There is today a need of producing rotor blades of a material, which may resist an aggressive environment, for instance, in the chemical process industry, and which are relatively light, resulting in that the fan, on which the rotor blades are mounted, may be operated at higher speed and that in certain cases, the rotor blades may also be made smaller and thus less expensive. Attempts have therefore been made to produce rotor blades of composite material, such as fibre reinforced plastic.

Through US 4877376 a rotor blade of fibre reinforced plastic is previously known, which has relatively low weight and may accordingly be operated at high speed. However, the fastening of the rotor blade is complicated, partly due to a bolt joint having bolts extending through an pressure flange, abutting against the plastic material, to a hub or an attachment device, and partly due to a shank, which extends into the attachment device and co-operates with means to provide a pre-stress of the rotor blade. In an aggressive environment such fastening is unsatisfactory, even if the material in the rotor blade is chemically resistant, the area around the pressure flange will be both chemically and mechanically affected. Thus, it has been shown that rotor blades, having fastening means of known kind, during high speed of the fan and thus subjected to great stress, tends to be destroyed by propagating cracks, arising in the area of the bolt joint.

Through US 4966527 a rotor blade of fibre reinforced plastic is also previously known, which has relatively low weight and may accordingly be operated at high speed. However, the fastening of the rotor blade is complicated, with fibres forming loops around several mounting elements near the blade root, which elements extend substantially parallel to the sides of the blade.

An object of the present invention is to provide a simple and durable fastening of a rotor blade made of composite material, which also resist an aggressive environmental.

An additional object is to improve the operation conditions of the rotor blade.

These objects are achieved according to the invention with a rotor blade, which is characterised in that said body is arranged to withstand a state of strain, acting in several axially different directions, and that said body extends, mainly perpendicular to the sides of the blade, through the foot to both sides of the blade-part, and comprising fastening means located on each side of the blade-part.

In a preferred embodiment, the foot of the rotor blade comprises at least two bodies, preferably made of metal, such as steel or similar, which effectively may withstand a state of strain, acting in several axially different directions. The two bodies extend perpendicular through the foot to both sides of the blade and suitably each body consists of a beam, having a rounded lower edge. The two bodies may also be integrated with each other and thus forming an H-shaped girder construction. Naturally, it is possible to use a body shaped like a plate, provided with recesses for the reinforcement means, or using only one beam, which by way of example is arranged oblique in relation to the blade.

The reinforcement means suitably comprise an amount of orientated fibres and consists in a preferred embodiment of at least a bundle carbon fibre, which during manufacturing of each rotor blade in a mould, is placed around the body and lead out over the sides of the blade.

Naturally, the reinforcement means may also be fastened to the body, for instance, by leading a bundle carbon fibre through a hole in the body, whereas it is fastened with a knot or similar, having a larger diameter than the hole.

The composition of fibres and plastic in the composite material of the foot of the rotor blade is preferably selected such that the composite material has an elongation by temperature adapted to the body. The composite material is suitable made of glass-fibre reinforced epoxy resin.

The invention will now be described closer with reference to the attached drawings, in which; figure 1 shows a partially cross-section, front view of a rotor blade according to the present invention, figure 2 shows a view from above of the rotor blade, figure 3 shows a side-view of the rotor blade, and figure 4 shows a cross-section of an area around the foot of the rotor blade, in larger scale.

The drawings illustrate a rotor blade 1 for attachment on a hub of a fan (not shown) or the like. The rotor blade 1 comprises a blade-part 2 and an integrated foot 3. The foot 3 of the rotor blade comprise two bodies 4, with fastening means 5. The two bodies 4 are preferably made of metal, such as steel or the like, which may withstand a state of strain, acting in several axially different directions. The two bodies 4 extend perpendicular in relation to the sides 7 of the blade, and through the foot 3 to both sides of the blade-part 2. An amount of reinforcement means 6 extends at least partly around the two bodies 4 and along the sides 7 of the blade. The fastening means 5 may suitably consist of holes through the two bodies 4, which are intended to co-operate with bolts (not shown) screwed into the hub of a fan or into an attaching means arranged thereto.

The rotor blade 1 is made of a composite material of fibre reinforced plastic. In a preferred embodiment the composite material consists of a reinforced glass-fibre in a matrix of epoxy resin, which according to the invention are reinforced with an amount of reinforcement means 6 of several equally orientated fibres. Preferably, the fibres are long and continuous, and may as an example be composed of carbon fibre, but also other fibres, for instance, fibres of aramide or similar may be used as reinforcement means. In the same way other polymer then epoxy resin may be used as matrix.

During production of the rotor blade 1 several layers of orientated glass-fibres are placed on each side of a mould, then the bodies 4 are arranged in one end of the mould. A bundle of reinforcement means 6 made of carbon fibre being placed around each body 4 and being lead along a plastic core 8 (fig. 4), which is arranged between the layers of glass-fibre, finally epoxy resin will be added.

Thus, the completed rotor blade 1 comprises a blade-part 2, consisting of a composite material, in shape of glass-fibre reinforced epoxy resin, provided with a core 8 of plastic and an integrated foot 3, which likewise consists of composite material and at least one body 4, and several reinforcement means 6 of carbon fibre.

Thus, the foot 3 of the rotor blade consists of the body 4, the reinforcement means 6 and the part of the composite material located around the body 4. Said body 4 extends, mainly perpendicular to the sides 7 of the blade, and through the foot 3, to both sides of the blade- part 2. By this, the body 4 forming a counterweight acting against the tendency of the blade-part 2 to turn around its own axle during operation. The body 4 is preferably made of metal, such as steel or similar, which may withstand a state of strain, acting in several axially different directions and has fastening means 5 on each side of the blade-part 2,

which, in the example shown, are shaped as a bolt-holes for each fastening bolt. The number of bolt-holes may vary from one to several bolt-holes on each side of the blade-part 2. As said above, the rotor blade 1 is fastened to a hub by means of the fastening bolts, which being inserted in the holes of the body 4 and being screwed into the hub or into an attachment means arranged thereto. Even if the composite material essentially surrounds the body 4, it is an advantage that the fastening bolts solely extends through the body 4 and that in the area of the bolts it does not exist any essential amount of composite material.

The rotor blade 1, described above, is light compared to earlier used rotor blades made of metal, and it has proved to withstand high speed without bursting of the foot at the area of the bolt-joint. The forces acting on the rotor blade 1 is transmitted via the reinforcement means 6, consisting of carbon fibre, being essentially stiff in its longitudinal direction, to the body 4, which may withstand a state of strain, acting in several axially different directions, and further via the fastening bolts to the hub. An important part of the invention is that the reinforcement means 6 being fastened to the body 4, either by extending around the body 4 or being attached to the body 4 in a suitable manner. It is also important that the reinforcement means 6 extends over a part of the length of the rotor blades.

To avoid undesired stress of the reinforcement means, the body being shaped as a beam, having rounded lower edges. It is possible to use only one beam, even if the figures show use of two beams. It is also possible that the two bodies are integrated with each other and thus form an H-shaped girder construction or that the body is shaped like a plate, provided with recesses for fastening of the reinforcement means.

The composition of fibres and plastic in the composite material of the foot 3 of the rotor blades is selected such that the composite material has a elongation dependent of the temperature, which is adapted to the body 4, in such way that the effect of the bodies expansion during different temperature conditions will be reduced as much as possible, i.e.

the composite material will follow the body 4 in its movement dependent of the temperature.