US3902253A

US3902253A - Lumber drying apparatus

Info

Publication number: US3902253A
Application number: US433888A
Authority: US
Inventors: Takeshi Sabuzawa; Toshiyuki Suzuki; Masayuki Kato; Teruji Muraki
Original assignee: Nippon Gakki Co Ltd
Current assignee: Nippon Gakki Co Ltd
Priority date: 1973-01-17
Filing date: 1974-01-16
Publication date: 1975-09-02
Anticipated expiration: 1992-09-02
Also published as: SE7400536L; SE405640B

Abstract

A lumber drying apparatus for drying lumber such as boards and squares to a desired final moisture content during the progressive transfer of the lumber through a drying section defined by an outer wall structure having an inlet at the green end and outlet at the dry end. The drying section is divided along the lumber transfer path into a plurality of drying compartments, with the atmospheric conditions of the drying compartments individually set according to a drying schedule predetermined by the kind and thickness of the lumber to be dried.

Description

United States Patent Sabuzawa et a1.

Sept. 2, 1975 LUlVmER DRYING APPARATUS Inventors: Takeshi Sabuzawa; Toshiyuki Suzuki; Masayuki Kato; Teruji Muraki, all of Hamamatsu, Japan Assignee:

Filed:

Nippon Gakki Seizo Kabushilki Kaisha, Hamamatsu, Japan Jan. 16, 1974 Appl. No.: 433,888

Foreign Application Priority Data Jan. 17, 1973 Japan 48-7536 Jan. 17, 1973 Japan 48-7537 Jan. 17, 1973 Japan 48-8107 Jan. 19, 1973 Japan..... 48-8771 Jan. 19, 1973 Japan..... 48-8772 Jan. 19, 1973 Japan..... 48-8773 Feb. 6, 1973 Japan 48-9376 Feb. 6, 1973 Japan 48-15276 US. Cl. 34/1; 34/77; 34/212;

34/219; 34/242 Int. Cl F261) 3/34 Field of Search 34/215, 216, 217, 210,

34/212,1, 77, 78, DIG. 19, DIG. 21, 218, 219, 242; 432/250;'160/l84; 432/8, 54; 55/32 [56] References Cited UNITED STATES PATENTS 942,150 12/1909 Tiemann 34/77 1,567,031 12/1925 Buensod 34/216 2,197,776 4/1940 Argabrite et a1... 34/216 2,799,096 7/1957 Scott 34/216 2,997,096 8/1961 Morrison et a1. 34/216 3,474,544 10/1969 Holden, Jr. et a1. 34/1 3,497,965 3/ 1970 Cortellessa 34/242 3,634,998 1/1972 Patterson 55/32 Primary Examiner-Carroll B. Dority, Jr. Assistant Examiner-Larry I. Schwartz Attorney, Agent, or FirmWaters, Schwartz & Nissen [5 7] ABSTRACT A lumber drying apparatus for drying lumber such as boards and squares to a desired final moisture content during the progressive transfer of the lumber through a drying section defined by .an outer wall structure having an inlet at the green end and outlet at the dry end. The drying section is divided along the lumber transfer path into a plurality of drying compartments, with the atmospheric conditions of the drying compartments individually set according to a drying schedule predetermined by the kind and thickness of the lumber to be dried.

23 Claims, 13 Drawing Figures 13 30 III 1 =12. 39 3 T- 8273?; l8 z I 2,

PATENTED SEP 2 I975 SHEET 3 0F 5 I G. 6b

FIG. 6a

PATENTED 21975 3,902,253 sum u, or 5 FIG. 7

FIG.

31 32 32a 32u /32Q PATENTED SEP 21975 sum 5 u; 5

om mm wN mp muw Um @323 m mm ow 33 mm LUMBER DRYING APPARATUS BACKGROUND OF THE INVENTION This invention relates to apparatus for drying lumber such as boards and squares and, more particularly, to a lumber drying apparatus, in which the lumber is passed through a plurality of drying comparments under different drying conditions preset according to a predetermined schedule to thereby reduce the moisture content of the lumber to a desired value.

The lumber such as boards and squares produced from logs is usually dried either by air seasoning or through an artificial drying system such as one using hot air.

