NO169383B - PROCEDURE AND DEVICE FOR CONTINUOUS STRENGTH GRAVITING OF CARBON FORMS - Google Patents

Abstract

A method is described for continuous graphitization of carbon-shaped bodies by means of electric resistance heating, in which the carbon-shaped bodies surrounded by a granular carbon material with a preferably circular-cylindrical or prismatic cross-section are passed in a vertical direction through a graphite furnace in the form of a string. and wherein the electric current by means of electrodes is supplied to the carbon shaped bodies through it. granular carbon material and out through the mold bodies. The method is characterized in that the strand formed by the carbon-shaped bodies (1,2) is passed through the furnace from below and upwards while the surrounding granular carbon material (3) is passed in countercurrent from above and downwards through the furnace. A device for carrying out the method is also described.

Description

Method and apparatus for coating glass fibres.

The present invention relates to a method and

an apparatus for coating glass fibres. This achieves that the loss of coating material to the environment is largely avoided, which results in a greater "concentration" of solids being placed on the fibers while the "migration" of solids is reduced.

According to the present method, coating material, which comprises a thixotropic gel, is brought to an applicator and is transferred to a fluid state by the effect of shear force, and further, glass fibers, preferably newly produced glass fibers, are drawn over the applicator in contact with the coating material, after which the coated glass fibers are immediately wound into a coil.

Cf. at 8a-25/01

This method can be carried out and is preferably carried out with such glass fibers which are completely newly produced (i.e. in direct connection with the fiber formation and, if the fibers are to be combined into strands, before the strand formation), but in reality the coating operation can be carried out at any time. The fibers thus do not need to be newly produced or in statu nascendi.

The coating solution resumes its gel-like state immediately after it is removed from the shearing forces. In connection with the invention, it has been found that fibers that are pulled over a surface coated with a thixotropic gel will produce a shearing effect in the gel film which will cause the fibers to be completely and uniformly covered with material. The uniformity that prevails in the thus formed coating is unexpected because fibers cannot be pulled over conventional gels to coat the fibers'. Conventional gels resist transfer from the gel body itself to the fibers and generally do not adhere to the back of the fibers. The part of conventional gels that is taken up by fibers that are pulled over these gels is retained on the fibers more by mechanical action than by adhesion. The. it has been discovered that thixotropic gels do more than just cover the surface that • is applied to the gel, and it has been discovered that the thixotropic materials flow to the back of the fibers where they adhere just as satisfactorily. The coatings that are formed by drawing the fibers over thixotropic gels are uniform at least to such an extent that the coated fibers will prevent wear during glass-to-glass contact during the formation, twisting and weaving of these glass fibers.

Several materials are known which give thixotropic gels. It has been found that almost all of these materials can be used to apply a gel to any of the previously used coating materials for fibers. The fibers that are pulled over these.

gels are not only adequately coated, but essentially none of the gel is lost in the process. The coating using thixotropic gels is therefore very effective and enables an economical use of materials that were previously thought to be too expensive for use as a coating on glass fibres. It has also been found that thixotropic gels contain a considerably higher percentage of solids than the previously known coating solutions. emulsions

or susosensi ons, can be satisfactorily placed on the fibres. The method according to the invention, where the fibers are pulled over thixotronic gels to transfer the material from the gel to the fiber surface, has so many advantages that it will make all the previously known methods for placing materials including <glass> fibers in the formation of these completely outdated. The possibility that thixotropic gels could be used to coat the fibers in a uniform manner has not been realized before, nor has it been possible to predict the many advantages associated with the method according to the invention.

