Patent Publication Number: US-2021164104-A1

Title: Continuous multiple tow coating reactor

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. application Ser. No. 15/713,758, which was filed on Sep. 25, 2017. 
    
    
     BACKGROUND 
     Fiber reinforced ceramic matrix composite (CMC) materials are finding a greater number of applications in high temperature oxidizing environments due to their material properties including, but not limited to, high temperature and oxidation resistance, high strength and creep resistance, high thermal conductivity and low weight. 
     An advantage of CMC materials compared to their corresponding monolithic materials is that such materials are significantly tough even though their constituents may be intrinsically brittle. This feature is achieved by utilizing an appropriate fiber/matrix interface coating(s) that arrest and deflect cracks formed under load in the brittle matrix and prevent early failure. Furthermore, the interface coatings protect the fibers from detrimental interactions with each other, with the matrix, and with the environment in the CMC component application(s). Therefore, interface coatings play an important role in the performance and lifetime of CMC materials during their applications. 
     The disclosure relates to a method and reactor system for applying a coating to a fiber, such as by chemical vapor deposition (CVD). 
     SUMMARY 
     A method for a tow coating reactor system according to an example of the present disclosure includes a reactor for receiving fiber tow and a wedge situated adjacent the reactor and configured to receive the tow at a tip end, such that as the tow moves across the wedge, the wedge spreads the tow into a plurality of sub-tows. 
     In a further embodiment according to any of the foregoing embodiments, the wedge includes a tapered portion including a tip in line with the fiber tow. 
     In a further embodiment according to any of the foregoing embodiments, the wedge includes an untapered portion downstream of the tapered portion. 
     In a further embodiment according to any of the foregoing embodiments, the wedge has a coating. 
     In a further embodiment according to any of the foregoing embodiments, the coating is a diamond-like carbon coating. 
     In a further embodiment according to any of the foregoing embodiments, the wedge includes a plurality of longitudinal grooves, and each of the plurality of longitudinal grooves configured to receive one of the plurality of sub-tows. 
     In a further embodiment according to any of the foregoing embodiments, the continuous line of fiber tow has a tow center axis, the wedge has a wedge center axis, and the tow center axis and the wedge center axis are aligned. 
     In a further embodiment according to any of the foregoing embodiments, the wedge includes a first half surface and a second half surface opposite the first half surface, and the wedge is positioned such that one of the plurality of sub-tows runs across the first half surface, and a second of the plurality of sub-tows runs across the second half surface. 
     In a further embodiment according to any of the foregoing embodiments, the wedge includes a plurality of longitudinal grooves, and each of the plurality of longitudinal grooves configured to receive one of the plurality of sub-tows. 
     In a further embodiment according to any of the foregoing embodiments, a second wedge is opposite of the reactor from the first wedge. 
     In a further embodiment according to any of the foregoing embodiments, the second wedge is configured to consolidate the plurality of sub-tows into a single tow. 
     In a further embodiment according to any of the foregoing embodiments, the wedge is configured to untwist the fiber tow, and the second wedge is configured to twist the plurality of sub-tows. 
     In a further embodiment according to any of the foregoing embodiments, the wedge includes a plurality of fins. 
     A method for coating a fiber tow according to an example of the present disclosure includes moving a fiber tow across a wedge to separate the fiber tow into a plurality of tub-tows and coating the plurality of sub-tows. 
     In a further embodiment according to any of the foregoing embodiments, the plurality of sub-tows is consolidated into a single tow. 
     In a further embodiment according to any of the foregoing embodiments, the wedge includes a tapered portion including a tip in line with the fiber tow. 
     In a further embodiment according to any of the foregoing embodiments, the tow is untwisted before the coating and the tow is twisted after coating. 
     A wedge configured to split a tow into a plurality of sub-tows according to an example of the present disclosure includes a tapered portion, an untapered portion adjacent to the tapered portion, a plurality of grooves provided by at least one of the tapered portion and the untapered portion, and each of the plurality of grooves is configured to receive one of the plurality of sub-tows 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  schematically illustrates an example tow-coating reactor system. 
         FIG. 2  illustrates a side view of an example wedge. 
         FIG. 3  illustrates a cross sectional view of the example wedge. 
         FIG. 4  illustrates a cross sectional view of the example wedge receiving sub-tows. 
