US3078653A

US3078653A - Wrapped elastic yarn

Info

Publication number: US3078653A
Application number: US125814A
Authority: US
Inventors: Preston F Marshall
Original assignee: Kendall Co
Current assignee: Kendall Co
Priority date: 1961-07-21
Filing date: 1961-07-21
Publication date: 1963-02-26
Anticipated expiration: 1980-02-26

Description

Feb. 26, 1963 P. F. MARSHALL WRAPPED ELASTIC YARN 5 Sheets-Sheet 1 Filed July 21, 1961 Feb. 26, 1963 P. F. MARSHALL WRAPPED ELASTIC YARN 3 Sheets-Sheet 2 Filed July 21, 1961 Feb. 26, 1963 P. F. MARSHALL 3,073,653

WRAPPED ELASTIC YARN Filed July 21, 1961 3 Sheets-Sheet 3 WINDUP WRAPPING YARN CONTRAC N CONDENSING FACTOR FACTO BEFORE RELAXATION WINDER SPEED F. P. M.

LET-O WRAPPING YARN /js' CORE YARN TENSION SECONDARY CORE ELASTIC CORE iiaited states hastens G 3,tl78,653 WRAPPED ELASTIC YARN Preston F. Marshall, Walpole, Mass, assignor to The Kendal! Company, Boston, Mass, a corporation of Massachusetts Fiied .l'uly 21, 1961, Ser. No. 125,814 '7 Glaims. (6i. 57-152) This invention is a continuation-in-part of my copending application, Serial Number 858,694, filed December 10, 1959, which relates to a novelty core-constructed yarn prepared from a filamentary material wrapped in a series of looped configurations about the axis of said yarn, and to a process and apparatus for producing said yarn without resorting to mechanical twisting devices. In carrying out this wrapping process, it is pointed out in application 858,694 that an inexpensive elastic yarn may be produced by wrapping a rubber core with rayon or nylon. The present invention relates to improvements and refinements in the preparation of wrapped elastic yarns.

More particularly, it relates to a product and process in which the degree of elongation and the modulus of a wrapped elastic yarn are controlled by the tensiouing effect of a wrapping strand or strands, said strand or strands being wrapped around the elastic core by a stream of fluid, without resorting to conventional twisting devices as are customarily used to wrap elastic yarns. The wrapping or tensioning yarn has no true twist around the elastic core, and an elastic yarn, wrapped by the process of this invention, may readily be maintained in stable configuration, at a predetermined state of extension, or at any intermediate degree of extension between full extension and substantially complete relaxation.

Due to the ease with which they are handled, and to the ready control of their elastic properties, yarns made according to this present invention are of particular suitability for the preparation of elastic fabrics used in knitted dress goods, gridles, bathing suits, supportive garments, and the like. Furthermore, the elastic yarn of this invention is characterized by a type of wrapping which imparts to the yarn a desirable softness and freedom from abrasive effect, esthetically and physically attractive in garments Worn next to the skin.

As a further consequence of the loop-like nature of the wrapping strand, as explained more fully herein below, the yarns of my invention are characterized by an ability to felt or lock together when woven or knitted into garments or industrial fabrics, such felting being of a nature and a degree not realizable with conventionally wrapped yarns, or with novelty yarns of the chenille type. Such fabrics are eminently suited for use as dampening roll covers, applicator pads, inner soles, filters, and other uses to which felts or felted fabrics are devoted.

It is an object of this invention to provide a wrapped elastic yarn which is stable and non-kinking in nature although only a single end of wrapping strand is applied to the elastic core.

It is a further object of this invention to provide an elastic cored yarn that is maintained permanently or temporarily in a predetermined degree of axial elongation by the looping configuration of the covering strand.

It is a further object of this invention to provide an elastic yarn with a fuzzy surface arising from pedicled loops projecting outwardly from the main axis of the yarn.

Another object of this invention is to provide an elastic Patented Feb. .26, 1963 yarn where the surface softness is maintained even when the yarn is extended beyond its relaxed state or more.

Still another object of this invention is to produce an elastic yarn with the drape and suppleness of an uncovered elastic yarn.

A further object of this invention is to provide a yarn of normally non-feltable components which is capable of being knitted, woven, or otherwise fashioned into fabrics which are characterized by the smooth and uniform surface associated with wool felts.

