Abstract:
A method of cleaning a carbon work piece includes the step of applying an acetone cleaning agent to the carbon work piece to remove debris therefrom. The removal of debris promotes adhesion between the carbon work piece and a subsequently applied coating. For example, other steps may precede the acetone cleaning step, such as submersing the carbon work piece in deionized water. In one example, a subsequent coating process deposits an alumina coating on the carbon work piece.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates to preparation of carbon components for a coating process and, more particularly, to cleaning the carbon component before the coating process with a cleaning agent having a relatively low viscosity for penetrating the carbon component and having a relatively low amount of volatile organic compound (“VOC”). 
         [0002]    Carbon components, such as carbon seals, are widely known and used in high speed machinery such as gas turbine engines. Typically, the carbon component is coated in a coating process with one or more layers that enhance the durability of the carbon component. To promote adhesion between the layer and the carbon component, the carbon component is cleaned with a cleaning agent before the coating process to remove debris from surfaces of the carbon component. 
         [0003]    Traditional cleaning agents have several drawbacks. For example, after cleaning with a traditional cleaning agent, such as methanol, the carbon component is dried at an elevated temperature for up to four hours to vaporize and remove any residual cleaning agent. The time and expense of drying equipment adds to the expense of the carbon component. Moreover, methanol includes relatively high levels of VOCs, which are often regulated by federal, state, or local governments. 
         [0004]    Therefore, what is a needed is a cleaning method that reduces or eliminates the need for extensive drying and uses a cleaning agent having cleaning effectiveness at least as good as that of existing cleaning agents but with lower amounts of VOCs. This invention addresses those needs while avoiding the shortcomings and drawbacks of the prior art. 
       SUMMARY OF THE INVENTION 
       [0005]    An example method of cleaning a carbon work piece includes the step of applying an acetone cleaning agent to the carbon work piece to remove debris therefrom. The acetone cleaning agent is of suitable viscosity to deeply penetrate pores of the carbon work piece to remove the debris. For example, cleaning with acetone may be preceded by other steps, such as rinsing or soaking the carbon work piece in deionized water. In one example, the carbon work piece is cleaned in preparation for depositing a coating thereon. In another example, the carbon work piece is ultimately used within a gas turbine engine, such as within a diffuser to seal a chamber having a bearing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows. 
           [0007]      FIG. 1  schematically illustrates selected portions of an example gas turbine engine. 
           [0008]      FIG. 2  shows a more detailed view of a bearing arrangement shown in  FIG. 1 , including a carbon composite seal. 
           [0009]      FIG. 3  shows a perspective view of an example carbon composite seal. 
           [0010]      FIG. 4  schematically illustrates pores of a portion of the carbon composite seal. 
           [0011]      FIG. 5  illustrates selected steps of an example cleaning process for preparing a carbon workpiece to be coated. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0012]      FIG. 1  illustrates selected portions of an example gas turbine engine  10  including a fan  11 , a compressor section  12 , a combustor section  14 , and a turbine section  16 . The gas turbine engine  10  operates in a generally known manner, feeding compressed air from a compressor section  12  to a combustor section  14 . The compressed air is mixed with fuel and reacts to produce a stream of hot gasses  18 . The turbine section  16  transforms the stream of hot gasses  18  into mechanical energy to rotate a drive shaft  20 , such as a turbine engine main shaft. The shaft  20  is coupled with the fan  11 , the turbine section  16 , and the compressor section  12  such that the turbine section  16  drives the fan  11  to produce thrust and drive the compressor section  12 . In this example, an exhaust nozzle  22  directs the hot gasses  18  out of the gas turbine engine  10 . An annular, non-rotatable case  24  provides support for the shaft  20  on a bearing arrangement  26 , such as a No. 1 bearing. 
         [0013]      FIG. 2  shows selected portions of the example bearing arrangement  26  shown in  FIG. 1 . In this example, the bearing arrangement  26  includes a bearing  36  located between the case  24  and the shaft  20  that provides support for the shaft  20 , which rotates about a central axis A. A seal arrangement  38  provides fluid restriction between a low pressure and temperature region (L) within a bearing chamber  40  and hot, high pressure region (H) outside of the bearing chamber  40 . 
         [0014]    In this example, a seal arrangement  38  includes a seal  42  that is non-rotatably secured to the case  24 . The seal  42  abuts against a piston ring  44  that rotates with the shaft  20 . In this description, one of ordinary skill in the art will recognize alternative gas turbine engine arrangements that will benefit from the examples disclosed herein. The seal  42  in this example includes a carbon composite seal member  46  secured to a metal backing  48 , as also depicted in  FIG. 3 . In other examples, or in other types of uses, the carbon composite seal member  46  is used without the metal backing  48 , or with another known type of backing. 
         [0015]    In this example, the carbon composite seal member  46  is made of graphitic carbon that is impregnated with a material that enhances the performance of the carbon composite seal member  46 . In one example the material includes phosphorous. In a further example, the phosphorous is a phosphorous salt. The phosphorous salt is located within pores within the graphitic carbon and functions to enhance durability of the carbon composite seal member  46 . 
