EP0062185B2 - Device for drafting a roving in spinning machines - Google Patents

Abstract

The present invention concerns a method for processing a fiber sliver in a drafting arrangement, and a drafting arrangement for implementing the method. The objective for a drafting arrangement, which can be adapted to a wide range of staple lengths, to draft a fiber sliver at high speeds, has led to the following features of the invention: (a) The fiber sliver is deflected simultaneously in the drafting process systematically in such a manner that, the fiber sliver can be inserted into the subsequently arranged funnel and the subsequently arranged pair of calender rolls without further deflection.

Description

The invention relates to a drafting device for spinning machines, in particular for drawing, for processing a sliver with a stacking area of cotton and / or plastic fibers in a preliminary and a main drawing zone, comprising drawing zones delimiting sub-cylinders arranged on a machine frame and above that assigned to each sub-cylinder Printing cylinder, wherein the first printing cylinder delimiting the main stretching zone is arranged so as to be displaceable and fixable on an arc around the axis of rotation of the corresponding lower cylinder.

DE-PS 1250315 shows and describes a drafting system with, viewed in the running direction of the sliver, an input cylinder pair, a middle cylinder pair and an output cylinder pair, each consisting of a lower cylinder and an associated pressure cylinder. The input and middle pairs of cylinders together form a leading, while the middle and output pairs of cylinders form a main stretching zone. The pair of input cylinders, viewed in the direction of travel of the sliver, can be moved linearly back and forth in order to change the length of the pre-stretching zone. Both cylinders can be moved independently of each other. The middle and the output lower cylinder are rigid, while the middle and the output pressure cylinder are arranged linearly displaceable in the same way as the input pressure cylinder. All three printing cylinders are vertically movable with respect to a base plate receiving the pedestals of the lower cylinders, so that when the printing cylinders are linearly displaced, in combination with the vertical mobility, they can perform a movement around the fixed or fixed lower cylinders. This makes it possible to change the length of the main stretching zone and to adapt it to a certain extent to the stack length. The output lower cylinder has a larger diameter than all other cylinders. The bearing blocks of the printing cylinders are arranged so as to be linearly displaceable on the bearing blocks of the lower cylinders. The pressure on the pressure cylinder is exerted by spring-loaded pressure pistons, which are attached to a swivel and lockable bracket.

In addition, CH-PS 426 570 shows and describes a drafting system with a pre-stretching and a main stretching zone, in which a pressure cylinder is arranged pivotably around the axis of a lower cylinder, as a result of which the loop of the sliver is lengthened or shortened. In order to be able to adapt the clamping line distances in the drawing fields which delimit the preliminary and main drawing zone to the fiber length of the fiber material to be processed, the mutual distances of the roller groups can be changed.

The increase in performance of a drafting system inevitably leads to an increase in Belt speed High belt speeds, e.g. of 800 m / min. or more of the stretched belt, ie at the outlet of the drafting system, results in high speeds of the drafting system cylinders and this in turn places higher demands on the mounting of the cylinders.

In addition to the speed and the load, the accuracy of the assembly is also decisive for the service life of a bearing, e.g. with respect to the parallelism of the pressure and sub-cylinders to one another and with regard to the exact alignment of the cylinder shafts to the elements driving the shafts.

If one looks at the drafting device of DE-PS 1250 315 from the above-mentioned points of view, it is found that for the displaceability or fixability of the bearing blocks for the input cylinder pair as well as the bearing blocks of the middle and output pressure cylinders, no special device for precise fixing is available is, so that these storage positions can only be set relatively inaccurately or only with special setting aids, neither shown nor described. However, the use of such aids is time-consuming, cumbersome and therefore unsatisfactory.

In addition, the mutual linear displaceability of the pressure cylinders with respect to the lower cylinders, in order to thereby change the clamping point spacings of the stretching zones, has the disadvantage that the spring forces of the pressure pistons, depending on the position of the pressure cylinders on the lower cylinders, as a result of changing force components in the radial direction different force on the tape.

Another disadvantage is the large diameter of the output cylinder, since this increases the distance between the clamping lines of the main stretching zone.

