CA2441553A1 - Method for drying timber - Google Patents
Method for drying timber Download PDFInfo
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- CA2441553A1 CA2441553A1 CA002441553A CA2441553A CA2441553A1 CA 2441553 A1 CA2441553 A1 CA 2441553A1 CA 002441553 A CA002441553 A CA 002441553A CA 2441553 A CA2441553 A CA 2441553A CA 2441553 A1 CA2441553 A1 CA 2441553A1
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- Prior art keywords
- timber
- drying
- compressed
- pressing
- drying process
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- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F26—DRYING
- F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
- F26B7/00—Drying solid materials or objects by processes using a combination of processes not covered by a single one of groups F26B3/00 and F26B5/00
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B27—WORKING OR PRESERVING WOOD OR SIMILAR MATERIAL; NAILING OR STAPLING MACHINES IN GENERAL
- B27M—WORKING OF WOOD NOT PROVIDED FOR IN SUBCLASSES B27B - B27L; MANUFACTURE OF SPECIFIC WOODEN ARTICLES
- B27M1/00—Working of wood not provided for in subclasses B27B - B27L, e.g. by stretching
- B27M1/02—Working of wood not provided for in subclasses B27B - B27L, e.g. by stretching by compressing
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F26—DRYING
- F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
- F26B2210/00—Drying processes and machines for solid objects characterised by the specific requirements of the drying good
- F26B2210/16—Wood, e.g. lumber, timber
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- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Life Sciences & Earth Sciences (AREA)
- General Engineering & Computer Science (AREA)
- Wood Science & Technology (AREA)
- Forests & Forestry (AREA)
- Drying Of Solid Materials (AREA)
- Chemical And Physical Treatments For Wood And The Like (AREA)
Abstract
A method for drying solid-wood timber (3), wherein the timber is compressed between pressing elements (10, 12) during the drying to reduce cracking, in which method the timber is compressed by an amount at least equal to the drying shrinkage of the timber, and in which method the timber consists of pieces of timber placed between the pressing elements and dried at the same time. By means of the pressing elements, the timber (3) is only compressed.
The pieces of timber (3) are arranged between the pressing elements in one or more tiers in the pressing direction so that the pieces of timber in the same tiers are pressed against each other during the drying process.
The pieces of timber (3) are arranged between the pressing elements in one or more tiers in the pressing direction so that the pieces of timber in the same tiers are pressed against each other during the drying process.
Description
4. F a~~~~ ~C~~w~~'.~. ~ ~ d4.~r.~
r ~' Ba~3~~rr~v~kr~ø~~:P ~~~t~~~~ ,:. pCT/FI02/OQ255 "- ~ 22-04-2003 METHOD FOR DRYING TIMBER
The present invention relates to a method for drying solid-wood timber as de fined in the preamble of claim 1, wherein the timber is compressed during the drying process.' The drying of solid-wood timber, such as planks, is carried out by heating the timber. Typically, the drying is implemented by first heating the timber at a lower temperature, e.g. 60°C, whereupon the temperature is raised gradually to a dry-ing temperature, which may typically be e.g. 70°C.
In the drying of timber, a big problem is the cracking of the timber. In prior-art methods, a "cautious" drying scheme is used in order to avoid cracking. In con-nection with the drying of timber, 'drying scheme' refers to the values to which the humidity of the drying air (the difference between dry-bulb and wet-bulb temperatures) is adjusted. A feature characteristic of the prior-art cautious dry-ing scheme is that, at the beginning of the drying process, the relative humidity of the air is high and it is reduced with the progress of the drying, the drying efFi-ciency being thus increased. During the drying process, the humidity of the dry-2o ing air is monitored by measuring the so-called "dry-bulb temperature" and "wet-bulb temperature". For example, for pine or fir timber having a thickness of mm, the difFerence between these temperatures is at present typically 4 -5°C at the beginning of the drying process and about 15°C at the end of it.
As it is necessary in drying processes generally used at present to employ a relatively "cautious" drying scheme to avoid producing cracks in the timber, the drying periods are long. For example, if pine planks having a cross-section of mm x 100 mm are dried to a 13-% final moisture level, then the drying period is typically 7 - 8 days.
When the drying temperature is raised to a level exceeding 100°C, the process is called high temperature drying, and clearly shorter drying periods are possi-ble, but in this case the problem with current methods is relatively heavy crack-ing of the timber, and especially internal cracking. The risk of cracking is the higher the thicker is the timber being dried.
