Patent Publication Number: US-2011048111-A1

Title: Method of leak testing aerospace components

Description:
STATEMENT OF GOVERNMENT INTEREST 
     This invention was in part produced through funding under a U.S. Government sponsored program (Contract No. N00019-02-C-3003) and the United States Government has certain rights therein. 
    
    
     BACKGROUND 
     The present invention relates generally to a method of leak testing components that have internal cavities and more particularly to a method of leak testing aerospace components that have internal cavities. 
     Aerospace electrical components are particularly difficult to leak test because in many instances they must be leak free prior to and after a molding process which bonds them to additional aerospace components. The electrical components must be leak free prior to the molding process to insure internal dimensional stability. This internal dimensional stability is important for maintaining good electrical contact between male and female electrical components when these components are interconnected. Additionally, aerospace electrical components should be leak free before and after the molding process to ensure that corrosive elements do not enter the interior of the electrical component and corrode the electrical contacts disposed therein. Conventional methods of leak testing, such as water submersion testing, may be difficult or impossible to perform after the electrical components have been bonded to additional aerospace components, or risk introducing corrosive elements into the interior of the electrical components. 
     Conventional leak testing methods carried out prior to the molding process also risk introducing contaminants to the external surfaces of the electrical components. These contaminants may negatively affect the strength of the bond formed between the electrical components and the additional aerospace components. Further complicating matters, aerospace electrical components typically have thin exterior walls to reduce component weight. The thin component walls can structurally fail if a large pressure differential is created between the internal pressure on the electrical component and the pressure external to the electrical component. 
     Because introducing contaminants or corrosive elements either internally or externally to the aerospace electrical components can impair component functionality, conventional leak testing can be rather destructive. If a leak occurs or contaminants are determined to have been introduced to the electrical component, the component is generally destroyed, increasing the component scrap rate. This increased scrap rate increases overall manufacturing costs. 
     SUMMARY 
     A method includes providing an aerospace electrical component having a wall and a feature that extends through the wall, introducing a detectable residue-free gas on a first side of the wall, and testing for the presence of the detectable gas on a second side of the wall. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional view of a gas turbine engine. 
         FIG. 2  is a perspective view of a section of an inlet case and an inlet strut of a gas turbine engine with an inlet shroud fairing exploded away to show portions of a heater system. 
         FIG. 3A  is a perspective view of an electrical connector. 
         FIG. 3B  is a sectional view of the electrical connector and the outer shell of the shroud fairing viewed along fluid communication element  3 B- 3 B of  FIG. 2 . 
         FIGS. 4A-4C  show alternative methods of leak testing the electrical connector. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows an embodiment of a gas turbine engine  10 . The engine  10  includes a casing  12 , inlet struts  14 , shroud fairings  16 , a fan  18 , a compressor section  20 , a combustion section  22 , a turbine section  24 , and rotors  26 . 
     In  FIG. 1 , the casing  12  surrounds the moving components of the engine  10  and defines an airflow passageway. Toward the inlet end of the engine  10 , the inlet struts  14  interconnect with the casing  12 . At least the leading edge of the inlet struts  14  are surrounded by and secured to the shroud fairings  16 . The fan  18  is disposed downstream of the inlet struts  14  and shroud fairings  16 . The casing  12  surrounds the compressor section  20 , the combustion section  22 , and the turbine section  24 , which are located downstream of the fan  18 . The rotors  26  extend within the casing  12  and interconnect with the fan  14 . The turbine section  24  turns the rotors  26 . The rotors  26  rotate about a rotational axis  28  to drive the fan  18  and compressor section  20 . 
     The inlet struts  14  may be oriented within the casing  12  to direct intake air into the forward part of the compressor section  20 . The shroud fairings  16  (which are wrapped around each of the inlet struts  14 ) may be heated to prevent the formation of ice on the surfaces of the shroud fairings  16 . The air passes between the struts  14  and fairings  16  and is compressed in the compressor section  20 . The compressed air is mixed with fuel and burned in the combustion section  22 . In the turbine section  24 , the gases from the combustion section  22  expand to rotate the rotors  26 , which in turn drive the fan  18  and compressor section  20 . 
       FIG. 1  merely illustrates one exemplary embodiment of a gas turbine engine that utilizes electrical components. Aerospace systems other than the propulsion system also utilize electrical components, and therefore, would benefit from the present invention. 
