.0 x 4.5 x 70.0 mm3

Alternating load conditions: 100 Hz

Number of cycles N

σ

σm

ax.

σsta

t.

2xσ

a

σa = ± 40 N/mm2

σmax = σstat + σa

Number of cycles N

F = 1

F = 1/2Laminate plane perpendicular to the plane of applied forceMedium: ultra-high-purity heliumMeasurement temperatures: 450 OC and 1200 OC

F = 1/2

sm

ax. (

MPa

) or

(N/m

m2 )

15

Resistance to temperature fluc-tuations

Compared with most ceramic andmetallic materials, ®SIGRABONDhas superior resistance to fluctua-tions in temperature. This is the pre-requisite for the successful use of thisclass of materials in high-tempera-ture applications. The thermal shockbehavior of homogeneous and crack-free materials is usually described bythe “first“ and “second“ thermalstress parameters R and R' respec-tively.

R = sY (1 -n)

R = sY (1 -n)

· lE ·a E ·a

where

sY tensile strength of the materialn transverse contraction numberE Young’s modulusa coefficient of thermal expansionl thermal conductivity.

R has the dimension of a tempera-ture and describes the maximumtemperature difference that the respective body can still just toleratein the thermal shock experiment.

R multiplied by the thermal con-ductivity gives R1 with the dimen-sion W/m·K. If typical material data,e. g. those for ®SIGRABOND 1501 G, are inserted into the above-mentioned equations, then,assuming that

sY = 350 MPaE = 75,000 MPan 0°/90° = 0.03aII, 1000°C = 0.3 · 10-6 K-1

l II, 1000°C = 28 W/m·Kthis yields the valuesR = 15,000 KR1 = 422,000 W/m

As hairline cracks in a materialdissipate the thermal stresses,materials with hairline cracks displaygood stability to temperaturefluctuations. This is true of®SIGRABOND. The equationsgiven in the foregoing are onlyapproximately applicable to com-posite materials. One outstandingexample of the resistance of CC tothermal shock is that of rocket noz-zles. On the start-up of a power unitthe CC is heated up to more than2000°C within about two seconds.

Figure 9

Specific heat of®SIGRABOND1001 G

Specific heat

0

0.5

1

1.5

2

2.5

0 400 600 800 1000200 1200 1400 1600 1800 2000Temperature OC

J/g

· K

16

Chemical properties

Purity

Essentially, CC materials consistentirely of the element carbon.Other elements are present only asimpurities introduced through theraw materials or production equip-ment employed. Exceptional purityis obtained in graphitized work-pieces, in other words componentsheated to well above 2000°C. Attemperatures as high as this, manysubstances vaporize. Consequently,only a few unwanted elementsremain behind in the graphitized®SIGRABOND.

High purity is an advantage in thefollowing applications:

• in the semiconductor industry; thesemiconductors are not impairedby elements that readily vaporize

• in high-tech projects such asfusion reactor linings; pure®SIGRABOND components havelittle effect on the quality of thefusion plasma.

• in chemical process equipment;the catalytic effect of the extra-neous elements on oxidation andcorrosion is minimized.

Typical ash contents and percentagesof the commonest elements presentin the ash quantities are set out inTable 5. The most important ele-ments are calcium (Ca), iron (Fe),sodium (Na), phosphorus (P) andsilicon (Si).

Material category ......G .....ZR

Typical ashcontent in ppm 300 to 600 10 to 30

Element Typical content Typical contentin ppm in ppm

Al 3 – 6 0.5 – 1.5

Ca 54 – 108 0.7 – 2.1

Fe 15 – 30 0.7 – 2.1

Na 30 – 60 1.6 – 4.8

Ni * 0.4 – 1.2

P 45 – 90 *

Si 18 – 36 4.0 – 12

Ti * *

other 135 – 270 2.1 – 6.3

Table 5

* below detection limit

17

Chemical resistance of®SIGRABOND

The graphitic nature of®SIGRABOND makes it highlyresistant to corrosive media. In Table6 we have listed media that usuallydo not attack graphite.

