DE2137614C3 - Process for the production of graphite lasers - Google Patents

Description

The invention relates to a new method for Production of graphite fibers with an improved modulus of elasticity and higher strength.

The cross-sectional shape of the well-known carbon fibers depends on the manufacture of the raw material. Generally these have carbon Fibers have a circular, oval, cocoon-like, or star-shaped cross-section. When carbon fiber This cross-sectional shape can be combined and twisted into a yarn or thread bundle, it is it is not possible to reduce the void space between the fibers or threads below a certain value. Because of the high rigidity of the carbon fibers, twisted yarns are made from the usual Carbon fibers of the cavity or porosity of the twisted yarns 40 to 70% or even more intertensioned state.

When the carbon fiber η to each other mainly are in point contact, takes place when applying pressure in a vertical direction give the twisted yarns a concentration of tension at the points of contact or tangent points the TVs. from which the twisted yarns or bundles of threads are made. For materials with Young's high modulus of elasticity, like carbon fiber, is this concentration of tension undesirable. There are various publications on the plastic deformation of carbon fibers by stretching in the fiber axis at high temperatures and in an inert gas atmosphere. However, it is not known how to measure the cross-sectional shape of such materials as carbon fibers, change with an extremely thin diameter and plastically deform them at extremely high temperatures can without deteriorating their mechanical properties. This has so far been found to be extremely difficult viewed.

The object of the invention is to provide a new method for producing graphite fibers of various types Cross-sectional shape and with a high modulus of elasticity and / or high mechanical strength create. This object is achieved by the invention.

The invention thus provides a process for the production of graphite fibers, which is characterized in that carbon fibers of circular cross-section with a strength of at least 71 cm ² and a value of the ratio of the apparent tensile strength of the twisted yarn to the average strength of the individual fibers of the twisted yarn from 0.03 to 0.5 twisted into a yarn and then at a temperature of at least 2000 C in an inert gas atmosphere a

jo subjected to tensile stress of at least 0.5 t cm ² .

If in the process according to the invention the carbon fibers in the fiber axis at high temperature exposed to a tensile stress, this tensile stress is converted into a force that the

Fibers compressed perpendicular to the fiber axis. This is based on the pressure with which the fibers change from a state of linear contact to a state of surface contact. While the cross-sectional shape of the carbon fibers used is generally circular or oval, that is to say almost circular, the fibers have a different polygonal cross-section after the method according to the invention has been carried out.
If the carbon fibers are subjected to tensile stress at a temperature of at least 2000 C, not only is a negative pressure exerted on the fibers in the fiber axis, but also a positive pressure along the cross-section of the twisted (iarnes. In this case, the Positive pressure along the cross-section of the twisted yarn turns the cross-section of the fibers into a different polygonal cross-section due to the mutual compressing action of the fibers, with the result that the fiber bundle as a whole is brought into a state in which each fiber is with the others Fibers are compactly bundled due to the deformed cross-sections of the individual fibers. This means that the individual fibers are not in punctiform contact with the other fibers in the longitudinal direction.

direction of the fibers, as is the case with conventional twisted yarn, but in a linear or are in planar contact with one another.

The positive pressure along the cross section of the fibers also increases the drawing force in the Longitudinal direction of the twisted yarn, i.e. a compression force on the individual fiber. If you have the When fibers are subjected to plastic deformation, they are subjected to these two in their longitudinal direction

Forces stretched further, growing and at the same time The graphite crystallites rejuvenate, resulting in a The increase in the modulus of elasticity leads to a considerable increase in the modulus of elasticity during stretching can be 700% or more depending on the stretching conditions. At the same time it is possible : a degree of crystal orientation of 90% or more to reach. Despite this considerable increase in the modulus of elasticity and the high orientation of the Crystallites can increase the mechanical strength of carbon fibers can be increased to a value of about 400%.