AMENDED SHEET
r ~' Ba~3~~rr~v~kr~ø~~:P ~~~t~~~~ ,:. pCT/FI02/OQ255 "- ~ 22-04-2003 METHOD FOR DRYING TIMBER
The present invention relates to a method for drying solid-wood timber as de fined in the preamble of claim 1, wherein the timber is compressed during the drying process.' The drying of solid-wood timber, such as planks, is carried out by heating the timber. Typically, the drying is implemented by first heating the timber at a lower temperature, e.g. 60°C, whereupon the temperature is raised gradually to a dry-ing temperature, which may typically be e.g. 70°C.
In the drying of timber, a big problem is the cracking of the timber. In prior-art methods, a "cautious" drying scheme is used in order to avoid cracking. In con-nection with the drying of timber, 'drying scheme' refers to the values to which the humidity of the drying air (the difference between dry-bulb and wet-bulb temperatures) is adjusted. A feature characteristic of the prior-art cautious dry-ing scheme is that, at the beginning of the drying process, the relative humidity of the air is high and it is reduced with the progress of the drying, the drying efFi-ciency being thus increased. During the drying process, the humidity of the dry-2o ing air is monitored by measuring the so-called "dry-bulb temperature" and "wet-bulb temperature". For example, for pine or fir timber having a thickness of mm, the difFerence between these temperatures is at present typically 4 -5°C at the beginning of the drying process and about 15°C at the end of it.
As it is necessary in drying processes generally used at present to employ a relatively "cautious" drying scheme to avoid producing cracks in the timber, the drying periods are long. For example, if pine planks having a cross-section of mm x 100 mm are dried to a 13-% final moisture level, then the drying period is typically 7 - 8 days.
When the drying temperature is raised to a level exceeding 100°C, the process is called high temperature drying, and clearly shorter drying periods are possi-ble, but in this case the problem with current methods is relatively heavy crack-ing of the timber, and especially internal cracking. The risk of cracking is the higher the thicker is the timber being dried.
AMENDED SHEET
One solution for reducing cracking in connection with the drying of timber is to compress the timber while it is being dried. As the timber is under compression during the drying process, it cannot undergo any warping or bending. Further-more, it retains its rectangular cross-sectional form, and e.g. a plank cannot be-s come convex, which means that less raw material is wasted at planing time.
Compression drying also allows a sawing procedure in which the core of the log remains in the middle of a plank. In this case, the core of the log and the juve nile wood near it, which is the weakest part of the wood material in respect of its properties, will remain completely hidden inside the plank and will not cause any harm in later use.
Specification WO 94/26485 discloses a method for form-drying of timber, espe-cially planks, in a hot press comprising an upper press plate, upper supporters supporting the upper press plate, a lower press plate and hydraulic cylinders for moving it. The surfaces of the press plates are heatable. Both press surFaces are covered with screens permeable to steam. The planks to be pressed are placed between the screens, and the pressing stroke is limited by stoppers placed at the ends of the press plates. In the method, moist timber is pressed into a desired shape while the timber is heated at the same time. The method 2o consists of two stages. During the first stage, the moist timber is pressed quickly into the desired shape under a high pressure against the gas-permeable sur faces until the final dimensions are reached, and after this pressing stage the timber is allowed to expand towards its original size. After this, the pressing is continued using a low pressure, which produces a change at least as large as the shrinkage resulting from the drying of the timber.
A drawback with the solution according to the specification in question is espe-cially the fact that the heat is conducted into the timber via the press plates, the compression and heating of the timber being thus both perFormed by means of 3o the press plates, i.e. as it were from the same source, which limits the usable heat sources to those in which the heat can be conducted via the press plates.
It is not possible to place several pieces of timber side by side or one over the other in the pressing direction between the press plates. In addition, the method is relatively slow, and when it is used, cracking still occurs in the timber, espe-3s cially in the drying of thicker timber, so the method is not applicable for the dry-ing of e.g. building logs.
Compression drying also allows a sawing procedure in which the core of the log remains in the middle of a plank. In this case, the core of the log and the juve nile wood near it, which is the weakest part of the wood material in respect of its properties, will remain completely hidden inside the plank and will not cause any harm in later use.
Specification WO 94/26485 discloses a method for form-drying of timber, espe-cially planks, in a hot press comprising an upper press plate, upper supporters supporting the upper press plate, a lower press plate and hydraulic cylinders for moving it. The surfaces of the press plates are heatable. Both press surFaces are covered with screens permeable to steam. The planks to be pressed are placed between the screens, and the pressing stroke is limited by stoppers placed at the ends of the press plates. In the method, moist timber is pressed into a desired shape while the timber is heated at the same time. The method 2o consists of two stages. During the first stage, the moist timber is pressed quickly into the desired shape under a high pressure against the gas-permeable sur faces until the final dimensions are reached, and after this pressing stage the timber is allowed to expand towards its original size. After this, the pressing is continued using a low pressure, which produces a change at least as large as the shrinkage resulting from the drying of the timber.
