US2132492A - Rayon structure - Google Patents

Description

C2620 TRENGTH IN Poumis Coeo STRENGTH 1N Pom-ms Oct. 11, 1938. H. PARKER 2,132,492

RAYON STRUCTURE Filed June 21, 1934 RAYcm CORD 22 v El YPTlAN 5m Co'lToN (0E0 INTERNEDIAT TFAND TWH5T (TURNS PER [NcH l5 CABLE TW|$T 4 Tumas P52 INch. 25

A Z3 CABLETWIST l0 Tums PER [NCH INTERMEDIATE; STI'ZAND TWlST (TURNS PER INCH) INVENTOR. I J-[ar0ld JLParker ATTO RN ELY.

Patented Oct. 11,1938

itAiroN STRUCTURE Harold B. Parker, Kenmore, N. E, assignor, by

mcsne assignments, to E. ii. du Pont de Nemours & Company, Wilmington, Deh, a. cor

poi-ation of Delaware Application June 2i, 1934, Serial No. 731,719 12 Claims. (Cl. 117-552) This invention relates to the art of twisting to the behavior of cotton threads which are doncontinuous filamentary threads and pertains parbled and twisted into cord. I ticularly to the doubling and twisting of strong This loss in strength can better be comprerayon. hended from 'a study of the following facts. An

Ingeneral, tires and various other rubber prodelemental thread of 275 denierfilament ucts have been reenforced with a fabric prestrong rayon having a twist of 7 turns per inch, pared from highly twisted cotton cord. In order prior to combining into a cord, may have an avto get the maximum strength from cotton, the cotton fibers from which the threads and cords are formed must be tightly twisted, the maximum strength of cotton cords being obtained when the intermediate strands, from which the cords are made, are relatively highly twisted. Cotton cords, adapted for use in the reenforcement of rubber vehicle tires, have been made, for example, by twisting elemental cotton threads of- 23 count to about 16 turns per inch and then, five of these threads being united to form a strand by twisting them together 20 turns per inch in the opposite direction, and finally three such intermediate strands being united to form the final cord by twisting 10 turns per inch in the direction opposite to the intermediate twist. This construction cord, commonly referred to as 23-5-8 construction, results in a cotton cord having a strength goer unit weight substantially equal to the strengthof the elemental thread, that ismthere is no appreciable loss in strength as a result of the high degree of twist.

Recentiy, it has been proposed that strong rayon threads be substituted for cotton threads in the preparation of cords to be used in the reenforcement of rubber. Inmaking cordfrom strong rayon which is comparable to,cotton cord of the 23-50%. construction, five threads of 2'75 denier-120 filament strong rayon;-twistecl to 7 turns per inch, are twisted together to about 20 turns per inch in a direction opposite to the twist in the threads. Three strands thus formed are then combined to form a cord by twisting them 10 turns per inch in a direction opposite to the strand twist and thus in the same direction as the thread twist. Such a cord is referred to as 275-5-3 construction, the number 2'75 designating the thread denier; 5, the number of threads making up the strand; and 3, the number of strands in the cable, It has been found, however, that when cords are prepared from strong. rayon in the manner described, the cords do not possess proportionately as muchstrength as the threads from which they are preparedthe cord strength per unit weight in some cases being only 50% of the original thread strength. This is directly contrary of 3 grams per denier- When this thread is combined into cord of the 275-5-3 construction according to the prior art method described above, the cord has a denier of about 5100 and the strength'per unit weight is only about half the thread strength, being 16 pounds, or about 1.42 grams per, denier.

One object of this invention comprises a new method of twisting strung rayon. Another object of the. invention rfiates to the making of strands, cords and the like, from strong rayon in such a manner that the tenacity per unit strands and cords made from strong rayon.

A further object of the invention pertains to the making of strands or-cords from strong rayon which have astrength per denier substantially equal to or nearly equal to the strength per denier of the original threads. Another object of the invention is to provide an improved cord structure. Other objects will be apparent hereinafter.