A considerable number of materials, both organic and inorganic, are known which give thixotropic gels and these materials are called thixotropic substances. The exact structure of gels in general and thixotropic gels in particular has not been fully elucidated, but it is believed that they form a network by means of secondary bonds that surround and enclose other materials including solvents. In some cases, the solvents, if these are polar, will unite with the network due to Van der Waal's forces to thus become cross-linked from one gel particle to another. In other cases, it is assumed that the gel particles are aligned under the influence of secondary forces so that the network is formed. In a thixotropic gel, shear forces break the secondary bonds so that the structure breaks down and so that it behaves like a solution. However, as soon as the shearing forces are removed, the materials realign themselves into a network that encloses the solvent and acts so that the mixture assumes a gel-like state. As previously indicated, thixotropic gels can be made in both aqueous and organic solvents so that thixotropic gels with partly different structures are formed. All types of thixotropic gels, regardless of solvents, can be used for filler coating of fibers and especially glass fibers during their formation. Since all material types that produce a thixotropic gel are called thixotropic substances and since all known thixotropic substances give gels that are suitable for coating glass fibers during their formation, these materials will be called thixotropic substances or thixotropic agents in the following.

The following is an example of an organic thixotropic substance which gives a suitable thixotropic gel with an organic solvent and which is also suitable for application to glass fibers during their formation.

Example 1

This material was made by mixing the polyvinyl acetate in 100 parts diacetone alcohol until the polyvinyl acetate was dissolved and then the rest of the diacetone alcohol was added. This material was introduced into a "Waring" mixer and "Thixcin R" was added to the mixer which was run at high speed, while the material had a temperature of approx. iJ3°C. This creates a very good thixotropic gel which can be pumped to a rounded surface over which glass fibers are drawn during formation. The thus coated fibers are provided with a film of thixotropic gel which completely covers the fibers and which, on evaporation of the solvent, leaves a film consisting of polyvinyl acetate which completely covers the fibers.

The following example shows that resins and other materials can be incorporated with the thixotropic substance to give the resins in the form of a gel.

Example 2

Epoxy (1) has the following formula where n=0:

Epoxy (.2) has the same formula with the exception that n = 3.

This material was made by mixing the epoxy polymer with the diacetone alcohol in a Waring mixer to give a solution and then adding Thixcin R. The mixer was run at high speed for five minutes at a temperature of about 44°C and the material produced was a good thixotropic gel which completely surrounded the glass fibers when drawn through the gel. Upon evaporation of the solvent, an epoxy resin-containing coating remained on the fibers.

The following examples show that essentially any resinous material can be converted into a thixotropic gel. These materials were made in substantially the same manner as described above, and they can all be uniformly coated on glass fibers to form a uniform resin film that completely surrounds and covers the fibers.

Example 3

The gel was made by dissolving the monazoline compound

in the isopropyl alcohol and then by adding the thixotropic agent. The material was mixed in a mixer for five minutes. The phosphoric acid was then added and thoroughly mixed to thus give the thixotropic gel. This material was found to uniformly cover glass fibers pulled through the material. »

The next example shows that resins and other materials can be incorporated into a thixotropic gel using the same thixotropic substance.

This material was made in the same manner as stated above and allowed to be coated evenly on glass fibers so that a uniform coating consisting of the epoxy and other components was formed.

The following is an example of an inorganic material that forms a thixotropic gel in an aqueous medium. This gel can also be coated evenly on glass fibers when these are drawn through the gel.

Example 12

This material is made by dispersing "Baymal" i

50 parts water. Ammonium hydroxide is added to 20 parts of water and these two materials are mixed in a mixing device for 10 minutes. The material formed is a thixotropic gel. Other substances such as cationic and nonionic lubricants and film formers such as starch or others may be added to give a thixotropic gel of the whole mixture.

The following is an example of an organic material that forms a thixotropic gel in an aqueous medium.

The thixotropic gel was made by mixing the polyvinyl alcohol in water at room temperature, after which the copolymer of methyl vinyl ether and maleic anhydride is added during 5 minutes of vigorous mixing. This material is a thixotropic gel and forms a uniform coating on fibers that are drawn through it.

The following is an example of another organic material that forms thixotropic gels in aqueous media.

Example lh

This material was made by heating the polymer solution and the polyamine-stearic acid condensate until it was dissolved. "L-77" was added followed by "Kelzan" and stirring was carried out until the latter was dissolved. This produced a thick emulsion in which a thixotropic material is dispersed in a thixotropic gel formed from "Kelzan" and water.

