GB2124716A - Bellows - Google Patents

Abstract

One-walled bellows of metallic material for absorbing axial, lateral and/ or angular movements which, in contrast to conventional bellows, consist of cast metal. Alterations in the wall thicknesses are thereby no longer, as previously, predetermined by the manufacturing method but may be selected in such away that they may be optimally adapted to the material stress prevailing in the bellows undulation. In the case of undulating regions which are predominantly under compressive stress the wall thickness is increased; in the case of undulating regions which are predominantly under tensile stress the wall thickness is decreased.

Description

SPECIFICATION Bellows This invention relates to a one-walled bellows of metallic material for absorbing axial, lateral and/or angular movements.

Bellows of metallic material are presently produced by taking a cylindrical metal tube and forming the desired undulating profile thereon by radial impressing or forcing out. The forming of the undulations occurs in this case for example by applying rollers from the outside and/or the inside to form the desired profile either in stages or continuously.

Since the material is expanded to different degrees during the shaping process, differences in the wall thickness occur along the undulating profile.

These differences in the wall thickness are predetermined with respect to the method and, depending on the method of production used, lead to reductions, to a greater or lesser extent, in the wall thickness at the peaks of the undulations or at the undulation troughs and/or flanks. Depending upon where the maximum stress of the bellows occurs in operation, this weakening of the wall thickness may reduce the loading capacity and the useful life of the bellows.

The main disadvantage, however, lies in that with the known bellows it is not possible to adapt the pattern of the wall thickness to the material stress in the bellows undulation.

The present invention provides a one-walled bellows of metallic material for absorbing axial, lateral and/or angular movements, wherein the bellows is cast.

By means of the present invention a one-walled bellows may be manufactured in which the wall thickness pattern along the undulating profile may be freely selectable and in particular be optimally adapted to the material stress in the bellows undulation.

The present invention is based on the unexpected discovery that, in contrast to the process of manufacturing bellows by radial pressing in or out, which has been conventional for approximately 80 years, it is instead possible to manufacture bellows by casting despite the thinness of their walls. In this way bellows with a wall thickness of approximately 2 to 3 mm and good accuracy of shape may be manufactured, there being complete freedom with respect to local changes in the wall thickness along the undulating profile. This means that casting enables undulation geometry to be realized which is technically and economically optimized almost without restriction. In addition, the advantage results that undulating profiles which are essentially deeper than was possible hitherto may be produced, since it is not necessary to deform the material.Finally, unsynmmetrical undulation shapes, in particular those with undercuts, may also be produced at no extra cost.

Advantageously the wall thickness is altered in a predetermined manner dependent upon the local material stresses of the bellows undulation. In particular the wall thickness may be dimensioned such that there is approximately the same material stress along the entire undulating profile.

In the case of undulating areas which are predominantly under compressive stress it is advisable to increase the wall thickness locally, whereas in the case of undulating areas which are predominantly under tensile stress it is advisable to reduce the wall thickness locally. Both measures may be combined with the aim of equalizing the non-homogeneous stress and expansion state in the bellows undulation to a lower level, i.e. to render uniform the stress and expansion pattern.

Preferably the bellows undulations have wall thickenings both at the folds and at the flanks. It has been shown in tests that relatively high meridian stresses occur not only at the inner and outer folds but also approximately at the centres of the flanks, predominantly when the bellows are under compressive stress.

Austenitic cast iron, light-metal casting, cast steel and bronze are predominantly used as the material for the cast bellows.

The invention will be further described, by way of example only, with reference to the accompanying drawings, in which figures 1 to 17 show in each case various undulations shapes in cross-section (axial sections with respect to the bellows) of bellows according to the invention.

Figure 1 shows local wall thickenings at the inner and outer folds as well as at the central flank region.

The meridian stresses occurring when the bellows is under compressive stress are thereby equalized optimally, such that the non-homogeneous stress and expansion state is rendered uniform and reduced to a lower level.

Figures 2 and 3 show corresponding wall thickness patterns in the case of reduced meridian stress orfor relatively high pressure in the case of diaphragm and torus bellows respectively.

When the bellows have a large diameter the peripheral stresses define the admissible pressure.

For this purpose it was hitherto necessary to insert separate reinforcement rings in the troughs of the undulations. By incorporating the reinforcement in the bellows wall as shown in figures 4 to 10 the additional expenditure with respect to the manufacture and assembly of separate reinforcement rings may be dispensed with. Bellows of this type, suitable for high peripheral forces, may thereby be manufactured more cheaply.

The undulating profile shown in figure 7 is, in addition, suitable for high movement stresses since the walls of the folds are thinner in comparison to those of the flanks. A wall thickness pattern for torus bellows, corresponding to figure 7, is shown in figure 11 and for diaphragm bellows in figure 2.

If both high compression strength and high mobilityare required an undulating profilewithoutturning points and the greatest possible meridian arc length is advantageous. Such a profile is illustrated in figures 12 and 13. Corresponding profiles for diaphragm bellows are shown in figure 2 and for torus bellows in figures 14to 17.

Claims (8)

1. A one-walled bellows of metallic material for absorbing axial, lateral and/or angular movements, wherein the bellows is cast.

2. A bellows as claimed in claim 1, having varying wall thicknesses in the fold and flank regions, wherein the wall thickness is altered in dependence upon the local material stress in the bellows undulation.

3. A bellows as claimed in claim 2, wherein the wall thickness is altered according to uniform maximum stress in the bellows undulation.

4. A bellows as claimed in any of claims 1 to 3, wherein the wall thickness is increased in the undulating regions predominantly under compressive stress.

5. A bellows as claimed in any of claims 1 to 4, wherein the wall thickness is reduced in the undulating regions predominantly under tensile stress.

6. A bellows as claimed in any of claims 1 to 5, wherein the bellows undulations have wall thickenings both at the folds and at the flanks.

7. A bellows as claimed in any of claims 1 to 6, made of austenitic cast iron, light-metal casting, cast steel or bronze.

8. A bellows according to claim 1, substantially as herein described with reference to, and as shown in, any of figures 1 to 17 of the accompanying drawings.