The invention relates to the method according to the introductory part of patent claim 1 for manufacturing a timber log.

In the prior art there is known a method for manufacturing a timber log- wherein a freshly cut log of wood is worked into a timber blank and this is dried in a drying oven with a temperature of most advantageously 40-60° C during several weeks, generally three weeks. After the drying stage, the moisture content in the wood is reduced to 10-15 %. The timber blank is worked into its final form, a log suited for building, such as a planed or round log, whereafter it is ready for use.

A drawback with the known method is its slowness. Another problem is the drying. The heart of a massive log dries remarkably slower than the surface part. In order to prevent the wood from splitting, the drying must be realized in a slow and controlled fashion, so that the inside of the log dries at the same pace as the surface.

The object of the present invention is to introduce a new method for manufacturing a log, owing to which method a log can be manufactured in a remarkably quicker fashion than before.

The method of the invention for manufacturing a log is characterized by the novel features enlisted in the independent patent claim.

In the method according to the invention for manufacturing a log, which log is meant to be used in building log houses or similar log structures, in the timber blank there is arranged a number of adjacent narrow, long and deep grooves running along the lengthwise direction of the timber blank, whereafter the timber blank is dried and worked to its final form to constitute a timber log.

A narrow and long groove here means a groove where the width-length ratio is for instance 1 : 100 or less. This kind of groove is made in the timber blank by means of a circular saw or a similar tool. A deep groove here means a groove where the width-depth ratio is for instance 1: 10 or less. Generally the grooves are arranged to extend in the vertical direction as far as the middle

section of the timber blank. It is also possible that the grooves extend throughout the whole timber blank.

It is an advantage of the invention that because parallel grooves extend deep into the wood material, this results in that at the drying stage, moisture is effectively removed of the middle part, heartwood, of the timber blank. It is a particular problem with drying massive pieces of wood that the outer layer dries faster than the heartwood, which generally leads to the splitting of the wood material. In the method of the invention, the drying of the heartwood is intensified, so that the drying takes place more evenly as regards both the outer layers and the heartwood, and thus the drying period can be remarkably shortened without a risk of splitting the wood. The drying period of a timber blank provided with parallel grooves is cut by 30-40 % and even more as compared to the drying period of a massive timber blank.

Another advantage of the invention is that the timber blank does not split when drying like a massive timber blank does. A particularly important factor with a timber blank and a log is that the vertical sides remain essentially unbroken and unsplit on the surface. This requirement set for the log is effectively realized by applying the present invention. Hence the quality of the timber blank and the log worked thereof is improved.

It is yet another advantage of the invention that the timber blank keeps well in measure and remains straight at the drying stage, it does not bend and twist as easily as a corresponding massive whole wood timber blank. Thus the quality of the timber blank and the final log is improved in this respect, too. A particularly advantageous feature from the point of view of the invention is to arrange the grooves in the timber blank (and further in the final log worked therefrom) in a symmetrical fashion. Now the possible twists and/or tendencies to bend owing to asymmetric working of the timber blank can be eliminated.

It is yet another advantage of the invention that the grooves are made in the timber blank so that they are not outwardly visible in a ready-made log when the logs are stacked for instance when building a wall or another similar construction. The grooves are arranged in the timber blank and in the log from either the bottom and/or top surfaces towards the heart, in which case the stacked logs cover the groove apertures.

It is yet another advantage of the invention that the natural good qualities of timber, such as a breathing composition and a pleasant appearance, are maintained.

A surprising advantage of the invention is the fact that the heat insulation capacity of the log manufactured of a timber blank is improved. The narrow grooves and advantageously the large number of parallel grooves, for instance six or more, effectively prevent heat from conducting in between the inner and outer surfaces of the log, and as a consequence the heat insulation capacity of this kind of log is clearly better than those of a massive whole wood log of the same size.

Yet another advantage of the invention is that the grooves are narrow, advantageously with a niinimum width of 5 mm, and relatively long, advantageously with a maximum length of 600-1,200 mm, in the lengthwise direction of the timber blank and the log. It is fairly simple to provide such grooves in the log; they can be sawn with a circular saw or a corresponding tool, for example adjacent grooves at the same time. Thus the creation of the grooves in the timber blank is a relatively simple and quick operation.

