YARN TENSIONING DEVICE IN THE FORM OF ROTARY DISCS

Abstract: A disc-type yarn tensioner consisting of one or more tensioning elements (2, 3) in series, each composed of a pair of idly-rotating mutually facing discs (4, 6) of which the first disc (4) is able to undergo only rotary movement whereas the second disc (6) is able to rotate, translate axially, and incline its axis of rotation by the effect of the engagement between a rotating cylindrical cavity and a fixed spherical surface (10).

Description: This invention relates to a yarn tensioning device which enables a constant regulated tension to be provided to a crude yarn during yarn production and finishing operations. This device is of particular importance in spooling because correct yarn tension regulation is essential for the proper outcome of this operation. In this respect, it should be noted that a crude semiprocessed yarn which is fed to a spooling operation still comprises considerable irregularities, which have to be at least substantially reduced during this stage. Tensioning devices are known in the form of a pair of discs pressed against each other, between which the yarn is passed. The pressure between the discs is adjustable by lever mechanisms, by gravity, by weights or by pneumatic pistons. In other more basic types, one of the discs is in the form of a non-rotating block. In a very common version, these devices are motorised by driving one of the two discs, the other being entrained by friction. The yarn passes substantially at the centre of the discs, and the tension is provided by the effect of the pressure, ie of the friction between the yarn and discs. The tensioning action is adjustable both by adjusting the pressure between the discs and by adjusting the speed at which the motor rotates the drive disc. However, this known device has considerable drawbacks because the tension is conferred in only one portion of the yarn, and thus in the case of hairy or powdery filaments the yarn deteriorates. So-called peeling occurs, and build-ups of fluff or accumulated dust become concentrated and entrained. In this case, the tensioning device itself creates or emphasises the irregularities, which instead should be reduced during spooling. In a more recent device, these drawbacks are reduced by disposing two pairs of mutually facing idle discs in sequence, these being rotated by the yarn itself which no longer slides at the centre of the discs but on a rotating pin of small diameter, so that the friction forces between the yarn and discs generate a tangential force which rotates the discs. By dividing the tensioning action into two positions, the tension can be applied progressively to the yarn rather than being concentrated in a single portion, thus reducing the tendency for peeling and for the formation of groups or build-ups. Only one of these idle discs is free to move axially and the pressure necessary for tensioning the yarn is applied to it, this normally being sufficient for the discs to be conveniently rotated by the yarn. The yarn tension is related to the resistance which the discs oppose to entrainment. When a concentrated irregularity in the yarn arrives, the axially mobile disc adapts to it by withdrawing axially. Contact between the yarn and discs is then limited to only that portion corresponding to the irregularity, and the tensioning action is correspondingly limited. The result is that at a concentrated irregularity in the yarn, the tension transmitted to the yarn tends to decrease. From FR-A-1 586 649 there is known a yarn tensioning device comprising two idly rotatable, mutually facing coaxial discs pressed against each other and entrained to rotate about a fixed pin by the movement of the yarn advancing therebetween, wherein the lower disc rests with its hub on a fixed flat surface and therefore rotates in a fixed rotation plane, and the upper disc, which is engaged by a bellows, encircles the fixed pin with considerable play, so that this latter disc besides being axially displaceable along the rotation axis defined by the pin, is also slightly tiltable with respect thereto. This construction allows in principle to maintain the engagement between the discs and the yarn also at the side opposite the one where an irregularity of the yarn causes the upper disc to displace under the action of the irregularity. However, at the high linear processing speeds of the yarn employed today, the tiltable disc, owing to its possibility of carrying out movements allowed by the play existing between the disc itself and the pin about which it rotates, tends to unacceptably vibrate, so that the proper tensioning effect on the yarn gets lost and only an unsatisfactory irregular tensioning action may be achieved. The purpose of the present invention is to provide a yarn tensioning device which enables the position of the pairs of discs to be adapted to the yarn irregularities while keeping them always in mutual engagement, i.e. while maintaining the tensioning action even in correspondence with such irregularities. This purpose is achieved by a device according to claim 1. The invention is described hereinafter with reference to Figures 1 and 2 which show a typical embodiment of the tensioning device of the invention comprising two consecutive tensioning elements 2, 3 each consisting of pair of idly rotatable, mutually facing coaxial discs 4, 6 pressed against each other. The invention can be implemented with one or more tensioning elements in series according to the required graduality of tensioning to be conferred to the yarn. The yarn 1 to be tensioned moves from right to left, encountering firstly the tensioning element 2 and then the tensioning element 3, these being identical. Each tensioning element has an idle upper disc 4 supported by an outer fixed ring 5 which allows it to rotate about a fixed rotation axis in a fixed rotation plane, i.e. not to undergo axial movement. Each tensioning element also has a lower disc 6 which is of more complicated construction and is axially displaceable along said fixed rotation axis and slightly tiltable with respect thereto. The terms "upper" and "lower" relate to the position shown in Figure 2. In actual fact, these discs are generally disposed vertically, with their axis of rotation horizontal. The disc 6 consists of a circular rotary ring 7 shaped with rounded edges consistent with the disc 4 with which it is in contact, at the centre of said ring 7 there being positioned a hollow cylindrical axial pin 8 which rotates rigidly with the disc 6. In the cylindrical cavity of the pin 8 there is disposed a fixed pin 9 - of transverse dimensions substantially less than those of the cavity of the rotary pin 8 - having a substantially spherical terminal end 10 of a size equal to the inner size of the coaxial cylindrical cavity of the rotary pin 8, so that the pin 8 slidably and rotatably engages the fixed surface defined by said end 10. The ring 7 is supported by a pad 11 of deformable material, for example felt, which connects it to a support cap 12 which in its lower part carries an element comprising an axial cylindrical cavity in which a support pin in the form of a piston 13 is disposed and slides in the direction of the arrow A within a cavity 14 kept under controlled pressure by feeding air at moderate pressure through a pipe 15. It is apparent that the compression force between the upper disc 4 and lower disc 6 can be adjusted by adjusting the pressure of the air fed through the pipe 15. The operation of the tensioning device according to the invention when a yarn irregularity reaches the tensioning device is described hereinafter. The yarn slides from right to left at high speed, being deviated in its path through a certain angle α on entering the tensioning element 2 and α′ on leaving the tensioning element 3. These angles must be of positive value in order to ensure that the yarn remains continually in contact with the rotary pins 8 of each tensioning element 2, 3. The length of the portion of yarn in contact with the pins 8 can be varied by varying the angles α and α′. The yarn advancing between the discs 4 and 6 entrains by friction the idle discs 4 and 6 to rotate, the entrainment force extered on the tensioning element corresponding to the tension transmitted to the yarn. The entrainment action can be increased or decreased by varying the compression force between the discs, ie by varying the pressure in the pipe 15. If for example a yarn irregularity indicated with obvious exaggeration by 16 - should reach the tensioning element disposed on the left and indicated by 3, the circular ring 7 tilts in accordance with the arrow B, firstly in a clockwise direction as the irregulariy traverses its right hand inlet edge and then in the opposite direction as the irregulariy traverses its left hand outlet edge. The opposite edge remains in any event engaged with the yarn as the tilting movement is both guided by the engagement between the substantially spherical surface of the terminal end 10 and the cylindrical cavity of the pin 8, and compensated by the deformable pad 11 and the travel of the piston support 13. It will be noted that even during passage of the yarn irregularity, the tensioning element remains engged and is entrained by the movement of the yarn, to thus transmit tension to the yarn continuously and reliably. In a modfied embodiment, the deformable element 11 which enables the effects of the concentrated yarn irregularities to be compensated and damped can be inserted into the first disc assembly, for example into the support for the fixed ring 5, instead of in the second disc assembly which is shown in Figure 2 in the lower position. In further modified embodiments, the compression between the two discs can be provided by springs or counterweights connected to suitable lever mechanisms.

