False twist device

Details False twist device False twist device

1999-05-26

2001-04-10

Calvert, John J. (Department: 3741)

Textiles: spinning, twisting, and twining

Apparatus and processes

False twist device

C057S077000, C057S339000

Reexamination Certificate

active

06212867

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to a false twist device for a synthetic multifilament yarn for use in false twist texturing machines.
In the case of false twist texturing machines, one starts out from the principle that, while advancing through a false twist device, the synthetic multifilament yarn is put in a twisted condition at, for example, more than 2,000 rpm, and heated in this twisted condition to the plasticization limit. Thereafter, it is again cooled to a temperature that is below the first-order transition point.
To impart a twist, a false twist device is used that is known from U.S. Pat. No. 4,235,071. The false twist device consists of three sets of disks that are each mounted on an axle for rotation in the same direction. The axles are arranged in the corners of an equilateral polygon, so that the disks overlap in the center thereof. In the center of the polygon, the yarn advances through the false twist device. In so doing, the yarn contacts the circumferential surface of the rotating disks, and is thus twisted. Heating and subsequent cooling in the false twist machine set the form predetermined by the twist impartation, so that after untwisting, a crimp remains in the yarn.
In this process, it should be taken into account that currently the false twist texturing machines process yarns of polyester, in particular, polyethylene therephthalate, polyamide 6 (Perlon) or polyamide 6.6 (Nylon). In so doing, the yarns are processed from partially oriented feed yarns. These partially oriented feed yarns are spun at a high speed and, consequently, subjected in the texturing machine only to a small draw ratio of less than 2:1 in the case of polyester, preferably less than 1.8:1 in the case of polyamides, preferably less than 1.3:1.
In this draw process, the polyester yarns are subjected in a heating zone to temperatures from 190° C. to 210° C., nylon yarns from 190° C. to 205° C., and perlon yarns to about 170° C.
The technological requirement that the effective yarn temperature in the heating zone must exceed 180° C., preferably 200° C. results at increasing yarn speeds and with the known cooling devices in that the yarn enters into the false twist device at an overly increased temperature. Upon its entry into the false twist device, the yarn temperature may be greater than 100° C.
The increased yarn advancing speeds during the false twist impartation necessitates higher yarn tensions to obtain a stable texturing process. Such yarn tensions can be realized by increasing the draw ratio, which leads again to undesired changes in the yarn properties (primarily low elongation).
It is therefore the object of the invention to further develop a false twist device of the initially described kind such that within a false twist zone in a false twist texturing machine, a stable yarn advance is realized at yarn speeds greater than 1,000 m/min, in particular above 1,200 m/min.
SUMMARY OF THE INVENTION
In accordance with the invention, a false twist device having the characteristic features of claim
1
accomplishes the object.
The invention is based on the recognition that while maintaining a stable process at an increased yarn speed, the yarn tension will have to be increased to a lesser extent, when the disks of a false twist device have a correspondingly large radius on their circumferential surfaces that are contacted by the yarn. In terms of measurements, one finds a reduction of the coefficient of friction. This is surprising, inasmuch as the radius of the circumferential disk surface—when viewed in the radial section of the disks—is unusually large, so that because the thereby caused lengthening of the contact length of the yarn wetted with a lubricant, one has to expect an increase in the coefficient of friction or the yarn tension (Euler law). In comparison therewith, it can be expected under the Eitelwein law that the coefficient of friction or the yarn tension depends exclusively on the looping angle, but not on the radius or the length of the looped surface. In fact, the reduction of the coefficient of friction or the yarn tension is based on the decreased inner friction in the yarn that is caused by a larger radius of curvature. The inner friction in the yarn results from the alternating bending stress of the yarn inside the false twist device. By increasing the circumferential surface radii, it is possible to reduce these alternating bending stresses accordingly. Since the alternating bending stress of the yarn increases at a smaller yarn diameter, it has shown that in proportion to the diameter dF of the twisted yarn, the radius r of the circumferential surface must have a certain magnitude, which is at least 35 times the diameter d
F
of the twisted yarn. In the following “circumferential surface” stands for that surface on the disk that is contacted by the yarn, outer surface for the entire disk surface (without the front ends).
Currently, false twist texturing machines process preferably polyester or polyamide yarns. In this connection, it is preferred to process polyamide yarns with deniers smaller than 170 dtex, and polyester yarns even with deniers greater than 170 dtex. In the case of a textured yarn with a denier greater than 170 dtex, a circumferential surface radius greater than 35 times the diameter of the twisted yarn, accomplishes the above object for processing polyester yarns.
To process polyamide yarns with advantage, the false twist device of the present invention preferably is constructed so that the circumferential surface radius is greater than 40 times the diameter of the twisted yarn.
In a particularly preferred embodiment of the false twist device according to the invention, the circumferential surface radius r is defined in relationship to the disk height h such that the center of the circumferential surface radius lies outside of the center plane of the disk, preferably between the inlet end edge and the center plane of the disk. With that, it is possible to realize, in particular in the case of disks with high coefficients of friction, that the circumferential surface is substantially the same as the outer surface, and that the yarn does not advance over the edges of the front ends. By imparting the twist, the yarn is influenced while looping the disk in such a manner that the yarn contacts the circumferential surface of the disk at a greater angle of slope and leaves the circumferential surface at a smaller angle of slope. Thus, because of the asymmetric configuration of the disk, only a shorter section of the toroidal surface is available on the inlet side than on the outlet side. With this configuration of the false twist devices, which is used preferably for disks of frictionally intensive materials, such as, for example polyurethane or rubber, it is possible to use the disks only in a certain installed position. To avoid installation errors during the assembly, the front ends of such disks are identified (for example, by an imprint annular groove, etc.).
To impart to the yarn, despite the high yarn speed the necessary twist (of, for example, more than 2,000 rpm) while maintaining an adequate process stability, the disks of a preferred further development of the false twist device are made of a heat-resistant elastomer. The heat resistance of the elastomer enables a yarn temperature on the disks greater than 100° C.
In a particularly preferred further development of the invention, the disks consist of a heat-resistant rubber, in particular nitrile-butadiene rubber saturated with hydrogen. This material is especially advantageous, since it is also especially wear-resistant and, moreover, possesses satisfactory frictional properties relative the synthetic multifilament yarns. It is therefore especially suited for processing yarns at high yarn speeds and high temperatures.


REFERENCES:
patent: 3705488 (1972-12-01), Sholly et al.
patent: 3901011 (1975-08-01), Schuster
patent: 4051655 (1977-10-01), Lorenz et al.
patent: 4115987 (1978-09-01), Taniguchi et al.
patent: 4195470 (1980-04-01), Sturhahn
patent: 4235071 (1980-11-01)

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