In addition, the drafting system has the disadvantage that in order to e.g. To be able to run in a can, an additional deflection of the belt after the drafting system is required, which is necessary for the belt at belt speeds of 13.3 m / sec. and more results in an additional, undesirable centrifugal load and thereby creates a procedural disadvantage.

Ultimately, a drafting device with three drawing zones is known from French Patent No. 1196 694, in which the lower cylinders, as well as the printing cylinders, are arranged opposite one another in concentric circles, the printing cylinders being located on the outer circle. Such drafting systems are used in roving or ring spinning machines and work at belt speeds at the exit of the drafting system of max. 40 m / min. in leader and max. 20 m / min. in ring spinning machines. The arrangement on concentric circles was chosen in order to obtain more space for printing cylinders of large diameter without increasing the distance between adjacent clamping lines. These Increasing the diameter reduces the risk of winding on the pressure cylinders of such drafting systems. At the inlet of the drafting system and in each drawing zone, an intermediate guide element is provided, on which the fiber sliver or the fiber sliver is deflected such that the fiber sliver or the fiber sliver passes the mentioned clamping lines in the tangential direction. The fiber sliver is deflected on a roller only on the last lower roller, seen in the running direction of the fiber sliver, and only after the clamping line.

The drawbacks of such a drafting arrangement are that the intermediate guide elements of - necessarily - small diameter cause excessive centrifugal forces at high belt speeds, and that the fiber sliver is still deflected on the last lower roller.

• daß alle Unterzylinder ortsfest auf dem Maschinenrahmen gelagert sind,
• daß auch der erste, die Vorverstreckzone begrenzende Druckzylinder in Laufrichtung des Faserbandes gesehen, auf einem Bogen um die Drehachse des entsprechenden Unterzylinders verschieb- und fixierbar angeordnet ist,
• daß die Unterzylinder derart angeordnet sind, daß das Faserband aus einer beim Einlauf des Streckwerkes im wesentlichen horizontalen Lage in eine beim Abgang vom ersten, die Hauptverstreckzone begrenzenden Unterzylinder im wesentlichen senkrechte Lage umgelenkt wird,
• daß der erste, die Hauptverstreckzone begrenzende Unterzylinder im Durchmesser derart gewählt ist, daß das darauf umgelenkte Faserband einen maximalen Radialbeschleunigungswert (r · ω²) von 400 m/s² aufweist,
• daß der Umschlingungswinkel des Faserbandes an den ersten, die Verstreckzonen begrenzenden Unterzylindern innerhalb der jeweiligen Verstreckzone maximal 45° beträgt,
• daß der Durchmesser des den zweiten die Hauptverstreckzone begrenzenden Unterzylinders im wesentlichen einem Drittel des Durchmessers des ersten Unterzylinders dieser Verstreckzone entspricht, und
• daß die zweiten, die Hauptverstreckzone begrenzenden Zylinder derart angeordnet sind, daß das Faserband darauf im wesentlichen keine Umlenkung erfährt.

To solve these disadvantages is the object of the invention. The invention, as characterized in the first claim, achieves the object in this way

• that all lower cylinders are fixed on the machine frame,
• that the first pressure cylinder, which delimits the pre-stretching zone, viewed in the running direction of the fiber sliver, is arranged so that it can be moved and fixed on an arc around the axis of rotation of the corresponding lower cylinder,
• that the lower cylinders are arranged in such a way that the fiber sliver is deflected from a position that is essentially horizontal when the drafting device is fed into a position that is essentially vertical when it leaves the first lower cylinder that delimits the main drawing zone,
• that the diameter of the first lower cylinder delimiting the main stretching zone is selected such that the fiber sliver deflected thereon has a maximum radial acceleration value (r · ω²) of 400 m / s²,
• that the wrap angle of the fiber sliver at the first sub-cylinders delimiting the stretching zones within the respective stretching zone is a maximum of 45 °,
• that the diameter of the second sub-cylinder delimiting the main drawing zone corresponds essentially to one third of the diameter of the first sub-cylinder of this drawing zone, and
• that the second cylinders, which delimit the main drawing zone, are arranged in such a way that the fiber sliver thereon undergoes essentially no deflection.

