Textiles: spinning – twisting – and twining – Apparatus and processes – Twist setting
Reexamination Certificate
1999-10-22
2002-03-12
Calvert, John J. (Department: 3765)
Textiles: spinning, twisting, and twining
Apparatus and processes
Twist setting
C057S290000, C057S333000, C057S350000, C028S178000, C028S271000, C028S281000
Reexamination Certificate
active
06354069
ABSTRACT:
TECHNICAL FIELD
The invention relates to a method and an apparatus for the air treatment of filament yarn with yarn treatment nozzles having a continuous miniaturized yarn duct into which compressed air or gaseous fluid is introduced and a dominant twisting flow is produced in the yarn duct.
STATE OF THE ART
The production of yarn from synthetic fibres involves quite a number of basic stages. The individual continuous filaments are extruded via spinnerets from hot liquid thermoplastic polymer raw material and are then solidified in a cooling stage. A desired number of filaments are then combined to form a single thread or yarn which is either cut into staple fibre or left as a continuous filament. The staple product will not be described in detail hereinafter. It is subjected to processing steps similar to those whose basic principle is known from conventional natural yarn production. The very fine filament produced under high pressure as well as the yarn produced therefrom has a number of basic properties. These prevent direct use of the solidified unstretched filaments for the production of textiles. A chain molecular structure with low pre-orientation of the chain molecules is formed polymerization of a filament. If a yarn of this type is subjected to a more pronounced tensile stress, a considerable permanent change of length occurs. A typical representative of such a yarn which is designated POY (pre-oriented yarn) can be plastically stretched by a factor of 1:1.5 to 1.8.
30 years ago, it was normal to produce an LOY quality which even had to be stretched in a ratio of 1:3 to 3.8. The stretching process is a stage of operation which is essential for subsequent use for the production of textiles as the fabric (produced from unstretched yarn) would obviously be locally permanently elongated when first stressed. The second property is that the molecular orientation can be permanently changed at yarn temperatures of about 200° C. and higher if the yarn is cooled immediately after an appropriate operation. The reduction in temperature below the glass transition point sets the changed molecular orientation produced under the influence of force so to speak. The third property is based on the second. The yarn is subjected to pronounced twisting in the hot state and a pronounced twist applied to the yarn. This operation has been employed worldwide for many decades and is known as the false twist method. Friction spindles are normally used as twisters nowadays. A spiral molecular orientation is created in the yarn owing to the twist which is forced mechanically on the yarn, so the individual filament can pass into a curved form after solidification and in the relaxed state, as shown schematically on the right of
FIG. 1
according to the state of the art. The main result of the helical molecular orientation produced in this way is that the relaxed yarn can take on bulkiness and a crimped structure. The resultant product is described as false-twist-textured yarn and imparts a textile character to the end product.
A further particular property of synthetic fibre yarns is that the individual filament is sometimes very thin. To achieve high productivity in an economic manner, many filaments are produced continuously from a corresponding number of spinnerets and at very high rates. The spinning rate was 1000 m/min in the 60s. This has increased continuously ever since and is now between 3000 and 8000 m/min. Two particular branches of processing, among others, have arisen for textured yarn production. In one case, texturing is linked directly with the spinning process; in the other case (for titres <1000, in particular <334), texturing has to be separated from the spinning process. There is an excessively large discrepancy between spinning rate (POY yarn 3-4000 m/min) and the possible texturing rate in the second case. Supply bobbins therefore have to be produced after spinning. Final stretching and texturing is then carried out with the supply bobbins, separately from the filament spinning process in position and time. With coarse textured yarns, so-called BCF (bulked continuous filament) yarns, texturing can be carried out directly after filament extrusion, cooling and elongation. Typical BCF production rates are from 2500 to 5000 m/min. Simultaneous and sequential stretch texturing is known during false twist texturing. A characteristic feature of the two methods is that a heating zone and then a mechanical friction spindle for twist production are arranged in the direction of travel of the thread. During sequential stretch texturing (
FIG. 1
a
) the yarn is stretched in a first stage and false twist texturing only carried out in a separate second stage (with respect to the yarn tension). As the twist acts in the direction of travel of the thread backwards to the next feed unit there before, a cooling zone can be arranged directly after the heating zone but in front of the twister. With simultaneous stretch texturing, stretching and texturing take place within the same stage, as shown in
FIG. 1
b
. The highest possible yarn velocities can be achieved at present with the mechanical friction spindle. However, there is a natural limit to performance dictated mainly by the looping, the maximum permitted tensile stress on the yarn and the frictional resistance relative to the twist discs. If the performance of the twist discs which is to be transmitted exceeds a permitted level, surging occurs. A proportion of the already produced false twist with the travelling thread skips over the twist discs forwards in the direction of travel of the thread. This leads to an instantaneously reduced thread tension and simultaneously to a reduced twisting action. This effect is ultimately noticed as a defect on the finished textiles owing to periodically repeated differences, for example in colour.
The described methods are a combination of heating/cooling and a mechanically produced change in the molecular orientation. In contrast, air jet texturing is known, for example, from EP-PS 88 254. Air jet texturing utilizes the forces of air, in particular shock waves at the outlet from an air nozzle. The shock waves produce filament loops uninterruptedly on each individual filament. During air jet texturing, the yarn is guided into the air nozzle with a large overfeed. This overfeed is required during air jet texturing for the loops being formed in all directions, even toward the interior of the thread. The stability of the looped yarn is ensured by the loop action, but in particular by filament on filament friction. Production of the bulkiness in the false twist textured yarn, on the other hand, is based on the newly formed helical molecular orientation. The character of air jet textured yarn and of false twist textured yarn differs greatly. The two yarn qualities have their own particular fields of application. Apart from the qualitative differences (of air jet textured and false twist textured yarns), a main distinction between the two methods resides in the constructional dimensions of the texturing device. The mechanical friction spindle has dimensions which are a multiple of those of said air jet texturing nozzles. The mechanical friction spindle has extremely rapidly rotating parts in relation to the air jet texturing nozzle which does not require moving parts for its operation. The most obvious drawback of the mechanical friction spindle resides in the width dimension. If a parallel bundle of threads comprising many threads needs to be processed, the corresponding device is very wide. In addition to conventional long and deep stretch texturing machines, special machines are also constructed, for example for warp stretching, with which well over 1000 threads can be processed in parallel in a depth of 1 to 2 metres, but without texturing spindles. The same applies to warping devices. Warp stretching devices with a tangle arrangement show that air treatment can be carried out in a minimum of space. The desired aim is therefore to develop a compressed air element of suitably small shape, in particu
Calvert John J.
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Heberlein Fibertechnology, Inc.
Hurley Shaun R
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