         FIG. 5  illustrates a cross sectional view of another example wedge. 
         FIG. 6  schematically illustrates another example tow-coating reactor system. 
         FIG. 7  is a flow chart of an example method for coating a fiber tow. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  schematically illustrates a system  10  for continuously coating tow fibers. The system  10  includes a reactor  12  positioned to receive a continuous line of fiber tow  14 . It was difficult previously to apply a uniform coating to a fiber tow. As will be described, the system  10  can uniformly coat the tow  14 , effectively splitting the tow into sub-tows and applying a uniform coating to each sub-tow. 
     The reactor  12  is configured to coat the fiber tow  14 . The fiber tow  14  is passed through a chamber  15  of the reactor  12 , and a reactant gas is injected into the chamber  15 . One example coating material is boron nitride, but one of ordinary skill having the benefit of this disclosure would realize that other coating materials, including but not limited to silicon nitride, silicon carbide, and boron carbide can be utilized. One example reactor  12  is a chemical vapor deposition (CVD) reactor, but one of ordinary skill having the benefit of this disclosure would realize that other reactors may be utilized. The reactant(s) used in the reactor  12  is/are determined by the desired coating. Some coatings may be produced by decomposition of a single reactant gas. For example, deposition of carbon may be accomplished by decomposition of a hydrocarbon, such as methane. A two-gas reaction may be used for other coatings. For example, a boron trichloride and ammonia reaction may be used to form boron nitride. A three gas reaction such as boron trichloride, ammonia and a silicon precursor may be used to form a desired coating. Silicon precursors include dichlorosilane, trichlorosilane, silicon tetrachloride, and silane. Hydrogen or nitrogen may be used to dilute precursor gases to control reaction speed and temperature. 
     The tow fibers  14  to be coated may be fibers made from one of SiC, carbon, alumina, aluminum silicate, mullite, and silicon nitride, as well as from other materials. The tow fibers  14  can have a diameter of from 4 to 25 microns. The tow fibers  14  may contain from 2 to 12000 fibers, depending on fiber type, size and intended use. 
     A tow-splitting wedge  16  is situated adjacent the reactor  12  to split the fiber tow  14  into a plurality of sub-tows  18  before the plurality of sub-tows  18  enter the chemical vapor disposition reactor  12 . The sub-tows  18  are spaced from one another while passing through the chamber  15  and receiving coating. Each sub-tow  18  may include a plurality of individual filaments that make up the fiber tow  14 . Alternatively, each sub-tow  18  may have one filament. The wedge  16  may include a tip  34  and is configured to receive the tow  14  at the tip  34 , such that as the tow  14  moves across the wedge  16 , the wedge  16  spreads the tow into a plurality of sub-tows  18 . 
     The tow-coating reactor system  10  is a continuous system, such that the fiber tow  14  runs from a take-off spool  20 , across the wedge  16 , through the chemical vapor deposition reactor  12 , and to a take-up spool  22 . The system  10  may further include a consolidator  24  between the reactor  12  and the take-up spool  22  for consolidating the coated sub-tows  18  back into a single tow  14  after the coated sub-tows  18  exit the reactor  12 . In one example, the consolidator  24  is substantially the same as the wedge  16  but oriented in the opposite direction. In another example, the consolidator  24  is a ring, such that the sub-tows  18  run through the inner diameter of the ring to be consolidated into a single tow  14 . In other examples, a consolidator  24  is not utilized. 
     The wedge  16  and consolidator  24  may be connected by a support  25 . In one example, the support  25  is a rotatable axle, such that the wedge  16  may be rotated as the tow travels across to untwist the tow  14  to form the sub-tows  18 . The consolidator  24  is rotated at the same speed in the same rotational direction to that of the wedge  16  to twist the sub-tows  18  back into an individual tow  14 . Alternatively, the support  25  may be fixed against rotation, such that only the geometry of the wedge  16  and the consolidator  24  function to split and combine the tow  14 . The sub-tows  18  may be substantially parallel to one another when in the reactor  12 . 
