EP0143466B2 - Apparatus for drawing bundles of synthetic yarns - Google Patents

Description

The invention relates to a device and a method according to the preamble of claim 1.

With such a drafting device for multifilament threads made of thermoplastic materials, more than a thousand threads can be drawn at the same time. This method is particularly useful when the threads are to be opened on warp beams after they have been drawn.

In this case, if the thread breaks, it is desirable to switch off the stretching and winding system immediately in order to avoid sympathy breaks and to prevent the broken thread end from running through the machine and from being unable to be tied up. However, the sudden machine downtime entails the risk that the remaining, unbroken threads, which rest on the heating devices of the drafting system at a standstill, will melt or will be damaged in such a way that they break during further operation of the drafting system or only during further processing .

On the other hand, it has been found that when stationary stretching pins are used, by which the stretching is effected, it is difficult to achieve a satisfactory uniformity of the stretched threads, since the threads are individually guided and stretched through the treatment zone when using stretching pins, particularly on stretch twisting machines will. Even if the above-described risk of thermal damage to other threads when a thread breaks cannot occur, there is an endeavor to be treated, in particular when opening a thread family on warp or warp beams, in which the uniformity of the thread properties is of particular importance all threads of the thread sheet under the same conditions, for which their stretching between roller drafting systems, in particular with the arrangement of heated rollers at the entrance of the stretching zone, has proven to be particularly suitable.

DE-A-1 946 863 describes forms of training of heated godets, referred to as rollers, of the type known for use on draw twisting machines. Such godets are known as supply mechanisms for individual threads, in particular on drawn twisting machines, and are not suitable for the joint treatment of a thread group composed of up to 1000 and more threads.

FR-A-2 444 733 describes a device in which a family of preferably wound elastomer threads are jointly subjected to a heat treatment by passing them over a heated plate. The individual threads of the thread sheet run at a distance from one another through the bores of a thread guide bar, which serves to separate the threads and is provided at both ends of the heated plate. When the thread sheet is stopped, the latter is lifted off the heated plate by lifting the two thread guide strips. Delivery mechanisms, between which the thread sheet would be stretched, or bobbin creels are not described.

In a device which has become known from FR-A-2 404 066, threads drawn off from a creel are combined to form a family of threads, passed over a first roller delivery unit, stretched in a subsequent heating box using an edge or cutting edge and then through further drafting system and a preparation station for further processing. When the thread sheet is stopped, the heating box opens to cool the thread sheet, for example in a water bath.

The invention is therefore based on the object to provide means for a device for stretching coulters of synthetic threads on which the threads are heated and stretched together as a thread coulter between a first roller delivery unit and a further roller delivery unit, in order to brake the line of threads to interrupt the flow of heat to the thread sheet.

This object is achieved according to the invention by a device for stretching yarn sheets made of synthetic threads, on which the yarns drawn off from a creel are heated and stretched together as a yarn sheet between two roller delivery units and in which means are provided on the devices for heating the yarn sheet to slow them down the thread coulter to interrupt the flow of heat to the thread coulter, solved by the fact that a pair of heating rollers with at least one heated roller is provided between the two delivery units, preferably one pair of unheated rollers being assigned to the pair of heating rollers, that one roller of the or each pair of rollers above and the other roller of the roller pair (s) is located below the thread sheet and that the rollers of one roller pair and possibly those of the other roller pair are each movable relative to one another in such a way that they enter the thread sheet from both sides and their path to the S or Z -Form v change, with the arrangement of two pairs of rollers at the end of the respective retracting movement only one pair of rollers is engaged with the thread sheet and the rollers of the second pair of rollers do not touch the thread sheet.

In one embodiment of the invention, devices are provided for this purpose, which enable a relative movement between the entire thread sheet and the heating roller when the drafting system is at a standstill in the sense of lifting off and when restarting in the sense of placing the thread sheet on the heating roller. Thereby the heating roller, which is in the working position when the thread sheet is running, can be brought out of the action of the thread sheet when the machine is braked. For example, a pair of rollers are used, at least one of which is a heating roller. This pair is advantageously located between the delivery plants. The rollers, which are aligned parallel to one another and transversely to the thread sheet, can be inserted into the thread sheet from opposite sides. When viewed from the side, the group of threads is deflected into an S or Z shape.

