Abstract:
A sprocket assembly for a roller conveyor comprising a hub and a sprocket plate, the hub having a central cylindrical bore for fitting onto a round shaft of a roller, the hub having provisions for rotationally and axially locking it on a shaft in a manner adequate to transmit torque to the shaft and rotationally drive the roller, the sprocket plate having peripheral teeth adapted to be interengaged with a drive chain and a central bore capable of receiving the shaft, the sprocket plate and hub being constructed and arranged to be removably joined together with the centers of their respective bores coincident, said hub and sprocket plate having complementarily shaped radially extending abutting surfaces enabling the sprocket plate to develop torque on the hub by compressive forces developed by the radially extending sprocket plate surfaces against the radially extending hub surfaces.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to improvements in powered roller conveyors and, in particular, to a novel drive sprocket arrangement for the rollers of such conveyors. 
       PRIOR ART 
       [0002]    Power driven roller conveyors are used in process equipment for conveying materials such as wet slurrys, mats, and so forth, through dewatering and/or drying stations. By way of example, wet or water laden materials conveyed by such conveyors are processed into wall board, ceiling tile, and the like as is known in the art. Commonly, the rollers of the conveyor are each driven through a sprocket fixed to its shaft. The sprockets are typically driven by a common endless chain. The service conditions in which the sprockets operate are adverse, often with no practical way for sealing the materials being processed away from the sprockets and for lubricating the sprockets. The operating conditions typically result in a wear rate that requires replacement of the sprockets every year or so and, in any event, far more routinely than an entire conveyor is replaced. 
         [0003]    Sprocket replacement is expensive in terms of both the cost of parts and labor. The sprockets typically occupy a crowded space and it is not easy to separate them from their respective shafts after they have been in service for any significant period. It is common for a mechanic to break the sprockets off, by striking blows with a hammer, rather than pulling them off, since it is difficult to grip them with a puller and it is not unusual for them to be tightly locked onto their shafts as a result of corrosion and the build-up of dirt and debris on the shafts. 
       SUMMARY OF THE INVENTION 
       [0004]    The invention provides a novel sprocket arrangement for a powered roller conveyor useful in a hot air dryer or like processing equipment. The sprocket arrangement of the invention comprises mating hub and sprocket plate elements that allow ready replacement of the sprocket plate after its service life has been exhausted while allowing the hub to remain fixed on its associated roller shaft. The invention departs from the time honored practice of replacing worn out integrated sprocket and hub units. By only replacing that part of a sprocket and hub drive unit that experiences significant, and in practice, inevitable wear, the invention affords substantial savings in both material and labor. 
         [0005]    Since only about half of the combined material of the sprocket and hub assembly is replaced, there can be significant savings in material costs. Moreover, the labor to replace a worn sprocket plate, in accordance with the invention, is considerably less than that involved in removing a prior art unitary sprocket and hub, typically frozen on to the roller shaft and difficult to reach because of obstructions posed by adjacent sprockets and other parts of the conveyor. 
         [0006]    The disclosed sprocket plate and hub elements have unique mating configurations that allow the sprocket plate to apply torque to the hub through abutting surfaces that are generous in size and effective radius so as to transfer forces by low compressive stresses rather than at concentrated points by shear forces. In one embodiment, the torque coupling between the sprocket plate and hub is isolated from machine screws used to hold these components together. Consequently, these fastener elements or screws can be of moderate size, thereby saving costs and effort needed for their original assembly and eventual removal when a sprocket must be replaced. In another embodiment, the sprocket and hub are configured to be coupled together without separate fasteners. 
         [0007]    The disclosed sprocket plate and hub arrangement solves a problem of removing a sprocket from an operational position where the hub has a maximum outside diameter larger than a minimum inside diameter of the sprocket plate. 
