DE2014116A1 - Drying process and system for wood veneers and similar material with a broadly varying moisture content - Google Patents

Description

Drying process and system for wood veneers and the like Material with a widely varying moisture content.

The invention relates to a system and a method for Drying wood veneer and similar sheet material, the initial moisture content of which varies over a wide range. In particular The invention relates to an arrangement of a high-capacity main dryer, in which a large percentage of the treated material falls to one Moisture content within a predetermined range without excessive Drying out is dried, and a secondary dryer lower capacity, which takes the remaining part of the underdried material from the execution point of the main drying chamber, to further bring the material to a certain level of moisture dry. An endless conveyor construction for the secondary dryer allows the undried material to be automatically transferred as many times as it is necessary to pass through the secondary drying chamber again in order to obtain the required dryness in the end product. While the embodiment of the invention disclosed here relates to the Drying of wood veneer relates, these lessons can of course also an advantage for a drying line or heat treatment of other sheet or strip materials apply, their

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Initial humidity varies over a wide range.

It has been a conventional method of production for many years drying veneers by handling the product in sheet form and layering it through a multi-deck front drying chamber to move. The veneer is usually scraped off a log using a lathe in a changeable manner Leaf things depending on the size of the desired multilayer board product. The outer layers of the trunk when separated from the Lathes are peeled off as young wood, which usually has a higher moisture content, while the inner ones Layers, known as heartwood, have a lower moisture content and generally have a slightly different structure and density. While with some types of woods the difference is not as great in moisture content between heartwood and young wood as in others, there is nevertheless a measurable difference in all cases, in fact.

In any type of wood that has a wide range of moisture content differences between heartwood and young wood, attempts are usually made to separate the two immediately, after the green veneer is cut off in sheet size. Typical-

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This segregation is wisely achieved, where possible, by using the natural color differences that exist between the core fluid young wood material but mostly by the trained eye of the sorter, which has certain different characteristics of the inner Recognizes wood in contrast to the outer layer. Although this removal of the heartwood from the young wood has heretofore been done by hand, moisture sensors have been developed to achieve this removal by hand. However, have such instruments so far in the industry has not yet found wide acceptance and it lacks the broad band splitting ability to handle the material, which has a wide range of moisture content.

Although there is veneer drying that is now carried out in the industry with wood material in tape form or as panels in a layered base, "the largest amount of layered veneer in sheet form" is handled in packs with single-layer leaves continuously introduced into multi-deck conveyor dryers. After a initial passage through the drying chamber, the filter sheet is read and stacked again in drying packs. Even where an initial selection of heartwood and young wood material has taken place, there is typically a wide difference in the

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Moisture content even after the veneer sheets have passed through the dryer for the first time. To the main part In fact, drying an ordinary batch to a satisfactory moisture level requires overdrying as much as 70% of the batch are reduced to a lower than desired humidity level · Based on the knowledge of a wide difference in humidity, the present in a veneer pack after the initial drying cycle The industry generally follows the practice of a small percentage of one pass as "re-drying" for the next Process. In conventional practice, this becomes a re-drying material (i.e. the material that could not be dried sufficiently in the initial drying run due to a higher than average initial moisture content) of that Weed out satisfactorily dried material and set aside until enough has accumulated to make a second Make passage for this material through the drying chamber. However, due to the treatment of this redrying material during the second drying process there are considerable Lent losses and fractures, large production losses and decreased drying efficiency such that the industry devotes only a small percentage of the material to redrying.

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Probably the main rejection of the process is re-drying of the veneer, in order to bring it to an acceptable level of its moisture content, in that, there, ß the main drying process of the green veneer in that. Production run on the dryer interrupted will. Also, the dryer itself must operate at a lower level of efficiency during the re-drying cycle because considerably reduced temperatures are required in the circulation of the drying medium in order to avoid overdrying to prevent this partially dried material.

Therefore, the invention is directed to a two dryer system Avoidance of the need for an initial selection of the veneer product " tes in the green state to the young wood with high moisture content to separate from the less moist heartwood material. the Two-dryer arrangement makes an efficient drying of the undried Material possible that results from the initial drying process without additional handling and without interrupting the production run of the green veneer through the drying system.