A drawback with the solution according to the specification in question is espe-cially the fact that the heat is conducted into the timber via the press plates, the compression and heating of the timber being thus both perFormed by means of 3o the press plates, i.e. as it were from the same source, which limits the usable heat sources to those in which the heat can be conducted via the press plates.
It is not possible to place several pieces of timber side by side or one over the other in the pressing direction between the press plates. In addition, the method is relatively slow, and when it is used, cracking still occurs in the timber, espe-3s cially in the drying of thicker timber, so the method is not applicable for the dry-ing of e.g. building logs.
The object of the invention is to achieve a method for the drying of solid-wood timber that can be used to dry sawn timber as well as other timber quickly and so that the cracking occurring in the timber can be minimized. The method of the invention is based on the idea that the timber is compressed at feast as much as the wood would shrink even otherwise when drying, and that the com-pression and drying of the timber are performed by means of separate devices.
The drying heat is supplied from a different source and not via the press plates as in specification WO 94/26485, so the drying of the timber can be performed using any drying method, to which only devices for producing the necessary compression are added. For drying, several pieces of timber are placed one over the other in the pressing direction by so that they are pressed against each other.
The details of the features characteristic of the method of the invention are pre-~5 sented in the claims below.
This allows a decisive expansion of the possibilities of application of the method. Different embodiments of the invention can be utilized in various proc esses, allowing economical solutions to be achieved when large amounts of 2o timber are to be dried.
The drying method disclosed in the present invention provides good possibilities of achieving more efficient drying of timber. The essential point is that the in-vention makes it possible to prevent cracking, both surface and internal crack-25 ing, allowing the drying to be effected using a drying scheme as efficient as possible, thereby substantially reducing the drying period required. For exam-ple, when the drying temperature is 70°C, then the wet-bulb temperature is 35°C or less, and when the drying temperature is 150°C, then the wet-bulb tem-perature is 90°C or less. The drying can also be performed using high tem-so peratures, which further reduces the drying periods. In respect of control of the drying, the method disclosed also simplifies the drying process as it allows con-tinuous use of a simple drying scheme as efficient as possible. Using the method of the invention, effective drying of even large pieces of timber, such as balks, is possible.
In the following, the invention will be described in detail by the aid of examples with reference to the attached drawings, wherein Fig. 1 presents a chamber drier designed for the drying of solid-wood timber, in which a method according to the invention for the drying of building logs is use, Fig. 2 presents an apparatus used for testing the method of the invention and illustrates the implementation of drying tests using planks placed edge to edge, Fig. 3 presents an apparatus used for testing the method of the invention and illustrates the implementation of drying tests using planks placed with their flat ~o sides againsfi each other, Fig. 4 presents an embodiment of the method of the invention wherein several logs placed one over the other can be dried simultaneously, and 15 Fig. 5 presents an embodimenfi of the method of the invention wherein several logs placed side by side can be dried simultaneously.
The drier presented in Fig. 1 comprises a chamber 2 placed in a drying plant building 1, which chamber is used for the drying of timber, such as balks 3 (not 2o shown in scale), planks or boards. At least one end of the chamber is provided with a door 4. The chamber is provided with radiators 5 together with the asso ciated piping and control valves for heating the air, and parallel fans 6 controlled e.g. by a frequency converter and serving to create an air circulation of a de sired type in the chamber. In addition, the chamber 2 may be provided with a 25 moistening apparatus 7 and exhaust and fresh air ducts 8.
According to the invention, timber is dried in a drying plant by heating the timber and simultaneously compressing it by means of a pressing apparatus 9 (not in scale). The compression pressure of the pressing apparatus is adjusted by so means of a control system (not shown) to a level such that it produces a con-traction of a magnitude, optimally 4 - 6 %, that is equal to the shrinkage result-ing from drying of the timber to prevent cracking, cupping, bending and warping of the timber.
35 The pressing apparatus comprises a press plate 10, hydraulic cylinders 11 and their control system for moving the plate, a fixed press plate 12 and a support-ing structure 13. The timber 3 to be pressed is placed between the press plates ,.. . ~~ ~,~°~'i~,~.~.'I-P i"';~''.~'c~.Y"t'i, S~E'~i~~~ / ' r > ~°~' ?~~t:~s~~4i~e~a~~ ~~~~6~~~a~~l~ ' and 12 in one or more layers and pressed by means of the hydraulic cylin-ders 1 1 from t he direction o f t he arrow while b eing s imultaneously h Bated. I f there are several layers, laths 13 are placed between layers. The pressing can be performed in one stage, i.e. the timber is compressed continuously until the 5 final dimension is reached, without letting it resile towards its original dimension before that. The compression can be started with a lower pressure, and the pressure is then increased during the drying process.
