Debarking/delimbing apparatus comprises at least one spool device mountable and rotatably driven about an axis and capable of removing bark from tree parts moved lengthwise across its axis. Each spool device has two end members rotatable about the axis and each of which supports the ends of several shafts which extend between the ends members parallel with the axis and equally spaced from and around the axis. Each of said shafts has, spaced along its length, a series of solid debarking elements, each element being eccentrically and rotatably mounted on its respective shaft so that when the spool device is rotated centrifugal forces will cause the elements to project outwardly from the device so as to contact tree part, the elements being provided with protrusions for scraping off bark. The spool device is arranged so that all of said elements are completely rotatable about said shafts without interference with each other or with any part of the device.

The present invention provides apparatus for removing bark and limbs from 
trees or tree parts. 
While the apparatus of this invention may have many different applications, 
a particular utility is in debarking and delimbing small trees, from about 
3 inches to about 12 inches diameter, which are to be used to produce pulp 
for paper making. For the production of good quality paper, it is required 
that almost all of the bark should be removed from the trees, i.e. all but 
about 0.5% of the bark. 
Various rather complex debarkers have been designed and made for removing 
bark from trees in pulp mills. However, the present invention is 
particularly concerned with a rather simple and readily mobile apparatus 
which can be used on mobile equipment used in the forest. 
There has been a trend in recent years to producing chips from trees in the 
forest itself, so that waste products, which are of course bio-degradable, 
can be immediately returned to the forest floor; this requires a mobile 
debarker. One kind of mobile debarker which has been used for this purpose 
is the so-called ring debarker, in which a ring, rotatable about its own 
axis, carries a series of arms which are pivotally mounted inside the ring 
and carry debarking tools which remove the bark from a tree trunk fed 
through the ring. While these are good for fairly large diameter tree 
trunks, on smaller sizes (e.g. 3 to 8 inches) the rate of production is 
rather slow, especially because only one trunk at a time can be fed 
through the debarker. 
For forestry processing of small sizes of wood, it is known to use a 
so-called flail debarker; this has the advantage that several trunks at a 
time can be fed through so giving adequate output. Such a flail device has 
one or two rotatable drums with a series of chains having their inner ends 
connected to the drum with the remaining chain loose so as to extend 
outwardly from the drums when the drums are rotated at a high speed. Trees 
to be delimbed and barked are passed, lengthwise, across such drums so 
that the chains strike the limbs and remove these and the bark. While 
these chain flails are commonly used they suffer from well known 
drawbacks. Firstly, they do not reliably remove 99.5% of the bark, 
especially from small trees, due to the random manner in which the chains 
hit the trees. Secondly, the chains frequently break, and replacing the 
chains involves a significant cost in operating such equipment. Chain 
breakage is caused in part by the fact that the chains strike not only the 
wood but also, after striking the wood, curl back and strike the drum, and 
also hit other chains. 
A most cost effective way of producing chips in the forest would be to set 
a flail unit adjacent to a chipper permitting the debarked stems to pass 
directly from the debarker to the chipper. However, this is impractical 
since pieces of broken chain entering the chipper could do serious damage. 
Examples of chain flails, for debarking/delimbing are shown in the 
following prior patents: 
Canadian Patent No. 
598,362, issued May 17, 1960 to Ontario Paper Company Limited; 
964,965, issued Mar. 25, 1975 to Stadnik; 
1,035,673, issued Aug. 1, 1978 to Larson; 
1,073,784, issued Mar. 18, 1980 to Forano Limitee; 
1,074,213, issued Mar. 25, 1980 to Forano Limitee; and 
1,080,584, issued July 1, 1980 to The Northern Engineering and Supply Co. 
Limited. 
Another type of flail device, although not using chains, is shown in 
Canadian Patent No. 1,189,765, issued on July 2, 1985 to Wilbur Peterson 
and Sons, Inc. 
The present invention provides a device which is particularly suitable for 
use in mobile forestry equipment for removing bark and limbs from small 
diameter trees. Large branches may also be debarked; hereafter, the term 
"tree parts" is used for both tree trunks or branches or portions thereof. 
The apparatus is similar to the flails described above in that it 
incorporates at least one rotatable device and means for rotating this, 
the device being equipped to debark and/or delimb a tree part fed 
longitudinally across the axis of rotation. However, the rotatable device 
does not have any chains or flexible elements subject to breakage; rather 
it has solid debarking elements which are eccentrically mounted on shafts 
and which are completely rotatable about the shafts without striking any 
other part of the device. The term "solid" is used herein in the sense of 
the dictionary meaning i.e. "a substance exhibiting rigidity", in contrast 
to the prior art flexible elements. Since the debarking elements are solid 
and do not strike anything other than the wood they are not subject to 
breakage. 
