A BLADE

TECHNICAL FIELD

This invention relates to a blade.

In particular, the present invention relates to a blade for use in the forestry industry.

BACKGROUND ART

Modem forestry practice often makes use of mechanical harvesters in order to fell trees, remove side limbs, and cut the trunk to various lengths, all in a single process.

Mechanical harvesters usually consist of a harvesting head attached to the end of the mechanical arm of a hydraulically operated machine, such as an excavator or wheeled harvester. The harvesting head is manoeuvred to the base of the tree where it grips the trunk and cuts it from the stump of the tree using a saw attached to the harvesting head. The tree trunk is then driven through the head and any side limbs are removed by de-limbing knives attached to the harvesting head. The trunk may also be manoeuvred into position over a stack and cut into lengths using the saw attachment to the harvesting head.

The tree trunk is gripped by a number of hydraulically driven wheels attached to the harvesting head. The outer contact surface of each wheel is placed against the tree trunk. The contact surface is configured to enhance the frictional force between it and the trunk of the tree, thus reducing slippage and increasing the rate at which the tree can be passed through the head.

There are a number of ways in which this is achieved. One method, known as thumb-style, uses a number of cone shaped protrusions from the contact surface

in order to provide a number of high pressure points against the trunk. The disadvantage of this type of wheel is that the pressure required to grip the trunk may damage the wood underneath. Slippage may also occur if the surface of the bark is hard and highly contoured, or alternatively if the surface is too smooth for the protrusions to grip effectively.

In situations where the protection of the outer layer of the wood is of prime importance, the wheels may be formed from rubber with cast chain overlays around the outer surface of the wheel.

The type of wheel selected depends on the use to which the timber will be put.

For wood to be used as timber planks there is generally a need to protect the outer layer so as to limit damage to the surface or wood near the surface. There is also a need in some of these circumstances to leave as much bark on the tree as possible to reduce staining of the timber. This situation typically applies to soft woods, for example pinus radiata.

In such instances a thumb-style or rubber wheel may be used.

In other situations the wood is chipped for use as feed stock for pulping. This typically applies to various hard woods, including eucalypts and acacias. In these situations it is desirable to remove the bark from the tree prior to chipping through the use of debarking wheels.

An example of a debarking apparatus is disclosed in US Patent 5,111 ,860.

Typically, the outer contact surface of a debarking wheel is configured to include a series of blades substantially oriented across the direction of rotation of the wheel. These blades are designed to penetrate into the bark of the trunk thus providing a firm grip on the trunk. This is required in order to provide enough grip to drive the tree through the harvester head to remove all the branches as well as to control

the trunk to enable accurate measurement of the trunk dimensions.

The compression action of the blades on the bark releases the bond between bark and trunk and to a degree also promotes fracture of the bark enabling its removal.

The blades are configured so as to cause the trunk to rotate as it passes through the head.

Rotation of the trunk improves the debarking action of the harvester head by exposing more bark to additional debarking devices, such as delimb knives mounted on the front of the harvester head, as the trunk moves through the harvesting head.

A regular unconnected pattern of cuts running longitudinally along the trunk would occur if there was no rotation. Instead, with this blade configuration the resulting trunk rotation leads a pattern of cuts which follows a substantially continuous helical path along and around the tree.

In operation several debarking wheels are used in order to hold the trunk. This results in rapid coverage of a large portion of the bark with each pass of the trunk through the harvesting head.

The combined effect of the pattern of cuts made by the blades and the pressure exerted by the debarking wheels is to compress, tear and fracture the bark from the outside of the trunk.

Surprisingly with all of the considerations detailed there are still a number of disadvantages with use of the conventional debarking wheel as described above. Depending on the type and condition of the tree, it may take several passes of the trunk through the head in order to remove most or all of the bark. This is time consuming and therefore adds additional cost.

In particular, problems are encountered with trees which have a particularly hard bark, or long and stringy bark - commonly found with hardwood trees such as eucalyptus and acacias.

Sections of bark often jam into the space between the knife edges on the surface of the wheel, leading to machine down-time while the bark is removed from the wheel.

An alternative method of debarking used in some cases is to remove the bark by manually making a cut through it in the direction of the grain of the wood, in order to open up a tear in the bark. The bark may then be manually removed by pulling it away from the trunk in a manner which propagates the tear along the direction of the trunk. The disadvantage with this method is that it is labour intensive and time consuming, as well as potentially dangerous to the labourers. As such it is not suited to modern forestry practice.