In the case of air seasoning or natural drying, where the lumber is left outdoors in the form of piles or stacks, a large stack area or drying yard is required. Also, in this case the drying or seasoning period cannot be controlled and, it is very long; for 2 or 3 years is required to season lumber of some kinds. Further, with whatever long seasoning period it is impossible to obtain a moisture content lower than the atmospheric equiliblium moisture content.

From this point of view almost all air seasoned lumber flnds use only as construction material and cannot be used as the material for interior furnishings, furni ture or musical instruments such as a piano where dimensional error in the material are unacceptable.

Accordingly, the controlled drying, particularly heated drying with hot air, has been adopted to readily obtain lumber suited for the material of interior furnishings, furniture and musical instruments.

The heated drying method, in contrast to natural drying, permits reducing the moisture content to a desired value suited to the use of the lumber in a greatly reduced drying period.

In this method, hot air whose moisture and temperature are artificially controlled is supplied to a drying compartment where the lumber to be treated is accommodated. From the standpoint of cost and finish of drying treatment. however, it to be usual for the lumber to be treated is preliminarily dried through natural drying. This means that there is still required a period of several weeks to several months to obtain dry lumber of satisfactory finish, that is, one with a moisture content (usually around 12 percent) suited for of furniture and musical instruments.

Therefore, a considerable number of drying compartments are needed to meet the demand for the dry lumber in the market. Also, a large stack area is still needed for the preliminary drying. Further, such laborconsuming operations as piling up the wet lumber in the drying yard and transferring lumber into and out of the drying compartment are inevitable.

SUMMARY OF THE INVENTION A primary object of the invention, accordingly, is to provide a lumber drying apparatus, which permits green lumber such as boards and squares to be dried during progressive passage thereof through a plurality of drying compartments individually held under different temperature and moisture conditions controlled according to a drying schedule predetermined by such factors as the kind and thickness of the treated lumber, whereby dry lumber with a desired moisture content and free from such undesired results as cupping, bowing end split, surface checks, inner checks and collapse may be obtained in a very short period of time of such order as expressed in terms of hours.

Another object of the invention is to widely reduce the drying period so as to meet the demand for dry lumber in the market, reduce the space required for drying and facilitate the management of lumber.

A further object of the invention is to obtain dry lumber at a greatly increased rate by providing a plurality of vertically spaced lumber transfer paths in the individual drying compartments.

Still another object of the invention is to improve the efficiency of drying and obtain uniform drying of lumber by increasing the inner diffusion of moisture with at least one high-frequency dielectric drying unit provided in the path of progressive transfer of the lumber through a succession of drying compartments.

Another object of the invention is to provide a lumber drying apparatus, in which the hot air in each drying compartment is partly recirculated through a duct partly exposed to the external atmosphere and provided with a moisture removing mechanism to circulate only dry hot air so as to eventually reduce the loss of thermal energy.

Another object of the invention is to provide a lumber drying apparatus, in which preparatory sections are provided adjacent the green end and dry end of the drying section, with a desired temperature gradient between the external atmospheric temperature and the temperature of the drying section established in each preparatory section, thereby preventing bowing, end split and like undesired effects that might result from sudden change of temperature and moisture content of the lumber.

Another object of the invention is to provide a lumber drying apparatus, in which each drying compartment is provided with heaters disposed on opposite sides of the lumber transfer path, deflecting members disposed to surround the outer side of the heaters and fans for hot air circulation, one fan provided on a central portion of the deflecting member on one side of the lumber transfer path and the other fans on opposite end portions of the deflecting member on the other side, thereby producing two hot air streams flowing in opposite directions within the drying compartment so as to dry the lumber uniformly and prevent bowing, end split and like undesired results.

Another object of the invention is to greatly improve the drying efficiency with the same space factor by providing a plurality of vertically spaced lumber transfer paths.

Another object is to provide a lumber drying apparatus, in which the individual drying compartments are vertically divided into a plurality of divisions by hori- BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a diagrammatic view outlining the principles of operation of the lumber drying apparatus according to the invention.