         [0008]    Still further, in one disclosed preferred embodiment, the sprocket plate is configured as a ring with a large open center to permit it to be removed, when worn out, by slipping it over its associated roller thereby affording flexibility in the steps that can be taken for sprocket plate replacement. This flexibility in the manner in which the sprocket plate can be removed allows a mechanic to choose the easiest way, off either end of a roll assembly for its removal, while still avoiding the removal of the sprocket hub. The ring-like structure of a sprocket plate significantly reduces its material content over that compared with integrated sprocket and hub units thereby reducing the cost of manufacture of replacement parts. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a simplified fragmentary elevational view of a roller conveyor fitted with one embodiment of the sprocket arrangement of the invention; 
           [0010]      FIG. 1A  is an elevational end view of the relationship of a sprocket plate to its associated roller in the arrangement of  FIG. 1 ; 
           [0011]      FIG. 2  is a fragmentary plan view of the conveyor arrangement of  FIG. 1 ; 
           [0012]      FIG. 3  is a fragmentary exploded perspective view of the conveyor of  FIG. 1 ; 
           [0013]      FIG. 4  is a side elevational view of a sprocket plate in accordance with a second embodiment of the invention; 
           [0014]      FIG. 5  is a cross-sectional view of a “half” sprocket plate taken in the plane  5 - 5  indicated in  FIG. 4 ; 
           [0015]      FIG. 6  is a cross-sectional view of a “full” sprocket plate taken in the plane  6 - 6  indicated in  FIG. 4 ; 
           [0016]      FIG. 7  is a side elevational view of a hub in accordance with the second embodiment of the invention; 
           [0017]      FIG. 8  is an edge view of the hub of  FIG. 7 ; 
           [0018]      FIG. 9  is a side view of a sprocket and hub assembly in accordance with the second embodiment of the invention; 
           [0019]      FIG. 10  is a fragmentary view, on an enlarged scale, of the sprocket and hub assembly where the sprocket plate is the “half” style of  FIG. 5 ; and 
           [0020]      FIG. 11  is a fragmentary view like  FIG. 10 , showing the “full” style sprocket plate of  FIG. 6 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]    Referring to the figures, there is shown a partial area of a roller conveyor  10  of the type used, for example, in dryers employed in the manufacture of drywall, particle, flake or chipboard, ceiling tile, and like products that are formed by drying a slurry or wet intermediate product. The conveyor  10  has cylindrical rollers  11  carried on respective concentric round shafts  12  mounted in bearings  13  as is conventional. Normally, a large number of rollers  11  are used in a conveyor but for simplicity only three are shown in the figures. It will be understood that a bearing  13  is provided at each end of each roller  11 . The rollers  11  are arranged parallel to one another in a common horizontal plane, typically, with a uniform center-to-center spacing. The rollers  11  can be mounted close to one another to adequately support the material being conveyed which is often in a weak state incapable of supporting itself across a significant span. 
         [0022]    Ordinarily, in a typical dryer, there are several vertically spaced layers or decks of rollers  11 . The rollers  11  of each level or deck are all driven in the same direction of rotation by a common chain  14 , which may be of the conventional roller type. Customarily, the chain  14  contacts only one or a limited number of teeth  16  of a sprocket  17  associated with a respective roller  11  at any given time. Usually, the rollers  11  of a level or deck are driven by a single chain at one side of the conveyor  10 . 
         [0023]    The sprockets  17 , in accordance with the invention, are assemblies of a sprocket plate  18  on which are formed the teeth  16 , and a hub  19  that is mounted on a roller shaft  12 . As will be described, the sprocket plate  18  and hub  19  are specially configured to interfit or mate with one another for a positive rotational drive between these elements and, alternatively, for passage of the sprocket plate axially completely over the hub. More particularly, the sprocket plate  18  has a spider-like internal bore  21  while the hub has a complementary external spider profile, characterized by radially extending legs or spokes  22  that can fit through the bore. 
         [0024]    Each hub  19  is preferably a metal body with a plurality of three internally radially extending legs or spokes  22 . The hubs  19  can be formed of any suitable material such as a ferrous metal like cast iron, cast steel, or hot roll steel. A bore  26  of the hub  19  is sized to fit the shaft  12  of a respective roller  11  which shaft typically is 1¼ inch in diameter. 
         [0025]    The sprocket bore  26  includes an internal keyway  27  for receiving a key  28 . The key  28  is also received in an external keyway in the shaft  12  as is conventional. A set screw  29  threaded into a radial hole  31  in the hub  19  locks against the key  28  and releasably fixes the hub  19  onto the shaft  12 . 