®SIGRABOND is not resistant tomedia with a powerful oxidizingaction (e.g. nitric acid, chlorine bleaching solution and oleum), espe-cially at elevated temperatures.

If ®SIGRABOND is going to be incontact with mixtures of substance

and if impurities are present, even invery small quantities, or if there aredoubts about stability, the suitabilityof the chosen materials should beverified by testing.

Some metals, especially the transitionmetals such as iron, nickel andcobalt, though also silicon, form car-bides at high temperatures in thepresence of carbon.

Interstitial compounds may occur ifcertain molecules or atoms are in-cluded in the graphite lattice. Amongthese may be concentrated acids,halogens or halogenides.

Inorganic substances

AcidsArsenic acidBoric acidFluorosilicic acidHydrobromic acidHydrochloric acidPerchloric acidPhosphoric acidSulfurous acidTetrafluoroboric acid

Salt solutionsAcetates of all common

metalsChlorides of all common

metalsFluorides of all common

metalsNitrates of all common

metalsNitrites of all common

metalsSulfates of all common

metalsSulfites of all common

metals

Miscellaneous substancesAmmoniaCarbon disulfide

Hydrogen bromide,gaseous

Hydrogen chloride,gaseous

Hydrogen sulfidePhosgenePhosphorus oxychlorideSodium thiosulfateSulfur dioxide, gaseousThionyl chloride

Organic substances

Aliphatic hydrocarbonsHeptaneHexane KeroseneMineral oilNaphthaPentanePetrol (gasoline)Synthetic petrol (gasoline)

Aromatic hydrocarbonsBenzeneTolueneXylene

Halogenated hydrocarbonsAllyl chlorideCarbon tetrachloride

ChlorobenzeneChloroformDibromoethaneDichlorobenzeneDichloroethaneDichloroethyleneEthyl chlorideEthylene chlorohydrineMethylene chloride TetrachloroethyleneVinyl chloride

Alcohols, thioalcohols(mercaptans), phenolsAmyl alcoholButanolEthanolGlycerineGlycolMannitolMethanolOctanolPhenolPropanol

EthersDiethyl etherDimethyl etherIsopropyl ether

Amines, nitro compounds, nitrites (CN compounds)AnilineAniline hydrochlorideCyanogen chlorideCyanuric chlorideDimethyl anilineEthanolamine (mono-, di-, tri-)Nitrobenzenep-NitrochlorobenzeneNitrotoluene

Aldehydes, ketonesAcetaldehydeAcetoneChloralChloral hydrateFormaldehydeGlyoxalParaldehyde

Carboxylic acidsAcetic acidAcrylic acidBenzoic acidButyric acidCaprylic acidChloroacetic acid (mono-, di-, tri-)Citric acidDichloropropionic acidFormic acid

Fumaric acid or maleic acid

Glycolic acidLactic acidLinoleic acidLinolenic acidMalic acidNicotinic acidOleic acidPalmitic acidPropionic acidSalicylic acid Stearic acidTannic acidTartaric acid

EstersButyl acetateButyl acrylateEthyl acetateIsopropyl acetateVinyl acetate and otheresters of acetic acid

Miscellaneous compoundsAmino acids such as folic

acidCarboxylic acid anhy-

drides such as acetic acidanhydride

Organic sulfonic acids such as

benzene-sulfonic acidtoluene-sulfonic acid

Table 6

18

Chemical properties

of movement and composition ofthe surrounding gas – e. g. moisturecontent and other factors.The resistance of ®SIGRABONDmaterials to oxidation is improvedby impregnation with anti-oxidationagents or coating with silicon carbide(SiC).

Protective coatings

Our company supplies®SIGRABOND materials with hardSiC protective coatings (see photobelow). The coatings adhere excel-lently to the CC and resist even highthermal and mechanical stresses.

Oxidation behavior

®SIGRABOND is used mainly in avacuum or protective gas. As nooxidizing gases are present, it doesnot oxidize.

