DE102005046879A1 - Method and device for preheating a scattered pressed material mat in the manufacture of wood-based panels - Google Patents

Abstract

The wood chips or the saw dust are distributed on a belt (1) in order to be transported to the pre-heating station. The mat created between perforated belts (2,3) is lifted and guided across a heating station. Hot fluid, preferably a water and air mix, is released through nozzles (5). The perforated belts (2,3) are pre-heated by being pulled along hot plates (4) in order to avoid condensation occurring at the belts (2,3) which are cleaned when returning after having delivered the mat to the press (7). ETAILED DESCRIPTION - An independent claim is given for a device used for pre-heating a chipboard sheet.

Description

The The invention relates to a method for preheating a scattered pressed material mat in the production of wood-based panels according to the preamble of claim 1 and an apparatus for performing the Method according to claim 7.

Method, Installations and devices for the adjustment of important production features such as Moisture, temperature, preactivation of the adhesive and the like a Pressgutmatte, which consists of scattered particles such as fibers and / or shavings are well known. Usually These are also used to a scattered Pressgutmatte so to compress that excess air is removed from the Pressgutmatte. For one, this is desired to avoid being in the inlet of a continuous press a high compression gradient leads to high flow velocities the repressed Air to uncontrollable shifts of the material and thus too non-uniform density profiles in the pressed material mat; the other is supposed to be during the pre-compression a uniform preset the parameters such as humidity and temperature are facilitated. Especially the influx of fluids such as water vapor, air or a water vapor / air mixture is facilitated if the scattered pressed material mat a certain degree of compaction which prevents inflowing fluids with their flow rates move the scattered crop unchecked.

Such a method and apparatus has been disclosed in DE 36 40 682 A1 already known. There, a pressed material mat is formed from a forming station, which is guided through a pre-press with endlessly circulating screen belts. There, the pressed material mat is compacted by means of unheated press plates and steamed with a steamer.

With DE 197 01 595 A1 is a plant for the preheating of a pressed material mat has become known, which deals primarily with the procurement and production of an adjustable climate for spraying the pressed material mat. In the climate distribution devices described there, which supply the used conditioned air to the pressed material mat, condensate drains are provided in order to prevent condensate from passing out of the climate distribution device into or onto the pressed material mat. This publication is directly related to the process EP 0 695 609 A1 , There, the preheating device used is specified in more detail, the screen belts used to transport the pressed material by the preheater.

The Screening belts be free lying in the return guided. This is common and known that the screen belts in the return mostly by brushes, Air bubbles or water jet bars are cleaned.

One Such screen belt consists for the most part Part made of plastic, but it can also be used a metal sieve become. The mesh size must be selected so that the scattered Particles (chips, fibers) can not fall through, but still a sufficient Gas permeability given is. The thickness of the sieve bands is usually 1 to 3 mm.

When Fluid can be a vapor / air mixture or water vapor (superheated or saturated) be used. The fluid can be bilateral, ie from above and below or from only one side of the Bedüsungsplatten in the Pressgutmatte flown become. The inflow area of the fluid over The width is usually the requirements of the production width and the material itself.

All plants described above have a significant disadvantage which can seriously affect production. It has it turned out that often to blockage by dust, glue or wood particles in the wire belts can come, even if the screen belt with brushes, air jets or Water jet cleaning in the filter belt return line is cleaned.

blockages to lead to an uneven penetration of the fluid in the mat. this leads to different consequences such as uneven heating and / or activation the adhesive, lack of softening of the particles and thus too Committee. The entire process of mat pre-heating can be clogged with a Screen belt no longer performed become.

Also if the problem of clogging by regular alternation of Pressgutmatten used in the way of a production change in the production of various Wood-based panels can be reduced, reinforced cleaning devices be used or even regular manual hand cleaning is provided, this leads Circumstance to an increase in the price of fixed costs in production.

