EP1432559B1

EP1432559B1 - Sawing method and apparatus

Info

Publication number: EP1432559B1
Application number: EP02718228A
Authority: EP
Inventors: Asko PERTTILÄ
Original assignee: Mairtek Ky
Current assignee: Mairtek Ky
Priority date: 2001-04-25
Filing date: 2002-04-25
Publication date: 2006-03-01
Anticipated expiration: 2022-04-25
Also published as: DE60209472T2; FI20010865A; RU2288836C2; FI20010865A0; RU2003134541A; WO2002085585A1; EP1432559A1; FI112453B; DE60209472D1; ATE318684T1

Abstract

The invention concerns a sawing method for compensating drying spirality of sawn timber. According to the invention, the drying spirality of a sawing blank and/or sawn timber sawn from a tree trun (1) is measured or estimated, and the tree trunk (1) is sawn with a counter spirality compensating the drying spirality, wherein the sawn surface (8) turns around the tree trunk so, that the angle (K) between the line segment (11) defined by saw blades/blade edges (2) and the comparative line segment (10) defined by the center point (6) of the cross-sectional profile of the tree trunk changes. The invention also concerns a sawing apparatus for compensating the drying spirality of sawn timber.

Description

The present invention concerns a sawing method according to the preamble of claim 1 for compensating the drying spirality of sawn timber.
The invention also concerns a sawing apparatus according to claim 8 for compensating the drying spirality of sawn timber, (see for example WO-A-0012230).
After a tree trunk has been sawn into sawing blanks like blocks, the sawing blank is sawn into desired sawn timber with a certain setting. When the sawn timber is dried to the moisture content depending on the usage (0...24%), it is often twisted propeller-like around its longitudinal axis. The propeller-like distortion of the sawn timber during drying is caused by many different factors, generally called spiral grain of the wood. The best description of the drying spirality is given by publication NR. 97 of VTT (Technical Research Center of Finland) of 1997; Decreasing the distortion of sawn timber by means of drying.
Tree trunk in this connection refers to pruned small sized wood, trunk or sawn logs (timber).
Trees almost always grow as twisted. Spirality is not constant, but it can be spiral even in different directions with the same wood species and within an individual tree. In the Northern Hemisphere, the cells of the heartwood usually are spiral to the left and the cells of the sapwood to the right, whereby it is difficult to foretell the direction and degree of spirality of a certain tree trunk. When the trunk then is chipped into a balk and the balk is sawn with a certain setting into sawn timber to be dried to a certain moisture content, the amount of drying spirality of the final dried sawn timber is not easily predictable. The biggest problem is caused when the sawn timber or the final products made of it are twisted already before delivery to the site. The construction work becomes more difficult and the final result does not correspond to the expectations. Waste of material and additional costs are caused for the carpentry, when both sides of the pieces must be straightened. According to the above-mentioned publication of VTT, the working losses and operation disturbances caused by distortion are evaluated to cause losses of several ten millions of marks in Finland annually.
In this connection, reference is made to the publication NR. 562 of VTT, by Pertti Viitaniemi, Twisting of spruce, Espoo 1988, disclosing factors having influence on the drying spirality of the sawn timber made of spruce. Drying spirality indicates twisting of sawn timber around its longitudinal axis. According to the publication, these factors having influence on the drying spirality are differences of the grain angles of different flats of the sawn timber and the amount of the juvenile wood in the sawn timber and the point, when the grain angle has reversed. On the last mentioned fact is affected, among other things, the growth rate and changes in the wind conditions. Juvenile wood is the part of the heart of wood, where the grains are twisted prominently and the cells shrink more in the longitudinal direction than those of normal wood during drying.
Shrinking during the drying occurs most of all in sawn timber, in which the heartwood is in the middle of the sawn timber piece. Drying spirality causes problems also with the sawn timber received from wood sawn on the equator and in the Southern Hemisphere. In the Southern Hemisphere the cells of trees twist in young trees to the right and later to the left. The same investigation shows, how the drying distortion, in other words the drying spirality is measured.
When using sawn timber with drying spirality for constructions, they are nearly always subject to construction defects due to the distortion of the sawn timber. If the sawn timber is after pressure drying exposed to changing moisture conditions or dries more, it twists still more, which impedes the final treatment and usage of the sawn timber.
There are several ways to measure the grain angle of the cells of a tree trunk an/or a sawn timber blank and a sawn timber piece. These measuring methods have been described e.g. in diploma work "Spiral grain-measuring and modeling", 18.12.1996 by Marjaana Sävilammi. The same publication discloses a definition for grain angle of tree, also used in this application, which means the deviation of the wood fiber, that is the wood cells from the direction of the longitudinal axis of the trunk in the plane of the tangential-longitudinal axis. Based on grain angles measured in certain points of the trunk, it is possible to forecast the average grain angle in the whole trunk. Instead of this, it is more difficult to forecast the average grain angle of sawn timber sawn from a tree trunk with a certain blade setting and the differences between the grain angles of different parts of the sawn timber (e.g. flat surfaces) and their influence on the spirality of the timber based on grain angle values measured from individual points of the trunk, since the drying spirality of sawn timber pieces is influenced among others by the aforementioned differences between the grain angles of the different flat surfaces of the sawn timber and the amount of the juvenile wood in the sawn timber, the location of the juvenile wood with respect to the cross-section of the sawn timber piece and the number of right-threaded and left-threaded growth rings in the sawn timber.
