Plastic and nonmetallic article shaping or treating: processes – Reactive gas or vapor treatment of work – Work is organic material
Patent
1998-09-04
2000-06-27
Theisen, Mary Lynn
Plastic and nonmetallic article shaping or treating: processes
Reactive gas or vapor treatment of work
Work is organic material
264102, 264109, 425371, B27N 318, B27N 324
Patent
active
060803444
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method for prepressing a formed web of finely-divided lignocellulosic fibrous material prior to finish-pressing the web in the continuous manufacture of board products.
BACKGROUND OF THE INVENTION
During the manufacture of different types of board products, a web or mat is generally formed which is prepressed prior to being passed into the heat press, in which the web or mat is pressed under a controlled surface pressure and/or controlled thickness at a temperature of between about 150 and 230.degree. C., while simultaneously applying glue. In order to obtain the requisite board properties, a continuous press is required which is flexible and with which a high surface pressure, among other things, can be applied during an early stage in the press. Thus, the thickness of the web or mat should be very close to the final press thickness even at this early stage of the process, i.e. the mat thickness must be very greatly reduced in the press entry section.
It is desired to avoid excessive pre-hardening of the surface layers without the risk of surface bulging or cracking in the material, due to enclosed air being rapidly pressed out. It has therefore been proposed in Swedish Patent No. 502,202 that subsequent to forming the fibrous material into a web, with subsequent first compression and expansion of the web, the web is successively recompressed in the entry section of a prepress to a density close to the density of the web after the first compression, and that the web is then transferred to the finishing press while controlling limited expansion of the web in the prepress expansion section.
An object of the present invention is to further improve this method, so as to enable the use of a shorter and less expensive hot press and to reduce the power requirement of the press.
SUMMARY OF THE INVENTION
In accordance with the present invention, this and other objects have now been accomplished by the invention of a method of prepressing lignocellulose-containing fibrous material which comprises forming the lignocellulose-containing fibrous material into a web, initially compressing the web to a first density and permitting expansion of the initially compressed web, recompressing the initially compressed web in an entry section of a prepress to provide a recompressed web having a second density approximating the first density, permitting the recompressed web to undergo controlled expansion to provide an expanded web in an expansion section of the prepress, injecting steam into the web within at least one of the entry and expansion sections of the prepress, and transferring the expanded web into a finishing press.
In accordance with one embodiment of the method of the present invention, the web includes an upper side and a lower side, and the method includes injecting the steam into the upper side of the web and withdrawing the steam from the lower side of the web.
In accordance with another embodiment to the method of the present invention, the web includes an upper side and a lower side, and the method includes injecting the steam into the upper side of the web in the entry section of the prepress, and injecting the steam into the lower section of the web in the entry section of the prepress. In a preferred embodiment, the method includes injecting the steam into the web in an expansion section of the prepress.
In accordance with another embodiment to the method of the present invention, the method includes injecting air into the web along with the steam.
BRIEF DESCRIPTION OF THE DRAWING
The invention can be more fully appreciated with reference to the following detailed description, which, in turn, refers to the drawing which is side elevational schematic representation of an apparatus for application of the method of the present invention.
DETAILED DESCRIPTION
Referring to the drawing, the entry section of a continuous hot press is shown therein, which typically includes front deflecting rollers 1 and hot plates 2. These hot plates 2 have an
REFERENCES:
patent: 5063010 (1991-11-01), Fischer et al.
patent: 5433905 (1995-07-01), Tisch
patent: 5711972 (1998-01-01), Schedin et al.
Sunds Defibrator Industries AB
Theisen Mary Lynn
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