     The reactor  12  may include a reactant inlet  26  for injecting the coating reactant into the chamber  15  and a reactant outlet  28  for the reactant exhaust to exit the chamber  15 . The reactant inlet  26  and the reactant outlet  28  may be parallel to the fiber tow center axis P. In the example, the reactant inlet  26  is located at the longitudinal end E A  of the chamber  15  and the reactant outlet  28  is located at the longitudinal end E B  of the chamber opposite the longitudinal end E A , such that the reactant flows within the chamber  15  in the direction F R  from end E A  toward end E B . The sub-tows  18  enter the chamber from end E B  and exit through end E A  such that the sub-tows  18  travel in the direction F T  from E B  to E A —opposite the reactant flow direction. Alternatively, the directions F R  and F T  may be the same. 
       FIG. 2  illustrates one example wedge  16  including a tapered portion  32  that converges to a tip  34 . In one example, the tip  34  is axially aligned with the fiber tow center axis P, with reference to  FIG. 1 , in line with the fiber tow  14 . The tapered portion  32  serves to gradually split the tow  14  radially outward into separate sub-tows  18  that are radially spaced from one another with respect to the tow center axis P, as the tow  14  travels from the point  34  to the wide end  35  of the tapered section  32 . The tow  14  is received at the tip  34 , such that as the tow moves across the wedge, the wedge spreads the tow  14  into the sub-tows  18 . 
     The wedge  16  may include a substantially untapered portion  36  downstream of the tapered portion  32 . The substantially untapered portion  36  has a substantially constant diameter as it extends axially. The substantially untampered portion  36  defined the maximum tow spread width for the sub-tows  18 . The wedge  16  may include one or more longitudinal grooves  38  each configured to receive a sub-tow  18 . The one or more longitudinal grooves  38  may extend axially from the substantially untapered portion  36  into the tapered portion  32  or, alternatively, be only within the substantially untapered portion  36 . 
       FIG. 3  shows a cross-sectional view of an example wedge  16 . The example wedge  16  includes four grooves  38 , such that the wedge  16  is configured to split a tow  14  into four sub-tows  18 . More or fewer grooves  38  for more or fewer sub-tows  18  may alternatively be used. In some examples, a range of two to eight grooves  38  may be used for a range of two to eight sub-tows  18  in the system  10 . 
     The wedge  16  may include a maximum diameter D. In some examples, the maximum diameter D is less than or equal to 0.5 inches. In some examples, the maximum diameter D is between 0.25 and 0.5 inches. 
       FIG. 4 , with continued reference to  FIGS. 1-3 , illustrates a cross sectional view of the wedge  16  splitting the fiber tow  14  into a plurality of sub-tows  18 . Each of the plurality of grooves  38  receives one or more sub-tows  18 . The sub-tows  18  are radially split such that each sub-tow  18  is spaced an increased distance from the tow center axis P relative to its distance from the center axis of the tow before contacting the wedge  16 . In the example, the tow  14  has a center axis P, the wedge  16  has a center axis A, and the center axis P and the center axis A are aligned, but other configurations are contemplated. 
     The wedge  16  radially splits the tow  14  into sub-tows  18 . The wedge  16  may include one half surface  40  and a second half surface  42  opposite the half surface  40 . The wedge  16  may be positioned such that one sub-tow  18  runs along the half surface  40  and at least one other sub-tow  18  runs along the half surface  42 . In the four grooved example, each half surface  40 ,  42  includes two grooves  38 . 
     In some examples, the wedge  16  may have a diamond-like carbon coating to create a smooth low-friction surface. A smooth surface facilitates reducing risk that the wedge  16  abrades or wears the individual filaments of each sub-tow  18 . The wedge  16  may include a core material of silicon nitride, silicon carbide, aluminum oxide, aluminum nitride, boron nitride, boron carbide, or other abrasion-resistant materials. A person of ordinary skill in the art having the benefit of this disclosure would recognize that other core materials could be used. 
       FIG. 5  illustrates a cross sectional view of an example wedge  216  for use in a system that twists and untwists a tow  14 . The wedge  216  includes a plurality of fins  44  that serve to increase friction between the wedge  216  and the sub-tows  18 . The friction facilitates maintaining the sub-tows  18  on the wedge  216 , evenly distributing the sub-tows  18  about the wedge  216  during twisting. The consolidator  24  may also include a plurality of fins  44 . 
