DE102010003212A1 - Producing a component made of a fiber composite material, comprises producing a green body with a matrix made of resin and carbon fibers incorporated into the matrix, and introducing the green body into a microwave oven - Google Patents

Abstract

The method for producing a component made of a fiber composite material, comprises producing a green body (7) with a matrix made of resin and carbon fibers incorporated into the matrix, introducing the green body into a microwave oven, and pyrolyzing the green body using pulsed microwave effect. The green body is produced at 150-260[deg] C by hot pressing, and is heated with a heating rate of 1400-2200[deg] C per hour using a microwave-absorbing susceptor (6, 10), which is positively contacted with the green body under interposition of an intermediate layer. The method for producing a component made of a fiber composite material, comprises producing a green body (7) with a matrix made of resin and carbon fibers incorporated into the matrix, introducing the green body into a microwave oven, and pyrolyzing the green body using pulsed microwave effect. The green body is produced at 150-260[deg] C by hot pressing, and is heated with a heating rate of 1400-2200[deg] C per hour using a microwave-absorbing susceptor (6, 10), which is positively contacted with the green body under interposition of an intermediate layer. The green body is pressed using the plate-shaped susceptor during the microwave effect. The green body is heated in heating zones at different heating rates. The green body is kept at a maximum pyrolysis temperature for a holding time of 10-20 minutes. The green body is heated in a first heating zone with a first heating rate of 2000[deg] C per hour at a temperature of 400[deg] C. The green body is heated in a second heating zone with a second heating rate of 1500[deg] C per hour at a temperature of 600[deg] C. The green body is heated in a third heating zone with a third heating rate of 2000[deg] C per hour at a temperature of 900[deg] C. The pyrolyzed green body is cooled with a cooling rate of 800[deg] C per hour, and is infiltrated at 1550-1750[deg] C under vacuum with silicon.

Description

The The invention relates to a method for producing a component made of a fiber composite material. It relates in particular to a method for pyrolysis of a green body.

The EP 0 915 070 A2 describes a method for producing a carbon fiber reinforced, ceramic molded body. For this purpose, first a green body is produced in which carbon fibers are contained in a matrix formed from a phenolic resin. The green body is pyrolyzed. As a result of the pyrolysis, a porous carbon skeleton remains from the matrix. The porous green body is then infiltrated with liquid silicon. The carbon of the matrix reacts with the liquid silicon to form silicon carbide. - The pyrolysis of the green body requires in the known method, a time of usually more than 30 hours. Apart from that, the pyrolysed green body does not have a particularly high dimensional accuracy.

The DE 199 29 666 A1 describes a method in which a thermoplastic fiber composite semi-finished product is heated by means of microwaves to a temperature in the range of 120 ° C. The heating by means of microwaves serves to cure the polymer used for producing the fiber composite semifinished product.

The EP 1 547 992 A1 describes a method of manufacturing a fiber composite component wherein a fiber-resin mixture is pyrolyzed with uncured resin. In this method, it is considered advantageous that the curing of the resin takes place during the pyrolysis process.

Also This method has the disadvantage that the pyrolysis process is time-consuming is. The porous green compact produced with it no particularly high form faithfulness.

task The invention is to the disadvantages of the prior art remove. In particular, a method is to be specified, which is a production of a component made of a fiber composite material With reduced time and cost allows. To Another object of the invention is a manufactured in the process Pyrolyzed green body one possible have high dimensional accuracy.

These The object is solved by the features of claim 1. Expedient embodiments of the invention result from the features of claims 2 to 14.

According to the invention, a method is proposed for producing a component from a fiber composite material with the following steps:
Production of a green body with a matrix of a resin and carbon fibers accommodated in the matrix,
Introducing the green body in a microwave oven and
Pyrolysis of the green body by means of pulsed microwave action.

at it is a "green body" within the meaning of the present invention, essentially one solid body in which the matrix-forming resin cross-links or has largely cured. The networking of the first flowable resin can by means of conventional Techniques, for example by adding a hardener, by the action of radiation, by temperature and pressure, in particular by hot pressing, and the like can be achieved.

