CA2362391C - Process and device for producing components and semi-finished products from synthetic graphite or ceramic granules, in particular for producing graphite tubes - Google Patents

Abstract

This invention relates to a process and a device for producing components and semi-finished product from synthetic graphite or from ceramic granules, in particular for producing graphite tubes, involving shaping of a material to be mixed preferably containing petroleum coke or graphite granules, by means of an extrusion press (22) or an extruder, wherein the process provides the following steps: a) Pre-pressing the material (20) to be mixed in static or quasi-static manner, flow movement of the material (20) to be mixed being stopped or impeded in such a way that particles previously irregularly arranged in the material to be mixed are initially aligned transversely to the direction of pressing, b) Pressing out of the pre-pressed material (20) to be mixed through an outlet opening (28) of the extrusion press (22) or the extruder in such a way that owing to adjusted flow properties of the material (20) to be mixed, the particles within the pre-compressed material (20) to be mixed realign, starting from their transverse alignment, by an angle (.beta.) of a maximum of 75.degree. in the direction processing.

Description

Process and device for producing components and semi-finished products from synthetic graphite or ceramic granules, in particular for producing graphite tubes Description State of the art The invention relates to a process and a device for producing components and semi-finished products from synthetic graphite or ceramic granules, in particular for producing graphite tubes or a component or semi-finished product made of synthetic graphite or ceramic granules, Graphite has very good electrical and thermal conductivity and has a very high level of chemical and thermal resistance. For this reason the material graphite is used, in the form of tubes for example, as a semi-finished product for chemical apparatuses. Tubular heat exchangers made from bundled graphite tubes therefore are known for example.

As graphite is a ceramic material, one of the minor advantageous characteristics of this material is a relatively low resistance to impulsive and dynamic loads, in particular, in order to improve the dynamic resistance of graphite tubes, it was proposed in accordance with DE 31 16 309 C2 to cover the tubes with carbon fibres, the connection with interlocking fit between the tube and the bundles of fibres being produced by means of a curable resin, in a manner similar to a laminate. This process is, however, relatively complex and therefore cost intensive.

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in accordance with a known process for producinq componerlts and semi finiahed producta from graphite, petroleum coke or graphite granules, for example, are uised, as raw maLeLia.lu which are comminuted and screened in a first atep.
Subsequently, the bulk startinq material wYlic:tl Yldb beeji cornminuted is mixed with a binding agent to form a viscous material to be mixed. For the stldUiu.y uf Lk1C uaLerial Lo be mixed which is obtained in such a manner and is ready f.or pieseilzq, Lor example to form a tube, this is fed into the supply chambar of an extrusion press and then cornpressPd hy m.eans of a plunger piston which cnn be moved longitudinally in a press housing in the direction ot an outlPt npPning and im pressed out as a virtually continuoua strand, for PxamplP in the form ot a tube. A scr w-type extruder which is coaxial to the press housing can also aeeume the prpa4ing out ot the material instead of a plunger piston.
As a result ot the forward movement of the plunger piston and the relativeJ.y good flowability of the material to be mixed, the predominantly elongate-shaped coke or graphite particles are aligned from the start in the case of extrusion pressinq or extrusion so dd to be pdLdllel Lu Llie direction of pressing in the flow field pointing towards the outlet operlirnq aild renuiin "frUZell" in l.YllS pU.41l.lUu .iu the subsequent production stages. As the main direction of thermal cOI1d11C:tiUI1 r'llIls TJriIItt1Z f ly dluilLJ Ll1C d11.y11111ei1L
1:lL
the material particles, the material properties of toLnponenl.s pressed in such a way consequently have strong anisotropies, x_e- whilst the t'hermal r.nnr3,ir.t-tivity nf an extrusion pressed heat exchanger graphite tube hae high va 1 oes owing tn t-he Proar.3nmi nanf-. part i n I P a I i gnmPnh para l lP l to the direction of pressing in axial longitudinal direcr.3on, ir_ ig cliaacivanr.agPoligly low, however, in the radial direction which ie important for heat transfcrcncc in heat exchanger tubes. Un the other hand, the alignment TT/90S NI1QV'1Q3QHIds HQ +67T88D6T9887 XV3 8T ;LT TO,60/CO

of the particles in the axial longitudinal direction has a favourable effect on the bending and tensile strength of the graphite components which is particularly advantageous in heat exchange tubes.
Conventional extrusion presses have a plunger piston which can be moved longitudinally inside a press housing, which plunger piston delimits a supply chamber which discharges into an outlet opening of a shaping mouthpiece of the press housing narrowing in the shape of a funnel in the direction of pressing, which funnel can be filled with material to be pressed and can be comminuted by its pressing movement.
Once the material to be pressed has been pressed out of the outlet opening, the plunger piston must be withdrawn completely from the press housing so the supply chamber can be refilled with material to be pressed. It goes without saying that the refilling process is complex and therefore the piston stroke and the supply chamber of such extrusion presses must be designed as large as possible for reasons of economy, in order to avoid frequent refilling.
Accordingly, the pressed part located in the supply chamber is relatively long, whereby the forward movement forces required to compress and press out the pressed part from the constricted outlet opening are high. In order to limit the pressing forces, the bulk material is accordingly free-flowing. Upon pressing out, a flow field is produced inside the supply chamber, in which flow field the graphite particles tend to align themselves parallel to the direction of pressing which, in tubes, in turn results in the already described undesired anisotropy of the graphite material.

3a Summary of the Invention In accordance with one aspect of the present invention, there is provided process for producing components and semi-finished products from synthetic graphite or from ceramic granules, involving shaping of a material to be mixed by means of an extrusion press or an extruder, the process comprising the following steps:
a) pre-pressing the material to be mixed in static or quasi-static manner, flow movements of the material to be mixed being stopped or impeded in such a way that particles previously irregularly arranged in the material to be mixed are initially aligned transversely to the direction of pressing, b) pressing out of the pre-pressed material to be mixed through an outlet opening of the extrusion press or the extruder in such a way that owing to adjusted flow properties of the material to be mixed, the particles within the pre-compressed material to be mixed realign, starting from their transverse alignment, by an angle ((3) of a maximum of 75 in the direction of pressing.

