Ultra high pressure water log debarking

A method and apparatus for hydraulically debarking logs is disclosed, in which water at a substantially constant, ultra high pressure of, say, at least 25,000 KPa, is caused to impinge upon, generally radially with respect to, the surface of a log to be debarked. The apparatus of a preferred embodiment has ultra high pressure nozzles mounted upon resilient members circumferentially surrounding the log to be debarked, the members being biassed radially inwardly of the leg to bear upon the undulating surface thereof, and to maintain the nozzles at a predetermined distance therefrom, thereby maintaining the impinging water at a constant ultra high pressure.

BACKGROUND OF THE INVENTION 
This invention relates to a method of and an apparatus for debarking logs. 
Due to an increasing shortage of large timber, substantial quantities of 
small-sized timber, and particularly hardwoods, are gradually emerging 
from anomynity as a distinctive and marketable commodity, as discussed in 
a paper entitled "Debarking of Eucalypts--A re-appraisal". by A Krilov, 
and published in Aust. For. J43(4) 1980--145-149. These new types of raw 
material, which have previously received little attention, are expected to 
form a much more important part of the world's timber supply in the near 
future. 
The cost of debarking large quantities of small, low volume timber, such as 
hardwoods, of poor configuration by conventional means, is ofter 
prohibitive. One way of achieving this cheaply and efficiency would be to 
use an appropriately designed hydraulic debarker. 
BRIEF DESCRIPTION OF THE PRIOR ART 
A known hydraulic debarking technique uses high pressure water jets to 
loosen and then remove bark from logs. Small logs of poor shape can be 
debarked cleanly and without excessive damage, which is not otherwise 
possible without removing a certain amount of good fibre. Such equipment, 
however, requires a larger water supply and is generally restricted to 
operations of a considerable size. Hydraulic debarkers can handle 
softwoods and numerous hardwoods well, particularly those with thin bark. 
However, they cannot effectively handle difficult hardwood species which 
also cannot generally be debarked by standard mechanical debarkers. 
Certain timbers, which in the present state of technology are considered to 
be extremely difficult to debark, include Eucalyptus paniculata which has 
a massive and very hard bark, E. pilularis and Syncarpia glomulifera with 
short to medium fibrous bark which adheres strongly to the cambial layers 
and long-fibre species, such as, E. agglomerata belonging to the botanical 
group of "true" stringybarks. 
The known use of high pressure water for log debarking and/or surface 
preparation or cleaning normally involves pressures of up to 20,700 kPa. 
An object of the invention is to provide a method of and apparatus for 
debarking timber which can effectively handle difficult hardwood species, 
such as those mentioned above, as well as efficiently debarking such 
timber in large quantities of small, low volume hardwoods of poor 
configuration with which known high pressure hydraulic debarkers cannot 
cope efficiently. 
Another object of the present invention is to provide a method of and 
apparatus for debarking timber, which reduces substantially the amount of 
water otherwise used in known forms of high pressure or other forms of 
debarkers. 
SUMMARY OF THE INVENTION 
Accordingly, one aspect of the invention provides a method of hydraulically 
debarking logs, wherein water at a substantially constant, ultra high 
pressure, of, for instance, at least 25,000 kPa, is caused to impinge upon 
and generally radially with respect to the surface of a log to be 
debarked. 
In accordance with another aspect of the invention, there is provided a 
hydraulic debarking apparatus including means for causing water to impinge 
upon and generally radially with respect to the surface of a log to be 
debarked at a substantially constant, ultra high pressure, of, for 
instance, at least 25,000 kPa. 
The substantially constant, ultra high pressure of the water impinging 
generally radially on the log surface can be of the order of 83,000 kPa, 
although lower pressures down to, say, 25,000 kPa, may be used 
successfully, depending upon the nature of the logs to be debarked. 
In a preferred embodiment of the invention, the means for causing the 
substantially constant, ultra high pressure water to impinge generally 
radially on the surface of a log to be debarked comprises at least one 
ultra high pressure nozzle which is maintained at a predetermined radial 
distance from the surface of the log during debarking, thereby maintaining 
the ultra high pressure of the water impinging generally radially upon the 
log surface at a substantially constant and desired value. 
