Abstract:
A multi-piece stargear assembly comprising a hub, a pair of arcuate toothed segments, and a lock ring, the hub having an internal bore, a keyway in the bore, and an external radially extending flange adjacent one end, the ring being configured to fit on an end of the hub opposite said one end, said segments being arranged around said hub, said flange and segments having mutually interlocking surfaces that enable the flange to resist axial and radial movement on said hub of said segments adjacent said flange, said ring and segments having mutually interlocking surfaces that enable the ring to resist axial and radial movement on said hub of said segments adjacent said ring.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to improvements in powered roller conveyors and, in particular, to replaceable drive gears for such conveyors. 
       PRIOR ART 
       [0002]    Board making processes such as those involved in the manufacture of veneer boards, typically use drying stations that have powered conveyors to transport moisture laden material through a hot air dryer. The conveyors in these applications are generally of the powered roller type with roller pairs driven in unison by meshed gears on respective roller shafts. The gears, sometimes called stargears, owing to their characteristic tooth shape, are subject to high wear rates because they operate in open environments exposed to the materials being conveyed and without the benefit of lubrication. 
         [0003]    Conventional dryer conveyor systems are configured such that the components exist in tight quarters and various parts are assembled successively on each roller shaft. The lack of clearance around the parts and the need to remove some parts for access to others makes it very difficult and time consuming to change the stargears in a conventional dryer conveyor. The task of removing and replacing stargears is considerable because associated shaft bearings and in some designs, sprockets must first be removed and this effort is compounded by the sheer number of such gears that exist in the typical dryer. Oftentimes, the sprockets and stargears themselves are oxidized to the roller shafts, making their removal particularly troublesome. From the foregoing brief discussion, it will be understood that there has been a long-standing need for a way to replace worn stargears with less labor and time than has heretofore been necessary. 
       SUMMARY OF THE INVENTION 
       [0004]    The invention provides a stargear assembly for use in powered roller conveyors that reduces the labor, time and material cost in replenishing worn gear teeth. The stargear assembly, in accordance with the invention, permits the renewal of worn gear teeth while leaving a base hub in place on the roller shaft for re-use with a new set of gear teeth. Since the invention permits the gear teeth to be removed and replaced without disturbing other components including bearings, bearing holders, and sprockets on the roller shafts, considerable savings in labor can be achieved and the risk or need to break or otherwise damage other components can be avoided. Further, the stargear teeth replacement elements, in the form of arcuate segments, are less expensive to produce than prior art pieces since they comprise less material and less machine work is required for their manufacture. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  is a schematic view of a pair of power driven rollers at a typical roller station in a dryer conveyor; 
           [0006]      FIG. 2  is a perspective view of a stargear assembly constructed in accordance with the invention; 
           [0007]      FIG. 3  is a side view, partially in section, of the stargear assembly; 
           [0008]      FIG. 4  is an end or axial view of the stargear assembly; 
           [0009]      FIG. 5  is an axial view of a hub of the stargear assembly; 
           [0010]      FIG. 6  is a side view partially in section, of the hub of  FIG. 5 ; 
           [0011]      FIG. 7  is an axial view of a stargear segment of the invention; 
           [0012]      FIG. 8  is a side view of the stargear segment of  FIG. 7 ; 
           [0013]      FIG. 9  is a cross-sectional view of the stargear segment taken in the plane  9 - 9  indicated in  FIG. 7 ; 
           [0014]      FIG. 10  is a diametral cross-sectional view of a lock ring of the stargear assembly; 
           [0015]      FIG. 11  is a diametral cross-sectional view of a modified lock ring; and 
           [0016]      FIG. 12  is a longitudinal cross-sectional view of a modified hub. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0017]    The invention resides in a multi-piece stargear assembly particularly suited for use in a roller conveyor  10  such as used in a veneer dryer. For purposes of clarity, only one pair of rollers  11 ,  12  are shown, but it will be understood that on each level or deck of the dryer, numerous roller pairs are arrayed parallel and closely spaced to one another at successive points or stations along the conveying path. The rollers  11 ,  12  are mounted on respective shafts  13 ,  14  which in turn are located in bearing supports  16 ,  17 . The lower shaft, conventionally, is carried in bearings  18  in lower portions of the supports  16 ,  17 , while the upper shaft  14  is confined in upper parts of the supports  16 ,  17 . A chain  21  power drives the lower shaft  13  through a sprocket  19  and similarly drives other sprockets associated with the other roller pairs in the same conveyor level or deck. 
