Abstract:
A stump grinding apparatus of the type adapted to be mounted in a frame on the end of a boom is described. The apparatus comprises a grinding wheel mounted between hubs keyed to a shaft that is connected though belts and gears to a source of motive power, such as a diesel engine. A pair of non-adjustable roller bearings are used to provide relative movement of the shaft and grinding wheel in the frame. The apparatus includes means for providing lubrication between relatively moving parts so that the life of the bearings and other component parts can exceed 5000 hours of use without failure. The shaft assembly includes dimensional tolerances that protect the moving parts from the ingress of dirt and other debris. The materials of construction are selected to also enhance trouble-free operation.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to the field of stump grinding machines, particularly with respect to the shaft assembly useful with a grinding wheel for grinding tree stumps. More specifically, it relates to such an assembly useful with a boom-end mounted stump grinder. 
     2. Description of the Related Art 
     It is known to provide a stump grinding apparatus to cut and dispose of tree stumps. The device finds use for agricultural applications, for proper lawn maintenance and care, and for site development. It is often required to lower a protruding stump to a level that is below grade so that it will not interfere with plowing, disking and other farm tasks. For pleasing appearance of residential lawns, stumps of dead and fallen trees must likewise be cut away to a point that is below grade to allow for soil to be placed thereover for seeding or planting. When used for site development, the apparatus removes the stumps, thereby permitting soil to be moved as needed. 
     Typically, such a device includes a rotatable grinding wheel having a plurality of cutting teeth disposed circumferentially about the wheel. The wheel can be powered by a chain drive, or by gear or belt, or may be at the end of a movable boom driven by a diesel or gasoline engine. The grinding wheel commonly encounters more than just wood when performing its tasks. The wheel may be brought into contact with rocks and all manner of buried debris, such as re-bar, wire, cinder block and other materials of construction. The stump grinding operation places tremendous radial and axial loads on the wheel, the drive shaft and other component parts associated with the wheel assembly. 
     One particular stump grinder is mounted on the end of an excavator boom and uses a self-contained diesel engine and a combination belt and gear drive to rotate the grinding wheel. The wheel is mounted on a drive shaft that is supported in a frame at the end of the boom. Grinders of this type are manufactured by Sneller Machine Co., Cleveland, Ohio, and are referred to as the Sneller Stump Mill. The drive shaft rotates in two sets of roller bearings. Because of the encounters with miscellaneous debris during grinding, the bearings are subject to tremendous lateral and axial stress. The bearings and grease seals are exposed to entanglement with wire that can become wrapped around the shaft and can damage or destroy the grease seals around the bearings, causing premature failure of the bearings. Furthermore, with improper tolerances and clearances between the rotating and non-rotating parts of the assembly, bearing wear can be substantial, thus necessitating shutdown and repair of the stump grinder. Because of the costs associated with the disassembly and repair of the equipment, and the associated non-productive time, ways are constantly being sought for reducing downtime. 
     BRIEF DESCRIPTION OF THE INVENTION 
     It is an objective of the present invention to increase the length of the in-service time intervals for a stump grinder. Another objective is to reduce the time and expense for maintenance of a stump grinder. 
     These and other objectives and advantages will become apparent upon a reading of the description that follows. 
     The present invention relates to a boom-end stump grinder utilizing a shaft assembly providing maintenance-free service. The invention furthermore relates to an improved shaft assembly for use with a boom-end stump grinder. 