• a. durch die Umlenkung des Faserbandes im Streckprozess, trotz hoher Bandgeschwindig­keiten am Auslauf des Streckwerkes, die Radial­beschleunigungswerte an den Umlenkungen im Streckwerk in für das Faserband tragbaren Grössen bleiben,
• b. durch die Umlenkung im Streckprozess das im wesentlichen horizontal einlaufende Faserband nach dem Streckwerk ohne zusätzliche Umlenkung und mit kurzem Abstand in den Trichter, respektive in das nachfolgende eine Messgrösse abgebende Kalanderwalzenpaar geliefert werden kann, so dass ein optimal kurzes Stück fehlerhaftes Band zwischen dem letzten Zylinderpaar und den Kalanderwalzen weiter gefördert werden kann,
• c. durch die starre Anordnung der Unterzylinder eine von der Montage her bleibende präzise Ausrichtung der Lager gewährleistet ist, die einen positiven Beitrag an die Lebensdauer der Lager und eine Verkürzung der Einstelldauer zur Anpassung an andere Stapellängen erbringt,
• d. durch die Verschiebbarkeit der Druckzylinder um den genannten Bogen eine Anpassung des Streckwerkes an die Stapellänge des Faserbandes möglich ist, ohne Veränderung der Position der Unterzylinder,
• e. bei einer gleichbleibenden Kraftrichtung de Druckzylinder relativ zur Achse des entsprech­enden Unterzylinders die Kraftwirkung auf das Faserband konstant bleibt.

The advantages achieved by the invention are essentially that:

• a. due to the deflection of the fiber sliver in the drawing process, despite high belt speeds at the outlet of the drafting system, the radial acceleration values at the deflections in the drafting system remain in sizes that can be carried by the fiber sliver,
• b. due to the deflection in the drawing process, the essentially horizontally entering sliver after the drafting device without additional deflection and with a short distance into the hopper, or into the following one Calender roller pair delivering the measurement variable can be supplied so that an optimally short piece of defective belt can be conveyed between the last cylinder pair and the calender rollers,
• c. The rigid arrangement of the lower cylinders ensures that the bearings are precisely aligned from the assembly, which makes a positive contribution to the life of the bearings and shortens the adjustment time to adapt to other stack lengths.
• d. due to the displaceability of the printing cylinders around the aforementioned sheet, it is possible to adapt the drafting system to the stack length of the fiber sliver without changing the position of the lower cylinders,
• e. with a constant direction of force de pressure cylinder relative to the axis of the corresponding lower cylinder, the force effect on the sliver remains constant.

An advantageous embodiment of the drafting arrangement consists in the arrangement of the pressure cylinders on the pivotable arm. This means that even wide fiber slivers can be easily and safely inserted into the drafting system.

Another advantageous embodiment consists in that the displaceable printing cylinders can be adjusted by means of rastering to adapt to the stack length, and the extent of the displacement can be measured by means of a scale, so that they can be displaced quickly and precisely, which, despite the displaceability of the printing cylinders, ensures precise parallel guidance of the Pressure cylinder to the lower cylinders guaranteed.

Furthermore, the displacement of the second pressure cylinder delimiting the main stretching zone on an arc around the axis of rotation of the corresponding lower cylinder enables the sliver to be tangentially fed into this cylinder pair, regardless of whether a push rod with positive or negative deflection of the sliver is used.

The small diameter of the second lower cylinder delimiting the main drawing zone has the advantage that, despite the also advantageous large diameter of the previous lower cylinder, an optimally short clamping distance can be achieved.

Further advantageous configurations are contained in the other claims.

• Fig. 1 eine Seitenansicht des erfindungs­gemässen Streckwerkes in Betriebsposition, halb­schematisch dargestellt,
• Fig. 2 eine Frontansicht des Streckwerkes von Fig. 1 in Betriebsposition, halbschematisch dar­gestellt,
• Fig. 3 ein Detail des Streckwerkes von Fig. 1 von derselben Seite her gesehen, halbschematisch dargestellt,
• Fig. 4 das Detail von Fig. 3, teilweise im Schnitt gemäss Linie A-A, halbschematisch dargestellt,
• Fig. 5 & 6 je eine Variante des Streckwerkes von Fig. 1, je als Ausschnitt von Fig. 1, vergrössert dargestellt.

