US2407100A

US2407100A - Drafting of fibers

Info

Publication number: US2407100A
Application number: US492425A
Authority: US
Inventors: Ernest L Richardson
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1943-06-26
Filing date: 1943-06-26
Publication date: 1946-09-03
Anticipated expiration: 1963-09-03
Also published as: GB624765A

Description

. Sept. 3, 1946. E. L..l RICHARDSON y DRAFTlNG 0F FIBERS Filed June 26, 1943 2 sneek-sheet 1 A.. .4 a. C v O k G l. Mv

P= tam-tant 7b mill compressed a/r `s'l/)uplv Inventar- Ernest L.Ri char=doh,

'by H f. 1Mb Attorney.

"f Hi y Sept 3, 1945A E. L. RICHARDSON. 2,407,100

DRAFTING 0E FIBERs Filed June 2e, 194s sheets-shet 2 o l O Y Inventor: Ernest L.. Richardson,

Y H is4 Attorneg.

Patented Sept. 3, V1946 DRAFTING OF FIBERS Ernest L. Richardson, Melrose, Mass., assignor to General Electric Company, a corporation of New York- Applicauon June 26, 194s,l seria1No-`49a425 This invention relates to the processing of fibers to form yarns or threads; more particularly to means employed in the drafting of fibers; and it has for an object the provision of a simple, reliable, inexpensive, and improved means of this character.

In certain of the preparatory steps in the processing of fibers to form ayarn or thread, a length of materials, such as a sliver or roving, containing an' array of fibers is subjected to a series of drafting operations before being converted into the final yarn or thread form.

When the material is made up into sliver form for the rst time, whether it be by means of carding or in any other way, it falls very far short of the ideal so far as regularity and uniformity of density are concerned. The constituent fibers are by no means perfectly mixed, and both long and short wave variations in thickness are considerable.-

Drafting is usually accomplished by passing a length of material containing an array'of fibers through successive pairs of drafting rollers which are driven at progressively higher speeds to cause the fibers to slide over one another and thereby decrease the overlap between each fiber and its neighbors. If a sliver or roving is first passed through the nip of one pair of rotating rollers and then through the nip of a second pair of rollers which is rotating live times as fast as the first pair, the issuing sliver or roving must be ve times as long and five times as thin. The draft in such case is five.

In spite of the use of many devices and methods intended to produce uniformity, the sliver from which the roving and finally the yarn or thread is produced contains thick portions and thin portions. The occurrence of thick and thin places really means that the draft, instead of being general in the fields between the nips of successive pairs of drafting rollers, is local. Where there is no draft, a thick portion results and where the draft is concentrated, athin portion results. The latter originates at some place within the drafting field between the hips of two successive pairs of drafting rollers Where the fiber cohesion is least, and results in the stream of `short fibers being separated into two parts'. The rear part moves slowly and the front part more rapidly. The concentration of the draftin therear portion allows the front portion to go forward undrafted, and the rear portion is drafted into a thin portion.

Accordingly, a further object of this invention is the provision of means for controlling the draft 12 Claims.

(Cl. lil-70) of the bers to eliminate or minimize these variations in thickness, thereby to improve the quality of the final product.

If all the fibers were of the same length, this could be accomplished by passing the length of material through two pairs of rollers, of which the spacing ofthe rollers is only just greater than the liber length. With such an arrangement, the tail of each fiber would no sooner leave the control of the rst pair of rollers, i. e. the entry or retaining rollers, than it would corne under the influence of the second pair, i. e. the drawing rollers. The changeover would be accomplished by a sudden acceleration on the part of the fiber from the speed of the first pair of rollers to the speed of the second pair. It would only be free from positive control by one or the other pair of rollers fora brief instant.

However, in practice the ideal of fibers of equal length is usually not realized. The spacing of the successive pairs of rollers cannot be less than the length of the longest fibers because otherwise they would be held simultaneously by both pairs of rollers and would be either broken or not drafted. The shorter fibers, constituting the great bulk of the material under treatment, are drafted under conditions that are very unsatisfactory. When within the drafting field between the two pairs of rollers, they are under no direct control by either pair of rollers and depend for their support and their movements entirely on the other fibers with which they are in contact.

