Abstract:
The present disclosure is directed to a pin joint component for a pin joint assembly that has improved wear surfaces, especially for those portions of the pin joint component surface that interface thrust rings, lips, and other adjacent wear components. The pin joint component comprises a first treated region that is formed by removing material from the wear surface of the pin joint component and replaced with clad material. Prior to this operation, a second treated region is formed by removing material from a section of the pin joint component distinct from the first treated region and performing a nitriding process thereon.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates generally to pin joint components. More particularly, the present invention relates to pin joint assembly collars, inserts, bushings, and track links that are treated with at least two distinct surface treatments. 
       BACKGROUND 
       [0002]    Pin joints are commonly used in numerous work machine applications, such as in track chains or undercarriage systems, linkage pins, or boom pin joints. Typically, the pin joint components are made of a general use steel with limited surface treatment. Moreover, multiple surface treatments on the same component or surface of a component are technologically challenging, as use of multiple surface treatments commonly encounters the problem of subsequent treatments offsetting the effectiveness of the earlier surface treatment(s). 
         [0003]    The vast majority of improvements related to improving pin joint wear resistance are directed to sealing technology, such as that disclosed in U.S. Pat. No. 7,121,555, issued to Yamamoto et al. Despite Yamamoto et al.&#39;s advances, they do not address improvements related to the pin joint components, and certainly not to creating a pin joint component with multiple surface treatments. 
       SUMMARY OF THE INVENTION 
       [0004]    In one aspect, the present disclosure is directed to a pin joint component comprising a main body having an outer wear surface including a first treated region and a second treated region proximate to the first treated region. The first treated region includes clad alloy material, while the second treated region includes a nitrided surface. 
         [0005]    In another aspect, the present disclosure is directed to a method for forming a pin joint component comprising the following steps: forging an alloy into the general shape of the pin joint component; removing material from a wear surface of the pin joint component to form a second treated region; nitriding the second treated region; removing material from the outer wear surface of the pin joint component to form a first treated region; and cladding an alloy to the first treated region. 
         [0006]    In yet another aspect, the present disclosure is directed to a pin joint assembly comprising a pin joint component that has a main body. The main body includes a wear surface with (i) a first treated region, (ii) a second treated region that is not co-planar with the outer wear surface, (iii) a shoulder between the first treated region and second treated region having a width of at least about 1 mm, and (iv) a channel between the shoulder and the second treated region. Further, the first treated region includes clad stainless steel alloy, and the second treated region includes a nitrided surface having a hardness of at least about 55 HRC and extends below the surface at least about 0.15 mm. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a schematic of a pin joint assembly. 
           [0008]      FIG. 2  is a schematic of the area of a pin joint assembly including a collar, an insert, and a seal assembly. 
           [0009]      FIG. 3  is a cross-sectional view of an insert of the present disclosure, with first and second treated regions. 
           [0010]      FIG. 4  is a cross-sectional view of the insert of the present disclosure having the second treated region exposed. 
           [0011]      FIG. 5  is a cross-sectional view of the insert of the present disclosure having the first and second treated regions exposed. 
           [0012]      FIG. 6  is a cross-sectional view of the insert of the present disclosure having the clad alloy applied to the first treated region. 
           [0013]      FIG. 7  is a cross-sectional view of the insert of the present disclosure having a channel disposed between the first and second treated regions. 
           [0014]      FIG. 8  is a cross-sectional view of a pin joint assembly including a bushing and track link prepared according to the present disclosure. 
           [0015]      FIG. 9  is a cross-sectional view of a pin joint assembly including a bushing and collar prepared according to the present disclosure. 
       
    
    
       [0016]    Whenever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
       DETAILED DESCRIPTION 
       [0017]    The pin joint component disclosed herein has utility in various work machine applications, as detailed below. The following example of the use of the pin joint component in a track laying machine&#39;s undercarriage system is for example only, and is not presented in a limiting sense. 