FIGS. 2a and 2b illustrate is a horizontal longitudinal sectional view, partly broken away, showing an embodiment of the lumber drying apparatus according to the invention, with a green end portion of the apparatus indicated at FIG. 2a and a dry end portion of the apparatus indicated at FIG. 212.

FIG. 3 is a sectional view taken along line IIIIII in FIG. 2a.

FIG. 4 is a vertical sectional view showing an embodiment of the curtain and high-frequency dielectric drying means provided between adjacent drying compartments.

FIG. 5 is a vertical sectional view showing an embodiment of the curtain provided in the inlet preparatory section in the apparatus according to the invention.

FIGS. 60 and 6b show an embodiment of the means for supplying lumber into the apparatus according to the invention,

FIG. 7 is a front view showing one of two hot air deflectors constituting the cover structure.

FIG. 8 is a sectional view, on an enlarged scale, showing an embodiment of the moisture removing means.

' FIGS. 9a and 9b are views similar to FIGS. 2a and 212 but showing a different embodiment of the lumber drying apparatus according to the invention.

FIG. 10 is a sectional view taken along line XX in FIG. 9a.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows, in block form, the lumber drying apparatus according to the invention. Reference numeral 1 designates an inlet preparatory section provided at the green end of the apparatus. Lumber 2 such as boards and squares produced from logs are directly fed into the inlet section 1. The interior of the inlet section 1 is held at a temperature of 40C to 50C. Numeral 3 designates an outlet preparatory section provided at the dry end of the apparatus. The dried lumber 2' with a moisture content reduced to a desired value is discharged from this section. Similar to the inlet section 1, the outlet section 3 is held at a temperature of 40C to 50C. A temperature gradient is provided between these sections on the one hand and drying compartments on the other hand as will be described later. The lumber 2 is transferred from the inlet section 1 to the outlet section 3 progressively through a succession of a plurality of drying compartments, for instance five compartments 4a to 4e, which are respectively held at different temperature and moisture conditions so that the lumber with an initial moisture content of nearly 100 percent may be dried stepwise until the moisture content is reduced to around 10 percent.

FIG. 2 shows a sectional view of part of the apparatus in FIG. 1. The outer walls 5 of the apparatus having the drying compartments 4a to 42 are made of a material which is free from thermally-caused chemical changes and still having a heat retention property, for instance metal, brick or concrete. The interior of the tunnel-like structure constituted by the outer walls 5 is divided into the drying compartments 4a to 40 by means of curtains 6a to 6d which will be described hereinafter in detail.

As shown in FIG. 2, a number of lumber feed rollers 7 each provided with a heat-resistant rubber coating are arranged in a row at desired intervals, for instance 1 meter, within and over the entire length of the inlet preparatory section 1, drying compartments 4a to 46 and outlet preparatory section 3. These feed rollers 7 extend horizontally and transversally and are rotatably supported at opposite ends between a pair of

support members

8 and 9. The feed rollers 7 may be provided at their one end with respective sprocket wheels in mesh with an endless chain for driving the feed rollers in synchronism with respect to one another.

While only a single roller conveyor type horizontal lumber transfer path may be provided, the drying efficiency may be multiplied by providing a plurality of such paths vertically spaced from one another, as shown in FIG. 3, with all the vertically spaced horizontal lumber transfer paths C C extending through individual drying compartments 4a to 42.

The curtains 6a to 6d defining the individual drying compartments 4a to 42 each consists of a pair of curtains spaced apart a desired distance and constructed such that the lumber being transferred can freely pass through them.

FIG. 4 shows an example of the construction of the curtains 6a to 6d. As is shown, each of the curtains in pair is constituted by vertically spaced shield members 14 individually corresponding to respective horizontal lumber transfer paths C C and secured to a pair support members 12 and 13 (only support member 12 being shown) and flap members 15 individually pivoted to the lower edge of the respective shield members 14 such that they each can open and close the gap between the adjacent shield members 14.