With the known carbon fibers there are differences between the theoretical values and the values found for the modulus of elasticity sj and mechanical strength. These values are given below:

Theoretical value
Found value

I lastizilätsmodui

9000 t / cnv

3000
7000 t / cra ²

Mechanical l'esligkcit

3 (K) O t cm ²
30 40th ^2nd

From the table it can be seen that although the known carbon fibers have a relatively high modulus of elasticity, the mechanical strength of the fibers is only " ₅ to", "of the theoretical value, even if one is based on the measured value of 200 t / cm ² for graphite whiskers. For this reason, it is believed that the mechanical strength of carbon fibers and graphite fibers depends on defects in the amorphous parts of the surface as well as in the interior of these fibers and less in the crystalline part of these fibers.

One might speculate that this increase in mechanical strength is due to both decrease dei -inen cavities or pores in the lasers as also the legends in the surface of the fibers vi Defect positions could be reached if nan during the deformation caused by compression of the fibers along with one another in a twisted state its length as well as in the fiber axis exerts a compression force, which is caused by a force in the Fiber axis alone can hardly be achieved. An increase in the modulus of elasticity without simultaneous Reducing the mechanical Festipkeil would thus be the greatest disadvantage of the previously known Graphite fibers overcome what would represent a particular advance.

Since the graphite fibers that can be produced by the process according to the invention have the aforementioned properties, it is possible to produce graphite fibers of superior quality, e.g. B. with a mechanical strength of 37 t / cm ² and a modulus of elasticity of 4600 t / cm ² . These values are still above the corresponding values for boron fibers, which have a mechanical strength of about 32 t / cm ² and a modulus of elasticity of about 4300 t / cm ² . Because of their excellent physical properties, these boron fibers make excellent reinforcing fillers.

Due to their polygonal cross-section and the compact filling of the fibers, which are peculiar to them Based on cross-sectional shape, the graphite fibers produced according to the invention are excellent as reinforcing fillers. These fibers can be used in a proportion of up to 80% or more than reinforcing fillers are used.

In practice, the method according to the invention is preferably carried out as follows. The temperature at which the carbon fibers are subjected to tensile stress is at least 2000 ^p C, preferably it is 2500 to 3500 C. The treatment is carried out in an inert gas atmosphere, e.g. B. in argon or helium carried out. If the carbon fiber has a high modulus of elasticity of ?,. B. have less than 0.9% of the ultimate tensile strength, the treatment temperature is preferably above 2900 "C, and the heat treatment must be carried out during such a period that the fibers are not damaged. Preferably, the carbon fibers to be treated are treated under such conditions the temperature, the twisting of the yarn and the tension so that sufficient plastic deformation is achieved within about one minute.

The carbon fibers used in accordance with the process can either contain carbon or graphite, but their cross-sectional shape must be circular and their tensile strength must be at least 7 cm ^2. The carbon content must be at least 90 percent by weight so that there is no reduction in strength! takes place during the treatment at the high temperatures. The average fiber length can be around 75 to 100 mm. The fiber length naturally depends on the number of fibers in the twisted yarn and the twisting conditions. The above specific values represent the shortest average length when the other conditions are within the preferred range.

Carbon fibers that meet the aforementioned conditions can be made from a wide variety of raw materials and using a wide variety of methods With regard to the condition in the method according to the invention that the cross-section If the fibers are to be circular, pitch carbon fibers are particularly preferred.

Carbon fibers with a highly irregular cross-sectional shape, ζ. Β star-shaped cross-section, do not result in graphite fibers with improved mechanical strength. Pitch carbon fibers produced at a high spinning speed and with a high draw ratio have a polygonal cross-section, whereby the carbon fibers can be intimately and compactly twisted together so that they can be used to produce graphite fibers with a high modulus of elasticity and high mechanical strength the inventive Vcr ^r Ahren particularly suitable.

This converts the tensile stress exerted in the axial direction of the twisted yarn into a compression force can be converted in a direction perpendicular to the fiber axis, as in the invention The process is aimed at, a certain suitable number of carbon fibers must be properly twisted will. If necessary, twisted yarns can be twisted together even further, so that one receives double twist.

If the twist is not done properly, it can be Inadequate conversion of the axial tensile stress into that acting perpendicular to the fiber axis Reach pressure compression force. It is difficult to quantify the various conditions which must be fulfilled in the yarn made of carbon fibers used according to the process, like first twist, second or further twist or number of threads or fibers to be twisted. However, it has been established that at a value of the ratio of the apparent tensile strength wedge of the twisted yarn to the average strength of each fiber or each thread from which the twisted Consists of yarn, d. H. the "conversion level" of 0.03 to 0.5 the method according to the invention with success can be carried out.

