CA1188888A - Method of carrying out the drying of wooden objects - Google Patents
Method of carrying out the drying of wooden objectsInfo
- Publication number
- CA1188888A CA1188888A CA000406834A CA406834A CA1188888A CA 1188888 A CA1188888 A CA 1188888A CA 000406834 A CA000406834 A CA 000406834A CA 406834 A CA406834 A CA 406834A CA 1188888 A CA1188888 A CA 1188888A
- Authority
- CA
- Canada
- Prior art keywords
- objects
- drying
- circulating air
- air
- unit
- 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.)
- Expired
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- Drying Of Solid Materials (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A method of drying wooden objects according to the invention shall be carried out in a closed treatment room with a supply of microwave effect which heats the objects stacked in a unit so that the moisture is pressed out and removed. Each unit is positioned in a cover of a heat insulation stuff which prevents cooling of the wooden objects by the air circulation in the room.
A method of drying wooden objects according to the invention shall be carried out in a closed treatment room with a supply of microwave effect which heats the objects stacked in a unit so that the moisture is pressed out and removed. Each unit is positioned in a cover of a heat insulation stuff which prevents cooling of the wooden objects by the air circulation in the room.
Description
'/01 . h6 rcT/~ E~ 1/00~
j:
A method of carrying out the dryinq of wooden ob jects The present invention i3 related ~o a method of drying wood in tho shape of boards, planks, etcetera.
A well-known method of drying timber is carried out by exposing the timber to dry hot-air currents which suck out the moisture of the wood. During such a 5 procedure the surfaces of the wooden objects will dry first which implies that the thin capillaries in the wood which keep the moisture will shrink at the surface and obstruc~ further transfer of moisture out of the wood. In such a well-known procedure (e.g. patent publication SE 319129) the hot-air drying i3 comp~eted with a high frequency treatment of the wood. By such high frequency heating it is 10 possible to achieve a temperature gradient in the load which i~ positive in the direction from the surface to ~h~ centre of the load. As the heat is then generated in the wood it is necessary to provide air to cool ths wood in order to create atemperature balance. The moisture is then pressed out instead of being s~lcked out as in the case of conventional hot-air drying when the temperature gradient i~
15 oppositely directed. The high frequency treatment according to ~he well-knownprocedure implies, however, just a partia~ advantage to the conventional drying~Some improvements of the procedure are achieved by the use of microwave heating for the drying. 1) The saving of time by microwave hea~ing can be essential; the drying period is often reduced to 20 9~ of the corresponding period 20 of hot-air drying. 2) The microwaves are self-adjusting i.e. the drier parts of the load absorb less effect than the moister ones. 3) The microwave drying gives a higher quality thanks to the fact that the occurrence of cracking and wrappedne~s is practically elirninated as both the temperature and the moisture gradients are essentially less than in the case of other drying methods. 4) The t.eatment costs 25 are considerably reduced by microwave drying thanks to the fact that a laying of bed laths is~eliminated and the improvement of quality allows a simplification of the subsequent manufacturing procedures. 5)1~1uch less energy consumption is a consequence of the use of microwaves, primarily owing to the fact that no need exists for heating air separa~ely, ~hat the air temperature in the drying room is 3û lower and thus the heat dissipation less, that the drying period is shorter and that the power of ventilators is reduced as the air circulation is used jus~ for removing the moisture, not for blowing air on the timber to suck out the moisture as in the case of ho~-air drying.
j:
A method of carrying out the dryinq of wooden ob jects The present invention i3 related ~o a method of drying wood in tho shape of boards, planks, etcetera.
