Techniques for pitch densification

In some examples, a method for densifying a material via pitch comprises inserting the material to be densified into a mold, wherein the mold is part of an apparatus. The apparatus may include a ram configured to apply a ram pressure sufficient to force a pitch into the mold to densify the material, a gas source configured to apply a gas pressure sufficient to force the pitch into the mold to densify the material, and a vacuum source operable to create a vacuum pressure in the mold at least prior to application of either the ram pressure or the gas pressure. The method may further comprise densifying the material in the mold via pitch using a selectable one of the ram, the gas source, the ram and the vacuum source, or the gas source and the vacuum source.

TECHNICAL FIELD

This disclosure relates to pitch densification and, more particularly, to pitch densification for carbon-carbon composites.

BACKGROUND

Carbon fiber-reinforced carbon materials, also referred to as carbon-carbon (C—C) materials, are composite materials that generally include carbon fibers reinforced in a matrix of carbon material. The C—C composite materials are found in many rigorous, high temperature applications. For example, the aerospace industry is known to employ C—C composite materials for manufacturing different aircraft structural components. Example applications include rocket nozzles, nose cones, and friction materials for commercial and military aircraft such as, e.g., brake friction materials.

In some examples, C—C composites are manufactured using either woven or non-woven carbon fibers. The carbon fiber may be arranged to define a shape of a resulting structural component and, as such, may be referred to as a preform. The preform may undergo different processing steps to increase the carbon content and density of the preform to transform the preform into a C—C composite component. For example, carbon may be added to the preform using one or more pitch densification processes. In general, a pitch densification process operates to impregnate the carbon fiber preform with pitch that is subsequently cooled and solidified to produce a dense, high carbon content C—C component.

Different pitch densification processes often involve different chemical and mechanical force loading. Different carbon fiber preforms may also exhibit different chemical and mechanical properties, for example, due to different material morphologies, different manufacturing techniques, or the manufacturing tolerances inherent in most fabrication processes. If a pitch densification process selected for a specific carbon fiber preform is too aggressive, the preform may be damaged during the pitch densification process. In applications where the performance and quality of C—C components take precedence, a damaged preform may generally be of little use and may be discarded.

SUMMARY

In general, the disclosure relates to apparatuses and techniques for densifying an article such as a carbon fiber preform with pitch. In some examples, a single apparatus may be configured to densify a carbon fiber article with pitch (referred to herein also as “pitch densification”) to form C—C composite material via multiple different pitch densification processes. For example, a single apparatus may be configured to perform each of resin transfer molding (RTM), a vacuum-assisted resin transfer molding (VRTM), or a vacuum pressure infiltration (VPI) to densify a carbon-based article with pitch all within the same mold of the densification apparatus.

To densify an article to a desired level using such an example apparatus, the article may be inserted within a mold cavity and subjected to one or more cycles of the same pitch densification process or multiple different densification processes. Depending on the particle densification process used, during a densification cycle, an apparatus may be configured to impregnate a carbon-fiber material with pitch within the mold cavity of the apparatus using ram pressure, gas pressure, vacuum pressure, or some combination thereof. For instances in which one or more cycles of two or more different pitch densification processes are used to densify a carbon fiber preform or other article, the article does not need to be removed from one apparatus and inserted into a separate apparatus to carry out different pitch densification processes. Instead, one or more cycles of each of the different densifications processes may be performed within the same mold cavity of an apparatus. In some instances, only a single type of pitch densification process (RTM, VRTM, or VPI) may be utilized to densify a preform. However, as a single apparatus may perform each type of pitch densification processes, the need for three separate apparatuses to perform each respective pitch densification process may be eliminated.

In some examples, a pitch densification process can be selected from among the plurality of different pitch densification processes based, for example, on the initial properties of an article to be densified. In some examples, the selected pitch densification process can be changed in-situ to a different one of the plurality of different pitch densification processes. In this way, an apparatus may adapt and respond to initial or changing properties of the material to be densified. As a result of the versatility of an apparatus configured to perform multiple pitch densification processes, improved C—C structural components may be formed with less attendant waste and component damage.

In some examples, a pitch densification apparatus may include a mold configured to receive both a preform (or other material to be densified) and a solid portion of pitch material. The apparatus may be configured to heat the solid portion of pitch material beyond the melting temperature of the pitch material within the mold. In some examples, the apparatus may also provide one or more pitch driving forces to further drive the melted pitch into the different pores of the material. By melting solid pitch in-situ, a low cost apparatus without external pitch melting equipment may be provided. Moreover, the amount of pitch provided to the material may be precisely controlled by eliminating transfer line loss and transfer line measuring inconsistencies associated with transferring melted pitch from a separate melt tank.

In one example according to the disclosure, an apparatus includes a mold configured to receive a material to be densified, a ram configured to apply a ram pressure to force a pitch into the mold to densify the material, a gas source configured to apply a gas pressure in the mold to force the pitch into the mold to densify the material, and a vacuum source operable to create a vacuum pressure in the mold at least prior to application of either the ram pressure or the gas pressure. According to the example, the apparatus is configured to densify the material in the mold using a selectable one of the ram, the gas source, the ram and the vacuum source, or the gas source and the vacuum source.

In another example according to the disclosure, an apparatus includes a mold configured to receive a brake disc preform, a ram configured to apply a ram pressure to force a melted pitch into the mold to densify the brake disc preform during at least one of a resin transfer molding cycle or a vacuum-assisted resin transfer molding cycle, an inert gas source configured to apply a gas pressure in the mold to force the melted pitch into the mold to densify the brake disc preform during a vacuum pressure infiltration cycle, and a vacuum source configured to create a vacuum pressure in the mold during at least one of the vacuum-assisted resin transfer molding cycle or the vacuum pressure infiltration cycle. According to the example, the apparatus is configured to densify the brake disc preform in the mold using a selectable one of the resin transfer molding cycle, the vacuum-assisted resin transfer molding cycle, or the vacuum pressure infiltration cycle.

In another example, a method is described that includes inserting a material to be densified into a mold, where the mold is part of an apparatus configured to densify the material using a selectable one of a resin transfer molding cycle, a vacuum-assisted resin transfer molding cycle, or a vacuum pressure infiltration cycle. The method includes selecting one of the resin transfer molding cycle, the vacuum-assisted resin transfer molding cycle, or the vacuum pressure infiltration cycle to densify the material in the mold, and densifying the material in the mold using the selected one of the resin transfer molding cycle, the vacuum-assisted resin transfer molding cycle, or the vacuum pressure infiltration cycle to densify the material to be densified.

In another example, an apparatus includes a mold configured to receive a preform and a solid pitch separate from the preform, a heating source thermally coupled to the mold, where the heating source is configured to heat the solid pitch above a melting temperature of the solid pitch within the mold to melt the solid pitch, and a gas source configured to apply a gas pressure in the mold to force melted pitch into the preform to densify the preform.

In another example, a method is described that includes inserting a preform into a mold, inserting a solid pitch into the mold, wherein the solid pitch is separate from the preform, heating the solid pitch to a temperature greater than a melting temperature of the solid pitch in the mold, densifying the preform within the mold by at least pressurizing the melted pitch.

In another example, a method is described that includes inserting a preform into a mold, where the mold is part of an apparatus configured to densify the preform using at least a vacuum pressure infiltration cycle, and inserting a solid pitch into the mold, where the solid pitch is separate from the preform, and wherein the solid pitch defines a shape substantially corresponding to a shape of the mold. The method also includes heating the solid pitch to a temperature greater than a melting temperature of the solid pitch within the mold, and densifying the preform within the mold using at least the vacuum pressure infiltration cycle to force melted pitch into the preform.

DETAILED DESCRIPTION

During fabrication of a C—C composite material component, a carbon-based fiber material may undergo multiple processing steps to arrange, strengthen, and densify the carbon-based fiber material into a formed component. In different examples, the carbon-based fiber material may be processed via chemical vapor deposition (CVD) to add carbon to the material, resin transfer molding (RTM) to impregnate the material with high pressure (e.g., between 500 psi and 3500 psi) pitch, or vacuum pressure infiltration (VPI) to impregnate the material with comparatively lower pressure (e.g., between 25 psi and 800 psi) pitch. In some examples, the carbon-based fiber material may be subject to a combination of these processes, or additional or different processes. For example, the carbon-based fiber material may be subject to CVD to strengthen the fibers with deposited carbon before the fibers are further subject to pitch densification using an RTM and/or VPI process.

In general, CVD may involve placing a carbon-based fiber material in a high temperature atmosphere with a carbon-containing precursor material for an extended period of time. As the carbon-based fiber material and the carbon-containing precursor material react and/or degrade, carbon is deposited on the carbon-based fiber material, strengthening the material and increasing the density of the material. In some examples, different processing parameters, e.g., different processing control tolerances or different material morphologies, result in inconsistent densities and strengths for different carbon-based fiber materials. For example, CVD may be simultaneously performed on multiple preforms of carbon-based fiber material within a CVD chamber. After the CVD process, each of the multiple preforms may exhibit some variance in density or strength from an average density or strength, with some preforms exhibiting characteristics farther from the average than other preforms. These differing characteristics may affect subsequent processing of the preforms.

A carbon-based fiber material may be subject to pitch densification in addition to, or in lieu of, CVD to densify the material. In a pitch densification process, a pitch is impregnated in the carbon-based fiber material. Different pitch densification processes generally involve different mechanical loading forces, e.g., associated with different pitch driving forces and different pressure gradients in the carbon-based fiber material associated with each particular process. If a carbon-based fiber material is not strong enough to withstand a particular pitch densification process, the carbon-based fiber material may shear apart or delaminate (e.g., in cases in which a carbon preform includes multiple layers) during the densification process, rendering the material unsuitable for forming a high-performance component. Further, if an incorrect amount of pitch is delivered to the carbon-based fiber material, the material may be under densified, also rendering the material unsuitable for forming a high-performance component.

In accordance with some examples described in this disclosure, a pitch densification apparatus may be configured to carry out a plurality of different processes for densifying a material with pitch. As described above, in some examples, an apparatus may be configured to densify a material using RTM, VPI, and VRTM. Each of these pitch densification processes is described further below. Such a pitch densification apparatus may use a variety of driving forces to impregnate a carbon-based fiber material with pitch within a mold of the apparatus. Example driving forces that may be used to impregnate a carbon-based fiber material with pitch within a mold of an apparatus include ram pressure, gas pressure, vacuum pressure, and combinations thereof.

As the example pitch densification apparatus is capable of impregnating a carbon-based fiber material with pitch using a variety of driving forces, the particular process or processes performed by the apparatus to densify a carbon-based fiber material with pitch may be tailored based one or more considerations. For example, in some cases, the strength of the carbon-based fiber material may be determined, e.g., by determining the density of the material, and the particular process or processes used to densify the respective material with pitch may be selected based at least in part of the strength of the material. In some examples, the strength of a material or other variable that may be useful in selecting the particular process may be determined by the apparatus. In other examples, the apparatus does not evaluate the strength of the carbon-based fiber material. For example, the strength of a material may be determined instead by an operator controlling the apparatus, and the operator may operate the apparatus to perform one or more pitch densification processes determined to be suitable based on the determined strength of the material.