If the threads or fibers of the yarn have an elongation at break of above 0.9%, the process according to the invention can be carried out at acceptable treatment temperatures and treatment times without damaging the twisted fibers or threads in the aforementioned range of the degree of conversion. However, if the fibers or threads have an elongation at break below 0.9%, the degree of conversion should preferably have a value of 0.07 to 0.2. The tensile strength of the twisted yarn should not be less than 0.5 t / cm ² . The fiber length of the sample for determining the tensile strength of the twisted yarn is half the average fiber length of the components of the yarn fibers or 300 mm. whichever value is the smaller.

When the twisted yarn is drawn in the direction of the fiber axis at the high temperatures, the yarn is plastically deformed by the compression force generated, which depends on the extent of the tensile stress that is exerted on the twisted yarn. The minimum tensile stress required to generate this compressive force is 0.5 t / cm ² . The process according to the invention cannot be carried out successfully below this value. The value mentioned depends somewhat on the treatment temperature. If this value is converted into a draw ratio at about 3000 C, it becomes greater than that of the twisted yarn by a factor of 1.4, if e.g. B. the length of the twisted yarn is shorter than the average length of each fiber or thread from which the twisted yarn, e.g. B. with thread yarn. With this yarn, the influence of the mutual sliding of the threads is negligible. When the average fiber length is shorter than the length of the twisted yarn, the apparent draw ratio of ordinary staple yarn becomes larger than the effective draw ratio. The consequence of this is that drawing by more than 1.6 times the length of the twisted yarn is required.

The invention is further explained in the drawings.

Fig. 1 shows the crystal orientation of graphite fibers, obtained under various conditions;

F i g. Figure 2 is an x-ray diffraction diagram of one made by the method of the present invention Graphite fiber;

F i g. 3 and 5 are photomicrographs of the cross section of graphite fibers made in accordance with the present invention :

F i g. 4 is a photomicrograph of the cross section: a graphite fiber produced by conventional methods.

From the drawings it can be seen that the nacl the process according to the invention produced Gm phil fibers intimately and compactly twisted together and are in nearly planar contact with one another stand. This is believed to be the reason for their excellent physical properties.

The examples illustrate the invention.

example 1

By cracking petroleum naphla at high temp temperatures is a pitch with 96.2 Gewichlspro / .eni Carbon, an average molecular weight of 870 and a softening point of 178 C. This pitch is produced with different spinning speeds and different draw ratios The working conditions are given in Table 1. The received Threads are then exposed to air, starting at room temperature up to 250 ° C with an increase in temperature heat-treated at 0.8 C / minute. flat this heat treatment, infusible due to the threads are made, they become charring (Carbonization) heated to 1000 C for 30 minutes in a nitrogen atmosphere.

The carbon threads obtained have an average mechanical strength of 7 to 8 t / cm ² , a modulus of elasticity of 550 to 650 tem ² , an elongation of 1.3%, a carbon content of 99% and a circular cross-section.

The carbon threads obtained were processed under the two conditions mentioned below and ^{graphitized in an argon atmosphere at temperatures of 2 "7} SO and 2800 C in a graphite tube heated by high-frequency induction heating

The carbon fibers are processed under the following conditions:

a) untwisted threads (sample No. 1, 2. 3, 4 and 4a in Table I),

b) 500 threads with an average length of 75 mm are subjected to a first twist (8.2 twists per 25.4 mm). A twisted yarn is obtained with a tensile strength of about 1.8 t / cm ² (strength ratio 0.24). Then three rows of the twisted yarn are subjected to a second twist to the extent of 5.8 turns / 25.4 mm (Sample No. 5 in Table I).

Samples 2 and 4, which have a length of 150 mm, are attached at one end thereof, and a weight is attached to the other end to produce a tensile stress of 0.7 t / cm ² . The samples are then heat-treated. This leads to an elongation of about 15%. For Sample No. 5 (twisted) d No. 4a (untwisted), the heat treatment is carried out under the same conditions as for Sample Nos. 2 and 4 until an elongation of about ^{1.3 t / cm 2 at a tensile stress of 1.3 t / cm 2} 80% is reached.