         [0026]    The sprocket assemblies  17  along the conveying direction alternate between two constructions or styles, one  36  lying outside, with reference to a zone occupied by the rollers  11 , of an imaginary vertical plane passing through the middle width of the chain  14 , and the other  37  lying to the inside of this imaginary plane. In other words, the inside and outside designations of these sprocket assembly styles  36 ,  37  is made with the understanding that parts on the side of the imaginary vertical mid-plane of the chain adjacent the rollers  11  are “inside” and parts on the other side of this imaginary plane are “outside”. To the extent that the features of the sprocket plates and hubs are the same or similar in shape or function, the same reference numerals will apply. The sprocket plates of both styles  36 ,  37  have essentially the same axial profile, including number of teeth and outside diameter. 
         [0027]    The sprocket assemblies  17 , as mentioned, are all driven in the same rotational direction so that their respective rollers  11  also revolve in this same direction. Adjacent leading edges of the hub legs or spokes  22 , with reference to their direction of rotation, are radially extending lugs or stops  41 . The lugs  41  are formed with abutment surfaces  42  that facing rearwardly with reference to their rotational direction, preferably lie in radial planes that are parallel to and pass through the center of rotation or axis of the hub  19 . The abutment surfaces  42  extend radially outward from an imaginary cylinder concentric with the hub axis and coincident with cylindrical surface segments  43  at the base or radially inward ends of the legs  22 . The abutment surfaces  42  terminate radially outwardly at cylindrical outer surface segments  45  of the legs  22  on a common imaginary cylinder concentric with the bore  26  and forming the major outside hub diameter. 
         [0028]    The sprocket plates  18  have asymmetric unidirectional teeth  16  that are shaped to provide a positive drive from limited tangential engagement of the chain  14 . Tips  56  of the teeth  16  represent the outside maximum diameter of the sprockets  17 . The sprocket plates  18  have central bores  57 . Arcuate surface areas  58  of the bore  57 , represent a major diameter area and three intervening arcuate surface areas  59  represent the minor diameter of the bore  57 . The internal sprocket legs  23  are equally angularly spaced and form the minor diameter areas  59  at their inner ends. As seen, the legs  23  span the arcuate space between the major diameter arcuate surfaces  58 . Leading abutment faces  61 , with reference to the direction of rotation of the sprocket assemblies  17 , extend between the inside diameter and outside diameter bore surfaces  58 ,  59  and preferably lie in flat planes that are radial to, pass through, and are parallel to a central axis of the sprocket plate  18 . 
         [0029]    In the illustrated embodiment, the hub legs  22  of either sprocket style  36  or  37 , are three in number and the sprocket plate legs  23  are of the same number. The arcuate extent of each hub leg  22  is slightly less than an arcuate gap  44  between the internal legs or spokes  23  of the internal sprocket plate bore  21 . This arcuate geometry of the hub and sprocket plate legs as well as the limited radial extent of these legs results in an outer hub profile that is complimentary to and slightly smaller than the interior bore  57  of the sprocket plate thereby enabling a sprocket plate to pass completely over a hub. 
         [0030]    A face  47  of the hub  19  lies in a flat radial plane transverse to the hub axis and serves as a seat or abutment surface against which the sprocket plate  18  is secured by machine screws  62 ,  63 . The sprocket plates  18  are removably assembled on corresponding hubs with the axes of these elements coincident and held in place by a set of the machine screws  62  or  63 . In the case of the outside style of sprocket assembly  36 , the sprocket plate  18  is held to the hub  19  with socket head machine screws  62  threaded into the sprocket plate and in the case of the inside style of sprocket  37  the sprocket plate  18  is held to the hub  19  by flat head machine screws  63  threaded into the hub. The screws  62 ,  63 , hold the respective sprocket plates  18  in abutting contact with the radial hub face  47 . It is this surface  47  from which the hub lugs  41  axially project. When mounted on a hub  19 , radial sprocket surfaces  61  abut the radial lug or abutment surfaces  42  enabling the torque developing forces imposed by the chain  14  to be transmitted to the hub with low compressive stresses imposed on these surfaces as a result of being relatively large and being disposed radially outwardly significantly from their rotational axis. Non-threaded clearance holes  66 ,  67 , that receive the machine screws  62 ,  63  in the hubs of the respective outside sprocket styles  36  or in the sprocket plates of the inside sprocket style  37 , ensure that the torque transmitted from the sprocket plate  18  to the hub  19  is isolated from the screws, it being understood that this torque is developed by the abutment surfaces  61 ,  42 . 
