The present disclosure relates to carbon/carbon composites, and more specifically, to systems and methods for manufacturing carbon/carbon (C/C) composites.
Composite bodies are utilized in various industries, including the aerospace industry. C/C composites are often produced as 2D structures, for example utilizing planar oxidized polyacrylonitrile (PAN) fiber-based preforms followed by carbonization and chemical vapor infiltration (CVI) densification.
According to various embodiments, a shape forming tool is disclosed, comprising a female forming tool, a first plug; a second plug, and a wedge. The female forming tool comprises a die recess, the female forming tool extends longitudinally along a longitudinal centerline of the female forming tool between and to a first end of the female forming tool and a second end of the female forming tool, and the female forming tool extends laterally between and to a first side of the female forming tool and a second side of the female forming tool. The first plug, the second plug, and the wedge are configured to be received by the die recess. The wedge is configured to be received by the die recess between the first plug and the second plug. The wedge extends longitudinally along a longitudinal centerline of the wedge between and to a first end of the wedge and a second end of the wedge. The wedge extends laterally between and to a first side of the wedge and a second side of the wedge. The first side of the wedge comprises a first tapered surface and the second side of the wedge comprises a second tapered surface. The first tapered surface of the wedge is configured to engage the first plug and the second tapered surface of the wedge is configured to engage the second plug. In response to the first tapered surface of the wedge engaging the first plug, the first plug is configured to move laterally toward the first side of the female forming tool. In response to the second tapered surface of the wedge engaging the second plug, the second plug is configured to move laterally toward the second side of the female forming tool.
In various embodiments, the female forming tool extends vertically between and to a bottom side of the female forming tool and a top side of the female forming tool.
In various embodiments, the die recess extends vertically into the female forming tool from a first top surface and a second top surface of the female forming tool to a recess surface of the female forming tool, wherein the first top surface and the second top surface are arranged on opposing sides of the recess surface at the top side of the female forming tool. The die recess extends longitudinally in the female forming tool between and to the first end of the female forming tool and the second end of the female forming tool. The die recess extends laterally in the female forming tool between the first side of the female forming tool and the second side of the female forming tool.
In various embodiments, the die recess extends into the female forming tool from a first top surface and a second top surface of the female forming tool to a recess surface of the female forming tool, wherein the recess surface comprises a radii surface forming a rounded, convex surface transition disposed between a sidewall portion of the recess surface and the first top surface of the female forming tool.
In various embodiments, the die recess is configured without any sharp corners or sharp transitions.
In various embodiments, the shape forming tool further comprises a caul plate configured to be disposed between the fibrous preform and at least one of the wedge, the first plug, and the second plug. The caul plate is configured to distribute a force between the wedge, the first plug, and/or the second plug and the fibrous preform during a pre-carbonization compression step.
In various embodiments, the first plug comprises a first angled surface configured to engage the first tapered surface of the wedge, and the second plug comprises a second angled surface configured to engage the second tapered surface of the wedge.
In various embodiments, the first tapered surface comprises a guide flange protruding therefrom, and the first angled surface comprises a guide slot configured to receive the guide flange for maintaining a longitudinal position and a rotational position of the first plug with respect to the wedge.
In various embodiments, the guide flange is disposed entirely within a laterally outermost boundary of the wedge.
In various embodiments, at least one of the wedge, the first plug, or the second plug comprises a threaded aperture at top side thereof for receiving a lifting apparatus whereby at least one of the wedge, the first plug, or the second plug is moved.
According to various embodiments, a shape forming tool is disclosed, comprising a female forming tool comprising a die recess, a first plug configured to be received by the die recess, a second plug configured to be received by the die recess, and a wedge configured to be received by the die recess between the first plug and the second plug. The wedge extends longitudinally along a longitudinal centerline of the wedge between and to a first end of the wedge and a second end of the wedge. The wedge extends laterally between and to a first side of the wedge and a second side of the wedge. The first side of the wedge comprises a first tapered surface and the second side of the wedge comprises a second tapered surface. The first tapered surface of the wedge is configured to engage the first plug and the second tapered surface of the wedge is configured to engage the second plug. In response to the first tapered surface of the wedge engaging the first plug, the first plug is configured to move vertically toward a bottom side of the female forming tool. In response to the second tapered surface of the wedge engaging the second plug, the second plug is configured to move vertically toward the bottom side of the female forming tool.