in the For the purposes of the present invention, the term "pulsed Microwave action "an exposure of the green body understood with microwaves, which is temporarily interrupted. Ie. the green body is during power up intervals with Microwaves applied. Two switch-on intervals are switched on Switch-off interval interrupted. The duration of the switch-on and switch-off intervals is variable. Even a radiated microwave power can from Switch-on interval to switch-on interval can be varied. advantageously, a turn-on interval has a duration in the range of 5 seconds to 300 seconds, more preferably from 10 seconds to 200 seconds. A switch-off interval advantageously has a duration in the range from 10 seconds to 600 seconds, preferably 20 seconds to 200 Seconds. At least during two consecutive turn-on intervals the same microwave power can be radiated. A switch-off interval between at least two consecutive turn-on intervals advantageously has the same duration. Likewise also at least two consecutive turn-off intervals the same Have duration. - The provision of the switch-off intervals allows a particularly gentle degassing of the green body. In particular, the formation and bursting becomes gas-filled Cavities avoided. The pyrolysed prepared according to the invention Green body is characterized by a high form loyalty out.

to Production of the green body becomes a carbon-rich Resin used. After pyrolysis of the green body remain from the matrix at least 40 wt.% Of carbon. Of the Carbon forms a porous framework which is traversed by the carbon fiber.

With the proposed method, the pyrolysis is surprisingly be drastically reduced. Using pulsed microwave exposure is it possible to have a green body inside to pyrolyze for a period of less than 1 hour. In order to a method for producing a component from a fiber composite material, especially a fiber composite ceramic, drastically shortened and thus considerably cheaper become.

To An advantageous embodiment of the invention is the green body by means of hot pressing at a temperature of 150 ° C to 260 ° C made. A pressing pressure is more advantageous Wise 10 to 20 bar. This allows the production exactly dimensioned green body. Networked during hot pressing the resin largely. The green body is largely non-porous and has a homogeneous structure.

To In another advantageous embodiment, the carbon fibers before the production of the green body at a Temperature in the range of 600 ° C to 900 ° C annealed. Annealing can last for 0.5 to 3.5 hours be carried out under a protective gas atmosphere, which is substantially is formed of argon or nitrogen.

Of Furthermore, it has proven to be expedient to use as the resin a resin selected from the following group is selected: phenolic resin, pitch, PMMA, PU, PAI. Especially is suitable for carbon-rich thermosets and pitch-based raw materials for use as a resin.

When Carbon fibers can be short fibers, continuous fibers, preimpregnated Woven fabrics and fabrics, knitted fabrics, nonwovens or the like. Processed carbon fibers be used.

To a further advantageous embodiment of the method is the Green body with a heating rate of 1400 ° C heated to 2200 ° C per hour per hour. The green body can be heated in particular in several stages, which are located in differentiate the heating rate.

To a further advantageous embodiment of the invention is for Heating the green body at least one microwave absorbing Susceptor used. Such a susceptor heats up as a result of Absorption of microwaves quickly increases and releases the absorbed Heat in particular in the form of IR radiation to the green body from. Apart from that, the green body is using of the susceptor heated by direct heat conduction and convection. Advantageously, the at least one susceptor, preferably with interposition of an intermediate layer, positive fit in contact with the green body. The intermediate layer is made of a material that has good thermal conductivity and has a high compressive strength. Because of the form-fitting Contact will be a particularly effective transfer of Heat from the susceptor to the green body reached. In this case, the green body is so both by the absorption of microwave energy and the Absorption of IR radiation, by direct heat conduction and convection heated up. The use of a susceptor in immediate Contact to the green body has advantageously the effect of having a temperature gradient between the green body and the environment during the heating phase particularly small is. As a result, occurring in the green body thermomechanical stresses kept small and a delamination the green body avoided even at high heating rates become.

To a further advantageous embodiment of the green body during microwave exposure, preferably by means of at least one plate-shaped susceptor, pressed. In order to can improve the dimensional accuracy of the green body become.

Of Furthermore, it has proven to be expedient that the Grunkörper in several, a different Heating rate having heating stages is heated. Within one and the same heating stage may have a first duration exhibiting first Shutdown interval can be used. At the end of each heating stage can a second shutdown interval with a second duration provided be. The second duration may be different from the first duration. she can in particular be larger or smaller than that first duration.

To A further advantageous embodiment provides that the green body at a maximum pyrolysis temperature for a hold time of 5 to 60 minutes, preferably 10 until 20 minutes, is held. The maximum pyrolysis temperature can for example in the range from 850 ° C to 1650 ° C, preferably in the range of 950 ° C to 1250 ° C, lie.

following becomes the pyrolyzed green body at a cooling rate of at least 750 ° C to 850 ° C per hour, preferably about 800 ° C per hour, cooled. The proposed high cooling rate further contributes to the acceleration of the method.

Subsequently can the pyrolyzed green body again at a temperature in the range of 1500 ° C to 1700 ° C, preferably 1600 ° C to 1680 ° C, pyrolyzed under vacuum become. This further pyrolysis serves to remove low molecular weight degradation products and to generate a particularly high reactivity of the Carbon.

