Abstract:
A method of measuring the clearance between a rotating component and a static component in a rotating machine. The method comprises installing a rub pin on an interior surface of the static component, operating the rotating machine such that the rotating component impinges on the rub pin, securing the rotating machine, and inserting an optical device to visually ascertain the length of rub pin remaining. The method reduces the time and cost of clearance determinations by avoiding disassembly or the degree of disassembly of the rotating machine required to conduct a clearance determination.

Description:
FIELD OF THE DISCLOSURE 
       [0001]    The present disclosure relates generally to methods of measurement, and more specifically to method of measuring clearance between rotating and static components in a machine such as a turbine machine. 
       BACKGROUND 
       [0002]    In a machine with rotating components it is often desirable to measure the distance between a rotating component and nearby static components of the machine. This distance, referred to as the clearance, is necessarily kept larger than a minimum clearance requirement such that the rotating component does not strike the static component during operation of the machine. However, relatively large clearances in rotating machines are also undesirable as they can reduce the efficiency of the machine. 
         [0003]    As an example, in a turbine engine the blades of the turbinomachinery rotate at high rates of speed relative to a static casing or shroud that houses the rotor. From a cold start to operating temperatures the various rotating and static components may undergo thermal expansion. It is therefore desirable that even at full operating temperatures a sufficient clearance is maintained. A sufficient clearance ensures that a rotating rotor blade does not strike the casing. However, in the case of a turbine engine, clearances larger than that sufficient to prevent blade impingement allow a flowpath for combustion gases to bypass the turbomarchinery such as compressor blades or turbine blades, thus reducing the efficiency of the turbine engine. The measurement of clearances is additionally beneficial when conducting performance diagnostics on turbomachinery. 
         [0004]    Understanding then that clearances are critical to the safe and efficient operation of rotating machines, it is desirable to be able to measure them. Unfortunately, in many rotating machines, access to the space between a rotating component and static component is extremely restricted. In many machines, accessing this space requires removal of at least a portion of the casing or shroud around the rotating component, which is typically a difficult, time-consuming, and expensive process. Additionally, as noted above there can be significant changes in clearances depending on whether a machine is at cold or operating temperatures. As it is generally not practicable to directly measure a clearance in an operating machine, it is necessary to have a method of measurement during operations that does not imperil the safe operation of the machine. 
         [0005]    Previous solutions to this problem include the use of rub pins. Rub pins are typically columnar shaped and formed from a soft metal or similar material which can be abraded when contacted by a rotating component during operation. A rub pin is affixed to a static component such that it is disposed in the space between a rotating component and the static component, and the machine is then started and brought to operating temperatures or pressures. Once the machine has been operated in a desired manner or for a desired length of time, the machine is secured and cooled down. The machine is then at least partially disassembled to allow for inspection and retrieval of the rub pin. Due to the impingement of a rotating blade on the pin, the pin will have worn down to indicate the clearance between the rotating component and static component. A measurement of the pin length, when measured between the worn end and the surface of the static component, is a measurement of the machine&#39;s clearance. Although effective at obtaining accurate clearance measurements, the use of rub pins is a time-consuming and expensive process because it requires securing and partially disassembling the machine to insert the pins, operating the machine, and then securing and partially disassembling the machine a second time to retrieve and inspect the pins. 
         [0006]    Another solution is described in European Patent Application 2,236,977. This application discloses a rub pin having at least one embedded wire which completes a circuit through the pin. When the pin is installed in the static component and protrudes into the rotating component path, the wire will be broken by blade impingement at a certain clearance. Breaking the wire causes an interruption in the circuit, which can be used as an indication that the clearance is insufficient or has surpassed a predetermined measurement. This solution is thus effective at monitoring machine performance for a single clearance, but does not provide a means for measuring over a wide range of clearances and additionally requires electrical circuitry for effective use. 
         [0007]    It is thus desired for an improvement in the art of measuring clearances which would enable such measurements to be taken in a safe and efficient manner. 
         [0008]    The present application discloses one or more of the features recited in the appended claims and/or the following features which, alone or in any combination, may comprise patentable subject matter. 
       SUMMARY 
       [0009]    According to an aspect of the present disclosure, a method of measuring clearance between a rotating component and a static component in turbomachinery without twice disassembling the static component comprises: disassembling, at least partly, the static component to position at least one rub pin in the static component, wherein the at least one rub pin has interval markings and is disposed having a proximal end of the rub pin extending toward the rotational path of the rotating component; operating the turbomachinery to achieve at least one steady-state operating parameter, said operating causing the rotating component to remove a portion of the rub pin; inserting an optical device into the static component without disassembly; and visually ascertaining, via the optical device, the number of interval markings between an interior surface of the static component and a terminal end of the rub pin formed by the removal of the a portion of the rub pin in the rotational path of the rotating component. 