In this preferred embodiment, each ultra high pressure nozzle is maintained 
at a predetermined distance from the surface of the log durng debarking by 
resilient means which bears against the log surface and to which each 
nozzle is fixed. Thus, as the profile of the log surface varies, according 
to its natural growth, the resilient means moves radially inwardly and 
outwardly with respect to the log surface upon which it bears, thereby 
maintaining each nozzle at a predetermined distance from the undulating 
log surface. As a consequence, the ultra high pressure of the water 
impinging generally radially upon the log surface is maintained 
substantially constant. 
Each ultra high pressure nozzle may be rotatable around the log, in a plane 
generally normal to the longitudinal axis thereof, during debarking. 
Alternatively, the log can be rotated about its own axis with respect to 
the or each nozzle.

DETAILED DESCRIPTION 
Referring now to the drawings, an ultra high pressure hydraulic debarking 
apparatus, designated generally at 10, is designed to operate with 
tree-length logs 1 of 100 to 350 mm diameter and a maximum length of 30 m. 
Prior to being fed individually to the debarking apparatus 10, the logs 1 
are loaded on to a "waterfall" or "cascade" type unscrambler deck (not 
shown) consisting of three sections which can be controlled individually. 
The log feed speed varies from 6.8 m/min on deck one to 18 and 25 m/min on 
deck two and three respectively. A rotating log loader (not shown) places 
each log separately on to a chain conveyor 11 which feeds each log to the 
input at the left hand end of the apparatus 10. 
Before describing the particular form of the hydraulic debarking apparatus 
10, some basic principles of fluid mechanics will now be considered in 
relation to achieving efficient practical application of water blasting 
techniques to the removal of the bark from the logs during their passage 
through the debarking apparatus. These principles govern the "debarking 
power" which can be applied when such factors as jet velocity, nozzle 
size, engine power and water delivery volume are specified. These and 
other factors are related to each other by equations whose solutions lead 
to the attainment of a correct balance of such factors, which, in turn, 
achieves debarking of the logs without causing any substantial surface 
breakdown of the timber. The following equation is of basic importance: 
EQU F=p.multidot.V.sup.2 
where 
F=debarking or impact force (Pa) 
V=velocity of the fluid (m/s) 
p=fluid mass density. 
This equation relates the velocity of the water jet delivered through a 
nozzle directly to the pressure of the fluid and nozzle orifice. It is 
important to recognise this relationship, because the desired pressure can 
only be achieved by the proper combination of nozzle orifice and pump 
volume. This can be illustrated as follows. 
Where a TC No. 5 nozzle operating at 531/min will produce a pressure of 
45,500 kPa, the same volume of water expelled through a TC No. 4 nozzle 
will develop 58,600 kPa, namely, 13,000 kPa more, using the same pump and 
engine. Most standard Triplex pumps used in water blasting today are 
capable of delivering 20 to 70 l/min at ultra high pressures which range 
from 27,000 to 69,000 kPa and sometimes reach 83,000 kPa. 
Another consideration of prime importance is the size of engine driving the 
pump. If the engine does not have sufficient power, then obviously 
pressure volume cannot be maintained. This is expressed by another simple 
but important relationship, namely,: 
EQU kW=P.multidot.V/C.sup.T 
where 
P=pressure at the nozzle (kPa) 
V=volume of fluid (l/min) 
C.sup.T =constant appropriate to the equipment used 
There is always a pressure drop between the pump and the nozzle, which 
depends upon a number of factors, the main ones being the size and length 
of hose used. Tables providing the technical characteristics of such hoses 
are available and it is important to use them, because the water blasting 
process may be a failure if the incorrect hose is fitted. 
Another factor of considerable importance in determining the effects of the 
water jets is the angle of incidence which is the angle of impact measured 
between each jet and the surface of the log. A range of such angles could 
vary between 90.degree. and 5.degree., in this particular application the 
most effective angle of incidence being 60.degree.. 
During use of the apparatus 10 on a pinus elliottii log, the importance of 
a substantially constant spacing between the nozzles and the log 1 to be 
debarked can be demonstrated. It has been found that there is an optimum 
distance for this factor which has to be kept constant, or at least 
substantially constant, during debarking. The actual distance required 
varies with the species of timber and the need to maintain this constant 
nozzle distance presented at one time a substantial practical problem, 
because of the variable sizes of the logs and the fast rate of feed 
through the debarking apparatus 10. 