The retaining rollers retain their hold upon the long fibers until they are in position to be taken by the drawing rollers. But with the short fibers there is no such control. They are released by the retaining rollers when they still have some distance, depending on their length, to go before it is their turn to be taken by the drawing rollers. The result is that they tend from time to time to be plucked forward in thick undrafted bunches, leaving behind them thin portions `composed mainly of the longer fibers. These thick bunches of short fibers tend to persist through theentire series of subsequent drafting operations.

Another object of the invention isthe provision 'of means for detecting variations in the density of the fibers of the length of material, and for providing an indication of the magnitude of such variations.

In carrying the invention into effect in one form thereof, a fluid such as air is caused to flow through the fibers of a length of material, such as 'al sliver, of which thefiber density is to be determined. The resistance offered by the array of bers to the flow of air is a measure of the fiber density, and thus by measuring variations in resistance to the flow of air through the liber array, the amount of variation from uniformity can be determined.

One form of the device for measuring the resistance to flow of air through the fibers comprises a member provided with a passageway through which the length of material passes. l

This member is recessed to provide a chamber in communciation with the passageway. Air from a suitable source of constant pressure is supplied through a restricted orifice to this passageway and escapes through the fibers. The air pressure in the chamber is a measure of the fiber density of the material passing through the passageway.

In a preferred form of the invention, the member containing the passageway is provided with a plurality of chambers which are in fluid communication with the passageway.

Another aspect of this invention is the automatic control of the drafting of the length of material to produce the desired degree of evenness in the draft and uniformity of the'product. In this aspect of the invention, a length of material containing an array of fibers is passed between a pair of drafting rollers which is driven at a predetermined speed by a suitable driving means and then through another pair of drafting rollers driven at a higher speed. A device such as described in the foregoing for detecting variations from a predetermined value in the density of the fiber array passing through the passageway is utilized to control the driving means for the pairs of drafting rollers to vary the draft in such a manner as to restore the fiber density to the predetermined value.

For a better and more complete understanding of the invention, reference should now be had to the following specification and to the accompanying drawings of which Fig. 1 is a simple diagrammatic sketch of an embodiment of the invention; Fig. 2 is a modification; and Fig. 3 is an enlarged view in section of the multiple chamber ow tube of the modifications of Figs. l and 2.

Referring now to the drawings, a length of material I0, such as a sliver, containing an array of loose fibers, is illustrated as being passed in the direction of the arrow II through the nip of a first pair of drafting rollers I 2, and then through the nip of a second pair of drafting rollers I3 to a subsequent stage in the processing. The distance between the nips of the pairs of drafting rollers I2 and I3 is greater than the length of the longest fibers in the array which constitutes the sliver Ill.

Although the drafting rollers may be driven by any suitable driving means, they are preferably driven by electric motors. As illustrated, the rst pair of drafting rollers I2 is driven at a suitable speed by means of an electric motor I4 which is illustrated as a shunt-wound direct-current motor to the drive shaft of which the bottom roller is connected through suitable driving connections illustrated as gearing I5, and the second pair of drafting rollers I3 is driven at a speed which may be assumed to be ve times the speed of the first pair of rollers by a similar motor I6 through similar reduction gearing I 'I.

The motors I4 and I6 are supplied from a suitable direct-current source which is represented in the drawings by the two conductors I8 and I9. The conductor I8 represents the positive side of the supply source, and the conductor I9 reprelli) sents the nega-tive side of the source. An adjustable potentiometer type resistor 20 is connected across the source I8, I9. The shunt field. windings I4a and I6a of the -motors I4 and I6 are connected in series relationship with each other across the source, and the armatures of these two motors are connected in parallel relationship between the positive side I8 of the supply source and the slider 20a of the potentiometer resistor. By varying the position of the slider 20a, the speeds of motors I4 and I6 can be adjusted up- Ward or downward to a desired level.