In any event, by utilizing multiple types of pitch driving forces, the apparatus can tailor a particular pitch densification process to the specific carbon-based fiber material. For example, for carbon-based fiber materials with relatively low initial densities, the apparatus may densify the material using VPI. A material with a low initial density may have less mechanical strength than materials with higher initial densities. Yet VPI may apply comparatively less mechanical force to the material during densification than other types of densification processes such as, e.g., RTM or VRTM. Conversely, for carbon-based fiber materials with relatively high initial densities, the apparatus may densify the material using RTM or VRTM. A material with a high initial density may have more mechanical strength than materials with lower initial densities. Further, a cycle of RTM or VRTM may add more pitch to the pores of the material during densification, thus densifying the material to a greater extent than VPI. In some additional examples, the apparatus may use two or more pitch densification processes to densify a specific carbon-based fiber material. For example, for carbon-based fiber materials with relatively low initial densities, the apparatus may first densify the material using VPI to densify and strengthen the material. The strengthened material may then be further densified within the same mold of the apparatus using RTM and/or VRTM. RTM and/or VRTM may increase the density of the material more rapidly than using VPI alone. However, VPI may strengthen and initially densify the material to withstand the forces of RTM and/or VRTM. As a result, a carbon-based material may be effectively densified while reducing or eliminating damage to the material.

In accordance with some examples described in this disclosure, a pitch densification apparatus includes mold that houses a material to be densified and a solid portion of pitch material within a mold cavity. The apparatus is configured to heat the solid portion of pitch material beyond the melting temperature of the pitch material within the mold cavity. In some examples, the solid portion of pitch material defines a shape substantially conforming to a cross-sectional shape of the material to be densified. In some examples, the pitch densification apparatus is configured to provide one or more pitch driving forces to drive melted pitch into the pores of the material to be densified. As a result, a precise amount of pitch may be added to the material to be densified without the cost and complexity of an external pitch melt tank and conveyance system.

An example apparatus configured to densify a material using one or more of a plurality of different pitch densification techniques will be described in greater detail with reference toFIGS. 2-4. An associated example technique is described below with reference toFIG. 5. In addition, an example technique and an example apparatus configured to densify a material using a mold configured to receive a solid portion of pitch in combination with a carbon-based fiber material is be described in greater detail with reference toFIGS. 6-9. However, an example aircraft brake assembly that may include one or more C—C composite materials manufactured in accordance with examples of this disclosure will first be described with reference toFIG. 1.

FIG. 1is a conceptual diagram illustrating an example assembly that may include one or more C—C composite material components formed in accordance with the techniques of this disclosure. In particular,FIG. 1illustrates an aircraft brake assembly10, which includes wheel12, actuator assembly14, brake stack16, and axle18. Wheel12includes wheel hub20, wheel outrigger flange22, bead seats24A and24B, lug bolt26, and lug nut28. Actuator assembly14includes actuator housing30, actuator housing bolt32, and ram34. Brake stack16includes alternating rotor discs36and stators38, which move relative to each other. Rotor discs36are mounted to wheel12, and in particular wheel hub20, by beam keys40. Stator discs are mounted to axle18, and in particular torque tube42, by splines44. Wheel assembly10may support any variety of private, commercial, or military aircraft.

Wheel assembly10includes wheel18, which in the example ofFIG. 1is defined by a wheel hub20and a wheel outrigger flange22. Wheel outrigger flange22is mechanically affixed to wheel hub20by lug bolts26and lug nuts28. Wheel12defines bead seals24A and24B. During assembly, an inflatable tire (not shown) may be placed over wheel hub20and secured on an opposite side by wheel outrigger flange22. Thereafter, lug nuts28can be tightened on lug bolts26, and the inflatable tire can be inflated with bead seals24A and24B providing a hermetic seal for the inflatable tire.

Wheel assembly10may be mounted to an aircraft via torque tube42and axle18. In the example ofFIG. 1, torque tube42is affixed to axle18by a plurality of bolts46. Torque tube42supports actuator assembly14and stators38. Axle18may be mounted on a strut of a landing gear (not shown) to connect wheel assembly10to an aircraft.

During operation of the aircraft, braking may be necessary from time to time, such as during landing and taxiing. Accordingly, wheel assembly10may support braking through actuator assembly14and brake stack16. Actuator assembly14includes actuator housing30and ram34. Actuator assembly14may include different types of actuators such as, e.g., an electrical-mechanical actuator, a hydraulic actuator, a pneumatic actuator, or the like. During operation, ram34may extend away from actuator housing30to axially compress brake stack16against compression point48for braking.

Brake stack16includes alternating rotor discs36and stator discs38. Rotor discs36are mounted to wheel hub20for common rotation by beam keys40. Stator discs38are mounted to torque tube42for common rotation by splines44. In the example ofFIG. 1, brake stack16includes four rotors and five stators. However, a different number of rotors and/or stators may be included in brake stack16. Further, the relative positions of the rotors and stators may be reverse, e.g., such that rotor discs36are mounted to torque tube42and stator discs38are mounted to wheel hub20.

Rotor discs36and stator discs38may provide opposing friction surfaces for braking an aircraft. As kinetic energy of a moving aircraft is transferred into thermal energy in brake stack16, temperatures may rapidly increase in brake stack16, e.g., beyond 200 degrees Celsius. With some aircraft, emergency braking may result in temperatures in excess of 500 degrees Celsius, and in some cases, even beyond 800 degrees Celsius. As such, rotor discs36and stator discs38that form brake stack16may include robust, thermally stable materials capable of operating at such temperatures. In one example, rotor discs36and stator discs38are formed of a metal alloy such as, e.g., a super alloy based on Ni, Co, Fe, or the like.

In another example, rotor discs36and/or stator discs38are formed of a C—C composite material fabricated according to one or more example techniques of this disclosure. In particular, at least one of rotor discs36and/or at least one of stator discs38may be formed from a carbon-based fiber material fabricated using a pitch densification apparatus, where the apparatus is capable of densifying the material using one or more of a plurality of different pitch densification processes. In some examples, at least one of rotor discs36and/or at least one of stator discs38may be formed using an example apparatus that includes a mold configured to receive both material to be densified and a solid portion of pitch material. By using an example apparatus according to this disclosure, a C—C composite component may be formed that defines a general shape of a rotor disc or stator disc.

Independent of the specific material chosen, rotor discs36and stator discs38may be formed of the same materials or different materials. For example, wheel assembly10may includes metal rotor discs36and C—C composite stator discs38, or vice versa. Further, each disc of the rotor discs36and/or each disc of the stator discs38may be formed of the same materials or at least one disc of rotor discs36and/or stator discs38may be formed of a different material than at least one other disc of the rotor discs36and/or stator discs38.

As briefly noted, rotor discs36and stator discs38may be mounted in wheel assembly10by beam keys40and splines44, respectively. Beam keys42may be circumferentially spaced about an inner portion of wheel hub20. Beam keys may be shaped with opposing ends (e.g., opposite sides of a rectangular) and may have one end mechanically affixed to an inner portion of wheel hub20and an opposite end mechanically affixed to an outer portion of wheel hub20. Beam keys42may be integrally formed with wheel hub20or may be separate from and mechanically affixed to wheel hub20, e.g., to provide a thermal barrier between rotor discs36and wheel hub20. Toward that end, in different examples, wheel assembly10may include a heat shield (not shown) that extends out radially and outwardly surrounds brake stack16, e.g., to limit thermal transfer between brake stack16and wheel12.

Splines44may be circumferentially spaced about an outer portion of torque tube42. Splines44may be integrally formed with torque tube42or may be separate from and mechanically affixed to torque tube42. In some examples, splines44may define lateral grooves in torque tube42. As such, stator discs38may include a plurality of radially inwardly disposed notches configured to be inserted into a spline.

Because beam keys40and splines44may be in thermal contact with rotor discs36and stator discs38, respectively, beam keys40and/or splines44may be made of thermally stable materials including, e.g., those materials discussed above with respect to rotor discs36and stator discs38. Accordingly, in some examples, example techniques of the disclosure may be used to form a beam key and/or spline for wheel assembly10. For example, a pitch densification apparatus, such as, e.g., apparatus50(FIG. 2), that is configured to densify a material using one or more of a plurality of different pitch densification cycles, may be used to form a C—C composite component that defines a general shape of beam key40and/or spline44. In some examples, a pitch densification apparatus, such as, e.g., apparatus300(FIG. 6), that includes a mold configured to receive both material to be densified and a solid portion of pitch material, may be used to form a C—C composite component that defines a general shape of beam key40or spline44.

FIG. 2is a conceptual block diagram illustrating an example pitch densification apparatus50. Apparatus50is configured to densify a material using one or more of a plurality of different pitch densification techniques. In particular, apparatus50is configured to densify a material via one or more of a resin transfer molding (RTM) process (represented inFIG. 2as resin transfer molding module58), a vacuum-assisted resin transfer molding (VRTM) process (represented inFIG. 2as vacuum-assisted resin transfer molding module60), and/or a vacuum pressure infiltration (VPI) process (represented inFIG. 2as vacuum pressure infiltration module62). In general, RTM module58, VRTM module60, and VPI module62are representative inFIG. 2of the various structural features and components in apparatus50that allow apparatus50to perform each of the respective processes to densify preform52. Examples of the structural features and components represented by RTM module58, VRTM module60, and VPU module62include those described herein with regard to each respective process.

However, while RTM module58, VRTM module60, and VPI module62are shown inFIG. 2as being separate from one another, it is contemplated that certain structural features and components of apparatus50may be utilized to perform more than one of the described processes. That is, while RTM module58, VRTM module60, and VPI module62are shown separately, components and structural features of apparatus50that allow for the respective processes to be performed are not necessarily exclusive to one or more process. In some examples, certain components and structural features of apparatus50may be used to perform two or more of RTM, VRTM, and VPI. As described below, in some examples, the combination of RTM module58, VRTM module60, and VPU module62include a ram to apply a ram pressure, a gas source to apply a gas pressure, and a vacuum source to create vacuum pressure selectively all within mold54to impregnate a material such as preform52with pitch.

Apparatus50includes mold54, which defines one or more mold cavities55that houses preform52(or other carbon-based material) to be densified by apparatus50. In some examples, preform52defines a shape corresponding to a shape of a finished component prior to being inserted into mold54. During operation of apparatus50, pitch56is pressurized in mold cavity55of mold54to fill the pores of preform52. In some examples, melted pitch56is conveyed into mold cavity55of mold54during operation of apparatus50to densify preform52. In other examples, as described in greater detail below, solid pitch may be inserted into mold cavity55of mold54at the beginning of a pitch densification cycle along with preform52. In either set of examples, apparatus may selectively pressurize the pitch in mold cavity55using one or more of RTM module58, VRTM module60, and VPI module62. In this manner, apparatus50may be used to increase the density of preform52by impregnating preform52with pitch to form a C—C composite component.

In general, C—C composite components include carbon materials reinforced in a carbon matrix. Accordingly, preform52or other materials densified by apparatus50may include, but are not limited to, woven and non-woven carbon-based fiber materials. The carbon-based fiber materials may, in some examples, be straight, chopped, granular, or otherwise shaped. In some examples, the carbon-based fiber materials may include a polyacrilonitrile (PAN) fiber. In other examples, the carbon-based fiber materials may include carbon fibers, pitch fibers, or combinations of the aforementioned fibers.

