Process and apparatus for producing a fiber web

A process for the production of a fiber web on a movable, gas-permeable surface of a continuous laydown belt which is under vacuum and which forms a distribution chamber. After the fibers are mechanically opened, the fiber flow is conducted into the distribution chamber by means of an air current and additional air currents are delivered to the distribution chamber. An additional air current is introduced into the distribution chamber for the purpose of preventing a lumping together of fibers prior to the laydown in the web while the carrying air current is delivered to the distribution chamber in a nozzle-shaped chute. After the fibers have been laid down in a web, the web is precompressed by means of a controllable vacuum.

BACKGROUND OF THE INVENTION 
The present invention relates to a process for the production of a fiber 
web on a movable, gas-permeable surface of a continuous laydown belt which 
is under vacuum and which forms a distribution chamber. After the fibers 
are mechanically opened, the fiber flow is conducted into the distribution 
chamber by means of an air current and additional air currents are 
delivered to the distribution chamber. 
German Preliminary Published Application 2 149 892 discloses a process of 
the above mentioned type for the production of fiber webs in which dry 
fibers are deposited on a gas permeable laydown belt which closes off a 
distribution chamber in downward direction. In this case, additional air 
currents are introduced into the distribution chamber to deflect the flow 
charged with fibers. These additional air currents are employed to prevent 
an uncontrollable fiber laydown in such a way that the fiber-charged 
vertical gas flow, when the distribution chamber is centered and in 
further travel in the direction of the laydown belt, follows a path 
similar to a ballistic curve or trajectory. This provides a separation of 
the incoming fibers according to their size in such a way that the coarser 
and heavier fibers are pushed farther out while the finer and lighter 
fibers are laid down via the shortest path to the laydown belt. This type 
of process makes an opening of the fibers impossible since, as a result of 
the different direction air currents, an agglomeraton of larger fiber 
particles or a clinging of smaller fiber particles to larger fiber 
particles is possible. When these bundles of fibrous lignocellulose 
particles are laid down in the web, a non-uniform web is obtained which in 
further processing to board-like articles leads to waste with respect to 
strength and density. 
SUMMARY OF THE INVENTION 
Based on the above, it is an object of the present invention to prevent 
lumping of unopened fibers prior to laydown in a web and at the same time 
to obtain a high density web. 
In particular, as a result of employing a second air current having the 
same direction as the first air current for opening and transporting the 
fibers lumping of the opened fiber prior to the laydown of the fibers in 
the web is prevented while a subsequent precompression of the loose web at 
maintained vacuum prevents a rebounding of the precompressed fiber mat 
obtained thusfar without the application of vacuum. 
The overall structure and processing parameters prevent sticking of the 
fiber to the walls of the chute in the feed area of the fiber. 
As a result of the arrangement of an alignment base, the air current is 
designed as a parallel current and the nozzle-shaped tapering of the chute 
walls causes any lumped fiber still present to be opened. The additional 
air intake opening in front of the front return of the continuous belt 
prevents opened fiber from uncontrolled arrival on the laydown belt. 
Additional vacuum units provided near a precompressing area enhance the 
precompression pocedure by gas evacution from the laid down fiber web. 
As a result of an air-permeable wall between the intake of the fiber and an 
additional air delivery opening, any caking of the fiber to be opened on 
the walls of the intake is prevented. 
As a result of the arrangement of at least one turbulence-causing device at 
the ceiling of the distribution chamber, fiber agglomerations are 
prevented because constantly new turbulence is produced.

DETAILD DESCRIPTION OF THE INVENTION 
The exemplified embodiment represented in the drawing shows a production 
installation for particle board manufacture in which a fiber cover layer 
produced, according to the invention, is deposited on a particle board 
core. Fiber webs produced according to the invention may also be 
manufactured into fiber boards alone wihtout a particle board core. 
In the present exemplified embodiment, fiber is deposited via a discharage 
1 into a supply bin 2 via a distribution device 3. As a result of the 
travel of a floor conveyor 4 corresponding to the direction of the arrow, 
the fiber 5 is transported against delivery rolls 6 where the fibers are 
preopened and delivered to an opening device 8 via a delivery chute 7. 
Fiber 5 is delivered through a chute 11 as a fiber flow 9 to an opening 
roll 10 which corresponds to the entire width of the future web. At least 
one side wall of the chute 11 consists of air-permeable material, and in 
the exemplified embodiment, the air-permeable material consists of a woven 
screen 12. Air also enters the opening device 8 through an additional 
opening 13. During the down flow of the fiber air also goes through the 
woven screen 12 so that caking of preopened fiber on the walls of the 
chute 11 is prevented. 
Near the opening roll 10, an air current from a fan 50 enters the opening 
device 8 via a delivery duct 14 and an alignment base 15. This aligned, 
parallel air current is directed onto preopened fiber 16 and carries the 
fiber through a chute 17 which tapers in the shape of an adjustable nozzle 
into a distribution chamber 18. As a result of the velocity change of the 
air current produced by the adjustable nozzle-shaped tapering and widening 
chute 17, the fiber carried along is subjected to opening forces so that 
any remaining unopened fiber is opened. Since interfering air currents do 
not enter this area as a result of other air currents, a lumping of the 
opened material is clearly prevented. The nozzle leading to the 
distribution chamber may be made adjustable by any well known means. 
Between the nozzle-shaped chute wall 19 and the return 20 of the laydown 
belt 21 moving in the direction indicated by the arrow, an additional air 
intake opening 22 is provided. This air intake opening also extends over 
the entire width of the fiber web to be formed. The air entering through 
intake opening 22 may be produced by an additional fan 23. Also a 
controlled amount of fiber may also be taken from the delivery duct 14 by 
a fan (not shown) and introduced into the distribution chamber 18 through 
the additional air intake opening 22. The additional air current prevents 
a caking of the opened fiber on the back of the nozzle-shaped chute wall 
19 and, moreover, prevents opened fiber from settling in an uncontrolled 
manner on the laydown belt 21 in front of vacuum units 24 arranged under 
the laydown belt. 
A fiber web 25 produced in this way in conducted under a leveling device 26 
on the laydown belt 21 and delivered to a precompression device 27. In the 
precompression device, a belt press 28 is provided which travels according 
to the indicating arrow and causes a precompression of the fiber web 25 in 
cooperation with additional controllable vacuum devices 29. As a result of 
the air evacuation, according to the invention, of the fiber web by the 
additional controllable vacuum devices 29, a rebounding of the 
precompressed fiber web 25 is prevented. The web is then conducted over a 
separating wedge 30 and combined with a particle board core 31 produced in 
a known manner at a uniting site 32. A blank obtained in this way can then 
be cut in a known manner and pressed into artificial wood boards. 
The present invention is not limited to the arrangement represented in the 
exemplified embodiment. Fiber boards without a particle board core may 
also be produced with such an apparatus. 
Moreover, at the ceiling of the distribution chamber 18, turbulence-causing 
devices 35 are provided in the form of rods or grids which prevent the 
development of turbulence which would result in an agglomeration of opened 
fiber which of necessity would lead to a production of a non-uniform fiber 
web.