GB2263726A - Cam cleats - Google Patents

Abstract

A cam for use in a cam cleat comprises an injection-moulded polymer reinforced with randomly oriented carbon fibres. The cam preferably has teeth with radii of between 0.40 and 0.75mm. A cam cleat comprising a pair of such cams preferably has a cam angle of about 15 DEG and face angles of about 70 DEG to 75 DEG . <IMAGE>

Description

CAM CLEATS This invention relates to improvements in the trianufacture of cam cleats.

Cam cleats are used particularly to secure lines on sailing craft. Cam cleats generally comprise a pair of cams rotatably mounted about a pair of adjacent shafts. The cams are normally spring biased towards each other, and adjacent faces include gripping teeth so that any line placed between the cams is held firmly in position.

In the past, cams have been manufactured from metals, particularly aluminium, but the cost of manufacturing cams using suitable metals is significantly more than the cost of using polymer plastic materials.

However, moulded polymer plastic cams, whether reinforced with minerals or glass fibres, have not to date achieved similar performance levels to those of cams made of metals or using metal teeth inserts in moulded plastics.

Accordingly, applications for and performance of plastic cams have been limited compared with metals. Plastic cams have had all or some of the following disadvantages: (a) the plastic is too smooth to grip some types of rope; (b) the plastic "burns out" when ropes are pulled rapidly through the cleat; (c) the plastic teeth have insufficient rigidity1 so that they deform as they grip the rope, letting it slip slightly and resulting in tooth and rope wear, which in turn results in more slipping; (d) when the plastic is reinforced with glass fibres, the fibres enhance gripping becaUse they are abrasive and because they increase the rigidity of the teeth, but they cause increased rope wear and the glass fibres themselves wear away over a relatively short period of time.

According to the present invention, there is provided a cam for use in a cam cleat, the cam comprising an injection-mouSded a polymer reinforced with randomly oriented carbon fibres.

Prior to the experimentation which resulted in the development of the present invention, it was believed that carbon fibres would be unsuitable for use in achieving the objects of the present invention, In particular, although it was known that carbon fibres are useful in stiffening plastics, it was thought that carbon fibres would result in cams having surfaces which were too smooth and slippery to provide a firm grip for a rope, especially if fibre glass fibres were not used or were used in reduced proportion. It was also known that the introduction of a high proportion of carbon fibre into a plastic composition can result in brittleness, and it was thought that cams incorporating carbon fibres might break too easily.

However, considerable experimentation and testing has resulted in the surprising conclusion that the use of carbon fibres together with a suitable polymer results in a cam having excellent performance characteristics. It has furthsrmore been found that, because there is less deformation of the gripping teeth when they are reinforced with carbon fibre, it is easier to remove a rope from the cam cleat when loaded.

The invention will hereinafter be described in greater detail by reference to the attached drawing which shows an example form of the invention. It is to be understood that the particularity of the drawing does not supersede the generality of the preceding description of the invention.

Figure 1 is a plan view of a cam cleat manufactured according to an embodiment of the present invention.

The cam cleat comprises two cams 1,2, which are spring biased towards each other. Facing edges 3,4 on the cams have teeth 5 which grip a rope when the rope is placed between the cams. Each cam is manufactured by injecting a polymer together with randomly oriented carbon fibres into a mould.

The suitability of the materials chosen for use in the present invention was determined after a considerable program of research in which a number of different materials were tested. Testing equipment included a cam cleat usage simulation machine, which enters a rope into a cam cleat, pulls it approximately one metre, removes tension from the "up" side of the rope so that the cleat is required to hold the rope from slipping with various loads (typically about 40 kg) and then re-tension the line, uncleats it and returns it to the start position. Each cycle of this operation is designed to simulate typical usage on sail craft.

The comparative testing was conducted over ten thousand cycles, a period which was intended to approximate roughly f ive years of normal yachting use.

In a preliminary laboratory test, 8 cam manufactured using a combination of a polymer with 40% glass fibre was compared with a cam manufactured using 40% carbon fibre instead of glass fibre. It was found that the sample which included carbon fibres exhibited the following improvements over the sample which included glass fibres: 50% improvement in tooth compression stiffness and flexural modulus; 408 reduction in co-efficient of friction; 45% reduction in self wear (tested against steel).

When the simulation testing machine described above was used, the carbon fibre sample exhibited the following improvements over the glass fibre sample: 40% less rope wear (removal, cutting and abrasion of rope fibres); 258 less wear of cam teeth themselves; 20t lower exit efforts (that is amount of force required to remove rope when loaded from cam cleat); and 10% higher maximum load (load at which rope slips).

