Device for pneumatically conveying and guiding a multifilament thread

A device for pneumatically conveying and guiding a multifilament thread has a closed conveying channel which has a thread inlet opening at one end and a thread outlet opening at the opposite end. An injector zone having at least one compressed air channel which opens into the conveying channel is formed between the thread inlet opening and the thread outlet opening, wherein the compressed air channel can be connected to a compressed air source. In order to avoid blowing air from flowing back from the injector zone at the thread inlet opening, a return flow channel is formed in a channel section of the conveying channel between the thread inlet opening and the opening of the compressed air channel, which return flow channel connects the conveying channel to ambient atmosphere.

The invention relates to a device for pneumatically conveying and guiding a multifilament thread as disclosed herein.

In melt-spinning processes or textile processes it is known for a running thread to be pneumatically guided and conveyed by means of a nozzle-type device. To this end, a compressed-air stream, which catches a thread entering through a thread inlet opening into a conveying duct and conveys said thread to a thread outlet opening, is inducted within the conveying duct. Depending on the positive pressure of the compressed air which is supplied to the conveying duct, a high conveying force is generated on the thread on account of the expanding compressed air. In the case of comparatively high positive pressures of the compressed air, a return stream is established within the conveying duct, which return stream exits from the thread inlet opening counter to the running direction of the thread. However, such return streams of the compressed air hamper the entry of the thread. It is known in particular that, on account of the returning air stream, individual broken filaments of the multifilament thread are hampered when entering the conveying duct.

This phenomenon is known in the prior art, with various attempts having been made at avoiding return streams of this type in the conveying duct. DE 22 36 957 A1 discloses a device for pneumatic conveying and guiding, in which the conveying duct in the region below the compressed-air supply has a cascade-type widening of the cross section. Therewith, return streams of the air to the thread inlet opening may indeed be reduced, but with the great disadvantage of reduced conveying capability.

DE 27 34 220 A1 discloses a further device for pneumatically guiding and conveying a multifilament thread, in which the conveying duct in an entry region has an aperture labyrinth which forms a plurality of expansion spaces. Therewith, throttling of the returning air stream is achieved, such that only reduced return streams arise at the thread inlet opening. However, additional apertures and throttles of this type in the conveying duct hamper thread entry by way of an accumulation of entrained ambient air on the thread, which facilitates a broken filament in breaking out into one of the expansion spaces.

It is now the object of the invention to refine a device of the generic type for pneumatically conveying and guiding a multifilament thread in such a manner that trouble-free entry of the thread and a high conveying effect are simultaneously possible in the case of high positive pressures of the compressed air.

This object is achieved according to the invention in that a return stream duct opens into a duct portion of the conveying duct, between the thread inlet opening and the mouth of the compressed-air duct, said return stream duct connecting the conveying duct to an ambient atmosphere.

Advantageous refinements of the invention are defined by the features and combinations of features disclosed herein.

The invention is based on the insight that rapid air streams preferably cling to walls and flow therealong. Such physical properties are also known as so-called Coand{hacek over (a)} effects. To this extent, the natural behavior of the stream within the conveying duct is used to obtain dissipation of the return stream into a return stream duct. Therewith, the return stream of the blower air can be diverted into an ambiance which is not critical to thread guiding.

In order for as large a proportion of the return stream from the conveying duct as possible to be able to be received, according to one advantageous refinement of the invention the return stream duct opens out having an inclination in the conveying direction of the conveying duct. The inclination of the return stream duct is substantially defined by an angle in the range of 5° to 40° between the return stream duct and the duct portion of the conveying duct between the thread inlet opening and the mouth of the compressed-air duct. Therewith, the deflection of the return stream from out of the conveying duct can be facilitated.

In order that the so-called Coand{hacek over (a)} effect catches a major part of the return stream in a particularly pronounced manner, the refinement of the invention in which the return stream duct and the conveying duct in the mouth region on the side facing the compressed-air duct form a transition face which is rounded is preferably implemented. Therewith, even slight negative pressures in the mouth region of the return stream duct, which lead to ambient air being suctioned from the thread inlet opening, can be generated. Guiding of the multifilament thread is particularly facilitated therewith.

The effectiveness of stream deflection can even be improved in that according to one advantageous refinement of the invention a supply stream duct opens into the duct portion of the conveying duct in the region of the mouth of the return stream duct, and in which the inflow duct connects the conveying duct to an ambient atmosphere. The additional air supply to the mouth region of the return stream duct facilitates stream deflection of the returning blower-air stream.

In order for radiation deflection caused by the Coand{hacek over (a)} effect on the wall of the conveying duct in the mouth region of the return stream duct to be amplified, the mouth of the stream duct lies opposite the mouth of the return stream duct, wherein the opening cross section of the mouth of the inflow duct is configured so as to be smaller than the opening cross section of the mouth of the return stream duct.

