Today, in press lines producing sheets of wood material, especially wood fiber board, conveyor weight meters are used for weighing the sheets. The conveyor weight meter weighs the conveyor and the sheet together. The speed of the press line has to be reduced at the weighing point.

The object of the present invention is to eliminate the drawbacks of prior-art solutions and to achieve a new method and apparatus for the weighing of sheets. According to the invention, the sheets are weighed in a cooling turn gear when the sheet has been turned to an upright position or at least to a nearly upright position. The details of the features characteristic of the method and apparatus of the invention are presented in the claims below.

Thanks to the invention, no conveyor weight meter is needed in the press line and thus the press line can be made shorter. The weighing accuracy is substantially better than in a conventional conveyor weight meter solution because only the sheet itself is weighed instead of weighing the relatively heavy conveyor together with the light sheets on it. The invention facilitates the implementation of the press line as the sheets are not weighed while they are moving on the press line conveyors and as it is no longer necessary to reduce the speed of the line to allow for weighing. In addition, the invention facilitates the modernization of factories where a continuous press is to be extended. The space that used to be occupied by the conveyor weight meter can be advantageously utilized to extend the press line without building an expensive addition. Moreover, the cooling turn gear often works in a stepwise manner, so the facts that the sheet stops moving and the vibrations damp out lead to an accurate weighing result.

In the following, the invention will be described in detail by the aid of an example with reference to the attached drawing, which presents a figure

showing a cooling turn gear according to the invention in end view.

Wood fiber board sheets are manufactured on a press line by pressing sheet preforms in a press or a continuous press, whereupon the sheets are sawn off to form blanks. After this, the sheets are conveyed on a conveyor into a cooling turn gear, in which the sheets are cooled down before being stacked.

The cooling turn gear comprises a frame 2 mounted on a base 1 and consisting of metal beams, e. g. three adjacent frame parts. Mounted in the frame is a cooling wheel 3, which rotates in a vertical orientation in an anti- clockwise direction as indicated by the arrow. The cooling wheel is rotated by a drive mechanism, which may consist of e. g. a squirrel-cage motor controlled by a frequency converter. The cooling wheel comprises a cylindrical barrel part 4 with radial supporting bars 5 connected to it to support the sheets 6 (the figure only shows some of the supporting bars, the entire circumference of the wheel being fitted with such bars).-As the sheets enter and leave the turn gear, they are guided by curved guide bars 7.

The cooling turn gear presented in the drawing comprises a weighing system 8 fitted on the horizontal top beams 2'of the frame so as to allow the sheets 6 to be weighed when they have been turned to a nearly upright position, i. e. in a position near the top dead center of the cooling wheel 3.

The weighing system 8 comprises weighing elements 9 placed upon the top beams 2'and fastened by one end to the ends of pivoted lever arms 10, and wheels 11 provided with e. g. rubber-like surface material upon the weighing elements. From the weighing elements 9, the measurement data is passed to the control system of the press line for determination of the weight of the sheets 6.

The weighing is performed as follows. As the cooling wheel 3 is turning, a sheet 6 in a top position climbs onto the wheels 11, with the edge of the sheet 6 resting on the wheels, whereupon the sheet 6 is weighed. As the cooling wheel 3 turns further, the weighing elements 9 are released and the next sheet advances to the weighing position.

If necessary, several thin sheets can be weighed at once if they are placed in the same gap between supporting bars. In this case, the average weight of the sheets can be determined.

It is obvious to the person skilled in the art that different embodiments of the invention are not restricted to the example described above, but that they can be varied within the scope of the claims presented below. The weighing can also be performed using a weighing system which is placed in a structure above the cooling wheel and which lifts the sheets off their support and weighs them.