Solid material comminution or disintegration – Processes – Wood and similar natural-fibrous vegetable material
Reexamination Certificate
2000-02-15
2001-11-06
Rosenbaum, Mark (Department: 3725)
Solid material comminution or disintegration
Processes
Wood and similar natural-fibrous vegetable material
C241S261300, C241S298000
Reexamination Certificate
active
06311907
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to disc refiners for lignocellulosic material. More particularly, the present invention relates to refiner plate segments for such an apparatus.
In high consistency mechanical pulp refiners, the wood fibers are worked between two relatively rotating discs on which refiner plates are mounted. The plates usually have radial bars and grooves. A large volume of steam is produced between the plates as a result of this refining work. For effective refining, the fibrous material must be retained between the plates on the bar surfaces despite the high velocity of the flowing steam, and the enormous centrifugal forces. Typically, the steam is exhausted via the grooves, and dams are provided in the grooves to interrupt material flow and thus improve the retention time of the material in the refining region.
In a typical refiner plate with radial bars and grooves, the bars provide impacts or pressure pulses which separate and fibrillate the fibers. The grooves enable radially directed feeding of the fibers and steam extraction. Near the perimeter of the plates, high radial steam flow and high centrifugal force both act to sweep the fibers outwardly from between the plates prematurely, thus reducing the refining effectiveness. The flow restrictions due to a small gap between opposed plates and fiber-filled grooves result in a steam pressure peak between the plates, located radially inward from the perimeter. This pressure peak is a major source of the refining thrust load, and can induce control instability at high motor loads. It is thus desirable that the steam generated during refining be discharged from the refining region as quickly as possible, while retaining the pulp within the region as long as possible.
SUMMARY OF THE INVENTION
Briefly stated, the invention includes a refiner plate which is constituted from a plurality of refiner plate segments, each of the segments formed with a pattern including a refining zone having a plurality of radially disposed bar segments. Each of the bar segments has oppositely disposed radially inner and outer ends. A chicane extends obliquely from the outer end of an inner bar segment to the inner end of an outer bar segment to form a zig-zag shaped rib. Adjacent ribs define a plurality of zig-zag shaped grooves alternating with the ribs. The chicanes define at least one substantially arcuate line extending radially and laterally across at least the refining zone.
It is an object of the present invention to provide a refiner plate for the face of a refiner disc, which facilitates the removal of steam while retaining the pulp in the refiner region to achieve satisfactory pulp quality.
This object is achieved by, in a preferred form, by providing chicanes that form a zig-zag flow path for most of the steam generated during the refining operation. A sloping leading face on each chicane directs the flow of the lignocellulosic material into the gap between the refiner plates for comminution on the grinding surfaces of the bars. Although the upwelling of lignocellulosic material into the refining gap restricts flow of steam through the gap in the vicinity of the chicanes, the chicanes are positioned to form arcuate lines extending to the peripheral edge of the disc. Consequently, steam may flow in the gap to the edge of the disc in the arcuate corridors formed between the lines of chicanes.
Accordingly, the object of achieving good fiber quality with good steam management is accomplished by providing chicanes that direct the fiber into contact with the grinding surface while providing a plurality of flow paths for directing steam through the refining gap to the peripheral edge of the disc. To the inventor's knowledge, no one previously provided chicanes that are distributed in a manner that facilitates steam flow in the refining gap.
Other objects and advantages of the invention will become apparent from the drawings and specification.
REFERENCES:
patent: 1114339 (1914-10-01), Bryant
patent: 5373995 (1994-12-01), Johannson
patent: 5425508 (1995-06-01), Chaney
patent: 0 179 041 (1986-04-01), None
patent: WO 88/06490 (1988-09-01), None
Alix Yale & Ristas, LLP
Durametal Corporation
Rosenbaum Mark
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