The invention is explained in more detail below, with reference to the appended drawings, wherein

figures la and lb are schematic illustrations of a log of wood and of a timber blank worked thereof, seen in perspective; figures 2a and 2b illustrate the timber blank in perspective when a groove is being sawn in it; figure 3 illustrates a grooved timber blank in perspective; figure 4 shows a transversal section A- A of the timber blank of figure 3; figure 5 shows a lengthwise section B-B of the timber blank of figure 4; figure 6 is a schematic illustration of the drying of timber blanks in a drying oven; figures 7a and 7b illustrate in perspective a log which is worked of the timber blank after drying; figures 8a and 8b are transversal sections C-C and D-D, respectively, of the logs according to figures 7a and 7b;

figure 9 shows a transversal section of a wall which is built of the logs illustrated in figures 7a and 8a; figure 10 shows a transversal section of a second timber blank; figure 11 shows a lengthwise section E-E of the timber blank of figure 10; figure 12 shows a transversal section of a third timber blank; figure 13 shoows a lengthwise section F-F of the timber blank of figure 12; figures 14a and 14b illustrate a fourth timber blank in perspective; figure 15 shows a transversal section G-G of a fourth timber blank; figure 16 shows a lengthwise section H-H of the timber blank of figure 15; figure 17 shows a fifth timber blank as seen from below; figure 18 shows a transversal section I-I of a fifth timber blank; figure 19 shows a lengthwise section J-J of the fifth timber blank; figure 20 illustrates a sixth timber blank in perspective; and figure 21 shows a transversal section K-K of the sixth timber blank.

Figures 1-8 illustrate a method according to the invention for manufacturing a log.

Figures la and lb show a log 1; la, lb, and the working plans drawn at the end thereof. According to figure la, the log of wood 1; la should be sawn into a timber blank 2; 2a which is quadrangular in cross-section and has a predetermined width 1 and height k. The width 1 and height k of the timber blank essentially correspond to the width and height of the planed log to be manufactured, but provisions for drying and working loss are taken into account in the measures. In figure lb, the log of wood 1; lb is meant to be turned into a round timber blank 2; 2a, circular in cross-section; the diameter d of the said timber blank essentially corresponds to the diameter of the round log manufactured of the log 1, when provisions for drying and working are taken into account. The conical shape of the original log is eliminated by working the log into an essentially cylindrical timber blank. The log, which is most advantageously peeled, can also be considered as a timber blank, particularly the blank of a round log.

The timber blanks 2; 2a, 2b worked of the log 1 are illustrated in figures 2a and 2b at a stage where a circular saw 3a, 3b is being used for sawing in the timber blanks 2; 2a, 2b essentially vertical grooves 4; 4a, 4b running along the lengthwise direction of the timber blank. The groove system is based on the idea that the timber blank 2; 2a, 2b is thought as divided, in the

transversal direction, into parallel groove zones 5; 5a, 5b, wherebetween there are left wood material zones 6; 6a, 6b. Both zones 5, 6, alternating in the transversal direction, are defined to be in cross-section at least roughly quadrangular areas which extend in the lengthwise direction of the timber blank from one end to another.

Advantageously the number of the parallel groove zones 5; 5a, 5b of the timber blank 2; 2a, 2b and at the same time the number of grooves 4; 4a, 4b is at least six. The number of grooves must be sufficient in order to ensure an effective drying. The parallel grooves 4 are arranged in the cross-section plane of the timber blank in the vertical middle area 7; 7a, 7b thereof, most advantageously in a symmetrical fashion (in the middle of the timber blank, with respect to an imaginary vertical axis and the vertical plane passing therethrough). On both vertical sides of the timber blank 2; 2a, 2b, there is left a relatively thick - thickness for instance 25-35 mm - and essentially unbroken side wood material layer 8; 8a, 8b; 9; 9a, 9b. In the case of a round log blank 2b, the maximum thickness of the side wood material layer can be remarkably larger, for instance 50-70 mm.

In this embodiment, each groove zone 5; 5a, 5b of the timber blank 2; 2a, 2b comprises one narrow and long groove 4; 4a, 4b, which extends from the surface of the timber blank to at least the middle area thereof. In this case the grooves 4; 4a, 4b belonging to the groove zones 5; 5a, 5b are arranged to extend, in the lengthwise direction of the timber blank, from the first end 23 a to the second end 23b thereof, so that they begin and end at a slight distance, at least, from the free ends of the timber blank 2; 2a, 2b.