To solve this problem, a novel component of the apparatus 10 was designed 
and built, the completed component's structure being a strongly made 
framework shaped in the form of a deep tapered, generally circular, 
open-ended basket-type cradle 13 with axially-extending, heavy duty metal 
bars 15 which are pivoted at the wider axial open end. This cradle 13 is 
fixed horizontally in the mouth of an "anti-thrash" tunnel 12. The wider 
open end of the cradle 13, into which each log 1 is fed longitudinally, 
narrows to a diameter at its other open end which is equal to a minimum 
log diameter size, because each bar 15 is urged radially inwardly by a 
bias provided by tensioned springs 16. The ends of the bars are curved 
slightly radially outwardly and eight jet nozzles are attached to each of 
them at predetermined locations. This ensures that, whatever the log size 
the ultra high pressure water strikes the log surface from the optimum 
distance of, say, 80 mm, in the particular case of pinus elliottii logs. 
In operation, logs 1 are conveyed through the cradle 13 to the downstream 
end of the cradle and log sections of minimum diameter pass under the jets 
without altering the size of the framework. Larger log sections force the 
bars radially outwardly, but because the spring bias keeps the bias 15 in 
constant contact with the log surface, the nozzles 19 maintain the correct 
distance from the log surface. This ingenious arrangement provides 
excellent working results. 
In more detail, and with particular regard to FIGS. 4 to 6 of the drawings, 
the axially-extending bars 15 are mounted, for radial pivotal movement at 
the upstream wider open end of the cradle 13, upon a framework 18, as 
shown in FIG. 4. At the other, downstream end of the cradle 13, each bar 
15 is provided with at least one radially inwardly directed nozzle 19. 
Each bar 15 is generally L-shaped with its shorter leg 20 arranged to bear 
against the surface of a log 1 to be debarked. The radially extending, 
longer legs 21 of adjacent pairs of bars 15 are connected together, at 
their outer ends, by the strongly tensioned springs 16 which bias the bars 
15 radially inwardly, such that the shorter legs 20 of the bars are 
maintained in bearing contact with the surface of the log 1. Each nozzle 
19 of each bar 15 is mounted on the longer leg 21 thereof, to be directed 
radially inwardly towards the log surface. Ultra high pressure water is 
supplied to the nozzles via suitable hoses 22. In this preferred 
embodiment, there are eight bars 15, although only six are shown in FIG. 
5, for reasons of clarity. 
In the non-working position of the cradle 13, as shown in FIGS. 4 and 5, 
the bars 15 are located in their radially innermost positions, owing to 
the radially inward bias of the tension springs 16. When a log 1 to be 
debarked is passed through the cradle 13, as shown in FIGS. 1 to 3 and 6, 
the bars 15 are urged radially outwardly due to the shorter legs 20 
thereof bearing upon the surface of the log. As the log 1 continues its 
passage through the cradle 13 upon the conveyor 11, the bars 15 are 
resiliently moved radially inwardly and outwardly in dependence upon the 
shorter legs 20 bearing against the undertaking surface of the log. In 
this way, the nozzles 19 are maintained at a substantially constant 
distance from the log surface, thereby maintaining the water impinging 
thereupon at a substantially constant, ultra high pressure to cause the 
required debarking of the log 1. As described above, the debarked log 1 
then progresses downstream through the anti-thrash tunnel 12. 
The debarked logs 1 are conveyed at a speed of 60 to 70 m/min through the 
anti-thrash tunnel 12, where a further series, preferably eight, of ultra 
high pressure water jets blast away any extraneous bark or other material 
remaining on the log surface. The jets are regulated to provide pressures 
of approximately 48,300 kPa which was found to be the most effective value 
for this particular debarking apparatus, although pressures of 69,000 kPa 
can be achieved with suitable motors, for instance, a three phase 415 volt 
power supply or a diesel engine. The volume of water used averages 227 
l/min. 
The ultra high pressure water is projected at a velocity of 396 m/s through 
No. 6 ring-type nozzles which have 1.5 mm openings and a 15.degree. fan. 
The water is delivered from a motor driven pump 30. 
In this particular water blasting arrangement, there is preferably a safety 
factor of 3:1 for the hoses and fittings and 4:1 for the nozzles. The jets 
are regulated automatically and the nozzles safety stop for machine 
pressure is controlled by an operator. 
The waste bark material removed from the logs by the ultra high pressure 
water jets is deposited under gravity on to a wide belt conveyor 14 which 
takes it to any suitable waste disposal area. Also, any chunks of thick 
bark can be collected periodically from underneath the waterfall or 
cascade deck and transferred to a central waste pile (not shown). 
