CA1248741A - Drafting system for yarns - Google Patents

Abstract

Drafting System for Yarns Abstract Drafting system for textile yarns and including a driven feed roll, a driven output roll, a low friction freely rotatable heated roll located between the driven feed roll and the driven output roll and operating at essentially the same surface speed as the driven feed roll, the freely rotatable heated roll being driven by engagement with the yarn and whereby sufficient yarn tension automatically is transferred upstream of the freely rotatable heated roll to pretension the yarn before it contacts the freely rotatable heated roll with drafting taking place near the location where the yarn leaves the freely rotata-ble heated roll to pass toward the driven output roll.

Description

De6criPtion Drafting Sy6tem for Yarns Technical Field The present invention is directed to a drafting eystem for yarns generally used for textile yarn6 and particularly i6 directed to a ~ystem for draf~ing yarn~, 6uch a~ polyester yarns, at speeds greater than 300 meters per minute up to 1500 meters per minute and greater.
Background There is con~iderable prior art in the drafting of yarns, and particularly for polyester yarn~. U.S.
Patent No. 3,539,680 discloses one system where 6peed~
disclosed are around 600 meters per ~inute to 1500 meter~ per minute: however, rela~ively ~peaking, this is a very expen~ive system requiring equipment and main~enance thak we think can be omitted with the system that we propose herein.
Pretensioning yarn in a drafting ~ystem before ~e yarn contact~ any heated device~ whether ~uch device be a fixed pin, a rotating roll, a stationary contact heater or other type of device, i6 an important contribution ~oward obtaining a uniformly dyeable and defect-free yarn. U.S. Patent No. 3,539,G~0 mentioned abo~e recogni~e~ the importance of æuch preten~ioning ~o a6 to minimize occurrence of "fluff~" and dyeing unevennes~ ~Col. 4~ lines 43-47). The patent discu~ses an arrangement for obtaining such preten6ion ~y providing the combination of a nip roller and a , .

delivery roller, and employing a ratio of peripheral ~peeds of the delivery roller to the heated feed roller within the range of l:l.OOl-1:1.030. Thus the patent discloses e~tablishing a pretension zone which i6 designed to draw the yarn slightly, as indicated by the given ratio range, in order to aehieve the required pretensioning. The patent indicates alternatively ~hat a thread brake or guide may be used if it can impart uniform and predetermined tension.
Other types of drafting systems employ heated pins, heated plates, and heated plates with separator rolls, all of which are well known. The quali~y of the yarn produced on these systems, however, has been found to be generally poor due to the high level of broken filaments and poor dye uniformity than that produced on a system such as represented by the above-mentioned U.S. Patent No. 3,539,68Q, and the problems of broken filaments and poor dye uniformity have been found to increa~e as the speed is increased. Broken filamentæ
tend to cause defects, which cause waste and los8 of time~
An objec~ of our invention is to provide a low ~ri~tion drafting ~y~em which provides au~omatic pretensioning of the yarn before the yarn contac~s any heated device and without employing t~e usual structures upstream from such heated device to provide ~uch pretensioning.
U.S. Patent No. 3,919,748 discloses an apparat~g for altering the length of a &ynthetic continuou~
filament or yarn strand. ~h~ apparatus co~prises a first strand feeding means involving a driven feed roll and a separa~or idler roll; a f ir~t heating means in ~he form of a heated roll connec~ed to and coaxial with the driven feed roll and having a ~eparator idler roll:
a second heating mean~ in the form o~ a heated pla~e over which ~he yarn strand slides: a second feeding means in the form o~ a driven roller and a ~eparator A

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idler roller; and a driven take-up spool. All of the embodiments in the patent, except one, show the "fir~t heating means", which is the heated roll, as being rigidly connected to the fir~t driven feed roll. The excep~ion i~ the embodiment ~hown in Fig. ~ where the "heated roller 20"' turn~ freely on stud 23 of the swinging arm 26 and is thus turned only by the yarn strand a~ the yarn strand loops around the heated roller. The pa~entee does not give any reason for t~e purpo~e of thi~ exception nor does he offer any advantage~. There i6 no recognition by the patentee, therefore, that preten~ioning of the yarn would automatically occur upstream of the heated roller 20 in the area between the exit of the yarn fitrand from the driven feed roll 17 ~Fig. 4) and the initial contact of the yarn strand with the heated roller 20l.
Although Fig. ~ does not illu6trate a separator idler roller, it i8 as6umed that it would be po~itioned as illustrated in Fig. 6. Also, although the patentee doe~ not indicate in his ~iscu~6ion of the embodimene of Fig. 4 that the separator idler roller for heated roller 20' would need to be independently rotatable from the 6e~arator idler roller for th~ driven ~eed roll 17, it is assumed that thi~ would be desirable.
In reference to Fig. 6, therefore, a "thread guide" 37 is proYided between the coaxially alisned driven feed roll and heated roller on one side and the ~eparator idler roller~ on the other 6ide which ~erves to displace the yarn ~trand from the driven feed roll to the heated roller. Since thi~ is probably a hig~
tension zone, thi6 ~read guîde in the embodiment of Fig. 4 will tend to damage the yarn strand which will lead to the generation of an excessive number oP broken filament~ in the yarn. The yarn 6trand filaments which are ~irectly in contact with t~e 6urfacs of the thre~d guide 37 will be damag~d to the ~} .