Blade setting in this application refers to the kind of sawn timber to be sawn up from a saw log received from a certain tree trunk/log. Depending on the diameter of the saw log, usually two or more battens or blanks or one balk and a variable number of boards are received. The (blade) setting used for the log depends on the sawing method and on the diameter of the log to be sawn. With respect to the settings, reference is made to the literature of the art.
Nowadays, the mostly used way to try to avoid the above mentioned drying spirality of sawn timber is to use a slow and even drying process. One disadvantage of this method is the slowing up of the drying process. In addition, attempts have been made to decrease the drying spirality of wood by stacking the timber under pressure during drying, so that the distortion is prevented. The problem with the above mentioned method is that there are stresses left in the wood, that can break up later, for example when the moisture content of the wood changes, thus causing twisting of the wood.
The object of the present invention is to solve the problems occurring in the technology of prior art referred to above. Thus, the main target of the invention is to provide a method and apparatus, by which it is possible to decrease spirality of the sawn timber without increasing the drying time or without leaving stresses in the wood, that could break up later.
The objects according to the present invention can be reached by means of a method according to claim 1 and an apparatus according to claim 8.
The method in accordance with the invention is based on the experience, that the influence of the grain angles of the saw logs to be sawn, on the drying spirality of the sawn timber can be forecast with certain accuracy. It is possible to measure, calculate and/or evaluate the drying spirality, and based on this grain angle values and other values measured and/or evaluated from the sawn timber it can be forecasted with adequate reliability. In a forecast, it is in most cases taken into account, how the grain angles discovered in the earlier sawn tree trunks have correlated with the drying spirality discovered in the dried sawn timber received from the same.
The method in accordance with the present invention is based thereon, that the angle between the line segment defined by the saw blades and the line segment defined by the mathematical center point of the trunk in the cross-sectional profile of the trunk, is subjected to a controlled deviation, which is the contrary to the estimated, measured or forecasted drying spirality of the trunk/sawing blank/sawn timber. When estimating the drying spirality, at least the following is preferably taken into account: grain angles, (saw blade) setting, drying degree of the sawn timber and the growth speed of the tree, which can be measured by means of automatic meters. In addition, generally also summer growth percentage, diameter of the trunk and the temperature of the trunk to be processed, quality, form, amount of knots of the trunk and the wood species are taken into consideration.
Sawing plane refers here to the plane defined by the longitudinal axis of the blades. In general the trunk is sawn in a certain sawing phase, like when sawing square timber, with two parallel blades, which means that there are also two sawing planes.
The certain reference line segment defined by the center of the cross-sectional profile of the trunk is mostly a fixed vertical or horizontal line, in case the trunk is moved forward on the sawing line without rolling it. In case the trunk is rolled, the reference line segment defined by the center of the trunk is selected to be any line segment passing via the mathematical center of the trunk.
In known sawing methods, the angle between the sawing plane defined by the blades and the longitudinal section plane defined by the center of the trunk remains unchanged during the sawing. The grain angle appearing in various parts of the sawn timber is variable, which causes stresses in the timber during drying of the timber, said stresses causing drying spirality.
In the sawing method in accordance with the present invention for compensating the drying spirality of the sawn timber, grain angles of the trunk are measured and/or estimated, and based on said grain angles, the drying spirality of the sawing blank and/or sawn timber is estimated or/and calculated. It is also possible to measure and/or estimate drying spiralities of the sawn timber in other ways. After that, the trunk is sawn with a counter spirality that compensates the drying spirality, whereby the sawn surface turns around the trunk so that the angle between the line segment defined by the saw blades and the comparative line segment defined by the mathematical center of the cross-sectional profile of the trunk changes.
In this connection the word "estimate" refers to functions, according to which the final drying spirality of the sawn timber is estimated based on some physical or chemical variable of the wood, eventually by means of computational tools. Often used for estimation are the earlier drying results of the wood.
As per method in accordance with the present invention, a counter spirality compensating the drying spirality of the sawn timber is sawn to the trunk. When sawing, it is thus possible to take into account the influence of the grain angles of the wood on the drying spirality of the dried sawn timber, which offers a prominent advantage of being able to provide a controlled counter spirality of the sawing blank, whereby the sawn timber made of the sawing blank is straightened and its quality is essentially improved. Also pressure stacking is used during drying for achieving straight timber.
