EP0562219B1

EP0562219B1 - Atomized resin binding method and system for making wood-shaving panels

Info

Publication number: EP0562219B1
Application number: EP92830551A
Authority: EP
Inventors: Roberto C/O Sia S.R.L. Bertola; Guido C/O Sia S.R.L. Goglino
Original assignee: SIA Srl
Current assignee: SIA Srl
Priority date: 1992-03-25
Filing date: 1992-10-01
Publication date: 1995-06-28
Anticipated expiration: 2012-10-01
Also published as: DE69203225D1; ITMI920712A0; EP0562219A1; BR9302541A; ES2077387T3; ITMI920712A1; AU4190593A; DE69203225T2; ATE124314T1; ZA934905B; CA2094940A1; CA2094940C; IT1254557B; CN1094350A; JPH0752111A

Abstract

The present invention relates to an atomized-resin binding method and system for making wood-shaving panels, characterized in that the method comprises the step of simultaneoulsy subjecting to heat and to an superheated pressurized steam dynamic pulse, the wood-shaving, glue and chemical mixture with a turbulent motion in the resin binding machine, so as to provide an atomized flow of particles having even physical characteristics. <IMAGE>

Description

BACKGROUND OF THE INVENTION

The present invention relates to an atomized resin binding method and system for making wood-shaving panels.
There are already known resin binding methods for making wood-shaving panels, which methods are carried out in systems essentially comprising a metering hopper for metering the wood-shavings obtained from dried wood, the hopper supplying with a continuous type of wood shaving flow a ribbon balance which is suspended from a load cell.
The balance continuously sends the value of the weight of the wood shavings supplied to the resin binding apparatus to an electronic processor device which, in order to hold the dry glue/dry wood shaving weight ratio constant, as set by the operator, drives the RPM's of a pump which supplies the resin binding apparatus with a glue mixture comprising water, a glue, and a curing paraffin mixture.
For making the panels there are conventionally used at least two systems for each panel making line: a system is used for resin binding the fine wood shavings, which will form the surfaces of the panel, whereas the other system is used for resin binding the larger size wood shavings which will form the inner portion of the panel.
Downstream of these systems there is provided a further forming system, preferably comprising four forming apparatus arranged with an in-line arrangement.
The first forming apparatus is provided for spreading on a forming ribbon or web a first layer of fine resin bond wood shavings, while the second and third forming apparatus are provided for applying two layers of resin bond wood shavings of larger particle size, whereas the fourth forming apparatus is provided for forming the last layer including fine particle wood shavings.
The thus formed "mattress" is entrained, by means of the ribbon or web which is continuously driven under the forming apparatus, inside a continuous pressing apparatus, comprising two steel ribbons sliding on two plates which are heated to a temperature which varies from 180°C to 240°C, with the same speed as the forming web or ribbon.
Under the combined effect of pressure and temperature, the resin bond wood shaving mattress is set owing to the curing of the resin, so as to provide a wood shaving panel.
Such a prior method, on the other hand, is affected by several drawbacks.
In particular, in winter time, the mattress temperature will decrease, with respect to a summer time, of about 20°C, so as to require an increased baking time and, accordingly, an increased operating time of the system, in particular from 4.8 sec/mm to 5.9 sec/mm, for a base thickness of 18 mm of the finished wood shaving panel.
A further drawback is that, periodically, the operation of the system must be interrupted in order to clean out the resin binding apparatus from resin and wood powder scales.
Yet other drawbacks are a comparatively low resin binding efficiency, and the requirement of using water delivered from refrigerator assemblies operating at about 5°C, in order to cool the resin binding apparatus jackets, since, because of the friction over-heating, the scales tend to set and deposit on the inner walls of these jackets, so as to cause the apparatus to be obstructed.
The mentioned forming apparatus, moreover, are also fouled because of a not optimal distribution of the binding resin on the wood shavings.
Yet another drawback is the requirement of using an expensive paraffin emulsion in order to reduce the amount of water absorbed by the finished product.

