KR960000033B1 - Controlled fiber distribution technique for glass matrix composites - Google Patents

Abstract

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Description

Fiber Reinforced Glass Substrate Composite Manufacturing Method

1 is a partial side cross-sectional view showing the final stage of the filament being forced through the nozzle portion of the molding apparatus of the present invention.

2 is a cross sectional view of a composite prepared according to the method of the present invention and a hot pressed composite illustrating the fiber distribution developed.

3 is a cross sectional view of a composite prepared according to the method of the present invention and a hot pressurized composite illustrating improved fiber separation.

* Explanation of symbols for main parts of the drawings

1: reservoir 2: injection nozzle

3: pupil 6: plunger

The present invention relates to a molding method, in particular a molding method of a fiber reinforced composite product.

Due to the scarcity and rising costs of conventional high temperature structural metals, attention has been focused on the development of nonmetallic fiber reinforced composites to replace conventional high temperature metal alloys. Metal substitutes, high strength fiber reinforced resins and high strength fiber reinforced metal matrix composites have been used commercially from sporting goods to the production of modern jet aircraft parts. However, one of the big problems with using these composites is the maximum utilization temperature.

Ceramics, glass and glass-ceramics are known in the art which can be used at high temperatures. However, the ceramic body has poor mechanical strength and always suffers from toughness and impact resistance. This has resulted in the production of composites consisting of substrates made of ceramic, glass or glass-ceramic materials with inorganic fibers that are continuously or discontinuously dispersed. The glass substrate composites described above are described in US Pat. Nos. 4,314,852 and 4,324,843. Glass-ceramic substrate-silicon carbide fiber composites made according to the technology of the foregoing patents exhibit physical properties that can be used in heat engines and other applications to significantly improve performance. However, for such applications, new manufacturing methods are needed to produce complex shaped parts with reinforcing fibers distributed in at least three directions to distribute the increased strength.

Although there have been great advances in this field, it is difficult to manufacture such improved composite products. In the past, continuous reinforcement of the composite article with fibers is accomplished using collimated fiber tape, pulp and paper impregnated and oriented with a glass-carrier slurry of the size to be cut and then laminated to a die for fine presses. However, this process is unsuitable for much more complex shapes and only possible when the fibers are in planar arrangement. It is also difficult to form cylinders and other complex shapes from the material.

In addition, careful pre-positioning of fiber reinforcements in resin, metal and glass-based composites is not necessary, and the random distribution of the segmented fibers gives the proper performance characteristics. It also enables the production of precisely shaped products quickly and inexpensively.

Co-transferred US Pat. No. 4,464,192 describes a process for producing fiber reinforced glass substrate composites of complex shape (eg curved or curved wall) by injection molding. However, there is a constant need to improve molding technology.

There has therefore been a continuing study on a fast and relatively simple method of preparing glass-based composites that are particularly suitable for molding such composites of complex shape.

The present invention relates generally to a method for producing discontinuous fiber reinforced glass substrate composites by injection molding using injection exposure which separates all yarns into individual fibers such that the composites have larger crack resistance. The method includes impregnating a continuous filament yarn with a glass substrate powder comprising glass, glass-ceramic powder or mixtures thereof. The impregnated multifilament yarns are discontinuously cut and exposed to temperatures sufficient to soften the substrate material. Sufficient shear force is generated on the die wall so that all the multifilament yarns are separated into their respective filaments because the yarns are replaced with molded bodies by applying sufficient pressure to the heated impregnated multifilament yarns. Molding pressure is maintained sufficiently to prevent the composite from relaxing until the glass reaches the strain point.

The present invention has made great progress in glass-based fiber reinforcement technology by providing a method for separating fibers into stronger composites.

The above and other features and advantages of the present invention will be described in detail with reference to the accompanying drawings.

Any glass that confers high temperature strength properties to the composite can be used in the present invention, but Corning 7740 or 7070 borosilicate glass (Corning Glass Wix, Corning, NY) is known to be suitable for the method according to the present invention. Similarly, Corning 1723 aluminosilicate glass is also known to be good. The borosilicate glass and aluminosilicate glass can be used with a -356 mesh size. Mixtures of the glasses and high silicate glasses (Corning 7913, 7930 and 7940 high silica glass and mixtures of the glasses can also be used. Borosilicate glasses are preferably used because their viscosity temperature properties improve flowability. .

