Patent Description:
As known, slivers with fibre length typically of <NUM> or longer and above all with fibre distribution as homogeneous as possible are required in air spinning systems. These characteristics of the upstream sliver allow obtaining good technical characteristics of the yarn, while the presence of short fibres significantly worsens such characteristics.

The drawing systems used are normally formed by three or more pairs of drawing and pressure cylinders, each of which performs a partial and progressive drawing of the sliver. The last pair uses belt systems which ensures greater delicacy in fibre parallelization and drawing.

The output fibre flow continuity is a fundamental requirement.

The drawing systems used in air spinning devices are derived in toto from those traditionally used in ring spinning and suffer from the same shortcomings, i.e. poor parallelization efficiency at high working speed and limited maximum obtainable drawing.

Carding roller drawing systems, instead, are used in open-end spinning systems to convey the fibres from the inlet to the rotor using the mechanical action of the teeth to tear the fibres from the sliver and the centrifugal action due to the high rotation speed to remove impurities and short fibres from the flow of fibres which enters into the rotor. In these systems, the continuous flow of fibres is not a fundamental requirement and nor is the presence of short or broken fibres. However, the systems with carding roller are more compact than those with rollers and above all the parallelization function of the fibres, ensured by the action of the teeth of the carding roller, is extremely effective and is not affected in any manner by the working speed or the imparted drawing amount. A drawing device according to prior art is disclosed for example by <CIT>.

The need is therefore felt to solve the drawbacks and limitations mentioned above with reference to the prior art.

Such need is met by a drawing method with carding roller for air spinning according to claim <NUM>.

Further features and advantages of the present invention will be more comprehensible from the following description of preferred embodiments given by way of nonlimiting examples, in which:.

Elements or parts in common to the embodiments described below will be indicated using the same reference numerals.

With reference to the aforementioned figures, reference numeral <NUM> indicates a drawing device for slivers <NUM> of textile fibres as a whole.

In particular, the drawing device <NUM> comprises a feeder device <NUM> of a sliver <NUM> to be drawn, comprising a feeder roller <NUM>.

The feeder roller <NUM> is driven so as to rotate about a rotation pivot thereof.

According to a possible embodiment, the feeder device <NUM> further comprises a nozzle or a mouth <NUM> which conveys the sliver <NUM> to be drawn towards the successive drawing processes.

The nozzle or mouth <NUM> defines a passage channel <NUM> for the sliver <NUM> together with the feeder roller <NUM>.

The nozzle or mouth <NUM> is preferably pressed towards the feeder roller <NUM> so as to apply a pressure which is as a function of the input web thread count.

The feeder roller <NUM>, by virtue of its motorized rotation, sets in motion the sliver web- <NUM>, which is fed at an input speed Vi.

The drawing device <NUM> further comprises a carding roller <NUM> comprising, on its outer side wall <NUM>, a plurality of teeth <NUM> arranged at a constant tangential pitch P. The teeth <NUM> are shaped so as to draw the sliver <NUM>.

The feeder roller <NUM> rotates and directly faces the carding roller <NUM> so as to feed the web to the carding roller <NUM> at said input speed Vi.

Preferably, the tangential pitch P between the teeth <NUM> of the carding roller <NUM> is comprised between <NUM> and <NUM>.

As explained below, this pitch P is particularly wide compared with the pitches of the solutions of the prior art: this reduces the complexity and cost of the carding roller <NUM>.

Preferably, said teeth <NUM> have a substantially triangular shape which protrudes from the outer side wall <NUM> of the carding roller <NUM>, according to a first front portion <NUM>, which directly faces the sliver <NUM>, and a second rear portion <NUM> which forms a vertex <NUM> with the first front portion <NUM>.

Preferably, said vertex <NUM> has a radial height <NUM>, measured with respect to the outer side wall <NUM> along a radial direction R passing through a rotation axis C of the carding roller <NUM>, comprised between <NUM> and <NUM>.

According to an embodiment, the first front portion <NUM> identifies a first angle β comprised between <NUM> and <NUM> degrees with radial direction R, passing through a rotation axis C of the carding roller <NUM>.

According to an embodiment, the second rear portion <NUM> identifies a second angle α comprised between <NUM> and <NUM> degrees with tangential direction T perpendicular to a radial direction R passing through the rotation axis C of the carding roller <NUM>.

The sliver <NUM> is fed by the feeder device <NUM>, at the input speed Vi according to a direction of advancement F agreeing with a direction of rotation S of the carding roller <NUM>.

