EP0271418B1 - Method for continuously producing core yarns on ring-spinning frames, the core yarns being composed of long fibres surrounded by an outer layer - Google Patents

Abstract

The core composed of long-fibre yarns, preferably obtained by cracking, is raised in twist during the actual spinning operation carried out continuously on a ring-spinning frame without reaching its critical twist coefficient alpha "0, the cover of the said core being made of long fibres or short fibres. The twist coefficient of the core yarn lies between 20 and 85. <IMAGE>

Description

The present invention relates to a process for obtaining continuous ring spinning of composite yarns with a core of long fiber yarns surrounded by an outer envelope.

• le procédé de filature sur continu à filer fibres longues à anneaux,
• le procédé de filature sur continu à filer fibres courtes à anneaux,
• et le procédé de filature à friction.

We know that the manufacture of composite yarns with a core surrounded by an outer envelope, more commonly known as "Core-spun", can be carried out according to three spinning processes:

• the spinning process on continuous spinning long ring fibers,
• the spinning process on continuous spinning short ring fibers,
• and the friction spinning process.

While the friction spinning process can use continuous, multi or monofilament filaments as well as fiber yarns and does not impart any twist to the core thread, the continuous ring spinning processes they use long fibers or short fibers, can use, as thread constituting the core, only continuous filaments, multifilaments or drawn monofilaments.

It should also be noted that these continuous ring spinning processes, by their very design, impart to the core wire a twist equivalent to that which the entire composite wire receives.

• Figure 1 représente, de façon très schématique, un fil composite avant que n'ait été impartie aucune torsion ni à l'âme ni à la couverture ;
• Figures 2 et 3 représentent, de façon également très schématique, plusieurs types de torsion appliqués à un fil composite dont l'âme a reçu une torsion Z.
• Figure 4 est une courbe représentant le résistance du filé composite en fonction du coefficient de torsion du fil d'âme.

The use of fiber spun yarns as a core in systems for making core-spun yarns on continuous ring spinning was therefore hitherto completely excluded, as will be demonstrated in the following with reference to the schematic drawing appended in which :

• Figure 1 shows, very schematically, a composite yarn before no torsion has been imparted either to the core or to the cover;
• Figures 2 and 3 show, also very schematically, several types of twist applied to a composite wire whose core has received a Z twist.
• Figure 4 is a curve representing the resistance of the composite yarn as a function of the twist coefficient of the core wire.

In the figures, the core is designated by 2 and the cover by 3 .

Figure 1 shows a composite wire element made a core 2 and covering fibers 3 , none of these elements having received torsion.

If we apply a torsion of coefficient α to the whole wire, i.e. T = α √Nm (T = number of turns / meter; Nm = metric number), the covering and the core, after application of the torsion, will have the same twist T. Now, when you twist a wire, there is a shortening effect which is a non-linear function of the twist.

Consequently, the elements 2 and 3 of initial length lo, will have a length l <lo after application of the torsion. Experience shows that the reduction in width has a value close to 5% for an α = 80. This variation is naturally independent of the direction of the torsion.

Let us take the case (Figure 2) where the core threads 2 are yarns of fibers (long or conical), whose twist in direction Z has a coefficient of twist in the interval 60 <α <90.

This interval covers the range of coefficients commonly used on ring spinning machines, whether long fibers or short fibers.

If a torsion is applied to the assembly in the same direction as the torsion applied to the core wire, therefore a torsion Z with a coefficient αʹ, included in the interval defined above, the core 2 will be overstrained compared to the cover 3 , and the reduction in length Δl of the core 2 will be greater than the reduction in length Δʹl of the cover 3 .

There will therefore be excess length of the cover 3 relative to the core 2 and it will thus appear "uncovered areas".

In the situation represented in FIG. 3, a torsion is applied to the assembly in the opposite direction to that applied to the core wire, ie a torsion S, with a coefficient also included in the interval defined above. We then observe the opposite phenomenon: in fact, the spool of the core 2 untwists, and therefore sees its length increase. At the same time, the cover 3 has its length reduced due to the effect of the twist. In this situation, there is excess length of the core 2 relative to the cover 3 , and appearance of exposed parts, as in the previous case.

In addition to the type of fault described above, it can be estimated that, in both cases, the resistance of the core wire 2 will deteriorate very quickly.

Indeed, in the case shown in Figure 3, this deterioration will occur by untwisting and passing through the point "0" of the core wire. Indeed, the staple fibers (long and a fortiori short of the cotton plants) are linked mechanically by the cohesion fibers to fibers given by the twist.