Oxidation occurs in the presence ofoxidizing gases at elevated temper-atures. Its intensity is governed bythe partial pressure of O2 and alsovaries depending on the materialtype used. In air, oxidation begins oncarbonized material at about 350°C,and on graphitized CC at about450°C. The rate of oxidationdepends also on the nature of thematrix carbon, the porosity, the cata-lytic effect of the impurities, the rate

19

Components madefrom ®SIGRABOND forfurnace construction

The following properties of CCmake it especially suitable for use infurnace construction:

• Heat resistance and stability tothermal shock

• Low mass, allowing short heatingand cooling times

• Strength, specific strength andfracture toughness

• Adjustable specific electricalresistance

• Low coefficients of thermalexpansion; hence negligible ther-mal stresses

Main uses

• Hard-metals sintering furnaces• CVD furnaces• Hot isostatic presses, hot presses• Furnaces for high-temperature

ceramics• Plants for the production of ultra-

high-purity silicon• Vacuum and protective gas fur-

naces for hardening and carburiz-ing steel

Typical components and theiradvantages

• Heating elements for temperaturesup to 2500°C; unlike brittle mate-rials these allow thin-walled light-weight structures (photo upperright)

• Thin charging plates and moun-tings; saving in space, greater usefulvolume for products, e. g. hardme-tals components

• Screws and threaded bolts withhigh fracture toughness; saving inweight; high-temperature strength(photo lower right)

• Pressure plates and female moldcavities for hot sintering presses

• Support structures and liningstrips for graphite felts

• Good combination potential of®SIGRATHERM graphite insu-lating felts and ®SIGRAFORMgraphite components (photo left)

• Brochure on ®SIGRABOND *charging systems and heating ele-ments in carbon fiber-reinforcedcarbon available on request

*carbon fiber-reinforced carbon

20

®SIGRABOND components forchemical processtechnology

The following properties of CC areimportant to its use in the chemicalindustry:

• Corrosion resistance at up to hightemperatures

• Strength even in low-thicknesscomponents

• Resistance to vibration

• Electrical conductivity (in electro-chemical processes)

Examples of CC components

• Structured packings for separationcolumns (European Patent No0499040) (photo upper right)

• Stirrers and feed pipes (photolower right)

• Support grids and other columninternals (photo left)

Advantages

• Textile materials made from car-bon fibers, e.g. mesh fabrics, canbe used to produce ®SIGRA-BOND materials with large opensurfaces. CC packings made ofsuch materials are highly effectivein separating liquid mixtures indistillation-rectification plants.

• The properties of ®SIGRABONDallow elegant design techniques tobe used. Components like gridscan be produced in lightweightdesigns which allow for disman-tling. This enables maintenancework on columns to be carried outthrough manholes without theneed to dismantle the entirecolumn.

• For chemical resistance, see Table 6.

21

Components madefrom ®SIGRABOND for the glass industry

The following properties of CC areespecially useful for applications inglassware manufacture:

• Stability to thermal shock, strength

• Unwettability by molten glass

• Low hardness and thermal con-ductivity; hence, no impairment ofthe glass surface

• Good porosity

• Impact toughness.

Components produced include

• Channeling systems to carry thegobbets of molten glass duringhollow glassware manufacture(photos left)

• Various contact element designsfor moving hot hollow glasswarearticles and / or tubes (photoright)

• Molds for crystal and lead crystaldrinking glasses (photo center).

Advantages of ®SIGRABOND inglass component manufacture

• A CC channeling system needs noinner cooling like metal scoops,for instance; neither does it needtreatment with short-lived paintsor paste finishes or spray coatingwith oil.

• The low weight of a fast-movingscoop reduces the mass momentof inertia and lowers the stressesimposed on the gobbet distribu-tion mechanism; moreover, light-weight troughs for the glass areeasy to install and remove.

• The mechanical and thermal stabil-ity prevents plastic deformation ofthe scoop at the gobbet impactpoint and ensures long service lifeas well as low glass contaminationfrom abraded carbon.

• The low thermal conductivity ofthe contact elements preventsrapid heat dissipation and thusavoids cooling cracks, even insensitive products.

• For further details, see our techni-cal information on hollow glass-ware production.