In accordance with another aspect of the present invention, there is provided device for producing components and semi-finished products from synthetic graphite or ceramic granules, containing an extrusion press with a plunger piston guided so as to be movable longitudinally inside a press housing, which plunger piston delimits a supply chamber with a diameter (D) which discharges into a constricted outlet opening with a diameter (d), which can be filled with material to be pressed and can be comminuted by its pressing movement, wherein the supply chamber has a separate supply opening arranged between a starting position and an end position of the plunger piston, and the ratio (D/d) of the diameter (D) of the supply chamber to the 3b diameter (d) of the outlet opening is smaller than or equal to 2.5.

In accordance with yet another aspect of the present invention, there is provided component or semi-finished product made from synthetic graphite or from ceramic granules, obtained by a process involving shaping of a material to be mixed by means of an extrusion press or an extruder, the process comprising the following steps:
a) pre-pressing the material to be mixed in static or quasi-static manner, flow movements of the material to be mixed being stopped or impeded in such a way that particles previously irregularly arranged in the material to be mixed are initially aligned transversely to the direction of pressing, b) pressing out of the pre-pressed material to be mixed through an outlet opening of the extrusion press or the extruder in such a way that owing to adjusted flow properties of the material to be mixed the particles within the pre-compressed material to be mixed realign, starting from their transverse alignment, by an angle (R) of a maximum of 75 in the direction of pressing.
Accordingly, some embodiments of the present invention provide a process and a device for producing components and semi-finished products from synthetic graphite or ceramic granules as a result of which the anisotropies present in the graphite material are reduced without the'strength of the material being reduced.

In some embodiments of the invention, owing to the pre-pressing process, as in the case of stamping presses, the graphite particles initially align themselves within the pre-compressed material block transversely to the direction of pressing. Owing to the low flowability of the material to be mixed.in the region of the constricted outlet opening of the extrusion press or the extruder upon pressing out, the graphite particles rotate out of their original transverse alignment only by a small angle in the direction of pressing, so that they are arranged substantially obliquely or spirally in relation to the central axis of the finished component.

As the predominant direction of the thermal conduction and resistance properties defined by the alignment of the particles is now no longer purely transverse or purely parallel to the central axis of the pressed component but rather is oblique thereto, a new type of graphite material with substantially lower anisotropy than before results.
This is because, on the one hand the obliquely oriented particles have a component transverse to the direction of pressing, which, for example, is favourable for the radial thermal conductivity of heat exchanger graphite tubes produced according to the process according to the invention. On the other hand, the components of the particles complementary thereto which point in the direction of pressing prevent the bending strength of the 5 graphite tubes being significantly reduced.

Some embodiments of the invention provide for the extrusion press to have a supply chamber with a supply opening for supplying material to be mixed, which supply opening is arranged between a start and an,end position of a plunger piston which can be reduced to the size of the supply chamber, the shaping of the material to be mixed comprising the following steps which form a cycle:

a) Metering of material to be mixed into the supply chamber with the aid of a metering device until this is completely filled when the plunger piston is in the starting position, b) Quasi-static pre-pressing of the material to be mixed in the supply chamber by slow forward movement of the plunger piston in order to align the particles transversely to the direction of pressing, c) Pressing out of a volume of pre-compressed material to be mixed through the outlet opening, which volume is smaller than the volume originally in the supply chamber, whereby, once the end position of the plunger piston in the supply chamber has been reached, a pre-compressed residual volume remains, d) Return of the plunger piston to the starting position and metering of new material to be mixed into an intermediate chamber between the pre-compressed residual volume and the plunger piston until the supply chamber is again filled completely, e) Continue with step b).

Owing to the rapid and quasi-continuous refilling potential by means of the supply opening, small quantities of material to be pressed can also be pressed economically by a single pressing stroke. High pressing forces are therefore no longer necessary, so the flowability of the material to be mixed can be reduced in a concerted manner.
Owing to the internal flow hindrance of the material to be pressed no pronounced flow field can form in which the graphite or granular particles could align parallel to the direction of flow. Rather, as already described above, the material to be pressed is pre-pressed almost statically, whereby the graphite particles align transversely to the direction of pressing before the material to be pressed leaves the supply chamber through the outlet opening. Owing to the inner flow hindrance of the pre-pressed bulk material it is advantageously obliquely aligned when it flows through the constricted outlet opening.

In accordance with a further embodiment, it is provided that the alignment of the particles transversely to the direction of pressing required at the start is brought about by pre-compressing the material to be mixed to form a block-shaped pre-pressed part, preferably by means of a stamping press and the pre-pressed part is then placed in a supply chamber of a piston extruder in order to then press it through the outlet opening to give it its shape.
Further embodiments provide that the material to be mixed is obtained by mixing a bulk starting material containing at least one particle size fraction of petroleum coke and/or graphite granules with a binding agent and additionally adding carbon fibres to the material to be mixed. By adding carbon fibres the resistance of the tytdjJI11Le c:otttpoiienLs caui be increased in an advantageous manner.

An addition of commercYally available auxiliary pressing agents supports the desired internal flow hindrance of the bulk rnet.erim1 to the PxtPnt that the wall triction ot the bulk material with the cylinder wall in particular is rCdtlCeCl and therefore A si-npppr flow is producetl Wt1iC11 hinders the alignment of the particles in the dircction of presging.

11"hp hinding agent_s used in the production of graphite components havc the object of connecting the colide i5 particles to one another by means of high wetting ability and thcrcforc of making them plactically deformable as well as ensuring the reQuired resistance of the components. The binding agent is conventionally added, for example, in liquid form, to the solids consisting of petroleum coke or graphite granules. The quantity of binding agent is metered at such a high rate in the state of ttic d.LL LtidL d relatively low impact pressure is produced inside the bupply e:2idaLbet ot Lbe exLrusion press. A material to be mixed having the conventionally high proportion of binding dyettL ltaa3 Llle d.ieatlvanLage, however, that owing to the good flowability of the bulk material the particles are aligned in Lhe direction ot pressing particularly well and in this way the formation of a strongly aninnt.rnpin prPgRing part is supported. Furthermore, the material shrinks greatly 10 d ring miirmprpuftnt pyrnlymi sa. Thn RPvPrP shrinkage furthermore has an unfavourable effcct on the atrcngthcning e.:ffPe-t nf the nArhnn fi hri-m i ntrnri r.PCI .