Prior to being inserted into apparatus50for densification, the material to densified within apparatus50may undergo processing to prepare the material for densification. According to one example, the material may be processed into preform52prior to being inserted into cavity55of mold54. Preform52may define a general shape of a desired finished component. For example, preform52may define a general shape of rotor disc36, stator disc38, beam key40, or another component of aircraft brake assembly10(FIG. 1). The shape may be a generally two-dimensional shape defined by a single layer of carbon-based fiber material. Alternatively, the shape may be a three-dimensional shape. For example, a plurality of layers of carbon-based fiber material may be stacked on top of one another to define a three-dimensionally shaped working piece.

In some examples, the working piece may be needled in a direction generally orthogonal to each of the plurality of layers to entangle fibers between layers. For example, the working piece may be subject to mechanical needling or hydroentanglement to entangle fibers between layers. In this manner, the working piece may be axially strengthened between different layers of the multilayer piece. The working piece may then be cut to define a preformed shape corresponding to that of a desired finished component. Alternatively, different layers of the multilayer preform may be cut prior to assembly, and the different layers may be combined to define a preformed shaped. In either case, the material to be densified may be processed to form preform52prior to being inserted into mold cavity55for pitch densification.

As another example of a processing step that may be performed on preform52or another material prior to being inserted into mold cavity55, preform52may undergo one or more cycles of chemical vapor deposition. Prior to or after being processed into preform52, the material that forms preform52may undergo chemical vapor deposition to strengthen and initially densify the material in preparation for further processing on apparatus50. In general, chemical vapor deposition (CVD), which may also be referred to as chemical vapor infiltration (CVI), involves placing preform52in a high temperature atmosphere with a carbon-containing precursor material for an extended period of time. In some examples, preform52may be placed in an oven operating under a blanket of inert gas, e.g., to prevent premature oxidation of preform52. After the oven reaches a suitable temperature, e.g., between 850 degrees Celsius and 1250 degrees Celsius, the inert gas may be replaced with a carbon-bearing gas. Example gases include, but are not limited to, methane, ethane, propane, butane, propylene, acetylene, and combinations thereof. As the hydrocarbon gas flows around and through the porous structure of preform52, a series of dehydrogenation, condensation, and/or polymerization reactions may occur, depositing carbon atoms on and through the surfaces of preform52. As the number of carbon atoms deposited on preform52increase, the fibers of preform52may strengthen and the density of preform52may increase.

In some examples, preform52may exhibit a density before chemical vapor deposition between approximately 0.4 grams per cubic centimeter (g/cc) and approximately 0.6 g/cc. After a cycle of chemical vapor deposition, preform52may exhibit a density between approximately 0.9 g/cc and approximately 1.45 g/cc. Different initial and post-processing densities are possible, however. In general, a cycle of chemical vapor deposition may be defined as a single densification during which perform52is infiltrated with pitch under one defined set of conditions (e.g., gas flow rates, temperature, time, etc.). While preform52may undergo multiple cycles of chemical vapor deposition, e.g., both before and/or after using apparatus50, each cycle of chemical vapor deposition may last an extended period of time. In some examples, a cycle of chemical vapor deposition may last between one and five weeks.

Regardless of the particular preprocessing steps used, preform52may be inserted into mold cavity55defined by mold54prior to being densified in apparatus50using RTM module58, VRTM module60, and/or VPI module62. Mold cavity55may define a shape generally corresponding to a shape of a desired finished C—C composite component. For example, mold54may define mold cavity55that has a shape generally corresponding to a shape of preform52. Mold54may include different ports for receiving pitch56in cavity55, venting air forced out of the pores of the material by pitch56, receiving pressurized gas, evacuating gas to create a vacuum pressure, or the like. During operation of apparatus50, preform52may be constrained within mold cavity55along with pressurized pitch56. In some examples, mold54may be separate from and insertable into apparatus50. In other examples, mold54may be integrally formed with apparatus50.

After being inserted into mold cavity55of mold54, apparatus50may densify preform52by impregnating preform52with pitch56. Pitch56may be a hydrocarbon-rich material that may be extracted, e.g., from coal tar and petroleum. Pitch56may also be synthetically produced. In different examples, pitch56may come from a single source (e.g., coal) or may be a combination of different pitches from different sources. In some examples, pitch56may be a mesophase pitch. In other examples, pitch56may be an isotropic pitch. Combinations of mesophase and isotropic pitches are also contemplated.

Pitch56may have a melting temperature greater than typical ambient temperatures. As such, pitch56may be heated to a flowable state prior to densification of preform52. In some examples, as described in greater detail below with respect toFIG. 6, pitch56may be added to apparatus50, and in particular mold cavity55of mold54, in a solid state along with preform52and then heated above the melting temperature in apparatus50during densification. In other examples, as described in greater detail below with respect toFIG. 3, pitch56may be heated above the melting temperature separately from apparatus50and conveyed into mold cavity55of apparatus50as a melted pitch. In some examples, pitch56may be heated to a temperature between approximately 200 degrees Celsius and approximately 450 degrees Celsius such as, e.g., between approximately 275 degrees Celsius and approximately 330 degrees Celsius to melt into a flowable state.

Apparatus50in the example ofFIG. 2is configured to densify preform52using a variety of pitch densification techniques. According to one technique, apparatus50is configured to densify preform52with pitch56using at least one cycle of RTM via RTM module58. In general, a cycle of RTM involves injecting pressurized pitch56into mold cavity55through one or more injection port defined in mold54. As described in greater detail below with respect toFIG. 3, during a RTM cycle, pitch56is pressurized using a ram such as, e.g., a piston or plunger. During a RTM cycle, a backstroke of the ram may create a vacuum that draws melted pitch56into a ram cavity. Alternatively, a ram cavity may be forcibly loaded with melted pitch, e.g., using an extruder screw. In either case, a forward stroke of the ram may apply a ram pressure, pressurizing pitch56and forcing pitch56into mold cavity55of mold54. The pressurized pitch56may travel through channels into mold cavity55of mold54, displacing air in mold cavity55and the pores of preform52. In this manner, preform52may be impregnated with pitch56by RTM, thereby increasing the density of preform52.

The operating pressure during a RTM cycle may be relatively high compared to other pitch densification processes provided by apparatus50, such as, e.g., a VRTM molding cycle and/or a VPI cycle. In some examples, a RTM cycle may involve a ram pressure (i.e., the amount of pressure that pitch56is pressurized to using a ram to force pitch56into mold cavity55of mold54) between approximately 100 pounds per square inch (psi) and approximately 5000 psi, such as, e.g., between approximately 500 psi and approximately 3500 psi.

A high pressure RTM cycle may effectively cause pitch56to infiltrate and impregnate the various pores of preform52. For example, before a RTM cycle, preform52may exhibit a density between approximately 1.0 g/cc and approximately 1.5 g/cc. After a cycle of RTM, however, preform52may exhibit a density between approximately 1.6 g/cc and approximately 1.8 g/cc, where a cycle of resin transfer molding may be defined as a single densification during which perform52is infiltrated with pitch under one defined set of conditions (e.g., gas flow rates, temperature, time, etc.). Further, densification via RTM within apparatus50may be rapid, e.g., compared to VRTM and/or VPI, in some cases lasting less than approximately 10 minutes such as, e.g., less than approximately 3 minutes per cycle. For example, when preform52exhibits small pore sizes, RTM may be able to drive pitch56into preform52at a faster rate than VRTM and/or VPI. However, if preform52is structurally weak prior to densification via apparatus50, the high pressure pitch56associated with a RTM cycle may result in the destruction of preform52, or damage to the structure of preform52, during densification. Without being bound by any particular theory, it is believed that as pitch56initially infiltrates preform52, a pressure gradient is created across preform52. The pressure gradient may cause internal stresses within preform52. If preform52is not strong enough to accommodate the internal stresses, all or sections of preform52may shear or different layers of preform52may delaminate, destroying the shape and mechanical strength of preform52. The internal stresses created within preform52may increase as the pressure of pitch56increases.

Therefore, to accommodate preforms with different types of properties, apparatus50may be configured to densify preform52using different densification techniques in addition to, or in lieu of, RTM. For example, apparatus50may densify preform52using one or more VRTM cycles via VRTM module60. A VRTM cycle may be considered a form of RTM cycle in which a vacuum pressure is created in mold cavity55of mold54at least prior to the beginning of the RTM cycle. By creating a vacuum pressure in mold cavity55of mold54at least prior to the beginning of RTM, the ram pressure required to densify preform52with pitch56during the RTM cycle may, in some examples, be lowered as compared to when vacuum pressure is not created in mold cavity55of mold54. Again not wishing to be bound by any particular theory, it is believed that air in mold cavity55of mold54, and in particular the pores of preform52, may create backpressure inhibiting the free flow of pitch56during densification. This backpressure may exacerbate a pressure gradient across preform52when initially injecting pitch into preform52. By creating a vacuum in mold cavity55of mold54at least prior to injecting pitch56into mold cavity55of mold54during a RTM cycle, a lower ram pressure may be accommodated while still suitably impregnating preform52with pitch56. Moreover, by creating a vacuum in mold cavity55at least prior to injecting pitch56into mold cavity55, the pores of preform52may be opened and air bubbles may be removed from preform52, allowing preform52to be densified while reducing or eliminating the possibility of damage (e.g., delamination) to preform52during the RTM portion of the VRTM cycle.

In some examples, a VRTM cycle may include reducing the pressure in mold cavity55to between approximately 1 torr and approximately 100 torr, such as, e.g., between approximately 10 torr and approximately 20 torr. In some examples, a RTM cycle performed after reducing the pressure in mold54may involve a ram pressure between approximately 500 psi and approximately 3500 psi, such as between approximately 750 psi and approximately 2000 psi, or between approximately 800 psi and approximately 1000 psi. Other pressures are contemplated, however, and the disclosure is not limited in this respect.

By first reducing the pressure in mold cavity55and then forcibly injecting pitch into mold cavity55, preform50may be densified with pitch. As with a RTM cycle, preform52may exhibit a density between approximately 0.9 g/cc and approximately 1.4 g/cc before densification. After a VRTM cycle, however, preform52may exhibit a density between approximately 1.5 g/cc and approximately 1.7 g/cc, where a cycle of VRTM may be defined as a single densification during which perform52is infiltrated with pitch under one defined set of conditions (e.g., gas flow rates, temperature, time, etc.).

