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WO2002081992A1 - Procede de sechage du bois d'oeuvre - Google Patents

Procede de sechage du bois d'oeuvre Download PDF

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Publication number
WO2002081992A1
WO2002081992A1 PCT/FI2002/000255 FI0200255W WO02081992A1 WO 2002081992 A1 WO2002081992 A1 WO 2002081992A1 FI 0200255 W FI0200255 W FI 0200255W WO 02081992 A1 WO02081992 A1 WO 02081992A1
Authority
WO
WIPO (PCT)
Prior art keywords
timber
drying
compressed
drying process
planks
Prior art date
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.)
Ceased
Application number
PCT/FI2002/000255
Other languages
English (en)
Inventor
Paavo Kontinen
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
TEKMAWOOD Oy
Original Assignee
TEKMAWOOD Oy
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by TEKMAWOOD Oy filed Critical TEKMAWOOD Oy
Priority to EP02708399A priority Critical patent/EP1373816A1/fr
Priority to CA002441553A priority patent/CA2441553A1/fr
Publication of WO2002081992A1 publication Critical patent/WO2002081992A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

Links

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
    • 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

Definitions

  • the present invention relates to a method for drying solid-wood timber as defined in the preamble of claim 1 , wherein the timber is compressed during the drying process.
  • the drying of solid-wood timber is carried out by heating the timber.
  • 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 drying temperature, which may typically be e.g. 70°C.
  • a "cautious" drying scheme is used in order to avoid cracking.
  • '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 drying 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 efficiency being thus increased.
  • the humidity of the drying 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 50-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.
  • the drying periods are long. For example, if pine planks having a cross-section of 50 mm x 100 mm are dried to a 13-% final moisture level, then the drying period is typically 7 - 8 days.
  • WO 94/26485 discloses a method for form-drying of timber, especially 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.
  • moist timber is pressed into a desired shape while the timber is heated at the same time.
  • the method consists of two stages.
  • the moist timber is pressed quickly into the desired shape under a high pressure against the gas-permeable surfaces 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 especially 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 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- cially in the drying of thicker timber, so the method is not applicable for the drying 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 least as much as the wood would shrink even otherwise when drying, and that the compression 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 drying method disclosed in the present invention provides good possibilities of achieving more efficient drying of timber.
  • the essential point is that the invention makes it possible to prevent cracking, both surface and internal crack- ing, allowing the drying to be effected using a drying scheme as efficient as possible, thereby substantially reducing the drying period required.
  • the drying temperature is 70°C
  • the wet-bulb temperature is 35°C or less
  • the drying temperature is 150°C
  • the wet-bulb temperature is 90°C or less.
  • the drying can also be performed using high tem- peratures, which further reduces the drying periods.
  • the method disclosed also simplifies the drying process as it allows continuous 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.
  • 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 sides against 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
  • Fig. 5 presents an embodiment 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 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 associated 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 desired type in the chamber.
  • the chamber 2 may be provided with a moistening apparatus 7 and exhaust and fresh air ducts 8.
  • 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 means of a control system (not shown) to a level such that it produces a contraction of a magnitude, optimally 4 - 6 %, that is equal to the shrinkage resulting from drying of the timber to prevent cracking, cupping, bending and warping of the timber.
  • 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 supporting structure 13.
  • the timber 3 to be pressed is placed between the press plates 10 and 12 in one or more tiers and pressed by means of the hydraulic cylinders
  • the pressing can be performed in one stage, i.e. the timber is compressed continuously until the 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, and timber 23 to be dried in the press, the pieces of timber being packed with their edges 24 (Fig. 2) or their flat sides 25 (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. In the following, two practical examples will be given to describe drying 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 temperature was increased to 70°C.
  • the duration of the heating stage was 2 h, and during this stage steam was supplied into the drier, so that no drying occurred at this 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 slides were fully open.
  • the "wet bulb temperature" was about 45°C, so the difference 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 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 compression pressure used was 3,3 bar.
  • the average final moisture level was 13.5%.
  • Table 1 The dimensions of the planks before and after the drying are shown in Table 1.
  • drying a plank dimensioned 50 mm x 100 mm at 70°C to a 13% final moisture level takes about 179 h.
  • 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%.
  • 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.
  • 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 temperature 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 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.
  • 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 start 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.
  • planks When the planks are placed in the drier with their flat sides against each other, the compression takes place in the thicknesswise direction and the planks must have a corresponding oversize in their thickness dimension.
  • 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 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.
  • a drying scheme as efficient as possible was used.
  • the drying time was 91 h.
  • the compression pressure was initially 6 bar, 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 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%.
  • the resulting shrinkage is greater than the shrinkage occurring due to drying of the wood.
  • the hardness of the timber can be increased.
  • the increase of hardness is the greater the greater is the compression shrinkage.
  • 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 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 between them, thus accelerating the drying process (not shown).
  • Screens 16 may be inserted between the surfaces to be placed together, which also accelerates the 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 hot drying, but that does not constitute any limitation of the application of the invention.
  • the method of the invention whereby timber is compressed during 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 drying, high-frequency drying, micro-wave drying, steam drying or any other method or their combination.
  • the embodiments may vary in the scope of the 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.
  • the timber to be dried consists of balks, which are sawn after the drying to produce boards and planks, 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 100 mm.