So that the thread coulter tension is maintained further when the heated rollers are disengaged, a dancer roller arrangement can be provided within the stretching zone. A similar, but unheated and possibly actively cooled roller pair is advantageously associated with the heated roller pair. Both work together in such a way that the heating roller pair is in contact with this while the coulter is unheated while the coulter is at rest. The movements take place in a coordinated manner, so that the immersing pair of rollers absorbs the slack caused by the extension of the other. By coordinating the coordinated movement of the two roller pairs with the current thread coulter speed in such a way that the full immersion of the heated rollers takes place only at the maximum stretching speed and corresponding intermediate positions are otherwise assumed, the adapted heat supply can be ensured in every operating state. The unheated and, if necessary, cooled roller pair can also be connected to a heating and cooling system together with the initial delivery plant or both delivery plants, it also being possible advantageously for the feed delivery plant to be heated.

The uncooled pair of rollers, which is only exposed to low operating loads, can be designed in a correspondingly simpler manner.

In a further embodiment, the or preferably each of the roller pairs is mounted on a respective carrier, namely at the ends thereof, and the carrier is about a pivot axis which is approximately in the middle between the rollers and parallel to them, with a pivot angle of at least 30 and maximum Can be swiveled 180 °. The pivoting movements of the heated and the unheated pair of rollers are coupled to one another and can be directed in opposite directions, with mirror-symmetrical arrangement also in the same direction; they can be started by braking or starting again.

Particularly advantageously, the sequence of the pivoting movement of the pair of rollers engaged in each case is controlled depending on the course of the thread coulter tension in such a way that a change in tension is substantially avoided during the change of engagement between the roller pairs assigned to one another.

For large stretching systems in which e.g. 1000 and more threads are drawn at the same time, in a further embodiment of the invention, mass-free or low-mass embodiments are proposed, in which the heating rollers themselves are not moved, that is to say the family of threads executes the required relative movement for lifting off the heating roller. Above all, however, it should also be ensured that the thread tension is not changed beyond the tolerable level by the insulation at a standstill. For this purpose, a lifting segment is assigned to the stationary heating rollers, which slides between the roller surface and the thread sheet when the machine is at a standstill. It also shields the thread sheet preferably from the heat radiation from the roller and at the same time separates it from it.

The lifting segment is adapted to the roller in the form of a jacket and forms with the roller a gap which prevents heat transfer to a sufficient extent.

The individual lifting segment has an extent in the circumferential direction which corresponds at least to the wrap angle of the thread sheet and is preferably approximately 4% to 20% larger.

The lifting segment is pivotally mounted on the axis of the heating roller itself or eccentrically to it. The thread coulter can partially wrap around the heating roller in the central swivel position of the lifting segment. When the drafting system is at a standstill, the lifting segment is preferably pivoted around the heating roller in the direction of travel of the thread sheet in such a way that it lifts the thread sheet from the heating roller and keeps it at a distance from the heating roller during standstill. When the system is started up, the lifting segment is pivoted further until it loses engagement with the thread coulter and returns to its neutral position. The swiveling movement of the lifting segment is initiated by its own drive, which is activated when the thread sheet is braked. You can now coordinate the time at which the drive comes into operation with the braking deceleration of the drafting system in such a way that the coulter itself brings the lifting segment into the standstill position and holds it there during standstill. When the drafting system is restarted, the thread sheet automatically transports the lifting segment out of the standstill position. Through these measures, the self-propulsion of the lifting segment can be limited to bringing the lifting segment into engagement with the thread sheet which is still running but has already been braked at a precisely coordinated point in time. The lifting segment also has the advantage that the thread sheet is kept under virtually unchanged thread tension during standstill. This avoids the risk of the threads becoming tangled.

