The present invention relates to a rotor blade to be attached to a hub in a rotor, such as a vane to be attached to a hub of a fan.
Fan blades are usually made of metal, for instance steel or aluminium. There is today a need of manufacturing fan blades of a material which is more chemically resistant than metal and consequently can resist a chemically aggressive environment in a better manner than metal, for instance in the chemical process industry. There is also a need of making the fan blades lighter, which means that the fan on which the blades are mounted can be operated at higher speeds, and that in some cases the fan can be made smaller and thus less expensive. Attempts have therefore been made to manufacture fan blades of composite material of fibre-reinforced plastic. These fan blades are chemically resistant and light, but it has proved difficult to fasten them to a hub of a fan in a satisfactory manner. The connection between blade and hub usually is a bolt connection with bolts, which extend through the base of the blade and are screwed into the hub or a holder arranged thereon. Such connections are known, for example from US-A-3 565 547. Regrettably, it has been found that the fan blades made of composite material tend to be destroyed at high speeds of the fan and thus great stress since cracks arise in the base of the blade in the area of the bolt connection.
A specific object of the present invention therefore is to provide a fan blade, which has the desired properties and besides can be attached to a hub of a fan in a satisfactory manner.
A more general object of the invention is to provide a rotor blade, which has the desired properties and can be attached to a hub in a rotor without breaking at high rotor speeds and when subjected to great stress.
According to the invention, this object is achieved by a rotor blade, which is characterised in that the rotor blade is made essentially of a composite material of fibre-reinforced plastic, that the base of the rotor blade comprises a metal ring with means for attaching the rotor blade to the hub, said ring having an opening, which has a cross-sectional area increasing in the direction away from the rotor blade, that a rigid reinforcing element is arranged in the opening of the ring, and that the composite material extends into the ring, reinforcing fibres in the base of the rotor blade extending into the opening of the ring between the reinforcing element and the wall of the opening essentially in parallel therewith.
In a preferred embodiment, the opening of the ring has the form of a truncated cone.
The reinforcing element suitably contains carbon fibres and, in a preferred embodiment, is formed of a carbon-fibre strand, which is rolled into a disk-shaped roll and which during manufacture of the rotor blade in a mould is arranged in the opening of the ring to press the reinforcing fibres in the opening in the direction of the wall of the opening.
The composition of the composite material of fibres and plastic in the base of the rotor blade is preferably selected such that the composite material therein has a linear expansion characteristic adapted to the metal ring. The composite material suitably is glass-fibre reinforced epoxy plastic. In a preferred embodiment, the glass-fibre reinforcement in the base of the rotor blade is supplemented with a carbon-fibre reinforcement with carbon fibres, which extend substantially transversely of the glass fibres in the glass-fibre reinforcement in the base.
The invention will now be described in more detail with reference to the accompanying drawings, in which
The drawings illustrate a fan blade 1, which is to be attached to a hub (not shown) in a fan (not shown) by means of four fixing bolts (not shown), which are to be screwed into the hub or a holder arranged thereon.
The blade 1 is made of a composite material of fibre-reinforced plastic. In a preferred embodiment, the composite material is a glass- and carbon-fibre reinforced epoxy plastic. However, it will be appreciated that other fibres than glass fibres and carbon fibres, e.g. aramide fibres, can be used as fibre reinforcement. It will also be appreciated that other polymers than epoxy plastic can be used as a matrix.
In the manufacture of the blade 1, two mats, each consisting of several layers of oriented glass fibres, and an intermediate plastic core 2 (Fig. 4) are placed in a mould, whereupon a circular ring 3 of metal, e.g. steel, is arranged in the mould at one end thereof. The ring 3 has an opening 4 which is conical in a truncated manner and is of a cross-sectional area increasing in the direction away from the mould. The glass fibres at the end of the mats closest to the ring 3 (this end constituting the base end of the completed blade 1) are introduced into the opening 4 of the ring 3 and are pressed against the wall of the opening 4. A "bundle" of glass fibres is arranged in the pointed portion A, indicated by dashed lines in Fig. 4, between the mat glass fibres pressed against the wall of the opening 4. A carbon-fibre strand, which is rolled into a disk-shaped roll and which is to form a rigid reinforcing element 5 in the completed blade 1, is arranged in the opening 4 of the ring 3 on the outside of the bundle of glass fibres in order to retain the glass fibres in the position when pressed in the direction of the wall of the opening 4. The mould is closed, whereupon epoxy plastic is injected so as to form the blade 1.
The completed blade 1 thus consists of a composite material 6 (including the area A) of glass-fibre reinforced epoxy plastic and having a core 2 of plastic and a reinforcing element 5 in the form of a carbon-fibre/epoxy-plastic composite.
The base of the blade 1 consists of the metal ring 3, the reinforcing element 5 and that part of the composite material 6 which is located in the opening 4 of the ring 3 and in which the glass fibres extend conically along the wall of the opening 4 between the wall and the reinforcing element 5, which prevents the glass fibres in the ring 3 from being pressed towards the centre of the ring when the blade 1 is subjected to great stress, and the body of the blade from being pulled out of the ring 3.
The ring 3 has a bolt hole 7 for each fixing bolt. As mentioned above, the blade 1 is attached to a hub by means of the fixing bolts, which are inserted into the holes 7 in the ring 3 and screwed into the hub or a holder arranged thereon. The above-described fan blade 1 is light compared with previously used metal blades, and besides it has appeared to withstand high speeds of the fan without its base breaking adjacent to the bolt connection.
The composition of fibres and plastic in the composite material 6 in the blade base is selected such that the composite material therein has a linear expansion characteristic which is adapted to the metal ring 3, thereby reducing as much as possible the effects of the expansion and contraction of the ring under various temperature conditions, i.e. such that the composite material is able to follow the ring 3 in the temperature-dependent movements thereof. To this end, the glass-fibre reinforcement in the blade base is, in a preferred embodiment of the fan blade 1, supplemented with a carbon-fibre reinforcement with carbon fibres, which in the manufacture of the blade in the mould are arranged among the glass fibres in the area of the ring 3 so as to extend in the completed blade 1 substantially transversely of these glass fibres in the composite material.