US2245191A - Manufacture of pubescent yarns - Google Patents

Description

June l0, 1941- E. G. GUENTHER Erm. 2,245,191

MNUFACTURE OF PUBESCE'NT YARNS Filed July 20, 1939 4 Sheets-Sheet 1 Ecyaf 6. @dni/7er s INVENToRs mf BY J- w E O n A h/enaw/ 6. FOM

June l0, 1941.

MAX/MUM STAPE E/YGTH /N INCHES E'. G. GUENTHER Erm. 2,245,191

MANUFACTURE OF PUBESCENT YARNS l Filed July 20, 1939 4 sheetS-Sheet 3 YARN W/TH ULT/MATE STRETCH/.5) 0F26 RRQ/1 D:

DRAFT MAX/MUM .STAP/ 5 LENGTH HATCH m) a STRETCH/.sj VAR/ABLE DRAFT Eqyof 6. 60e/#her h/enae// Fah/ INVENTORJ' BY y ATTOR EYS June 10, 1941.

MAX/MUM STAPLE LENGTH /Y /NCHES' (D E. G. GUENTHER ET AL.

MANUFACTURE OF PUBESCENT YARNS Filed July 20, 1939 4 Sheets-Sheet 4 MAX/MUM STAPLELE/YGTH \57RE7'CH/6)=26`% PATCH/R) VAR/ABLE' INVENTORS BY mww ATTO EYS Patented June 10, 194i.

MANUFACTURE or PUBESCENT YARNS Edgar G. Guenther and Wendell G. Faw, Kingsport, Tenn., assignors to Eastman Kodak Company, Rochester, N.- Y., a corporation of New Jersey Application July 2o, 1939, serial No. 285,572

(ci. 21a-1) 9 Claims.

This invention relates to the production of` synthetic staple yarns, and more particularly, to an improved method for the production of a synthetic staple yarn closely simulating spun yarn in its physical characteristics.

As is Well known, numerous processes have been proposed for the manufacture of synthetic l to various operations such as opening, picking,

carding, drafting, drawing, combing, gilling, re-

ducing, roving and spinning operations to produce f the final spun yarn. Such processes require the use of a great deal of complicated machinery has several serious disadvantages. For example, since the process involves attenuating each of the broken filaments throughout its length to the breaking point, the natural or inherent ability of the material to stretch is thus lost in the stretchbreaking step. This results in the filaments being left with little life, especially when woven in the form of yarn into a fabric. In fact, the residual stretch is so low in most cases' that yarn spun from such laments has insufficient stretch or elasticity to permit its use on knitting or Weaving machines. Another disadvantage is the fact that notonly is a. majority of the staple fibers resulting from the'above-mentioned stretch-breaking operation too short for the production of a satisfactory type of yarn, but also an undesirable amountof y or very short staple is produced which tends to reduce thestrength of the ultimate which is expensive to operate and maintain.-

Furthermore, most of` these steps or processes are extremely injurious to' the synthetic 'fiber ma-` be employed;

terial, some operations-breaking a portion of the laments into extremely `short lengths or y,

while others stretch the filaments so much that several methods have been proposed for Ithe co`n`v version of rovingsor strands ofcontinuousfila ments into staple lengths without breaking'the essing steps.

yarn and to produce slubs in spinning, knitting, .l

the yarn may.- l

and weavingoperations in which This invention has as a continuous process whereby aicommercially satisfactory `synthetic spun yarn -may :be produced directly from a strand or roving of continu-` ous synthetic filaments with, a minimum of procl A` further object is vto provide a means of so controllingthe operation of .i thev stretch-breaking process as to produce staple fibers vof any desired average length. A `still further vobject ris toproduce a vspun yarn having. a commercially satisfactory degree of residual y stretch, tensile strength, elasticity, and `other properties. Another object is to produce a spun continuity of the roving. In one of such processes, a rovingof substantiallyv parallel' continuous filaments is fed to a series Aof sei-,'s-*ofdrafting rolls, the sets beingseparated'apartfromeach other a predetermined distance andthe suc--l`l` cessive sets being operatedat such peripheral speeds as results in stretching the individual ilaments -to and beyond their breaking points and reducing them to staple lengths. -The operation. of the process is such that 'a random distribution of breaks occurs at points of natur-'alor induced Weakness in the filaments, with the result that the continuity of the sliver is maintained. The

