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The present invention concerns a device to control the yarn at the outlet of yarn feeders, particularly an "antiballoon" device apt to contain the weft yarn at the outlet of weft yarn feeders for looms.

More specifically, the invention arose from the need to set up an antiballoon device to be applied at the outlet of measuring weft feeders for fluid jet looms, particularly air looms, so as to stop the forming of balloons - which are quite frequent and create serious inconveniences - as a result of the yarn being unwound in defile from such feeders.

There is known to be an increasingly widespread use of fluid jet looms, particularly air looms, for weaving a constantly rising number of different articles; it is also known that such looms work at increasingly higher speeds.

The higher working speeds determine an increase in the speed of weft yarn insertion and, consequently, a higher yarn unwinding speed from the winding unit of the measuring weft feeder. The weft yarn is wound on said winding unit into successive turns, so as to form a yarn reserve, and is subsequently unwound therefrom in defile, which often gives rise - due to the high unwinding speed - to the forming of balloons.

The negative consequences of the forming of balloons are substan¬ tially the following:

- the unwinding weft yarn could rub against parts of the measuring weft feeder which should not be touched in normal unwinding conditions, with possibility for the yarn to get caught in such parts; and

- there could be an increase in the tension of the yarn being unwound, determined by the centrifugal forces acting on said yarn.

In practice, this determines irregular conditions in the weft yarn which do not allow it to regularly reach the side of the fabric being woven opposite to that of weft insertion.

Such irregular conditions can substantially occur in two ways:

- times taken for the weft yarn to reach the other side of the fabric.

which are not constant in respect of the weft insertion cycle; and - non perfect settlement of the weft yarn inserted in the loom shed.

To overcome these drawbacks - which become more and more evident the higher the loom speed and the smaller the yarn count, due to increase in the centrifugal force action - it is known to use antiballoon devices consisting of hollow elements having an approximately frustoconical shape which, positioned downstream of the measuring weft feeder, perform the function of containing and controlling the balloon formed by the unwind¬ ing weft yarn.

Figure 1 of the accompanying drawings shows an antiballoon device 1 according to known technique, applied just downstream of the measuring weft feeder 2: the weft yarn T - after having been drawn from the spool or reel R, and wound by the winding arm 4 onto the winding unit 3 of the feeder 2 - is unwound from said unit 3 thanks to the main nozzle 5 mount¬ ed on the loom being fed by said feeder 2.

The antiballoon device 1 is fixed to the upper part of the measu¬ ring weft feeder 2 by way of a support bracket 6, which may eventually allow its adjustment in an axial sense so as to suitably vary the dis¬ tance of the device 1 from the winding unit 3-

Nevertheless, the presence of the device 7 to stop the yarn T - which must forcedly be positioned close to the area of yarn outlet from the winding unit 3 - makes it impossible to totally envelop said winding unit 3, whereby there is still the possibility of a "residual" balloon (indicated by B in fig. l) being formed.

The inner surface of the antiballoon device 1 is moreover apt to create friction forces by rubbing of the weft yarn, hence increasing the tension of the yarn T at its outlet from the device 1 , which may cause delays in the times taken for the weft yarn to reach the other side of the fabric being woven, or increases in the feeding pressure of the loom nozzle 5 to make up for the increased yarn resistance to unwinding and thus obtain correct times of weft yarn arrival at the other side of the fabric.

To overcome these drawbacks there are already known to be special configurations of the antiballoon device which tend to reduce friction between the yarn and the wall of said device. By way of example, the following configurations of the antiballoon device are illustrated with reference to figures 2 to of the accompanying drawings:

- Fig. 2 shows the device in the form of a frustoconical element with double taper:

- Fig. 3 shows the device approximately in the form of a semiellipsoidal element;

- Fig. 4 shows the device in the form of a frustoconical element, with its inner wall provided with projecting parts, generally of a more or less hemispherical shape and variably arranged over the whole, or over part of the surface of said wall.

This last known configuration of the antiballoon device is more appreciated, in that the projections arranged in the intrados of the frustoconical element tend to reduce the surface of contact with the weft yarn, correspondingly limiting the friction forces involved.

