This invention relates to a method of and apparatus for delimbing and debarking tree trunks and branches. The apparatus includes two elongated rotors which are parallel to, spaced from each other and mounted for rotation in the housing, flexible flail elements on the rotors, means for driving the rotors in contra rotation and a roller guide arrangement on the housing for guiding elongated tree trunks and branches between the rotors to be delimbed and debarked by the flail elements on the rotors.

FIELD OF THE INVENTION 
This invention relates to a method of and apparatus for delimbing and 
bebarking elongated tree trunks and branches. 
BACKGROUND TO THE INVENTION 
Debarkers which include a ring rotor which carries internal cutting blades 
which are inwardly biased and through which one log at a time is axially 
fed to be debarked by the rotating blades is known. Problems with 
debarkers of this type is, however, that the bark cutting blades are 
expensive and need to by professionally sharpened and further that the 
cutting pressure of the blades on the bark generally increases 
proportionally with the diameter of the logs being debarked so that the 
timber of large diameter logs is damaged and the bark on small logs is not 
properly removed. Logs having a diameter less than 50 mm normally cannot 
be debarked with these machines. Additionally, wet bark is more easily cut 
than dry bark resulting in wet (freshly cut) timber being damaged by the 
cutting blades and bark which is dry not being adequately removed. Another 
time consuming problem associated with debarkers of the above type is that 
they are incapable of delimbing logs. The logs therefore need to be 
manually delimbed before being fed into the rotor of the machine. 
OBJECT OF THE INVENTION 
It is the object of this invention to provide a method of and apparatus for 
simultaneously delimbing and debarking a plurality of tree trunks and 
branches to minimise the problems mentioned above with known debarkers. 
SUMMARY OF THE INVENTION 
Debarking apparatus according to the invention includes a housing, two 
elongated rotors which are parallel to, spaced from each other and mounted 
for rotation in the housing, flexible flail elements on the rotors, means 
for driving the rotors and a guide arrangement on the housing for guiding 
elongated timber members between the rotors to be delimbed and debarked by 
the flails on the rotors. 
Further according to the invention the flail members on the rotors are 
spaced from each other in the axial directions of the rotors with the 
lengths of the flail elements being such that the circumferences of their 
paths of rotation overlap each other in the space between the rotors. 
Conveniently the flail elements are lengths of metal chain. 
Still further according to the invention the rotor drive means is adapted 
to drive the rotors in opposite directions of rotation with the direction 
of rotation of each rotor, on a line which is normal to and intersects 
both rotor axes, being in the same direction and in the direction in which 
a timber member is guided from the guide arrangement between the rotors. 
The timber element guide arrangement conveniently includes two hoirizontal 
and parallel guide rollers with at least one of the rollers being attached 
to the housing for movement towards and away from the other, means biasing 
the movable roller towards the other and means for driving at least one of 
the rollers to feed a timber element placed between the rollers into the 
housing. The housing may additionally carry a second pair of horizital and 
parallel output rollers on the opposite side of the flail rotors to that 
on which the guide rollers are situated with at least one of the output 
rollers being attached to the housing for movement towards and away from 
the other. 
Preferably each roller of each pair of rollers is movably attached to the 
housing for movement towards and away from the other roller in its pair 
with each roller in each pair being biased towards the other. 
Yet further according to the invention the debarking apparatus includes 
means for driving each of the guide and output rollers to drive a timber 
element in a uniform direction through the housing. Preferably each of the 
guide and output rollers is fixed to a drive shaft and the rotor driving 
means is a hydraulic motor on at least one of the drive shafts of each 
pair with the motors being interconnected for series operation so that the 
driven rollers rotate at a common speed. 
There is also provided according to the invention a method of operating the 
above debarking apparatus in which the rotors are rotated in 
contra-rotation with the peripheral velocity of each of the flail chains 
on the rotors being between 20 and 40 meters/second. If flexible elements 
other than chains are used as flails it will be necessary empirically to 
determine the optimum rotor speed for debarking logs of various degrees of 
wetness.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The debarking apparatus of the invention is shown in the drawings to 
consist of a wheeled chassis 10, a housing 12, flail rotors 14 and 16, a 
rotor drive arrangement 18, a log guiding arrangement 20 and an output 
roller arrangement 22. 
