GB2029932A

GB2029932A - Rollers

Info

Publication number: GB2029932A
Application number: GB7929709A
Authority: GB
Original assignee: JM Voith GmbH
Current assignee: JM Voith GmbH
Priority date: 1978-09-02
Filing date: 1979-08-28
Publication date: 1980-03-26
Also published as: DE2838427A1; FI792712A; JPS5536696A

Abstract

In a roller for pressure-processing material webs, especially paper webs, with equalisation of the bowing under load, having a hollow cylindrical rotating casing 1 with a support element 4, pressure pistons 3 are guided in cylindrical bores in the support element and shoes 2 supported on the pressure pistons are provided, with a venting pressure chamber 12 equipped with a seal 14, 15 between each shoe and pressure piston. Each shoe can be readily inclined so that it always rests against the casing, and a single shoe may extend over the length of the casing. At least one of the two surfaces formed by the pressure piston and the shoe in the venting pressure chamber, e.g. surface 13 in the vicinity of its contact surface, is constructed at least approximately as a cylindrical or spherical surface. <IMAGE>

Description

SPECIFICATION Roller for pressure-processing material webs, especially paper webs The invention relates to rollers for the pressureprocessing of material webs, especially paper webs, with equalisation of the bowing under load, of the type which has a hollow cylindrical rotating casing with a support element extending through it and supported at its two ends, wherein for the transmission of pressure between the casing and the support element pressure pistons guided in cylindrical bores in the support element and sliding shoes supported in the pressure pistons provided, and wherein between each shoe and pressure piston there is a venting pressure chamber equipped with a seal.

This type of pressing roller may bow due to the compression pressure, and this might result in problems, especially when processing paper webs.

For this reason, a so-called floating roller has come into use, wherein shoes which extend over the whole length of the roller or several shoes arranged adjacent to each other and supported individually on pessure pistons and pressed from the inside towards the roller casing. By supplying a pressure medium between the casing and the shoe or shoes, a hydrostatically "floating" mounting is obtained. Corresponding to the bowing under load of the support element, the shoe can thus be inclined so that it always rests against the casing.

As friction arises during the relative movement between the shoe and the pressure piston, due to the great pressure forces prevailing there is a danger that a corresponding incline cannot always be guaranteed. For this reason, it is already known from German Laid-Open Patent Specification No. 22 45 597 to provide a venting pressure chamber between the pressure piston and the shoe. In this way, the coupling between the pressure piston and the shoe is partially vented so that th friction forces are reduced. The venting pressure chamber is this instance is sealed by an annular seal which lies in a plane passing through the centre of rotation of the coupling.

However, this design has the d.isadvantage that a supporting coupling is required for the ncessary inclining movement between the pressure piston and the shoe. Despite a venting pressure chamber, this coupling is still heavily loaded. Moreover, such a coupling would be difficult to use in practice where only one shoe which extended over the entire length of the casing were being used.

The present invention is therefore based on the problem of producing a roller of the type described in the introduction in which the necessary inclining movement of the shoe is guaranteed, and which is suitable both for individual shoes and also for shoes which extend over the entire length of the casing.

According to the invention, a roller of the type described is characterised in that at least one of the two venting pressure chamber surfaces formed by the pressure piston and the shoe, in the vicinity of its contact surface, is constructed at least approximately as a cylindrical or spherical surface. With the construction according to the invention a special supporting coupling can be dispensed with. The shoe is now supported on the cylindrical or spherical surface and can "roll away" on it. In this way the shoe can adapt itself to the path of the casing in a simple manner. In this instance the venting pressure chamber ensures that too high forces do not arise in the vicinity of the supporting surface. The construction according to the invention is suitable both for a plurality of shoes distributed over the length of the casing as well as for a single shoe which extends right across.In addition, the shoe runs more smoothly on the pressure piston, that is, the inclining movement is more even, as secondary forces with a braking effect are reduced or entirley eliminated.

In a development of the invention, provision is made for the pressure piston or the shoe to be equipped with a sealing ring in the vicinity of the contact surfaces. This provides a simple seal for the venting pressure chamber.

Another sealing possibility consists in arranging a hydrostatic seal which forms part of the contact surface, between the pressure piston and the shoe.

In this way, a contact-free and friction-free seal is obtained.

In one embodiment of a hydrostatic seal according to the invention, the hydrostatic seal consists of at least one annular dome-like projection pointing in the direction of the other sealing component. In this instance, the dome-like projection can be arranged either on the pressure piston or on the shoe.