Figures 3, 4 and 5 illustrate a timber blank 2; 2a after the grooves 4 are worked, for instance sawn, in the planned groove zones 5 thereof in the fashion illustrated in figure 2a. In cross-section the timber blank 2; 2a is quadrangular, but it can also be a round, cylindrical timber blank 2b, as is indicated by dotted lines in figure 4. Now the grooves 4 are arranged to extend from the top surface 2c of the timber blank to a relatively small distance, for instance 1/5 of the height k of the timber element, from the bottom surface 2d of the timber blank. The bottom part 10 of the timber blank now interconnects the vertical wood material zones 6 in between the grooves 4. On the sides of the timber blank 2, there are also left the side wood material layers 8, 9. The grooves 4 begin (and end) at a distance a from the

end 23; 23a, 23 b of the timber blank. Advantageously the distance is of the order 5-15 cm.

Next the timber blank 2; 2a, 2b, provided with a number of parallel grooves 4, is dried.

The timber blank is dried in similar fashion as sawn goods in general. The timber blanks 2; 2a, 2b are stacked to suitable drying piles in a drying carriage, whereafter they are put in a drying oven with a temperature of the order 40-60° C. When the moisture content of the timber blanks is reduced to for instance 15 %, they are removed from the oven. It is pointed out that owing to the grooves 4, the timber blank 2; 2a, 2b is not massive, uniform wood material anymore, but is divided into fairly thin wood material sections: to wood material zones 6; 6a, 6b and to side wood material layers 8; 9; 8a, 9a; 8b, 9b. Now the timber blank 2; 2a, 2b can be dried nearly as quickly as a sawn wood piece of the same size as the side wood material layers 8, 9. The side wood material layers 8, 9 are the thickest uniform wood material parts in the timber blank 2; 2a, 2b.

Figure 6 illustrates an advantageous way of drying a timber blank. For drying, the timber blanks 2, 2a are piled for instance in splinted drying stacks 11 in a carriage 13. In the drying stack 11, the timber blanks 2; 2a rest on top of each other, side against side, so that in between them there are placed strips 12. Moreover, the timber blanks 2; 2a are arranged in the drying stack 11 so that there are two blanks 2; 2a side by side, i.e. they form the adjacent stack elements 1 la, 1 lb, and that the top surfaces 2c of the timber blanks 2; 2a are directed outwards from the drying stack 11, and likewise the grooves 4 in the groove zones 5 open outwards therefrom. The drying stack 11 is pushed in the carriage 13 into the drying oven 14, and the hatch thereof (not illustrated in the drawing) is closed. Drying air is blown into the drying oven 14 for example through air channels 15, 16 provided at the sides thereof. The blowing of drying air is most advantageously carried out in the lengthwise direction of the grooves 4, so that drying air (arrows) has access to penetrate into the grooves 4 of the timber blanks 2; 2a to wash the grooves and/or to circulate therein. This intensifies the drying of the heart of the timber blanks 2; 2a.

After drying the timber blanks, each blank is worked to a log with a desired profile. A quadrangular timber blank 2; 2a is processed into a planed log 17, in which case the top edges of the timber blank 2; 2a are cut to form for example slanted areas 18, and a provision 19 is cut in the bottom surface thereof, as is apparent from figures 7a and 8a. In similar fashion, the cylindrical timber blank 2b with a round cross-section is processed into a round log 20 so that it reaches its final diameter, and a provision 21 is cut on its bottom surface, as is apparent from figures 7b and 8b.

The ready-made log, such as a planed log 17, is used to construct for instance the frame of a building. In this case the logs 17 are stacked, a strip of insulation 23 is matched therebetween, and they are tenoned together to form a compact structure, as is seen in the cross-section of a log wall 22 in figure 9. Now the grooves 4 remain hidden inside the wall structure. One log 17b laid on top of another log 17a covers the grooves 4 in the central area 7 of the log 17a.

A second timber blank 31 suited in the production method according to the invention, is illustrated in figures 10 and 11. In each groove zone 5 of the timber blank 31, there are provided two narrow, long and deep grooves 25, 26. The first groove 25 of each groove zone 5 is arranged to extend from the top surface 3 la of the timber blank 31 downwards to the central area of the timber blank, and the second groove 26 from the bottom surface 3 lb of the timber blank 31 upwards to the central area of the timber blank. In between the grooves 25, 26, in the middle of the timber blank, there now remains a relatively narrow horizontal middle part 27, which interconnects the parts 29, 30 of the wood material zone 6 located in between the grooves 25, 26. The cross-section of a planed log 3 lc processed of the timber blank 23 is indicated with dotted lines in figure 11.