These connections are, in fact, the consequence of the inter-free friction forces. The untwisting therefore leads to a dislocation of the yarn of fibers placed in the core.

. Il existe, en effet, une caractéristique propre à chaque famille de fibre que l'on peut représenter par la courbe de la figure 4, dans laquelle la résistance en décanewtons est portée en ordonnée, le coefficient de torsion étant porté en abscisse. L'équation de cette courbe F = f (α") possède un maximum. La valeur αő` correspondant à ce maximum est appelée coefficient critique. Pour toute valeur telle que α">α $\genfrac{}{}{0ex}{}{\text{"}}{\text{o}}$

, on constate une diminution de la résistance.In the case shown in Figure 2, we see that the resistance of the yarn decreases very quickly, when the twist coefficient of the core thread exceeds the critical value α $\genfrac{}{}{0ex}{}{\text{"}}{\text{o}}$

. There is, in fact, a characteristic specific to each family of fibers which can be represented by the curve of FIG. 4, in which the resistance in decanewtons is plotted on the ordinate, the coefficient of torsion being plotted on the abscissa. The equation of this curve F = f (α ") has a maximum. The value αő` corresponding to this maximum is called the critical coefficient. For any value such as α"> α $\genfrac{}{}{0ex}{}{\text{"}}{\text{o}}$

, there is a decrease in resistance.

It is obvious that this critical coefficient depends on the type of fiber and yarn used and is therefore a characteristic specific to each textile product.

The object of the invention is to provide a composite yarn with a core of long fibers spun surrounded by a cover of long fibers or of short fibers, in which the cover perfectly covers the core without any exposed part thereof, has good strength, and in which there is a good bond between the core and the cover.

To this end, the process which it relates to consists of starting from a core made of long fiber yarn, the torsion coefficient of which is substantially lower than its critical torsional coefficient, and from covering the core made of long fibers or short fibers, and to carry out the torsional mounting of the core during the same spinning operation carried out on continuous ring spinning, this twisting being such that the total coefficient of twist of the core thread is lower at its critical coefficient of torsion.

Another object of the invention is to determine a method of calculating the total twist coefficient of the core yarn, so as to be able to optimize the twist coefficient of the fiber yarn to be used as the core yarn in order to obtain a optimum resistance.

(loi de Koechlin)

la torsion du fil complet est de :

$\text{Tʹ =αʹ√Nʹm (2)}$

la torsion totale du fil d'âme est de :

$\text{Tʺ = T + Tʹ (3)}$

Soit, par ailleurs, le pourcentage de l'âme par rapport au fil complet :

en posant

le titre du fil d'âme devient :

This is how if:
α 'is the coefficient of the complete wire,
N'm is the title of the complete thread,
Nm is the title of the core thread and
α is the coefficient of the core wire,
the twist of the core wire is:

$\text{T = α√Nm (1)}$

(Koechlin's law)

the twist of the whole yarn is:

$\text{Tʹ = αʹ√Nʹm (2)}$

the total twist of the core wire is:

$\text{Tʺ = T + Tʹ (3)}$

In other words, the percentage of the core in relation to the complete thread:

by asking

the title of the core thread becomes:

et la torsion totale du fil d'âme de :

The twist of the core wire, as a function of Nʹm and h is:

and the total twist of the core wire of:

We can then calculate the total coefficient α ʺ of the core wire as follows:

Now, according to equation (5):

If we carry this value in equation (8), we have:

We therefore see that αʺ is a function of three variables: α, αʹ and h, and is independent of the metric number of yarns.

We have seen above that the coefficient of torsion above which there is a decrease in resistance must be such that:

${\text{α ≦ α "}}_{\text{o}}$

If one places oneself at the limit, and by fixing the values of h and αʹ, (which can be predetermined), it is possible to calculate the value of α, that is to say of the coefficient of torsion of the yarn of fibers to be used for the core yarn to obtain optimum resistance. This value is given by equation (10):

We know, moreover, and from experience that to have total coverage of the soul, we must have:

For example, if we choose 90 as the value of '(this is a current value in spinning to obtain yarn with a closed structure); we'll have :

$\text{α = 80 - 90 √0.3 = 30.7}$

In the long cracked fiber technique, such a yarn is entirely feasible, and suitable for entering as a core yarn in a Corespun composite yarn.

Thus, the twist coefficient of the long fiber yarn intended to form the core of the composite yarn is equal to the value of the critical twist coefficient of this yarn, reduced by the product of the value of the total coefficient of twist of the composite yarn and of the square root of the proportion of core thread in the composite thread.

