Plastic and nonmetallic article shaping or treating: processes – Forming articles by uniting randomly associated particles – Stratified or layered articles
Patent
1991-06-13
1993-02-09
Theisen, Mary Lynn
Plastic and nonmetallic article shaping or treating: processes
Forming articles by uniting randomly associated particles
Stratified or layered articles
264109, 264120, 425335, 425371, 425372, B32B 2102, D04H 170
Patent
active
051851156
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a method and apparatus for manufacturing inorganically or organically bonded wooden materials.
BACKGROUND OF THE INVENTION
Continuous methods and devices for manufacturing materials from substances containing cellulose, and/or lignocellulose, with the addition of binders are known. Typically, a mixture of particles, binders, and additives is spread on a horizontal belt which is moving at a suitable speed, and the mixture is then compressed. For example, Siempelkamp-Contiroll presses and Kusters compresses work on this principle. In this flat extrusion method, the pressure compressing the fleece acts perpendicularly to the plane of the panel. Manufacture of chipboard by this method proceeds continuously. The spreading and mixing stations required to produce multilayered panels are arranged sequentially. After compression, when gypsum binders are used, a panel must remain in the calibrating press until hydration is largely complete. The specific hydration conditions in gypsum binders cause hydration to begin when the water of hydration is added. The start of hydration and the total hydration time are closely linked. The ratio is approximately such that the total hydration time is three times as long as the time before stiffening begins. Consequently, a faster start of hydration also means the shorter hydration time. The length of a retaining unit, i.e., a calibrating press, required to obtain the dimensions of the panels to be bonded, is therefore a function of the total hydration time and is directly linked to the start of hydration. The earlier hydration can begin, the shorter the calibration press can be made or similarly the higher the feed rate that can be selected. When spreading stations are arranged sequentially, limits are imposed on the rapid start of hydration for design reasons. In other words, when hydration begins later, total hydration lasts longer, and the calibration unit must also be made longer. Ordinary press lengths are approximately 50 m. This length is disadvantageous.
In addition to this continuous flat extrusion method, extrusion methods are known in which the pressure is exerted parallel to the plane of the panel in such fashion that the wood chips are pressed continuously by a heated strand or channel with a rectangular or differently-shaped section producing the chipboard. This method is the so-called Okal method. In this method the chips are metered and fed into a perpendicular compression channel and compressed by a cyclically operating piston. The chips thus compressed migrate through a heated molding channel whose length is set so that the chips are glued sufficiently firmly. Pressing times are relatively short, since the development of heat causes the chips to be glued together at the surface. The resultant strength makes it possible for the binding process not to have to proceed to the middle of the panel while the panel is within the press. The quantity of heat stored at the surface of the panel is sufficient to cause the panel to be bonded all the way to the core of the panel after leaving the press. In this method, despite the relatively short pressing times, there are the disadvantages that an additional device, a punch, must be used; that the friction between the lining of the channel and the fleece reaches levels many times higher than desirable; and that the orientation of the chips of the panels produced by the Okal method runs perpendicular to the plane of the panel, resulting in limited bending strengths of the panels thus produced. This is highly disadvantageous.
SUMMARY OF THE INVENTION
The invention relates to a process for producing panels having a high bending strength to the species and a device for working the process in such fashion that the device is very compact and short.
The use of a relatively short calibrating press in the present invention is made possible by the fact that the mixing and spreading assemblies are arranged parallel to or above one another so that the mixtures required for manufactu
REFERENCES:
patent: 2728939 (1956-01-01), Behr
patent: 3216059 (1965-11-01), Voelskow
patent: 4216179 (1980-08-01), Lamberts et al.
patent: 4923656 (1990-05-01), Held
Fraunhofer-Gesellschaft zur Forderung der Angewandten Forschung
Theisen Mary Lynn
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