Method and device for rejoining yarn with high efficiency in an open-end spinning machine

Abstract: A method for rejoining yarn in an open-end spinning machine in which the rejoining is effected by feeding intact fibres to the rotor (12) but preceding the rejoining by an operation in which the sliver (3) is cleared and the carder (2) is cleaned by the high-vacuum suction nozzle (19) brought into correspondence with the air intake port (18).

Description: This invention relates to a device and a method for rejoining yarn in an open-end spinning machine, and more particularly to a device and a method for preparing the fibre sliver which forms the feed before joining or rejoining the yarn to enable spinning to restart. Open-end spinning machines comprise spinning stations each having a feed roller feeding a fibre sliver to a toothed carder which rotates at high speed and separates the sliver into individual fibres. The individual fibres are pneumatically fed to a hollow spinning rotor which is provided with an inner groove within which the fibres are deposited in layers by the effect of the centrifugal force generated by the rotor rotating at very high speed; To start spinning, an already formed yarn is initially inserted through a channel located substantially on the axis of rotation of the rotor, and centrifugal force propels the free end of the yarn to the periphery, ie into the groove where it encounters the fibre layer; on drawing out the yarn the fibres become joined to the yarn, acquiring twist in the section between the groove and the exit channel to produce new yarn. In the known art the spinning machine is provided with yarn-feeling sensors which for every yarn breakage cause the fibre sliver feed roller to stop, as described for example in IT-A-791 993. However the separating carder continues to rotate even if yarn production is interrupted. In the known art the method used for rejoining the yarn and restarting production comprises firstly cleaning the spinning rotor, in which irregularities or dirt build-up have probably occurred. This cleaning is done either by opening the roller, clamping it and then using suitable tools such as brushes, suction nozzles, spatulas etc., or by keeping the roller closed and using an air blast. After cleaning, a fibre layer suitable for forming new yarn is rebuilt in the spinning rotor while under movement, and the interrupted yarn end is reinserted when the rotor has reached suitable speed, to "fish out" this fibre layer and again produce yarn. This operation is conducted either manually, in non-automated spinning machines, or automatically by devices located for example on mobile carriages which patrol the plurality of spinning stations along the machine face in the case of automated machines, as described in US-A-3 810 352 and US-A-3 950 926. A technical problem common to both automated and non-automated spinning machines is that the fibre feed sliver which has been halted on yarn breakage, with its feed roller at rest, remains with its end exposed to the action of the separating carder. Generally, the rejoining operation is commenced with variable delay because the rejoining operation requires in the case of non-automated spinning machines the operator, or in the case of automated spinning machines the carriage, to arrive in front of the spinning station at which the operation is to be carried out. The operator or carriage can be a variable distance away, or may be engaged in other operations. During this variable waiting time the end of the feed sliver continues to undergo separation, without advancing, and is depleted of fibres, which are gradually removed by the carder teeth. When the sliver is reused in that state for restarting the spinning, the fibre layer newly deposited in the rotor groove and used for rejoining purposes gives rise to thinner or fatter weakened portions and thus to an irregular joint, with the result that the produced yarn is of poor quality. The sliver depletion varies in accordance with the waiting time for commencing the operation, and the layer initially deposited in the rotor groove consequently varies. According to the known art this variability in the consistency of the fibre sliver re-fed to spinning is overcome by means of a brief prefeed of sliver during the initial stage of the rejoining operation. This prefeed enables the state of the sliver to be equalized by consuming that portion of sliver which in the meantime has remained exposed to the action of the carder, so restoring the state of the sliver as if the yarn breakage had taken place at the moment the rejoining operation commences. In this respect it must be remembered that after the equalization to produce a constant sliver not influenced by the variable waiting time far the commencement of the rejoining operation, the sliver remains at rest and exposed to the action of the carder, which continues to rotate, for the time period between the sliver prefeed and the return to normal feeding to deposit the new fibre layer for rejoining purposes. The