According to the method, in addition, the grain angles of the sawing blank are generally measured and/or estimated before sawing and immediately after sawing or already during sawing, and based on the mentioned grain angles, the compensation of the drying spirality is adjusted by turning the angle between the sawing plane and the longitudinal section plane defined by the center line of the trunk. Thus, when measuring the spirality of the trunk, also measurements of the sawn surface of the balk or some other sawing blank immediately after the sawing, or even during the sawing can be utilized. Thereby the grain angle of the cells of the trunk at the sawing point can be measured and the influence of the grain angle on the drying spirality of the sawn timber made of the respective sawing blank can be mathematically calculated and forecast. The grain angle is preferably measured immediately after the saw blade like balk chipper.
The invention also concerns a sawing apparatus for compensating the drying spirality of the sawn timber, whereby the sawing apparatus comprises a feeding device and a receiving device and saw blades. In this sawing apparatus, it is possible to change the angle between the sawing plane defined by the saw blades and the longitudinal section plane defined by the center of the trunk attached to the feeding device and the receiving device. In addition, the sawing apparatus comprises a measuring device for measuring and/or estimating the grain angles of the trunk. Preferably the sawing apparatus further comprises a data processing system having means for saving the measured and/or estimated grain angles of the trunk and for comparing those with earlier measured grain angles of trunks.
The counter spirality to the sawing blank can be made either so that the trunk is rolled by means of the feeding and receiving means of the trunk moving system or, alternatively, so that the rolling of the trunk is prevented and the log or the trunk is fed to the sawing device the butt or top ahead by means of the trunk moving system, and the saw blade(s) like balk chipper blades turn with respect to the longitudinal section plane defined by the center of the trunk, thus achieving the same result as by rolling the trunk.
The above-mentioned methods can also be used simultaneously together. The total rolling angle, by which the trunk has been rolled, can preferably be calculated mathematically by measuring the length of path and the speed of the trunk during the sawing, as well as the momentary rolling angle from the angle between the sawing plane and the comparing plane defined by the center line of the trunk used in the comparison. The rolling angle of the trunk can also be identified optically by using a reference line drawn onto the end or sides of the trunk.
If the trunk is not rolled, but the saw is rolled around the trunk, the local rolling angle and the total rolling angle calculated thereof, can be received by technical, mathematical and mechanical means.
Figure 1 describes operation of the method in accordance with the present invention, realized with a sawing apparatus in accordance with the invention.
Figure 2 illustrates the sawn surface achieved by means of the method.
Figure 3 illustrates the sawing co-ordinate used in the apparatus described in figure 1.
In the following, the practical implementation of the method in accordance with the present invention will be illustrated with reference to figure 1. The (saw) log 1 is brought to the saw table 3 through feeding device 4 of the log moving means. In the case of said figure, blades 2 of the balk chipper and the feeding device 4 and the receiving device 7 of the log moving means saw by means of two blades the trunk into a balk with a certain spirality. The spirality of the balk is achieved by rolling the log 1 by means of the feeding device 4 and the receiving device 7 as regards to the sawing plane defined by the blades 2, with respect to the sawing table 3. Thereby the balk receives a sawn surface turning around the trunk as described in figure 1. The sawn surface is described in more detail in figure 2. After the blades 2 of the balk chipper there is provided a receiving device 7, which further rolls the trunk after it has passed the feeding device 4. The receiving device 7 can be in its basic design either a roller 9, which can be turned in respect of the sawing plane 6 or a wheelwork 9, which can be rolled along the sawn surface 8. The sawing planes are defined by the blades 2 of the balk chipper. The spirality is made to the certain trunk length based on the desired rolling angle, where by the turning angle defines the dimension of the counter spirality to be processed to the length of the trunk.
The sawn surface 8 processed to the balk by means of the apparatus in accordance with figure 1 is illustrated in figure 2. The sawn surface 8 turns propeller-like around the centerline L of the trunk, said line being defined by the center point 6 of the sawn balk.
The co-ordinates used in the apparatus of figure 1 are described in more detail in figure 3 illustrating the log at its sawing point as a schematic cross-sectional figure. A line section 11 is defined by the saw blades 2 of figure 1. A comparative line segment 10 is defined by the mathematical center point of the trunk. The comparative line segment 10 can be determined e.g. mathematically. When the trunk is rolled around its centerline, the angle K between the comparative line 10 drawn on the cross-sectional profile and the line parallel to the blades changes. Angle K is formed between the comparative line and the lines defined by blades, said angle expressing how much the sawing plane has rolled compared to the comparative plane defined by the comparative line segment.