The invention may be more clearly understood by referring to the drawings herein.

FIGURE 1 is a drawing of the apparatus used to produce the yarn.

FIGURE 2 is an enlarged cross-sectional view, partially cut away, of one part of the apparatus called the vortex chamber.

FIGURE 3 is a cross-sectional view of FIGURE 2, showing the process of wrapping.

FIGURES 4, 5, 6 and 7 are cross-sectional views of FIGURE 2 taken in the horizontal plane BB showing the wrapping operation in four phases of the development of a typical wrapping cycle.

FIGURE 8 is a perspective view of the wrapped yarn of the invention, idealized and simplified to show the fundamental equality of right-hand and left-hand turns of wrapping strand around the core strand.

FIGURE 9 is a diagrammatic perspective view, partially broken away, of a yarn of the present invention when the wrapped elastic yarn has been extended.

FIGURE 10 is the relaxed version or" FIGURE 9.

FIGURE 11 is a cross-sectional view of FIGURE 10.

FIGURE 12 is a highly enlarged hypothecated perspective view of the composite yarn during processing.

FIGURE 13 is a flow sheet of the process of FIGURE 1 showing the operational information that is recorded in table form in Examples 1 through 6 of the specification.

Referring first to the drawing of FIGURE No. 1, the elastic core it) may be one or more strands of natural rubber or of a synthetic rubberlike material which has sufficient elasticity to make it suitable for the purposes to which elastic yarns may be put. This core 10 is supplied from a package 12 and threaded over star wheels of

conventional design

14 and 16 up through a vortex chamber 13, and around the

star wheels

20 and 22 through a guide 24 to a winder 26. Oneor more covering strands 23 are furnished from a yarn package 30 and partially wrapped around the feed wheel 32 and fed into the vortex chamber 18. A secondary core yarn 34 from the supply.

package 36 may be threaded around the star wheel 38 and fed with the elastic core it into the vortex chamber 18. This second core yarn 34 is omitted in many of the examples described below. In operation, to carry out the method of the invention, the core elastic strand 10 is fed by the

star wheels

14 and 16 more slowly than it is withdrawn by the

star wheels

20 and 22 of the take-up mechanism and thus passes through the vortex chamber 18 in a state of tension. The covering strand 28 is delivered by the feed wheel 32 at a linear speed that is usually some 5 to 50 times faster than the linear delivery rate of the take-

up star wheels

20 and 22. The wrapping strand 28 covers the elastic core 10 within the vortex tube and the composite yarn emerges from thevortex tube to complete its travel through the mechanism as a single composite strand 40. The winder 26 operates at a slower speed than the take-

up star wheels

20 and 22, thus allowing the composite strand to contract a specified amount before being packed in bobbin form.

The heart of the operation is the vortex tube 18 shown in FIGURES 2 through 7. In FIGURE 2, the inside chamber of the tube has a cylindrical wall 42 with a pair of

tangential openings

44 and 46 thereinto and

end walls

48 and 50 having

openings

52 and 54. As a means for creating a longitudinally extended whirling body of fluid in said chamber, the tangential chamber opening 44 is connected to a source of fluid pressure by the tube 56. The preferred tangential direction of the air stream, coupled with the generally cylindrical shape of the chamber, creates a miniature tornado in the vortex chamber with a rapidly revolving stream of air circulating around the inside walls.

The wrapping strand 28 is drawn into the chamber through the inlet 46 by the rotating air mass. The rate at which the strand 28 enters the chamber is less than the velocity of the rotating air as measured at the periphery of the chamber. This slippage between the air velocity and the yarn velocity can be deduced from the fact that the portion of the strand 28- located outside of the chamber is under considerable tension, and this tension apparently acts to reduce the entering velocity of the strand 10. High-speed motion pictures show that the strand 28 after entering the chamber tends to maintain a circular path around the chamber wall 42 for about oneqnarter of a turn. An element of the yarn once inside the chamber and removed at least 90 from the point of entry, should be free to accelerate to a speed more nearly matched to the peripheral speed of the rotating air. This can be deduced from the fact that once the yarn has passed through at least 90 of chamber arc, the axial tension of the yarn no longer can effectively retard the speed of rotation since the forces of the air are now tending to accelerate the yarn at some angle to its axis. Referring to FIGURE 4, the covering strand 28, in theconfiguration shown, under the accelerating forces of the air, is apparently moved into the configuration of a loop 58 shown in FIGURE 5'.