The following is an example of a starch material that has been converted into a thixotropic gel.

This mixture is made by boiling the starch to the boiling point and then quenching with cold water. "Carbopol"

dispersed in a liter of water and added to the boiled starch. "L-77" is also diluted with water and then added to the mixture. This mixture is thoroughly stirred and then added to starch until all air has been expelled from the mixture. Ammonium hydroxide is then slowly stirred into the mixture. The mixture forms a thixotropic gel which provides a very uniform coating on fibers that are drawn through the gel.

This material was made by premixing "Benagua" and "Avicel-C" powders and then adding this mixture to water in an "Eppenback" mixer run at top speed. This produced a very heavy thixotropic gel which may contain other materials such as starches etc. when applied to glass fibers in the manner described above.

According to the present invention, an apparatus is also provided for carrying out the above-mentioned method and this apparatus is characterized by a) an applicator consisting of a rotatably stored roller arranged to receive a thixotropic gel material and glass fibers to be coated with said material, b) a cutting surface which is placed close to the applicator roller so that a narrow gap is provided between the cutting surface and the jacket surface of the applicator roller, c) a device for feeding thixotropic gel material to the jacket surface of the applicator roller, d) a device for pulling glass fibers over the jacket surface of the applicator roller, and e ) a support structure for the applicator roller.

Conventional applicators cannot be used to apply thixotropic gels to glass fibres. It was not actually known before the apparatus according to the invention was made, that thixotropic gels could be satisfactorily applied to glass fibres. Normal thixotropic gels are gels at ambient temperature when given the opportunity to assume static conditions. When a shear force of sufficient magnitude affects these gels they return to solutions; and when the shear force is removed they are immediately converted into a gel. It will be seen that a pad or wick type applicator will not cause a thixotropic gel to move to the part from which the gel is removed by pulling fibers over the applicator. It will also be seen that an endless belt moving into a gel body will tend to take the gel with it in an uneven manner and carry it along in this state to an area where the gel is removed by the fibers. It has also been found that the applicator of the conventional roller type does not work satisfactorily, and the reasons for this were not entirely clear before the present invention.

The invention will be explained in the following with reference to the drawings where

Figure 1 is a plan view of an apparatus for implementation

of the invention;

figure 2 is a cross-section taken approximately along the line 2-2 of figure 1;

Figure 3 is a plan view of another embodiment of the present apparatus;

figure H is a cross-section taken approximately along the line 4-4 of figure 3; and

figure 5 is a graphical representation showing how the shear force varies with the shear rate for thixotropic gels that break down at different viscosities.

The applicator shown in Figures 1 and 2 generally consists of an applicator roller 10 over whose front flat fibers are drawn. The roller 10 may be of any suitable diameter and has a section over which the fibers are drawn and this has a diameter of approximately 12 mm. A thixotropic gel is passed through passage 14 to a narrow gap 16 which communicates with the side of the roller opposite to that over which the fibers are drawn. Because the fibers remove the thixotropic gel from the roller at a relatively slow rate, the thixotropic gel passing through passage 1H is at all times in the gel state. The thixotropic gel is preferably fed through the passage 14 by means of a positive displacement pump to ensure a uniform supply regardless of resistance, and the passage 14 preferably has a uniform cross-section along its entire length. The roller 10 has enlarged parts 18 and 20

at opposite ends so as to provide shoulders 22 and 24 respectively which confine the gel to the middle section 12 over which the fibers are drawn. The applicator roller 10 is supported in a housing 26 which may be made in any suitable manner and, as shown in the drawing, is formed of top and bottom center plates 28 and 30 which are separated by a u-shaped gasket 32. The open end of the u-shaped packing 32 forms the gap 16 through which the gel is fed to the middle section 12 of the roller 10. The housing 26 also comprises opposite side bars 34 and 36 respectively, which are suitably attached to the sides of the plates 28 and 30, in which the extended parts 18 and 20 of the roller 10 are stored. The roller 10 comprises an axially projecting part 38 which projects from the side bar 36 and is provided with a tongue 40 which is intended for engagement when the roller is to be driven. A drive shaft 42 on a motor-driven unit 44 engages with the tongue 40 to thus drive the roller.