duration of this time interval is rigorously constant in the case of automated spinning machines in which the rejoining operation is robotized and generally carried out by a mobile carriage, and substantially constant where the operation is carried out by an operator who has acquired sufficient manual ability. During this constant time interval the sliver is subjected to deterioration by the carder. This deterioration is a drawback which is not very important from the point of view of the quantity of residual fibres present in the sliver end because this can be remedied by controlling the time interval between the restoration of the sliver feed and the "fishing out" of the fibre layer in the rotor cavity by the yarn end. This drawback cannot however be totally overlooked from the point of view of the quality of the residual fibres present in the sliver end. It must be remembered that the duration of the interval between prefeed and restoration of spinning in current automated open-end spinning machines is of the order of 10 seconds, and the carder has therefore a considerable time available for this deterioration action on the end of the halted sliver. In this respect it has been found that one of the most important causes of defective joining, even using the prefeed practice, is that the sliver end, which remains subjected to the action of the carder for the entire duration of the said interval, is also subjected to qualitative deterioration because the sliver fibres are not only removed but also shortened, so that the new fibre layer deposited in the rotor cavity on restoring the sliver feed and which is used for the actual rejoining is formed from fibres of inferior quality as it also comprises a considerable amount of fibres shortened by the action of the carder rotating an the sliver which is at rest during the waiting time for the rejoining. This drawback is particularly marked if fine yarns of high metric count are produced, for which the prefeed practice does not allow a reliable joint of good quality. The joining operation must be frequently repeated because the joint is either not made or breaks. In DE-A-3 104 444 and DE-A-3 436 295 it is proposed to firstly deviate during the rejoining operation those fibres of the damaged portion of the sliver exposed to the action of the carder during the waiting period by not allowing them to reach the spinning rotor, so allowing the spinning rotor to receive only the undamaged fibres of the sliver portion which was not under the action of the separating carder while at rest. According to DE-A-3 104 444 this deviation is done by suction channels which open into the pneumatic conveying path which the fibres separated by the carder take in travelling to the rotor, and by blowing nozzles which act against the normal movement of the fibres towards the rotor. This device results in considerable complications both in the spinning device and in its operation. In DE-A-3 436 295, which reflects the closest prior art, the deviation is done by using an aperture in a duct tangential to the carder to remove the impurities. The impurities, such as dust, sand and dirt, are more subject to the action of centrifugal force as they are heavier and more compact than the separated fibres. The impurities are thus projected outwards through this tangential duct which connects to a suction manifold in which a slight vacuum is maintained sufficient to induce an air stream powerful enough to convey the impurities but not to suck the fibres from the carder. This vacuum is by way of example a few tens of mm. of water column or a few mm. of mercury expressed as static vacuum. The suction manifolds of the spinning units converge into a large central duct under vacuum which collects all impurities and conveys them to a collection box and distributes the suction to the various spinning units. According to DE-A-3 436 295 a tubular suction nozzle is inserted into the suction manifold until its mouth engages the aperture of the tangential duct to shut off the suction manifold, and after it has been inserted in position the suction is applied to the damaged fibres. This device and method are not free of drawbacks because the suction nozzle carried by the service carriage must be carefully constructed and positioned with great accuracy relative to the spinning station, and in addition travels a long distance in positioning itself within, and withdrawing from, the suction manifold, so extending the duration of the rejoining cycle. In addition there is disturbance to the initial spinning conditions, both due to the lack of suction for the impurities precisely during and immediately after the rejoining operation when the suction nozzle withdraws to its rest position to again engage the frontal air intake port, and due to the consequent pressure pulsations which arise when the air intake port is released. The present invention provides a device and a method for rejoining yarn in an open-end spinning machine which enables the rotor to be supplied with totally intact