SUMMARY OF THE INVENTION

Accordingly, the aim of the present invention is to overcome the above mentioned drawbacks, by providing such a system and method allowing to greatly reduce the baking time, with a consequent great increase of the making efficiency, and which do not involve any interruption of the making operation in order to clean the resin binding and forming apparatus.
Within the scope of the above mentioned aim, a main object of the present invention is to provide such a resin binding method and system which allow to obtain a very great operating efficiency, with a consequent improvement of the mechanical characteristics of the finished wood shaving panel.
Another object of the present invention is to provide such a resin binding method and system providing an improved spreading of the mattress by the forming apparatus, with consequent improved thickness tolerances of the raw panels at the outlet of the pressing machine.
Yet another object of the present invention is to provide such a method and system which allow to overcome the requirement of using any paraffin emulsion.
Yet another object of the present invention is to provide such a method and system which do not include refrigerators for cooling the water circulation jackets of the resin binding apparatus.
According to one aspect of the present invention, the above mentioned aim and objects, as well as yet other objects, which will become more apparent hereinafter, are achieved by an improved system for making wood shaving panels, characterized in that said system provides for the use of a high temperature fluid which preferably comprises pressurized steam, said fluid being conveyed into a resin binding apparatus in order to increase the temperature of the wood shavings, glue materials and chemical aids, which are so mixed as to provide a wood shaving panel.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages of the invention will become more apparent hereinafter from the following detailed disclosure of a preferred, though not exclusive, embodiment thereof, which is illustrated, by way of an indicative, but not limitative example, in the accompanying drawings, where:

Figure 1 illustrates a schematic diagram of a conventional system for continuously pressing and making wood shaving panels;
Figure 2 illustrates a schematic diagram of a prior resin binding system for making panels;
Figure 3 illustrates a schematic diagram of other parts of a system for continuously making wood shaving panels;
Figure 4 illustrates a schematic diagram of a resin binding system for carrying out the method according to the present invention;
Figure 5 is a schematic cross-sectioned side view illustrating a vessel for steam processing wood shavings according to the invention;
and
Figure 6 is a top cross-sectional view illustrating the above vessel coupled to a steam condensate separating device.

DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference to the figures of the accompanying drawings, and, more specifically to Figure 2, prior resin binding systems for making wood shaving panels conventionally comprise a dry wood shaving metering hopper 1 which supplies with a continuous flow of dry wood shavings a ribbon balance 2, suspended from a load cell 3.
The balance 2 is provided for continuously sending the data related to the weight of the wood shavings supplied to the resin binding apparatus, to an electronic processor, which, in order to hold the dry glue/dry wood shaving weight ratio constant, as it has been set by the operator, will control the RPM's of a pump 5 which supplies the resin binding apparatus 4 with a glue mixture comprising, in particular, water, a glue and a curing paraffin emulsion.
For each layer of the mattress being formed along the making line of the wood shaving panel there are conventionally used one or more resin binding systems of the above disclosed type.
Some resin apparatus are used for resin binding the fine wood shavings, which will form the outer surfaces of the panel, and one or more of said resin binding apparatus will be used for resin binding the wood shavings having a larger particle size, and which will form the mattress or mattresses provided for forming the inner portion of the panel.
Downstream of the above disclosed apparatus, there is provided a forming system 6 which essentially comprises four forming apparatus 7, 8, 9, 10 arranged in an in-line arrangement.
The first forming apparatus 7 is provided for spreading on a forming ribbon 11 a first layer of fine resin bond wood shavings, while the second 8 and third 9 forming apparatus are provided for forming two resin bond wood shaving layers of larger particle size, and, finally, the first forming apparatus 10 is provided for forming the last layer of fine wood shavings.
The thus formed mattress 12 is entrained, by means of the forming ribbon 11 which is continuously driven under the above forming apparatus, inside a continuous pressing apparatus 13 comprising two steel webs or ribbons 14 sliding on heated plates 15 with the same speed as the forming ribbon 11.
Under the combined effect of pressure and temperature, the resin bond wood shaving mattress 12 is set, owing to the curing of the resin, so as to provide a finished wood shaving panel.
As stated, however, the above prior making method is affected by several drawbacks.
In particular, in winter time, the temperature of the mattress 12 decreases, with respect to the summer time temperature, of about 20°C, thereby involving a corresponding increase of the baking time and, accordingly, of the system operating time from 4.8 sec/mm to 5.9 sec/mm, for a base thickness of 18 mm of the finished wood shaving panel.
With reference to Figure 3, 4, 5 and 6, the nebulized resin binding system and method according to the present invention substantially provide to simultaneously subject to heat and an additional dynamic pulse, of even and diffused nature, the mixture of wood shavings, glue and chemical aids which is subjected to a turbulent motion provided by the stirrer 16 operating inside the resin binding apparatus 4.
In particular, the heat is applied by injecting pressurized steam (at a preset pressure from 0.1 to 13 bars) and, in a preferred embodiment, the steam is super-heated to a temperature which can be preset by the operator (at 120-200°C) and being moreover pre-processed.
This is preferably obtained by means of a steel injector 17, arranged perpendicularly to the flow direction, and provided with a nozzle having an inner diameter of 8-10 mm, at a distance of about 300 mm from the inlet hopper 18 in the resin binding apparatus, at a short distance upstream of the injectors for loading the glueing mixture, with respect to the material advancement direction as impressed by the stirrer 16.
The mentioned pre-processing is performed inside a suitable steel cylindric vessel, or turbomixer 19, which, according to a preferred, though not exclusive, embodiment has an inner diameter ⌀ = 350 mm, a height of about 600 mm and a thickness of about 10 mm.
This turbomixer vessel 19 comprises two nozzles 20 and 21 which are arranged tangentially of the vessel surface and, in its inside, deflecting fins 22 and 23.
Moreover, coupled to the vessel there is provided a condensate separating device 24, arranged upstream of the vessel and in which there are separated the steam fractions which would deposit on the ducts of the system.
More specifically, the nozzle 20 allows super-heated steam to be introduced into the vessel, whereas the nozzle 21 is provided for introducing the several chemical aids or adjuvants.
A mixing of the super-heated steam and the chemical adjuvants is performed at the central region of the vessel, because of the provision of the above mentioned deflecting fins 22 and 23 which operate so as to hold the chemical adjuvants separated from the super-heated steam flow, during the first step in which these adjuvants are conveyed to the vessel for processing the steam.
In particular, the chemical adjuvants comprise surface active agents 25, preferably ethylene and methylene glycoles.
These adjuvants are used for modifying the surface condition of the water so as to properly control the thermal balance of this water during the different year seasons, in the pressing step.
Moreover, there are also used catalyzer substances 26 in order to accelerate the curing of the glueing mixture and there are also used cleansing substances 27.
The latter are used, in particular, for cleaning all of the downstream arranged apparatus.
There are also used water-repellant substances 28, in order to provide the wood shaving panel with an improved resistance against water.
From the atomized mixture formed as above disclosed, having even physical characteristics and conveyed through said injector 17 into the resin binding apparatus 4, there are transferred the condensation heat and momentum, by impact, to the dry wood shavings, which are progressively impregnated by the glueing mixture, under the effect of mutual slipping, impacts and of the turbulent motion occurring between the several substances introduced into the resin binding apparatus 4.
The main feature of the present invention consists substantially of the injection of the superheated steam, which allows to achieve several great advantages.
Firstly, as it is introduced into the resin binding machine, the steam will expand, so as to heat the glueing mixture and render it more "malleable".
The steam, moreover, causes the wood pores to also expand, so as to allow the glue and other chemical adjuvants to properly enter these pores.
Accordingly, it is obtained an improved binding efficiency, which will provide the finished wood shaving panel with very good mechanical characteristics, as well as a great resistance against ageing and moisture.
Moreover, the steam provides an optical spreading of the chemical adjuvants through the mattress, without negatively affecting the catalysis of the binding resin.
The introduction of super-heated steam into the resin binding apparatus, provides moreover a good lubrication of its walls, preventing them from being fouled, and this without the requirement of using cooled water, since exclusively tower water at 30°C is used, as necessary for cooling the water jackets of the resin binding apparatus.
Moreover, it is provided to actuate, by means of the steam progressively condensing on the inner wall of the cylindric jacket 4' of the resin binding apparatus 4, a continuous laminar meatus with lubricating action on the wood shaving flow toward the outlet 29 to the forming station 6.
One of the main advantages of the present invention is that the steam provides a great reduction of the baking time.
In fact, the super-heated steam will cause, in a very advantageous manner, and mainly in winter time, an increase of the mattress temperature of about 20°C, with a corresponding increase of the operating efficiency of about 20%, in the term of the amount or yield of made panels.
A further important aspect of the invention is that the disclosed method also allows to obtain a great reduction of the formaldehyde contents of the finished product.
From the above disclosure it should be apparent that the invention fully achieves the intended aim and objects.
The invention as disclosed is susceptible to several modifications and variations, all of which will come within the scope of the inventive idea as defined by the appended claims.
Moreover, all of the details can be replaced by other technically equivalent elements.
In practicing the invention, the used material, provided that they are compatible to the intended use, as well as the contingent size and shapes can be any according to requirements.