In the plant according to the present invention, the first dryer , which is of the conventional multi-deck conveyor type, acts as the main

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dryer through which all of the green veneer material goes, which can either be sheet or tape. The operating parameters (ie conveying speed, drying air temperature and circulation flow) of this main dryer are set so that only the veneer material with a low initial moisture content is completely dried during the passage through it. A conventional moisture scanner is placed at the exit of the main dryer to differentiate the fully dried material, typically 30-50% of the passage of the main apparatus, depending on the types of the remainder requiring further drying. The material, which has been satisfactorily dried during passage through the main dryer, as determined by the moisture scanner, is pulled from the conveyor, read out into packages, and is then ready for application to multilayer wood panels. The remaining material, which has been marked as insufficiently dried by the moisture scanner, makes its way through a secondary dryer, which, in contrast to the main dryer, has a lower capacity. In the transition of the material from the main to the auxiliary dryer by means of the conveyor , the underdried material is in no way handled or packed in any way and therefore the likelihood of breakage is considerably reduced, if not completely eliminated.

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In the embodiment of the invention for handling veneer panels in contrast to a veneer tape, the For the arrangement between the main dryer aisle and the entrance to the secondary " dryer designed so that the grain orientation of the leaves in Is rotated by 90 ° with respect to the direction of flow, so that e.g. when the material is initially advanced through the main tumbler with the grain orientation parallel to the direction of flow

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it gets into the secondary dryer, with the grain ~

runs at right angles to the flow in the secondary dryer. Where that

Material treated as veneer tapes would, on the other hand, be the Main * and secondary trousers are accordingly arranged in one line

and there would be no change in grain direction in the transition of the material from the main to the secondary dryer enter.

The secondary dryer of the in-line dryer assembly according to the present invention is designed to have a closed loop _ for the material entering the second dryer. These Endless construction of the secondary dryer »made possible by a endless conveyor belt that carries the veneer material in a vertical direction arranged elliptical orbit through an overflow drying chamber leads "allows" the veneer to automatically pass through the secondary

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through the dryer as many times as necessary, to reduce the moisture content to a satisfactory level. The repeated passage of the material through the secondary dryer " is necessary because despite the selection that occurs at the end of the drying process of the Main dryer, the material that reaches the secondary dryer, still has a high moisture content, which varies over a wide range. About the moisture content of the material After it has passed through the secondary dryer to monitor, a second moisture scanner is at the exit end of the again rotating conveyor of the secondary system arranged to the material determine the moisture content of which is still above the desired level. In a typical type of wood, 70% of the Veneer material entering the secondary dryer will be satisfactorily dried after a single pass, but the remaining ones 30% requires at least a second pass through the secondary drying chamber.

As mentioned earlier, there are one major major advantages of the Primary-secondary dryer systemj, as summarized above, in that the veneer product is not damaged by the treatment during the drying process. No more veneer

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material in a harmful way overdies, as it does with conventional Attachments is the case to have a minimum amount of re-drying Material to be preserved and thus undesirable effects in the Veneer panel production in relation to excessive glue consumption, and Removal of glue due to glue drying and poor veneer surfaces are avoided. Finally, the most significant advantage of the present system is the efficiency of the drying process too see, which is greatly increased if the material that goes through the plant is only dried to the desired moisture level and not well below this level. The length of time during which the veneer material is exposed to the drying medium is also reduced, as a result of which higher production speeds are possible or conversely, the operating range of the drying chamber can be reduced will increase by more than 20-30% while maintaining the same volume Veneer material is treated as the material dried by conventional drying equipment.

It is therefore a primary object of the present invention to provide a novel one To make the method and apparatus available for achieving improved continuous drying at high speed of wood veneer or similar sheet material that has a wide variety of

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ending moisture content.

It is another object of the present invention to provide necessity to avoid the separation of green veneer young wood from veneer hardwood before the drying process by means of the application of a Primary-secondary drying system that provides more uniform drying of the veneer material than could previously be achieved.

Another important object of the present invention is that Making available a veneer drying system that is more efficient and has higher production speeds than the previously known systems.

A key feature of the present invention is that the Veneer material with initially high moisture content is automatically fed through a main drying chamber to a secondary drying chamber for a further drying process, whereby the material that is not sufficient after passing through the secondary dryer is dried, is automatically fed through the secondary dryer as many times as it is necessary to achieve the desired moisture level to achieve, with the entire measure without «ine

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additional handling or manual intervention can be carried out.