For the purpose of varying the relative speeds of the pairs of drafting rollers I2 and I3, in response to variations from a predetermined value in the density of the bers in the sliver Iii, a suitable speed regulating device 2I is provided for controlling the relative speeds of motors I4 and I6. This speed regulating device 2| comprises a stack of disks of a resistance material, such as carbon. The carbon stack 2I is connected in series relationship with a permanent resistor 22 across the supply source I8, I9, and the common point 2Ia between the carbon stack 2l and the resistor 22 is connected to the common point |412 between the field windings I4a and IIia by means of a conductor 23. The carbon stack 2| is mounted on a support 24 and is provided with a cap 25 to which a rod 26 passing through the center of the carbon stack is suitably secured. When pressure is applied to the carbon stack 2 I, as by means of a downward pull on the rod 2, the resistance of the carbon stack is decreased and conversely, when the pressure on the carbon stack is released, the resistance is proportionately increased.

From the connections described in the foregoing, it will be seen that the carbon. stack 2! is in parallel with the shunt eld winding Illa of the motor I4 and in series with the shunt field winding I6a of the motor I6. Thus, when pressure is applied to the carbon stack 2| to decrease its resistance, the excitation of the shunt field winding Ma, is weakened and that of the shunt eld winding ISa is increased. As a result, the speed of the motor I4 is increased and the speed of the motor I6 is decreased. The increase in the speed of the motor I4 and the decrease in the speed of the motor I6 produce corresponding changes in the speeds of the pairs of drafting rollers I2 and I3, and thereby decrease the draft of the bers in the drafting eld between these pairs of rollers.

Likewise, when the pressure on the carbon stack 2I is released to increase its resistance, the excitation of the field winding I4a is increased and the excitation of the field winding I 6a is correspondingly decreased. This causes the speed of the motor I4 and the drafting rollers I 2 driven thereby to decrease and the speed of the motor I6 and the drafting rollers I3 driven thereby to increase. The decrease in the speed of the drafting rollers I2 and the increase in the speed of the drafting rollers I3 produce an increase in the draft of the sliver in the drafting eld between the two pairs of rollers.

The pressure on the carbon. stack 2l is varied by means of a pressure responsive diaphragm device 2l in response to variations in fluid pres-n sure produced by a flow tube device 28 in response to variations from a predetermined value in the density of the sliver I0. Although the flow tube detecting device 28 may be made in any suitable way, .it is illustrated as comprising a pipe T member 28a which is provided with an insert 28h. The insert member 22D is tapered from. botl'i ends toward the center to provide a flow tulo-cy passageway for the passage of the sliver 513, and

5 is recessed between the entering and leaving ends of the tube to provide a chamber v28o in commuM nication with the passageway through which the sliver i0 passes.

A fluid, such as air. is supplied from a suitable source, such as the mill supply, through a retricted orice 29 to the chamber 28C in the flow tube device 28.

The pressure ofthe air supplied to the chamber 28C through the oriiice 29 is maintained substantially constant by means of a pressure regulating device 3B, which is included in the pipe connections between the source and the orifice 29. valve 39a which is loadedby means of a spring 30h. The bleed valve 30a is yfastened to one end of a lever 30C, the opposite 1end of which is provided with a knife edge which rests in thebottom of a .V-shapedslot in afblock 30d to provide for pivotal mcvementof the Vlever 39o.` 'One end of the loading spring 3B?) is 'secured to a stationary part, such. for example as the pipe and the other end is attached to a screw 39e which passes through the lever 39e and is provided with a nut 30] for adjusting the tension of f the spring to provide the desired loading of the valve. The valve 306i has a maximum movement of approximately 0.003 inch so that the change in spring gradient is negligible.

With variable inlet air pressure from the supply source throughthe throttling valve 327 the spring loading is adjusted for the desired pressure, and the throttling valve 32 is adjusted to give a small opening of the bleed valve corresponding to the minimum inlet pressure.` With? increase in the inlet pressure, the bleed valve opens a very small amount to dispose of the increased iiow passed by the throttling valve and thereby maintains a substantially constant supply pressure to the orifice 29.