22

®SIGRABOND components for high-tech applications

CC material originated in aerospaceprojects. To successfully manufactureand use rocket nozzles and heatshields, for instance, the materialsused must be

• extremely heat-resistant

• exceptionally stable to thermalshock and

• fracture-resistant.

CC meets these requirements excel-lently. Other important properties ofCC are its

• vibration resistance

• low density and

• adjustable thermal conductivity.

The different high-tech applicationsdemand high-performance materialswith a wide variety of thermal con-ductivity values. A heat shield needsvery low values, e.g. 5 W/m·K, whereas a protective “tile“ in a fusionreactor requires values above300 W/m·K. No isotropic base

material exists which could be modi-fied to give such a wide thermal con-ductivity range. ®SIGRABONDmaterials, however, can be adaptedto give optimum solutions.

The following noteworthy components have beenfabricated from ®SIGRABONDmaterials:

• 5-meter form for the super-plasticshaping of titanium sheet at above900°C

• cladding for rocket combustionchambers

• gas rudders and thrust deflectorsfor military aircraft (photo left)

• cladding elements for the JointEuropean Torus nuclear fusionreactor in the UK (photo upperright)

• expansion nozzle of a hypersonicpropulsion unit (photo lowerright).

23

Criteria for designing with CC materials

The design possibilities afforded byCC depend on the conditions of use,in particular high temperatures, theproperties of the material and the

opportunities for shaping.®SIGRABOND is a frequent choicewhen peripheral conditions rule outthe use of other materials for high-temperature furnace construction orchemical process technology.

Designing with®SIGRABOND

Quality assurance

Our commitment to quality

Machining

The individual production stages arefully documented in descriptions ofmanufacturing operations. Thereproducibility of ®SIGRABONDproduct quality is ensured by follow-ing these instructions in everydayworking practice.

Semi-finished and finished productsare monitored with non-destructiveand destructive test methods. Asboth measuring techniques and test

methods are closely geared to prac-tical conditions of application andfollowed meticulously,®SIGRABOND is highly reliable inuse. As a relatively new class ofmaterial, CC is not yet used on alarge scale.

Our aim is to supply customersworldwide with products and ser-vices of maximum benefit.

®SIGRABOND is usually machinedwet with hard-metals or diamondtools. If there are a large number ofworkpieces and their contours aresuitable, water-jet cutting can also berecommended. SGL Carbon hasmany years’ experience of machiningcarbon and graphite workpieces inall sizes, including very large dimen-sions. We can offer our customersthe benefits of this experience. Thecarbonizing and graphitizing opera-

tions produce a form of skin on®SIGRABOND which is slightlydenser than the materials beneath.The roughness depths of these outerskins are virtually identical, regard-less of the material grade. When CCis machined (by turning, milling orgrinding), the internal structure ofthe material is exposed. The rough-ness depths of such machined sur-faces are less than those of the outerskins.

Table 7Typical roughness depths of ®SIGRABOND materials in mmm

RY Ra

Unmachined 40 to 50 10 to 20(outer skin)

Machined 25 to 40 5 to 15

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Design of components

Hints on designing with®SIGRABOND

• Choose a suitable ®SIGRABONDmaterial grade to match knownrequirements or experience

• Aim to use monolithic, i.e. unitaryconstruction and select shell-typeor axially symmetrical or othercomponent geometries producedby filament winding

• Use screw-type joints (no solder-ing, welding or bonding)

• Take advantage of SGL Carbon´sexperience in component design.

To comply with the foregoingpoints, the information and proce-dures given below should be notedand adhered to:

• Material grades

®SIGRABOND 1001, 1501, 1601,1701, 2001, 3001 and 4001; depen-ding on their letter suffix (see p.31)these material grades can be heat-treated up to 1000, 2000, 2200 and2700°C. Special materials are pos-sible such as ®SIGRABONDgrades combining unidirectionallayers and fabric layers in a com-posite material.