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extent that they will break in the subsequent drafting of the yarn strand.
Another object of the invention, therefore, is to insure that there is no frictional contact ~ade with the yarn in the area between the exit of the yarn from the input feed roll and the initial contact of the yarn with the freely rota'able heated roll.
Still another object of our invention is to provide a low maintenance drafting system.
A further object of our invention is to provide a drafting system which will operate satisfac~orily from a mechanical quality and dye uniformity standpoint, at speeds up to 1500 meters per minute and greater.
A still further object is to provide a less expensive drafting system for providing textile yaxns of equivalent quality to those made by the process disclosed in U.S. Patent No. 3,539,680.

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Disclosure of In~ention In accordance with the present invention, we provide a drafting system for yarn which has a driven feed roll for feeding the yarn at a predetermined speed; a driven output roll for ~orwarding the yarn at a second predetermined speed greater than the first-mentioned speed; a low friction freely rotatable heated rollr the surface of which is heated to a pre-determined temperature, the freely rotatable heated roll being located between the driven feed roll and the driven output roll; and a separator roll spaced adjacent to the freely rotatable heated roll and wherein the yarn is wrapped a plurality of times around the freely rotatable heated roll and the separator roll. The surface speed of the freely rotatable heated roll is operating slightly faster than the surface speed of the driven input roll with the freely rotatable heated roll being driven by engagement with ~L2~37'~

the yarn. As a result. sufficient yarn ten6ion automatically is tran~ferred upstream of ~he freely rotatable heated roll to pretension ~he yarn before it contacts the freely rotatable heated roll. Drafting takes place near the loca~ion where the yarn leaves the freely rotatable heated roll to pass toward the driven output roll.
The e~sential feature~ of the above described drafting system are:
(a) the steady ~tate resi6tance t~ turning of the freely rotatable heated roll plus the separator roll, as measured by stress on the yarn being drafted, i6 no more than 0.25 grams/denier(drafted yarn) and is preferably <0.15 grams/denier(drafted yarn), (b) t~e start-up resistance. which is primarily the inertia of the freely rotatable heated roll, i6 no more than 0.000113 Pounds x s~uare foot or denier(drafted yarn~
4.B6xlQ-5 newtons x metres sauared and is preferably denier(drafted yarn) approximately 0.000045 pounds x sQUare foot or denier(drafted yarn) 1.86xlO-5 ne~tons x metres squared a8 obtained from denier(drafted yarn) the equation T = CWk2a denier ~drafted yarn~
wherein T - torque (length x force~per unit denier C = constan~ depending on units selected k = radius of gyration (unit~ of len~th~
a = angular acceleration (radian6 per second squared) weight (units of mas6~, .

(c~ the coefficien~ of friction betwee~ the yarn and the sur~ace of the ~reely rotatable heated roll, as mea~ured on a Rothschild Friction Te~ter (ba~ed on ; :
, :
.

capstan equation) using 180 cGntact at a yarn speed of 10 metres/minute, is greater than 0.57, (d) the separator roll being located at a position relative to the freely rotatable heated roll and rela-tive to the direc~ion of the path of yarn movementsuch that the angle of contact of the yarn with the surface of the freely rota,able heated roll is > 30 on the first wrap and is >30 on the last wrap before the yarn leaves the freely rotatable heated roll, and (e) there is no frictional contact made with the yarn in the area where pretension occurs between the location where the yarn exits from the driven feed roll and the location where the yarn makes initial contact wi~h the freely rotatable heated roll.
More specifically, the separator roll is located at a position relative to the freely rotatable heated roll and relative to the direction of the path of yarn movement so as to be either within the angular specification designated 2 + 6 ~ as shown in Fi~. ~a of the drawings, or so as to be within quadrant ~a", as shown in Fig. 4b of the drawings.
A device for thermally stabilizing the yarn may be located between the freely rotatable heated roll and the driven output roll, or the driven output roll may be heated so as to thermally stabilize the yarn, or the yarn may be thermally stabilized after the yarn leaves the driven output roll.
In the drafting system disclosed herein, greater than 60 percent and preferably 80 to 95 percent of the yarn draw tension is trans~erred upstream of the freely rotatable heated roll to pretension the yarn before the yarn touches the heated roll. It is impor-tant to realize that in the proposed drafting system of this invention it is the low ~riction character o~
the freely rotatable heated roll that enables the ~2~