and impurity-free fibres for the rejoining operation, without having the above drawbacks of the device and method of DE-A-3 436 295. The device and method of the present invention have the features claimed in claims 1 and 4, respectively. The device and method are described with reference to Figure 1 which shows a spinning unit during its normal operation, and Figure 2 which shows the spinning unit during the rejoining cycle. The spinning unit consists of a fixed support 1 in a cavity of which a rotary separating carder 2 is positioned, provided along its outer cylindrical surface with saw-toothing to separate the fibres of the feed sliver. The fibre sliver 3, originating from an underlying chamber not shown on the figures, is fed along a fixed guide 4 by a feed roller 5 which rotates in an anticlockwise direction in order to feed the sliver towards the carder 2. The feed roller 5 is preferably provided with knurling on its cylindrical surface to increase the dragging effect on the sliver, contact between the sliver 3 and roller 5 being ensured by an approach member 6 the surface of which is kept in proximity to, but not in contact with, the cylindrical surface of the roller 5 by a suitable pneumatic or elastic device not shown on the figures, so that the sliver 3 is guided into contact with the cylindrical surface of the roller 5. In the practical embodiment the approach member 6 is a sliding block with a concave surface facing the roller 5. In this manner the sliver 3 is fed to the carder 2, which separates it into individual fibres. The individual fibres travel through an interspace 7 surrounding the carder 2 and are conveyed pneumatically through a channel 8 to the cavity of the spinning rotor 9, which rotates at very high speed. A vacuum is generated within the cavity of the rotor 9 by the effect of its speed and perforations 10, or by the action of a separate suction source, and sucks the fibres separated by the carder 2, withdrawing air both from the interspace 7 and through an aperture 11. Inside the rotor 9 the fibres are subjected to high centrifugal force and are urged towards the periphery where they collect in an annular groove 12 to form a layer of suitable size. An already formed yarn is then inserted through a channel 13 at the commencement of spinning. The free end of the yarn is urged by centrifugal force to the periphery of the rotor where it encounters the fibre layer, the yarn then being withdrawn for example by a pair of rollers 14. The fibres join to the inserted yarn end and acquire twist along the path between the annular groove 12 and the axis of the rotor 9, where the exit channel 13 is located. The produced yarn 15 is extracted and collected in packages or bobbins by a collection system, not shown on the figures. The impurities which escape the carder 2 are discharged by centrifugal force from the aperture 11, which connects a substantially tangential duct 16 to a suction manifold 17. As visible in the drawings, the tangential duct 16 provided in the fixed support 1 departs from the carder cavity downstream of the feeding region of the sliver 3 and upstream of the spinning rotor 9. The suction manifold 17 extends in the fixed support 1 between an air intake port 18 and a suction port proximate to the rollers 14. Conveying air is drawn into the manifold 17 through the air intake port 18 by the effect of the vacuum downstream of the manifold 17, indicatively about 50 mm of water column, in the direction of the light arrows shown in Fig. 1. When a breakage occurs in the yarn 15, a sensor not shown on the figures causes the feed roller 5 to stop and halts collection of the yarn 15 in known manner. The yarn-feeling sensor also calls the service carriage to the spinning station in which yarn breakage has taken place, to effect the yarn rejoining operations in accordance with the cycle described heretofore. During the intervention cycle the roller 5 remains at rest and the end of the sliver 3 is progressively depleted and degraded by the carder 2, which continues to rotate. At the same time the rotor 9 is halted to enable its groove 12 to be cleaned. Thus the pneumatic conveying action in the groove 12 which sucks the fibres from the channel 8 to the rotor 9 ceases, and the fibres removed from the slivers 3 by the rotary carder 2 at least partly remain on the carder 2 and in the interspace 7. According to the present invention, for the yarn rejoining operation a high-vacuum suction nozzle 19 carried on the service carriage of the spinning machine is brought into generally axial alignment with the air intake port 18 and is able to approach to, and withdraw from, the spinning unit in accordance with the double-direction light arrows shown in Fig. 2. The mouth of the suction nozzle 19 is therefore movable and stoppable in facing and sealing engagement with the outer surface of the fixed support 1 at the intake port 18. When the rotor 9 has been cleaned and before returning it to the speed at which the new fibre layer is to be deposited for the actual