In accordance with the present invention debarking/delimbing apparatus 
comprises at least one spool device mounted so as to be rotatably driven 
about an axis and capable of removing bark and/or limbs from a tree part 
moved lengthwise relative to the spool device across its axis, each spool 
device having two end members supporting the ends of several shafts which 
extend between the two end members, with these shafts being parallel and 
equally spaced from the rotational axis of the device and from each other. 
Each of the shafts has, spaced along its length, a series of debarking 
elements each eccentrically and rotatably mounted on a respective shaft so 
that when the spool device is rotated centrifugal force causes the 
elements to project outwardly from the device into contact with the tree 
part. The elements are provided with tooth-like protrusions for scraping 
bark off the tree part. The elements are completely rotatable about the 
shafts without interference with each other or any part of the device. 
Preferably, the spool device has three shafts all equally spaced from its 
rotational axis, and the debarking elements of each shaft are staggered 
with respect to elements of the two other shafts so that elements of 
adjacent shafts can overlap without interfering with each other. 
The spool device may be used as a single unit with a tree part or several 
tree parts being passed over or under the spool device while this is being 
rotated, thus removing bark or limbs from one side of the tree parts. The 
device will remove bark from practically one half of the tree part. The 
tree parts can then be turned around and the remaining bark removed with 
another pass. Preferably, however, two spool devices are used and the tree 
parts are passed between these so that the devices act on opposite sides 
of the tree parts. The spool devices may be directly opposite each other 
or may be staggered. If they are directly opposite each other, the 
separation of their axes will be such that rotatable elements of one of 
the spool devices closely approach but do not touch the rotatable elements 
of the other device. With a staggered arrangement, the spool devices may 
be set so that their debarking elements pass beyond the centre line of the 
tree part so that the two devices effectively remove all the bark.

FIG. 1 illustrates how two spool devices in accordance with the invention 
can be arranged to act on single or multiple tree trunks, and shows 
guiding and feeding means for the tree trunks. However, it is to be 
understood that the spool devices which are at the heart of this invention 
can be used in different ways, either singly, or in pairs as shown in FIG. 
1, and for example the spool devices can be used in generally similar 
manners to the flail devices shown in the above mentioned Canadian patents 
Nos. 598,362, 1,073,784, and 1,189,765. 
The apparatus shown in FIG. 1 includes a base member 10 carrying two side 
plates 12, the rear most being shown. The two side plates support a lower 
guide plate 14 which guides tree parts T between a lower roller 16 and an 
upper roller 18. These feed rollers are mounted on pivotal arms 19 which 
are spring urged to keep the rollers in firm contact with the tree parts. 
Similar feed rollers 16' and 18' are provided at the outlet end of the 
apparatus, these being similarly mounted. All of the feed rollers have 
small projections or studs to assist in gripping the tree, and all are 
driven by suitable means such as by sprocket chains connected to motors to 
move the tree part through the apparatus in the direction shown. 
Preferably, the studs or projections on the feed rollers are arranged in a 
spiral pattern which tends to rotate the tree part as this is fed through 
the apparatus, between the lower and upper spool devices S1 and S2 made in 
accordance with the invention, and which are arranged between the two sets 
of rollers. The lower spool device is fixedly mounted on support 30, 
whereas the upper spool device is mounted on a pivoting arm 32. However, 
depending on the range of tree sizes being used, both spool devices may 
have fixed axes. 
The spool devices S1 and S2, which are identical to each other, will now be 
more particularly described with reference to FIGS. 2 and 3. As shown in 
these drawings, each spool device has two end support members 40 which are 
in the form of circular plates, each plate having an outwardly projecting 
central stub shaft 42. These stub shafts are rotatable in the mounting 
means 30 and 32 shown in FIG. 1, and means, not shown, are provided for 
rotating the spools at a speed which will depend on the sizes of the 
spools but will usually be about 200-300 RPM, in the direction indicated 
in FIG. 1; i.e. in the same direction as the feed rollers. The speed of 
movement of the periphery of the spool devices (indicated at P) will 
however be much faster than the speed of movement of the tree part caused 
by the rollers. The stub shafts terminate at the end plates so there is a 
clear central area between the end plates in which the debarking elements 
can move. 
The two end plates 40 of each spool device fixedly support three shafts 44 
which are equally spaced from the axis of the stub shafts 42 and which are 
equally spaced around the end plates, i.e. each subtends 120.degree. with 
the adjacent shaft. 