In this manner, the teeth of the carding roller <NUM>, during rotation, cling to the sliver web- <NUM> and draw it according to its direction of advancement F.

This operating condition is opposite to the known solutions in which the teeth oppose the direction of advancement of the web.

Advantageously, the carding roller <NUM> is driven in rotation so as to have a peripheral speed or extraction speed Ve on the teeth <NUM> equal to the product of the input speed Vi times the total drawing St of the sliver <NUM>, so that the drawing of the sliver web- <NUM> takes place entirely on the carding roller <NUM>.

Therefore, the Ve value must remain about <NUM>% of the product of the input speed Vi times the total drawing St.

Preferably, the Ve value must remain about <NUM>% of the product of the input speed Vi times the total drawing St.

Even more preferably, the Ve value must remain about <NUM>% of the product of the input speed Vi times the total drawing St.

Total drawing St means the ratio between the count of the yarn to be produced and the input sliver count.

The drawing device <NUM> further comprises an extraction cylinder <NUM> placed downstream of the carding roller <NUM> and of the sliver <NUM>.

In other words, the carding roller <NUM> receives the sliver <NUM> from the feeder device <NUM> and, by rotating in the same direction as the direction of advancement F of the sliver <NUM>, pulls and draws the sliver <NUM> towards the extraction cylinder <NUM>, arranged downstream of the carding roller <NUM> and of the sliver <NUM> with respect to said direction of advancement F of the sliver <NUM>.

It is worth noting that the carding roller <NUM> and the extraction cylinder <NUM> rotate in mutually opposite directions of rotation S,G. In particular, the extraction cylinder <NUM> rotates in a counter-rotating direction G with respect to the direction of rotation S of the carding roller <NUM>.

The successive removal of the fibres of the sliver <NUM> is facilitated and improved by virtue of the counterpoised rotations of the carding roller <NUM> and of the extraction cylinder <NUM>.

For this purpose, the extraction cylinder <NUM> has a specific shape.

In particular, the extraction cylinder <NUM> defines an inner cavity <NUM> and has a perforated side wall <NUM>, provided with a plurality of holes <NUM> communicating with the inner cavity <NUM>, adapted to create a suction flow in order to facilitate the detachment of the fibres from the carding roller <NUM>. In particular, the inner cavity <NUM> is connected to a vacuum source so as to create a suction flow through said holes <NUM> which facilitates the removal of the fibres from the carding roller <NUM>.

It is apparent that the opposite rotation between carding roller <NUM> and extraction roller <NUM> further facilitates such detachment of the fibres of the sliver <NUM> from the carding roller <NUM>.

For this purpose, said holes <NUM> are circular holes having a diameter comprised between <NUM> and <NUM>.

According to an embodiment, said holes <NUM> are arranged according to a matrix diagram along a pair of directions perpendicular to each other, and are spaced apart according to a first and a second pitch L1, L2.

Preferably, said first and second pitches L1, L2 are comprised between <NUM> and <NUM>.

Preferably, said first and second pitches L1, L2 are equal to each other.

According to a possible embodiment, one of said directions of the matrix diagram is parallel to a rotation axis W of the extraction cylinder <NUM>.

Obviously, the rotation axes W, C of the extraction cylinder <NUM> and the carding machine <NUM> are respectively parallel to each other.

Generally, the perforated side wall <NUM> of the extraction cylinder <NUM> has holes <NUM> arranged along an extraction band <NUM> having an axial thickness H, parallel to the rotation axis W of the extraction cylinder <NUM>, comprised between <NUM> and <NUM>.

In relation to the relative arrangement of carding roller <NUM> and extraction cylinder <NUM>, preferably with respect to a direction Q joining the rotation axes C, W of the carding machine <NUM> and of the extraction cylinder <NUM>, the vertices <NUM> of the teeth <NUM> and the side wall <NUM> of the extraction cylinder <NUM> are distant by a pitch <NUM> comprised between <NUM> and <NUM>.

A conveying device <NUM> is arranged downstream of the extraction cylinder <NUM> equipped with an output roller <NUM> which turns in idle manner and facilitates the extraction of the yarn from the extraction cylinder <NUM>.

A spinning apparatus for the successive operations to be performed on the yarn may be advantageously arranged downstream of the drawing device <NUM>.

The operation of the drawing device according to the invention will now be described.

In particular, as mentioned, the feeder device sends the sliver <NUM> at an advancement speed Vin through the nozzle or mouth <NUM>. The advancement speed Vin of the sliver web- <NUM> also corresponds to the tangential rotation speed of the feeder roller <NUM> at its point of contact with the sliver itself.

