GB2404926A - Calender nip adjustment mechanism - Google Patents

Abstract

To set and adjust a nip gap between a pair of rolls 12, 14 in a calender, a screw jack device 30 is mounted between the bearing blocks 16, 18 mounting the rolls 12, 14 at each side thereof. A spindle 36 is threadedly engaged with a wheel nut 32 held captive in a housing 34, and a worm shaft 38 is used to rotate the nut 32 to raise and lower the spindle 36. Contact mode or gap mode operation of the nip is possible, as is calibration to a nip gap display on a position indicator 50.

Description

CALENDER NIP ADJUSTMENT MECHANISM

This invention concerns an arrangement for setting a gap between a pair of rolls of a calender and more particularly for adjusting that gap to meet different operating requirements.

The invention is particularly applicable to calender use in a final stage of paper making for controlled reduction in thickness whilst improving the surface smoothness of paper in a finishing operation. In these situations it is often desirable to create and maintain a small gap between the rolls, i.e. a nip gap, instead of having a closed nip which is used in many other situations.

However, the invention is also applicable to any other calender, either in the field of paper making or paper treatment, or in any other field, such as for plastics or rubber or non-woven textile materials, where a nip gap may be required.

Typically, in an open frame calender an upper roll is mounted between fixed bearing blocks while the lower roll is mounted between bearing housings which are themselves mounted upon pivotal arms so as to be swingable from a lower nip-open condition to an upper nip-closed condition. The pivoting of the lower roll is accomplished by hydraulic cylinders or pneumatic bellows acting on these arms.

These hydraulic or pneumatic actuators effectively load the lower roller, i.e. urge it towards contact with the upper roller.

In other calendars, such as closed frame calendars, where there is less access to the rolls, a screw jack mechanism may be used to load the rolls. This may involve moving the upper roll downwards towards the lower roll, as disclosed in US 4,627,262.

Hitherto, in order to set a gap between the rolls in a closed frame, hydraulically loaded, paper finishing calender, a system of wedges has been used. These are located between the bearing blocks mounting the upper and lower rolls, with sloping surfaces of the upper and lower wedges in contact with each other. The precise setting of the nip gap is achieved by sliding the upper and lower wedges relative to each other.

The nip gap needs to be changed for different runs of material, depending on its thickness and other operating parameters, and in respect of different rolls. Rolls of different size may be fitted into the calender depending on the calendering operation required. When this occurs, the distance between the blocks mounting the upper and lower rolls may vary substantially, by several cm, even though the range of nip gaps required may be only a few mm. The wedge system is then unsatisfactory as the wedge taper cannot accommodate the required range between the mounting blocks.

Packing pieces have to be inserted behind the wedges when the distance between bearing blocks exceeds the possible adjustment of the wedges. This introduces a safety risk for operators. Also, measurement of the roll diameters to ascertain whether and how much packing is required and maintaining precision in the nip gap distance can then be a problem. s

An object of the present invention is to provide a way of setting and of adjusting a nip gap which does not affect roll loading but allows for a greater range of adjustment and is more accurate than hitherto. Another object is to provide a way of setting and of adjusting a nip gap in a more efficient and safer manner than hitherto.

With these objects in view the invention provides a calender comprising a pair of rolls providing a nip therebetween, each roll having first and second opposed ends, respective bearing blocks mounting the first and second ends of each roll, means for loading the bearing blocks of one roll so as to move and/or press that one roll towards the other roll, and a separate nip gap setting/adjustment mechanism comprising respective screw jacks mounted between the respective bearing blocks at the first and second ends of the rolls.

Thus the nip gap setting/adjustment mechanism, which is mounted between the upper and lower bearing blocks, is separate from the roll loading means which is operative to exert force on the bearing blocks of one roll from a location which is remote from the other roll, i.e. pressing the lower blocks upwards from below, or less commonly, pressing the upper blocks down from above.

The proposed mechanism of the invention acts in a similar manner to the aforesaid wedge system, but more efficiently and safely, to keep the rolls apart under a loaded condition, rather than affecting the loading function as must be the case in the arrangement shown in US 4,627,262.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which: Fig 1 is a partial end view showing a preferred embodiment of the nip gap adjustment device of the present invention mounted in a calender; Fig 2 is a plan view of the adjustment device of Fig 1 and part of the calender below line A-A in Fig 1; Fig 3 is a cross-section along line B-B in Fig 1 in the direction indicated; and Fig 4 is a schematic end view, to a much reduced scale compared to Figs 1 to 3, of the entire calender in which respective nip gap adjustment devices as shown in Figs 1 to 3 is mounted.

