Abstract:
Disclosed herein is a ring cutter for a tunneling apparatus, the ring cutter formed by a process in one form comprising several steps. In one form, this mold is sacrificial, and may be a pair of parallel cylinders such as an outer and an inner cylinder with a gap there between. In one manufacturing process, a single mold is used to produce multiple cutters which are cast simultaneously within the single mold. In one form, the mold is formed in the final shape of the cutter, such that the cutter requires no further machining to be used in a tunneling apparatus. Another step being: disposing a volume of powdered metal, such as a nickel based alloy, into the mold. The powdered metal may then be subjected to isostatic gas pressures, and elevated sintering temperatures simultaneously (HIP) with the isostatic gas pressure to consolidate the powdered metal.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims priority benefit of U.S. Ser. No. 61/372,208, filed Aug. 10, 2010. 
     
    
     BACKGROUND OF THE DISCLOSURE 
     a) Field of the Disclosure 
       [0002]    The present invention pertains to a roller cutter assembly for rock boring machines. Rock boring machines have a plurality of these cutter assemblies mounted on a rotatable cutterhead. Conventionally, each cutter assembly includes a shaft which is adapted to be secured to the cutterhead, a hub mounted on bearings for rotation relative to the shaft and the cutterhead, and a cutter ring being fixedly secured to the hub. The rock breaking elements on the cutter ring can be a so-called disc cutter with a peripheral cutting edge. These cutter element arrangements are generically termed “cutter rings”. 
         [0003]    Furthermore, this disclosure relates to an improved cutting surface used in the field of cutting, severing or breaking up of naturally occurring solid, hard Earth (ground) material. Such cutting, severing or breaking up of solid, hard material generally comprises forming an opening or cut in native material of larger cross-sectional surface area than the effective cutting area of the cutting means by movement of the means parallel to the exposed surface, and forming a large passageway into the earth by continuously advancing a cutting device by means of a vehicle or the like, the cutting means forming the entire passageway in an uninterrupted advance movement as the vehicle or the like follows the cutting means into and along the passageway. In this disclosure, the cutter rings are formed in a process of hot isostatic pressing of powder metal. 
       SUMMARY OF THE DISCLOSURE 
       [0004]    Disclosed herein is a ring cutter for a tunneling apparatus, the ring cutter formed by a process in one form comprising several steps. One step of the process being the step of providing a mold of the cutter, the mold may be cylindrical, or may be more in the shape of the final cutter. In one form, this mold is sacrificial, and may be a pair of parallel cylinders such as an outer and an inner cylinder with a gap there between. In one manufacturing process, a single mold is used to produce multiple cutters which are cast simultaneously within the single mold. In one form, the mold is formed in the final shape of the cutter, such that the cutter tip requires no further machining to be used in a tunneling apparatus. Another step being: disposing a volume of powdered metal, such as a nickel based alloy, into the mold. The powdered metal may then be subjected to isostatic gas pressures, and elevated sintering temperatures simultaneously (HIP) with the isostatic gas pressure to consolidate the powdered metal. In this step, the pressures used may be up to 7,350 PSI, 15,000 PSI, 45,000 PSI, or more in some applications. Argon gas may be used in the HIP process. The temperatures may exceed 900° F. or even 2,400° F. In one form the elevated temperatures are sufficient to sinter the powdered metal. One additional step being to subject the consolidated powdered metal to an austenitization process. The temperatures used in the austenitization process may exceed 1650° F. 
         [0005]    Also disclosed is a method of fabricating a cutter ring for a tunneling device, the method comprising several steps. One step may be: securing an mold about the circumference of an inner ring so as to create a cavity defined by the mold and a surface of the inner ring. This step followed by a step of filling the cavity with an alloy, which is in powder form, to form a cutter ring assembly; then sealing the cavity; then heating the cutter ring assembly to a selected temperature while applying pressure as a HIP process. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a highly schematic cross-sectional view of one portion of one embodiment of an improved cutter ring. 
           [0007]      FIG. 2  is a highly schematic cross-sectional view of one embodiment of a step in production of a plurality of improved cutter rings as shown in  FIG. 1 . 
           [0008]      FIG. 3  is a highly schematic cross-sectional view of one portion of one variation of an improved cutter ring, as shown in  FIG. 1 . 
           [0009]      FIG. 4  is a highly schematic cross-sectional view of one portion of another variation of an improved cutter ring, as shown in  FIG. 1 . 
           [0010]      FIG. 5  is a highly schematic cross-sectional view of one portion of another embodiment of an improved cutter ring. 
           [0011]      FIG. 6  is a highly schematic cross-sectional view of one embodiment of a step in production of a plurality of improved cutter rings, as shown in  FIG. 5 . 
           [0012]      FIG. 7  is a highly schematic cross-sectional view of one portion of one variation of an improved cutter ring, as shown in  FIG. 5 . 
           [0013]      FIG. 8  is a highly schematic cross-sectional view of one portion of another variation of an improved cutter ring, as shown in  FIG. 5 . 
           [0014]      FIG. 9  is a cutaway view of one embodiment of an improved cutter ring mounted to an additional structure. 