Fig. 1 is a graphic illustration of the relative strength of strong rayon cord compared with that of cotton cord, plotted against intermediate strand twist. Fig. 2 is a graphic illustration of strong rayon'cord strength plotted against intermediate' strand twists, for cords of diifere'nt cable twist.

It has been discovered, in accordance with the present invention, that strands and cords may be formedff'om strong rayon thread without losing any great amount of the efiective strength of the thread, by imparting to the thread and/or strands a low degree of twist. Although strands and cords having a low degree of twist do not, in general, possess the same high degree of elasfailure as highly twisted structures, it is highly important,'for many uses where high elasticity and high elongation are not required, that the plied structures possess a tenacity, both at ordinary temperatures and at elevated temperatures, per unit of weight, as close to the tenacity of the elemental threads as possible. Since this result can be achieved by the low-twisting method of the-present invention, it greatly increases erage dry tensile strength at room temperature weight is greatlyin excess of that of prior art ticity and high percentage elongation before the utility of cords and the like made from strong whether a twist is a high twist or a low twist is by reference to the helix angle. Helix angle" is defined in an article An Introduction to the Micro-Analysis of Yarn Twist by E. R. Schwarz, published in the Journal of. the Textile Institutefor March, 1933. Using the equation developed by the above author, the helix angle for the strands which have been twisted 20 turns per inch and prior to being twisted into cord of the 275-5-3 construction, is approximately 40.

The twist (calculated by the equation referred to in said article) required for structures of different deniers to produce a 40 helix angle are summarized in the following table:

Number or vDenier 1 turnsper inch The intermediate strands described above in connection with the production of cord of the 275-5-3 type from strong rayon, have a denier.

of 1660 when twisted 20 turns per inch, and possess a high twist. g

a For the purposes of this invention, low twist, whether in a strand or in a cable, signifies a helix angle not higher than 33 as computed by the equation given in the publication above referred to.

In. applying the principles of the invention, elementary threads of strong rayon having a twist comparable to about 4 to 7 turns in a thread ot the 2'75 denier-120 filament type, are twisted to a low degree of twist to give a strand structure. when it is desired to twist the strands into cord. it is generally preferred that the cord structure also have a low degree of twist.

In strands prepared from 5 threads 275 denier-120 filament strong rayon, the twist will not be more than about 12 turns per inch, and will preferably be from 3 to 10 turns. In cords prepared from 3 of these strands, where'it is desired to have a low twist in the cord, the twist of will not be more than about 6 turns, and will preferably be about 4 to 6 turns per inch, or the amount of cable twist to give a balanced structure will be imparted to the cord, this twist, in

general, being about half the number of turns which were put in the strand twist. V

The following examples are given by way of illustrating modes of practicing the invention: (Example I.An undesulfured, unbleached; 2'15 denier-120 filament thread is prepared as described in my co-pending application, Serial No.

676,463. After washing the thread acid-tree, it

is treated in any suitable manner with a 0.2% aqueous solution of olive 'oil soap and dried. The

7 thread has a dry tenacity of about 3 grams per denier at room temperature anda dry elongation opposite direction turns per inch, three of these intermediate strands then being combined 5 by twisting in the reverse direction to 4 turns per inch to form a cord of the cable type. The denier of this cord is about 4100 or 19% less than that of a cord of the 275-5-3 construction constructed with an intermediate twist of 20 turns and a cable twist of 10 turns per inch, and yet the total tenacity is in the neighborhood of 45% greater, e. g. 23.2 lbs. (2.5 grams per denier) as compared with 16 lbs. (1.42 grams per denier) for prior art strong rayo'n cord, with a dry elongation at room temperature 'at the breaking point of about 10% as compared with the elongation of the highly twisted prior art cord of about 26%.