In various embodiments, in response to the first tapered surface of the wedge engaging the first plug, the first plug is configured to move laterally toward a first side of the female forming tool. In response to the second tapered surface of the wedge engaging the second plug, the second plug is configured to move laterally toward a second side of the female forming tool.
In various embodiments, a total height of the wedge, measured along a vertical direction, is equal to that of the first plug and the second plug.
According to various embodiments, a method for manufacturing a C/C part is disclosed, the method comprising positioning an oxidized PAN fiber preform with a female forming tool, the female forming tool comprising a die recess, and forming the oxidized PAN fiber preform into a shaped body. The forming comprises moving a first plug at least partially into the die recess, the oxidized PAN fiber preform disposed between the first plug and the female forming tool, moving a second plug at least partially into the die recess, the oxidized PAN fiber preform disposed between the second plug and the female forming tool, and moving a wedge between and against the first plug and the second plug along a first axis. In response to the wedge pressing between and against the first plug and the second plug, the first plug and the second plug move in opposite directions along a second axis substantially perpendicular to the first axis. In response to moving the first plug and the second plug along the second axis, the oxidized PAN fiber preform is compressed between the first plug and the female forming tool and between the second plug and the female forming tool.
In various embodiments, movement of the wedge along the first axis further causes the first plug and the second plug to move parallel to the first axis.
In various embodiments, in response to the wedge moving along the first axis, compressing the oxidized PAN fiber preform between the wedge and the female forming tool.
In various embodiments, the first plug and the second plug are in direct contact with the oxidized PAN fiber preform when the wedge is pressed between and against the first plug and the second plug.
In various embodiments, the method further comprises gripping the oxidized PAN fiber preform with a gripper plate, wherein a lateral end of the oxidized PAN fiber preform is held between the gripper plate and a clamping surface of the female forming tool.
In various embodiments, a first layer of the oxidized PAN fiber preform is held by the gripper plate and a second layer of the oxidized PAN fiber preform is slidable against the clamping surface of the female forming tool.
In various embodiments, the method further comprises applying water to the oxidized PAN fiber preform prior to the oxidized PAN fiber preform being formed into the shaped body.
In various embodiments, the method further comprises applying heat to the oxidized PAN fiber preform for a predetermined duration while the oxidized PAN fiber preform is held in compression in the die recess.
In various embodiments, the method further comprises moving the shaped body into a graphite fixture, performing a carbonization process on the shaped body, and depositing carbon on and within the shaped body via a chemical vapor infiltration process while the shaped body is secured in the graphite fixture.
The foregoing features and elements may be combined in various combinations without exclusivity, unless expressly indicated herein otherwise. These features and elements as well as the operation of the disclosed embodiments will become more apparent in light of the following description and accompanying drawings.
All ranges and ratio limits disclosed herein may be combined. It is to be understood that unless specifically stated otherwise, references to “a,” “an,” and/or “the” may include one or more than one and that reference to an item in the singular may also include the item in the plural.
The detailed description of exemplary embodiments herein makes reference to the accompanying drawings, which show exemplary embodiments by way of illustration and its best mode, and not of limitation. While these exemplary embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, it should be understood that other embodiments may be realized and that logical, chemical and mechanical changes may be made without departing from the spirit and scope of the invention. For example, the steps recited in any of the method or process descriptions may be executed in any order and are not necessarily limited to the order presented. Moreover, many of the functions or steps may be outsourced to or performed by one or more third parties. Furthermore, any reference to singular includes plural embodiments, and any reference to more than one component or step may include a singular embodiment or step. Also, any reference to attached, fixed, connected or the like may include permanent, removable, temporary, partial, full and/or any other possible attachment option. Additionally, any reference to without contact (or similar phrases) may also include reduced contact or minimal contact.
As used herein, “fiber volume ratio” means the ratio of the volume of the fibers of the fibrous preform to the total volume of the fibrous preform. For example, a fiber volume ratio of 25% means the volume of the fibers in the fibrous preform is 25% of the total volume of fibrous preform.
As used herein, the term “fiber density” is used with its common technical meaning with units of g/cm3 or g/cc. The fiber density may refer specifically to that of the individual fibers in the fibrous preform. The density will be measured, unless otherwise noted, by taking the weight divided by the geometric volume of each fiber. The density may refer to an average density of a plurality of fibers included in a fibrous preform.
As used herein, “CVI/CVD” may refer to chemical vapor infiltration and/or chemical vapor deposition. Accordingly, CVI/CVD may refer to chemical vapor infiltration or deposition or both.