         [0010]    In some embodiments the clearance is determined for steady-state operating parameters temperature, pressure, rotational speed of the rotatable component, or output of the turbomachinery. 
         [0011]    According to an aspect of the present disclosure, an optical rub pin comprises a base adapted to be received and affixed to a stationary component of a turbomachine; an elongated portion extending from the base and adapted to project radially inward from the stationary component; the elongated portion comprising a plurality of visual indicators, each representing a predetermined interval; wherein the plurality of visual indicators are adapted to be worn away by contact with a rotating component of a turbomachine. 
         [0012]    In some embodiments the plurality of visual indicators are distinguished from adjacent ones of the plurality of visual indicators by a characteristic selected from the group consisting of texture, color and text. In some embodiments the plurality of visual indicators are notches or engravings defining the predetermined intervals. In some embodiments the predetermined intervals are constant. In some embodiments the predetermined intervals are approximately 0.002 inches. In some embodiments the characteristics of plurality of visual indicators alternates to more easily distinguish between adjacent intervals. In some embodiments the characteristic is unique to one of the plurality of visual indicators. In some embodiments the plurality of visual indicators comprise a coating over the elongated portion. In some embodiments the plurality of visual indicators are bands surrounding a central rod. In some embodiments the plurality of visual indicators are a core within a bore in the elongated portion. In some embodiments the plurality of visual indicators are arranged sequentially along a longitudinal axis of the elongated portion. In some embodiments the color of each of the plurality of visual indicators is associated with a predetermined distance. In some embodiments the plurality of visual indicators comprises a clearance visual indicator, the clearance visual indicators forming the terminal portion of the elongated portion most distant from the base. 
         [0013]    According to another aspect of the present disclosure, a method of determining the clearance between a blade and shroud of a turbomachine comprises inserting an optical device through a port in the turbomachine; visually ascertaining, via observing with the optical device, a characteristic of one or more of a plurality of visual indicator on an optical rub pin, wherein the optical rub pin comprises a base adapted to be received and affixed to an interior of the shroud; an elongated portion extending from the base and adapted to project radially inward from the shroud, wherein the plurality of visual indicators comprise at least a portion of the elongated portion; determining the clearance based on the ascertained characteristic on a terminus of the optical rub pin. 
         [0014]    In some embodiments the characteristic is selected from the group consisting of color, texture, contour and text. In some embodiments the characteristic alternates between adjacent visual indicators. In some embodiments the plurality of visual indicators define a plurality of intervals. In some embodiments the plurality of visual indicators are notches or engravings defining the predetermined intervals. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The following will be apparent from elements of the figures, which are provided for illustrative purposes and are not necessarily to scale. 
           [0016]      FIG. 1A  is a schematic profile view of a rotating machine with installed rub pin in accordance with some embodiments of the present disclosure. 
           [0017]      FIG. 1B  is a detailed schematic profile view of a rotating machine with installed rub pin in accordance with some embodiments of the present disclosure. 
           [0018]      FIG. 1C  is a side schematic cutaway view of a rotating machine with installed rub pin in accordance with some embodiments of the present disclosure. 
           [0019]      FIG. 2  is a side profile view of a rub pin in accordance with some embodiments of the present disclosure. 
           [0020]      FIG. 3  is a side schematic cutaway view of a rotating machine with installed rub pin and an optical device partly disposed in the rotating machine in accordance with some embodiments of the present disclosure. 
           [0021]      FIG. 4  is a block diagram of a method in accordance with some embodiments of the present disclosure. 
           [0022]      FIGS. 5A, 5B, and 5C  are embodiments of a rub pin according with some embodiments of the present invention. 
       
    
    
       [0023]    While the present disclosure is susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described in detail herein. It should be understood, however, that the present disclosure is not intended to be limited to the particular forms disclosed. Rather, the present disclosure is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosure as defined by the appended claims. 
       DETAILED DESCRIPTION 
       [0024]    For the purposes of promoting an understanding of the principles of the disclosure, reference will now be made to a number of illustrative embodiments illustrated in the drawings and specific language will be used to describe the same. 
         [0025]    This disclosure presents embodiments to overcome the aforementioned deficiencies in clearance measuring systems and methods. More specifically, the present disclosure is directed to systems and method of measuring clearances between a rotating component and static component which limits or eliminates the disassembly of the machine required to effectively measure the clearance. Limiting machine disassembly reduces the time and cost associated with measuring the clearance. 