' sliver emerging from the last setof rolls consists into spun yarn, especially since it enables a roving of continuous filaments to be converted .directly to a continuous spinnable sliver, nevertheless, it

yarn composed of synthetic staple fibers in which the majority of the fibers have not been attenuated to the point where they have experienced an undesirable loss o'f their-'inherent stretch characteristics, tha'tis, such 'a lossas wouldI de-I prive them of Athe abilityto be stretched to a certain extent when present in Woven or knitted fabrics. An additional object is -to produce synthetic staple f'lbers having an improved physical form.. ,Other objects will appear hereinafter. r These objects are accomplished by thefollowing invention, which in its broader aspects, comprises the discovery that the staple length of the fibers produced 'in Vthe continuous stretch-breaking process andthe physical characteristics' of these fibers, partiularly the residual stretch, may be controlledA by controlling the relationship between the linear speeds "of the respective sets of rolls employed. vThis relationship can be expressed by anobject ,to vimprove upon the stretch-breaking lmethod vof producing. staple fibers from synthetic :yarns and to providey an equation which. when plotted, graphically illustrates how, among other things. the staple length of the fibers depends upon the draft employed.

In order that the distinctions between our process and the stretch-breaking processes of the prior art shall be made clear, it is desirable at this point to define various terms employed in describing .our invention. Taking the stretchbreaking operation in which a strand or roving of continuous ilaments is passed between two successive sets of rolls as typical of such processes, the term ratch as indicated above, is the distance between the center lines of the sets of rolls between which the actual stretch-breaking action takes place. g

inasmuch as the yarn is always stretched or drafted in the stretch-breaking process, the forward set of rolls must always operate at a greater peripheral speed than the rearward set. Draft" may, therefore, be defined as the ratio of the peripheral velocities of the two sets of rolls. i. e., the quotient of the peripheral velocity of the forward set of rolls divided by the peripheral velocity of the rearward' set. For example, if the speed of the rear rolls is taken as unity and the speed of the forward rolls is half again as great asthat of the rear rolls, the ratio of the two speeds is as 1.5 to 1. 'I'he draft is therefore 1.5.

As is well known, every synthetic yarn has its own individual inherent physical characteristics such as tensile strength, resiliency, ability to stretch and the like. When a fiber of a given yarn is stretchedI to the breaking point, for example, it is evident that its original stretch characteristics are inevitably altered. In other words, if the filament is stretched to any extent, whether to the breaking point or to less than the breaking point,vit is bound to lose at least some of its ability to stretch. 'I'he amount of stretchability which is still left in the yarn after stretch breaking may be referred to as its residual stretc The matter of stretch and residual stretch will be made clear by' the following illustrations.

The percentage stretch or elongation which a yarn undergoes under a given load, which may be equivalent to, or less than the breaking load, may be computed as follows:

As an example, a -inch length of. yarn is subjected to a load sufficient to elongate it to twelve f inches. The percent stretch would be 'Ihe residual stretch of a yarn, for the pur,-

it has been subjectedl to the stretch breaking operation. In other words, it represents the ultimate original ability of the yarn to be stretched or elongated without breaking. y

The elasticity of a yarn may be defined as theA tendency to return to its original length after having been stretched an amount which is insumcient to cause permanent elongation. 'I'his may be expressed as a percentage of the original length. Thus, if a 10-inch length of yarn is stretched to 10.2 inches and the load is removed, the yarn returns to its original length of 10 inches, and if the yarn will not'return if stretched to more than 10.2 inches, we may express the percent elasticity as It is important to note that a 'yarn composed of filaments which have been so completely stretched as to have lost all of their residual stretch will have substantially no ability to stretch. If a fabric woven from such yarn is subposes of the present invention, may be defined In considering the mathematical relationships existing between staple length and draft for a X 100 5 residual stretch jected toa severe stress, it cannot give and, if the stress is severe enough, the fabric will rupture. It isthus highly important that all yarns must display a certain amount of give under stress, either because of retention of some ability to stretch, or residual stretch, or because of retention of some of their original elasticity or resiliency, or both, in order for fabrics produced therefrom to be commercially usable.