The effect is improved if the pivot axis of the lifting segment is eccentric to the associated roller and in a plane which is determined by the roller axis and the end of the wrap angle. In this way, the lifting segment is relatively far away from the heated surface when the thread sheet is running and therefore remains cool, while when swung in the lifting position it comes into a position in which it can be only a short distance from the surface of the roller but pushes between the roller and the thread sheet and separates them from the roller surface. As a result, the lifting only leads to an even lower hearing of the thread pulling forces.
The minimum distance between the roller surface and the inner surface of the lifting segment should - depending on the general or roller dimensions - be about 0.5 to 2 mm in the lifting position and about 10 to 25 mm in the swung-out position; the latter must ensure that the lifting segment does not heat up too much in the pivoted-out position. This is supported by a structure of the lifting segment, which makes it a heat insulator. It can consist, for example, of a reflection layer, an insulation layer and a wear-resistant thread running layer from the inside to the outside; the edges running transversely to the thread coulter are expediently made of wear-resistant material, since when they first engage the thread coulter they have to endure the relatively high relative movement of the threads as wear-free as possible.

In a mechanically simple design and reliable working design, the lifting segment is a flat structure, i.e. Cloth, foil, pliable mat or the like. With a finite length and a width that corresponds to the working width of the heated roller. This flexible sheet has good insulating properties. When the brake breaks or the brake is started up, it is guided, clamped and transported away by a drive device with its broad side into the gap between the roll surface and the thread sheet running onto the roll surface, until the roll comes to a standstill. The fabric must be as long as the length of the thread coulter after the thread breaks or the brake is started. When the device is restarted, the surface area Ide is thrown off the roller and falls down without further obstructing the thread sheet. It can be seen that the length of the insulating sheet material should essentially be limited to the outlet path of the thread group so that the heating of the threads starts immediately when the device is restarted. The particular advantage I of this embodiment is above all to be seen in the fact that the fabric practically does not increase the thread tension and is also able without effort to withstand the forces caused by the thread tension. The drive is also very simple, especially since the moving masses are very low.

Another advantageous exemplary embodiment provides a heating roller, which is hollow on the inside and connected to a circuit for a liquid heating medium. The heating medium is heated outside of the heating device by a suitable heater. According to the invention it is provided that in a branch of the heating medium circuit which is parallel to the heater, a cooling device or preferably a cooling container, preferably even a cooled container, is provided which contains enough heating liquid to at least partially fill the heating device and reduce the temperature of the heating device in this way to ensure that the threads are no longer damaged. Valve devices are provided in the heating circuit, which are connected to thread break monitoring directly or via the machine drive and through which the liquid circuit, in which the heating device is switched on, is switched from the heating branch to the cooling branch when the thread breaks or the machine stops.

The advantage of this embodiment also lies in the fact that no mechanical parts have to be moved to switch off the heating effect when the machine is at a standstill. The movement of mechanical parts is always associated with considerable vibrations of the machine and also leads to changes in the thread tensile forces acting on the thread group. The threads can get confused.

Depending on the operating temperature of the heating device on the one hand and the temperature of the cooled heating medium in the cooling container or the cooling device, a single filling of the heating device with the cold heating medium is sufficient.

However, circulation of the actively cooled heating medium can also be provided with constant further cooling. If e.g. the heating device is only used to fix the stretching point in polyester threads, so it has a temperature that is in the range of 100 °. In this case, a temperature reduction of 20 to 30 ° is already sufficient to prevent damage to the threads, even if the thread is not used for a long time.

3-way valves in front of and behind the heater or the cooling container are preferably used as valve devices.

It is known that the elongation occurs when a synthetic thread, in particular a thread made of polyester and polyethylene terephthalate, is stretched in a narrow range in the longitudinal direction. The length of this area depends on the spinning orientation of the thread. For threads with a low spinning orientation, a so-called bottle neck of a few millimeters in length is created. For threads with a ho In spinning orientation, flow zones of greater length are formed. In any case, the change in length occurs only after the threads overflow through the heating device. To support the task according to the invention of avoiding the contact of undrawn thread areas with the heating device at a standstill, a method is further proposed as an exemplary embodiment in which, in the event of a thread breakage, the thread transport devices, i.e. delivery and drafting units, are braked to a standstill and then moved back so far be that a stretched thread length, that is, such thread material comes into contact with the heating device at a standstill, which lies behind the flow zone in the thread running direction.