         [0026]      FIG. 1A  is a schematic profile view of a rotating machine  100  with installed rub pin  102  in accordance with some embodiments of the present disclosure. Rotating machine  100  comprises a rotating component  104  and static component  106 . In the illustrated embodiment, rotating component  104  is a compressor having a shaft  108  and plurality of blades  110  coupled thereto. For simplicity of the illustration, only a single compressor blade  110  is shown. Although the illustrated rotating component  104  is a compressor, the present disclosure is equally applicable to other rotating components  104  such as fans and turbines. 
         [0027]    Static component  106  is illustrated as a casing, such as a compressor engine casing. In some embodiments static component  106  is a shroud, mount, engine block, or similar structure. Static component  106  may also be referred to as a stationary component. 
         [0028]    Each blade  110  of the rotating component has a tip  112  at the radially-outward end of the blade  110 . This furthest extension of the blade  110  defines the travel path  114  of the rotating component  104 . The distance between the travel path  114  and the radially inner surface  116  of static component  106  is the clearance  120 . During operation of rotating machine  100 , the diameter of travel path  114  is susceptible to change. Travel path  114  is illustrated in  FIG. 1A  in a cold, non-operating condition of the rotating machine  100 . As many rotating machines  100  typically operate at relatively high temperatures, the rotating component  104  is likely to undergo thermal expansion during operation that results in an expanded travel path  114  and thus in a reduced clearance  120 . Additional operational transients such as changes in power demand or operating pressures of the rotating machine  100  will cause changes in the travel path  114 . 
         [0029]      FIG. 1A  illustrates a rub pin  102  disposed in rotating machine  100 . Rub pin  102  is installed in rotating machine  100  by affixation to static component  106 . In some embodiments rub pin  102  is affixed to static component  106  by insertion into predefined grooves or bores, or by adhesive, or a combination. 
         [0030]    Rub pin  102  is installed in rotating machine  100  such that a distal end  123  is affixed to or inserted into static component  106  and a proximal end  125  extends toward the rotational path of blade  110 . In some embodiments rub pin  102  is aligned with a radius of shaft  108 . In some embodiments, the proximal end  125  of rub pin  102  extends into the rotational path of blade  110 . The rotational path of blade  110  is defined by the travel path  114  of rotating component  104 . 
         [0031]      FIG. 1B  is a detailed schematic profile view of a rotating machine  100  with installed rub pin  102  in accordance with some embodiments of the present disclosure.  FIG. 1C  is a side schematic cutaway view of a rotating machine  100  with installed rub pin  102  in accordance with some embodiments of the present disclosure. As discussed above with reference to  FIG. 1A , both  FIGS. 1B and 1C  illustrate a rub pin  102  affixed to radially inner surface  116  of static component  106  and extending toward the rotational flow path of rotating component  104 . Clearance  120  is the distance between the tip  112  of blade  110  and the radially inner surface  116 . Blade  110  is coupled to and rotates about shaft  108 . 
         [0032]      FIG. 2  is a side profile view of a rub pin  102  in accordance with some embodiments of the present disclosure. Rub pin  102  comprises a distal end  123 , proximal end  125 , and elongate portion  127  extending between distal end  123  and proximal end  125 . Distal end  123  can also be referred to as the base of the rub pin  102 . In some embodiments rub pin  102  is marked by a plurality of indicator lines  129 , which divide rub pin  102  into a plurality of intervals  131 . In some embodiments, indicator lines  129  are evenly spaced and intervals  131  are of equal size. An exemplary interval is approximately 0.002 inches. 
         [0033]    In some embodiments indicator lines  129  are etched or notched into rub pin  102 . In some embodiments, indicator lines  129  and intervals  131  are colored to provide a high contrast, such as white intervals  131  and black indicator lines  129 . In some embodiments intervals  131  alternate coloring to be more prominently visible. In some embodiments indicator lines  129  are marked with measurements, as measured from distal end  123 . The rub pin  102  may be formed of brass with the intervals marked with engraving or notches as shown in  FIG. 2  In the embodiments in which the intervals are indicated by color, the color may be applied as a coating, for example with paint, or may be from layers of an abradable core as shown in  FIG. 5A , or external bands being made of differently colored material press fit onto a central rod as shown in  FIG. 5B  The rub pin  102  may also be constructed from multiple different materials that are visually distinguishable by color or texture as shown in  FIG. 5C . Intervals  131  may alternate methods of visually distinguishing between adjacent intervals  131  for example by alternating interval  131  color, texture, notching, or a combination of these distinguishing characteristics. In some embodiments, an interval  131  has a distinguishing characteristic that is unique to that interval  131 . In some embodiments visual indicators  129  and intervals  131  are arranged along a longitudinal axis of the rub pin  102 . In some embodiments the color of an interval  131  is associated with a predetermined distance or length of rub pin  102 . 