         [0016]    To further enhance the durability of the carbon composite seal member  46 , a coating  50  is deposited onto outer surfaces of the carbon composite seal member  46 . In one example, the coating  50  includes aluminum oxide or other suitable inorganic coating to enhance the durability of the carbon composite seal member  46 . For example, the coating  50  is deposited using a known thermal spray technique. 
         [0017]    The carbon composite seal member  46  (i.e. a carbon work piece) is cleaned prior to depositing the coating  50  in order to promote adhesion between the graphitic carbon and the coating  50 . The cleaning generally removes debris from the surfaces of the carbon composite seal member  46  and infiltrates into pores  52  of the graphitic carbon to remove debris that may be within the pores  52 , as shown schematically for example in a partial view of the carbon composite seal member  46  in  FIG. 4 . 
         [0018]    Referring to  FIG. 5 , an example cleaning process  58  is shown. In this example, the carbon composite seal member  46  is first submersed in deionized water  59  at a step  60 . In one example, the carbon composite seal member  46  is soaked in the deionized water  59  for about 30 minutes to wash away phosphorous salt residing on the outer surfaces of the carbon composite seal member  46 . Removal of the phosphorous salt from the surfaces prevents the phosphorous salts from interfering with the adhesion between the coating  50  and the graphitic carbon. 
         [0019]    At step  62 , the carbon composite seal member  46  is removed from the deionized water and brushed using a brush  63  to remove any air bubbles on the outer surfaces of the carbon composite seal member  46 . For example, the bubbles may inhibit the deionized water  59  from carrying debris out of the pores  52  and also prevent the deionized water  59  from infiltrating the pores  52  to remove the debris. 
         [0020]    At step  64 , the carbon composite seal member  46  is again soaked in deionized water  65  to further remove debris and to rinse existing debris from the surfaces. In one example, the carbon composite seal member  46  is soaked in the deionized water  65  for about 30 minutes. Upon removal from the deionized water  65  at step  66 , the carbon composite seal member  46  is dried in air, for example. In one example, ambient, dry air is blown over the surfaces of the carbon composite seal member  46  to dry it. 
         [0021]    After drying, the carbon composite seal member  46  is submersed in an acetone cleaning agent  70 . In this example, the carbon composite seal member  46  is completely submersed in the acetone cleaning agent  70  such that the acetone can penetrate into the pores  52  of the graphitic carbon to remove debris that is lodged therein. In one example, the acetone is supplied by Union Carbide and has a viscosity at 25° C. of about 0.306×10 −3 Pa·s. In some examples, the viscosity may vary by as much as 25% or even more, depending on the supplier and whether the acetone is mixed with other substances. 
         [0022]    The viscosity of the acetone permits it to penetrate into the pores  52  of the graphitic carbon to remove debris therefrom. Prior cleaning agents that are more viscous are not able to penetrate as far into the pores  52 , and therefore are not able to achieve the desired level of cleaning that is possible using acetone. For example, the relatively low viscosity of the acetone permits it to penetrate a farther distance into the pores  52  compared to methanol or water. That is, the distance of penetration depends at least partially on the viscosity of the cleaning agent. Additionally, the acetone also provides the benefit of having a relatively lower amount of volatile organic compounds (“VOC”) compared to other type of cleaning agents. 
         [0023]    In one example, the acetone cleaning agent is equal or greater than 99% pure. Using acetone of this purity prevents the acetone from leaving residue on or within the carbon composite seal member  46  from impurities in the acetone. 
         [0024]    In another example, the acetone cleaning agent  70  used at step  68  is used over several cleaning cycles for different carbon composite seal members  46  proceeding through the cleaning process  58 . In this example, the acetone cleaning agent  70  is periodically inspected to ensure it is of suitable quality to properly clean the carbon composite seal members  46 . For example, a characteristic of the acetone cleaning agent  70  is measured periodically to determine whether or not it is contaminated. For example, the specific gravity of the acetone cleaning agent  70  is measured and the acetone cleaning agent  70  is discarded in favor of new acetone cleaning agent  70  if the specific gravity is above a threshold level. In one example, the threshold level is about 0.87 (e.g., wherein the initial specific gravity is about 0.79). 
         [0025]    In the illustrated example, the carbon composite seal member  46  is then removed from the acetone cleaning agent  70  and dried. For example, dry ambient air is blown over the surfaces of the carbon composite seal member  46  to blow off any remaining acetone cleaning agent  70  or vaporize the acetone cleaning agent  70  from the surfaces thereof. 
         [0026]    In this example, the carbon composite seal member  46  is then transported to equipment for depositing the coating  50 . In one example, if the carbon composite seal member  46  cannot be coated within a certain time period, the carbon composite seal member  46  is stored in an oven at an elevated temperature, such as 350° F.±25° F., until it can be coated. This prevents the carbon composite seal member  46  from absorbing moisture that may inhibit adhesion between the coating  50  and the graphitic carbon. 
         [0027]    Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.