A well-known method of drying timber is carried out by exposing the timber to dry hot-air currents which suck out the moisture of the wood. During such a 5 procedure the surfaces of the wooden objects will dry first which implies that the thin capillaries in the wood which keep the moisture will shrink at the surface and obstruc~ further transfer of moisture out of the wood. In such a well-known procedure (e.g. patent publication SE 319129) the hot-air drying i3 comp~eted with a high frequency treatment of the wood. By such high frequency heating it is 10 possible to achieve a temperature gradient in the load which i~ positive in the direction from the surface to ~h~ centre of the load. As the heat is then generated in the wood it is necessary to provide air to cool ths wood in order to create atemperature balance. The moisture is then pressed out instead of being s~lcked out as in the case of conventional hot-air drying when the temperature gradient i~
15 oppositely directed. The high frequency treatment according to ~he well-knownprocedure implies, however, just a partia~ advantage to the conventional drying~Some improvements of the procedure are achieved by the use of microwave heating for the drying. 1) The saving of time by microwave hea~ing can be essential; the drying period is often reduced to 20 9~ of the corresponding period 20 of hot-air drying. 2) The microwaves are self-adjusting i.e. the drier parts of the load absorb less effect than the moister ones. 3) The microwave drying gives a higher quality thanks to the fact that the occurrence of cracking and wrappedne~s is practically elirninated as both the temperature and the moisture gradients are essentially less than in the case of other drying methods. 4) The t.eatment costs 25 are considerably reduced by microwave drying thanks to the fact that a laying of bed laths is~eliminated and the improvement of quality allows a simplification of the subsequent manufacturing procedures. 5)1~1uch less energy consumption is a consequence of the use of microwaves, primarily owing to the fact that no need exists for heating air separa~ely, ~hat the air temperature in the drying room is 3û lower and thus the heat dissipation less, that the drying period is shorter and that the power of ventilators is reduced as the air circulation is used jus~ for removing the moisture, not for blowing air on the timber to suck out the moisture as in the case of ho~-air drying.
- 2 ~
According to this invention, there is provided in the method of drying wood objects by subjecting the objects to microwave energy in a treatment space while circulating air in said space, the improvement comprising covering said objects with a cover of a heat insulating material that is pervious to moisture and to said microwave energy, whereby said objects are separated from said circulating air.
According to another aspect of this invention there is 10 provided a method for drying wooden objects comprising the steps of: (a) stacking said wood objects close to each to form a unit; (b) covering ~aid unit with a cover of a heat insulating material which permits the penetration therethrough of microwaves and water vapor; (c) pushing said cover unit in a 15 microwave treatment room; (d) supplying microwave energy to said treatment room; and (e) circulating air in said treatment room externally of said cover.
The cross-section areas of the load inside the 20 insulation in any direction may be of a value of some penetration depths at most of the used microwave frequency.
When this is for instance 915 MHz this measure will be about 1 meter. The microwaves penetrate the insulation without attenuation and are absorbed in the load. Thanks to this an 25 even drying is achieved which is lenient and brings about great technical advantages owing to less occurrence of cracking and wrappedness in the wood.
- 2a ~
The preferred embodiment of this invention is illustrated in the accompanying drwings in which:
Fig. 1 is a vertical section of a treatment room for treating a package of wood, and Fig. 2 is a view similar to Figure 1 showing treatment of a stack of wood.
The physical quantities to be used in carrying ou-t a method here referred to are microwave effect, temperature and time, in addi-tion condensation of moisture is assumed to be provided. Microwave effect is supplied from a microwave generator which works in an established frequency range.
15 Condensation is achieved by means of a cooling apparatus and ventilator arrangement. The procedure is carried out in a treatment room 10 to which a microwave source 11 and an air circulation system 12 are connected. There is also a carrier 13 for a load 14 to be treated in the room. The inner walls of the 20 room are designed for a high reflection of microwaves and a good sealing to the environment so that the waves cannot leak out.
The load is disposed in a parcel (Fig. 1) or stacked (Fig. 2) on the carrier which in the shown embodiment is a carriage of preferably dry wood with wheels of metal. The distance from the 25 wheels to the load need to be a couple of vacuum wavelengths in - 2b -order not to make the distortions in the field from the metal objects dominating. The carriage is used for moving the load into and out of the treatment room. If other conveying means are used the carrier can be a common stand. The wooden objects (Fig. 1) shall be in close contact with each other as a sufficient vaporization still occurs and the moisture is removed by the air circulation. The microwave heating is self-adjusting in the way that drier parts of the load absorb less effect than moist parts. The objects can be kept together by bands or in 10 other ways exposed to a pressure in order to further reduce the warpedness of the dried product. If certain parts of the load have ~c ~ o~ c~r~/~c E~3~ /on3~9 -~
uneven moisture this will be equilibrated during the drying procedure. Closely packed objects are during the heating heated to a higher temperature than freelystrayed objects which would be cooled individually by the air circulation. The wooden ~urfaces are protected from the cooling air circulation by an insulation 5 cover 16 around the wooden objects. Thanks to this a more even temperature andmoisture gradient is achieved which makes ;t possible to obtain a higher quality, reducea the energy consumption of the drying process owing to smaller heat di~sipation to the enYironment and allows the use of 3 higher wood temperature than what is used in conventional drying. The moisture of the wood is evaporatedlû more rap;dly at the obtained higher temperature, penetrates the insulation and is removed by the air current. Owing to the fact that the moisture is evaporated more rapidly the treatment time will be shorter and the procedure more economic.