Erample II .-An undesulfured, regenerated cellulose thread, prepared as described in Example I, is dried and then twisted to 7 turns per inch. Five of these single threads are combined with twisting while drawing them through a water bath in any suitable manner so that they are combined to form an intermediatestrand having a twist of 8 turns per inch opposite to the twist initially put in the thread. Three of these intermediate strands are then twisted together in the wet state, in the'direction opposite to that used in the formation of the intermediate strand, to 4 30 turns per inch. The resulting cord strength per denier is about 29 lbs. (2.56 grams per denier), or 80% greater than that of previously known strong rayon cords of the same character which have been dry twisted in a single operation and which have 20 turns, intermediate twist and 10 turns cable twist. The tenacity of the cord produced in accordance with this example is about 2.56 grams per denier. Furthermore, the diameter of the cord is 40 approximately 15% less than that of the highly twisted cord just referred to; the diameter 0! which is 0.034 inch, and therefore a greater number of cords per inch can be used in preparing a fabric for use in tires, for belting, or other simi- .lar uses, thereby imparting additional strength and durability to such articles.

. Example III .Six unit threads prepared as described in Example I are doubled and twisted in the reverse direction to 5 turns per inch and m then formed into a cable by combining three of these intermediate strands and again reversing the twist to 4 turns per inch. Although this cord contains 18 unit threads instead of 13, the size of the cord is no greater than that of the cord of the 275-5-3 construction prepared according to H the prior art with high twist, either in diameter or in weight per unit length, but the strength of this cord is about 29.8 pounds or about 2.63

grams per denier, being nearly double that of the comparable prior art strong rayon cord.

. Example IV.--Five unit threads as described in Example I are doubled, twisting them together in the reverse directionto '7 turns per inch, and then formed into a cable by combining three of these strands and again reversing the twist to 10 7 turns per inch. This cord is characterized by low strand twist as in the preceding examples and differs because of the high cable twist. The

reduction in the intermediate strand twist results in obtaining a cable having about 19 lbs. strength, or 1.8 grams per denier, beingan increase in strength of about 20% over high twist cord. The maintenance of the high degree'of twist in the cabling gives the requisite spiral formation to greases the cord structure which is essential where elasticity in the cord is desired.

Example V.Four unit threads prepared as described in Example I are doubled and twisted togather in the reverse direction to the thread twist to turns per inch. Three of these strands are then combined and twisted together in the direction opposite to the strand twist to 10 turns perinch. The cord so'formed is somewhat stronger 10 than the cord produced with high intermediate strand twist and having the same number of unit threads, but as in the preceding example, the cord has the desired spiral formation, with good elasticity.

Example VI.The formation of the cord in this example is the same as in Examples IV and V, except that both the strand twisting and cord twisting operations are carried out in the wet state. By twisting the threads in the wet state,

- the twist is set, the structure is condensed, and the cord is as easily handled as a cord prepared of balanced structure.

Example VII.--Instead of starting. with the thread used in the preceding examples, 1100 denier-480 filament thread, having a gram per denier strength of about 3 grams and twisted to '10 turns per inch, is used. Three of these threads are plied together with a twist of 10 turns in the direction opposite to the twist of the thread. This cord has a strength of about 20.2 lbs. (2.4 grams per denier). .It has a diameter of 0.031 inch and a gram per meter weight of 0.42.

Example VIII.-Three 1400 denier-600 filament threads, having a gram per denier strength as of about'3.0 and a twist of 4 turns per inch, are

combined bytwisting in the direction opposite to the thread twist to 2 turns per inch. This cord hasa strength of about 27 lbs., or 2.72 grams per denier. 40 My invention is described primarily in the preparation of cable type cords wherein the twist is reversed in each succeeding operation, but it is, of course, as applicable to the hawser type in which the twist is in the same direction in the first two operations and is reversed in the third. It will thus be seen from the examples that the invention is characterized by twisted structures of unusually high strength. In considering the prior art, it should be understood that the loss in effective cord strength is due to two things,

(1) the degradation of the yarn because it is twisted too tightly, andv (2) the position of the threads or strands in the cord. I have found by untwisting numerous cords, and again testing the elemental threads that the loss of strength due to degradation is in general about 30% when cords are prepared according to the prior art. when cords are prepared according to my invention, there is'no appreciable degradationof the 0" thread, for in numerous instances when threads are removed from cord by untwisting the cords and tested, these threads show the same strength as they possessed before doubling and twisting.