The cause of the clogging is condensation in the sieve belt when passing the fluid to preheat the pressed material mat. It can then lead to caking of dust or fine particles and powdery adhesive from the outer layers of Preßgutmatte in the wire belt. The water in the screen belt acts as an adhesive or collector for dust, fine particles and like. In particular, when using phenol powder in the cover layer, this leads to blockages of the screen belt, since the adhesive cures in the screen belt. It may even come to the formation of built-up edges (known from metal cutting machining), which leave impressions with their tips in the pressed material, which are still visible after the final pressing.

The but condensed water in the sieve can also on the Preßgutmatte dripping and water marks only on the pressed material and thus on the lead produced wood-based panel itself. This wood-based panel is then broke and must be eliminated during visual inspection become. But since small water spots in the visual inspection of a several square meters Wood panel quite overlooked can be this can lead to the delivery of defective goods and accordingly Loss of image of the producer lead.

Of the present invention, the object is a method for preheating a pressed material mat and a device for carrying out the method to develop the above-mentioned disadvantages and thus a Bonding by condensed water in the sieve belts in Connection with foreign substances or glue prevents and continues the Occurrence of water spots on the finished wood-based panel avoids.

The Task for the process is solved by that the screen belts before entering the area of fluid supply to an approximately equal or higher Temperature be brought as the condensation temperature of the preheating used fluids.

The Task for the device for implementation of the method is solved by that for warming the screen belts in front of the spraying plates Heating devices is arranged.

With the Siebbandvorwärmung invention is the screen belt temperature before the entry of the screen belt into the spraying area of the preheating device so raised, that they are bigger or is equal to the condensation temperature of the fluid.

If the wire belt preheat is not performed, condensation of the fluid will occur at a wire belt temperature below 100 ° C (when using a water-steam mixture) or when using steam-air mixture below the dew point the screen belts. The condensation does not stop until the filter belt is heated above the dew point or above the boiling point (about 100 ° C) with steam. For example, condenses on 1 m ² filter belt made of plastic about 30 g of water when heated from 40 ° to 100 ° C.

Remains the screen belt dries in the area of the injection of the fluid a blockage of the screen belt by glue and dust not more on, because no water for bonding glue and dust is present in the screen belt. The mat preheating can be carried out safely. Water stains on the plates are avoided.

ever according to ambient temperature in the area of the preheater, length of the Siebbandrücklaufes and the feed rate of the wire belt cools that Screen belt in the screen belt return to 30 ° -70 ° C from. Especially but also when starting up the preheating after a production stop (maintenance, emergency stop ...) is the Filter belt cooled to ambient temperature. To avoid this The disadvantage is a passive heat tunnel in the return the screen belts to be ordered.

It can be permanent Production operation but also come that cold screen belts suddenly one be called Fluid flow are exposed.

at a cold sieve, the condensed amount of water is greater than in a slightly heated Screen belt. Therefore, the water staining and the risk of contamination especially big here. In addition to the starting operation has also a width adjustment of preheating by adding external plate areas proved a problem. When a wider mat is to be steamed and outer chambers be connected, a similar Situation as when starting the preheater ago. In the Design of the preheating device Alternatively, you can also support the preheating by the heat tunnel be incorporated. To voltage spikes in the power supply during startup could be avoided an active heat tunnel in an energy balance. That would not only mean that the screen belt protected against ambient dust, but could already warmed to a basic temperature.

Further advantageous measures and embodiments of the subject matter of the invention will become apparent from the dependent claims and the following description with the drawing.

It demonstrate:

1 In a schematic side view a plant for the production of wood-based panels with representation of the preheating device,

2 in a schematic side view of another embodiment of the preheating and

3 in a schematic side view, the use of a heat tunnel in the preheater.

1 shows the schematic structure of a production plant for wood-based panels with one on a forming belt 1 by means of a forming station 10 Streubaren Pressgutmatte (not shown), which can then be introduced into the preheater. In the process, the pressed material mat is removed from the sieve belts 2 and 3 taken and pulled through the preheater. In addition to a possibly necessary pre-compaction (not shown) of the just-scattered pressed material mat, the pressed material mat is removed by means of one of the spraying plates 5 exiting hot fluid, for example, a water vapor / air mixture heated. To create condensation in the screen belts 2 and 3 To avoid this, these are before the Bedüsungsplatten 5 by means of heating plates 4 heated, which have a temperature of 90 ° to 200 ° C. After the preheating device, the preheated pressed material mat becomes a continuously operating press 7 or handed over to a clock press to perform the necessary compaction and curing in a wood-based panel. Otherwise, the sieve belts are in the return by means of a cleaning device 9 cleaned. Preferably, this is done immediately after the deflection to facilitate the cleaning. Here are the conventional cleaning methods with brushes, air or water or a combination of these methods.