As another pitch densification technique, apparatus50may be configured to perform one or more cycles of VPI via VPI module62. During a VPI cycle, mold cavity55may be reduced to vacuum pressure to evacuate the pores of preform52. In some examples, a vacuum pressure between approximately 1 torr and approximately 100 torr, such as, e.g., between approximately 10 torr and approximately 20 torr may be created. With the pores of preform52ready to receive pitch56, mold cavity55may be flooded with pitch56. In examples where a portion of solid pitch is provided in mold cavity55, as will be described with reference toFIG. 6, flooding may be accomplished by heating pitch56above the melting temperature of pitch56. In examples where pitch56is conveyed to mold54in a flowable state, as will be described with reference toFIG. 3, flooding may be accomplished, e.g., by pressurizing a tank of pitch56, mechanically conveying pitch56, or allowing a vacuum pressure in mold cavity55to draw pitch56into mold cavity55to begin infiltrating preform52. After flooding, a gas such as, e.g., an inert nitrogen gas, can be used to pressurize pitch56in mold cavity55. In some examples, a gas pressure between approximately 10 pounds per square inch (psi) and approximately 1000 psi, such as, e.g., between approximately 300 psi and approximately 700 psi may be used. Pressurization may help pitch56travel through the different pores of preform52. In this manner, apparatus50may be used to density a material through one or more cycles of VPI.

In some examples, preform52may exhibit a density between approximately 0.4 g/cc and approximately 0.6 g/cc prior to densification. On the other hand, after a VPI cycle, preform52may, in some examples, exhibit a density between approximately 1.5 g/cc and approximately 1.8 g/cc. A cycle of vacuum pressure infiltration (62) may be defined as a single densification during which perform52is infiltrated with pitch under one defined set of conditions (e.g., gas flow rates, temperature, time, etc.).

Because a VPI cycle does not include the use of ram pressure to drive pitch56into preform52, the densification cycle may be gentler on preform52compared to other types of densification cycles such as RTM and VRTM. This may provide versatility by allowing apparatus50to process preforms exhibiting different types of physical characteristics. For example, a VPI cycle may be performed on a preform52that does not undergo a chemical vapor deposition strengthening process prior to being densified on apparatus50. As another example, VPI cycle may be used on a preform52that is not suitably strengthened during a chemical vapor deposition process. In other words, a comparatively preform52may be densified using one or more VPI cycles. Additional uses are contemplated for vacuum pressure infiltration cycle.

In general, apparatus50may densify preform52with pitch within mold cavity55using one or more of RTM module58, VRTM module60, and VPI module62. In some instances, apparatus50may densify preform52with pitch to a desired density using one or more cycles of the same process (i.e., one of RTM, VRTM, and VPI). Following the densification of preform52, another preform may be inserted in mold cavity55and apparatus50may densify the another preform with pitch to a desired density using one or more cycles of the same process, where the process is different from that used to densify the preceding preform52. For example, apparatus50may densify the another preform using VRTM or VPI, when the preceeding preform52was densified with RTM. In this manner, apparatus50embodies a single apparatus that is capable of performing all of RTM, VRTM, and VPI to densify preform52within mold54, e.g., rather than requiring three individual apparatuses to carry out each of the respective pitch densification processes. In some examples, apparatus50may densify preform52using two or more of RTM, VRTM, and VPI. For example, after being inserted into mold cavity55, apparatus50may perform one or more cycles of VPI to densify preform52to a desired density followed by one or more cycles of RTM and/or VRTM to further densify preform52. Alternative combinations of RTM, VRTM, and VPI are possible to densify preform52, as will be appreciated by those of skill in the art.

By providing different types of pitch densification driving forces, apparatus50may be able to densify preforms with a range of different characteristics. In some examples, selection of one or more of RTM, VRTM, and VPI cycles may be based on an initial density of preform52prior to densification within apparatus50. As described above, the initial density of preform52may be indicative of an initial strength of preform52. Further, preform strength may indicate the ability of a specific preform to withstand a specific densification technique without substantiating structural damage.

The strength of preform52may vary, e.g., based on the specific materials and processing steps used to form preform52. The forces associated with a specific densification technique may also vary, e.g., based on the specific densification apparatus used and the specific processing parameters selected. However, in some examples, preform52may be able to withstand the forces of associated with RTM if preform52has an initial density greater than or equal to 1.0 g/cc. In some examples, preform52may be able to withstand the forces of associated with VRTM if preform52has an initial density between approximately 0.8 g/cc and approximately 1.0 g/cc. In some further examples, preform52may be able to withstand the forces of associated with VPI even if preform52exhibits a density less than or equal 0.8 g/cc such as, e.g., less than approximately 0.5 g/cc. These density values may vary based on a variety of factors such as, e.g., the overall volume of preform52, however, and it should be appreciated that the disclosure is not limited in this regard.

In some examples, the density of preform52may be determined external to apparatus50and a particular densification cycle (RTM, VRTM, or VPI) may be selected based on the externally determined density, e.g., by operator entry. In other examples, however, apparatus50may include processor59that determines a density of preform52and automatically select one or more of RTM, VRTM, and/or VPI cycles based on the determined density of preform52. In one example, apparatus50may include a scale (not shown) that weighs preform52within cavity55. The volume of preform52may be separately entered into apparatus50, e.g., by an operator, and processor59of apparatus50may determine the density based on the entered volume and the measured weight from the scale. In another example, apparatus50may include instrumentation to determine both a weight and volume of preform52, and processor59of apparatus50may receive measured data and determine a density of preform52. In additional examples, processor59of apparatus50may be communicatively coupled to different instrumentation of apparatus50such as, e.g., a density meter, to determine the density of preform52.

Independent of the process used by apparatus50to determine the density of preform52, processor59of apparatus50may compare the determined density to one or more threshold density values stored in memory61associated apparatus50. In some examples, the threshold density values may correspond to different density thresholds that allow preform52to withstand a force associated with of one or more of RTM, VRTM, and VPI, as discussed above. Based on the comparison, processor59of apparatus50may select a specific densification cycle to densify preform52with pitch within cavity55.

FIG. 3is a schematic diagram illustrating an example pitch densification apparatus100. Pitch densification apparatus100is configured to densify a material using one or more of a plurality of different pitch densification techniques. Apparatus100is an example of apparatus50(FIG. 2) and illustrates various components that may be included in apparatus50and configured to densify preform52with RTM, VRTM, and VPI. In the example ofFIG. 3, apparatus100is connected to a separate pitch melt apparatus102, which supplies melted pitch to apparatus100during a pitch densification cycles. In different examples, however, apparatus100may include an integrated pitch melt system or, as described in greater detail below with respect toFIG. 6, a portion of solid pitch may be placed in the mold of apparatus100.

In general, press platens104A and104B apply pressure from opposing directions to constrain the various features of apparatus100during a pitch densification cycle. One or both of press platens104A and104B may move in the Z-direction illustrated onFIG. 3to allow mold114to open at a mold parting line sealed by mold parting seal160, e.g., to insert or remove preform113from mold cavity115of apparatus100. Press platens104A and104B may be integrally formed (i.e., permanently connected) with other features of apparatus100, or press platens104A and104B may be separate features, as illustrated inFIG. 3. In other words, press platens104A and104B may be purpose-built or may be part of a standard press to which other components of apparatus100are added.

Press platen104A and104B are connected to bolster106and clamp plate108B, respectively. In turn, bolster106is connected to clamp plate108A, while clamp plate108B is connected to bolster ejector plate116. In general, bolster106and bolster ejector plate116may function to define cavities for receiving and housing various features of apparatus100. For example, bolster106defines a cavity to receive ram cylinder106and bolster ejector plate116defines cavities to receive ejector pins118. Bolster106and bolster ejector plate116may protect the various features from the pressing force of press platens104A and104B during operation of apparatus100.

Clamp plates108A is interposed between bolster106and backing plate110. Clamp plate108B, by contrast, is interposed between bolster ejector plate116and insulating plate112B. Clamp plates108A and108B function to clamp different features of apparatus100from moving out of alignment.

Apparatus100includes backing plate110interposed between clamp plate108A and insulating plate112A. Backing plate110defines cavities for receiving and housing various features of apparatus100. For example, backing plate110defines a cavity to receive pitch pressurization ram122, vacuum line control cylinder124, vacuum line control rod126, gas feed control cylinder130, gas control rod132, pitch feed control cylinder134, and pitch control rod136. Backing plate110may protect the different features from the pressing force of press platens104A and104B during operation of apparatus100.

Mold114is located between insulating plates112A and112B. Insulating plates112A and112B may limit thermal transfer away from mold114, e.g., to help mold114retain heat during a pitch densification operation. Accordingly, insulating plates112A and112B may, in some examples, be formed from a low thermal conductivity material. To further limit thermal transfer away from mold114, connection lines extending between mold114and other features of apparatus100may, in some examples, be provided with insulating seals162, as shown inFIG. 3. Insulating seals162may prevent thermal transfer through openings in insulating plates112A and112B.

Mold114is configured to receive a material to be densified, such as, e.g., preform113, by apparatus100. Mold114is an example of mold54(FIG. 2). Mold114defines one or more mold cavities115that house preform113(or other carbon material) to be densified. Mold114may be formed of soft tooling materials such as, e.g., a polyester or an epoxy polymer. Alternatively, mold114may be formed of hard tooling materials such as, e.g., cast or machined aluminum, nickel, steel, titanium, or the like. Mold114may define different channels for conveying pitch, venting air, drawing a vacuum, receiving pressurized gas, or the like to mold cavity115.

During one or more pitch densification cycles, a vacuum pressure may be created in mold cavity115for at least part of the densification cycle. Accordingly, apparatus100may include vacuum hardware connectable to a vacuum source to create a vacuum pressure in mold cavity115. In the example ofFIG. 3, vacuum hardware is provided by vacuum line control cylinder124, vacuum line control rod126, and vacuum port128. Vacuum port128provides a connection point between vacuum source125, which is operable to create a vacuum in mold114, and in particular mold cavity115, that contains preform113. Vacuum line control cylinder124is connected to vacuum line control rod126. In operation, vacuum line control rod126may be controllably actuated in the Z-direction shown onFIG. 3to selectively place vacuum source125in pressure communication with mold cavity115, thereby controlling a vacuum pressure created in mold cavity115. In different examples, vacuum line control cylinder124may be a single acting cylinder, which uses a compressible fluid to actuate vacuum line control rod126in one direction and a spring to return vacuum line control rod126to a return position, or a double acting cylinder, which uses a compressible fluid to both extend and return vacuum line control rod126. In different assemblies according to the disclosure different vacuum control hardware may be used, and the disclosure is not limited in this respect.

From time to time, a pressurized gas may be applied to pitch in mold cavity115to help densify preform113, e.g., during a VPI cycle. To control the pressurized gas, apparatus100may include gas control hardware connected to a pressurized gas source. In the example ofFIG. 3, for instance, apparatus100includes gas feed control cylinder130, gas control rod132, and gas port133. Gas port133connects gas source129, which supplies pressurized gas, to mold cavity115that contains preform113. In various examples, gas source129may be a source of pressurized inert gas including, but not limited to, nitrogen, helium, argon, carbon dioxide, or the like. Gas control rod132is connected to gas feed control cylinder130. In operation, gas control rod132may be controllably actuated in the Z-direction shown onFIG. 3to selectively place gas source129in fluid communication with mold cavity115, thereby controlling a gas pressure created in mold cavity115. In different examples, gas feed control cylinder130may be a single acting cylinder or a double acting cylinder, as discussed above with respect to vacuum line control cylinder124. Further, as similarly discussed above with respect to the vacuum control hardware in apparatus100, in different assemblies according to the disclosure, different features may be used to control pressurized gas flow to mold cavity115, and the disclosure is not limited in this respect.

