US3406436A - Crimping process - Google Patents

Description

1968' G. R. CLARKE, JR 3,406,436

GRIMPING PROCESS Filed Nov. 30, 1965 v INVENTOR GEORGE R.CLARKE,JR.

ATTORNEY United States Patent F ABSTRACT: on THE DISCLOSURE A: process for regulating the crimp frequency of compaction-crimped yarn. Uncrimped yarn is fed into a stuffer box at a constant rate and emerges in'the form of a plug from which crimped yarn is taken up at a constant rate. The crimp frequency (crimps per inch) imparted to the yarn in the stuffer box inversely determines the distance downstream from the discharge port at which the crimped yarnunfolds from the plug. This distance (and hence also the crimp frequency) can be kept within a fixed control region by controlling the amount of resistance offered by the gate ofthe stuflier box to the compressive force of the compacted yarn therewithin, e.g., by varying the weight placed on the gate.

This invention relates to a process for crimping a strand or multiple of strands of fibers. More particularly, this invention relates to a process for controlling the crimping of synthetic fibers, e.g. nylon, so that the crimp frequency, in terms of 'crimps per inch, is uniform throughout the yarn.

Compression crimping has recently been used on a large scale to impart to synthetic or man-made fibers, e.g. thermoplastic yarn, a bulk or crimp giving the appearance of a wool-like fiber. In the known processes of compaction crimping, e.g. Those using a stutfer box, the yarn so crimped is characterized by some lack of uniformity in crimp frequency throughout the length of the yarn. Specifically, artificial man-made fibers, e.g. nylon, which after being spun are drawn to orient the polymer molecules, are characterized by a relatively smooth surface whichis crimped'to give the'yarn a wool-like appearance using, in many commercial operations, a stutfer box. Generally, this process is performed by feeding the'y'arn in a semi-plastic state through nip rolls which impart a nip to the fiber. The yarn passes through the nip rolls into a box called a stuifer box wherein it' is "compacted with previously advanced yarn under compaction and the unoccupied yolume of the stuffer box is maintained at a minimum using a discharge'gate which resists egress of the yarn and thus determines' the compaction of the yarn. The yarn is taken up by conventional winders on conventional bobbins, or the like,"at a rate less than the feed'rate of theyarn'to the stuffer box through the'nip rolls. Many factorsin fluence thebehavior of the yarn in a stuffer box, which determine the degree of crimp imparted to it and the crimp frequency. For instance, it has been found that in com mercial operation using a'sta'ndard-stuffer box that the crimp frequency can varyusing the .same feed rate of yarn through the nip rolls, the ,same stuffer box, same temperatures and the same take 'up ,rate. The reason for these'changes in crimp frequency it not known .but it is believed that processing conditions pres nt in the polymerizin'g, spinning and drawing operations effect the yarn behavior in the crimping step so as to change the crimp frequency to a different value. It is also believed that water present in the form of atmospheric moisture may also effect the crimp frequency. However, by far the majority of reasons for variations in crimp frequency at constant process conditions are still unknown.

It has been proposed to maintain the crimp frequency 3,406,436 Patented Oct. 22, 1968 constant by varying the feed rate of the yarn into the stuffer box via the nip rolls together with adjusting the take-up rate, thus maintaining a substantially constant degree of compaction of the yarn within the stuffer box. This method of control of crimp frequency is not desirable in that it involves a substantial number of moving parts in the apparatus employed to achieve the regulation of feed and take-up. It also suffers from the disadvantage that when the feed rate of the yarn to the stuffer box is decreased to a level below the normal process operating rate there is a decrease in the amount of crimped yarn produced per given unit time. Also, when the take-up rate is decreased to keep the crimp frequency uniform an increase in duration of fiber exposure to heat treatment results which may cause fiber non-uniformities, It is therefore desirable to maintain the crimp frequency constant while keeping the feed rate of uncrimped yarn constant and, at the same time, maintaining a constant take-up rate of freshlycrimped yarn.