In this case it is advantageous if the seal consists of two projections arranged one behind the other with a space lying between them for the reduction of pressure. In this way, a controlled reduction of pressure is obtained, since the pressure reduction space lying between ensures an appropriate gradual reduction of pressure.

In the following two construction examples of the invention are explained in more detail, with reference to the accompanying drawings, in which Figure 1 is a partial cross-section through a roller with one embodiment of pressure transmission according to the invention.

Figure2 is a partial cross-section through a roller with asecond embodiment of pressure transmission according to the invention.

Referring now to Figure 1,the pressure roller of this embodiment has a hollow cylindrical rotating casing 1 which is supported below the pressing slit from the inside by a plurality of shoes 2 distributed over the whole length of the roller and on the periphery of the roller. For this purpose, the shoe 2 is pressed against the casing 1 by a pressure piston 3 which slides in a support element 4, the inner member. The shoe is provided with a channel 5 which is connected via a pressure line 6 to a pressure chamber 7 formed by the piston 3 and the support element 4. A main line 8 supplies the pressure chamber 7 and thus also the channel 5 with pressure fluid. A bearing film on which the casing "floats" is thus formed in the channel 5.

On either side of the channel 5 there are pockets 9 and 10 for centering the shoe 2, each pocket being connected via capilliary lines 11 to the channel 5. If then on one side of the shoe the gap between the shoe 2 and the casing 1 becomes greater, increased pressure fluid comes out of the pocket lying on this side. The shoe 2 adjusts itself in this way back into the correct position.

Aventing pressure chamber 12 is aranged between the shoe 2 and the pressure cylinder 3. The surface of the pressure piston 3 which faces the shoe 2 is constructed in the vicinity of the contact surface as a spherical surface 13. As a seal for the venting pressure chamber 12 the shoe 2 has two projections 14 and 15 arranged behind one another, with a pressure reduction chamber 16 between them. The projections 14 and 15 are of dome-like design and form for the shoe 2 the contact surface which co-acts with the contact surface 13. At the same time they form a hydrostatic bearing.The shoe 2 can therefore adjust itself freely on the cylindrical surface 13 on the pressure piston 3 according to the bowing under load of the support element 4, the projections 14 and 15 rolling off or sliding accordingly overthe spherical surface 13 of the pressure piston 3.

Referring to Figure 2, the second embodiment is substantially of the same design. Unlike in the first embodiment shown in Figure 1, the shoe 2 now has an approximately spherical surface 17 pointing towards the pressure piston 3. In the vicinity of the similarly spherical contact surface 18 of the pressure piston 3 there is also a sealing ring 19. lfth shoe is designed as a strip extending right across the entire length of the casing, cylindrical surfaces, preferably in the axial direction of the casing, are adequate for the contact surfaces 13, 14, 15 or 17, 18 respectively.

Only when there is a plurality of separate shoes distributed over the length of the casing are separate associated spherical surfaces necessary, and since the inclining movements are reduced, it may sometimes suffice for the surfaces to be only approximately spherical.

Claims

1. A roller for the pressure-processing of material webs, especially paper webs, with equalisation of the bowing under load, of the type which has ahollow cylindrical rotating casing with a support element extending through it and supported at its two ends, wherein for the transmission of pressure between the casing and the support element pressure pistons guided in cylindrical bores in the support element and shoes supported on the pressure pistons are provided, and wherein between each shoe and pressure piston there is a venting pressure chamber equipped with a seal, characterised in that at least one of the two surfaces formed by the pressure piston and the shoe in the venting pressure chamber, in the vicinity of its contact surface, is constructed at least approximately as a cylindrical or spherical surface.

2. A roller according to Claim 1, characterised in that the pressure piston or the shoe, in the vicinity of the contact surfaces, is equipped with a seal.

3. A roller according to Claim 1, characterised in that between the pressure piston and the sliding shoe there is a hydrostatic seal which forms part of the contact surface.

4. A roller according to Claim 3, characterised in that the hydrostatic seal consists of at least one annular dome-like projection pointing towards the other sealing part.

5. A roller according to Claim 4, charaterised in that the seal consists of two projections arranged one behind the other with a pressure reduction chamber lying between them.

6. A roller for the pressure-processing of material webs constructed, arranged and adapted for use substantially as hereinbefore described, with referpence to Figure 1, or Figure 2, of the accompanying drawings. ~~~~~~