ItA will be evident that residual stretch is a quite diiferent property from elasticity. As indicated above, elasticity is the power of the yarn or filament material to return to its original llength after having been extended an amount insumcient to cause permanent elongation, whereas residual stretch is the ability of the yarn to be elongated without breakingwithout reference to its ability to return to its original length. Cellulose acetate and similar cellulose derivative filaments, however, retain a small amount of elasticity, even though stretched to the breakin point.

'I'he present invention is based upon a recog, nition of the above-described properties of synthetic yarns and upon a discovery of 4certain steps which constitute an entirely new principle in the stretch-breaking process. As indicated above, the principal defect of the hitherto known stretch-breaking processes is that they afford no means of control over the staple length, except by an adjustment of the ratch, and, no control over the residual stretch and elasticity of the staples of the stretch broken product. We

have discovered that by carryingout the stretch breaking operation in such manner `that the staple length is made dependent upon the draft employed, the residual stretch characteristics of. the staple fibers may be controlled and a yarn of `almost any desired residual stretch within the limits of zero and the original inherent stretch of the yarn dealt with, may be produced. This is a most outstanding and unexpected discovery. especially since it makes possible the conversion of a strand or roving `of `continuous filaments directly into a pubescent or villous type 'of spun. yarn of commercially usable quality and physical characteristics and having substantially all of the valuable properties of a spun yarn produced from natural fibers without the necessity of going through a multitude of complicated carding, drafting, spinning and the like operations of the older textile practice. It should be particularly pointed out that, while our process is capable of converting a strand or roving of continuous filaments into spinnable slivers of. more or less loose construction and suitable for further drafting and spinning operations,4 the principal value of our process is in its adaptability to the conversion of continuous filament yarns directly into pubescent or villous spun yarns of commercial quality.

In the follow-lng examples and description, we

'have set forth several of the preferred embodiments of our invention, but they are included only for the purpose of illustration and not as a limitation thereof.

In the accompanying drawings,

Fig. 1 is a diagrammatic representation of the essential parts of an apparatus suitable for carrying out theprocess of our invention.

Fig. 2 is a view illustratingthe outward appearance of a typical pubescent yarn obtained by our process. Y

Fig. 3 is a diagrammatic view of two sets of stretch breaking rolls such as shown in Fig. 1 and also illustrating graphically the terms employed in the equation showing the'relationship between maximum and minimum staple length and draft for a given ratch.

Fig. 4 is a diagrammatic view similar to Fig. 3 and including additional data on the equation.

Fig. 5 is a view similar to Figs. 3 and 4, but illustrating in greatly exaggerated' proportions the theoretical form of a single lament undergoing stretch breaking in accordance with our invention.

Fig. 6 is a curve plotted from the equation expressing -the relationship existing between the maximum staple length and draft for a given ratch. l

Fig. '7 is a family of. curves plotted from the equation and illustrating the results obtained by stretch. breaking yarns of different original stretch.

Fig. 8 is a family of curves plotted from the equation and illustrating the. results obtained by employing different ratches in the stretch breaki DSR(1 ,+)V A f Lmax=-R (D- 1-) 1+S Wherein (Figs. 3 and ratch, is the ratio Y, Velocity 0f thefront rolls Velocity of the back rolls and s is stretch. when-this equation-is plotted,

a curve such as'illustrated in Fig. 6is obtained. Assuming a ratch of 3", the maximum staple length obtainable for a given draft may be read directly from the curve. For example, if one wishes to produce a product having a maximumv staple length of 10", one would employ a draft of. approximately 1.25. For a product having a much shorter maximum staple length, say 6", one would employ ya draft of about 1.47.

The curve of Fig. 6illustrates especially well the effect of change of draft on the maximum staple length, particularly for the longer lengths. It will be noted that when the draft reaches the approximate vicinity of 1.20, the'curveundergoes a rather sharp change in slope, that is, the lower the draft, the longer the staple length, until at a point corresponding to 'a draft of about 1.13, no stretchbreaking is possible since the maximum staple length has become infinity.

