Abstract:
A component including a surface subject to wear by an electrically conductive wear counterface ( 50 ). The component comprises a substrate ( 10 ); one or more material layers ( 32 ) overlying the substrate ( 10 ); a wear surface layer ( 16 ) overlying the one or more material layers ( 32 ); a first pair of spaced apart and electrically open wear sensor conductors ( 12/14 ) disposed in the substrate ( 10 ), in the one or more material layers ( 32 ), or in the wear surface layer ( 16 ); a first wear warning electrical circuit ( 68/69/70/74 ) for communicating with the first pair of conductors ( 12/14 ) for providing a first wear warning; and wherein when the wear counterface ( 50 ) has worn overlying layers, the wear counterface ( 50 ) interconnects the first pair of conductors ( 12/14 ) to activate the first wear warning circuit ( 68/69/70/74 ).

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to sensors for detecting surface wear in one or both contacting surfaces of a machine, where at least one of the contacting surfaces comprises a conductive material. 
       BACKGROUND OF THE INVENTION 
       [0002]    Relative motion between contacting components in a machine (e.g., high performance machines or engines) can result in excessive wear of one or both components. For example, components subjected to high frequency and low frequency vibrations may result in excessive wear of component attachments or mating surfaces. The component wear, if left undetected, can cause component and machine malfunctions. For example, spring clips in combustion turbine engine experience surface wear from contact with other components due to operational vibrations and dynamic forces. 
         [0003]    In some applications, component wear can be controlled to acceptable levels by using lubricants, by employing materials with high resistance to wear and/or by design features that limit motion and contact and resulting component wear. However, there are many situations where relative motion cannot be eliminated, such as in brake linings, meshing gears, contacting sliders and slip fits; wear is unavoidable in such applications. 
         [0004]    Knowledge of the wear condition of critical components can be used to avoid forced outages due to unexpected component failures. Such knowledge also enables the machine to be shut down for repair of the worn components at a convenient scheduled time, rather than continuing operation until a component is worn beyond repair or an emergency shut down is required. Significant costs can be saved by both avoiding forced outages and by ensuring the worn parts can be repaired instead of scrapped when a scheduled outage is performed. 
         [0005]    The extent of wear and the suitability of the component for continued service can be determined by visual and/or dimensional inspection. In some applications, wear indicators are embedded within or proximate one or more of the contacting surfaces. For example, in the context of brake linings, wear limit notches or “squealers” generate an audible warning when a predetermined amount of lining wear has occurred. 
         [0006]    However, there are many applications where periodic inspection is not feasible due to such factors as, for example, time and labor expenses, cost of inspection and operational disruptions due to inspection down time. In addition, visual and audible warnings are not always feasible monitoring solutions, as is the case when monitoring internal components of a gas turbine engine. Thus, there is a need for a system that can monitor component wear while the component is in an operational state. 
         [0007]    Wear sensors mounted in one or both of the wearing components can advantageously provide real-time monitoring of component wear during machine operation. These sensors measure the amount of wear that occurs in regions prone to wear and notify an operator when a preselected amount of wear has occurred. The sensors improve machine reliability and enable more accurate maintenance planning. Such monitoring also improves safety and reduces operating and maintenance costs by indicating a maintenance requirement before any component damage occurs. Real time wear monitoring also avoids unscheduled outages. 
         [0008]    A conductive wear sensor is described in commonly-owned U.S. Pat. No. 7,270,890, entitled, Wear Monitoring System with Embedded Conductors. The patent describes a sensor comprising a closed circuit conductive trace that is transformed to an open circuit condition when a counterface wears through the conductive trace. While this sensor has many applications, frequently both members of a wear couple (i.e., two components in contact along the wear surface) are electrically conductive metals. An open circuit cannot be detected in such an electrically conductive component. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The invention is explained in the following description in view of the drawings that show: 
           [0010]      FIGS. 1-3  illustrate three different embodiments according to the present invention. 
           [0011]      FIGS. 4-7  illustrate successive steps of a process for applying a wear sensor of the present invention to a substrate. 
           [0012]      FIG. 8  illustrates a cross-sectional view of a substrate including the wear sensor of the present invention. 
           [0013]      FIGS. 9-11  illustrate wear stages of a substrate surface caused by motion of a wear counterface. 
           [0014]      FIG. 12  illustrates a cross-sectional view of a substrate worn by a wear counterface. 