transmission of a significant portion of the draw tension upstream of the freely rotatable heated roll, thereby providing automatic or inherent pretensioning of the yarn.
The drafting system may include a low friction freely rotatable heated roll that is an air bearing, or it may be a ball bearing or any other low friction bearing arrangement. "Air bearing~ and ~ball bearing~
are expressions used herein to describe a heated roll that may be supported for rotation either by an air bearing arrangment or a ball bearing arrangement.
~ here the yarn being processed is polyest~r yarn, the predetermined temperature for the surface of the freely rotatable heated roll ~ill be about 80C to about 120C, and the temperature for the device or thermally stabilizing the yarn is such that the yarn temperature is about 120C to about 220C as it leaves the thermally stabilizing device.

Brief Description of the Drawings The details of our invention will be described in connection with the accompanying drawings, in which Fig. 1 is a schematic elevational view of a prior art drafting system employing a pinch roll such as that disclosed in the above-mentioned U.S. Patent No. 3,539,~80;
Fig. 2 is a schematic elevational view of a prior art drafting system employing a heated pin;
Fig. 3 is a schematic elevational view of the drafting system of the present invention employing a low friction freely rotatable heated roll and a post stabilizing device; and Figs 4a and 4b are schematic diagrams ill~strating preferred locations for the separator roll relative to the freely rotatable heated roll and relative to the direction o~ the path o yarn movement.

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Best Mode for Carrying Out the Invention Fig. 1 represents a prior art drafting system 10 such as disclosed in U.S. Patent No. 3,539,680 in which a pretension zone for the yarn being processed is established between a nonheated godet roll 12 and a heated godet roll 14 and its separator roll 16, and a pinch roll 18 bearing against the heated godet roll 14 serves to minimize variability of the yarn drafting by preventing the drafting of the yarn 20 from extending upstream of the location of the pinch roll 18. The godet roll 22 and its separator roll 24 serve as an output roll arrangement for forwarding the yarn to a winder (not shown). Guides for the yarn are shown at 26 and 28, and 30 designates the separator roll for the nonheated godet roll 12.
Fig. 2 represents a prior art drafting system 32 which employs a heated stationary pin 34 between a nonheated godet roll 36 and its separator roll 38 and a nonheated godet roll 40 and its separator roll 42, the latter two serving as an output roll arrangement for forwarding the yarn 44 to a winder (not shown).
Another nonheated godet roll 46 and its separator roll 48, as well as yarn guides 5~ and 52 are shown located upstream of the first-mentioned nonheated godet roll 36.
The drafting systems of Figs. l and 2 will be discussed later in relation to the drafting system of the present invention following a discussion of the essential features of the invention.
In Fig. 3, which represents the proposed drafting system 54 o the present invention, the yarn 56 is shown being guided over yarn guides 58 and 60 to a nonheated godet roll 62 and its adjacent separator roll 64. The yarn then passes ~o a low friction freely rotatable heated roll 66 and its adjacent separator roll 68 to be wrapped a plurality of times therearound before passing to the nonheated godet roll or output roll 70 and its adjacent separator roll 72 to be forwarded to a winder (not shown).
The yarn may be thermally stabilized by a device such as that represented at 74, which may be a slit or plate heater having either contact or noncontact with the yarn. Typical temperatures to be employed with a contact heater, when the yarn being processed is poly-ester, are such that the yarn temperature will be about 120C to about 220C, and the freely rotatable heated roll surface temperature will be about 80C to about 120C as the yarn leaves the stabilizing device.
Alternatively the device for thermally stabilizing the yarn may be a device for heating the driven output roll; thus the driven output roll may be a heated godet roll. It is also within the scope of the inven-tion that such heated godet roll may be a stepped godet roll such that controlled shrinkage may take place during thermal stabilization, or the ya~n may be thermally stabilized after it leaves the output roll 70 and its separator roll 72.
As heretofore pointed out, we have discovered so~e essential features that must be present in our draft-ing system in order for our system to be effective.We have not found these features present in the prior art nor recognized by the prior art.
First, the steady state resistance to tuxning of the ~reely rotatable heated roll plus the separator roll, as measured by stress on the yarn being drafted, must be no more than 0.25 grams/denier(drafted yarn) and preferably ~s <0.15 grams/denier(drafted yarn).
Obviously, the steady state resistance to turning has two components: (1) bearin~ resistance and (2) air drag, with air drag being mor~ sensitive to operatiny speed.

