Previously known are, among others, from the Finnish patent specification FIX 101322, a framework for calenders, where the calender rolls are pressed against each other by a hyd- raulic cylinder affecting the bearing housings of the rolls. The bearing housings of the uppermost roll, among the bearing housings of the rolls, are firmly fixed to vertical pillars and the attachment of the lowest roll is by means of sliding guides carried out in vertical pillars so that in controlling the push force of the cylinder the nip force can be controlled that presses the rolls against each other and is direction the bearing housings of the lower roll.

By means of such a solution nip forces of different magnitudes can be produced in adjusting the hydraulic pressure. However, by means of the solution the stiffness of the system, for instance to avoid vibration, cannot be controlled. Supports or mutual flexibilities between bearing housings and frame cannot be adjusted.

Although wanted, with load cylinders the lower roll cannot be supported, e. g. flexibly or rigidly, since the cylinder has only a bearing power controlled each time by means of hyd- raulic pressure.

To be able to observe and control the vibration of rolls, to change the flexibility and stiffness of the system and to change the suspension of the bearing housings, one has arrived at a new solution regarding the suspension of bearing housings, which solution is characterized in that the bearing housing of the first roll is by means of the first arm supported'in the frame, which arm is from its other end fixed to the frame by a joint and the first end supported in the frame by means of a load cell and, further, the apparatus has a locking unit loading said end against said load cell, and the bearing housing of the second

roll is supported in the frame by means of another arm, which arm is from its other end fixed to the frame by a joint, and to support the second arm in the frame there is in the apparatus a knee-joint linkage affecting the magnitude of nip load and supporting the second arm, the knee-joint of which linkage is affected by a power required to increase or decrease the angle of the knee-joint.

Other embodiments of the invention are presented in the dependent claims.

The advantage of the apparatus as per this invention is that both by normal operation of the apparatus and by dynamic testings of tht ápparatus the stiffness properties of the system can be modified. The same loading device can support the roll either stiffness or flexibly, while keeping the nip load unchanged. On the other hand, the nip load is fully adjustable and, similarly, different support stifmesses of roll can be freely chosen for each chosen nip load. The apparatus is suitable for dynamic examination of calenders and for continuous use in a production plant, whereby the system stiffness can be easily changed, while the rotation speeds of rolls are changing, on changing the nip load or, when for instance, as a result of wear due to long term operation, the stiffness of system must be changed to avoid vibrations.

In the following the invention is disclosed with reference to the enclosed drawing, where Fig. 1 is the apparatus viewed from one end.

Fig. 2 is the apparatus and rotary system diagonally viewed from the side.

Figure 1 shows a calender with two rolls viewed from the end, whereby the first roll, i. e. the upper roll 4, has a bearing housing 7, by means of which roll 4 is fixed to first arm 5.

Arm 5 is from its other end by means of a joint fixed to frame post 1. The other end of the first arm rests by means of load cell 10 on a support shelf in the post. By means of hydraulic cylinder 8 the first arm 5 can be loaded in pulling it against load cell 10.

The second roll 3, i. e. the lower roll, is by means of bearing housing 7 fixed to second arm 2. The second arm 2 is from its one end fixed to post 1. The other end of the second arm can move freely between the two supporting shelves of the right side post without touching

the support shelves during normal operation. The second arm 2 is supported by means of knee joint linkage 9. The joint linkage 9 is kept in a wanted angle 0. The angle must be greater than zero.

By means of hydraulic cylinder 6 linkage 9 is pushed with the knee joint making the angle smaller in order to support second arm 2 and at the same time to produce nip load between the rolls. Stiffness i. e. flexibility of linkage 9 can be gained adjusting the knee joint angle 0. When roll 3 and 4 dimensions remain constant and the attachment of first arm 5 unchanged, the knee joint angle 8 is adjusted by increasing or decreasing the thickness of adjusting plate 15 underneath the lower knee joint bracket. The thickness of adjusting plate 15 is so chosen that it produces the angle 0 wanted. If the aim is to retain same nip load, the hydraulic pressure of cylinder 6 must also be changed. The stifffiess of the system grows, when the angle 8 decreases, and flexibility grows, when the angle A increases.

So that cylinder 6 would remain horizontal, the position of cylinder 6 is in regard to frame I adjustable in the vertical direction by means of set screws I6. Also between cylinder 6 bracket and frame 1 adjusting plates must be used if one wants to keep the cylinder piston position in cylinder, i. e. the distance of the cylinder bracket constant. Then also the hydraulic stiffness of cylinder remains constant, while knee joint angle 6 is changing.

By choice of the cylinder 6 hydraulic pressure the nip force wanted can be produced.

Cylinder 8 is the locking cylinder of upper arm 5 and the tractive force by which it pulls the upper arm 5 end against load cell 10 is chosen substantially greater than the nip force.

For instance, cylinder 8 can be replaced by a spring, as a cup spring set, weights or similar, which cause required pretension against load cell 10.

The nip force produced by cylinder 6 tends to lighten the load of load cell 10. The nip force can be counted from the load difference between cylinder 8 and load cell 10. Due to the solution first arm 5 and the bearing housing 7 of first arm 4 are tensioned, while rolls are rotating and first arm 5 having great stiffness.

To locking cylinder 8 a pressure accumulator can be added that allows cylinder 8 to yield if for some reason or other overloading occurs in the first roll. An overload situation occurs, when first arm 5 does not any more press load cell 10. Almost in this situation, at the latest, the locking cylinder 8 should be adjusted to yield against the pressure accumulator.

By normal working situation arm 5 presses the load cell by substantial force. Detection of proper rigidity for the system is done after the assembly in choosing the angle 8 and the pressures of cylinders 6 and 8.

Figure 2 shows an apparatus including rotary arrangements. Both rolls 3 and 4 are rotated by means of an own motor 14, a gearing 13 and an articulated shaft 11, 12.-, The motor operations and the rolls form a torsional vibration system that receives impulses from tooth contact situations of the gearing, from torque formation of electric motors and from variations of the reeling resistance of roll covers. In order to control and observe torsional vibrations, between gearing 13 and the articulated shaft a coupling 17 has been installed, the flexing and damping qualities of which can be varied within limits wanted.

Control of nip force and retain of set value is adjusted, for instance in transmitting the signal out of load cell 10 to the proportional valve that controls the pressure of the pushing side (+) of cylinder 6. In the chamber of cylinder 6 secondary side (-) a certain pressure is maintained, if one wants to use said chamber to damp passive vibration.

The invention is not restricted to the enclosed embodiment but many modifications are possible within the inventional concept presented in the claims.