US2641025A - Apparatus and method for drafting fibers - Google Patents

Description

June 9, 1953 J. c. BUSBY, JR 2,641,025

APPARATUS AND METHOD FOR DRAFTING FIBERS Filed Oct. 29, 1947 I SOURCE INVEN JOHN C. BUSB ATTORNEY Patented June 9, 1953 APPARATUS AND METHOD FOR. DRAFTING v FIBERS John C. Busby, IL, United States Navy, Salisbury, N. 0.

Application October 29, 1947, Serial No. 782,938

11 Claims. (01. 19-66) (Granted under Title 35, U. S. Code (1952),

see. 266) This invention relates in general to textile machinery and more particularly to a method and apparatus for the drafting of textile or other fibers. By drafting is meant the process of drawing out and reducing the weight per unit length of a sliver or roving or web or mass of fibrous material.

The major defect in existing drafting systems is the lack of control of short fibers. It is well known in the textile art that by using two sets of rolls, the front ones revolving at a higher surface speed than the back ones, a sliver may be drafted. The resultant product, however, is of imperfect uniformity because the front rolls tend to grip and accelerate the long fibers and to leave the short fibers behind. This results in the short fibers accumulating and coming through in bunches or masses, giving rise to what is known in the trade as drafting waves. Attempts have been made to remedy this condition by extending the nip of the rear set of rolls through carrier aprons and similar devices on the theory that, by carrying all fibers forward while permitting the longest to be accelerated without disturbing the others, a system of more or less uniform drafting could be attained. Such methods are apparently helpful, for by using them it is possible to draft uniformly up to fifty (that is, the drafted sliver has as much weight per unit length as the original sliver or roving). However, construction problems are such that very short fibers (of the order of 6 mm. and below) are still uncontrolled. Hence, drafting waves will still occur, although on a lesser scale than with ordinary apparatus.

Another major difliculty in the present methods of drafting has to do with the amount of sliver that can be processed through one set of rolls. From one viewpoint there must be enough grip or friction between fibers and rolls or between fibers and carrier aprons to prevent slippage, thereby placing a definite limitation on sliver size. From another viewpoint, it has been necessary to reduce roll sizes in order to attain a short space between roll nips, thereby to control short fibers to such an extent that the rolls have had to be run at greater and greater R, P. M. to attain a suitable production speed. Because of this factor, machine development has now reached the serious state where on some frames the front set of drafting rolls are being run at their maximum practicable speed. The speed of the front rolls has thus become the tem.

Accordingly, a primary object of the present invention is to overcome the disadvantages of the existing methods and apparatus for drafting textile and other fibers.

A more particular object is to provide a method and apparatus for controlling short fibers during the operation of drafting slivers of fibrous material.

Another object is to provide a method and apparatus for the drafting of much heavier slivers than are capable of being drafted by existing methods and apparatus.

Another object is to obtain higher production and greater efficiency in the drafting of textile and other fibers.

These and other objects will become apparent from the following description when taken with the accompanying drawing which illustrates in schematic form an embodiment of drafting apparatus in accordance with the present invention.

I have discovered that by properly establishing electrostatic forces in the drafting region, a system of drafting that approaches perfection in uniformity is achieved. By using a modified set of drafting rolls and creating an electrostatic attraction between the fibers comprising the original sliver and the region around the nip of the front rolls, each individual fiber, regardless of size, is pulled loose from the sliver ending as soon as it is free of the back-roll nip. The fiber, as it is pulled loose, is simultaneously straightened and accelerated toward the front-roll nip. The method thus permits each fiber to be handled individually. To express the matter differently, there are no uncontrolled fibers. Hence all fibers, regardless of length, even the shortest, are pulled forward by the electrostatic forces.

The process of drafting in accordance with my invention will now be described in connection with roll-drafting apparatus of the ordinary type as shown in the drawing. The block identified by numeral It) represents humiditycontrol apparatus, through which the sliver to be drafted II is fed. I have found that the condition of the roving is very important in successful electrostatic drafting inasmuch as the speed with which fibers can acquire a charge is proportional to their electrical conductivity. The conductivity, in turn, is a complex function of the condition of the fibers with respect to temperature and moisture content. At the present stage of my development, it is impossible to give any definite laws regarding these factors except that the type of fiber, the speed of the back set of rolls, the impurities in the fiber, and the strength of the electrostatic forces are very im portant. It can be pointed out, however, that the conductivity must be high enough to enable the fiber to ac uire a definite charge before it loses contact with the back rolls.