           [0015]      FIGS. 13-19  illustrate cross-sectional views of various embodiments of wear sensors for different applications. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    Before describing in detail the particular methods and apparatuses related to an open circuit wear sensor for use with a conductive counterface in accordance with various aspects of the present invention, it should be observed that the present invention, in its various embodiments, resides primarily in a novel and non-obvious combination of hardware and method steps. Accordingly, the hardware and method steps have been represented by conventional elements in the drawings, showing only those specific details that are pertinent to the present invention so as not to obscure the disclosure with details that will be readily apparent to those skilled in the art having the benefit of the description herein. 
         [0017]    The following described embodiments are not intended to define limits of the structures or methods of the invention but to provide only exemplary constructions. The embodiments are permissive rather than mandatory and illustrative rather than exhaustive. 
         [0018]    According to the present invention, an open circuit wear sensor, comprising for example two proximate wear sensor conductors configured in an open-circuit arrangement, is formed in a dielectric substrate or a conductive substrate. In the latter application, the wear sensor conductors are insulated from the conductive substrate. In either case, a dielectric layer (a wear surface or wear coating) is formed over the wear sensor conductors and when the wear surface is worn by a conductive wear counterface, the conductors are exposed and the counterface interconnects (bridges) or shorts the conductors. This action completes a circuit and provides an indication (a wear indication) that the wear surface has been breached. 
         [0019]    Generally, the wear surface (also referred to as a wear resistant coating or simply a wear coating) is defined as the outermost material layer that contacts the wear counterface. A material of the wear surface may be conductive or insulative. As applied to the present invention, in the former situation, the wear sensor conductors are insulated from the conductive material of the wear surface. In any case, the wear sensor conductors of the present invention are disposed below the wear surface, within the wear surface, within the substrate or within a material layer between the substrate and the wear surface. 
         [0020]    A wear indicator connected to the conductors is energized only when the dielectric material is breached and the wear sensor conductors are shorted by the wear counterface. The wear indicator is not energized when the conductors are open. 
         [0021]    The wear sensor conductors may be deposited on or within any coated or uncoated substrate material, on or within any material layer, or within the wear layer material. For example, the wear sensor conductors may be disposed with a trench formed in the material. Although a material of the substrate and the wear layer may be conductive or insulative as described above, a material of the wear counterface must be electrically conductive (or comprise an electrically conductive region) to short the conductors and activate the wear indicator. 
         [0022]      FIG. 1  illustrates a cross-sectional view of a dielectric substrate  10  and normally-open proximate wear sensor conductors  12  and  14 , two elements of a wear sensor, formed on an upper surface  10 A of the substrate  10 . A dielectric wear surface layer  16  (the wear surface layer may also be referred to as a wear resistant coating layer) is formed over the upper surface  10 A and the conductors  12  and  14 . A wear counterface (not illustrated) wears the wear surface  16  during operation of the substrate  10 , shorting the conductors  12  and  14  to close an external circuit and operate the wear indicator, as further described below. 
         [0023]    In another embodiment, the conductors  12  and  14  are disposed within the wear surface  16  between an upper wear surface  16 A and a lower wear surface  16 B. See  FIG. 2 . In yet another embodiment, the conductors  12  and  14  are disposed within, over or under a material layer disposed between the upper surface  10 A of the substrate  10  and the lower wear surface  16 B of the wear surface  16 . 
         [0024]      FIG. 3  illustrates the wear sensor conductors  12  and  14  embedded within the non-conductive substrate  10 . The surface  10 A is worn by the wear counterface until the conductors are exposed and the wear counterface interconnects or shorts the conductors  12  and  14  to activate the wear indicator as explained below. 
         [0025]      FIG. 4  begins a sequence of figures illustrating process steps for fabricating the normally-open circuit wear sensor conductors on or within a conductive substrate according to the present invention.  FIG. 4  illustrates an exposed surface  30 A of a conductive substrate  30  or a conductive coating overlying a substrate. The exposed wear surface  30 A is worn during operation of the substrate and thus wear sensor conductors are formed on or embedded within the exposed surface  30 A, suitably insulated from the conductive substrate. 
         [0026]    As illustrated in  FIG. 5 , a dielectric material region  32  is formed on the exposed surface  30 A. In one embodiment the dielectric region  32  is about 1-10 mils thick. See also the cross-sectional view of  FIG. 8 . 
