Drive assembly for a web spreading roll

Abstract: Spreading rolls are used in conjunction with, e.g., finishing equipment of paper mills to assure sufficient and constant cross-machine tension for the web running over guide rolls. Spreading is required due to web width variations caused by the coating, drying and calendering steps. A spreading roll comprises a curved shaft (1) with its radius of curvature vector aligned in the machine direction and rotary driven roll segments (6) mounted in bearings on the shaft. The roll segments are coupled to each other and they are driven about the shaft by a synchronous belt drive. The curvedness of the shaft complicates the design of a synchronous belt drive, and hence, the present invention concerns such a synchronous belt drive assembly for a web spreading roll that is free from angular nonalignment between the driving and the driven toothed pulley. The invention is based on mounting the driven toothed pulley (8) in bearings on the bearing housing of the curved spreading roll shaft and then coupling the pulley (8) with the outermost roll segment (6) using a flexible coupling (10).

Description: The present invention relates to an assembly according to the preamble of claim 1 for driving the spreading roll of a moving web. Spreading rolls are used in conjunction with, e.g., finishing equipment of paper mills to maintain sufficient and constant web tension also in the cross-machine direction for the web running over guide rolls. Spreading is required due to web width variations caused by the coating, drying and calendering steps. Moreover, the machine-direction tension of the running web tends to cause slight centripetal contraction of the web toward its center. A spreading roll comprises a curved shaft with its radius of curvature vector aligned in the machine direction and rotary driven roll segments mounted in bearings on the shaft. The roll segments are coupled to each other and they are driven about the shaft by a synchronous belt drive. The synchronous belt drive assembly comprises a toothed pulley coupled to the outermost rotary roll segment of the spreading roll, a drive motor, a toothed pulley mounted on the drive shaft of the motor and a toothed belt. The toothed pulley driving the rotary roll segments is mounted in bearings on the curved shaft and connected by a nonflexible coupling to the outermost roll segment. The drive motor is mounted on, e.g., the bearing housing of the shaft end bearing of the curved roll. As the web passes over the spreading roll, each roll segment imposes on the web a force with a magnitude dependent on its orientation relative to the web and directed toward the edge of the web thus tensioning the web in the cross-machine direction. The rotational speed of the spreading roll must be exactly controlled according to the web speed to avoid overtensioning the web and to achieve desired web tensioning in the cross-machine direction. Due to the strict accuracy requirement set for the spreading roll speed, a toothed belt must be used for driving the spreading roll. Use of a V-belt drive is impossible, because the inherent slip of a V-belt drive makes accurate speed control impossible. Use of a roller chain drive is hampered by pulsating speed variations which are intolerable in this kind of application. Slip-free and accurate speed control of the spreading roll is easily achieved by virtue of a toothed-belt drive. A major shortcoming of synchronous belt drives currently used for driving a spreading roll is the unavoidable nonalignment of the driven toothed pulley mounted on the end of the curved roll shaft relative to the driving toothed pulley mounted on the end of the drive motor shaft. The driven pulley is inherently parallel to the edge of the outermost roll segment and these elements are conventionally coupled to each other in a fixed manner. The driving toothed pulley of the drive motor is difficult to align in line with the driven toothed pulley, and in practice, an angular misalignment remains between the pulleys, whereby the life of the toothed belt will be drastically shortened by wear due to misalignment. The orientation of the driven pulley will change with the radius of curvature adjustment of the spreading roll shaft, which necessitates the mounting of the drive motor on an adjustable base with an alignment facility of the drive assembly pulleys. Such a mandatory alignment complicates the drive assembly construction and increases the labour required in the radius of curvature adjustment of the spreading roll. It is an object of the present invention to achieve such a synchronous belt drive assembly for a web spreading roll that is free from angular nonalignment between the driving and the driven toothed pulley. The invention is based on mounting the driven toothed pulley in bearings on the bearing housing of the curved spreading roll shaft and then coupling the pulley with the outermost roll segment using a flexible coupling. More specifically, the assembly according to the invention is characterized by what is stated in the characterizing part of claim 1. The invention provides significant benefits. The principal benefits of the present invention include a simplified construction of the drive assembly for a spreading roll and the elimination of angular nonalignment between the toothed pulleys. The toothed pulley driving the roll segments can be mounted in fixed bearings, whereby its alignment will not change during a radius of curvature adjustment of the curved spreading roll. Resultingly, the drive motor can be mounted on a fixed base, whereby the adjustment requirements are reduced to belt tension adjustment alone. As the alignment of the drive motor need not be adjusted during the radius of curvature adjustment of the spreading roll, this adjustment step of the spreading roll will be faster. Furthermore, the permanent elimination of angular nonalignment between the pulleys results in substantial increase in belt life. When desired, the assembly can be easily modified for the use of parallel belts and pulleys. In the following the invention is described in greater detail with reference to the annexed drawing illustrating a partially sectional side view of the drive assembly according to the invention. With reference to Fig. 1, the end of a spreading roll driven by a drive motor 5 is shown. The curved shaft 1 of the roll is mounted in bearings by means of a ball-and-socket bearing 2 supported by a bearing housing 3, 4. The bearing housing 3, 4 has a mounting flange 4 on which are mounted a drive motor 5 and a driven toothed pulley 8 in a bearing 7. The driving pulley 11 is mounted on the shaft 13 of the drive motor 5 and the toothed pulleys 8, 11 are coupled to each other by means of a toothed belt 12. The driven pulley 8 is coupled to the outermost roll segment 6 of the curved spreading roll with the help of a flexible coupling 9, 10. The coupling comprises mounting flanges 9 by which it is connected to the driven toothed pulley 8 and the roll segment 6, respectively, and a flexible bellows 10 joining the mounting flanges. The bellows can be made from rubber or other suitable, resilient material. This arrangement permits permanent mounting of the driven pulley 8, and thus, accurate alignment relative to the driving pulley 11, which is extremely important in terms of reliable function of a synchronous belt drive assembly. The flexible coupling 9, 10 is capable of transmitting the driving torque from the driven pulley 8 to the roll segment 6 notwithstanding a possible angular nonalignment between these two coupled elements. Furthermore, a change of such angular nonalignment during the radius of curvature adjustment of the spreading roll has no effect on the function of the drive assembly by virtue of the flexible coupling. The assembly according to the invention can be varied in many ways. The structure of the flexible coupling 9, 10 can be modified as required, and a great number of different types of flexible couplings are available commercially. Furthermore, the mounting of the driven toothed pulley and the drive motor on the bearing housing or other similar fixed structure can be implemented in a desired manner, and in fact, the design of the assembly must be fitted to the design of the spreading roll and the space constraints. The number of pulleys and belts can be varied according to the power to be transmitted.