Experimentation further revealed that the results obtained for the carbon fibre cams were comparable with and/or better than those achieved using metals such as aluminium in a cam cleat of similar design.

The testing revealed that, for some types of plastics, the use of reinforcing glass fibres tended to improve the heat performance; that is, the plastic was less susceptible to "burn out" when a rope was pulled quickly through the cleat.

It was found that the use of carbon fibres improved the heat performance further. It is thought that a reduction in "burn out" can be achieved by the rapid conduction of heat away from the friction heat source, that is the teeth.

It was found that the effectiveness of cam cleats incorporating carbon fibres was increased when careful attention was paid to the radii of the teeth and the angles of the faces, and when the polymer used in the plastic was adjusted to suit the carbon fibres. In particular, the following adjustments were made to the cam design: (a) Cam angles were reduced. The cam angle is the angle between an imaginary line intersecting the two cam pivot axes and an imaginary line between a cam pivot axis and the tooth on the same cam penetrating most into the rope.The cam angle in a fibreglass-reinforced cam cleat is typically 2De to 30", The use of carbon fibres in accordance with the present invention has allowed for a reduction in cam angle to approximately 159, (b) The teeth on the cams were rounded to increase the surface area of the cam in frictional contract with the rope, and to reduce the likelihood of breakage of sharp corners brought about by the brittleness of plastics having high carbon fibre content. The teeth on fibreglass-reinforced cam cleats frequently have radii of the order of 0,2mm.When carbon fibres are used according to the present invention, it has been found that, for large cams, the tooth radius is preferably about 0.75mm; for medium-sized cams the tooth radius is preferably about 0.55mm; and for small-sized cams the tooth radius is preferably about 0.40mum.

(c) Face angles were increased and made more open, increasing the surface area in contact with the rope and increasing the rigidity and resistance to breakage of the teeth by providing more material in compression directly behind the face of each tooth. It was also found that more open face angles improve heat dissipation through the carbon fibres and polymer from the tip of each tooth. The face angles on fibreglass-reinforced cam cleats are frequently of the order of 45". When carbon fibres are used in accordance with the present invention, the face angles are preferably about 700 to 75 .

(d) The cam stops limiting the rotation of the cams were increased in size to protect against the possibility of the cam stop being broken off when subjected to high cleating loads. This eliminates the potential brittleness attributable to use of a high-carbon-fibre content plastic. For fibreglass-reinforced cam cleats of medium size, cam stops are typically 3mm x 3mm to 6mm x 3mm in size, with some being as small as 3mm x 2mm, When carbon fibres are used according to the present invention, it is preferred that the cam stops be about lOmm x 5mm for medium or large cam cleats, and about 6mm x 3mm for small cam cleats.

In order to ensure that the cams had sufficient gripping ability, it was found desirable to choose a polymer which had a high coefficient of friction but good abrasion resistance. The preferred relative proportions of polymer and carbon fibres were approximately 608 polymer and 40% carbon fibres.

It is believed that the higher mum load characteristics achieved with the carbon fibre cams was attributable to the increased stiffness of the teeth, and the lower wear was attributable to the smoothness and natural lubricating properties of the carbon fibres, the ease with which ropes could be removed from the carbon fibre cam cleat was thought to be attributable to the lesser amount of deformation undergone by carbon fibre reinforced teeth.

It is to be understood that various alterations, additions and/or modifications may be introduced into the parts previously described without departing from the ambit of the present invention.

Claims (8)

CLAIMS:

1. A cam for use in a cam cleat, the cam comprising an injection-moulded polymer reinforced with randomly oriented carbon fibres.

2. A cam according to claim 1 wherein the cam cleat has teeth which have radii between about 0.40mm and about 0.75mm.

3. A cam according to claim 1 wherein the cam cleat has teeth which have radii between about 0.55mm and about 0.75mm.

4. A cam cleat comprising a pair of cams according to any one of claims 1 to 3 wherein the cam angle is approximately 15".

5. - A cam cleat comprising a pair of cams according to any one of claims 1 to 3 wherein the face angles are about 700 to 750

6. A cam cleat according to claim 4 wherein the face angles are about 700 to 750.

7. A cam cleat according to any one of claims 4 to 6 further comprising a pair of carbon-fibre reinforced cam stops which are approximately lOmm x 5mm in size.

8. A cam cleat substantially as herein described with reference to the drawing.