With reference to Fig 4, a preferred form of calender to which a preferred embodiment of the nip adjustment mechanism of the invention is fitted comprises a frame 10 onto which an upper roll 12 and a lower roll 14 are mounted to provide a nip therebetween. The upper roll 12 is mounted to the frame 10 by a fixed bearing block 16 at each end thereof. The lower roll 14 is mounted between respective bearing blocks 18 at its opposed ends, and these blocks 18 are mounted to the frame 10 by pivotal arms 20. A respective hydraulic cylinder 22 is mounted below each of the lower bearing blocks 18, in this case on a base 11 of the frame, to pivot same between a lowered, nip-open position and an upper nip-closed position, in which the rolls 12, 14 may contact each other, or be held apart by a specified narrow gap, as will be explained. The hydraulic cylinders 22 also load the lower roll 14 by exerting a continuous upward force thereon to provide pressure in the nip.

The lower roll 14 can be lowered to the nip-open condition, by release of hydraulic pressure in the cylinders 22, whenever required. This also enables removal and replacement of the lower roll 14 for different calendering operations.

This style of calender, in which the rolls 12, 14 are mounted to one side of the frame and there is relatively easy access to the rolls and their mounting means, is referred to as "open frame".

A nip adjustment device 30 in accordance with the invention is shown schematically, mounted between the bearing blocks 16, 18, in Fig 4. In practice, the adjustment mechanism for the calender consists of two such devices 30, one mounted at each side of the machine, between the upper and lower bearing blocks 16, 18 at the opposed ends of the rolls 12, 14. While the arrangement at only one end is shown in the drawings, it is to be understood that the arrangement at the other end corresponds, is mirror symmetrical thereto, and is intended to be operated in synchrony therewith.

With reference to Figs I to 3, the device 30 comprises a screw jack in the form of a wheel nut 32 held captive in a housing 34 so as to be rotatable, but prevented from axial movement, and a screw threaded spindle 36 which is threadedly engaged with the nut 32 and is caused to move axially through the nut 32 upon rotation of the nut.

The jack also comprises a worm shaft 38, which extends into the housing 34 and meshes with external teeth on the wheel nut 32 to bring about rotation of the captive nut 32. The worm shaft 38 itself has a wheel 40 at its free end which can be turned manually to rotate the shaft 38 and thereby move the spindle 36 up and down, relative to the housing 34, as viewed in the drawings.

At its upper end the spindle 36 is connected to a stop plate 42 by way of a part- spherical thrust bearing 44 of conventional form. A bellows-like flexible sealing sleeve 46 is fitted around the spindle 36, between the mounting plate 42 and the housing 42. This protects the jack mechanism from ingress of water and other debris which could affect is reliability.

The nut housing 34 is mounted onto a base 48. A key 49 is located in the base 48 and is capable of engagement with the spindle 36 to prevent its rotation. In this way the spindle 36 can be secured in position once it has been adjusted to a required height of projection upwards from the nut 32.

A digital position indicator 50 is mounted onto the worm shaft 38 prior to the hand wheel 40. This can be programmed to detect revolutions of the worm shaft 38 and calibrated to determine the nip gap (gap between rolls 12, 14) to which this corresponds. It includes a digital display, such as an LED or LCD display, which will show the nip gap.

In use, as shown in Figs 1 and 3, the screw jack device 30 is mounted to the lower bearing block 18 by way of the base 48. As previously mentioned, there will be a respective device 30 at each side of the calender. Proximity switches 51 are incorporated into each device 30 to detect whether the spindles (lacks) 36 are retracted or extended.

To enable the nip gap to be set accurately the first step is to fully lower the respective spindles 36 to the position shown in broken lines in Fig 3. This is accomplished by turning the handwheels 40 at each side of the calender and is detected by means of the proximity switches. The hydraulic cylinders 22 are then actuated to raise the lower roll 14 and close the nip (i.e. rolls 12, 14 in contact) at minimum load. Using the handwheels 40 to turn the worm shafts 38, the gap setting spindles 36 are then raised until the stop plates 42 just contact the underside of the upper roll mounting blocks 16. This will be apparent from an increase in the force required to turn the handwheels 40. At this point the display in each indicator 50 should be set to "zero".

The calender nip should then be opened again, by release of the hydraulic cylinders 22. Each handwheel 40 can then be turned to extend the jacks to give the required mp gap.

