Patent Publication Number: US-2020290835-A1

Title: Qualification and repair station

Description:
FIELD 
     Embodiments of the present disclosure generally relate to continuous tow processing systems and in particular to systems for qualification and repair of individual filament defects in a multi-filament tow prior to depositing coatings on a tow material. 
     BACKGROUND 
     Ceramic matrix composites (CMCs) are comprised of ceramic fibers embedded in a ceramic matrix. CMCs were developed to address limitations with conventional technical ceramics that prohibit use at high-temperatures and in oxidizing environments. Conventional unreinforced technical ceramics, including alumina, silicon carbide, aluminum nitride, silicon nitride, and zirconia, have low crack resistance and therefore fracture easily under mechanical and thermo-mechanical loading. These material limitations can be addressed by integrating multi-strand long ceramic fibers to enable greater elongation to rupture, fracture toughness, thermal shock resistance, and dynamic fatigue resistance. 
     Non-oxide polycrystalline ceramic fiber, typically silicon carbide (SiC) fiber, is used as continuous-length structural reinforcement in ceramic matrix composites (CMC). SiC-based ceramic fiber for CMC manufacture has small diameter, high thermal conductivity, low surface roughness, and a carbon-free surface. Furthermore, SiC-based ceramic fiber has high tensile strength as-produced, at high temperature, under high mechanical stress, and in oxidizing environments. 
     Chemical vapor infiltration (CVI) is used to produce an environmental barrier in the form of a thin conformal encapsulation layers on ceramic fibers. In general, the coated fiber has mechanical, thermal, and chemical advantages to un-coated fiber. Boron nitride (BN) and carbon-containing crack-deflecting interfacial coatings on SiC-based fiber surfaces improve SiC-based fiber oxidation resistance at high temperatures. 
     However, the inventors have observed that defects such as broken or loose filaments and non-uniformities in the polyvinyl acetate (PVA) coating on the multi-filament SiC tow (e.g., an untwisted bundle of continuous filaments) can cause perturbations in the coating process. Such perturbations can lead to problems such as non-uniform coating thickness and filaments sticking together. Furthermore, broken or loose filaments will create fuzz in the tow transport system which can cause further filament breakage and tow rupture. 
     Accordingly, the inventors have provided improved apparatus for qualification and repair of multi-filament tow. 
     SUMMARY 
     Apparatus for qualification and repair of multi-filament tow are provided herein. In some embodiments, an apparatus for inspecting and repairing a multi-filament tow includes a first spool having a multi-filament tow wound on the first spool; a first tow tensioner following the first spool to impart a predetermined tension on the multi-filament tow; a de-sizing chamber comprising a heater to heat the multi-filament tow to a first temperature suitable for removing a coating on the multi-filament tow; an inspection chamber configured to inspect the multi-filament tow for defects; a repair chamber configured to repair the defects in the multi-filament tow; a second tow tensioner following the repair chamber to impart a predetermined tension on the multi-filament tow; and a second spool following the second tow tensioner to collect the multi-filament tow. 
     In some embodiments a method of inspecting and repairing a multi-filament tow, includes de-spooling a multi-filament tow from a first spool; heating the multi-filament tow to a first temperature suitable for removing a coating on the multi-filament tow in a de-sizing chamber; inspecting individual filaments of the multi-filament tow for defects in an inspection chamber; if a defective filament is found, repairing the defective filament in a repair chamber or removing the defective filament from the multi-filament tow; and spooling the multi-filament tow exiting the repair chamber onto a second spool. 