A third timber blank 32 suited in the production method according to the invention is illustrated in figures 12 and 13. Each groove zone 5; 5a, 5b of the timber blank 32 is provided with a narrow, long and deep groove 33; 33a, 33b; 34. In this embodiment, in the parallel groove zones 5a, 5b separated by the wood material zones 6, the grooves 33, 34 are arranged so that in the first groove zone 5a, the groove 33; 33a, 33b is arranged to extend from the bottom surface 32b of the timber blank 32 upwards, to relatively near the top surface 32a of the timber blank, and in the second groove zone 5b the groove

34 is arranged to extend from the top surface 32a of the timber blank 32 downwards, to relatively near the bottom surface 32b of the timber blank. This alternating groove arrangement is repeated horizontally throughout the timber blank 32. A cross-section of a planed log 32c processed of this timber blank 32 is indicated with dotted lines in figure 12.

A third timber blank 32 is advantageously realized so that the grooves 33a, 33b nearest to the vertical sides of the timber blank 32 are directed from the bottom surface 32b of the timber blank towards the top surface 32a. It is an advantage of this arrangement that the first grooves in the top surface of the log processed of the timber blank are fairly far away from the vertical sides, which makes it difficult for possible rain water to flow into the grooves. It is well known that water in the grooves causes rotting of the wood.

A fourth timber blank 36 suited in the production process according to the invention is illustrated in figures 14a, 14b, 15 and 16. In this embodiment, in the groove zone 5; 5a, 5b of the timber blank 36 there are arranged successive narrow, long and deep grooves 37; 371, 372, 373; 38; 381, 382, 383, and therebetween, in the lengthwise direction, wood material tongues 39; 391, 392; 40, 401, 402, which tongues are short in comparison with the length of the grooves; the said tongues are arranged so that the wood material tongues 39; 391, 392; 40; 401, 402 of adjacent groove zones 5; 5a, 5b are located essentially in the same wood material tongue area 41; 411, 412 on the transversal plane of the timber blank 36.

In this embodiment, figures 14a, 14b, 15 and 16, the grooves 37, 38 in adjacent groove zones 5a, 5b separated by wood material zones 6 are arranged so that in the first groove zone 5a, the groove 37 is made to extend from the bottom surface 36b of the timber blank 36 upwards to fairly near the top surface 36a of the timber blank, and in the second groove zone 5b the groove 38 is made to extend from the top surface 36a of the timber blank 36 downwards to fairly near the bottom surface 36b of the timber blank 36. This alternating groove system is repeated horizontally throughout the timber blank 36, as is apparent from figures 15 and 16. A cross-section of a planed log 36c processed of this timber blank 36 is indicated with dotted lines in figure 15.

The ratio of the lengths of the wood material tongues 39, 40 of the groove zone 5; 5a, 5b to the lengths of the grooves 37, 38 in the lengthwise direction of the timber blank 36 is advantageously of the order 1:5-1:15. The length of the wood material tongues 39, 40 of the groove zone 5; 5a, 5b in the lengthwise direction of the timber blank 36 is of the order 10-15 cm, but it can also be smaller, and respectively the length of the grooves 37, 38 in the lengthwise direction of the timber blank 36 is of the order 60-120 cm. The advantage of this embodiment is that the rigidity and cohesion of the timber blank and of the log processed thereof are improved as compared to earlier applications. It is another advantage that the log processed of the timber blank can be cut to measure at the wood material tongues 41.

Figures 17, 18 and 19 illustrate a fifth timber blank 43 suited in the production process according to the invention. In each groove zone 5 of the timber blank 43, there are provided, in principle in the same fashion as in the previous embodiments of figures 14A, 14B, 15 and 16, successive narrow, long and deep grooves 44; 441, 442, 443; 45; 451, 452, 453, and therebetween, in the lengthwise direction, wood material tongues 46; 461, 462; 47; 471, 472, which tongues are short when compared with the length of the grooves. In this embodiment, the grooves 44, 45 of adjacent groove zones 5a, 5b are arranged to be directed from the bottom surface 43b of the timber blank 43 towards the top surface 43a. Now the cross-section of the timber blank 43 at the grooves 44, 45 corresponds to figure 18. Moreover, in this embodiment the grooves 44; 441, 442, 443; 45; 451, 452 and the wood material tongues 46; 461, 462; 47; 471, 472 belonging to the groove zone 5 of the timber blank 43 are arranged so that the wood material tongues 46; 461, 462; 47; 471, 472 of adjacent groove zones 5a, 5b are placed in an at least partly overlapping fashion with respect to each other in the transversal direction of the timber blank 43. Now the wood material tongues 46; 461, 462; 47; 471, 472 do not form a uniform wood material tongue area throughout the timber blank in the transversal direction thereof, as was the case in the embodiment of figures 14a, 14b, 15 and 16, but the wood material tongues 46; 461, 462; 47; 471, 472 of adjacent groove zones 5a, 5b overlap with the grooves 44; 441, 442, 443; 45; 451, 452, as is illustrated in figures 17, 18 and 19. A cross-section of a planed log 43c processed of this timber blank 43 is indicated with dotted lines in figure 18.