A major advantage of the present invention is that the entire passage of wood veneer ^ on a rolling basis takes place without interruption of the production line and that despite the fact that the initial moisture content of the veneer material, that is dried varies over an extremely wide range.

Another important part of the present invention is that the wood veneer is dried effectively on a continuous basis Production line to an acceptable moisture content, without that 'the material is too recimated, "'."

The foregoing objectives und'andere, Merfemale uuu Vorteil® present invention-.sollen from the following description of an embodiment with reference to the accompanying drawings yield. In the drawings:

Fig. 1 is a plan view of a schematic representation of a Main-secondary "Troekiieranlage" according to the present Invention;

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FIG. 2 shows a plan view of an embodiment of the secondary dryer part of the system according to FIG. 1;

Figure 3 is a front view of the secondary dryer design according to Fig. 2;

FIG. 5A is an enlarged view of the conveyor structure shown in FIG. 3; FIG.

Fig. 4 is an enlarged sectional view taken along line 4-4 in Fig. 2;

FIG. 4A is an enlarged view showing the drying chamber of FIG. 4 in detail.

In Fig. 1, a veneer dryer system is shown according to the teachings of the prior invention. The main dryer, generally designated 10, may be of a conventional type, such as is used for drying wood veneers, for example . Such a dryer vird by the applicant and sold under the trade name U III JET, eggs aiii = .η iVlshräeck dryer comprising the gas ooer eampfbehe ^ i ur> e-ne Vie ?? .. äiü of Having drying sections.

As already mentioned, the heirlcbsparRxneter of the main dryer 10 can be set,>? O dai? a typical unsorted hardwood and young wood? "£ rg an gi. * i;" · ■.; .. r ^ u fed to entrance 11

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between 30-50% is dried satisfactorily without too much Drying out after going through the main drying chamber. In other words, the part of the passage that initially becomes one low moisture content, completely dried to the required moisture level by treatment in the main dryer 10. After exiting the main dryer 10, the veneer material is individually through at the outlet 12 of the main dryer a conventional humidity sensor 15 scanned, which between those pieces of veneer that have been dried to or below a certain moisture content and those that have yet another Need drying, carry out an excretion. In a well-known Moisture sensing device is the partially dried material oversprayed with a water-soluble colored dye so that easy distinction can be made. A suitable one Moisture sensing device for use in this case is the applicant's Moore Oregon Continuous Check Moisture Detector, described in brochure no. 6608.

After passing the moisture sensor 15, the veneer " material - that in the present embodiment in the form of sheets is traded, transferred to the conveyor 20, where its alignment

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is changed by 90 relative to the initial direction of movement. This changes the orientation of the veneer grain relative to the path of movement of the material through the secondary dryer 30. If thus typically the grain orientation of the veneer through the main dryer 10 was parallel to the direction of movement, the changes right angle rotation shown at 20a, the veneer orientation, see above that when passing through the secondary dryer 30, the neck grain runs at right angles to the direction of movement.

Before reaching the secondary dryer 30, the veneer material passes a separation station, denoted by 25a ... h, where separators remove the unmarked completely dried veneer parts according to conventional Separate sorting out procedures. The remaining veneer material, Marked as insufficiently dried, is brought into the entrance 31 of the secondary dryer 30 by the conveyor 20. As As best shown in FIGS. 2 and 3, the partially dried veneer panels 18 are fed to the feed 31 of the secondary dryer 30 through a Conveyor belt 35 transported in a closed elliptical path, first upwards and then through a heat treatment chamber mounted above 36, then down and past a second clumsiness checker 37 of a conventional type, to then at an extraction station 3 9 to get past and finally back to the beginning the endless path. ,

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Thus, in the system arrangement described above, all of the partially dried veneer materials received from the main dryer 10 are passed through the drying chamber of the secondary dryer 30, where their moisture content is further reduced "if the material has ever been satisfactorily dried after the initial pass through the secondary drying chamber 35" it from dsm conveyor belt 35 through separator at the separation station 39 on rollers 39a ,. .f (Fig. 1), from where it came to the support area of a SchicMholitafel. On the other hand, the sensor material still wet for use is the second moisture sensor 37 m6rfcfes? S tmA uom & aw? © h 'üim sponsor voi? ls © i aa d © r

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chamber 36 above a platform 41 (i.e. 2, 5 - 3 m above the ground) mounted by means of a frame made of support beams 42 and cross members 43.

