DRYER FOR DRYING VENEER PANELS

Abstract

A dryer for drying veneers including a plurality of sections in which drying means for drying the veneers are present, wherein at least one of the sections there is a means for generating a negative pressure in the respective section.

Claims

1. A dryer for drying veneers, comprising a plurality of sections in which drying means for drying the veneers are present, wherein in at least one of the sections there is a means for generating a negative pressure in the respective section.

2. The dryer according to claim 1, wherein the means comprises at least one suction device or fan for sucking air out of the interior of the respective section.

3. The dryer according to claim 1, wherein the at least one fan is arranged on the upper side of the respective section.

4. The dryer according to claim 2, wherein the at least one fan is arranged in each case above a circulating air fan.

5. The dryer according to claim 1, wherein means are provided for sealing the interior of the respective section.

6. The dryer according to claim 5, wherein the means comprise seals on a chain for driving rollers in the region of an end-side outer wall of the respective section.

7. The dryer according to claim 5, wherein the means have sealing devices for sealing rollers in the region of the end-side outer wall.

Description

[0037] The invention is explained in more detail below in an embodiment example with reference to the drawings:

[0038] FIG. 1 shows a schematic top view of a veneer dryer according to the invention with a plurality of sections,

[0039] FIG. 2 shows a section with a plurality of nozzle boxes for drying the veneers,

[0040] FIG. 3a, b show seals for sealing transport chains on the end walls of the sections, and

[0041] FIG. 4a, b show the transport of veneers in the area of the end walls of the sections and seals.

[0042] A veneer dryer 1 (FIG. 1) has, for example, a conveyor extending over the entire length of the drying system shown in FIG. 1, which comprises several belt, roller or chain conveyors 1 arranged one above the other. The direction of passage is illustrated by an arrow A. Along the conveyor device, starting in the direction of passage of the arrow A, a number of sections 3, for example up to about twenty sections, which are all operated at essentially the same temperature, are arranged one after the other downstream of an inlet zone 2; downstream of a section 4 follows a sealing zone 5, which is operated at a slight overpressure, for example 10 to 30 Pa above normal pressure or ambient air pressure, and a cooling zone 7, which consists of three sections 8. The number of sections 3, 4 is usually between five and twenty-five.

[0043] Each of the sections 3 to 8 has its own housing. In particular, the sections 3, 4 each have partitions 9 through which they are connected to each other and have, for example, 2 to 2.5 m in length built up.

[0044] In sections 3, 4, the pressure inside is lowered significantly with respect to the surrounding normal air pressure, as indicated above, in order to prevent vapors, solvent vapors and the like from evaporating and particles condensing therefrom from settling out of the veneers.

[0045] Each section 3, 4, 5 is provided with or is in communication with a means for generating dry air. Sections 3, 4 each have a recirculating air fan 10 (FIGS. 1, 2) for generating a flow of drying air within the respective section 3 or 4. A heating device 11 is provided in each section 3, 4, via which the air in the section 3, 4 is heated either directly (heating coil of an electric heater or burner) or indirectly (via steam, thermal oil or hot water).

[0046] Furthermore, each section 3, 4 is provided with a device for exhausting the heated air saturated with moisture and solvents from section 3, 4, the vapors. This device is either an exhaust fan associated with each individual section 3, 4 or a central exhaust and extraction system, by each section 3, 4 individually or at least a plurality of sections 3, 4 combined into groups, exhausts and extracts the vapors.

[0047] In accordance with the embodiment shown in FIG. 1, three groups of sections 3, 4 arranged one behind the other are combined, the vapors of which are each discharged together in groups via lines 12, 13 and 14 to a central exhaust air valve 15 and from this to a stack 16. Each of the lines 12 to 14 is equipped with a throttle valve 17 in order to be able to control or regulate the amount of extracted air.

[0048] The sealing field 5 is also connected to a heating device 18, through which warm air supplied via a supply air valve 19 is introduced into the sealing field 5 under slight positive pressure. Three cooling zones 20 are arranged downstream of the sealing field 5.