We have found that by applying the abovedescribed mathematical formula, which we 'have derived from purely theoretical considerations,

vto the actual practical process ofy stretch breaking, they results obtained check closely with the theoretical and we are enabled to produce a greatly improved`yarn in which the staple fibers have a much greater average length, a higher residual stretch and less fly. Such a product obviously has far more life and resiliency when woven into a fabric than many of the yarns produced according to priorv art methods in which the staple bers have been completely attentuated throughout their length to the breaking point of the individual filaments as is the case with many of the prior art products. However, the novelty of our process isnot alone based upon the physical characteristics of the staple fibers obtained, but primarily upon the fact that we are enabled to producea villous or pubescent yarn closely simulating actual spun yarn by the continuous stretch-breaking process and still obtain a product which is sufciently close to spun yarn in its physical characteristics as to render it commercially satisfactory.

In other words, one of the principal features of our invention is the obtaining of a manufacturing advantage by virtue of Vthe fact "that we can feed a continuous roving or strand of filaments through the stretch breaking rolls and obtain continuously and without any other operations whatever, a product closely simulating spun yarn. This is a wholly novel and unexpected result which is, so far as We are aware, nowhere disclosed nor suggested in the prior art. Our invention will be more fully understood by reference to Fig. 1 of the drawings illustrating a simple form of mechanism in which the process may be carried out. The numeral l designates a supply spool from which a strand or roving R composed of a pluralityof continuous filaments and having a twist of about 1/2 vturn per inch, is

Y Y yarn as it enters the rolly should be vregulated to `five or ten grams, depend-ingon thesize of yarn beingvdrafted. The strand thenpasses to a series of setsof'rolls A and-B constituting the "stretch breaking mechanism per se. 1

Rolls A and B are f xedly ,mountedonshafts rotatably mounted in suitable bearings (not drical steel surface, and -are connected to rotate together at the same speed, gear 8 .being driven by gear 9 supplied with a suitable source of power (not shown). Roll 6 is so mounted with relationship to roll 1 as to provide for adjustable clearance and tension by means of spring tension member III pivotally mounted on shaft II. Shaft I I is fixed to bracket I2 which, in turn, is screwed to the frame 5.- YThe tension member is also attached through arm I3 to the shaft of roll 6 as illustrated, tension being controlled by means of adjusting screw I 4 threaded through a projecting boss I5 of bracket I2 in such manner as to bear on the upper surface of member III.

Set B comprises rolls I1 and I8 rotatably mounted on frame 5 similarly to rolls 6 and l. The same type of adjustable tensioning device is provided for regulating tension between rolls II and I8 as that employed in connection with rolls 8 and 1.

Roll I1 may be provided with a calf-skin cover I9, while roll I8 is preferably an unprotected steel roll with a smooth surface.` Roll I1 is driven through frictional contact with roll I8. Roll I8 is provided with a gear 20 fixedly mounted on its shaft .and meshing with gear 2| which is a part of change. gear mechanism 2I-2I'. rotatably mounted on shaft 22, gear 2I in turn meshing with and being driven by gear 8. The relationship of the number of teeth on the respective gears is such that the peripheral velocity .of rolls B is always greater than that of rolls A, thus providing a draft on the yarn strand which passes between the two sets of rolls. Should it be desirable to change the draft, that is,-the speed of rolls B with respect to rolls A, a suitable change gear may be substituted for 2I2I' in a manner well-known to those skilled in the art. v

The yarn strand or roving R after passing through the two sets of rolls emerges as al tension by the tensioning device 4, thence between rolls A and rolls B where the filaments are all stretch broken. The particular draft employed may beq selected by reference to the curve of Fig. 6. Incidentally, the mechanism illustrated in Fig. 1 may be provided with adjusting mechanism is well within the knowledge of those skilled in the art and need not be described in detail here.

'I'he pressure existing between rolls I1 andy I8 is at all times much higher than that between rolls l and 1. This will vary with the denier of the laments comprising the roving and with the denier of the roving or strand of filaments fed into the apparatus. The principle is illustrated by the following table in which `the pressure on the yarn is given for rolls 6 and 1 and for the rolls II and Il.