Fig. 2 and 3 present a laboratory-size apparatus, which has been used to carry out drying tests. The apparatus comprises a framework 21, a hydraulic press 22 producing the required pressure, a nd timber 23 to b a d ried in the press, the pieces of timber being packed with their edges 24 (Fig. 2) or their flat sides (Fig. 3) placed against each other. The drying is implemented by pushing the entire framework into a drier, applying a pressure and starting the drying proc-ess. I n t he following, four p ractical a xamples w ill b a g iven t o d escribe d rying tests.
Example 1. The sawn timber to be dried consisted of pine planks measuring 50 mm x 100 mm. The planks were placed in the drier in the manner shown in Fig.
2, with their edges 24 against each other. The drying temperature was 70 °C.
The drying process was started by a heating stage, during which the tempera-ture was increased to 70°C. The duration of the heating stage was 2 h, and dur-ing this stage steam was supplied into the drier, so that no drying occurred at this stage. After the heating stage, a drying scheme as efficient as possible was used. The control values were such as to keep the temperature at 70°C, and the exhaust and fresh air dampers were fully open. Upon the lapse of 2 h after the start of the drying, the "wet bulb temperature" was about 45°C, so the differ-ence between the dry-bulb and wet-bulb temperatures was 25°C, and after a nearly full day of drying the wet-bulb temperature was 35°C, so the difference so between the dry-bulb and wet-bulb temperatures was 35°C, and it remained so until the end of the drying process. The total drying time was 76 h. The com-pression pressure used was 3,3 ~ bar. The average final moisture level was 13.5%. The dimensions of the planks before and after the drying are shown in Table 1.
The drying heat is supplied from a different source and not via the press plates as in specification WO 94/26485, so the drying of the timber can be performed using any drying method, to which only devices for producing the necessary compression are added. For drying, several pieces of timber are placed one over the other in the pressing direction by so that they are pressed against each other.
The details of the features characteristic of the method of the invention are pre-~5 sented in the claims below.
This allows a decisive expansion of the possibilities of application of the method. Different embodiments of the invention can be utilized in various proc esses, allowing economical solutions to be achieved when large amounts of 2o timber are to be dried.
The drying method disclosed in the present invention provides good possibilities of achieving more efficient drying of timber. The essential point is that the in-vention makes it possible to prevent cracking, both surface and internal crack-25 ing, allowing the drying to be effected using a drying scheme as efficient as possible, thereby substantially reducing the drying period required. For exam-ple, when the drying temperature is 70°C, then the wet-bulb temperature is 35°C or less, and when the drying temperature is 150°C, then the wet-bulb tem-perature is 90°C or less. The drying can also be performed using high tem-so peratures, which further reduces the drying periods. In respect of control of the drying, the method disclosed also simplifies the drying process as it allows con-tinuous use of a simple drying scheme as efficient as possible. Using the method of the invention, effective drying of even large pieces of timber, such as balks, is possible.
In the following, the invention will be described in detail by the aid of examples with reference to the attached drawings, wherein Fig. 1 presents a chamber drier designed for the drying of solid-wood timber, in which a method according to the invention for the drying of building logs is use, Fig. 2 presents an apparatus used for testing the method of the invention and illustrates the implementation of drying tests using planks placed edge to edge, Fig. 3 presents an apparatus used for testing the method of the invention and illustrates the implementation of drying tests using planks placed with their flat ~o sides againsfi each other, Fig. 4 presents an embodiment of the method of the invention wherein several logs placed one over the other can be dried simultaneously, and 15 Fig. 5 presents an embodimenfi of the method of the invention wherein several logs placed side by side can be dried simultaneously.
The drier presented in Fig. 1 comprises a chamber 2 placed in a drying plant building 1, which chamber is used for the drying of timber, such as balks 3 (not 2o shown in scale), planks or boards. At least one end of the chamber is provided with a door 4. The chamber is provided with radiators 5 together with the asso ciated piping and control valves for heating the air, and parallel fans 6 controlled e.g. by a frequency converter and serving to create an air circulation of a de sired type in the chamber. In addition, the chamber 2 may be provided with a 25 moistening apparatus 7 and exhaust and fresh air ducts 8.
According to the invention, timber is dried in a drying plant by heating the timber and simultaneously compressing it by means of a pressing apparatus 9 (not in scale). The compression pressure of the pressing apparatus is adjusted by so means of a control system (not shown) to a level such that it produces a con-traction of a magnitude, optimally 4 - 6 %, that is equal to the shrinkage result-ing from drying of the timber to prevent cracking, cupping, bending and warping of the timber.
