Abstract:
A system for recirculating lubricant to cool and lubricate a pellet mill including: a die; first and second roller assemblies received by the die; and a main shaft in communication with the roller assemblies, a pump, and a reservoir. The system provides fluid to a cavity formed between an inner surface of the plurality of bearings, an inner surface of the roller shell, a liner and a seal on each end of the roller shaft of each of the roller assemblies. Fluid fills the cavity through a first passage of the roller shaft of the roller assembly until fluid can enter a second passage of the roller shaft of the roller assembly. From the second passage, fluid may flow out of the roller shaft and roller assembly to another roller assembly or back to the main shaft.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention pertains to the field of pellet mill machines. More particularly, the invention pertains to lubrication and cooling of bearings and roller shafts in pellet mill machines. 
         [0003]    2. Description of Related Art 
         [0004]    Pellets are used for different purposes, for example for fuel, animal bedding or for animal feed. Pellets are comprised of a compressed raw material. The raw material is a biomaterial, which may be for example dried feed components, wood, sawdust or other wastes from sawmilling and other wood products manufacture. 
         [0005]      FIGS. 1-2  show a conventional roller shaft with a single grease outlet. Typically, the roller shaft  2  is surrounded by a bearing, which is received by a roller shell. The roller shaft  2  has a single passage  4  that runs approximately half the length of the roller shaft  2  with an inlet  6  and an outlet  8 . 
         [0006]    When the roller shaft  2  is manually greased or greased automatically, grease enters the passage  4  of the roller shaft through the inlet  6  and travels through the passage and out the outlet  8  to an outside surface  9  of the roller shaft  2 , which is surrounded by at least one bearing, and to a surface between the bearing and the roller shell. 
         [0007]    To manufacture pellets, raw biomaterial is fed into a pellet mill to a pelleting chamber formed between a die, a main shaft and a pair of roller assemblies. Each roller assembly includes a roller shaft  2  surrounded by bearings, which are received within a roller shell. The outer surface of the roller shell compacts the raw biomaterial into the holes of the die as the die rotates and causes the roller shells of the roller assemblies to rotate through the bearings on the fixed roller shafts  2 . As the raw biomaterial is extruded through the holes of the die, the biomaterial is heated, melting the biomaterial and allowing the biomaterial to be formed as a pellet. Knives cut the pellets as they are extruded from the die. 
         [0008]    During the pelleting process, the roller assemblies are subject to high temperatures. The bearings of the roller assemblies need to be replaced often due to warping resulting from high heat used during the pelleting process. Currently, bearings need to be replaced after 80 to 250 hours of operating time. The number of hours is based on the material being used to make the pellets. 
         [0009]    To compensate for the high temperatures of the pelleting process, the prior art roller shaft  2  has a single grease exit hole  8  along its shaft  2  and a user has to grease the roller shaft  2  manually approximately every fifteen minutes during operation. The grease lubricates the bearings, but does not cool the bearing or dissipate the heat from the bearing. The grease that exits the roller assemblies can be in excess of 500° F. Furthermore, having to manually grease the machine every fifteen minutes is tedious and labor intensive for a user. 
         [0010]    While an automated greater may be used to continuously grease the shaft  2  within the roller shell, the grease can enter the pellets being made. This is unacceptable for some uses of the pellets (for example pellets used as animal bedding and animal feed) and the grease that is continually pumped into the shaft  2  is good for only one use, which can become very expensive for the user. Furthermore, the automated greasing does not remove any of the intense heat that can warp the bearings. 
         [0011]    In some conventional pellet mill machines, temperature sensors are present within the roller shafts, and if the temperature within the roller shafts reaches a specific temperature which can damage the bearings, the machine will shutdown in order to cool and attempt to preserve the bearings, limiting production of pellets. 