In the designs shown in figures 1 and 2, the

the extended portions 18 and 20 of the roller 10 inwards from the side bars 34 and 36 respectively and the upper and lower center plates 28 and 30 are provided with notches as at 46 and 48 to provide clearance for these plates. The gasket 32 surrounds the notched parts

46 and 48 to confine the gel to the central portion 12 of the roller which is within the shoulders 22 and 24. In the embodiments of Figure 1

and 2, the roller 10 is placed mainly in the lower center plate 30 and is arranged so that the upper surface of the section 12 of the roller as far as it is protrudes above the top surface of the bottom plate 30. The upper plate 28 is flat and is extended over the upper part

of the roller 10. Clearance is provided between the roller 10 and the top plate 28 and this is due to the separation created between the plates 28 and 30 due to the thickness of the gasket 32. The lower plate 30 therefore forms a socket for the roller 10 which mainly surrounds the roller. The lower plate 30 also comprises a lower

edge 50 helps to hold the gel on the roll after the part of the roll in contact with the fibers separates from the gel.

A blanket of hot air is passed from the heated

bushing down to the applicator of the moving glass fibres. It has been found that this carpet of moving air has a detrimental effect on the gel film on the roll surface and it has also been found that the heat associated with this can dilute the gel to such an extent that an uneven coating occurs on the fibers. These effects are overcome in the embodiment shown in Figures 1 and 2 by allowing the front surface of the top plate 28 to be slanted upwards and backwards so as to form a pocket. A baffle plate 54 which may be made of a pliable metal or elastic plastic material is attached to the top surface of the upper plate 28. The baffle plate 54 preferably has a portion that projects forward and upward to deflect the warm air blanket from the fibers. The baffle plate 54 also increases the dead air space immediately above the roller. Air that is not led away from the fibers expands and swirls into the pocket to thus reduce the speed of the moving air that exists between the moving fibers. The designs in Figures 1 and 2 also include a passage 56 for cooling water in the upper center plate 28 to prevent heat being transferred to the gel. A suitable cooling water inlet 58 is provided on the back of the top plate 28 and the passage 56 returns to an outlet 60 which is also located on the back of the plate 28. It has also been found that, unlike previously known roller applicators, the applicator of the present invention removes air bubbles from the gel that is fed to the roller. It should be noted that the applicator according to the invention has a cutting surface 60 located close to the surface of the roller between the area 16 where the gel is placed on the roller and the area where the fibers remove the gel from the roller surface. This surface 60 is preferably adjacent to the top surface of the roller and this will now be explained.

It will be seen that the thixotropic gel immediately changes to a solution when a predetermined shearing force acts on the gel. The apparatus in Figures 1 and 2 is designed to provide this shearing force between the surface 60 and the top surface of the roller.

After the shear force has been produced, air bubbles, which were retained by the gel structure, are carried to the surface of the solution before the shear force is removed and the material leaves the shear area at surface 60. A clear gel is therefore left on the roll surface and this gel is then moved downwards to the area where it comes into contact with the moving fibers.

Figure 5 shows the effect of shear forces on thixotropic materials. At low shear forces, the gel is elastically deformed and under the influence of somewhat greater shear forces, the gel is permanently deformed. However, no particular dilution of the material occurs and this area is illustrated by the shaded field which is limited by the coordinates and the curve 62. Real solutions have the properties shown by the radial lines. Radial lines 64 denote different viscosities. At a certain shear force, generally illustrated by curve line 66, gels of different consistencies will have been completely transformed into a solution. Between the curved lines 62 and 66, the materials will be a mixture of solution and gel. The shear action on a typical thixotropic material is shown at lines 68 and 70. When a shearing force of increasing magnitude acts on a free thixotropic gel body, this gel will deform elastically until it reaches a yield stress shown at point 72. Then the speed of movement increases ( defined as shear rate) with increasing shear force (shown by line 68).