Since this wrapping is made by a strand doubled into a loop, the collapsing of a loop around the circumference of the core strand necessarily involves no net true twisting of'the wrapping strand. Examination of the nature of the'wrap shows frequent reversals of direction, amounting to many reversals per inch. A possible explanationof this is shown in FIGURES 5 and 6. It will be noted that as a'leading loopSS is formed in FIGURE 5, there is automatically formed an arc, bend, or incipient loop 59 which is headed in a direction opposite to the direction of loop 58. In FIGURE 6, the'loop 58 has narrowed in the process of collapsing around the core yarn, while the bend 59 has simultaneously elongated into an oppositelydirected loop.

Since the core strand isnot being twisted, and the wrap ping strand is being applied only in looped form, it is obvious that whatever the relative lengths of

loops

58 and 59, there must be as many right-hand turns of wrapping strand as there are left-hand turns, as is illustrated in FIGURE 8'. This is true not only considering the net effect on the total length of wrapped yarn, but the fre-- quent reversals of direction of wrap effected by this invention means that right-hand and left-hand turns average out in small subsections of length. By this means, a stabilized and non-kinking wrapped yarn can be produced with a single wrapping strand, whereas conventional wrapping requires two strands running in opposite direc tions, one balancing the torque imparted by the other.

While a loop 58 is winding around the core 10, FIG- URE 7,- another loop 60 is being formed and the process is repeated. In FIGURE 7 the loop 59 of FIGURE 6 is not shown: actually loop 59 is now wrapped around the core yarn 10 but is concealed by the overwrap of loop 58. As these

loops

58, 59 and 60 are formed at high speed, they apparently tend to be located one on top of another as shown in FIGURE 3 in side view and in FIGURE 7 in plan view. These

loops

58, 59 and 60 are then carried upward and out of the chamber. Since to date high-speed motion pictures have failed to photographically stop these high-speed yarns, the above explanation of the workings of the chamber must be considered hypothetical and the claimed invention must remain independent of this hypothetical explanation. It can be pointed out, however, that the existence of highspced loops 56 and 60 is sustained by the observation that high-speed motion pictures taken at 8000 frames per second and projected at 24 frames per second failed to stop the motion of these loops in a one-quarter inch diameter vortex chamber. It can be calculated that had the loops been rotating at the peripheral velocity at which strand (.10) enters the chamber, the photographs should have stopped the motion.

The wrapping of a doubled strand around the elastic core does not always proceed until the end of the loop islaid down in a smooth, radially wrapped configuration. Due to slight irregularities in the yarn components, or to occasional instances of turbulence in the air stream, loops may become twisted around their own doublestrand axis. This forms what I call a pedicled loop, and is illustrated in FIGURES 9, 10, 11, and in enlarged form in FIGURE 12.

As may be seen in FIGURE 12, a multiplicity of the doubled-back ends may form loops 66 with twisted pedicles which arefrequently intertwisted with adjacent pedicled loops as at 68 and 70. The

loops

66, 68, and 70, etc., extend generally perpendicular to and radially of the tensioned central elastic core strand 10 from the central axis of the yarn, and outwardly there beyond. In the so-wound and twisted wrapping strand, the individually looped strand portions may be partially entangled, snarled, and interlocked with adjacent looped portions as shown at 74 and 76 in FIGURE 12, so as to resist unwinding. This resistance to slippage and unwinding, together with the packed nature of wrapped loops against wrapped loops, is another factor which enables the wrapped yarn of this invention to be stable and non-shrinking even when thecore is highly tensioned.

The characteristic wrapping of the yarn of this invention may be seen in FIGURE 9, which represents the yarn of FIGURE 10 extended about In FIGURE 9, the wrapping strand is disposed in the form of more or less smoothly wrapped bundles of loops, 62, which wrap around the core strand 10, interspersed with radially-extendingpedicled loops 61 extending outward from and perpendicular to the axis of the core strand. Both FIGURES 9 and 10 are magnified several times for illustrative purposes. Where a very fuzzy yarn is desired, the formation of more radially extending pedicled loops is encouraged by increasing the air pressure which feeds the wrapping strand. Whether this is due to induced turbulence or not, excess air pressure usually creates a wild yarn characterized by many radially-extending loops.