It is the object of this invention, therefore, to provide a process for crimping yarn wherein the crimp frequency is maintained constant in the yarn despite the presence of the aforementioned unknown factors which influence crimp frequency.

It is still another object of this invention, therefore, to

' provide such process for crimping nylon or other synthetic yarn in an economical manner whereby the yarn s0 crimped is characterized by a high degree of uniformity of crimp frequency.

It is still another object to provide a process for crimping yarn by compaction to provide uniformity of crimp frequency in the yarn wherein the feed rate of the yarn to the zone of compaction and the take-up rate of winders, etc. are maintained constant.

These and other objects of this invention will become apparent from the following complete description of my invention, accompanying drawing and appended claims.

This invention contemplates a process for regulating the crimp frequency of compaction-crimped yarn, said process comprising: crimping the yarn in a zone of compaction so as to form a plug, maintaining an unfolding point of the yarn from the plug within a predetermined region by varying the resistance of the zone of compaction against the yarn therein while maintaining the feed rate of the yarn to the zone of compaction and the take-up rate of the yarn from the plug constant.

My process is preferably performed by passing uncrirnped yarn, e.g. nylon into a conventional staffer box or other confined region having a movable wall or gate, with weights attached to the gate to adjust its pressure against the yarn within the stuffer box, thereby adjusting the resistance of the zone of compaction against the yarn. Different yarns, because of processing conditions, contribute different resistance against the zone of compaction, thereby necessitating greater or lesser gate pressure.

In a preferred embodiment of my invention, the yarn is withdrawn from the zone of compaction in the form of a plug, e.g. on a conveyor belt and taken up downstream from the zone of compaction.

More specifically, my process is directed to controlling the crimp frequency by controlling the unfolding point of the yarn from the yarn plug which issues from the discharge end of the stuffer box on, for example, a standard endless conveyor belt. When, due to the unknown factors effecting crimp frequency, the unfolding point of the yarn from the plug, which is selected to be within an arbitrary control region, but is dependent upon feed rate and take-up rate, moves upstream, it is an indication, as I have discovered, of an increase in crimp frequency. On the other hand, I have also discovered that when the unfolding point of the yarn from the plug moves downstream of this arbitrarily selected control region for the tion ofa decrease in crimp frequency.-I have further-discovered that the unfolding point of the yarn from the plug can be maintained within a predetermined region, and hence the crimp frequency can be kept generally constant by controlling the force on the upper stuifer box gate'acting against the compacted yarn. As a result, there is a substantially constant total volume of yarn in the stuifer box. Crimping yarn with an essentially constant yarn plug unfolding point as herein prescribed insures, uniform crimp. It will be observed that according to my process the crimp frequency of the yarn is maintained uniform without adjusting the yarn feed rate to the stuifer box or the rate at which the yarn is withdrawn from the plug form.

My invention will be more readily understood by reference to the accompanying drawing which is a side view of a stulfer box partially broken away wherein 2 is the overall stuffer box into which yarn 4 is fed via nip rolls 6 and 8. Gate 10 which is bounded by sides 12 and 14 and is hinged at 16 using pin 18. The gate has afiixed thereto vertical bar 20 on which weight 22 and 24 are placed. The yarn so crimped within stuflfer box 2 by compaction issues at discharge port 26 onto endless conveyor belt 28 moved by rolls 30 and 32 which are driven by a motor (not shown). The crimped yarn unfolds from the yarn plug at some point A in the accompanying drawing. When, because of conditions which affects crimp frequency, the yarn unfolding point changes from con trol point A to point B there is observed, as discussed above, an increase in crimp frequency. To account for this, sufiicient weight is taken off gate 10, thereby increasing the volume of the stuifer box and decreasing the crimp frequency, to adjust it to the frequency desired and thereby cause the unfolding point of the yarn to move back downstream toward point A. When, on the other hand, the unfolding point moves downstream from point A say to point C, suificient weight is applied to gate 10 over vertical bar 20 to bring the unfolding point back upstream toward point A. If the unfolding point is allowed to remain at point C, a lower crimp frequency than desired is imparted to the yarn.