In addition to or in lieu of using pressurized gas to pressurize pitch in mold cavity115, apparatus100may use pitch pressurization ram122to pressurize a pitch in mold cavity115, e.g., during a RTM cycle. Pitch pressurization ram122may be a piston, plunger, or other device for applying a mechanical compression force to pitch. Pitch pressurization ram122is shown in an extended state inFIG. 3. In operation, pitch pressurization ram122may be controllably actuated back and forth in the Z-direction shown onFIG. 3. Upon being retracted, pitch pressurization ram122may define a ram cavity for receiving pitch. Pitch may be loaded into the ram cavity using a variety of loading forces including, e.g., a vacuum created by retracting pitch pressurization ram122or a pressure differential between pitch tank142and the ram cavity. In any event, upon loading the ram cavity, pitch pressurization ram122may be actuated forward (extended) to pressurize pitch in the ram cavity, injecting the pitch through a pitch injection port in mold114(not shown inFIG. 3).

Pitch pressurization ram122is connected to ram cylinder120. Ram cylinder120functions to actuate pitch pressurization ram122. Ram cylinder120extends through bolster106, clamp plate108A, insulating place112A, and mold114. In some examples, ram cylinder120may be a pneumatic cylinder for converting pneumatic power into mechanical power for actuating pitch pressurization ram122. In other examples, ram cylinder120may be a hydraulic cylinder for converting hydraulic power into mechanical power for actuating pitch pressurization ram122. In yet further examples, ram cylinder120may be replaced by a different mechanical actuating force such as, e.g., a ball and screw arrangement.

To control pitch delivery to mold cavity115, apparatus100may also include pitch flow control features. For example, apparatus100includes pitch feed control cylinder134, pitch control rod136, and pitch port137. Pitch port137provides a connection point between pitch tank142and mold cavity115that contains preform113. Pitch control rod136is connected to pitch feed control cylinder134. In operation, pitch control rod136may be controllably actuated in the Z-direction shown onFIG. 3to selectively place pitch tank142in fluid communication a ram cavity (i.e., a void area created be retracting ram122), which in turn is in fluid communication with mold cavity115. In this manner, the flow of pitch to mold cavity115may be controlled. In different examples, pitch feed control cylinder134may be a single acting cylinder or a double acting cylinder, as discussed above with respect to vacuum line control cylinder124and gas fee control cylinder130. Further, as also noted above with respect to the vacuum control features and the gas control features in apparatus100, in different assemblies according to the disclosure, different features may be used to control pitch flow to mold114, and the disclosure is not limited in this respect.

In the example ofFIG. 3, pitch melt apparatus102supplies pitch port137with melted pitch. Pitch melt apparatus102includes pitch tank142, pitch feed inlet144, temperature control jacket146, and pitch liquefaction system148. Pitch discharge valve140connects pitch melt apparatus102to pitch port137of mold114. Pitch tank142may receive solid pitch through pitch feed inlet144. In some examples, temperate control jacket146may heat pitch tank142. In other examples, pitch tank142may be heated using additional or different heating elements, such as, e.g., direct tank heating or internal tank heat coils. Pitch may liquefy as pitch tank142is heated above the melting point of the pitch in the tank.

After densifying preform113, pressure may be released from press platens104A and104B to allow mold114to be opened. In some examples, mold114may be removed from apparatus100before opening the mold to extract a densified preform113. In other examples, a portion of mold114may be opened while mold114resides in apparatus100. For example, inFIG. 3, mold114may be opened in apparatus100on a parting line sealed by parting seal160. To facilitate removal of a densified preform113in these examples, apparatus100may include ejector pins118. Ejector pins118may be controllably actuated in the Z-direction shown inFIG. 3to help eject preform113from mold114.

In operation, apparatus100may be used to densify preform113in the same mold cavity115of mold114using one or more of a RTM cycle, a VPI cycle, a VRTM cycle, or combinations of these cycles, as described above with respect to apparatus50inFIG. 2. For example, apparatus100may densify preform113in mold cavity115via a RTM cycle. During a RTM cycle, preform113may be placed into mold cavity115. Mold114may then be compressed between press platens104A and104B to seal mold cavity115for the densification cycle. Pitch may be melted by pitch melt apparatus102, and in particular pitch tank104, with heat supplied from temperature control jacket146. Upon actuating pitch pressurization ram122into a retracted position, pitch discharge valve140may be opened and pitch feed control cylinder134may be controlled to actuate pitch control rod136, thereby placing pitch tank142in fluid communication with a cavity created by the retracted pitch pressurization ram122. After filling the ram cavity with pitch, pitch pressurization ram122may be actuated forward to apply a ram pressure to force pitch into mold cavity115. As pitch enters mold cavity115, air in the pores of preform113may evacuate, e.g., through vacuum port128or a separate vent port on mold114(not shown inFIG. 3). In this manner, preform113may be pitch densified via a RTM cycle within mold cavity115of apparatus100.

Apparatus100may also be used to densify preform113using a VRTM molding cycle, as described with respect toFIG. 2. In a VRTM cycle, preform113may be placed into mold cavity115and pitch may be melted in pitch melt apparatus102, as described above with respect to a RTM cycle. A pressure in mold cavity115may be reduced to vacuum by controlling vacuum line control cylinder124to actuate vacuum line control rod126. Upon actuating vacuum line control rod126, mold cavity115may be placed in pressure communication with vacuum source125through vacuum port128. Pitch pressurization ram122may be retracted and a cavity created by the retracted pitch pressurization ram122filled with pitch. Thereafter, pitch pressurization ram122may be actuated forward to pressurize pitch in the ram cavity, injecting the pitch through a pitch injection port into mold cavity115and into the vacuum pressure conditions previously established in mold114. In this manner, preform113may be pitch densified via a VRTM cycle within mold cavity115of apparatus100.

Apparatus100may also be used to densify preform113using a VPI cycle, as also discussed with respect toFIG. 2. In a VPI cycle, preform113may be placed into mold cavity115and pitch may be melted in pitch melt apparatus102, as described above with respect to a RTM cycle. A pressure in mold cavity115may be reduced to vacuum by controlling vacuum line control cylinder124to actuate vacuum line control rod126. Upon actuating vacuum line control rod126, mold cavity115may be placed in pressure communication with vacuum source125through vacuum port128. Pitch pressurization ram122may be retracted and a cavity created by the retracted pitch pressurization ram122filled with pitch. As the cavity created by the retracted pitch pressurization ram122is in fluid communication with mold cavity115(e.g., through a pitch injection port in mold114not shown inFIG. 3) the vacuum in mold cavity115may draw the pitch from the ram cavity into mold cavity115, thereby filling mold cavity115with pitch. With mold cavity115filled with pitch, vacuum line control cylinder124may be controlled to actuate vacuum line control rod126to close vacuum port128. Thereafter, gas feed control cylinder130can be controlled to actuate gas control rod132. Gas control rod132can actuate to open gas port133, placing mold cavity115housing preform113in communication with pressurized gas source129. In this manner, preform113may be pitch densified via a VPI cycle within mold cavity115of apparatus100.

With the example features described above, apparatus100is configured to pitch density a preform using at least one of a RTM cycle, a VRTM cycle, or a VPI cycle. As described above with respect to apparatus50(FIG. 2), a specific pitch densification cycle may be selected for apparatus100based on an initial density of preform113. In some examples, apparatus100may be configured to determine a density of preform113and automatically select a specific pitch densification cycle based on the determined density. Accordingly, apparatus100may include a scale (e.g., load cell) and/or any additional features to determine the weight, volume, or density of preform113.

Apparatus100, as outlined above, may include features for pitch densifying a carbon-based fiber preform using a pitch densification cycle selected from a plurality of different pitch densification cycles. As shown, apparatus100may be a modular assembly configured to be used with standard press platen104A and104B. That is, apparatus100may include different modular components configured to be assembled and inserted between press platens to form apparatus100. In different examples, however, apparatus100may include different modular components or non-modular components in addition to or in lieu of the components illustrated and described with respect toFIG. 3. Therefore, although apparatus100includes various example components, different configuration are contemplated.

As an example of the additional or different features that may be included in an apparatus according to the disclosure,FIG. 4is a schematic diagram illustrating an example of apparatus100(FIG. 3) with example thermal management features for controlling the temperature of mold114. Because pitch is generally solid at ambient temperatures, an apparatus that includes thermal management features may help melt pitch or keep pitch in a flowable state until pitch suitably permeates the various pores of preform113. In other words, in examples where pitch is externally melted and conveyed to mold114, as shown inFIG. 4, thermal management features may help keep the pitch in a flowable state until the pitch infiltrates the pores of preform113within mold cavity115. Conversely, in examples where a portion of solid pitch is supplied in mold cavity115prior the start of a densification cycle, as described in greater detail with respect toFIG. 6, thermal management features may help increase the temperature of mold114until mold114is above the melting temperature of the pitch in the mold.

In the example ofFIG. 4, apparatus100includes heater tubes180and cooling tubes182for heating and cooling, respectively, mold114. Heater tubes180may extend through at least a portion of mold114and be in thermal communication with mold114. Heater tubes180may define a conduit configured for fluid communication with a thermal transfer agent. A thermal transfer agent may include, but is not limited to, steam, oil, a thermal transfer fluid, or the like. Heater tubes180may be cast or machined into mold114, or may be inserted into apertures defined by mold114. Heater tubes180may be formed of a thermally conductive material including, but not limited to, copper, aluminum, and alloys thereof. In operation, a thermal transfer agent may be heated in apparatus100or externally to apparatus100(e.g., in a furnace or heat exchanger) and conveyed through heater tubes180. The heat of the thermal transfer agent may conduct through heater tubes180, mold114, and preform113. In this way, mold114, including preform113and pitch in mold cavity115, may be conductively heated by heater tubes180. In various examples, a thermal transfer agent may be heated to a temperature greater than approximately 150 degrees Celsius, such as, e.g., a temperature greater than approximately 250 degrees Celsius during a pitch densification cycle of apparatus100.

After completing one or more pitch densification cycles on apparatus100, preform113may be saturated with liquid pitch and excess pitch may remain in mold cavity115. To facilitate easy and rapid removal of a densified preform113from apparatus100, cooling tubes182may be provided on apparatus100to cool and solidify melted pitch. In some examples, heater tubes180may be used as cooling tubes by conveying a comparatively cool thermal transfer agent through heater tubes180after densification. In other examples, however, apparatus100may include separate cooling tubes182. Separate heating tubes180and cooling tubes182may allow apparatus100to operate faster than when apparatus100includes shared heating and cooling tubes by reducing thermal cycling times.

Cooling tubes182may be similar to heating tubes180in that cooling tubes182may extend through at least a portion of mold114and may be in thermal communication with mold114. Cooling tubes182may also define an aperture configured for fluid communication with a thermal transfer agent, which may be the same thermal transfer agent received by heater tubes180or a different thermal transfer agent. In operation, the thermal transfer agent may be conveyed through cooling tubes182. As a result, mold114, including preform113and pitch in mold cavity115, may be conductively cooled by cooling tubes182.

