METHOD AND ARRANGEMENT FOR FORMING A FIBRE MAT

Abstract: The invention relates to a method and an arrangement for continuously forming a fibre mat for the manufacture of fibreboard or the like, comprising feeding out fibre material from a dosing arrangement and depositing the material on the surface of a moving conveyor belt. The mat is formed by rotating forming rolls (1, 3, 4, 6; 21, 23, 26), located above the conveyor belt and transverse to its direction of movement, which work in the deposited material. The invention is characterized in that the material is distributed in the fibre mat in controlled manner with the aid of at least one screw-type rotating forming roll (3, 4; 23).

Description: METHOD AND ARRANGEMENT FOR FORMING A FIBRE MAT The present invention relates to a method and an arrangement for continuously forming a fibre mat for the manufacture of fibreboard or the like, in which fibre material from a dosing arrangement is deposited on the surface of a moving conveyor belt or web in accordance with the preamble to patent claim 1 and patent claim 3, respectively. The invention also relates to a forming roll intended for use in such an arrangement, as defined in patent claim 13. When manufacturing fibreboard in accordance with the dry method (MDF, HDF, LDF, etc.), the fibre mat is formed on a moving conveyor belt and subsequently compressed by means of hot pressing. The mat can be formed in a single homogeneous layer or in several layers having different properties for fibre, glue, moisture, etc. Such a fibre mat can also be formed on top of other types of mats such as OSB (Oriented Strand Board), wafer-board, particle board, etc., to produce a soft surface layer. The mat is usually formed in a passive manner, i.e. by just distributing the fibres on a moving belt or wire and then adjusting the thickness of the mat by removing fibres from the upper surface of the mat. It can be formed, for instance, by the fibres being transported in an air current from a fibre bin and deposited on a wire while air is simultaneously sucked through the wire, or by the fibres being deposited purely mechanically after being fed from a dosing bin onto a number of distributing rolls which spread the fibres down onto a forming belt in order to form a mat on the belt. There also exist other arrangements comprising a combination of pneumatic and mechanical systems. A common problem is that, if its cross section is studied, it will be observed that a fibre mat produced in this way has pronounced irregularities. This may be due to differences in the type of raw material and to local process conditions, which may have such a great influence that the cross section of the formed mat may differ considerably from installation to installation as regards charac- ter and appearance. The fibre mat may, for instance, exhibit an excess of material at the outer edges while at the same time exhibiting a deficiency of material in the middle, or vice versa. In other cases it may exhibit an excess of material along one outer edge while the other outer edge exhibits a deficiency of material. In order to obtain a uniform mat, therefore, the problem of achieving redistribution of the fibre material in the mat must be solved. This may be a matter of transporting fibres from one area where there is an excess of material to another area where there is a deficiency, for instance, or vice versa. SE-C-511 259 and SE-C-508 504 show mechanical formers comprising a number of forming rolls operating at different levels above and to a certain extent in the fibre mat, to be already known for levelling the upper surface of the formed mat. According to SE-C-508 504 these forming rolls are provided with a number of inclined plates that penetrate down into the mat. According to SE-C-511 259 the forming rolls are instead provided with a number of variously shaped forming blades that penetrate down into the mat. However, both these known mechanical formers produce what is more like a whisking effect and no real distribution or transport of fibres in the transverse direction of the mat occurs. The problem of achieving a uniform mat thus remains. The object of the present invention is to solve the above-mentioned problems. This is achieved by a method having the characterizing features defined in claim 1 and by an arrangement as defined in claim 3, having the characterizing features defined therein. Since, in accordance with the present invention, at least one of the rotating forming rolls in the arrangement is of screw-type, the advantage is gained that, with the aid of this forming roll, material can be transported in the transverse direction of the mat from an area with excess material to an area deficient in material. The screw-type roll thus in principle acts as a feed worm and consider- ably more material can be transported/moved than is possible with known arrangements. The material in the mat is also distributed in a controlled manner so that a preferably uniform mat is obtained. In accordance with the invention the desired controlled distribution of the material in the fibre mat is obtained by controlling the rotation speed and/or direc- tion of rotation of said at least one screw-type forming roll and/or its vertical placing in relation to the fibre mat and/or lateral placing transverse to the direction of movement of the conveyor belt. Controlling the direction of rotation of the screw-type roll enables control of the direction in which the fibres are to be moved transversely across the fibre material. Adjusting the height of the screw-type roll in relation to the fibre mat enables control of the quantity of fibre to be moved. The quantity of fibre to be moved can also be controlled by adjusting the speed of rotation of the screw-type