A considerable loss in strength is also due to the 5 position of the threads or the strands inthe cords. If the twist is high, then the pull on the cord is largely across the thread or strand rather than in the direction of the length of the thread or strand, or the stress applied to the cord acts 7 upon the elementary parts largely in the directiofiof lesser strength. On'the other hand, when c ords are prepared according to my invention,

i. e. with a low'degree of twist, the threads and strands comprising the cord extend substantially 1 in the direction of the cord and-when a force is denier, the cords being of the tion. In these cords, the amount or cable twist applied, the elemental parts can better resist it, for, in this case, the force will act to a much greater degree in the direction of greatest strength.

Experimental tests show that cotton cord of 5 the 23-5-3 construction attains its maximum strength when the intermediate strands are twisted to about 16 turns per inch prior to being doubled and twisted into cord. Cord of the 275-5-3 construction, made from strong rayon thread, as described above, has its maximum strength when the intermediate strand twist is from 0 to about 5 or 6 turns per inch prior to forming cord from the strands, and the strength gradually decreases as the amountof strand twist increases beyond this range. The curves shown in Fig. l of the drawing graphically illustrate the strength of comparable rayon and cotton cords under various conditions of intermediate twist, the rayon cords being prepared from rayon threads or yarn having a strength of 3 grams per 275-5-3 construcis adjusted in each case so as to give a balanced cord. Generally, this is secured when the cable .25

is approximately one-half the intermediate WIS In Fig. 1, the ordinates represent strength of the cord in pounds and the abscissae represent .the number of turns per inch imparted to the intermediate strand prior to being twisted into cord of the construction described.

To illustrate furtherthe eifect of strand twist on cord strength, I prepared cords with constant cable twist, but varied the twistimparted to the 35 intermediate strand prior to the cord-forming operation. These cords were all prepared by twisting 5 threads of 275 denier-120 filament strong rayon having a strength of 3 grams per denier, and having a thread twist of 7 turns per 40 inch, into strands having a varied intermediate strand twist, then twisting three of the strands int-o cable by imparting a constant cable twist in a direction, opposite to the twist of the strands. The curves shown in Fig. 2 graphically illustrate 45 the results, the ordinates representing the cord strength in pounds and the abscissae represent ing the twist in turns per inch imparted to the intermediate strands prior to the cord-formin operation.

It will be noted from Fig. 2 that, as the intermediate strand twist is kept constant, the strength of the cord increases as the twist in the cable decreases. Also, as the cable twist is kept constant, the strength in the cord increases as 55 the twist in the intermediate stranddecreases.

It will thus be seen that it is'possible to attain the same cord strength in a cable having a twist of 10 turns per inch as in a cable having a twist. of 4 turns per inch Wherethe strand twist in Q the former is approximately 7 turns per inch less than the strand twist in the latter. Hence, where it .is desirable to produce a cable having a higli degree of elasticity and elongation, asin Ex-. amples IV, V and VI, this result can be attained, while still preserving a high tenacity for the cord, by'imparting a low twist to the intermediate strand prior to the cord-forming operation.