At the foundation level of the apparatus 10, used water from the ultra high 
pressure debarking method flows under gravity in to an open concrete drain 
(also not shown) which channels it through a series of gratings into a 
sediment trap (not shown) where large pieces of solid waste are filtered 
from the water. It is then pumped up to a head station (not shown) from 
which it flows slowly through a series of settling ponds down to a main 
water holding pond. In the settling ponds, the remaining dirt and fines 
soon fall to the bottom and the water is finally clarified by using a 
flocculating agent, preferably, "Actizyme" (additive K) which is added 
periodically at the rate of 25 kg per million liters of water used. The 
total cost of this additive is negligible. 
The "clean" water from the main water holding pond is then pumped up to a 
storage tank and subsequently fed by gravity to the nozzles through 
suitable filters. This recycling system, therefore, solves the two 
problems of high water usage and accelerated machinery wear. So successful 
has been the recycling process, that water losses, monitored over a 
considerable period, have been not more than 2% of the total water 
throughput, such losses mainly being due to evaporation. 
As can be seen from FIGS. 1 and 2, an additional anti-thrash tunnel 12' can 
be located downstream of the first anti-thrash tunnel 12. This further 
tunnel 12' can also be provided with ultra high pressure water nozzles and 
a suitable cradle arrangement 13' as in the case of upstream tunnel 12. 
A number of trials employing the inventive apparatus and method have been 
carried out and these are detailed in the following Example. 
EXAMPLE 
Timber 
Several short logs ranging between 65 and 140 mm mid-diameter were cut from 
the following five species: Ironbark (E. paniculata), blue-leaved 
stringybark (E. agglomerata) white mahogany (E. acmenioides), blackbutt 
(E. pilularis) and turpentine (Syncarpia glomulifera). Three samples of 
each species were collected and provided a gradient of debarking 
difficulty, due mainly to the different thickness of bark. Samples 
dimensions, bark characteristics and relevant observations are noted in 
Table 1. 
All samples were harvested in the shortest possible time (within 24 hours), 
marked, hermetically enclosed within polythene bags and prepared for 
testing the next day. 
TABLE 1 
__________________________________________________________________________ 
3 4 5 6 7 8 
Dimensions 
1 Diameter Thickness 
Sample 
2 top 
butt 
Length Volume 
top 
butt 
9 10 
No. Timber species 
mm mm m m.sup.3 
mm mm Bark type 
Observations 
__________________________________________________________________________ 
1 E. paniculata 
130 
140 
1.26 
0.018 
10 10 Massive & ridged, 
Top branches from a large 
2 E. paniculata 
75 
90 
1.86 
0.010 
10 10 hard fallen tree; 
3 E. paniculata 
85 
85 
1.38 
0.008 
8 8 very dry, knotty and hard 
4 E. agglomerata 
115 
125 
1.25 
0.014 
10 12 Long stringy 
Top branches from tree with 
5 E. agglomerata 
85 
85 
1.17 
0.007 
6 8 400 mm butt diameter 
6 E. agglomerata 
70 
75 
1.36 
0.006 
7 8 
7 E. acmenioides 
125 
130 
1.20 
0.015 
10 10 Short stringy 
Small tree with 150 mm 
8 E. acmenioides 
95 
105 
1.03 
0.008 
7 9 butt diameter 
9 E. acmenioides 
65 
75 
1.26 
0.005 
6 7 
10 Syncarpia glomulifera 
120 
140 
0.92 
0.012 
10 10 Coarsely fibrous, 
Small tree with 200 mm 
11 Syncarpia glomulifera 
105 
115 
1.15 
0.011 
15 16 thick, furrowed 
butt diameter 
12 Syncarpia glomulifera 
115 
125 
1.50 
0.017 
12 13 
13 E. pilularis 
140 
165 
1.04 
0.019 
8 10 Finely fibrous, 
Small tree with 400 mm 
14 E. pilularis 
125 
150 
0.95 
0.014 
7 10 stringy butt diameter 
15 E. pilularis 
90 
130 
0.90 
0.009 
7 8 
16 E. paniculata 
105 
115 
1.02 
0.010 
12 14 as above Top branches from a 
17 E. paniculata 
120 
120 
0.97 
0.011 
15 15 fallen tree of 500 mm 
18 E. paniculata 
100 
120 
0.97 
0.009 
10 16 butt diameter 
__________________________________________________________________________ 
Equipment 
The equipment consisted of: 
(a) An American Aero anti-corrosive, stainless steel high-pressure pump, 
model FE85 Triplex, capable of three outputs, which were easily adjustable 
in practice: 
______________________________________ 
Pressure kPa Maximum flow l/min 
______________________________________ 
69,000 37.8 
48,300 53.0 
34,500 71.9 
______________________________________ 
The pump power ends were heat-treated, alloy steel crankshafts, with large 
bearings for high frame load capacities. The connecting rods were made of 
nodular iron and fitted with precision-type split insert bearings and 
extra-large hardened and ground wrist pins. The piston-type crossheads 
were over-sized for reduced wear. The simplified design permitted complete 
field maintenance by semi-skilled personnel. 