In the preferred practical embodiment, as illustrated, the worm/wheel ratio is selected so that thirty revolutions of the worm shaft 38 result in one revolution of the wheel nut 32. The pitch of the spindle screw thread is chosen so that one turn of the handwheel 40 will extend the spindle by 0.004 inches, so one quarter turn of the handwheel will increase or decrease the nip gap by 0.001 inches. Obviously other ratios and pitches can be selected to give appropriate gap changes in exact units per quarter turn or full turn of the handwheel, as desired, these figures being only by way of example and having been chosen for ease of calculation by operators.

Once the required nip gap has been set, the rolls 12, 14 can be "closed" again. In other words the hydraulic cylinders 22 can be operated to raise the lower rolls 14, although the rolls 12, 14 will no longer make contact owing to the interposition of the raised jack mechanisms. The calender is then ready for operation in nip gap mode.

Whenever rolls are changed or are replaced after regrinding the jack devices 30 must be "zeroed" again and the nip gap set afresh by the sequence of steps just described.

Of course, even with the screw jack devices 30 fitted, the calender can still be operated in the nip closed condition (i.e. rolls 12, 14 in contact prior to material passing therebetween) by simply retracting the spindles 36 of the devices 30.

When the calender is used in a paper making or paper finishing process, the rolls are generally of considerable width, e.g. 5 metres, and one of the rolls is likely to incorporate deflection compensation means to counter the roll deflection which always occurs at such widths and would otherwise lead to uneven pressure across the width of the roll. In the illustrated embodiment of calender, the lower roll could be such a deflection compensating roll. The compensation means would be internal to the roll shell and hydraulically operated, with linkage to the hydraulic means for loading the lower roll. Such linkage is only appropriate when the nip is operating in contact mode, and means can be provided to automatically decouple the hydraulic loading and deflection compensation means when the nip is to operate in gap mode, as provided for by the screw jack devices of the invention.

The foregoing is illustrative and not limitative of the scope of the invention and many variations in details of the screw jack mechanism are possible within the scope of the amended claims. In particular it may be advantageous to fit a pneumatic gun or other operating means in addition to or instead of the handwheel so that operators can have powerassistance to turn the worm shaft. Also, a comparable screw jack nip adjustment mechanism to that described could be fitted to a closed frame calender.

Claims (16)

1. A calender comprising a pair of rolls providing a nip therebetween, each roll having first and second opposed ends, respective bearing blocks mounting the first and second ends of each roll, means for loading the bearing blocks of one roll so as to move and/or press that one roll towards the other roll, and a separate nip gap setting/adjustment mechanism comprising respective screw jacks mounted between the respective bearing blocks at the first and second ends of the rolls.

2. A calender according to claim 1 wherein the means for loading the bearing blocks are hydraulic or pneumatic.

3. A calender according to claim 1 or 2 wherein each screw jack comprises a spindle threadedly engaged in a retained wheel nut, the nut being rotatable to adjust the height of the spindle.

4. A calender according to claim 3 wherein each screw jack further comprises a worm shaft, which is operatively engaged with the wheel nut in order to rotate the wheel nut and raise or lower the spindle.

5. A calender according to claim 4 wherein each screw jack further comprises means enabling manual actuation of the worm shaft.

6. A calender according to any of claims 3 to 5 wherein each screw jack includes a flexible seal around the spindle.

7. A calender according to any preceding claim wherein each screw jack includes an indicator device to indicate the height of the jack and/or the nip gap.

8. A calender according to any preceding claim wherein one roll of the pair incorporates deflection compensating means.

9. A device for setting and adjusting a nip gap in apparatus having a pair or rolls, each having first and second opposed ends mounted in respective bearing blocks, the device comprising a screw jack adapted for mounting between the bearing blocks of the two rolls at the first or second ends thereof and having a spindle threadedly engaged in a retained wheel nut, the nut being rotatable to adjust the height of the spindle so as to set the distance between the bearing blocks to which the jack is mounted.

10. A device according to claim 9 wherein the jack includes a worm shaft operatively engaged with the wheel nut to rotate the latter and raise or lower the spindle.

11. A device according to claim 10 wherein the jack includes a manual actuator for the worm shaft.

12. A device according to any of claims 9 to 11 wherein the jack includes a flexible seal around the spindle.

13. A device according to any of claims 9 to 12 wherein the jack includes an indicator device to indicate the height of the jack.

14. A device according to any of claims 9 to 13 wherein the jack includes an indicator device capable of calibration to indicate the nip gap between the rolls mounted from the bearing blocks between which the device is to be fitted.

15. A calender having a nip gap setting mechanism substantially as hereinbefore described with reference to and as illustrated by the accompanying drawings.

16. A device for setting and adjusting the roll nip in a calender or the like substantially as hereinbefore described with reference to and as illustrated by Figs 1 to 3 of the accompanying drawings.