Method of Processing Timber

Abstract

A method of processing timber comprises cutting a log into at least one elongate block of timber having a square or rectangular cross section and an elongate axis, cutting said at least one block into

Description

FIELD OF THE INVENTION This invention relates to a method of processing timber and in particular to an improved method of cutting elongate timber blocks cut from logs into a plurality of planks. BACKGROUND OF THE INVENTION When cutting logs into timber products it is known to cut an elongate block of wood (initially cut from a log) into a plurality of planks by the use of several saw blades mounted in vertically spaced parallel relationship, such that the block is cut into a stack of planks simultaneously as it is passes said saw blades. The stack of planks formed from the block can subsequently be wrapped for onward transportation to a customer. This provides a quick and efficient method of producing a stack of planks from one elongate block of timber. However, a problem with this known method of cutting elongate timber blocks into a plurality of planks is that sawdust becomes trapped between the planks as they are cut because the planks are not separated from one another between cutting and wrapping. This sawdust is unwanted by the customer and increases the size and weight of the stack of planks due to the thickness of the sawdust, increasing transportation costs. Furthermore, the trapped sawdust absorbs moisture and, where the planks are treated with a preservative after cutting, the sawdust absorbs the expensive treatment chemicals. Furthermore, the value of the trapped sawdust is lost as a product in its own right. However, removal of the trapped sawdust typically requires separation of the planks in the stack. This loses the advantages of retaining the planks formed from a single block in their stacked configuration following cutting and is therefore undesirable. SUMMARY OF THE INVENTION According to the present invention there is provided a method of processing timber comprising cutting a log into at least one elongate block of timber having a square or rectangular cross section and an elongate axis, cutting said at least one block of timber into a plurality of vertically stacked planks by conveying the block past a plurality of saw blades mounted in vertically spaced, parallel relationship; conveying the stack of planks in a direction transverse to said elongate axis; in a first rotation step, rotating the stack of planks through 90° about said elongate axis such that sawdust trapped between the planks falls out under gravity; collecting the thus released sawdust for subsequent use; in a second rotation step, rotating the stack of planks through 90° about said elongate axis such that the stack of planks is returned to a vertically stacked configuration; and wrapping the stack of planks for onward transportation to a customer. The stack of planks may be vibrated, shaken or otherwise disturbed to facilitate the release of sawdust trapped between the planks between said first and second rotation steps. Preferably said first and second rotation steps are carried out by a conveying device. In one embodiment, said first and / or second rotation steps may be carried out by conveying said stack of planks over a stepped or ramped conveying surface. In the second rotation step, the individual planks of the stack may tip over a step or ramp in said conveying surface consecutively, moving from a vertical to a stacked horizontal orientation, to further facilitate removal of sawdust trapped between the planks. Preferably the method further comprises the step of converting the sawdust collected following the first rotation step of the stack of planks into pellets for use as a fuel. The stack of planks may be treated with a treatment chemical following the second rotation step. BRIEF DESCRIPTION OF THE DRAWINGS A method of processing timber in accordance with an embodiment of the present invention will now be described, by way of example only with reference to the drawings, in which: - Figure 1 is a schematic view of the step of cutting a block of timber into a stack of planks in accordance with an embodiment of the present invention; and Figure 2 is a schematic view of the step of removing sawdust from between the planks of the stack. DETAILED DESCRIPTION OF THE DRAWINGS The present invention provided a method of processing timber in a sawmill comprising cutting a log into at least one elongate block of timber having a square or rectangular cross section and an elongate axis, simultaneously cutting said at least one block of timber 2 into a plurality of vertically stacked planks or boards 4 by conveying the block past a plurality of saw blades 5 mounted in vertically spaced, parallel relationship. The saw blades 5 may comprise circular blades, preferably mounted coaxially, or band saws. Each stack may comprise between 6 and 10 planks. The thus formed stack of planks 4, with the planks in the stack arranged horizontally in a vertically stacked relationship, is then conveyed in a direction transverse to said elongate axis and, in a first rotation step A, rotated through 90° about said elongate axis such that planks are arranged vertically and the sawdust trapped between the planks falls out under gravity. The thus released sawdust 14 is collected for subsequent use. In a second rotation step B, the stack of planks 4 is rotated through a further 90° about said elongate axis such that the stack of planks 4 is returned to a vertically stacked configuration with the planks arranged horizontally. The stack of planks 4 is then conveyed onwards to a wrapping station, whereat the stack of planks is wrapped with securing straps for onward transportation to a customer. As illustrated schematically in Figure 2, the first and second rotation steps A,B may be carried out by a conveying device, for example by conveying said stack of planks 4 over a stepped or ramped conveying surface, wherein the stack tips over a respective stepped or ramped portion 8,10 of said conveying surface to facilitate each of said first and second rotation steps A,B. In the second rotation step B, the individual planks of the stack may tip over the step or ramp consecutively to further facilitate removal of sawdust trapped between the planks. In the second rotation step, each block of planks or boards may pass over a step allowing each board to individually drop and thus incurring disturbance which will allow a lot of the sawdust to fall out from between the planks. Preferably the stacks of planks 4 may be conveyed over said stepped or ramped portions of the conveying surface at a rate of approximately 75m / min such that the first and second rotation steps take place over a period of approximately 3 seconds. The stack of planks may be vibrated, shaken or otherwise disturbed to release sawdust trapped between the planks between said first and second rotation steps with the planks arranged vertically. This may be achieved by the acceleration and deceleration imparted to the stack of planks as it is tipped over said stepped or ramped portions 8,10 of the conveying surface. Preferably sawdust 14 disturbed and removed from between the planks is collected, for example by means of a conveyor belt 12 located beneath said conveying surface, and conveyed for subsequent processing as a separate and useful product. In a preferred embodiment at least a portion of the collected sawdust is made into wood pellets for use as a fuel. A portion of the collected sawdust may be used as an energy source for the sawmill, said sawdust being burnt in a boiler to heat water to be used as a heat source, for example for drying kilns, and to drive a steam turbine coupled to an electricity generator. The stack of planks may be treated with a treatment chemical following the second rotation step, avoiding wastage of the treatment chemical which would be otherwise absorbed by the trapped sawdust between the planks. The invention is not limited to the embodiment described herein but can be amended or modified without departing from the scope of the present invention.