Another glass substrate material useful in the process of the invention is glass ceramics. During densification of the moldings, the substrate retains its glass shape, thereby avoiding fiber damage and promoting densification at low pressures. After densification to the desired fibrous-substrate tissue, the glass substrate is converted into a crystalline state and the extent and extent of the crystal is controlled by the substrate composition and the heat treatment process employed. Various glass ceramics can be used in this method. However, when using silicon carbide fibers, it is important to control strict limits on the amount and activity of titanium in the glass. Therefore, if silicon carbide fibers and titania nucleating agents are used, the titania should be inert or kept below 1% by weight. This can be achieved by simply replacing another titania such as zirconia or adding an agent to prevent the titania from reacting toward the silicon carbide fibers. In some cases, however, it is necessary to eliminate or prevent the influence of titania on silicon carbide fibers in order to obtain composites having high temperature strength properties. Conventional lithium aluminosilicates are good glass-ceramic, but conventional glass-ceramics such as aluminosilicates, magnesium aluminosilicates and their compounds are also used as long as the ceramic substrate material is free of titanium (up to about 1% by weight) or blocked. Can be. Co-transmitted US Pat. No. 4,324,843 is incorporated herein by reference. It is desirable to use lithium aluminosilicates because of their improved compatibility with carbon and silicon carbide fibers.

Generally the starting glass-ceramic material can be obtained in the form of a glass powder. However, if the glass-ceramic material is obtained in crystalline form, it is preferred to melt the material into a glass form, solidify and pulverize before forming the slurry according to the present invention to form a powder form in which -325 mesh is desired. In selecting a glass-ceramic material, it is important to select one that can be densified into a glass shape with a low viscosity sufficient to fully solidify and then transform into a complete crystalline state. However, it is also possible to convert the starting crystal powder into the glass state during preheating before applying pressure to densify.

Blast furnace stable fiber materials can be used in the process according to the invention, but silicon carbide, alumina or silicon nitride, carbon fibers and the like are particularly preferred. Particularly preferred are multifilament carbon yarns having an average filament diameter of 10 mu, for example between about 7 and 10 mu. Hercules Incorporated, Wilmington, Delaware, produces yarns of 1000, 3000, 6000 or 12000 per tow and an average diameter of 8μ. The average strength of the fiber is about 2758 MPa. Yarn has a density of about 1.84 g / cm ² and an elastic modulus of about 379 GPa. It is preferable to use HMU ^™ of Hercules Incorporated for compatibility with substrate glass. Fiber whiskers such as whiskers of F-9 silicon carbide from Acro Chemicals (Great South Carolina) or SNW-silicon nitride of Tateo Chemical Industries Ltd. of Japan can also be used.

Polymeric binders can also be used in the present invention that readily dissolve or disperse in any particular carrier and provide a lubricant to facilitate cold press. It is known that latex acrylic polymers and especially Roflex ^™ latex acrylics (Long and Haas Coporation, Philadelphia, PA) are suitable for the binder used in the process of the present invention. Likewise preferred are Carbowax ^TM (Carbide Coporation) polymer series and Carbowax 4000 in particular. In addition, inorganic binders that are easily dissolved or dispersed in any particular carrier can also be used in the present invention. Colloidal silica solution and The Dogx ^TM (E. I. Dupont Denemours, Delaware) are known to be suitable binders for the methods of the present invention. Therefore, a carrier material compatible with the binder may be used, and water is also preferable.

Although the amount of the material may vary, the slurry is prepared so that the glass substrate powder, the binder and the carrier liquid impart a strong mixture when added to the fibers. In general, the amount of glass added is sufficient to give a fiber concentration of about 15% to about 50% by volume when the carrier liquid and binder are removed. Typically, the slurry contains about 1.80 ml of carrier liquid (preferably water) and about 0.2 ml of organic binder for each gram of -325 mesh glass powder. The final molded article generally contains from about 50% by volume to about 85% by volume, preferably 70% by volume, of glass substrate.

The fiber tow then passes through the glass-binder-water slurry in such a way that the slurry saturates the fiber tow. When the typical ratios described above are used, the fiber tow is impregnated with an amount of glass sufficient for the volume percent of the glass to be between 50 and 85 volume percent. The impregnated tow is then wound up on a mandrel and dried. The dried tow is subdivided into lengths useful for the intended molding. The length to be chosen depends on the minimum mold wall thickness (eg cylinder wall thickness). The mold composition should be short enough to prevent aggregation when penetrating the mold wall. The fiber tow preferably has a length of about 0.635 cm to 2.54 cm and preferably a mold wall thickness of about 0.254 cm of fiber tow, less than 1.27 cm.

The mold composition is heat-treated to remove residual water and binder and then placed in the reservoir chamber of the molding apparatus shown in FIG. According to FIG. 1 the glass mixture is placed in the tool reservoir 1 and the tool is heated up to the temperature described below and pressurized through the plunger 6 so that the heated mixture is injected into the cavity 3 through the injection nozzle 2. Is moved to). The mold composition may also be hot pressed to form suitable billets.