In 2 found in a further embodiment heated deflection drums 6 instead of the heating plates 4 , The tail pulleys 6 can be heated, for example, with steam or thermal oil, so that sufficient heat energy to the filter belts 2 and 3 can be transferred. Of course, a combination of both heaters is conceivable, wherein the respective screen belt is heated to a temperature above 90 ° C.

In 3 is in the return of the preheater a heat tunnel 8th arranged. This can be either active (heating) or passive (insulating). In an active application, the screen belts can already be preheated for a start-up operation and thus support the other heating devices.

Not indicated was a heater for the Bedüsungsplatten 4 , This is to prevent a condensation in the Bedüsungsplatten 4 itself can take place and thus drops of water fall on the pressed material mat (from above) or be taken by the injection of the fluid (from below). Incidentally, depending on the design of the system, the forming belt 1 be executed as a wire belt and quasi in a pass through the preheater the wire belt 3 replace below. This can be used especially when in the forming station 10 when using a pneumatic scattering excess air through the forming belt 1 is to be sucked off, so that the pressed material can be distributed in order on the forming belt.

1

forming belt

2

screen belt above

3

screen belt below

4

heating plate

5

Bedüsungsplatte

6

Umlenktrommel

7

continuous working press

8th

heat tunnel

9

cleaning device

10

forming station

Claims (13)

A process for the continuous preheating of a scattered pressed material mat in the continuous production of wood-based panels, but mainly for the production of particleboard / fiberboard, in which offset from a starting mixture of chips and / or fibers from a scattering station on a continuously moving forming belt with a binder Pressgutmatte forms, this Pressgutmatte after preheating and possible pre-compression between scattering station and the main press using pressure and heat in the main press is brought into the final shape and cured, characterized in that the screen belts in the preheating before entering the range of Fluid supply be brought to an approximately equal or higher temperature than the condensation temperature of the fluid used for preheating. Method according to claim 1, characterized in that that the respective screen belt is heated to a temperature above 90 ° C. Method according to claim 1, characterized in that that for warming of the respective screen belt before contact with the pressed material mat this over a hot plate with a temperature of 90 ° to 200 ° C is drawn. A method according to claim 1, characterized gekenn records that in order to heat the respective screen belt prior to contact with the pressed material mat, this is deflected and heated with a heated deflection drum. Method according to claim 1, characterized in that that for heat conservation the respective sieve belt in the return through a passive heat tunnel is pulled. Method according to claim 1, characterized in that that for heating the respective filter belt in the return in an active heat tunnel warmed up becomes. Device for preheating a continuously scattered pressed material mat prior to entry into a continuously operating press ( 7 ) or a cycle press consisting of one or two endlessly circulating gas-permeable screen belts ( 2 . 3 ) and above and / or below arranged Bedüsungsplatten ( 5 ), characterized in that for heating the respective screen belt ( 2 . 3 ) in front of the spraying plates ( 5 ) are arranged one or more heating devices. Device for preheating according to claim 7, characterized in that the heating device consists of a heating plate ( 4 ) consists. Device for preheating according to claim 7, characterized in that the heating device from a heated deflection drum ( 6 ) consists. Device for preheating according to claim 7, characterized in that a heater for the Bedüsungsplatten ( 4 ) is arranged. Device for preheating according to claim 7, characterized in that in the return of the screen belts ( 3 . 4 ) an active heat tunnel ( 8th ) is arranged for heating. Device for preheating according to claim 7, characterized in that in the return of the screen belts ( 3 . 4 ) a passive heat tunnel ( 8th ) is arranged for isolation. Device for preheating according to claim 7, characterized in that the forming belt ( 1 ) is designed as a screen belt and is guided by the device for preheating.