APPARATUS FOR SCATTERING FIBRES, SUCH AS CHIPS

This invention relates to an apparatus for scattering fibres, such as e.g. chips, by means of which apparatus chips are scattered through one or more sets of rollers as a chip mat onto a moving belt conveyor or equivalent and in which scattering flowing gas, such as e.g. air, is utilised. The object of the apparatus according to the invention is to improve the scattering result of a roller-scattering apparatus in manufacturing chipboards by levelling the swirling of air inflowing to the scattering chamber.

Roller scattering as such is known from specification Fl 90746 which describes an apparatus for scattering fibres or chips as a mat together with a binder onto a scattering belt conveyor, in which apparatus there is one set of rollers consisting of at least three rollers parallel to each other and in which set of rollers there are adjustable roller gaps. Between the set of rollers and the belt conveyor, there is an air flow which is provided by air suction or by combining air blowing and air suction.

If this air flow known as such is not utilised, the material freely dropping down swirls uncontrollably when displacing air causing irregularity and dents to the chip mat which substantially weaken the quality of the surface layer of the board.

From specification Fl 20040698 are known a method and an apparatus applying the method in scattering chips as a chip mat together with a binder onto a belt conveyor, in which apparatus chips are scattered through one or more sets of rollers and gas flow, in which gas is e.g. air, is utilised and in which the gas flow is guided to at least two substantially chamber-like spaces which are located above and below at least one set of rollers and in which at least one chamber-like space the direction of the gas flow is opposite to the ones of the other chamber-like spaces.

Typical of roller scattering compared with conventional wind scattering is good scattering accuracy (small variations in the basis weight of the scattered mat), because the fractionation of the chip is principally performed mechanically by

means of the set of rollers instead of substantially based on the air flow as in wind scattering. In wind scattering, air flows are problematic. The air flow easily becomes too swirling and weakens the scattering accuracy (scattering quality) because forceful swirls transfer chip particles uncontrollably.

In implemented roller-scattering arrangements, it has been possible to keep the drop height H of the chip in the chamber between the set of rollers and the scattering belt conveyor advantageously very small (typically e.g. 300 mm). Only air suction has been required below the chamber. It has been possible to keep the flow speed of suction air reasonably low (typically less than 1 m/s). Because the chamber has been shallow and the flow speed of air relatively low, the volume flow of air arranged below the set of rollers has remained at an advantageously low level. Because of these reasons, the swirling occurring in air flows and weakening the scattering accuracy has been kept adequately small and thus the scattering accuracy has remained good.

Nowadays, greater and greater demands are made for the quality of the surface of the chipboard in some coating forms (aiming at cost savings). Such a form is, inter alia, the so-called "direct printing" in which onto the surface of the board is printed on top of a thin priming layer e.g. a wood-imitation pattern directly by means of the multi-colour printing method. Currently because of cost saving, one also aims at coating boards with coating films or paint layers thinner than earlier. With board types applicable for the above-mentioned coating purposes, the surface to be coated has to be extremely dense and there can exist only so small particles that all of the chips are able to pass through typically e.g. a rectangular 1.0-mm screen mesh and from these typically e.g. 70% has to pass through a 0.5-mm screen mesh. A special critical requirement is also that the above-mentioned particles have to be adequately thin e.g. max. 0.3 mm. The requirement of thinness comes partly from the fact that, in grinding the board from the surface or e.g. in edge machining, a possibly loosening piece cannot leave behind too large a hole which would be visible e.g. as a surface defect after thin coating or would appear as a disturbing edge fraying e.g. when sawing the coated board. A thin, advantageously leafy or fibrous chip form also decreases the surface porosity of the board and thus reduces e.g. the consumption of paint in coating and improves the creation of

a strong glue/chip bond decreasing the loosening of particles. Therefore, a thick e.g. cubic chip form is poor in this relation.

Indefinable swirling weakening scattering accuracy which occurs in air flows is emphasised in conventional wind scattering in which relatively tall wind chambers (typically over 2 m) and typically higher air flow speeds than in roller scattering and particularly active blowing at the feed end of the chip have to be used for providing adequate fractionation. Usually, one has to install screen meshes which level air swirling into the wind-scattering chambers. They are awkward to use, they increase costs and tend to be blocked easily because they have to be positioned in a dusty space. The need for maintenance of wind scattering is great compared with roller scattering because of dusting caused by the active blowing. Many times, the line has to be stopped for cleaning the blowing heads and meshes in order to restore the weakened scattering accuracy back to a tolerable level.

The above-mentioned patent Fl 90746 describes as some advantageous embodiments a way in which, in addition to the set of rollers, into connection with it is arranged wind scattering or in which in connection with roller scattering solely suction or combined air blowing and suction is used. The present invention relates to the latter embodiment in which, in connection with roller scattering, either suction or combined air blowing and suction is used.

In order to fulfil the above-mentioned requirement of the thinness of chips, in roller scattering the drop height H of the chips has to be increased case-specifically for obtaining an adequate amount of thin chips to be selected and transferred when dropping in a desired area on the surface of the chipboard. However, the heightening of the chamber increases the swirling of air being sucked inside the chamber, which can in certain situations weaken the scattering accuracy.

By means of the invention, one tries to solve the above-mentioned problems by means of roller scattering by maintaining its good characteristics compared with the conventional wind scattering.

In the invention, in roller scattering, the inflow profile of an air inflow opening at the tail end of the set of rollers in the cross section of a suction opening is levelled by means of an auxiliary device to be positioned in front of it in order to calm the chamber swirling to an acceptably low level, whereby the variation of the basis weight of the mat can be kept in an advantageously low level typical for roller scattering and, at the same time, an advantageous scattering result already described earlier is obtained.