The restricted orifice 29 is preferably mounted in one arm of a pipe T 33, and a similar restricted orifice 34 is mounted in the other arm of the pipe T. This other arm of the pipe T leads to atmosphere through a pipe 35 and an adjustable needle valve 36. p

When the needle valve 36 is completely closed, there is no flow through the orice 34 and the pressures on both sides of the orice 34 are equal to the supply pressure.

The lower chamber of the diaphragm device 2l is connected through a pipe 3l and an adjustable needle valve 38't0 the pipe 35, and therefore, the fluid pressure in the lower chamber is equal to the regulated supply pressure when valve ,35 is 'f closed. rFhe upper chamber of the diaphragmdevice is connected through a pipe 39 to the pipe di) through which air is supplied from the restricted orifice 29 to the chamber 28e of the iow tube detecting device 28. Consequently, the pressure in the upper chamber of the diaphragm device 3l is substantially equal to the pressure in chamber 28C. The two diaphragms 2lb and 21o are mechanically connected together by means of a yoke 21d which moves to take up a position corresponding to the magnitude of the diiference in pressure in the upper and lower chambers. Since the supply pressure is maintained constant, the diaphragm device may therefore be considered to be responsive to variations in the pressure in the chamber 28e of the flow tube detecting device. l

As illustrated in Fig. l, the pressure applying rod 26 of the speed regulating device 2| is secured to the yoke 21d by suitable fastening This pressure regulator comprisesa bleed means. The connections between the yoke 21d and the pressure applying rod 26 `are such that4 a decrease in pressure in chamber 28o produces a corresponding increase in pressure c-n the carbon stack, and an increase in pressure in the chamber 28c produces a corresponding decrease in pressure on the stack. 1

A pressure responsive indicating device, such as a Bourdon gauge 4l is connected to the pipe 4D leading to the pressure chamber 28o, for the purpose of providing a Visual indication of the pressure in the chamber 28oA and the density of the fibers of the sliver I il passing through the passageway of the flow tube detecting `device 29.

For the purpose of providing support andrestraint of the shorter iibers in the drafting elds between the pairs.ofdraftingrollers l2 and I3, without fracturing the longer fibers in the drafting eld, a iiow tube nozzle device 42 is provided.

A's shown in Fig. 3, the flowrtube device 42 diifers from the'flowtube device 2B of Fig. 1 in that the sizes of the sliver flow passages in the inSertSrllZa and 42bin the entering and leaving ends of the tube are different and also in the provision'of a plurality of internal barriers 42C and 42d which" are substantially equally spaced between the ends to provide a plurality of air chambers 42e, 42j, and 42g. The barriers 42o and 42d are provided with centrally disposed passages which are graduated in size such that when centrally aligned with the passages in the insert 42a and 42h, a passageway the size of which decreases uniformly fromthe entering to the leaving end is provided for the sliver l0. The end inserts 42a and 42h and the internal barriers may be made Vof steel and their surfaces which constitute the passageway for the sliver may be chromium plated to minimize resistance to the flow of the sliver. Y 3

`Air is supplied to the chambers 42e, 421, and 42g from a` manifold; 43 which in turn is connected by means of a pipe 44 `to the source of regulatedair supply, i. e., to the pipe 3l at` the` outlet endof the regulator 39. l.. Y

Thefflow .tube device 42 is mounted in the drafting eld between the rst and second pairs of drafting rollers so that the center line of the `passagewayof. the tube is aligned with the nips of the first and second pairs of drafting rollers. It is of suchsize that it occupies almost the entire space between the rst and second pairs of drafting rollers. f

, l With the foregoing understanding of the ele- A across the restricted orifice 29 will result in a relative speed of the pairs of drafting rollers I2 and i3 such as to draft the fibers just that amount that will result in delivering drafted sliver of the correct fiber density to the iiow tube detecting device 28.

