Method and equipment in crawling operation of a press felt in a paper machine

The invention concerns a method and an equipment in crawling operation of a press felt in a paper machine.

The press felt is passed as a closed loop through the nip between the centre roll and a press roll in the paper machine, and the drive of the felt is produced by means of the nip drive. In connection with replacement of felt, the new felt is moistened before the start of the operation proper, and at the felt-moistening stage the felt is run with a low crawling speed by means of a separate drive gear while the press nip is open. In prior art, the drive gear has consisted of an electric motor, whose speed of rotation has been lowered by means of a reduction gear, the output shaft of said gear being further connected to a mechanical cylinder-operated coupling. Through the coupling, the movement of rotation has been transferred further to the axle of the drive roll of the felt.

As the mechanism mentioned above has been formed by coupling the constructional units of the mechanism one after the other, the constructional length of the mechanism has become detrimentally long. Further, the mechanism has consisted of a number of individual components, for which reason the susceptibility of failure of the equipment has been relatively high. In connection with the cylinder operation of the coupling, separate limit detectors have been used. By means of the use of the detectors, in the prior-art solutions, switching-on of the main drive of the felt has been prevented in situations in which the auxiliary drive is still in operation. The detectors have been susceptible of contamination, in which case the data on limit positions given by the detectors have not always been reliable.

In the present application, attempts have been made to find an improvement for the crawling operation of a press felt. In the application, a novel method and an equipment in accordance with the method are described, wherein the coupling and the drive gear consist of the same unit. The equipment does not comprise a separate disconnecting coupling, a separate gearbox, or a separate drive unit, but these consist of one unit. Thus, it has been possible to make the whole drive unit of simple construction and of short constructional length. Since the number of units susceptible of failure is lower, the operation of the equipment is considerably more reliable than the prior-art electro-mechanical crawling-drive system.

The method in accordance with the invention for crawling operation of a press felt is mainly characterized in that, when the paper machine is not being run and the nip between the centre roll and the press roll in the paper machine is open, the felt is moved, so as to moisten the new felt, by means of the crawling drive by rotating the drive roll, the axle of the drive roll being permanently connected with a drive rim, and that, in the method, during crawling operation, the drive wheel of a hydraulic device is brought into engagement with the drive rim, and, when the crawling drive of the felt is not in operation, the drive roll is switched to the free revolving position by shifting the drive wheel of the hydraulic device, which drive wheel is operationally connected with the drive rim, apart from the drive rim.

The device in accordance with the invention for crawling operation of a press felt is mainly characterized in that the equipment comprises a hydraulically displaceable drive wheel, which is operationally connected with the drive rim, and at least one spring, whereby, in view of effecting the position of free rotation of the drive roll of the felt, the spring is fitted to keep the drive wheel apart from the drive rim, the arrangement of equipment operating both as means of rotation of the drive rim and as a coupling device for the drive roll for crawling operation of the felt.

The invention will be described in the following with reference to some preferred embodiments of the invention illustrated in the figures in the accompanying drawings, the invention being, however, not supposed to be confined to said embodiments alone.

Figure 1A is shows the location of the device of the invention in a paper machine.

Figure 1B shows an equipment in accordance with the invention for crawling operation of a press felt as viewed in the machine direction.

Figure 2 shows a first preferred embodiment of the invention, wherein the hydraulic mechanism is displaced hydraulically so that the drive wheel that rotates the drive rim is brought into contact with the drive rim.

Figure 3A shows a second preferred embodiment of the device in accordance with the invention, wherein the drive rim is rotated by means of a cam mechanism.

Figure 3B shows the equipment of Fig. 3A in a position of free rotation, wherein the main drive of the press felt may be switched on.

