GB1592578A - Method and apparatus for manufacturing unidirectionally fibre reinforced resin products - Google Patents

Description

(54) METHOD AND APPARATUS FOR MANUFACTURING UNIDIRECTIONALLY FIBER REINFORCED RESIN PRODUCTS (71) We, TOSHITAKA FUJII, KENICHI HIGUCHI, and HARUYUKI FUJII, all citizens of Japan, residing at No. 417, Gonose-cho, Nishiwaki-shi, Hyogo-ken; No. 2 17, 7chome, Shinimazato, Ikuno-ku, Osaka-shi, Osaka-fu; and No. 417, Gonose-cho, Nishiwaki-shi, Hyogo-ken, Japan, respectively, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a method for manufacturing fiber reinforced synthetic resin products, more particularly unidirectionally orientated fiber reinforced synthetic resin products and an apparatus for manufacturing the same.

It has been already proposed to manufacture unidirectionally fiber reinforced synthetic resin products by employing fibers of high tensile resistance. e.g., carbon filaments, metal fibers, chemical fibers, etc. as reinforcing fibers and coating or impregnating these fibers with a thermosetting resin such as phenolic resin or a cold-setting resin such as an epoxy resin. This conventional method, however, has a serious problem that the fibers are forcibly retracted to be slackened and partially subjected to compression in the longitudinal direction thereof by the surrounding resinous material due to its shrinkage at curing and heat shrinkage after heat curing, and accordingly the fibers are molded in the state that the fibers are partially bent or relaxed in case a linear expansion coefficient of the fibers employed is smaller than that of the resinous material employed. Since the fibers cannot bear the compression when they are compressed in the longitudinal direction thereof, the fibers, after the resinous material is cured and shrunk, are rendered nonlinear, wavy or irregularly curved and are fixed in the resinous material in the relaxed state. Accordingly. though the fibers appear to be orientated in the longitudinal direction of the molded product, the fibers are in fact set in the relaxed state and not disposed properly in linear parallel relation.

Therefore, the products thus obtained are not uniform in strength and accordingly cannot be homogeneous and cannot have the desired strength. Thus, it can be said that an effect of the real unidirectional fiber reinforced resin product cannot be attained with the conventional method.

Accordingly the present invention provides a method for manufacturing an elongated unidirectional fiber reinforced synthetic resin product, including the steps of winding around a mandrel a prepreg sheet of fibers orientated in one direction and impregnated with resinous material so that the fibers are orientated substantially parallel to the longitudinal axis of the mandrel, applying tension to the fibers and fully curing the resinous material whilst keeping the fibers under tension. Thus initial deflection of the fibers is minimized by applying initial tension to the fibers during curing and the products thus obtained are uniform in strength and quality and have sufficiently high strength.

For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Fig. 1 is an enlarged fragmentary longitudinal sectional view of a pipe wall of a tubular product; Fig. 2 is an enlarged fragmentary cross sectional view of the pipe wall of Fig. 1; Fig. 3 is an enlarged fragmentary longitudinal sectional view of prepreg sheet with fillers incorporated therein; Fig. 4 and 5 are enlarged fragmentary views partly in longitudinal section of a tubular product in accordance with a conventional method; Fig. 6 and 7 are similar enlarged fragmentary views partly in longitudinal section of a tubular product in accordance with the present invention: Fig. 8 is a side view partly in section of a mandrel in accordance with the present invention; Fig. 9 is a side view of the mandrel of Fig.

8 with resin impregnated cloth wound therearound; and Fig. I() shows cross and longitudinal sectional views of a clamp employable for the mandrel of Figs. X and 9; Referring now to the drawings. there is illustrated a prcfcrred embodiment of the present invention.

Fig. 1 and 2 show one form of a general tubular product in longitudinal section and cross section. respectively. Numeral 1 designates fibers and numeral 2 a resinous material. Though a laminate structure formed of three layers is shown in Figs. I and 2, the number of laminations may be suitably selected according to necessity.