rejoining operation, an energetic suction action is applied at the intake port 18, spaced from the tangential duct 16, in the direction of the dark arrows shown in Fig. 2. The suction action is controlled by a time-operated solenoid valve, not shown on the figures but arranged in the duct containing the nozzle 19, under a vacuum much higher than that maintained in the manifold 17 during normal operation, the high suction being provided by a suction source to which the nozzle 19 is connected. The levels of static vacuum which enable a good joint to be made are indicatively between 300 and 900 mm of water column and preferably between 450 mm and 700 mm. The energetic suction action through the tangential duct 16 allows removal from the carder 2 and interspace 7 of all the fibres deposited there during the stages preceding the intervention cycle, ie those in which the sliver 3 was deteriorated by the action of the carder 2. Immediately afterwards, the sliver 3 is again moved forward by the roller 5 to the carder 2 while maintaining the interspace 7 under energetic suction, and the rotor 9 is restarted. The deteriorated fibres present at the leading end of the sliver 3 are thus combed away by the carder 2, and drawn towards the aperture 11 and nozzle 19. After the deteriorated portion has been removed, the suction action of the nozzle 19 is shut off and this latter can be removed, to restore normal vacuum in the manifold 17. The fibres separated by the carder 2 again flow to the rotor 9, which in the meantime has reached the required speed for depositing the new layer of intact fibres in the groove 12 and has restored its pneumatic sucking action through the channel 8. The fibres thus fed to the rotor 9 are perfectly intact and allow a better quality of joint. As can be seen, the nozzle 19 does not have to travel long distances or be accurately positioned. Sealing is ensured by a soft annular gasket. The time required for cleaning the carder 2 and interspace 7 and for removing the damaged fibres from the sliver 3 is very short, with an indicative total of less than 7 seconds. Using the device and method of the invention, high-efficiency joints have been obtained even on fine yarns, with a metric count of 40-80, to the extent of more than 95% as shown by subjecting them to joint tests. In the case of medium yarns, this efficiency reached 99%.

Claims: A device for rejoining yarn in an open-end spinning machine comprising a spinning rotor (9) on a fixed support (1) and a separating carder (2) rotatable within the fixed support (1) and fed with a fibre sliver (3) by a feed roller (5) to produce individual fibres which are fed to the spinning rotor (9) by pneumatic conveying, the carder (2) being housed in a cavity of the fixed support (1) provided with a substantially tangential duct (16) departing from said cavity downstream of the feeding region of the sliver (3) and upstream of the spinning rotor (9) for removing impurities and deteriorated fibres, said tangential duct (16) opening with an aperture (11) into a suction manifold (17) extending in said fixed support (1) between an air intake port (18) and a suction port, and further comprising a suction nozzle (19) carried by a service carriage of the spinning machine for providing a suction in said tangential duct (16) for removing deteriorated fibres before rejoining the yarn, characterised in that the suction mouth of said suction nozzle (19) is movable and stoppable in facing and sealing engagement with the outer surface of said fixed support (1) at said intake port (18) in generally axial alignment therewith. A device as claimed in claim 1, characterised in that said suction nozzle (19) is connected to a suction source providing a static vacuum of between 300 and 900 millimetres of water column. A device as claimed in claim 1 or 2, characterised in that said suction nozzle (19) is provided with a time-operated solenoid valve for controlling the beginning and the end of the suction action. A method for rejoining yarn in an open-end spinning machine by means of a device as claimed in one of the preceding claims, in which the rejoining is effected by returning the yarn end into contact with a layer of fibres newly deposited in the groove (12) of the rotor (9) after having cleaned the rotor (9) and in which before depositing the new layer of fibres in the groove (12) of the rotor (9) both the fibres still contained in the cavity which encloses the carder (2) and the deteriorated fibres at the leading end of the sliver (3) moved forward by the feed roller (5) are removed by suction applied through the tangential duct (16) and the new fibre layer consisting of intact fibres is deposited when the suction action ceases, characterised in that said suction is applied at said suction port (18) spaced from said tangential duct (16).

Inventors: FERRO FRANCESCO, PERUCH CLAUDIO, FERRO, FRANCESCO, PERUCH, CLAUDIO
Applicants: SAVIO MACCHINE TESSILI SRL, SAVIO MACCHINE TESSILI S.R.L.
Application year: 1989
Main classification: D01H4
IPC codes: D01H4