         [0018]    A multi-piece stargear assembly  26  of the invention is mounted on each shaft  13 ,  14  of a roller pair or station. The stargears  26  are meshed with one another and thereby enable some of the power imparted to the associated sprocket  19  to be transferred to the mating upper roller  12  causing it to counter-rotate in synchronization with the lower roller  11  driven directly by the sprocket. The stargear assemblies  26 , used on the lower and upper shafts  13 ,  14 , are identical. A stargear assembly  26  has a characteristic long gear tooth profile enabling the gear teeth of mating assemblies to stay engaged with one another while the center-to-center distance between their respective shafts  13 ,  14  varies somewhat as a function of the presence and the thickness of the web of material passing between the rollers  11 ,  12 . 
         [0019]    Each stargear assembly  26  comprises a hub  27 , a pair of gear segments  28 , and a locking ring  29  all of which can be formed of ductile iron. The hub  27  is cylindrical in its general form with a central cylindrical bore  31  sized to fit closely on a shaft  13  or  14 . The bore  31  includes a key slot  32  for receiving a square key that is also received in a corresponding slot in the shaft  13 , or  14 . The exterior of the hub  27  is concentric with the bore  31  and has a radially extending circular flange  33  at one end, cylindrical arcuate surface segments  34  along its mid-section, and an externally threaded portion  36  on an end opposite the flange  33 . The surface segments lie diametrally opposite one another and between a pair of diametrally opposed lugs or stops  37 . The lugs extend radially from the cylindrical surface segments  34  to an imaginary cylinder corresponding to an outer surface  38  of the flange  33 . One of the lugs  37  has an internally threaded hole  39  to receive a set screw that can bear on a key in the slot  32 . An inner radial face  41  of the flange  33  is formed with arcuate grooves  42  of constant rectangular cross-section concentric with the bore  31  and extending from lug  37  to lug  37 . The formation of the grooves  42  create arcuate retaining lips  43 . The inner sides of the grooves  42  have radii equal to the radius of the cylindrical surface segments  34  at the mid-section of the hub such that they present a smooth continuation of these mid-section surfaces. The axial length of the lugs, measured from the flange  33  is preferably somewhat less than the distance to the threaded portion  36 . 
         [0020]    The lock ring  29  is a circular element relatively short in its axial direction, and is formed with an internally threaded circular bore  44 , an outer cylindrical surface  46  concentric with the bore, and opposite radially extending end faces  47 ,  48 . The threads of the bore  44  are cut to mate with the external threads on the hub  27 . The outer cylindrical surface  46  has angularly spaced radially oriented blind holes  49  to receive a wrench by which the lock ring  29  can be tightened or loosened on or off the hub  27 . The lock ring  29  has a counter bore  51  at a side or end that forms an inner cylindrical surface  52  and an annular lip or projection  53 . 
         [0021]    The gear segments  28  are preferably identical and have radially elongated uniformly arcuately spaced teeth  56  being five (5) in number and with a nominal common pitch diameter of 7½″. At the roots of the teeth  56  is an arcuate cylindrical base  57  that serves as a bridge connecting the teeth. An inner cylindrical surface  58  of the base  57  has a radius closely fitting the radius of the hub surface segments  34 . 
         [0022]    The face width of the teeth  56  is about one-half the axial length of the hub  27 . With particular reference to  FIGS. 8 and 9 , a radial face  61  of the segment  28  has an axially projecting lip  62  that at its inside forms part of the cylindrical surface  58  and that ha a cylindrical outer surface  63 . At its opposite radial face  66 , the segment  28  has an arcuate groove  67  of constant rectangular cross-section concentric with the interior cylindrical surface  58 . 
