Bark press

A bark press including a frame and supporting rollers rotatably carried on the frame. These rollers support a rotatable dewatering drum, within which is eccentrically located a press roll, the outside surface of this press roll and the inner surface of the dewatering drum defining a press gap therebetween. The outside surface of the dewatering drum carries at least one ratchet circle with which at least one pressure cylinder cooperates. One end of this pressure cylinder is supported by the frame of the press and the opposite end rotating the dewatering drum step by step through the ratchet circle.

The present invention concerns a bark press comprising a frame and 
supporting rollers rotatably carried therein, supporting a rotatable 
dewatering drum within which is eccentrically located a press roll, the 
outer surface of this and the inner surface of the dewatering drum 
defining a press gap therebetween. 
In the course of rising energy prices, more and more attention has been 
paid to improving the energy economy in the wood conversion industry. One 
of the significant targets is a better utilization of bark by burning. 
Prior to burning, endeavours have been made to remove as much water as 
possible so that the efficiency of the bark boiler might be high. 
Dewatering of the bark by mechanical pressing is an advantageous 
procedure. Therefore, the significance of the functioning of bark presses 
and of the dry matter content of the bark produced has increased. 
It is known in the prior art to use bark presses in which compression is 
effected between two eccentrically displaced cylindrical surfaces. The 
outer surface is perforated so that water may run off. Presses like these 
function well, and using them it is possible to obtain dry matter content 
40-55%, depending on bark type. The presses of the prior art are, however, 
encumbered by drawbacks that are associated with their drive means. The 
drive is usually an electric motor, rotating the dewatering drum through a 
gear transmission. Since the rotational speed of the dewatering drum is 
low, the gear transmission must be large. Therefore, the price of the 
drive means is high. In addition, the consumption of energy per ton of 
bark treated is great. The drive means is susceptible to trouble because 
it has to operate in conditions which are wet and most unclean. For the 
same reason, the wear of moving components takes place rapidly. 
The object of the present invention is to provide a new type of bark press 
which is free of the drawbacks mentioned in the foregoing. The invention 
is characterized in that the dewatering drum carries on its outer surface 
at least one ratchet circle wherewith in cooperation is at least one 
pressure cylinder, one end of this pressure cylinder being carried on the 
frame of the press, and the opposite end rotating the dewatering drum step 
by step through the agency of the ratchet circle. 
As to the initial cost, the bark press of the invention is inexpensive if 
compared to presses of the prior art. The energy consumption per ton of 
treated bark is a fraction of the energy consumption of presses of the 
prior art. The press of the invention is reliable in service. Virtually no 
disturbances may occur in its drive means. 
The dewatering drum may have on its circumference one or more parallel 
ratchet circles. Accordingly, there may be one or more pressure cylinders. 
In any case, it is important that the ratchet circle or circles are 
located symmetrically so that no flexural forces act on the dewatering 
drum. In case there are more than one ratchet circle and pressure 
cylinder, the rotation of the drum can be made continuous by arranging the 
pressure cylinders to operate out of synchronism so that at any moment at 
least one pressure cylinder is pushing the drum in the direction of 
rotation. Nevertheless, it is to advantage if the press has no more than 
one ratchet circle and one pressure cylinder. In that case the movement of 
the drum is interrupted while the pressure cylinder is executing its 
return motion. During this time the water can drain from the bark bed in 
the press gap and pass through the perforated dewatering drum. The 
movement of the press cylinder in the direction in which it rotates the 
dewatering drum is considerably slower than its return movement.

In the drawing, the reference numeral 1 refers to the frame of the bark 
press, in which two support rollers 2 are rotatably carried. Upon these 
rests freely a dewatering drum 3 provided with a great number of water 
draining holes. The ends of the dewatering drum carry outwardly pointing 
bracing rings 4. On the circumference of the dewatering drum 3 has been 
affixed an encircling ratchet circle 5, located symmetrically with 
reference to the drum ends, as seen in FIG. 2. The ratchet circle 5 
cooperates with a pressure cylinder 6, the lower end of which is carried 
by the frame 1 and to the free end of its piston rod 7 being affixed a 
fork 8. The fork 8 carries a transversal pin 9, which during the work 
stroke of the pressure cylinder engages with the teeth of the ratchet 
circle 5 one after the other. 
Inside the dewatering drum 3 is eccentrically located a press roll 10. The 
shaft of the press roll is carried in one end of a beam 11 to be freely 
rotatable. The beam 11 is rotatably carried in the frame 1, and at its 
opposite end is located a pressure cylinder 12, the lower end of which is 
supported by the frame 1. Thereby, the beam 11 constitutes a two-armed 
lever. With the aid of the pressure cylinder 12, the pressure between the 
dewatering drum and the press roll 10 acting on the bark mat can be 
regulated. In addition, the pressure cylinder 12 permits spontaneous 
movements of the press gap. 
The ends of the dewatering drum 3 are closed by means of stationary, 
circular plates 13 and 14, affixed to the frame 1. The plate 13 has an 
aperture for the bark feed conveyor 15 and another aperture for the bark 
exit conveyor 16. In addition, both plates have an aperture 17, 18 
respectively, for the shaft 19 of the press roll 10. These apertures are 
elongated so that the shaft of the press roll may move. 
The bark feed conveyor 15 and the exit conveyor 16 are screw conveyors. The 
conveyor tubes 20 and 21 terminate at the plate 13, but the conveyor 
screws 22 and 23 extend into the dewatering drum 3 up to the opposite 
plate 14. 
The wet bark is introduced into the space confined by the dewatering drum 
and the plates 13 and 14 by means of the conveyor 15, wherefrom it falls 
into the press volume formed by the dewatering drum 3 and the press roll 
10. The bark goes into the press gap where the highest pressing force 
prevails. The dewatering drum 3 is supported by one of the supporting 
rollers 2 at the very press gap. The water escapes through the dewatering 
drum 3, and the pressed bark ascends on the inside surface of the drum up 
to the exit conveyor 16. The press roll 10 rotates by effect of friction 
in synchronism with the dewatering drum 3. The pressure prevailing in the 
press gap is regulated with the aid of the pressure cylinder 12. The 
inside of the dewatering drum 3 may during the operation of the press 
contain greater or lesser quantities of bark. This is immaterial because 
the pressure cylinder 12 keeps the pressure constant in the press gap. 
It is obvious to a person skilled in the art that various embodiments of 
the invention may vary within the scope of the claims stated below. For 
instance, the apertures for the bark feed conveyor and for the exit 
conveyor may equally be located on different sides of the dewatering drum, 
if space utilization so requires.