US3383849A

US3383849A - Rope strand or yarn and method of making same to reduce its whip-back characteristic at rupture

Info

Publication number: US3383849A
Application number: US571640A
Authority: US
Inventors: Stirling James
Original assignee: Individual
Current assignee: Individual
Priority date: 1966-08-10
Filing date: 1966-08-10
Publication date: 1968-05-21
Anticipated expiration: 1985-05-21

Description

May 21, 196

FIG.5

J. STIRLING 393339849 OPE STRAND OR YARN AND METHOD OF MAKING SAME TO REDUCE ITS WHIP-BACK CHARACTERISTIC AT RUPTURE Filed Aug. 10, 1966 James Stirling ATTORNEY United States Patent 3,383 849 ROPE STRAND 0R YARN AND METHOD OF MAK- ING SAME TO REDUCE ITS WHIP-BACK CHAR- ACTERISTIC AT RUPTURE James Stirling, 109-26 209th St., Queens Village, N.Y. 11429 Filed Aug. 10, 1966, Ser. No. 571,640 19 Claims. (Cl. 57-144) This invention relates in general to a safety strand or yarn and method of making the same and more specifically to a safety rope strand and method of making same in which the whip-back characteristic that results at rupture is substantially minimized.

It is well known that rope strand or yarn constructed by known conventional methods result in the core yarns of the strand being substantially shorter than the yarns formed in the succeeding cover layers. Accordingly, when the strand formed by conventional methods is stressed, the core yarns, being shorter, are subjected to greater stresses. For this reason, failure of the strand first occurs in the core yarns. Under continuing or increasing loads, failure of the strand then proceeds rapidly and progressively to the succeeding core-covering layers proceeding from the core to the outermost layer. Therefore, when a break occurs initially in the core yarns, a tremendous overload is instantly transferred toward the outer cover layers to result in a whip-back of relatively high intensity, the amount or degree of whip-back varying in accordance with the material of which the strand is formed, and with the number of yarns making up the outermost layer. The whip-back characteristic, however, is most noticeable and most dangerous in wire rope, nylon rope, and fine polypropylene filament (Prolene) rope. Because of the severe whip-back characteristic which is inherent in conventionally formed rope strands, many serious accidents have resulted therefrom. T 00 often such accidents have resulted in the death of the victim who happened to be in the way of the whiplashing rope when it ruptured. This dangerous situation is further aggravated in that the initial indications of this potentially dangerous rope condition are not rendered readily apparent by visual inspection, because such failure or rupture initiates in the inside or core yarns and continues progressively outwardly from the core yarn to the outermost cover layer yarns.

It is, therefore, an object of this invention to provide an improved rope strand or yarn construction and method of forming the same in which the whip-back characteristic of the finished rope strand is substantially minimized when rupture occurs.

Another object of this invention is to provide an improved rope strand construction and method of forming the same wherein the twist or pitch per unit length of the yarn in the respective layers is adjusted relative to one another so that maximum elongation of the yarn in the respective layers at break is progressively determined whereby the maximum elongation in the respective yarn layers is progressively increased in going from the outermost layer to the core to insure that failure of the strand will first occur in the outermost layer and then progress successively through the remaining layers inwardly toward the core.

Another object of this invention is to provide an improved rope strand or yarn construction and method of forming the same in which the length of the specific yarns making up the respective layers of the finished strand or yarn is progressively increased in going from the outermost layer to the core when formed throughout of yarn material having similar elastomeric properties.

Another object of this invention is to provide a rope construction formed entirely of synthetic material in 3,383,849 Patented May 21, 1968 which the yarn forming the core and each of the succeeding layers utilize dissimilar synthetic materials having varying degrees of stretch wherein the synthetic material having the greatest degree of stretch at break is utilized in the core, and the dissimilar materials making up the other respective layers of the strand are arranged so that the stretch of the materials in each of the respective layers is progressively decreased in going from the core to the outermost layer.