Second, ehe start-up resi~tance, w~ich is primarily the inertia of the ~reely rotatable heated roll, i5 no more than 0.000113 pounds x ~quare foot or denier(drafted yarn) 5 4.86x10-5 newton6 x metres s~uared and i~ pre~erably denier(drafted yarn) approximately O.Q00045 ~ounds x square foot or denier(drafted yarn) 1.86xlO-5 newtons x metre6 sq~red a~ obtained from denier(drafted yarn) the equation T - CWk2a denier (drafted yarn) wherein T = torque (length x force)~per unit denier C = constant depending upon the units 6eleceed k = radius of ~yration (unit~ of length) = angular acceleration (radian~ per 6econd squared) W = weight (unit~ of ma~s)~

For a given yarn at stare-up, the torque iB
approxima~ely constant and i8 generated by sliaing frictional contact with the free~y rotatable ~ea~ed roll. Thus, the re~istance to turning i~ directly proportional to Wk . The torque generated ~o accelerate the freely rotatable heated roll iP also proportional to denier because the area in contact with the heated roll increase~ as the denier increa~e~.
Thu6, ~pecifying that the pound~ x ~quare foot/denier(drafted yarn) ~newton6 ~ metres squared~-denier~drafted yarn)] 6hould not exceed a given number, i~ equivalent to caying that ~he angular acceleration will equal or exceed a minimum value and thereby 35 minimi~e ~tare-up time for the freely ro~at~ble ~eated roll.

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Third, the coefficient of friction between ~he yarn and the surface of the freely rotatable hea~ed roll, a~
mea6ured on a Roth~child Friction Tester (ba6ed on capstan equation~ u6ing 180 contact at a yarn 6peed of 10 metres~minute, is greater ~han 0.57, and i6 prefer-ably in the range of 0.75 to 0.95. The capstan equa-tion i~ well-known, but will be mentioned here a6 bein~
T2 = e~
T
wherein T2 = ten~ion of the yarn on the side of the capstan where yarn i6 being pulled Tl = tension of the yarn on ~he other ~ide of the capstan e = base of natural logarithm = coefficient of friction ~ = angle of wrap in radians The high coefficient of friction insures that t~e yarn will not slide on ~.he freely rotatable heated roll during the fir~t wrap and thereby undesirably initiate a kind of two-stage drafting. Thi6 also hel~s increa~e the ~orque at star~-up which minimizes the ~ime for ~he freely rotatable heated roll ~o accelerate ~o steady ~tate.
Fourth, the separator roll 6hould be located at a ~06ition relative to the freely rotatable heated roll and relative to the direc~ion of the path of the yarn movement ~uch that the angle of contact with the 6urface o~ the freely rotatable roll i6 ~30 on the fir~t wrap and i6 230~ on ~he la~t wrap before the yarn leaves the freely rotatable heated roll, Note, for example, the angle of contact llxll, which would be on the firfit wrap in Fig6. ~a and gb, and the angle of contact "y", which would be on the last wrap in Figs.
4a and 4b.
.

As also heretofore pointed out, the separator roll is located at a position relative to the freely rotatable heated roll and relative to the direction of the path of yarn movement so as to be either within the angular specification designated + , as shown in Fig. 4a of the drawings (no'e path of yarn 56 in Fig. 4a), or so as to be within quadrant "a~, as shown in Eig. 4b of the drawings (note path of yarn 56 in Fig. 4b). The reason for the yarn being in quadrant ~a~ in Fig. 4b, for èxample, is that the yarn has a longer contact with the heated roll on the last wrap and thereby helps insure that no drating will take place before the yarn leaves the freely rotatable heated roll. The distance between the separator roll and the freely rotatable heated roll should be mini-mized with about one (1) to two (2) inches ~2.54 centimeters to 5 centimeters) being reasonable~
Fifth, there is no frictional contact made with the yarn in the area where pretension occurs between the location where the yarn exits from the driven feed roll and the location where the yarn makes initial contact with the freely rotatable roll. This ~eature is quite essential hecause any interference in this critical area, such as shown by the thread guide 37 in Fig. 6 of U.S. Patent No. 3,919,748, as heretofore discussed, will cause damage to the yarn resulting in filament breakage in the subsequent drafting of the yarn.
The drafting systems of the prior art will now be discussed and compared with the drafting system of the present invention. Be~ore doing so, however, we want to point out that the feed system for our inven~ion does not have to be powered godetsl as is often true in the prior art, but can be of any o~ the lesser-costing devices used on false twist texturing machines, (i.e. rubber cots on shafts, casablancas)O

