GB2206945A - Disc springs - Google Patents

Abstract

Discs 1 in springs according to the invention are made of resilient plastics material, preferably reinforced with fibre, and are without central apertures, having instead a substantially flat land 2 at the centre. A guide element of the spring may comprise a tube 4 enclosing the spring, or may comprise guide rods which pass through off-centre apertures in the discs. <IMAGE>

Description

Disc Springs This invention relates to disc springs.

A disc spring comprises discs formed as shallow truncated cones or like dished elements which in use are loaed so as to be distorted axially. Loading causes progressive distortion of the element about a guide rod passing through a central aperture in it until ultimately the element is flat. Discs springs have been in use for decades. Their discs have been made of steel or (for use in unusual conditions) special metallic materials such as chrome-molybdenum alloys, but there have been proposals that they should be made of resilient plastics material, preferably incorporating fibrous reinforcement (eg high-modulus glass, carbon or aramid fibres) which might be in the form of a fabric, so that the fibres would lie generally in the plane of the disc.

We have found that disc springs made as just outlined fail prematurely, owing to the propagation of cracks or delamination at the edge of the central aperture through which the guide rod passes.

According to the present invention, we dispense with such a central aperture, leaving a substantially flat land in its place. The guide means may comprise a tube which encloses the spring, or guide rods or the like which pass through the apertures in the discs which are displaced from the disc flat centres or lands. Thus, m number of apertures disposed about the disc centre may be provided, say half-way down the conical slope of each disc, through which a corresponding number of guide rods or the like may pass. For example, 3 apertures could be disposed so that lines joining them to the disc centre would be inclined at 12"0 to one another.

By the invention stresses arising from the presence of the aperture are reduced, and in consequence the rate and life of the disc springs are increased.

A wide variety of plastics materials, either thermoplastic or thermosetting, may be employed in making the discs; for example polyether sulphone, polyetherimide, polyetheretherketone, epoxy and polyester resins. They enable a wide selection of spring properties to be obtained by varying such features as modulus and thickness, and are easily moulded to disc form by conventional press or injection moulding procedures.

As in conventional disc springs, the discs will usually be stacked in pairs face to face with their margins abutting to define a space between the members of a pair.

If desired however, some can be stacked in continuous contact to provide a thicker distortable element.

Similarly, discs of different properties can be assembled in a stack to form a spring whose behaviour changes progressively, or stepwise, in a predictable and controlled manner during the compression produced by loading. Multi-rate or variable rate springs can alsD be obtained by including in the stack spacer elements made for example from compressible elastomers or hard polymers.

The invention is further illustrated with reference to the accompanying drawing, which is an axial section of one form of disc spring and to the following example.

Example A glass-fibre woven fabric (224 ends per 10 cm; 8-end 2 satin weave; 0.23 mm thick; weight 297g/m ) was then impregnated with a solution of epoxy resin (Ciba-Geigy MY 750) in methyl ethyl ketone containing hardener (HT 972).

Excess resin solution was squeezed from the impregnated fabric by passing it between rollers and the material was then heated at 1000C for 25 minutes to remove solvent and part-cure the resin. Fifteen circular pieces (150 mm diameter) were cut from the sheet thus obtained. The pieces were superimposed one upon another, and the assembly was press cured in a conical disc mould with 0 flattened centre at 150 C for 10 minutes under a pressure of 0.7 MPa. The resulting disc was 3mm thick with a flat centre of 50mm in diameter. The angle made by the flat land with the conical wall was 1700.

To make a spring, discs (numbered 1 in the accompanying drawing) having central flat lands 2 are assembled as pairs, in alternating arrangement, with their margins 3 abutting and enclosing a space 3a, in a guide 4 in the form of a steel tube closed by a steel base 5.

A spring such as just described can be made from 6 pairs of discs assembled in a tubular guide. Such a spring has a length of 156mm and a typical rate of 70KN/m.

Claims (6)

1. A disc spring in which the discs are of resilient plastics material and have a central unapertured substantially flat land.

2. A disc spring according to claim 1, in which the spring guide means comprises a tube which encloses the spring.

3. The disc spring according to claim 1, in which the spring guide means comprises guide rods or the like which pass through apertures in the discs which are displaced from the disc land.

4. A disc spring according to claim 1,2 and 3 in which the plastics material is reinforced with fibre.

5. A disc spring according to claim 4 in which the fibre is incorporated in a fabric.

6. A disc spring substantially as described with reference to the Example and drawing herein.