Another object of this invention is to provide a rope strand and method of making the same formed of either natural and/or man-made fibers in a manner to insure that the yarns of similar elastomeric properties in the finished strand are rendered progressively longer in going from the core to the outside layer so that when the rope breaks in service the break will occur first in the outside yarns, and then progress successively inwardly toward the core yarns.

Another object of this invention is to provide a rope strand construction and method of forming the same utilizing dissimilar materials wherein the twist or the pitch of the yarns in the core and in each of the succeeding layers is governed by the known elastomeric properties of the different materials used therein to insure that the rope strand will break from the outside of the strand toward the core.

Another object of this invention is to provide a rope strand or yarn construction and method of forming the same in which the strand or yarn breaks or fails initially in the outermost layer and then progresses inwardly toward the core so that the whip-back is restricted from any free movement until the tremendous overload is transferred to the core yarns so that the resultant whip-back is only that which is normal for whatever material is used in the relatively few core yarns.

Another object is to provide a strand or yarn construction capable of sustaining greater loads and less whipback than conventionally made ropes.

Other features and advantages will become more readily apparent when considered in view of the drawings and description in which:

FIG. 1 shows a piece of three-strand rope with one strand marked off to show the general pattern of an individual cover yarn.

FIG. 2 is an enlarged cross-section of the rope taken along line 22 of FIG. 1.

FIG. 3 illustrates a piece of three-strand rope in which the lays of the respective individual components thereof are emphasized.

FIG. 4 is a modified showing of a strand formed with 3-ply yarn with Z twist made of 3 singles of S twist.

FIG. 5 is a diagrammatic showing of a rope strand or yarn construction in which the respective layers of yarn for a unit length of strand are illustrated in an expanded relation to illustrate the correlation of individual yarn length and pitch of the respective yarn elements in each of the respective strand layers per unit length of strand.

Referring to the drawings, there is illustrated in FIG. 1 a length of rope 10 embodying the improved rope strand and/ or yarn construction of this invention. The illustrated rope construction 10 is made up of three strands 11, 12 and 13. One of the strands 11 is marked off as indicated at 14 to show the general pattern of an individual cover yarn. Accordingly, the outside cover yarn 14 is shaded darker to illustrate how it shows up on the outside and travels in a spiral around the outside of the strand going from the inside of the rope and reappearing on the outside again in a distance approximately equal to the lay of the rope.

FIG. 2 illustrates the cross-section of the rope of FIG. 1. It will be noted that each of the respective strands 11,

12, 13 comprises a

core

11A, 12A, 13A and a plurality of concentrically disposed layers including an

intermediate layer

11B, 12B, 13B and an

outermost cover layer

11B, 12B, 133. Each of the respective layers is formed of several ends or yarns which are twisted in layers concentrically disposed one on another about a common axis. While only one intermediate layer is shown, it will be understood that more than one intermediate layer may be provided depending upon the size of the desired rope.

FIG. 3 illustrates, for example, a rope construction in which the respective direction of twist of the individual rope components making up the rope are emphasized. In the illustrated example it will be noted that three strands 11, 12, 13 are twisted together so that they slope upwardly and to the right to define a right or Z-twist, as it is normally referred to in the art. For illustrative purposes, a Z is superimposed on the lay of strands 11, 12, and 13. Accordingly, the yarns in the cover or outermost layer of each of the respective strands 11, 12, 13 are laid so that they slope upwardly and to the left with a left or S-twist or lay. This is indicated by the S formed on the individual strands 11, 12 and 13. It will be noted that if the respective layers are formed of single yarns, then the respective single yarns are twisted or laid with a twist which is opposite tothat of the layer which includes it. For example, if the outer cover is formed of single yarns and the individual ends therein are laid with a left twist, the twist of the individual single yard making up the outer cover layer is to the right or Z-twisted. This is shown in FIG. 3 at 15 where the cover yarn of the strand is magnified.

