Press for the continuous production of boards

In a press for the continuous production of boards according to the invention passages (11) are provided between the press belts (1) of the press and the supporting surfaces (10) thereof, said passages being completely filled with bearing balls and merging into return passages (12) so that the balls may carry out complete orbital motions.

BACKGROUND OF THE INVENTION 
The present inventions relates to a press which operates continuously to 
produce boards and wherein the material to be pressed is fed into a press 
slot between two movable surfaces of which at least one is defined by an 
endless belt, preferably of steel, which at the press slot is supported by 
a supporting surface in such a manner that it cannot increase its distance 
from the opposed moving surface. 
The press herein is a press by means of which boards, such as particle 
boards, plywood boards, fiber boards and the like, may be pressed and 
various kinds of boards may be laminated and provided with a surface 
layer. In all such cases the boards or the board blanks must be subjected 
to pressure. The boards or the board blanks may constitute an endless web 
or constitute pieces of finite length and fed into the press one after the 
other. 
In order to obtain, for boards of the kind indicated, a more flexible and 
simpler method of manufacture and processing, proposals have been made to 
replace the conventional multiple opening presses by continuously 
operating presses. The invention relates to such a continuously operating 
press. 
If the press belt slides against a supporting surface there will be 
friction between the surface of the press belt and the supporting surface 
and such friction will brake the movement of the belt and generate therein 
a significant tensile stress and hence considerably limit the compression 
pressure. To a certain extent successful efforts have been made to reduce 
such friction by pumping an oil or air film between the belt and the 
supporting surface, but this entails considerable sealing problems and 
allows of not interspaces between the boards or width variations. A 
technically better solution has been obtained by introducing a number of 
roller chains between the belt and the supporting surface, such chains, 
like roller bearings, reducing the friction between the belt and the 
supporting surface to a minimum. The disadvantage of the last-mentioned 
solution primarily is that the roller bearings or roller rods must be 
specially made and require extremely high precision leading to very high 
manufacturing costs. Also, the guiding of the press belt and the rollers 
or roller rods will require sensitive and costly extra equipment. 
SUMMARY OF THE INVENTION 
The present invention has for its purpose the improvement and 
simplification and hence the reduction of the costs of the last-mentioned 
type of continuously operating presses, and features the provision of 
endless passages filled with recirculating ball bearings over which the 
press belts ride.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The press shown by the drawings consists of two endless steel belts 1 which 
define a press slot therebetween. The belts 1 move about end rollers 2 and 
3. The end rollers 3 shown to the right in FIG. 1 are driven and both 
rotate at the same rate. To prevent the belts from sliding with respect to 
end rollers 3 the belts are pressed against the rollers by means of 
pressure chambers 4. To offset the pressure force on the rollers and the 
bearings thereof caused thereby pressure chambers 5 of the same size are 
provided on opposite sides of rollers 3. Another method of obtaining 
sufficient friction force between the belts and the driven rollers 
consists in very forcefully stretching the belts between rollers 2 and 3, 
but this entails certain disadvantages, such as large bearing loads, 
larger rollers 2, a larger belt tension and increased difficulties in 
guiding the belts. 
The board material to be pressed in the example shown consists of a 
particle mat 6 which is fed into the press slot between press belts 1. The 
mat emerges from the slot in the shape of finished particle board material 
1. At the press slot, the press power is transferred to press plates 9 and 
thence to upper and lower press beams 8 which are interconnected on the 
press sides. The upper press portion may be elevated or lowered by means 
of screws, wedges or by hydraulic means for obtaining the intended height 
for the press slot between the press belts 1. 
To avoid friction between belts 1 and the surfaces 10 supporting the belts 
of press plates 9 there is, between the belts and the surfaces, a passage 
11 which is filled with bearing balls. Following the press slot with 
respect to the direction of transport, passage 11 merges into a return 
passage 12 between spacer plates 13 and 14, the mutual spacing of which is 
somewhat larger than the diameter of the balls. Return passage 12 is also 
completely filled with balls and forms with passage 11 an endless passage 
filled with balls. In the operation of the press the balls circulate along 
endless paths at half the rate of press belts 1. 