Pressure roll i7 v and 18 Filament Pressure d roll (gend The roving or strand R, after passingbetween thetwo sets of rolls A and B emerges/as a completely stretch-broken, villous, Vor pubescent type of yam closely simulating spun yarn. Such a product is illustrated in Fig. 2 and, as may be seen, possesses a distinctly hairy exterior due to numerous projecting ends of stretch-broken staple fibers.

At this point it is desired to point out that our invention is further distinguished from all related processes of the prior art by the fact that we may employ a low draft, preferably within the range of L20-1.30, with the optimum at about 1.27, as'compared to drafts of the order of 5 or 6 recommended in the prior art. It will of course be understood that the particular draft selected will depend upon the ratch employed and also upon the inherent original stretch characteristics of the yarn dealt with as well as upon the ultimate stretch characteristics desired in the nished product.

It will thus be seen that our process involves a number of variables and no hard and fast rules can be laid down in general terms to meet all conditions. It may be said, however, that in.

general for any given value of ratch or inherent stretch, we prefer to keep the draft within the indicated limits. Furthermore, we are enabled to define our invention and the necessary relationships in the process by means of simple algebra as outlined in detail near the end of this specification. i

The conditions of operation of our process will be more fully understood by reference to the curves of Figs. 6, 'I and 8. Referring to Fig. 6, the maximum staple length varies with the draft in accordance with the curve. As previously indicated, at a point a little beyond a draft of 1,13, no break in the filaments occurs. Therefore, inl order to obtain a stretch-broken product, it is necessary with the indicated ratch, to keep above a draft of this value.l It will thus be'seen that the longer staple lengths are produced with the lower drafts. Conversely, a draft ofthey order ofl 2.00 gives a maximum staple length, with the indicated ratch, of approximately four inches.

As previously explained, the curve of Fig. 6

is based upon ideal, conditions and ideal filaments. In actual practice there will ofcourse be a progressive variation in the staple lengths present in any given length of the finished pubescent yarn obtained by our process, .from

staples of the maximum length down to staples of very short length. This is due to the fact that all of the filaments do not break so as to have the maximum length and the breaking occurs more or less at random. Non-uniformity is also to be accounted for by unavoidable slippage, damaged iilam'ents'present' in the original strand or roving and the fact that at break the filaments actually snap back to a certain extent, since they retain atleast a certain small amount of their original elasticity even after rupture.

Referring to Fig. 7. it will be seen that each type of yarn dealt with gives a characteristic stretch-breaking curve, and in the main, follows the general law of the above-described equation. It will be seen from this family of curves that the smaller the original inherent stretch of the yarn, the lower will be the draft required to produce a maximum staple length.

Referring to Fig. 8, it will be seen that as the ratch is varied, the maximum staple length obtainable varies considerably. From this family of curves, it will be seen that the lower the ratch the lower will be the draft required to produce a staple of given maximum length.

It should be noted that, while the curves of Figs. S, '1, and 8 are plotted from mathematical data obtained by substituting various values in the equation, it is noteworthy that the results obtained in the actual practice of our process tally closely with the theoretical values represented by these curves.

The nature of a filament which has been stretch broken in accordance with our process will be more fully understood by reference to the theoretical diagram of Figure 5. Assuming that the continuous filament enters rolls A and emerges at the right of rolls B, it will be seen that the first increment of the staple will be unstretched, while the last increment of the staple after breaking will have been fully stretched or attenuated to its breaking point. The complete staple therefore will have been progressively stretched from its extreme right end to its extreme left end, thus retaining a very considerable proportion of its original inherent or rovings which may be combined and subjected to the stretch-breaking operation in such manner as to form a yarn. Numerous other modifications of our process and product will be apparent to those skilled in the art.

Our product as illustrated in Fig. 2 may, therefore, be regarded as characterized, among others, by the following speciiic features: (l) There are no continuous laments, the product thus closely resembling true spun yarn produced from natural staples, (2) the laments vary in length, (3) the majority or average of the filaments are longer than it has heretofore been possible to produce on even the worsted or spun silk systems employing natural fibers and are definitely longer than the.

majority of filaments present in the prior art' stretch-broken products, (4) the yarn is a drafted product, that is, produced by a continuous process in which a roving or strand of continuous lilaments is fed into the apparatus and emerges in the form of a spun yarn, (5) the yarn has a high degree of stretch because of retention of a high proportion of its original stretch and resiliency, the product is stronger than any other spun yarn prc duct of which we are aware, and (6) the yarn is :tronger than yarns produced by the prior art due to less degradation of the filament, to longer average length of the filaments comprising the yarn, and to the greater evenness of the final yarn.