As shown in FIG. 3, each of the three shafts 44 supports a series of 
debarking elements 46, each equally spaced along the shaft by spacer 
members 48. The elements are referred to as being "debarking" since this 
is their main function, although they will also remove limbs from small 
trees. As shown in FIGS. 2 and 2a, each debarking element is generally in 
the form of a disc having an eccentric bore 47, close to one side of the 
disc, by which it is rotatably mounted on its shaft. The eccentricity of 
each disc is preferably at least one half its radius. The discs are 
provided with blunt, roughly square edged teeth 48 which extend from an 
outer end of the disc, i.e. that part most removed from the shaft, to 
close to the inner end, at least beyond a point roughly level with the 
shaft, taken on a line normal to the axis of the disc between the shaft 
and its end. The discs are provided with teeth on both sides of the 
leading and trailing edges; although only the teeth on one edge are 
operative in one position of the disc, this allows the arrangement to be 
reversed when the teeth on one side are worn. As will be seen by reference 
to FIG. 2a, the teeth can be formed by cutting material from an initially 
circular disc. 
The size of the discs 46, and their eccentricity, is chosen so that each 
disc can rotate through 360.degree. on its shaft without interfering with 
the other shafts or spacers thereon. Also, the discs on the respective 
shafts are staggered so that the discs of one shaft cannot interfere with 
those of another shaft although they overlap. Since all the discs are 
identical, this means that the discs of each shaft must be spaced apart 
more than the width of two discs. The teeth on the discs may be offset at 
either side of the disc, thus increasing the effective width, and the disc 
spacing must of course allow for this. For example, a disc of one quarter 
inch width may have its teeth offset by 1/4 inch at each side of the disc, 
giving it an effective width of 3/4 inch. This offset allows discs to be 
relatively light even for a large effective width. Additional lightness 
may be achieved by forming a central aperture in the disc as shown at 49 
in FIG. 2a. If discs are too heavy they may damage the wood. The spacing 
of 3/4 inch discs would be about 1 inch for each disc on the spool, or 3 
inches for each disc on one shaft, giving 1/4 inch clearance between 
overlapping discs. 
The operation of the apparatus can be understood with reference to FIGS. 2 
and 3. The spools S1 and S2 will be rotated in the directions shown in 
such a way that action of the debarking elements on the tree part T 
assists this in its passage through the apparatus. The spools are rotated 
at such speed to ensure that centrifugal force normally maintains the 
discs extended from their shafts, as illustrated in FIG. 2 for discs 46a 
and 46b. The discs 46c are those which, at the instant shown, are 
performing the debarking function. Those discs, for example disc 46c', 
which are adjacent the sides of the tree trunk contact this when almost 
fully extended from the spool device, and are deflected only by a small 
amount in their rotation. However, those discs such as 46c" which are 
adjacent the centre line of the trunk, contact this as the associated 
shaft approaches the trunk and are then pivoted backwards as illustrated 
in FIG. 2. During this pivoting movement several of the teeth 48 
successively contact the tree bark and remove this with a scraping motion. 
As the spool rotates the debarking elements gradually become clear of the 
trunk and centrifugal force returns them to the outwardly extended 
position. 
FIG. 3 shows a spool mounted so that the outer most reach of its debarking 
elements is just short of the centre line of the tree trunk. The maximum 
radial amount by which the discs can move, to accommodate the radius of a 
tree trunk without the spool moving, is equivalent to twice the 
eccentricity of the discs. For example, if 12 inch discs are mounted at a 
3 inch eccentricity, they can accommodate tree trunks having a radius of 6 
inches and therefore a diameter of 12 inches, without the spools moving 
apart. Assuming that the upper spool is movably mounted, as shown, larger 
trunks can be accommodated but they will not be completely debarked at a 
single pass. 
FIG. 4 shows how two spool devices, mounted as shown in FIG. 1, can be used 
to debark both sides of several small tree trunks or tree parts 
simultaneously. The ability to debark several small tree trunks 
simultaneously is a great advantage of this type of apparatus as compared 
to ring debarkers which can only debark one tree trunk at a time. 
It is important to note that in accordance with the invention the debarking 
elements do not, in operation, contact anything other than the wood. This 
provides a great advantage as compared to chain flails where the chains 
hit the drums and hit each other and are subject to much abrasion and 
breakage. 
While it is convenient to form the debarking elements from discs, this is 
of course not essential and other shapes could be used provided that the 
elements have a generally convex arrangement of several teeth which can 
scrape off bark. 
It is also possible that in larger sizes of spool, an additional support 
plate may be provided between the end plates 40, to give extra support to 
shafts 44. 
It is also contemplated that a debarker/delimber may have two sets of spool 
devices as described, having different disc sizes. These may rotate in 
opposite directions, with the larger spool rotating in the direction which 
assists the tree part in its movement. 
The apparatus as described will also remove the limbs from small trees. For 
larger trees, it is contemplated that debarking would be preceded by a 
delimbing step. Many types of delimbers for large trees, which do not 
remove bark, are already known, and some such devices may be combined with 
the debarking apparatus of this invention so that trees can be delimbed 
and debarked simultaneously.