The graphical illustrations previously dis cussed, i. e. Figs. 1 and 2, have not taken into account the increase in size of the cord resulting from increased twist. If the cords were compared on the same diameter or weight basis, the decrease in strength at higher twists would be' even more marked. The table below con- TABLI I Variation in strength of'rayon cord with twist Pounds Strength Inter- Cable is? h Dlamebased on Grams mediate Denier twist number ter cord constant per twist of Dues in inches diameter denier constant at 5100 10 16. 0 0. 034 14. 3 l. 42 4860 8 l8. 7 0. 033 17. 8 l. 75 4650 6 20. 9 0. 0325 20. 3 2. 03 4450 4 22. 6 0. 032 22. 6 2. 31' 4250 2 24. 1 0. 0315 24. 8 2. 66

The cord referred to in the above table-is of the 275--3 construction and was prepared from thread of 275 denier-120 filament strong rayon having a strength. of about 3 grams per denier, according to the method described above for preparing cord of this construction.

The cord produced in accordance with my invention has unusually high tensile strength both in the wet and dry state and at both room temperature and at elevated temperatures. For instance, cords prepared as previously described herein have strengths in the dry state at room temperature of from about 18 to 27 pounds or even more, or from 1.7 grams per denier up. As a ready means of comparison, I have chosen a cord having a diameter of 0.032 which is approximately the diameter of the cords produced according to the examples in this application. (See column 5 in the table above.) It is to be understood, of course, that this measurement will vary in different laboratories in accordance with diiferent methods oi testing, but the values will be in the same proportion. A prior art cord, having this diameter and made by prior art twisting method, described in the first part of this specification, by twisting threads of 275 denier-I20 filament strong rayon into strands having a'twist of 20 turns per inch, and then forming a cable from these strands by twisting turns per inch in a direction opposite to the twist in the intermediate strand, in order ta form acord of the 275-5-3 construction, has a strength, at best, not substantially in excess of 16 pounds, whereas acord, similar in every respect to this prior cord, but having the low strand twist and the low cable twist characterizing the preferred cord of the present invention, may have a strength of 24 pounds, and even considerably higher. a

In addition to the highstrength of this cord, it shows very little tendency. to grow or become permanently elongated when subjected to a load 'over long periods oftlme. In fact, comparing this growth with prior art cords, whether they be made from long fiber Egyptian Sak cotton or from the same high tenacity artificial yarn, it has been found to be from one-half to .onefourth as much. These properties make the cord admirably suited for uses wherein such characteristics are desired. For instance, this cord maybe woven or otherwise fabricated into belting, or it may be used as a 'reenforc'ing means in numerous materials, such as .Bakelite or other plastic compositions, rubber, etc.

Although the cord of my invention does not ordinate to strength and where it is not subj ected to shocks similar to those of ordinary road surfaces. I have found that a cord in which the strand twist only is lowered, such as is described in Examples IV, V and VI, gives particularly good service in this type of tire.

.The cord of .my invention may also be used to good advantage in belting, especially in fan belts and other power belts which must withstand severe tensile loads which may, however, be substantially uniform. In this case, also, little growth of the cord is advantageous for then the belt will not stretch under the constant heavy strain and require adjustment of the pulleys,

' etc. at frequent intervals. The novel strong rayon cords have the further inherent advantage of high density for a given strength, this property, for example, making the cord well suited for use in V-type driving belts, where it is desirable to have the strength-producing reenforcing members located at the neutral axis and being of as small dimensions as is possible without sacrifice of too great an amount of strength. Comparative tests on the V-type belting just discussed, utilizing on the one hand, high grade cotton cord, and, on the other hand, the novel cord of this invention, show that the belting reenforced with cotton alone stretches several times as much as when the reenforcement on the neutral axis is the novel cord of the present invention prepared from strong rayon by the method previously discussed. Driving belts, or equivalent driving means, may be made entirely from the novel rayon cord, or they may comprise the cord (which may be in the form of a fabric) imbedded in rubber to form reenforced rubber belting.

This low twist cord is especially useful for the formation of woven belts, i. e. belts which are formed from a number of woven plies built up by weaving or braiding the plies together at the time they are being woven. The cord of this invention maybe used in combination with cotton cords or threads which may, for instance, be the filler threads while the low twist rayon cord is the Warp thread, or the low twist rayon cord may be used in both the filler and the warp.