In general, there are currently two primary methods of manufacturing carbon/carbon (“C/C”) materials. The first method involves the layup and cure of a carbon fiber, phenolic resin matrix composite, followed by pyrolysis and subsequent phenolic resin infiltration and pyrolysis cycles. Multiple resin infiltration, cure, and pyrolysis cycles are typically used until the part achieves the desired density. The second method involves fabrication of an oxidized polyacrylonitrile fiber (OPF) or carbon fiber preform, followed by carbonization (for OPF preforms) and chemical vapor infiltration (CVI) densification. The chemical vapor infiltration cycles are continued, in conjunction with machining the preform between infiltration cycles if desired, until the desired part density is achieved. Combinations of these two basic process methods are also in use and may include variations in preform architecture, infiltration resin type, and chemical vapor infiltration conditions. A third method may involve a combination of the two aforementioned processes including layup and cure of a carbon fiber, phenolic resin matrix composite, followed by pyrolysis, and CVI densification.
After a fibrous OPF preform (also referred to herein as a fibrous preform) is made, it is carbonized to convert the OPF into carbon fibers. Typically, fibrous preforms are carbonized by placing the preforms in a furnace with an inert atmosphere. As is well-understood, the heat of the furnace causes a chemical conversion which drives off the non-carbon chemical species from the preform. The resulting preform generally has the same fibrous structure as the fibrous preform before carbonizing. However, the OPF have been converted to 100%, or nearly 100%, carbon. After the preform has been carbonized, the preform is densified. In general, densification involves filling the voids, or pores, of the fibrous preform with additional carbon material. This may be done using the same furnace used for carbonization or a different furnace. Typically, chemical vapor infiltration and deposition (“CVI/CVD”) techniques are used to densify the porous fibrous preform with a carbon matrix. This commonly involves heating the furnace and the carbonized preforms, and flowing hydrocarbon gases into the furnace and around and through the fibrous preforms. As a result, carbon from the hydrocarbon gases separates from the gases and is deposited on and within the fibrous preforms. When the densification step is completed, the resulting C/C part has a carbon fiber structure with a carbon matrix infiltrating the fiber structure, thereby deriving the name “carbon/carbon”.
C/C parts of the present disclosure are formed using OPF fabrics that are shape-formed prior to carbonization. C/C parts of the present disclosure may be formed using multi-axial, non-crimp, stitch-bonded, OPF fabrics that are shape-formed prior to carbonization. C/C parts of the present disclosure may be particularly useful for high temperature aerospace applications, such as for re-entry vehicle applications or other high temperature applications such as where a hot gas impinges on the vehicle after being rapidly compressed and heated as a result of a high pressure bow shock in front of the vehicle. C/C parts of the present disclosure may be especially useful in these applications because of the superior high temperature characteristics of C/C material. In particular, the carbon/carbon material used in C/C parts is a good conductor of heat and is able to dissipate heat generated during high temperature conditions. Carbon/carbon material is also highly resistant to heat damage, and thus, may be capable of sustaining forces during severe conditions without mechanical failure.
Application of OPF-based carbon-carbon composites has been generally limited to simple flat structures including C/C aircraft brake disks. C/C components including leading edges, structural members and other contour-shape carbon composites are often produced as 2D structures (i.e., flat, planar components); however, these materials tend to maintain low interlaminar properties. A shape formed 3D C/C part offers opportunity for similar in-plane C/C properties with higher interlaminar properties than 2D C/C.
With reference to
With reference to
The wedge 124 is configured with a wedge-shaped geometry; e.g., the first side 136 comprises a first angled surface 144 (also referred to herein as a first tapered surface) and the second side 138 comprises a second angled surface 146 (also referred to herein as a second tapered surface) such that the wedge 124 is tapered toward the bottom side 140. In various embodiments, the first side 136 further comprises a first vertical surface 148 and the second side 138 comprises a second vertical surface 150 such that the wedge 124. The first angled surface 144 may intersect with the first vertical surface 148 at a horizontally extending (e.g., along the X-axis) interface. The second angled surface 146 may intersect with the second vertical surface 150 at a horizontally extending (e.g., along the X-axis) interface.