Different pitch densification apparatuses and pitch melt techniques have been described in relation toFIGS. 2-4.FIG. 5is a flow chart illustrating an example method for densifying a material with an apparatus configured to densify a material according to one or more densification techniques selected from a plurality of different densification techniques. For ease of description, the method ofFIG. 5for pitch densifying a material with an apparatus configured to operate according to a plurality of different pitch densification cycles is described as executed by apparatus100(FIGS. 3 and 4). In other examples, however, the method ofFIG. 5may be executed by apparatus50(FIG. 2) or apparatuses with different configurations, as described herein.

As shown inFIG. 5, preform113may be inserted into mold cavity115of a densification apparatus (220), and the initial density of preform113may be determined (222). Based at least part on the density of preform113(222), a densification cycle may be selected (224). In accordance with the selected cycle (224), apparatus100may then carry out one or more of a RTM cycle (226), a VPI cycle (228), and/or a VRTM cycle (230) on preform113within mold114.

The technique ofFIG. 5includes inserting preform113into mold cavity115of pitch densification apparatus100(220). In different examples, mold114may be removable from pitch densification apparatus100or integrally formed with pitch densification apparatus100. Preform113or other material to be densified by apparatus100may be a carbon-based fiber material, a carbon-based non-fiber material, or a non-carbon-based material. In some examples, the material may be a woven or non-woven layered material. A plurality of different layers of the layered material may be stacked on top of one another. The plurality of different layers may be shaped, needled, and/or otherwise mechanically affixed together to define preform113. In one example, preform113may define a shape generally corresponding to finished brake rotor disc36or finished brake stator disc38(FIG. 1). In another example, preform113may define a shape generally corresponding to finished beam key40for securing a finished brake disc rotor to a wheel assembly. In yet other examples, preform113may define different shapes, as will be appreciated by those of ordinary skill in the art.

The technique ofFIG. 5includes determining an initial density of a material to be densified (222). An initial density may be indicative of the initial strength of the material and may indicate the ability of the material to withstand a specific densification technique. In some examples, an initial density of the material may be determined outside of densification apparatus100prior to inserting the material into mold cavity115of apparatus100(220). In other examples, the initial density of the material may be determined by densification apparatus100after inserting the material into mold cavity115of apparatus100(220). Pitch densification apparatus100may include, e.g., a scale, density meter, or other features for determining the initial density of the material.

After determining an initial density of preform113(222), one or more of a plurality of different densification cycles (RTM, VRTM, and/or VPI) can be selected to densify preform113. The one or more of the plurality of different densification cycles may be manually selected (e.g., by an operator) or automatically selected (e.g., by densification apparatus100). Further, the one or more of the plurality of different densification cycles may be selected based on a variety of different factors including, e.g., operating cycle times for each of the different densification cycles, the preprocessing steps performed on the material to be densified, the cost associated with each densification cycle, or other factors. According to example ofFIG. 5, however, the technique includes selecting a densification cycle based on the determined density (224). In some examples, a processor of apparatus100may compare the determined density to one or more thresholds density values stored in a memory associated with apparatus100. In other examples, a processor of apparatus100may compare the determined density to one or more threshold ranges stored in a memory associated with densification apparatus100. In either set of examples, different thresholds or threshold ranges may correspond to different density thresholds that allow preform113to withstand a force associated with one or more of RTM, VRTM, and VPI, as discussed above with respect toFIG. 2. Accordingly, a processor of apparatus100may select a specific densification cycle by comparing the determined density to one or more thresholds or threshold ranges.

Based on the selected densification cycle, apparatus100may densify the material in mold cavity115according one or more of a RTM cycle (226), a VPI cycle (228), and/or a VRTM cycle (230). During a RTM cycle (226), for example, pitch may be melted in pitch melt apparatus102and conveyed to apparatus100. Alternatively, one or more heating features may operate to melt solid pitch within mold cavity115, as described in greater detail with reference toFIG. 6. In either case, pitch pressurization ram122may be actuated into a retracted position during RTM cycle (226). Melted pitch may fill a cavity created by the retracted pitch pressurization ram122. Thereafter, pitch pressurization ram122may be actuated forward to apply a ram pressure to force pitch into mold cavity115. In some examples, pitch pressurization ram122may apply a ram pressure between approximately 500 psi and approximately 5000 psi. As a result, pressurized pitch may infiltrate the different pores of the material in mold cavity115. In this manner, apparatus100may densify the material via RTM cycle (226).

In VRTM cycle (230), a pressure in mold cavity115may be reduced to vacuum by controlling vacuum line control cylinder124to actuate vacuum line control rod126, thereby placing mold cavity115in fluid communication with vacuum source125. Thereafter, pitch pressurization ram122may be retracted and a cavity created by the retracted pitch pressurization ram122filled with pitch. Pitch may be melted in pitch melt apparatus102and conveyed to apparatus100. Alternatively, pitch may be melted directly in mold cavity115. As with resin transfer molding cycle (226), forward actuation of pitch pressurization ram122may pressurize pitch in the ram cavity, injecting the pitch through a pitch injection port in mold114into the vacuum pressure conditions previously established in mold cavity115. In this manner, apparatus100may densify the material via a VRTM cycle (230).

During a VPI cycle (228), a pressure in mold cavity115may be reduced to vacuum by controlling vacuum line control cylinder124in apparatus100to actuate vacuum line control rod126, thereby placing mold cavity115in fluid communication with vacuum source125. Pitch may flood mold cavity115during the vacuum cycle. For example, pitch may be conveyed from melt apparatus102to mold cavity115during the vacuum cycle. Alternatively, pitch may be melted in mold cavity115during the vacuum cycle to flood mold cavity115. In either example, with mold cavity115filled with pitch, the vacuum line may be closed and gas feed control cylinder130controlled to actuate gas control rod132. Actuation of gas control rod132may place mold cavity115in communication with pressurized gas source129. The pressurized gas may cause melted pitch in mold cavity115to infiltrate the different pores of the material to be densified. In this manner, apparatus100may densify material in mold cavity115with a VPI cycle (228).

Preform113may be densified with a single cycle of RTM (226), VPI228), or VRTM (230). Alternatively, preform113may be densified with multiple cycles of RTM (226), VPI (228), and/or VRTM (230) without being removed from mold cavity115of apparatus100. The same RTM (226), VPI (228), and/or VRTM (230) cycle may be repeatedly performed on apparatus100to densify preform113, or at least one cycle of one densification process (i.e., RTM (226), VPI (228), VRTM (230)) used to densify preform113may be different than at least one other cycle of one other densification process used to densify preform113, while preform113is housed within mold cavity115.

In this respect, in some examples, the techniques ofFIG. 5may be repeated after a first cycle of densification on apparatus100by again determining the density of preform113in apparatus100after a cycle of densification (222). In some examples, a processor of apparatus100may compare the determined density to one or more thresholds density values or ranges of threshold values stored in a memory associated with apparatus100. The different thresholds or threshold ranges may correspond to different density thresholds that allow preform113to withstand a force associated with one or more of RTM, VRTM, and VPI, as discussed above. Accordingly, a processor of apparatus100may select a densification cycle (RTM, VRTM, and/or VPI) by comparing the determined density to one or more thresholds or threshold ranges. The densification process may be the same process used for a first densification cycle on preform113, or the densification process may be different than the densification process used for the first densification cycle on preform113.

In some examples, different densification processes may be used to densify preform113without removing preform113from mold cavity115. For example, a processor of apparatus100may determine a density of preform113(222) and compare the determined density to one or more threshold density values or range of density values stored in a memory associated apparatus100. Based on the comparison, apparatus100may select a RTM cycle, a VRTM cycle, and/or a VPI cycle to pitch densify preform113(224). After performing the selected pitch densification cycle, the processor of apparatus100may again determine the density of preform113(222) and compare the determined density to one or more threshold density values stored in a memory associated apparatus100. Based on this further comparison (224), the processor of apparatus100may determine that one or more additional cycles of pitch densification are warranted. The processor of apparatus100may then select one or more additional pitch densification cycles to perform on preform113based on the threshold comparison, and the one or more cycles may be the same or may be different than the initial pitch densification cycle. In this manner, apparatus100may change pitch densification processes to adapt to the changing density of preform113without removing preform113from mold114. Alternatively, after comparing a determined density of preform113to one or more thresholds, apparatus100may determine that preform113has reached a suitable density and that no further densification is necessary. In some examples, preform113may undergo pitch densification until preform113reaches a density between approximately 1.6 g/cc and approximately 1.7 g/cc.

By pitch densifying a material according to one of a plurality of different selectable pitch densification cycles, the technique ofFIG. 5may allow apparatus100to densify materials that exhibit different physical characteristics. In some examples, this may allow weak materials that may otherwise by discarded to be processed using lower force densification techniques. In additional examples, this may allow for the fabrication of low cost C—C composite materials, e.g., by eliminating material waste, by eliminating the capital costs associated with multiple densification machines, and by eliminating processing steps during the fabrication of C—C composite material.

Techniques for pitch densifying a material using a selectable one of a plurality of different pitch densification processes have been described. In additional examples according to the disclosure, techniques are provided for pitch densifying a material using an apparatus that includes a mold configured to receive both a material to be densified and a portion of solid pitch material. The apparatus may be the same as the apparatuses described above or the apparatus may be different. In some examples, the apparatus is configured to heat the solid portion of pitch material beyond the melting temperature of the pitch material. As a result, the apparatus may melt pitch in-situ. By melting pitch in-situ, a low cost apparatus without external pitch melting equipment may be provided. Furthermore, by providing a portion of solid pitch material, a material may be densified with a precise amount of pitch, resulting in a high performance C—C composite component manufactured within tight pitch tolerances.

FIG. 6is a conceptual block diagram illustrating an example pitch densification apparatus300in accordance with the disclosure that includes a mold configured to receive a material to be densified and solid pitch. In particular,FIG. 6illustrates apparatus300including preform52, mold54, solid pitch302, gas source304, vacuum source306, and heating source308. Mold54defines mold cavity55. Preform52and solid pitch302may be inserted into mold cavity55for pitch densification. Heating source308is thermally coupled to mold54and, in particular, solid pitch302in mold cavity55. Heating source308is configured to heat solid pitch302above a melting temperature of solid pitch302. Gas source304is connected to mold54and configured to apply a gas pressure in mold cavity55to force melted pitch into preform52to densify the preform. Vacuum source306is connected to mold54and configured to create a vacuum pressure in mold cavity55at least prior to application the gas pressure from gas source304.

As described in greater detail below, apparatus300is configured to pitch densify preform52without using external pitch melting equipment. Preform52and a portion of solid pitch302may be inserted into mold cavity55defined by mold54of apparatus300. In some examples, preform52and the portion of solid pitch302may be separate. In some examples, the portion of solid pitch302may define a shape substantially corresponding to a shape of mold cavity55. Heating source308may heat mold54, and in particular solid pitch302, above a melting temperature of solid pitch302to fill mold cavity55with melted pitch. Further, apparatus300may apply one or more driving forces to force the melted pitch into the different pores of preform52while preform52resides in cavity55, thus producing a densified material. In different examples, apparatus300may be configured to densify preform52with a portion of solid pitch302using one or more of a RTM cycle, a VRTM cycle, or a VPI cycle, e.g., as described above with respect toFIGS. 2 and 3. For ease of description, however, apparatus300in the example ofFIG. 6is shown with gas source304and vacuum source306, which may each be used singly or may be used in combination, e.g., during a VPI cycle.