         [0031]    As seen in  FIG. 2 , and as discussed, the inside and outside styles  37 ,  36  of the sprocket assembly  17  can alternate along the feed direction of the conveyor  10  to permit a relatively large sprocket diameter to be used in proportion to the center-to-center distance of the shafts  12 . By offsetting the sprocket assemblies  17  to either side of a center plane of the chain  14 , the sprocket plate  18  of one assembly does not interfere with the sprocket  18  or hub  19  of an adjacent sprocket assembly even where, as shown, the center-to-center distance of adjacent shafts  12  is less than the combined radius of a sprocket and a radius of essentially any part of the sprocket hub on the adjacent shaft. This geometry thereby allows relatively large sprockets to be used and, in turn, reduces the forces required of the chain on the sprocket teeth to develop a given level of torque. 
         [0032]    At least the sprocket plates  18  on the outer sprocket assemblies  36 , and preferably the sprocket plates on the inner sprocket assemblies  37 , are able to be passed completely over their associated hubs  19  for purposes of removal and replacement. 
         [0033]    The sprocket plates  18  can experience relatively high wear rates due to their operating environment and from time-to-time may need to be replaced. Both the inside and outside sprocket plates can be changed without removal of their associated hubs. Moreover, removal and replacement of these plates can be readily accomplished because the machine screws  62 ,  63  securing these plates on their respective hubs can be conveniently reached from the outside, i.e. the space outward of the chain  14 , with the convention that the conveyor rollers  11  are to the inside. 
         [0034]    With the invention, replacing each of the sprocket plates  18  is a simple matter of removing three screws  62  or  63 , and separating the plate from its hub. The need for breaking the hub loose from its fit on a shaft  12  is eliminated. Prior to assembly, the screws  62 ,  63 , can be coated with a suitable protective sealant so that the risk of corrosion in the threaded holes in the sprocket plate  18 , or hub  19  is reduced. The torque between the sprocket plate and hub developed by the chain force is transmitted between the radial abutment faces  42  and  61  and is preferably isolated from the screws by appropriately dimensioning the parts and especially as mentioned, the clearance holes. Typically, where desired, the shaft  12  can be lifted slightly for access to any of the machine screws  63  on the inside sprocket plates.  FIG. 4  shows that a sprocket plate  18  can be removed by sliding it axially over the respective roller  11 . This optional method of removal is permitted where, as shown, the minor inside diameter of the sprocket plate is slightly larger than the diameter of the roller. This geometry can be used on the inside sprocket assembly  37  enabling the inside sprocket to be removed, for example, while the adjacent outside sprockets remain in place or can be used on both inside and outside sprocket assemblies for greater flexibility in maintenance or replace operations. 
         [0035]    In many instances, the rollers  11  can be spaced apart far enough to allow the sprockets of each roller to be in-line, i.e. in a common plane without interference. In this case, the width or thickness of a sprocket plate can be double that shown in the figures, while still using the illustrated chain and the axial sprocket plate profile can be the same as that of the described and shown sprocket plates. Such a wide or full width sprocket plate is conveniently used with the inside sprocket style hub illustrated in  FIG. 2 . 
         [0036]      FIGS. 4-11  illustrate a second embodiment of a sprocket assembly  70  that has structure and function analogous to that of the assembly  17  described in connection with  FIGS. 1-3 . The sprocket assembly  70  comprises a sprocket plate  71  and a hub  72  each of which is made from a suitable material such as steel or other ferrous metal. The sprocket plate  71  and hub  72  can be cast, stamped, forged, machined or otherwise made into their respective shapes as desired. The sprocket plate  71  has peripheral unidirectional teeth  73 , distributed about its geometric center, to cooperate with the roller chain  14  like that shown in  FIGS. 1 and 3 . The hub  72  has a keyed cylindrical bore  74  with an associated set screw  76  for locking a key  77  onto a shaft such as the shaft  12  shown in  FIGS. 1 and 3 . When assembled on the hub  72 , the ring-like sprocket plate  71  has its teeth  73  concentrically disposed about the axis of the bore  74 . 