         [0034]    In some embodiments indicator lines  129  do not extend completely from proximal end  125  to distal end  123 ; in some embodiments this indicates to a user the depth to which the rub pin  102  should be inserted into a bore or groove in static component  106 . 
         [0035]    As discussed above, at least one rub pin  102  but preferably a plurality of rub pins  102  are installed in a rotating machine  100  while the rotating component  104  is not rotating. In some embodiments, a rotating machine  100  must be at least partially disassembled or opened to provide access for installing rub pin  102 . With rub pin(s)  102  installed, the rotating machine  100  is operated based on predetermined operational parameters. For example, in some embodiments it is desirable to measure clearance  120  for the rotating machine  100  operating at a standard operating pressure and temperature. The rotating machine  100  is therefore operated for a sufficient time to reach standard operating pressure and temperature, and can then be secured to obtain a reading of the rub pin  102 . 
         [0036]    In other embodiments it is desirable to measure clearance  120  for the rotating machine  100  during a specified transient, such as a rapid increase or decrease in power demand from the rotating machine  100 . The rotating machine  100  is therefore operated to meet the operational parameters of the specified transient, and then is secured to obtain a reading of the rub pin  102 . 
         [0037]    Rub pins  102  provide effective and inexpensive means for measuring clearances  120  through a wide range of operating conditions and allow for a wide range of clearance testing to be performed. 
         [0038]      FIG. 3  is a side schematic cutaway view of a rotating machine  100  with installed rub pin  102  and an optical device  300  partly disposed in the rotating machine  100  in accordance with some embodiments of the present disclosure. Optical device  300  is used to ascertain the length of the rub pin  102  following operation of the rotating machine  100  likely to cause reduction in the rub pin  102  due to impingement of blade  110 . 
         [0039]    As shown in the illustration, optical device  300  is preferably inserted into rotating machine  100  through an inlet or exit of the machine, such as through an exhaust duct  309 . Where optical device  300  is inserted through a normal flow path of the rotating machine  100  it is unnecessary to disassemble the rotating machine  100  to read the rub pin  102 , thus saving time and cost when determining clearance. If the rub pin  102  cannot be read by inserting optical device  300  through an inlet or exit of rotating machine  100 , it is preferable to insert optical device  300  using the least instrusive (i.e. requiring the least disassembly) manner possible. For example, optical device  300  may be inserted through a small access port rather than completing a teardown of rotating machine  100 . These access ports are commonly provided in turbomachinary. 
         [0040]    In the illustrated embodiment, optical device  300  comprises a work station  301 , fiber optic cable  302 , and optical element  304 . Optical element  304  allows a user stationed at work station  301  to view rub pin  102  via a video connection. In some embodiment, optical element  304  is capable of taking still photographs of rub pin  102  or other components of rotating machine  100 . In some embodiments optical device  300  is a boroscope. 
         [0041]    Clearance  120  between a rotating component  104  and static component  106  is determined by counting the indicator lines  129  or intervals  131  between the radially-inner surface  116  of static component and a newly-formed terminus  311  of rub pin  102 . Terminus  311  is formed by blade  110  impinging on rub pin  102 , causing the removal of some portions of the rub pin  102 . Terminus  311  is created due to the closest approach of the blade  110  to static component  106  and thus the minimal clearance  120  during the operation of the rotating machine  100 . Once the number of indicator lines  129  or intervals  131  is visually ascertained, that number can be multiplied by the known length of the interval  131  to obtain a total length of the rub pin  102  and thus clearance  120 . In embodiments where rub pin  102  is designed with non-uniform intervals, rub pin  102  is visually inspected to determine its length, either by reading markings on the rub pin  102  or by visually comparing the rub pin  102  to a template or copy. 
