GB2272707A - Improved composite bearing materials - Google Patents

Abstract

Polyester fibre felt is used as a reinforcement for cured organic resin composites for use as bearing materials, e.g. for shafts in marine applications. The felt may be needled or stitch bonded. A phenolic or polyester resin may be used.

Description

Improved composite bearing materials This invention relates to fibre reinforced composites of the kind wherein textile fibres are employed as reinforcement in a polymeric matrix material. In particular the invention is concerned with non-asbestos composite bearings based on a thermoset resin matrix and including an organic fibre reinforcement.

Fibre reinforced composite bearings of the above kind are wellknown. They find utility in such applications as marine propeller shaft bearings. For this latter application whether lubricated by oil or water, it is usual to produce the composite article from cloth impregnated with a curable resin, typically a phenolic resin. This is then converted to a composite material by one of two routes. Firstly, it may be rolled around a mandrel to form a thick walled tube. Secondly, several layers may be superposed, to make a flat or curved sheet. In both cases, the resin impregnant is thereafter cured under heat and pressure to yield an essentially rigid product which may thereafter be sawn, or machined into bearing components.

Asbestos cloth was traditionally employed as reinforcement for composites intended for marine bearing applications where water is the primary lubricant. However, attempts to replace asbestos by, for example, woven polyester fabrics, have not been entirely successful, primarily for cost reasons. Polyester fibres are vulnerable to chemical attack by adventitious material in the resin system, such as free phenol, in the case of phenolic resins. Also, polyester fabric is relatively expensive and lacks the resin absorbing high surface area and structural mass of asbestos cloth.

It is an object of the present invention to provide an improved non-asbestos composite bearing.

According to this invention, a non-asbestos fibre-reinforced composite bearing comprises a cured organic resin binder including a felt of polyester fibres as reinforcement.

The felt may be a needled or a stitch bonded felt, the latter being preferred. Surprisingly, it has been found that such a felt can replace an expensive conventional woven polyester fabric with no significant deterioration in properties.

Particularly preferred resins include polyester resins and phenolic resins containing less than about 2% by weight of free phenol.

Examples In order that the invention be better understood, four preferred embodiments of it will now be described with reference to the following Examples. The first two Examples utilised a thermally bonded polyester fibre felt having a density of 150g/m2.

In Example 1, the felt was impregnated with a phenolic resin containing less than 2% of free phenol and press cured into a laminate slab containing 21 layers of felt.

Example 2 was made in exactly the same way, but used an unsaturated polyester resin instead of the phenolic resin.

In both cases, laboratory equipment was used to make the laminates.

The products were tested by conventional means, with the following results.

EXAMPLE 1 EXAMPLE 2 Resin content approx % 56 50 Tensile Strength MPa 59 64 Compressive Strength MPa 306 263 Impact Strength kJ/m2 52 40 Bond Strength kN 2.55 (4.92mm) 2.4 (5.31mm) Water Absorption % Wt 1.75 1.13 Swell 200C % thickness 0.46 0.38 Swell 800C % thickness 1.54 1.42 Density g/cm3 1.33 1.26 Note that bond strength was measured on the sample thickness in parenthesis, by pressing a steel ball into the sample until failure occurred.

The above test results were fully commensurate with those obtained using much more expensive polyester fabrics. The tensile strength was slightly lower, although for bearing applications, this is not critical, because behaviour in compression is more important.

The products were readily sawn/machined into bearing components.

The performance of the latter, particularly in water-lubricated marine applications was very acceptable.

Examples 3 and 4 both used a stitch bonded polyester felt, the bonding being carried out with a polyester thread at a stitch density of about 2.5 per inch. This was processed on production equipment as follows.

EXAMPLE 3 A cured laminate sheet was made from a stitch bonded polyester felt of density 350g/m2 and a phenolic resin content of 60%, by weight. On testing it exhibited the following properties.

Tensile strength 40 MPa Compressive strength 250 MPa Impact strength 25 kJ/m2 Bond strength 3.5 kN (on a sample thickness of 6.35mm) Water absorption 2% Swell at 200C as % of thickness 0.5 Swell at 890C as % of thickness 1.0 Density 1.31 g/cc The finished sheet was cut into generally trapezoidal section staves which were assembled side by side in a supporting cage to form a tubular bearing, the performance of which in a waterlubricated marine shaft bearing application was very satisfactory.

EXAMPLE 4 A tube was made from a stitch bonded polyester felt of density 200g/m2 and a phenolic resin content of 70% by weight, the method employed being to wrap the felt under tension onto a mandrel. The wrapped felt was baked in an oven at 1350C. The cured tube produced by removing the mandrel had the following properties.

Compressive strength 180 MPa Bond strength 4.5 kN (on a sample thickness of 6.35mm) Density 1.31 g/cc Its other properties were generally commensurate with those listed in relation to Example 3. The performance of a waterlubricated bearing made from the tube by cutting/machining was also good.

Claims (6)

1. A non-asbestos fibre reinforced composite bearing comprising a cured organic resin binder including a felt of polyester fibres as reinforcement.

2. A non-asbestos composite according to claim 1 wherein the felt is a needled felt or a stitch-bonded felt.

3. A non-asbestos composite according to claim 1 or claim 2 wherein the resin is a phenolic resin.

4. A non-asbestos composite according to claim 3 wherein the phenolic resin contains less than 2% by weight of free phenol.

5. A non-asbestos composite according to claim 1 or claim 2 wherein the resin is an unsaturated polyester resin.

6. A non-asbestos composite bearing substantially as described with reference to the Examples.