The particle material in the form of wood chips or wood fibers manufactured in a desintegration plant is transported to a forming station, which comprises a batching unit for batching the material flow down on a continuous forming web, on which a mat of the particle material is formed. The mat is thereafter compressed in one or several presses, to which it is continuously transported by the forming web. The final pressing to a finished board takes place in a hot press.

In the board industry, a production plant for board is requested to be able to manufacture board of varying width in response to the specifications of the customer.

In conventional production plants different width are manufactured by first forming a mat on the forming web, thereafter compressing the mat and finally removing the edge strips by means of circular saws or mills. These edge strips are again desintegrated and then transported back to the batching system via pneumatic or other transporting means. This system usually is called'mat-trimming".

Mat-trimming has the disadvantage of high energy conumption, because it requires much energy for compressing, desintegration and transport. Furthermore, as a result of the staying-time of the particle material on the forming web and of the fact, that the material again must be desintegrated, the material has not the same quality as the main flow which is mixed at the re-circulation to the batching system. Another disadvantage is that at multi-layer forming, i. e. at forming stations where mats for board with special surface layers are manufactured, the fiber material intended for surface layers is mixed with fiber material intended for central layers at the recirculation to the batching system.

US, A, 3 057 022 shows a mat forming system where the mat width is controlled by partition walls in the forming station. The material falling outside the partition walls is transported back to a storage chamber. However, this method required an extensive transport system. Further, material recycled from the forming station will be mixed with new material in the storage chamber which is a disadvantage.

The present invention has the object to bring about a method and a device at board manufacture, where the board width can be adjusted in a simple manner and at the same time the afore-mentioned shortcomings are avoided. This is achieved according to the invention in that the intended board width is determined already at the forming of the mat in the outlet from the batching unit. The characterizing features of the invention are apparent from the attached claims.

The invention is described in greater detail in the following, with reference to some embodiments shown in the drawings. The description refers to the MDF- process, but the invention can be applied also to the manufacture of other board.

Fig. 1 shows schematically a conventional plant for the manufacture of MDF; Fig. 2 shows an apparatus according to the invention; Figs. 3 and 4 show two different embodiments by cross-section according to III-III in Fig. 2; Fig. 5 is a cross-section according to V-V in Fig. 4; Fig. 6 shows another embodiment of the invention.

Th conventional plant shown in Fig. 1 is intended for the production of MDF. The plant comprises a storage bin 10 with an outfeeder 11, a batching unit 12 with a batching web 13, feed rolls 14 and a distribution chamber 15. Below the batching unit 12, an endless forming web 16 is provided which runs about a plurality of rolls 17, one of which is driving.

On the forming web 16 a fiber mat 18 is formed. A mat compressor 19 is located in connection to the forming web 16 and comprises upper and lower compression webs 20,21 as well as upper and lower compression rolls 22,23. After the mat compressor 19 a system for mat-trimming 24 is located. Thereafter a hot press 25 is provided for finally pressing the fiber mat to a finished board. A recycling system with a collector 26, transport line 27 and fan 28 is arranged for returning removed edge strips from the mat-trimming 22 to the storage bin 10.

Fig. 2 shows a device according to the invention. The batching unit 12 with the distribution chamber 15 is here formed with a width corresponding to the maximum width which a fiber mat can have. In the distribution chamber 15 vertical partition walls 30 are arranged, which extend in the direction of movement of the forming web and are offset in lateral direction. By these partition walls 30 the width of the fiber mat 18 and, thus, also the width of the finished board are determined. When mats and board of a smaller width are to be manufactured, the partition walls are moved inward whereby the distance between the walls is the intended mat-width. The partial amount of the fiber flow from the batching unit 10 which drops outside the movable partition walls 30, is taken care of in an expedient transport unit 32 for diverting the partial amount of the material in the distribution chamber 15.

Fig. 3 shows the invention according to which the separated partial amount of the fiber flow is recycled, distributed and deposited directly as a surface layer of the mat by means of the transport unit 32.

At the embodiment shown in Figs. 4 and 5, the transport unit 32 is formed with an opening 35, the width of which is adjusted together with the partition walls 30, so that it places the separated partial amount of the fiber flow on the upper side of the formed mat directly without re-circulation to the batching unit 12.

Another alternative is shown in Fig. 6. This embodiment differs from the embodiment according to Figs. 4 and 5 in that it places the separated partial amount of the fiber flow on the forming web 16 before the distribution chamber 15, which implies that this layer will be located on the lower side of the fiber mat 18 formed by the distribution chamber 15.

The invention, thus, implies that the fiber material in its entirety can be utilized for the forming of a fiber mat, without any part of it having to pass through the mat compressor 19 or being discharged from the distribution chamber 15. The invention further implies that multi-layer board can be manufactured at optimum. At multi-layer forming one forming station is used for each layer. The diversion of the partial amount of the fiber flow which at the forming drops outside the intended board width implies, that is has the same quality as the fiber material in the main flow and, therefore, can be re-used in the same forming station without quality problems.

According to the invention, no system for mat-trimming is needed no extensive transport system for fiber recirculation is needed. The energy demand for mat compression is reduced, because the formed mat has the intended width already from the start.

The invention, of course, is not restricted to the embodiments shown, but can be varied within the scope of the claims.