Accorc9i ngl y, i n arnorr3anr.P wi r.r a development of the invcnti.on the matcrial proportion of the addcd binding agent is low and is between 5 and 32 wt. t of the total TT/'OTS 1QNIV1T3Q$Ibf 2IQ +67T6679TZ867 ZY3 tZ :Lt T0 , 60/EO

mass of the material to be mixed. This has the advantage that the material to be mixed shrinks less during the subsequent pyrolysis on the one hand, and, on the other hand, is less flowable, so the desired flow hindrance of the material to be mixed is effectively supported by a lower proportion of liquid binding agent and the tendency of the graphite particles to align themselves parallel to the direction of flow, is reduced. During later pyrolysis, the situation where the carbon fibres present in the component resulting from the material to be mixed become ineffectual owing to shrinkage is additionally effectively prevented.

A further development of some embodiments of the invention provides that the bulk starting material and the binding agent and further raw materials to form the material to be mixed are mixed by a mixer with low shearing effect, for example a tumble mixer or a Rhon wheel mixer.
The result is a particularly gentle mixing process, shearing or breaking off of the carbon fibres added to increase the component resistance being avoided in particular. Furthermore, the individual components are mixed particularly thoroughly with the aid of tumble mixers, so no undesired accumulations of carbon staple fibres form.

Finally, in some embodiments, the bulk starting material is comminuted and screened before mixing in such a way that it effectively contains a first particle size fraction with particle sizes greater than 0 mm and less than 60 m and with a material proportion of 20 to 100 wt. % of the bulk starting material, and a second particle size fraction with particle sizes of 60 m to 750 m and a material proportion of 0 wt. % to 34 wt. % of the bulk starting material and a third particle size fraction'with particle sizes greater than 750 pm to 2,000 pm and a material proportion of 0 wt.
% to 46 wt. % of the bulk starting material. By producing a bulk starting material containing coarser particles, the material to be mixed resulting therefrom is less viscous and consequently a higher level of internal friction is produced during the subsequent pressing process which prevents a rapid discharge of the material to be mixed through the outlet opening of the extrusion press. As a result, the desired pre-compression of the material to be mixed is supported effectively.

In some embodiments, owing to the rapid and quasi-continuous refilling potential of the extrusion press by means of the supply opening, smaller quantities of material to be pressed can also be pressed economically with a single piston stroke and consequently pressing can be carried out with forces which are lower compared with the state of the art. An increase in the flowability of the material to be mixed in order to limit the pressing forces is therefore no longer necessary. Rather, in contrast, the flowability of the material to be mixed can be reduced in a concerted manner in order to prevent the formation of a pronounced flow field in which the graphite particles could align in an undesired manner parallel to the direction of flow.
Furthermore, the desired particle alignment can be best achieved with a ratio D/d of the diameter D of the supply chamber to the diameter d of the outlet opening smaller than or equal to 2.5.

Conventional extrusion presses extend in vertical direction in order to be able to uniformly fill the supply chamber from above with material to be mixed after removal of the plunger piston. In order to be able to press out continuous 5 components, for example tubes, the height of such vertical extrusion presses must, however, be appropriately large.
In contrast, in some embodiments, the longitudinal extent of the extrusion 10 press is arranged substantially parallel to the horizontal and the supply opening of the supply chamber to be arranged substantially transversely thereto. Owing to the horizontal arrangement of the extrusion press, its height is advantageously slight and continuous components of almost any length can be pressed out. On the other hand, the filling of the supply chamber in the vertical direction ensures that the material to be mixed is uniformly distributed there.

Drawings Embodiments of the invention are described in more detail in the description below and illustrated in the drawings, in which:
Fig. 1 shows a flow diagram of a part of the production process of graphite components;

Fig. 2 shows a schematic sectional view through an extrusion press according to the.invention for pressing material to be mixed in an embodiment with completely filled supply chamber;

Fig. 3 shows the extrusion press of Fig. 2 during pre-compression;

Fig. 4 shows the extrusion press of Fly. 2 during extrutsion r Fig. 5 shows the extrusion press of Fig_ 2 during the refillinq proc:cub;

Fiq. 6u2iuws av.LeLun exLruder tor shaping the material to be mixed;
FicJ _ 7 shows a single-gVrew-t.yrP Pxi-nicipr tor shaping the material to be mixed.

Descriptioa of the embodiments 1s The flow diagram in accordance with Fig. 1 shows the first production stages of the process according to the ilivCllLlUt1 for producing comportentC and cemi-finished goods from graphite or ceramic granules, with graphite tubes for use in heat exchangers having been produced in accordance with a preferred embodiment. Numerous production attemptb wiLYa various raw materials and production stages wero carried ouL fui. L2ila VuLNOse, oL which only some are deacribed below by way of example.
Petroleum coke, for example, was used as bulk starting mal.erial which was initially calcined, i.e. was calcined at 1,200 to 1,400 C in a rotating tubular kiln or revolving hearth furnace 2, for example, and was then temporarily stored in a silo 4. In a subsequent stage, the bulk starting ttmaterial was comminuted by rotary crusherr. 6 or impact grinding mills, for example, and screened in sieves $ in such a way i-hat frnr.ti nnaa of different particle sizes resulted which were temporari].y stored in bins 10 which we!rp RP.parmtn from one anofihPr.

9T/'COS N1QvxaQ3IM ?IQ +69T889CT3869 ZV'3 6Z :LT TO, 60/90 The ytdilulutttelry oL petroleum coke and graphite granules which have been comcninuted and screened is listed in Table 1 bcluw wiLh I.hc aid or three test exam8les in each case and the particle sizes are clasaified in four ranges, in each caFaa 0-Ft1 jtm, 60-700 m, 200-400 -lm and 4UU-750 4m. In accorcidzlc:c wiLYl d fijdL euib=odimcnt in which petroleum coke servea exclueaively as bulk starting material, the largest particles had a diameter rnt.wPPn 4Q0 ltm and 750 m, wherein 45 wt. t of the material proportion were smaller than 60 Et.m and 55 wt. I material proportion of the bulk startinq matericil weLe yLCdLet t11a-E1/eyLLal to 60 m. Petroleum coke was also used as raw matcrial in a 3ccond cmbodiment in which the largest particles were sotnewhat smaller than 400 m and the material proportiom of particles s-ttdllet ttidii 60 m was 44 at.t and that of particles greater than/equ.til tu 60 lim wa:3 56 wt.W. Finally, when using graphite granules du sLaLL.isiy LnaLerial Lhe largest particles reached a size of 750 m, with the material proportion of particles yLCnLet Lllan/equal l.0 60 tn being 45 wt. % and the fraction of ptLrticleu stad1leL Lrldil 60 uL Leinq 56 wL.%.

