GOVT. POLY. HISAR AYM NOTES

NEW SPINNING PROCESSES

• Introduction

New spinning processes have been available In a practicable from for twenty years, and yet by the largest amount of short-staple yarn is still spun on conventional machines. These are mostly developments dating from period 1760-1830, in particular:

• Mule spinner;

• Flyer- spinning machine;

• Cap- spinning machine

• Centrifugal –spinning machine machine;

• Pot-spinning machine; and ring frame.

SUMMARY OF NEW SPINNING PROCESSES

• Spin-twist and self twist systems are typical worsted-spinning processes. Bobtex and periloc systems give yarns with a woollen- spun character, but with higher strength. The Parafil and Dref-2 processes must also be allocated to the coarse-yarn sector. All other methods produce yarns for the short-staple market segment. From this group the following gave prospecis for practical operation:

• Rotor spinning (already very widespread)

• Friction spinning

• Wrap spinning (to a certain extent), end

• False- twist spinning.

Rotor spinning is considered separately in this volume.

The other more promising candidates will be treated in somewhat greater detail in following description.

OPEN-END-SPINNING PROCESSES

In all other spinning processes, an uninterrupted stream of fibre proceeds continuously, but with gradual attenuation , from the feedstock to the take –up package. In open-end-spinning this flow of fibres is interrupted, the fibre strand being opened to individual fibres at a predetermined position , usually by means of an opening roller. This enables twist to be imparted by rotation of the yarn end , which in turn leads to significantly higher speeds of rotation.

However the break in fibre flow also leads directly to one of the most important and difficult tasks in open-end spinning , namely, the necessity to re-collect the fibres, which is essential to the formation of a new fibre stand. This very tricky problem of open-end spinning can be dealt with as described below.

A constant stream of separated fibre is allowed to flow to a rotating yarn end. The Brush-like, open yarn end grasps the fibres brought into contact with it and continuously binds movement. The continuously formed yarn has only to be withdrawn and taken up on a cross-wound package. On the basis of the device used to reassemble the separated fibre, distinctions are drown between:

• Rotor spinning

• Electrostatic spinning

• Friction spinning , and

• Disc spinning

ELECTROSTATIC SPINNING

In the process based on the Battelle principle , a roving (2) derived from the roving frame is passed to a conventional double-apron drafting arrangement(3) and is subjected to a draft of 180-200. The fibres exit freely from the front cylinder. They must then be collected to from the front cylinder. They must then be collected to from a fibre strand and twisted to from a yarn. The first of these operations is performed by the electrostatic field, and twisting is carried out at a twist – imparting unit(6).

Twisting presents no problems . The complexity of this method lies wholly in the electrostatic field generated between the front roller and the twist element (6) by earthing the front roller and applying a high voltage (about 30000-35000 V) to the twist element. When the fibres enter this field, they take up charge and from dipoles, i.e. one end becomes positively charged and the other negatively charged . An open yarn end (5) projects from the twist element into the field. This yarn is negatively charged and is therefore always attracted to the front roller.

There is this a relatively high degree of fibre straightening between the front roller and twist element. Fibres leaving the roller are atiracted to the yarn as a result of the charges carried by the two parts. They join continuously to the yarn. Since the yarn rotates, the fibres are bound in . A yarn is formed continually and is withdrawn by withdrawal rollers (8) to be passed to a take-up device (9) for winding into a cross wound package.

FIEGER OF ELECTRO-SPINNING PRINCIPLE

AIR-VORTEX SPINNING

In this spinning method (Fig.3), yarn is formed by an air vortex in a tube (1).For this purpose, air is sucked into the tube through tangential slots(2). The air moves upwards along the tube wall in a spiral and finally arrives at the upper tube seal(3). Since exit from the tube is prevented by the seal , the air then flows to the centre of the tube and moves down again to an aspirator. An air vortex (5), rotating continually in the same direction, is generated at the seal(3).

Opened fibre material is allowed to enter the system through an opening (4). The rising air stream grasps this material and transports it upwards into the vortex (5). To form a yarn, an open yarn end is passed into the tube through a passage in the upper seal(3). The vortex grasps this yarn end and whirls it round in circles in the same way as the fibre . Since the upper yarn length is rotation, each revolution of the yarn end in the vortex inserts a turn of twist into the yarn.

Formation of the fibre strand itself arises because the rotating open yarn end in the vortex is presented with a multiplicity of floating fibres, which are caught by the bound in fibres of the yarn end and are thus continuously twisted in .

One associated problem is the correct, ordered binding in of the fibres, i.e., achieving adequate strength in the yarn . For this reason , synthetic fibre of the highest attainable uniformity are mainly used . A second deficiency is variability in twist level in the spun yarn; twist can very within a very wide range. A major advantage of the process is the absence of any kind of rapidly rotating machine parts.