When the shear force reaches a value corresponding to the point of intersection between the line 68 and the curve 66, the thixotropic material will have been completely changed into a solution and then the material will behave like a real solution. When the shearing force is reduced, the shearing effect decreases in the same way as in solutions of specific viscosity, and certain parts of the material will begin to build up a gel network when the shearing force falls below the curve 66. The material thickens as it flows, and it flows as if it were a resolution as indicated by line 70. The space between lines 68 and 70 can be compared to a hysteresis effect and is an indication of the amount of gel structure present. It will be seen that if the shear action produced by the shear surface 60 is above and to the right of the curve 66, the thixotropic material will behave as a solution so that air bubbles are allowed to rise to the surface of the material. Separation of air bubbles therefore takes place.

It has been found that if the roll is either driven positively at high speed or is rotated freely at the high speed of the fibers, parts of the roll will become dry. The roller 10 in the embodiment of Figures 1 and 2 is therefore driven at a slow speed to ensure that all parts of the section 12 of the roller are covered with the thixotropic gel.

The reason why dry spots appear on the surface

of the roller when it is rotated at high speed, is believed to be due to the shearing effect in the area where the material is fed to the roller. The thixotropic gel is passed through the roller 16, which is of course stationary. With reference to Figure 4, it can be seen that the thixotropic material thins as the shearing effect increases. Since the shearing effect is highest at the roll surface, a thin lubricating film develops on the roll surface and the gelatinous gel network is held back by the stationary surfaces around the gap 16 and does not attach to the roll. By reducing the relative speed between the roller and the stationary surfaces, the gel network is caused to extend to the roller surface to thus provide a transfer of gel from the stationary surface to the roller surface.

Certain advantages occur when the roller applying gel to the fibers is allowed to rotate freely. An advantage is that the gel flow automatically stops when the fibers are no longer pulled over the roll surface. Figures 3 and 4 show an embodiment where the applicator roller can be rotated by the fibers at high speed, and thixotropic gel is nevertheless led to the applicator roller without dry spots forming on it. The parts of the design shown in Figures 3 and 4 which are similar to the corresponding parts of the design in Figures 1 and 2 are designated by the same number provided with a mark. The embodiment of Figures 3 and 4 differs mainly from the embodiment of Figures 1 and 2 in that thixotropic gel is fed to the applicator roller 10' by a feed roller 80 which is positively driven by a motor, not shown, so that a surface velocity is provided which, in relation to the surface of section 12 of the applicator roller falls within the area between curves 62 and 66

on Figure 5 - By varying this relative speed, the amount of thixotropic gel that is fed to the applicator roller 10' can be regulated. The feed roller 80 has a width that is smaller than the distance between

the shoulders 22' and 24' and protrude below the extended elbows 18'

and 20'. When the surface of the feed roller 80 can be moved faster than the surface of the roller 10' (provided the relative speeds are as described above), the roller 80 preferably has a surface speed less than that of the roller 10' to facilitate over-

guiding gel to the roller 10 from a stationary surface. The Waltz 80

can further be fed by a number of rollers which are individually rotated at progressively lower speeds to achieve a continuous gel transfer.

In the versions in Figures 3 and 4, gel is brought to the surface

on the roller 80 from the underside on the surface. By supplying gel from the outside from the underside of the roller surface, the gel network will be strongest at the surface of the roller so that it is maintained on the surface even if the speed of the roller in relation to the surrounding stationary surfaces is above and to the right of the curve 66 in figure 5 - The gel can be fed to the roller 80 in any suitable manner, and is fed as shown in the drawing from a feed passage 82 located in the central axis of the roller 80. The roller 80 may have an axially projecting passage 84 and a plurality of radial branches 86 which are in communication with the roller surface. The branches 86 are preferably continuously offset in relation to each other so that the gel only needs to

spread out in the longitudinal direction of the roller at a minimum distance. In out-

in the arrangement shown in the drawings, three rows of branch passages 86 are arranged at a distance of 120° from each other

and the respective passages in each row are shifted in length-

the direction relative to the passages on the other two rollers.