Moreover, the additional supply air is inducted in a substantially transverse manner into the conveying duct, such that the supply stream duct in the mouth region encloses an angle in the range of 80° to 100° with the conveying duct.

The device according to the invention is particularly suitable for immediately carrying out further treatment of the thread in a melt-spinning process, since both broken filaments as well as loops protruding from the composite thread may pass without hindrance into the thread inlet opening of the conveying duct. To this extent, the refinement of the invention in which the conveying duct by way of the thread outlet opening opens into a stuffer box, by way of which the thread is compressible to a thread plug, is preferably implemented. This variant of the device is used for crimping threads and is preferably used in the manufacture of carpet yarns.

A first exemplary embodiment of the device according to the invention is schematically illustrated in a cross-sectional view inFIG. 1. An elongate closed conveying duct2, which at an upper end is connected to a thread inlet opening3and at the lower end is connected to the ambiance by way of a thread outlet opening4, is configured in a nozzle body1. The thread inlet opening3has an inlet funnel15in order for entry of a thread into the conveying duct2to be facilitated. The conveying duct2may be configured as a bore or as a groove, wherein the nozzle body could be constructed so as to be integral or in multiple parts.

Two mirror-symmetrically configured compressed-air ducts5.1and5.2, which open into the conveying duct2at an inclination, are provided in an upper third of the conveying duct2, between the thread inlet opening3and the thread outlet opening4. The mouths10.1and10.2of the compressed-air ducts5.1and5.2are opposite one another on the wall of the conveying duct2. By way of the opposite ends, the compressed-air ducts5.1and5.2are connected to at least one compressed-air connector opening7via supply ducts6.1and6.2. A compressed-air source (not illustrated here) can be connected to the nozzle body1by way of the compressed-air connector opening7.

The mouths of the compressed-air ducts10.1and10.2on the conveying duct2form the so-called injector zone9in which compressed air meets for the first time a thread which is guided within the conveying duct2. The region above the injector zone here is defined as the thread entry zone8, and the region below the injector zone9is defined as the expansion zone11.

In order to be able to pneumatically guide and convey a thread within the conveying duct2, compressed air is supplied via the compressed-air ducts5.1and5.2. A blower-air stream in the direction of the thread outlet opening4is created in the portion of the conveying duct2of the injector zone9. In order to support the blower-air stream, the duct portion of the conveying duct2in the region of the expansion zone11advantageously has a widening of the duct, such that additional acceleration of the blower air arises.

On account of the pulse-type inflow of compressed air in the injector zone, comparatively high back pressures are created which cause a return stream of the blower air in the direction of the thread inlet opening3. In order for the returning blower-air stream to be kept away from the region of the thread inlet opening3, a return stream duct12is provided in the nozzle body1.

The return stream duct12, which opens into the conveying duct2at an inclination in the conveying direction, is configured in the thread entry zone8, in the duct portion of the conveying duct2between the thread inlet opening3and the mouth of the compressed-air duct10.1and10.2. The conveying direction of the conveying duct2is identified by a vertical arrow inFIG. 1.

The inclination of the return stream duct12inFIG. 1is identified by the angle α. The angle α is in a range of 5° to 40°, so as to be able to receive a returning blower-air stream resulting from the injector zone9at the mouth13of the return stream duct12.

In order for the dissipation of the returning blower-air stream into the return stream duct12to be facilitated, a rounded transition face24, which is effective in relation to the conveying duct2, is molded on the mouth13of the return stream duct12. Wall contours of this type are particularly suitable for automatically guiding the return stream of blower air, which is guided on the wall of the conveying duct2, into the return stream duct13by way of the so-called Coand{hacek over (a)} effect. In the case of high stream velocities of the blower air, negative pressure is formed here between the wall and the stream, such that the return stream from out of the conveying duct2is diverted into the return stream duct12. Additionally, on account of negative pressure in the mouth region of the return stream duct12, suction which acts on the thread inlet opening3is generated. This suction effect facilitates thread entry into the conveying duct even in the case of multifilament threads having broken filaments or projecting filament loops.

In order for dissipation of the returning blower-air stream to be facilitated, the return stream duct12has a duct cross section which is larger than a duct cross section of the conveying duct2in the mouth region of the return stream duct12. Therewith, additional widening of the cross section can be implemented in order to accelerate the return stream of blower air.

The exemplary embodiment of the device according to the invention as perFIG. 1is suitable for pneumatically guiding and conveying individual multifilament threads or a group of a plurality of multifilament threads or a group of filaments within a melt-spinning process. There is thus the possibility that the nozzle body is formed by two nozzle halves which lie opposite one another in order to form a groove-like conveying duct. Therewith, groups of threads and filaments can also be advantageously guided.