     The invention relates to a mounting arrangement for the cutter wheel of a stump grinder. The arrangement is a shaft assembly that comprises a shaft having an inboard end adapted to engage a rotational power source, and an outboard end distal from the power source. An inboard hub is mounted on the shaft for rotation therewith and an outboard hub likewise is mounted on the shaft for rotation therewith. Each hub includes a radially extending flange defining a gap between the two flanges to receive a cutter wheel. An annular cast iron shell surrounds the shaft and is separated therefrom by an inboard roller bearing and by a layer of lubricant. The shell is separated from the inboard hub by a labyrinth typically filled with grease. A second annular cast iron shell surrounds the shaft and is separated therefrom by an outboard roller bearing and a layer of lubricant. The shell is separated from the outboard hub by a second grease labyrinth. The shaft and hubs are rotationally movable with respect to the two cast iron shells. Typically, both the inboard bearing and the outboard bearing are non-adjustable double roller bearings. The labyrinths are located axially between the two cast iron shells and the respective inboard or outboard hubs. A gap is maintained between each of the shells and the shaft. This gap is no greater than about 0.100, and preferably no more than 0.080″, and is filled with lubricant supplied from the labyrinth. Likewise, a gap is maintained between each of the cast iron shells and an axially extending portion of the respective hub. This gap is no greater than about 0.150, and preferably no more than 0.125″, and contains lubricant supplied from the labyrinth. The length of the axially extending portion of each hub is at least about 1″. 
     In another aspect of the invention, a shaft assembly is adapted to be mounted on a stump grinder frame and comprises a cutter wheel secured between two hubs, the hubs mounted for rotation with a shaft. The shaft has an inboard end adapted to engage a rotational power source, and an outboard end. The two hubs comprise an inboard hub and an outboard hub, each hub including a radially extending flange defining a gap between the two flanges to receive the cutter wheel. An inboard cast iron shell surrounds the shaft and is separated from the shaft by an inboard roller bearing and by a layer of lubricant. The inboard shell is separated from the inboard hub by a grease labyrinth. An outboard cast iron shell surrounds the shaft, and is separated therefrom by an outboard roller bearing and by a layer of lubricant. The shell is separated from the outboard hub by a grease labyrinth. The two cast iron shells are adapted to be mounted in a frame at the end of the boom. Preferably, the inboard bearing and the outboard bearing are non-adjustable double roller bearings. A gap is maintained between each of the shells and the shaft of no greater than about 0.080″, and the gap is filled with grease supplied from the labyrinth. Similarly, a gap is maintained between each of the shells and an axially extending portion of the respective hub of no greater than about 0.125″, wherein the gap contains lubricant supplied from the labyrinth. The length of the axially extending portion of each hub preferably is at least about 1 inch. An annular sleeve engages and surrounds the outboard end of the shaft. The sleeve has a radially outwardly extending flange at one end thereof that abuts a shoulder on the shaft, and has external threads at the opposite end to receive a lock washer and nut. The shaft and sleeve are keyed to prevent rotational slippage of the sleeve on the shaft. The inner race of the outboard bearing is press fit on the outer surface of the sleeve and abuts the radially outwardly extending flange of the sleeve. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectioned view of the shaft assembly of the present invention; and 
     FIG. 2 is an enlarged view taken along line  2 - 2 ′ of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention relates to a boom end stump-grinding wheel mounted on a shaft driven by a power source, such as an internal combustion diesel engine. The stump grinder will not be described in detail but is the type typically used on the Sneller Stump Mill. It has a 2″ thick by 42″ diameter cutter wheel mounted on a shaft driven by an internal combustion engine, such as a 200 or 275 horsepower Cummins diesel engine. The engine is joined to a drive shaft onto which the cutter wheel is assembled. Through a series of belts and gears, the engine drives the grinding wheel at a rotational speed of about 500 to 800 RPM. 
     The bearings used in the Sneller Stump Mill typically are non-adjustable, two row, tapered roller bearings having a one piece double outer race, and two inner races. The faces of the inner race are extended so that they abut, thereby eliminating the need for a separate inner race spacer. Bearings of this type are available from various manufacturers, such as The Timken Company of Canton, Ohio. To function properly, these bearings require proper lubrication. For this purpose, each bearing is lubricated by grease supplied from two separate reservoirs, each of which is designed to avoid leakage and to protect from ingress of dirt and debris. According to the present invention, it has been found that the stump grinder can be used for 5000 hours or more without bearing failure or before fatigue spall develops. At 500 revolutions per minute, this is equivalent to at least 15 million revolutions. 
     Turning now to FIG. 1, there is shown the overall shaft assembly  10  mounted within two arms  12   a  and  12   b  of a frame of the stump grinder. The frame arm and the boom and are not part of the present invention but are identified as representative of the environment in which the present invention is used. 