Apparatus300is configured to receive a material to be densified, which in the example ofFIG. 6is shown as preform52(FIG. 2). As described above, preform52may be a carbon-based fiber material. The carbon-based fiber material may be arranged as a plurality of stacked layers. The plurality of stacked layers may or may not be needled together. In addition, preform52may or may not undergo chemical vapor deposition prior to being inserted into mold cavity55. Preform52may define a general shape of a desired finished component including, e.g., a general shape of rotor disc36, stator disc38, beam key40, or another component of aircraft brake assembly10(FIG. 1).

Preform52is inserted into mold cavity55of mold54along with solid pitch302. Solid pitch302is an example of pitch56, described with respect toFIG. 2. Solid pitch302may be cold (e.g., at ambient temperatures) or solid pitch302may be heated, e.g., to reduce heating time on apparatus300. In general, when solid pitch302is heated prior to being inserted into mold cavity55, solid pitch302is heated to a temperature below the melting temperature of solid pitch302. In other words, solid pitch302is in a solid state when placed in mold cavity55. In this manner, solid pitch302may be easily handled and controllably measured, e.g., to place a precise amount of pitch into mold cavity55.

In some examples, solid pitch302may be placed in mold cavity55with preform52. The solid pitch302may be placed in mold cavity55prior to or after placing preform52in mold cavity55. For example, solid pitch302may be placed in mold cavity55and then preform52may be placed on top of solid pitch302. Alternatively, preform52may be placed in mold cavity55and solid pitch302may be placed on top of preform52. In another example, solid pitch302may be placed around a side of preform52. Regardless of the specific arrangement, the single portion of solid pitch302may melt during the operation of apparatus300to flood mold cavity55with melted pitch.

Solid pitch302may be a single piece of pitch or divided into multiple portions of solid pitch. As described in greater detail with reference toFIG. 8, in some examples, multiple portions of solid pitch302(e.g., two, three, four, or more) may be placed in mold cavity55. Different portions of the multiple portions of solid pitch302may be arranged next to each other, or different portions may be separated from one another, e.g., by preform52. For example, different portions of solid pitch302may be arranged around different surfaces of preform52(e.g., a top and bottom surface of preform52, or top, bottom, and side surfaces of preform52, or different hemispheres of preform52). In some examples, arranging different portions of solid pitch302around preform52may result in a substantially uniform distribution of melted pitch around preform52after melting solid pitch302. This may produce a C—C composite material with a more uniform density than a C—C composite material manufactured with a single portion of solid pitch material.

Independent of the specific number of portions of solid pitch302placed into mold cavity55, in some examples, solid pitch302and preform52may be separate components when inserted in mold cavity55. In other words, in various examples, solid pitch302and preform52may be separate components that may be separately placed in mold cavity55or connected components that may be separate in the sense that solid pitch302and preform52are not materially integrated. By separating solid pitch302from preform52, preform52may undergo different processing steps, e.g., needling, charring, or chemical vapor deposition, that would otherwise melt or physically disturb solid pitch302without pressurizing the pitch in a bounded area to pitch densify preform52. Moreover, in some examples, providing solid pitch302separate from preform52may allow an existing mold54or an existing apparatus300to be adapted to the techniques of this disclosure without requiring additional capital costs. That being said, in other examples, solid pitch302and preform54may be integrated into a single component that may be inserted into mold cavity55. In one example, solid pitch302may be mixed with carbon-based fibers used to form preform52prior to forming preform52. In another example, one or more layers of solid pitch302may be inserted between one or more layers of carbon-based material used to form preform52, thereby forming an integrated component of carbon-based fiber and solid pitch. Additional examples are possible.

Solid pitch302may define any suitable size and shape. In some examples, solid pitch302may be a powder. In other examples, solid pitch302may have a defined shape. Solid pitch302may be a block of pitch material, a disc of pitch material, rods of pitch material, pellets of pitch material, or any other shape. In some examples, as described in greater detail with respect toFIGS. 7A and 7B, solid pitch302may define a shape substantially corresponding to a shape of mold54such as, e.g., a shape substantially corresponding to a cross-sectional shape of mold cavity55. When solid pitch302defines a shape substantially corresponding to a cross-sectional shape of mold cavity55, solid pitch302may, in some examples, be comparatively thinner than when solid pitch302defines a different shape. A thinner solid pitch302may, in some cases, melt faster than a comparatively thicker solid pitch302, e.g., facilitating faster cycling times on apparatus300.

In some examples, mold cavity55defines a shape corresponding to a general shape of a desired finished component (e.g., as described with respect to preform52). Example finished components include, but are not limited to, rotor disc36, stator disc38, and beam key40(FIG. 1). Because solid pitch302may, in some examples, defines a shape substantially corresponding to a cross-sectional shape of mold cavity55, solid pitch302may also define a shape corresponding to a general shape of a desired finished component.

In one example, rotor disc36and/or stator disc38may define an annular cross-sectional shape. An annular cross-sectional shape may facilitate placement of rotor disc36and/or stator disc38in aircraft brake assembly10(FIG. 1). Accordingly, solid pitch302may also, in some examples, define an annular shape.FIGS. 7A and 7Bare conceptual diagrams illustrating an example in which solid pitch302has an example annular shape312.FIG. 7Aillustrates annular shape312in the X-Y cross-sectional plane.FIG. 7Billustrates annular shape312in a corresponding X-Z cross-sectional plane taken alone the A-A cross-sectional line shown onFIG. 7A.

In the X-Y cross-sectional plane shown onFIG. 7A, solid pitch302forms a ring that defines annular shape312. Annular shape312includes inner diameter314and outer diameter316. The specific dimensions for annular shape312may vary, e.g., based on the size of rotor disc36and/or stator disc38. However, in some examples, solid pitch302may define annular shape312with inner diameter314between approximately 6 inches and approximately 13 inches. In some examples, solid pitch302may define annular shape312with outer diameter316between approximately 9 inches and approximately 25 inches. Other values and shapes are contemplated, however, and is should be appreciated that the disclosure is not limited to using a solid pitch that has any particular size or that defines any particular shape.

While the disclosure is not limited to a solid pitch302that has any particular dimensions, as briefly noted above, in some examples, a thinner solid pitch302may melt faster than a comparatively thicker solid pitch302. Accordingly, solid pitch302may have controlled thickness dimensions. Thickness dimensions for solid pitch302may, in some examples, be measured in a direction orthogonal to a cross-sectional plane defining a shape for solid pitch302. For example, with respect to solid pitch302defining annular shape312in the example ofFIG. 7A, a thickness of solid pitch302may be measured in the Z-direction shown onFIG. 7B. As seen in the example ofFIG. 7B, solid pitch302may define thickness318in the Z-direction illustrated. In some examples, solid pitch302may define a thickness318between approximately 0.25 inches and approximately 1.0 inch. Other values according to the disclosure are possible though. Further, it should be appreciated that although thickness326is described with respect toFIG. 7B, other solid pitches according to the disclosure may define thickness326, or a different thickness, regardless of the specific cross-sectional shape the pitch defines in the X-Y cross-sectional plane.

Independent of the specific shaped defined by solid pitch302, solid pitch302may be shaped using any variety of techniques. In one example, prior to being inserted into mold cavity55, pitch may be liquefied, poured into a mold, and cooled to define a shape for solid pitch302. In another example, a portion of solid pitch may be milled to define a shape for solid pitch302. In a further example, pitch may be resin transfer molded to define a shape for solid pitch302. Resin transfer molding may be accomplished on a dedicated resin transfer molding apparatus. Alternatively, in examples where a pitch densification apparatus is configured to pitch densify a material using a resin transfer molding cycle (e.g., apparatuses50and100described above with respect toFIGS. 2 and 3, respectively) a pitch may be molded on a pitch densification apparatus to define a specific shape for solid pitch302using the apparatus. In other words, the pitch densification apparatus may be used to mold a billet of solid pitch302in addition to, or in lieu of, being used to later pitch densify a material with the molded portion of solid pitch302.

For example, with reference toFIG. 3for ease of description, pitch densification apparatus100may be used to mold a portion of solid pitch302that defines a shape of mold114. Pitch may be melted in pitch melt apparatus102and conveyed to apparatus100. Pitch pressurization ram122may be retracted to define a cavity for receiving the melted pitch. Without preform113in mold cavity115, pitch pressurization ram122may be actuated forward to inject pressurized pitch into mold cavity115of mold114. After allowing the injected pitch to cool and solidify, solid pitch302may be removed from mold114. In this manner, pitch may be resin transfer molded on pitch densification apparatus100to form solid pitch302that defines a shape substantially corresponding to a shape of mold cavity115. In different examples, solid pitch302may be resin transfer molded on different pitch densification apparatuses, including those described in this disclosure. It should be appreciated, however, that alternative techniques can be used to form solid pitch302, and the disclosure is not limited to any particular techniques for forming solid pitch302.

Using solid pitch302in pitch densification apparatus300(FIG. 6), in accordance with this disclosure, may allow preform52to be densified with a precisely controlled amount of pitch. Unlike pitch densification techniques that require transferring melted pitch, pitch densification using a portion of solid pitch302may not involve pitch loss during transfer or melted pitch measuring errors. Rather, solid pitch302may be precisely weighed and the weight of solid pitch302adjusted before being inserted into mold54. In this manner, the amount of pitch supplied to a particular component may be controlled within a narrow range of tolerances.

In general, any suitable amount of solid pitch302may be inserted into mold cavity55with preform52. The amount of solid pitch302inserted into mold cavity55may vary based on a variety of factors including, e.g., the size of preform52, the characteristics of solid pitch302, and the desired density for a finished C—C composite component. Further, it should be appreciated that the amount of solid pitch302may vary with the number of preforms52inserted into mold cavity55. Accordingly, if mold54is configured to receive multiple preforms52(e.g., two, three, four, or more), the amount of solid pitch302inserted into mold cavity55may increase.

As noted with reference toFIG. 6, mold54is configured to receive preform52and solid pitch302. Mold54may have a variety of different configurations and may be formed of a variety of different materials (as discussed with respect toFIG. 2). Further, the specific shape and size of mold54may vary, e.g., based on the shape and size of preform52, the shape and size of solid pitch302, and the number of portions of solid pitch302intended to be added to mold54.

FIG. 8is a conceptual diagram illustrating a cross-section of one example of mold54in accordance with the disclosure. As depicted in the example ofFIG. 8, mold54includes mold cavity55that is defined between first portion320and second portion322, which are separable at parting line324, e.g., to open mold54for adding or removing solid pitch302and preform52. Mold54includes top surface326, bottom surface328opposite top surface326, pressure port330, and vent ports332. Pressure port330is in fluid communication with gas source304to receive pressurized gas. Vent ports332may be in fluid communication with vacuum source306to create a vacuum pressure in mold cavity55or, e.g., a venting line to vent air in preform52as melted pitch infiltrates the pores of preform52. Within mold cavity55in the example ofFIG. 8are first portion of solid pitch302A, second portion of solid pitch302B, and preform52, which is shown as an annular shaped preform52. First portion of solid pitch302A is adjacent top surface326, second portion of solid pitch302B is adjacent bottom surface328, and preform52is interposed between first portion of solid pitch302A and second portion of solid pitch302B. By interposing preform52between first portion of solid pitch302A and second portion of solid pitch302B, different surfaces of preform52may be exposed to substantially similar amounts of melted pitch after solid pitch302melts. This may improve the uniformity with which preform52is densified.

