Abstract:
A system and method of manufacturing improved wear ring assemblies and positive pressure shaft seals. The wear ring assemblies are made from stacked layers of flat metal. Different shaped component parts of the wear ring assemblies are cut from various sheets of metal. The component parts are stacked to form different sections of the wear ring assemblies. The stacked component parts are welded or otherwise bound together. The resulting sections of the wear ring assemblies are then assembled to form the annular structure of a full wear ring assembly. The result is a wear ring assembly that is both easy and inexpensive to produce.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   In general, the present invention relates to the structure of seals that are used around rotating shafts. More particularly, the present invention relates to the manner and method by which such shaft seals are manufactured. 
   2. Description of the Prior Art 
   The prior art is replete with machines, equipment and component parts that require a seal be formed around a rotating shaft. As such, over the years, many shaft seal designs have been developed for a wide array of rotating shaft applications. Many shaft seals, such as those used on automobile engines are designed as part of the engine and are actively lubricated and cooled by the running of the engine. However, in many applications, shaft seals are needed in isolated applications where active lubrication and cooling are either not available or are not desirable. 
   Two of the most common families of isolated shaft seal designs are packed seals and positive pressure seals. Typically, neither packed seals nor positive pressure seals require active lubrication or cooling. A packed seal is the type of shaft seal used in most plumbing valve fixtures. With a packed seal, packing material is placed around the shaft and the packing material is compressed against the shaft until the packing material is so dense that foreign material cannot pass through the packing material. Such shaft seal designs work well but add significant friction to the rotating shaft. Accordingly, such shaft seals are typically only used with shafts that turn only on occasion or rotate at very low speeds. If such packed seals were used on shafts that turn quickly, the friction would rapidly heat the seal to a point where the seal or shaft would fail. 
   Positive pressure shaft seals add much less friction to a rotating shaft than do packed seals. Accordingly, positive pressure seals can be run at much higher shaft rotation speeds without concerns of friction heat causing the seal to fail. 
   Referring to  FIG. 1 , a typical prior art positive pressure seal assembly  10  is shown. In the prior art, an elastomeric seal  12  is clamped directly onto a rotating shaft  14 . The elastomeric seal  12  is interposed between two wear rings  16  that have smooth external faces. The wear rings  16  and the elastomeric seal  12  are placed in an annular housing  18 , wherein the interior of the housing  18  is kept above ambient pressure. As the shaft  14  turns, the elastomeric seal  12  on the shaft  14  turns, as do the wear rings  16  surrounding the elastomeric seal  12 . The wear rings  16  move against the interior of the housing  18 . Foreign material is prevented from entering the seal by the contact of the wear rings  16  against the interior of the housing  18  and the positive pressure within the housing  18 . 
   Although positive pressure shaft seals have many advantages over packed seals, they tend to be significantly more expensive than simple packed seals. One of the most extensive elements in a positive pressure shaft seal is the wear ring. The wear rings are typically machined from solid blanks of stainless steel. Each wear ring has a complex internal configuration that enables the wear ring to engage and retains the elastomeric seal. Furthermore, the wear rings have external surfaces that must be polished smooth to reduce wear friction. It is the cost of properly manufacturing the wear rings that often is a limiting factor in economically producing positive pressure shaft seals. 
   A need therefore exists for an improved way to produce wear rings in a positive pressure shaft seal that reduces both the cost and complexity of manufacture. This need is met by the present invention as described and claimed below. 
   SUMMARY OF THE INVENTION 
   The present invention is a system and method of manufacturing improved wear ring assemblies and the positive pressure shaft seals that utilize the improved wear ring assemblies. The wear ring assemblies are made from stacked layers of flat metal. Different shaped component parts of the wear ring assemblies are cut from various sheets of metal. The component parts are stacked to form different sections of the wear ring assemblies. The stacked component parts are welded or otherwise bound together. The resulting sections of the wear ring assemblies are then assembled to form the annular structure of a full wear ring assembly. Since the wear ring assemblies are made from cut pieces of flat metal that are bonded together, little or no machining is required to produce the structure of the wear ring assemblies. The result is a wear ring assembly that is both easy and inexpensive to produce. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the present invention, reference is made to the following description of exemplary embodiments thereof, considered in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a partially fragmented perspective view of a prior art positive pressure shaft seal; 
       FIG. 2  is a partially fragmented perspective view of a positive pressure shaft seal in accordance with the present invention; 
       FIG. 3  is a perspective view of a wear ring assembly in accordance with the present invention; 
       FIG. 4  is an exploded view of the embodiment of the wear ring assembly shown in  FIG. 3 . 
       FIG. 5  is an exploded view of a subassembly of the wear ring assembly in accordance with the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIG. 2 , a positive pressure shaft seal assembly  20  is shown in accordance with the present invention. The shaft seal assembly  20  contains an elastomeric seal  22  that is clamped around a rotating shaft. The elastomeric seal  22  is interposed between two opposing wear ring assemblies  24 . As will be later explained, the wear ring assemblies  24  are not machined from a solid blank of metal, but are rather assembled out of component pieces. 
   Each wear ring assembly  24  has a face surface  26  that is smooth. The wear ring assemblies  24  and the elastomeric seal  22  are placed within a housing  28 . The housing  28  has interior surfaces  29  that abut against the face surfaces  26  of the wear ring assemblies  24 . The interior surfaces  29  of the housing  28  can be polished metal or can be lined with a low friction bearing material such as Teflon, Surlyn or Kevlar. 