As long as the density of the sliver owing through the flow tube detecting device 28 remains constant at the desired value the rate of flow of air from the chamber 28o in opposite directions through the entering and leaving inserts of the iiow tube will remain constant and consequently the pressure in the chamber 28C will remain constant and the diaphragm pressure responsive device 21 will therefore not change the pressure i -sity of the bers'entering the passageway of the ow tube device 28 tends to increase. As a result of this tendency of the liber density to increase, the'flow of air from the chamber 23e through the fibers in both directions will be proportionately restricted and this will cause the pressure in the chamber 28e to increase. The resulting increased pressure in the chamber 28e decreases the pressure drop across the restricted orifice 29 thereby tending to equalize the pressure in the upper and lower chambers 21h and 21e of the diaphragm device 21 and permitting the yoke 21d to move upwardly and relieve the pressure on the carbon stack 2|. The relief of pressure on the carbon stack 2| causes its resistance to increase correspondingly thereby weakening the excitation of the field winding Ita of the motor I 5 which drives the second or drawing pair of drafting rollers I3. As a result of the increase in the resistance of the carbon stack 2 I, the voltage drop across the carbon stack 2| is increased, thereby increasing the voltage applied to the eld winding Ida of the motor I4 whichv drives the rst or retaining" pair of drafting rollers I2. The decrease of excitation of the eld winding IGa produces a corresponding increase in speed of the motor I6 and conversely the increase in the excitation of the field winding I4a produces a corresponding decrease in the speed of the motor As a result, the draft of the bersin the drafting field between the pairs ofrollers I2 and I3 is increased and the increased draft elongates and thins the thick portion of the sliver, and thereby reduces the fiber density of the sliver delivered to the ow tube detecting device 28. This action continues as long as the density of the sliver is greater than the desired predetermined value. When the fiber density of the sliver returns to the predetermined desired value, the pressure in the chamber 28e returns to the normal value and the diaphragm pressure responsive device 21 responds to actuate the carbon stack .".I to restore the original Speed relationship of the draft roller driving motors I4 and I6. If a portion of the sliver which is relatively thinner than the normal value approaches the now tube device, the density of the bers entering the passageway of the flow tube device tends to decrease so that the bers will offer less resistance to the ow 0f air from the chamber 28o to atmosphere. This will cause the pressure in the chamber 28e to decrease, thereby increasing the -pressure drop across the restricted orifice 29. As a result of the increased pressure drop across the orifice 2S, the diaphragm pressure responsive device 21 will increase the pressure on the carbon stack 2| to decrease its resistance. This increase in pressure on the carbon stack increases the excitation of the field winding ISa of motor I 6 and decreases the excitationof the field winding I 4a of motor I II. As a result, the speed of the motor IG which drives the drawing drafting rollers I3 will decrease correspondingly and the speed of the motor IIiI which drives the retaining drafting rollers I2 will increase. This produces a decrease in the draft of the fibers in the drafting eld between the pairs of rollers I2 and I3, and as a result, the fiber density of the sliver delivered from the drafting rollers I3 will be increased correspondingly. When the density of the bers of the sliver within the passageway of the ow tube detective device 28 returns to the normal value, the pressure in the chamber 28e will be restored to the normal predetermined value. Likewise the pressure drop across the restrictedorice 29 will be restored to the normal value and the diaphragm pressure responsive device 21 will again relieve the pressure on the carbon stack 2| to restore the speeds of the motors I4 and I6 to the relative values which produce the required draft of the fibers when the sliver has the correct fiber density.

The foregoing actions are repeated whenever the fiber density of the sliver delivered from the second pair of drafting rollers I3 deviates from the normal predetermined value.

Since the pressure in the upper chamber of the diaphragm device 21 is equal to the pressure in the chamber 28e and the pressure in the lower chamber of the diaphragm device is equal to the pressure ahead of the orifice 251, the diaphragm device in eiect balances the pressure in the chamber 23e against the pressure ahead of the orifice 29 as a reference pressure. By varying the opening of the needle valve 35, the reference pressure with` which the pressure in the chamber 28C is compared can be varied as desired, thereby to provide for adjustment of the automatic correcting means t0 hold any desired value of ber density.