A fifth timber blank suited in the production process according to the invention is illustrated in figures 20 and 21. In this embodiment, in the groove zone 5; 5a, 5b of the timber blank 48, there are provided successive narrow and long grooves 49; 491, 492, and in the lengthwise direction therebetween, there are provided wood material tongues 50; 501, which tongues are short in comparison with the length of the grooves. The said tongues are arranged so that the wood material tongues 50; 501 of adjacent groove zones 5; 5a, 5b are located essentially in the same wood tongue area 51; 511 on the transversal plane of the timber blank 48. In this embodiment, the grooves 49 of the groove zone 5 of the timber blank 48 are made to pass through the timber blank 48, from the bottom surface 48b to the top surface 48a thereof, and/or vice versa. In between two groove zones 5; 5a, 5b, there is now left a wood material zone 6. A planed log 48c processed of this timber blank 48 is indicated with dotted lines in figures 20 and 21.

The width of the grooves 4; 25, 26; 33, 34; 37, 38; 44, 45; 49 of the timber blank 2a, 2b; 23, 32, 36, 43, 38 is 5 mm at the maximum, advantageously 3.0- 4.0 mm, but they can be even narrower, such as 1.0-1.5 mm. The width of the wood material zones 6; 6a, 6b located in between the grooves in the transversal direction of the timber blank 2a, 2b; 23, 32, 36, 43, 48 is 10 mm at the maximum, advantageously 5-8 mm.

The number of adjacent grooves 4; 25, 26; 33, 34; 37, 38; 44, 45, 49 in the timber blank 2a, 2b; 23, 32, 36, 43, 48 is at least six, advantageously ten, even twelve or more.

The adjacent grooves 4; 25, 26; 33, 34; 37, 38; 44, 45; 49 of the timber blank 2a, 2b; 23, 32, 36, 43, 48 are arranged on the transversal plane of the timber blank, symmetrically in the middle area 7; 7a, 7b thereof, so that at the sides of the timber blank, there is a relatively thick - with a thickness of for instance 20 mm, advantageously 25-30 mm - and essentially unbroken side wood material layer 8, 9; 8a, 9a; 8b, 9b (for example figures 2a and 2b).

The grooves 4; 25, 26; 33, 34; 37, 38; 44, 45, 49 of the timber blank 2a, 2b; 23, 32, 36, 43, 48 are advantageously arranged to begin and start at a slight distance, such as 5-15 cm, from the free end 23; 23a, 23b of the timber blank, as is illustrated in the drawings.

When seen from the side, the grooves 4; 25, 26; 33, 34; 37, 38; 44, 45, 49 of the timber blank 2a, 2b; 23, 32, 36, 43, 48 are at both ends provided with curved parts 28, as is apparent from figures 5, 11, 13 and 16, among others. The grooves 4; 25, 26; 33, 34; 37, 38; 44, 45; 49 are made in the timber blank 2a, 2b; 23, 32, 36, 43, 48 advantageously by means of one circular saw blade (cf. figures 2a and 2b) or with several parallel circular saw blades, which blades are pressed to a suitable depth into the timber blank while working the grooves. According to the shape of the said blades, both ends of the grooves 4; 25, 26; 33, 34; 37, 38; 44, 45; 49 obtain their curved shape. Now the ends of the timber blank 2a, 2b; 23, 32, 36, 43, 48 are left unbroken, so that for instance at a protruding log corner, the ready-made log appears as a normal massive log.

In the above specification, the invention is explained mainly with reference to a few preferred embodiments, but it is naturally clear that the invention can be modified in many different ways within the scope of the inventional idea defined in the appended patent claims. For instance, the timber blanks illustrated in the drawings are essentially quadrangular in cross-section, but they can also be round or oval or have some other geometric shape.