Claims

An improved system for making wood shaving panels, characterized in that said system provides for the use of a high temperature fluid, comprising pressurized steam, which is conveyed to a resin binding apparatus, in order to increase a temperature of a wood shaving mass, of glue materials and other chemical adjuvants, which are so mixed as to provide a wood shaving panel.
An improved system according to Claim 1, characterized in that said system provides for the use of a high temperature water steam injector, arranged perpendicularly to a movement direction of said wood shaving mass to be mixed in said resin binding apparatus.
An improved system, according to Claim 2, characterized in that said pressurized steam injector is arranged upstream of injector means for loading a glue mixture, with respect to an advancing direction of a wood shaving and glue mixture, said mixture being driven by toothed stirring means arranged according to a spiral like generatrix line.
An improved system, according to Claim 1, characterized in that the steam flow, as it expands through said resin binding apparatus, transmits a dynamic pulse to the wood shaving and glue mass in said resin binding apparatus.
An improved system, according to Claim 1, characterized in that said super-heated steam is mixed with chemical adjuvants, said mixing being performed in a mixing vessel arranged upstream of the injection nozzle and in turn connected to a condensate separating device.
An improved system, according to Claim 5, characterized in that said mixer vessel is provided with a steam nozzle or duct arranged tangentially of the wall for processing said steam, said steam being conveyed at the front of a second duct, also tangentially arranged, and therethrough there are conveyed said chemical adjuvants which are mixed with said steam in said vessel.
An improved system, according to Claim 5, characterized in that inside said steam processing vessel there are arranged deflecting fins which hold the chemical adjuvants separated by said steam flow at the start of the introduction of said steam, so as to provide an even mixing of said steam with said chemical adjuvants.
An improved system for making wood shaving panels according to Claim 1, characterized in that said system further comprises an injector adapted to inject steam having a pressure from 0.1 to 13 bar and being super- heated to a temperature from 120°C to 200°C.
An improved system for making wood shaving panel, according to Claim 1, characterized in that said system comprises a vessel to which there are conveyed surf ace active substances, catalyzer substaces, cleansing and water-repellant substances, so as to form an atomized mixture adapted to be successively conveyed to said resin binding apparatus.
An improved system for making wood shaving panels, according to Claim 9, characterized in that said nebulized mixture transfers condensing heat and momentum, by impact, to dry wood shavings progressively impregnated by said glue mixture, under the effect of slipping forces, mutual impacts and turbulent motion in said resin binding apparatus, said atomized particle flow having even physical characteristics.
An improved system for making wood shaving panels, according to Claim 1, characterized in that in said system, by means of progressively condensed steam on the inner wall of the cylindrical jacket of the binding apparatus, there is actuated a continuous laminar meatus, having a lubricating effect on the resin bond wood shaving flow directed toward the outlet arranged toward a forming station.
An improved system for making wood shaving panels, according to Claim 1, characterized in that said system further comprises cooling means for water cooling said resin binding apparatus.
An atomized resin binding method for making wood shaving panels, characterized in that said method comprises the steps of simultaneously supplying heat and an even and diffused dynamic pulse to a mixture of wood shavings, glue and chemical adjuvants, subjected to a turbulent motion, produced by a stirrer operating inside the resin binding apparatus, and providing said heat and dynamic pulse by means of an injection into said resin binding apparatus of a pressurized water steam, said steam being super-heated and pre-processed upstream of the loading zone of the glue mixture, with respect to the advancing direction of the material as said stirrer operates.
An atomized resin binding method for making wood shaving panels, according to Claim 13, characterized in that said method comprises the step of pre-processing said super-heated steam inside a suitable cylindric vessel, preferably made of steel, into which there are loaded surface active agents, as well as catalyzer substances, cleansing and water repellant substances, so as to provide an atomized mixture to be then introduced into said resin binding apparatus.
An atomized resin binding method, for making wood shaving panels, according to Claim 13, characterized in that said super-heated water steam is introduced into said vessel through a nozzle, whereas a second nozzle is adapted to facilitate the introduction into said vessel of said surface active agents, as well as said catalyzer, cleansing and water repellant substances.
An atomized resin binding method for making wood shaving panels, according to Claim 13, characterized in that said method further comprises the step of transferring condensing heat and a momentum of said atomized mixture, by impact, to dry wood shavings progressively impregnated by a glue mixture under the effect of sliding forces and mutual impacts as generated by a turbulent motion in said resin binding apparatus, so as to provide an even physical characteristic particle atomized flow.
An atomized resin binding method for making wood shaving panels according to Claim 13, characterized in that said method further comprises the step of actuating, by means of said steam progressively condensing on the inner wall of the cylindric jacket of the resin binding machine, a continuous laminar meatus having a lubricating action on the resin bond wood shaving flow toward the outlet to the forming station.
An atomized resin binding method for making wood shaving panels, according to Claim 13, characterized in that said method provides, in a preferred embodiment thereof, the step of injecting super-heated and pre-processed water steam by means of one or more injectors, with the nozzle arranged perpendicularly to the flow direction, at a short distance upstream of the loading station of the glue mixture, and operating at a temperature which can be preset in an overall range of technically used values.