DE2705336A1 - CARBON FIBER REINFORCED SCREW - Google Patents

Description

270B336

SlGRI ELEKTROGRAPHIT GMBH Meitingen, the ' I S: ";:') ''

Carbon fiber reinforced screw

The invention relates to a screw made from a carbon fiber containing composite.

For the frictional connection of elements made of a composite material reinforced by carbon fibers and for connecting these elements to structural parts made of a different material, screws have become known which consist of a material reinforced by carbon fibers. So far, such screws have been produced by first making plates or cylinders from a composite material containing the carbon fibers in an essentially unidirectional orientation and working the screws out of these bodies, where the length of the screw coincides with the direction of the carbon fibers. Screws with such a fiber orientation have considerable tensile and flexural strengths, since d: <_ shear strength, however, is relatively small, but threads of screws with a carbon matrix already on the surface during machining and individual threads become under Load easily sheared off.

To improve the shear strength of composite materials is or, known, e.g. plates or pipes in uniform,

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to wrap layers at an angle. From these Screws carved out of bodies can have a greater shear strength, especially in the thread area have, but at the expense of tensile and flexural strength, the reduction of which is generally not permitted can be.

The invention is based on the object, while maintaining the high tensile and flexural strength Shear strength of screws made from a carbon fiber reinforced Improve composite material.

The object is achieved with a screw of the type mentioned in that the in a matrix distributed carbon fibers in the screw core towards are arranged on the longitudinal axis of the screw and extend in the thread at an acute angle to the longitudinal axis.

According to a preferred development of the invention, the angle is equal to the pitch angle of the thread. According to the invention, the matrix of the composite material preferably consists of carbon. Other suitable Matrix materials are, for example, curable synthetic resins such as epoxy resins and phenol-formaldehyde resins. According to the invention, the term carbon fibers is also understood to mean graphite fibers which consist of K (jh lens tof fibers produced by a thermal process will. Finally, screws according to the invention are not limited to special thread shapes and pitches.

in screws according to the invention are the advantages of a composite material with unidirectional arranged

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:; l.'irkuriq:;! auorri unci one of several networked against each other Combined material containing fiber layers, the screw core preferably tensile and bending stresses and the threads absorb shear stresses, which results in undiminished tensile and flexural strength of the screw core, a significantly higher shear strength of the thread turns is achieved.

As reinforcing fibers for screws according to the invention are especially carbon or graphite fibers with

a tear strength y 2 kN / mm, which is optionally impregnated and coated after a surface treatment to improve the interlaminar shear strength with a curable synthetic resin such as epoxy, furan or phenolic resin, laid out in layers and then after drying and partial hardening of the resin to form panels or cylindrical rods are pressed. After complete hardening of the resin matrix, which is expediently carried out in the temperature range between about 150 and 200 ° C, cylinders are machined from the raw bodies containing about 40-70% by volume of unidirectional carbon fibers, the diameter of which is equal to the core diameter of the respective screw; The screw head can be produced in the same operation in a known manner. Now a layer consisting of morose layers is drawn onto the core in a winding process made of synthetic resin-impregnated yarns or rovings up to the desired outer diameter of the screws. In this layer, the carbon fibers run at an acute angle to the longitudinal axis of the screw core, preferably at

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the angle speaks the pitch angle of the screw. After the resin has hardened, the thread is then cut in a known manner.

For the production of screws with a carbon matrix screws containing a resin matrix are used to carbonize the resin in an inert atmosphere heated to about 1000 ° C. As the resin matrix shrinks under these conditions, correction is generally needed the dimensional changes require reworking. According to a different method are therefore used as the matrix material Used for screws made from carbon fiber reinforced carbon, coal tar pitch coke. The carbon fibers are impregnated with a tar pitch, laid out in layers and made into plates or cylindrical rods pressed. After appropriate processing, pitch-impregnated rovings or yarns are then applied to the blanks several layers are wound up or the blanks are first carbonized and then processed and provided with wrapping layers. In the second case there is a second heating to the carbonization temperature necessary. The thread is cut after the last carbonization.

In the following, production and properties are described according to the invention by means of examples and a drawing Screws described.

example 1

Carbon fiber rovings with 10,000 filaments were laid out to form ribbons, ^{impregnated with the commercially available resin system Epikote R} DX 210 / Epikure ^R DX 137, dried for 30 minutes at a temperature of 80 ° C. and in a

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The mold is heated to 140 ° C under a pressure of 0.7 N / mm. From the raw body, the fiber content of which was approx. 60 % by volume, rods with a cross section of 10 × 10 mm were cut in the direction of the fiber flow and the rods were turned to a diameter of 9 mm. High strength carbon fibers with 3000 filaments that

were impregnated with the commercially available resin system Araldit LY 556 / MY 051, were then under a to ei. 8j wound against the cylinder axis inclined direction and in the winding layers after a hardening process a thread with a helix angle of 5 is cut after 15 hours. The flexural strength of the screw

2 core was 1300 to 1500 N / mm, the flexural strength

2 speed of the thread 450 to 500 N / mm.

Example 2

Unidirectional carbon fiber fabric tapes were coated in a press mold with finely ground hard pitch, which softened at a temperature above 180 C. and heating the assembly in an oven to about 300 C and then under a pressure of 0.7 N / mm compressed. The raw bodies were then heated to 550 ° C. under a pressure of 25 bar and cooled and twice impregnated with a coal tar pitch with a softening point of approx. 60 ° C. After every Impregnation step, the bodies were pressurized to 550 ° C and after the second impregnation to complete Carbonization of the carbon matrix heated to approx. 1000 ° C without pressure. As described in example 1 Cylindrical rods were made from the raw body, whose reinforcement fibers parallel to the longitudinal

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ai'hse dor cylinders were arranged. High strength carbon fibers 3,000 filaments were then dry wound onto the cylindrical cores at an angle of 85 ° and the layers are impregnated with pitch, carbonized and the thread cut as described above. With a fiber content of approx. 60% by volume, the screws had the following properties:

core 500 thread N / mm Flexural strength 400 - 000 4 50 N / mm Elasticity
module 110 110,000

As illustrated schematically in the drawing, the carbon fibers 2 run parallel in the screw core 1 to the longitudinal axis of the screw. The reinforcing fibers follow in thread 3 the thread pitch. Compared with known screws made of a composite material dor screw core and thus the strength of the screw unchanged, the shear strength of the thread turns however, is wio the comparative example shows essential greater.

For shearing off a thread on average force to be used:

Matrix unidirectional wound

Fiber orientation threads

Resin 2,800 N 4,400 N

Carbon 500 N 850 N

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ErI i ruJufKjr.qc screws stand out next to the Great strength thanks to excellent corrosion resistance and screws with a carbon matrix, thanks to their high thermal stability the end. The screws are particularly suitable as a connection between elements made of composite materials, Ceramic, carbon and graphite, which are exposed to particular thermal and chemical loads are.

J claims
1 figure

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Claims (3)

270b336 Claims (ί.) Screw made of a composite material containing carbon fibers, characterized in that the carbon fibers distributed in a matrix are arranged in the screw core in the direction of the screw's longitudinal axis and extend in the thread at an acute angle to the longitudinal axis. 2. Screw according to claim 1, characterized in that the angle is equal to the pitch angle of the thread is. 3. Screw according to claim 1 and 2, characterized in that the matrix is made of carbon consists. PA 77/2 Dr.We / häu 809832 / OAde ORIGINAL INSPECTED