         [0027]    A wear sensor  38  comprising two wear sensor conductors  40  and  42 , see  FIG. 6 , is formed on an upper surface  32 A of the dielectric material region  32 . In one embodiment a thickness of material forming each conductor  40  and  42  is about 1-6 mils. 
         [0028]    A dielectric layer  46  (which can serve as the wear surface layer or wear coating) is formed over the wear sensor conductors  40  and  42  and completely or partially over exposed regions of the upper surface  32 A. See  FIGS. 7 and 8 . A thickness of the dielectric layer  46  is selected responsive to the wearability of the dielectric layer material, wear characteristics of the wear counterface and the amount of contact force developed between the dielectric layer  46  and the wear counterface during operation. Preferably, material of the wear surface layer  46  can be removed (by machining back the layer  46  for example) such that the wear surface layer  46  has a desired thickness. 
         [0029]    As shown in  FIG. 7 , the dielectric layer  46  covers a region  40 A and  42 A of each conductor while regions  40 B and  42 B are exposed to form connection regions for connecting additional wear sensor components as described below. 
         [0030]    Although end regions  40 C and  42 C of the conductors  40  and  42  are illustrated in  FIG. 7  as terminating proximate end regions of the dielectric material region  32 , according to other embodiments the conductors extend to end regions of the substrate  30  when suitably insulated from any substrate conductive material they may contact. In these embodiments the conductors may be considered as extending beyond boundaries of the wear sensor  38 . 
         [0031]      FIGS. 9-11  illustrate operation of the wear sensor of the present invention.  FIG. 9  depicts the wear sensor  38  and the substrate  30 . Before wear occurs the dielectric layer  46  (which may also act as a wear surface layer or wear coating) is intact. 
         [0032]      FIG. 10  illustrates an orientation of an electrically conductive wear counterface  50  relative to the substrate  30  and a direction of wear motion indicated by an arrowhead  52 . Although a cylindrical wear counterface is illustrated, this is not required as the wear counterface can have any shape, e.g., a cylinder or a flat surface. It is only required that during operation, the substrate  30  and the wear counterface  50  contact along a line or a plane. A point-wear contact, such as a sphere contacting a flat surface, may not provide the desired functionality of the present invention as the sphere may not be able to contact and interconnect the wear sensor conductors. The line or plane contact interface enables the wear counterface  50  to simultaneously contact (and short together) both conductors  40  and  42 . 
         [0033]    When the dielectric wear surface layer  46  is worn through, see  FIGS. 11 and 12 , regions  40 D and  42 D of the respective wear sensor conductors  40  and  42  are exposed and simultaneously contacted by the electrically conductive wear counterface  50 . This action completes a circuit including a power source  70  and a wear indicator  74 . When energized, the wear indicator  74  indicates that wear of the dielectric wear surface layer  46  has reached to the depth of the wear sensor conductors  40  and  42 . As shown in  FIG. 11 , conductors  68  and  69  associated with the power source  70  and the wear indicator  74  are connected to the regions  40 B and  42 B of the respective conductors  40  and  42 . 
         [0034]    According to another embodiment, the conductors  68  and  69  are not required, as a wireless transceiver is connected to the regions  40 B and  42 B for transmitting a wireless signal when the wear conductors  40  and  42  are shorted by the wear counterface. The signal is received by an external receiver for activating a wear indicator. 
         [0035]    A material of the substrate  30  may comprise a dielectric or a metal, as described above, or another material such as a ceramic or ceramic matrix composite. An appropriate deposition process for forming the wear sensor conductors on these substrate materials may be accordingly selected, as is known in the art. 
         [0036]    In an application where a conductive layer  104  (see  FIG. 13 ) is disposed over the substrate  30 , the wear sensor conductors  40  and  42  are formed in a dielectric layer  106  (i.e., in a trench in the dielectric layer  106 ) or above the dielectric layer  106  (as illustrated in  FIG. 13 ), that insulates the wear sensor conductors  40  and  42  from the conductive layer  104 . The wear surface  46  is formed over the wear sensor conductors  40  and  42 . As in the embodiments described above, the wear surface  46  is worn away by contact with the wear counterface (not shown in  FIG. 13 ). 