The invention is explained in more detail below on the basis of illustrated exemplary embodiments. It shows:

• 1 is a side view of the drafting system according to the invention in the operating position, shown semi-schematically,
• 2 is a front view of the drafting arrangement of FIG. 1 in the operating position, shown semi-schematically,
• 3 shows a detail of the drafting arrangement of FIG. 1 seen from the same side, shown semi-schematically,
• 4 shows the detail of FIG. 3, partly in section along line AA, shown semi-schematically,
• FIGS. 5 & 6 each show a variant of the drafting arrangement from FIG. 1, each as a detail from FIG. 1, shown enlarged.

A drafting system 1 comprises a machine frame 2, on which the arm parts 4 forming a double arm are pivotably mounted by means of a hinge pin 3.

The arm parts 4 each comprise an arch part 5 and an arch part 6 and an end part 7. A notch 8 is provided on the end part 7 for receiving a fixing bolt 9 each. The fixing bolt 9 is part of a pneumatic cylinder 10. The fixing bolt 9 is designed as a part matching the notch 8 and serves to fix the double arm in the working position shown in solid lines in FIGS. 1 and 2. The operating position of the double arm is shown in Fig. 1 with dash-dotted lines.

Lower cylinders 11, 12, 13 and 14 are rotatably mounted on machine frame 2 by means of axes 15, 16, 17 and 18. The lower cylinders 11, 12, 13 and 14 are individually driven (not shown).

The arcuate parts 5 each contain an arcuate guide slot 19 coaxial with the axis 15 and the arcuate portions 6 each have an arcuate guide slot 20 coaxial with the axis 17. The guide slots 19 serve to guide one pair of bearing blocks 21 and 22 (only part of the pair in FIG 2), while the guide slots 20 serve to guide a pair of bearing blocks 23. In the end part 7, a guide slot 60 coaxial with the axis 18 is provided for guiding a pair of bearing blocks 25.

A pair of bearing blocks 22 is arranged at the entrance of the drafting system and a pair of bearing blocks 24 at the transition from the arch part 5 to the arch part 6 on the double arm 4.

Seen in the running direction of the sliver 26 (indicated by the arrow in FIG. 1), the drafting system 1 comprises in the following sequence a pressure roller 27, rotatably mounted in the bearing block pair 22, a first pressure cylinder 28 delimiting the beginning of the pre-stretching zone, rotatably supported in the bearing block pair 21, one the end of the pre-stretching zone defining second pressure cylinder 29, rotatably supported in the pair of bearing blocks 24, a first pressure cylinder 30 delimiting the beginning of the main stretching zone, rotatably supported in the pair of bearing blocks 23 and a second pressure cylinder 31 delimiting the end of the main stretching zone, rotatably supported in the pair of bearing blocks 25.

The cylinders 11 and 28 form the first, viewed in the running direction of the sliver, the cylinders 12 and 29 the second, the pre-stretch zone delimiting sliver.

The cylinders 13 and 30 form the first, the cylinders 14 and 31 the second, the main stretching zone delimiting fiber sliver.

The bearing block pairs 24 and 22 are arranged in a fixed manner, while the bearing block pairs 21 and 23, respectively, the guide slots 19 and 20, respectively, are arranged so as to be movable and fixable again to adapt to the length of the sliver to be processed. In addition, this is Bearing block pair 25 arranged in the guide slot 60 so as to be movable and fixable again, in order to ensure the tangential entry of the sliver despite the changeable entry position of the sliver, caused by the displacement of the pressure cylinder 30.

In order to ensure the parallelism of the pressure cylinders 28 and 30, respectively, to the lower cylinders 11 and 13, viewed in the radial direction to the axes 15 and 17, on the one hand, raster teeth 32 and 32 are shown on the arc parts 5 and 6 (FIGS. 3 and 4). and a raster scale 33 corresponding to the number of teeth and, on the other hand, a raster device 34 which engages in the teeth 32 is provided on the bearing block pairs 21 and 23. This grid device 34 is assigned to each individual bearing block of the bearing block pairs 21 and 23. Such a bearing block comprises a bearing block lower part 35 with a guide opening 36 for receiving and guiding a shaft bearing 37 of a pressure cylinder shaft 38. Each pressure cylinder shaft 38 serves to receive the pressure roller 27 and the pressure cylinders 28, 29, 30 and 31.

