HIGH-SPEED FALSE-TWISTING

Abstract: A system for applying a false twist to a continuously traveling yarn-strand utilizing a plurality of twist imparting, moving elements arranged in such a manner that the yarn-strand is only rolling rather than sliding over any of its twist imparting surfaces. The false twisting system does not use any twist-restricting, stationary guides between the different twisting members, but uses in their place other yarn-twisting elements, which are properly angled in relation to their preceding and their subsequent twisting members. Extremely long contact lines between the yarn-strand and the twisting-elements are provided to reduce the specific pressure on the yarn to enable a gentle, low tension and high-speed operation of the false-twisting process.

Description: HIGH-SPEED FALSE-TWISTING Technical Field and Background of the Invention This invention relates to a system for applying a false twist to a continuously traveling yarn-strand, and more particularly to a system for passing the yarn-strand in frictional contact over moving surfaces. For many years, synthetic yarn-strands have been textured by first heating the yarn-strand while it is in a twisted configuration and subsequently cooling it to "freeze" the chain molecules in their twisted configuration, while the yarn-strand is thereafter untwisted. The temporary twist in a typical false-twist texturing machine is generated for example by guiding the yarn-strand around a series of rotating discs and the frictional forces rotate the yarn-strand around it's own axis. The contact length of the yarn-strand with the twisting elements on todays texturing-machines is usually relatively short and the yarn-strand is in most cases pulled lengthwise over the surface of the twist imparting elements. For these reasons, the yarn-strand is slipping substantially on these twist imparting surfaces. This slippage, together with the high contact pressure from the twist-imparting elements, results in frictional damage of the yarn-strand, which can be seen as rubbed off particles known as "snow". The process speed on todays false-twist texturing machines is restricted by this high contact pressure and the "snow" generating slippage. Summary of the Invention It is an object of the invention to impart twist to a moving yarn-strand over an extended length of the yarn- strand in order to reduce the specific frictional forces imparted to the yarn-strand. It is another object of the invention to assure that the surface of the yarn-strand is moving in the same direction as the twist imparting surfaces. It is another object of the invention to eliminate sliding motion of the yarn-strand on the twist imparting surfaces. It is another object of the invention to control the tension in the yarn-strand through the proper geometrical configuration of the twist imparting surfaces. It is yet another object of the invention to eliminate all twist-restricting guides on the twisted yarn- strand through the proper geometrical arrangement of the twist imparting mechanical elements. These and other objects of the invention are achieved in the preferred embodiments disclosed below by ensuring that the contact surfaces of all twist imparting elements move in the same direction as the contact-surface of the processed yarn-strand and by application of sufficient contact area between the yarn-strand and the twist imparting elements by the application of several twist- imparting elements, which are arranged in angular and cpaced apart relation to each other. According to one preferred embodiment of the invention, 4 (four) friction rolls are arranged in a square configuration. Means are included to rotate these rolls. The rotation direction of these 4 (four) friction rolls are from the inside of the roller square upward. The yarn- strand is wrapped in a spiral around the outside of the first friction roll and passes through the inside of the roller square to the second friction roll. The yarn-strand is then wrapped in like fashion around the second friction roll and so forth. The yarn-strand can be wrapped several times around the 4 (four) friction-rolls to maximize the twist applying contact surface of the friction imparting friction rolls. It is understood that a system of fewer or more than 4 (four) rolls can be applied. According to another preferred embodiment of the invention, the 4 (four) friction rolls are of conical shape, where the incoming yarn-strand