US 3538552 A
Description (OCR text may contain errors)
Nov. 10,1970 v J. L.'FOLEY CARDING DEVICE .7
Filed March 5, 1969 OSCILLATING CYLINDER FOR EDGEWISE MOTION OF DOFFING ROLL MAIN CYLINDER OSCILLATING 2 SheetsSheet 1 Nov. 10, 1970 J. FOLEY I 3,538,552
CARDING DEVICE Filed March 3,-1969 2 Sheets-Sheet 2 United States Patent U.S. Cl. 19-163 1 Claim ABSTRACT OF THE DISCLOSURE As a carding auxiliary, an auxiliary toothed roll of relatively small diameter is set adjacent to, but not in contact with, the doffing cylinder of a conventional textile carding machine. The auxiliary roll is provided with a device by means of which it can be caused to oscillate back and forth across the dofiing cylinder face at a rate of 100 to 1000 cycles per minute, at a surface speed which is slower than the surface speed of the doffing cylinder. By this means, the highly-parallelized fiber orientation of a conventional card web is perturbed, and a more nearly equalized lengthwise to crosswise strength ratio is realized in carded webs and nonwoven fabrics made therefrom.
This is a continuation-in-part of my copending application Ser. No. 689,402, filed Dec. 11, 1967, now abandoned.
This invention relates to a process for improving the ratio of longitudinal strength to lateral strength in carded webs of textile-length fibers. Particularly, it relates to a method for more nearly equalizing the longitudinal and lateral strengths in bonded nonwoven fabrics prepared from such webs.
In the preparation of nonwoven fabrics, it is common practice to feed a thick lap or sheet of textile length fibers, weighing up to 500 grams per square yard, to a fiber-rearranging device such as a card, garnett, or air-lay device, which forms the fibers into a thin web or fieece with a weight attenuation of about 100 to 1. Among web-forming devices, the card is perhaps the most commonly used.
A conventional textile card comprises a cylinder, three to four feet in diameter and of any desired width, covered with a multiplicity of fine bent wires called teeth or card clothing. A lap of fibers is fed by means of a socalled licker-in roll to this main cylinder, which picks up and carries a fleece or Vail of fibers. The fibers are also workui upon by auxiliary rolls or flat strips covered with wire teeth and set in close proximity to the circumference of the main cylinder. The fibrous web is removed from the cylinder by a dotting device, conventionally a secondary wire-covered cylinder tangential to the main cylinder and revolving in the opposite direction. From the doffer, the web is removed and sent for further processing by a vibrating comb.
The conventional textile card or carding machine was primarily devised to exert a two-fold effect. First, it cleaned an array of fibers such as cotton or wool, removing considerable dirt, other foreign matter, and short fibers. Secend, it tended to parallelize nad rearrange the fibers, which was a desirable consequence since the fibrous web was customarily drafted and spun into yarn in a multi-stage process. With the advent of the nonwoven fabric industry, however, many cards were converted from their original function of preparing a sliver of parallel fibers to delivering a plurality of full width webs to a conveyor belt, for subsequent bonding to form a nonwoven sheet. One of the advantages of carding, parallelization of fibers, became a distinct disadvantage in the preparation of nonwoven fabrics. Spun yarns have strength only in the "ice lengthwise direction, whereas the majority of nonwoven fabrics must have at least some minimal tensile strength in the transverse or cross-web direction. The problem is particularly acute in the case of nonwoven fabrics prepared from man-made fibers, which, although they may be crimped, are generally straighter and much more readily oriented than natural fibers such as cotton.
A further complication is that the conventional processing of bonded nonwoven fabrics consists of a set of stages-conveying, saturating, drying, winding, etc.- all of which impose a further drafting and parallelizing effect on the fibrous web. If a web is carefully removed from the doifer of a card and is bonded without drafting or distortion, the longitudinal (machine direction) tensile strength may be only 3 or 4 times the lateral (cross direction) tensile strength. If the same web is subjected to a normal multi-stage bonding operation, tensile strength ratios will be found which are 10 to 20 to 1, machine direction to cross direction.