The speed with which a fiber acquires the requisite charge in an electrostatic field of given strength is a function of the electrical conductivity of the fiber. Hence, the conductivity of the fiber must be increased by the addition of moisture if it falls below the requisite amount. As a general rule. raw cotton will draft satisfactorily if its moisture content will remain in equilibrium with an atmosphere maintained at 20 C., 75% relative humidity, and 760 mm. of mercury pressure. On the other hand, fibers of acetate rayon will require a greater moisture content than cotton. It should also be pointed out that in some cases it may be necessary to pre-treat fibers with various substances, e. g., soluble elec trolytes, to increase their conductivity. Such treatment allows running at lower moisture content, thereby causing the coefficient of friction between fibers to be somewhat less, which, in turn, reduces the amount of charge required to achieve satisfactory drafting. The humidifying apparatus 10 may not be necessary in many cases where the atmospheric conditions are such that a relatively high humidity is present and in cases when fibers of normally high conductivity are being slowly drafted in an electrostatic field of unusually great strength.

After passing through the humidifying apparatus ID, the sliver H is drawn into the drafting machine by the conducting back rolls [2 and 13, which are rotated in opposite directions by driving means (not shown). Rolls 12 and 13 are grounded as shown and serve as one of the electrodes between which an electrostatic field is established. The front rolls l4 and I are constructed in the form of a cylinder of a material having very high resistance. As illustrated in the drawing, the rolls are constructed of hard rubber. These rolls also are rotated in the directions indicated by driving means, which are not shown. Disposed within the cylindrical rolls l4 and I5 are electrodes Hi and H which are respectively connected to high voltage sources [8 and I9. Two sources of high voltage are shown in the drawing to eleminate confusion. but it is to be understood that both electrodes maybe connected to a single voltage source. It will be apparent from the position of electrodes l5 and I! with respect to the grounded rolls !2 and I3, that an electrostatic field is established therebetween.

In operation, as the back rolls [2 and I 3 are rotated in the direction indicated, fibers constituting the roving H are brought forward by the rolls. The spaced relation of rolls I2 and IS with respect to electrodes [6 and IT, by the well-known phenomena of electrostatic induction, produces a concentration of negative charges on the interior surfaces of cylinders l4 and I5 in the region of the electrodes; a concentration of positive charges on the outer surfaces of cylinders l4 and IS; a concentration of negative charges on that portion of rolls l2 and I3 nearest electrodes l6 and I1; and a concentration of positive charges on that portion of rolls [2 and i3 furthest removed from electrodes l6 and IT. As a consequence of the grounding of rolls l2 and IS, the positive charge on that portion of rolls l2 and I3 furthest removed from electrodes l6 and I! will escape to .4 ground, whereby rolls I2 and I3 retain an effective negative charge. As each individual fiber is brought into the electrostatic field by rolls l2 and I3, it acquires a negative charge in the following manner: Just as the fiber emerges from the nip of rolls l2 and (3, one end thereof is momentarily in contact with one or the other of rolls [2 and i 3, and the other end extends in the general direction of electrodes l6 and IT. At this instant, because of the conductivity of the individual fiber and the phenomena of electrostatic induction, a concentration of negative charges appears at the end of the fiber nearest the electrodes and a positive charge appears at the end thereof which contacts rolls I! or I 3. As previously stated, that area of rolls I 2 and 13 which would contact the fiber as it passes between the rolls will have a concentration of negative charges thereon, with the attendant result that the positive charge on the fiber will escape to the rolls [2 and i3. As the fiber is pushed forward by the fibers behind it and is released by the rolls, it enters the region between the back and front rolls carrying a negative charge. The amount of charge acquired depends principally on the strength of the electrostatic field, but also depends to a lesser extent on other factors such as fiber shape and the degree of ionization of the air. Since the fibers are all charged negatively, a force of attraction exists between the fibers and the electrodes l6 and H, which propels them toward the front rolls. Since all the fibers acquire a charge of like sign, they tend mutually to repel one another whereby they are separated from each other, both laterally and longitudinally, thus preventing escape of the negative charges thereon by conduction to the positive outer surface of the front rolls. Each fiber, then, may be considered to traverse the region between the back and front rolls independently of each other fiber, thus materially reducing, if not eliminating, the friction between any two adjacent fibers and permitting drafting of fibers that could not otherwise be handled with the relatively small forces which can be developed in electrostatic fields. It is thus seen that, during the time the fibers are freely suspended in the region between the back and front rolls, they are simultaneously separated by electrostatic repulsion and accelerated toward the front rolls by electrostatic attraction. As the fibers approach the front rolls, they are collected at the nip of these rolls, where they hang momentarily before becoming discharged by the positive charge appearing at that region of the rolls. Because of the proximity of the nip of rolls l4 and I5 to electrodes [6 and I1, this charge may be sufficient, in addition to neutralizing the negative charge, to impart a slight positive charge to the fibers, whereby they are repelled from the rolls. During this period of time, the rotation of the front rolls brings the fibers through the nip and into a region of ionized air created by any of the well-known commercial static-charge neutralizers indicated by 20 and 2|. Such neutralizers may work on the principal of ionizing the air through bombardment of alpha rays generated by radioactive strips, or they may function by corona discharge from sharply pointed metallic wires energized with a high-potential alternating current. Alternate construction, eliminating the necessity of the neutralizers, is theoretically possible since the only requirement in this particular embodiment is that once the fibers are drawn through the front roll nip, they no longer have any charge. Discharging electrodes 22 and 23, which are connected to ground, and