On the platform 41 a heat treatment chamber is provided which comprises a first section 45 in which a heated air medium is directed at high speed against the surfaces of the veneer material in order to evaporate the moisture therefrom, and a second section 55 in which ambient air is circulated to cool the veneer and remove any remaining moisture. As best shown in Figures 4 and 4A, a pair of centrifugal fans compromise 46 in the heating section 45 air, which can also be heated to high temperatures (usually above 180 C) by a non-exhaustedU th gas burner is heated. The compressed heated air is then in a first filling he comb 47 and from there into an associated air box 48 pressed laterally on each side of the veneer material being moved through the central core area. As 4A shows the veneer 18 is brought through the center of the chamber by means of opposing conveyor belts 35k and 35b which pass through a roller mechanism 49 are supported and driven.

The heated air exits the respective air boxes 48 at a high level

I. 1

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Speed, usually 750-3000 m per minute, through a Plurality of nozzles 52 which are staggered and spaced to direct the heated air perpendicular to the horizontal surfaces of the moving veneer material 18. the Nozzle action with high speed and high temperatures produces an effective and fast drying of the partially dried Veneer material and due to the flow of the boundary layers apart, which occur due to the sharp right angle impingement of the jet streams on the flat surface of the sheet material the drenching effect is very thorough. The used high ones Air temperatures considerably above those conventionally selected lying in veneer dryers are not harmful because the moisture is quickly pushed out of the interior of the veneer material and is quickly evaporated from the surface, creating a cooling effect arises, which is the limit area from damage or discoloration protects. A detailed illustration of the drying phenomena is disclosed in US Pat. No. 3,199,213, to which in this respect Should be referred to »

After hitting the veneer material, the air sweeps sideways across the surface and passes from the central core area into corresponding second filling passages 51 and thereafter to the inlet side of the

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opposing centrifugal fan 46 to the circulation path to complete. The moisture carried away by the veneer material in the drying process and collected in the gas medium is then vented to atmosphere through a flue pipe 53.

After passing through the heating section 45, the veneer material arrives in the adjacent cooling section 55 of the same design, adding unheated ambient air at high speed by means of jet streams at right angles against the corresponding surfaces of the veneer sheets in order to remove the remaining moisture to be carried away. In this cooling section, the air is blown in the same way as in the heating section by means of a centrifugal fan 56 is circulated and the moisture-laden air is vented to the atmosphere through separate exhaust ducts 58, which are provided in the cooling section.

The conveyor mechanism 35, the veneer material 18 in a The closed loop path passing through the secondary dryer 30 is generally of conventional design and uses powered and idler rollers suitably driven as is known. To the veneer material 18 during its passage "

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To secure through the heat treatment chamber where high velocity jet streams occur, the veneer is preferably forced in a sandvich fashion by a conveyor belt 35 which, as shown in Figure 4A, rests on the top and bottom of the material during this portion of the movement . In its arcuate vertical passage from the above-mounted drying chamber to the moisture sensing and separating stations arranged on the floor and back again, the veneer material is guided, as shown in FIG closely spaced rollers 35 and which are arranged along the arcuate path. Due to the nature of the conveyor mechanism shown in Fig. 3, it can be seen that the veneer sheets 18 continue their circulation in the closed path between the drying chamber and the separation station, ie the material is removed from the conveyor belt. m

Addressed during the described Ausführungsforni the present invention "Hf tin system * for treatment of veneers in sheet form, this system can also apply for the treatment of in tape form by alignment of the main and Sekundärin a linear arrangement and in such a modification,

009841/1241 ORIGINAL INSPECTED

that the elliptical path that the conveyor belt of the secondary dryer covered, is adapted to the longer tape lengths.

In an operating example of the primary-secondary dryer system according to the present invention samples of mixed virgin and heartwood veneer with a range of initial moisture, which ranged from 35 - 158% (based on the dry substance weight of the veneer, as it is in practice in conventional industry), fed to the main dryer unit. The operating parameters of the main Dryer units were set so that only the material with the lowest initial moisture is completely dried in this unit became; thus the material went from the original 35% moisture content to a satisfactory moisture level of 4% therein Passage through the main unit was reduced and the material was then removed from the facility. The veneer material from the beginning However, 158% moisture content was only partially dried to 22% moisture content after passing through the main dryer and this moist material was further transported through the secondary dryer

where it finally reaches a satisfactory humidity of 3 1/2% was brought in two passes. Material with a moisture content between these two extremes required a single one

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Passing through the secondary dryer to the desired moisture level to reach. In this way, all of the mate rial to a satisfactory moisture level within a low Dry in the range of 2-4% moisture content, with no material underdried and no material undergoing further treatment than required re-drying material.