The lower bearing block 35 is also designed as a cylinder, with a piston 39, an associated piston rod 40, a spring 41, a compressed air connection 42 and a ventilation opening 43.

A cylinder block upper part 44, which is fixedly connected to the bearing block lower part 35, serves as the end of the cylinder.

A guide pin 45 belonging to the grid device 34 is firmly screwed into the bearing block upper part 44 by means of thread 46 and serves to guide a grid part 47. A compression spring 48 clamped between the grid part 47 and a guide pin upper part 45.1 presses the grid part 47 against the bearing block upper part 44. The grid part 47 can be against the Force of the spring 48 can be lifted off the upper bearing block 44.

The raster teeth 32 provided on the arch parts 5 and 6 engage in the teeth 49 provided in the raster part 47 when the raster part 47 rests on the bearing block upper part 44.

Furthermore, two guide pins 50 are pressed into the bearing block upper part 44, which protrude into the guide slots 19 and 20, respectively, and which are selected in diameter in such a way that the individual bearing block 21, 23, 25 is guided precisely along the guide slot 19, 20, 60 results.

A fixing screw 51 with nut 52 fixes the individual bearing blocks on the arch parts 5 and 6, or respectively on the end part 7.

If the bearing block pairs 21 and / or 23 are now to be moved, the fixing screw 51 (FIGS. 3 and 4) is loosened, the raster part 47 is lifted along the guide bolt from the upper bearing block part 44 by manual force against the force of the spring 48, and the bearing block pair 21 is manually lifted and / or 23 on the arch part 5 or 6, guided along the guide slot 19 or 20. The degree of displacement can be read on the raster scale 33.

The bearing block pairs 24, 25 and 22 comprise the same elements as the described bearing block pairs 21 and 23 with the exception that the raster device 34 is omitted.

The bearing block pairs 24 and 22 are arranged in a fixed manner. The mobility of the bearing block pairs 25 will be described later.

Furthermore, the sliver 26 after the last sliver clamping point, given by the cylinders 14 and 31, is combined in a hopper 53 and passed on to a rotatably mounted pair of calender rolls 54 known per se. The pair of calender rolls 54 consists of a fixedly arranged calender roll 55 and a calender roll 56 arranged displaceably therefrom.

The funnel 53 is arranged such that it can be tilted in the direction of the arrow B and projects with the sliver outlet part 57 into the sliver feed gap (not shown) of the pair of calender rolls 54.

When the roller 56 is displaced away, the funnel 53 can be tilted in order to be able to comfortably guide the strip discharged from the last rollers 14 and 31 into the funnel.

The drafting device 1 can also be provided with a so-called push rod 58 (FIG. 5) which, provided in the main drawing zone, deflects the fiber sliver positively and in the process guides the fibers within the drawing zone as an aid. A positive deflection is to be understood as a deflection with a radius directed away from the machine frame 2. The push rod 58 is provided in the main stretching zone in such a way that when the clamping stretch of the main stretching zone is extended, given by the clamping points of the cylinder pairs consisting of the cylinders 13 and 30, or respectively 14 and 31, by pushing back the pressure cylinder 30 against that in FIG. 1 Position shown with dash-dotted line, the deflection around the push rod 58 is reduced. The reduction in the deflection ends when the distance connecting the push rod 58 and the clamping point between the cylinders 13 and 30 forms a tangent to the circumference of the cylinders 13 and 30. This first clamping distance is indicated in FIG. 5 by the arrow E, while the maximum clamping distance. of 85 mm is reached at the point indicated by the arrow F.

When the push rod 58 is used, the bearing block pair 25 is positioned or fixed in such a way that the sliver 26 is tangentially caught by the cylinders 14 and 31.