clearers of flannel or felt 24 and 25 are preferably provided to keep fibers from clinging to and lapping around front rolls l4 and I5. Since the sliver delivered by the front rolls I4 and I5 is likely to be spread apart into a flat ribbon-like configuration, it may be necessary to draw it through a condenser, which may take the form of a trumpet as indicated at 26. The drafted sliver 21 thus formed is carried forward by the driven rolls 28 and 29 to be delivered to a spindle or package for twisting or further treatment (not shown).

It is thus apparent that my invention, which provides a controlled handling of all fibers regardless of length, prevents the bunching of fibers during the drafting process, thereby eliminating drafting waves. The apparatus and method herein disclosed therefore provide for uniform sliver or roving at the output of the drafting machine. It is further apparent that since the fibers are controlled in the region of the roll nip by an electrostatic field, the rolls may be made larger in diameter, thereby providing a high surface speed with a low rotational speed, thus permitting very high-speed production. By referring to the drawing, it will be seen that my invention provides a method of separating the fibers from other materials or objects with which the fibers may be in contact. If, for example, pieces of metal, vegetable matter, sand, or other waste enter the apparatus with the sliver, the said waste will not usually acquire sufficient charge to enable it to move to the nip of the front rolls [4 and I5, and it will consequently drop down out of the path of the forward moving fibers. The waste may be collected in a receptacle (not shown) and disposed of later if desired. Furthermore, there is naturally some tendency for all fibers passing through rolls or coming in contact with aprons or other objects to cling to the rolls, aprons, or other objects. This tendency is known in the art as the tendency towards lapping, and fibers are said to lap around rolls. My inven tion overcomes the tendency towards lappingespecially around the back ro1lsby use of electrostatic forces which tend to direct the fibers forward away from the rolls through which the fibers pass.

It is obvious that there will be many possible methods of employing electrostatic forces to aid in the drafting process. I have illustrated a single embodiment to show how my invention may be utilized with roll-drafting equipment of the ordinary type. It is, therefore, to be understood that the example given is not to be construed as a definition of the invention, but merely illustrative of a form that the invention may take, and that the spirit and scope of the invention is to be limited only by the appended claims.

The invention described herein may be manufactured and used by or for the Government of the United States of America for Government purposes without the payment of royalty thereon or therefor.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. Apparatus for drafting textile fibers or the like comprising a first pair of driven conducting and grounded rolls between which said fibers are fed, a second pair of driven rolls of cylindrical form in spaced relationship to said first pair of rolls, said second pair of rolls being constructed of an insulating material, a pair of electrodes respectively disposed within said second pair of cylindrical rolls, and means for applyin a voltage to said electrodes thereby establishing an electric field between said electrodes and said first pair of rolls.