       SUMMARY OF THE INVENTION 
       [0012]    A system and method for recirculating lubricant to cool and lubricate a pellet mill machine comprising: a die; a main shaft received by die comprising a first passage and a second passage extending a length, the first passage in fluid communication with a pump and the second passage in fluid communication with a reservoir; and at least a first roller assembly and a second roller assembly received within the die. 
         [0013]    Each roller assembly includes a roller shaft; a plurality of bearings mounted on the outer surface of the roller shaft, forming a cavity between an inner surface of the plurality of bearings, a liner and a seal; and a roller shell surrounding the plurality of bearings and the roller shaft. The roller shell is rotatable relative to the roller shaft and the die. 
         [0014]    Each roller shaft of a roller assembly has a first passage for receiving lubricant, extending a length of the roller shaft and outputting lubricant through a first hole to an outer surface of the roller shaft; a second passage for receiving lubricant parallel to the first passage, extending a length of the roller shaft and outputting lubricant through a second hole to an outer surface of the roller shaft. The first hole is preferably spaced at least 90 degrees apart from the second hole along the outer surface of the roller shaft. 
         [0015]    The first passage of the main shaft is in fluid communication with the first passage of the first roller assembly through a first line and the second passage of the main shaft is fluid communication with the second passage of the second roller assembly through a second line. The second passage of the first roller assembly is in fluid communication with the first line of the second roller assembly through a third line. 
         [0016]    During operation, lubricant flows from the pump to the first passage of the main shaft, through the first line to the first passage of the roller shaft of the first roller assembly, and out of the first passage through the first hole to the outer surface of the roller shaft. The lubricant exiting the first hole lubricates and bathes the inner surfaces of the plurality of bearings surrounding the roller shaft of the first roller assembly, fills the cavity, and enters the second hole of the second passage of the roller shaft of the first roller assembly. 
         [0017]    Lubricant from the second hole flows into the second passage of the roller shaft of the first roller assembly, through the third line to the first passage of the roller shaft of the second roller assembly, and out of the first passage through the first hole to the outer surface of the roller shaft of the second roller assembly. The lubricant exiting the first hole lubricates and bathes the inner surfaces of the plurality of bearings surrounding the roller shaft of the second roller assembly, fills the cavity and enters the second hole of the second passage of the roller shaft of the second roller assembly and flows through the second line to the second passage of the main shaft and to the reservoir. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  shows a side view of a conventional roller shaft of a pellet mill machine. 
           [0019]      FIG. 2  shows a front view of a conventional roller shaft of a pellet mill machine. 
           [0020]      FIG. 3  shows an exploded view of the roller assembly of an embodiment of the present invention. 
           [0021]      FIG. 4  shows a side view of a shaft of an embodiment of the present invention. 
           [0022]      FIG. 5  shows a front view of a shaft of an embodiment of the present invention. 
           [0023]      FIG. 6  shows a schematic view of the recirculating oil flow path through the roller assemblies of a pellet mill machine. 
           [0024]      FIG. 7  shows an exploded view of the roller assemblies of the present invention relative to the die of the pellet mill machine. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0025]      FIG. 7  shows an exploded view of roller assemblies  120   a ,  120   b  in an embodiment of the present invention relative to the die  122  and the main shaft  127  of the pellet mill machine. A die  122  defines a cavity  123  in which at least a pair of roller assemblies  120   a ,  120   b  which are mounted on a carriage  124  that has a front support  128  and a back support  129 . Also mounted to the carriage  124  is the main shaft  127 . The main shaft  127  is rotated by a quill drive assembly  130 . The die  122  has a plurality of openings  125  circumferentially and axially spaced for receiving biomaterial from within the cavity  123  compressed between the roller assemblies  120   a ,  120   b  and an interior surface  126  of the die  122 . Upon relative rotation of the die  122  and the roller assemblies  120   a ,  120   b , biomaterial is extruded through the openings  125  and forms pellets along the outside of the die  122  which are removed by blades (not shown) along the outside of the die  122 . 