Thus the diaphragm pressure device 21 responds to all variations in the pressure within the chamber 2te produced by deviations of the ber density of the sliver from the predetermined value, to initiate changes in the relative speeds of the pairs of drafting rollers I2 and I3 to counteract such deviations. These deviations may occur at such a rate that a hunting action will be set up. However, this hunting action is overcome by adjustment of the needle valve 38 in the pipe connection between the lower chamber of the diaphragm device 21 and the pressure supply source to provide a restriction to the now of fluid between the source and the lower chamber. This produces a dash-pot action which minimizes the tendency to hunt.

The supply of air under pressure from the manifold 43 tothe air chambers 42e, 42j, and 42g of the multi-chamber flow tube device 4L' provides support and restraint for the shorter fibers in the array of fibers between the pairs of drafting rollers I2 and i3. Owing to the fact that Within the air chambers 42e, 42j, and 42g the sliver Iii is surrounded by air under pressure, a slipping restraint or grip is imposed upon the fibers which keeps the loose or wild bers bound into the mass and creates a condition favorable to consistent and uniform draft.

The slipping grip imposed upon the portion of the sliver within the passageway of the flow tube 2 b-y the air pressure within the chambers 42e, i321, and 112g allows the long fibers to be drawn forward freely and also allows the short fibers entering the second pair of drafting rolls I3 to beA moved forward with respect to the shorter fibers which have not yet entered the drafting rolls I3 and thereby provides even and consistent drafting of all the fibers within the drafting field. In the modification of Fig. 2, the flow tube de` tecting device 25 of Fig. l is eliminated, and the functions of the flow tube detecting device 28 and the flow tube device 42 are performed by a single multi-chamber flow tube device 4S, which is identical in structure with the flow tube device 42 of Figs. 1 and 3. This is accomplished by connecting the manifold 41 into one arm of a pipe T 48 which contains restricted orifices (not shown) in the upper and lower arms thereof which are identical in structure with the corresponding restricted orifices 29 and 34 of Fig. 1 and perform the same function. Likewise the throttle valve 49, fluid pressure regulator 50, the pressure responsive diaphragm device l, the carbon stack motor speed regulating device 52, and the needle valves 53 and 54 are identical in structure Wi-th the corresponding elements in Fig. 1 and perform the same function. The motors which drive the first and second pair of drafting rollers 55 and 56 and their electrical control circuit are omitted from Fig. 2 in the interest of simplicity. They are identical in structure with the motors of I4 and IB and associated control circuits respectively of Fig. 1.

In operation, the diaphragm device 5| responds to variations in fluid pressure in the chambers of the multi-chamber iiow tube device 46 which are produced by deviations from a predetermined value in the density of the` fibers of Vthe sliver within the passageway to actuate the carbon stack regulating device; 52 to vary the relative speeds of the electric motors which drive the pairs of drafting rolls 55 and 56 in the same manner as in the previously described operation of the modification of Fig. 1.

Since the ow tube device 46 of the modification of Fig. 2 is identical with the flow tube device l2 of the modification of Fig. 1, and since it is mounted in the same position between the first and second pairs of drafting rollers 55 and 56, it also performs the same function of support and restraint of the shorter fibers in the drafting field without danger of fracturing. the longerfibers. Ans in the modification of Fig. 1, a Bourdon gage 51 or other pressure responsive indicating device is employed to provide a visual indication of the fluid pressure in the chamber of the multi-chamber device 46. Since the pressure of the air supplied through the orifice in the pipe T 48 to the chambers of the device 46 is maintained constant by means of the pressure regulator 593, the fiuid pressure in the chambers of the flow tube device 46 is therefore a measure of the density of the bers of the sliver and consequently the dial of the gage 51 may be calibrated in units of ber density.

In Calibrating the dial o-f an indicating device, such as the devices 4I and 5'! of Figs. 1 and 2, respectively, it is feasible to use the total fiber cross-section of the sliver as a measure of density. When density is so considered, the calibration is identical for all types of fiber, except for insignificant differences owing to the variation in the air fiow coeicient caused by variation in fiber surface friction. The density of a given type of fiber is also frequently measured in terms of weight (in grains) per yard and a different calibration for each type of material is required on account of the varying specific gravities of fibers of different materials.

