ARRANGEMENT FOR BELT CONTROL

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of PCT application No. PCT/EP2007/052432, entitled “ARRANGEMENT FOR BELT CONTROL”, filed Mar. 15, 2007, which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an arrangement for treating a paper, board, tissue or other fibrous web in a machine for producing and/or finishing the same, the arrangement including an endlessly circulating belt with a high flexural rigidity which wraps around a rotatably mounted control roll with a wrap angle, at least one end of the control roll being mounted such that it can be displaced along an adjusting travel in order to set the belt tension.

2. Description of the Related Art

Control rolls of this type have been known and are intended to influence the belt run with regard to limiting the lateral run-off of the belt parallel to the roll axis.

It is primarily belts with a high flexural rigidity, in particular at right angles to the belt running direction, which are subjected to high flexural stresses, reducing the lifetime of the belt.

In addition, in the case of belts with high rigidity, transversely with respect to the belt running direction, there is the risk of sliding on the control roll.

What is needed in the art is to improve the belt run with the lowest possible flexural stress, in particular transversely with respect to the belt running direction.

SUMMARY OF THE INVENTION

The present invention, provides an arrangement for treating a paper, board, tissue or other fibrous web in a machine, the arrangement including an endlessly circulating belt which wraps around a rotatably mounted control roll having a wrap angle lying between 90° and 180° and the adjusting direction of the control roll lying approximately perpendicular to the bisector of the wrap angle.

The wrap angle corresponds to the difference between 180° and the angle between the belt running on and running off with regard to the control roll. As a result of the relatively large wrap of the control roll, higher frictional forces can also be transferred to the belt, which sharply reduces the risk of the belt sliding on the control roll. The linear adjustment of the mounting approximately perpendicular to the bisector minimizes the change in the belt length and thus, the increase in stress associated with the latter.

In this case, the angle between the adjusting direction and the bisector may lie between 60° and 120°, between 80° and 100° and between 85° and 95°. The thicker and wider the belt, the less the adjusting direction should deviate from the perpendicular to the bisector. The reason for this lies in the rigidity of the belt, influenced substantially by the width and the thickness.

In order to limit a change in the belt length, the adjusting travel may be at most 60 mm long. Depending on the width of the belt and specific requirements, both bearings of the control roll may be adjusted or else only one bearing may be adjusted and the other remain fixed. In the event that both bearings are adjusted, the bearings should be adjusted in opposite directions.

Because of the flexural stress problems, the arrangement of the present invention may be suitable for belts of which the modulus of elasticity is greater than 100 kN/mm2, or greater than 190 kN/mm2. Furthermore, for the same reason the arrangement of the present invention may be suitable for belts which are wider than 2 m and/or have a thickness of more than 0.5 mm or more than 0.8 mm.

The belt in the arrangement of the present invention may be formed as a steel belt and may also be impermeable.

The belt of the arrangement of the present invention may be pressed by a pressure element against a supporting element running with it, and the fibrous web, on its own or together with one or more functional belts, may run between the supporting element and the belt. This permits the dewatering or drying of the fibrous web. The pressure element may be formed by a stationary pressure chamber filled with a pressurized fluid, the pressure chamber being open toward the belt and sealed off with respect to the belt.

The supporting element should be formed by a rotating supporting roll. In this case, the control roll should be arranged before the supporting roll, the length of the belt from the control roll as far as the supporting roll being less than one third less than one quarter of the overall belt length.

In order to prevent the belt from sliding on the control roll and/or a guide roll arranged before or after the control roll, the control roll or the guide roll may have a roll cover, which may be a rubber cover, with high friction, preferably with a μ of more than 0.2. In addition, improved adhesion is achieved if the roll cover has grooves. In this case, the grooves should run axially parallel or with a herringbone geometry.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawing, wherein:

FIG. 1 illustrates a schematic cross section through the arrangement of the present invention.

Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrates one embodiment of the invention and is not to be construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, and more particularly to FIG. 1, there is shown a drying arrangement of a paper machine for drying fibrous web 1.

This is formed by supporting element 8 in the form of a cylindrical, rotating and heated supporting roll and impermeable, endlessly circulating belt 2 wrapping around the supporting roll.

In addition to fibrous web 1, two water-absorbing functional belts (not shown) are guided through the press nip formed by belt 2 and the supporting roll, running between fibrous web 1 and belt 2.

In the wrap region of belt 2, opposite the supporting roll, there is arranged pressure element 9 in the form of a pressure hood, having a pressure chamber filled with fluid.

This pressure chamber is sealed off with respect to belt 2 by seals, so that the fluid of the pressure chamber, open toward belt 2, presses belt 2 toward the circumferential surface of the supporting roll.

Cooling of belt 2 is carried out by the fluid, so that intensified condensation occurs in the water-absorbing functional belts. In this way, the water evaporated from fibrous web 1 via the heating by the supporting roll can be led away simply via the functional belts.

Before and after the pressure hood, belt 2 is pressed against the supporting roll by guide roll 10 in each case. This leads to the compression of the nip between belt 2 the and supporting roll and improves the guidance of belt 2 and the functional belts.

Since the pressure hood is arranged to be stationary, the seal with respect to belt 2 must be lubricated. It is carried out here via leakage of the fluid, water here, from the pressure chamber.

The pressure in the pressure chamber lies between 0.3 and 5 bar. Thermally conductive belt 2 is formed by a steel belt, which has a width of several meters and a thickness of 0.8 mm.

The modulus of elasticity of belt 2 is more than 200 kN/mm2. In order to control the belt run and the belt tension, belt 2 is led around control roll 3 that is rotatably mounted on both sides and is arranged before the supporting roll. Wrap angle 5 of belt 2 is around 140°, it being possible for both bearings of control roll 3 to be displaced over adjusting travel 7. In this case, wrap angle 5 corresponds to the difference between 180° and angle 12 between the belt running on and running off with regard to control roll 3.

In order to minimize the change in the length of the belt and, therefore, also the increase in tension transversely with respect to the belt running direction at the edge of the belt during an adjustment of the bearings, the adjusting direction of the mountings of control roll 3 is approximately the same as perpendicular 6 to bisector 4 of wrap angle 5.

In order to effectively counter belt 2 running off transversely with respect to web running direction 11, the mountings are adjusted in opposite directions, so that the average length of the belt is stretched as little as possible. Maximum adjusting travel 7 lies between +30 and −30 mm around a central position and is thus 60 mm. As a result of these measures, in particular in the case of such rigid belts 2, the result is optimum conditions with regard to minimal flexural stress, little change in belt length and high transmitted frictional force between belt 2 and control roll 3. The flexural stresses generally increase with wider belts 2.

While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.