An unexpected advantage in the utilization of the covered yarns of this invention lies in the manner in which the radially-extending loops facilitate felting or yarn-to-yarn entanglement when such yarns are fashioned into a fabric. With a minimum amount of fulling, or in some'cases with a simple steaming and pressing operation, the loops on one yarn are caused to entangle or interlock with the loops on adjacent yarns. This-not only causes yarn-to-yarn mechanical adhesion within the fabric, but also creates a novel felt-like surface which may simulate a smooth, tightly woven, high count fabric even though the calculated arithmetical cover factor of the actual fabric is relatively low.

An additional unexpected advantage residing in fabrics fashioned from the yarns of the invention lies in the extraordinarily high and fieecy nap that can be raised thereon by a conventional napping operation, and the tightness with which the napped yarns are locked to the base or core yarn. This appears to be due to the fact that the radially-extending loops of wrapping yarn ofier a ready surface to the teeth of the napping machine, being readily available to these teeth without the need for digging into or abrading the yarn surface as is the case where the wrapping yarn is oriented generally parallel to the axis of the core strand. Although the radial loops are wrapped around the core strand, they are for the most part capable of further elongation when engag-ed with the wire teeth of a revolving napping roll. Apparently the pull of the tooth elongates the loop, with a consequent ti htening of the involuted loop base where it is wrapped around the core.

Elongation of the loop proceeds until the resistance of the constantly tightening loop base is greater than the pull of the napping tooth on the loop, whereupon the loop is broken, usually at nor near its tip. In this way, extremely fleecy and firmly anchored naps can be raised on base fabrics made from the yarns of the present invention.

PRE-ELONGATED WRAPPED ELASTIC YARNS The geometry of the winding which apparently results from the practise of this invention appears to be the means by which the wrapping yarn is able to accomplish the task of holding an extended elastic core yarn in a predetermined state of extension, thus providing the unexpected novelty of a wrapping configuration which can hold an elastic core in a state of extension while remaining soft and appealing to the touch. Turning to FIG- URE 9, this can probably be explained in the following manner: The wrapping strand 28 is applied to the core in a series of closely spaced bundles of tight wrappings 62 and pedicled loops 61, each bundle 62 consisting of a multiplicity of turns formed by the wrapping of a single loop. These series of bundles are applied during a time when the elastic core is held in a state of stretch, during which this stretch has caused a decrease in the diameter of the elastic core. Two desirable results follow from this geometric configuration of the wrappings on a tensioned core.

First, the bundles of wrappings pinch the core so that, when the force which was applied to stretch the core is removed, the core is unable to regain its original unstretched diameter and, thus, is hindered from contracting to its original relaxed length.

Secondly, when the core is allowed to contract the individual bundles of wrappings 62 are brought closed together until they interact, one against the other, to resist any further contraction of the core.

Another consequence of the nature of the wrapping of this invention is that it offers little or no resistance to the extensibility of the final wrapped product. Conventionally, elastic yarns are wrapped with at least two strands of a continuous filament yarn which fit more or less snugly like a sleeve on the core. The extent to which such a yarn can be extended is geometrically limited by the diameter of the core and by the angle which the wrapping strand makes with the core. In order to produce a conventional wrapped yarn with substantial elongation, it is necessary that the elastic core be stretched to near the desired ultimate elongation during the wrapping process, so that suflicient turns of wrapping yarn can be accommodated. A conventional Wrapped yarn, therefore can be extended only to the approximate point to which the elastic core was extended during the wrapping process.

ln the wrapped yarns of the present invention, however, the loops of wrapping strand provide a slack-wrap portion which comes into play when the yarn of this invention is extended. In the unextended condition, the loops and convolutions are held more or less snugly against each other by the retraction of the core, which having been Wound under tension, tends to contract in length until suficient jamming of the looped wrapping prevents further contraction. Extension of the yarn of this invention results in a freeing-up of the jammed condition: loops are free to be extended in the direction of elongation, and the yarns are observed to demonstrate a built-in slack which gives and recovers as an elongating force is applied and removed.