           [0015]      FIG. 10  is a view of a worn cutter ring and associated structures. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0016]    Disclosed herein is an improved cutter ring for tunneling devices, such as the cutter rings disclosed, for example, in U.S. Pat. Nos. 3,787,101 and 7,401,537, incorporated herein by reference, the understanding of which will allow one of ordinary skill in the art to readily understand the application and benefits of the disclosed cutter rings and methods of manufacture thereof. Such tunneling devices are well known in the art for mining, tunneling for subway trains, and similar applications. These ring cutters differ in function and application from both drag bits, and tri-cone boring bits attached to a down hole shaft. As the cutter rings directly engage the surface of hard rock for cutting and tunneling therethrough, the cutter rings wear out and require replacement. This is obviously detrimental to the operation of the device as tunneling cannot occur during the replacement process. As is shown in U.S. Pat. No. 3,787,101, these cutter assemblies are removably attached to the drilling machine through a mounting portion well described in this patent. Additionally, the assembly is comprised of a replaceable outer portion, described herein as the cutter ring itself, and a larger hub assembly. 
         [0017]    Looking to  FIG. 9  of this disclosure, a cutter ring  20  is shown having a cutting edge  22 , which rolls over the rock face during operation (tunneling). As shown, the cutter ring  20  is fixedly and removably attached to a hub  24  in one form by way of an interference fit with adjoining surfaces  26 . In one form, a first lip  28  prohibits movement of the cutter ring  20  relative to the hub  24  in a first longitudinal direction  30 , while a second lip  32  prohibits movement of the cutter ring  20  relative to the hub  24  in a second longitudinal direction  34 . As shown, the hub  24  is mounted through a plurality of bearings  36  to a housing  38 . The housing  38  is rigidly fixed to or formed as part of a larger structure which interconnects a plurality of cutting assemblies  40 , on a cutter head. This is only one example of a cutter ring assembly utilizing the disclosed improvements. 
         [0018]    Looking to  FIG. 10 , of cutting assembly  40 , generally comprising a cutter ring  20  and hub assemblies  24 , is shown. It can be seen in this figure that the cutting edge  22  of the replaced cutting assemblies is well worn from the original shape shown by the dashed line, and requires sharpening or replacement before being replaced into the larger structure for tunneling or drilling. 
         [0019]    Traditionally these cutter rings are formed by forging, casting, or machining. This disclosure describes several cutter rings formed using a powder metal process utilizing hot isostatic pressure sintering of the powder metal. Powder metallurgy is a forming and fabrication technique consisting of three major processing stages. First, the primary material is physically powdered, divided into many small individual particles. Next, the powder is injected into a mold wherein the end part is formed by applying pressure, high temperature, long setting times (during which self-welding occurs), or any combination thereof. 
         [0020]    Hot isostatic pressing (HIP) is a manufacturing process used to reduce the porosity of metals and influence the density of many ceramic materials. This improves the material&#39;s mechanical properties and workability. 
         [0021]    The HIP process subjects a component to both elevated temperature and isostatic gas pressure in a high-pressure containment vessel. The pressurizing gas most widely used is argon, although other gasses may be used. An inert gas is used so that the material does not chemically react with the gas. The chamber and metal therein is heated, causing the pressure inside the vessel to increase. Many systems use associated gas pumping to achieve the necessary pressure level. Pressure is applied to the material from all directions (hence the term “isostatic”). 
         [0022]    For processing castings, the inert gas is applied between 7,350 psi (50.7 MPa) and 45,000 psi (310 MPa), with 15,000 psi (100 MPa) being most common. Process soak temperatures range from 900° F. (482° C.) for aluminum castings to 2,400° F. (1,320° C.) for nickel-based superalloys. When castings are treated with HIP, the simultaneous application of heat and pressure eliminates internal voids and microporosity through a combination of plastic deformation, creep, and diffusion bonding. Primary applications are the reduction of microshrinkage, the consolidation of powder metals, ceramic composites and metal cladding. Hot isostatic pressing is also used as part of a sintering (powder metallurgy) process and for fabrication of metal matrix composites. 
         [0023]    Disclosed herein is an improved method for making an improved cutter ring  20 , which is more wear resistant than any known cutter rings. Two embodiments will be utilized to describe this process, with multiple variations of both embodiments. 
         [0024]    The first embodiment is shown in  FIG. 1 , with variations shown at  FIGS. 3 and 4 .  FIG. 2  generally shows one method for simultaneously producing several cutter rings of this first embodiment. 
         [0025]    The second embodiment is shown in  FIG. 5 , with variations shown at  FIGS. 7  and eight.  FIG. 6  generally shows one method for producing this second embodiment. 
         [0026]    A process to simultaneously manufacture several copies of the cutter ring of the first embodiment  42  is perhaps most easily understood by looking to  FIG. 2 . As shown, a plurality of first embodiment cutter rings  44  ( a - h ) are simultaneously produced in a canister, around an inner tube  46 . An inner tube  46  is provided, whereupon a thin canister (mold)  48  is then attached at either (or both) end ( 50   a  or  50   b ) to the inner tube  46 , whereupon a volume of powder metal  52  is disposed in the gap  54  between the canister  48  and the inner tube  46 . Where upon, this assembly is subjected to hot isostatic pressing as described above. The powder metal then consolidates and securely bonds to the wrought inner tube  46  during the HIP process. Once complete, the assembly  56  is cut along lines  58  to form unique cutter rings  44 . Additionally, the assembly  56  is machined following the HIP/sintering step and/or forged to form the outer surface  58  of the individual cutter rings  44 . 