contacts the larger diameter of the friction rolls. The purpose of the conical shape of the friction rolls is to reduces the tension of the yarn-strand during the twisting action. According to another preferred embodiment of the invention, the 4 (four) friction rolls are of convex and/or of concave shape to affect the tension during the twisting action in a desired fashion. According to yet another preferred embodiment of the invention, a second set of 4 (four) friction rolls are located underneath the first set in order to double the number of contacts of the yarn-strand with the friction applying rolls. According to another preferred embodiment, 2 (two) or more parallel friction rolls are rotating in the same direction, around which the yarn-strand is wrapped in spiral fashion. According to yet another preferred embodiment, 2 (two) or more friction rolls are rotating in the same direction and point with their axes towards a point, located towards the exit of the yarn-strand, to facilitate the sliding off of the yarn-strand. According to yet another preferred embodiment of the invention, the yarn-strand is wrapped alternately around a rotating ring and around rotating friction pins in order to insert false twist into the yarn-strand. According to yet another preferred embodiment of the invention, the polygonal arrangement of the friction rolls are replaced by a moving endless belt around which the yarn-strand is wrapped. According to another preferred embodiment, a friction disk is located between 2 (two) parallel friction rolls, around which the yarn-strand is wrapped. Brief description of the drawings Some of the objects of the invention have been set forth as above. Other objects and advantages of the invention will appear as the description of the invention proceeds when taken in conjunction with the following drawings, in which: FIG. 1 is a perspective view of the false-twisting system with 4 (four) friction rolls, according to the present invention. FIG. 2 is a top view of the false-twisting system with 4 (four) friction rolls, according to the present invention as shown in FIG. 1. FIG. 3 is a top view of the false-twisting system with 4 (four) friction rolls with added guiding pins, according to the present invention. FIG. 4a is a perspective view of the yarn entrance of the false-twisting system with a diagram of the velocity- vectors at the yarn-entrance. It shows the velocity of the surface of the yarn-strand and of the surface of the friction roll, according to the present invention. FIG. 4b is a perspective view of the yarn exit of the false-twisting system with the velocity-vectors at the yarn-exit. It shows the velocity of the yarn-strand of the surface of the friction roll, according to the present invention. FIG. 5 is a perspective view of the false-twistincr system with 4 (four) friction rolls of conical design, according to the present invention. FIG. 6 is a perspective view of the false-twisting system with a second set of 4 (four) friction rolls located underneath the first set, according to the present invention. FIG. 7a shows in top view a false-twisting system with a driven rotating friction ring and 4 (four) friction rolls, according to the present invention. FIG. 7b shows in a side view the false-twisting system, according to FIG. 7a. FIG. 8a is a perspective view of a false-twisting system with a pair of rotating friction rolls, according to the present invention. FIG. 8b is a perspective view of a false-twisting system with two driven friction rolls, arranged in angular position to each other, according to the present invention. FIG. 9 shows in top view a false-twisting system with a driven friction belt, according to the present invention. FIG. 10a shows in bottom view a false-twisting system with two driven friction rolls and a driven friction disk in between, according to the present invention. FIG. 10b shows the false-twisting system as shown in FIG. 10a from the front. FIG. 10c shows in perspective view from underneath the false-twisting system as shown in FIG. 10a. FIG. lOd shows a variation of the unit as shown in FIG. 10a, FIG. 10b and FIG. 10c. It is provided with 2 (two) friction disks (14) . One friction disk (14) can be ■adjusted along the axes of the friction rolls (2) . Spreading the 2 (two) friction disks (14) further apart, increases the twist level in the yarn (1) and visa versa. FIG. lla shows the yarn-path around a friction roll in front-view. FIG. lib