Background of the invention

[0001] The invention relates to a circular saw blade to be used in a canter-edger, the blade comprising a disc-like blade body and having a plural number of blade teeth on an outer circumference thereof. Between successive blade teeth, there are sawdust spaces with bevelled edges. Further, back surfaces of the blade teeth are provided with bevels for managing sawdust.

[0002] The invention also relates to a blade element for. a circular saw blade of a canter-edger and a blade unit for a canter-edger.

[0003] The field of the invention is described in more detail in the preambles of the independent claims.

[0004] At sawmills, logs are cut into timber of different lengths. In a first handling step the logs are fed through a canter-edger in which two sides of the log facing away from each other are machined to remove some of the surface layer. With the canter-edger, a log is shaped before the actual sawing to produce a rectangular saw blank, i.e. a cant. The canter-edger has at least two blade units facing each other, each unit comprising a sawing blade and a chipper. The canter-edger may be provided with vertical blade units and horizontal blade units. The saw blade saws a surface piece of a desired width from the log surface, the chipper blades then chipping the cut piece into wood chips. The saw blade is typically a circular blade to provide a saw blank of a good surface quality. A problem with circular saw blades, known as front blades, used in canter-edgers is that the chippings cause blade breaks and degrade sawing quality.

Brief description of the invention

[0005] It is an object of the invention to provide a novel and improved canter-edger saw blade, a blade element belonging thereto, and, further, a canter-edger blade unit.

[0006] The saw blade of the invention is characterized in that larger sawdust spaces are provided at the end of a sawing cycle than at the beginning of the sawing cycle.

[0007] The blade element of the invention is characterized in that the blade element is provided with sawdust spaces of unequal volumes and that the blade surface is provided with at least one sawing cycle with larger sawdust spaces at the end of the sawing cycle than at the beginning of the sawing cycle.

[0008] The blade unit of the invention is characterized in that the saw blade is provided with larger sawdust spaces at the end of each sawing cycle than at the beginning of the sawing cycle.

[0009] According to an idea, the volume of a sawdust space in the saw blade is larger at the end of a sawing cycle than at the beginning of the sawing cycle. In other words, the size of the sawdust space is dimensioned to take into account the amount of sawdust produced during a sawing cycle, the amount being at its largest before the cutting by the chipper blade takes place.

[0010] An advantage of this is that the sawdust spaces of the saw blade are capable of receiving sawdust during a sawing cycle better than before, particularly at the end of the sawing cycle. As a result of appropriately dimensioned sawdust spaces in the saw blade and controlled production of sawdust less stress is caused to the blade teeth. This provides an opportunity to reduce the thickness of the saw blade. Hence major savings in raw materials may be achieved, as less sawdust is produced thanks to a smaller saw-slit. Sawing with a thin blade produces more chips, which attract a substantially better price than sawdust.

[0011] Moreover, the management of sawdust improves the saw cut of the saw blank and thereby timber quality. High-quality timber, in turn, naturally allows a better price to be obtained than timber in which sawdust penetrated between the saw blade and the saw blank has caused an uneven surface and dimensional variation to the blank.

[0012] In addition, the disclosed solution may be applied to increase chip length and hence new demands set by those further processing chippings can be met. A sawmill gets a better price from long chips than from short ones.

[0013] According to an embodiment, a radial distance from the outer edge of the saw blade to the bottom of the sawdust spaces is greater at the end of a sawing cycle than at the beginning of the sawing cycle. This means that the height of the blade teeth increases during a sawing cycle in a spiral manner but without changing the outer diameter of the saw blade. As the distance at the bottom of the sawdust space increases, the volume of the sawdust space increases accordingly.

[0014] According to an embodiment, a radius of curvature at the bottom of the sawdust spaces is greater at the end of a sawing cycle than at the beginning of the sawing cycle. Changes made to the radius of the curved sawdust space bottom allow the volume of the sawdust space to be acted on. The longer the bottom radius, the greater is the volume of the sawdust space.

[0015] According to an embodiment, the volume of the sawdust spaces increases evenly during a sawing cycle. In that case the height of a blade tooth, for example, may grow linearly between a starting point and an end point of the sawing cycle. Also the radius of curvature of the sawdust space bottom may grow evenly on a sawing cycle portion.