In cases where the bark is to be removed, it would be useful to have provided an apparatus which could achieve effective and timely removal thereof as part of the mechanical harvesting process.

All references, including any patents or patent applications cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinency of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents form part of the common general knowledge in the art, in New Zealand or in any other country.

It is acknowledged that the term 'comprise' may, under varying jurisdictions, be attributed with either an exclusive or an inclusive meaning. For the purpose of this

specification, and unless otherwise noted, the term 'comprise' shall have an inclusive meaning - i.e. that it will be taken to mean an inclusion of not only the listed components it directly references, but also other non-specified components or elements. This rationale will also be used when the term 'comprised' or 'comprising ¹ is used in relation to one or more steps in a method or process.

It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.

Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.

DISCLOSURE OF INVENTION

According to one aspect of the present invention there is provided a wheel for the removal of a surface layer from an item, the wheel having one or more primary blades oriented substantially across the direction of rotation of the wheel when in operation,

characterised in that

the wheel includes a secondary cutting blade oriented substantially in the same direction as the direction of rotation of the wheel when in operation.

Reference throughout the specification shall now be made to the surface layer as being bark, the item as being a tree trunk or branch and the use of the present invention in relation to the forestry industry. However, it should be appreciated that the principles of the present invention could be applied to other industries and items. For example, the present invention could be used to strip outer layers from pipes and wires.

In a preferred embodiment the wheel is a debarking wheel.

Throughout this specification reference to a debarking wheel should be understood to mean a wheel configuration use in conjunction with a harvesting head in order to grip the trunk (or in some cases a branch) of a tree and to remove a surface layer from it.

The aggression of the debarking wheels can be varied by adjusting the hydraulic pressure applied on the wheels. The operator can increase or decrease the clamping pressure applied to the wheels depending on the bark conditions and the effectiveness of the wheels.

Reference shall be made to the wheel including a contact surface, defined as the outer surface formed around the circumference of the wheel and extending between the outer edges of the wheel.

Throughout this specification reference to a blade should be understood as a device configured to form a cutting edge.

It is the contact surface of the wheel which is configured to include one or more primary blades oriented substantially across the direction of rotation of the wheel.

It is envisaged that in preferred embodiments of the present invention the primary blades are of a similar shape and design to that used with conventional debarking wheels. However, this should not be seen as limiting as the principles of the present invention can be used in conjunction with primary blades of other designs.

A purpose of the primary blades is to cut into the bark so as to provide a firm grip on the tree trunk. This reduces the slippage than may occur with other types of wheel, thus increasing the accuracy of movement of the trunk through the

harvesting head. This is required in order to provide enough grip to drive the tree through the harvester head to remove all the branches and control the trunk to enable accurate measurement of the trunk dimensions.

This is important, especially for rapid acceleration and deceleration of the trunk whilst providing accurate measurement, as is required for efficient operation of the head.

Often the primary blades on a debarking wheel are curved. When the wheel rotates, the orientation of the primary blades relative to same provides a force across the direction of rotation of the wheel. This induces a spin to the tree trunk so that it rotates as it moves through the harvesting head.

In the present invention the debarking wheel includes at least one secondary cutting blade orientated substantially in the same direction as the direction of rotation of the wheel.

Preferably the secondary cutting blade is configured to cut through the bark of the tree.

The primary purpose of the secondary blade is to cut through and open up a tear in the bark as the blade moves over the bark.

The orientation of the secondary blade is such that it cuts through and opens the bark between and substantially perpendicular to the cuts made by the primary blades and roughly parallel to the grain direction of the bark.

In a preferred embodiment one or more secondary blades are oriented in the direction of rotation of the wheel and aligned so as to form a continuous or quasi continuous cutting surface around the circumference of the contact surface of the debarking wheel.

This arrangement results in a continuous or quasi continuous cut through the bark which extends substantially or all of the length of the trunk, and through the pattern of cuts made by the primary blades, as the trunk passes through the harvesting head.

In some applications it may be preferable that the debarking wheel includes more than one secondary cutting blade as described.

One advantage of this arrangement is that the cuts of the secondary blades open up the bark between the compressed and damaged bark of the primary blades. This, combined with the mechanical action of the primary blades, enhances the likelihood of fracture of the bark from the trunk, thus reducing the number of passes required to debark the trunk. A reduction in the number of passes of the trunk through the head is a major advantage in operating costs and harvesting time.

Another advantage of this arrangement is that the cuts formed by the secondary blades are oriented along the grain of the bark, which runs longitudinally along the trunk, so that the bark breaks off the trunk in long strips.