In this connection it is to be noted that when the layers comprising fibers and a resinous material are laminated around a mandrel having a profile corresponding to the inner surface of a tubular product to be obtained and the laminate is subjected to curing to set the resinous material according to the conventional method to obtain a molded article having the structure as shown in Figs. I and 2, the resinous material is caused to shrink and the fibers 1 are inevitably slackened or relaxed as shown in Fig. 4 for the reason as mentioned above. Stresses acting on the resinous material 2 and the fibers 1 are indicated by arrows 3 and 4. In particular a compression stress 3 acts on the fibers 1 and a tensile stress 4 acts on the resinous material 2. As mentioned above, the fibers 1 can only withstand a limited compression stress.

When a bending moment M acts on the tubular product due to its own weight or external force applied thereto, the fibers 1 located on the tight side are stretched and the fibers 1' located on the slack side or compressed side are retracted. As far as the degree of the deformation is relatively small, only the relaxation rate of the fibers 1 is decreased and no tensile stress due to the tension of the fibers 1 themselves is yet exerted. Accordingly, the tubular product resists the bending by the actions of the tensile stress 4 and the compression stress 4' of the resinous material 2. However, the modulus of the resinous material, for example with respect to KEVLAR--49 (trademark and trade name of aromatic polyamide type fibers manufactured and sold by Du Pont Co., U.S.A.), is 1.3x 106 kg/cm2. Accordingly, the tubular product is liable to be distorted or deflected as long as tension is not exerted on the fibers.

As the bending moment M gets larger and tension is exerted on the fibers I on the tight side in Fig. 5, the fiber stress 3 is changed to a tensile stress and first effectively imparts a reinforcing function to the fibers.

In Figs. 8 to 10, one preferred mode of method and apparatus for manufacturing a tubular product according to the present invention is shown. Fig. 8 shows one example of a mandrel formed in a tapered shape varying its diameter along its length. Of course a mandrel of uniform diameter from end to end may be employed in the present invention according to necessity. Numeral 6 designates a main member of the mandrel which has an internal screw thread 7 at its one end portion and a groove 8 at its other end portion on the periphery thereof. Numeral 9 designates an auxiliary mandrel member. A shaft 11 with a head passes through a central hole of the auxiliary mandrel member 9 and has a screw 13 at its one end passed through a flange 12 formed integrally with the auxiliary mandrel member 9. The screw 13 is screwed into the thread 7 until the flange 12 abuts against the main mandrel member 6 and the auxiliary mandrel member 9 is slid to a position where it contacts the flange 12. The auxiliary mandrel member 9 also has a groove 10 on the periphery thereof. A prepreg sheet 14 formed of fibers orientated in one direction and impregnated with resinous material is wound around the mandrel so as to dispose the fibers substantially in parallel with the axial direction of the mandrel.

In Fig. 9, the prepreg sheet 14 wound around the mandrel is fixed at its end portions by clamps 15, 15, which are dividable into complementary members as shown in Fig. 10, by removing screws 17. The clamping positions correspond to the grooves 8 and 10. As the head of the shaft 11 is rotated in the direction to disengage the screw 13 from the thread 7, the auxiliary mandrel member 9 is spaced away from the main mandrel member 6 and tension is imposed on the fibers of the prepreg sheet 14.

In order easily to obtain a suitable tension, the number of rotations of the screw 13 is advantageously determined preliminarily with reference to the length of the mandrel.

The prepreg sheet 14 is then subjected to full curing by heating or at normal temperature while keeping the fibers under tension, subsequently cooled, and cut where indicated at 16, 16' in Fig. 9. The clamps 15, 15 are then opened and the surplus scraps removed to allow the central tubular product to be taken off. The inner structure of the thus obtained tubular product is shown in the enlarged sectional views of Figs. 6 and 7.