         [0018]    Track laying machines utilize articulating track chains for propelling the machine over terrain during operation in, e.g., construction, mining, oil/gas, forestry, and other rugged operating environments. Such track chains are typically utilized in pairs disposed on each side of the machine. The track chain comprises a series of subassemblies, the number of which is determined by the desired length for a given application, with the opposite ends of each track chain being mechanically coupled together using master links to form a closed loop that typically extends about a drive sprocket and at least one idler. Each subassembly includes a track pin assembly, an inner and outer link, and a track shoe. As shown in  FIG. 1 , track pin assembly  10  includes a track pin  11 , a bushing  12 , a collar  14 , and an insert  13 , which is sometimes also referred to as a collar. Insert  13  includes a first end region  15 , a wear edge  16 , and a bore  17 . Insert  13  may be fixed relative to track pin  11  so that insert  13  will not rotate or move axially relative to track pin  11 . For example, insert  13  may be press fit onto, welded to, adhesive or chemically bonded to track pin  11 , or another known manner of attaching two mechanical components. Over the course of operation, the constant metal-to-metal contact of the moving pin joint components can result in significant wear, even when measures are taken to minimize friction between these components. 
         [0019]    With reference to the drawings,  FIG. 2  shows a cross section of a prior art track pin assembly component, specifically an insert  13  having a main body and wear surface  16  that is exposed to the operating environment, and collar  14 . In prior art configurations, a thrust ring  21  is disposed adjacent to wear surface  16 . Moreover, a lip  23  may also be disposed adjacent to wear surface  16  as part of a seal assembly  26 , which also includes load ring  24  and can  25 . When wear surface  16  is untreated, thrust ring  21  and lip  23  may unacceptably wear the wear surface  16  because, in the case of thrust ring  21 , it is formed of a harder alloy than wear surface  16 . In the case of lip  23 , wear surface  16  may corrode because of environmental factors, such as exposure to basic or acidic slurries. Accordingly, as shown in  FIG. 3 , insert  13  includes a first treated region  31  that interfaces with lip  23  of the seal assembly and a second treated region  32  that interfaces thrust ring  21  on wear surface  16 , with a shoulder  33  disposed between first treated region  31  and second treated region  32 , wherein first treated region  31  and second treated region  32  are generally parallel to one another, but may not be co-planar. 
         [0020]    To form insert  13 , the general shape is formed with a forging and annealing process. Any suitable alloy may be used, such as, e.g., steels, including carbon steels and chromoly steels. Additional cold working is typically performed to further form insert  13 , such as green turning and knurling insert  13 . 
         [0021]    Referring to  FIG. 4 , material is removed from a portion of wear surface  16  that will form second treated region  32  after an optional neutral hardening step. The material removed may form any suitable shape for second treated region  32 , such that second treated region  32  is non-planar with respect to wear surface  16 . As shown in  FIG. 4 , one such shape is generally rectangular with an optional radial portion cut near shoulder  33 . The depth of the material removal may be any suitable depth, and in one example the depth of material is at least about 0.1 mm, such as at least about 0.15 mm or 0.20 mm. 
         [0022]    After said material removal step, second treated region  32  undergoes a nitriding step. The nitriding step includes standard steps known in the art in nitriding techniques such as gas nitriding, liquid or salt bath nitriding, ion nitriding, or plasma nitriding.  FIG. 4  shows an embodiment wherein gas nitriding is employed to nitride the surfaces of insert  13  exposed to the gas nitriding process. The nitrided second treated region  32  has an average apparent hardness of at least about 45 HRC, such as at least about 47 HRC or even at least about 50 HRC. By “apparent hardness,” this is the hardness garnered from a typical test using the HRC scale, which may be skewed downward because of the relatively thin layer of the nitrided second treated region  32  on the softer substrate, which may have a hardness of only about 42 HRC or less. The actual hardness of just the second treated region  32  may be substantially higher, such as at least about 55 HRC or even at least about 65 HRC. 
         [0023]    The second treated region  32  extends below the surface of second treated region  32  at least about 0.1 mm deep, such as at least about 0.15 mm deep or at least about 0.20 mm deep. This nitrided case  41  is shown as the line that traces the contours of the outer surfaces of insert  13  in a somewhat or substantially uniform manner because of the gas nitriding process. Other nitriding processes may not result in such a substantially uniform case depth and may, in some processes, be localized solely to second treated region  32 . It will be appreciated that the case may not represent a distinct drop in hardness resulting from the nitriding, but that the drop in hardness may be gradual. 