         [0037]      FIG. 14  illustrates an application where a substrate  130  and a wear surface  134  both comprise an electrically conductive material. A dielectric layer  138  and a dielectric layer  140  are interposed between the substrate  130  and the wear surface  134 . The wear sensor conductors  40  and  42  are disposed over the dielectric layer  138  and within the dielectric layer  140 . The dielectric layer  138  insulates the conductors  40  and  42  from the conductive substrate  130 . The dielectric layer  140  insulates the conductors  40  and  42  from the conductive wear surface  134 . As in the other presented embodiments, the wear counterface wears the wear surface  134  and the dielectric layer  140 , completing a circuit between the wear sensor conductors  40  and  42  to provide a wear indication. 
         [0038]    In an alternative embodiment the wear sensor conductors are disposed within a trench formed in the dielectric layer  138 . 
         [0039]    The wear sensor conductors of the present invention may be deposited on the substrate or within the wear-resistant layer (e.g., a metal, ceramic, or cerment coating) or another material layer using a thin film deposition process such as plasma spraying, electron beam physical vapor deposition, chemical vapor deposition, pulsed laser deposition, mini-plasma, cold spray, direct-write, mini high velocity oxy-fuel, or solution plasma spraying, for example. 
         [0040]    In certain applications of the present invention the substrate is fixed while the wear counterface moves while in contact with the substrate. Since the wear counterface closes a conductive path between the two wear sensor conductors disposed within the stationary substrate, it is unnecessary to construct an electrical circuit (with attendant conductors) within the moving wear counterface and connect that circuit to external electrical devices (e.g., a power source and a wear indicator). This invention thus avoids the use of elements typically employed to electrically connect to a moving or rotating element, (e.g., brushes and slip rings). All installation and maintenance actions related to the wear sensor conductors are performed on the stationary substrate. 
         [0041]    The various sensor conductors described herein may be formed as follows.
       1. If the substrate has a high dielectric constant, as with an insulating ceramic such as Al 2 O 3 , the sensor conductors may be deposited directly on the substrate as illustrated in  FIG. 1 .   2. If the substrate does not exhibit a sufficiently high dielectric constant, an electrically insulating layer or dielectric layer is formed on the substrate surface using a material such as an oxide ceramic with high dielectric/insulating properties e.g., Al 2 O 3 , Yttria-stabilized Zirconia (YSZ), and MgAl 2 O 4 .   3. After completing step 1. or 2., the sensor conductors are deposited using an electrically conducting material with a high oxidation resistance at the operational temperature of the substrate and the counterface. For example Ni—Cr is electrically conducting and suitable for operation to about 500° F. (260° C.). This material is therefore suitable for use with a gas turbine combustor spring clip assembly operating below the 500° F. threshold. In this application, an exemplary sensor conductor thickness is in a range of about 10-50 microns, with 10-25 microns a preferred thickness in one embodiment. The wear sensor conductors may be formed by subtractive etching of a conductive surface or application of electrically conductive materials, for example by spraying.   4. Optionally a wear coating, such as an alloy of Cr 2 C 3 —NiCr or WC—Co, or commercial products known as Stellite 6B or T800 is deposited over the sensor conductors.       
 
         [0046]    In another embodiment, a trench or groove  160  is formed in a wear substrate  162  for receiving wear sensor conductors  170  and  172 . See  FIG. 15 . The wear substrate  162  further comprises a wear surface  174 . A width W 1  of the trench or groove  160  is smaller than a width W 2  of the wear surface  174  to minimally impact the wear behavior of the wear substrate  162  and the wear surface  174 . 
         [0047]    If the wear substrate  162  comprises conductive material, a trench bottom region  160 A and trench sidewall regions  160 B and  160 C comprise an electrically insulating material  166  that insulates the wear sensor conductors  170  and  172  from each other and from the conductive substrate  162 . 
         [0048]    In  FIG. 16  a conductive wear coating layer  180  overlies the wear substrate  162 , with an exposed surface of the wear coating layer  180  forming the wear surface  174 . The trench or groove  160  is disposed in the wear coating layer  180  as illustrated. In this embodiment a depth D 1  of the trench  160  is less than a thickness T 1  of the wear coating layer  180  to minimize impact on the wear behavior of the wear coating layer  180 . 
         [0049]    In both the  FIGS. 15 and 16  embodiments after the trench or groove  160  is formed, a dielectric material is formed in the trench  160  by any means known to those in the art, such as thermal spray, solution spray, direct-write, vapor deposition, or slurry casting to coat the bottom surface  160 A and the sidewall surfaces  160 B and  160 C. Conductive traces are formed to serve as the wear sensor conductors  170  and  172  and additional dielectric material is formed over the conductive traces. The exposed surface of the dielectric material may be machined flush with the wear surface  174 . 