       FIG. 6  schematically illustrates a second example tow-coating reactor system  110  including a reactor  112  positioned to receive multiple continuous lines of fiber tow  114 . In the example, there are two continuous lines of fiber tow  114 . The reactor  112  is configured to provide coatings to the fiber tows  114 . The fiber tows  114  are passed through a chamber  115  of the reactor  112 , and a reactant gas is injected into the chamber  115 . 
     Tow-splitter wedges  116  are positioned to split each fiber tow  114  into a plurality of sub-tows  118  before the plurality of sub-tows  118  enter the chemical vapor disposition reactor  112 . The tow-coating reactor system  110  is a continuous system, such that the fiber tows  114  runs from take-off spools  120 , across the wedges  116 , through the chemical vapor deposition reactor  112 , and to take-up spools  122 . The system may further include consolidators  124  between the reactor  112  and the take-up spools  122  for combining the sub-tows  118  back into single tows  114  after the sub-tows  118  exit the reactor  112 . 
     The wedge  116  and consolidator  124  may be connected by a support  125 . In one example, the support  125  is a rotatable axle, such that the wedge  116  may be rotated as the tow travels across to untwist the tow  114  to form the sub-tows  118 . The consolidator  124  is rotated at the same speed in the same rotational direction to that of the wedge  116  to twist the sub-tows  118  back into an individual tow  114 . Alternatively, the support  125  may be fixed against rotation, such that only the geometry of the wedge  116  and the consolidator  124  function to split and combine the tow  114 . The sub-tows  118  may be substantially parallel to one another when in the reactor  112 . 
     The reactor  112  may include a reactant inlet  126  for injecting the coating reactant into the chamber  115  and a reactant outlet  128  for the reactant exhaust to exit the chamber  115 . In the example, the reactant inlet  126  is located at the longitudinal end E A  of the chamber  115  and the reactant outlet  128  is located at the longitudinal end E B  of the chamber opposite the longitudinal end E A , such that the reactant flows within the chamber  115  in the direction F R  from end E A  toward end E B . The sub-tows  118  enter the chamber from end E B  and exit through end E A  such that the sub-tows  118  travel in the direction F T  from E B  to E A —opposite the reactant flow direction. Alternatively, the directions F R  and F T  may be the same. 
       FIG. 7  illustrates a flow chart of a method  200  for coating a fiber tow, which, in some examples, may be used with any of the systems or components in this disclosure. At  210 , the method includes moving a fiber tow across a wedge to separate the fiber tow into a plurality of sub-tows. At  220 , the method includes coating the plurality of sub-tows. 
     The method  200  may further include consolidating the plurality of sub-tows into a single tow. 
     The method  200  may further include untwisting the tow before entry into the chemical vapor deposition reactor. The method may further include twisting the tow after exit from the chemical vapor deposition reactor. 
     The systems and methods in this disclosure allow for a fiber tow to be split into radially separated sub-tows. By radially separating the sub-tows, a more uniform interphase coating of the fiber tow may be achieved. Reactants diffuse inside the sub-tows more easily as a result of the radial separation because the inner filaments of the tow are more accessible to the reactants. This results in improved performance and lifetime of the CMC materials having these fibers because the interface coatings are more uniform. In addition, a better precursor utilization will be achieved. 
     As can be seen from the above description, a continuous CVD interface coating system and method for the fabrication of CMC composite parts has been presented. The system and method described herein can improve the performance and lifetime of CMC materials during their applications due to the manner in which the interface coatings are formed more uniformly on the tow fibers. The system and process described herein can allow improvements in the thickness distribution of interface coatings. 
     Although example geometries for tow-splitting wedges are disclosed, one of ordinary skill in the art having the benefit of this disclosure would recognize that other components could be used to radially split a tow  14  into a plurality of sub-tows  18 . 
     Although the systems and methods disclosed involve closed chemical vapor deposition processes, one of ordinary skill in the art having the benefit of this disclosure would recognize that the components disclosed, including but not limited to the wedge  16 , could also be used with open chemical vapor deposition processes. 
     Although the different examples have the specific components shown in the illustrations, embodiments of this disclosure are not limited to those particular combinations. It is possible to use some of the components or features from one of the examples in combination with features or components from another one of the examples. 
     One of ordinary skill in this art would understand that the above-described embodiments are exemplary and non-limiting. That is, modifications of this disclosure would come within the scope of the claims. Accordingly, the following claims should be studied to determine their true scope and content.