[0049] Alternatively, each section 3, 4 is equipped with its own exhaust fan or other means for extracting vapors, which is designed in a manner known to the skilled person so that these are extracted along the length of all sections in accordance with the desired drying profile.

[0050] In each of the sections 3, 4, air flows from a recirculation fan 10 (FIG. 2), the flow direction of which is indicated by an arrow B, to the heating device 11, where it is heated. From the heating device 11, the air is led into a pressure chamber 21. The pressure chamber 21 serves to distribute the air uniformly to the individual levels of a drying chamber 23 equipped with nozzle boxes 22. The air is thereby forced into the nozzle boxes 22, from which it is blown perpendicularly onto the veneers passing through the drying chamber 23 between the nozzle boxes 22 via perforated nozzles arranged on the upper and lower sides of the nozzle boxes 22, respectively. The veneers rest on support rollers and are conveyed perpendicular to the viewing plane of FIG. 2 by means of a transport device (not explained in detail here). The support rollers are arranged between and slightly above the nozzle boxes 22 so that the drying air flows between the support rollers onto the veneers.

[0051] To ensure optimum flow and introduction of the drying air from a ceiling box 24 into the pressure chamber 21 and from this via the nozzle boxes 22 along the veneers into a suction chamber 25, the width of the pressure chamber 21 is greater in relation to the width of the suction chamber 25.

[0052] By means of the exhaust stack, part of the drying air is extracted so that the air pressure inside each of the sections 3, 4 can be lowered by up to 300 Pa. The simultaneous extraction of the substances contained in the drying air prevents them from settling on the inner walls of sections 3, 4 or elsewhere. In this way, any corrosion is avoided. The exhaust air is preferably sucked out of the suction chamber of the first fan 10.

[0053] The drying air extracted by the fan 25 is preferably passed through a filter system (not shown here) in which corrosive constituents of the drying air are selectively separated out so that the cleaned drying air can be fed back into the system where required.

[0054] An adjustable flap 26 is arranged at the end side of those sections 3, 4 whose neighboring section is to have or can have a different negative pressure, in order to be able to adjust the air pressure, the temperature as well as the moisture content and/or further parameters inside the respective section 3, 4.

[0055] If the veneers are transported by rollers or conveyor belts driven by chains, these are also largely sealed in the area where the chains emerge from the end walls of those sections 3, 4 where pressure differences are to be expected, in order to maintain the negative pressure in the sections 3, 4 as far as possible.

[0056] In a guide area 27 (FIG. 3a) of a chain 28, the latter has a free cross section 29. At the exit of the chain 28 from the wall of the respective section 3, 4, sealing plates 30, 31 are provided above and below the chain 28, which are additionally equipped with elastic sealing lips or sealing lamellas 32 towards the chain 28.

[0057] For the transport of veneers 36, pairs of rollers 33, 37 and 34, 38 (FIG. 4a) are used, between which the veneers 36 are passed. According to the invention, in order to largely limit leakage of the respective one of the sections 3, 4 at the inlet and outlet of the veneers 36, respectively, and to contain the loss of negative pressure inside the respective one of the sections 3, 4, sealing devices 39, 40 are provided, which cooperate with the rollers 34 and 38 on the lower and upper sides of the veneers 36, respectively, in order to prevent air from entering the respective one of the sections 4 to 6 through the open slot 41 provided in the area of an end-side outer wall 42.

[0058] The sealing devices 39 comprise, for example, a plurality of bristles 43 formed, for example, from animal hair or from metal wire, or lamellae formed, for example, from rubber or plastic. The bristles 43 are bundled by a support 44, which is preferably attached to the inside of the outer wall 42.

[0059] The measures provided according to the invention to maintain a substantial negative pressure in sections 3, 4 can be realized in all types of veneer dryers, for example in the veneer dryer already mentioned at the beginning, disclosed in WO 03/025484 A1, or in the veneer dryer known from WO 2005/047793 A1, which discloses a loop-shaped guiding of the veneers between two conveyor belts.