The decision how much and to which direction the log 1 has to be rolled, depends on the twisting of the tree during its growth, that is the spiral grain angles and its location in the wood material (heartwood /sapwood) and the differences between the grain angles of the cells. Because the grain angles are mostly measured relatively close to the surface of the trunk or the sawing blank, and the sawn timber is dried later, the influence of the grain angles measured or estimated in a fresh trunk or sawing blank like balk on the spirality of dried sawn timber must be generally estimated. The estimation is preferably performed with a data processing system using fuzzy self-learning logic. The program must consider at least the respective blade setting, because the sawn timber received of a certain trunk results in different drying spiralities with different sawn timber pieces, depending e.g. on the amount of juvenile wood and dextro-spiral wood in these sawn timber pieces. Because the spirality in a certain trunk can change many times, it must be known or estimated either empirically or mathematically, how and in which part of a certain sawn timber piece the wood material with the different grain angle will be located. A self-learning data processing system can be utilized here, for controlling the controlling logic of the angle between the sawing plane and the comparative plane defined by the centerline of the trunk in the sawing process. In this kind of a self-learning data processing system, that is a system using fuzzy logic, the sawing history of the previous sawing blanks/sawing timber pieces and the drying history and the drying spirality of the sawn timber are taken into account, and, based on the grain angles of the sawing blank or trunk, the drying spirality of the sawn timber is estimated.
In a data processing system for controlling in a log sawing process the control logic of the means for changing the angle between the sawing plane and the comparative plane defined by the center line of the trunk, also the outer dimensions of the trunk or the sawing blank and the final drying percentage of the sawn timber must be generally taken into account. The total spirality of the trunk can be measured, detected and calculated by using different measuring methods. By means of these measuring values and mathematical formulas and based on programmatic measures, the rolling of the trunk 1 with respect to the sawing plane 6 is performed by using the feeding device 4 and the receiving device 7. When rolling the log, the instantaneous turning angle between the comparative plane 10 fixed in the trunk and the sawing plane 6 illustrated more clearly in figure 2 is changed, and said rolling angle can be calculated from the angle between the comparative plane and the sawing plane. In most cases the rolling is performed so that the instantaneous rolling angle is changed evenly, when the trunk moves forward on the sawing line. The respective rolling moment, rolling angle and the rolling mechanics is dependent on the mechanical and programmatic solutions of the sawing apparatus and the data processing device and control logic connected thereto (not shown in the drawing).
The rolling of the log implemented by means of the measuring methods and the measuring values based thereon, as well as by means of the feeding device 4 and the receiving device 7, is based on the blade setting, drying degree of the sawn timber, growth speed of the tree, density of the growth rings of the tree, base and top measures, cross-grain, crooked-growth, amount of snags and knots, ovality, coning angle, grain angles of the sapwood and/or heartwood cells, age, summerwood and juvenile wood percentage, moisture content, temperature of the log, final moisture content of the sawn timber, quality of logs, species of wood, experimental and statistical measuring history and material, as well as on the combinations and/or partial weightings of the above mentioned measuring values.
Taken into account when controlling the magnitude of the rolling angle of the log 1 at a certain moment is the grain angle and form/quality data given by the measuring device 5 of the spirality, and the distance of the feeding device 4 from the sawing point, the instantaneous rolling angle and rolling moment. The measuring device 5 can be located even in a different room than the saw and the feeding device 4 itself. In that case, however, the measured logs and their measuring information must be saved, and the moving of the logs on the sawing line followed, so that when the log comes to the blades of the balk chipper 2, the respective data and rolling angles can be fed to the feeding device 4 and the receiving device 7. There can be a number of measuring devices 5 of the grain angle, and grain angles can be measured with them also from the sawn timber, and these results can be used for adjusting the rolling degree of the feeding device 4 and the receiving device 7.
The method in accordance with the invention further preferably comprises evaluation of the sawing result, mathematical evaluation, recognition of the sawn spirality and measuring of the grain angles of the cells of the wood immediately after sawing, and, based thereon, eventual readjustment of the rolling of the log by means of the feeding device 4 and the receiving device 7, based on the feed-back.
The most advantageous place for measuring the spirality is immediately after the receiving device 7. Thus, the spirally sawn balk can be sawn immediately on the same sawing table or on a separate sawing table to sawn timber, or this sawing can be performed later. The sawing to sawn timber is performed according to the chosen blade setting. The sawn timber has then certain spirality. When the sawn timber is dried into the chosen drying degree (generally 0-30 %), it is straightened during the drying.
Above is described only one embodiment of the sawing method according to the present invention and of the sawing apparatus used therein, but it will be clear for skilled in the art, that the invention can be implemented in many other ways within the scope of the invention, which is defined by the appended claims.
Thus, the receiving device 7 can also be a knife or rail control running on the surface of the log along the sawing line and turned according to the spirality sawn to the log. The knife is preferably suitable for total device solutions with a band saw and a rotary saw. Instead of a balk chipper, also other possible saws like band saws and/or rotary saws and/or circular saws can be used.