The physical characteristics of the stretchbroken yarn produced in accordance with our process will be more fully understood by reference to the following table:

Comparative physical properties stretch. The length of the staple produced will,

, as previously explained, vary in accordance with the draft and also in accordance with the point at which the staple breaks between rolls A and B. Accordingly, an infinite number of actual staple lengths is possible depending upon the point between the two rolls that the break actually occurs.

Regardless of the matter of length, or relative length as between individual staple fibers in the finished yarn,- the fact remains that we are enabled to produce a finished product having greater residual stretch because of the progressive stretching of aY majority of the filaments, than is possible in any known stretch-breaking process in which all or substantially all the filaments are attenuated or stretched throughout their length to the breaking point, as is the case with all high draft stretch breaking. No one, so far as we are aware, has ever recognized the necessity of keeping the draft as low as possible in order to provide for retention of a high degree of residual stretch in the finished staple product.

As stated, we are enabled by the practice of our process to convert a roving or strand of continuous laments directly into a yarn closely simulating true spun yarn.' On the other hand, if desired, we may employ a plurality of strands It will be readily observed that a yarn stretch broken on the low draft principle of the present invention has a markedly increased strength and elongationas compared to yarns produced according to either the prior art high draft method, or simply by cutting the yarn into the required staple lengths. In the case of a 10G-denier strand of two-denier laments, for example, the strength in grams per denier of our product is 1.4, as

compared to .'70 gm. per denier for the high draft product. In other words, our yarn is twice as strong as the high draft material.

A comparison of the elongation, that is, the percent of stretch which the yarn is capable of undergoing, shows that our product possesses almost four times the elasticity or stretchability of the high draft material. It is also interesting to compare the properties of our product with a typical cut staple product. In the case of a 300- denier strand of three denier laments as indicated by the above table, our product has nearly twice the strength of the cut staple material and nearly twice the elongation. On the other hand, the cut staple yarn is roughly equivalent to the high draft material, but neither of the two lastmentioned products are in any sense of the word comparable to the material produced in accordtremely important in the manufacture4 of durable and satisfactory fabrics. A

Another interesting comparison between the characteristics of the prior art products and products produced in accordance with our invention and illustrating certain characteristics which distinguish our process from prior processes may be obtained by reference to the diagrams of Fig. 9. 'I'hese diagrams 'represent stretch-broken yarn samples in which the individual fibers have been separated in such a way as to indicate a gradation of all lengths from shortest to longest.

Under the column designated A is indicated the stretch-broken fibers present in a sample of yarn produced in accordance with the instant invention in which a ratch of three inches and a draft of 1.15 is employed to stretch break a cellulose acetate yarn having an inherent stretch of 25%.

Under the column designated B is shown a.

-inc es and adraft of five, the yarn having an inherent stretch of 26%.

Under the column designated D is illustrated another product produced in accordance with the high draft prior art method in which the ratch 1 is eight inches, the draft five and the yarn has an inherent stretch of 26%.

These diagrams illustrate very strikingly the improvement in the quality of the yarn made possible by our process, since it will be noted that the average staple length (as indicated by the dotted line marked Av.) is always greater than the ratch (indicated by the solid line R). In accordance'with our invention, it is necessary only to alter the draft in order to alter the average or maximum staple length.

In the case of the'prior art process, on the other hand, in which a high draft is employed, the maximum staple length is only slightly greater than the length of the ratch and the average in each case is much less. According to the prior art, it is always necessary to lengthen the ratch to increase the average or maximum staple length.

However, the outstanding difference between the samples A and B representing the instant in- Avention and the samples C and D representing .the prior art is that amajlority of the staple fibers of samples A and B have a much higher residual stretch and resiliency than the bers of samples C and D. In fact each of the staple fibers of the prior art have been attenuated throughout its length to the breaking point and has substantially no residual stretch or resiliency and therefore no life In fact, a product such as the material of samples C and D has proved to be entirely unsatisfactory in actual use in fabrics due to its lack of ability to stretch and to its lack of resiliency. The pubescent yarn of samples A and B on the other hand has been proved to have such a marked residual stretch and resiliency as to make it readily adaptable for use in fabrics of many kinds.