As an example, for a conventionally wrapped elastic yarn to be capable of elongating 400%, or to five times its untensioned length, the elastic core must be elongated and held to this extension during the wrapping process. This limits the production speed of the processing equipment.

Due to the built-in looped slack of the unique wrapping of this invention, however, an elastic core need be extended in the wrapping process only or so, or merely suihcient extension to prevent whipping of the core in the air stream, in order for a Wrapped yarn to be produced which can be subsequently elongated- 500% or more. Since the speed of the wrap of this invention does not involve a twisting device, wrapping is very rapid. For this reason, the lower the degree of elongation that must be imparted to the elastic core in the wrapping process, the higher are the economies of the process.

It will be apparent to one skilled in the art that wide variations may be effected in the texture, pretensioning, and denier of the finished composite yarn by adjusting the speeds and other parameters of the process. The following examples, in tabular form, are based on the process of FIGURE 1 as represented schematically by the fiowsheet of FIGURE 8.

in the following examples listed in Table 1, three types of vortex tube were used. Type A was a cylindrical glass chamber inch in diameter and inch in height, with tangential air and wrapping yarn inlets of 0.040 and 0.020 inch in diameter, respectively. Type B was a cylindrical chamber of Kel-F, a fluorocarbon polymer manufactured by the M. W. Kellog Company, and had the same dimensions as Tube A except that the tangential yarn inlet was 0.016 inch in diameter. Type C was glass, with the same chamber dimensions as Types A and B, but with tangential air and yarn inlets of 0.027 and 0.031 inch in diameter, respectively.

Core yarn tension is measured by the relative speeds of the take-up wheel 20 and the input letoff wheel 16 of FIGURE 1.

The wrapping yarn condensation factor is a measure of the number of feet of wrapping yarn being drawn into the vortex tube over letoff wheel 32, compared with the number of feet of wrapped composite yarn leaving the vortex tube via takeup wheel 20.

The windup contraction factor is a measure of the degree of relaxation which the yarn is allowed to undergo between the letoil wheel 20 and the winder 26.

Lycra yarn is a trademark for a polyurethane yarn manufactured by E. l. du Pont.

Table 1 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Vortex tube type- A. B.. 13.- B B. Core 10 type 75's rnbber...- 44s rubbcr Lycra, Q0 d Lycra, 420 d Lycra, 420 (1. Core 10 input 252 Lp m 31l.p m 37.5 f.p.m 37.5 t.p.m. Gore 3-1 type Nyl g i 260 d None Ngio p 70 d. None. co 341 m 23s i 'm 119 pin Type of wrap Nylon 70 d. Nylon 70 d. Nylon d. Rayon 75 (1. Nylon 20 d.

34 ill. 34 fil. 7 ill. 30 til. 7 ill. Wrap input 3,773 i. p.m.. 3,758 f. p.m. 3,758 f.p.m 3,758 i.p.m. 3,758 i.p.m.-. 3,758 f.p.m. Air pressure 40 p.s.1 50 ps1 6O p.s.i. 50 p.s.i------ 80 p.s.i so p.s.i. Core yarn tension stretch factor Zero 5.0 times 5.04..- 5.04..- .0-.. 5.04. Wrapping yarn condensation factor before rclaxa- 14.97 t1mcs.. 23.8 19.9 5.96 5.97 19.9.

Speed or wrapped yarn leaving vortex tube 252 i.p.m 158 i.p.m 1S9 f.p m 530 {p m 030 [.p m 139 {.p 111 Speed of wrapped yarn at windup 252 fp m 140 in m 169 {.p m 520 f.p m 310 L1) m 169 tip in Windup contraction factor Zero 1.4%-- 10.6% 17.5% 50.8% 10.6%. Total denier of final product, relaxed 2,108" ,046..- 1,140 1,673 3,950 2. Air consumption measured by flow meter 33 cu. it. hr. 29 cu. ft. 11L..- 31 cu. ft. hr 29 cu. ft. hr 26 cu. ct. hr-.. 31 cu. ft. hr.