The graphite fibers obtained in this way show considerable differences; this is from Table II can be seen from which the superiority of the graphite fibers produced by the process according to the invention (Sample no. 5) emerges

Table I.

sample

No.

2
3
4th
5
4a

Spin speed
of
Interlinking Stretching
ratio Twist Graphitization procedure temperature (m / min) applied
Tensile stress cc :) 250 400 (t / cm ² ) Melt spinning 270 250 400 - Melt spinning 270 2 (K) O 4 (M) O 0.7 Centrifugal process 3! 0 2000 4000 Centrifugal process 310 2000 4000 twisted 0.7 Centrifugal process 310 2000 4000 1.3 Centrifugal process 310 1.3

train
strength Table Il strain Cross-sectional shape sample
No. (t cmM _ Elastic
power module _ .. j% L_ 3.7 _U / cm ² | 1.5 circular 1 2.1 250 1.0 circular 2 6.5 270 1.5 circular 3 17.0 430 0.9 circular 4th 29.0 2000 0.8 polygonal 5 18.0 3600 0.8 circular 4a 2300

Sample Nos. 1.3 and 5 were examined for their crystal orientation by X-ray diffraction. the Results are shown in FIG. 1 reproduced.

The reason for the significant differences in the physical properties of those listed in Table II listed samples is difficult to explain. The sharp drop in mechanical strength in the Sample Nos. 1 and 2 presumably depends on the irregular arrangement of the aromatic rings in the pitch used. also from the slow spinning speed and the low draw ratio, as a result, crystal growth is rather irregular at high temperatures and even with the application of an external tensile stress, crystal orientation is difficult to occur; see. Curve 1 in FIG. 1. Another explanation for the sharp drop in mechanical strength in the Samples 1 and 2 is the. that in the crystals during crystal growth, fine pores to a large extent or cavities arise. This phenomenon may be related to the increase in diameter of the threads by a value of about 10 to 20%, which can be observed during the heat treatment is.

In the case of samples 3.4 and 5, those at high spinning speeds and stretching ratios are obtained, there is less possibility of that relatively large defects are formed on the thread surface. This shows that the most fibers obtained by slow spinning speed and low draw ratio There is a much greater possibility for such errors due to a change in the fiber structure cannot be eliminated during graphitization. This also seems to be the cause of the different Properties between the graphite fibers of Samples Nos. 1 and 2 and the graphite fibers of samples # 3 and # 4.

Have the twisted graphite fibers (sample no. 5) produced by the method according to the invention The following three main differences compared to graphite fibers, which are obtained after conventional graphitization treatments were manufactured:

1. The mechanical strength of the fibers is improved. This improvement in strength is believed to be due to the reduction in defects in the fiber surface and the number of fine pores in the interior of the fibers caused by the compressive forces exerted on the fibers. This improvement can also be seen from the different specific gravity of more than 0.2 g / cm ³ of samples 4, 4 a and 5.

2. It is possible according to the method according to the invention. To greatly stretch graphite fibers without affecting their mechanical strength; see curve 5 in FIG. 1. When creating a crystal orientation in ordinary graphite fibers that gives the fibers a modulus of elasticity of more than 3500 t / cm ² , it is usually difficult to achieve a mechanical strength of more than 22 t / cm ² . When this value is reached, the elongation is only about 0.5%. The improvement in this regard gives a particularly favorable picture in the tear diagram of molded bodies which have been produced from materials which contain the graphite fibers produced according to the invention as a reinforcing filler. 3. The fibers are mutually compressed so that their originally circular cross-section merges into hexagonal or other polygonal cross-sectional shapes. As a result, the fiber bundle is intimately and compactly united, as shown in FIG. 3 can be seen. If, for example, the fibers of sample no. 5 produced according to the invention are considered, the degree of compactness of the fiber bundle reaches a value of 88%, while with the graphite fibers produced by conventional methods only a value of 62% is achieved. This fact is important if the fibers are to be used as reinforcing fillers, since they can then be incorporated into the molding compound in a relatively high proportion of the mixture. For example, when using the fibers of samples No. 4 and 4a, it is very difficult to incorporate more than 65% of an epoxy resin, while the fibers of sample No. 5 produced according to the invention can be incorporated into the epoxy resin in an amount of more than 50%.