Notable material properties

• Extreme thermal stability

• Sensitivity to oxidation

• High specific tensile strength andrigidity

• Low density

• Low interlaminar shear strength(ILS)

• Open porosity

• Quasi-plastic fracture behavior

• Anisotropic properties

Figure 10

25

• Monolithic designs

The following points should benoted:The green production operationsinvolve processing thin, large-surface-area semi-finished materi-als (woven fabric or unidirectionalprepreg). The number of layers ofsemi-finished material will dependon the component design butshould not be more than neces-sary; this will obviate the need tocut away excess layers later bymachining, thereby damaging thesupporting fibers. Allowanceneeds to be made during greenproduction for localized thicken-ing, narrowing or reinforcing ribs(see Figure 11).

Also employed in green produc-tion processes is a wind-up tech-nique for high-strength structures(material grade 2001). This isnormally used to produce com-ponents of axially symmetricalgeometry or other geometrieswhich are machined according tothe same principles as shell-type/large-surface-area compo-nents. No components with long-fiber reinforcement (material grades 2001, 1501 and 1601)should include any curves inwhich the carbon fiber is bentthrough a radius of less than 3mm. The use of compression mol-ding for materials reinforced withchopped fibers (grades 3001 ad4001) is an inexpensive green pro-duction method. Material grades 3001 and 4001 can bemachined by cutting techniqueswithout loss of strength.

Figures 11

Typical thickenedareas created byadded layers, ribs of varying thickn-ess and differencesin the number oflayers used

26

Designing with®SIGRABOND

• Joints

Joints of exceptional tensilestrength can be formed with loop-shaped CC tensioning elementsthat utilize the high tensilestrength of the carbon fibers effi-ciently and are tensioned with®SIGRABOND wedges. Themost usual method of producingeffective joints, however, is withthreaded bolts. The inherent an-isotropy of the bolts needs to beallowed for. The alignment of thereinforcing layers in nuts, bolts

and screws is shown by thedrawings in the section “Formssupplied“. As a rule, the reinforc-ing fibers in a screw joint connec-tion, say, two CC sheets with CCscrews are perpendicular to eachother (see Figures 12 and 13). Aslong as the materials forming thejoint are a suitable combinationand if due regard is paid to com-ponent dimensions, bolt or screwdesign, assembly forces and theassembly instructions, then theresulting screw joints will performreliably at up to 2000°C.

Figure 13Figure 12

Examples of permitted tighteningtorques for bolts and screws with

metric threads are given in Table 8below.

Notes on tightening torques

Bolts with hammer heads are used inall kinds of mechanical securingapplications for CC components atextremely high temperatures.

Bolts with countersunk heads arepreferred for the screw mounting ofCC heating conductors because ofthe low electrical contact resistivityattainable and small space require-ment.

If the tightening torques given aboveare greatly exceeded, the followingtypical forms of failure occur:

• torsional fracture of the bolt if theexposed thread length is relativelylarge, e.g. 50 mm with M 10

• stripping of the bolt thread if theexposed thread length on the boltis short

• damage to the bolt head if bolts ofthe countersunk type are used.

Talble 8

M 8 to M 12 with hammer head 4.0 Nm

M 8 to M 12 with countersunk head 0.8 Nm

Permitted tightening torques for screws and bolts made frommaterials grades 1001 G and 1501 G

27

• Values for component design

Two important factors in the designof components are the

• effective bearing strength values(see Table 9) and the

• shear strength values of bolts (see table 10).

The tables (below) give values forvarious grades of ®SIGRABONDmaterial.

Notes on effective bearingstrength values

The quasi-plastic fracture behaviorof CC differs markedly from thefracture behavior of homogeneousceramic material or that of metals.As shown in the stress-strain graph,some of the reinforcing fibers maybreak before the tensile strength atfracture of the whole component isreached, but such premature break-ing does not lead to disastrous crackpropagation or consequent total

materials failure. This „benign“ frac-ture behavior is also a factor in theeffective bearing strength, inasmuchas the relative widening of a drillholemay amount to several percent with-out sudden failure of the remainingloadbearing cross-section. Indeed,the tensile stress on the remainingloadbearing cross-section often fallsfar short of its tensile strength atfracture, even after allowing for thenotch effect of the drillholes. Thisnotch effect roughly halves the prop-erty values given in Table 2.