After braking the thread path, a stretched piece of thread is moved back into the area of the heating device. It should be pointed out that the measure proposed here can be used in conjunction with the measures previously described in the context of this application if it is found that, despite the measures, the family of threads is still exposed to temperatures which the threads in the undrawn state do not present without the danger can endure damage.

The invention is explained in more detail with reference to the accompanying drawings, in which:

Fig. 1 shows a schematic representation of an embodiment of the device according to the invention. The heating device consists of two rollers 25, which are both heated, parallel to one another and can be pivoted together about a common axis 29 lying in one plane with the two roller axes and running parallel to them. For this purpose, both rollers 25 are rotatably fastened in a frame 27 indicated by levers in the drawing, the axis of rotation 29 of which is the common axis.

An unheated, possibly also cooled roller pair 26 is assigned to the heated roller pair 25 and has the same structure. Both pairs of rollers 25 and 26 are installed in the stretching zone between the feed mechanisms 4 and 5. Their frames 27 and 28 either run parallel to one another or are arranged mirror-symmetrically to one another.

In both cases, their pivot axes 29 and 30 preferably run in the connecting plane 34 between the two delivery mechanisms 4 and 5, so that in each case one roller 25 or 26 of each pair of rollers can be inserted into the thread sheet 43 from below and the other from above. With the thread sheet 43 running, the heated roller pair 25 engages with it, describing the path 31; the unheated rollers 26 are out of function. If the thread sheet is now braked, the pivoting movement of both pairs of rollers 25, 26 is preferably initiated synchronously with the start of the braking. The heated pair 25 moves out of the thread sheet and at the same time the unheated pair 26 moves in, the path of the thread sheet 1 changing in accordance with the dash-dot line 32. Both paths 32 and 33 have the same length, so that the family of threads remains taut. This process can advantageously be controlled in dependence on the thread coulter tension in such a way that it essentially does not change. If the frames 27 and 28 are arranged in parallel, the pairs of rollers 25, 26 move in opposite directions, and if the arrangement is mirror-symmetrical, their movement is rectified.

Instead of fastening both rollers of the roller pairs 25, 26 to a common swivel frame 27 or 28, the rollers can also be arranged independently of one another. A heating roller and a cooling roller are then each below, the associated second rollers above the thread sheet. Such an arrangement requires separate guide and movement mechanisms for each of the rollers 25, 26 and is therefore more complex than that previously described. However, it offers the possibility of a sensitive control of the thread heating by more or less deep immersion of the rollers in the thread sheet, whereby the respective wrap angle can be changed.

In the embodiments of the invention described so far, certain disadvantages result from the fact that relatively large masses have to be moved, which can lead to considerable acceleration forces when moving the rollers because of the usual very fast braking processes. This is remedied by an embodiment of the invention in which the heating devices are no longer moved themselves, but the thread sheet is separated from them by appropriate devices and measures, which leads to the heat supply to the thread sheet being interrupted. Figures 2 to 5 serve to explain this embodiment.

2 shows an arrangement in which, for illustration, a heating plate underneath the thread sheet 43 brought. The respective inner, the heating plate facing rollers 47 and 48 of the two delivery mechanisms 4 and 5 are assigned in more detail lifting segments which are pushed when braking between the rollers 47 and 48 and the thread sheet 43 and lift them from the heating plate so far that their influence on the thread group becomes insignificant. The heating plate can therefore be stationary.