9T/~n5 NNVIQHQSIM ?Id +89T66TCTZ889 XYd 89;LT Td, 80/CO

Fractioa 0-60 60-200 200-400 00-750 [ m7 Petro aum coke, 45 21 14 Material proportion [wt. U
Petroleum co e, 4 32 24 0 Material proportion (wt. %]
Graphite 55 17 qranules, Materia.l proportiu:i [wt_ Table ls Granulometry of the bulk starting materials by way of example In Table 2 below the rnir-imnim posFi h I P parriniP sizes detcrmincd in the course of the teate arc denoted by "A"
and the maxi,murn passi h1 e rArti n I P Ri ?PR arP ciPnotea by "B" , these beizig particlee with which a till 3ufficicnt l o rnmpnnPnt resistance notlld be achieved and a shaping of the graphitc material was otill Jjuot poaoible. Therefore, the particle size ~raetionp between 0 and 60 m in the smallest possihlr grAin F;i'P A t-ngPthPr nnnnpieci 100 wt. t ot material proportion of the bulk stiarting matcrial, grain oizc3 coar3cr than 60 m not occurring on the other hand.
In contrast, a dubstantially widcr band of 0 to 2,000 m resulted with the largest possible grain size R, t.hp finnnt fractions between 0 and 60 [tm tagri-.hPr maaking up 20 wt. ik of the material proportion, the meciiua--bizea fs.&cl,iotls ot FT/50S ATATVI[:iQaIM ?IQ '*OYi889CiZ8SV 7CV3 OC ;LT Tq, 60/90 = CA 02362391 2001-09-04 60 m Lu 750 m together making up 34 wt. '6 of the material proportion auci l.tiC (:udLtiCGiL fracL'ions between 750 m and z,uUO m together making up 46 wt. t of the materidl proportion of the bulk starting material.
Preeb on 0 10 10 40 40 60 60 200- 100- 750- 1000-[PLMI 'lUU 400 750 1000 2000 A 60 4u u u 0 0 0 0 fraoti.onp [wz. irl 3 10 7 15 0 9 2.1 75 fractionrs [wt- ie]

Table a: Maximum and minimum granulcmtctLy uf l.2ie Lulk tStd= t iii.y utdLeL idl As cmeryces fLuut T tblc 3 dilrl Fig. 1 the petroleum coke or the graphite granules 1 were mixed fQ1.1.owi ng i-hei r zGCiuuLluu ill el'lae and screening with a binding agent 12, for example phenolic resin, Nc1volAkO, tyPP SP 222, tlow paths 20-100 mm, the binding agent being finely ground with an addition of 8& herxAmPthylrnP tPl-raminP (He-ca), produced by nakelite AG, Germany or pitch of the BX 95 typc, SP >
30 C, produced by Rutgcra, Ccrmany. In addition, siaed carbon staple fibreo 'I d, pre!frrAh Iy STf;RAFILQD fibres ot the type C-25-300G EPY produced by OGL TeChnik GmbH, acrmon.y were added to the bulk ist.Prting mat.Prlal in anme tesr_e, which fibres have a diameter of 8 rn and a length of 6 mm.
Fljlally, aii auxiliary pressiiig agent 16, for example in the form of paraffin oil with a viscosity of 60 ml'a = 3 at 20 C
or in the form of Stearin", laboratory product rtearic acid", was additionrslly adcieci Zu uutue ur l.hc tests to reduce the wall friction- Mixing took place with a slow-DT/905 xHvxaaaiat ud +67i6679TZ88D zv3 os;ct to. tiarco running Rh8n wheel mixer 18 with mixing baffles in the form of perforated plaLe c:iceues aL iuuui LctupcrdLLure or witlz a Lwo-armed mixer at a temperature of 80 C, whereby a material to be mixed 20 which i.a ready for pressing is b obtained as a result.

Furthermore, Table 3 altows the LiuiLeLidl pLuliurLions of the raw material of the material 20 to be mixed as were used in the teNts. Ac:c:uidiu,yly, Llic uwLerial proportion of the bulk 10 starting material consisting of the various particle size fidc:Liuua wae beLween 65 auid 95 wt.% and the material proportion of the binding agent was betwPedn 5 anci '32 w1- .
uL Lhe LoLal niass of the inaterial 20 to be mixed. In so far as carbon staple fibres 14 were ar9c9Pr.9, thpi r matPrial 15 proportion wan 0 to 15 wt. %, in the caee of the auxiliary pressing agent 1E, 0 to 5 wt. *_ Thr mat-rriA1 >.c1 r.n hP mixed wa4 shapPd by an extrusion pretis 22 illustrated in croee-acction in Fig. 2 with a zU plunger piston 26 which can be moved in the longitudinal direction ineide a prcea houoing 24, which plungcr pioton delimits a supply chamber 3U which disCharges into an outlet opening 28 of the press housing 24 which ir constricted in contrast, which supply chamber can be filled with material to be pressed and can be comminuted by its pressing movement. The longitudinal extenc of the extrusion preos 22 it; subr.tantially parallel to the horizontal-The press housing 24 comprises a cylindrical portion 32 wiLtt diduteLeL D.yulaiuy Ltie pluxxyer pisLon 26 and a tunnel-shaped portion 34 which is provided, for example, at its eud witlt a LubulctL suuL11NLCue 36 wiLh diameter d forming tho outlet opening 28.