10 fiber density `of alength of material without utilizing variations in the density from a predetermined value as signals to actuate automatic controlling mechanism. In such cases, the only apparatus necessary is a flow tube detecting device, a source of constant fiuid pressure for supplying fluid to the detecting device, a restricted orifice in the connection between the source and the; detecting device, and a device for measuring and indicating fluid pressure in the detecting device. The detecting device may be of the same type as the device 28 or may be of the multiple chamber type, such as device 42 of Fig. 1, and maybe located at any point at which it is desired to measure the density of the fibers. In

other Words,` for cases in which it is desired only to-measure the density of the fibers, apparatus such as is shown in Figs. 1 and 2 may be employed with the pressure diaphragms and speed regulating features omitted.

Although in accordance -withA the provisions of the patent statutes this invention is described in` concrete form and the principle thereof is explained together with the best mode in which it is now contemplated applying that principle it willbe understood that the elements shown and described are merely illustrative and that the invention is not limited thereto since alterations and modifications will readily suggest themselves to persons skilled in the art without departing from the true spirit of this invention or from the scope of the annexed claims.

What I claim asignew and desire to secure by Letters Patentof the United States is:

1. In combination, means for'drafting a length of material containing an arrangement of fibers comprising a rst pair of drafting rollers, a second pair of drafting rollers mounted in spaced relationship with respect to said first pair of roll- Vto unevenness in successive portions of said length of material, and means responsive to said varying pressure for controlling said driving means to vary the relative speeds of Asaid pairs of rolls to diminish said unevenness.

2. In Vcombination with means fordrafting a length of material containing an array of loose fibers comprising first and second pairs of drafting rollers mounted in spaced relationship through which said length of material passes in succession, means for driving one of said pairs of rollers at one speed and the other pair at a different speed, a source of substantially constant fluid pressure, a member provided with a passagewayfor said length of material having a chamber. connected to said source and communicating with said passageway for producing variations in fluid pressure in said chamber in response to departures in the density of` said length of material from a predetermined`va1ue,and means responsive to said Variations in fluid pressure for varying the relative speeds of said pairs of drafting rollers to restore said predetermined `value of density of said length of material. i

3. In combination with means for drafting a length `of material containing an array of loose fibers comprising first and second pairs of drafting rollers mounted in spaced relationship through which saidlength of material passes in i1 succession, means for driving one'of said pairs of rollers at one speed and the other pair at a different speed, a member providing a passageway for said length of material having a chamber communicating with said passageway, a source of substantially constant fluid pressure for supplying a fluid to said chamber, and means responsive to changes in the resistance of said length of material to the passage of said fluid for varying the relative speeds of said pairs of drafting rollers to maintain the density of said length of material substantially constant.

4. In combination with means for drafting a length of material containing an array of loose fibers comprising first and second pairs of drafting rollers for said length of material mounted in spaced relationship, electric motor means for driving one of said pairs of rollers at a predetermined speed and the other pair at a different speed, a member providing a passageway for said length of material having a chamber communieating with said passageway, a source of substantially constant fluid pressure for supplying fluid to said chamber to provide variations in the pressure in said chamber corresponding to variations in the density of said material from a predetermined value, and means responsive to said pressure variations for controlling said motor means to vary the relative speeds of said pairs of rollers to restore the density of said materialto said predetermined value.

5. In combination with means for drafting a length of material containing an array of loose fibers, comprising first and second pairs of drafting rollers for said length of material mounted in spaced relationship, a first electric motor for driving said rst pair of rollers at a predetermined speed, a second electric motor for driving said second pair of rollers at a, different speed, a member providing a passageway for said length of material having a chamber communicating with said passageway, a source of substantially constant pressure for supplying a iiuid to said chamber to provide variations in fluid pressure corresponding to variations from a predetermined value in the density of said length of material, and means responsive to said pressure variations for varying the relative speeds of said motors to restore the density of said length of material to said predetermined value.