The mathematical description by which our invention is exactly and clearly definable will now be outlined. In the first place the equation:

which was discussed above is developed as follows:

The sections of unstretched filament marked X and Y in Fig. 3 pass through the rolls B and A, respectively, by the time that rupture occurs. Since rolls B are moving faster than rolls A, X is greater than Y. In fact, both X and Y are in practice much longer than shown; X may even be longer than R and extend beyond rolls A in Fig. 3, but for convenience X and Y are shown quite short. The same mathematical analysis applies to all cases.

As shown in Fig. 4, the original portions X and Y are stretched Ato X and Y', respectively, at the time of rupture. Starting as shown in Fig. 3, the first infinitesimal part of X which is fed through Linux: R

l rolls B is unstretched; the last infinitesimal part fed through, just before rupture, is fully stretched, i. e. by a stretch factor l-l-S. The Whole length X' is stretched by an amount equal to the average of its first and last infinitesimal The portion between Y' and rolls B is made up of what was originally R-X and is fully stretched to (1+S) (R-X). -Therefore from Since the rollers B and A have a relative velocity (draft) D, the amount fed out at B equals D times the amount fed 'in at A, i. e. X=DY; therefore from Equations 1 and 4:

DSR

=R+(1+)X and therefore from Equation 6:

Ds1z 1+ig Lmax:

' .2, the draft of This is the equation previously given for Lmx in terms of draft D, stretch S, and ratch R.

Now having developed this equation we are able to adjust the draft and ratch to give any desired Lum. Furthermore, in order to produce a satisfactory yarn we have found that the longest staples should be made up so that at least 35% of their length is not full stretched, i. e. X should be at least 35% of Lmax. Of course this means that when a filament breaks at rolls A, it is made up of 35% of a portion not fully stretched, but if on the average it breaks half way between rolls A and B, the not-fully-stretched portion is about 50% of its length. (In this mathematical discussion, we are not considering fly such as might occur by a double break between the rolls.)

In a preferred embodiment of the invention, the longest staples are at least 50% not fully stretched and the average complete staple is at least 66% not fully stretched, i. e. X is at least 60% of Lmax.

Taking the case where X' must be at least 50% of Lmax, then from Equation '7 R must be less Therefore Therefore the preferable embodiment wherein i X' is at least 50% of Lmax is provided as long as the draft D is less than In fact if the draft D is less than 1+2S the X' will be atleast 40% to 60% of Lmxfor all ordinary values of S.

From a practical point of view we now consider the average yarn wherein rupture occurs in any one filament when it is stretchede26%, i. e., S -.26. In this case, if X is to be 50% of Imax,

the draft D must be less than 1.475 by Equation 8.

In practice a draft less than 1.5 gives practically this desired degree of quality and any draft of less than 2 gives X at least 35% of Lmx.

If the draft is exactly rtg it is obvious from the equation that Lmax is infinite and that "gio rupture will occur for any values of D less than this. Therefore D must be greater than Since most yarns have a-stretch S greater than any machine should be greater than 1.1. J g.:

If We consider the hypothetical case where the draft is infinite (in practice to 1 would be considered infinite draft) we note from Equation '7. that :1.23 R when S=.26

In fact even when tlle draft is as low as 5 or 6 (the lowest draft suggested by the prior art),

MFR

=l.31 R when S=.26

and if'D is infinite,

which is not much better than with innnite draft.

In this latter case X is only less than 1.5,. gives-the superior results which we have discovered. 1

In the previously mentioned optimum conditions wherein the draft is 1.27 for yarn whose filaments have a stretch S=.26

stretched fraction is only 19% leaving 81% of each filament still capable of being stretched.

It is to be understood that the apparatusand process herein described for practicing our invention are merely illustrative and many changes in both may be made within the scope of our For example, various types of rolls equipped with various types of surface coverings and with different drives may be employed with equally satisfactory results as with the apparatus illustrated in Fig. `1. The continuous yarn converted into pubescent yarn in accordance with our process may be any type of synthetic continuous yarn, such as that composed of the various types of viscose, cellulose acetate and other cellulose organic derivative yarns. We find that cellulose acetate yarn lends itself particularly well to conversion to a pubescentyarn of the type herein described by means of our process.

