Wood pulper with constant wood feed

The invention concerns a wood pulper of the kind in which wood is fed via a hopper having advancing elements arranged on two opposite sides by which wood is advanced to a grinding stone. The invention is characterized in that said advancing elements comprise a plurality of driven shafts which are arranged parallel to and adjacent each other substantially transverse to the feed direction, said shafts being equipped with a plurality of toothed discs lying adjacent to each other. This arrangement enables the driving force to be distributed over a plurality of feed shafts, so that a continuous compression can be obtained which increases as the wood feeds through the hopper.

BACKGROUND OF THE INVENTION 
The present invention relates to a wood pulper of the kind in which wood is 
fed via a hopper having advancing elements arranged on two opposing sides 
by which the wood is advanced to a grinding stone. 
A wood pulper of this kind is described, for example, in German Published 
Patent Specification No. 1,461,582. In this pulper, the wood is advanced 
to the grinding stone by advancing elements consisting of endless 
revolving contoured chains having projections thereon, which pick up a 
pile of wood and press it against the grinding stone. There is a 
difference in speed between the chain speed and the wood speed which 
increases with increasing compression towards to the surface of the 
grinding stone, however, and this results in an uneven compression of the 
wood and thus uneven loading of the contoured chain. Although virtually no 
force is expended by the contoured chain in the feed-in or starting zone 
of the hopper, the force expended rises approximately parabolically from 
approximately the center of the hopper onwards. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide an advancing device for a 
wood pulper, which achieves reliable and even compression of the wood, and 
which is trouble-free in operation. 
The wood pulper according to the present invention is characterized in that 
the advancing elements comprise a plurality of driven shafts which are 
arranged parallel to and adjacent each other, substantially transverse to 
the feed direction, said shafts being equipped with a plurality of toothed 
discs lying adjacent to each other. 
This characteristic feature enables the driving force to be distributed 
over a number of feed shafts, instead of only two as in the case of wood 
pulpers of the prior art. In this way, a continuous compression can be 
obtained, which increases evenly stepwise from the first shaft to the 
last. In addition, the feed device of the wood pulper according to the 
present invention can be made very robust and reliable in operation. 
The drive motor and the mounting of the shafts can be arranged outside the 
hopper so as to protect these parts from chemical attack, and to enable 
maintenance to be carried out on them easily. Also, they can be replaced 
very rapidly, in a simple manner, if required. 
Although a wood holder for long wooden beam cutters is already known from 
German Published Patent Specification No. 2,312,013, in which toothed 
discs are arranged on two opposing walls in a supply and feed hopper, in 
that case a different field of application is involved, and, in addition, 
the purpose of the application is different. Thus, in said German 
Specification No. 2,312,013 a machining appliance for long wooden beams is 
described, wherein the beams are cut by blades attached to a blade 
carrier, and the advance feed is effected by a pressing piston. On the two 
sides of the hopper, i.e. for engaging on the end faces of the wooden 
beams, there are several toothed discs. These toothed discs, which are not 
driven, are not used to advance the wood, but only serve to smooth out the 
feed speed or to hold the speed constant over the width of the hopper. 
They are provided to ensure that the cut pieces always have the same 
thickness across their width, and are also intended to prevent the wood 
from slipping or tipping when the blades are resting on it. 
According to the present invention, provision is made for the shafts to be 
arranged in such a way that the toothed discs engage on the circumference 
of the pieces of wood. This feature is intended to provide a smooth 
advance by ensuring a trouble-free feeding, especially when the wood is of 
different lengths. 
According to a further feature of the invention, provision can also be made 
for each of the shafts to be driven independently of each other. This 
feature makes it possible to continue to operate even when the drive for 
one shaft has failed. Moreover, if required, it is possible to operate at 
different rotary speeds, and therefore at different feed speeds and/or 
compression pressures. 
It is advantageous if the toothed discs on adjacent shafts are arranged 
offset from each other in a direction transverse to the feed direction. 
This feature ensures that the toothed discs are arranged virtually 
alternately in interstices, which enables them to hold the wood even 
better. A further improvement in the feeding of the wood can be achieved 
if the toothed discs on shafts which lie opposite to each other are also 
offset from each other in a direction transverse to the feed direction. 
According to a further feature, a pulp duct is located underneath the 
pulping zone, and a trough with a variable immersion depth is arranged 
underneath the grinding stone. In known wood pulpers, the wood pulp 
produced is removed via a collecting trough, but thickening often takes 
place in the trough, and the grinding stone becomes smeared. It is 
desirable for a continuous pulping process, however, that the surface of 
the stone should not become smeared. In accordance with this further 
feature, the trough is arranged in such a way that the wood pulp produced 
by the grinding stone is removed beforehand directly into a pulp duct, 
without further contact with the surface of the stone. The trough is thus 
used only to moisten the surface of the stone appropriately with water 
and/or suspension. 
It is advantageous in this case for a water supply line to open out into 
the trough, which makes it possible to maintain the consistency in the 
trough so as to maintain the quality of the pulp constant. The effect on 
quality is obtained indirectly in this case, by means of the fiber/water 
film carrier out of the trough by the surface of the stone. This ensures 
that the previously-selected constant conditions always prevail in the 
vicinity of the grinding zone. If required, production water, or pulp with 
a controlled consistency, can be supplied via the water supply line.

DETAILED DESCRIPTION 
The wood 1 to be pulped is supplied via a hopper 2 with a feed aperture 3 
to a grinding stone 4 of the wood pulper. The hopper 2 is equipped both on 
its upper face and on its opposed lower face with a number of shafts 5 
arranged adjacent each other, on each of which a number of toothed discs 6 
are arranged adjacent each other. The toothed discs 6 can be constructed 
as gear-wheels, discs with projections, cams, or the like. FIG. 1 
illustrates a suitable prior art tooth structure on one of discs 6. 
As shown in FIG. 2, the toothed discs 6 on adjacent shafts are offset from 
each other so that they engage in the intermediate spaces between the 
adjacent shafts. It can also be seen from FIG. 2 that the shafts which lie 
opposite to each other in the vertical direction are also equipped with 
toothed discs which are offset from each other. Each shaft 5 is equipped 
with one or two drive motors 7, preferably in the form of a hydraulic 
motor, although other types of motors may be used. For reasons of space, 
the drive motors 7 may be arranged at alternate ends of adjacent shafts. 
Underneath the grinding stone, a trough 8 is located which is equipped with 
a flap 9, the height of which can be adjusted. The height of the flap 9 is 
chosen so that the immersion depth of the grinding stone 4 can be selected 
between zero and twenty centimeters. Furthermore, a water supply line 10 
opens out into the trough 8, through which washing water or a suspension 
can be supplied for the controlled adjustment of the stock density in the 
trough 8. A wiper blade 11, which can be combined with a spray tube 12, is 
used to wipe off any wood pulp which might possibly adhere to the grinding 
stone in the pulping zone, from which the wood pulp feeds into a pulp duct 
13. 
While this invention has been described as having a preferred design, it 
will be understood that it is capable of further modification. This 
application is, therefore, intended to cover any variations, uses, or 
adaptations of the invention following the general principles thereof and 
including such departures from the present disclosure as come within known 
or customary practice in the art to which this invention pertains and fall 
within the limits of the appended claims.