Various expedients are resorted to for improving What will hereinafter be referred to simply as the strength ratio, it being understood that this refers to the ratio of strength in the machine or longitudinal direction to the cross or lateral direction. One expedient is to disperse the fibers in more or less random orientation into an air stream, from which they are collected on a perforated rotating drum by suction. Such devices are expensive, and while satisfactory at speeds of around 10 yards per minute, they produce Webs of poorer quality at speeds of 30 yards per minute, due to clumping and poor dispersion of fibers.
Another common method of improving the strength ratio is by means of a cross-laying device, whereby a fullwidth web of oriented fibers is mechanically pleated back and forth across a conveyor belt to build up a composite batt in which the average angular displacement of the fibers is alternated. Such devices again are slow, cumbersome, and are suitable only for batts of substantial thickness where fold marks and overlap ridges are not 0bjectionable.
It is with improvements in the art of producing fibrous webs and bonded nonwoven fabrics of more nearly equal ized machine direction and cross direction tensile strengths that the present invention is concerned. It is a primary object of the invention to provide a process and a device which will rearrange an array of substantially parallelized textile-length fibers to produce an array in which the ratio of cross-direction strength to machine-direction strength is improved.
Basically, the process of this invention involves equipping a conventional card doffer cylinder with an auxiliary cylinder, with its main axis parallel to the axis of the card doffer, so that the auxiliary cylinder is tangential to the doifer surface. The auxiliary cylinder is preferably clothed with metallic clothing, rather than wire clothing in which there is a bend or knee in the wires, and it rotates in the same direction as the doffer, but more slowly, as explained below. The teeth of the metallic clothing are preferably of neutral pitch. In addition to its rotary motion, however, it is caused to oscillate in a back-and-forth reciproeating motion across the surface of the dotfer, from which it picks up the fibrous web and imparts to the parallelized fibers a periodic wave pattern. This perturbs the highly oriented configuration, so that even after the normal pulling and drafting associated with saturation bonding and drying, the tensile strength in the machine direction is only 3 to 5 times the tensile strength in the cross direction, instead of the 10 to 1 to 20 to 1 ratio normally experienced.
The invention will be better understood with reference to the following description and drawings, in which:
FIG. 1 is a perspective view of the oscillating auxiliary roll showing its general relationship to the doifer of a card.
FIG. 2 is a schematic and stripped-down cross-sectional view of the card cylinder, card dotfer, and auxiliary roll.
FIG. 3 is a cross-sectional representation of the structure of the auxiliary roll in the preferred form of this invention.
Referring to FIG. 1, a conventional cylinder and dotfer (12) are shown as comprising the essential elements of a card, the additional features of flats, or rollertop card workers and strippers, not being shown. Mounted on end brackets 15, tangentially across the doifer is the oscillating auxiliary roll 14, clothed with so-called metallic clothing. The oscillating auxiliary roll is small in comparison with the doifer, being of the order of 4 to 6 inches in diameter, and is long enough to cover the full surface of the dotfer 12 at the extremes of its traverse. The oscillating auxiliary roll 14 is mounted in proximity to, but not in tooth-to-tooth engagement with, the doffer with a clearance of between .007 inch and .075 inch, .012 inch being a suitable clearance when processing fibers such as 1% inch long viscose rayon.
As mentioned above, the auxiliary roll 14 has a surface speed of rotation which is less than the surface speed of the doffer cylinder 12, so that the carded web tends to build up in a rolling action as shown at 13 in FIG. 2. This roll-up action, in the form of an inverted letter U, starts at the point at which the auxiliary roll and the doifer are tangent. The fibrous web, borne counterclockwise by the rotating doffer, follows the doffer for one-half inch or more before being diverted downward by the action of the air currents around the smaller auxiliary roll. It has been surmised that it is this reversal of direction, combined with the side-shucking action of the oscillating auxiliary roll, that causes the reworking and realignment of the fibers in the gap between the two rolls. Whatever the reason, it has been found that if the auxiliary roll is rotating at a surface speed which is equal to or up to 10% slower than the dofier, little or no equalization of lengthwise to crosswise tensile strength occurs in the web. If the auxiliary roll is rotating at a surface speed which is 35% or more slower than the doifer, the doffing becomes irregular and parts of the fibrous web tend to cling to the rotating dofier and not be stripped off by the influence of the auxiliary roll. My preferred operating condition, therefore, is that the auxiliary roll shall rotate at a surface speed which is between 10% and 35% slower than the dolfer. This also has the effect of increasing the weight of the finished web over the weight which would normally be delivered by stripping with a reciprocating comb in the conventional manner.
