Abstract:
A hybrid metal/composite centrifuge is described which can be designed and manufactured for large sizes which have traditionally been of metal construction only. The hybrid metal/composite centrifuge combines an “all composite”, fully disposable, centrifuge rotor with a reusable metal center tube which retains the rotor bearings. This design combines a fully disposable composite rotor, for example made of an incinerable plastic material, with a removable and reusable metal centertube.

Description:
FIELD 
       [0001]    A composite, disposable centrifuge rotor that is useable in a centrifuge filtration system is described. 
       BACKGROUND  
       [0002]    Centrifuge filtration systems for filtering fluids, such as lube oil, are known. These devices generally include a centrifuge rotor formed by an outer rotor shell sealed to a rotor base, and a centertube that extends between a center of the rotor base and a center of the rotor shell. Some centrifuge designs do not have a centertube. The centrifuge rotor is rotatably disposed on a shaft for rotation relative to the shaft. 
         [0003]    The market for a large diameter centrifuge rotor is dominated by very expensive “all metal” designs due to the mechanical stress limits inherent in composite centrifuge rotors which would not normally have the strength to survive heavy duty requirements. Currently there are size limitations to the use of a fully composite centrifuge rotor. Among these limitations are performance characteristics, holding capacity and material cost. As the size requirement increases beyond these limitations, the typical material choice for key components of a rotor is metal which adds cost to the manufacturing process. The result is an expensive, heavy, non-disposable rotor with significant maintenance activity required at regular service intervals. 
         [0004]    Centrifuge designs are known that utilize a metal centertube which retains the bearings. However, in these designs, the rotors are all metal. 
         [0005]    An all composite, incinerable insert cartridge that is installable in a metal rotor is known from the CS44000 ConeStaC™ centrifuge insert cartridge available from Cummins Filtration. However, the CS44000 is not a pressure vessel. Rather, it is just an incinerable service component that is held within a metal rotor shell and metal centertube/baseplate assembly. 
       SUMMARY  
       [0006]    A hybrid metal/composite centrifuge rotor is described which can be designed and manufactured for large sizes which have traditionally been of metal construction only. The rotor is useable in a centrifuge filtration system for filtering a fluid including, but not limited to, lube oil. 
         [0007]    In one embodiment, the hybrid metal/composite centrifuge combines an “all composite”, fully disposable, large diameter centrifuge rotor with a reusable metal centertube which retains the rotor bearings. This design combines a fully disposable composite rotor, for example made of an incinerable plastic material, with a generally permanent, reusable metal centertube which provides greater resistance to internal pressure when compared to a composite only centrifuge rotor. The employment of a metal centertube to provide support adds strength to a composite rotor and provides a lower cost, disposable alternative to large diameter centrifuges that utilize “all metal” rotors. 
         [0008]    In one embodiment, a centrifuge includes a composite rotor made entirely from incinerable material, where the rotor includes a first opening at one end and a second opening at an opposite end. A metal centertube supports the composite rotor, and includes a first end that extends through the first opening of the rotor and a second end that extends through the second opening of the rotor. A first bearing is mounted on the centertube at the first end thereof and a second bearing is mounted on the centertube at the second end thereof for rotatably supporting the metal centertube, and the centertube is removably mounted on the rotor. 
         [0009]    The composite rotor can be used in place of a higher cost, higher maintenance rotor and is able to withstand pressure load distributions present in a large diameter centrifuge. 
         [0010]    The reusable metal centertube assembly provides a “backbone” for the composite rotor and has bearings mounted thereon instead of on the rotor to allow for a fully disposable, fully incinerable centrifuge rotor. 
     
    
     
       DRAWINGS  
         [0011]      FIG. 1  is an exploded view of components of the hybrid metal/composite centrifuge along with a shaft. 
           [0012]      FIG. 2  is a cross-sectional view of the composite rotor with the metal centertube installed. 
           [0013]      FIG. 3  is a cross-sectional view of the composite rotor with the metal centertube removed. 
           [0014]      FIG. 4  is a perspective view of the metal centertube assembly used to support the composite rotor. 
       
    
    