Claims

1. A method of processing timber comprising cutting a log into at least one elongate block of timber having a square or rectangular cross section and an elongate axis,5 cutting said at least one block of timber into a plurality of vertically stacked planks by conveying the block past a plurality of saw blades mounted in vertically spaced, parallel relationship; conveying the stack of planks in a direction transverse to said elongate axis; in a first rotation step, rotating the stack of planks through 90° about said elongate axis such that sawdust trapped between the planks falls out under10 gravity; collecting the thus released sawdust for subsequent use; in a second rotation step, rotating the stack of planks through 90° about said elongate axis such that the stack of planks is returned to a vertically stacked configuration; and wrapping the stack of planks for onward transportation to a customer.15 2. A method of processing timber as claimed in claim 1, wherein the stack of planks is vibrated, shaken or otherwise disturbed to release sawdust trapped between the planks between said first and second rotation steps.

3. A method of processing timber as claimed in claim 1 or claim 2, wherein said first20 and second rotation steps are carried out by a conveying device.

4. A method of processing timber as claimed in claim 3, wherein said first and / or second rotation steps are carried out by conveying said stack of planks over a stepped or ramped conveying surface.

255. A method as claimed in claim 4, wherein, in the second rotation step, the individual planks of the stack tip over a step or ramp in said conveying surface consecutively, moving from a vertical to a stacked horizontal orientation, to further facilitate removal of sawdust trapped between the planks.

306. A method as claimed in any preceding claim, comprising the step of converting the sawdust collected following the first rotation step of the stack of planks into pellets for use as a fuel.

7. A method as claimed in any preceding claim, wherein said stack of planks is treated with a treatment chemical following the second rotation step.

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