All piping connections were straight boss threads with SAE O-ring seals to 
eliminate stress and prevent leakage. The pump was fitted with a 138,000 
kPa pressure gauge and safety relief valve, set to open at 20% above 
maximum machine discharge pressure. At a safety factor of 3:1 the pump was 
stressed against accidents to some 1.2 million kPa. 
(b) A movable two-stroke Detroit Diesel Allison, model WBD-90, fitted with 
a supercharged engine type GMC 3-53 Diesel running at 2000-2100 RPM, 
necessary to operate the high-pressure pump. 
(c) Single operator control gun model P-10-M, fitted with the appropriate 
nozzle, and designed for pressures not greater than 69,000 kPa. 
Trials Testing Procedure 
Whilst each log was securely fixed before debarking began, the hydraulic 
pump was adjusted to the medium range pressure of 48,300 kPa. At this 
pressure it was capable of developing a maximal flow of 53 l/min. 
To reduce water losses, the control gun was fitted with a stainless steel 
No. 6 jet nozzle with 15.degree. fan and 1.57 mm diameter opening. At a 
relatively high pressure (48,300 kPa), this nozzle produced a water flow 
of not greater than 28.4 l/min. 
Debarking of each sample was timed. The number of passes per log were 
counted and the debarking time per strip noted. As pump-nozzle flow 
capacities were known, this information enabled the water requirements per 
species to be determined. It also provided a fair indication of the 
relative difficulty of bark removal from the samples. 
Results 
The final results of the debarking trials are given in Table 2, as follows: 
TABLE 2 
__________________________________________________________________________ 
7 
4 5 6 Volume 
Debarking time 
Total 
of water 
3 In volume 
required to 
1 Debarked normal 
of water 
debark 
Sample 
2 length 
Per strip 
operation 
used 1 mm length 
8 
No. Timber species 
m S S.sup.a 
l l Observations 
__________________________________________________________________________ 
1 E. paniculata 
+ -- -- -- -- +Sample used to adjust 
system. 
No times were taken 
2 E. paniculata 
1.00 7-11-11-17-19 
13 24.5 24.5 Both values only 
indicative: 
3 E. paniculata 
1.38 15-17-19-22 
18 34.0 24.6 extremely dry, 
weather-hardened 
Sample 
4 E. agglomerata 
1.25 6-6-10-10-11-12- 
11 20.7 16.5 Bark is detached in long 
strips of 
13-17 various length. Adherance 
of the 
5 E. agglomerata 
1.17 5-8-9-9-10-12 
9 17.0 14.5 inner bark great. No 
particular 
6 E. agglomerata 
1.36 7-8-9-10 9 17.0 12.5 problems 
7 E. acmenioides 
1.20 6-7-7-7-7-7-10- 
8 15.1 12.5 Bark is detached in short, 
separate 
10 fibers of 200-300 mm. 
Adherance 
8 E. acmenioides 
1.03 7-7-8-10-11 
9 17.0 16.5 of the inner bark similar 
to 
9 E. acmenioides 
1.26 5-5-5-5 5 9.4 7.4 previous. No problems 
10 Syncarpia glomulifera 
0.92 3-3-4-4-5-7-7 
5 9.4 10.2 Debarking easy. Bark is 
detached 
11 Syncarpia glomulifera 
1.15 5-6-7-7-10-10 
8 15.1 13.1 in long (up to 1.00 m) and 
wide 
12 Syncarpia glomulifera 
1.50 7-8-8-8-13-15 
10 18.9 12.6 (50-100 mm)strips or small 
chunks. Wood surface clean 
13 E. pilularis 
1.04 3-4-5-7-7-8-9-9- 
9 17.0 16.3 Debarking difficult. Great 
10-10-11-12-12 adherance of bark 
falling-off in 
14 E. pilularis 
0.95 5-6-9-11-11-12- 
12 22.6 23.7 tufts similar to E. 
acmenioides. 