6. In combination with means for drafting a length of material containing an array of loose fibers comprising first and second pairs of drafting rollers for said length of material mounted in spaced relationship, driving means for said pairs of rollers, a member mounted between said pairs of rollers providing a passageway for said length of material and having a chamber communicating with said passageway, a source of substantially constant fluid pressure for supplying fluid to said chamber to produce variations in uid pressure corresponding to variations from a predetermined value in the density of said length of material, and means responsive to said variations in fluid pressure for controlling said driving means to vary the relative speeds of said drafting rollers to restore the density of said length of material to said predetermined value,

7. In combination, means for drafting a length of material containing an array of loose fibers comprising first and second pairs of drafting rollers for said length of material, driving means for said pairs of rollers, a member providing a passageway for said length of material and having a chamber communicating with said passage- 12 way, a member having a restricted oriee, a source of substantially constant fluid pressure for supplying fluid through said orifice to said chamber to produce variations in the fluid pressure drop across said orifice in response to variations from a predetermined value in the density of said length of material, and means responsive to said variations in fluid pressure drop across said orifice for controlling said driving means to vary the relative speeds of said drafting rollers to restore the density of said material to said predetermined value.

8. In combination, means for drafting a length of material containing an array of loose fibers comprising first and second pairs of drafting rollers for said length of material, driving means for said pairs of rollers, a member mounted between said pairs of rollers provided with a passageway for said length of material and having a chamber communicating with said passageway, a member having a restricted orifice, a source of substantially constant fluid pressure for supplying fluid through said orifice to said chamber thereby to produce variations in the pressure drop across said orifice corresponding to variations from a predetermined value in the density of said length of material, and means responsive to said variations in pressure drop for controlling said driving means to vary the relative speeds of said drafting rollers to restore the density of said length of material to said predetermined value.

9. In combination, means for drafting a length of material having an array of loose bers comprising first and second pairs of drafting rollers for said length of material, driving means for said rollers, a member provided with a passageway for said length of material recessed to provide a plurality of chambers between the inlet and outlet of said member communicating with said passageway, a source of substantially constant fluid pressure for supplying fluid to said chambers thereby to produce a variation in the fluid pressure in said chambers in response to variations from a predetermined value in the density of said length of material, and means responsive to said variations in fluid pressure for controlling said driving means to vary the relative speeds of said pairs of rollers to restore said predetermined value of density.

l0. In combination, means for drafting a length of material having' an array of loose fibers comprising first and second pairs cf drafting rollers for said length of material, driving means for said rollers, a member provided with a passageway for said length of material recessed to provide a plurality of chambers between the inlet and outlet of said member communicating with said passageway, a member having an orifice, a source of substantially constant fluid pressure for supplying uid through said orifice to said chambers thereby to produce variations in the fluid pressure drop across said orifice in response to variations from a predetermined value in the density of said length of material, and means responsive to said variations in pressure drop for controlling said driving means to vary the relative speeds of said pairs of rollers to restore the density of said material to said predetermined value.

11. In combination, means for drafting a length of material containing an array of bers comprising rst and second pairs of drafting rolls for said length of material, driving means for said pairs of rollers, a member mounted between said pairs of rollers having a passageway for said length of material and recessed to provide a plurality of chambers surrounding said passageway and communicating therewith, a source of substantially constant iiuid pressure for supplying fluid to said chambers thereby to produce variations in fluid pressure in response to variations from a predetermined value in the density of said material for controlling said driving means to vary the relative speeds of said pairs of drafting rollers to restore said density of said material to said predetermined value,

12. In combination, means for drafting a length of material containing an array of fibers comprising first and second pairs of drafting rollers for said material, driving means for said pairs of rollers, a member provided with a passageway for said length of material and recessed to provide a chamber in communication therewith, an orisaid predetermined value, and anti-hunting means comprising a variable restriction in the connections between said pressure responsive device and said orifice.

ERNEST L. RICHARDSON.