Sprocket construction for conveyor rollers

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.

BACKGROUND OF THE INVENTION

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

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.

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

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.

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.

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.

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.

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.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the figures, there is shown a partial area of a roller conveyor10of 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 conveyor10has cylindrical rollers11carried on respective concentric round shafts12mounted in bearings13as is conventional. Normally, a large number of rollers11are used in a conveyor but for simplicity only three are shown in the figures. It will be understood that a bearing13is provided at each end of each roller11. The rollers11are arranged parallel to one another in a common horizontal plane, typically, with a uniform center-to-center spacing. The rollers11can 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.

Ordinarily, in a typical dryer, there are several vertically spaced layers or decks of rollers11. The rollers11of each level or deck are all driven in the same direction of rotation by a common chain14, which may be of the conventional roller type. Customarily, the chain14contacts only one or a limited number of teeth16of a sprocket17associated with a respective roller11at any given time. Usually, the rollers11of a level or deck are driven by a single chain at one side of the conveyor10.

The sprockets17, in accordance with the invention, are assemblies of a sprocket plate18on which are formed the teeth16, and a hub19that is mounted on a roller shaft12. As will be described, the sprocket plate18and hub19are 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 plate18has a spider-like internal bore21while the hub has a complementary external spider profile, characterized by radially extending legs or spokes22that can fit through the bore.

Each hub19is preferably a metal body with a plurality of three internally radially extending legs or spokes22. The hubs19can be formed of any suitable material such as a ferrous metal like cast iron, cast steel, or hot roll steel. A bore26of the hub19is sized to fit the shaft12of a respective roller11which shaft typically is 1-¼ inch in diameter.

The sprocket bore26includes an internal keyway27for receiving a key28. The key28is also received in an external keyway in the shaft12as is conventional. A set screw29threaded into a radial hole31in the hub19locks against the key28and releasably fixes the hub19onto the shaft12.

The sprocket assemblies17along the conveying direction alternate between two constructions or styles, one36lying outside, with reference to a zone occupied by the rollers11, of an imaginary vertical plane passing through the middle width of the chain14, and the other37lying to the inside of this imaginary plane. In other words, the inside and outside designations of these sprocket assembly styles36,37is made with the understanding that parts on the side of the imaginary vertical mid-plane of the chain adjacent the rollers11are “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 styles36,37have essentially the same axial profile, including number of teeth and outside diameter.

The sprocket assemblies17, as mentioned, are all driven in the same rotational direction so that their respective rollers11also revolve in this same direction. Adjacent leading edges of the hub legs or spokes22, with reference to their direction of rotation, are radially extending lugs or stops41. The lugs41are formed with abutment surfaces42that 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 hub19. The abutment surfaces42extend radially outward from an imaginary cylinder concentric with the hub axis and coincident with cylindrical surface segments43at the base or radially inward ends of the legs22. The abutment surfaces42terminate radially outwardly at cylindrical outer surface segments45of the legs22on a common imaginary cylinder concentric with the bore26and forming the major outside hub diameter.

The sprocket plates18have asymmetric unidirectional teeth16that are shaped to provide a positive drive from limited tangential engagement of the chain14. Tips56of the teeth16represent the outside maximum diameter of the sprockets17. The sprocket plates18have central bores57. Arcuate surface areas58of the bore57, represent a major diameter area and three intervening arcuate surface areas59represent the minor diameter of the bore57. The internal sprocket legs23are equally angularly spaced and form the minor diameter areas59at their inner ends. As seen, the legs23span the arcuate space between the major diameter arcuate surfaces58. Leading abutment faces61, with reference to the direction of rotation of the sprocket assemblies17, extend between the inside diameter and outside diameter bore surfaces58,59and preferably lie in flat planes that are radial to, pass through, and are parallel to a central axis of the sprocket plate18.

In the illustrated embodiment, the hub legs22of either sprocket style36or37, are three in number and the sprocket plate legs23are of the same number. The arcuate extent of each hub leg22is slightly less than an arcuate gap44between the internal legs or spokes23of the internal sprocket plate bore21. 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 bore57of the sprocket plate thereby enabling a sprocket plate to pass completely over a hub.

A face47of the hub19lies in a flat radial plane transverse to the hub axis and serves as a seat or abutment surface against which the sprocket plate18is secured by machine screws62,63. The sprocket plates18are removably assembled on corresponding hubs with the axes of these elements coincident and held in place by a set of the machine screws62or63. In the case of the outside style of sprocket assembly36, the sprocket plate18is held to the hub19with socket head machine screws62threaded into the sprocket plate and in the case of the inside style of sprocket37the sprocket plate18is held to the hub19by flat head machine screws63threaded into the hub. The screws62,63, hold the respective sprocket plates18in abutting contact with the radial hub face47. It is this surface47from which the hub lugs41axially project. When mounted on a hub19, radial sprocket surfaces61abut the radial lug or abutment surfaces42enabling the torque developing forces imposed by the chain14to 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 holes66,67, that receive the machine screws62,63in the hubs of the respective outside sprocket styles36or in the sprocket plates of the inside sprocket style37, ensure that the torque transmitted from the sprocket plate18to the hub19is isolated from the screws, it being understood that this torque is developed by the abutment surfaces61,42.

As seen inFIG. 2, and as discussed, the inside and outside styles37,36of the sprocket assembly17can alternate along the feed direction of the conveyor10to permit a relatively large sprocket diameter to be used in proportion to the center-to-center distance of the shafts12. By offsetting the sprocket assemblies17to either side of a center plane of the chain14, the sprocket plate18of one assembly does not interfere with the sprocket18or hub19of an adjacent sprocket assembly even where, as shown, the center-to-center distance of adjacent shafts12is 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.