U.S. Patent No. 4,053,27~ discloses a hea~ed air bearing that in principle would be suitable Por practice ~f t~e ~resen~ invention. ~lthough t~ere i6 no disclo~ure in the patent where the thermocouple would be positioned to assure pre~etermined ~urface temperatures, we would ~uggest employing a thermocouple internally of the roll with its probe being positioned just beneath the surface of the roll such as disclosed in U.~. Patent No. 3,879,594 or Patent No. 3,296,418, for example. Air bearings or rolls are al~o shown in U.S. Patent~ No. 4,013,326, No. 3,753,517, and No.
3,560,066. Ball bearing rolls may also be used and are conventional in the art, ~uc~ as shown in U.S. Patent No. 3,296,418. The design o~ such roll, ~owever, must be o~ very low friction.
The freely rotatable heated roll 66 (Fig. 3) in our invention i6 wrapped with sufficient wraps to ensure heating of the yarn to approximately ~he surface temperature of the heated roll~ Drafting of the yarn 56 takes place near the point where the yarn leaves t~e heated roll 66 for the last time on it~ way koward t~e outpu~ roll 70.
The output roll may be con6tru~ted in the same manner a the input roll, thus costs will be mini~i~ed and ~uch construction will be simpli~ied because the godet rolls shown do not reguire heating thu~
maintenance will be reduced a~ compared to maintenance required for heated godet rolls. Obviously, ~he latter statement will only be partially true if the thermally stabilizing device should be incorPorated in t~e output roll ~o ma~e it in effect a heated godet roll.
The following drafting sy8tem8 were evaluated:
(1) a drafting sy6tem including a heated godet roll ~aving a 0.5 meter circumference and a pinch xoll ~uch a6 disclosed in U.S. Patent No. 3,539,680 and illus-'~
-, ;. ,~ , , .

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trated in Fig. 1; (2) the same drafting system as in (1) except the pinch roll was removed (not shown in the drawings); (3) a drafting system including a stationary 40 millimeter diameter heated stationary pin having a flame-coated ceramic surface, such as disclosed in Fig. 2; (4) the same drafting system as in (3) except that a stationary 80 millimeter diameter heated stationary pin was used; (5) a drafting system including a 70 millimeter diameter freely rotatable heated roll was used, such as is illustrated in Fig. 3.
A polyester (from polyethylene terephthalate polymer) POY (partially oriented yarn) was used to evaluate ~he drafting systems. See U.S. Patent No. 4,245,001 for a description of the polymer and spinning conditions for making the POY. The numbers shown in the tables below are highly dependent upon the quality of the polymer from which the yarns were spun and the spinning process from which they were made. Thus the true significance of these numbers is determined only by looking at the relative values among the systems as opposed to the absolute numbers.
As noted in the tables, no post stabilization device was used in obtaining the results shown in thé tables.
The drating systems were evaluated with the above-aescribed yarn to determine optimum drafting conditions for each system at 400 meters per minute and at 1000 meters per minute drafting speeds~ The drafting system of our invention ran so smoothly at 1000 meters per minute that we see no problems in running it up to 1500 meters and greater. After optimum drafting conditions were determined for each system~ the systems were then compared to each other, as shown by the tables below.

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Table 1 Drafting Conditions for Polyesler POY
270 denier/30 filaments Preheating Broken Filaments Temperature(ct./1000 m) %
Set Pt., C X** S*** Uster Heated Air Bearing100 2.33 1.66 3.12 8 wraps 120 1.89 1.17 1.95 645/1000 m/m 140 0.33 0.50 0.66 150* 0.11 0.33 0~67 160 0.11 0.33 0.7~
Heated Air Bearing120 0.67 1.32 0.62 8 wraps 140* 0.00 0.00 0v78 258/400 m/m 150 2.78 1.56 0.77 160 ll.OU 4.73 0.79 80 mm Hot Pin 70 9.67 3.00 6.92 1-360 wrap 80 14.11 3.98 7.23 645/1000 m/m 90 19.67 3.~0 7.18 80 mm Hot Pin 70 4.89 2.09 5.60 `1-360 wrap 80 2.67 2.34 5.20 258/400 m/m 100* 4.00 2.34 2.24 120 14.22 4.27 1.00 40 mm Hot Pin 80 12.87 3O94 6.97 1~360 wrap 90 28.33 6.40 7.25 645/1000 m/m 100 45-44 8.68 7.20 120 100.33 10.6~ 6.62 140 127.67 14.57 5.40 40 mm Hot Pin 70 3.44 1.81 6.78 1-360 wrap 80 6.44 3.50 6.R3 258/400 m/m 90 5.44 2.40 6.20 100 4.44 2.60 ~.20 Heated Godet (no pinch) 80 1~33 1.41 3.33 8 wraps 95 1.00 1.32 ~.72 645/1000 m/m 100 0.56 0.73 1.82 110* 1.56 0.88 0.73 120 43.3 8.66 U.68 7-~