         [0037]    The hub  72  has a central core  78  with a generally circular exterior surface  79  concentric with the bore  74  and with a plurality of three equally angularly spaced legs  81  extending radially outwardly from this core surface  79 . The legs  81  have radially outer surfaces  82  lying on a common imaginary cylinder concentric with the bore  74 . Between the legs  81  are arcuate spaces  83 . As shown in  FIGS. 8 ,  10  and  11 , the legs  81  each have a slot  84  at mid-length in the axial direction of the bore  74 . Each hub leg slot  84  is open at one arcuate side of the leg  81  and adjacent the cylindrical surface  82 . Each slot  84  has a bottom  86  concentric with the bore  74  on a radius equal or larger than the radius of the core  78 . In an angular direction with respect to the axis of the bore  74  the slot  84  ends to form a generally radially oriented abutment surface  87  that can be semi-cylindrical or otherwise somewhat rounded, when viewed in a plane transverse to the radial direction, for ease of manufacture. 
         [0038]    The sprocket plate  71  is ring-like in form and has a plurality of three radially inwardly extending equally angularly spaced legs  89 . The legs have inner surfaces  91  on a common imaginary cylinder concentric with the geometric center of the body of the sprocket plate  71 . Arcuate spaces or gaps  92  between each sprocket plate leg are larger in profile than the profile of a hub leg  81 . The sprocket plate legs  89  have leading edges  93  in a rotational sense that are generally radial with respect to the center of the sprocket plate  71 . As indicated in  FIG. 5 , showing a sprocket of “half” thickness, the legs  89  lie in a plane that is offset from the plane of the peripheral teeth  73  a distance that preferably is at least equal to the thickness of the sprocket in the base area of the teeth. The spaces  92  are radially bounded by surfaces  94  lying on a common imaginary cylindrical surface concentric with the center of the sprocket plate  71 . The surfaces  94  form the major inside diameter or bore of the sprocket plate while the surfaces  91  form the minor inside diameter of the sprocket. 
         [0039]    As the case with the sprocket and hub shown in  FIGS. 1-3 , the major and minor inside diameters of the sprocket plate  71  are at least as large as the major and minor outside diameters of the hub  72 . This relationship, in addition to the gaps between the sprocket legs  89  being larger than the arcuate widths of the hub legs  81  enables the sprocket plate  71  to pass completely over the hub  72 . 
         [0040]    The sprocket plate  71  is assembled on the hub  72  by angularly aligning its legs  89  with the hub spaces  83  and slipping it onto the hub until the plane of the legs  89  is coincident with the plane of the hub grooves or slots  84 . The sprocket plate  71  is then rotated relative to the hub  72  in a manner similar to a bayonet connection such that the sprocket plate becomes rotationally coupled to the hub with the radial edge abutment faces  93  on the sprocket legs  89  abutting respective end walls or abutment surfaces  87  at the arcuate ends of the hub slots  84 . The sprocket plate  71  can be releasably locked in position on the hub  72  with a roll pin  95  received in holes drilled through the hub and sprocket plate parallel to their axis. 
         [0041]      FIGS. 5 and 10  illustrate a “half” width sprocket that can be used as described earlier where the roller shaft centers are close and inside and outside half width sprockets are alternately mounted from shaft-to-shaft. The sprocket of  FIG. 5  can be an outside sprocket and a complementary inside sprocket can be configured as a mirror image of it. A “full” sprocket useful when the conveyor roller spacing is large is illustrated in  FIGS. 6 and 11 . It is desirable to proportion the hub  72  widthwise in the manner shown such that its axial length is three times the nominal thickness of a half sprocket at the base of the teeth or 1½ times the width of a full sprocket at the base of its teeth and it is symmetrical about a mid-plane perpendicular to the axis of the bore  74 . This length permits the hub  72  to be used with both inside and outside style sprockets without interference with an adjacent sprocket as well as with full width sprockets. 
         [0042]    It will be understood that sprocket plates of the style illustrated in  FIG. 4  can be readily removed from a hub for replacement while the hub remains locked on a shaft. Removal of a sprocket plate  71  only requires the roll pin  95  to be knocked out and the sprocket plate to be rotated in a reverse direction relative to the hub until its legs  89  are aligned with the spaces  83  between the hub legs  81  and then moved axially off of the hub. 
         [0043]    It should be evident that this disclosure is by way of example and that various 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, in the embodiment of  FIGS. 1-3 , the sprocket plate can be retained against the hub by elements other than machine bolts such as a wedge or a horseshoe clip. The invention is therefore not limited to particular details of this disclosure except to the extent that the following claims are necessarily so limited.