The molding composition may be pressurized at high temperature to form a suitable billet to remove the carrier liquid and binder in a suitable atmosphere after injection molding. In some cases a suitable mold that can be injection molded without further pre-densification by simply mechanically mixing finely divided fibers (or whiskers) and glassy powders, such as those that can be achieved in suitable blends, depending on the size and shape of the part to be manufactured. Compounds can be formed. However, low density mixtures (usually about 10% of the mold density) require very large mold degradable devices.

The mold composition is ready for injection molding, even in a pre-solidified form without tackiness. The mold apparatus (including the mold) is heated to a temperature sufficient to soften the glass substrate to have a viscosity of about 10 ³ to 10 ⁵ pois. Where the pois is the absolute viscosity in units of cgs equal to 0.1 Pa.S. If the viscosity of the glass substrate is about 10 ⁵ pois or more, the viscosity may be too high and the injection nozzle may be clogged. If the viscosity of the glass substrate is less than about 10 ³ pois, the fluidity is so good that separation of the fibers and the substrate occurs. The conventional glass and ceramic described above generally require a temperature of about 900 ° C to 1500 ° C. However, good carbon fiber-borosilicate glass substrates require temperatures of about 1000 ° C to 1250 ° C.

The molten glass substrate / fiber mixture is placed in a mold of the desired shape through the injection nozzle. The nozzle is formed such that sufficient die wall (nozzle wall) shear forces are generated (ie molded into a curved shape) such that all (i.e. at least about 90%) finely divided multiple filament yarns are separated into their respective filaments (ie, curved to form). As it moves through it, it is created by the frictional drag exerted by the injection nozzle wall on the mold sculpture. This frictional force allows the fiber toe to separate into individual filaments so as not to damage the filaments. In order to achieve this shear separation optimally, the injection nozzle comprises tubular openings at both ends, and the inner surface is preferably in the form of a cylinder. Any cross-section nozzle with adequate volume will yield suitable results, but a good cross-sectional shape is preferably a circular cross section to concentrate the die-wall shear force.

In the case of a circular cross-section injection nozzle, an optimum result is obtained when the diameter of the nozzle is shorter than the cutting length of the fiber tow because the force is applied to the tow heat in the nozzle to optimize the tow separation. For example, when a nozzle diameter of about 0.75 cm to about 1.00 cm in a tow of about 1.25 cm to about 1.50 cm is long, separation occurs in all filaments and a uniform mixture is produced.

Similarly, the length of the nozzle must be equal to or greater than the bundle length to align the tow. Injection nozzle lengths that are too long for the toe length or nozzle diameter given above will make the mold apparatus larger than necessary, but the nozzle length should be at least about 1.50 cm. The pressure applied to the plunger of the mold apparatus should be sufficient to completely solidify the mold composition in the reservoir. This causes the mold composition to move into the molded die cavity through the injection nozzle. The exact range of pressure depends on the exact composition of the substrate glass, the fiber percentage and the temperature at which pressure is applied. In a good carbon fiber-borosilicate glass substrate mixture containing from about 15% to about 30% by volume of fibers and pressurized at about 1000 ° C to about 1150 ° C, a pressure of about 7 MPa to about 17 MPa is fully injected and formed. The composition hardens in the die cavity. Applying pressure below this range will block the injection nozzle and incompletely fill the die cavity. Applying pressure above this range will result in excessive stress on the mold apparatus. Note that there is a correlation between the nozzle diameter and the nozzle length and the pressure applied. When high pressure is applied, small diameter nozzles or long nozzles or both can be used successfully.

For good composition the mold is generally maintained at about 1100 ° C. to 1250 ° C. until it is filled. From about 0.25 hour to about 1.0 hour in the aforementioned composition. Once filled, it should be cooled at a rate of about 15 ° C./min to about 30 ° C./min, because excessively high cooling rates result in excessive cracking of the glass substrate. Usually the pressure exerted on the glass substrate / fiber composition is maintained enough to prevent the composition from relaxing until the strain point of the glass is reached. Strain points are defined in ASTM C336 and C598. The strain temperature is also at the bottom of the annealing range, with a viscosity of about 10 ^14.5 poWs. A pressure of about 7 MPa to about 17 MPa is preferably applied for about 2 hours, depending on the particular glass composition and the mold temperature used to prevent delamination of the compositional structures that can form pores.

EXAMPLE

The weight of 18.7g and Magna ^TM dynamite graphite fibers type HMU (Delaware, Wilmington material heokyu leasing encodings Va'a-o-federated) (3,000 filaments per tow) are suitable speed for the yarn having a length of 85.4m (about 6.5m / min) The fibers resulting from passing through the flame of the furnace bunsen burner are removed, the fiber yarns are released from the feed spool, the raw yarns are immersed in the stirred slurry and the saturated yarns are immersed in the glass-water-binder slurry by winding the saturated yarns in the winding mandrel. The slurry consists of 200 g Corning 7740 borosilicate glass powder of -325 mesh, 25 g of redox colloidal silica and 250 ml of distilled water. Sufficient slurry is impregnated along the yarn to add 52.7 g of glass. The saturated yarn is dried to remove water on the cold mandrel.