Table 1 continued Heated Godet (with pinch) 105 0.00 0.00 0.93 8 wraps 110* 0.00 0.00 0.73 645/1000 m/m 115 0.33 0.50 0.72 Heated Godet (no pinch) 60 17.77 7.97 2.65 8 wraps 80 9.56 2.96 2.60 258/400 m/m 90 0.11 0.33 1.31 95* 0.44 0.53 0.86 100 4.33 2.45 0.95 110 102.20 17.75 0.93 120 393.10 63.07 1.45 Heated Godet (with pinch) 90 0.22 0O44 1.40 8 wraps 95* 0.11 0.33 0.88 258/400 m/m 100 0.78 1.64 0.80 *optimum conditions **mean of nine (9) separate measurements on 1000 meters of drawn yarn ***standard deviation no post stabilization was used in obtaining ,hese results 7~1 a) o a) ~ ~ o ~ ~o ~ o ~ ~ ~
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Table 1 shows the Uster uniformity and broken filament results from the different drafting systems and the conditions evaluated using a partially oriented yarn (POY) of polyester (270 denier/3 filaments from polyethylene terephthalate)D
Table 2 shows the Uster uniformity and broken filament results at various numbers of wraps on the surface of the 70 millimeter dia~eter heated air bearing or heated roll. Optimum drafting conditions for various POY yarns using the 70 Inillimeter diameter heated air bearing are shown in Fig. 3.
In reference to Table 1 again, in general as the temperature of the drafting device increases, the level of broken filaments for the yarn decreases, passes through a minimum and then increases. The Uster uniformity behaves similarly. The drafting conditions which gave the minimum Uster uniformity and broken filament level was chosen as the optimum drafting condition, and it is indicated with a single asterisk in Table 1. The 70 millimeter diameter heated air bearing was found to perform as well as the heated godet with the pinch roll and better than either of the t~o heated pins or the heated godet roll without a pinch roll.
The number of wraps on the heated air bearing was found to be an important variable as shown in Table 2.
The optimum number of wraps was found to be eight for a drafting speed of 1000 meters per minute, draw ratio of 1.55X and a set point of the heated air bearing of 150C Increasing the number of wraps above eight did not appear to lower the Uster uniformity or the broken filament level. Also shown in Table 2 is th~ draw tension be~ore and after the heated air bearing as a function of the number of wraps. For the above condi-tions and eight wraps, the tension before the heatedair bearing or the pretension was found to be about 42 7~

grams with the tension after the heated air bearing being about 100 grams. Obviously, this particular combination of yarn, number of wraps, speed, etc., causes an unusually large drag to exist on the heated roll. In this case a tension of 60 grams or higher would be preferred. It will be noted that as the wraps increased after eight, the pretension increased.
A speed check with a Strobe light showed the heated air bearing or freely rotatable heated roll surface to be moving only slightly faster than the feed roll.
This was very surprising to us. This feature occurs because the dynamic stress strain curve of the undrawn yarn was found to be Hookean over the tension ranges encountered before the yarn makes contact with the heated roll and under these conditions the yarn exhibits a very high dynamic modulus.
The best operating temperatures for the yarns when drafting on the 70 millimeter diameter heated air bearing using eight wraps are shown in Table 3.
Higher speed or larger total deniers were found to require higher operating temperature o~ the heated air bearing or heated roll. Therefore, each yarn wi~l have its own particular optimum temperature settings.
Actual surface temperature of the heated air bearing or heated roll, as measured with a contact thermocouple (not shown) immediately after stopping the ro.ating surface ~see Table 3), was lower than the set point temperature. "Set point temperature~ is the temperature established within the heated roll, and does not mean the surface temperature of the roll~
This difference was caused by the location of the thermocouple which was in the unit core rather than in the rotating surface.
Dyed socks made from the yarns which were drawn on the heated air bearing or heated roll at 1000 meters per minute bad exce-llent uniformity. They were found to be superior to the yarns produced on ~he fixed heat pins and equivalent to those produced on the heated godet sy~t~m without a pinch roll.
The following is an example of an ef~ective draft-ing system as disclosed herein.

~AMPLE 1 One freely rotatable heated roll was constructed using ball bearings. The diameter of the roll was 10 70 m~ and it6 Wk was 0.0045 lb6 x ft or O.OQl86 newtons x metres 6quared.
The roll had a poli~hed chrome surface wi~h a coefficient of friction of O.~S. This roll was used to draft polyester filamen~ yarn under the ~onditions listed below:
Draw ra~io - 1.60X
Pin temperature (6et point) - 100C
Stabilizatio~ plate temperature - 160C
Speed - 300 m~min The measured percent of draw ~ension transferred upstream into the pretension zone was about 92S.
The feed yarn wa6 22~(140)/25 POY
The yarns produced dyed uniformly and con~ained les~
25 than 0.3 bro~en filamPnts per pound of yarn. Start-up was also adegu~te.
The following exampl~ are used to determine and define important variables related to the ~ucces~ul operation of the drafting ~ystem di~closed herein.
~AMPLE 2 Another freely rotatable heated roll wa6 con-6tructed u~ing ball bearing~. The diame~er of the roll was 70 mm and its Wk2 was al~o 0.0045 1~6. X ft.2.
35 The surface, however, was plas~a coated ceramic with a coefficient of friction of 0.29. When running a temperature series on the roll, an unusual phenomenon was observed. The feed yarn was 225(140)/25 polyester POY.
Draw ratio - 1.6GX
Stabilization plate temperature - 140C
Speed - 800 m/min The measured percent of draw tension transferred upstream into the pretension zone was about 85%.
The separator roll was located as shown in Figure 3 such that the wrap angle for the first wrap was approximately 30.
Set Point on In Out Speed SurEace Speed 15Roll C M/Min of Roll M/Min 110 50n S48 Notice that at 100C and below the surface speed of the roll differs from the input speed by about 2%.
This 2~ represents the elastic ex~ension o~ the POY
under the pretension load. This elastic extension is the reason the roll operates slightly faster than the feed roll speed. However, at llO~C and above, there is some obvious drafting of the yarn taking place 3Q before it establishes good frictional contact wi~h the surface of the roll. This two stage drafting behavior is undesirable.
Two ways were found to eliminate this undesirable behavior. The first was to increase the wrap angle on the first wrap to 270 or more. This is not a very practical method. The second approach was to use a ~2~