2. Apparatus for drafting textile fibers or the like comprising a first pair of cooperating driven conducting and grounded rollers between which said fibers are fed, a second pair of cooperating hollow cylindrical rollers constructed of insulating material and disposed in spaced relationship to said first pair of rollers, a pair of electrodes respectively disposed within said second pair of rollers, means for applying a high potential to said electrodes thereby establishing an electrostatic field between said electrodes and said first pair of rollers, means for discharging any static charge which may appear on said second pair of rollers, and means to ionize the air at the nip of said second pair of rollers furthest disposed from said first pair of rollers.

3. A method of drafting fibrous material comprising the steps of treating said material with soluble electrolytes, establishing an electrostatic field between two opposed electrodes, feeding said treated material into the region between said electrodes, separating the individual fibers of said material by mutual electrostatic repulsion within said region, and collecting said fibers.

4. A method of drafting fibrous material comprising the steps of treating said material with a soluble electrolyte, establishing an electrostatic field between two opposed electrodes, feeding said treated material into the region between said electrodes, separating the individual fibers by mutual electrostatic repulsion and simultaneously accelerating said fibers through said region, and thereafter collecting said fibers.

5. A method of drafting fibrous material, which comprises the steps of treating said material with soluble electrolyte, establishing an electrostatic field between spaced electrodes, advancing said treated material into the region between said electrodes, imparting a charge of like sign to each of the fibers of said material initially upon entry into said region, separating the individual fibers by mutual electrostatic repulsion while in said region and simultaneously accelerating said fibers through said region, thereafter collecting said fibers and removing the charge therefrom.

6. Apparatus for drafting textile fibers or the like comprising, a first pair of driven grounded conducting rolls between which said fibers are fed, a second pair of hollow driven rolls constructed of insulating material disposed in spaced relationship to said first pair of rolls, and means disposed within the rolls of said second pair for producing an electrostatic charge on the outer surface of said second set of rolls and establishing an electrostatic field extending between said first and second pairs of rolls.

"7. Apparatus for drafting textile fibers or the like comprising, a first pair of cooperating driven rolls between which said fibers are fed, a. second pair of cooperating driven hollow rolls constructed of insulating material and disposed in spaced relationship to said first pair of rolls, and means positioned within the roller of said second pair for establishing an electrostatic field extending between the mutually directed nips of said first and second pairs of rolls.

8. Apparatus for drafting textile fibers or the like comprising a first pair of driven conducting and grounded rolls between which said fibers are fed, a second pair of hollow driven rolls spaced from said first pair of rolls and constructed of insulating material, and means disposed within each of said second pair of rolls for establishing 7. an electrotatic field extending between said first and second pairs of rolls.

9. Apparatus for drafting textile fibers or the like comprising, a first pair of driven conducting and grounded rolls between which said fibers are fed, means for treating said fibers before being fed between said first pair of rolls, a second pair of hollow driven rolls spaced from said first pair of rolls and constructed of insulating material, and means disposed within each of said second pair of rolls for establishing an electrostatic field extending between said first and second pairs of rolls.

10. Apparatus for drafting textile fibers or the like comprising, a first pair of driven conducting and grounded rolls between which said fibers are fed, a second pair of hollow driven rolls spaced from said first pair of rolls and constructed of insulating material, and means disposed within each of said second pair of rolls for producing an electrostatic charge of like sign on each of said second pair of rolls and establishing an electrostatic field extending between said first and second pairs of rolls.

11. Apparatus for drafting textile fibers or the like comprising, a pair of hollow driven cylindrical rolls constructed of insulating material,

References Cited in the file of this patent UNITED STATES PATENTS 15 Number Name Date 1,549,875 Home Aug. 18, 1925 1,968,861 Strang Aug. 7, 1934 2,151,273 Hess Mar. 21, 1939 2,153,358 Whitehead Apr. 4, 1939 20 2,385,873 Melton Oct. 2, 1945 2,442,880 Schwartz June 8, 1948 2,450,409 Baymiller Oct. 5, 1948 2,542,331 Heinsch Feb. 20, 1951 FOREIGN PATENTS 25 Number Country Date 872,301 France Feb. 9, 1942

Images