       FIG. 2  is a perspective view of a portion of an outer case  30  and an inner case  31  interconnected by one inlet strut  14 .  FIG. 2  also includes an exploded perspective view of one shroud fairing  16 . The inlet strut  14  includes an electrical probe (or plug)  32 . The shroud fairing  16  includes a heater mat  34 , an electrical connector (or jack)  36 , and an outer shell  38 . The heater mat  36  includes heating elements  40  and has a leading edge  42 . 
     The inlet strut  14  extends radially inward from the annular outer case  30  to the annular inner case  31 . The electrical probe  32  projects from the leading edge portion of the inlet strut  14  is complementary to and inserts into the electrical connector  36  when the shroud fairing  16  is assembled on the inlet strut  14 . The insertion of the electrical probe  32  in the electrical connector  36  allows an electrical connection to be formed therebetween. 
     The shroud fairing  16  includes the U-shaped folded heater mat  34 , which surrounds and wraps the leading edge portion of the inlet strut  14 . The electrical connector  36  is one particular exemplary type of electrical component, selected from the many aerospace electrical components, which can benefit from the method of leak testing described herein. In  FIG. 2 , the electrical connector  36  is disposed between the folded sides of the heater mat  34 , adjacent the leading edge of the heater mat  34 . The electrical connector  36  interconnects with the heater mat  34  and is electrically connected to the electrical elements  40  adjacent the outer radial edge of the heater mat  34 . In one embodiment, the outer shell  38  is a ply composite matrix and is molded or otherwise formed over the heater mat  34 . 
     The bond that interconnects the electrical connector  36  and the heater mat  34  can be accomplished by resin transfer molding. Alternatively, the electrical connector  36  can be joined to the heater mat  34  by another type of molding such as compression molding. The electrical connector  36  can also be joined to the heater mat  34  by, for example, autoclaving, welding, brazing, soldering, mechanical crimping/stapling or adhesives. The heater mat  34  and electrical connector  36  may be constructed from any suitable polymeric material or composite polymer matrix. The metallic heating elements  40  extend along the radial length of the heating mat  36  (either along the outer surface or internally within the mat  36 ) and may be sputtered, insert molded, or adhesively bonded to the heating mat  36 . In  FIG. 2 , the heating elements  40  are deposited within the heating mat  36  and are therefore illustrated with dashed lines. 
     When the shroud fairing  16  is assembled, the leading edge  42  of the heater mat  34  or a leading portion of the outer shell  38  abuts the inlet strut  14 . The sides of the heater mat  34  and outer shell  38  extend rearward around a portion of each inlet strut  14  and may be secured thereto by fasteners or adhesive. The electric probe  32  extending from the inlet strut  14  inserts into the electrical connector  36  to supply power to the heating elements  40 . The heating elements  40  provide heat along the entire length of the outer shell  38  thereby preventing the formation of ice on the exterior surface of the outer shell  38  and in any space between the heater mat  34  and the inlet strut  14 . 
       FIG. 3A  is a perspective view of the electrical connector  36 .  FIG. 3B  is a sectional view of the heater mat  34  and the electrical connector  36 . The electrical connector  36  includes a top wall  44 , a bottom wall  46 , end walls  47   a  and  47   b , sidewalls  48   a  and  48   b , an aperture  49 , a plug  50 , and electrical contacts  51 . The top wall  44 , bottom wall  46 , and sidewalls  48  define an interior cavity  52 , which has an open end  52   a  and for receiving the electrical probe  32  and a closed end  52   b.    
     The top and bottom walls  44  and  46  of the electrical connector  36  body extend generally parallel to each other between the folded sides of the heater mat  34 . The sidewalls  48   a  and  48   b  extend generally perpendicularly between the top and bottom walls  44  and  46 . The outer surfaces of portions of the walls  44 ,  46 ,  47   a ,  47   b ,  48   a  and  48   b  may be chemically or adhesively bonded, molded, autoclaved, welded, brazed, soldered, mechanically crimped/stapled/fastened, or otherwise affixed to the heater mat  34 . In one embodiment, the plug  50  fills aperture  49  in endwall  47   b  to form closed end  52   b  of interior cavity  52 . The electrical contacts  51  extend through the sidewalls  48   a  and  48   b  from the interior cavity  52  to the exterior of each of the sidewalls  48   a  and  48   b  and are electrically connected to the electrical elements  40  of the heater mat  34  ( FIG. 2 ). Together the walls  44 ,  46 ,  47   a ,  47   b ,  48   a ,  48   b  and the plug  50  form the interior cavity  52 , which receives the electrical probe  32  when the shroud fairing  16  is assembled on the inlet strut  14  ( FIG. 2 ). More specifically, the electrical probe  32  extends through the open end  52   a  into the interior cavity  52  when the shroud fairing  16  is assembled on the inlet strut  14 . 