So, the carding roller <NUM> is driven in rotation, according to a direction of rotation S, in a direction agreeing with the direction of advancement F of the sliver <NUM>.

The difference in speed between the tangential or extraction speed Ve of the teeth <NUM> of the carding roller <NUM> and the advancement speed Vi of the sliver <NUM> determines the total drawing St of the sliver <NUM>.

Moreover, the sliver <NUM> is then passed from the carding roller <NUM> to the extraction cylinder <NUM> which, as seen, rotates in direction of rotation G opposite to the direction of rotation S of the carding roller <NUM>.

The perforated extraction cylinder <NUM>, which delimits the inner cavity <NUM>, has a perforated side wall <NUM>, provided with a plurality of holes <NUM> communicating with said inner cavity <NUM> and with a vacuum source.

The removal of the fibres of the sliver <NUM> from the carding roller <NUM> is facilitated by virtue of the vacuum and also by the opposite rotation of the extraction cylinder <NUM> according to a direction of rotation W opposite to the direction of rotation S of the carding roller <NUM>.

The rotation speed of the extraction cylinder <NUM> is such that the tangential speed on the side wall <NUM> is approximately equal to the tangential speed of the teeth <NUM> of the carding roller <NUM>.

The fibres of the sliver <NUM> is then conveyed from the inner cavity <NUM> output from the extraction cylinder <NUM>, towards the conveying device <NUM> and the output roller <NUM>.

As can be appreciated from the description above, the present invention allows overcoming the drawbacks presented in the prior art.

The use of the carding roller in the conditions and manner described in the present patent ensures a "soft" manipulation of the fibres, minimizing the possibility of breakage thereof and ensuring the continuity of the fibres at the input of the subsequent spinning units.

This condition of continuity and the reduced presence of short fibres can be obtained by virtue of the operating condition of the present invention according to which the carding roller works at a linear speed equal to the product of the sliver input speed times the total drawing of the sliver ± <NUM>%.

As long as the linear speed value is within <NUM>% of such a value, yarn continuity is obtained, with fibres of longer length and with a minimum risk of breakage thereof.

Advantageously, the present invention allows obtaining a high-quality yarn, according to the desired count because fibre continuity is always ensured. In other words, although the drawing is obtained in a single step on the carding roller, the fibres are drawn rapidly but progressively and above all continuously. The result is a homogeneous and uniform yarn free of broken fibres and/or short length.

Advantageously, the solution of the present invention envisages that the carding roller rotates according to a direction of rotation agreeing with the direction of rotation of the sliver of fibres: in this manner, it is possible to significantly increase the working speed and drawing amount compared to the solutions of the prior art, without incurring the risk of damaging the fibres.

Advantageously, the fibres of the sliver are drawn practically entirely on the carding roller, which for this purpose is provided with teeth which are not very dense compared to prior art solutions.

This reduces the production costs of the carding roller itself. Furthermore, the fibres are less stressed and can be drawn in a more progressive manner than in the solutions of the prior art.

This therefore strongly limits the risk of obtaining broken and thus "short" fibres due to the excessively abrupt mechanical action of the teeth of the carding roller.

Moreover, by virtue of the fact that the entire drawing action is performed by the carding roller, it is possible to reduce the overall dimensions and the overall costs of the drawing device.

Claim 1:
Method of drawing a textile fibre sliver web- comprising the steps of:
- providing a feeder device (<NUM>) of a sliver (<NUM>) to be drawn,
- providing a carding roller (<NUM>) comprising, on an outer side wall thereof (<NUM>), a plurality of teeth (<NUM>) arranged at a constant tangential pitch (P), suitable for drawing said sliver (<NUM>),
- preparing an extraction cylinder (<NUM>) placed downstream of the carding roller (<NUM>) and of the sliver (<NUM>),
- providing the feeder device (<NUM>) with a feed roller (<NUM>), facing the carding roller (<NUM>), which rotates so as to feed the sliver to the carding roller (<NUM>) at an input speed and according to a direction of advancement (F) concordant with respect to said rotation direction (S) of the carding roller (<NUM>),
the method being characterized by:
- driving the carding roller (<NUM>) in rotation so as tc have a peripheral speed on the teeth or extraction speed equal to the product of the input speed for the total drawing of the sliver ± <NUM>%, so that all the drawing of the sliver takes place on the carding roller,
- the total drawing being the ratio between the count of the yarn to be produced and the count of the sliver in input.