Fig. 1A shows the location of the crawling-drive roll 10 of the press felt H in the press section. When the nip N between the centre roll K and the roll T in the paper machine is open, the felt is operated by means of the drive roll 10, for example, to moisten the felt. The roll 10 is a so-called crawling-drive roll. During operation of the paper machine, the felt is operated by means of the nip N, and in such a situation the roll 10 is in a position of free rotation.

Fig. 1B shows the crawling-drive device of the press felt as viewed in the machine direction. The press felt H is operated by the press-felt drive roll 10, whose axles 10a are mounted in bearings 11. The drive roll 10 receives its rotation drive directly from the drive rim 20, whose body 20a is connected to the roll 10 axle 10a. Around the equipment, there is a protective housing 13. The equipment rests on a cantilevered frame beam 12, while the trame beam 12 is attached to the frame R.

Fig. 2 shows a first preferred embodiment of the crawling-drive device in accordance with the invention. The drive shaft 15 of the hydraulic motor 14 is connected with a drive wheel 19. The hydraulic motor 14 is provided with an input connection 18a and an output connection 18b for fluid. The hydraulic motor 14 is displaced by means of a cylinder device 17, preferably by means of a hydraulic cylinder. When the hydraulic cylinder 14 is extended to its full stroke length, in the way shown in the figure, the drive wheel 19, preferably a cogwheel, placed on the output shaft 15 of the hydraulic motor 14 is brought into engagement with the drive rim 20, preferably a toothed rim. When the pressure in the hydraulic cylinder 17 is removed, the spring 23 between the piston 21 of the hydraulic cylinder 17 and the cylinder end 22 shifts the drive wheel 19 out of contact with the drive rim 20. Thus, the arrangement operates both as a drive gear for the roll 10 and as an overrunning clutch. When the crawling operation of the felt H is not on, the spring 23 shifts the drive wheel 19 out of contact with the drive rim 20, in which case the drive roll 10 is in the position of free rotation.

Figure 3A shows a second preferred embodiment of the crawling-drive device. The drive rim 20 comprises a wave-shaped inside rim form 24. Inside the drive rim 20, there is a drive unit 25, which comprises a number of drive pistons 26a,26b..., at whose ends there are cam-wheels 27a,27b... . The rotation of the drive rim 20 is produced by passing pressurized fluid through the inlet opening to the distributor 28 and from the distributor 28 further into the cylinders 29a,29b... . Some of the drive pistons 26a,26b... are in the work stage and push the cam-wheels 27a,27b... against the drive rim 20. The cam-wheels 27a,27b... that are in the work stage force the drive rim 20 into a revolving motion. After the pistons 26a,26b... have performed their full stroke, the distributor 28, which revolves synchronously with the drive rim 20, closes the inlet of fluid into the piston 26 that has completed its work stage and opens the exhaust opening to the fluid space of said piston. In a corresponding way, the distributor 28 opens the flow passage for the pressurized fluid into the piston 26 that is in the bottom position in its cylinder.

When pressurized fluid is not being passed to the distributor 28 and, through the distributor, into the pistons 26a,26b..., in the way shown in Fig. 3B, the springs 30a,30b... press the pistons 26a,26b... into their bottom positions in the cylinders 29a,29b... and keep the cam-wheels 27a,27b... placed at the ends of the pistons 26a,26b... apart from the drive rim 20. In such a case, the drive rim 20 can be rotated freely so that the system does not cause an operating resistance to the movement of rotation. The cam mechanism permits a drive system in which the drive device and the disengaging coupling constitute a single unit. When the press felt H is switched to the main drive, the fluid spaces E₁,E₂ at both sides of the pistons 26a,26b... are kept free of pressure. In such a case, the springs 30a,30b... press the pistons 26a,26b... to their bottom positions in their cylinders 29a,29b... and keep them there. The drive rim 20 and the press-felt H crawling-drive roll 10 connected to the rim 20 permanently by means of the body 20a can revolve freely at a high speed during normal operation of the paper machine while the felt H is driven by means of the nip N between the centre roll K and the press roll T in the press.