     DESCRIPTION  
       [0015]    With reference to  FIGS. 1-4 , the hybrid metal/composite centrifuge  10  includes a composite rotor  12  and a centertube assembly  14 . In use, the centrifuge  10  can be rotatably mounted on a shaft  16  for rotation relative to the shaft. 
         [0016]    The composite rotor  12  is an all incinerable construction that allows the rotor to be incinerated for disposal. The rotor  12  can be made of any suitable incinerable material, such as an incinerable plastic. The rotor  12  includes a first opening  20  at one end and a second opening  22  at an opposite end for receipt of the centertube of the centertube assembly. 
         [0017]    In the illustrated example, the rotor  12  includes an upper, outer rotor shell  24  that is sealed along a base edge thereof to a lower rotor base  26  along a seam  28 . The outer rotor shell  24  and the lower rotor base  26  rotate together and define an interior space  29  in which the centrifugal separation occurs. The first opening  20  is formed centrally in the outer shell  24  while the second opening  22  is formed centrally in the lower base  26  coaxial to the first opening. 
         [0018]    The shell  24  and the base  26  essentially form a pressure containment vessel during use. The shell  24  and the base  26  can be formed with features to achieve separation of contaminants from the fluid being filtered. For example, in the case of lube oil that is to be filtered, the shell  24  and the base  26  can include jet drive features to cause rotation of the rotor  12  to effect the separation. The construction and operation of features in centrifuge rotors to achieve separation of contaminants from the fluid are well known to those of ordinary skill in the art. Examples of centrifuge rotors are disclosed in, for example, U.S. Pat. Nos. 7,674,376 and 7,566,294. 
         [0019]    The centertube assembly  14  includes a metal centertube  30  having a first end  32  that in use extends through the first opening  20  and a second end  34  that in use extends through the second opening  22 . A first bearing  36  is mounted on the centertube  30  at the first end and a second bearing  38  is mounted on the centertube at the second end for rotatably supporting the metal centertube on the shaft  16  for rotation about the axis of the shaft. 
         [0020]    A suitable radial seal  40 ,  42 , for example an elastomeric o-ring, x-ring, x-rings, a wiper seal, or the like, is mounted on the centertube  30  at each of the first end  32  and the second end  34 , with the radial seals sealing with respective sealing surfaces  60 ,  62  on the rotor to seal between the centertube and the rotor. The sealing surface  60  is defined by a circumferential shoulder on the shell  24  that defines the first opening  20 . The sealing surface  62  is defined by a circumferential wall  64  that extends upwardly from the base  26  in a direction toward the first opening  20  and that defines the second opening  22 . 
         [0021]    The centertube  30  is generally hollow to allow passage of the shaft  16 . Openings  66  are formed in the centertube to allow fluid to flow from the interior space  29  into the interior of the centertube  30 , and then through flow passages  31  formed in the shaft  16 . The openings  66  are located on the centertube  30  between the seals  40 ,  42 , for example closer to the seal  40  than to the seal  42 . In the illustrated example, the openings  66  are located on the centertube  30  at a location just beneath the seal  40 , and are located at a step-down region  33  of the shaft  16  where the outer perimeter of the shaft  16  is reduced. Although the shaft  16  is illustrated as being circular when taken in cross-section, the shaft  16  can have any shape including, but not limited to, square, octagonal, oval, etc. 
         [0022]    In addition, the centertube  30  is illustrated as being cylindrical with a circular outer and inner perimeter, and being substantially hollow. However, the inner perimeter of the centertube  30  can have any shape that allows the shaft  16  to fit therethrough, including generally matching the shape of the shaft  16 . Further, the outer perimeter of the centertube  30  can have any shape including, but not limited to, square, octagonal, oval, etc. Likewise, the openings  20 ,  22  are illustrated as being circular, but they can have any shape, such as square, octagonal, oval, etc., that allow passage of and sealing with the centertube  30 . 
         [0023]    The centertube  30  is removably mounted on the rotor  12  to allow it to be reused. In particular, the first end  32  of the centertube is threaded  50 . A retainer clip  52  is mounted on the centertube at the second end  34 , and a threaded collar  54  is engaged with the threads  50  at the first end  32  that in use removably clamps the rotor  12  on the centertube  30  between the threaded collar and the retainer ring. At the same time, the seals  40 ,  42  seal with the sealing surfaces  60 ,  62  so that the rotor  12  forms a pressure containment vessel. 
         [0024]    The reusable centertube  30  contains the bearings  36 ,  38 , for example bushings, which can be made from a low cost, drawn metal tubing construction. In contrast, the rotor  12  is constructed from fully composite components that can be incinerated. The rotor can have any conventional features including, but not limited to, jet drive features in centrifuges available from Cummins Filtration, Inc. 
         [0025]    The hybrid centrifuge  10  is different because the bearings are no longer held in the separable composite rotor  12 . This difference helps to make the rotor  12  fully disposable and incinerable upon removal. Further, the inclusion of radial seals between the centertube  30  and the composite rotor  12  enables pressure containment while still allowing for easy disassembly. 
         [0026]    The shaft  16  and centertube  30  are illustrated as full flow designs. However, the shaft and centertube could be designed to implement split flow where the percentage of flow entering the collection chamber relative to the percentage of flow bypassing the collection and going to jet drive nozzles is controlled as described in U.S. Pat. No. 7,377,893. 
         [0027]    The invention may be embodied in other forms without departing from the spirit or novel characteristics thereof. The embodiments disclosed in this application are to be considered in all respects as illustrative and not limitative. The scope of the invention is indicated by the appended claims rather than by the foregoing description; and all changes which come within the meaning and range of equivalency of the claims are intended to be embraced therein.