If the respective layers of the strand are formed of a plied yarn as indicated at 16, then the plied yarn 16 which makes up the respective layers is twisted in the direction opposite to that which the yarn in a given layer is laid, with a single of the plied yarn 17 being twisted in the direction opposite to the twist or lay of the plied yarn. For example, if the cover layer 11C is formed of a plurality of plied yarns and the cover yarns are twisted with a left or S lay as shown in FIG. 3, then the individual plied yarns 16 are plied to the right with a Z-twist, whereas the individual singles of the plied yarns are formed with a left or S-twist. Thus, it will be noted that the twist of the individual yarns in each of the respective layers of the strand is always opposite that of the layer which includes the same.

FIG. 5 is a schematic showing of a strand construction, e.g. strand 11 embodying the instant invention. As shown in FIG. 5, for purposes of description, a linear unit length of a finished strand measured along the axis thereof is identified as L and the respective layers of the strand, i.e. 11A, 11B, and 110 are each illustrated in an expanded or stretched out relationship rather than in a concentric overlying relationship as would be the case in an actual construction. The present invention contemplates that a rope strand construction, be it made of either natural and/or man-made fibers, is constructed so that in a strand formed of yarns having similar elastomeric properties, the yarns in the respective layers are made progressively longer in going from the outside layer toward the core so that when the rope breaks in service, the break will occur from the outside layer 11C and progress inwardly toward the core 11A. To attain this relative relationship of length in the respective layers of the strand, the pitch of the yarn in the respective layers is controlled. Thus, as it is evidenced in FIG. 5, the individual length of the respective twisted yarns YL YL and YL in the core layer 11A, the core cover layer 11B, and the outermost layer 11C, is determined by the respective pitch P P P of the yarn in each of the respective layers. It will be noted therefore that actual linear length LY of the yarn in the core layer 11A is greater than the actual linear length of the yarns LY in layer 1113 and that the length YLg of yarns in layer 11B is still greater than the length of yarn YL in layer 11C. It is to be further noted that the number of ends or yarns YL twisted in making up the core 11A are generally much fewer than the ends or yarns YL making up the layer 11B, and that the number of ends or yarns LY making up the layer 11B is still less than the number of yarns or ends LY making up layer 110, as noted in FIG. 2. By way of example, if a strand is made up of 48 ends, 6 such ends may define the core, 18 may be disposed in the layer about the core, and 24 disposed in the outermost or cover layer.

It will then be noted that when a rope whose strands are constructed as described herein is subjected to a breaking stress the rupture will start from the outside since these yarns are the shortest and subjected to the greatest stresses. Continued breaking loads imparted on the strand 11 cause the rupture to progress inwardly toward the core. In doing so, the free movement of the whip-back for the progressively ruptured yarns YL in the outer layer will be restricted till final separation takes place in the core yarns YL Thus the whip-back characteristic of the strand constructed as herein described is restricted until the overload is transferred to the core yarns YL so that the resultant whip-back is only that which is normal for the material used in the relatively few core yarns YL In the event that the strand 11 is to be formed of dissimilar materials, i.e. material having different elastomeric properties, it will be understood that the pitch P P P of the yarns in the core 11a and in each of the succeeding

layers

11B, 11C will be governed by the known elastomeric properties of the difierent materials used. By controlling the pitch in the respective layers the length of the respective yarns therein can be determined to insure that the rope strand will break first in the outermost layer and thence progress inwardly toward the core.

If the strand 11 is formed entirely of synthetic yarns in which the core and the one or more of the layers twisted about the core are respectively formed of dissimilar synthetic materials, the synthetic material having the greatest degree of stretch at break is utilized in the core and the other dissimilar material or materials of other varying degrees of stretch are arranged so that the yarn material with the least stretch at break forms the outside layer, and the material of intermediate degrees of stretch being arranged so that the degree of stretch progressively diminishes from the core to the outermost layer.

The relative stretch at break for the more commonly used synthetic materials in rope construction listed in the order from greatest to least stretch are Prolene, nylon, polypropylene (mono-filament), polyethylene, and polyester.

For example in a synthetic 3-layer strand formed in accordance with this invention from a combination of Prolene, nylon and polyester fibers, the core yarns would be formed of Prolene, with nylon placed in corecover yarns and the polyester placed in the outermost layer.