         [0026]      FIGS. 3-5  shows a roller shaft assembly  120  in an embodiment of the present invention. The roller assembly  120  includes a roller shaft  102 , a plurality of bearings  110 ,  111  mounted on an outer circumferential surface  109  of the roller shaft  102 , and roller shell  112  surrounding the bearings  110 ,  111  and the roller shaft  102 . 
         [0027]    The roller shaft  102  includes two parallel passages  103 ,  104  of a length approximately equal to half the length of the roller shaft  102 , although slightly longer or slightly shorter passages may also be used along an axis parallel to the axis C-C of the roller shaft  102 . Each of the passages  103 ,  104  are formed by closed end bores, with the open ends  105 ,  106  of the passages  103 ,  104  in fluid communication with a main shaft  127 . 
         [0028]    Passage  103  is connected to the outer surface  109  through opening  115  of the roller shaft through a passage  107  perpendicular to the axis of the C-C of the roller shaft  102  and the passage  103 . Passage  104  is connected to the an outer surface  109  through opening  108  of the roller shaft through a passage  113  perpendicular to the axis of the C-C of the roller shaft  102  and the passage  104 . 
         [0029]    The stationary roller shaft  102  is received by a front bearing  110  maintained in place on the roller shaft  102  through a collar  116  and seal  114  and a back bearing  111  through retaining rings  118 , which maintain the spacing of the front bearing  110  relative to the back bearing  111  on the roller shaft  102 . The bearings  110 ,  111  and the roller shaft  102  are held within a groove  117  of the roller shell  112  by locking the bearings  110 ,  111  into place relative to the roller shell  112  though a lock nut  138  which engages a lock washer  136 , which is adjacent a seal  134  and bears against a lock nut liner  132  adjacent the back bearing  111 . The pellet machine preferably has two roller assemblies  120   a ,  120   b , which are received within a cavity  123  formed by a die  122  as shown in  FIG. 7 . 
         [0030]    The collar  116  and the lock nut liner  132  may be coated with a sealant to prevent leakage of lubricant from the roller assembly  120 . 
         [0031]    Lubricant flows from the main shaft  127 , through open end  105  to passage  103 . From passage  103 , lubricant flows through passage  107  and out hole  115 , lubricating the inner surface  110   a ,  111   a  of the bearings  110 ,  111 , and a seal  114  and lock nut liner  132 . Once the lubricant reaches hole  108 , lubricant flows into passage  113 , through passage  104  and through open end  106 , allowing lubricant to recirculate between passages  103  and  104 , the main shaft  127  and the other roller assembly, ensuring a constant flow of lubricant to the inner surfaces  110   a ,  111   a  of the bearings  110 ,  111  on each of the roller shafts. As the lubricant recirculates, the inner surfaces  110   a ,  111   a  of the bearings  110   a ,  111  are bathed with lubricant and cooled. 
         [0032]      FIG. 6  shows the flow of lubricant recirculating through the roller assemblies  120   a ,  120   b  and the main shaft  127  of the pellet mill machine. The main shaft  127  has two parallel passages  162 ,  164  extending the entire length of the main shaft  127  along an axis parallel to a central axis C-C of the main shaft  127 . The first passage  162  is in fluid communication with a heat exchanger  158  at one end and a first passage  103   a  of a first roller assembly  120   a  through a line  166 . The second passage  164  of the main shaft  127  is in fluid communication a reservoir  150  at one end and a second line  104   b  of the second roller assembly  120   b  through line  170 . A second line  104   a  of the first roller assembly  120   a  is connected to the first line  103   b  of the second roller assembly  120   b  through line  168 . 
         [0033]    During operation of the pellet mill machine, pump  154  pumps lubricant through a filter  156  to a heat exchanger  158 . From the heat exchanger  158 , lubricant flows to the first passage  162  of the main shaft  127  and flows out through line  166  to the first passage  103   a  of a first roller assembly  120   a.    