After drying, the impregnated yarn is removed from the winding mandrel and cut to an average tow length of 1.25 cm. The subdivided mold composition is placed in a chamber in a reservoir of a mold apparatus similar to that of FIG. The injection nozzle in this embodiment has a diameter of 0.95 cm and a length of 1.25 cm. The injection molding apparatus is placed in a high temperature vacuum press and heated to 1275 ° C. and a pressure of 14 MPa is pressed against the plunger and maintained for 30 minutes. The furnace is then powered off and the pressure is removed when the assembly cools to 500 ° C. The assembly is then cooled to room temperature and the injection molded part is removed from the mold.

According to one embodiment which improves composition performance from the present invention, the load bearing capacity of the parts of the three composition samples is measured by compressing the part between the flat roller and the steel chisel tip. Two samples made in accordance with the present invention have a load bearing capacity of 5930N and 8145N. The third sample produced by the one-way hot pressing process of the same composition has a load bearing force of 1713N.

The increased strength of the composition prepared according to the invention is due to at least two factors. Using injection nozzles improves fiber distribution for more uniform reinforcement. This is illustrated in the cross-sectional comparative example of the above-described composition shown in FIG. The three-dimensional arrangement shown in figure a of FIG. 2 is preferred because the arrangement gives isotropic reinforcement. In contrast, mainly the planar magnification shown in Figure b of Figure 2 is undesirable because it does not reinforce vertically to the arrangement. As described above, when the injection nozzle is used, the fiber tow is separated into each filament. This compares the microstructure of hot pressed composition B (without non-isolated fibers) with the injection molding composition as shown in FIG. The composition is similar to the composition described above, but in this case the tow length is 0.64 cm and the injection nozzle has a diameter of 0.48 cm and a length of 2.72 cm.

The process according to the invention is particularly suitable for producing complex shapes. It is particularly suitable where more reinforcement is needed than two-dimensional reinforcement in conventional hot pressed compositions. This is because the reinforcing fibers can be widely spread and the fibers can be dispersed homogeneously by separating into individual filaments. Typical complex shapes made in accordance with the method of the present invention are cylinder shapes such as cylinder liners and gun barrels, bulky or thick walls such as hollow vessels such as cups and spark plugs and igniter insulators and compressor protection.

The present invention facilitates the production of purely shaped products since a die consisting of complex multiple parts with complex shapes can be used in contrast to hot press processing. The present invention not only provides a suitable method for producing complex shapes of fiber reinforced glass substrate composites by mass production, but also the product has strength in three dimensions by random orientation of the fibers in three dimensions. In addition, by randomly distributing the fibers three-dimensionally, the reinforcement performance of the component of the composite shape is improved.

Discrete fiber reinforced composites of the state of the art include fiber bundles of up to 12,000 filaments. These bundles become woven microstructures containing substrate rich zones through which shaping is easily transmitted. The present invention described above allows the bundle to be broken down into individual filaments and distributed evenly on the substrate. This results in a good strength and homogeneous composite.

Finally, the method allows for fast part manufacturing since multiple part cavities are supplied from a single reservoir. This increased manufacturing speed reduces manufacturing costs. The present invention also enables good dispersion of the fibers while using high tow starting yarns (cheaper than small toe yarns). Thus, the present invention has made great progress in the field of fiber reinforced glass substrate composite molding.

The present invention can be variously modified without departing from the scope and spirit of the invention.

Claims (5)

a) impregnating a continuous multifilament yarn with a slurry consisting of glass, glass-ceramic powder or mixtures thereof; b) subdividing the impregnated multifilament yarns into discrete lengths; c) exposing the granular impregnated multifilament yarns to a temperature sufficient to soften the substrate; d) Sufficient die wall shear force to pressurize the impregnated multifilament yarns such that all of the filament yarns are separated into their respective filaments sufficient to cause the heated subdivision impregnated multifilament yarns to be transferred to the mold through a curved injection nozzle. Discontinuous fiber, characterized in that it is produced, and e) maintaining a mold pressure sufficient to prevent the release of the composite until the glass reaches the strain point to produce a composite having a large crack resistance. Reinforced glass substrate composite manufacturing method. The method of claim 1 wherein the yarns are subdivided into lengths from about 0.635 cm to about 2.54 cm. The method of claim 1, wherein the granular impregnated yarn is exposed to a temperature sufficient to reach a glass viscosity of about 10 ³ to 10 ⁵ pois. The method of claim 1 wherein the mold pressure is about 7 MPa to about 17 MPa. The method of claim 1, wherein the mold is maintained at a temperature of about 900 ° C. to about 1500 ° C. until the mold is filled.

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