Landscapes

  • 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

L'invention porte sur un procédé de séchage du bois d'oeuvre (3) solide comprimé entre des éléments de presse (10, 12) pendant le séchage afin de réduire le craquelage. Le bois d'oeuvre est comprimé par une quantité au moins égale au retrait de séchage du bois d'oeuvre et le bois d'oeuvre utilisé est constitué de pièces de bois placées entre les éléments de presse et séchées en même temps. Grâce aux éléments de presse, le bois d'oeuvre (3) est uniquement comprimé. Les pièces de bois d'oeuvre (3) sont disposées entre les éléments de presse selon un ou des alignements vertical(aux) dans le sens de presse de manière que les pièces de bois d'oeuvre dans le même alignement vertical soient pressées les unes contre les autres pendant l'opération de séchage.
PCT/FI2002/000255 2001-03-26 2002-03-26 Procede de sechage du bois d'oeuvre Ceased WO2002081992A1 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
EP02708399A EP1373816A1 (fr) 2001-03-26 2002-03-26 Procede de sechage du bois d'oeuvre
CA002441553A CA2441553A1 (fr) 2001-03-26 2002-03-26 Procede de sechage du bois d'oeuvre

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FI20010611A FI20010611A0 (fi) 2001-03-26 2001-03-26 Menetelmä puutavaran kuivaamiseksi
FI20010611 2001-03-26

Publications (1)

Publication Number Publication Date
WO2002081992A1 true WO2002081992A1 (fr) 2002-10-17

Family

ID=8560833

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/FI2002/000255 Ceased WO2002081992A1 (fr) 2001-03-26 2002-03-26 Procede de sechage du bois d'oeuvre

Country Status (4)

Country Link
EP (1) EP1373816A1 (fr)
CA (1) CA2441553A1 (fr)
FI (1) FI20010611A0 (fr)
WO (1) WO2002081992A1 (fr)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2006099737A1 (fr) * 2005-03-24 2006-09-28 9051-8127 Québec Inc. Dispositif de pression et utilisation dans un systeme de sechage de bois
WO2011065845A1 (fr) * 2009-11-25 2011-06-03 Wood Engineering Technology Limited Produits de bois d'œuvre d'ingénierie, composants et méthodologies
EP2252848A4 (fr) * 2008-03-12 2014-10-08 Paprotec Oy Procédé et dispositif de séchage d ebois de sciage et séchoir

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1994026485A1 (fr) * 1993-05-18 1994-11-24 Valtion Teknillinen Tutkimuskeskus Procede de sechage et de compression pour la mise en forme du bois

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1994026485A1 (fr) * 1993-05-18 1994-11-24 Valtion Teknillinen Tutkimuskeskus Procede de sechage et de compression pour la mise en forme du bois

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2006099737A1 (fr) * 2005-03-24 2006-09-28 9051-8127 Québec Inc. Dispositif de pression et utilisation dans un systeme de sechage de bois
EP2252848A4 (fr) * 2008-03-12 2014-10-08 Paprotec Oy Procédé et dispositif de séchage d ebois de sciage et séchoir
WO2011065845A1 (fr) * 2009-11-25 2011-06-03 Wood Engineering Technology Limited Produits de bois d'œuvre d'ingénierie, composants et méthodologies
US10189177B2 (en) 2009-11-25 2019-01-29 Wood Engineering Technology Limited Engineered timber products, components and methodologies
US11325276B2 (en) 2009-11-25 2022-05-10 Wood Engineering Technology Limited Engineered timber products, components and methodologies

Also Published As

Publication number Publication date
FI20010611A0 (fi) 2001-03-26
CA2441553A1 (fr) 2002-10-17
EP1373816A1 (fr) 2004-01-02

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