         [0034]    From the first passage  103   a  of the first roller assembly  120   a , lubricant flows to passage  107  and out hole  115  to the outer surface  109  of the roller shaft  102   a , filling a cavity between an inner surface  110   a ,  111   a  of the bearings  110 ,  111 , collar  116  with seal  114 , lock nut liner  132  with seal  134  and an inner surface of roller shell  112 , lubricating the inner surface  110   a ,  111   a  of the bearings  110 ,  111 . Once the lubricant fills the cavity to a point in which lubricant enters hole  108 , lubricant recirculates to passage  113 , to the second passage  104   a  and out of the first roller assembly  120   a.    
         [0035]    From the first roller assembly  120   a , lubricant flows through line  168  to the first line  103   b  of the second roller assembly  120   b . From the first line  103   b  of the second roller assembly  120   b , fluid flows to passage  107  and out hole  115  to the outer surface  109  of the roller shaft  102   b , filling a cavity between an inner surface  110   a ,  111   a  of the bearings  110 ,  111 , collar  116  with seal  114 , lock nut liner  132  with seal  134  and an inner surface of the roller shell  112 , lubricating the inner surfaces  110   a ,  111   a  of the bearings  110 ,  111 . Once the lubricant fills the cavity to a point in which lubricant enters hole  108 , lubricant recirculates to passage  113 , to the second passage  104   a  and out of the second roller assembly  120   b  to the second passage  164  of the main shaft through line  170 . 
         [0036]    The used lubricant then flows from the second passage  164  of the main shaft  127  to a reservoir  150 . From the reservoir  150 , the lubricant is filtered  152  and sent to the pump  154 . 
         [0037]    In an alternative embodiment, the heat exchanger is not present and the filtered lubricant is sent directly to the first passage  162  of the main shaft  127 . 
         [0038]    In one embodiment, the reservoir  150 , filters  152 ,  156 , pump  154  and the heat exchanger  158  may be located outside of the pellet mill machine. In an alternative embodiment, the reservoir  150 , filters  152 ,  156 , pump  154  and the heat exchanger  158  may be part of the pellet machine. For example, the pump  154  may be the pump present in a gearbox of the pellet mill machine. 
         [0039]    By recirculating the lubricant, the bearings  110 ,  111  of the roller assemblies  120   a ,  120   b  are bathed in lubricated and cooled without exposing the biomaterial used to make pellets to the lubricant. 
         [0040]    Since the lubricant is filtered after recirculating through and bathing the roller assemblies  120   a ,  120   b , the lubricant may be reused, saving the user of the pellet mill machine the cost of using the lubricant one time only as in the automated greasing or manually greasing of the prior art. Furthermore, by having the lubricant recirculate and bathe the bearings, the temperature of the lubricant after it has circulated through the roller assemblies  120   a ,  120   b  is significantly lower, decreasing warping and wear of the bearings  110 ,  111 . For example, the oil exiting the roller assembly of the present invention is approximately 125° F. in comparison to approximately 300-450° F. in conventional, prior art designs as shown in  FIGS. 1-2 . 
         [0041]    Also, the bearings of the present invention last in excess of 300 hours of operation before having to be replaced. Decreasing the time spent having to change the bearings, which involves cooling the machine down and changing the bearings, costing a user at least one full day of production every 80 to 250 hours of production. 
         [0042]    Furthermore, by recirculating and bathing the roller assemblies  120   a ,  120   b  with lubricant, the bearings do not reach very high temperatures, enabling the production to be maintained and due to the low temperatures that are present, production may be increased approximately a quarter ton an hour. The rate of production of pellets of a pellet mill machine of the present invention is approximately half a ton an hour and the bearings have been used in excess of 300 hours without having to replace the bearings, in comparison to 120 hours of production before having to replace the bearings. 
         [0043]    Accordingly, it is to be understood that the embodiments of the invention herein described are merely illustrative of the application of the principles of the invention. Reference herein to details of the illustrated embodiments is not intended to limit the scope of the claims, which themselves recite those features regarded as essential to the invention.