         [0050]    In the embodiments of  FIGS. 15 and 16  if the wear substrate  162  and/or the wear coating layer  180  are not electrically conductive, it is not required that the material  166  comprise an electrically insulating material. 
         [0051]    In yet another embodiment, the wear sensors  170  and  172  are formed in separate trenches  190  and  192  in the substrate  162 , as illustrated in  FIG. 17 . 
         [0052]    In still another embodiment, the wear sensors  170  and  172  are formed in separate trenches  193  and  194  in the wear coating layer  180 , as illustrated in  FIG. 18 . 
         [0053]    In yet another embodiment, the wear sensor comprises two pairs of wear sensor conductors, each conductor pair formed at a different depth below a surface of the coating or a surface of the substrate. See  FIG. 19 . 
         [0054]    When a material layer  200  above a first or upper-most conductor pair  202  and  204  is breached, the counterface shorts or interconnects the first conductor pair  202  and  204  and closes an electrical circuit to actuate a first wear indicator, indicating that the material layer  200  has worn to a depth d 1 . A top surface  208 A of a material layer  208  is now exposed. When the wear counterface wears the first conductor pair  202  and  204  and wears a portion of the material layer  208  above a second conductor pair  222  and  224  a different electrical path is completed when the wear counterface interconnects the conductors  222  and  224 . This action energizes a second wear indicator indicating the material layer  208  has been worn to a depth d 2 . Additional conductors can be disposed at different depths to provide a graded indication of the wear depth. Different maintenance actions can be performed depending on the depth of material wear. 
         [0055]    The teachings of the present invention can also be employed where two contacting or proximate components vibrate, the vibrations bringing the two components into contact and wearing one or both of the components. 
         [0056]    The teachings of the present invention can also be employed in a system where two components are in a close proximal relationship during normal operation. Operational anomalies cause the two components to contact, which can lead to operational difficulties. The conductive sensors of the present invention are formed in a first one of the components and when contacted by a second component, the conductive sensors are shorted and an alarm activated. In this application it may advisable to form the conductive sensors in a trench as illustrated in  FIGS. 15 and 16  or in two trenches as illustrated in  FIGS. 17 and 18 . As the top surface of the conductive sensors is worn away, additional conductive sensor material is available to provide the contact alarm. 
         [0057]    In yet another embodiment, it may be desirable to orient the wear conductor sensors relative to a direction of motion of the wear counterface to preclude any smearing of the material of the conductor sensors. Such smearing may bridge the gap between the conductors, shorting the conductors and obviating the shorting function of the wear counterface. 
         [0058]    Thickness dimensions are set forth herein for certain of the material layers. However, it is recognized that these dimensions are not critical to the functionality of the present invention. The thickness of the wear sensor conductors (e.g., conductors  40  and  42 ) is also not critical to the functionality of the present invention, except that a duration of the short (as determined by a thickness of the conductors before the conductors are completely destroyed by wearing) must be sufficiently long to provide an indication of the short, thereby warning that the wear surface has worn away. 
         [0059]    The various material layers described above according to the various embodiments may comprise a thermal barrier layer, a substrate layer, a dielectric layer, a wear coating layer (a wear resistive coating or a wear surface), a conductive layer, a ceramic layer or any other layers known in the art. A material of each of these layers may be selected based on the application, proximate materials, and expected wear affects of the wear counterface. Also, material layers below the wear surface are selected based on the application and the proximate layer materials. 
         [0060]    As used herein the terms “open” and “short” when applied to electrical circuits do not require a respective infinite resistance and a zero resistance. The terms are intended to suggest a very high resistance (e.g., greater than about several mega-ohms) through which little current flows or a very low resistance (e.g., less than about 100 ohms) through which a considerable current flows. The actual values of resistance and current in any particular application are dependent on the materials comprising the conductors, the substrate and the wear counterface and on the configuration of the electrical circuit. Also, the term “interconnect” as used herein requires a connection between two conductors through which current can flow. An interconnect does not necessarily require a short circuit. 
         [0061]    One application for the present invention includes a gas turbine having rotating turbine blades that may wear a surrounding shroud. Mounting the wear sensor of the present invention in material layers comprising the shroud provides a wear warning when the shroud has been worn by the blades to a depth of the wear sensor. 
         [0062]    While various embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.