For even greater effect the twist of the respective layers of the synthetic yarn may likewise be varied so that the pitch of the respective layers is progressively adjusted or controlled from the core to the outside layer only by the correct amount which insures that the break will occur from the outside in toward the core. In this manner maximum strength is attained with minimum whip-back.

It will be appreciated and understood that the concept herein described with respect to a strand construction may also be applied to the construction of the yarn per se, which may be used in the strand structure. For purposes of discussion, a three-ply yarn is regarded as a miniature three-strand rope with similar structural features, and single yarns are considered analogous to a rope strand inasmuch as single yarns are built up by individual fibers or ends in numbers commensurate with the size desired, just as a rope strand is built up of individual yarns in numbers commensurate with the size of rope strand desired. Therefore, the same concept embodied herein with respect to the rope strand may be carried out in single yarn construction and/ or in singles before plying.

As the instant invention is applied to single yarn construction, the twist of the plurality of fibers or ends constituting the core and the respective covering layer or layers of fibers where each has similar elastomeric properties, is progressively increased in going from the outside cover layer to the core to insure that the fibers in the outermost covering layer will reach their maximum elongation and rupture first, with the maximum elongation of each of the succeeding layers of the yarn being reached successively in going from the outermost layer to the core. Similarly, when dissimilar fibers are used in a single yarn construction, the twist of the fibers constituting the core and each succeeding layer of layers of the yarn is governed by the known elastomeric properties of the material used in the respective layers thereof in such a way as to insure that the break will occur from the outside in toward the core, instead of from the core out to the covering layers as is the case when such single yarns are conventionally twisted.

The whip-back at breaking stress for yarns, either singles or plied, when made in accordance with this invention, is noticeably less than the whip-back of conventionally twisted yarns.

rom the foregoing it can be appreciated that when the break occurs in a strand made in accordance with this invention, the rupture starts from the outermost strand layer and progresses inwardly toward the core thereby restricting the free movement of the whip-back of the rup tured outside yarns until separation takes place in the core yarns. The instant invention further contemplates minimizing the whipback of the core yarns by constructing the core yams in accordance with this invention as the invention applies to the single yarn construction hereinbefore described. It is to be noted that the strength of the single yarns made in accordance with this invention is somewhat less than the strength of the single yarns made in accordance with my Patent 3,201,930 wherein substantial equality of the fiber length was desired. Therefore, for optimum results in reducing whip-back while still maintaining high strength, the invention as it applied to single yarns structure should only be used in the yarns in the core.

In accordance with this invention care should be exercised in controlling the twist in a rope strand to avoid twisting the inside yarns more than that necessary to insure that the break will progress from the outside toward the core, particularly in the type of strand structure where the core and the covering layer or layers are all twisted in the same direction. In rope utilizing the strand construction of this invention, any overtwist going toward the inside would enhance the danger of failure in the splicing test as prescribed by Federal Specifications MILR17343C for nylon rope. To avoid the danger of failure in this splicing test and to permit a considerable margin of error in manufacturing rope strand of this invention, the twist of the yarns constituting the core and the direction of twist for the covering layer or layers may be alternated or varied so that the outside covering layer of the strand is twisted opposite to the direction in which it is layed in the rope which includes the strand. It should be noted that the yarns used in different stages of the strand structure are twisted or plied in the direction that is opposite to the stage in which they are used.

The method of making the improved strand of rope in accordance with this invention comprises the steps of progressively twisting a plurality of ends or yarns to form a core having a predetermined pit-ch, e.g. P to result in a particular number of turns per unit length necessary to attain a given length YL which is predetermined by the physical characteristics of the material making up the core. A plurality of other yarns are simultaneously and successively twisted about the axis of the core in a concentric layer about the core layer whereby the pitch P of the succeeding core-covering layer is controlled so that in a finished strand L the unit length of yarns YL in the core-cover layer 11B is proportional to that of the core yarns so that where materials having similar elastomeric properties in the respective layers are utilized, the length of the yarn YL in the core-covering layer 1113 is proportionately shorter by a predetermined amount to the length of the yarn YL in the core. Thus, when the strand is subjected to a breaking stress, any break or rupture will occur first in the outermost layer and progress inwardly toward the core.