     In some embodiments, an apparatus for inspecting and repairing a multi-filament tow includes a first spool having a multi-filament tow wound on the first spool; a first motor coupled to the first spool to rotate the first spool and unwind the multi-filament tow from the first spool; a first tow tensioner following the first spool to impart a predetermined tension on the multi-filament tow; a first pitch control in-line with the first spool, between the first spool and the first tow tensioner, to allow the multi-filament tow to de-spool in a controlled manner; a first tension sensor in-line with the first spool, between the first pitch control and the first tow tensioner to measure a force induced on the multi-filament tow by the first tow tensioner a de-sizing chamber comprising a heater to heat the multi-filament tow to a first temperature suitable for removing a coating on the multi-filament tow; a first pulley in-line with the first spool between the first tow tensioner and the de-sizing chamber; an inspection chamber configured to inspect the multi-filament tow for defects; a repair chamber configured to repair the defects in the multi-filament tow; a second tow tensioner following the repair chamber to impart a predetermined tension on the multi-filament tow; a second pulley in-line with the first spool between the repair chamber and the second tow tensioner; a second tension sensor in-line with the second pulley and following the second tow tensioner to measure a force induced on the multi-filament tow by the second tow tensioner; a second pitch control in-line with the second pulley and following second tension sensor to allow the multi-filament tow to spool onto a second spool in a controlled manner; a second spool following the second tow tensioner to collect the multi-filament tow; and a second motor coupled to the second spool to rotate the second spool and wind the multi-filament tow onto the second spool. 
     Other and further embodiments of the present disclosure are described below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present disclosure, briefly summarized above and discussed in greater detail below, can be understood by reference to the illustrative embodiments of the disclosure depicted in the appended drawings. However, the appended drawings illustrate only typical embodiments of the disclosure and are therefore not to be considered limiting of scope, for the disclosure may admit to other equally effective embodiments. 
         FIG. 1  depicts a schematic of an apparatus for qualification and repair of multi-filament tow in accordance with some embodiments of the present disclosure. 
         FIG. 2  depicts a flowchart illustrating a method of inspecting and repairing a multi-filament tow in accordance with some embodiments of the present disclosure. 
     
    
    
     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. The figures are not drawn to scale and may be simplified for clarity. Elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation. 
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure advantageously provide improved apparatuses for qualification and repair of multi-filament tow. Embodiments of the present disclosure advantageously identify and remove or repair defects of individual filaments prior to exposing the multi-filament tow to a barrier coating process. Embodiments of the present disclosure advantageously provide improved uptime, throughput, and yield as well as improved quality tow. 
     For example, embodiments of the present invention provide an automated system for qualifying incoming ceramic tow for subsequent environmental barrier formation via chemical vapor infiltration. Conventional equipment for ceramic tow chemical vapor infiltration (CVI) relies on in situ repair at the time of tow break or tow jump, resulting in low CVI system productivity. Embodiments of the present invention improve CVI system performance by qualifying and repairing tow ex situ (in advance of initiating the CVI process). Tow, specifically SiC-based ceramic fiber, is de-spooled from a conventional spool (or bobbin), desized (stripped of poly-vinyl acetate (PVA), poly-vinyl alcohol, epoxy, PVA blended with polyethylene oxide), optically characterized for breaks, breaks repaired using various polymer splicing technology, and then transferred to a processing reel and/or otherwise conveyed to the CVI process. 
       FIG. 1  depicts an example of a system  100  for qualification and repair of multi-filament tow in accordance with some embodiments of the present disclosure. In some embodiments, the multi-filament tow is a bundle of continuous filaments, for example ceramic fibers (e.g., alumina, silicon carbide, aluminum nitride, silicon nitride, zirconia). In some embodiments, the system  100  is within an enclosure  134  that can be evacuated to allow the system  100  to run under a vacuum to avoid chemical reaction between the atmosphere and the multi-filament tow  102 . In some embodiments, the temperature and the humidity within the enclosure can be regulated in order to minimize oxidation of the multi-filament tow  102 . 