Although stripper rolls with an oscillating action have been proposed in the prior art to doif or transfer webs from one moving surface to another, so far as I am aware it has not been appreciated that by slowing down the surface speed of the oscillating roll relative to the speed of the roll to be doifed, a pronounced realignment of the fibers occurs, with a desirable decrease in the ratio of lengthwise to crosswise tensile strength in the fibrous web.
The auxiliary roll 14 may be integral with its shaft, with the assembly rotating and traversing as a unit. My preferred method, however, is to reduce the mass of the traversing assembly by having the shaft rotate only, confining the traversing motion to the surface of the auxiliary roll. This preferred assembly is shown in FIG. 3, where the auxiliary roll 14 is shown as comprising a splined inher shaft 40, supported on the frame of a card doffer by the bearing supports 42, 42. Mounted concentrically with the shaft 40 is a shell or tube 44, carrying the metallic clothing (not shown). It is this tube which oscillates as it rotates, the heavy central shaft rotating only. The shell 44 may be of a light weight metal such as aluminum.
The oscillating or reciprocating motion is imparted to the outer shell 44 of the auxiliary roll by coupling only 4 the shell with a thrust bearing 46, which may be a standard propellor shaft or automobile front wheel type bearing.
The bearing 46 is in turn coupled to a yoke 48, which is caused to oscillate by any one of a number of conventional oscillating or reciprocating devices, not shown, such as an oscillating piston or cylinder, a four bar linkage, or an eccentric crank shaft. This latter arrangement generates a sinusoidal pattern in the fibrous web: various other devices, such as eccentric cams, may be used to generate different patterns. The thrust bearing and yoke assembly 46 and 48, are designed for high stresses and reciprocating motion of up to 1,000 cycles per minute.
Linear motion bearings or bushings 50, 50 are mounted concentrically with the shaft 40, and may be rigidly coupled therewith. Rotary motion is imparted to the shaft 40 by means of a belt coupled with the pulley 52, which may be coupled to the card dofi'er drive. Alternatively, the pulley 52 may be driven independently, to allow a surface speed on the auxiliary roll which may be varied plus or minus about 25% of the card doffer speed.
The distance traversed by the auxiliary roll 14 across the face of the doffer 12 will govern the amplitude of the wave pattern imparted to the fibers. Even relatively small traverses, compared to the width of the roll, will yield significant improvement in the tensile strength ratio. A convenient working traverse distance is from 0.75 to 1.5 inches.
Although a conventional reciprocating comb 20 is shown as part of the apparatus in FIGS. 1 and 2, its function therein is not the function which a comb usual- 1y exerts in conventional carding, where it is used to remove an intact fibrous web from the doifer and deliver it for further processing. The web removal in the present process is effected by the auxiliary roll 14, as shown by the path of the fibrous web 24 in FIG. 2. Since the auxiliary roll and the dotfer do not touch each other, the primary instruments of web removal are presumably windage and the tendency of interengaged fibers to follow each other in the machine-direction pull. The comb 20 does assist in clearing the roll 14 when the apparatus is started up, but once the apparatus has reached operating speed, its use may generally be dispensed with.
The length of the fibers processed into card webs by the process of this invention, defined as fibers of textile length, will customarily lie between 0.5 inch and 4 inches, preferably between 1 and 2 inches. Web speeds of 10 to 50 yards per minute are realized, with an amplitude of displacement action of 0.75 inch to 1.5 inches. The frequency of oscillation of the auxiliary roll across the face of the dolfer may be varied from to 1,000 or more cycles per minute. Using 2 inch fibers, a web speed of 30 yards per minute, and an oscillation speed of 750 cycles per minute, the average fiber, presumed to be originally oriented perfectly parallel to the machine direaction of the web, will be subjected to both a right-to-left and a left-to-right traverse of the auxiliary roll.