In accordance with this invention, one or more layers may be simultaneously twisted in concentric layers upon the core 11A and each other whereby the pitch, i.e. the number of turns per unit length in each succeeding layer from the core to the outermost layer is progressively controlled in accordance with the known elastomeric properties of the materials so that in breaking or rupturing, the break will occur from the outermost layer and progress inwardly toward the core.

In making rope having dissimilar materials the pitch of the yarns in the core and in each of the succeeding layers is governed by the known elastomeric properties of the different materials used, to insure that the rope strand will break from the outside of the strand and progress inwardly toward the core.

In the event that synthetic yarns are used the invention contemplates the utilization of the physical properties of the respective synthetic fibers making up the rope strand to effect the relative proportional elongation of the rope yarns or fibers at break so that the yarns in each layer will attain their maximum elongation at break successively in going from the outside layer inwardly toward the core. In such instances, the material having the greatest stretch is used in the core and the materials having progressively decreasing amounts of stretch are utilized in the succeeding layers in going from the core to the outermost layer. It is, of course, contemplated that the twist of the respective layers making up the strand and/or yarn can be twisted in the same direction or opposite directions, and that the method is equally applicable in making strand or yarn of synthetic and/or natural fibers.

In making strand or yarn of synthetic fibers the method described contemplates the utilization of the physical properties of the respective synthetic fibers to effect the relative degree of proportional elongation at break so that rupture of the respective yarns will occur progressively in the respective stages in going from the outermost layer and inwardly toward the core.

The method herein also contemplates the construction of individual core yarns of a given strand in accordance with the instant invention to further minimize Whip-back of the core yarns 'at rupture.

The method herein described can be readily performed on the apparatus disclosed in my prior Patents 3,097,472 and 3,251,178 by utilization of the appropriate gear ratio for each state or table of the apparatus.

From the foregoing it will be noted that whereas the disclosure in my Patent No. 3,201,930 related to a method of constructing a strand or yarn in which substantial equal elongation of the respective fibers at break was described for attaining maximum strength, the instant invention contemplates a strand construction and method wherein the pitch of the yarn in the respective stages thereof is controlled to attain a progressive or varying degree of maximum elongation of the respective yarns in each of the respective stages of the strand and/or yarn to insure that at rupture the strand will fail in the outermost layer first, and thence progress inwardly to the succeeding stages in going from the outermost layer inwardly toward the core to minimize the whip-back characteristic of a rupture strand to that of the relatively few yarns which define the core thereof, and the whip-back being further reduced by carrying out the structure of the invention to the individual yarns making up the core.

In another form of the invention maximum strength with reduced whip-back can be attained in a strand construction in which all the yarns in the respective layers surrounding the core and each other are made substantially equal as disclosed in my US. Letters Patent No. 3,201,930, with the core yarns only made longer than the yarns in the covering layers in accordance with the disclosures herein. With this type of strand construction, maximum strength is attained because of the equality of length of the respective yarns in the covering layers, and which when rupture does occur, the free movement of the whiplash of the covering layers is restricted until the core yarns, which are longer, break. If desired, further reduction in whiplash can be attained when the invention is applied or carried out in the construction of the respective yarn elements which made up the core of a given strand.

While the instant invention has been described with respect to the various embodiments disclosed herein, it will be appreciated and understood that variations and modifications may be made without departing from the spirit or scope of the invention.

What is claimed is:

1. A rope strand comprising a core including a plurality of yarns twisted about a common axis at a predetermined pitch per unit length, and

a layer of individual yarn elements twisted about said common axis onto and about said core whereby the pitch per said unit length of said layer of yarn is adjusted in relationship to the pitch per unit length of said core measured along said common axis so that the individual yarns in said covering layer attain their maximum elongation first and the maximum elongation will be reached by the succeeding layers of yarn in succession going toward the core. 2. The invention as defined in claim 1 wherein the yarns in said core and in said layer are formed of a material having substantially similar properties of stretch whereby the length of the individual yarn in said layer and said core is progressively longer going from the outside of the strand layer toward the core.

