FI83739B - Gluing process - Google Patents

Abstract

The invention relates to a process for gluing veneer sheets, which sheets are used for the production of plywood. In the process, regard is paid to various sheet parameters, on the basis of which adjustment is made to the glue dosage and/or composition. The sheet parameters are constituted by moisture content, wood type, position of the veneer sheet in the set and the purpose of use of the veneer.

Description

1 83739

Liimoitusmenetelmä

The invention relates to a gluing method for gluing wood veneers used in the manufacture of plywood.

5

The stack used for the production of plywood is formed from plywood sheets which are glued in an appropriate manner on the lower and / or upper surface before being introduced into the stack, or, depending on the position in the stack, not glued.

In the application of glue to veneer, roller and syringe film application methods are used, the most common of which are roller application and spray application. In roll application, the sheet to be glued is passed between a pair of rollers, with which rolls the glue is transferred to the lower and upper surface of the sheet. In spray application, on the other hand, the sheet is guided through a device in which an adhesive jet is directed at its upper surface to glue the upper surface. In film application, the veneer passes through the adhesive-20 film.

In connection with the production of plywood, it is also known to apply an adhesive to a veneer from a perforated extruder nozzle as a pressed line array, as well as as a foamed product applied in a corresponding manner.

The methods of adjusting the amounts of glue used in connection with these gluing methods are based on run-specific adjustments, in which the glue dosage of the gluing device is set to empirical values. Dosing values are only changed when the stacking program changes. Experiential dosage amounts have been selected to achieve at least a certain application rate in proportion to the acceptable adhesive seam.

However, such a dosing regimen is wasteful. The requirement of minimum strength without differentiation of driving conditions will inevitably lead in part to additional gluing for some veneers or barn sections. On the other hand, an excess of glue does not improve the quality of the glue joint, but may even degrade it.

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The object of the present invention is therefore to develop gluing control in order to reduce the above-mentioned drawbacks, i.e. to achieve optimal gluing by taking into account veneer variables.

10

According to the invention, a control is connected to the control of the gluing apparatus, which, on the basis of the information received, is able to change the gluing control in connection with the formation of the stacking, in particular on a sheet-by-sheet basis.

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An essential part of the control device is a microprocessor or similar control device capable of logical conclusions. Various veneer and process information can be entered for this device. The veneer information can be, for example, the moisture value measured from the veneer, the veneer thickness information, the information on whether it is softwood veneer or birch veneer, and as an alternative veneer / process information, whether the veneer is going to be surface veneer or middle veneer. part of the internal structure.

The moisture content of the veneer entering the barn is essential for a uniform end product result. Although the aim is to dry the veneers to the same degree of dryness, there are in practice significant variations in humidity between the veneers. The varying moisture contents of the different parts of the bedding are important, above all, in the hot-pressing plywood stage. If, on the other hand, information on the moisture content of each veneer entering the gluing 35 can be fed to the gluing device, the variation in the moisture content in the gluing can be significantly smoothed out, and in particular the amount of glue that gives the best glue joint can be applied.

Adhesives used in the manufacture of plywood usually contain about 50% water, so that a mere change in the amount of adhesive-5 can cause noticeable changes in the moisture contents of the stacking parts, which amount changes do not yet affect the strength of the joint to be formed. Another, and more effective way is to increase the amount of water to be glued when the veneer is becoming drier than usual.

In gluing, it may also be appropriate to vary the amount of glue applied to the veneer depending on the veneer information on the origin of the veneer. In the case of softwood veneer-15 lu, it needs more glue than the corresponding birch veneer. Likewise, the thickness of the veneer affects the amount of glue required. More glue must be applied to thick veneer than to thinner veneer in order to achieve the same gluing result. The amount of glue can also be adjusted on the basis of the process information, in that the aim is to apply less glue to the veneers entering the middle part of the stack than to the veneers in the thicker one. The forced water with the glue causes its own problems during the hot pressing stage of the stack, and above all it would be advantageous if there was no excess water in the inner part of the stack.

It may further be advantageous to be able to affect the composition of the adhesive applied to the veneers entering the barn at different points, in that it may be desirable to mix an additional component with the veneers coming to some parts of the barn. Such an additional component in plywood is, for example, termite protection. According to the current practice, the termite protection is premixed with the macro-composition of the adhesive, in which case the component in question will be added to the adhesive of all the veneers of the stack without any change. However, this substance would actually only be necessary

Claims (6)

1. A method for controlling the veneer sheet sizing in connection with veneer manufacture, characterized in that the adhesive dosage at the sizing device is controlled under the control of a device making logical decisions, which device controls the glue quantity control in accordance with the received information on veneer and / or process information. -tert. 10 2. A method according to claim 1, characterized in that the control device measures the moisture content of the veneer sheet coming in to the adhesive. 15 3. A method according to claim 1 or 2, characterized in that the thickness of the veneer sheet coming from the control device is measured on the control device. 4. A method according to claim 1, 2 or 3, characterized in that the tiling of the veneer sheet is measured by the control device. 5. A method as claimed in claim 1, 2, 3, or 4, characterized in that the control device is measured to determine the position of the veneer sheet coming to the glue. Method according to Claim 1, 2, 3, 4, 5 or 6, characterized in that the component or additive substances of the adhesive are mixed during the bonding process.