The separate objscts (Fig. 2) of the load can be positioned at a distance 15 from each other so that open;ng gap~ and hence air space are formed in the load~
Such opening gaps can be established by putting laths (bed laths) 15 between Lhelayers of boards or the like when these are piled up. The openinq gap~ establish air channels in the load which is thus thoroughly aired when the ventilator i workinq.
The relative humidity in the air is high (typlcally more than 80 %) but to 2û make the air continuously absorb vapour, the systern is provided with a condensat-ing apparatus in the form of a cooling element 17. As th2 circulation system is closed the same air is cùnducted in a circuit between the load and the cooling element. The air circulates at a low speed as the air current just shall remove moisture9 a relatively small Yentilator la can thus be used~
The insulation material mentioned in the foregoing shall have the property of letting vapour through. The choice of one of several such ma~erials should bemade case by case, as an example it is noted that packing material in the form of undulated cardboard boxes has a sufficient heat insulating caoacity in combinaton with diffusibility. As an example of wooden objects packed and dried in boxes with 30 those properties furniture details and parquet blocks are menticned. The drying procedure is then the last step in a manufacturing process which thanks to this method can be shortened and simplified.
According to this invention, there is provided in the method of drying wood objects by subjecting the objects to microwave energy in a treatment space while circulating air in said space, the improvement comprising covering said objects with a cover of a heat insulating material that is pervious to moisture and to said microwave energy, whereby said objects are separated from said circulating air.
According to another aspect of this invention there is 10 provided a method for drying wooden objects comprising the steps of: (a) stacking said wood objects close to each to form a unit; (b) covering ~aid unit with a cover of a heat insulating material which permits the penetration therethrough of microwaves and water vapor; (c) pushing said cover unit in a 15 microwave treatment room; (d) supplying microwave energy to said treatment room; and (e) circulating air in said treatment room externally of said cover.
The cross-section areas of the load inside the 20 insulation in any direction may be of a value of some penetration depths at most of the used microwave frequency.
When this is for instance 915 MHz this measure will be about 1 meter. The microwaves penetrate the insulation without attenuation and are absorbed in the load. Thanks to this an 25 even drying is achieved which is lenient and brings about great technical advantages owing to less occurrence of cracking and wrappedness in the wood.
- 2a ~
The preferred embodiment of this invention is illustrated in the accompanying drwings in which:
Fig. 1 is a vertical section of a treatment room for treating a package of wood, and Fig. 2 is a view similar to Figure 1 showing treatment of a stack of wood.
The physical quantities to be used in carrying ou-t a method here referred to are microwave effect, temperature and time, in addi-tion condensation of moisture is assumed to be provided. Microwave effect is supplied from a microwave generator which works in an established frequency range.
15 Condensation is achieved by means of a cooling apparatus and ventilator arrangement. The procedure is carried out in a treatment room 10 to which a microwave source 11 and an air circulation system 12 are connected. There is also a carrier 13 for a load 14 to be treated in the room. The inner walls of the 20 room are designed for a high reflection of microwaves and a good sealing to the environment so that the waves cannot leak out.