roll in relation to the linear speed, i.e. the speed of movement of the conveyor belt. All these advantages are achieved with the present invention. Furthermore, since the screw-type roll can be moved laterally, the possibility of moving material is also increased and, with more than one screw-type roll, the advantage is also gained of having variable forming width. The term "forming width" refers to the distance along the transverse direction or width of the conveyor belt where forming may take place. In accordance with a first embodiment the arrangement comprises at least two screw-type forming rolls, each of which has an effective forming length that is less than the maximum forming width of the conveyor belt. By "effective forming length" is meant the distance in longitudinal direction of the screw-type roll, transverse to the direction of movement of the mat, along which the screw- type roll can transport material and thus contribute to forming the mat. Each screw-type forming roll preferably has an effective forming length that is a proportion of the maximum forming width of the conveyor belt, which proportion is substantially directly proportional to the number of screw-type rolls. If an arrangement comprises two screw-type forming rolls then each of these has a forming length corresponding to approximately half the maximum forming width of the conveyor belt. The screw-type forming rolls together preferably also have a maximum effective forming length that corresponds substantially to the maximum forming width of the conveyor belt. In general it can be said that the number of screw-type rolls is chosen taking into consideration the width of the conveyor belt. The screw-type forming rolls are preferably displaced in relation to each other, in the direction of movement of the conveyor belt. They are preferably arranged so that they at least partly overlap each other. In accordance with a second embodiment the arrangement comprises a screw-type forming roll comprising two roll sections with oppositely directed screw form. The forming roll(s) are advantageously included in a forming head and surrounded preferably by ordinary forming rolls seen in the direction of movement of the conveyor belt. A primary placing may be as rolls Nos. 4 and 5 seen from the entry to the forming head. The arrangement also comprises drive means for driving the screw-type forming roll or each of the screw-type forming rolls separately. The screw-type forming roll(s) can also be rotated individually and independently of each other in forward or backward direction. This offers the advantage, for instance, that two screw-type rolls can be driven in opposite directions so that material is transported from both outer areas of the mat, in towards the middle of the mat, or vice versa, by rotating the rolls in the opposite directions. The speed of rotation of the screw-type forming roll(s) is preferably variable. The rolls are preferably also movable in lateral direction, transverse to the direction of conveyance, as mentioned above. They can also advantageously be individually vertically movable so that the working depth in the mat can be controlled. This allows for none, or only one of the rolls to influence the forming, when desired, by raising the other screw-type roll(s) above the upper surface of the mat. Other features and advantages will be clear from the subordinate claims. The present invention will now be described in detail with reference to the accompanying schematical drawings, illustrating embodiments of the invention by way of example, in which Fig. 1 illustrates schematically, seen from above, a first embodiment of an arrangement comprising screw-type forming rolls in accordance with the present invention, Fig. 2 illustrates schematically, seen from above, a second embodiment of an arrangement comprising one screw-type forming roll in accordance with the present invention, and Fig. 3 illustrates the arrangement in Fig. 1 , seen from the side. Fig. 1 shows a forming head used for continuously forming a fibre mat for the manufacture of fibreboard or the like. Below this forming head is a moving conveyor belt with a surface for receipt and deposition of fibre material supplied from above, i.e. above the forming head, usually from a dosing bin provided with a feed-out device for the fibre material. The forming head comprises a number of forming rolls 1 , 3, 4, 6 for forming the surface of the fibre mat. These forming rolls are arranged in the transverse direction of the conveyor belt, and preferably have the same diameter. They are preferably arranged stepwise, as illustrated in Fig. 3. The forming roll situated lowest is at the inlet end of the forming head, marked with an arrow A. At the inlet the conveyor belt passes in through the forming head and fibre material is supplied from above. The fibre mat becomes thicker as the material is added from above in the forming head, and the forming rolls gradually assume higher positions, which gives a stepwise arrangement seen from the side (see Fig. 3). To enable such a stepwise arrangement to be obtained the ends of the forming rolls are generally attached to a lifting beam 7 on each side of the forming head, and the height of this lifting beam in relation to the upper side of the mat is controlled by means of two jacks 9 arranged one at each end of the lifting beam. However, the forming rolls 3, 4 can preferably be raised or lowered individually. This is achieved with the aid of parallel jacks 8. Obviously, there is nothing to prevent the arrangement being designed so that all the forming rolls can be raised and lowered individually if so desired. The first embodiment illustrated in Fig. 1 comprises two screw-type forming rolls 3, 4, which may also be termed