GB2063889A

GB2063889A - Fibre reinforced plastics

Info

Publication number: GB2063889A
Application number: GB8037449A
Authority: GB
Original assignee: SKF Kugellagerfabriken GmbH
Current assignee: SKF GmbH
Priority date: 1979-11-30
Filing date: 1980-11-21
Publication date: 1981-06-10
Also published as: DE2948239A1; IT1134438B; IT8026200A0; JPS5686953A; FR2470785A1

Abstract

The invention provides a fibre reinforced plastics comprising a thermoplastics resin containing up to 25% by weight of glass fibres and up to 15% by weight of carbon fibres. The invention also includes a cage for a rolling bearing made from such a plastics.

Description

SPECIFICATION Fibre reinforced plastics The invention relates to a fibre reinforced plastics and to a cage for a rolling bearing made from such a plastics.

The prior art contains reference to the addition of fibrous substances to various thermoplastic synthetic resins in order to improve various properties, e.g.

wear resistance, temperature stability and sliding friction. However, only a single fibrous admixture is ever mentioned and only general recommendations for the use of these materials are given.

The prior art also contains a reference to a friction-bearing material for a sliding bearing which can be combined with various fibrous materials including carbon or glass fibres, but contains nothing about which percentage compositions can give which special properties.

Also the prior art contains a reference to another friction-bearing material for a sliding bearing which contains various admixtures, some of them mixed, which are said to improve the properties of the material, particularly at room temperature.

In the case of a cage for a rolling-bearing however, some of the physical properties required of the material are quite different from the requirements for a sliding bearing, and therefore the materials proposed for the prior art sliding bearings cannot be directly used for rolling-bearing cages. Cage materials must have high bending strength, tensile strength and temperature stability and must also be elastically deformable in most applications. In addition, the material itself must be cheap and simple to process. Known glass-fibre of carbon-fibre reinforced thermoplastics have considerable advantages - e.g. higher tensile strength, bending strength, heat stability and long-term properties - over the base thermoplastics material when used in rollingbearing cages, but they often fail to meet the increased requirements.Elastic deformability is a particularly important property of cages having projections for retaining the rolling members, or for the cage itself. The elasticity, however, decreased when the proportion of fibrous materials increases.

For this reason, elastically deformed parts of a rolling-bearing cage may break immediately or after a short period of operation in a rolling bearing, resulting in premature failure of the rolling bearing.

This occurs particularly in the case of carbon-fibre reinforced plastics, which contain high proportions of fibres in order to give other properties such as thermal and dimensional stability.

Elastic deformability is also an important property when producing an object by injection-molding. In order to use known, insufficiently deformable, materials for moulded objects meeting the aforementioned requirements, it is necessary to construct complicated moulding tools which, when they comprise multiple slides, have to be removed before the object can be taken out, particularly in the case of undercut recesses in injection-moulded objects (e.g.

pockets of rolling-bearing cages with retaining projections).

In view of the aforementioned requirements, known fibre reinforced plastics are preferred as a material for rolling bearing cages but they have inadequate resistance to ageing. The-requirements are frequently contradictory, particularly in the case of a rolling-bearing cage material.

The invention provides a fibre reinforced plastics comprising a thermoplastics resin and glass and carbon fibres, there being up to 25% by weight of glass fibres and up to 15% by weight of carbon fibres. The invention provides a plastics which is easy to process, resiliently deformable within certain limits without suffering permanent changes, resistant to ageing even at elevated temperatures and when acted upon by foreign substances, and resistant to impacts, collisions and the like.

Preferably the weight of glass fibres is in the range of 15 to 20%, and the weight of carbon fibres is in the range of 5 to 10%. The thermoplastics synthetic resin may be a polyamide.

The invention also includes a cage for a rolling bearing made from a fibre reinforced plastics according to the invention.

The percentage weights of fibres used throughout this specification are based on a percentage of the weight of the plastics including the fibres.

The plastics according to the invention has the following improved properties relative to known compositions: greater elastic deformability greater resistance to ageing, and greater impact strength.

In addition, important properties of known fibrereinforced plastics can be substantially maintained or even improved, e.g. the following: good heat stability, low coefficient of thermal expansion, great bending strength, great tensile strength, low wear coefficient, low friction coefficient, good thermal conductivity, and ease of processing.

In the case of the plastics according to the invention the elastic deformability, which is important for rolling-bearing cages having retaining projections, can advantageously be increased until, e.g.

in the case of roller-bearing cages having projections formed on the webs for holding the rollers, there is no risk that the projections will break or be permanently deformed when the rollers are snapped in.

The improvement in elastic deformability also resuits in critical advantages in the design of the injection-moulding tools. Many complicated tools, which have hitherto had to be movable, can be simplified or need not be movable, since the elastic resilience of the plastics can be used when the finished roliing-bearing cage is taken from the mould.

Consequently, even complicated tools for forming under-cuts can be snapped loose during release from the mould, or alternatively the cage can be taken from the injection-moulding tool.

In addition, a critical improvement is made in the resistance to ageing, compared with known rein forced plastics. In the case of rolling bearings, it is particularly important for the life of the cage to match the life of the other bearing components.

An improvement is also made in the impact strength of a rolling-bearing cage, which may suffer instantaneous local peak loads, caused by the rolling members. As a result of its great toughness, the fibre reinforced plastics according to the invention can withstand these loads without harmful plastic deformation.

The plastics according to the invention, besides having improved properties; is thus suitable for large-scale production because it comprises simple, cheap basic materials and is thus economic for many plastics products. The described plastics is of use not only in rolling-bearing cages, as given by way of example, but whenever a material has to meet high requirements and must also be cheap.

Claims

1. A fibre reinforced plastics comprising a thermoplastics resin and glass and carbon fibres, there being up to 25% by weight of glass fibres and up to 15% by weight of carbon fibres.

2. Afibre reinforced plastics as claimed in Claim 1, wherein the weight of glass fibres is in the range of 15 to 20%, and the weight of carbon fibres is in the range of 5 to 10%.

3. A fibre reinforced plastics as claimed in Claim 1 or 2, wherein the thermoplastics resin is a polyamide.

4. Acagefora rolling bearing made from afibre reinforced plastics as claimed in any preceding claim.