According to one embodiment of the invention, the twist coefficient of the core wire is between 20 and 85.

It can be noted that, with the "Core-spun" yarn thus obtained, the aforementioned drawbacks: excess of length of the core relative to the cover, or excess of length of the cover relative to the core, disappear with the possibility of making, for example, a wire whose torsional coefficient is close to 30, therefore with fibers very slightly inclined relative to the core of the wire.

The present invention will be better understood and its advantages will emerge clearly from the example which follows which illustrates it without in any way limiting it.

The material intended to constitute the core consists of a spun of long fibers of high modulus aramid, Nm 90.

   la valeur h étant de 0,3 on a k = 30 %.The critical torsional coefficient for this material is: ${\text{αʺ}}_{\text{o}}\text{= 80}$

the h value being 0.3 we have ak = 30%.

The metric number (Nʹm) of the cover made of a mixture of short cotton fibers and flame retardant viscose, which represents 70% of the whole "Core-spun" yarn is N dem = 27.

The coefficient of torsion αʹ determined on the complete yarn and necessary in short fiber spinning is 90.

- α √h ; α = 80 - 90 √0,3 = 30,7
The calculation of the coefficient α of the core wire (equation 10) gives:

α = α $\genfrac{}{}{0ex}{}{\text{"}}{\text{o}}$

- α √h; α = 80 - 90 √0.3 = 30.7

The core thread will therefore have the following twist:

$\text{T = α √Nm; T = 30.7 √90 = 291 t / m Z direction}$

The complete wire will be twisted

$\text{Tʹ = αʹ √Nʹm; Tʹ = 90 √27 = 467 t / m Z direction}$

The total twist of the core wire will be

$\text{Tʺ = T + Tʹ; Tʺ = 291 + 467 = 758 t / m}$

et l'on retrouve donc le coefficient critique ${\text{αʺ}}_{\text{o}}\text{= 80}$

précédemment déterminé.The core wire after the twist has risen therefore has a coefficient

and so we find the critical coefficient ${\text{αʺ}}_{\text{o}}\text{= 80}$

previously determined.

It is also possible to determine the quite remarkable resistance of the "Core-Spun" wires thus obtained.

The resistance of a composite short cover fiber depends only on the resistance of the core wire.

Yes :
RʹKm is the kilometric resistance of the complete wire in Km,
RKm is the mileage resistance of the core wire,
Fʹ is the breaking resistance of the whole wire,
and F the breaking strength of the core wire,

The core wire after ascent in torsion has an RKm = 120, therefore

This resistance is quite remarkable for a yarn whose cover of short fibers made of cellulosic fibers represents 70%. Such a yarn made of 100% short fibers would have an RKm of the order of 18 km.

In long fiber coverage, a slight doping of the total resistance of the wire is obtained.

We can understand the advantage of the process according to the invention which makes it possible to obtain, on conventional ring spinning equipment, core-spun composite yarns whose core is made of long synthetic fibers yarns from all sources and whose cover can be made of any known synthetic, artificial or natural fiber, whether in the short fiber system or the long fiber system. There are no discovered parts.

The wires thus obtained, which can be obtained in a plate of metric numbers between 1 and 100 have, moreover, and as said above, a quite remarkable resistance.

Claims (6)

1. A process to obtain a composite yarn with a core surrounded by an exterior envelope, characterized in that it consists in commencing with a core (2) produced from long fibre yarn, the torsion coefficient of which is appreciably less than its critical torsion coefficient, and with a covering (3) of the core (2) produced from long or short fibres, and to perform the twisting of the core during the actual operation of spinning continuously performed on ring-spinning frames, this torsion being such that the total torsion coefficient of the core yarn is less than its critical torsion coefficient.
2. A process according to Claim 1, characterized in that the torsion coefficient of the long fibre yarn intended to form the core of the composite yarn is equal to the value of the critical torsion coefficient of that yarn less the value of total torsion coefficient of the composite yarn multiplied by the square root of the proportion of core yarn in the composite yarn.
3. A process according to either of Claims 1 and 2, characterized in that the torsion coefficient of the long fibre yarn intended to form the core of the composite yarn is of the order of 30.
4. A process according to any of Claims 1 to 3, characterized in that the proportion of yarn core in the composite yarn is less than or equal to 0.3.
5. A process according to any of Claims 1 to 4, characterized in that the core of the composite yarn is formed of long fibre yarn of high modulus aramide.
6. A process according to any of Claims 1 to 5, characterized in that the fibres constituting the core are obtained by breaking.

Images