Of the Pyrolysed green bodies can be described below in conventional At a temperature in the range of 1550 ° C to 1750 ° C, preferably about 1650 ° C, under vacuum with silicon or metallic alloys are infiltrated. As a result, converts The carbon formed during pyrolysis in silicon carbide around. It becomes a carbon fiber reinforced silicon carbide ceramic educated.

following Embodiments of the invention with reference to the drawings explained. Show it:

1 a schematic cross-sectional view of a first arrangement for carrying out the method,

2 a schematic cross-sectional view of a second arrangement for carrying out the method,

3 a temperature course over time and

4 a temperature and microwave power curve over time.

In 1 and 2 is a microwave source 1 about one with a cutting disc 2 , which may be made of quartz glass, sealed waveguide, for example 2a with a reaction chamber 3 connected. The reaction chamber 3 has an outer shell made of steel, which on its inside with a carbon felt 4 is provided. On the side facing the interior of the carbon felt 4 is at least a graphite foil 5 appropriate. With the reference numerals 6 is an upper susceptor plate and with the reference numeral 10 a lower susceptor plate, which may be made of silicon carbide, for example. One of the two susceptor plates 6 . 10 can also be replaced by a plate with a high thermal conductivity, such as AlN. In 1 is between the susceptor plates 6 and 10 positive fit of the green body 7 inserted. The green body 7 has, for example, external dimensions of 300 mm × 300 mm × 15 mm.

The from the susceptor plates 6 and 10 and the interposed green body 7 existing layer sequence is with the interposition of an insulating plate 13 on one with grooves 11 provided rotatable stamp 12 supported. The grooves 11 For example, in two mutually perpendicular directions in the stamp 12 be provided.

With the reference number 8th is one of a through the graphite foil 5 limited reaction chamber 3 Leading gas discharge line, which leads to a thermal Gasnachverbrennungseinrichtung 9 leads. The reaction chamber 3 is with a gas-tight door 17 locked. The reference number 14 denotes one on the waveguide 2a discharged gas supply line.

At the in 2 shown second device are between the susceptor plates 6 and 10 and the green body 7 each fiber mats 16 inserted, the z. B. from Al ₂ O ₃ , can be made. On the upper susceptor plate 6 is another insulation board 13 placed on which a rotatable plunger 15 suppressed.

To produce a pyrolyzed green body, the procedure is as follows:
First, a green body 7 prepared by a carbon-rich polymer or resin having a carbon content of z. B. more than 40 wt.%, Preferably more than 50 wt.%, Mixed with carbon fibers or a carbon fiber-formed fabric, knitted fabric, nonwoven or the like. Infiltrated with it and is subsequently subjected to a molding process. The molding process may be a conventional molding process, as known in the plastics arts. Preferred is a shaping by means of hot pressing. If phenolic resin is used as the resin, the hot pressing at a pressure of 5 to 25 bar, preferably 10 to 20 bar, and a temperature of 150 ° C to 250 ° C, preferably 160 ° C to 200 ° C, take place. The hot pressing can under a protective gas atmosphere, for. As nitrogen atmosphere, take place for a period of 1 to 10 hours.

According to an advantageous embodiment of the hot-pressed green body 7 subsequently annealed at a temperature of 200 ° C to 300 ° C for a period of 1 to 20 hours, preferably 5 to 15 hours, in air. This further increases the degree of crosslinking of the resin and creates shrinkage cracks.

The green body 7 will then be in the in 1 brought shown arrangement. By means of pulsed microwave radiation, the green body 7 according to the in 3 heated temperature profile shown. During heating, the reaction 3 or furnace chamber with nitrogen at a rate of 20 to 30 l / minute rinsed.

How out 3 it can be seen, the temperature profile consists of three heating stages. During a first heating step, the green body becomes 7 heated at a heating rate of 2000 ° C per hour to a temperature of about 400 ° C. During a subsequent second heating stage, the heating rate is 1500 ° C per hour. The second heating step reaches up to a temperature of about 600 ° C. In a subsequent third heating step of the green body by 7 heated again at a heating rate of about 2000 ° C, up to a maximum pyrolysis temperature of 900 ° C. The green body 7 is held at the maximum pyrolysis temperature for about 10 minutes. Thereafter, the pyrolyzed green body is cooled at a cooling rate of about 800 ° C / hour. The pyrolysis process takes, as from the 3 and 4 can be seen, a total of about 90 minutes.