PT/LOS NllNV1QaQaIm ?IQ +69T68TCTZ$87 %Yd OC :LT TO, 60/CO

Ra1r mater a Property Raage Petroleum co e ranu otnetry Max mum pdrt c e m ze graphite granulas 0.04 to 2 mm Quantity 65-95 wt. %
B n ng agen Type Pitch, SP > 3o"C
Phenolic recin, Phenolic resin-Novolaks flow path 20-100 tcar-tlan . .y 5-3-1 wt. ~k arbon fibres Fibre lengths 0.2-15 mm rP- .rPa .mPn _ s zed, sizings su t e for incorporating in pitch and/or phenolic resins Quantity 0-15 wt.
yx1 :L ary Type ara in oi ,,. t-r~ri n pressing agent Quanl.lLy 0-5 wt.

Table 3: Type and material prcpui 4lutiri tiL l.1xc c;onlponellts Uf ttie uidtrz'idl Lu ba mixcLl The supply Chamber 30 is eeaentially formed by a space enclosed by the cylindrical and funnel-SYaared sPcrf-i on 12, 34 and delimited by a preseing face 38 of the plunger piston 26 pointing towards the out.t rt oprni ng 'l.H anr? i g ar its largest when the plunger piston 2G ie in a starting position illustrated in Fig. 2 which is as far from the outlet opening 20 ae possible.

A counter mandrel 40 iC coaxially received inside the tubular mouthpiece 36 at a radial distance to the latter's inncr pcriphcral face to form the tube, which counter mandrel projects at least partially into the cylindrical portion 32 of the preocs houcing 21 with its end facing towards the plunger piston a6 and tapers there. The fuiuiel-DT/805' NiNV7Q3Q3IM i1Q +OVTG6V6T980T Z'tl'd TC ;LT TO,00/C0 shaped portion 34, the tubular mouthpiece 36 and the counter mandrel 40 together form a shaping mouthpiece 42 of the extrusion press 22. The shaping mouthpiece 42 is connected in a heat conducting manner to heating devices 43 to heat material to be mixed which has been pressed through the shaping mouthpiece 42, the heating device 43 of the tubular mouthpiece 36 being heat insulated from the heating device of the funnel-shaped portion 34.

The ratio D/d of the diameter D of the cylindrical portion 32 of the press housing 24 to the diameter d of the tubular mouthpiece 36 is smaller than or equal to 2.5.
The ratio of the diameter d of the tubular mouthpiece 36 to its length 1 is preferably smaller than or equal to 1 and the funnel-shaped portion 32 has a cone angle a of 35 .

The supply chamber 30 has a separate supply opening 46 connected to a metering device 44, via which supply opening material to be pressed can be supplied in metered fashion to the supply chamber. The supply opening 46 is designed as a through hole in a wall 48 of the cylindrical portion 32 of the press housing 24 transversely to the horizontal longitudinal extension of the extrusion press 22 and is extended radially outwards by a funnel-shaped filling tube 50 in which a cellular wheel sluice 44 forming the metering device is received.

The individual stages illustrated schematically in Fig. 2 to Fig. 5 which form a pressing procedure are now to be described below. Initially, the plunger piston 26 is in a starting position in accordance with Fig. 2 which is as far away from the outlet opening 28 as possible, so the supply chamber 30 assumes its maximum size. In a first stage, material to be mixed with irregularly aligned particles is metered into the supply chamber 30 via the cellular wheel se sluice 44 until the upply chamber is comLalPtply filled.
Then the metered material to be mixed is compressed by forward movement of the plunger piston 26, fnr PXarnplP at a continuous forward movement speed s of a maximum of 4 m/min, as shown in Fig. 3- Owing to r.hP high proportion of coarse-grained fractions of the graphite granulca or pPtrolPilm coke which has been comminuted, which bring about a relatively high level of inner friction in the material to ,bP pressed, discharging ot the material to be mixed through the conotrictcd outlet opening iA initially prevented. Consequently a quasi-static compression results, for which reaoon the previouply irregularly aligned particles in the material to be mixed, for exanwle c:dubuil fibrec and graphite particles can, Eimilarly to when pressing in a stamping press, only aliyn trau,-sveLsely Lu the direction of forward movement or prescing.

As the plunger piston 26 moves with a, for example, continuous forward movement speed towax=dts Llie uuLlCL
opening 28, after a certain period of time, the situation illustrated in Fiy. 4 zesulLa Iu w1li0a iL lias reached its end position and pre-compressed material to be mixed discharges through the outlet opening 28, pasaing the counter mandrel 40, whereby it is shaped into a continuous tube 52. Owing to the internal flow hindrance, the particles previously aligned transversPly to the AirPnr.inn of pressing, realign inside the material to be mixed in 411C'h a way that thr_y assume a slightly altered oblique position and now exhibit a direction component in the direction at pressing based on their longitudinal extent.
Obliquc position ahould be undcrotood here to mean an angular alignment 0 greater than 0 and smallsr than/equal to 750 to a plane pcrpcndicular to the longitudinal axiE of the tube-VT/OTS NNVl1HQ3Idf aQ +87T86TCTZ889 rVd ZC ;LT TO, 60/CO

in order to achieve sufficient thermal conductivity of the graphite tubes 52 in radial direction, d tou dCVCLC
alignment of the particles in the direction of the longitudinal axis is unfavourable. Cdre is CX(Jtealetll.ly Lu be taken that the external friction acting on the pre-compressed nuitcrial to bc niixeci ib da luw dd puasible, Lhe internal friction on the other hand being as high as PcesivlC, fui CXdtLlp3.C Ly daailicll caL Lhe auxiliary pressing agent 16. The aim is the formation of a stopper flow in the interior of the aupply chamber 30.