roll surface with a higher coefficient of friction. A
polished chrome surface roll was constructed with a coefficient of friction of 0.85. No two-stage draft-ing was observed with this surface. Thus, combina-S tions of increased wrap angle and/or increasedcoefficient of friction between the yarn and the roll surface can be used to eliminate the two-stage drafting.
The invention has been described in detail with particular reference to preferred embodiments thereof, bu~ it will be understood that variations and modifi-cations can be effected within the spirit and scope of the invention.

7~

SUPPLEMENTARY DISCLOSURE

As taught in the principal disclosure a drafting system is pro~ided for yarn which has a driver feed roll for feeding yarn at a predetermined speed; a driven output roll for forwarding the yarn at a second predetermined speed ~reater than the first-mentioned speed; a low friction freely rotatable heated roll, the surface of which is heated to a predetermined temperature, the freely rotatable heated roll being located between the driven feed roll and the driven output roll; and a separator roll spaced adjacent to the freely rotatable heated roll and wherein the yarn is wrapped a plurality of times around the freely rotatable heated roll and the separator roll. The surface speed of the freely rotatable heated roll is operating slightly faster than the surface speed of the driven input roll with the freely rotatable heated roll being driven by engagement with the yarn. As a result, sufficient yarn tension automatically is transferred upstream of the freely rotatable heated roll to pretension the yarn before it contacts the freely rotatable heated roll. Drafting takes place near the location where the yarn leaves the freely rotatable heated roll to pass toward the driven output roll.
One of the essential features of the above described system is the start-up resistance, which is primarily the inertia of the freely rotatable heated roll, which is 0 000113 pbunds x square foot no more than denier ~drafted yarn) or 4.86 x 10 5 newtons x metres squared and is preferably denier tdrafted yarn) 0 000075 pounds x square foot no more than denier (drafted yarn) or 3 10 x 10- newtons x metres squared, still more preferably denier (drafted yarn 0 000045 pounds x square foot is no more than denier (drafted yarn) or -S.D. 24-::IL2~

denier ~drafted yarn) 0.000030 pounds x square foot no more than denier (drafted yarn) or .
1.24 x 10 5 newtons x metres squared as obtained from denier (drafted yarn) CWk2a the equation T = denier (drafted yarn) wherein T = torque (length x force)/per unit denier C = constant depending on units selected k = radius of gyration (units of length) a = angular acceleration (radians per second squared) W = weight (units of mass).
For a given yarn at start-up, the torque is approximately constant and is generated by sliding frictional contact with the freely rotatable heated roll. Thus the resistance to turning is directly proportional to Wk2. The torque generated to accelerate the freely rotatable heated roll is also proportional to denier because the area in contact with the heated roll increases as the denier increases. Thus, specifying that the pounds x square foot/denier (drafted yarn) ~newtons x meters squared/denier (drafted yarn)] should not exceed a given number, is equivalent to saying that the angular acceleration will equal or exceed a minimum value and thereby minimize start-up time for the freely rotatable heated roll~
Obviously, start-up performance, as the denier of the feed yarn is decreased, becomes poorer unless the Wk2 sf the freely rotatable heated roll is reduced correspondingly.
The following additional example is provided of an effective drafting system as disclosed.

One freely rotatable ~eated roll was constructed using ball bearings. The diameter of the roll was 70 mm and its Wk2 was 0.0045 lbs. x ft 2 or 0.00186 newtons x meters squared.

-S.D. 25-~ .

37~

The roll had a polished chrome surface with a co-efficient of friction of 0.85. This roll was used to draft polyester filament yarn under the conditions listed below:
Draw ratio - 1.60 x Pin temperature (set point) - 100C
Stabilization plate temperature - 160C
Speed - 300 m/min.
The measured percent of draw tension transferred upstream into the pretension zone was about 92%.
The feed yarn was 96(60)/20 POY.
The yarns produced dyed uniformly and contained less than 0.3 broken filaments per pound of yarn. Start-up was marglnal.