509 628 / 1S

Example 2

The following eight kinds of different starting material are used to produce carbon fibers under the conditions given in Table IH used:

ArI des
Exit dialcrials

Statement

Obtained by heating the reverse oil obtained from the splitting of ethylene was, to a temperature of 360 C / 10Torr, for the separation of low-boiling Factions

Obtained by heating a tar that is produced when naphtha is cracked 380'C / 10 Torr, for the separation of low boiling points Factions

Obtained by heating heavy anthracene oil with air to 200 ^° C. in the presence of 5 percent by weight of solid ammonium nitrate and then separating off the low-boiling fractions at 350 ° C./10 Torr

Obtained by heating petroleum pitch to 380 ° C / 10 Torr to separate low boiling points Factions

Type of starting material

10

Manufacturing

Obtained by extracting coal pitch with chloroform for separation low molecular weight substances and then heating the extracted for 3 hours Pitch to 150 ° C, 3 hours heating to 200 C and 1 hour heating 300 "C under reduced pressure

Obtained by treatment of distilled return oil obtained at the partial hydrogenation of tar, which occurs when crude oil is cracked, with 10 percent by volume Air containing nitrogen dioxide for one hour at 100 ° C. and subsequent treatment of the oil for one hour with ammonia at 200 ° C. and finally separation of the low-boiling points Fractions at 350 C / 10 torr

Obtained by pyrolysis of polyvinyl chloride at 405 ° C. in a stream of inert gas

Obtained by reacting 45 parts by weight of phenanthrene and 55 parts by weight Chrysene in the presence of 10 percent by weight aluminum chloride as a catalyst and subsequent refining

Art Original painting middle
Molecular
weight E. Table HIa air Tem
temperature
(C) Time
(Hours.) Physical properties of the carbon dioxide fascia tensile strenght
(t / cm ² ) carbonization end
lempcralur
("C) orientation PI 590 ching-
Point
Γ C) Air + O ₃ (10%) > 300 15th Atmosphere
sphere 750 no attempt P-2A CX- + H
(%) 530 230 Air + NO ₂ (3%) > 280 5 N ₂ 800 no No. P-2 B 95.2 530 160 Working conditions at Air -I- NO ₂ (10%) > 230 4th Ar 1000 no 1 P-2 C 95.0 530 160 Meltable + NH ₃ > 110 0.25 N ₂ ICKK) no 2 95.0 160 the atmosphere Air + Cl ₂ (20%) > 200 N ₂ 3 P-3 95.0 500 Air + NH ₃ (30%) 30th 0.5 8.0 800 4th P-4 800 140 Air + SO ₃ (50%) > 280 2 8.5 H ₂ 750 4a P-5 93.03 510 210 HClO ₄ + H ₂ O (10%) 100 0.5 11.5 NH ₃ 1000 5 P-6 92.90 620 150 H ₂ O + NH ₄ NO ₃ (10%) 30th 1.0 12.0 Ar 1500 6th P-7 91.0 700 170 + Air 100 0.5 Ar 2O00 7th P-7 94.81 700 175 NaQ > 23O 2 Ar 8th P-8 93.98 520 175 Table IHb 100 0.5 950 9 93.98 210 strain
<%) N ₂ 9a attempt 95.8 2.6 10 No Strand thickness
(Micron) 2.5 3.0 3.1 1 9.0 2 8.5 3 8.9 4th 8.3 4a

11th

continuation

12th

attempt Slang thickness Physical properties of the K ohlensloff fibers No. (Micron) strain tensile strenght 8.0 (%) (l / cm ² ) 5 7.9 2.9 9.5 6th 9.1 2.9 8.1 7th 8.3 2.3 8.9 8th 7.9 2.7 14.1 9 2.5 15.0 9a 8.9 10 2.4 10.0

orientation

no
no
no
no
very low

no

Remarks:

1. Spinning process: The carbon fibers are produced using the melt spinning process with simultaneous application of centrifugal force and rapidly flowing hot air. The spinning speed is 2000 m min., the stretching ratio is 5000.