It will be realized that my process can be performed at any temperature suitable for crimping of the yarn involved, feed rate of yarn to stuifer box, take-up rate of yarn from plug form, etc., and using other types of apparatus for crimping by compaction. It should also be realized that various means for regulating the force exerted on the stuffer box gate can suitably be employed. These include use of a pneumatic cylinder in which the air pressure is regulated to give the desired force on the stuffer box gate; and standard spring mechanisms adjustable by a screw whereby the different tensions of the spring cause different forces to be exerted upon the stuifer box gate.

In order to illustrate in detail the nature and manner of practicing my invention, the following example is presented.

20 ends of 1050 denier, 70 filament, /2 Z twist polycaproamide (Nylon 6) at a temperature of 90 C. were fed into a stuffer box similar to that shown in the accompanying drawing at a feed rate of 1425 ft./minute and wound-up on a yarn package at 1160 ft./minute. The gate pressure was varied during the process run to vary the resistance against the yarn, thereby maintaining substantially constant yarn volume in the stuffer box. The weights placed on the stuifer varied between 1.5 lbs. and 5.0 lbs. The yarn received a uniform crimp having 14 crimps/inch controlled within 12.0 crimp/inch on 20 separate stuifer box units for several months. Necessity for continuous tests by quality control labs was eliminated due to the crimp process of this invention.

It will be realized that my invention can be utilized in -other' crimping processes, e.g. jet crimping with or without pre-chemical treatment, gear crimping, etc. The method of controlling the CIimpin the case of jet crimping involves maintaining a pair of micro-switches or other sensing means, one proximatethe jet and the other downstream from the desired unfolding point, but within the zone of compaction. If the plugmovesdownstream, it actuates the, microswitch' which adjusts presure via the jet against the yarn. If the plug backs up, it. actuates the switch proximate the jet to decrease pressure against the yarn. In the case of gear crimping, the crimp is regulated by increase or decrease, of pressure on the yarn via the gears. This can be done using weights or adjustable spring loaded means which apply tensionto-the' yarn via the gears. In the case of knife-edge crimping, the weightor pressure resistance is maintained by adjusting the position laterally of the knife-edge against the yarn. I

It. can vbe readily seen from the above that I have provided a new and useful processfor controllingcrimp frequency of yarn crimped by compaction. It is-seen that my process can be easily performed, does not necessitate large expenditures for equipment anddoes not require any cutting down periodically in production rate.

The terms and expressionswhich have been employed are used as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, to exclude any equivalents of the. features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed. 1

What is claimed is: I

1. A process for regulating the crimp frequency of compaction-crimped yarn comprising:

(a) feeding yarn to a zone of compaction at a constant rate;

(b) crimping the yarn in the zone of compactionso as toform a plug; Y

(c) withdrawing the plug from the zone of compaction; and I (d) taking up the crimped yarn from the plug at a constant rate, and at a distance from the zone of compaction which is kept within a fixed control region by varying the resistanceof the zone of compaction to the yarn therein.

2. A process according to claim lwherein:

an increase in the distance of the control region from the zone of compaction is reversed by increasing the resistance .of the zone of compaction to the yarn therein; and

a decrease in the distance of the control region from the zone of compaction is reversed by decreasing the resistance of the zone of cornpaction to theyarn therein., I

3. A process according to claim 2 wherein the plug is withdrawn from the zone of compaction on .a conveyor belt. p

4. A, processaccording toclaim .2 wherein theresistance of the Zone of compaction is varied utilizing weights. r

5. A process accordingto claim 2 wherein the yarn isnylonf I j p I References Cited s -UNITED STATES'PATENTS LOUIS K. RIMRODT, Primary Examiner.

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