Table 9

Tensile force in 0° direction Tensile force in 45° direction

Material grade Hole diam. Pressure on With relative Pressure on With relative[mm] hole face widening of hole hole face widening of hole

[MPa] [%] [MPa] [%]

1501 G 5 90 2.3 80 2.78 80 1.7 50 1.5

10 70 1.5 30 0.7

2001 G 5 140 2.4 85 2.38 100 1.7 50 1.4

10 85 1.5 30 1.1

Effective bearing strength values of various ®SIGRABOND grades

28

Design of components

Notes on the shear strengthof bolts

The listed shear strength values inMPa are mean values calculatedfrom a relatively large number ofmeasurements. These values aredefined as the first permitted mate-rial damage (see stress-strain graph– Figure 2).

As the bolts are machined fromsheet, they have a privileged direc-tion like screws, owing to the orien-tation of the layers. If the fabriclayers are aligned in the direction oftesting, they give higher measuredvalues than those for fabric layersaligned at right angles to the testdirection. The values given in thetable are minimum strength values,as the fabric layers in these boltswere aligned perpendicularly to thedirection of testing (Figure 14).

Figure 14

Shear strength values of various ®SIGRABOND grades in MPa

Material grade

Bolt diameter 1001 G 1501 G 1601 G

8 mm – 47 36

10 mm 22 41 51

14 mm 27 34 45

Table 10

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Forms supplied anddimensions

Standard sheet dimensions

Material grade 1001 1501 1601 1701

Length I [mm] 1005Width b [mm] 1005

Thickness d [mm]

0.7 ± 0.2 1.2 ± 0.2 1.6 ± 0.2 2.5 ± 0.2 3.0 ± 0.34.0 ± 0.4 5,0 ± 0.5 5.5 ± 0.5 7.5 ± 0.7 10 ± 1.0

12.5 ± 1.1 15 ± 1.3 20 ± 2.0 30 ± 3.0

Special formats can be produced for material grades 1001 G, 1501 G and 1601 G up to2500 mm length and 80 mm thickness.

Standard L profiles

Material grade 1601 GS

Length l [mm] 1000 + 3; 1000; 2000Side length s [mm] 65 ± 1Thickness d [mm] 1.3 ± 0.2

Standard U profiles

Material grade 1601 GS

Length l [mm] 1000 + 3; 2000 + 4Side length s [mm] 60 ± 1Thickness d [mm] 1.3 ± 0.2Base width b [mm] 20 ± 1; 30 ± 1; 40 ± 1

Hot pressing matrices

Material grade 2001 GV

Typical inner diameter [mm] 125 220 275 325 550

Typical wall thickness 50 mm

Standard pipe dimensions

Special formats can be supplied for pipes made from material grades 1501 G, 1601 G, 2001 G and 2302 G up to 1600 mm diameter and 2500 mm length.

Standard H profiles

Material grade 1601 GS

Length l [mm] 1000Side length s [mm] 105; 44Thickness d [mm] 1,3

30

Forms supplieddimensions

given to the ®SIGRABONDmaterial’s anisotropic and ceramicproperties. Please ask us for ourdetailed drawings; special designson request.

The measurements and tolerancesare largely in line with the stan-dards for metal screws. In thedesign of all securing elements,however, due consideration is

NutsStandards:M8 to M16

Threaded bolts Threaded rods

Cheese-head(pan-head)screws

Hammer-head screws

Countersunk-head screws

n ±

0.2

S 2 -

0.5

n ±

0.2

laminate layer

31

The information contained in this brochure is based on our present state of knowledge and is intended to provide general notes on our products and their uses. It should therefore not be construed as guaranteeing specific properties of the products described or their suitability for a particular application. Any existing industrial property rights must be observed. The quality of our products is guaranteed under our “General Conditions of Sale“

® registered trademark of SGL Carbon Group companies

05 2004 / 2 NÄ / E / Printed in Germany

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SGL CARBON GmbH

Werner-von-Siemens-Straße 1886405 Meitingen/GermanyPhone+49 (8271) 83-1703Fax +49 (8271) 83-2244www.sglcarbon.com