The supply opening 46 is preferably arranged between the starting position and the end position ot the p1ungpr piston 26, so that, in its end position in accordance with Fig. 4, it has at itast partially passed the supply opening 46 and is in the region of the end of the cylindrical portion 32 ot the press housing A4, whereby the supply chambcr 30 ia diaconncctcd from the aupply opening 46. The piston stroke is preterably dimensioned such that a volume of prcaocd matcrial to be mixed ie preCOed out of the outlet opening 28 which is smaller than the volume of material to be mixed originally metered into the supply chamber 30, so a residual volume of material to be ud.xed which has been pressed into the funnel-shaped portion 34 of the press housing 24 remains in the supply ctiatcLber 30.
Finally, the plunqer piston 26 is rapidly retuztieci Lu ILb starting poaition, whereby the supply opening 46 is c:c[upleLCly expuaCd, dU e2iuwii wiLli LYie dia ut Fi g. 5. The intermediate space 54, which has now been produced between the resa.dual volume of the material to be mixed remaining in the funnel-shaped portion 34 and the pressing face 38 of the plunger piston 26 pointing towards the outlet opening 29, is now filled with new material 20 to be mixec9 by mPann of the metering device 44 until the supply chamber 30 is aga i n nomp l Pi:P ly f.3.J.1 Pci . As i:he rPmaining volume ot the IT/TTS NNVNHQHIm 2iQ +6IT8696TZ867 RV,3 ZB;LT T0, 80iCt7 material to be mixed of the previouo preeaing procedure has already been pre-compressed in the tunnel-shaped portion 34, a diecharge barrier is formed for the newly filled volume of material to be mixed against which the pluiiyer 5 piston 26 now presses from the other side. Therefore, the newly filled, still slightly compressed volunie of tnateridl to be mixed is compressed by the advancing piston movement, so the particles can aliqn tranbversely befuz.e Ltie iesiaudl volume of the previous pressing procedure remaining in the 10 funnel-shaped portion 34 and constituting a stopper is pressed out. After the plunger piston 26 has reached its end position the cycle described starts from the beginning ag tin _ 1 S Tn adcii i-i nn tn the ahovP-clPgcrihPd extrusion press 22, also used for tshaping material to be mixed was a piston extruder 56 illtistrated in Fig. 6 with a plunger piston 60 which can bc movcd longitudinally in3idc an cxtruder houcsing 58, which piston delimits a supply chamber 62 which discharges 20 into an outlct opening 61 which ie conctricted on the opposite side and which supply chamber can be filled with matcrial to bc prccced and can be Coaun.inuted by itc pressing movement. The extruder housing 58 comprises a cylindrical portion 64 guiding the plunger piston 60 and a funriel-shapld portion 66 with a cone angle y of preferably 300, which is provided at ita end with a tube stump 68 fnrming the cnit:lPt opening 61, thP supply chamber 62 being substantially formcd by the inncr opacc cnclo3cd by the cylindrical and tunnel-shaped section 64, 66 and delimited by a prc3sing face 70 of the plungcr pi3ton 60 pointing towards the outlet opening 61. In contrast to the prcvioualy dc3cribcd cxtruaion prca3 22, the cupply chamber 62 is substantially longer, so greater forces are necessary for preooing and the forward movement opeed c is likewise higher.

VilZTS Nll1i"HQ3IdA gQ +6VT66'D~TZS6V %'tl3 C~ -LT TO, G0/'CU

ziI Lllt LeSLs in w111G11 Lhe piSLon exLruder 56 was used, the material to be mixed was initially statically pre-cUaLPtebued iLL d t3LdltlpillH ptesb kiiuwtt lurl' se (noL sllowll) in order Lo achieve aui aligiiLneiiL oL the graphite particles and carbon fibres transverse to the direction of pressing_ Subsequently, the pre-compressed pre-pressed part adapted to the size of the 5upply chamber 62 o.f, the piston ext.riir.7Pr S6 was introduced into the supply chamber by withdrawing the p1 iingrr pi nr.nn F,e) e~niT t-Pr tn r.hP r7i rPnr.i nn nf prPgging through an end rear aperture 72 coaxial with thc piston axis and then passing the pre-pressed part through the same aperturc and placcd in the supply chambcr 62. The particlcn were realigned inLo an oblique position as in the previously described extruAion preOQ 22 by the subsequent forward movement of the piston and the resulting pressing out of material to be mixed through the outlet opening 61.
Fig. 7 shows a single-screw-type extruder 74 as was used to shape the material to be mixed in some of the teuts.
Instead of a plunger piston the single-screw-type extruder 74 Yldb d t.Udxl.dlly tuLciLill,y PtC~bLLtC WUtLIt 78 111l31.L~e dL11 extruder housing 76_ Table 4 gives an overview of the parameters used and aLLaiiied iu 17 LeetLr3 Lu ptuduvC gidi.pli_iLe Lubes. In the test denoted by the serial number 8, for example, a tnateri.s1 to be mixed, the total material of which consisted of E37 wt. ~
grAjahi t.e with s maximum pa.r_ t i.cl,e Bi Qe of 0_ 75 mm Anrl 1 A wt.
* of binding agent in the form of Novolak, 1 wt.W paraffin ni 1 Anr.l '>. wt.* r.Arhnn tibres ot C, mm i n 1 pngr.h waR prpg4Pd to form a graphite tube in accordance with the process illustrated in Fig. 2 to Fig. 5. The metered individual comporient were mixed at room temperature to form a material to be mixed with the ith8n wheel mixer la leig. 1).
Thc rclative flowability of the material to be mixed was 9T/CT5 ATN'tl'IQBQ3Ids tiQ '*69T669CTZ8Cf'D gY3 CC ;LT T0 , 60/9O

0.38. After shapinr.~ by means of thP Pxtrusion press 22, the graUliil.C Lube was fired (coked) in an clcctriCally heated kiln with protective furnace gas rinsing (nitrogen) to 800 C.
The r cult of Test No _ 8 were grapbi t.e fi.tihPg with a thermal cvriclucl.ivity ot 84 W/(m x K) in the direction of preocing or length of the tube and 81 W/(m x K) transversely to the direction of presesing or length of the tube, a ratio of thermal conductivities along/t.ranmvPrRP to the direction of pressing oL 1.04 being produced. The anglc bctwccn the carbon fihrPs and the direction ot pressing or length of t hP tiibe was approximately ts 5 , i.e. the initially traravrrsaP I y aligned particles (corresponding to 90 ) were realigned by approximately 5 in the di rPr..t.i nn of pressing.
'1'he bursting pressure of the graphite tube dtuuuiil.ecl Lo 68 bar.