shows the yarn-path in a side-view. Description of the preferred embodiment and best mode Referring now specifically to the accompanying drawings, FIG. 1 and FIG. 2 illustrate how the yarn (1) is wrapped around the friction rolls (2) , starting with the entering yarn (4) and leaving the twisting unit with the exiting yarn (5) . The yarn (1) is wrapped 3 (three) times around the 4 (four) friction roll (2) . Often it is of advantage to use separation pins (3)as shown in FIG. 3, especially for the start-up. These separation pins (3), when properly placed, will not touch the yarn (1) after the start-up. In false-twisting, the yarn (1) is in twisted state before it enters the false-twisting unit. After leaving the twisting unit, the yarn (1) has no twist. This means that the entering yarn (4) is rotating around it's own axis. However, the exiting yarn (5) is not rotating around it's own axis. FIG. 4a and FIG. 4b indicate the velocity of the yarn (1) and the friction roll (2) . If no slippage exists between the yarn (1) and the surface of the friction rolls (2) , the surface velocity (6) of the roll is equal the resultant of the components of the axial yarn velocity (10) and the tangential yarn velocity (11) . The axial yarn velocity (10) of the exiting yarn (5) is equal the surface velocity of the roll (6) and the tangential yarn velocity (11) is zero, since the exiting yarn (5) does not twist around it's axis. A better suited configuration for the slippage-free twisting of yarn (1) is shown in FIG. 5 with the tapered rolls (13) . The taper of the tapered roll (13) allows to compensate for the lower axial yarn velocity (10) of the entering yarn (4) , as compared to the axial yarn velocity (10) of the exiting yarn (5) . The taper of the tapered roll (13) is also affected by the shrinkage of the yarn (1) due to the cooling, as well as due to the twisting and can be properly selected for a desired tension characteristic during the twisting of the yarn (1) . For example, a smaller diameter of the tapered roll (13) at a specific location results in higher tension down-stream. FIG. 6 shows how the number of contacts of the yarn- strand can be doubled with a second set of secondary friction roll (12) underneath the standard friction roll (2). In FIG. 7a and FIG. 7b, a friction ring (7) and 4 (four) friction studs (8) replace the friction rolls (2) . 4 (four) drive pins (9) rotate counter-clockwise and drive the friction ring (7) . 4 (four) friction studs (8) rotate also counter-clockwise. The yarn (1) is alternately wrapped around the friction ring (7) and the friction studs (8). Another alternative method is shown in FIG. 8a and FIG. 8b, where two opposite friction rolls (2) are omitted. In FIG. 8a, the 2 (two) friction rolls (2) are parallel and in FIG. 8b, the 2 (two) friction rolls (2) are slightly angled towards each other for better feeding of the yarn (1). Still another alternative method is shown in FIG. 9 where the friction disk (14) of FIG. 7a and FIG. 7b is replaced by an endless belt (21) , driven by drive rolls (20) . The yarn (1) can be wrapped several times around the belt if so desired. In FIG. 10a, FIG. 10b, FIG. 10c and FIG. lOd, two opposite friction rolls (2) as shown in FIG. 1 are replaced by one or more friction disks (14) . The yarn (1) passes first around the friction disk (14) and is then wrapped around the first friction roll (2) ; from there it passes around the front side of the friction disk (14) and around the second friction roll (2) . The yarn (1) leaves the twisting unit after a last wrapping around the back-side of the friction disk (14) . The twist level can be increased by the application of a larger friction disk (14) and visa versa. To easily adjust the twist level, two friction disks (14) are used, of which at least one can be adjusted in the direction of the axis of friction roll (2) as shown in FIG. lOd FIG. 11a and FIG. lib show the yarn path (18) around a friction roll (2) . The yarn (1) makes contact with the friction roll (2) at the entrance contact point (15) and leaves the surface of the friction roll (2) at the exit contact point (16) . The radial force (19) presses the yarn (1) in contact with the surface of the friction roll (2) and imparts added twist to the yarn (l) through the frictional force. The added twist, imparted by this portion of the false-twisting unit, makes the yarn-spiral steeper and can be seen as the angle of added twist (17) .