12-13-13-13-15-16 Wood surface unclean, 
irregular 
15 E. pilularis 
0.90 5-7-13-13-14-14- 
13 24.5 27.2 and extensively damaged by 
spray 
14-15-16 
16 E. paniculata 
1.02 5-7-9-14 9 17.0 16.6 Relatively easy debarking. 
Bark is 
17 E. paniculata 
0.97 7-7-10-10-12 
10 18.9 19.4 detached in large, solid 
chunks. 
18 E. paniculata 
0.97 7-8-12-14 
11 20.7 21.3 similar to Syncarpia. 
Greater 
volume of water is 
necessary to 
carry off thick 
__________________________________________________________________________ 
bark 
*Rounded to the next top value 
Note that in Table 2, column 4 represents debarking times clocked 
separately for the number of strips or passes needed to debark a given 
sample cleanly. These preliminary tests were carried out with only one jet 
nozzle, so that in a normal operation with a regular log feed the expected 
debarking time should be an average of the figures given in column 4. This 
value is noted in column 5. 
The total volume of water delivered, which was necessary to debark a green 
sample, is given in column 6. It was calculated by multiplying the average 
time used in a normal operation (column 5) by four. The factor four 
represents the number of jets required for debarking logs of small to 
medium diameter in normal practice. As the results obtained correspond to 
the variable length of each sample, these figures were adjusted to a basic 
reference length of 1.00 m for each timber species (column 7) 
Analysis of column 7 in Table 2 shows clearly that the species tested can 
be arranged in an order of difficulty of debarking, which is given in 
Table 3 (Note that E. paniculata samples 2 and 3 are excluded, as they 
were special cases), as follows: 
TABLE 3 
__________________________________________________________________________ 
3 
1 Mean water consumption 
4 
Sample 
2 per 1.00 m length 
Relative difficulty 
5 
No. Timber species 
1 of bark removal.sup.a 
Observations 
__________________________________________________________________________ 
10-12 
Syncarpia glomulifera 
11.9 1 
7-9 E. acmenioides 
12.1 2 
4-6 E. agglomerata 
14.5 3 
16-18 
E. paniculata 
19.1 4 Standard sample 
13-15 
E. pilularis 
22.4 5 
1-3 E. paniculata 
24.5 Not considered 
Extreme case 
__________________________________________________________________________ 
.sup.a 1 easy; 5 difficult 
The conclusions of Table 3, column 4 are confirmed, qualitatively and 
quantitatively by practical observations. 
One of the objects of this trial was to assess the feasibility of debarking 
certain timbers, which are known to be difficult in this respect. The 
results given above show that this object was achieved, and that debarking 
by means of an ultra-high pressure water jet is clearly practicable. These 
findings are numerically represented and commented upon in columns 7 and 8 
of Table 2. 
The specific example of E. paniculata extremely dry, weather-hardened 
samples No. 1, 2 and 3, selected to test the eventual capability of a 
hydraulic debarker in dealing with an extremely difficult bark under the 
worst possible conditions, is obvious. All these samples were debarked 
neatly and without too many problems. The practical experiments with other 
species only amplified and confirmed this fact. 
The volume of water required to debark these timbers is not excessive. In 
fact, it is substantially less than that currently used by conventional 
hydraulic debarkers processing softwoods. It seems important, however, to 
note, that the estimations given in Table 2, column 7, do not necessarily 
represent the total volume of water which would be required for debarking 
one meter of any particular species in practice. In a closed circuit, 
supplied with an adequate filtering system, a small hydraulic debarker 
should be capable of limiting water losses to not more than 20% of the 
indicated values. 
The behavior of various bark types under a high velocity water jet is 
different for each species. It has been observed that the shredding which 
occurs, is related to the specific structure of the bark and its adherence 
to the cambial layer. These factors also have a great influence on the 
average water consumption per unit length of sample (Table 3, column 3). 
The effect of variable log diameters, which is reflected to some extent by 
the number of passes per sample, is of a lesser importance and therefore 
is not considered further. 