In the embodiment of FIG. 4, in the space between the pair of curtains constituting each of the curtains 6a to 6d, there extend rollers 16 each belonging to the corresponding one of the horizontal lumber transfer paths C C and rollers 17 co-operating with the associated rollers 16 to clamp the lumber. The

rollers

16 and 17 are driven in synchronism with the afore-mentioned feed rollers 7 each provided with a sprocket wheel 10 in mesh with an endless drive chain 11. The rollers 17 may also be provided for the respective rollers 7, as shown in FIG. 4, so as to insure feeding of the lumber and to prevent it from warping. Also, there are provided in the space between the pair of curtains on the outlet side of the

rollers

16 and 17 electrode pairs for high-frequency dielectric drying each provided for each lumber transfer path and consisting of electrodes 18a and 1812 vertically spaced apart a desired distance.

Referring back to FIG. 2,

heaters

19 and 20 having a heater fin for drying the lumber are provided along the opposite sides of the lumber transfer path or paths in each of the drying compartments 4a to 4e. The outer side of each of the

heaters

19 and 20 is covered by a cover structure consisting of hot

air deflecting members

21 and 22. Of the pair of cover structures for each drying compartment, one is provided with

suction fans

23 and 24 located in the vicinity of the opposite ends of the compartment, and the other cover structure is provided with a suction fan 25 located to face the center of the compartment. These fans 23 to 25 serve to provide circulation of hot air, and they are independently driven from a motor 26 as shown in FIG. 3. The hot air deflecting members 21 are so arranged as to cause the air sucked by the

fans

23 and 24 to flow along the members 21 and to circulate toward the suction fan 25, and the hot air deflecting member 22 is so arranged as to cause the air sucked by the fan 25 to flow along the member 22 and to circulate toward the

fans

23 and 24.

Numerals

27 and 28 designate nozzles, from which hot air, cool air or steam may be issued to adjust the atmospheric condition of the drying compartment. These

nozzles

27 and 28 are provided in the path of hot air circuh tion caused by the fans 23 to 25, that is, on the inner side of the associated cover structure of the hot

air deflecting members

21 and 22.

The cover structure carrying the

fans

23 and 24 is provided with ventilation ports 29, as is typically shown in FIG. 7, communicating with a space 30 defined be tween the cover structure and the outer wall 5. The space 30 communicates with the suction side of the fan 25 provided in the other cover structure through a duct 31, which is provided with moisture removing means 32, as is most clearly shown in FIG. 3. The hot air in the drying compartment, is thus partly led through the ports 29 into the space 30 and relieved of moisture in its flow through the moisture removing means 32 in the duct 31 back to the drying compartment. The moisture removing means 32 is provided in a major portion of the duct 31 extending above the outer wall 5.

FIG. 8 shows an embodiment of the moisture removing means 32. It comprises a number of vertical fins 32a vertically depending from the top wall of the duct 31 and slanted fins 32b arranged between adjacent vertical fins 32a and extending from the bottom wall of the duct 31 in an inclined direction such as to redirect the hot air stream. These

fins

32a and 32b are naturally cooled by the external atmosphere.

The other cover structure carrying the fan 25 is also provided with ventilation ports 33 communicating with

spaces

34 and 35 defined between the cover structure and outer wall 5, the

spaces

34 and 35 communicating with the suction side of the

fans

23 and 24 through

re spective ducts

36 and 37, which are provided with respective

moisture removing means

38 and 39 similar to the one as mentioned above.

The inlet preparatory section 1 is provided with a plurality of curtains 40 arranged in a row in the direction of travel of the lumber, and the outlet preparatory section 3 is also provided with a similar arrangement of curtains 41. The curtains 40 have the same construction as the curtains 41, as typically shown in FIG. 5. As is shown, each curtain comprises vertically spaced shield members individually corresponding to respective horizontal lumber transfer paths C C and secured at the opposite ends to a pair support members 42, and flap members 44 of such a material as heatresistant rubber are individually pivoted to the lower edge of the respective shield members 43 such that they each can open and close the gap between the adjacent shield members 43. These curtain arrangements are provided for establishing a desired temperature gradient between atmospheric temperature and the temperature of the

drying compartment

4a or 4e, whereby adverse effects of a sudden change of temperature and moisture conditions on the lumber may be prevented.

The operation of the apparatus of the above construction according to the invention will now be described.