Furthermore, the drafting system 1 can be provided as a variant to the push rod 58 with a push rod 59 (FIG. 6) which deflects the fiber sliver negatively. With this solution, the deflection of the sliver given by the push rod remains constant. In order to allow the fiber sliver to be tangentially gripped by the cylinders 14 and 31 in this variant as well, the bearing block pair 25 is shifted into the position shown in FIG. 6. The upper guide pins 50 lie in this position (in the viewing direction according to FIG. 1 seen) of the bearing block pair 25 at the upper end (not visible) of a guide slot 60 provided in both end parts 7, while for the variant with the push rod 58 the lower guide pins 50 of the bearing block pair 28 rest against the lower end 61 (FIG. 6) of the guide slots 60 .

In this way, the same drafting system is suitable for the use of both push rod variants without changing a part.

A pneumatic cylinder 62, which is pivotally connected to the machine frame 2 and whose piston rod end part 63 is connected to the two arm parts by means of a rod 64, serves to lift the arm parts 4 into the operating position shown in dash-dotted lines in FIG. 1 and thus to introduce a sliver into the drafting system 4 is connected.

The fiber sliver is placed over the lower cylinders 11, 12, 13, 14 and the funnel 53 tilted in the direction B for introduction into the drafting system in the open position of the drafting system.

The drafting system is closed again by reversing the function of the cylinder 62 and locked again by reversing the function of the cylinder 10.

After start-up in slow speed, the drawn material is fed into the hopper 53 and into the pair of calender rolls 54. The stretch value can then be switched to production.

The term "short to long staple fibers" is intended to mean cotton and chemical fibers with a staple length of up to 80 mm.

For those lower cylinders that form the beginning of the pre-stretching zone or the main stretching zone, a diameter of 90 mm is selected, so that even when processing fibers with a stack length of 80 mm, a wrap angle of the sliver on the mentioned lower cylinder of experience can be guaranteed by a maximum of 45 degrees.

With wrap angles of more than 45 degrees, the rope friction between the fiber sliver and the lower cylinder becomes too great when the lower cylinders are corrugated.

The high belt speed mentioned at the beginning result in high centrifugal forces, i.e. high radial acceleration values.

For example, at a belt speed of 1000 m / min. at the outlet of the drafting system and a diameter of 90 mm for the first sub-cylinder 13 of the main drawing zone and a draft ratio for the drawing zone of 4: 1, a radial acceleration value on the first sub-cylinder 13 of a _r = r · ω² = 385 m / Sec², which corresponds to an approx. Corresponds to 38 times the acceleration due to gravity.

If you wanted to use a drafting system according to the prior art mentioned, which with 1000 m / min. Deflect the sliver emitted with a radial acceleration value of a _r = 385 m / Sec.², so a deflection radius would have to be of 720 mm can be selected, which would be unfavorable in terms of device.

In order to obtain an optimally short clamping distance for stretching fibers with short stack lengths, despite the advantageous large diameter of the first lower cylinder 13 of the main stretching zone, a diameter was chosen for the second lower cylinder 14 of the main stretching zone which was essentially one third of the diameter of the first lower cylinder mentioned 13 corresponds, for example of 28 mm.

By choosing a small diameter for this cylinder 14, the high belt speeds result in high speeds, which in turn results in high radial acceleration values. However, since the deflection of the sliver on this cylinder is zero or a few degrees of angle, and therefore no or a very small sliver mass has to be deflected, no or relatively small centrifugal forces (Z = m · r · ω²) arise for the self-contained sliver. The situation is different for detached individual fibers directed away from the cylinder 14 from the self-contained sliver. Such fibers are deflected until the deflected mass results in a centrifugal force that is greater than the adhesive forces between the fibers and the cylinder.

To counteract a possible electrostatic charging of the fibers, ionizers can be used in a manner known per se.