4 shows in addition to the temperature profile, as in 3 shown is the course of microwave power over time. How out 4 is apparent, the microwave power or the microwaves is pulsed irradiated. The duration of a turn-on interval is typically 0.5 to 5 minutes. A first duration of a first switch-off interval is expediently 10 seconds to 10 minutes. Between the first and the second heating stage and the second and the third heating stage, a second switch-off interval is selected whose second duration is greater than the first duration of the first switch-off interval within the respective heating stages. Between the heating stages, the second duration of the second switch-off interval is, for example, 1 to 5 minutes; within the heating stages, the first duration of the first switch-off interval is, for example, 10 seconds to 1 minute.

How farther 4 it can be seen, the irradiated microwave power is increased from one heating stage to the next heating stage. It can also be increased within a heating stage. The irradiated microwaves may have a frequency in the range of 0.3 to 300 GHz. They are both through the green body 7 itself, but especially by the Suszeptorplatten 6 and 10 , absorbed.

In particular, during the first and second heating phase are in the green body 7 translaminare cracks and channels created which allow degassing, without causing delamination. To even out the on the green body 7 acting temperature can this by means of the punch 12 be continuously rotated.

In particular green body 7 , which have a greater tendency to delamination, in the in 2 be pyrolyzed device shown. By means of the pressure stamp 15 on the upper susceptor plate 6 Applied pressure can be the green body 7 be kept in its form during pyrolysis. The between the susceptor plates 6 and 10 inlaid fiber mats 16 contribute to a uniform pressure introduction to the green body 7 at. Pointed contacts between the green body 7 and the susceptor plates 6 and 10 are avoided. The pressure distribution on the green body 7 is particularly homogeneous.

LIST OF REFERENCE NUMBERS

1

microwave source

2

cutting wheel

2a

waveguides

3

reaction chamber

4

carbon felt

5

graphite foil

6

upper susceptor

7

green body

8th

gas discharge line

9

Gasnachverbrennungseinrichtung

10

lower susceptor

11

groove

12

stamp

13

insulation

14

gas supply

15

plunger

16

fiber mat

17

door

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - EP 0915070 A2 [0002]
• - DE 19929666 A1 [0003]
• EP 1547992 A1 [0004]

Claims (14)

Method for producing a component from a fiber composite material with the following steps: production of a green body ( 7 ) with a matrix of a resin and carbon fibers accommodated in the matrix, introduction of the green body ( 7 ) in a microwave oven ( 3 ) and pyrolyzing the green body ( 7 ) by means of pulsed microwave action. Method according to claim 1, wherein the green body ( 7 ) is produced by means of hot pressing at a temperature of 150 to 260 ° C. Method according to one of the preceding claims, wherein a resin is used as the resin, which consists of the following Group is selected: phenolic resin, pitch, PMMA, PU, PAI. Method according to one of the preceding claims, wherein the green body ( 7 ) is heated at a heating rate of 1400 ° C to 2200 ° C per hour. Method according to one of the preceding claims, wherein the green body ( 7 ) by means of at least one microwave-absorbing susceptor ( 6 . 10 ) is heated. Method according to one of the preceding claims, wherein the at least one susceptor ( 6 . 10 ), preferably with the interposition of an intermediate layer ( 16 ), positively with the green body ( 7 ) is in contact. Method according to one of the preceding claims, wherein the green body ( 7 ) during microwave exposure, preferably by means of at least one plate-shaped susceptor (US Pat. 6 . 10 ), is pressed. Method according to one of the preceding claims, wherein the green body ( 7 ) is heated in a plurality of a different heating rate having heating stages. Method according to one of the preceding claims, wherein the green body ( 7 ) is maintained at a maximum pyrolysis temperature for a hold time of 5 to 60 minutes, preferably 10 to 20 minutes. Method according to one of the preceding claims, wherein the green body ( 7 ) is heated in a first heating stage at a first heating rate of about 2000 ° C per hour to a temperature of 350 ° C to 450 ° C, preferably about 400 ° C, heated. Method according to one of the preceding claims, wherein the green body ( 7 ) is heated in a second heating step following the first heating stage at a second heating rate of about 1500 ° C per hour to a temperature of 550 ° C to 650 ° C, preferably about 600 ° C. Method according to one of the preceding claims, wherein the green body ( 7 ) is heated at a second heating rate of about 2000 ° C per hour to a temperature of 850 ° C to 1650 ° C, preferably about 900 ° C in a second heating step following the third heating stage. Method according to one of the preceding claims, wherein the pyrolyzed green body ( 7 ) is cooled at a cooling rate of at least 750 ° C to 850 ° C per hour, preferably about 800 ° C per hour. Method according to one of the preceding claims, wherein the pyrolyzed green body at a temperature in the range of 1550 ° C to 1750 ° C under vacuum is infiltrated with silicon.

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