The invention relates to clarifying the line force between two rotating rollers pressed against each other by calculation means or by measuring means. The aim of the invention is to produce a calculation model in order to calculate stresses existing in the other roller caused by evenly distributed line force in the said roll. By means of the method as per the invention the stresses of the other roller are worked out by calculation from a spot, where they can also be determined.

Previously known as method for determination of line force distribution is observation of product driven through roller, whereby from the features of its cross profile the evenness of compression between rollers is concluded. The weakness of such distribution of line force noticed from the end product is that the cross profile of the end product depends also on many other circumstances than distribution of line force. Correcting the distribution into better evenness is difficult, since by means of cross profile observation it is not yet possible, for instance, to solve the necessary change of the roller crowning.

Further, as previously known method is a static nip paper test, whereby from paper pressed between rollers the distribution of compression force is interpreted. This tests gives also only guidance for the change of crowning, it is hard to carry out and does not pay any notice to the effect of the turning of rollers on line force distribution.

For clarification of the crowning shape necessary for roller calculation formulas are known, into which factors due to bearing support and bend of the roller are included.

However, it has not been possible to verify the evenness of line force distribution in a real situation, i. e. on conducting the web between turning rollers. Accordingly, in modern technique the crowning is accepted, which has been made in the roller according to values given by the calculations.

The compression force of roller by nip contact against another roller is previously adjusted into roller by means of pushing shoes arranged at a distance from each other, by means of which from roller inside the roller mantle has been pushed on the nip line. Since for the pushing shoes different pushing forces has been arranged, it has been possible to adjust the distribution of line force. The disadvantage of this is that only after observing the cross profile of the end product one has with great delay been able to correct the distribution of pushing forces of the pushing shoes and thus influence the distribution of line force.

By means of the method according to this invention the above presented problems are solved and a significant improvement for clarifying the distribution of line force and for correcting the distribution into better evenness, as well as for adjustment in real time. The invention is characterized in what is disclosed in the claims.

The advantage of the method according to the invention is that the control of line force, i. e. nip pressure, improves decisively, since the corresponding stress distribution caused by uniform line force distribution in the other roller in the web lateral direction is presented by means of the calculation formula and corresponding stresses are also measured from said roller. When as stress field the cylinder inner surface of the roller to be measured is chosen, it is, for instance, possible to measure from it by means of stress- strain flaps the stresses in axial and tangential directions. The stresses of corresponding inner surface are also calculatory favourable to be determined, when bending, depression by nip contact and flattening due to line force are used as the cylinder roller load.

By means of the method according to the invention the process of paper manufacture is improved, where the quality of paper can be made smoother as before over the whole web breadth. The crowning shapes of rollers can be made to correspond better to the need and it is possible to determine more accurately the necessary correction of crowning. If there is in the factory an active, for instance by means of pushing shoes working load determining the line force in real time, by means of the method as per the invention an adjustment in real time for this is achieved, when in the counter roller continuous measuring of stress is arranged.

In the following the invention is disclosed with reference to the enclosed drawing, where Fig. 1 shows the pair of rollers from the side.

Fig. 2 shows a part of the pair of rollers in profile, where there is in the other roller a pushing shoe arrangement, by means of which the line force distribution is adjusted.

Fig. 3 shows the roller stress distribution horizontally.

Fig. 4 shows distribution of line force of the pair of rollers.

Fig. 5 shows the roller crowning shape.

Fig. 6 shows the distribution of pushing force.

Figure 1 shows the rotatable pair of rollers 1,2 of a paper machine supported by means of body 4 so that at least the roller fastening with bearings in body 4 can be moved vertically. By means of forces directed to the bearings the rollers 1,2 can be pressed against each other, whereat nip contact is formed between the rollers. The rollers are cylinder rollers with a length of L. On the inner surface of the other cylinder roller stress- strain flaps are fixed, from which information of the inner surface stress state appearing by chosen distribution in roller lengthwise direction can be achieved. As output in this invention stresses are wanted, which in nip contact point represent stresses formed into the roller inner surface. Since roller 2 is rotating the wanted stress values are received by cycles only once per revolution. However, stress values are at their maximum value in nip connect point, so that their peak values are easily distinguished from information by the stress-strain flaps.

Figure 2 shows a construction, where into the other roller (roller causing nip pressure) a dead core 6 is placed, to which hydraulically working pushers 7 have been fixed at a distance from each other and which by means pushing shoes 8 push the roller I mantle against roller 2. Roller 1 is fastened with bearings to roll on core 6. There is in a portion of roller 2 fixed stress-strain flap detectors 3, which are most suitably at the roller 2 pusher 7,8 in the roller lateral direction.

If there is in the roller a known crowning and it is assumed that the line force is evenly divided by line contact between rollers 1,2 and the construction of both rollers, the supports of bearings and stiffening impacts of roller ends are known, in the invention a calculation model drawn up on basis of this situation is utilized, which as result of calculation gives the stress values of roller 2 inner surface at strain flaps 3, while said spots are on the nip line. When the basis is that the line force is evenly divided by nip connection the calculation model, by means of which the inner surface stress values are solved, becomes relatively accurate and sufficient for the aimed purpose.

Since the corresponding stress values of roller 2 can according to the invention also be measured, the accuracy of the calculation can be solved by means of practical tests. As a most useful application the calculation model gives, used in another direction, the distribution of line force by nip connection of known rollers, when into the calculation model stress values from counter roller 2 are recorded. By means of the calculation model it is possible to find out as of from the stress values measured from roller 2 the shape of the necessary crowning shape so that the line force would be distributed evenly.

If it is the question of a solution according figure 2, where the zone adjustment of line force is carried out by means of hydraulic pushers 7,8 inside the roller, it is possible by means of shell stress values measured from counter roller 2 to draw up an adjustment separately for each pusher 7 and so achieve active adjustment and line force control. By means of the adjustment a result is aimed, where at stress-strain flaps 3 the stress values are formed into same values as achieved by calculation into these points in the situation, where the line force has been assumed to be evenly distributed. When from stress-strain flaps 3 stress values are received continuously and the algorithms of the calculation model can be quickly solved by means of a computer, it is possible by means of the adjustment arrangement to adjust the pressures of pushers 7 in real time. Since there are several pushers and the adjustment of one effects the function of the adjacent ones, the adjustment arrangement must make some adjustment cycles in order to achieve sufficient accuracy.

Figure 3 shows diagrammatically along roller length L stresses measured by means of strain flaps 3 in the axial direction 8a and the radial direction 8r. The stress values of corresponding points are also determined by means of the calculation modeL Figure 4 shows distribution of line force Fn all over the roller. Certain stress values in Figure 3 correspond to each line force value and vice versa, when the same roller pair is observed.

Figure 5 shows a crowning shape on roller outer surface.

Figure 6 shows diagrammatically the distribution of pushing force Fp.

If the calculation model applied to a known pair of rollers gives a reliable result and yielding, bending and flattening of rollers are in control, in one embodiment the measuring of stress can be restricted only to the roller centre, whereat, knowing the calculated roller features, from the stress values of the roll centre other stresses active along the roller length can be determined.