35 The pressing apparatus comprises a press plate 10, hydraulic cylinders 11 and their control system for moving the plate, a fixed press plate 12 and a support-ing structure 13. The timber 3 to be pressed is placed between the press plates ,.. . ~~ ~,~°~'i~,~.~.'I-P i"';~''.~'c~.Y"t'i, S~E'~i~~~ / ' r > ~°~' ?~~t:~s~~4i~e~a~~ ~~~~6~~~a~~l~ ' and 12 in one or more layers and pressed by means of the hydraulic cylin-ders 1 1 from t he direction o f t he arrow while b eing s imultaneously h Bated. I f there are several layers, laths 13 are placed between layers. The pressing can be performed in one stage, i.e. the timber is compressed continuously until the 5 final dimension is reached, without letting it resile towards its original dimension before that. The compression can be started with a lower pressure, and the pressure is then increased during the drying process.
Fig. 2 and 3 present a laboratory-size apparatus, which has been used to carry out drying tests. The apparatus comprises a framework 21, a hydraulic press 22 producing the required pressure, a nd timber 23 to b a d ried in the press, the pieces of timber being packed with their edges 24 (Fig. 2) or their flat sides (Fig. 3) placed against each other. The drying is implemented by pushing the entire framework into a drier, applying a pressure and starting the drying proc-ess. I n t he following, four p ractical a xamples w ill b a g iven t o d escribe d rying tests.
Example 1. The sawn timber to be dried consisted of pine planks measuring 50 mm x 100 mm. The planks were placed in the drier in the manner shown in Fig.
2, with their edges 24 against each other. The drying temperature was 70 °C.
The drying process was started by a heating stage, during which the tempera-ture was increased to 70°C. The duration of the heating stage was 2 h, and dur-ing this stage steam was supplied into the drier, so that no drying occurred at this stage. After the heating stage, a drying scheme as efficient as possible was used. The control values were such as to keep the temperature at 70°C, and the exhaust and fresh air dampers were fully open. Upon the lapse of 2 h after the start of the drying, the "wet bulb temperature" was about 45°C, so the differ-ence between the dry-bulb and wet-bulb temperatures was 25°C, and after a nearly full day of drying the wet-bulb temperature was 35°C, so the difference so between the dry-bulb and wet-bulb temperatures was 35°C, and it remained so until the end of the drying process. The total drying time was 76 h. The com-pression pressure used was 3,3 ~ bar. The average final moisture level was 13.5%. The dimensions of the planks before and after the drying are shown in Table 1.
Thicknessmm Width m~
Be innin After Chan a % Be innin After d Chan a d in in 52.5 52.2 -0.6 104.7 99.5 -5.0 Table 1.
No surface or internal cracks had appeared in the planks.
When a conventional drying method is used, drying a plank dimensioned 50 mm x 100 mm at 70°C to a 13% final moisture level takes about 179 h.
Thus, by the drying method of the invention, the drying time can be reduced to less than half the time needed in conventional drying.
The thickness and width of the planks have changed so that the thickness has been slightly reduced and the width has been reduced by 5%. As compared ~5 with conventional drying, the total shrinkage is of the same order, but shrinkage has only occurred in one direction (i.e. in the direction in which the plank was compressed), which has to be taken into account when determining the sawing dimension of the plank.
2o Example 2. Pine planks dimensioned 50 mm x 100 mm were dried using the compression method of the invention. The planks were placed in the drier in the manner shown in Fig. 2, with their edges against each other. The drying tem-perature was 150°C, and the temperature was increased right from the start as fast as possible. A drying scheme as efficient as possible was used. At the final 25 stage of the drying process, the wet-bulb temperature was about 90°C. The drying time was 20 h. The pressure used was 2.0 bar.
The actual drying was followed by a cooling stage, during which the pressure was still maintained until the internal temperature of the planks fell below 100°C.
so This procedure prevents the occurrence of a steam explosion at the time of de-pressurization. The average final moisture level of the planks was 4.7%. No surface or internal cracks appeared in the planks.
Be innin After Chan a % Be innin After d Chan a d in in 52.5 52.2 -0.6 104.7 99.5 -5.0 Table 1.
No surface or internal cracks had appeared in the planks.
When a conventional drying method is used, drying a plank dimensioned 50 mm x 100 mm at 70°C to a 13% final moisture level takes about 179 h.
Thus, by the drying method of the invention, the drying time can be reduced to less than half the time needed in conventional drying.
The thickness and width of the planks have changed so that the thickness has been slightly reduced and the width has been reduced by 5%. As compared ~5 with conventional drying, the total shrinkage is of the same order, but shrinkage has only occurred in one direction (i.e. in the direction in which the plank was compressed), which has to be taken into account when determining the sawing dimension of the plank.