FIGS. 3 and 4 show two different possibilities for assigning the lifting segment 33 to the roller 47 or 48 to be covered. In the embodiment according to FIG. 3, the pivot axis 45 of the lifting segment 33 coincides with the roller axis 50, the lifting segment therefore moves with the same Distance to the roller surface. In the illustration, the covering area 49 of the lifting segment 33 extends beyond the looping area 44 of the thread sheet 43 when it runs over the heating roller 25 or 26. The drawn-out lifting segment 33 has been pushed between the thread sheet 43 and the roller surface and shields the stationary thread sheet 43 against the roller 47 or 48. With the thread sheet running, the lifting segment 33 assumes the position 33A shown in broken lines. The covering area 49 of the lifting segment 33 is dependent on the respective wrap angle or area 44. If possible, it should be about 4% to 20% larger than the wrap angle 44; this is only possible at wrap angles 44 that are smaller than 180 °, but this should be the normal case.

FIG. 4 shows an embodiment of the lifting segment 33, in which the pivot axis 46 of the lifting segment 33 lies parallel to the roller axis 50 at a certain distance from it. It is arranged in a plane 35 which is determined by the roller axis 50 and the bisector 35 of the wrap angle 44. It is thereby achieved that the distance 37 between the roller surface and the inside of the lifting segment 33 in the lifting position is smaller than the distance 28 in the position 33A pivoted away (shown in broken lines). The minimum distance 37, which is also determined by the size relationships, is approximately 0.5 to 2 mm in the lifting position and the distance 38 in the pivoted-away position is at least approximately 10 to 25 mm.

If the rollers 47, 48 of FIG. 2 are designed as heating rollers, the action according to the invention of the lifting segment 33 is supported if it is constructed as a heat insulator, as shown in FIG. 5. It consists from the inside to the outside of an inner reflection layer 41, an insulation layer 40 and a wear-resistant thread running layer 39. The edges 42 running transverse to the thread sheet 43 preferably consist of wear-resistant material.

4A serves to explain the exemplary embodiment in which the lifting segment is designed as a flexible sheet 80. The heated roller 60 is shown, which is rotatably supported and driven in bearings, not shown. The roller 60 is partially wrapped around the threads 3 of a thread family. On the axis 45 of the roller 60, a lever 81 and 82 is freely rotatably mounted on both end faces. Each lever is firmly connected to a gear 83. The gear 83 is driven by gear 84 and swing motor 85. A gear wheel corresponding to 84 and swivel motor corresponding to 85 is therefore also provided for the lever 82. Both motors are started synchronously and with the same phase position in the direction of rotation of the roller 60 when the braking system of the device engages in the event of a thread break.

At the ends of the levers 81, 82 there is a hook 86 and 87, respectively. The insulating surface ide 80 is hooked into the hook. The fabric is flexible so that it can adapt to the diameter of the roller 60. It can be a cloth, foil, mat or the like. act. On the one hand, it has the heat resistance in order to be able to endure the temperature of the roller 60. On the other hand, it has good insulating properties in order to prevent or substantially hinder the heat flow from the roller 60 onto the thread sheet. In the event of a thread breakage or when the brake is started up, the motors 85 are also started briefly, so that the broad side 88 of the fabric is clamped in the tip of the gap between the thread sheet and the surface of the roller 60 and by the roller 60 or thread sheet 3 is transported further.

It should be noted that the hooks 86 and 87 lie outside the roll length and essentially on the radius of the roll 60. The length 89 of the fabric 80 is now dimensioned such that it essentially corresponds to the runout of the thread family. So if the lever 81, 82 retract and clamp the sheet 80 in the gap between the surface of the roller 60 and the thread sheet 3 when the thread breaks and the brake is applied, the sheet is carried so far that it touches the peripheral area touched by the threads completely covers the roller. Otherwise, the length is dimensioned such that when the device is restarted, the heating of the threads, i.e. the direct heat-conducting contact between the roller 60 and the thread sheet starts again at a desired point in time. It may therefore be desirable to make the fabric longer than the loop length of the roller. However, the length of the fabric is preferably limited to the looping length both with regard to the maximum and with regard to the minimum.

It can be seen that such a device can also be used with rollers which are wound around from below by the thread sheet, such as with the first roller 60 in the thread path according to FIGS. 7A, 7B. In this case, the fabric hangs on the levers 81, 82. By lowering the levers 81, 82, the free one falls Broadside 88 under the force of gravity of the sheet 80 in the gap between the thread sheet 3 and the roller surface and is now clamped and transported on. Then the levers 81, 82 - as in the case described above - are dragged on without a drive.