A number of observations on the behavior of the bark during debarking 
operation, is provided in Table 2, column 8. These observations show that 
the shredding qualities of Sample No.'s 4-6, 7-9, 10-12 and 16-18 bark 
types are basically different and that the shredding of bark fibers is 
characteristic for each particular timber species. 
Thus, it is to be noted that Sample No.'s 7-9 bark type is cleanly 
separated by the water jet into individual fibers of short length (200-300 
mm). The physical aspect of this bark and the degree of defibration are 
such, that the product obtained is readily utilizable. This material seems 
to have a great potential for the manufacture of a cheap insulating board. 
In contrast, the bark type of E. agglomerata was removed in long strips of 
varying length, which could be used for such purposes as land fill. 
The bark type of E. paniculata came off in solid chunks. These were quite 
regular in appearance and should have been usable as they were, for mulch, 
ground cover and other purposes. Syncarpia glomulifera chunks were 
somewhat longer. 
Whilst most of the selected species were debarked well and with relative 
ease, E. pilularis presented a few problems. The separation of the bark 
from the wood was extremely difficult. It did not break down either into 
smaller pieces of characteristic shape or into separate fibers. Unlike 
other species, blackbutt bark was not entirely removed by the first pass 
of the jet: the inner bark hung down in torn fragments, while the other 
bark stuck out in hairy tufts, mixed with splinters from the damaged 
surface of the wood. Subsequent passes increased the damage to the log 
surface, without wholly removing the bark. The damage to the wood was 
such, that no attempt was made to remove all the bark by repeated 
application of the jet. The surface resulting from this treatment was 
rather unclean, irregular and more or less severely battered. The contrast 
between this species and the others tested, was very striking. 
These results indicated clearly that at given nozzle characteristics, the 
pressure of 48,300 kPa was too high for this particular species. 
It is, however, premature to conclude that E. pilularis cannot be 
efficiently debarked by hydraulic means, in that a lower water jet 
pressure, combined with a more suitable nozzle size and an adjusted nozzle 
geometry, may solve this problem. 
Further improvements may be achieved by appropriate modifications in water 
flow pressure, number of nozzles, nozzle size, shape of the jet opening 
and the degree of the spray fan. 
In this respect it is possible to reduce the total water consumption for 
debarking to about 20% of that used previously, by adequate removal of 
waste particles. Pollution control could be incorporated at the filtering 
stage of this process without any inconvenience. 
Conclusions 
These trials have allowed certain conclusions to be drawn as to the 
technical advance provided by the present invention which can be 
summarized as follows: 
1. A clear demonstration that most of the small diameter hardwoods selected 
can be efficiently debarked by an ultra high pressure water jet. Even the 
most recalcitrant timber species, such as long fibered "stringybarks" can 
be debarked, which cannot be done by standard mechanical equipment. It is 
expected, therefore, that the majority of less problematic hardwood barks 
can be removed efficiently by this inventive method. 
2. Timbers tested can be ranked in order of the difficulty of removal of 
their bark. 
3. Although the cleanness of the debarked surface varies greatly within the 
range of species tested, the quality of debarking is far superior to that 
produced by other known equipment of any sort. 
4. The fibers of certain bark types, such as that of E. acmeniodides or E. 
paniculata, are removed by the water jet in a form which should be 
utilizable without any further processing. Significant progress towards 
greater utilization of hardwood barks is made possible by these findings. 
It is to be appreciated that, although the embodiment described above, with 
reference to the accompanying drawings, relies upon the resilient radial 
movement of the bars 15 to maintain the nozzles 19 at a predetermined 
distance from the surface of a log 1 to be debarked, thus maintaining the 
impinging debarking water at a substantially constant, ultra high 
pressure, other suitable means may be provided to maintain the ultra high 
pressure of the water at a constant value as it impinges on the log 
surface. For instance, radially inwardly biassed sensors may be used on 
the cradle to determine the undulating profile of the log surface at any 
given time and to adjust the pressure of the water issuing from the 
nozzles, which could be fixed upon the cradle, and with respect to the log 
surface, thereby maintaining the pressure of the water impinging upon the 
log surface at a substantially constant value. 
Modifications may be made in this invention without departing from the 
scope and spirit thereof. While the invention has been shown and described 
in terms of certain particular structures and arrangements, the invention 
is not to be limited to those particular structures and arrangements 
except insofar as they are specifically set forth in the following claims.