cross-section correcting rolls or screws, included in a forming head where they are surrounded by ordinary forming rolls. These ordinary forming rolls may be rolls of the wing-roll or wobble-roll type. The screw-type rolls can be likened to feed worms and thus consist of a rotatable shaft provided externally with flanges forming a screw thread. In this embodiment the two screw-type forming rolls 3 and 4, respectively, are arranged one after the other in the direction of movement of the conveyor belt. The advantage of this arrangement is that the rolls can be arranged to slightly overlap each other. In the second embodiment, illustrated in Fig. 2, the arrangement comprises one screw-type forming roll 23 which may be described as consisting of two roll sections 24, 25 with a common shaft, the respective screw threads being oppositely directed, i.e. with left and right threading, respectively. This screw-type forming roll 23 is included in a forming head with other, previously known, forming rolls 1 , 6, in the same way as in the first embodiment. With such a forming roll, material in the mat can be moved from the edges of the mat towards its middle, or vice versa. The purpose of this embodiment is to illustrate that it is feasible to have only one screw-type forming roll. Alternatively the two sections of this screw-type forming roll could be separately suspended and driven. There is naturally nothing to prevent the two parts of the forming roll being threaded in the same direction. The movement of material then occurs from one edge of the mat to the other edge. Both in the case of the forming rolls 3 and 4 in the first embodiment and of the forming roll 23 in the second embodiment, the direction of rotation and speed of rotation of each roll can be chosen and controlled separately, independently both of the speed and direction of rotation of the other screw-type forming roll and of the speed and direction of rotation of the other forming rolls. Separate driving and control of each screw-type roll is therefore generally provided. In the first embodiment, illustrated in Fig. 1 , each screw-type roll covers approximately 50% of the maximum forming width; i.e. the first screw-type roll 3 covers the first 50 per (0-50%) of the maximum forming width, and the second screw-type roll 4 covers the other 50 per cent (50-100%) of the maximum forming width. The forming width of the rolls can be varied by making the screw-type rolls 3, 4 in this embodiment displaceable in lateral direction seen in the direction of movement of the conveyor belt, as indicated by an arrow B, i.e. axially with respect to the rolls. It is thus possible to increase the area where the rolls overlap if desired. It is also possible easily to vary the embodiment in Fig. 1 so that the screw-type rolls can be displaced axially to produce a gap between the rolls where the formation of the mat is unaffected. It is thus possible to obtain variable forming width. To achieve individual raising and lowering of a screw-type roll, one posi- tion potentiometer per screw-type roll is generally used to measure its vertical height in relation to the fibre mat produced, as well as jacks, as mentioned earlier. Alternatively, separate jacks may be used for raising the left and right ends of the roll and, in that case, two separate potentiometers per roll. This enables vertical adjustment of the roll with a variable angle for the left and right sides, i.e. the roll can be set with an axial inclination transverse to the direction of movement of the conveyor belt. In this way a systematic fault causing one edge of the fibre mat to be thicker than its other edge can be compensated. If no correction is required the screw-type roll(s) can be fully raised so that they do not work the mat. When the screw-type rolls are used for compensating irregularities in the fibre mat, the direction of rotation of the screw-type rolls is chosen so that each roll moves material from the area where an excess of material exists, to an area where there is a deficiency of material. The speed of rotation of the screw-type rolls is chosen taking into consideration the linear speed and the quantity of material to be moved. The vertical position of the screw-type rolls is also adjusted in relation to the height of the mat, with regard to the amount of material to be moved. The equivalent is naturally applicable to the case using only one screw- type forming roll. It would of course be perfectly possible to have a forming head with more than two screw-type forming rolls. The number of forming rolls depends to a great extent on the width of the conveyor belt. The variations possible as regards forming width, etc., can naturally also be increased by means of an arrangement having more than two screw-type forming rolls. In that case they may be displaced in relation to each other as shown in Fig. 1. It is also possible to combine the two embodiments. In the examples illustrated the forming rolls are arranged stepwise. However, there is nothing to prevent them from being arranged at the same level. It should be pointed out that in certain cases it may be possible for two screw-type forming rolls to have a common drive, for instance. However, this generally entails certain limitations in the possibility of redistributing the fibre material in the mat in different ways. The screw-type rolls may naturally also be used, if so desired, for pro- ducing a fibre mat that does not have a completely uniform profile, e.g. a wedge- shaped cross section. The present invention shall not be considered as limited to the illustrated embodiments, which are supplied only by way of example, but can be varied in all manner of ways obvious to one skilled in the art, within the scope of the append- ed claims.