Claims

A sawing method for compensating the drying spirality of sawn timber, characterized in that
- the drying spirality of a sawing blank and/or sawn timber sawn from a tree trunk (1) is measured or estimated and

- the trunk (1) is sawn with a counter spirality compensating the drying spirality, whereby the sawing surface (8) is turned around the trunk so that angle (K) between the line segment (11) defined by the saw blades/blade edges (2), and the comparative line segment (10) defined by the center (6) of the cross-sectional profile of the trunk changes.
The method in accordance with claim 1, characterized in that grain angles of the trunk (1) are measured and/or estimated, and based on said grain angles, the drying spirality of the sawing blank and/or sawn timber is estimated or/and calculated.
The method of any of the aforementioned claims, characterized in that the angle (K) is changed by rolling the tree trunk (1) around its longitudinal axis, by means of a feeding device (4) and a receiving device (7).
The method of any of aforementioned claims, characterized in that the angle (K) is changed by turning the blades/blade edges (2) of the sawing device with respect to the center line (L) of the tree trunk.
The method of any of the aforementioned claims, characterized in that in said method, additionally, the grain angle of the sawing blank is measured and/or estimated immediately after the sawing or during the sawing, and, based on said grain angle, the counter spirality compensating the drying spirality is adjusted by changing the angle (K) between the line segment (11) defined by the saw blades and the center line (L) of the tree trunk.
The method of any of the aforementioned claims, characterized in that the grain angles are estimated and/or measured by means of an optical method like laser measuring or a method based on electrical characteristics of the wood, like a capacitance sensor.
The method of any of the aforementioned claims, characterized in that based on the grain angles of the tree trunk (1), the drying spirality of the sawing blank and/or sawn timber is estimated or/and calculated taken into account the drying degree of the sawing blank and/or sawn timber, conic angle of the tree trunk, growth speed of the tree, type and quality classification of the sawn timber to be sawn from the sawn blank and/or grain angle measurements of earlier tree trunks and the drying spirality generated to the sawn timber based on those.
A sawing apparatus for compensating the drying spirality of sawn timber, wherein said sawing apparatus comprises saw blades and a transferring device of wood including a feeding device (4) and a receiving device (7), characterized in that the sawing apparatus comprises measuring means for measuring and/or estimating grain angles of the tree trunk and means for sawing a sawn surface (8) turning around the tree trunk so, that the angle (K) between the line segment (11) defined by the saw blades or blade edges (2) and the comparative line segment (10) defined by the center line (6) in the cross-sectional profile of the tree trunk changes.
The sawing apparatus of claim 8, characterized in that means for sawing the sawing surface turning around the tree trunk comprises a rolling device in the feeding device and in the receiving device for rolling the trunk.
The sawing apparatus of any of the claims from 8 to 9, characterized in that the sawing apparatus further comprises a data processing system including means for saving the measured or/and estimated grain angles of the tree trunk and for comparing those with earlier measured grain angles of tree trunks.