         [0027]    In the first variation  60  shown in  FIG. 3 , a different method of manufacture is disclosed wherein a formed outer cover (mold)  62  is welded or otherwise attached to the machined inner ring  66 . In one form, the outer cover  62  is formed of sheet metal or an equivalent. A volume of powder metal  64  forming a core is then disposed into the void formed between the outer cover  62  and the upper surface of the inner ring  66 . This assembly  76  is then subjected to an HIP process, such as described above, bonding the powder metal into a unitary structure which is also chemically and mechanically bonded to the inner ring  66  forming a unitary cutter ring which will require minimal machining on the bore to achieve a final product. The outer cover  62  will quickly be worn away in use, or may be removed prior to installation of the cutter ring  20  upon a hub  24 . The production process may be completed by submitting the assembly  76  to an austenitization process. In one form, the temperatures used in the austenitization process exceed 1650° F. 
         [0028]    By changing the temperature for austenitization, the austempering process can yield different and desired microstructures. A higher austenitization temperature can produce a higher carbon content in austenite, whereas a lower temperature produces a more uniform distribution of austempered structure. The carbon content in austenite as a function of austempering time has been established 
         [0029]    In the second variation  68  shown in  FIG. 4 , yet another method of manufacture is disclosed wherein a cover  70  is welded or otherwise attached to the inner ring  74  and substantially encompasses the inner ring  74  and an open region defined by the cover  70  and the radially outward surface of the ring  74 . Once again, a volume of powder metal  72  is disposed within an open region. As with previous embodiments, the assembly  78  is then subjected to an HIP process, such as described above, to form a cutter ring. Again, the outer cover  70  may quickly be worn away in use, or may be removed prior to installation of the cutter ring  20  upon a hub  24 . This process also may be completed by submitting the assembly  76  to an austenitation process. In one form, the temperatures used in the austenitization process exceed 1650° F. As with the first variation, this assembly also may not require additional machining between the HIP/sintering step and installation. 
         [0030]    In the second embodiment  80 , shown in  FIGS. 5-8 , the entire cutter ring  82  is formed of a solid and unitary powder metal structure. 
         [0031]    In one form of production as shown in  FIG. 6 , the cutter rings  82  are formed by providing a longitudinally oriented tubular canister  84 , having an inner surface  86 , an outer surface  88  and end surfaces  90 A,  90 B. A volume of powder metal  92  is disposed within the tubular canister and subjected to an HIP process, such as described above, forming a long tube of powder metal material from which individual cutter rings  82   a - 82   h  are cut and machined. Again, the outer cover will quickly be worn away in use, or may be removed prior to installation of the cutter ring upon a hub. The process may be completed by submitting each ring  82  to an austenitation process. In one form, the temperatures used in the austenitization process exceed 1650° F. 
         [0032]    In the first variation  90  of the second embodiment, shown in  FIG. 7 , a formed canister (mold)  92  is formed as a ring having the cross sectional shape, the upper portion of which is generally as shown in  FIG. 7 . Into this canister is deposited a volume of powder metal  94 . The entire assembly  96  is then subjected to the HIP process, such as that disclosed above, whereupon a unitary, singular cutter ring  90  is formed. In one form, the canister  92  is formed of sheet metal. As with the previous embodiments, the outer cover will quickly be worn away in use, or may be removed prior to installation of the cutter ring upon a hub  24 . The process may be completed by submitting the assembly  76  to an austenitation process. In one form, the temperatures used in the austenitization process exceed 1650° F. 
         [0033]    Alternatively, a second variation  98  of the second embodiment  80 , shown in  FIG. 8 , is disclosed. This second variation  98  is formed by providing a formed sheet metal canister  100 , which is substantially rectangular in cross section. Into this canister  100  is deposited a volume of powder metal  102 . This assembly  104  is then subjected to the HIP process, such as that described above. The resulting assembly  104  is then machined or forged to the contour generally shown at  106 , resulting in a unitary structure, singular cutter ring. The outer cover is removed prior to or during machining of the ring to the final cutter shape. The process is then completed by submitting the machined ring to an austenitation process. In one form, the temperatures used in the austenitization process exceed 1650° F. 
         [0034]    The term sacrifice used herein is defined as the surrender or destruction of something prized or desirable for the sake of something considered as having a higher or more pressing value. In this case, the mold, or a portion thereof, may be sacrificed to more easily produce a very hard cutter ring with potentially less expense than with a non-sacrificial mold. 
         [0035]    While the present invention is illustrated by description of several embodiments and while the illustrative embodiments are described in detail, it is not the intention of the applicants to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications within the scope of the appended claims will readily appear to those sufficed in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and methods, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of applicants&#39; general concept.