         [0023]    As particularly seen in  FIG. 3 , the hub  27 , gear segments  28 , and lock ring  29  are assembled in a manner that locks the segments on the hub. The projecting lip  62  on the radial face  61  of a gear segment fits into the groove  42  on the inner radial face  41  of the hub flange  33 . Similarly, the part of the lock ring surrounding the counter bore  51  projects into the groove  67  on the segment base  57 . The arcuate length of the gear segment base  57  is complimentary to that of the spacing between the hub lugs  37 , such that abutment between the ends of a segment base  57  and the lugs  37  prevents rotation of the segments relative to the hub. When a stargear assembly  26  is first installed on a shaft, the segments  28  and lock ring  29  can already be in place on the hub  27  as described in connection with  FIG. 3 . The assembly  26  is slipped over a shaft  13  to the correct axial position and locked in place by tightening a set screw in the tapped hole  39 . In some conveyor designs such as shown in  FIG. 1 , the sprocket  19  is outboard of a stargear assembly  26  while in others, the stargear assembly is positioned on the opposite end of a roller from where the sprocket is attached. Typically, the bearings and bearing supports for the rollers  11 ,  12 , are outboard of the stargears. 
         [0024]    With use, the stargear segments  28  wear out requiring their replacement, typically at times when other parts at the roller stations are not in need of replacement. The invention permits the gear teeth, when worn out, to be replaced without removal of any associated sprocket  19 , bearings  18 , or bearing supports  16 ,  17 . Removal of a worn set of gear segments  28  is accomplished, in accordance with the invention, by unscrewing the lock ring  29  away from the gear segments  28  and off of the hub  27 . With the ring  29  off the hub  27 , the segments  28  can be moved axially away from the hub flange  33  until the projecting lip  62  is completely out of the hub flange groove  42  and is then moved radially completely away from the hub  27 . A new set of gear segments  28  can be installed on the hub  27  by reversing this sequence. 
         [0025]    When the stargear parts are fully assembled, the gear segments  28  are locked in position against movement on the hub  27  and, consequently, against movement relative to the shaft  13  or  14  on which they are mounted. The fit between the inner cylindrical surface  58  of the gear segment  28  and the outer cylindrical surface segments  34  of the hub prevents radial inward movement of the segments. The interfitting or telescoping relation between the projections and corresponding grooves prevents any outward radial movement or axial tilting movement of the gear segments relative to the hub. Specifically, the hub lips  43  radially restrain the gear segment lips  62  at one side of the segments  28  and the annular ring lip  53  received in the segment grooves  67  radially restrains the other side of the segments. The segments  28  are axially confined by the radial surfaces of the hub flange and lock ring abutting the opposed radial faces of the segments, respectively. Angular movement of the segments  28  on the hub  27  is prevented by abutting contact between the end faces of the segments and the sides of the stop lugs  37  that lie in planes generally chordally oriented with respect to the axis of the hub  27 . 
         [0026]      FIGS. 11 and 12  illustrate examples of modifications a hub  71  and lock ring  72  of the invention. These hub and lock ring components  71 ,  72  serve the same functions in assembly with the stargear segments  28  as do the earlier described hub and lock ring components  27  and  29 . Structural features of these modified components that are identical with those of the earlier described components are given the same numeral designations as previously used. The hub  71  has a peripheral groove  73  of V-shaped cross-section adjacent its cylindrical end  74  distal from the flange  33 . The lock ring  72  has a smooth cylindrical bore  76  sized to slip over the cylindrical end  74  of the hub  71 . Diametrally opposed pointed set screws  77  (only one is seen in  FIG. 11 ) are assembled in radial tapped holes in the lock ring  72 . The set screws  77 , when tightened, extend into and lock on the peripheral groove  73 , thereby securing the stargear segments  28  on the hub  71 . 
         [0027]    It should be evident that this disclosure is by way of example and that various other changes may be made by adding, modifying or eliminating details without departing from the fair scope of the teaching contained in this disclosure. For example, the lock ring, as an alternative to the machine threads of the bore  44  or the set screws  77 , can be retained on the hub by a bayonet style connection, by a snap ring, or by other known collar retention arrangements. The invention is therefore not limited to particular details of this disclosure except to the extent that the following claims are necessarily so limited.