Textiles: spinning – twisting – and twining – Apparatus and processes – Twist setting
Reexamination Certificate
1999-04-05
2001-04-03
Calvert, John J. (Department: 3741)
Textiles: spinning, twisting, and twining
Apparatus and processes
Twist setting
C057S280000
Reexamination Certificate
active
06209302
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a yarn false twist texturing machine used in the production of synthetic yarn. Such machines typically comprise a plurality of side-by-side processing points (also referred to as stations)—usually up to 216.
False twist texturing machines of said type comprise a plurality of processing points—usually up to 216 processing points—which are arranged adjacent to one another along the length of the machine. Each of said processing points comprises a first delivery mechanism and a second delivery mechanism. The first delivery mechanism withdraws the yarn from a supply bobbin and delivers it into a false twisting zone. The second delivery mechanism draws the yarn out of the false twisting zone and delivers it to a take-up device, the yarn speed and the stretching of the yarn being determined by the speed ratio between the second and first delivery mechanism.
When texturing synthetic yarns, yarn speeds are customary which demand both a suitably long heating zone and a suitably long cooling zone. In the false twisting process, the quality of the achieved crimping is influenced particularly by the yarn tensile force prevailing in the individual regions inside the false twisting zone. Thus, for example, it is known that a low yarn tensile force not yet jeopardizing the stable yarn course is required in the heating zone for achieving good crimping. On the other hand, it has also been observed that increasing the yarn tensile force, say, in the region of the cooling rail produces improved results. It would therefore be desirable to adjust a yarn tensile force in the false twisting zone which leads to good results both during the heat treatment and during cooling.
From EP 0 638 675 a false twist texturing machine is known which comprises a twist-stopping device in the form of a rotatable transport roller inside the false twisting zone.
Although this does achieve the effect that the friction force exerted by the twist-stopping device upon the yarn leads only to a slight variation of the yarn tensile force, the absolute value of the yarn tensile force in the false twisting zone is substantially dependent upon the draw ratio adjusted between the first and second delivery mechanisms. Thus, a variation of the yarn tensile force in the false twisting zone would be achievable only by varying the yarn speed.
An object of the invention is accordingly to provide possible ways of influencing or controlling the yarn tensile force prevailing in the false twisting zone substantially independently of the yarn speed.
A further object of the invention is to achieve a piecing facility which is particularly protective of the yarn, gentle yarn processing and hence higher texturing speeds. It is likewise an object of the invention to provide a false twist texturing machine, in which each processing point is easily controllable independently of the adjacent processing points.
SUMMARY OF THE INVENTION
The above and other objects and advantages of the present invention are achieved by the provision of a yarn false twisting apparatus and method which comprises a false twisting zone composed of an elongate yarn heater, an elongate cooling plate, a false twist unit, and a yarn feed system for advancing the yarn through the false twist zone. A twist stopping device is positioned upstream of the yarn heater for stopping the twist which runs back in the yarn from the false twist unit. The twist stopping device comprises a rotatable transport roller about which the yarn is at least partially wrapped, and a drive for controlling the rotation of the roller so that the yarn may be braked or advanced thereby.
The false twist texturing machine according to the invention and the texturing method according to the invention are notable in particular for the fact that the yarn tensile force inside the false twisting zone is variable independently of the draw ratio adjusted between the take-off delivery mechanism and the delivery mechanism disposed downstream of the false twisting zone. In such case, the false twist generated in the yarn runs back to the extent necessary for producing the crimping in the yarn. The twist-stopping device is therefore disposed immediately upstream of the heating device. The yarn tensile force in the yarn is influenced by the friction ratios between the running yarn and the peripheral surface of the driven transport roller. The transport roller may, in said case, be driven in such a way that the peripheral speed of the transport roller is lower than the yarn speed. The yarn would therefore be conveyed with a sliding friction component over the peripheral surface of the transport roller. An increase of the yarn tensile force is thereby achieved in the false twisting zone.
For the eventuality that the peripheral speed of the transport roller is equal to the yarn speed, a deflection of the yarn which is substantially neutral in terms of the yarn tensile force is effected by the twist-stopping device. In the false twisting zone the yarn tensile force is effective which results from the speed ratio adjusted between the take-off delivery mechanism and the second delivery mechanism.
In order to produce a low level of yarn tensile force in the false twisting zone, it is necessary to drive the transport roller in such a way that the peripheral speed of the peripheral surface is greater than the yarn speed. The result is a slip between the yarn and the peripheral surface of the transport roller, leading to a reduction in the yarn tension. Said method variant would also be suitable for producing a preliminary stretching in the yarn between the take-off delivery mechanism and the twist-stopping device.
To enable the twist torque of the yarn to be absorbed, a corresponding counter-torque has to be generated by the twist-stopping device. This is achieved in a particularly advantageous manner in that the yarn in the wrap region of the transport roller is conveyed in a zigzag manner on the peripheral surface of the transport roller. At each deflection point this produces between the yarn and the transport roller a friction which counteracts substantially only the transverse forces of the yarn.
The zigzag yarn running track on the peripheral surface of the transport roller may be realized in a particularly advantageous manner by means of individual yarn guide elements disposed on the periphery of the transport roller. It is thereby possible to realize any desired form of yarn excursion at right angles to the yarn running direction. The maximum excursion of the yarn is then determined by the overlap of opposing guide edges. The number of deflections is determined by the relative spacing of the yarn guide elements.
In a preferred development, the yarn guides take the form of rings which are mounted from both ends onto the driven transport roller carrying them. They may, in said case, between them form the yarn running track or be so shaped that the yarn running track is formed by suitable, laterally attached extensions emanating radially from the ring inner surfaces.
In a further preferred embodiment, the transport roller takes the form of two discs, which at their outer edges have laterally projecting yarn guide elements and are so arranged relative to one another on a drive shaft that a zigzag yarn running track is produced at a peripheral surface formed by the yarn guide elements.
In order to influence the wrap of the yarn around the yarn guide edges of the yarn guide elements, it is particularly advantageous when the yarn guide elements are of an adjustable design. It is therefore possible, given only a slight wrap of the peripheral surface of the transport roller, to produce in the yarn a high friction torque for absorbing the twist torque of the yarn.
The yarn may be pieced in a particularly gentle manner onto the transport roller by a movable yarn deflection device which is disposed directly in the yarn course upstream or downstream of the transport roller in such a way that the angle of wrap at the transport roller is variable by means of the deflecti
Berges Dietrich
Bruske Johannes
Lorenz Hellmut
Wortmann Thomas
Alston & Bird LLP
Barmag AG
Calvert John J.
Welch Gary L.
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