B S.D. 26-

Claims (13)

We Claim:

1. A drafting system for yarn comprising:
driven feed means for feeding said yarn at a predetermined speed driven output means for forwarding said yarn at a second predetermined speed greater than said first-mentioned pre-determined speed; a low friction freely rotatable heated roll, the surface of which is heated to a predetermined temperature, said freely rotatable heated roll being located between said driven feed means and said driven output means and a separator roll spaced adjacent to said freely rotatable heated roll and wherein said yarn is wrapped a plurality of times around said freely rotatable heated roll and said separator roll: and the surface speed of said freely rotatable heated roll is operating slightly faster than the surface speed of said driven input means, with said freely rotatable heated roll being driven by engagement with said yarn and whereby sufficient yarn tension automatically is transferred upstream of said freely rotatable heated roll to pretension said yarn before it contacts said freely rotatable heated roll with drafting taking place near the location where said yarn leaves said freely rotatable heated roll to pass toward said driven output means, and wherein:

(a) the steady state resistance to turning of the freely rotatable heated roll plus separator roll, as measured by stress on the yarn being drafted, is no more than 0.25 grams/denier (drafted yarn), (b) the start-up resistance, which is primarily the inertia of the freely rotatable roll, is no more than or as obtained from the equation wherein T = torque (length x force)/per unit denier C = constant depending on units selected k = radius of gyration (units of length) a = angular acceleration (radians per second squared) W = weight (units of mass), (c) the coefficient of friction, between the yarn and the surface of the freely rotatable heated roll as measured on a Rothschild Friction Tester (based on capstan equation) using 180°
contact at a yarn speed of 10 metres/minute, is greater than 0.57, (d) the separator roll being located at a position relative to the freely rotatable heated roll and relative to the direction of the path of yarn movement such that the angle of contact of the yarn with the surface of the freely rotatable heated roll is >30° on the first wrap and is >30° on the last wrap before the yarn leaves the freely rotatable heated roll, and (e) there is no frictional contact made with the yarn in the area where pretension occurs between the location where the yarn exits from the driven feed means and the location where the yarn makes initial contact with the freely rotatable heated roll.

2. A drafting system as defined in Claim 1 wherein said steady state resistance to turning of the freely rotatable heated roll plus separator roll, as measured by stress on the yarn being drafted. is <0.15 grams/denier(drafted yarn), and said start-up resistance is no more than

3. A drafting system as defined in Claim 1 wherein said coefficient of friction is in the range of 0.75 to 0.95.

4. A drafting system as defined in Claim 1 wherein said separator roll is located at a position relative to the freely rotatable heated roll and relative to the direction of the path of yarn movement so as to be within the angular specification designated shown in Fig. 4a of the drawings.

5. A drafting system as defined in Claim 1 wherein said separator roll is located at a position relative to the freely rotatable heated roll and relative to the direction of the path of yarn movement to so as to be within quadrant "a" shown in Fig. 4b of the drawings.

6. A drafting system as defined in Claim l and including means for thermally stabilizing the yarn.

7. A drafting system as defined in Claim 6 wherein said means for thermally stabilizing the yarn is located between said freely rotatable heated roll and said driven output means.

8. A drafting system as defined in Claim 6 wherein said means for thermally stabilizing the yarn is a means for heating said driven output means.

9. A drafting system as defined in Claim 1 wherein greater than 60 percent of yarn draw tension is transferred upstream of said freely rotatable heated roll.

10. A drafting system as defined in Claim l wherein 80 to 95 percent of yarn draw tension is transferred upstream of said freely rotatable heated roll.

11. A drafting system as defined in Claim 1 wherein said low friction freely rotatable heated roll is supported for rotation on an air bearing.

12. A drafting system as defined in Claim l wherein said low friction freely rotatable heated roll is supported for rotation on ball bearings.

13. A drafting system as defined in Claim 6 wherein said yarn is a polyester yarn and said predeter-mined temperature for said surface of said freely rotatable heated roll is about 80°C to about 120°C
and the temperature for said means for thermally stabilizing said yarn is such that the yarn temperature is about 120°C to about 220°C as the yarn leaves said means for thermally stabilizing said yarn.

CLAIMS SUPPORTED BY THE SUPPLEMENTARY DISCLOSURE

S.D. 14. A drafting system as defined in claim 1 wherein said steady state resistance to turning of the freely rotatable heated roll plus separator roll, as measured by stress on the yarn being drafted, is <0.15 grams/denier (drafted yarn), and said start-up resistance is no more than or S.D. 15. A drafting system as defined in claim 1 wherein said steady state resistance to turning of the freely rotatable heated roll plus separator roll, as measured by stress on the yarn being drafted, is <0.15 grams/denier (drafted yarn), and said start-up resistance is no more than or