     The system  100  comprises a multi-filament tow  102 , wound on a first spool  104 . The first spool  104  is coupled to a first motor  114  to rotate the spool and unwind the multi-filament tow  102  from the first spool  104 . The multi-filament tow  102  passes through a first pitch control  106  which controls the de-spooling of the multi-filament tow  102  to minimize or prevent damage to the multi-filament tow  102  and to allow the individual filaments in the multi-filament tow  102  to maintain their position relative to each other during de-spooling. In some embodiments, the first pitch control  106  is positioned with respect to the first spool  104  to maintain the multi-filament tow  102  in a substantially horizontal orientation. In some embodiments, the first pitch control  106  comprises opposing pulleys or rollers that rotate as the multi-filament tow  102  passes through. The distance between the opposing pulleys is dependent on the thickness of the multi-filament tow  102 . In some embodiments, the first pitch control  106  further comprises a sensor to measure the length (i.e., amount) of the tow that has passed through the first pitch control  106 . 
     The system  100  further comprises a first tension sensor  108 . In some embodiments, the multi-filament tow  102  passes from the first pitch control  106  to the first tension sensor  108 . In some embodiments, the first tension sensor  108  is positioned approximately level with the first spool  104  such that the multi-filament tow  102  travels substantially horizontally from the first spool  104  to the first tension sensor  108 . In some embodiments, the first tension sensor  108  is a tension strain gauge coupled to an idler pulley to measure the force on the multi-filament tow  102 . 
     In some embodiments, a first tow tensioner  110  is provided to control the tension on the multi-filament tow  102 . For example, in some embodiments, the first tow tensioner  110  provides about  0 . 4  Newton of tension on the multi-filament tow  102  as measured by the first tension sensor  108 . In some embodiments, the first tow tensioner  110  is placed below the height of the first tension sensor  108 . In some embodiments, the first tow tensioner  110  is a pulley having a movable axial position in order to increase or decrease the tension on the multi-filament tow  102 . In some embodiments, the first tow tensioner  110  is coupled to a third motor that moves the first tow tensioner  110  to control the linear distance between the first tow tensioner  110  and the first tension sensor  108 . For example, increasing the distance between the first tow tensioner  110  and the first tension sensor  108  idler pulley will increase the tension on the multi-filament tow  102  while decreasing the distance between the first tow tensioner  110  and the first tension sensor  108  idler pulley will decrease the tension on the multi-filament tow  102 . Tension control during spooling and unspooling provides uniform conditions for de-sizing, inspection, repair and re-spooling. In some embodiments, the first tow tensioner  110  is configured to move in a substantially vertical direction.  FIG. 1  shows the first tow tensioner  110  placed a first vertical distance below the height of the first tension sensor  108 ; however, the first tow tensioner  110  may alternatively be placed above the first tension sensor  108 , with the multi-filament tow  102  wrapped around the idler pulley in the opposite direction. 
     The multi-filament tow  102  passes over a first pulley  112 , which may for example be at about the height of the first spool  104 , and into a de-sizing chamber  116 . Within the de-sizing chamber  116 , the multi-filament tow  102  is heated to a temperature of about 500 to about 1000 degrees Celsius to remove the polyvinyl acetate (PVA) coating on the multi-filament tow  102 . The PVA coating holds the individual filaments in a bundle. The de-sizing chamber  116  may heat the multi-filament tow  102  using any suitable heating mechanism capable of heating the multi-filament tow  102  to about 500 to about 1000 degrees Celsius, such as a heat exchanger, heat lamps, or the like. 
     Once the PVA coating is removed, the multi-filament tow  102  passes through an inspection chamber  118  and then through a repair chamber  120 . Within the inspection chamber  118 , the multi-filament tow  102  is inspected for defects such as breaks in individual filaments in the multi-filament tow  102 . The inspection chamber  118  uses an optical detection process for identifying and quantifying defects in the multi-filament tow  102 . In some embodiments, the defective filaments may be physically marked or the location of the defective filaments may be measured, for example in meters or other suitable units, and recorded. Within the repair chamber  120  the identified defect is repaired or removed. For example, in some embodiments, a broken filament is removed from the multi-filament tow  102  and guided to a reject path for disposal or, if possible, to be re-spooled and re-used. 