Features characteristic of the invention are presented in detail in the accompanying claims.

Next, the invention is described in more detail by referring to the accompanying drawings in which

Fig. 1a shows the travel/swirling of air in roller scattering in a known arrangement in which no element has been used for levelling the swirling of air. Chips are fed from a scattering chamber 9 by means of feed rollers 7 and a dosing conveyor 6 onto a set of rollers 1 from which they drop between individual rollers onto a belt conveyor 2 or equivalent. On top of the belt conveyor, a chip mat 4 is formed of dropped chips. The distance between the set of rollers 1 and the belt conveyor is designated with H in the figure. The travel direction of air is according to arrows from left to right and air, which is sucked into a chamber-like space 5 between the set of rollers 1 and the belt conveyor 2 or equivalent, exits from a suction slot between the belt conveyor 2 and the dosing conveyor 6 which slot is designated with reference number 8. Depending on the height and width of the chamber-like space 5 and on other factors, such as the form of the speed profile of the air flow being sucked into the chamber-like space in the inlet opening, air swirls in the chamber-like space which swirling is shown in the figure by thickened arrows.

Fig. 1b shows an embodiment according to the invention in which, for levelling the swirling of inflowing air, into the chamber-like space 5 in front of the inflow opening of air being sucked, before the tail end of the set of rollers 1 (the left end of the set of rollers) are installed one or more elements 3, 3 ^' levelling the inflow profile of air. As the inflow profile of air being sucked into the chamber-like space 5 i.e. the

direction and speed of the air flow is levelled before the chamber-like space by means of one or more elements 3, 3 ^' levelling the inflow profile, air travels without swirling through the chamber-like space 5 until the outlet slot 8, the swirling remaining adequately small. The travel of air is designated with a thickened arrow in the figure. The element 3, 3' levelling the inflow profile of air can consist of e.g. a perforated plate, a mesh, a honeycomb structure or equivalent. The element 3, 3 ^' levelling the swirling of air can also be constituted by combining perforated plates, meshes and honeycomb structures in different ways.

Figs. 2a, 2b and 2c show some advantageous embodiments of the invention. (The scattering chamber of fibres is not shown in the figures because it is not substantial from the viewpoint of the invention).

Fig. 2a shows the levelling of the inflow profile of air according to the invention by using a level head 10 in which there are perforated plates, meshes and honeycomb structures or equivalents 3, 3 ^' to level the inflow profile of air and, in front of them, at least one auxiliary blower 13 for improving the levelling result and for compensating the pressure loss caused by the perforated plates or equivalent. If the pressure loss is too great, the chamber-like space can become too underpressurised. This, for its part, can lead to uncontrollable air leaks e.g. from the side edges of the chamber 5 into the chamber. According to the figure, the perforated plates, meshes, honeycomb structures or equivalent 3, 3 ^' and the auxiliary blowers 13 are installed in front of the opening of the chamber-like space 5 or in its vicinity, whereby the air flow which travels in the chamber-like space 5, between the set of rollers 1 and the belt conveyor or equivalent 2, is obtained non- swirling enough. The level head is movable in the vertical direction, whereby if the chip mat 4 is higher in the vertical direction, such as shown in Fig. 2b, the level head 10 can be raised (or lowered, if the height of the chip mat is low).

Many times in scattering lines, also the width of the scattered chip mat 4 can be decreased by means of a narrowing apparatus. In such cases, the effective working width of the levelling elements according to the invention, e.g. perforated plates or equivalents, can be arranged also adjustable e.g. by narrowing blocking

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6 plates (not shown in the figures) pushable from the vertical edges in front of the elements 3, 3 ¹ in a desired way.

The auxiliary blowers 13 can be joined to or be separate from the elements 3, 3 ^' levelling the inflow profile of air. In the latter case, these elements can be, if required, adjusted separately in the vertical direction. The element levelling the inflow profile of air substantially fills the whole cross-section area of the chamber- like space 5.

Fig. 2c shows an advantageous embodiment according to the invention in which with reference number 11 is designated a cross-flow blower installed at the level head 10 which blower in itself produces an adequately regular flow profile, whereby there is necessarily no need for perforated plates or equivalent elements 3, 3' between the cross-flow blower and the opening. Reference number 12 designates in the figures a protective mesh known as such.

Figs. 3a and 3b show an embodiment according to the invention for levelling the swirl of air flow in which to the level head is joined a perforated plate, mesh, honeycomb structure or equivalent and, in this case, three auxiliary blowers. Figure 3a is a front view of the level head. Figure 3b is a side view of the level head.

According to Fig. 3a, the level head 10 comprises a blower application 13 (an auxiliary blower e.g. axial blower) which is installed in a pipe 19. A fitting 17 joins the pipe 19 and an air chamber 16 in which there are elements 3, 3 ^' levelling the inflow profile of air. A framework of the level head is designated with reference number 14, and a frame part is designated with reference number 18. At the lower edge of the air chamber 16 can be installed a lath-like body the purpose of which is to prevent the travel of air flow between the lower edge of the air chamber and the chip mat (not shown in the figures). By means of a spindle motor 15, the cross- flow blower can be lowered or raised, if necessary, because the framework part is installed movably in relation to the frame part 18 which is fixedly installed on a support surface or equivalent.

Figs. 3a and 3b show a level head which includes three blower applications, but there can also be one or two blower applications, or even more if required. The rotating speed of the blower application is arranged adjustable for optimising the levelling of the inflow profile. If there are several blower applications, the rotating speed of each application can be adjusted together or each separately.

It is well known by those skilled in the art that the different embodiments of the invention are not solely limited to the examples described above, and thus they may vary within the scope of the appended claims.