3. The invention as defined in claim 1 wherein the yarns in said core and in said layer are formed of dissimilar materials and the respective twist of the yarns in the core and in the succeeding layers is governed by the known elastomeric properties of the different materials used so as to insure that the rope strand breaks from the outside of the strand toward the core.

4. The invention as defined in claim 3 wherein the yarn formed of a material having the greatest stretch at its breaking stress is utilized in the core,

and that the other layer surrounding said core utilizes yarn formed of a material having a progressively decreasing degree of stretch at break.

5. An improved safety strand of rope having a minimum of whip-back when a break occurs comprising a plurality of layers including a core and at least one layer,

said core including a plurality of yarns twisted about a common axis at a predetermined pitch per unit length, and

said layer being formed of individual yarns concentrically twisted about said core and each other about said common axis whereby the pitch per unit length of said layer is adjusted relative to the pitch per unit length of said core measured along said common axis so that the yarns in said layers attain their maximum elongation progressively from the outermost layer in before the yarns in said core attain their maximum elongation to insure that the yarns in said layers and in said core break successively from the outermost 5% layer to the core when said strand is subjected to a breaking load.

6. The invention as defined in claim 5 wherein said yarns in said core and said cover layer have similar elastomeric properties,

and the length of the respective yarns in said layer and in said core increase progressively from the outside of the strand to the core.

7. The invention as defined in claim 5 wherein the yarns in said core and said layer are formed of dissimilar material whereby the twist in said core and said layer is governed by the known elastomeric properties of the material from which the respective yarns of said core and said layer are formed so that the strand will break from the outside of the strand toward the core.

8. The invention as defined in claim 5 wherein the respective yarns in said core comprise of a plurality of fibers,

a portion of the fibers in said core yarns twisted to define a core for said core yarns and another portion of said fibers in said core yarns being twisted about said twisted core fibers of said core yarn whereby the pitch per unit length of said fiber layer of said core yarn is adjusted relative to the pitch per unit length of said core fiber in said core yarn so that the fibers in said fiber layer attain maximum elongation before the fibers in said fiber core to insure that said core yarns break from the outside of the core yarns to the inside thereof.

9. The invention as defined in claim 1 and including a second cover layer twisted about said first-mentioned layer about said common axis whereby the pitch er unit length of the respective layers and said core is adjusted relative the pitch per unit length measured along said axis so that the yarns in each of said cover layers and in said core attain their respective maximum elongation successively from the outermost layer toward the core to insure a progressive breaking of the strand from the outermost layer to the core.

10. The invention as define-d in claim 1 and including a plurality of concentric cover layers of yarn twisted about said first-mentioned cover layer about said common axis whereby the pitch per unit length of the respective cover layers and said core is adjusted relative to the pitch per unit length measured along said axis so that the yarns in each of said cover layers and in said core attain their respective maximum elongation successively from the outermost layer of the strand to the core of the strand, whereby the breaking of the strand occurs progressively from the outermost layer to the core.

11. The invention as defined in claim 1 wherein the yarns in said core and in said cover layer are formed of material having dissimilar properties of stretch. whereby the yarn material having the greatest stretch is utilized in the core and the material of the yarn used in said layer having a lesser degree of stretch.

12. The invention as defined in claim 1 wherein the yarns forming the core are twisted about said axis in one direction and the yarns lai-d onto the core being twisted about said axis in the opposite direction.

13. The invention as defined in claim 10 wherein the yarns forming the core are twisted in one direction; and the yarns in each of the other succeeding layers are twisted in a direction relative to said core in a manner such that the outermost layer of the strand is twisted opposite to the lay of a rope including the strand.