       FIGS. 4A to 4C  are sectional views of the electrical connector  36  showing alternative methods of leak testing the electrical connector  36 . In addition to the components already described, the electrical connector  36  shown in  FIGS. 4A-4C  includes a second plug  54  which has a port  56  therein. 
       FIG. 4A  illustrates a first method of leak testing the electrical connector  36 . The method shown in  FIG. 4B  includes a fluid communication element  58 A, a container  60 A, and a detector  62 A. 
     The second plug  54  is temporarily placed in the open end  52   a  of the electrical connector  36  to hermetically seal the interior cavity  52  during the duration of the leak testing. Once testing is completed the second plug  54  may be removed. The port  56  extends through the second plug  54  to interconnect with the fluid communication element  58 A. The fluid communication element  58 A may include any means of transferring a gas including tubing or piping. 
     The fluid communication element  58 A transfers the detectable residue-free gas from the container  60 A (such as a balloon or tank) through the port  56  to the interior cavity  52 . The container  60 A acts as a gas source to provide a detectable amount of the residue-free gas to one or several electrical connectors  36 . The detector  62 A, for example a commercially available helium mass spectrometer (if helium is used as the detectable gas), is moved externally around the walls  44 ,  46  and  48  and plugs  50  and  54  to check for detectable leaks. 
     More particularly, the second plug  54  is inserted into open end  52   a  to hermetically seal the internal cavity  52 . Any plug which has a shape capable of mating with open end  52   a  to hermetically seal the interior cavity  52  may be used. The second plug  54  may be, for example, a silicone, rubber, or foam insert. 
     By way of example, the second plug  54  may have a flange with a gasket (which abuts the trailing edges of the top and bottom walls  44  and  46  when the second plug  54  is inserted into the open end  52   a  of the interior cavity  52 ) and/or may be tapered such that the second plug  54  contacts the walls  44 ,  46 ,  47   a ,  48   a  and  48   b  when inserted to a sufficient depth within the internal cavity  52 . As the second plug  54  is inserted into open end  52   a , the surface of the second plug  54  in contact with the walls  44 ,  46 ,  48   a  and  48   b  increases while the spacing of the walls  44  and  46  remains generally constant. The tapered second plug  54  creates a hermetic seal when the second plug  54  is inserted a sufficient distance within the internal cavity  52 . Alternatively, a range of different expandable plugs such as part numbers 5300+ or 6200+ from Shaw Plugs may be used to create a hermetic seal depending on the testing requirements and geometry of the electrical component. 
     The fluid communication element  58 A transfers the detectable residue-free gas from the container  60 A through the port  56  to the interior cavity  52 . In one embodiment, container  60 A is configured to provide between about 1 psi and about 5 psi (about 6.895 kPa and about 34.47 kPa) of detectable gas to the internal cavity  52  of the electrical connector  36 . The only limitation on the pressure provided to the internal cavity  52  is that the pressure differential created should be sufficiently low to maintain the structural integrity of the walls  44 ,  46 ,  47   a ,  47   b ,  48   a , and  48   b  and plugs  50  and  54 . If a leak is present in the electrical connector  36 , the detectable gas from the internal cavity  52  will flow from the cavity  52  to the exterior of the electrical connector  36  as a result of the increased pressure of the internal cavity  52  (which results from the addition of the detectable gas) relative to the external pressure on the electrical connector  36 . Any gas that escapes from the interior cavity  52  of the electrical connector  36  eventually comes into contact with the detector  62 A as it is moved about the electrical connector  36 . The detector  62 A is capable of indicating the presence of the gas based on this contact to the operator. 
     A gas is detectable if it is capable of being tested for in a fluid medium such as air. Examples of detectable gases (in addition to helium) may include: carbon dioxide, methane, carbon monoxide, di-nitrogen-monoxide, hydrogen, xenon, argon, neon, and sulfur hexafluoride. 