Claims: An assembly for driving a web spreading roll, said roll comprising a curved shaft (1) mounted in bearings at the ends of the curved shaft and a number of rotary driven roll segments (6) mounted in bearings on the shaft (1), said drive assembly comprising a drive motor (5), at least one drive toothed pulley (11) mounted on the shaft (13) of the drive motor (5), at least one driven toothed pulley (9) coupled to at least one roll segment (6) for driving said roll, and at least one toothed belt (12) which couples the toothed pulleys (8, 11) to each other, characterized by the driven toothed pulley (8) is mounted by means of at least one bearing (7) to a fixed structure so that the alignment of the pulley relative to the driving toothed pulley (11) remains constant, and the driven toothed pulley (8) is coupled to the roll segment (6) by means of a flexible coupling (9, 10). An assembly as defined in claim 1, characterized in that the drive motor (5) and the driven toothed pulley (8) are mounted on the bearing housing (3, 4) of the curved shaft (1). An assembly as defined in claim 1 , characterized in that the flexible coupling comprises a flexible bellows (10) and two mounting flanges (9) for connecting the bellows (10) to the driven toothed pulley (8) and the roll segment, respectively. An assembly as defined in claim 1, characterized in that the flexible coupling comprises a flexible bellows (10) directly connected to the driven toothed pulley (8) and the roll segment, respectively.

Inventors: ESKOLA TIMO, KURKINEN LEO, ESKOLA, TIMO, KURKINEN, LEO
Applicants: VALMET CORP, VALMET CORPORATION
Application year: 1995
Main classification: D21F7
IPC codes: D21F7, D21F1, B65H23