Claims: A yarn tensioning device for production and finishing operations on crude yarn, and in particular for spooling, comprising one or more tensioning elements (2,3) each composed of a pair of idly rotatable, mutually facing coaxial discs (4,6) pressed against each other and entrained to rotate by the movement of the yarn (1) advancing therebetween, the first disc (4) having a fixed rotation axis and fixed rotation plane and the second disc (6) being arranged axially displaceable along said rotation axis and slightly tiltable with respect thereto, characterised in that the second disc (6) has a hollow cylindrical axial pin (8) rigid therewith and slidably and rotatably engaging a substantially spherical fixed surface (end 10) located inside the pin (8) and having a size equal to the inner size of the pin (8). A yarn tensioning device as claimed in claim 1, characterised in that the first disc (4) is rotatably supported by an outer fixed ring (5) and the second disc (6) comprises a circular ring (7) having rounded edges, and in that in the cylindrical cavity of said hollow cylindrical axial pin (8) there is arranged a fixed pin (9) having transverse dimensions substantially less than the inner transverse dimensions of said cavity and a terminal end (10) of substantially spherical shape defining said fixed surface. A yarn tensioning device as claimed in claim 1, characterised in that the second disc (6) is supported by a support cap (12) pressed toward the first disc (4). A yarn tensioning device as claimed in claims 2 and 3, characterised in that a deformable pad (11) is inserted between the circular ring (7) of the second disc (6) and the support cap (12). A yarn tensioning device as claimed in claims 3 or 4, characterised in that the support cap (12) is carried by a fluid-operated piston (13).

Inventors: BADIALI, ROBERTO, COLLI, LUIGI, MONEGO, SERGIO
Applicants: SAVIO S.P.A.
Application year: 1987
Main classification: B65H59
IPC codes: B65H59