It has now been found that the forming of a residual balloon can be almost entirely prevented - simultaneously reducing to a minimum the friction forces acting on the weft yarn - by adopting an antiballoon device of the last mentioned type, wherein the parts projecting from the intrados have a special and original configuration.

Said device forms the object of the present invention and consists of an element having a frustoconical surface, characterized in that a plurality of ribs project from its inner wall and substantially extend along the generatrices of its surface.

Preferably, said ribs are distributed in a uniform manner, or in sets, over the directrices of said surface, extending through at least half of the length of the generatrices of said surface.

The invention will now be described in further detail, by mere way of non-limiting example, with reference to two preferred embodiments thereof, illustrated on the accompanying drawings, in which:

Fig. '1 —is a diagrammatic view of a yarn feeder equipped with an antiballoon device according to known technique:

Figs. 2, 3 and 4 are external views of some known embodiments of antiballoon devices;

Fig. 5 is an external view of a preferred embodiment of the anti¬ balloon device according to the present invention;

Fig. 6 is a part section view of the same device, along the line V -VI of fig. 5; and

Fig. 7 is an external view of another embodiment of the antiballoon device according to the present invention.

With reference to figs. 5 and 6 of the accompanying drawings, the antiballoon device according to the present invention consists of an element 10 having a frustoconical surface, onto the intrados of which there are formed a plurality of ribs 11 extending along generatrices of said surface, the ribs being distributed in a uniform manner over the directrices of said surface.

The ribs 11 extend over a considerable length of said frustoconical element 10 and are apt to project to a constant extent (as shown), or to a variable extent, from the intrados of said element 10; also their sec¬ tion can be either constant or variable. Furthermore, the ribs 11 can extend exactly along the generatrices of the frustoconical surface of said element 10 - as shown - or else they can be slightly inclined in respect of said generatrices.

The extension of the ribs 11 along the generatrices of the frusto¬ conical surface of the element 10 defines, inside said element, an ideal low friction surface. In fact, thanks to such ribs, the weft yarn is pre¬ vented from contacting a wide surface of the element 10. At the same time, the forces generating through contact of the weft yarn with the ribs 11 - having the aforespecified configuration - provide the advantage of drastically reducing the formation of a "residual" balloon between the winding unit of the weft feeder and the inlet to the antiballoon device. The positive results obtained - as far as low tension of the weft

yarn being unwound and. thus, possibility to insert the weft yarn into the loom shed in short times and with low levels of fluid pressure feed¬ ing the loom nozzles - undoubtedly lead to a greater economy in loom operation and guarantee a constant quality of the fabric.

Tests have proved that the use of an antiballoon device as that described heretofore allows, compared to conventional devices, to reduce the weft insertion times by about i . when using cotton with a Ne 20 count, and up to about 10%, when using thicker cotton with a Ne 5 count.

Fig. 7 shows an alternative embodiment of the antiballoon device according to the invention. As seen, said device consists of an element 12 formed by associating two frustoconical surfaces 13 and 14. of diffe¬ rent taper, through an intermediate radiusing surface 15- Ribs 16 and 17. formed on the intrados of each of the surfaces 13 and 14. extend along the generatrices of said surfaces, while the radiusing surface 15 is smooth and comprises no ribs or projections.

Many other embodiments of the invention are of course possible, or variants could be introduced in the ones already described. For instance, as mentioned, the ribs - which, in the described embodiments are shown with a constant section, uniformly projecting from the intrados of the element forming the device and extending exactly along the generatrices of its surface - could instead be slightly inclined in respect of said generatrices, could project from said surface to a variable extent over their length, and could even vary in section or shape. Likewise, instead of one or more sets of ribs evenly distributed over the directrices of the surface of said element - as in the described embodiments - groups of ribs could be unevenly distributed over the directrices of said surface.

Furthermore, instead of a single homogeneous set of ribs 11 - as in the embodiment of fig. 5 - or of two distinct homogeneous sets of ribs 16 and 17 - as in the embodiment of fig. 7 - the device could comprise more sets of ribs, equal or different, possibly penetrating into each other.

It is understood that all these variants falL within the protection scope of the present invention.

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