The fibers 1 are disposed and fixed linearly and are not slackened or relaxed. Numeral 3 shows a tensile stress of the fibers 1 and numeral 4 to compression stress of the resinous material 2. As compared with the conventional product of figures 4 and 5, it can be seen that the directions of the stresses are reversed.

Fig. 7 shows the same tubular product subjected to a bending moment M. Even when the load is relatively small, the tensile stress 3 is exerted on the fibers 1 of the tight side and the tensile stress 3' is left, though reduced. Accordingly, the fiber stress always acts on the tubular products correspondingly to the external forces applied. Thus, the degree of distortion of the tubular product due to a tension or a bending depends mainly upon the modulus of the fibers and the initial distortion can be much reduced.

Fig. 3 shows one form of prepreg sheet with fillers 5 incorporated in a resinous material 2 which is employed where the resinous material is possibly subjected to plastic deformation in a long time due to the compression stress exerted on the resinous material 2. In Fig. 3, numeral 1 also designates fibers. As the fillers 5, there are advantageously employed fine particles having a high modulus, for example, hollow molten particles or solid particles of alumina.

These particles are incorporated in the resinous material so as to be adjacent each other and not only impart to the resinous material 2 a high compression strength and a high modulus but also prevent creep which is possibly caused when the resinous material is continually subjected to a stress.

The products thus obtained according to the present invention have excellent unidirectionally fiber reinforced characteristics and excellent performances and are advantageously utilized as fishing rods or pipes for chemical industries.

WHAT WE CLAIM lS: 1. A method for manufacturing an elongated unidirectional fiber reinforced synthetic resin product, including the steps of winding around a mandrel a prepreg sheet of fibers orientated in one direction and impregnated with resinous material so that the fibers are orientated substantially parallel to the longitudinal axis of the mandrel. applying tension to the fibers and fully curing the resinous material whilst keeping the fibers under tension.

2. A method according to claim I. in which the application of tension to the fibers is discontinued when the resinous material has been cured. and the cured product is then removed from the mandrel.

3. A method as claimed in claim I or claim 2, wherein tension is applied to the fibers by longitudinally extending the mandrel on which the prepreg sheet is wound and secured.

4. An apparatus for carrying out the method of claim 1, which comprises a mandrel, clamping means for securing a prepreg sheet, having fibers orientated in one direction and impregnated with a resinous material, around the mandrel and means for applying a tension to the fibers of the prepreg sheet while the resinous material is being fully cured, 5. An apparatus as claimed in claim 4, wherein the mandrel is formed of two members and the tension applying means includes means for spacing the two members of the mandrel apart from each other to extend the length of the mandrel.

6. An apparatus as claimed in claim 5, wherein the means for spacing the two members of the mandrel comprises an inner screw thread formed in one end of one member of the mandrel; a hole formed centrally in the other member of the mandrel which is adapted to align with said inner screw thread when assembled; a shaft adapted to be slidably inserted through said hole and provided at its one end with a protruding head, at its another end with a screw adapted to mesh with said inner screw thread and intermediate the ends with a flange adapted to abut against said end of said one member of the mandrel when the screw is engaged with the inner screw thread.

7. An apparatus as claimed in claim 6, wherein the clamping means is in the form of two dividable complementary members and adapted to be snugly fitted to grooves each formed on the peripheries of the end portions of the one and the other members of the mandrel, respectively, to secure the prepreg sheet therebetween.

8. An elongated unidirectionally fiber reinforced resin product whenever made by the method claimed in any one of claims 1 to 3.

9. A method according to claim 1, substantially as hereinbefore described with reference to any one of the accompanying drawings other than Figures 4 and 5.

10. Apparatus according to claim 4, substantially as hereinbefore described with reference to any one of the accompanying drawings other than Figures 4 and 5.

