Ejector device

TECHNICAL FIELD

The present invention refers to an ejection nozzle for transport of fibre thread pieces by means of compressed air, e.g. reinforcement material for manufacturing fibre reinforced plastic products, from a cutter to a moulding cavity, which nozzle is provided with a common flow duct for the compressed air and the fibre thread pieces.

BACKGROUND OF THE INVENTION In robot-controlled production of fibre reinforced plastic products, fibre thread pieces are fed out into a moulding cavity while being oriented, so that the strength of the fibres is utilized efficiently in the finished product. Compressed air is used for the transport of the cut fibre pieces from the cutter to the moulding cavity.

If the pressure/speed of the compressed air is not sufficiently high at the cutter, static electricity will make fibre pieces stick to the vicinity of the cutter, so that the feeding out is stopped up. This may be economically seriously damaging if the operations at a production line which depends upon said plastic details, is also influenced by the production loss.

However, if air pressure/speed is too high at the moulding cavity, fibre pieces may be oriented wrongly in said cavity, simply by being blown away from their intended location, or because they are deflected from the mould surface by having to high kinetic energy.

The problems can be reduced if it is possible to maintain an optimal distance between the feed out apparatus and the

moulding cavity. However, this is hardly ever possible, e.g. because of lack of space.

THE TECHNICAL PROBLEM One object of the present invention is therefore to provide an apparatus for feeding out fibre thread pieces from a cutter, which makes it possible to maintain a high air pressure/velocity at the cutter and at the same time avoid that the fibres end up wrong in the moulding cavity, or outside the same.

THE SOLUTION

For this purpose, the apparatus according to the invention is characterized in that the flow duct runs past at least one reflector surface for the air flow, and that at least one opening for evacuation of air to the surroundings is located along the flow duct.

DESCRIPTION OF THE DRAWINGS The invention will be described here below with reference to an embodiment shown in the accompanying drawings, in which Fig. 1 is a side view of a damper unit according to the invention. Fig. 2 is an end view of the damper unit in Fig. 1, and Fig. 3 shows a series of units according to Fig. 1 and

2 joined together into an ejector nozzle.

DESCRIPTION OF EMBODIMENTS

The ejector nozzle shown in Fig. 3 is used mounted upon a not shown robot arm, for feeding out fibre thread pieces from a likewise not shown cutter to a moulding cavity. The robot arm is preferably freely movable in space and is controlled by a programmable micro processor.

The ejector nozzle in Fig. 3 is carried by and is supplied with compressed air and fibre thread pieces via an ejector

tube 10. The nozzle comprises in the shown embodiment a series of three damper units 11.

Together, the ejector tube 10 and the damper unit 11 form a flow duct with varying diameter for the compressed air and the fibre thread pieces. Thus, the ejector tube 10 form a first section of the flow duct, which protrudes into and carries a first damper unit 11. This damper unit in its turn protrudes into and carries a second damper unit, which in its turn carries a third damper unit 11.

As is shown in Fig. 1 and 2, each damper unit 11 comprises a first cylindric tube part 12 and a second tube part 13 with a cross section 13 which is reduced in relation to the first tube part 12. The tube part 13 forms a bracket means with three radially protruding wings 14.

The tube part 13 with the bracket means 14 is entirely protruding into the cylindrical tube part 12 on the next following damper unit 11, in such a way that the wings 14 are centring the units along a common longitudinal axis.

The cylindrical tube part 12 and the tube part 13 with the bracket means 14 are interconnected via tube part 15 which tapers conically in the direction of flow. In its position of use, the tube part 15 which tapers in the direction of air flow forms a reflection surface for the air flow, so that it is slowed down. Thus, the tube part 15 creates a local increase in pressure in front of the mouth of the flow duct tube part 13, which forces air to flow back along the outside of the ejector tube 10 and the outside of the previous damper unit tube part 13, respectively, between the three wings 14 and to evacuate to the surrounding atmosphere. For this purpose, there are also holes 16 drilled in the cylindric tube part 12.

While the air stream in this way is slowed down step by step via the damper units 11, the fibre thread pieces which have initially been accelerated by the air stream may on the whole maintain its kinetic energy during the passage through the ejector nozzle. This implies that the range is maintained for the fibre pieces, and that the air flow at the end of the ejector nozzle is so reduced, that it is not able to disturb the already transported fibres in the moulding.

It is simple to adapt the ejector nozzle according to the invention to different modes of application by selecting a suitable number of damper units.

The invention is not limited to the above described embodiment, but several variants are possible within the scope of the accompanying claims. For example, the tube parts 12, 13 of the damper units do not have to be cylindric. The shape of the reflector surface 15 can also vary within wide limits. The holes 16 are not necessary for the invention, because air can leave between the end edge of the tube part 12 and the outside of the reflector wall 15. Also, the diameter of the tube parts 13 may vary between the damper units 11 along the flow duct, so that the last tube part 13 in the direction of flow has a reduced diameter.