The secondary blades promote a split in the bark directly under the wheels which spreads and releases the bark from areas which have been directly and indirectly contacted by the wheels

The walls of the primary and secondary blades are preferably angled with respect to each other to a degree that small bark fragments do not wedge between the knives and clog the debarking wheels

In operation the harvesting head will include a number of debarking wheels placed around the circumference of the tree. With each wheel configured according to the present invention, a series of cuts, equal to the number of wheels, will be

formed through the bark by the secondary blades, along and around the trunk as it passes through the harvesting head. This has the effect of slicing the bark into thin helical strips around the trunk and along the grain.

The action of the primary blades is to compress and release the bond between the bark and the trunk and to fracture some of the bark. This combined action of the two set of blades leads to an enhancement of the cutting and fracturing of the bark over that achieved by the primary blades alone. The result is that the bark is removed in large strips.

An advantage of the current invention over the prior art is more efficient removal of the bark, resulting in a reduction in the number of passes required to debark the tree. The reduction in the number of passes increases the productivity of the harvester head and reduces the damage to the tree trunk

Another advantage of the present invention is that there is a less down time as the present invention considerably lessens the chances of bark becoming stuck within the harvester head and debarking wheels. As identified earlier, this requires considerable manual input to remove, is potentially dangerous and significantly cuts into the efficiency of the device.

Yet another advantage of the present invention is that the secondary cutting blade is in preferred embodiments formed as part of the debarking wheel along with the primary cutting blades when the debarking wheel is cast. As this is not an add on feature it is robust, does not require attaching and does not significantly affect the cost of manufacture of a debarking wheel.

BRIEF DESCRIPTION OF DRAWINGS

Further aspects of the present invention will become apparent from the following description which is given by way of example only and with reference to the accompanying drawings in which:

Figure 1 shows a perspective view of a debarking wheel; and,

Figure 2 shows a perspective view of a debarking wheel according to the present invention; and,

Figure 3 shows a perspective view of a debarking wheel according to another aspect of the present invention; and,

Figure 4 shows a representation of a pattern formed by a debarking wheel; and,

Figure 5 shows a representation of another pattern formed by a debarking wheel according to the present invention; and

Figure 6 shows a harvesting head incorporating three debarking wheels according to the present invention.

BEST MODES FOR CARRYING OUT THE INVENTION

Figure 1 shows a perspective view of a conventional debarking wheel generally indicated by arrow (1). A disc (2) rotates about an axle (3), which during operation is attached to a harvesting head (see Figure 6).

The disc (2) has an outer contact surface (4) on which a set of primary blades (5) are orientated across the direction of rotation of the disc (2) about the axle (3).

Figure 2 shows a perspective view of the current invention applied to a debarking wheel (1). The current invention differs from the conventional debarking wheel

shown in Figure 1 , by the addition of a blade (6) orientated substantially in the same direction as the direction of rotation of the wheel (2) about the axle (3).

Figure 3 shows an expanded view of the current invention as applied to a debarking wheel (1) including a set of secondary blades (6) aligned in a direction substantially the same as the direction of rotation of the wheel such that the blades from a continuous or quasi continuous cutting surface around the circumference of the debarking wheel (1).

Figure 4 shows a representation of the type of pattern of cuts (7) left on a tree trunk (8) that result from use of a conventional debarking wheel (1), as shown in figure 1. In the example shown in figure 4 the tree trunk is moving past the debarking wheel (1) in a direction shown by the arrow, and is rotating in an anticlockwise direction.

Figure 5 shows a representation of the type of pattern on the tree trunk (8) created by the current invention as applied to a debarking wheel (1) as shown in Figure 3. The pattern is as shown in figure 4, with the addition of a continuous or quasi continuous helical cut (9) created by the secondary blades (6). The resulting cut (9) across the sequence of cuts (7) formed by the primary blades (5) opens a tear in the bark thus facilitating fracture and removal of the outer surface of the trunk (8) due to mechanical fracture.

Figure 6 illustrates a harvesting head generally indicated by arrow (10) which includes three debarking wheels (1) in accordance with the present invention. The primary blades (5) and secondary blades (6) can be readily seen.

In use, a tree trunk (not shown) is positioned between the arms (11 ), and wheels (1) and supported to a degree by the front knife (12)

The wheels (1) move towards each other to bear against the outer surface of the trunk. Rotation of the wheels (1) spin the trunk in addition to propelling it through the head (10). This action also causes the blades (5) and (6) to bite into the bark, assisting to strip same from the trunk as previously described.

Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope of the appended claims.