         [0024]    After nitriding of second treated region  32 , insert  13  undergoes another material removal step whereby material is removed from wear surface  16  in the area that will generally become first treated region  31 . Specifically, as seen in  FIG. 5 , a portion of wear surface  16  will be retained as shoulder  33  while material is removed from wear surface  16  on the side of the shoulder distal from second treated region  32 . Shoulder  33  should be of a width sufficient to prevent subsequent steps during treatment of first treated region  31  from significantly interacting with second treated region  32 . Generally, shoulder  33  should be at least about 1 mm wide, such as at least about 2 mm wide or at least about 3 mm wide. 
         [0025]    Referring again to  FIG. 5 , the material removed from wear surface  16  leaves a cavity  51  in wear surface  16  that is generally rectangular in shape, with an optional radial portion cut at either or both ends of the cavity. The cavity  51  is of a depth of between about 0.10 mm and about 4.0 mm, such as between about 0.8 mm and about 3.0 mm. The width of the cavity  51  is between about 1.0 mm and about 12.0 mm, such as between about 2.0 mm and about 10.0 mm or even between about 3.0 mm and about 7.5 mm. 
         [0026]    After this step, a cladding operation is used to fill cavity  51  formed in wear surface  16  with an alloy suitable for abutting lip  23  of a seal assembly. Specifically, stainless steel alloys or other corrosion resistant alloys are suitable for deposition as powder or wire feed stock using a cladding process. During the cladding operation, second treated region  32  is protected from any material runoff or splatter from the cladding process by the shoulder and, optionally, by placing a cap over the nitrided surface of second treated region  32 . The resulting insert  13  is shown in  FIG. 6 , which shows how first treated region  31  has alloy clad to first treated region  31  to fill the cavity and produce build-up of additional alloy material  61 . 
         [0027]    The additional build-up of clad material is then removed with a cold working step of, e.g., hard turning. During this processing step, it is likely and anticipated that material will be removed from wear surface  16  as well, such that the final surface of wear surface  16 , clad surface of first treated region  31 , and shoulder  33  all undergo material removal. However, the amount of material removed is less than the depth of second treated region  32  so that first treated region  31  and second treated region  32  remain substantially parallel, yet non-planar with respect to one another. A final honing or polishing step may also be included. A channel may optionally be formed between shoulder  33  and second treated region  32 , as shown in  FIG. 7 . This channel may help with seating of adjoining features, such as thrust ring  21 . 
         [0028]    As seen in  FIG. 8 , a similar process may also be applied to other pin joint components, as insert  13  is reconfigured for this particular application. Specifically, the surface of bushing  12  that may interface with lip  23  and thrust ring  21  may undergo two similar localized processes. In particular, material is removed from a portion of the edge of bushing  12  that will form second treated region  32 . The material removed may form any suitable shape for second treated region  32 , such that second treated region  32  is non-planar with respect to the edge of bushing  12 . One such shape is generally rectangular with an optional radial portion cut near shoulder  33 . 
         [0029]    After said material removal step, second treated region  32  undergoes a nitriding step, followed by another material removal step whereby material is removed from the edge of bushing  12  in the area that will generally become first treated region  31 . 
         [0030]    The material removed from bushing  12  leaves a cavity that is generally rectangular in shape, with an optional radial portion cut at either or both ends of the cavity. A cladding operation is then used to fill the cavity formed in bushing  12  with an alloy suitable for abutting lip  23  of a seal assembly. Build-up of additional alloy material  61  is expected during the cladding operation. 
         [0031]    The additional build-up of clad material is then removed with a cold working step of, e.g., hard turning. During this processing step, it is likely and anticipated that material will be removed from bushing  12  as well, such that the final surface of the edge of bushing  12 , clad surface of first treated region  31 , and shoulder  33  all undergo material removal. However, the amount of material removed is less than the depth of second treated region  32  so that first treated region  31  and second treated region  32  remain substantially parallel, yet non-planar with respect to one another. A final honing or polishing step may also be included. 