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Claims (9)

20H116 "Ji claims 1.J A method for continuously drying flat material with a widely varying moisture content, characterized by passing the material through a first drying chamber in which only the part of the material which initially has a low moisture content is completely dried to a predetermined moisture content, while the higher moisture content material is partially dried; By selecting the material after passage through the first chamber to the completely dried material the partially dried material VCN to distinguish, by dag Srtfernen of the completely dried portion of the material from the conveyor, troti by a continuation of the partially &; ne '. eii material through a second drying chamber, by re-marking the material after passing through the second drying chamber to distinguish the fully dried material from the partially dried material, by removing from the conveyor only that portion of the material that has passed through the second drying chamber complete is dry and by repeating the previous steps, until the remaining material is completely dried. *; 009841/1241 2OH116 .μ 2. The method according to claim 1, characterized in that «that the Wood veneer is peeled from a trunk «the heartwood and Has young wood, and that the operating parameters of the first drying be adjusted so that, about 70% of the material after Run is completely dried. 3. The method according to claim 1 or 2, characterized in that the material is dried in the second drying chamber by the action of a plurality of DÜeenstrÖme of heated air at high speed, the streams impinging approximately at right angles to the corresponding main surface of the material. 4. The method according to claim 3, characterized in that the Material is plywood, and that the nozzle flows in the second Drying chamber a speed between 750 and 3000 m per minute and one time over 180 ° C. 5. Plant for performing the method according to any one of claims 1-4, characterized by a first drying chamber with an associated device for setting the operating parameters to control the drying, through a second drying 008041/1: 249: -.- ORJGiNALlNSPECTED 20Κ11Θ u 21 chamber of much less capacity than the first «with one associated device for setting the operating parameters for the control of the drying, by a conveying device for the trust · « porting the material in a web to and through the first drying chamber, then to and through a second drying chamber and then again to the entrance of the second drying chamber, with the material progressing through the second drying chamber circulates until it is removed from the conveyor, through a first moisture * sensing device at the outlet of the first drying chamber « to distinguish the material dried to a predetermined moisture content from the partially dried material and by a second moisture sensor at the output of the second Drying chamber to distinguish the fully dried material from the partially dried material. 6. Plant according to claim 5, characterized in that the second « Drying chamber has a first section in which the » The material transported through is exposed to a multiplicity of jet streams which at high speed are approximately at right angles to the main flat surface of the material are directed, and a second Section in which a multitude of jet streams of unheated air 009841/1248 20 t * ti 8.; »■ at the same speed at right angles to the cooling on the main surfaces of the material is directed. 7. Plant according to claim 5 or 6 with a drying chamber, which has a core area through which a conveyor moves the material. leads, with a plurality of nozzles spaced apart in the chamber and are connected to a source of heated compressed air, characterized in that the chamber is supported by a framework is arranged above the floor, that the conveyor is arranged in a vertically extending closed path, so that the Material after passing through the core area of the. chamber is moved down under the chamber and finally back down back up to the inlet of the chamber, 8. Plant according to claim 7, characterized in that the moisture scanner to distinguish the fully dried material from the partially dried material at the exit of the chamber « Core areas is arranged, and that a separating station under the Chamber is provided in the open area where the completely dried material from the conveyor «marked by the moisture scanner is removable. ' 00914171248 ORIGINAL INSPECTED 20H118 _W ith 9. Plant according to one of claims 1-8, characterized in that that the material as it moves through the drying chamber between a pair of läligs extending, parallel Belts are guided, which guide the material in a sandwich manner «and that · when moving the material! between the top-mounted secondary drying chamber and the floor longitudinally extending belt parts lie over the material and this against a plurality of closely spaced idler rollers press, which are in arc-shaped paths between the drying chamber and the floor » rtickführbahn are arranged. ORIGINAL (NSPECTEp 008841/1249 ^ * f. \ äk & ml