2o Example 2. Pine planks dimensioned 50 mm x 100 mm were dried using the compression method of the invention. The planks were placed in the drier in the manner shown in Fig. 2, with their edges against each other. The drying tem-perature was 150°C, and the temperature was increased right from the start as fast as possible. A drying scheme as efficient as possible was used. At the final 25 stage of the drying process, the wet-bulb temperature was about 90°C. The drying time was 20 h. The pressure used was 2.0 bar.
The actual drying was followed by a cooling stage, during which the pressure was still maintained until the internal temperature of the planks fell below 100°C.
so This procedure prevents the occurrence of a steam explosion at the time of de-pressurization. The average final moisture level of the planks was 4.7%. No surface or internal cracks appeared in the planks.
Example 3. Pine planks dimensioned 50 mm x 100 mm were dried using the compression method of the invention. The planks were placed in the drier in the manner shown in Fig. 3, with their flat sides against each other. The drying temperature was 150°C, and the temperature was increased right from the starfi as fast as possible. A drying scheme as efficient as possible was used. At the final stage of the drying process, the wet-bulb temperature was about 90°C. The drying time was 20 h. The pressure used was 2.0 bar.
The actual drying was followed by a cooling stage, during which the pressure 1o was still maintained until the internal temperature of the planks fell below 100°C.
The average final moisture level of the planks was 15.2%. The dimensions of the planks before and after the drying process are shown in Table 2.
Thicknessmm) Width mm .
Be innin After Chan a % Be innin After d Chan a d in in 52.1 49.3 -5.4 104.6 103.8 -0.8 Table 2.
When the planks are placed in the drier with their flat sides against each other, 2o the compression takes place in the thicknesswise direction and the planks must have a corresponding oversize in their thickness dimension.
On the surface of the flat sides of the planks, small cracks of a length of about 10 cm had appeared at the ends. There were no cracks in the core parts of the flat sides nor in the edges. The planks had no internal cracks.
Example 4. The sawn timber to be dried consisted of pine planks measuring 50 mm x 100 mm. The planks were placed in the drier in the manner shown in Fig.
2, with their edges against each other. The drying temperature was 70 °C. The so drying process was started by a heating stage, during which the temperature was increased to 70°C. The duration of the heating stage was 2 h, and during this stage the drier was supplied with steam, so that no drying occurred at this stage. After the heating stage, a drying scheme as efficient as possible was used. The drying time was 91 h. The compression pressure was initially 6 bar, _ ,~.- _.
~~~fiyi-~ a'a~~;.-a~'i ~~~'~~~,:g ..
- " , ~ 0 6U~~~~~~i~~u~P 1~~,~~ci~~g~CPPA ;, g 22-04-2003 and it was increased gradually at intervals of one full day, and at the end of the drying process the pressure was 18 bar.
The average final moisture level of the planks was 11.9%. The planks had been s compressed in their widthwise direction by 14.3%. Their thickness had been increased by 2.4%. The Brinell hardness of the flat side surfaces of the planks had been increased by 18%.
When the timber to be dried is compressed with a high pressure, typically in the range of 6 - 20 bar, the resulting shrinkage is greater than the shrinkage occur-ring due to drying of the wood. In this way, the hardness of the timber can be increased. The increase of hardness is the greater the greater is the compres-sion shrinkage.
15 The drying of timber can be carried out either by placing the pieces of timber with their edge surfaces against each other, in which case the drying takes place via the flat sides, or by placing them with their flat sides against each other, in which case the drying takes place via the edge surfaces. This makes it possible to have the timber dried via desired surfaces, which in some cases has 2o an advantageous effect on the properties of the timber.
Fig. 4 illustrates a case where several balks 3 are placed one over the other in the direction of compression with their edges 14, 15 against each other. The surfaces to be placed together can be machined so that steam can escape from 2s between them, thus accelerating the drying process (not shown). Screens 16 may be inserted between the surfaces to be placed together, which also accel-erates t he drying process, as shown in Fig. 5, which illustrates the drying of several balks placed side by side with their lateral surfaces 17 against each other or against the pressing surfaces.
The practical examples described above relate to normal drying and high_tem-perature drying, but that does not constitute any limitation of the application of the invention. The method of the invention, whereby timber is compressed dur-ing drying by an amount at least equal to the shrinkage, is applicable for use regardless of the drying method itself. The drying method may be vacuum dry-ing, high-frequency drying, micro-wave drying, steam drying or any other method or their combination. The embodiments may vary in the scope of the __ . _ iap~d : m<3.'~-,','.°a't r, t'.~~s.';r; ~~
BU'JC~ uP"D~~it~,,-a~~8 ~,~,~..a~~:.>~~~, pCT/FI02/00255 .,~
. , 9 ~ 22-04-2003 claims presented below. The invention can also be used to dry e.g. a balk or a similar blank before its being planed to form a building log or sawn to produce sawn timber.