The chassis 10 of the debarking arrangement is shown fragmented in FIG. 1 
but includes on its left hand side, not shown, a tow hitch arrangement for 
connecting the chassis to a tow bar on a vehicle and a telescopic leg 24 
which is adjustable in length for supporting the chassis free of the 
towing vehicle. 
The flail rotors 14 and 16 are each journalled for rotation in the end 
walls of the housing and are more clearly shown in FIG. 3 to consist of 
drive shafts 26 which are journalled for rotation in bearings which are 
mounted on the housing end walls, hub elements 28 which are shaped as 
shown in FIG. 3, flail chains 30 and locking rods 32. 
The hub elements 28 each include a boss section 34 which spaces one hub 
element from the adjacent hub element to provide a peripheral slot or 
groove 36 between adjacent hub elements. Each of the hub elements includes 
four equally spaced holes adjacent its periphery and, in the bore through 
it, a key way slot. 
To assemble the rotors 14 and 16, a lock nut 40 is located at one end of 
the shafts and the hub elements 28 are slipped sequentially onto the 
shafts 26 over a key 42 which locks the hub elements against rotation to 
the shafts 26. When the shafts 26 are fully loaded with the hub elements a 
second lock nut 40 is tightened up against the hub elements to hold them 
in frictional engagement with each other. A terminal link of each of the 
flail chains 30 is now located in a slot 36 between the hub elements with 
the chains on each of the rotors 14 and 16 being out of phase with each 
other as shown in FIG. 2. The locking rods 32 are now fed through the 
registering holes 38 in the hub elements and through the terminal links of 
the chains 30 to lock the chains 30 to the hubs of the rotors. 
The flail chains of this embodiment of the invention are between 10 and 15 
mm chain and it has been found to be critically important to the invention 
that the circumferential paths of the flail chains 30 overlap each other 
as shown in FIG. 1 and 2 of the drawings. The degree of overlap has been 
found, with chains having a length of about 350 millimeters, to be about 
one quarter of the diametrical distance between the ends of two opposed 
chains on a common rotor. The degree of chain overlap may of course by 
varied from one application to another. 
The rotors 14 and 16 are releasibly connected to the drive arrangement 18 
through couplers 43. The portions of the end wall which carries the free 
ends of the rotor shafts are bolt-on cover plates, not shown, which carry 
the shaft bearings and which, when the shafts 26 are disconnected from the 
couplers 43, are removed so that the rotors with their flails may simply 
be withdrawn from the housing 12 for chain replacement and general 
maintenance. 
The rotors 14 and 16 are driven in contra-rotation as shown by the arrows 
in FIG. 2 by a gear train of the drive arrangement 18 which is adapted, at 
44 in FIG. 1, for attachment to the power take-off coupling of a tractor 
or other convenient prime mover. 
The drive shaft 26 of the rotor 16 is coupled to the impeller of a 
hydraulic pump 45. 
The housing 12 carries on one side, as is more clearly seen in FIG. 4, an 
inlet chute 46 through which logs are fed into the debarker. 
The log guide arrangement 20 and the output roller arrangement 22 each 
consist of guide rollers 48, 50 and 52, 54 respectively. Each of the four 
rollers include peripheral gripping formations for driving a log without 
slippage. The rollers of the guide arrangement 20 and output roller 
arrangement 22 are each located in a sub-assembly or sub-housing 56 which 
is pivotally connected at opposite ends to the end walls of the housing 12 
at 58. The lower roller sub-housings 56 of each pair of rollers is 
upwardly biased by springs 57, as shown in FIG. 4. The upper sub-housings 
56 of the upper rollers of each pair are downwardly biased towards the 
rollers beneath them under gravity. The sub-housings 56 and so the rollers 
which they carry are prevented from coming into contact with each other by 
suitable stops on the end walls of the housing which are not shown in the 
drawings. 
Each of the rollers 48 to 54 is fixed to a drive shaft 60 with each of the 
drive shafts 60 being driven by a hybraulic motor 62. It is of course 
possible to operate the machine reasonably efficiently by driving only one 
shaft 60 of each pair of rollers. 