The

heaters

19 and 20 and air blown from the

nozzles

27 and 28 are controlled according to the drying schedule predetermined by the kind and thickness of the lumber to be dried. In each drying compartment, air heated by the heater 20 and hot air blown from the nozzles 28 tend to proceed across the lumber transfer path toward the

fans

22 and 23 due to the suction effect thereof. Also, air heated by the heater 19 and hot air blown from the nozzles 27 tend to proceed toward the opposite side of the compartment clue to the suction ef feet of the fan 25 facing the center of the compartment. Thus, with the fans 23 to 25 operating, a flow of hot air is provided within the

individual drying compartments

4a and 46 in the manner as shown by the arrows in FIG. 1, with the air flowing toward the fan 25 being divided by the deflecting member 22 into branch streams flowing in opposite directions.

Since the arrangement of the fans and deflecting members is reversed for alternate drying compartments, the direction of flow of hot air is also reversed for alternate drying compartments.

The speed of feed of the lumber, that is, the speed of rotation of the feed rollers 7 constituting the lumber transfer paths C C is also controlled according to the kind and thickness of the lumber. The lumber 2 is introduced through the curtains 40 in the inlet preparatory section 1 into the first drying compartment 4a, and by the time it leaves the first drying compartment 4a, it is dried to a predetermined moisture content clue to the corresponding temperature and moisture of the at mosphere in the first drying compartment 4a. Similarly, the moisture content of the lumber is progressively reduced as it passes through the atmospheres in the following drying compartments 4b to 4e after the predetermined drying schedule. The lumber 2' taken out through the outlet preparatory section 3 following the last drying compartment 46 thus has a moisture content suited for the interior furnishings, furnitures and musical instruments.

Also, as the lumber passes through a high-frequency electromagnetic field set up between the

electrodes

18a and 18b provided between adjacent drying compartments, it is internally heated due to the dielectric loss induced, thus increasing the inner vapor pressure and promoting the inner diffusion, so that fluctuations in the final moisture content may be extremely reduced.

FIG. 6a and 6b show an embodiment of means for introducing lumber 2 into the roller conveyor type hori zontal lumber transfer paths C, C in the inlet preparatory section 1. It has a vertically movable platform 45 movable to the levels of the individual horizontal lumber transfer paths C C and provided with a lumber loading cylinder 46. In operation, lumber 2 is conveyed from a lumber mill 47 through a conveyor 48 to the platform 45, and after a predetermined number of lumber pieces of are aligned on the platform, the platform may be moved by a suitable drive means 45 to the level of the intended lumber transfer path and the loading cylinder 46 is operated to push the aligned pieces lumber into the intended lumber transfer path.

A specific example of the use of the apparatus according to the invention for drying agathis lumber (with a moisture content of percent) with a thickness of 16 mm will now be given.

The drying schedule is set as is listed in Table 1 below.

Note: Degree Dry bulb temp. -wet bulb temp.

The agathis lumber was progressively transferred through the individual drying compartments at a transfer speed of 3.6 meters per hour and the retention time in each drying compartment was set to 4 hours. Table 2 lists the moisture contents obtained when the lumber leaves the individual drying compartments.

Table 2 5 Moisture content (7m First drying compartment 4a 65 Second drying compartment 4b 40 Third drying compartment 4c 20 Fourth drying compartment 4d 12 Fifth drying compartment 4e 8 As is evident from this example, it is possible to dry agathis lumber with initial moisture content of 95 per- 15 cent into dry lumber with a moisture content of 8 percent which is suitable as material for musical instruments or the like, in about hours.

FIG. 9 and 10 show another embodiment of the lumber drying apparatus according to the invention. In these Figures, similar parts to those shown in FIGS. 2 and 3 are designated by like reference numerals and are not particularly described in any further detail. Similar to the previous embodiment, the outer wall constituting the individual drying compartments is made from such material as metal, brick or concrete free from thermally caused chemical changes and having a high heat insulation property, and the successive drying compartments 4a to 4e are defined by the curtains 6a to 6d. In this embodiment, the drying compartments 4a to 4e are each vertically divided into two divisions by horizontally extending partition member P, as shown in FIG. 10. The spaces 10 in both the vertical divisions are connected to common duct 31 provided with moisture removing means 32. The duct 31 is 5 forked on the side of the moisture removing means 32 opposite the spaces into two branches, one being led to the fan 25 in the upper division, and the other branch indicated at 31a being led to the fan 25 in the lower division. Except for the removal of the moisture which is commonly effected both for the upper and lower divisions, the operation is the same as in the previous embodiment.