In some cases it may be expedient to cool the rollers of the output delivery unit 5 in order to avoid possible changes in the thread structure caused by the heat, such as uncontrolled post-condensation. Likewise, a certain preheating of the yarn sheet 43 entering the drawing zone can be advantageous. In order to be able to correctly measure the heating of the thread sheet 1 in all operating states, the possibility is advantageously provided, for example by changing the effective wrap angle 44 or partially covering or the like to adapt the heat effect on the thread sheet 43 to the respective current thread sheet speed. In the embodiment according to FIG. 1, this is possible, for example, to a large extent by the extent to which the coordinated pivoting process of the two roller pairs 25, 26 takes place, since the wrap angle 44 varies widely from simple contact to maximum depending on the immersion depth Wraps can vary.

The system for stretching a sheet of threads according to FIGS. 7A and 7B is only shown schematically. On a gate 51 there is a variety of e.g. 1000 - supply spools 52, of which the threads 53 run through suitable thread guides, thread tensioners and thread monitors (not shown). The threads are drawn off by the first pair of rollers 54 and then fanned out in groups and passed through nozzle bars 57 lying one above the other in planes. The multifilament threads are each swirled in a so-called "tangle nozzle" in these nozzle bars. This will close the thread, i.e. the cohesion of the individual filaments of each thread is improved and the smoothness and stretchability are improved.

In the exemplary embodiment, an overflow rod 71 is arranged upstream and downstream of each nozzle bar. The overflow rods 71 are connected to the nozzle bar in a manner not shown.

Following the air swirling, all the threads are brought together again in one plane, which is done by means of two overflow rollers 58. The threads are then drawn off through the input rollers 59 of the drafting system. This is followed by the heated rollers 60, which are heated to approximately 90 ° for processing polyester threads. The threads then pass through a heating plate 61, on which they are heated to more than 120. The heating plate 61 is pivotally mounted on the support device 62. It can be lifted off the thread sheet by the drive device 63 - a pneumatic cylinder-piston unit is shown. The drive device 63 is controlled as a function of thread monitors. The output rollers 65 follow behind the deflection roller 64. The peripheral speed of the output rollers 65 is greater than the peripheral speed of the input rollers 59 or heated rollers 60 by the stretching ratio.

The thread family is then fed via a comb 68 to a warp beam 67 of the tree plant 66.

According to the invention it is provided that either lifting segments according to FIGS. 3, 4, 5 or an insulating flat structure according to FIG. 4A are provided for the insulation of the heated rollers 60 at a standstill or that the heated rollers 60 are heated with a liquid and that valve devices are provided by which the heated liquid can be exchanged very quickly for cold liquid, these valve devices being operationally connected to the thread break monitoring of the drawing system. The hot liquid is e.g. Water, since only temperatures up to 100 ° are desired. Water is also suitable as the cold liquid, cold being understood here as a temperature at which the threads lying on the rollers 60 are no longer damaged.

It should be noted that the surface speed of the rollers 60 can be set independently of that of the rollers 59 and 65, which is known per se from the stretching technology for plastic threads, in particular polyester threads.

6 shows the heating and cooling circuit of the rollers 60. The rollers 60 are hollow on the inside and connected to a heating circuit via corresponding slip ring couplings. The heating circuit is fed by the pump 70. When the pump 70 is in operation, a liquid heating medium circulates through the heater 71 and is kept at a constant temperature by appropriate temperature measuring and regulating devices. A possible thread breakage, even of only one of the threads of the thread family, is detected by the thread sensor 72. Depending on its output signal, the solenoid-operated 3-way valves 73 and 74 are changed over in such a way that the heater is removed from the liquid circuit and instead the cooler is switched into the liquid circuit. The cooler can be an active cooler. However, it may be it is also sufficient to provide a sufficiently large liquid container in which heating liquid is kept at room temperature. A heat exchanger may also be necessary or useful for this. The heating liquid from the cooling container or cooler is now conveyed into the rollers 60. It is sufficient - depending on the heat capacity of the masses and the temperature of the heating roller 60 and the cooling temperature of the liquid conveyed from the cooling container 75 and the desired temperature reduction - that the roller 60 is once filled with the cold liquid.