At least the sprocket plates18on the outer sprocket assemblies36, and preferably the sprocket plates on the inner sprocket assemblies37, are able to be passed completely over their associated hubs19for purposes of removal and replacement.

The sprocket plates18can 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 screws62,63securing these plates on their respective hubs can be conveniently reached from the outside, i.e. the space outward of the chain14, with the convention that the conveyor rollers11are to the inside.

With the invention, replacing each of the sprocket plates18is a simple matter of removing three screws62or63, and separating the plate from its hub. The need for breaking the hub loose from its fit on a shaft12is eliminated. Prior to assembly, the screws62,63, can be coated with a suitable protective sealant so that the risk of corrosion in the threaded holes in the sprocket plate18, or hub19is reduced. The torque between the sprocket plate and hub developed by the chain force is transmitted between the radial abutment faces42and61and is preferably isolated from the screws by appropriately dimensioning the parts and especially as mentioned, the clearance holes. Typically, where desired, the shaft12can be lifted slightly for access to any of the machine screws63on the inside sprocket plates.FIG. 4shows that a sprocket plate18can be removed by sliding it axially over the respective roller11. 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 assembly37enabling 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.

In many instances, the rollers11can 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 inFIG. 2.

FIGS. 4-11illustrate a second embodiment of a sprocket assembly70that has structure and function analogous to that of the assembly17described in connection withFIGS. 1-3. The sprocket assembly70comprises a sprocket plate71and a hub72each of which is made from a suitable material such as steel or other ferrous metal. The sprocket plate71and hub72can be cast, stamped, forged, machined or otherwise made into their respective shapes as desired. The sprocket plate71has peripheral unidirectional teeth73, distributed about its geometric center, to cooperate with the roller chain14like that shown inFIGS. 1 and 3. The hub72has a keyed cylindrical bore74with an associated set screw76for locking a key77onto a shaft such as the shaft12shown inFIGS. 1 and 3. When assembled on the hub72, the ring-like sprocket plate71has its teeth73concentrically disposed about the axis of the bore74.

The hub72has a central core78with a generally circular exterior surface79concentric with the bore74and with a plurality of three equally angularly spaced legs81extending radially outwardly from this core surface79. The legs81have radially outer surfaces82lying on a common imaginary cylinder concentric with the bore74. Between the legs81are arcuate spaces83. As shown inFIGS. 8,10and11, the legs81each have a slot84at mid-length in the axial direction of the bore74. Each hub leg slot84is open at one arcuate side of the leg81and adjacent the cylindrical surface82. Each slot84has a bottom86concentric with the bore74on a radius equal or larger than the radius of the core78. In an angular direction with respect to the axis of the bore74the slot84ends to form a generally radially oriented abutment surface87that can be semi-cylindrical or otherwise somewhat rounded, when viewed in a plane transverse to the radial direction, for ease of manufacture.

The sprocket plate71is ring-like in form and has a plurality of three radially inwardly extending equally angularly spaced legs89. The legs have inner surfaces91on a common imaginary cylinder concentric with the geometric center of the body of the sprocket plate71. Arcuate spaces or gaps92between each sprocket plate leg are larger in profile than the profile of a hub leg81. The sprocket plate legs89have leading edges93in a rotational sense that are generally radial with respect to the center of the sprocket plate71. As indicated inFIG. 5, showing a sprocket of “half” thickness, the legs89lie in a plane that is offset from the plane of the peripheral teeth73a distance that preferably is at least equal to the thickness of the sprocket in the base area of the teeth. The spaces92are radially bounded by surfaces94lying on a common imaginary cylindrical surface concentric with the center of the sprocket plate71. The surfaces94form the major inside diameter or bore of the sprocket plate while the surfaces91form the minor inside diameter of the sprocket.

As the case with the sprocket and hub shown inFIGS. 1-3, the major and minor inside diameters of the sprocket plate71are at least as large as the major and minor outside diameters of the hub72. This relationship, in addition to the gaps between the sprocket legs89being larger than the arcuate widths of the hub legs81enables the sprocket plate71to pass completely over the hub72.

The sprocket plate71is assembled on the hub72by angularly aligning its legs89with the hub spaces83and slipping it onto the hub until the plane of the legs89is coincident with the plane of the hub grooves or slots84. The sprocket plate71is then rotated relative to the hub72in a manner similar to a bayonet connection such that the sprocket plate becomes rotationally coupled to the hub with the radial edge abutment faces93on the sprocket legs89abutting respective end walls or abutment surfaces87at the arcuate ends of the hub slots84. The sprocket plate71can be releasably locked in position on the hub72with a roll pin95received in holes drilled through the hub and sprocket plate parallel to their axis.

FIGS. 5 and 10illustrate 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 ofFIG. 5can 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 inFIGS. 6 and 11. It is desirable to proportion the hub72widthwise 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 1-½ 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 bore74. This length permits the hub72to be used with both inside and outside style sprockets without interference with an adjacent sprocket as well as with full width sprockets.

It will be understood that sprocket plates of the style illustrated inFIG. 4can be readily removed from a hub for replacement while the hub remains locked on a shaft. Removal of a sprocket plate71only requires the roll pin95to be knocked out and the sprocket plate to be rotated in a reverse direction relative to the hub until its legs89are aligned with the spaces83between the hub legs81and then moved axially off of the hub.

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 ofFIGS. 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.