In Example 1 above in the table, it is noted that the rubber core is run under zero extension. Under such conditions, this low extension would normally allow the slack elastic core yarn to be whipped around by the rotating air and destroyed. This tendency has been eliminated by the addition of a second core yarn 34, as shown in FIGURE 1, of relatively inextensible material. By feeding this second core yarn under tension in close proximity to the elastic core yarn 10, the rotational velocity imparted to the elastic core yarn by the vortex tube results in the elastic core yarn twisting itself about the second core yarn 34 and being carried through the vortex tube supported in this manner.

In Example 2, it is noted that the core yarn is so tightly covered that it is held in highly extended condition. This does not mean that the resulting composite yarn is not elastic, but that the stretch factor imparted to the elastic core during the wrapping process in the vortex chamber is preserved and locked in by the wrap, so that when the composite final yarn is fully relaxed, the elastic core therein is five times the length it would show if the wrapping yarn were removed. I have found that tightly-wrapped, highly-extended yarns of this type may be treated with hot water or steam to plasticize the wrapping, whereupon the elastic core is free to contract further to as much as 50% of its dry, highlycxtended condition. This is particularly advantageous when it is desired to add further elasticity to fabrics fashioned from highly-extended yarns.

A very useful effect can be obtained from the use of theyarn of Example 3, where the Lycra elastic core is reinforced with a nylon strand, during the wrapping process. The auxiliary core yarn acts as a limit control by limiting the elongation that the composite yarn may undergo, during subsequent knitting or weaving operations. Such a limitation in elasticity enhances the evenness of the fabricating operations and the evenness of the fabricated structure. After fabrication, the fabric may be mechanically extended to the point where the auxiliary, relatively inelastic core is ruptured by being strained beyond its tensile limit. In this sense, the auxiliary core serves as a scaffolding yarn, the restraining effect of which is eliminated after it has served its purpose. By proper selection of the auxiliary core, various resistances to breaking may be developed: for instance, a 75 denier 3O filament rayon auxiliary core is relatively frangible, being readily ruptured by moderate distortion, resulting in the relaxation of the composite yarn and added elasticity in fabrics woven therefrom. Fabrics fashioned from the nylon auxiliary core of Example 3 may be treated to intermittent, zonal, or selected discontinuous overstrains to allow only certain composite yarns, or sets of yarns, to relax, with the formation of puckered or shirred effects. 7

Having thus described my invention, I claim:

1. A- wrapped elastic yarn comprising at least one continuous, generally straight, central elastomcric core strand extending generally axially of said yarn, and at least one continuous wrapping strand associated with said core strand in the form of a multiplicity of closely adjacent portions doubling back and wound in doubled configuration around and in intimate contact with said core strand, said doubled configuration providing an equal number of right-hand and left-hand turns of said trapping strand around said core strands whereby the wrapping strand of said wrapped elastic yarn is essentially free of true twist around said elastic core.

2. A wrapped elastic yarn comprising at least one continuous, generally straight, central elastomeric core strand extending generally axially of said yarn, and at least one continuous wrapping strand intimately associated with said core strand in the form of a multiplicity of closely adjacent portions consisting of doubled loops wrapped around the circumference of said core strand for a multiplicity of turns, said doubled loops being collapsed into the general form of closely spaced and partially overlapping helices, said helices being characterized by an equal number of right hand and left hand turns about said core strand, whereby the wrapping strand of said wrapped elastic yarn is essentially free of true twist around said elastic core.

3. A wrapped elastic yarn comprising at least one continuous, generally straight, central elastorneric core generally axially of said yarn, and a continuous wrapping strand intimately associated with said core strand in essentially non-slipping contact with said core strand, said wrapping strand being disposed around the circumference of said core strand in a series of wrapped loops which are wrapped around the circumference of said core yarn in a multiplicity of turns, said multiplicity of turns possessing no true net twist around the core strand with respect to the individual wrapping strand direction, said wrapped elastic yarn being relatively stable and non-kinking although wrapped with but a single wrapping strand.