The thread or cord of my invention has in addition to high strength and low elongation, the desired durability, suppleness, smoothnessof surfaceand resistance to-abrasion required for thread or cord to be used in weaving harness.

There are numerous other uses to which this cord may be put without departing from the spirit of my invention. For instance, in the manufacture of spinning buckets, such as are used in the rayon industry, reenforcing material is frequently molded in the Bakelite or other plastic composition used, to improve the strength of the structure. Here again, it is desired that the cord be strong and at the same time be incapable 01' L2 4 grams per denier.

The following table sets forth the physical properties of an illustrativestrong rayon thread which is compared with a normal rayon thread:

Strong Normal rayon rayon thread thread Dry ianacity, grams per denier 2. 95 1. 64 Dry elongation, percent ,8. 21. Wet tenacity, grams per denien. 1. 66 0.82 Wet elongation; percent. 12. 0 30. 8

As further illustrative examples of strong rayon thread, reference is made to those described in my co-pen'ding application, Serial No. 676,463, filed June 19, 1933.

The low twisting methods comprising the present invention are susceptible of considerable variparts to the thread a high degree of softness and 'ation. ,They may be applied to the twisting of threads of different denier, for example, threads having a denier as lowas 30, or as high as 1100 or even 1600 or higher, or the number of threads twisted into strands, or the number of strands twisted into cords may be varied. Likewise, the number of plying operations to produce the final product may be three or more, especially where low denier threads are used. Similarly, the new methods may be applied to the twisting of threads having a low filament-deniene. g. 30-denier-30 filament, 120 denier-100. filament, 275 denier-250 filament, and other threads having a filamentdenier of the same order of magnitude. The new twisting method may likewise be used in conjunction with the various common devices, such as tensioning weights on the creel which support spools of threads or strands which are to be twisted into the plied structure. While the processes described in this invention are of most marked advantage in the case of strong rayon yarn having a low dry elongation at room temperature, i. e. 12% .or lower, strong rayon having a high dry elongation, for example, 16%, can be twisted according to the novel method vantage. I

While the invention has been specifically described with relation to the plying' of threads of strong rayon obtained from viscose, it may also be applied to the twisting of strong artificial yarn produced by the cuprammonium process, or of any other artificial yarnshaving physical characteristics' comparable to those of strong rayon. In ExampleI, the use of a finish comprising an aqueous solution of olive oil soap has been dis-,

closed. It is preferred that a finish be used on the thread, and particularly a finish which imslipperlness, e. g. soap, vegetable oil, or other lubricating material. The strong rayon referred to in the above examples and to which the twisting processes of this invention may be most beneficially applied, is prepared as described in the co-pending application referred to above, and has av strengthv of about 3 grams per denier.

All the comparisons and discussions herein which refer to cotton relate to Egyptian Sak cotton-which exhibits far superior characteristics when twisted into strands and cords than other types of cotton. When compared with the cotton with 'adare even more remarkable.

The term room temperature, whenever referred to throughout the specification and claims, is intended to be 75 F. I

When the terms elongation and percentage elongation are referred to, they signify elongation at the breaking load.

The term strong rayon wherever used throughout the specification and claims is intended to define rayon having a tenacity at ordinary room temperature, of at least 2 /2 grams per denier. Throughout the specification, when reference is made to strong rayon thread withou t further qualification, it is to be understood that the thread has a twist of the order of 2-7 turns per inch. It is preferred that the strong thread have 7 turns per inch. It will be understood, however, that in some cases, this invention may be practiced with advantage with a strong rayon thread having no substantial twist.

- Referring throughout the specification and claims to dry thread strength at room temperature, or its equivalent, this is intended to indicate the tenacity attained in the following manner:

The thread is reeled under uniform tension in 450-mete'r skeins; these skeins are conditioned for 3 hours in an atmosphere maintained at 60% relative humidity'and 75 F.; the skeins are then weighed to determine the denier which is defined as the weight in grams of 9000 meters.

