Plastic and nonmetallic article shaping or treating: processes – Forming articles by uniting randomly associated particles – Plural – intermittent pressure applying
Patent
1990-05-15
1991-07-23
Theisen, Mary Lynn
Plastic and nonmetallic article shaping or treating: processes
Forming articles by uniting randomly associated particles
Plural, intermittent pressure applying
264115, 264121, 425 821, 425 831, B29C 4326, B29C 4334
Patent
active
050341758
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to methods for manufacturing fiber board sheets. More particularly, the present invention relates to methods for manufacturing fiber board sheets from lignocellulose-containing material such as wood, straw, bagasse, etc., using the dry method. Still more particularly, the present invention relates to an apparatus for manufacturing fiber board sheets from lignocellulose-containing material.
BACKGROUND OF THE INVENTION
Fiber board sheets designated as the MDF (medium density fiber board) type are conventionally producing fiber in a defibrator, drying the fiber together with resin, wax, etc. in a tube drier, and transporting the dried fiber by means of a pneumatic or mechanical conveying system to a fiber bin, from which it is discharged in a controlled manner to a conveying system for feeding same to a mat-laying station, in which a fiber mat is formed in a controlled manner.
The thus-formed fiber mats are subsequently hot-pressed in the production line to form a complete MDF-sheet. Multi-layer sheets are also manufactured in a corresponding manner. In these processes a considerable amount of energy is employed from the drying step all the way to the forming step, for both the drying itself and in order to effect the conveying of the dried material. The moisture content of the fibers prior to the drying is about 100%, and after the drying is about 10%.
Because of the special requirements placed on the drying procedures required for the drying of fibers, it is not possible to use the more energy-efficient driers which are used, for example, in the particle board industry, but one is essentially limited to the use of a tube drier. This type of drier, however, requires a great amount of energy per ton of fiber. This energy is normally produced in a steam boiler, hot oil boiler, or the like, with the energy then being transferred to the drying gas by means of a heat exchanger.
Upon their discharge from the drier, the dried fibers generally have a temperature of between about 60 and 70 .degree. C. After being handled in the manner described above, the temperature of the fibers then drops to around room temperature. During the subsequent hot pressing the fiber mat must then be reheated to a temperature above about 100.degree. C. in order to bring about the intended curing of the resin which is required in order to obtain a sheet having sufficient strength. For these reasons, not only is additional energy lost, but at the same time the heating time in the hot press is rather long, and therefore the rate of production is restricted.
An object of the present invention is to reduce the energy demand during the manufacture of fiber board sheets while utilizing the dry method.
SUMMARY OF THE INVENTION
These and other objects are achieved in accordance with the present invention by maintaining the temperature of the fibers at a high level after the drying step and substantially continuously up to the forming step. Furthermore, one significant aspect of the present invention in which a two-step drying press is employed permits separation of the drying gas from the fibers during the second drying step using a device of a reduced size. Furthermore, the drying gas can be maintained at a dryer condition, and a higher press capacity is achieved thereby.
In accordance with the present invention, a method has thus been discovered for manufacturing fiber board sheets from defibered lignocellulose-containing material comprising drying the defibered lignocellulose-containing material with heated gas in a tube dryer, transferring the dried lignocellulose-containing material directly to a forming station, and forming the dried lignocellulose-containing material into a fiber web at the forming station such that the temperature of the dried lignocellulose-containing material is substantially maintained from the drying step to the forming station. In a preferred embodiment, the defibered lignocellulose-containing material is mixed with a binding agent. Preferably, the method in
REFERENCES:
patent: 3903229 (1975-09-01), Mark
patent: 4407771 (1983-10-01), Betzner et al.
Sunds Defibrator Industries Aktiebolag
Theisen Mary Lynn
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