A further exemplary embodiment of the device according to the invention for pneumatically conveying and guiding a multifilament thread is illustrated inFIG. 2. In the device shown inFIG. 2, the nozzle body1could also be formed from two nozzle halves, wherein the view of the illustration inFIG. 2would correspond to a plan view of one of the nozzle halves. Independently of the type and construction of the nozzle body1, a conveying duct2which extends between a thread inlet opening3and a thread outlet opening4is configured within the nozzle body1. An injector zone9having the compressed-air ducts5.1and5.2is configured in the first third of the conveying duct2. The compressed-air ducts5.1and5.2are connected to a compressed-air connector opening7by way of the supply ducts6.1and6.2.

A return stream duct12is configured in the nozzle body1, in the region of the thread entry zone8of the conveying duct2. The return stream duct12extends between a return stream opening14, which is connected to the ambiance, and the one mouth13in the conveying duct2. The mouth region of the mouth13and the inclination angle α of the return stream duct21is implemented so as to be substantially identical to the aforementioned exemplary embodiment, so that no further explanations are included to this end.

An inflow duct16opens out on the wall of the conveying duct2, which is opposite the mouth13of the return stream duct12. The inflow duct16here extends between a mouth17on the conveying duct2and an inflow opening18which connects the inflow duct16to the ambiance. The inflow duct16, opposite the mouth13of the return stream duct12, opens out into the conveying duct2in a substantially orthogonal manner. The inclination angle of the inflow duct16inFIG. 2is identified by the angle β. The angle β is in a range of 80° to 100°.

A connector body21, which in the extension of the conveying duct2forms a stuffer box19, is disposed below the nozzle body1. In an exemplary manner, the connector body21is illustrated as an additional component to the nozzle body1. In principle, there is also the possibility for the connector body21to be integrated in the nozzle body1.

Independently of the constructive implementation, the thread outlet opening4of the conveying duct2opens out in a substantially concentric manner in relation to the stuffer box19. The stuffer box19is formed by an air-permeable stuffer box wall20which is surrounded by a relief chamber22. The relief chamber22is connected to the ambiance by way of a relief opening23.

The exemplary embodiment of the device according to the invention which is illustrated inFIG. 2is used for texturizing multifilament synthetic threads in stuffer boxes. To this end, compressed air is supplied during operation via the compressed-air connector opening7to the compressed-air ducts5.1and5.2, such that blower air in the conveying direction is generated within the conveying duct2. A thread which is guided in the conveying duct2is pneumatically conveyed by the blower air and is guided into the stuffer box19with high energy. Within the stuffer box19, the multifilament thread is stuffed to form a thread plug, wherein the filaments are deposited in bows and loops on the surface of the plug. The thread plug is compressed on account of the blower air, wherein ventilation occurs via the air-permeable stuffer box wall20.

The returning blower-air stream from the injector zone9in the direction of the thread inlet opening3is deflected via the mouth region of the mouth13of the return stream duct12and exhausted via the return stream duct12into the ambiance. Ambient air is suctioned, on the one hand, from the thread inlet opening3and from the inflow duct16, on account of negative pressure which is generated thereby in the conveying duct2. Deflection of the returning blower-air stream is particularly supported by the ambient air which flows transversely via the inflow duct16into the conveying duct2, such that substantially the entire returning blower-air stream can be dissipated via the return stream duct13into the ambiance.

It is essential here for the mouth17of the inflow duct16to have an opening cross section which is smaller than the mouth13of the return stream duct12, which preferably is configured so as to be opposite thereto. It is therewith achieved that the blower-air return stream advantageously bears on the opposite wall and thus an intensified Coand{hacek over (a)} effect for deflecting the stream arises.

The exemplary embodiment which is illustrated inFIG. 2is particularly suitable for compressed-air operated texturizing nozzles for manufacturing BCF yarns. In melt-spinning processes of this type, processing speeds of beyond 2500 m/min are reached, requiring a corresponding conveying and traction effect. To this end, positive pressures of the blower air in the range of 4 to 5 bar are achieved in the injector zone9of the conveying duct2, in order to maintain a corresponding conveying power. The comparatively high positive pressure within the injector zone9demands corresponding strong return streams of blower air into the thread entry region8, which are advantageously deflected from the conveying duct2by way of the interaction of the return stream duct12and the inflow duct16.

The duct cross sections of the conveying duct2, of the return stream duct12, and of the inflow duct16, which are illustrated in the exemplary embodiment as perFIGS. 1 and 2, are exemplary. It is essential here that deflection of the return stream of the blower air between the thread inlet opening3of the conveying duct2and the injector zone9is possible on account of the Coand{hacek over (a)} effect.

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