     A gas is residue-free if it does not have (solid, liquid, or gas) constituents that negatively interfere with the bond strength between the electrical component and the aerospace component to which the electrical component is bonded. Thus, a gas would not be residue-free if it has constituents which interfere physically to weaken the bonding interface. Similarly, a gas would not be residue-free if it has constituents that interfere chemically with the covalent bonding at the intersection of the component surfaces or inhibit the cure of any polymer(s) the components may utilize. Several examples of solid or liquid constituent residues that inhibit bonding (and are therefore contaminants) include: waxes, oils, salts, oxides or organometallics. 
     The method of leak testing shown in  FIG. 4A  allows the electrical connector  36  to be leak tested prior to and after the bonding of the electrical connector  36  to the heater mat  34  ( FIGS. 2 and 3B ). For example, a balloon may simply be fluidly connected to the electrical connector  36  after the electrical connector  36  has undergone the resin transfer molding process which can be used to bond the connector  36  to the heater mat  34  ( FIGS. 2 and 3B ). The method of leak testing described also increases the likelihood of that the electrical connector  36  will have internal dimensional stability because a low pressure differential internal and external to the electrical connector  36  can be utilized. The internal dimensional stability of the electrical connector  36  may also be preserved because the leak testing method described can occur prior to the molding process (which has the potential to fill the internal cavity  52  with polymer and resin if a leak is present in the electrical connector  36 ). Additionally, because a residue-free noncorrosive gas is utilized, the risk that corrosive elements will enter the interior cavity  52  of the electrical connector  36  is reduced. This reduces the likelihood of that the electrical contacts  51  will later corrode. The residue-free gas also reduces the likelihood that contaminants will be introduced to the external surfaces of the electrical connector  36  during leak testing. Thus, the method of leak testing described herein does not negatively impact the strength or durability of the bond between the electrical connector  36  and the heater mat  34 . 
       FIG. 4B  shows another method of leak testing the electrical connector  36 . The method shown in  FIG. 4B  includes a fluid communication element  58 B, a container  60 B, a detector  62 B, a support surface  64 A, a seal  66 A, and a containing element  68 . The support surface  64 A has a first port  70  and a second port  72  extending therethrough. 
     The second plug  54  is temporarily placed in the open end  52   a  of the electrical connector  36  and the electrical connector  36  is disposed such that the second plug  54  abuts the support surface  64 A. The support surface  64 A may be a structural aerospace member or a metallic base testing plate. The hermetic seal  66 A is disposed around the second plug  54  between the endwall  47   a  and the support surface  64 A. The containing element  68  (such as a bell jar) is placed over the electrical connector  36  and contacts the support surface  64 A to define an enclosed space around the electrical connector  36 . 
     The first port  70  extends through the support surface  64 A to communicate with the enclosed space within the containing element  68 . Another portion of the first port  70  interconnects with the fluid communication element  58 B which interconnects with the container  60 B. 
     The second port  72  aligns with the port  56  in the second plug  54  and is in fluid communication therewith. A portion of the detector  62 B is disposed immediately adjacent to or in direct communication with the second port  72 . The detector  62 B, for example a commercially available helium mass spectrometer (if helium is used as the detectable gas), is capable of indicating the presence of the gas based on this contact to the operator. 
     In one embodiment, the containing element  68  is capable of creating a hermetic seal between the enclosed space and the external environment which allows the enclosed space to be positively or negatively pressurized. The fluid communication element  58 B transfers a detectable residue-free gas from the container  60 B (which may be, for example, a balloon or a tank disposed external to the containing element  68 ) through the first port  70  to the enclosed space within the containing element  68 . In one embodiment, container  60 B is configured to provide between about 1 psi and about 5 psi (about 6.895 kPa and about 34.47 kPa) of detectable gas to the containing element  68  of the electrical connector  36 . The only limitation on the pressure provided to the containing element  68  is that the pressure differential which results should be sufficient to maintain the structural integrity of the walls  44 ,  46 , and  48  and hermetic seal  66 A. If a leak is present in the electrical connector  36 , the detectable gas within the containing element  68  will flow from the enclosed space within the containing element  68  to the interior cavity  52  of the electrical connector  36  as a result of the increased pressure within the containing element  68  (which results from the addition of the detectable gas) relative to the internal pressure on the electrical connector  36 . In another embodiment, container  60 B is configured to provide a pressure differential of about 1 psi and about 5 psi (about 6.895 kPa and about 34.47 kPa) between the pressure of the containing element  68  and the pressure of the interior cavity  52  of the electrical connector  36  (which maybe evacuated or pressurized to several hundred psi). Any detectable gas that enters the electrical connector  36  eventually contacts the detector  62 B, which indicates the presence of the gas to the operator. 