     Upon exiting the repair chamber  120 , multi-filament tow  102  passes over a second pulley  122 , which for example may be at the height of the first spool  104 , and to a second tow tensioner  124 . The second tow tensioner  124  may be placed below the height of the second pulley  122 . In some embodiments, the second tow tensioner  124  is a pulley having a movable axis to control the distance between the second tow tensioner  124  and the second pulley  122 . In some embodiments, the second tow tensioner  124  provides about  0 . 4  Newton of tension on the multi-filament tow  102  as measured by the second tension sensor  126 . In some embodiments, the second tow tensioner  124  is coupled to a fourth motor that moves the second tow tensioner  124  to control the distance between the second tow tensioner  124  and the second pulley  122 . Increasing the distance between the second tow tensioner  124  and the second pulley  122  will increase the tension on the multi-filament tow  102  while decreasing the vertical distance between the second tow tensioner  124  and the second pulley  122  will decrease the tension on the multi-filament tow  102 . In some embodiments, the second tow tensioner  124  moves in a substantially vertical direction. 
     The multi-filament tow  102  passes over a second tension sensor  126 . In some embodiments, the second tension sensor  126  is a tension strain gauge coupled to an idler pulley which measures the force induced by the second tow tensioner  124 . The multi-filament tow  102  then passes through a second pitch control  128  which allows the multiple filaments to spool onto the second spool  130  in a controlled manner preventing damage to the multi-filament tow  102  and allow the individual filaments to maintain their position relative to each other during re-spooling. In some embodiments, the second pitch control  128  comprises opposing pulleys or rollers. The multi-filament tow  102  passes in-between the pulleys or rollers. In some embodiments, the second pitch control  128  further comprises a sensor to measure the position of the multi-filament tow  102 . 
     The multi-filament tow  102  is wound onto a second spool  130 . The second spool  130  is coupled to a second motor  132  to rotate the spool and wind the multi-filament tow  102  onto the second spool  130 . In some embodiments, the second spool is a large diameter spool which provides less bending stress on the multi-filament tow. Once the entire spool of multi-filament tow  102  has been inspected and repaired the spool can be further processed. For example, the inspected and repaired spook can be placed in a chemical vapor deposition chamber to deposit barrier materials on the filaments. 
       FIG. 2  depicts a flowchart illustrating a method  200  of inspecting and repairing a multi-filament tow in accordance with some embodiments of the present disclosure. At  202 , the multi-filament tow is de-spooled from the first spool. At  204 , the multi-filament tow is heated to a first temperature of about 500 to about 1000 degrees Celsius to remove the polyvinyl acetate (PVA) coating on the multi-filament tow. The PVA coating removal may be accomplished, for example, as discussed above with respect to the de-sizing chamber  116 . 
     At  206 , individual filaments of the multi-filament tow are inspected for defects. The inspection of the filaments can be performed in the inspection chamber  118  as discussed above. For example, within the inspection chamber  118 , the multi-filament tow  102  is inspected for defects such as breaks in individual filaments in the multi-filament tow  102 . The inspection chamber  118  uses an optical detection process for identifying and quantifying defects in the multi-filament tow  102 . In some embodiments, the defective filaments may be physically marked or the location of the defective filaments may be measured, for example in meters or other suitable units, and recorded. 
     At  208 , it is determined if a defective filament has been found. If a defective filament has not been found, the multi-filament tow is spooled onto a second spool at  212 . If a defective filament is found, the defective filament is repaired or removed at  210 . The defective filament can be repaired or removed, for example, in the repair chamber  120  discussed above. In some embodiments, the defective filament, such as a broken filament, is removed from the multi-filament tow and guided to a reject path for disposal or, if possible, to be re-spooled and re-used. 
     While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof.