WO2009060298A2

WO2009060298A2 - Drafting unit

Info

Publication number: WO2009060298A2
Application number: PCT/IB2008/002986
Authority: WO
Inventors: Umberto Micheletti; Paolo Savio
Original assignee: Atex Spa; Convivium Gmbh
Priority date: 2007-11-09
Filing date: 2008-11-07
Publication date: 2009-05-14
Also published as: CN101910482A; CN101910482B; WO2009060298A3; ITUD20070213A1

Abstract

A drafting unit (10) for drafting discontinuous textile fibers comprises a first pair of feed rolls (12) that feed a sliver or strip (18) toward a second pair of drafting rolls (14) that draft the sliver or strip (18). The drafting unit also comprises a control device (11) to control the drafting disposed between the first pair of feed rolls (12) and the second pair of drafting rolls (14), which comprises a third pair of control rolls (20, 22), of which a first roll (20) on one side of the sliver or strip (18) and a second roll (22) on another side of the sliver or strip (18). The control rolls (20, 22) act on the sliver or strip (18) arriving from the first pair of feed rolls (12) in order to take it at a determinate speed of feed toward the second pair of drafting rolls (14).

Description

"DRAFTING UNIT"

* * * * *

FIELD OF THE INVENTION

The present invention concerns a drafting unit of the perfected type used in spinning discontinuous fibers, particularly linen, which allows an effective control of the fibers, particularly the short fibers.

BACKGROUND OF THE INVENTION

It is known that a process for spinning natural fibers provides to eliminate the impurities, to mix the components, to separate fibers by carding, to order the fibers by combing, to refine and regularize the structure by drafting, to consolidate the structure by inserting the twist and winding the yam formed on a suitable holder (spooling).

In particular, from a sliver of a determinate weight in grams a yarn is achieved by means of drafting, subsequent twisting and final spooling. Before drafting, the production of high quality counts, particularly linen, provides that the sliver, before being introduced into the drafting zone, is immersed in a tank filled with water (damp spinning). This operation facilitates the separation of the bundle of fibers, improving the running thereof and promoting the drafting action to which the sliver is subjected. In particular, the drafting operation progressively refines the combination of fibers, until the desired final count is achieved, using two pairs of rolls, feed rolls and drafting rolls, separated by a gap and rotating at different speeds.

The drafting is given by the ration between the speed of the drafting rolls and the speed of the feed rolls, where the speed of the former is always greater than the speed of the latter. In this way the count at exit is lower than the count at entry.

In a drafting zone defined by the gap between feed rolls and drafting rolls we have:

- fibers gripped by the feed rolls that advance at the speed imparted by the feed rolls;

- fibers gripped by the drafting rolls that advance at the speed imparted by the drafting rolls;

- fibers gripped both by the feed rolls and by the drafting rolls, which should break;

- floating fibers not gripped either by the feed rolls or by the drafting rolls.

In ideal conditions, every fiber with a tail that passes the gripping line of the feed rolls should move at the speed imparted by them until its head reaches the gripping line of the drafting rolls, in which case it will be subjected to an instantaneous acceleration to the speed imparted by the drafting rolls.

In practice, on the contrary, some of the floating fibers change speed before they reach the level of the drafting rolls, because they are dragged by those already gripped by the latter, and it is this premature and uncontrolled acceleration that constitutes a defective drafting, giving rise to a supplementary irregularity on the whole.

The pairs of feed rolls and drafting rolls are pressed against each other in order to effectively hold the respective gripped fibers.

Therefore, the movement of the floating fibers is regulated by the friction exerted in the points of contact between them and with the fibers gripped by feed rolls and drafting rolls. A floating fiber will remain under control for as long as it moves at the speed imparted by the feed rolls, that is, for as long as the static friction holding the fibers gripped by the feed rolls remains higher than the dynamic friction of the fibers gripped by the drafting rolls running along them. In order to achieve in practice a drafting that approaches ideal drafting conditions, that is, which delays as much as possible the acceleration of the floating fibers, it is possible to perform a free-zone drafting or a controlled-zone drafting.

Free-zone drafting, advantageously only for low drafting ratios due to the presence of the floating fibers, is based on the reduction of the gap between feed rolls and drafting rolls.

Controlled-zone drafting provides to improve the adherence of the fibers in the drafting zone, in particular near to the drafting rolls, where the fast fibers already gripped by the drafting rolls can make their action felt more. To this purpose, control devices are known, of the type with a zone of needles, used in the wool industry, and belt devices or curvilinear drafting zones used in the cotton industry. Drafting for discontinuous fibers, like that of better known preparation cycles, for cotton and wool, compared with them has three fundamental differences:

- large gap between entrance and exit of the feed rolls and drafting rolls, for considerable lengths of the fibers;

- the sliver between feed roll and drafting roll is traditionally controlled by belts or mobile gills, with a speed synchronous with that of the feed roll;

- in the case of linen fibers, the bundles of fibers, due to the effect of the mechanical actions of the gills and the grip of the rolls, tend to divide and shorten, with considerable modifications.

Therefore, the control of the fibers not only provides a complex system using belts or gills, but is not very effective, Indeed, it does not prevent a substantial number of short fibers, only partly controlled, from being disturbed in their regular movement toward the drafting rolls by the fibers that are accelerated due to the effect of the drafting itself.

Hence, in the field of discontinuous fibers, particularly that of linen, there is a great need for a better control of the fibers, particularly of short fibers, in the drafting zone, with respect to what is currently known.

On the other hand, the solutions used in the wool and cotton industries for controlling drafting cannot be used with appreciable results in the drafting of discontinuous fibers, due to the non-uniform length of the linen fibers, the high dispersion of the diameter and length of this latter type of fiber (in the case of linen, comprised between about 18 micron and 50 micron, whereas, for example, in the case of wool it is comprised between about 19 micron and 28 micron), the substantial variations in the average and long term of the count of the sliver entering and, last but not least, the presence of water on the sliver in damp spinning.

Purpose of the present invention is to achieve a drafting unit for drafting discontinuous fibers, in particular linen, which allows a suitable control of the fibers in the drafting zone, particularly of short fibers, which is easy to produce, use and maintain, and is limited in cost. The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.

SUMMARY OF THE INVENTION The present invention is set forth and characterized in the independent claims, while the dependent claims describe other characteristics of the invention or variants to the main inventive idea.

In accordance with the above purpose, a drafting unit for drafting discontinuous textile fibers, in particular linen, comprises a first pair of feed rolls able to feed a sliver or strip, formed by the textile fibers, at a determinate speed of feed, toward a second pair of drafting rolls able to draft the sliver or strip fed by the pair of feed rolls.

According to the invention, positioned between the first pair of feed rolls and the second pair of drafting rolls, a draft control device is provided, which comprises at least a third pair of rotary control rolls, of which a first roll is located on one side of the sliver or strip and is mounted on a frame, and a second roll is located on another side of the sliver or strip and is supported by support means connected to the frame. According to the invention, the control rolls act on the sliver or strip arriving from the first pair of feed rolls in order to take it to a determinate and controlled speed of feed toward the second pair of drafting rolls.

In a first form of embodiment of the invention, the two control rolls are disposed substantially longitudinal with respect to the axis of feed of the sliver, and are reciprocally disposed so as to create a deviation, of an adjustable quantity, along the axis of feed of the sliver.

In other words, the control rolls are disposed one with respect to the other with the respective circumferences slightly staggered and, in projection, at least slightly overlapping, so that a change of direction is imparted to the sliver passing through, with respect to the ideal line of feed defined by the line joining the gaps of the drafting rolls upstream and downstream.

By adjusting the entity of the change of direction, that is, by modifying the reciprocal position of the axes of the control rolls, the entity of the control action exerted on the sliver is consequently adjusted, and in particular in the bundle of fibers that make up the sliver, in the segment between the first and second pair of feed rolls and drafting rolls,

In another embodiment of the invention, the control rolls are disposed substantially aligned with each other on an axis substantially orthogonal, or at most inclined, with respect to the axis of feed of the sliver, and exert a pressure of adjustable entity on the sliver passing through.

In this embodiment, a preferential variant provides that an elastic means is provided mounted on the frame and in cooperation with the support means of the second roll so as to constrain the second roll elastically in order to regulate the pressure exerted by the pair of rolls on the sliver or strip.

The drafting unit according to the present invention allows a suitable control of the fibers in the drafting zone, particularly of short fibers, and is easy to produce, use and maintain, and is of limited cost. In fact, the adjustability of the deviation in the travel in one case, and the adjustability of the action of the elastic means in the other case, are relatively easy to actuate and allow an effective regulation of the control exerted on the fibers during drafting. This stabilizes the drafting forces that act on the fibers.

The present invention thus ensures an effective control of the fibers, since it considerably reduces, if not totally eliminates, the effect of the uncontrolled movement of the fibers which are still in the drafting zone but no longer subject to the control, or gripping, of the feed rolls.

With the present invention, the pressure exerted on the sliver or strip is high enough to ensure a total control of the constant and equal movement of all the fibers contained in the sliver or strip and not yet gripped by the drafting rolls.

The present invention increases the precision of control of discontinuous fibers, in particular linen, of any length and diameter, during the drafting step made on spinning machines for discontinuous fibers. In particular, the present invention is able to control much more precisely, compared with the state of the art, the bundle of fibers during the final stage of drafting, irrespective of their length and diameter.

The present invention allows to increase the drafting ratios with respect to the state of the art, thanks to the improved control of the short fibers and the irregularities in the sliver in general. Furthermore, the present invention allows to spin in the same spinning machine a wide range of discontinuous fibers, in particular with regard to their fineness and length, and also a reasonably extensive range of sliver or strip weights. The present invention produces yarns with superior properties of regularity, in both the short and long term.

The present invention reduces the formation of neps on the yam and the shagginess of the yarn, and moreover increases the quality, compactness and resistance thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other characteristics of the present invention will become apparent from the following description of a preferential form of embodiment, given as a non-restrictive example with reference to the attached drawings wherein: - fig. 1 is a schematic representation of a drafting unit according to the present invention associated with a spinning machine for discontinuous fibers;

- fig. 2 shows a first form of embodiment of the invention;

- fig. 2a shows an enlarged detail of fig. 2;

- fig. 3 is an enlarged detail, shown schematically, of the drafting unit in fig. I ; - fig. 4 is a front view of part of the drafting unit in fig. 2;

- fig. 5 is a lateral view of the part in fig. 4;

- fig. 6 is a plane view from above of the part in fig. 4.

DETAILED DESCRIPTION OF A PREFERENTIAL FORM OF

EMBODIMENT With reference to fig 1, a drafting unit 10 according to the present invention is mounted in a spinning machine 100 for linen. The drafting unit 10 receives a sliver or strip of linen 18 fed from a bobbin 16, after immersion in a tank 17 full of water (damp spinning) and passing through a sliver-guide.

The sliver 18 comprises discontinuous fibers of linen, long and short, with a varying count, varying diameter, comprised between about 18 micron and 50 micron, and also with a varying length, comprised between 20 mm and 100 mm.

By long fibers we mean fibers with a length comprised between 50 mm and 100 mm.

By short fibers we mean fibers with a length comprised between 20 mm and 50 mm.

The sliver 18, once subjected to drafting in the drafting unit 10, is sent, passing through a yarn-guide 19, to a spinning frame 21 where it continues in the preparation of the linen yarn. The sliver 18, at least inside the drafting unit 10, follows a determinate direction of feed S, substantially rectilinear (figs. 2a and 6),

The drafting unit 10 comprises, in a traditional manner, a pair of feed rolls 12 which receive the sliver 18 from the sliver-guide and grip it, which are counter- rotary clockwise and with a synchronous speed to impart a determinate speed of feed to the sliver 18.

Downstream of the pair of feed rolls 12, again in a traditional manner, a pair of drafting rolls 14 are provided, which receive the sliver 18 and grip it; they are counter-rotary clockwise and with a synchronous speed to impart a determinate drafting speed to the sliver 18, greater than the speed of feed. The ratio between drafting speed and speed of feed determines the drafting.

The distance or gap between the feed rolls 12 and the drafting rolls 14 is adjustable, by moving the feed rolls 12, for example by actuating the slider 35

(fig. 2), according to the significant parameters of the sliver 18, for example length and diameter. This allows the fibers to run correctly, which are gradually gripped by the drafting rolls 12.

Between the two pairs of rolls 12 and 14, the drafting unit 10 comprises a control device U , to control the drafting zone.

The control device 11 comprises two rotary rolls, a first roll 20 and a second roll 22, positioned as shown in figs. 2-6, so as to control the advance of the bundle of fibers that make up the sliver 18, imparting thereto a desired speed, so as to control the drafting thereof effectively .

The speed of rotation of the first roll 20 and the second roll 22 is equal to or greater, preferably slightly greater, than that of the feed rolls 12. According to one embodiment, the speed of rotation of the rolls 20, 22 is greater by about l%-30% than the speed of the feed rolls 12.

The first roll 20 is made to rotate by means of a wheel 30 that derives its rotation, possibly increasing the speed thereof, directly from the mechanism, not shown in the drawings, that makes the feed rolls 12 rotate. In particular, a train of gears is provided that transmit, precisely, the movement of a command gear mounted in the drafting zone of the spinning machine 100 to a primary gear, consisting of the wheel 30, keyed onto the inlet shaft of movement to the drafting unit 10. The whole may be commanded by an independent motor, or by a gear keyed onto a commanded shaft upstream of the spinning machine and suitably disposed so as to command the control device 11, or again by a gear keyed onto an already existing shaft, such as for example the shaft that feeds the sliver or the shaft of traditional drafting belts.

In the embodiment shown in figs. 2, 2a, the two rolls 20 and 22 are disposed substantially longitudinal with respect to the direction of feed of the sliver 18, and in particular are disposed one with respect to the other so as to create a slight deviation along the direction of feed defined by the line that joins the gaps between the feed rolls 12 and the drafting rolls 14.

As shown in the detail in fig. 2a, the first roll 20 defines a first gap, or deviation, with an adjustable entity "U", which determines a first slight change of direction of the sliver 18 with respect to the direction defined between the rolls 12 and 14, while the second roll 22 imparts a second gap or deviation with an adjustable entity ^ui2", which is normally the same value and the opposite direction to "il". It comes within the field of the invention that one or the other of the gaps "il" and "i2" can have a value of zero, so that only one of the two rolls 20 or 22 modifies the direction of feed of the sliver 18 in its travel between the feed rolls 12 and the drafting rolls 14. The possibility of regulating the position of one and/or the other of the rolls 20 and 22 with respect to the direction of feed of the sliver 18, thus modifying the entity of the gaps "il" or "i2", makes it possible to control the tension and speed of the fibers of the sliver 18 at entry to the drafting rolls 14, thus ensuring an optimum control of the fibers during the final stage of drafting, irrespective of their length and diameter.

The variant shown in figs. 3-6 concerns another form of embodiment in which the rolls 20 and 22 are disposed substantially orthogonal to the axis of feed of the sliver 18 in the segment comprised between the feed rolls 12 and the drafting rolls 14, and exert thereon a pressure of an adjustable entity. In the embodiment shown, the first roll 20 is mounted by means of a relative mandrel 23 on a fixed frame 24, with an axis of rotation X substantially orthogonal to the direction of feed S of the sliver 18. A return gear is provided, not shown in the drawings, that transfers the rotation motion from the first roll 20 to the second roll 22.

The second roll 22 is supported by one or two levers 26 with an axis of rotation X' substantially orthogonal to the direction of feed of the sliver 18 and parallel to the longitudinal axis X of the first roll 20. The second roll 22 is mounted by means of a relative mandrel 25 with a circular section housed with its ends in an oblong eyelet 27 made at the ends of the two levers 26, which extends along a transverse axis 2.

The levers 26 are connected to each other by a pin 28, which in turn allows the pivoting thereof, around an axis of rotation X" (fig. 5), to the fixed frame 24. For an effective control of the fibers of the sliver 18, the pair of rolls 20 and 22 are positioned at a distance as close as possible to the drafting rolls 14. This distance must be the shortest possible in order to ensure that the short fibers are also controlled.

In this way, when the long fibers of the sliver 18 are gripped by the drafting rolls 14 and are drafted, the short fibers, instead, are held by the rolls 20 and 22 and do not run with the long fibers. This ensures that all the fibers not yet gripped by the pair of drafting rolls 14 advance in a controlled and uniform manner, without preventing the fibers that have in fact been gripped from running. This prevents the premature advance of the fibers that are not yet gripped, obtaining the desired effect of controlling the draft, particularly on the short fibers.

Both in this solution and also in the one shown in figs. 2 and 2a, the shape of the rolls 20 and 22 is also defined as a function of the use in damp spinning, as in fig. 1, but also dry spinning, and with a wide range of twists and weights of the sliver and strip. The external surface of the rolls 20 and 22 can be grooved and knurled, or completely smooth, according to the drafting needs and the type of sliver to be drafted.

The material the rolls 20 and 22 are made of is preferably a hard material and with anti-adhesive and anti-static properties, which covers at least the external surface.

The sizes of the rolls 20 and 22 are about 10 mm in length and about 10 mm in diameter, understood as the external diameter of the gear that receives motion from the wheel 30. A contrasting bar 31 protrudes from the rear of the lever 26 that supports the roll 22.

A spring 32 is mounted under the contrasting bar 31, of the metal helical type, pre-loaded with a determinate elastic force. The contrasting bar 31 rests on said spring 32. The spring 32 normally thrusts the bar 31 in the direction indicated by the arrow F in fig. 4. The thrust on the bar 31 is translated into a rotary torque applied on the levers 26, in the direction indicated by the arrow G and with its fulcrum in correspondence with the axis X".

In this way, the levers 26 tend to keep the second roll 22 always in contact with the sliver 18, according to the elastic properties of the spring 32 and the elastic force exerted by it on the bar 31.

Therefore, the levers 26 and hence the roll 22 have the possibility of rotating or pivoting around the axis X" in a determinate angular range, if a force greater than the elastic force of the spring 32 acts on the roll 22. In this way, a variable but controlled pressure is exerted on the sliver 18 below.

Any lack of uniformity, or any variation in the count, diameter or volume of the sliver 18 translates into a discontinuity of motion, and therefore a force acting on the rolls 20 and 22, along the transverse axis Z as indicated by arrow P in fig. 4, which is thus damped and absorbed, thanks to the levers 26 and the elastic action of the spring 32, Therefore, the axis X' of the roll 22 tends to move slightly both by a first transverse component along the axis Z, and also by a second component, parallel to the axis of feed S of the sliver 18, thus determining a slight tendency to rotate of the roll 22, which allows the damping. It is clear that the roll 22 must in any case always stay gripping the sliver 18, to ensure the control of the fibers, however the elastic absorption allows this grip to be dynamically adaptable to the conditions of the sliver 18.

The use of the roll 22 damped by the spring 32 allows to modulate the gripping level effected by the rolls 20 and 22, and to regulate the pressure exerted on the sliver 18, to allow a controlled running of the gripped fibers. In particular, the roll 22 ensures an optimum and variable contact between fiber and fiber, which allows the free running of only the fibers already gripped and accelerated by the roll 22.

The elastic force with which the spring 32 is preloaded can be selectively regulated, advantageously variably and progressively, according to the properties of the sliver 18 subjected to drafting. To do this a regulation nut 33 is provided in a threaded seating 34 under the spring 32, able to thrust the latter upward.

The nut 33, according to how much it is screwed into/out of the relative threaded seating 34, determines a greater or lesser compression of the spring 32.

The use of the spring 32 as an elastic absorption element of the irregularities acting on the roll 22 must not be understood in a restrictive sense of the present invention. Indeed, instead of the spring 32 it is possible to use any other elastic element whatsoever, having predetermined elastic properties. For example as elastic element a gas spring can be used, a leaf spring device, a fluid-dynamic piston mechanism or other.

One form of embodiment of the present invention, instead of the spring 32, provides to use an element made of elastomer material, rubber or other, the elastic properties of which are known. A preferred elastomer material is expanded polyurethane with air, which gives long duration and reliable repeatability of the elastic properties.

The control device 11 is advantageously assembled in a box-like body 15, preferably made of hard and anti-static plastic material, suitable both for damp and dry spinning, easily mounted, stably, in the drafting zone, and also selectively removable for cleaning, maintenance, adjustment and replacement.

It is clear that modifications and/or additions of parts may be made to the drafting unit 10 as described heretofore, without departing from the field and scope of the present invention.

Claims

1. Drafting unit for drafting discontinuous textile fibers, in particular linen, comprising:

- a first pair of feed rolls (12) able to feed a sliver or strip (18), formed by the textile fibers, at a determinate speed of feed, toward a second pair of drafting rolls (14) able to draft the sliver or strip (18) fed by the pair of feed rolls (12), characterized in that it comprises a control device (1 1) to control the drafting disposed between the first pair of feed rolls (12) and the second pair of drafting rolls (14), said control device (11) comprising at least a third pair of rotary control rolls (20, 22), of which a first roll (20) on one side of the sliver or strip (18) and a second roll (22) on another side of the sliver or strip (18), said control rolls (20, 22) being able to act on the sliver or strip (18) arriving from the first pair of feed rolls (12) in order to take it at a determinate speed of feed toward the second pair of drafting rolls (14).

2. Drafting unit as in claim 1, characterized in that said two control rolls (20, 22) are disposed substantially longitudinal with respect to the axis of feed of the sliver (18), and are reciprocally disposed so as to create a deviation of adjustable entity along the axis of feed of the sliver (18).

3. Drafting unit as in claim 2, characterized in that said two control rolls (20, 22) are disposed one with respect to the other with the respective circumferences slightly staggered and, in projection, overlapping.

4. Drafting unit as in claim l _s characterized in that said two control rolls (20, 22) are disposed substantially orthogonal with respect to the axis of feed of the sliver (18), elastic means (32) being provided so as to elastically constrain the assembly position of the second roll (22) so as to regulate the pressure exerted by the pair of rolls (20, 22) on the sliver or strip (18).

5. Drafting unit as in claim 4, characterized in that the elastic means comprises a preloaded spring (32).

6. Drafting unit as in claim 5, characterized in that it comprises an adjustment element (33) to adjust the elastic force of the spring (32).

7. Drafting unit as in claim 4, characterized in that said elastic means comprises an element (32) made of elastomer material.

8. Drafting unit as in claim 7, characterized in that the elastomer material is based on expanded polyurethane with air.

9. Drafting unit as in any claim hereinbefore, characterized in that the support means of the second roll (22) comprises levers (26) connected by a pin (28) and pivoted, by means of the pin (28), to a supporting frame (24).

10. Drafting unit as in claim 9, characterized in that said levers (26) have oblong eyelets or holes (27) at the ends, the second roll (22) being mounted on the levers (26) by means of a mandrel (25) housed in said oblong eyelets or holes (27), so as to allow the movement thereof for a determinate vertical travel.

11. Drafting unit as in any claim hereinbefore, characterized in that the speed of feed determined by the third pair of control rolls (20, 22) is substantially equal to the speed of feed determined by the first pair of feed rolls (12).

12. Drafting unit as in any claim from 1 to 10, characterized in that the speed of feed determined by the third pair of control rolls (20, 22) is greater than the speed of feed determined by the first pair of feed rolls (12).

13. Drafting unit as in claim 12, characterized in that the speed of feed determined by the third pair of control rolls (20, 22) is substantially equal to the speed of feed determined by the second pair of drafting rolls (14).

14. Drafting unit as in claim 13, characterized in that the speed of the third pair of control rolls (20, 22) is greater by about l%-30% than the speed of the first pair of feed rolls (12).

15. Drafting unit as in any claim hereinbefore, characterized in that the diameter of each roll of the third pair of rolls (20, 22) is comprised between about 8 mm and 12 mm.

16. Drafting unit as in any claim hereinbefore, characterized in that the length of each roll of the third pair of rolls (20, 22) is comprised between about 8 mm and

12 mm.

17. Drafting unit as in any claim hereinbefore, characterized in that the surface of each roll of the third pair of rolls (20, 22) is knurled.

18. Drafting unit as in any claim hereinbefore, characterized in that the surface of each roll of the third pair of rolls (20, 22) has a central channel.

19. Drafting unit as in any claim hereinbefore, characterized in that the surface of each roll of the third pair of rolls (20, 22) is smooth.

20. Drafting unit as in any claim hereinbefore, characterized in that at least the surface of each roll of the third pair of rolls (20, 22) is made of a hard material, with anti-adhesive and anti-static properties.

21. Drafting unit as in any claim from 9 to 20, characterized in that the first control roll (20) mounted on the supporting frame (24) is fixed with respect to the sliver or strip (18) and the second roll (22), mounted on support means (26) connected to the frame (24), is mobile with respect to the first control roll (20), the elastic means (32) controlling the movement of the second roll (22) with respect to the sliver or strip (18).

22. Method for drafting discontinuous textile fibers, in particular linen, by means of a drafting unit (10) as in any claim hereinbefore, comprising:

- a first step of drafting a sliver or strip (18), formed by the textile fibers, by means of a first pair of feed rolls (12) able to feed a sliver or strip (18) at a determinate speed of feed, toward a second pair of drafting rolls (14) able to draft the sliver or strip (18) fed by the pair of feed rolls (12), characterized in that it also comprises

- a step of controlling the drafting by means of a control device (11) disposed between the first pair of feed rolls (12) and the second pair of drafting rolls (14), wherein the control step provides a second drafting step by means of at least a third pair of rotary control rolls (20, 22), of which a first roll (20) on one side of the sliver or strip (18) and a second roll (22) on another side of the sliver or strip (18), said control rolls (20, 22) acting on the sliver or strip (18) arriving from the first pair of feed rolls (12) in order to take it at a determinate speed of feed toward the second pair of drafting rolls (14).

23. Method as in claim 22, characterized in that it provides to use two control rolls (20, 22) disposed substantially longitudinal to the axis of feed of the sliver

(18), and disposed one with respect to the other so as to create a deviation of adjustable entity along the axis of feed of the sliver (18).

24. Method as in claim 22, characterized in that it provides to use two control rolls (20, 22) disposed substantially orthogonal to the direction of feed of the sliver ( 18), and wherein the pressure exerted by the pair of rolls (20, 22) on the sliver or strip (18) is adjusted during the second drafting step by elastically constraining the second roll (22) by means of elastic means (32) provided mounted on the frame (24) and cooperating with the support means (26) of the second roll (22).