2. Charging time: 6 hours.

The carbon fibers produced according to Table III a contain more than 90% carbon and haber a more or less circular cross-section. According to the invention, these carbon fibers are twisted and graphitized. The working conditions and the results are summarized in Tables IVa and IVb It can be seen from Table IVb that graphite fibers having excellent properties are obtained.

Table IVa

attempt
No.

Type of fibers or threads

SG SG FG SG FG SG

SG SG SG FG FG FG FG FG

Material,
No. Titer,
the Vi
yarn
number rdrillun
Three
25.4
first ; sbedingi
lung /
mm
second P-2B 6000 3 7.0 5.0 P-2B 6000 3 5.0 3.7 P-7 1000 1 ._ 3.0 P-2C 500 10 11.7 8.0 P-6 1000 1 3.0 P-8 (500 χ 3)
1500 6th 11.7 /
7.8 6.4 P-3 6000 3 5.0 3.7 P-3 6000 3 5.0 3.7 P-3 6000 3 5.0 3.7 P-28 500 3 0.5 0.3 PI 500 3 7.3 5.0 P-2A 500 3 7.3 5.0 P-4 500 3 7.3 5.0 P-5 500 3 7.3 5.0

Total litcr. the

18 18 1000 5 1 9

18th

18th

18th

1

1

1

1

1500

Table IVb

relationship

of strength

0.03

0.10

0.50

0.10

0.10 0.10 0.10 0.48 0.25 0.25 0.25 0.25

Graphing conditions

Tem Ver Behan temperature stretching lungsz CC) relationship (Sec. 3200 2.3 300 3200 2.5 10 2800 2.0 10 2800 2.0 120 2900 1.4 20th 3200 1.6 10 3000 1.2 10 3000 1.6 10 3000 2.0 10 2500 2.3 90 3000 2.0 120 3000 2.0 120 3000 2.0 120 3000 2.0 120

Tensile stress

(l / cm ² )

0.52

1.4

1.0

1.2

0.7

0.6

0.3 0.8 1.0 3.0 U U 1.1 1.1

attempt Zugfcstigkcil
(t / cm *) Physical Properties the graphite fibers No. 37.5
30.7
23.5
21.6 strain modulus of elasticity
(t / cm ² ) 1
2
3
4th 20.1 0.77
0.69
0.50
0.98 4850
4500
4700
2200 5 18.6 1.08 I860 6th 12.3 0.99 1890 7th 1.20 1000

Cross-sectional shape

polygonal
polygonal
polygonal
polygonal
(partly circular)

polygonal
(partly circular)

polygonal

(partially

circular

13th 2 137 614 l \ modulus of elasticity
(t / cm *) Crush cut shape 1840 polygonal continuation (partly circular] attempt tensile strenght
(t / cm ^) Physical properties of graphite fibers 2500 polygonal No. 16.8 strain (partly circular) 8 ■ ■ 0.91 5700 polygonal 20.7 (partly circular) 9 0.83 3500 polygonal 27.4 (partly circular) 10 0.47 3850 polygonal 20.8 (partly circular) 11th 0.58 3950 polygonal 21.1 (partly circular) 12th 0.55 3 «00 polygonal 23.2 (partly circular) 13th 0.59 20.8 14th 0.53

Notes to Table IVa:

1. SG = staple fiber yarn (fiber length 200 mm).

2. FG = thread yarn.

3. Experiments 2 and 3 as well as 5 to 9 were carried out with a device in which the upper and lower part of a vertical standing induction furnace with a 200 mm long uniform heating zone <i the sealed room is available. Outside the furnace there is a "Nelson" roller to heat and stretch the carbon threads at the same time? U can, while continuously advancing them.

4. Experiment No. 6: Threads made of carbon with a titer of 500 denier become 25.4 mm with a twist of 11.7 turns twisted. Three rows of such a twisted yarn are made. These three yarns are then double twisted, taking them a reverse twist of 7.8 turns / 25.4 mm is imparted.

F i g. 2 shows the X-ray diffraction diagram and FIG. 3 is a photomicrograph of graphite fibers; which were prepared according to the method according to the invention according to Experiment No. 1 in Table IV. These Fibers show a maximum modulus of elasticity and very high mechanical strength, but not a low one Strain.