I The tests for determining tenacity and elongation are made on a 'Suter single strand strength I and elasticity tester with an oil plunger controlled pull. The rate of fall of the plunger is 1 foot per minute, and the distance between the clamps is adjusted for an 18-inch length of yarn. In .makingthe dry test, five single strands from each of the above skeins areitested separately. These are clamped in the tester and ,ttretched until the yarn breaks; Both the breaking load in grams and the percent elongation may be read directly from scales on the machine.

Grams per, denier are obtained by dividing the speciflcally referred to herein, are used, different numerical resiilts may be obtained, but the relative improvementover the prior art will be of the same order, regardless of the method ing used.

It will be readily understood from a study of of test- .the specification that by the practice of the various features of this invention, there are obtained rayon strands and rayon cords from strong rayon which have highly improved physical characteristics, as compared with strong rayon twisted according to conventional twisting methods.

Rayon strands, and more particularly rayon cords, v

produced according to this invention, are extremely useful as reenforcing means in the production of various articles which may or may not contain rubber. Thus, they may be used as reenforcing cord or fabric in rubber tires, in hose, in belts, such as fan beltsor other power belts and conveyer belts, in loolnharness, and" gen'- desired to utilize the properties of the novel twisted structures. The high hot strength of my new strands and cords make them of particular value when used in reenforced articles whichoperate at a high temperature, such as pneumatic vehicle tires, steam hose, and conveyer belts used for the handling of hot materials. 7

Any variation or modification which conforms to the spirit of the invention is intended to be included within the scope of the claims.

' I claim:

1. A strand plied from strong rayon thread and having a degree of twist exhibiting a helix angle not in excess of 33.

2. A cord plied from strong rayon thread and having a degree of twist exhibiting a helix angle not in excess of 33.

3. Astrand plied from strong rayon thread, said strand having a degree of twist exhibiting a helix angle not in excess of 33 and having aneffective strength per unit of cross-section not substantially less than the original thread strength.

4. A cord plied from strong rayon thread, said cord having a degree of twist exhibiting a helix angle not in excess of 33 and having an effective strength per unit of cross-section not substantially less than the original thread strength. 5; A cord plied from strong rayon thread, said cord having a degree of twist exhibiting a helix angle not, in excess of 33 and having a strength in excess ofv 2 grams per denier.

6. A cord plied from strands having a degree of twist exhibiting a helix angle not in excess of 33, said strands' comprising strong rayon thread.

erally in the manufacture of articles where it is '7. A cord plied from strands having a degree of twist exhibiting a helix angle not in excess of 33", said strands comprising strong rayon thread. said cord also having a degree of twist exhibiting a helix angle not in excessof 33.

8. A cord plied from strands having a degree of twist exhibiting a helix angle not in excess of 33, said strands comprising strong rayon thread, said cord having a degree of twist exhibiting a helixangle in excess of 33.

9. A cord of the 275--5-3 construction plied from strong rayon threads, characterized in that the strands have been given a degree of twist exhibiting a helix angle not in excess of 33 prior to the cord-forming operation, and the cord has a degree of twist exhibiting a helix angle in excess of 33.

10. A twisted structure comprising several rayon threads having a dry strength of at least 2.5 grams per denier, said thread having a denier of at least 1100 and a denier per filament of between 1 and 2.5, such threads being twisted together to a degree of twist exhibiting a helix angle not in excess of 33.

11. A plied, twisted structure having a degree of twist exhibiting a helix angle not in excess of 33 and comprising several strong rayon threads having no substantial twist.

12. A plied, twisted structure having a degree of twist exhibiting a helix angle-not in excess of 33 and comprising several strong rayon threads having no substantial twist, said threads having a denier of at least 1100.

moron. PARKER.

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