With reference to
In various embodiments, the first side 156 is shaped to conform to a geometry of a side surface of the female forming tool 122. In various embodiments, the first side 156 comprises a vertical surface. However, first side 156 may be at an angle with respect to a vertical direction depending on the desired shape of the final C/C part. The second side 158 may comprise an angled surface 164 configured to engage (e.g., directly contact) first angled surface 144 whereby preform compressing forces (represented by arrows 192 in
Although illustrated as extending between and to the step 168 and the vertical surface 166, it is further contemplated that angled surface 164 may extend between and to the top side 162 and the bottom side 160 of second plug 128. In this regard, step 168 and vertical surface 166 may be omitted in various embodiments. For example, with momentary reference to
With reference to
The female forming tool 122 is configured with at least one die recess 182; e.g., an aperture such as a pocket, a channel, a groove, etc. The die recess 182 of
The recess surface 186 is a concave or concave-convex surface and may have a curved geometry; e.g., a three-dimensional (3D) curvature. The recess surface 186 of
In various embodiments, the recess surface 186 comprises a radii surface 181 which forms a rounded, convex surface transition between a sidewall portion 185 of the recess surface 186 and the female forming tool top surface 184. The fibrous preform may be bent around or over radii surface 625. Radii surface 181 may minimize wrinkling of the fibrous preform 110 during the forming process. Radii surface 181 may extend between and to the female forming tool first end 170 and the female forming tool second end 172. In various embodiments, an angled surface 183 oriented at an angle (e.g., between 5 and 75 degrees) with respect to the female forming tool top surface 184 is disposed between the radii surface 181 and the female forming tool top surface 184. Angled surface 183 may extend between and to the female forming tool first end 170 and the female forming tool second end 172.
With reference to
Methods for manufacturing a C/C part of the present disclosure include pre-carbonization compression of a fibrous preform 110. Fibrous preform 110 may comprise polyacrylonitrile (PAN) or OPF fibers extending in three directions and leaving a plurality of pores or open spaces and may be prepared for shape-forming, compression, and carbonization. In various embodiments, fibrous preform 110 is formed by stacking layers of PAN or OPF fibers and superimposing the layers (e.g., by stacking sheets of fabric). The layers may be needled perpendicularly to each other (i.e., along the Z-direction) with barbed, textile needles or barbless, structuring needles. In various embodiments, the layers are needled at an angle of between 0° and 60° (e.g., 0°, 30°, 45°, and/or 60°) with respect to the Z-direction to each other. The needling process generates a series of z-fibers through fibrous preform 110 that extend perpendicularly to the fibrous layers. The z-fibers are generated through the action of the needles pushing fibers from within the layer (x-y or in-plane) and reorienting them in the z-direction (through-thickness). Needling of the fibrous preform may be done as one or more layers are added to the stack or may be done after the entire stack of layers is formed. The needles may also penetrate through only a portion of fibrous preform 110, or may penetrate through the entire fibrous preform 110. In addition, resins are added, in various embodiments, to fibrous preform 110 by either injecting the resin into the preform following construction or coating the fibers or layers prior to forming the fibrous preform 110. The needling process may take into account needling parameters optimized to maintain fiber orientation, minimize in-plane fiber damage, and maintain target interlaminar properties.
After needling the fibrous preform 110, the non-woven fibrous preform 110 may be both compressed to higher fiber volume ratio and formed to shape in a single-step shape-forming process (i.e., using the shape forming tool of the present disclosure). It should be understood, moreover, that fibrous preforms 110 not subject to needling prior to pre-carbonization compression are also within the scope of the present disclosure.
After the fibrous preform 110 is placed over the female forming tool 122, the wedge 124, first plug 126, and second plug 128 are placed over the fibrous preform 110 and into the female forming tool 122, thereby beginning the shaping and compressing of the fibrous preform 110 as the fibrous preform is pressed into the female forming tool 122. In various embodiments, the wedge 124 may be first placed into the female forming tool 122 to push the fibrous preform 110 down to the bottom of the recess surface 186. In various embodiments, the fibrous preform 110 may also be first pushed down to the bottom of the recess surface 186 by hand.
With reference to
Each gripper plate 204 may include a first plate portion 206 oriented substantially parallel with a clamping surface 208 of the female forming tool 122. A grip surface 210 of the gripper plate 204 may be configured to contact the fibrous preform 110. The grip surface 210 may be configured with a relatively high coefficient of static friction and/or kinetic friction, whereas each female forming tool clamping surface 208 may be configured with a relatively low coefficient of static friction and/or kinetic friction. The grip surface 210, for example, may be textured whereas each female forming tool clamping surface 208 may be smooth; e.g., polished. The grip surface 210 may also or alternatively be formed from a material with a higher coefficient of static friction and/or kinetic friction than the material of the female forming tool 122.