     The assembly  10  includes a shaft  14  having a drive end  14   a  connected through belts and gears to the engine output (none of which is shown). Next to the drive end  14   a , the shaft includes a first threaded surface  14   b  that receives a nut  16  and a lock washer  18 . The nut and washer abut a ring  20  on which a grease seal  22  runs. An inboard, tapered roller bearing  26  is pressed on to the shaft  14  until the inner race abuts a shoulder  14   c  on the shaft. An end cap  24  is bolted or otherwise secured to a flange  29  of an inboard cast iron shell  28  and serves to limit any axial movement of the outer race of the bearing  26 . The nut  16  threaded onto the shaft prevents the axial movement of the inner race. The outer race of the bearing is fitted into a recess formed by and between the cast iron shell  28  and the outer plate  24 . 
     An inboard hub  30  is mounted on a tapered portion  14   d  of the shaft  14 . The hub is separated from the shell  28  by a labyrinth  32  filled with grease. The labyrinth includes a first layer of grease in the narrow gap  32   a  between the shaft  14  and the cast iron sleeve  28 . This gap has a radial width d 1  less than about 0.10 inches and preferably less than 0.08 inches, and is filled with grease from the labyrinth. Grease from the labyrinth also fills a gap  32   b  between the shell  28  and the axial flange  30   a  of the inboard hub  30 . This gap d 2  is less than about 0.15 inches and preferably is less than 0.125 inches. A grease seal  34  forms the separation between the labyrinth  32  and a grease reservoir  36 . A double seal  38  separates the bearing from the reservoir  36 . 
     A cutter wheel  40  (shown in outline) is mounted on a rim  30   b  of the inboard hub  30 . An outboard shell  42  made of cast iron abuts a shoulder  14   e  on the shaft  14 . The shell  42  is supported in the second arm  12   b  of the frame. An outboard hub  44  slips around a bolt ring  46  that abuts a shoulder  14   e  of the shaft  14 . The bolt ring  46  is secured to the inboard hub by a plurality of bolts  48  which draw the left-hand hub  30  against the tapered portion  14   d  of the shaft  14  to insure a tight fit between the hub and the shaft. A slotted keyway (not shown) in the outboard hub and the shaft engages a key in a manner that is well known in the art, serving to prevent relative rotation of the outer hub with respect to the shaft  14 . Obviously, with the two hubs bolted together, the inner hub is prevented from slippage as well. A plurality of bolts  78  and nuts  80  secure the cutter wheel  40  between the two hubs  30 ,  44 . 
     It has unexpectedly been discovered that using cast iron instead of steel for the annular inboard and outboard shells  28 ,  42  serves to prevent freeze welding of the stationary shells to the rotating steel shaft. 
     The outer end  14   f  of the shaft  14  receives a sleeve  50  having a flange  50   b  which abuts shoulder  14   g  on the shaft. The sleeve is prevented from relative rotation with respect to the shaft by the key  74  engaging slots that form a keyway  76  in the shaft and sleeve. The outer end of the sleeve  50  is threaded on the exterior surface  50   a  to receive a nut  52  and lock washer  54 . The outboard bearing  64  is press fit on to the sleeve  50  and is secured in place by the nut  52  threaded on to the sleeve. The lock washer  54  prevents the nut from coming loose. The use of the threaded sleeve has been found to minimize maintenance problems by reducing the likelihood of the outboard bearing becoming loose on the shaft. A loose outer bearing has been found to place a substantial additional strain on the inboard bearings and on the shaft. This can cause breakage of the shaft at the inboard end. Furthermore, any lateral forces applied through the grinder wheel or hub to the shaft when the shaft is suspended only in the inboard bearing can cause serious misalignment of the shaft and damage to the drive train. 
     A flanged outer cap  70  is secured to the outer shell  42 , preferably with the use of bolts (not shown) passing through the flange  72  to protect the shaft from dirt and debris. In like manner, the cap  70  and shell  42  are secured to the outboard arm  12   b  of the frame of the stump grinder using suitable fastening means, such as bolts (not shown). 