9i/DiS NiN'tlM:iIdd 2IQ +69T68TCT9889 %Y,3 CC ;LT i0 , 60/CO

9ar a gaw mater ai~
Hp. Quantity in [wt. t]
Co ~, qrap t~ p ea 1[ovo Freasing aid C-fibre ap ng y extrusion presa hite Q.P. P na pw+ sr rdera n o Longtk 6mm < 0.75 mm 110~C + S} Hem i 78 - 20 - 2 2 eo - ia - 2 Ctosrin b 85 - 12 1 2 Shapinq by pi ton extruder ammr tic c.r. rna 8ow+ e:
< 0.75 ca iio c + a'k no=

eo 1e a -R2. - 19; 1 7.

5 ap ng by screw-type exzru er w z conical mouthpiece araphi eo < u.75 mm - =

ap ng by screw- ype extru er w I~ eDDe mou p eCe t eGroletm cokQ M.P. r ao powder lns~ffin oil Length 0 mm c 0.75 mm 1 1 Aef! + 8# He7ts is 6g 30 - -etro sm coke c 0.4 mm Table 4, =rest parametere VT/TOS 11iNb'KBC[HIds 2iQ +8TT8896TZ88V gVS OD;LT T0, 60/CO

Ser]al jLe]ati+-e Car- C9raphtc- Therxral conduclivity C-fl~re trstiu$
No. flowaUdlity boni- imtion [N'I(m xioJ allprnrn pressure vf tha fa- l J ~*l II7aie'da1 i0 dDII
be mi1fR (1 in dira:fim of c>anevGtaely to Ratto along/
prexmtng ehe direcdaa of txamvaryaly pr=dnm by exesusioa prem Sbaping 1 0 60 40 1.3 appmx. 41 2 0.98 no 55 42 1.3 appror- 60 _LMS 3 0. es 58 52 1.1 iOX. 61 -4 0.75 oe 67 61 1.1 approx. 75 45 f1 4 nn 67. 59 1.05 49 B 0.32 ex uu 64 62 1.03 ~19.80 GG
7 0148 r~ ~n 67 f.S mx R 70 8 0.38 s ycs 84 81 1.04 VPLUJL. 68 Shs m extYULli's U.7'l es no 31 41 1.2 - 34 0.72 aa s6 51 1.1 - -11 U 6' 311 1.07 a x- 73 56 12 0.45 ea 65 64 1.02 a rox.80 65 5 acaew eurtutcr th conic MEu 13 2.0 as yoo 60 23 2 .4 - 40 ,a n w.rrw-rypr cxrni rr wil it rrxrilt iCCC
14 3.0 ra y- 110 90 1.22 - _ 41 1S 2.4 ea es PS 64 1.4 a .3f.1 57 itS 2.8 es 120 90 1.33 - -17 2.7 se 110 95 1.16 x.30 33 Continuatioa of 1'ablo 4 5 For the purpose of compzriaon, a reference tert is denoted by tYie uulabez 13 lu w2il.c:li Wttdp.1LL,y l:Ji by u-Ca113 uf d ki4l.cw-type extruder in accordance with the state of the art with a 30" r-nni ca1 shaping rnnl.ithri Rr..s. Nn r.rtr'hnn fi hrPg arP
t1(3dCC2 tU the ltit-ttCZ'j.til to be LIIiXC[2. Ay CIIlCL4]Cti ft Vut L11C
l0 table, graphite tubes are produced in which the thermal uuuducLiviLy in LlLe ditat~LiUsI uL Lhe lengLh of the tube was 2.4 times the thermal conductivity transverse to the direGLion of Lhe 1eLiyLh oL LiLe LuL'e - a considerably higher pronounced material anisotropy therefore compared with TPAt.
No. 8 with a ratio along/transverse of 1.04.

9i/ZOS NNt+1t3Q3IM 2IQ +67T809CTZ80y XVd Oy :LT T0 , WCO

= CA 02362391 2001-09-04 In contrast, the Bcrew-type extruder 74 in accordance with Fig. 7, with stepped instead of coziic:al .411dpluy uwuL.1ljiie4e was ueed to press the material to be mixed in the course of Test No. 14. As a result, a substaul.idlly uwLe favuuLaLle 5 ratio of thermal conductivity along/transverse to the (3iLCC:uiUi1 uf PLeUbitiy uf 1.22 vuuld be achieved.

Au aClvanl,ageously balanced thermal conductivity ratio of 1.02 was also achieved with Test No_ 12 in w'hir.h thP
10 material to be mixed had a relative flowability of 0.4S and shaping was by means of the pi s1-nn rxtriiciPr 56 in accordance with Fig. 6, the material to be mixcd having benn rrP-c-nmprPssPr9 i n a gtampi ng prPgg.=rhP binding agent fraction of the material (Novolak) to bc mixcd wao low at 15 15 wL. t, in addition, 2 wt. t of carbon fibres and 1 wt. V of auxiliary prc33ing agcnt wcrc addcd. Asn angle of approximately B0 was produced between the carbon fibres rmhrdded i n r.hP grsphi r.P mar.Pri a1 and r.hP ciirPc:t.ion of the length of the tube, i.e. the particles initially aligncd Au Lransversely owing to the block compression in the stamping press (corresponding to 90 ) were realigned by 100 in the direction of preasing. In addition, at 65 bar the bur3ting pressure was subsr_antially higher than in the state of the art (Tent No. 13).
2b Thc paramctcr3 of the furthcr tc3to can be inferred from the table, whereby, to sum up, it can be stated that the typically pronounced anisotropy for the graphite materials of the state of the art could be significantly reduced by using the process according to the invention. As a result, graphite components were produced with substantially hiqher thermal conductivity transversely to the direction of pZ'Cbuiliy, c111d d3 d LCtlllll. uf L11C dtIlULiUtt aL cal"1]UA L].17ZeS
to the material to be mixed, graphite tubes with higher burstinq preasures cUuld wz'coveL Le LJivciuc:Ctl.

DT/SOS xm'tl'1Q3Q3IA1 ?id +6VTCfO9CT9887 ZVd TV;LT TO, 60/EO

Claims (22)

CLAIMS:

1. Process for producing components and semi-finished products from synthetic graphite or from ceramic granules, involving shaping of a material to be mixed by means of an extrusion press or an extruder, the process comprising the following steps:

a) pre-pressing the material to be mixed in static or quasi-static manner, flow movements of the material to be mixed being stopped or impeded in such a way that particles previously irregularly arranged in the material to be mixed are initially aligned transversely to the direction of pressing, b) pressing out of the pre-pressed material to be mixed through an outlet opening of the extrusion press or the extruder in such a way that owing to adjusted flow properties of the material to be mixed, the particles within the pre-compressed material to be mixed realign, starting from their transverse alignment, by an angle (.beta.) of a maximum of 75° in the direction of pressing.