[0016] According to an embodiment, the volume of the sawdust spaces grows stepwise during a sawing cycle. In that case the height of a blade tooth, for example, may first remain constant at the beginning of the sawing cycle and then grow by one, two or more steps before the end point of the sawing cycle. Also the radius of curvature of the sawdust space bottom may grow stepwise during a sawing cycle portion.

[0017] According to an embodiment, the volume of the sawdust spaces grows exponentially during a sawing cycle. Hence the height of a tooth blade, the radius of curvature of the sawdust space bottom, or both, may grow exponentially during a sawing cycle portion.

[0018] According to an embodiment, the saw blade comprises one sawing cycle. This kind of front blade is used when the blade unit of the canter- edger is provided with only one chipper blade.

[0019] According to an embodiment, the saw blade comprises a plural number, for example two, three, four or more, sawing cycles. This kind of front blade is used when the blade unit of the canter-edger is provided with a plural number of chipper blades. The number of the chipper blades shows directly the number of the sawing cycles.

[0020] According to an embodiment, the saw blade comprises a blade body on whose outer circumference blade teeth are formed. Hence the blade body is a single uniform circular plate.

[0021] According to an embodiment, the saw blade comprises a blade ring having the shape of a substantially circular ring. The blade teeth are on the outer circumference of the blade ring, their outermost tips forming one outer diameter. The blade ring may be provided with one, two, three, four or more sawing cycles.

[0022] According to an embodiment, the saw blade comprises two, three, four or more blade segments substantially having the shape of a circular ring sector. The blade teeth are on the outer circumference of the blade segment and their outermost tips follow the same circular arc.

[0023] According to an embodiment, one blade segment corresponds to one sawing cycle. Hence one blade segment portion is provided with sawdust spaces having volumes unequal in size.

[0024] According to an embodiment, the thickness of the saw blade is 4 mm or less. If the saw blade is formed of blade components, i.e. of one or more blade elements, they also have the same thickness as above.

Brief description of figures

[0025] Some embodiments of the invention are described in greater detail in the attached drawings, in which

Figure 1 is a schematic view of a principle of a canter-edger seen from a longitudinal direction of a log;

Figure 2 is a schematic side view of a detail of a saw blade which is meant for a canter-edger and in which the height of the blade teeth changes on a sawing cycle portion;

Figure 3 is a schematic side view of a detail of a second saw blade which is meant for a canter-edger and in which the radius of curvature of the sawdust space bottom changes on a sawing cycle portion;

Figure 4 is a schematic side view of a blade unit with a saw blade and two chipper blades;

Figures 5a to 5c are schematic side views of some embodiments of a saw blade; and

Figure 6 is a schematic side view showing a saw blade made of four blade elements and different alternatives for a graph running through the bottoms of the sawdust spaces.

[0026] In the figures, some embodiments of the invention are shown simplified for the sake of clarity. Like reference numerals refer to like parts in the figures.

Detailed description of some embodiments of the invention

[0027] Figure 1 shows a structure of a canter-edger from a longitudinal direction of a log 1. The canter-edger comprises rotating blade units 2 that allow the log 1 to be shaped into a saw blank, i.e. a cant, having a substantially rectangular cross-section. Each blade unit 2 of the canter-edger comprises a sawing circular blade 3, known as a frontal blade, and a chipper part 4, which may be conical. The saw blade 3 first saws a surface piece 5 of a desired width from the surface of the log 1 , chipper blades 6 arranged to a chipper part 4 then chopping the sawn surface piece 5 into chippings. The saw blade 3 and the chipper blades 6 are interconnected and rotate simultaneously as the blade unit 2 is driven. Depending on the application, one or more chipper blades 6 may be provided. A portion of the saw blade 3 between the chipper blades 6 is called a sawing cycle 7. When a chipper blade 6 cuts the surface piece 5, a new sawing cycle always begins thereafter.