We claim:

1. A lumber drying apparatus comprising an outer wall structure defining a drying section having at least one lumber transfer path, said outer wall structure preventing leakage of hot air from said drying section, curtain means in said drying section to divide the same along said lumber transfer path into a plurality of dry- 5 ing compartments, heating means for heating the interior of each said drying compartment, and means for producing circulation of hot air in each said drying compartment including a first fan located on one side of the lumber transfer path substantially at a position in a transverse central plane of the compartment, second and third fans located on the other side of the lumber transfer path substantially at positions symmetrical to each other with respect to said transverse central plane, first deflecting means disposed on opposite sides of said first fan for dividing the flow of hot air with respect to said first fan, said first deflecting means including side walls which incline inwardly into the compartment in a direction away from the center thereof towards the second and third fans, and second deflect- 5 ing means disposed between said second and third fans for redirecting the fiow of hot air between said second and third fans and said first fan such that two circulating paths of air traveling in opposite directions are produced in each compartment, said second deflecting means including further side walls which incline inwardly into the compartment in a direction away from the second and third fans towards the center of the compartment.

2. The lumber drying apparatus according to claim 1, wherein said drying section has a plurality of vertically spaced lumber transfer paths.

3. The lumber drying apparatus according to claim 1, which further comprises at least one high-frequency dielectric drying means in said lumber transfer path.

4. The lumber drying apparatus according to claim 1, wherein said curtain means dividing the drying section into a plurality of drying compartments each comprises a pair of upright support members on opposite sides of the lumber transfer path, a transverse shield member secured to said support members, and a flap member made of heat-resistant material and pivoted to the lower edge of said transverse shield member.

5. The lumber drying apparatus according to claim 1, comprising duct means for recirculation of part of the hot air for each of the drying compartments, said duct means partly extending to the outside of the outer wall structure and exposed to external atmosphere, and moisture removing means in the exposed portion of said duct means.

6. The lumber drying apparatus according to claim 1, wherein said outer wall structure further defines an inlet preparatory section adjacent the inlet end of the drying section, said inlet preparatory section being divided into a plurality of divisions by curtain means arranged one after another in the direction of transfer of lumber, such that a temperature gradient between external atmospheric temperature and the temperature of the drying section is established in said inlet preparatory section.

7. The lumber drying apparatus according to claim 1, wherein said outer wall structure further defines an outlet preparatory section adjacent the outlet end of the drying section, said outlet preparatory section being divided into a plurality of divisions by curtain means arranged one after another in the direction of transfer of lumber, such that a temperature gradient between the temperature of the drying section and external atmospheric temperature is established in said outlet preparatory section.

8. The lumber drying apparatus according to claim 5, wherein said moisture removing means comprises a number of vertical fins vertically depending from the top wall of the duct means and slanted fins between adjacent vertical fins and extending from the bottom wall of the duct means in an inclined direction such as to redirect the hot air stream.

9. The lumber drying apparatus according to claim 6, wherein said curtain means dividing the inlet preparatory section into a plurality of divisions each comprises a pair of upright support members on opposite sides of the lumber transfer path, a tranverse shield member secured to said support members, and a flap mmember made of heat-resistant material pivoted to the lower edge of said tranverse shield member.

10. The lumber drying apparatus according to claim 7, wherein said curtain means dividing the outlet preparatory section into a plurality of divisions each comprises a pair of upright support members on opposite sides of the lumber transfer path, a tranverse shield member secured to said support members, and a flap member made of heat-resistant material pivoted to the lower edge of said transverse shield member.

11. The lumber drying apparatus according to claim 1, wherein each said drying compartment is provided with moist air supply nozzles.