The chassis 10 carries a hydraulic oil header tank 64 from which oil is 
pumped by the pump 45 on the drive shaft of the rotor 16 in series through 
each of the four hydraulic motors 62 so that both rollers of the log 
guiding arrangement 20 and the rollers of the roller arrangement 22 all 
rotate at a common speed. The roller hydraulic circuit includes a first 
valve, not shown, by means of which the speed of the rollers may be 
increased or decreased and a second valve for stopping, forwarding and 
reversing the direction of rotation of the rollers. Obviously, the rollers 
of each pair are rotated by their motors in opposite direcitons, as shown 
by the arrows in FIG. 2, to feed logs placed between them in a uniform 
direction through the housing. 
In use, the debarker of the invention is towed to a log pile in a 
plantation, where it may be disconnected from the towing vehicle, and the 
leg 24 is adjusted to level the chassis 10. The coupling 44 is connected 
to the power take-off of a tractor or other suitable prime mover which may 
be a motor which is permanently mounted on the chassis 10. The drive 
arrangement 18 is activated by what ever driving source is attached to the 
coupling 44 to drive the rotors at a speed of between 750 and 600 
revolutions per minute. With the chain length described above the 
peripheral speed of the flail chains is, at the lower end of the speed 
range, about 20 meters/second and at the upper end of the speed range 
about 40 meters/second. The actual speed selected will depend on the 
degree of wetness of the elongated timber elements to be debarked and 
delimbed by the debarker. For very dry wood the speed of the rotors would 
be adjusted towards the upper end of the speed range and for wet wood 
towards the lower end of the speed range. 
The hydraulic pump 45, which is driven through the driving arrangement 18, 
pumps hydraulic fluid from the tank 64 through the series connected motors 
62 back to the tank 64 and so on to rotate the guide and output rollers at 
a common feed and output speed. Logs to be debarked are now fed plurally 
into the inlet chute 46 between the rollers 48 and 50, which are moved 
apart by the logs, to enable the logs to be entrained by the rotating 
rollers through the space between the flail rotors 14 and 16 to the output 
roller arrangement 22. The direction of drive of the flail rotors, as 
shown by the arrows in FIG. 2, assists the passage of the log through the 
housing towards the output roller arrangement. The output rollers engage 
the leading end of the log, move apart to accommodate it, and because they 
are rotating at the same speed as the rollers of the log guiding 
arrangement, ratard acceleration imposed on the logs by the flails in the 
housing. The rotating flails pulverise and beat the bark from the logs on 
their passage through the housing without undue damage to the timber of 
the logs. The underside of the housing 12 is open and the fragmented bark 
is dropped through the base of the housing onto the ground below the 
chassis 10. The distance between the rollers of the guide arrangement 20 
and those of the output roller arrangement 22 is, in this embodiment of 
the invention, in the order of 1,2 meters enabling relatively short logs 
and branches to be debarked and delimbed. 
In a second embodiment of the invention, which is not illustrated, each of 
the pivoted sub-housings 56 could include a pair of rollers, as opposed to 
the single rollers illustrated in the drawings, with the rollers of each 
pair being parallel to and spaced from each other in the direction of log 
travel through the housing 12 so that logs or branches gripped between 
opposed pairs of guide arrangement rollers are held horizontally and 
presented centrally between the rotors 14 and 16 and also so that the 
debarked logs leave the output rollers horizontally. In this embodiment it 
is probably only necessary to drive one roller of each pair of rollers to 
provide adequate log speed. 
If the debarker is to be statically mounted at a fixed location input and 
output conveyors could be arranged adjacent the debarker for feeding logs 
into and away from the debarker. A bark conveyor could also be located 
beneath the housing to clear flailed bark from beneath the debarker. 
The invention is not limited to the precise details as herein described. 
For example the upper roller 54 of the output roller arrangement 22 and 
perhaps even the roller 48 of the feed arrangement need not be driven and 
could be a split across its length or one or both rollers of each pair 
could be clad with resilient rubber sleeves instead of the log gripping 
formations shown in the drawings to grip logs of various diameters which 
are fed simultaneously into the machine. It is only necessary that the 
rollers of the feed and output roller arrangements frictionally engage the 
logs which are passed through the housing to deccelerate their movement 
from the housing.