In general, mold54, and in particular mold cavity55of mold54, may be configured to receive preform52with any size or shape. Mold cavity55may also be configured to receive any number of portions of solid pitch302. In some examples, mold cavity55is defined by a recessed area in top surface326, bottom surface328, and/or another surface of mold54to accommodate both solid pitch302and preform52in mold cavity55.

After inserting solid pitch302and preform52into mold cavity55, solid pitch302may be heated above the melting temperature of solid pitch302by heating source308. Heating source308is thermally coupled to mold54and, in particular, solid pitch302in mold cavity55of mold54. As used in this disclosure, the phrase “thermally coupled” means that heating source308is arranged such that thermal energy provided by heating source308may transfer to mold54during operation of apparatus300.

In general, heating source308may be any source or sources of thermal energy that may operate to increase the temperature of solid pitch302above the melting temperature of solid pitch302. For example, heating source308may be a convection heating source, an electromagnetic induction heating source, or an infrared heating source. In some examples, heating source308may include heating tubes180(FIG. 4). A thermally transfer agent may be heated in apparatus300or conveyed to apparatus300(e.g., from an external furnace, heat exchange, or the like) and passed through heater tubes180. As a result, thermal energy may be conductively transferred from the thermal transfer agent, through heater tubes180, through mold54, and into solid pitch302, thereby increasing the temperature of solid pitch302. In other examples, different heating sources may be used in addition to or in lieu of heating tubes180. For example, heating source308may be a fired burner or an electrical resistance heater. In still other examples, heating source308may be a radio frequency energy source (e.g., microwave energy source) that heats solid pitch302with radio frequency energy. In additional examples, heating source308may be an induction heater that inductively heats mold54, which in turn heats solid pitch302. For example, heating source308may be an electromagnetic induction heater configured to operate in the range of approximately 350 hertz to approximately 600 hertz, such as, e.g., between approximately 400 hertz and approximately 560 hertz, although operating ranges are possible. Additional or different heating sources may be used in an apparatus according to the disclosure.

Heating source308is configured to heat solid pitch302above the melting temperature of solid pitch302within mold cavity55of mold54. The melting temperature of solid pitch302may vary based on the chemical composition of the specific solid pitch inserted into mold cavity55of mold54. That being said, in some examples, solid pitch302may exhibit a melting/softening temperature between approximately 110 degrees Celsius and approximately 330 degrees Celsius. As such, heating source308may, in some examples, be configured to heat solid pitch302to a temperature greater than 110 degrees Celsius such as, e.g., to a temperature between approximately 285 degrees Celsius and approximately 330 degrees Celsius.

Apparatus300may apply one or more driving forces to force melted pitch into the different pores of preform52in order to densify preform52while preform52resides in mold cavity55. In some examples, a driving force may be a pressurized ram force (e.g., pitch pressurization ram122shown inFIG. 3). For example, as solid pitch302melts in mold cavity55, pitch pressurization ram122may be actuated against mold54(e.g., in the z-direction illustrated inFIG. 3) to compress mold54and the melted pitch in mold cavity55. In this manner, melted pitch in mold cavity55may be pressurized, causing the pitch to infiltrate the different pores of preform52to densify preform52. In other examples, different pitch driving forces may be used in addition to, or in lieu of, pitch pressurization ram122.

In the example ofFIG. 6, apparatus300is configured to densify preform52using one or both of gas source304and vacuum source306. Gas source304and vacuum source306are in fluid communication with mold cavity55, e.g., to control the pressure in mold cavity55. In some examples, vacuum source306is configured to create a vacuum pressure in mold cavity55before solid pitch302melts in mold cavity55or while solid pitch302is melting in mold cavity55. By creating a vacuum in mold cavity55before or while solid pitch302melts in mold cavity55, melting pitch may be drawn into the different pores of preform52, thereby densifying preform52. In some additional examples, gas source304is configured to apply a gas pressure in mold cavity55to force melted pitch into the different pores of preform52to densify preform52. Gas source304may be a source of pressurized inert gas including, but not limited to, nitrogen, helium, argon, carbon dioxide, or the like. Gas source304may apply a gas pressure in mold cavity55before or after solid pitch302melts, or while solid pitch302is melting in mold cavity55. The gas pressure may pressurize the pitch in mold cavity55to densify preform52.

In still other examples, apparatus300may be configured to use gas source304and vacuum source306in combination, e.g., during a VPI cycle, as described above with respect toFIGS. 2 and 3. Vacuum source306may create a vacuum in mold cavity55at least prior to the application of gas source304, e.g., while solid pitch302is melting. After mold cavity55is flooded with melted pitch, vacuum source306may be disengaged and gas source304may be activated to pressurized the melted pitch in mold cavity55. In this manner, apparatus300may be configured to densify preform52while preform52is housed in mold cavity55using at least one VPI cycle.

The gas pressure created in mold cavity55by gas source304and the vacuum pressure created in mold cavity55by vacuum source306may vary, e.g., based on the size of preform52, a desired density of preform52, and the specific solid pitch inserted into mold cavity55. However, in some examples, gas source304may be configured to apply a gas pressure in mold cavity55between approximately 10 pounds per square inch (psi) and approximately 1000 psi, such as, e.g., between approximately 300 psi and approximately 700 psi. In some examples, vacuum source306may be configured to create a vacuum pressure in mold cavity55between approximately 1 torr and approximately 100 torr. Other pressures are possible though, and the disclosure is not limited in this respect.

Different pitch densification techniques using an apparatus that includes a mold configured to receive both a material to be densified and one or more portions of solid pitch have been described in relation toFIGS. 6-8.FIG. 9is a block diagram illustrating an example technique for densifying a material with such an apparatus. For ease of description, the technique ofFIG. 9for pitch densifying a material with an apparatus that includes a mold configured to receive both a material to be densified and a portion of solid pitch is described as executed by apparatus300(FIG. 6). In other examples, however, the method ofFIG. 9may be executed by apparatus50(FIG. 2), apparatus100(FIG. 3) or apparatuses with different configurations, as described herein.

As shown inFIG. 9, preform52may be inserted into mold cavity55(350) and solid pitch302may be inserted into mold cavity55(350). Once inserted, solid pitch302is heated to a temperature greater than a melting temperature of solid pitch302within mold cavity55(354), and preform52is densified within mold cavity55by pressurizing the melted pitch (356) to impregnate preform52with the melted pitch.

The technique ofFIG. 9includes inserting preform52into mold54of pitch densification apparatus300(350). In different examples, mold54may be removable from pitch densification apparatus300or integrally formed with pitch densification apparatus300. Preform52may be a carbon-based fiber material, a carbon-based non-fiber material, or a non-carbon-based material. In some examples, preform52may be defined by a plurality of different layers of carbon-based fiber material that may be shaped, needled, and/or otherwise mechanically affixed together. Preform52may define a shape generally corresponding to a shape of a desired finished component. In one example, preform52may define an annular cross-sectional shape, which may generally correspond to finished brake rotor disc36or finished brake stator disc38(FIG. 1). In another example, preform52may define a shape generally corresponding to finished beam key40for securing finished brake rotor disc36to wheel assembly10. In yet other examples, preform52may define different shapes, as will be appreciated by those of ordinary skill in the art.

Solid pitch302may be inserted into mold cavity55before inserting preform52into mold cavity55, after inserting preform52into mold cavity55, or both before and after inserting preform52into mold cavity55. Alternatively, solid pitch302may be inserted into mold cavity55(352) at the same time preform52is inserted into mold cavity55(350). In some examples, solid pitch302and preform52may be separate materials joined into a single component, e.g., attached on a shared surface, that is inserted into mold cavity55. In other examples, solid pitch302and preform52may be separate materials separately inserted into mold cavity55. Solid pitch302may be a powder or may be a defined shape. In some examples, solid pitch302defines a cross-sectional shape substantially corresponding to a cross-sectional shape of mold54. In any event, after inserting preform52into mold cavity55(350) and inserting solid pitch302into mold cavity55(352), mold cavity55may be sealed, e.g., by pressing a first mold portion over a second mold portion to create a bounded mold cavity55for pitch densifying preform52with melted pitch from solid pitch302.

The technique ofFIG. 9further includes heating solid pitch302with heat source308to a temperature greater than a melting temperature of solid pitch302. In some examples, a thermal transfer agent is conveyed through heater tubes180of apparatus300and the heat from the thermal transfer agent conductively heats solid pitch302. In other examples, solid pitch302is heated with a microwave induction heater. In still other examples, solid pitch302is heated with a fired burner, electrical resistance heater, or other source of thermal energy. Regardless of the source of thermal energy, heat source308melts solid pitch302above a melting temperature of solid pitch302.

Apparatus300is configured to densify preform52within mold cavity55by at least pressurizing the melted pitch within mold cavity55(356). In one example, gas source304applies a gas pressure in mold cavity55to pressurize melted pitch in mold cavity55. The gas pressure may force the melted pitch into preform52to densify preform52. In some examples, vacuum source306creates a vacuum pressure in mold cavity55at least prior to the application of the gas pressure. A vacuum pressure in mold cavity55at least prior to the application of the gas pressure may help draw pitch into the pores of preform52. A vacuum pressure in mold cavity55at least prior to the application of the gas pressure may also help remove air from the different pores of preform52. This may allow a lower pressure gas source304to be used when densifying preform52, which may, e.g., accommodate a structurally weaker preform52.

Used in combination, gas source304and vacuum source306may be controlled to densify preform52with one or more VPI cycles. In one example, vacuum source306creates a vacuum pressure in mold cavity55as solid pitch302is heated with heating source308(354). After solid pitch302is substantially melted, vacuum source306is disengaged, and pressure source304is used to apply a gas pressure in mold cavity55. In this manner, apparatus300may densify preform52with melted pitch.

Examples of different pitch densification apparatuses and pitch densification techniques have been described. In different examples, techniques of the disclosure may be implemented in different hardware, software, firmware or any combination thereof In some examples, techniques of the disclosure may be implemented within one or more processors, including one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), or any other equivalent integrated or discrete logic circuitry, as well as any combinations of such components. In some examples, techniques of the disclosure may also be embodied or encoded in a computer-readable medium, such as a computer-readable storage medium, containing instructions. Instructions embedded or encoded in a computer-readable storage medium may cause a programmable processor, or other processor, to perform the method, e.g., when the instructions are executed. Computer readable storage media may include random access memory (RAM), read only memory (ROM), programmable read only memory (PROM), erasable programmable read only memory (EPROM), electronically erasable programmable read only memory (EEPROM), flash memory, a hard disk, a CD-ROM, a floppy disk, a cassette, magnetic media, optical media, or other computer readable media.

Various modifications of the illustrative examples, as well as additional examples consistent with the disclosure, will be apparent to persons skilled in the art upon reference to this description.