However, there may also be a continuous or temporary circulation with active cooling of the umlau liquid can be provided. In a preferred embodiment it is provided that a temperature sensor 76 is provided in the circuit in front of the pump 70, by means of which the drive 77 of the pump 70 is switched off when a desired temperature is reached.

To explain the further exemplary embodiment of the invention, after which, in the event of a standstill, a return of the yarn feed mechanisms is required such that only stretched material comes into contact with the heating device, reference is also made to FIG. 7B.

As already stated, the rollers 60 of the delivery mechanism and the heating plate 61 are heated. It can be assumed that depending on the degree of spinning orientation of the delivered threads, the change in length, i.e. the flow between the last roller 60 and the heating plate 61 takes place. It is assumed that the flow zone extends to the heating plate 61. This means that in the case of a standstill undrawn thread material lies both on the heated rollers 60 and on the entrance area of the heating plate 61. For this reason, after the rollers 59, 60 and 65 have come to a standstill, the system is briefly put into operation with the opposite direction of movement, the transmission ratio between all the rollers 59, 60, 65 being switched to 1: 1. This return movement continues until there is no undrawn thread material on a heating device. This means that if the rollers 60 are not cooled, the return movement is continued until the flow zone is again in front of the rollers 60. However, if - as described above - cooling of the rollers 60 is provided in the event of a standstill, the return movement need only be carried out to such an extent that the flow zone comes to lie between the rollers 60 and the entrance of the heating device 61, i.e. a shorter return path is sufficient. With this procedure it is possible to avoid the rollers being cooled and / or the heating plate being lifted off the threads. However, it must be added that this method can only be used if the temperatures required for the stretching can be borne by the stretched thread material for the expected duration of the disturbance without damage. This insensitivity to temperature depends on the thread material; the level of the temperatures also depends on the material, but also depends on the other stretching parameters and the desired end product. The process described has been found to be readily applicable and advantageous for polyethylene terephthalate threads which have been spun at a take-off speed of more than 3500 m / min and which have thereby obtained a relatively high spinning orientation.

To restart the system after the fault has been remedied, the delivery mechanisms 60 and 65 are first started up in synchronism, i.e. with a transmission ratio of 1: 1, until the threads, i.e. the flow zone has reached exactly the position in which the standstill occurred. The number of forward rotations of the rollers 60, 65 with the transmission ratio 1: 1 thus corresponds to the number of reverse rotations previously carried out with the transmission ratio 1: 1. The normal operating state is then restored. It should be mentioned that the warp beam 67 must also take part in the reverse rotation and the forward rotation, its speed being adapted to the permissible thread tension of the thread family.

Claims (13)

1. A device for stretching groups of synthetic threads, the threads being simultaneously drawn in a group (43) from a bobbin creel (51) and heated and stretched between a first roller delivery device (4) and a second roller delivery device (5), the devices for heating the group of threads (43) being provided with means for stopping the heating of the threads (43) when they are slowed down, characterised in that a pair of heating rollers (25, 25) comprising at least one heated roller is disposed between the two delivery devices (4, 5), an unheated pair of rollers (26, 26) being associated with the heated pair (25, 25), one roller (25; 26) out of each pair of rollers (25, 25; 26, 26) is disposed above and the other roller (25; 26) of each pair of rollers (25, 25; 26, 26) is disposed below the group of threads, and

the rollers in each pair (25, 25; 26, 26) are movable relative to one another so that a roller can be inserted into the group of threads (43) on both sides and the path of the threads can be changed to an S or Z, and at the end of each moving-in movement only one pair of rollers (25, 25; 26, 26) is in engagement with the group of threads (43) whereas the other pair of rollers (26, 26; 25, 25) are not in contact with the group of threads (43), and where

the pair of heating rollers (25, 25) is in engagement with the group of threads (43) when they are moving, whereas the unheated pair (26, 26) is in engagement when they are slowed down.