     Permanent lubrication is provided between the outboard hub  44  and the cast iron shell  42 , and between the shell  42  and the outboard bearing  64 , in the same manner as previously described in connection with the lubrication surrounding the inboard bearing  26  and the stationary components. The hub  44  is separated from the shell  42  by a labyrinth  56  filled with grease. The labyrinth supplies grease to the narrow gap  56   a  between the shaft  14  and the shell  42 . This gap is less than about 0.10 inches and preferably less than 0.08 inches. A layer of grease fills the narrow gap  56   b  between the shell  42  and the outboard hub  44 . The radial thickness of the second gap is less than about 0.15 inches and preferably less than about 0.125 inches. The grease seal  60  forms the separation between the labyrinth  56  and a grease reservoir  58 . The double seal  62  prevents grease from working into the bearing from the reservoir  58 . 
     The inboard hub  30  and the outboard hub  44  each have an axially extending flange portion ( 30   a ,  44   a ) that has a width d 3  that extends at least about one inch along the axis of the shaft. This extended flange has unexpectedly been found to prevent cable or wire, often encountered at a construction site, from winding around the shaft and working its way into a labyrinth. It also serves to provide an improved seal to prevent the leakage of grease between the steel hubs and the cast iron shells. Maintaining a preferred clearance of 0.125 inches or less between the relatively moving parts further reduces the likelihood of leakage of grease or the ingress of dirt and debris into the labyrinth. 
     The device may be assembled in the following manner. The inboard hub  30  is slipped into place around the tapered portion  14   d  of the shaft  14 . The cutter wheel  40  is slipped onto the rim  30   b  of the hub. The outboard hub  44  is placed around the outboard end of the shaft until it abuts the shoulder  4   e  of the shaft. The hubs are then drawn together with a plurality of bolts  48  that extend through holes aligned in the outboard hub and the wheel, and that are threaded into tapped holes in the inboard hub  30 . The shaft sub-assembly is mounted in the arms  12   a ,  12   b  of the frame. The inboard shell  28  is placed around the shaft. The grease seal  34  is inserted into place and the second grease seal  38  is placed over the shaft. The inboard bearing  26  is pressed onto the shaft until it abuts the shoulder  14   c  on the shaft  14 , after which ring  20  is threaded on to the shaft. The outer grease seal  22  is placed therearound and the inboard end plate  24  is bolted through the flange  29  of the inboard sleeve  28  into the frame arm  12   a . The lock washer  18  is placed around the shaft and nut  16  is threaded on to the shaft and is tightened to anchor the inboard bearing securely in position. 
     In like manner, the outboard shell  42  is placed around the shaft. The grease seal  60  is inserted into place and an additional grease seal  62  is placed over the shaft. The sleeve  50  is pressed onto the outboard end of the shaft and is prevented from slipping on the shaft by a key  74  inserted into a slotted keyway  76  in the shaft and the sleeve. The sleeve  50  includes a flange  50   b . The outboard bearing  64  is pressed on the sleeve  50  until the bearing abuts the flange  50   b  and the flange  43  on the outboard shell  42 . A nut  52  and lock washer  54  secure the outboard bearing in place. This arrangement of the external threads on the sleeve and the nut to secure the outboard bearing in place unexpectedly reduces the likelihood of damage to the inboard end of the shaft. 
     The end cap  70  includes a flange  72  having a plurality of holes that match up with corrresponding holes in the flange  43  of the outboard shell  42  and the arm  12   b  of the frame. A plurality of bolts (not shown) are used to secure the outboard end of the shaft assembly to the frame. 
     After the components have been assembled, the grease reservoir and labyrinth are filled with grease by providing grease fittings and passages extending through the bearing housings and into the reservoirs. The grease is then forced into each of the reservoirs, and from there passes through the grease seals ( 34 ,  60 ) into the labyrinths. As part of the routine maintenance of the assembly, it should be regreased on a regular basis after a few hours of operation. 
     While the invention has been described in combination with embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing teachings. Accordingly, the invention is intended to embrace all such alternatives, modifications and variations as fall within the spirit and scope of the appended claims.