What we claim is:

1. A low draft process of producing a synthetic pubescent yarn closely simulating true spun yarn, which comprises converting a strand or roving of continuous filaments to staple lengths by passing the filaments between drafting rolls operating at a draft insumcient to attenuate the majority of the staples throughout their lengths to the breaking points, said draft being such that the average length of the stretch-broken staples produced in the process is appreciably greater than the length of the ratch employed.

2. The process of producing a synthetic pubescent. yarn closely simulating true spun yarn, which comprises converting a strand or roving of continuous filaments to staple lengths by passing the filaments between drafting rolls operating at a draft insuflicient to attenuate the majority of the staples throughout their lengths to their breaking points, said draft being such that the average length of the stretchbroken staples produced in the process is appreciably greater than the length of the ratch employed and between and 1+2S, where S refers to the inherent original stretch of the yarn treated.

3. The process of producing a synthetic pubescent yarn closely simulating true spun yarn, which comprises converting a strand or roving of continuous filaments to staple lengths by passing the filaments between drafting rolls operating at a draft linsufficient to attenuate the majority of the staples throughout their lengths to their breaking points, said draft being such that the average length of the stretchbroken staples produced in the process is appreciably greater than the length of the ratch employed and less than S2 (1ra) where S refers to the original inherent draft of the yarn treated.

4. The process of producing a synthetic pubescent yarn closely simulating true spun yarn, which comprises converting a strand or roving of continuous filaments to staple lengths by passing the filaments between drafting rolls operating at a draft insufiicient to attenuate the majority of the staples throughout their 5. The process of producing a syntheticv pubescent yarn closely simulating true spun yarn, which comprises converting a strand or roving of continuous `filaments to staple lengths by passing the filaments between drafting rolls operating at a draftinsufcient to attenuate the majority of the staples throughout their lengths to their breaking points, said draft being such that the average length of the stretchbroken staples produced in the process is appreciably greater than the length of the ratch employed and less than 1.5 where S refers to the inherent original stretch of the yarn treated.

6. The process of producing a synthetic pubescent yarn closely simulating true spun yarn, which comprises converting a strand or roving of continuous fliaments to staple lengths by passing the filaments between drafting rolls operating at a draft insuiilcient to attenuate the majority of the staples throughout their lengths to their breaking points, said draft being such .that the average length of the stretchbroken staples produced in the process is appreciably greater than the' length of the ratch employed and between lating true spun yarn comprising a strand composed of staple fibers, the majority of which have not been attenuated throughout their lengths to the breaking point, each of the fibers of this incompletely attenuated -majority having a residual stretch which varies progressively from one end of the fiber length to the other.

8. A synthetic pubescent yarn closely simulating true spun yarn comprising a strand composed of staple fibers, the majority of which have not been attenuated throughout their lengths to the breaking pointand have a high residual stretch and resiliency, andthe average of which bers have at least 35% of the material of which they are composed attenuated to a degree less than full attenuation.

9. A synthetic pubescent yarn closely simulating true spun yarn comprising a strand composed of staple fibers, the majority of which have not been attenuated throughout their lengths to the breaking point and have a high residual stretch and resiliency, and the average of which fibers have at least 35% of the material of which they are composed attenuated to a degree corresponding to 35-80% attenuation.-

EDGAR G. GUENTHER.

WENDELL G. FAW.

CERTIFICATE 0E CORRECTION.' Patent No. 2,215,191. June 1o., 19m.

EDGAR G. GUE'NTHER, ET AL.

It is hereby certified that erroreppears in the printed specification of the above nwnber'ed patent requiring oor'rectionas follows Page 5, second column, in the table, last column thereof, for"9." read -9.5; page T, first column, line 2l, for "60%" read 50%--; and that the said Letter-s Patent shouldbe read with this correction therein that the same may conform to the record of the oase in the Patent Office.,

Signed and sealed this 19th day of August, A. D. 19ML Henry Van Arsdale,

(Seal) Acting Commissioner of Patents.

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