2. A device according to claim 1, characterised in that the movements of the two pairs of rollers (5, 6; 7, 8) are coupled together, occur in opposite directions and can be started by slowing down or restarting the group of threads (1).

3. A device according to claim 2, characterised in that the sequence of motion of each pair of rollers (5, 6; 7, 8) in engagement is controllable independently of the variation in the tension of the threads, so as substantially to avoid a change in tension during a change of engagement.

4. A device according to any of claims 1 to 3, characterised in that the heated and/or the unheated pair of rollers is disposed on a supporting device (frames 27, 28) which is pivotable through 30 to 180° around an axis (29, 30) disposed between and parallel to the rollers.

5. A device for stretching groups of synthetic threads, the threads being simultaneously drawn in a group (43) from a bobbin creel (51) and heated and stretched between a first roller delivery device (4) and a second roller delivery device (5), the devices for heating the group of threads (43) being provided with means for stopping the heating of the threads (43) when they are slowed down, characterised in that a lifting-off segment (15) surrounding the heated roller (25; 60), like a jacket, preferably at a distance (37; 38) therefrom, is provided as a means for interrupting the flow of heat between the heated roller (25; 60) and the group of threads (1), and the length (29) of the segment in the peripheral direction of the rollers at least overlaps the loop area (25) of the group of threads (1) and preferably is about 4% to 20% greater, the segment being pivotable around an axis parallel to the roller axis, and in that the pivoting axis (26) of the lifting-off segment (15) is disposed eccentrically (18) to the associated roller (5, 6; 27, 28) and lies in a plane defined by the roller axis and the bisector (17) of the loop angle (25).

6. A device according to claim 5, characterised in that the minimum distance (19; 20) of the lifting-off segment (15) from the roller surface is 0.5 to 2 mm in the lifted-off position (19) and about 10 to 20 mm in the pivoted-away state (20).

7. A device according to any of claims 5 to 6, characterised in that the lifting-off segment (15) is constructed as a heat insulator and preferably, in the outward direction, comprises at least one reflecting layer (23), an insulating layer (22), and a wear-resistant layer (21) over which the threads run.

8. A device according to any of claims 5 to7,
characterised in that a compensating roller is provided for compensating fluctuations in thread tension and/or changes in position in the region between the feed delivery device (2) and the outlet delivery device (3).

9. A device according to claim 5, characterised in that the lifting-off segment is an insulating, flexible planar structure which is pulled between the group of threads and the heating device when the machine stops.

10. A device for stretching groups of synthetic threads, the threads being simultaneously drawn in a group (43) from a bobbin creel (51) and heated and stretched between a first roller delivery device (4) and a second roller delivery device (5), the devices for heating the group of threads (43) being provided with means for stopping the heating of the threads (43) when they are slowed down, characterised in that the heating rollers (60) are heated via lines to a heater (71) for liquid heating medium away from the heating rollers, and a cool container (75) containing a cold heating medium is connected in parallel with the heater (71) via a valve arrangement, preferably a three-way valve, and the valve arrangement is controllable in dependence on a thread-breakage monitor so that if the thread breaks the cold heating medium is fed to the heating rollers (60).

11. A device according to claim 10, characterised in that the pump in the liquid circuit is disposed in front of the branches of the circuit containing the heater and the cool container.

12. A device according to claim 11, characterised in that a temperature sensor projects into the liquid circuit in front of the pump, and the pump can be switched off in dependence on temperature.

13. A method of stopping a device according to any of claims 1, or 10, characterised in that the roller delivery devices (4, 5) are slowed down until they stop, after which the first delivery device (4) is rotated backwards for a few revolutions until the non-stretched length of thread which has already passed the heating device has returned in front of the heating device, whereas the downstream delivery devices (5) are connected so as to be freely rotatable or are preferably rotated backwards, likewise with a transmission ratio of 1:1.

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