12. The lumber drying apparatus according to claim 1, wherein said first, second and third fans are suction fans. I

13. The lumber drying apparatus according to claim 12, wherein said first deflecting means are disposed on opposite sides of said first fan and adapted to divides a stream of hot air proceeding toward said first fan into two branch streams flowing in opposite directions toward the respective second and third fans, and said second deflecting means between said second and third fans redirects hot air proceeding from said second and third fans toward said first fan, thereby producing the circulation of hot air.

14. The lumber drying apparatus according to claim 1, wherein each said drying compartment further com prises heater means disposed in the path of convection of hot air along said first and second deflecting means.

15. The lumber drying apparatus according to claim 1, wherein said second deflecting means in each said drying compartment defines a space with respect to the outer wall structure and is provided with a ventilating port communicating with said space, and also wherein duct means for recirculating part of the hot air is provided for each said drying compartment, said duct means partly extending to the outside of the outer wall structure and exposed to external atmosphere, whereby the hot air in each drying compartment is partly recirculated through said ventilating port, said space and said duct means to said first fan.

16. The lumber drying apparatus according to claim 15, wherein said duct means includes in its portion exposed to external atmosphere with a moisture removing means constituted by a number of vertical fins vertically depending from the top wall of the duct means and slanted fins between adjacent vertical fins and extending from the bottom wall of the duct means in an inclined direction such as to redirect the hot air stream.

17. The lumber drying apparatus according to claim 2, wherein each said lumber transfer path is constituted by a number of feed rollers arranged in a row.

18. The lumber drying apparatus according to claim 12, wherein said second deflecting means in each said drying compartment defines a space with repsect to the outer wall structure and is provided with a ventilating port communicating with said space, and also wherein duct means for recirculating part of the hot air is provided for each said drying compartment, said duct means partly extending to the outside of the outer wall structure and exposed to external atmosphere, whereby the hot air in each drying compartment is partly recirculated through said ventilating port, said space and said duct means to said first fan.

19. The lumber drying apparatus according to claim 18, wherein said duct means includes in its portion exposed to external atmosphere a moisture removing means constituted by a number of vertical fins vertically depending from the top wall of the duct means and slanted fins between adjacent vertical fins and extending from the bottom wall of the duct means in an inclined direction such as to redirect the hot air stream.

20. The lumber drying apparatus according to claim 1 wherein said first deflecting means extends along said one side of the associated compartment and said second deflecting means extends along the other side of the associated compartment.

21. The lumber drying apparatus according to claim 20 wherein said side walls of the first deflecting means have end portions which gradually slope inwardly into the compartment in a direction away from said first fan.

22. The lumber drying apparatus according to claim 4 wherein said first fan and said second and third fans are on alternately opposite sides of adjacent compartments.

23. The lumber drying apparatus according to claim 22 wherein the side walls of the first deflecting means of one compartment join the side walls of the second deflecting means of an adjacent compartment at the juncture of these compartments.

l l l

Claims

1. A lumber drying apparatus comprising an outer wall structure defining a drying section having at least one lumber transfer path, said outer wall structure preventing leakage of hot air from said drying section, curtain means in said drying section to divide the same along said lumber transfer path into a plurality of drying compartments, heating means for heating the interior of each said drying compartment, and means for producing circulation of hot air in each said drying compartment including a first fan located on one side of the lumber transfer path substantially at a position in a transverse central plane of the compartment, second and third fans located on the other side of the lumber transfer path substantially at positions symmetrical to each other with respect to said transverse central plane, first deflecting means disposed on opposite sides of said first fan for dividing the flow of hot air with respect to said first fan, said first deflecting means including side walls which incline inwardly into the compartment in a direction away from the center thereof towards the second and third fans, and second deflecting means disposed between said second and third fans for redirecting the flow of hot air between said second and third fans and said first fan such that two circulating paths of air traveling in opposite directions are produced in each compartment, said second deflecting means including further side walls which incline inwardly into the compartment in a direction away from the second and third fans towards the center of the compartment.

12. The lumber drying apparatus according to claim 1, wherein said first, second and third fans are suction fans.

14. The lumber drying apparatus according to claim 1, wherein each said drying compartment further comprises heater means disposed in the path of convection of hot air along said first and second deflecting means.