[0028] Figure 2 shows a detail of the outer circumference of the saw blade with a plural number of blade teeth 8 comprising a frontal surface 9 and a back surface 10. A blade tooth may have a tip part 11 that has been sharpened to provide a chipping surface or, alternatively, the tip of the blade tooth may be provided with a replaceable blade bit 12. Between successive blade teeth 8 there is a sawdust space 13. Both the back surface 10 of a blade tooth and the bottom 14 of the sawdust space 3 may be provided with bevels 15a and 15b, respectively, sloping from the outer edge of the blade to a side 3a facing the chipper part. The purpose of these bevels 15a, 15b is to guide sawdust away from the bottom of the sawdust space. Towards the end of a sawing cycle sawdust is not always capable of leaving the sawdust space well enough because at that point the blade teeth are between the saw blank and the surface piece and therefore lateral flow of sawdust is not possible. The saw blade 3 of the invention has a larger sawdust space 13 on the end part of the sawing cycle and therefore it is capable of receiving sawdust that cannot move away from the sawdust space 13. Distance L at the bottom 14 of the sawdust space 13 may grow towards the end of the sawing cycle, the volume of the sawdust space 3 thus increasing at the same time. A graph P running through the bottoms 14 of the sawdust spaces is marked in the figure by a line of dots and dashes.

[0029] In the embodiment of Figure 3 the radius of curvature R of the bottom of the sawdust space is smaller at the beginning of the sawing cycle than at its end. The radius of curvature R allows the volume of the sawdust space 13 to be acted on.

[0030] There are also other ways of arranging larger sawdust volumes to the end of a sawing cycle. The saw blade may be provided with a varying pitch of teeth. In that case a gap between the blade teeth may be ar- ranged to be wider at the end of a sawing cycle than at the beginning of the sawing cycle.

[0031] Figure 4 shows a blade unit 2 comprising an annular saw blade 3 and two chipper blades 6. In that case the saw blade 3 has two sawing cycles 7a and 7b, both of them having deeper bottoms of sawdust spaces 13 at the end part of the sawing cycle than at the beginning of the sawing cycles. In that case the height Ln of the blade teeth is greater at the end of the sawing cycles. Hence the circular blade 3 according to the figure has two spiral sawing cycles 7a, 7b.

[0032] Figures 5a to 5c show alternative constructions, highly simplified for the sake of clarity, of saw blades 3 of the invention. Figure 5a shows a blade 16 having the shape of a circular plate with blade teeth formed directly thereto. Figure 5b shows a blade element 17 having the shape of a circular ring that may be directly attached to a canter-edger, or it may be first attached to a disc-like blade body and then to a canter-edger. Further, the solution of the invention may be applied to circular saw blades of Figure 4c comprising two or more blade elements 8a to 18d having the shape of a circular ring sector. For the sake of clarity, Figures 5a to 5c do not show the blade teeth on the outer circumference of the saw blade and the sawdust spaces. In addition, arrows 6 in Figures 5a to 5c show where the chipper blades set when the saw blade is attached to the chipper part in the blade unit. In addition, fastening surface KP of the blade elements 17, 18, sawing surfaces SP and element body T are marked in Figures 4, 5b and 5c.

[0033] Figure 6 shows four blade elements 18a to 18d in the form of sectors of which the outermost portion of the saw blade 3 may be formed. Lines of dots and dashes P1 to P4 on a portion of the blade elements 18a to 18d depict different ways of arranging the depths of the sawdust space bottoms. Graph P1 in the blade element 18a illustrates that the bottoms of the sawdust spaces may change stepwise during a sawing cycle 7a. Graph P2 in the blade element 18b illustrates that the distance D of the bottoms of the sawdust spaces from the outer circumference may change evenly during a sawing cycle 7b towards the end part of the sawing cycle. Graph P3 in the blade element 18c illustrates an exponential change in the depth of the sawdust spaces. The blade element 18d represents prior art solutions in which the bottoms of the sawdust spaces extend on an equal distance from the outer edge. [0034] It should be mentioned that one application of a canter-edger in connection with sawing machines is what is known as a profiling machine, which also comprises a circular saw blade and a chipper blade. Consequently, the subject matter disclosed in this application also applies to a profiling device.

[0035] In some cases, features disclosed in this application may be used as such, irrespective of other features. On the other hand, when necessary, the features disclosed in this application may be combined to provide various combinations.

[0036] The drawings and the related description are only intended to illustrate the idea of the invention. The details of the invention may vary within the scope of the claims.