Claims: CLAIMS 1. A method for continuously forming a fibre mat for the manufacture of fibreboard or the like, comprising feeding out fibre material from a dosing arrangement and depositing the material on the surface of a moving conveyor belt, the mat being formed by rotating forming rolls (1 , 3, 4, 6; 21 , 23, 26) located above the conveyor belt and arranged transverse to the direction of movement of the belt, said rolls working the deposited material, characterized in that the material is distributed in the fibre mat in controlled manner with the aid of at least one screw-type rotating forming roll (3, 4; 23). 2. A method as claimed in claim 1 , characterized in that the desired controlled distribution of the material in the fibre mat is obtained by controlling the rotation speed and/or direction of rotation of said at least one screw-type forming roll (3, 4; 23) and/or its vertical placing in relation to the fibre mat and/or lateral placing transverse to the direction of movement of the conveyor belt. 3. An arrangement for continuously forming a fibre mat for the manufacture of fibreboard or the like, comprising a dosing arrangement with feed-out device, a moving conveyor belt with a surface for receipt and deposition of the fibre material from the feed-out device, and rotating forming rolls (1 , 3, 4, 6; 21 , 23, 26) arranged between the conveyor belt and the feed-out device, transverse to the direction of movement of the belt, characterized in that at least one of said forming rolls (3, 4; 23) is screw-type. 4. An arrangement as claimed in claim 3, characterized in that it comprises at least two screw-type forming rolls (3, 4), each of which has an effective forming length that is less than the maximum forming width of the conveyor belt. 5. An arrangement as claimed in claim 4, characterized in that each screw- type forming roll (3, 4) has an effective forming length that is a portion of the maximum forming width of the conveyor belt, which portion is substantially directly proportional to the number of screw-type rolls. 6. An arrangement as claimed in either of claims 4-5, characterized in that at least two of the screw-type forming rolls (3, 4) are displaced in relation to each other in the direction of movement of the conveyor belt. 7. An arrangement as claimed in claim 3, characterized in that it comprises a screw-type forming roll (23) comprising two roll sections with oppositely directed screw form. 8. An arrangement as claimed in any one of claims 4-7, characterized in that it comprises drive means for driving the screw-type forming roll or each of the screw-type forming rolls (3, 4; 23) separately. 9. An arrangement as claimed in any one of claims 3-8, characterized in that the screw-type forming roll, or the screw-type forming rolls (3, 4; 23) individually and independently of each other, can be rotated in forward or backward direction. 10. An arrangement as claimed in any one of claims 3-9, characterized in that the screw-type forming roll, or the screw-type forming rolls (3, 4; 23) individually and independently of each other, can be driven at variable speeds of rotation. 11. An arrangement as claimed in any one of claims 3-10, characterized in that it comprises means (8) for raising and lowering the screw-type forming roll or each of the screw-type forming rolls (3, 4; 23) individually and independently of each other. 12. An arrangement as claimed in any one of claims 3-11 , characterized in that the screw-type forming roll or one or more of the screw-type forming rolls (3, 4; 23) individually and independently of each other, is laterally displaceable transverse to the direction of movement of the conveyor belt. 13. A forming roll designed for an arrangement for continuously forming a fibre mat for the manufacture of fibreboard or the like, comprising a dosing arrangement with feed-out device, a moving conveyor belt with a surface for receipt and deposition of the fibre material from the feed-out device, and rotating forming rolls arranged between the conveyor belt and the feed-out device, transverse to the direction of movement of the belt, characterized in that it is a screw-type forming roll.

Inventors: ANDERSSON LEIF, MATHIASSON MIKAEL, ANDERSSON, LEIF, MATHIASSON, MIKAEL
Applicants: ANDERSSON LEIF, MATHIASSON MIKAEL, VALMET FIBERTECH AB, ANDERSSON, LEIF, MATHIASSON, MIKAEL
Application year: 2001
Main classification: B27N3
IPC codes: B27N3