F i g. 4 shows a photomicrograph of the cross section of the test No. 7 (comparative test) manufactured graphite fibers. F i g. Figure 5 is also a photomicrograph of the cross section of the present invention manufactured graphite fibers, in which the cross-sectional shape is generally polygonal and partial is circular.

Experiments Nos. 1, 2 and 3 show the results when the ratio of the strength of the twisted yarn within the designated range. Experiments 5 and 6 show the results where the minimum draw ratio is applied to filamentary yarn and staple yarn became. Experiments 7, 8 and 9 are examples of the deformation of the fiber cross-section, when the draw ratio is changed. Experiment No. 10 shows the influence of the heating temperature on the graphite fibers when they are heat-treated at a relatively low temperature. Experiments Nos. 11 to 14 were carried out to examine the influence of the starting material on the physical To investigate properties of graphite fibers. From Table IVb it can be seen that with the exception of the comparative test 7, the graphite fibers produced by the method according to the invention have excellent strength and modulus of elasticity.

Example 3

Carbon fibers made from material P-20 in Table HI of Example 2 are heated in the manner shown in Table V in two stages. After completion of the first heating treatment, the graphite fibers of Test Nos. 1 and 2 show a tensile strength of about 14 t / cm ² and 18 t / cm ^2, respectively, and an elongation of less than 0.9%, although the cross-sectional shape remained almost circular.

The graphite fibers are then twisted and subjected to the second heating stage. I'm trying No. 3, the graphite fibers are twisted after the first heating stage and au!

a higher temperature heats air in the first er overheating. The physical properties of the graphite obtained after the second heating stage fibers are listed in Table VI.

Table V

attempt

No.

Type of fibers or threads

Heat treatment (1) temperature

Γ C)

thread

2500

Tensile stress (t / cm ² )

Type of fibers or threads

Thread yarn
(Relationship
strength 0.07)

Heat treatment (II) temperature

_ ΓΟ ___

3000

Tensile stress (l / cm ² )

1.0

15th

continuation

fl

attempt Heat treatment (I) Old of the fibers temperature Tensile stress Type of fibers Heat treatment ") 11) Tensile stress No. or threads ("C) (t / ccn ² ) or threads (t / cm ² ) thread 2800 1.0 Thread 1.0 2 (Relationship the firm speed 0.2) Thread yarn 2700 1.1 Thread yarn 1.6 3 (Relationship the firm speed 0.3) temperature CC) 3200 2900

Table VI

attempt
No. Tear
strength
(t / cm ² ) 1 29 2 25th 3 24

modulus of elasticity

(l / cm ² )

5800

4200

3500

0.50

0.60

0.69

Transverse

shape of rabbits

or threads

polygonal,

partially

deformed

the same.

The filamentary yarns used in this example are made as follows:

About 300 threads are subjected to a first twist, and then 3 rows of the obtained twisted yarns combined and twisted further. After the second heating stage, the Graphite yarn from Trial No. 3 twisted back into its original three yarns. It was determined, that the yarn was in a slightly wavy form. If you are using this yarn again heated to 3000 ° C under a very low tension, it returns to its straight shape, the threads however, retain the twist in the yarn.

For this purpose 3 sheets of drawings

Claims (3)

itent claims: 1. Vedahrdblztr Manufacture of graphite fiber yarns with a high modulus of elasticity and high strength, whereby carbon fibers are raphitized with simultaneous stretching, because it indicates that carbon fibers with a circular cross-section with a strength of at least 7 t / cm ² and eJuem value of the ratio of the apparent tensile strength of the twisted yarn to the average strength of the individual fibers of the twisted yarn of 0.03 to 0.5? u a yarn twisted and then at a temperature of at least ⁰ C 2QOO in einej faertgasatraosphäre a tensile stress of at least 0, 5 t / cm ³ underwJi. 2. The method according to claim I, characterized in that the yarn is subjected to a tensile stress of at least 0.7 t / cm ² while it is being heated. 3. The method according to claim 1, characterized in that the yarn is heated to a temperature heated by at least 2500 C.