14. A method of making an improved safety rope element that has a minimum of whip-back when a break occurs in one continuous operation comprising the steps of twisting a plurality of ends to form a core,

simultaneously twisting a covering layer of individual ends onto said core,

and simultaneously varying the pitch of the core and said layer of ends about said core whereby the pitch from the core to the outermost layer is progressively controlled in accordance to the elastomeric properties of the respective fibers in said core and said layer so that the ends in said outermost layer attain their maximum elongation before the ends in said core whereby said rope element under a breaking load breaks progressively inwardly from the outermost layer to the core.

15. The method as defined in claim 14 and including the steps of forming the ends making up the core of a material having less stretch than the material making up the ends in said layer.

16. A method of making a multiple-layer rope strand comprising the steps of rawing a plurality of yarn from a source,

twisting said yarns as they are drawn from the source to form a core,

forming said twist so as to have a predetermined pitch per unit length of said core, simultaneously pulling another plurality of yarn having substantially similar elastomeric properties as the yarn forming said core from another source,

twisting said second-mentioned yarns about said core to form a covering layer therefor as said core is formed,

controlling the pitch of each layer and said core per unit length from the core to the outermost layer so that the yarns in said core and said layers attain their respective maximum elongation progressively from the outermost layer to the core to insure a progressively inwardly breaking of the yarns in the respective layers from the outside of the strand.

17. The method as defined in claim 15 wherein the yarns of the respective layers are formed of material having dissimilar elastomeric properties, wherein the stretch of the material of the yarns making up the respective layers is progressively decreased from the outside in.

18. The invention as defined in claim 1 and including:

additional layers of individual yarn elements twisted about said common axis onto and about said core and said core covering layer whereby the pitch per unit length of said core covering layer and said additional layers is governed by the known elastomeric properties of the respective yarns in said core covering layer and said additional layers so that each of said yarns in said layer surrounding said core is substantially uniformly stressed at a given maximum load and which when rupture occurs therein, the free movement of the whiplash of said covering layers is restricted until the core yarns break.

19. The invention as defined in claim 18 wherein the core yarns include a plurality of individual ends,

a portion of said ends being twisted about a common axis at a predetermined pitch per unit length, and

a second portion of said individual ends being laid in a layer twisted about the said ends defining the core of the core yarns whereby the pitch per unit length of the layer of said yarn ends is adjusted relative the pitch of the ends of the core of said yarns measured along the common axis so that the individual ends in said core layer attain maximum elongation before that of the ends in the core of said core yarns.

References Cited UNITED STATES PATENTS 728,399 5/1903 Kirsch 57l44 809,386 l/l906 Metcalf 57l44 2,133,071 10/1938 Anderson et al. 57l53 2,190,854 2/1940 Whitlock 57-144 2,281,036 4/1942 Hetzel fl 57-144 2,433,864 3/1948 Reed 57l44 3,071,919 l/l963 Lord 57l44 XR 3,197,953 8/1965 Dawbarn et a1. 57--l44, XR 3,201,930 8/1965 Stirling 5715 XR 3,323,301 6/1967 Jackson 57-144 FRANK J. COHEN, Primary Examiner.

D. WATKINS, Assistant Examiner.

Claims

1. A ROPE STRAND COMPRISING: A CORE INCLUDING A PLURALITY OF YARNS TWISTED ABOUT A COMMON AXIS AT A PREDETERMINED PITCH PER UNIT LENGTH, AND A LAYER OF INDIVIDUAL YARN ELEMENTS TWISTED ABOUT SAID COMMON AXIS ONTO AND ABOUT SAID CORE WHEREBY THE PITCH PER SAID UNIT LENGTH OF SAID LAYER OF YAN IS ADJUSTED IN RELATIONSHIP TO THE PITCH PER UNIT LENGTH OF SAID CORE MEASURED ALONG SAID COMMON AXIS SO THAT THE INDIVIDUAL YARNS IN SAID COVERING LAYER ATTAIN THEIR MAXIMUM ELONGATION FIRST AND THE MAXIMUM ELONGATION WILL BE REACHED BY THE SUCCEEDING LAYERS OF YARN IN SUCCESSION GOING TOWARD THE CORE.