Claims: I claim: 1. A method of false twisting a continuously traveling yarn-strand by friction comprising the steps of: (a) Guiding the yarn-strand around several rotating, twist imparting members; (b) positioning each subsequent twist imparting member at such an angle and spaced apart from the preceding twist imparting member that the twisting yarn-strand is not pulled with a sliding motion from the preceding twist imparting member. 2. A method of false twisting a continuously traveling yarn-strand by friction according to claim 1, comprising the step of selecting the surface speed of the twist imparting member to control the yarn-strand tension during the twisting process. 3. A method of false twisting a continuously traveling yarn-strand by friction according to claim 1, comprising the step of placing the preceding twist imparting member and the subsequent, twist imparting member at such an angle that the desired twist-level is achieved. 4. A method of false twisting a continuously traveling yarn-strand by friction according to claim 1, comprising the step of selecting sufficient long frictional contact between the yarn-strand and the twist imparting member, to assure a low tension level in the processed yarn-strand. 5. A method of false twisting a continuously traveling yarn-strand by friction according to claim 1 without the need of twist inhibiting, stationary guides. 6. A method of false twisting a continuously traveling yarn-strand by friction according to claim 1, comprising the step of selecting the number of contact surfaces between the yarn-strand and the twist imparting surfaces through change in thread-up of the yarn-strand. 7. A method of false twisting a continuously traveling yarn-strand by friction comprising the steps of: (a) Guiding the yarn-strand around several rotating, twist imparting members; (b) Guiding the yarn-strand around at least one twist imparting member more than once for twist insertion. 8. A method of false twisting a continuously traveling yarn-strand by friction according to claim 7, comprising the step of selecting the surface speed of the twist imparting member, to control the yarn-strand tension during the twisting process. 9. A method of false twisting a continuously traveling yarn-strand by friction according to claim 7, comprising the step of placing the preceding twist imparting member and the subsequent, twist imparting member at such an angle, that the desired twist-level is achieved. 10. A method of false twisting a continuously traveling yarn-strand by friction according to claim 7, comprising the step of selecting sufficient long frictional contact between the yarn-strand and the twist imparting member, to assure a low tension level in the processed yarn-strand. 11. A method of false twisting a continuously traveling yarn-strand by friction according to claim 7, without the need of twist inhibiting, stationary guides. 12. A method of false twisting a continuously traveling yarn-strand by friction according to claim 7, comprising the step of selecting the number of contact surfaces between the yarn-strand and the twist imparting surfaces through change in thread-up of the yarn-strand. 13. An apparatus for the false twisting of a continuously traveling yarn-strand by friction comprising: (a) a set of driven rolls with their axes arranged in polygona1 arrangement; (b) wrapping the yarn-strand in spiral shape around the rotating rolls. 14. An apparatus for the false twisting of a continuously traveling yarn-strand by friction according to claim 13, comprising an approximate conical shape of the rolls for tension control of the yarn-strand. 15. An apparatus for the false twisting of a continuously traveling yarn-strand by friction according to claim 13 comprising: (a) a second set of driven rolls spaced apart from the first set of rolls; (b) these rolls of the second set rotate in the same direction as the rolls of the first set; (c) wrapping the yarn-strand around both sets of rolls. 16. An apparatus for the false twisting of a continuously traveling yarn-strand by friction comprising: (a) a pair of approximately parallel rotating rolls; (b) wrapping the yarn-strand in spiral shape around the rotating rolls. 17. An apparatus for the false twisting of a continuously traveling yarn-strand by friction comprising: (a) a rotating ring; (b) several rotating pins arranged outside the rotating ring, turning in the same direction as the ring; (c) wrapping the yarn-strand in spiral shape, alternating between wrapping the yarn-strand around the inside of the rotating ring and around the outside of the rotating pins. 18. An apparatus for the false twisting of a continuously traveling yarn-strand by friction comprising: (a) a moving endless belt arranged in the shape of a polygon; (c) several rotating drive pins to drive the endless belt; (b) wrapping the yarn-strand in spiral form around the outside of the endless belt. 19. An apparatus for the false twisting of a continuously traveling yarn-strand by friction comprising: (a) a pair of driven rolls with their axes arranged in approximately parallel arrangement; (b) at least one friction-disk between the two rolls, whereas the axis of the friction disk forms an approximate right angle with the axes of the rolls. 20. An apparatus for the false twisting of a continuously traveling yarn-strand by friction according to claim 19, comprising: (a) the selection of the proper speed of the twist imparting members to control the yarn-strand tension during the twisting process. 21. An apparatus for the false twisting of a continuously traveling yarn-strand by friction according to claim 19, comprising: (a) a friction-disk large enough to achieve the desired twist-level. 22. An apparatus for the false twisting of a continuously traveling yarn-strand by friction according to claim 19, comprising: (a) two friction-disks where at least one friction- disk can be adjusted in the direction of the axes of the driven rolls to achieve the desired twist-level. 23. An apparatus for the false twisting of a continuously traveling yarn-strand by friction according to claim 19, comprising: (a) a none cylindrical shape of the rolls to achieve the desired tensions in the yarn-strand during its passage around the twisting-elements.

Inventors: NIEDERER KURT W, NIEDERER, KURT, W.
Applicants: NIEDERER KURT W, NIEDERER, KURT, W.
Application year: 1991
Main classification: D02G1
IPC codes: D02G1