Claims (13)

1. Drafting mechanism for machines for a spinning mill, especially drawing frames, for processing a fiber sliver with a staple range of cotton and/or synthetic fibers in a break draft zone and in a main draft zone comprising bottom rollers (11, 12, 13, 14) mounted on a machine frame (2) and bounding drafting zones and, above the bottom rollers, pressure rollers (28, 29, 30, 31) associated with respective bottom rollers, the first pressure roller (30) bounding the main drafting zone being movably and fixedly arranged on an arc (20) about the axis (17) of the corresponding bottom roller (13), characterized in that

- all bottom rollers (11, 12, 13, 14) are journalled at fixed locations on the machine frame (2);

- in that the first pressure cylinder (28) bounding the break drafting zone, as viewed in the direction of travel of the fiber sliver (26), is also displaceably and fixedly arranged on a arc (19) around the axis of rotation (15) of the corresponding bottom roller 11 ;

- in that the bottom rollers are so arranged that the fiber sliver is diverted from a substantially horizontal disposition at the infeed into the drafting mechanism into a substantially vertical disposition at the exit from the first lower cylinder (13) bounding the main drafting zone;

- in that the diameter of the first bottom roller (13) bounding the main drafting zone is so chosen that the fiber sliver diverted thereon has been maximum radial acceleration value (r · ω²) of 400 m $$\frac{\text{m}}{\text{s²}}$$

;

- in that the wrap angle of the fiber sliver at the first bottom cylinders (11, 13) bounding the drafting zones amounts to a maximum of 45° within the respective drafting zone;

- in that the diameter of the second bottom cylinder (14) bounding the main drafting zone corresponds essentially to one third of the diameter of the first bottom cylinder (13) of this drafting zone; and

- in that the second cylinders (14, 31) bounding the main drafting zone are so arranged that the fiber band experiences substantially no deflection thereon.

2. Drafting mechanism according to claim 1, characterised in that the pressure rollers (28, 29, 30, 31) are movably and fixably arranged on a double arm (4) pivotably mounted on the machine frame (2).

3. Drafting mechanism according to claim 1 characterised in that the second pressure roller (31) defining the main drafting zone is also movably and fixably arranged on an arc (60) about the axis of rotation of the corresponding bottom roller (14) and the arc is a guide slot (60) in the double arm (4).

4. Drafting mechanism according to claim 1 characterised in that at the infeed of the fibre sliver into the drafting mechanism a pressure roller (27) is provided engaging the first bottom roller.

5. Drafting mechanism according to claim 1 characterised in that a press rod (58, 59) is provided in the main drafting zone in such manner that the fibre sliver (26) undergoes a diversion

6. Drafting mechanism according to claims 1 and 2 characterised in that the arcs provided on the double arm (4) are guide slots (19, 20, 60).

7. Drafting mechanism according to claims 1 to 6 characterised in that at least each pressure roller (28, 30) defining the start of the break and main drafting zones is movable on the double arm (4) by means of bearing members (21, 23) receiving the shafts (38) of the pressure rollers (28, 30), which bearing members are guided in the guide slots (19, 20).

8. Drafting mechanism according to claim 6 characterised in that the double arm (4) has retainer teeth (32) arranged concentrically to the guide slots to position those bearing members (21, 23) which receive the first pressure rollers (28, 30) defining the break and main drafting zones.

9. Drafting mechanism according to claim 8 characterised in that each bearing member (21, 23) is provided with a retaining device (34) engaging in the retainer teeth.

10. Drafting mechanism according to claim 9 characterised in that the retaining device (34) comprises a guide pin (45) screwed onto the upper portion (44) of a bearing element and a retaining portion (47) engaging in the retaining teeth and movably guided by this pin, together with a spring (48) so tensioned between the guide pin and the retaining portion that the retaining portion (47) engages in the retaining teeth (32) due to the force of the said spring.

11. Drafting mechanism according to claims 2 and 4 characterised in that bearing members (22) are provided on the double arm (4) to receive the pressure roller (27).

12. Drafting mechanism according to claim 5 characterised in that the press rod (58) is so arranged that, upon increase in the clamping distance of the main drafting zone by shifting back of the first pressure roller (30) defining the main drafting zone, the diversion around the press rod (58) decreases up to a first clamping distance (E) and then remains constant (Fig. 5) up to a maximum clamping distance (F) of 85 mm.

13. Drafting mechanism according to claim 5 characterised in that the press rod (59) is so arranged that, upon increase in the clamping distance of the main drafting zone through shifting back of the first pressure roller (30) defining the main drafting zone, the diversion around the press rod (59) remains constant (Fig. 6).

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