This does not imply that each fiber is bent or displaced into a waved configuration. If tensile ratios were a precise reflection of fiber orientation, it would not be expected that a displacement of to inches from a straight-line orientation would bring about a substantial increase in cross-direction tensile strength in a test where the machine jaw clamps may be 2 to 4 inches apart.
The principal effect seems to be an increase in the number of points at which the fibers cross over each other, with a corresponding increase in the fiber-to-fiber bonds responsive for resistance to tensile stress in the cross direction.
Nonwoven fabrics made according to the process of thls invention display tensile and elongation properties which are more characteristic of a fibrous web with random or isotropic distribution than of a highly oriented carded fibrous web. That is, there is a decrease in the absolute value of the dry machine direction tensile strength and in increase in the absolute value of the cross direction tensile strength, leading to a lower tensile strength ratio. In many uses to which nonwoven fabrics are put,
such as fashioning into disposable garments, a balance of machine direction and cross direction tensile strengths is very important, since the stresses encountered in wearing the garments may run in the machine or the cross direction in different sections of the garment. In such nonwoven fabrics made from conventional card webs, the machine direction tensile strength usually turns out to be well in excess of what is needed, because the efiort to build up the cross direction tensile strength, by binder choice or hinder concentration, fortifies the strength in both directions indiscriminately. The equalization elfected by the process of this invention will be illustrated by the following example.
EXAMPLE I Three nonwoven fabrics were prepared from 1%; inch long crimpted viscose rayon fibers, with a base fiber weight of 25 grams per square yard saturated with grams per square yard of an acrylic latex binder for a total dry weight of 45 grams per square yard. Sample A was prepared using three conventional card webs plied together. Sample B consisted of three card webs each of which had been passed through the process of this invention, using an oscillation amplitude of one inch and a frequency of 250 oscillation cycles per minute, with the surface speed of the auxiliary roll set at 30% less than the surface speed of the doeiter. Sample C was prepared on a Rando Webber, adjusted to deliver the desired weight of a random array of fibers.
All details of handling the webs during the saturation and drying stages were identical. In the following analysis of the physical constants of the three products, M.D. and C.D. refer to machine direction and cross direction respectively; tensile strengths are in pounds per inchwide strip on an Instron Tester, and tear strengths were measured by the tongue-tear method.
Inspection of the above figures will indicate that the process of this invention assists in bridging the gap in tensile properties between a highly oriented web of fibers and one which has been laid down in random fashion.
Having thus disclosed my invention, I claim:
1. A method of improving the lengthwise to crosswise strength ratio of fibrous webs doifed from a rotating cylindrical surface which comprises:
carrying an oriented fibrous web on a first rotating cylindrical surface, removing said web from said first cylindrical surface by means of a second rotating cylindrical surface, said second rotating cylindrical surface being spaced a discrete distance from said first rotating cylindrical surface and out of physical contact therewith,
and rotating at a surface speed of between and of the surface speed of said first rotating cylindrical surface,
the removal of said web from said first surface by said second surface being accomplished by oscillating said second surface axially back and forth across said first surface while both cylinders are rotating in the same direction,
the amplitude of oscillation of said second surface being between 0.75 and 1.5 inches and the frequency of oscillation being at least cycles per minute,
whereby the fibrous web is doffed and the fiber pattern thereof is simultaneously transformed from a parallelized linear pattern to a wave-like pattern.
References Cited UNITED STATES PATENTS 250,896 12/1881 Dempster et al. 1999 409,918 8/ 1889 Carpenter 1998 576,262 2/ 1897 Fennessey et al. 19-106 XR 788,555 5/1905 Pitts 19-163 853,854 5/1907 Ainley 19106 1,199,513 9/1916 Walsh 19145.5 XR
FOREIGN PATENTS 605,288 11/ 1934 Germany. 917,615 2/ 1963 Great Britain. 1,084,789 9/ 1967 Great Britain.
DORSEY NEWTON, Primary Examiner U.S. Cl. X.R. 19--106