Plastic article or earthenware shaping or treating: apparatus – Preform severing means – Means forming from bulk and downstream severing means
Reexamination Certificate
1998-12-17
2001-10-09
Nguyen, Nam (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Preform severing means
Means forming from bulk and downstream severing means
C425S331000, C425SDIG002, C100S905000
Reexamination Certificate
active
06299430
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to pellet mills for agglomerating individual ingredients or mixtures (feed material) by compacting and forcing the ingredients or mixtures through die openings and particularly relates to a pellet mill having rollers within the die cavity and which rollers have bearings and bearing lubricant cooled by a cooling medium injected into the roller shafts.
BACKGROUND OF THE INVENTION
Conventional pellet mills typically employ a rotating ring die with stationary rollers within a die cavity defined by the ring die. Feed material within the cavity is extruded through the openings of the ring die to form pellets. Particularly, the feed material is conventionally fed by gravity from a feed chute into the die cavity where the feed material lies in nips between the ring die and rollers within the cavity. Rotation of the ring die causes rotation of the rollers about fixed shafts within the die cavity, causing the feed material in the nips to be extruded through the ring die apertures to the outside diameter of the die, thereby forming pellets. In another form of a pellet mill such as disclosed in a companion U.S. patent application Ser. No. 09/192,436, filed Nov. 16, 1998 of common assignee herewith, the disclosure of which is incorporated herein by reference, the rollers within the die cavity are mounted on a carriage for rotation about the die cavity relative to a fixed ring die.
In both types of pellet mills, the rollers are subject to high temperatures resulting from the pelleting process. Bearing failures in the pellet mill rollers have become an increasing problem, particularly in view of demands for higher product throughput and faster continuous operation. Cooling the bearings with forced oil lubrication has not proven reliable, as shaft oil seals often fail as a result of the harsh environment of the pelleting die cavity. A grease lubricant can also be used in the bearing. However, grease does not cool the bearing or dissipate heat and, in fact, can generate heat as a result of friction when a large volume of grease is forced into the roller bearing ways. Consequently, there has developed a need for apparatus for effectively cooling the roller bearings in a pellet mill.
BRIEF SUMMARY OF THE INVENTION
In accordance with the present invention, the shafts on which the rollers are mounted are provided with a cooling medium injection apparatus for forming cooling medium supply and return passages. Particularly, the supply and return passages for the cooling medium are provided in a single bore formed in and through one end of each roller shaft at a location which is either coaxial with or offset from and parallel to the axis of the shaft. Preferably, the supply and return passages are concentric with one another, with the supply passage lying within the return passage. Particularly, the injection apparatus includes a coupling at the end of each shaft for securing the supply and return passages to a cooling medium supply source and a return reservoir, respectively, and an elongated tube projecting from the coupling. By providing a single drilled bore hole in each shaft from one end of the shaft, the internal tube of the injection apparatus may be inserted into and spaced from the walls of the bore hole. In this manner, the annular passage between the tube and the bore hole wall formed the return passage while the tube per se forms the supply passage. With the end of the tube spaced from the end of the bore hole, the cooling medium, preferably water, may be supplied into the tube and returned from the shaft via the annular passage for cooling the bearings.
Grease for lubrication purposes is also provided the bearings for the rollers. The cooling medium therefore not only cools the bearings but also cools the supplied lubricant.
In a preferred embodiment according to the present invention, there is provided a pellet mill comprising a ring die defining a die cavity, the ring die having an axis and circumferentially and axially spaced die openings, a carriage mounting a plurality of rollers in the die cavity, the rollers being mounted on shafts carried by the carriage and having axes parallel to the axis of the ring die, a feeder for supplying feed material into the die cavity, a drive for rotating one of the ring die and the carriage relative to one another for extruding feed material in the nips between the ring die and the rollers through the die openings to form pellets, bearings disposed between each shaft and the rollers, cooling medium supply and return passages in each of the shafts generally parallel to the axes thereof and a cooling medium inlet carried by the shaft for supplying a cooling medium to the supply passage and a cooling medium outlet carried by the shaft for receiving heated cooling medium from the return passage.
In a further preferred embodiment according to the present invention, there is provided a pellet mill comprising a ring die defining a die cavity, the ring die having an axis and circumferentially and axially spaced die openings, a roller in the die cavity, the roller being mounted on a shaft having an axis parallel to the axis of the ring die, the shaft having a bore hole opening through one end of the shaft, a feeder for supplying feed material into the die cavity, a drive for rotating one of the ring die and the roller relative to one another for extruding feed material in the nip between the ring die and the roller through the die openings to form pellets, bearings disposed between the fixed shaft and the roller, a cooling medium transmission device for supplying a cooling medium to the shaft for cooling the bearings and including a tube receivable in the bore hole and spaced from walls of the shaft defining an annular passage thereby defining a cooling medium supply passage through one of the tube and the annular passage and a cooling medium return passage through another of the tube and the annular passage and a cooling medium inlet carried by the device for supplying a cooling medium to the supply passage and a cooling medium outlet carried by the device for receiving heated cooling medium from the return passage.
Accordingly, it is a primary object of the present invention to provide a novel cooling injection apparatus for the rollers of a pellet mill whereby a cooling medium can be supplied and returned along the roller shafts for cooling the bearings and any supplied lubricant to the bearings.
REFERENCES:
patent: 2670697 (1954-03-01), Meakin
patent: 2887718 (1959-05-01), Curran et al.
patent: 3354845 (1967-11-01), Schultz
patent: 3467031 (1969-09-01), Hafliger
patent: 5009586 (1991-04-01), Pallmann
patent: 5292240 (1994-03-01), Capelle
patent: 5585124 (1996-12-01), Bittner
Consolidated Process Machinery, Inc.
Heckenberg Donald
Nguyen Nam
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