Claims (16)

1. Method for coating glass fibres, characterized in that coating material, which comprises a thixotropic gel, is fed to an applicator and transferred to a fluid state by the effect of shear force, and that glass fibres, preferably newly produced glass fibres, are drawn over the applicator in contact with the coating material, after which the coated glass fibers are immediately wound into a coil. 2. Method according to claim 1, characterized in that the coating material is a thixotropic gel, which is formed by mixing a gel-forming and a non-gel-forming material, preferably with the addition of a solvent that dissolves both materials. 3. Method according to claim 1, characterized in that the coating material is a thixotropic gel consisting of a dispersion of a) an emulsion of a non-gel-forming material in b) a gel-forming material. 4. Method according to any one of claims 1-3> characterized in that a rotatably stored roller is used as the applicator, that said coating material, which comprises a thixotropic gel, is transferred from an application surface arranged close to the applicator roller to said roller, while this roller is preferably rotated at such a speed that the relative speed between the application surface and the roller surface is less than the shear speed at which the thixotropic gel is transferred to a fluid state, whereby the glass fibers are pulled over the applicator roller carrying the coating material. 5.. Method according to claim 4, characterized in that the cutting effect is provided by means of a cutting surface which is brought to act on the coating material applied to the applicator roll. 6. Method according to claims 1-5, characterized in that the coating material is applied to the applicator roller from a feeding roller arranged next to and parallel to this, which is also rotatable and which preferably rotates at a lower surface speed than the applicator roller. 7. Method according to any one of claims 4-6, characterized in that the rotation of the applicator roller is provided by means of the glass fibers being pulled over the surface of the applicator roller. 8. Apparatus for carrying out the method according to any one of claims 1-7, characterized by a) an applicator consisting of a rotatably supported roller (10, 10'), arranged to receive a thixotropic gel material and glass fibers to be coated with said material, b) a cutting surface (60, 60') which is placed close to the applicator roller so that a narrow gap (16) is provided between the cutting surface and the mantle surface of the applicator roller, c) a device (14, 80) for feeding thixotropic gel material to the applicator roller mantle surface, d) a device for pulling glass fibers over the applicator roller's mantle surface, as well as e) a support structure (26, 30, 30') for the applicator roller. 9. Apparatus according to claim 8, characterized in that the applicator roller (10, 10') is arranged horizontally and that the cutting surface (60, 60') is placed up to the highest point of the applicator roller's mantle surface. 10. Apparatus according to claim 8 or 9, characterized in that the gel feeding device consists of a gel supply channel 14 (which opens at the slot 16). 11. Apparatus according to claim 8 or 9, characterized in that the gel feeding device (80) is arranged for applying the thixotropic gel material to the surface of the applicator roller (10') at a location at a distance from and in the direction of rotation of the applicator roller before the zone where the applicator roller comes closest to the cutting surface ( 60'). 12. Apparatus according to claim 8 or 11, characterized in that the gel feeding device consists of another rotatably stored roller (80) arranged next to and parallel to the applicator roller (10') for turning in the preferably opposite direction to the applicator roller, whereby this gel feeding roller (80) is stored in the same support structure (30') as the applicator roller (10') and whereby the support structure preferably comprises a profiled block (30') with profile contours intended for accommodating the two rollers. 13- Apparatus according to claim 12, characterized in that the feed roller (80) is designed with an internal line (84, 86) for supplying thixotropic gel material to its mantle surface. 14. Apparatus according to claim 12 or 13, characterized in that the applicator roller (10') is arranged to rotate with a greater surface speed than the feed roller (80). 15. Apparatus according to any one of claims 12-14, characterized in that the two rollers (10'80) are arranged to rotate at a relative speed in relation to each other which is less than the shear speed at which the thixotropic gel is transferred to easily flowing state. 16. Apparatus according to any one of claims 8-15, characterized in that the applicator roller (10, 10') has end parts (18, 20, 18'20') with a larger diameter than the roller part (12, 12') between these end parts.