Paper making and fiber liberation – Apparatus – Running or indefinite length product forming and/or treating...
Reexamination Certificate
1999-03-01
2001-06-05
Nguyen, Dean T. (Department: 1731)
Paper making and fiber liberation
Apparatus
Running or indefinite length product forming and/or treating...
C162S374000, C277S407000, C277S944000, C277S946000
Reexamination Certificate
active
06241854
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a composite for forming a sealing strip for use in a suction roll of a papermaking machine.
BACKGROUND OF THE INVENTION
In a continuous papermaking machine such as a Fourdrinier machine, paper sheets are formed by passing a fiber and water slurry from a headbox onto a mesh screen and draining off the water to form a sheet of paper fiber. The sheet is then moved through a press section with rollers that expresses the water, and a dryer section to reduce the moisture content from about 60% to about 5%. The dried sheet is then fed to a high-speed calendar for compaction and finishing.
The drying section is typically composed of a series of revolving suction rolls. A screen belt that supports the paper sheet passes over the suction rolls at high speed. A suction roll is generally composed of a stationary vacuum box that is centrally disposed inside a perforated cylinder or shell. The vacuum box has a slot opening and a sealing strip on either side of the opening. The sealing strips are pressed against the inner surface of the perforated shell to form a seal so that, as the perforated shell rotates about the vacuum box, water from the paper sheet is drawn through the holes of the shell and the slot opening into the vacuum box. Due to the continuous abrasive contact with the inside surface of the rotating shell, the sealing strips become worn out after a relatively short time and must be replaced, which requires a complete shutdown of the machinery.
Attempts have been made to develop sealing strips having increased durability and a longer life. U.S. Pat. No. 4,714,523 (Sawyer) discloses a sealing strip made of a wear-resistant material with a narrow inlay strip of polytetrafluoroethylene (PTFE; Teflon™) that is exposed along the surface of the edge of the sealing strip. The PTFE strip rubs against the inside surface of the shell to lubricate the interface of the two elements and reduce friction. Although useful, a drawback of this sealing strip is that the PTFE insert strip can wear down to below the contact surface such that the PTFE insert is no longer effective in contacting and lubricating the shell surface. Another drawback is that the sealing strip requires an initial time interim for the PTFE to become distributed over the surface to provide a level of lubrication that allows a smooth interaction between the rotating shell and the sealing strips.
Therefore, an object of the invention is to provide a composite for forming a sealing strip for mounting in a suction roll of a papermaking machine that is highly durable and has increased compatibility and reduced abrasion against the inside surface of the perforated cylinder of a suction roll. Another object is to provide a sealing strip that will provide a high level of lubrication substantially immediately upon use and throughout the life of the sealing strip.
SUMMARY OF THE INVENTION
These and other objects are achieved by the present invention which is directed to a composite for forming a sealing strip for use in a suction roll of a papermaking machine that has extended usability and wear, and a low coefficient of friction. Also provided is a sealing strip formed from the composite that can be used to seal a juncture between a vacuum box and a perforated cylindrical shell of a suction roll. Further provided are methods of making the composite and the sealing strip.
The composite is a blend of a nitrite rubber, graphite, and carbon black with silicone oil and/or polytetrafluoroethylene (PTFE, e.g., Teflon™) dispersed throughout, and optional additives and processing aids as desired. Optionally, but preferably, the composite can include a phenolic resin for increased hardness and flexural properties. The ingredients are compounded together and can be processed into a sealing strip, for example, by extrusion or compression molding. The composite includes an effective amount of silicone oil and/or polytetrafluoroethylene ranging from a trace amount to about 30 wt-% to provide a sealing strip that has the silicone oil and/or polytetrafluoroethylene distributed throughout the contact surface, and a low frictional coefficient of about 0.02-0.06.
Advantageously, a sealing strip formed from the composite has reduced coefficient of friction substantially immediately upon use which increases the life of both the sealing strip and the perforated shell as compared to conventional sealing strips. Use of the present sealing strips in a suction roll will also reduce the amount of heat that is generated from the contact of the sealing strip with the shell surface.
REFERENCES:
patent: 2578551 (1951-12-01), Hornbostel
patent: 4714523 (1987-12-01), Sawyer, Jr. et al.
patent: 4915787 (1990-04-01), Branyon et al.
patent: 5515619 (1996-05-01), Kahl et al.
patent: 5580424 (1996-12-01), Snellman
patent: 5876566 (1999-03-01), Frawley, Jr.
Appleton International, Inc.
Nguyen Dean T.
Whyte Hirschboeck Dudek SC
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