   The housing  28  of the shaft seal assembly defines an interior chamber  30  that communicates with a pressurized gas source. Accordingly, the pressure within the housing  28  is maintained at a level higher than that of the pressure surrounding the exterior of the housing  28 . 
   Referring to  FIG. 3 , it can be seen that the wear ring assembly  24  is a complex annular structure. The face surface  26  of the wear ring assembly  24  has an outside diameter D 1  and an inside diameter D 2 . A cylindrical wall  32  extends upwardly from the peripheral edge of the back of the face surface  26 . However, although the cylindrical wall  32  has the same outside diameter D 1  as does the face surface  26 , the cylindrical wall  32  has an inside diameter D 3  that is larger than that of the inside diameter D 2  of the face surface  26 . The result is a ledge structure where the interior of the face surface  26  creates the base of a ledge structure and the interior of the cylindrical wall  32  creates the sides of the ledge structure. The existence of this ledge structure is necessary for the wear ring assembly  24  to properly engage and retain the elastomeric seal  22 ( FIG. 2 ). 
   Referring to  FIG. 4 , it can be seen that each of the ring assemblies  24  is comprised of two interconnected subassemblies  34 . Each subassembly  34  is a semi-annular structure comprised of a plurality of stacked elements  35 ,  36 ,  37  ( FIG. 5 ). Each of the three stacked elements is, itself, semi-annular. However, the position of each of three stacked elements is staggered. This causes the two ends  38 ,  39  of each subassembly  34  to form half of a finger lap joint. When two subassemblies  34  are connected, the ends  38 ,  39  of the staggered layers intermesh and complete the annular shape of the wear ring assembly  24 . The structure of the two subassemblies  34  is identical. Accordingly, each of the two subassemblies  34  can be manufactured in the same manner using identical processes, parts and tooling. 
   The two subassemblies  34  are held together by set screws  40  that pass through some of the layers in the ends  38 ,  39  of the subassemblies  34  that intermesh. Screw holes  42  are formed in the ends  38 ,  39  of the subassemblies  34 . The screw holes  42  only properly align when the two subassemblies  34  are correctly intermeshed. Consequently, when the set screws  40  are set in place, a person can be assured that the full wear ring assembly  24  has been assembled properly. 
   Referring to  FIG. 5 , it can be seen that each ring subassembly  34  is made from three stacked ring layers  35 ,  36 ,  37 . The first layer  35  forms the face surface  26  (FIG.  3 )of the each ring subassembly  34 . The first layer  35  is semi-annular in shape and is cut from a sheet of polished metal. Sheets of polished metal, such as stainless steel, are readily and inexpensively available for commercial use in different gauges. 
   The second layer  36  of each ring subassembly  34  and the third layer  37  of each ring subassembly  34  are both cut from a different stock of sheet metal than is the first layer  35 . The gauge of the metal used to create the second and the third layers  36 ,  37  can be thicker than that used to create the first layer  35 . Furthermore, the sheet of metal used to create the second and third layers  36 ,  37  need not have a polished finish. 
   The second layer  36  and the third layer  37  are semi-annular and have identical dimensions. However, the second and third layers  36 ,  37  are not uniformly stacked atop the first layer  35 . Rather, the first layer  35 , second layer  36  and third layer  37  are all staggered. In this manner, the ends of the first layer  35 , second layer  36  and third layer  37  terminate at different points. This creates the staggered ends  38 ,  39  ( FIG. 4 ) of the ring subassemblies  34  that enable the ring subassemblies  34  to intermesh when connected. 
   The first layer  35 , second layer  36  and third layer  37  are preferably made of stainless steel or another corrosion resistance metal. Sheets of the selected metal are provided for the first layer  35 , second layer  36  and third layer  37 . All three layers  35 ,  36 ,  37  can be cut from the same sheet of metal. However, it is preferred that the first layer  35  be cut from a first polished sheet and a second sheet of metal is used to create the second and third layers  36 ,  37 . 
   In the preferred embodiment, the first, second, and third layers  35 ,  36 ,  37  are cut from sheets of metal using a laser cutter or a water abrasion cutter. In this manner, the sheets of metal can be cut to close tolerances and need not be further machined in any secondary operation. 
   Once the three layers  35 ,  36 ,  37  of metal are obtained they are stacked together in the form of the wear ring subassembly  34  ( FIG. 4 ). Once so configured, the three layers  35 ,  36 ,  37  are spot welded or otherwise bound together at different points. After the three layers  35 ,  36 ,  37  are bound together, the screw holes at the ends of each ring subassembly  34  are drilled and tapped. Once the ring subassemblies  34  are created, they are interconnected and mechanically bound with the set screws  40  to form a complete wear ring assembly  24 . The wear ring assembly  24  can then be used to create the overall shaft seal. Since the wear ring assemblies  34  are made from standard sheets of metal and require no complex machining, the cost of the wear ring assemblies  34  is significantly lower than wear ring assemblies currently commercially available. Since the wear ring assemblies are less expensive than prior art alternatives, the completed shaft seal assembly can be manufactured at a cost lower than prior art alternatives. 
   It will be understood that the embodiment of the present invention shaft seal assembly that is described and illustrated herein is merely exemplary and a person skilled in the art can make many variations to the embodiment shown without departing from the scope of the present invention. For example, the illustrated example shows three layers used to create each subassembly. It will be understood that any plurality of layers can be used. Furthermore, the wear rings shown contain only two subassemblies. It will be understood that any number of subassemblies can be created that assemble together into the annular shape of the wear ring assembly. All such variations, modifications and alternate embodiments are intended to be included within the scope of the present invention as defined by the appended claims.