The load is disposed in a parcel (Fig. 1) or stacked (Fig. 2) on the carrier which in the shown embodiment is a carriage of preferably dry wood with wheels of metal. The distance from the 25 wheels to the load need to be a couple of vacuum wavelengths in - 2b -order not to make the distortions in the field from the metal objects dominating. The carriage is used for moving the load into and out of the treatment room. If other conveying means are used the carrier can be a common stand. The wooden objects (Fig. 1) shall be in close contact with each other as a sufficient vaporization still occurs and the moisture is removed by the air circulation. The microwave heating is self-adjusting in the way that drier parts of the load absorb less effect than moist parts. The objects can be kept together by bands or in 10 other ways exposed to a pressure in order to further reduce the warpedness of the dried product. If certain parts of the load have ~c ~ o~ c~r~/~c E~3~ /on3~9 -~
uneven moisture this will be equilibrated during the drying procedure. Closely packed objects are during the heating heated to a higher temperature than freelystrayed objects which would be cooled individually by the air circulation. The wooden ~urfaces are protected from the cooling air circulation by an insulation 5 cover 16 around the wooden objects. Thanks to this a more even temperature andmoisture gradient is achieved which makes ;t possible to obtain a higher quality, reducea the energy consumption of the drying process owing to smaller heat di~sipation to the enYironment and allows the use of 3 higher wood temperature than what is used in conventional drying. The moisture of the wood is evaporatedlû more rap;dly at the obtained higher temperature, penetrates the insulation and is removed by the air current. Owing to the fact that the moisture is evaporated more rapidly the treatment time will be shorter and the procedure more economic.
The separate objscts (Fig. 2) of the load can be positioned at a distance 15 from each other so that open;ng gap~ and hence air space are formed in the load~
Such opening gaps can be established by putting laths (bed laths) 15 between Lhelayers of boards or the like when these are piled up. The openinq gap~ establish air channels in the load which is thus thoroughly aired when the ventilator i workinq.
The relative humidity in the air is high (typlcally more than 80 %) but to 2û make the air continuously absorb vapour, the systern is provided with a condensat-ing apparatus in the form of a cooling element 17. As th2 circulation system is closed the same air is cùnducted in a circuit between the load and the cooling element. The air circulates at a low speed as the air current just shall remove moisture9 a relatively small Yentilator la can thus be used~
The insulation material mentioned in the foregoing shall have the property of letting vapour through. The choice of one of several such ma~erials should bemade case by case, as an example it is noted that packing material in the form of undulated cardboard boxes has a sufficient heat insulating caoacity in combinaton with diffusibility. As an example of wooden objects packed and dried in boxes with 30 those properties furniture details and parquet blocks are menticned. The drying procedure is then the last step in a manufacturing process which thanks to this method can be shortened and simplified.
Claims (6)
1. In the method of drying wood objects by subjecting the objects to microwave energy in a treatment space while circulating air in said space, the improvement comprising covering said objects with a cover of a heat insulating material that is pervious to moisture and to said microwave energy, whereby said objects are separated from said circulating air.
2. The method of claim 1 wherein said step of circulating air comprises propelling air in a circuit between a cooling element and said treatment space without connection with the atmosphere outside of said space, whereby water removed from said objects by the circulating air condenses on said cooling element.
3. The method of claim 1 further comprising maintaining the temperature of the circulating air to be lower than that of the wooden objects.
4. A method for drying wooden objects comprising the steps of:
a) stacking said wood objects close to each to form a unit;
b) covering said unit with a cover of a heat insulating material which permits the penetration therethrough of microwaves and water vapor;
c) pushing said cover unit in a microwave treatment room;
d) supplying microwave energy to said treatment room;
and e) circulating air in said treatment room externally of said cover.
a) stacking said wood objects close to each to form a unit;
b) covering said unit with a cover of a heat insulating material which permits the penetration therethrough of microwaves and water vapor;
c) pushing said cover unit in a microwave treatment room;
d) supplying microwave energy to said treatment room;
and e) circulating air in said treatment room externally of said cover.
5. The method of claim 4 wherein said step of circulating comprises propelling air in a circuit between a cooling element and said unit without connection with the atmosphere outside of said treatment room, whereby water removed from said unit by said circulating air condenses on the cooling element.
6. The method of claim 4 wherein said step of circulating comprises maintaining the temperature of circulating air in said treatment room to be lower than that of said wood objects.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000406834A CA1188888A (en) | 1982-07-07 | 1982-07-07 | Method of carrying out the drying of wooden objects |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000406834A CA1188888A (en) | 1982-07-07 | 1982-07-07 | Method of carrying out the drying of wooden objects |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1188888A true CA1188888A (en) | 1985-06-18 |
Family
ID=4123174
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000406834A Expired CA1188888A (en) | 1982-07-07 | 1982-07-07 | Method of carrying out the drying of wooden objects |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1188888A (en) |
-
1982
- 1982-07-07 CA CA000406834A patent/CA1188888A/en not_active Expired
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEC | Expiry (correction) | ||
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