2. Process according to claim 1, for producing graphite tubes.

3. Process according to claim 1 or 2, wherein the material to be mixed contains petroleum coke or graphite granules.

4. Process according to any one of claims 1 to 3, wherein the material to be mixed is pre-pressed statically to form a block-shaped pre-pressed part by means of a stamping press.

5. Process according to claim 4, wherein the pre-pressed part is then placed in a supply chamber of a piston extruder in order to press it through the outlet opening to give it its shape.

6. Process according to any one of claims 1 to 3, wherein the extrusion press has a supply chamber with a supply opening for supplying material to be mixed, which supply opening is arranged between a start and an end position of a plunger piston which can be used to reduce the size of the supply chamber, the shaping of the material to be mixed comprising the following steps which form a cycle:

f) metering of material to be mixed into the supply chamber with the aid of a metering device until it is completely filled when the plunger piston is in the starting position, g) quasi-static pre-pressing of the material to be mixed in the supply chamber by slow forward movement of the plunger piston in order to align the particles transversely to the direction of pressing, h) pressing out of a volume of pre-compressed material to be mixed through the outlet opening, which volume is smaller than the volume originally in the supply chamber, whereby once the end position of the plunger piston in the supply chamber has been reached a pre-compressed residual volume remains, i) return of the plunger piston to the starting position and metering of new material to be mixed into an intermediate chamber between the pre-compressed residual volume and the plunger piston until the supply chamber is again filled completely, j) continuation with step b).

7. Process according to any one of claims 1 to 3, wherein the material to be mixed is shaped by a single-screw-type extruder, the outlet opening of which, viewed in the direction of pressing, is tapered by at least one step hindering flow movements of the material to be mixed.

8. Process according to any one of claims 1 to 7, wherein the material to be mixed is obtained by mixing a bulk starting material containing at least one particle size fraction of at least one of: petroleum coke and graphite granules, with at least one binding agent, the bulk starting material having a material proportion of 65 to 95 wt. % and the binding agent having a material proportion between 5 and 32 wt. % of the total mass of the material to be mixed.

9. Process according to claim 8, wherein carbon fibres are additionally added to the material to be mixed before pre-pressing, these carbon fibres having a material proportion of 0 to 15 wt. % of the total mass of the material to be mixed.

10. Process according to claim 8 or 9, wherein auxiliary pressing agents are additionally added to the material to be mixed before pre-pressing, the auxiliary pressing agents having a material proportion of 0 to 5 wt. %
of the total mass of the material to be mixed.

11. Process according to any one of claims 8 to 10, wherein the bulk starting material and the binding agent and further raw materials are mixed by a slow-running mixer.

12. Process according to claim 11, wherein the bulk starting material and the binding agent and further raw materials are mixed by a tumble mixer or by a Rhön wheel mixer.

13. Process according to any one of claims 8 to 12, wherein the bulk starting material is comminuted and screened before mixing in such a way that it essentially contains a first particle size fraction with particle sizes greater than 0 mm and smaller than 60 µm and with a material proportion of 20 to 100 wt. % of the bulk starting material, and a second particle size fraction with particle sizes of 60 µm to 750 µm and a material proportion of 0 wt. %
to 34 wt. % and a third particle size fraction with particle sizes greater than 750 µm to 2000 µm and a material proportion of 0 wt. % to 46 wt. %.

14. Device for producing components and semi-finished products from synthetic graphite or ceramic granules, containing an extrusion press with a plunger piston guided so as to be movable longitudinally inside a press housing, which plunger piston delimits a supply chamber with a diameter (D) which discharges into a constricted outlet opening with a diameter (d), which can be filled with material to be pressed and can be comminuted by its pressing movement, wherein the supply chamber has a separate supply opening arranged between a starting position and an end position of the plunger piston, and the ratio (D/d) of the diameter (D) of the supply chamber to the diameter (d) of the outlet opening is smaller than or equal to 2.5.

15. Device according to claim 14, for producing graphite tubes.

16. Device according to claim 14 or 15, wherein the longitudinal extent of the extrusion press is arranged substantially parallel to the horizontal and the supply opening of the supply chamber is arranged substantially transversely thereto.

17. Device according to any one of claims 14 to 16, wherein the press housing comprises a cylindrical portion guiding the plunger piston and a funnel-shaped portion which is provided at its end with a tubular mouth-piece forming the outlet opening, the supply chamber being substantially formed by the space enclosed by the cylindrical and funnel-shaped portion and delimited by a pressing face of the plunger piston pointing towards the outlet opening when the plunger piston is in a starting position which is as far away from the outlet opening as possible.

18. Device according to claim 17, wherein the supply opening is designed as a through passage in a wall of the cylindrical portion and is extended radially outwards through a funnel-shaped filling tube, in which a cellular wheel sluice forming a metering device is received.

19. Device according to claim 18, wherein the ratio of the diameter (d) of the tubular mouthpiece to its length (1) is smaller than or equal to 1 and the funnel-shaped portion has a cone angle of (a) 30 to 35°.

20. Component or semi-finished product made from synthetic graphite or from ceramic granules, obtained by a process involving shaping of a material to be mixed by means of an extrusion press or an extruder, the process comprising the following steps:

a) pre-pressing the material to be mixed in static or quasi-static manner, flow movements of the material to be mixed being stopped or impeded in such a way that particles previously irregularly arranged in the material to be mixed are initially aligned transversely to the direction of pressing, b) pressing out of the pre-pressed material to be mixed through an outlet opening of the extrusion press or the extruder in such a way that owing to adjusted flow properties of the material to be mixed the particles within the pre-compressed material to be mixed realign, starting from their transverse alignment, by an angle (.beta.) of a maximum of 75° in the direction of pressing.

21. The component or semi-finished product according to claim 20, comprising a graphite tube.

22. The component or semi-finished product according to claim 20 or 21, wherein the material to be mixed contains petroleum coke or graphite granules.