To describe an embodiment in which the timber to be dried consists of balks, which are sawn after t he d tying to produce boards and p tanks, the following practical example is presented.
Example 5. Pine balks measuring 105 mm x 182 mm were dried with their flat sides placed against each other. The drying temperature was 70°C and an effi-cient drying scheme was used. The drying period was 14 days, at the end of which the balks had an average moisture level of 14.9%. After being dried, a balk can be cut e.g. by sawing two boards measuring 28 mm x 100 mm from either side of it, the portion left between them forming a plank of 63 mm x mm.
The actual drying was followed by a cooling stage, during which the pressure 1o was still maintained until the internal temperature of the planks fell below 100°C.
The average final moisture level of the planks was 15.2%. The dimensions of the planks before and after the drying process are shown in Table 2.
Thicknessmm) Width mm .
Be innin After Chan a % Be innin After d Chan a d in in 52.1 49.3 -5.4 104.6 103.8 -0.8 Table 2.
When the planks are placed in the drier with their flat sides against each other, 2o the compression takes place in the thicknesswise direction and the planks must have a corresponding oversize in their thickness dimension.
On the surface of the flat sides of the planks, small cracks of a length of about 10 cm had appeared at the ends. There were no cracks in the core parts of the flat sides nor in the edges. The planks had no internal cracks.
Example 4. The sawn timber to be dried consisted of pine planks measuring 50 mm x 100 mm. The planks were placed in the drier in the manner shown in Fig.
2, with their edges against each other. The drying temperature was 70 °C. The so drying process was started by a heating stage, during which the temperature was increased to 70°C. The duration of the heating stage was 2 h, and during this stage the drier was supplied with steam, so that no drying occurred at this stage. After the heating stage, a drying scheme as efficient as possible was used. The drying time was 91 h. The compression pressure was initially 6 bar, _ ,~.- _.
~~~fiyi-~ a'a~~;.-a~'i ~~~'~~~,:g ..
- " , ~ 0 6U~~~~~~i~~u~P 1~~,~~ci~~g~CPPA ;, g 22-04-2003 and it was increased gradually at intervals of one full day, and at the end of the drying process the pressure was 18 bar.
The average final moisture level of the planks was 11.9%. The planks had been s compressed in their widthwise direction by 14.3%. Their thickness had been increased by 2.4%. The Brinell hardness of the flat side surfaces of the planks had been increased by 18%.
When the timber to be dried is compressed with a high pressure, typically in the range of 6 - 20 bar, the resulting shrinkage is greater than the shrinkage occur-ring due to drying of the wood. In this way, the hardness of the timber can be increased. The increase of hardness is the greater the greater is the compres-sion shrinkage.
15 The drying of timber can be carried out either by placing the pieces of timber with their edge surfaces against each other, in which case the drying takes place via the flat sides, or by placing them with their flat sides against each other, in which case the drying takes place via the edge surfaces. This makes it possible to have the timber dried via desired surfaces, which in some cases has 2o an advantageous effect on the properties of the timber.
Fig. 4 illustrates a case where several balks 3 are placed one over the other in the direction of compression with their edges 14, 15 against each other. The surfaces to be placed together can be machined so that steam can escape from 2s between them, thus accelerating the drying process (not shown). Screens 16 may be inserted between the surfaces to be placed together, which also accel-erates t he drying process, as shown in Fig. 5, which illustrates the drying of several balks placed side by side with their lateral surfaces 17 against each other or against the pressing surfaces.
The practical examples described above relate to normal drying and high_tem-perature drying, but that does not constitute any limitation of the application of the invention. The method of the invention, whereby timber is compressed dur-ing drying by an amount at least equal to the shrinkage, is applicable for use regardless of the drying method itself. The drying method may be vacuum dry-ing, high-frequency drying, micro-wave drying, steam drying or any other method or their combination. The embodiments may vary in the scope of the __ . _ iap~d : m<3.'~-,','.°a't r, t'.~~s.';r; ~~
BU'JC~ uP"D~~it~,,-a~~8 ~,~,~..a~~:.>~~~, pCT/FI02/00255 .,~
. , 9 ~ 22-04-2003 claims presented below. The invention can also be used to dry e.g. a balk or a similar blank before its being planed to form a building log or sawn to produce sawn timber.
To describe an embodiment in which the timber to be dried consists of balks, which are sawn after t he d tying to produce boards and p tanks, the following practical example is presented.