To prevent, in the upper press portion, the steel belt loaded by the balls 
from falling down on account of gravity when the press is empty or only 
partly filled with board material, passages 11, 12 at their lateral edges 
are contiguous to ducts 17 which are connected to a source of negative 
pressure. As is evident from FIG. 2a and 2b duct 17 at return passage 12 
is defined by U-section members 15 and at the press slot by section 
members 18. The latter also define the width of ball passage 11 and 
additionally exhibit a duct 21 which is conncted to a blower with a filter 
which effectively prevents foreign matter from penetrating into 
sub-pressure duct 17 and into ball passage 11. By means of seals 19 and 20 
section members 18 are sealed against steel belt 1. The lower press 
portion preferably also is provided with the corresponding equipment 15, 
17, 18, 19 and 20 to stabilize the steel belt and to prevent foreign 
matter from entering ball passages 11 and 12. 
As is also evident from FIG. 2a and 2b the width of return passage 12 is 
defined by lateral rails 16 which control ball passage 12 by means of 
screws and/or springs to keep it filled with balls to its maximum 
capacity. 
If the press is empty or only partially filled with board material and if 
for some reason the sub-pressure is lost, yoke 22 prevents steel belt 1 in 
the upper press portion from falling down and the balls from flowing out 
of the press. 
Ball passages 11 and 12 and the lateral ducts 17 connected thereto as well 
as the source of negative pressure may be partly or completely filled with 
lubricant, preferably oil. 
In most presses the board material must be exposed to high temperature heat 
at the same time as it is being pressed. In a press according to the 
invention this may be brought about by heating press plates 9 in about the 
same manner as in conventional multiple opening presses, i.e. by means of 
electrical resistor elements or ducts for hot steam, hot water or hot oil 
provided within the press plates. The heat then is conducted in ball 
passage 11 on one hand through the balls and on the other hand through the 
air surrounding them to the press belt and through the latter to the board 
material. Additional heat may be supplied by heating the air in the 
negative pressure source and forcing the heated air to circulate through 
ball passage 11 by means of a pump. A still better heat input is obtained 
if the air in spaces 11, 12 and 17 is replaced by oil that is heated in 
connection with the source of negative pressure. 
Finally, the steel belt may be heated before it enters the press slot. 
If in any place the width of return passage 12 is reduced the speed of the 
balls will increase correspondingly. 
Preferably the press belt is an endless steel belt, and the diameter of the 
balls preferably is 2-5 times the thickness of the steel belt. If, for 
instance, the thickness of the steel belt is 1.5 mm the ball diameter 
preferably is 3-7 mm. The maximum size of the balls is limited in the 
first place by the steel belt beginning to bend at a high surface pressure 
and with an increased distance between the points of support. On the other 
hand, the size of the balls has no effect on the degree of their indenting 
the steel belt or the supporting surface and hence not on the rolling 
effect thereon. When the slot space according to the invention is filled 
with balls to its maximum capacity, the steel belt and the steel 
supporting surface without any risk of a rolling effect will stand a press 
surface pressure that is more than sufficient for normal pressing 
requirements. However, when required, substantially higher press surface 
pressures may be permitted if already when made the steel belt and/or the 
supporting surface are provided with longitudinal pre-rolled grooves 
corresponding to the diameter and rolling paths of the balls. 
As is evident to the expert, the embodiment of the invention described may 
be modified and varied in many ways within the scope of the invention. 
Thus, the moving surfaces defining the upper and lower press slots may 
differ mutually quite considerably. From the point of view of the 
invention it is essential that at any rate one of the surfaces is 
constituted by a press belt. This does not necessarily have to be a steel 
belt but it is of essential importance that the face of the belt against 
which the balls roll is of a sufficiently hard material. The other face of 
the belt may be of some other material that is more suitable with respect 
to the board material to be pressed. 
A substantial improvement as regards the practical use of the press is 
obtained by subjecting ball passages 11 and 12 to negative pressure as 
shown in FIG. 2a.