     The method of leak testing shown in  FIG. 4B  allows the electrical connector  36  to be rapidly leak tested on a pass/fail basis. The method of leak testing described also reduces failure and scrap rates of the electrical connector  36  due to structural failures (such as wall collapse) because testing may be conducted with a low pressure differential internal and external to the electrical connector  36 . Additionally, because a residue-free noncorrosive gas is utilized, the risk that corrosive elements will enter the interior cavity  52  of the electrical connector  36  is reduced. This reduces the likelihood of that the electrical contacts  51  will later corrode. The residue-free gas also reduces the likelihood that contaminants will be introduced to the external surfaces of the electrical connector  36  during leak testing. Thus, the method of leak testing described herein does not negatively impact the strength or durability of the bond between the electrical connector  36  and the heater mat  34 . 
       FIG. 4C  shows yet another method of leak testing the electrical connector  36 . The method shown in  FIG. 4C  includes a fluid communication element  58 C, a container  60 C, a detector  62 C, a support surface  64 B, a seal  66 B, and a positive or negative pressure displacement device  74 . The support surface  64 B has a port  76  extending therethrough. 
     Similar to the method shown in  FIG. 4B , the second plug  54  is temporarily placed in the open end  52   a  of cavity  52  of the electrical connector  36 , and the electrical connector  36  is disposed such that the second plug  54  abuts the support surface  64 A. The support surface  64 A may be a structural aerospace member or a metallic base testing plate. The hermetic seal  66 B is disposed around the second plug  54  between the top and bottom walls  44  and  46  and the support surface  64 B. A portion of the detector  62 C is disposed immediately adjacent to or in direct communication with the port  76 . The port  76  extends through the support surface  64 B and aligns with the port  56  in the second plug  54  and allows for fluid communication between the internal cavity  52  and the detector  62 C. The negative pressure displacement device  74  is also disposed in fluid communication with the port  76  upstream of the detector  62 C. 
     The fluid communication element  58 C, for example a gas probe, piping or tubing, communicates with the container  60 C. As it is moved externally around the walls  44 ,  46 ,  47   a ,  47   b ,  48   a  and  48   b  of the electrical connector  36 , fluid communication element  58 C supplies detectable quantities of gas externally to the electrical connector  36 . In one embodiment, between about 1 psi and about 5 psi (about 6.895 kPa and about 34.47 kPa) of detectable gas is supplied externally to the electrical connector  36 . 
     If a negative pressure displacement device  74 , for example a vacuum pump, is utilized, the interior cavity  52  of the electrical connector  36  may be evacuated or its pressure may be reduced to create a pressure differential between the interior of the electrical connector  36  and the pressure external to the connector  36 . If a leak is present in the electrical connector  36 , the detectable gas introduced externally to the electrical connector  36  from the fluid communication element  58 C will flow from the external environment to the interior cavity  52  of the electrical connector  36  as a result of the reduced pressure of the interior cavity  52  within the electrical connector  36  relative to the external pressure. Gas that enters the electrical connector  36  eventually contacts the detector  62 C, which indicates the presence of the gas to the operator. 
     The method of leak testing shown in  FIG. 4C  reduces failure and scrap rates of the electrical connector  36  due to structural failures (such as wall collapse) because testing may be conducted with low pressure differential internal and external to the connector  36 . Additionally, because a residue-free noncorrosive gas is utilized, the risk that corrosive elements will enter the interior cavity  52  of the electrical connector  36  is reduced. This reduces the likelihood of that the electrical contacts  51  will later corrode. The residue-free gas reduces the risk of introducing contaminants to the external surfaces which may interfere with the bonding of the electrical connector  36  to the heater mat  34  ( FIGS. 2 and 3B ). Thus, the method of leak testing described herein does not negatively impact the strength or durability of the bond between the electrical connector  36  and the heater mat  34 . 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.