The grip surface 210 of
In various embodiments, and with reference to
With reference to
In various embodiments, guide flanges 302 may comprise a tapered geometry such that the guide flange 302 becomes wider as it extends further from the second angled surface 346. Guide flange 302 (and guide slot 304) may be shaped like a dovetail. In this manner, wedge 324 may be mechanically locked from lateral movement (e.g., along the Y-direction) with respect to the second plug 328. Moreover, the guide flanges 302 and guide slots 304 provide rotational alignment (e.g., about the X-axis) of the second plug 328 with respect to wedge 324 (i.e., to keep the plug(s) from tipping over and rotating either clockwise (for the RH plug) or counterclockwise (for the LH plug). However, guide flanges 302 may be non-tapered or may be tapered such that the guide flange 302 becomes narrower as it extends further from the second angled surface 346, such that the wedge 324 is free—as to the guide flange 302—to move laterally away from the second plug 328.
Guide slot 304 may extend across the angled surface 364 and the vertical surface 366. The back surface 306 of the guide slot 304 may be a linear surface along the direction of travel of the guide flanges 302 with respect to the second plug 328.
With reference to
With reference to
In various embodiments, female forming tool 122 may comprise one or more lifted corners 130 at least partially defining the recess surface 186. The lifted corner 130 may extend from a sidewall of the female forming tool 122 to a bottom wall of the female forming tool 122. One or more of the first plug 126 and/or the second plug 128 may comprise a corresponding cutout or beveled corner 131 shaped to be complementary to the lifted corner 130. In this manner, the fibrous OPF preform 110 may be formed to have a similarly shaped contour or lifted corner 113.
With reference to
In step 502, the fibrous preform 110 is provided. Fibrous preform 110 may be configured as a multi-layered preform. The preform 110 of
Each layer of material 111 may share a common (e.g., the same) construction and/or material makeup. Each layer of material 111 in the stack 114, for example, may be formed by a sheet/layer of fibrous material; e.g., non-woven oxidized polyacrylonitrile (PAN) fibers. However, one or more layers of dissimilar construction may also be included (e.g., a non-woven with a chopped fiber mat sacrificial material).
In step 504, the fibrous preform 110 is arranged with the female forming tool 122. The fibrous preform 110 is disposed on the female forming tool 122 at its top side 180 (see
In various embodiments, moisture is added to the fibrous preform 110 during the shape-forming process. For example, a sizing agent comprising a fluid and/or fluid vapor such as water, steam, and/or polyvinyl alcohol may be applied to the fibrous preform 110 (e.g., before being shape formed). Adding the sizing agent to the fibrous preform 110 may dampen the fibers thereof which tends to relax the fibers of the fibrous preform thereby aiding in the bending, forming, and/or stretching of the fibrous preform. Adding the sizing agent to the fibrous preform 110 may tend to reduce wrinkling of the fibrous preform 110. Sizing may help to protect the fiber from handling damage and provide lubricity allowing the fibers to slide easily during preforming/compaction and aid in preventing wrinkling and kinking. Sizing agents of the present disclosure include water soluble polymers. The sizing agent may comprise a water solution. The sizing agent and may comprise long chain alcohols such as polyvinyl alcohols, modified starch, cellulose gum such as carboxymethyl cellulose, modified wax, acrylates, and/or mixtures thereof. In various embodiments, up to about 700 mL (23.7 fluid oz) of water or more may be applied to the fibrous preform 110, though the amount of water is a variable parameter based on a variety of factors, including the size and volume of the fibrous preform 110. In various embodiments, approximately 1 milliliter (ml) of water may be added for every 2.5 cubic inches of fibrous preform (1 ml/2.5 in3), wherein the term approximately as used in this context can only mean±0.5 ml. Stated differently, between 0.5 ml and 1.5 ml of water may be added to the fibrous preform for every 2.5 cubic inches of fibrous preform. However, it should be understood that other amounts of water or sizing agent may be added to the fibrous preform without departing from the scope of the present disclosure. Moreover, the fibrous preform may be preconditioned in a humidity chamber at a humidifying temperature (e.g., between 100° F. (37.8° C.) and 200° F. (93.3° C.)) and a relative humidity (e.g., between 75% and 90% humidity). Adding the sizing agent to the fibrous preform 110 may tend to reduce wrinkling of the fibrous preform 110 and support stabilizing the preform into the desired shape. In this manner, the fibrous preform 110 may be compressed to higher fiber volume ratio and formed to shape using heat, moisture, and pressure into contoured shapes using tool 120 as desired for a particular C/C part application.
The fibrous preform 110 may be pushed down (in the negative Z-direction) to the bottom of the recess surface 186 of the female forming tool 122 (see
In the arrangement of
In step 506, the fibrous preform 110 is formed into the shaped body 116. During this formation step 506, wedge 124, first plug 126, and second plug 128 may move (e.g., downward) vertically from the (e.g., open) position of
As the wedge 124 continues to vertically move to its (e.g., closed) position of
Moreover, as the wedge 124 continues to vertically move to its (e.g., closed) position, the first plug 126 and the second plug 128 may be moved laterally outward (see
During the pressing, the gripper plates 204 may selectively grip the fibrous preform 110 and its stack 114 of the layers of material 111. Each gripper plate 204 and its grip surface 210 of
The differential movement between the layers of material 111 in the stack 114 may be tuned by individually activating and deactivating the gripper plates 204 depending on the specific configuration of the die recess 182, the contact surfaces of the first plug 126, second plug 128, and/or wedge 124 and/or material properties of the fibrous preform 110 and its stack 114.
In various embodiments, each of the gripper plates 204 may move along a single axis; e.g., vertically up and down. In other embodiments, one or more or all of the gripper plates 204 may each move along multiple axes; e.g., vertically up and down, horizontally side to side, and/or horizontally in and out, etc. One or more of all of the gripper plates 204 may also or alternatively each rotate about one or more axes; e.g., the X-axis, the Y-axis and/or the Z-axis.
In various embodiments, with the wedge 124 in the closed position, the shape forming tool 120 and shaped body 116 may be heated to the shape forming temperature (e.g., loaded into an oven) for a predetermined duration (e.g., between an hour and 24 hours in various embodiments). Dead weight (e.g., apparatus 115) may be applied to the top sides of the wedge 124 (or in various embodiments, the wedge 124, first plug 126, and second plug 128) while the compressed assembly is in the oven so that the wedge 124, first plug 126, and second plug 128 are biased toward the female forming tool 122 as the shaped body 116 compresses and/or shrinks over time. In this manner, the wedge 124, first plug 126, and second plug 128 continually apply a compressing force to the shaped body 116.
In various embodiments, the heating and load application may occur at the same time by loading the assembly into a heated platen press and allowing the action of the press to drive the wedge 124 into the closed position while the assembly is simultaneously being heated.
In step 508, the shaped body 116 is released from the shape forming tool 120 and moved to a graphite fixture. The wedge 124, first plug 126, and second plug 128, for example, are moved vertically away from the female forming tool 122. The wedge 124, first plug 126, and second plug 128 may be moved vertically away from the female forming tool 122 using a lifting apparatus coupled to the respective wedge 124, first plug 126, or second plug 128. For example, with momentary reference to
Shape forming tool 120 may form the fibrous preform 110 into the shaped body 116 comprising a final, or near final, shape of the desired C/C part. In various embodiments, the shaped body 116 comprises a U-shape cross-sectional geometry (e.g., in the Y-Z plane). In various embodiments, the shaped body 116 comprises a complex curvature, depending on the geometry of the recess surface 186 of the female forming tool 122. With reference to
The shape forming tool 120 and its components 122, 124, 126, 128 are described above using the terms “bottom” and “top” with reference to exemplary orientations in the drawings. The present disclosure, however, is not limited to any particular formation system orientations. For example, in other embodiments, the wedge 124, first plug 126, and second plug 128 may alternatively be configured as a bottom die and the female forming tool 122 may alternatively be configured as a top die.
After being shape-formed using the shape forming tool 120, the shaped body 116 may be moved from the metallic shape forming tool 120 to a similarly shaped graphite fixture which is configured to maintain the compressed shape of the shaped body 116 during a subsequent carbonization process. The components of the graphite fixture 620 may be made from a graphite material suitable for withstanding carbonization and/or densification temperatures. With reference to
Graphite fixture 620 may comprise contoured surfaces similar to those of the shape forming tool 120. In this manner, graphite fixture 620 is configured to maintain the shape of the shaped body 116 previously achieved using the shape forming tool 120. Graphite fixture 230 may be configured to further compress the shape-formed fibrous preform 110 beyond that which might typically be achieved without compression. In various embodiments, graphite fixture 620 comprises a first member 232 and a second member 234. Shaped body 116 may be held in compression by placing a dead weight 615 onto graphite wedge 624 to evenly apply compressive forces onto shaped body with graphite wedge 624, graphite first plug 626, and/or graphite second plug 628, generally as described with respect to
In various embodiments, the graphite fixture 620 is designed such that the wedge 624 sits up (i.e., proud of or protruding above the plugs 626, 628) at the beginning of carbonization. During carbonization, the fibrous preform 110 will shrink (e.g., decrease in thickness). As this shrinkage is occurring, the influence of the dead weight 615 on the wedge 624 will drive the wedge(s) 624 and plugs 626, 628 down and out (laterally toward the female forming tool sidewalls) to continue to apply pressure to the fibrous preform 110.
In step 510, and with the shaped body 116 secured in compression within graphite fixture 620, the shaped body 116 may be carbonized to maintain shape and decrease fiber volume. In various embodiments, shaped body 116 together with graphite fixture 620 may be placed in a furnace for carbonization. The carbonization process may be employed to convert the fibers of the shaped body 116 into pure carbon fibers, as used herein only “pure carbon fibers” means carbon fibers comprised of at least 99% carbon. The carbonization process is distinguished from the densification process described below in that the densification process involves infiltrating the pores of the shaped body 116 and depositing a carbon matrix within and around the carbon fibers of the shaped body 116, and the carbonization process refers to the process of converting the fibers of the fibrous preform 110 into pure carbon fibers.
The shape-formed fibrous preform 110 may be carbonized by placing the shape-formed fibrous preform 110 in a furnace with an inert atmosphere. In general, the carbonization process involves heating the shape-formed fibrous preform 110 in a furnace to a temperature greater than about 1,600 degrees Celsius (2912 Fahrenheit). Typically, an inert atmosphere of nitrogen, argon or a vacuum is provided in the furnace during the carbonization process. The heat of the furnace causes a chemical conversion of the OPF that converts the fibers to carbon fibers and drives off other chemicals. Although it is sometimes preferred that the fibers in the carbonized fiber preform be 100% carbon fiber, it is generally acceptable for a less than full conversion to take place. The resulting carbonized fiber preform generally has the same fibrous structure as the fibrous preform before carbonizing. During carbonization, the total mass and the total fiber volume in each fibrous preform is typically reduced due to the loss of non-carbon compounds.
Fiber density of the fibrous preform 110 may increase during carbonization (e.g., from about 1.37 g/cc in OPF state to about 1.77-1.85 g/cc after carbonization, depending on the final carbonization temperature). In various embodiments, the OPF fibers shrink during carbonization, as OPF may have a char/carbon yield of around 50%. As used herein “char/carbon yield” means the remaining mass of the OPF after degrading the OPF using the carbonization process.
After carbonization, the carbonized shaped body 116 may be densified using chemical vapor infiltration (CVI), as described in further detail below. After carbonization, shaped body 116 may be densified. In various embodiments, the shaped body 116 is removed from graphite fixture 620 prior to densification. In various embodiments, the shaped body 116 is placed in a perforated graphite fixture during one or more densification runs. The shaped body 116 may be densified with pyrolytic carbon by CVI using optimized process conditions to maintain shape and support efficient carbon densification. In general, densification involves filling the voids, or pores, of the fibrous preform with additional carbon material. This may be done using the same furnace used for carbonization or a different furnace. Typically, chemical vapor infiltration and deposition (“CVI/CVD”) techniques are used to densify the porous fibrous preform with a carbon matrix. This commonly involves heating the furnace and the carbonized preforms, and flowing hydrocarbon gases (e.g., at least one of methane, ethane, propane, butane, and/or the like, as described herein) into the furnace and around and through the fibrous preforms. In various embodiments, the CVI/CVD process may include a temperature gradient. In various embodiments, the CVI/CVD process may include a pressure gradient. In various embodiments, the CVI/CVD process may include a temperature and a pressure gradient.
CVI/CVD densification may be conducted in a vacuum or partial vacuum (e.g., at pressures of 1-15 torr) or in an inert atmosphere at a temperature in the range from about 900° C. to about 1100° C. (1,652° F. to about 2,012° F.), and in various embodiments in the range of up to about 1,000° C. (1,832° F.) (wherein the term about in this context only means+/−100° C.) for a period of time in the range from about 150 hours to about 650 hours, and in various embodiments, in the range from about 300 hours to about 500 hours (wherein the term about in this context only means+/−24 hours).
As a result, carbon from the hydrocarbon gases separates from the gases and is deposited on and within the fibrous preforms. Typically, the densification process is continued until the preform reaches a density in the range from 1.6 to 1.9 grams per cubic centimeter (g/cc), and in various embodiments, a density of approximately 1.80 g/cc. When the densification step is completed, the resulting C/C part has a carbon fiber structure with a carbon matrix infiltrating the fiber structure, thereby deriving the name “carbon/carbon.”
After a first CVI/CVD cycle of 300 to 500 hours, an intermediate heat treat is typically performed, in the same furnace. This heat treat (>1600° C.) serves to dimensionally stabilize the shaped body 116, increase its thermal properties, and increase its porosity for subsequent densification. The shaped body 116 may then be machined to open the porosity further, to help allow for final density to be achieved using only one more CVI/CVD cycle. Part densities after first machining may be in the range of 1.4 to 1.7 g/cc, depending on the part thickness, overall size, and placement within the furnace. Typical, average density range is 1.55-1.65 g/cc.
The densification process may be continued until the preform reaches a desired density, for example in the range from 1.7 to 1.9 grams per cubic centimeter (g/cc), and in various embodiments, a density of approximately 1.80 g/cc. The CVI/CVD process may be continued with the shaped body 116 removed from the perforated graphite fixture. In this manner, the outer surfaces of the shaped body 116 may be more directly exposed to the gas flow. Moreover, the shaped body 116 may be machined in between carbon CVI densification processes (e.g., between fixtured carbon CVI densification and non-fixtured carbon CVI densification and/or between successive non-fixtured carbon CVI densification processes). Machining (e.g., grinding, sanding, milling, grit blasting, etc.) the shaped body 116 may be performed to achieve a final desired part shape. Machining the shaped body 116 may be performed to expose voids, or pores, of the shaped body 116 so as to facilitate infiltration with additional carbon material during subsequent carbon CVI densification. When the densification step is completed, and the desired density is achieved, the resulting C/C part has a carbon fiber structure with a carbon matrix infiltrating the fiber structure, thereby deriving the name “carbon/carbon.”
Following the CVI/CVD densification process, the C/C part may undergo a final heat treatment (FHT) process. This may be done using the same furnace used for densification or a different furnace. If done using the same furnace, the flow of hydrocarbon gases would be stopped following the end of the densification process and the temperature increased. FHT may be conducted in a vacuum or partial vacuum (e.g., at pressures of 1-15 torr) or in an inert atmosphere at a temperature in the range from about 1200° C. to about 2600° C. (2,921° F. to about 4,712° F.), and in various embodiments in the range from about 1400° C. to about 2200° C. (2,552° F. to about 3,992° F.) (wherein the term about in this context only means+/−100° C.) for a period of time in the range from about 4 hours to about 14 hours, and in various embodiments, in the range from about 8 hours to about 12 hours (wherein the term about in this context only means+/−2 hours). In various embodiments, the FHT process imparts high temperature dimensional stability to the final C/C part. In various embodiments, the FHT process imparts desired thermal properties associated with thermal shock such as high thermal conductivity, high heat capacity, and/or high emissivity.
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Systems and methods are provided. In the detailed description herein, references to “various embodiments”, “one embodiment”, “an embodiment”, “an example embodiment”, etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. After reading the description, it will be apparent to one skilled in the relevant art(s) how to implement the disclosure in alternative embodiments.
Benefits, other advantages, and solutions to problems have been described herein with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any elements that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as critical, required, or essential features or elements of the invention. The scope of the invention is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more.” Moreover, where a phrase similar to “at least one of A, B, or C” is used in the claims, it is intended that the phrase be interpreted to mean that A alone may be present in an embodiment, B alone may be present in an embodiment, C alone may be present in an embodiment, or that any combination of the elements A, B and C may be present in a single embodiment; for example, A and B, A and C, B and C, or A and B and C. Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. No claim element herein is intended to invoke 35 U.S.C. 112(f) unless the element is expressly recited using the phrase “means for.” As used herein, the terms “comprises,” “comprising,” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
This application claims priority to, and the benefit of, U.S. Provisional Patent Application Ser. No. 63/212,264, entitled “SHAPE FORMING NON-WOVEN OPF PREFORM,” filed on Jun. 18, 2021. The '264 application is hereby incorporated by reference in its entirety for all purposes.
Number | Date | Country | |
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63212264 | Jun 2021 | US |