         [0032]    Referring again to  FIG. 8 , similar localized processes may also be applied to another pin joint component, such as the inner surface of a track link  81  may interface with lip  23  and thrust ring  21  may undergo two similar localized processes. In particular, material is removed from a portion of track link  81  that will form second treated region  32 . The material removed may form any suitable shape for second treated region  32 , such that second treated region  32  is non-planar with respect to the side of track link  81 . One such shape is generally rectangular with an optional radial portion cut near shoulder  33 . 
         [0033]    After said material removal step, second treated region  32  undergoes a nitriding step, followed by another material removal step whereby material is removed from the side of track link  81  in the area that will generally become first treated region  31 . 
         [0034]    The material removed from track link  81  leaves a cavity that is generally rectangular in shape, with an optional radial portion cut at either or both ends of the cavity. A cladding operation is then used to fill the cavity formed in track link  81  with an alloy suitable for abutting lip  23  of a seal assembly. Build-up of additional alloy material  61  is expected during the cladding operation. 
         [0035]    The additional build-up of clad material is then removed with a cold working step of, e.g., hard turning. During this processing step, it is likely and anticipated that material will be removed from track link  81  as well, such that the final surface of the edge of track link  81 , clad surface of first treated region  31 , and shoulder  33  all undergo material removal. However, the amount of material removed is less than the depth of second treated region  32  so that first treated region  31  and second treated region  32  remain substantially parallel, yet non-planar with respect to one another. A final honing or polishing step may also be included. 
         [0036]    Referring now to  FIG. 9 , similar localized processes may also be applied to another pin joint component, such as a collar  14 , which is reconfigured along with insert  13  in this particular setting. Such a pin joint assembly may be referred to as a cartridge assembly. Collar  14  may interface with lip  23  and thrust ring  21 , and may undergo two localized processes similar to the one described above for insert  13 . In particular, material is removed from a portion of collar  14  that will form second treated region  32 . The material removed may form any suitable shape for second treated region  32 , such that second treated region  32  is non-planar with respect to the side of collar  14 . One such shape is generally rectangular with an optional radial portion cut near shoulder  33 . 
         [0037]    After said material removal step, second treated region  32  undergoes a nitriding step, followed by another material removal step whereby material is removed from the side of track link  81  in the area that will generally become first treated region  31 . 
         [0038]    The material removed from collar  14  leaves a cavity that is generally rectangular in shape, with an optional radial portion cut at either or both ends of the cavity. A cladding operation is then used to fill the cavity formed in collar  14  with an alloy suitable for abutting lip  23  of a seal assembly. Build-up of additional alloy material  61  is expected during the cladding operation. 
         [0039]    The additional build-up of clad material is then removed with a cold working step of, e.g., hard turning. During this processing step, it is likely and anticipated that material will be removed from collar  14  as well, such that the final surface of the edge of collar  14 , clad surface first treated region  31 , and shoulder  33  all undergo material removal. However, the amount of material removed is less than the depth of second treated region  32  so that first treated region  31  and second treated region  32  remain substantially parallel, yet non-planar with respect to one another. A final honing or polishing step may also be included. 
       INDUSTRIAL APPLICABILITY 
       [0040]    The insert  13  formed according to the present disclosure is especially suitable for use in a pin joint assembly for use in an undercarriage system of a tracked machine. For example, the insert may be part of the pin joint assembly described above as part of the endless track system used on a track type tractor, a tracked excavator, and other tracked work machines. 
         [0041]    Moreover, insert  13  of the immediate disclosure may be employed in any setting with a similar pin joint configuration where a thrust ring or other similar hard component abuts insert  13 , leading to excessive wear during operation. Such examples include the above described bushing, track link, or collar surfaces. 
         [0042]    Testing has shown that the dual treatment of wear surface  16  with a first treated region  31  and a second treated region  32  according to the present disclosure may increase wear resistance of the treated surface of the pin joint component by ten times over conventional pin joint component designs. 
         [0043]    Although the present disclosure has been described with reference to exemplary 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. For example, although different exemplary embodiments may have been described as including one or more features providing one or more benefits, it is contemplated that the described features may be interchanged with one another or alternatively be combined with one another in the described exemplary embodiments or in other alternative embodiments. The present disclosure described with reference to the exemplary embodiments and set forth in the flowing claims is manifestly intended to be as broad as possible.