II. A resin product according to claim 8, substantially as herein before described with reference to any one of the accompanying drawings other than Figures 4 and 5.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (10)

**WARNING** start of CLMS field may overlap end of DESC **. shows a tensile stress of the fibers 1 and numeral 4 to compression stress of the resinous material 2. As compared with the conventional product of figures 4 and 5, it can be seen that the directions of the stresses are reversed. Fig. 7 shows the same tubular product subjected to a bending moment M. Even when the load is relatively small, the tensile stress 3 is exerted on the fibers 1 of the tight side and the tensile stress 3' is left, though reduced. Accordingly, the fiber stress always acts on the tubular products correspondingly to the external forces applied. Thus, the degree of distortion of the tubular product due to a tension or a bending depends mainly upon the modulus of the fibers and the initial distortion can be much reduced. Fig. 3 shows one form of prepreg sheet with fillers 5 incorporated in a resinous material 2 which is employed where the resinous material is possibly subjected to plastic deformation in a long time due to the compression stress exerted on the resinous material 2. In Fig. 3, numeral 1 also designates fibers. As the fillers 5, there are advantageously employed fine particles having a high modulus, for example, hollow molten particles or solid particles of alumina. These particles are incorporated in the resinous material so as to be adjacent each other and not only impart to the resinous material 2 a high compression strength and a high modulus but also prevent creep which is possibly caused when the resinous material is continually subjected to a stress. The products thus obtained according to the present invention have excellent unidirectionally fiber reinforced characteristics and excellent performances and are advantageously utilized as fishing rods or pipes for chemical industries. WHAT WE CLAIM lS:

1. A method for manufacturing an elongated unidirectional fiber reinforced synthetic resin product, including the steps of winding around a mandrel a prepreg sheet of fibers orientated in one direction and impregnated with resinous material so that the fibers are orientated substantially parallel to the longitudinal axis of the mandrel. applying tension to the fibers and fully curing the resinous material whilst keeping the fibers under tension.

2. A method according to claim I. in which the application of tension to the fibers is discontinued when the resinous material has been cured. and the cured product is then removed from the mandrel.

3. A method as claimed in claim I or claim 2, wherein tension is applied to the fibers by longitudinally extending the mandrel on which the prepreg sheet is wound and secured.

4. An apparatus for carrying out the method of claim 1, which comprises a mandrel, clamping means for securing a prepreg sheet, having fibers orientated in one direction and impregnated with a resinous material, around the mandrel and means for applying a tension to the fibers of the prepreg sheet while the resinous material is being fully cured,

5. An apparatus as claimed in claim 4, wherein the mandrel is formed of two members and the tension applying means includes means for spacing the two members of the mandrel apart from each other to extend the length of the mandrel.

6. An apparatus as claimed in claim 5, wherein the means for spacing the two members of the mandrel comprises an inner screw thread formed in one end of one member of the mandrel; a hole formed centrally in the other member of the mandrel which is adapted to align with said inner screw thread when assembled; a shaft adapted to be slidably inserted through said hole and provided at its one end with a protruding head, at its another end with a screw adapted to mesh with said inner screw thread and intermediate the ends with a flange adapted to abut against said end of said one member of the mandrel when the screw is engaged with the inner screw thread.

7. An apparatus as claimed in claim 6, wherein the clamping means is in the form of two dividable complementary members and adapted to be snugly fitted to grooves each formed on the peripheries of the end portions of the one and the other members of the mandrel, respectively, to secure the prepreg sheet therebetween.

8. An elongated unidirectionally fiber reinforced resin product whenever made by the method claimed in any one of claims 1 to 3.

9. A method according to claim 1, substantially as hereinbefore described with reference to any one of the accompanying drawings other than Figures 4 and 5.

10. Apparatus according to claim 4, substantially as hereinbefore described with reference to any one of the accompanying drawings other than Figures 4 and 5.

II. A resin product according to claim 8, substantially as herein before described with reference to any one of the accompanying drawings other than Figures 4 and 5.