Example 5. Pine balks measuring 105 mm x 182 mm were dried with their flat sides placed against each other. The drying temperature was 70°C and an effi-cient drying scheme was used. The drying period was 14 days, at the end of which the balks had an average moisture level of 14.9%. After being dried, a balk can be cut e.g. by sawing two boards measuring 28 mm x 100 mm from either side of it, the portion left between them forming a plank of 63 mm x mm.
Claims (10)
1. Method for drying solid-wood timber (3, 23), wherein the timber is heated and compressed, wherein the compression is performed between pressing elements (10,12,22) during the drying to reduce cracking, in which method the timber is compressed by an amount at least equal to the drying shrinkage of the timber, and in which method the timber consists of pieces of timber placed between the pressing elements and dried at the same time, characterized in that the pieces of timber (3, 23) are arranged between the pressing elements in one or more layers in the pressing direction so that the pieces of timber in the same layer are pressed against each other during the drying process, and the timber is heated with heating means (5) separate from the pressing ele-ments, whereby heating and compressing are performed by separate means so that by means of the pressing elements the timber (3, 23) is only compressed.
2. Method as defined in claim 1, characterized in that the drying is performed in a drying space (2) provided with a pressing apparatus (10-14) for compressing the timber during the drying process.
3. Method as defined in claim 1, characterized in that the timber is compressed with an increasing compression force during the drying process.
4. Method as defined in claim 1, characterized in that the compression is per-formed in a single stage so that the timber is compressed continuously until the final dimension is reached, without interruptions allowing the timber to resile.
5. Method as defined in claim 1 for the drying of especially sawn timber, char-acterized in that the timbers are placed with their edge surfaces (24) against each other, so that the drying takes place via the flat sides.
6. Method as defined in claim 1 for the drying of especially sawn timber, char-acterized in that the timbers are placed with their flat sides (25) against each other, so that the drying takes place via the edge surfaces.
7. Method as defined in claim 1, characterized in that the surfaces to be placed together have been worked to accelerate the drying process so that steam can effectively escape from between the surfaces.
8. Method as defined in claim 1 for the drying of timber, characterized in that screens (16) are fitted between the surfaces placed together to accelerate the drying process.
9. Method as defined in claim 1, characterized in that the timber consists of a plank, beam or balk, which is worked further after the drying to p roduce e.g.
sawn timber and/or a building log.
sawn timber and/or a building log.
10. Method as defined in claim 1, in which method the timber is dried by adjust-ing the difference between its dry-bulb and wet-bulb temperatures, character-ized in that the difference between the dry-bulb and wet-bulb temperatures is so adjusted that it exceeds 15°C. at least at the final stage of the drying process.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FI20010611A FI20010611A0 (en) | 2001-03-26 | 2001-03-26 | Method for drying timber |
| FI20010611 | 2001-03-26 | ||
| PCT/FI2002/000255 WO2002081992A1 (en) | 2001-03-26 | 2002-03-26 | Method for drying timber |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2441553A1 true CA2441553A1 (en) | 2002-10-17 |
Family
ID=8560833
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002441553A Abandoned CA2441553A1 (en) | 2001-03-26 | 2002-03-26 | Method for drying timber |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP1373816A1 (en) |
| CA (1) | CA2441553A1 (en) |
| FI (1) | FI20010611A0 (en) |
| WO (1) | WO2002081992A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102883861A (en) * | 2009-11-25 | 2013-01-16 | 木材工程技术有限公司 | Engineered timber products, components and methodologies |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA2502252A1 (en) * | 2005-03-24 | 2006-09-24 | 9051-8127 Quebec Inc. | Wood stabilizer apparatus |
| FI123090B (en) * | 2008-03-12 | 2012-10-31 | Paprotec Oy | Method and apparatus for drying wood and drying plant |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FI91947C (en) * | 1993-05-18 | 1994-09-12 | Valtion Teknillinen | Method for shape drying of wood |
-
2001
- 2001-03-26 FI FI20010611A patent/FI20010611A0/en unknown
-
2002
- 2002-03-26 WO PCT/FI2002/000255 patent/WO2002081992A1/en not_active Ceased
- 2002-03-26 EP EP02708399A patent/EP1373816A1/en not_active Withdrawn
- 2002-03-26 CA CA002441553A patent/CA2441553A1/en not_active Abandoned
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102883861A (en) * | 2009-11-25 | 2013-01-16 | 木材工程技术有限公司 | Engineered timber products, components and methodologies |
Also Published As
| Publication number | Publication date |
|---|---|
| EP1373816A1 (en) | 2004-01-02 |
| WO2002081992A1 (en) | 2002-10-17 |
| FI20010611A0 (en) | 2001-03-26 |
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| FZDE | Discontinued |