4. A wrapped elastic yarn comprising at least one continuous, generally straight, central elastomcrie core strand extending generally axially of said yarn, and at least one continuous wrapping strand intimately associated with said core strand in the form of doubled-back loops wound for a multiplicity of turns around the circumference of said core strand, the doubled and looped configuration of said wrapping strand imparting no true twist of said wrapping strand around said core strand; said looped Wrapping being further characterized by being grouped into bundles in the form of overlapping helices, wherein at least some of the ends of said loops are pedicled and extend generally perpendicular to and outward from the central axis of said wrapped yarn, whereby a fuzzy surface is imparted to said wrapped yarn.

5. A wrapped elastic yarn comprising at least one continuous, straight, pro-extended central elastomeric core strand extending generally axially of said yarn, and at least one continuous wrapping strand associated with said core strand in the form of a multiplicity of closely adjacent portions doubling back and wound in doubled configuration around and in intimate contact with said core strand, said doubled configuration being characterized by an equal number of right-hand and left-hand turns around said core, whereby the wrapping strand of said wrapped elastic yarn is essentially free of true twist around said elastic core strand, said elastic core strand being maintained in stable pic-extended condition by the intimacy of contact therewith of said wrapping strand.

6. A wrapped elastic yarn comprising at least one continuous, generally straight, central elastomeric core strand and at least one relatively frangible continuous, generally straight, central non-elastic core strand, said core strands extending generally axially of said yarn, and at least one continuous wrapping strand associated with said core strands in the form of a multiplicity of closely adjacent portions doubling back and wound in doubled configuration around and in intimate contact with said core strands, said doubled configuration of the wrapping strand being characterized by an equal number of right-hand and lefthand turns around said core strands, whereby the wrapping strand of said wrapped elastic yarn is essentially free of true twist around said core strands.

7. A wrapped elastic yarn comprising at least one continuous, generally straight, pre-extended central elasto meric core strand and at least one relatively frangible,

continuous, generally straight, central non-elastic core strand, said core strands extending generally axially of said yarn, and at least one continuous wrapping strand associated with said core strands in the form of a multiplicity of closely adjacent portions doubling back and wound in doubled configuration around and in intimate contact with said core strands, said doubled wrapping configuration being characterized by an equal number of right-hand and left-hand turns around said core strands, whereby the wrapping strand of said wrapped elastic yarn is essentially free of true twist around the core strands, said elastic core strand being maintained in stable preextended condition by the intimacy of contact therewith of said wrapping strand.

References Cited in the file of this patent UNITED STATES PATENTS 1,943,437 Hopkinson Jan. 16, 1934 1,966,585 Gibbons July 17, 1934 2,588,361 Cooper Mar. 11, 1952 2,902,819 Ross Sept. 8, 1959 3,013,379 Breen Dec. 19, 1961 FOREIGN PATENTS 71,986 France Oct. 5, 1959 861,327 Great Britain Feb. 15, 1961

Claims

7. A WRAPPED ELASTIC YARN COMPRISING AT LEAST ONE CONTINUOUS, GENERALLY STRAIGHT, PRE-EXTENDED CENTRAL ELASTOMERIC CORE STRAND AND AT LEAST ONE RELATIVELY FRANGIBLE, CONTINUOUS, GENERALLY STRAIGHT, CENTRAL NON-ELASTIC CORE STRAND, SAID CORE STRANDS EXTENDING GENERALLY AXIALLY OF SAID YARN, AND AT LEAST ONE CONTINUOUS WRAPPING STRAND ASSOCIATED WITH SAID CORE STRNDS IN THE FORM OF A MULTIPLICITY OF CLOSELY ADJACENT PORTIONS DOUBLING BACK AND WOUND IN DOUBLED CONFIGURATION AROUND AND IN INTIMATE CONTACT WITH SAID CORE STRANDS, SAID DOUBLED WRAPPING CONFIGURATION BEING CHARACTERIZED BY AN EQUAL NUMBER OF RIGHT-HAND AND LEFT-HAND TURNS AROUND SAID CORE STRANDS, WHEREBY THE WRAPPING STRAND OF SAID WRAPPED ELASTIC YARN IS ESSENTIALLY FREE OF TRUE TWIST AROUND THE CORE STRANDS, SAID ELASTIC CORE STRAND BEING MAINTAINED IN STABLE PREEXTENDED CONDITION BY THE INTIMACY OF CONTACT THEREWITH OF SAID WRAPPING STRAND.