         [0042]      FIG. 4  is a block diagram of a method  400  in accordance with some embodiments of the present disclosure. Method  400  starts at block  401 , and proceeds to block  403  where a rub pin  102  is positioned in an interior surface of a static component  106  of the rotating machine  100 . In some embodiments, the interior surface is radially inner surface  116 . In other embodiments, the interior surface is any surface facing a rotating component and between which a clearance is desired to be obtained. In most rotating machines  100 , at least some disassembly of the machine  100  will be required in order to have access to an interior surface of the static component  106  to position the rub pin  102  according to step  403 . Rub pin  102  is positioned to have a proximal end  125  extending toward the rotational path (travel path  114 ) of the rotating component  110 . In some embodiments, rub pin  102  is positioned such that the proximal end  125  extends into the rotational path of the rotating component  110 . 
         [0043]    After the rub pin  102  is positioned and the rotating machine  100  is re-assembled as required, the rotating machine  100  is operated at step  405 . Operation of the rotating machine  100  during clearance testing can take many forms. In some embodiments, a steady-state clearance is desired and the rotating machine  100  is operated at steady-state conditions (i.e. various machine parameters are within their normal operating bands) for a set period of time. In some embodiments, clearance measurements are desired for various machine transients such as power fluctuations. A testing regimen for this period of operation may require taking the rotating machine  100  through a series of different transients or through multiples of a single type of transient in order to obtain a clearance measurement. As one example, at step  405  the rotating machine  100  can be operated in a cold burst, which for many machines such as turbine engines is the transient which causes the largest clearance closure (i.e. the smallest clearance between rotating component  104  and static component  106 ). A cold burst test in most machines will provide a measurement of the minimum anticipated clearance for that machine. 
         [0044]    After the rotating machine  100  is operated and secured, at step  407  an optical device  300  is inserted into the rotating machine  100  without disassembling the static component  106 . Optical device  300  is preferably inserted into rotating machine  100  through an inlet or exit of the machine, such as through a working fluid intake duct or an exhaust duct  309  as illustrated in  FIG. 3 . Where optical device  300  is inserted through a normal flow path of the rotating machine  100  it is unnecessary to disassemble the rotating machine  100  to read the rub pin  102 , thus saving time and cost when determining clearance. If the rub pin  102  cannot be read by inserting optical device  300  through an inlet or exit of rotating machine  100 , it is preferable to insert optical device  300  using the least instrusive (i.e. requiring the least disassembly) manner possible. For example, optical device  300  may be inserted through a small access port rather than completing a teardown of rotating machine  100 . This minimally intrusive inspection also saves time and cost over the prior art. 
         [0045]    At step  409  optical device  300  is used to visually ascertain a characteristic of the rub pin  102 . For example, optical device  300  may be used to visually ascertain a number of indicator lines  129  or intervals  131  between the interior surface (i.e. radially inner surface  116 ) of the static component  116  and a terminus  311  or terminal end of rub pin  102 . Terminus  311  is formed by blade  110  impinging on rub pin  102 , causing the removal of some portions of the rub pin  102 . Terminus  311  is created due to the closest approach of blade  110  to static component  116  and thus the minimal clearance  120  during the operation of the rotating machine  100 . In Step  409 , the interval indicator line or color may be determinative of the minimal clearance  120 . In some embodiments, the characteristic of the rub pin  102  which is visually ascertained at step  409  is one of color, texture, text, or material. 
         [0046]    A user operates the optical device  300  to visually ascertain a characteristic of the rub pin  102  which is used to determine the clearance. For example, the optical device  300  may be used to visually ascertain the number of indicator lines  129  or intervals  131  on rub pin  102 . Once the number of indicator lines  129  or intervals  131  is visually ascertained, that number can be multiplied by the known length of the interval  131  to obtain a total length of the rub pin  102  and thus clearance  120 . In embodiments where rub pin  102  is designed with non-uniform intervals, rub pin  102  is visually inspected to determine its length, either by reading markings on the rub pin  102  or by visually comparing the rub pin  102  to a template or copy. 
         [0047]    Method  400  ends at step  411 . 
         [0048]    The present disclosure provides many advantages over previous systems and methods of measuring clearances between rotating and static components. Knowing the clearance measurement in rotating machinery can be critical to determining how well the machine is performing and can indicate ways to improve performance, particularly for rotating blades in turbine engines. The present disclosure provides a system and method of measuring clearances that avoids the complexity of previous systems such as multi-tip capacitance sensors, microwave sensors, and eddy current transducers. The present disclosure additionally provides for a faster, less labor-intensive method of measuring clearances than the traditional use of rub pins. The method of the present disclosure avoids the need for multiple, sequential teardowns or disassemblies of a rotating machine. 
         [0049]    Although examples are illustrated and described herein, embodiments are nevertheless not limited to the details shown, since various modifications and structural changes may be made therein by those of ordinary skill within the scope and range of equivalents of the claims.