FRICTION SPINNING

Operating principle this process belongs to the open-end group because the fibre strand (draw frame sliver) must be opened completely to individual fibres and then reassembled to a new strand (yarn). The formation of a new strand is carried out by using suction to bring the individual fibres into engagement with the rotating open end of the yarn, e.g., by perforated drums. Binding-in of fibres, and imparting strength, are effected by continual rotation of the yarn in the converging region of two drums. The rotation of the yarn arises from the rotary movement of the two drums and is generated by frictional contact at the drum surface . Yarn formed in the convergent region by collecting fibres and binding them in must be constantly withdrawn and wound to a cross-wound package.

• FEED

Multiple-sliver feed improves evenness but also leads to high costs and the need for a very high degree of opening.

• OPENING

Opening is performed as for rotor spinning. In this case also, straightening of the released fibres, and the degree of longitudinal orientation exert a strong influence on the yarn characteristics.

• FIBRE TRANSPORT

The fibres can move to the collecting device in free fight with (Masterspinner, of Platt Saco Lowell) or without (Dref-2) guidance by a dust. Free flight of the fibres without guidance in a duct leads to fibre disorientation, which affects not only the yarn characteristics but also the spinning limit.

FIBRE COLLECTION The fibres are drown by a suction air stream towards the collecting surface and the open yarn end (fig.5(a), (b), and (c)). In rotor spinning, the fibres are additionally accelerated during collection and are thereby straightened, but in friction spinning the opposite happens. The fibres come into contact with a surface that is moving more slowly then are the result is fibre-buckling and deterioration in fibre orientation.

CHAPTER 2 ROTOR SPINNING

OBJECTS OF THE ROTOR SPINNING

The rotor spinning machine is unlike any other machine in the short-staple spinning mill in the range of tasks it has to perform, namely, all the basic operations:

• Opening(and attenuating) almost to individual fibres(fibre separation),

• Cleaning(optionally),

• Homogenizing thought back-doubling

• Combining i.e., forming a coherent linear strand from individual fibres,

• Ordering(the fibres in the strand must have an orientation as far as possible in the longitudinal direction),

• Improving evenness through back-doubling

• Imparting strength by twisting and

• winding

PRINCIPLE OF OPERATION

In the conventional spinning processes, the fibre strand at the infeed is Maintained as a coherent structure and is merely attenuated during spinning. In rotor spinning , the fibre strand is opened to individual fibres. This task is performed mainly by the opening roller(5). This task is performed clothed with needles or (more commonly) saw-teeth, combs through the fibre beard projecting from the nip between the feed roller and the trough; it transports the plucked fibres to the feed tube(8).

An air flow is needed for further transport of the fibres to the rotor(9).This generated by a central fan that draws air by suction through leads(13) from each rotor box(15).To facilitate generation of this underpressure, the rotor box must be hermetically sealed as far as possible. Most of the transport air enters at 2 and at 6.

The suction stream in the feed tube (8) lifts the fibres off the surface of the opening roller(5) and leads them to the rotor. In the course of this movement, both the air and the fibres are accelerated because of the convergent form of the feed tube.

This represents a second draft following the nip trough / Opening roller and giving further separation of the fibres. Moreover, partial straightening of the fibres is achieved in this air flow . A third draft arises upon arrival of the fibres on the wall of the rotor because it contributes significantly to good orientation of the speed of the fibre. This is a very important feature because it contributes significantly to good orientation of the fibres. The last straightening of good orientation of the fibre slides down the rotor wall into the groove under the influence of the enormous centrifugal force

s at work within the rotor.

THE OPENING UNIT

The projecting fibre beard takes on a wedge-shaped form . combing out will be more intensive and even:

• The thinner the fibre strand (sliver fineness),

• The more parallel the fibre arrangement (two draw frame passages are better than one).

• The more highly straightened the fibres (without crimping),

• The smoother the fibres(lustrous or delustred),

• The shorter the clamping distance, and

• The higher the rotational speed of the roller.

There are, however, limits to the last-named factor, because excessive rates of rotation not only bring no corresponding increase in the opening effect (asymptotic curve) out also lead to disadvantageous effects, such as:

• Tearing out of fibre bunches,

• Fibre deterioration or even fibre damage,

• Melt spots in processing synthetic fibres owing to the heat generated by friction between metal and fibres, and

• Fibre-buckling (failure of removal from the clothing points) at the fibre-feed tube, because the peripheral speed of the roller is greater than the air-flow speed in the suction tube (feed passage) (see section 2.3.2.4).

On the other hand not only do unduly low opening-roller rotational speeds lead to deterioration in the yarn characteristics but there is also a simultaneous increase in the risk of lap formation.

YARN FORMATION

Depending upon the arrangement of the feed tube, the fibres can move into the rotor in one of two ways:

• Axially

• Tangentially

In axial feed, centrifugal force distributes the fibres within the collection groove in a purely random fashion and in accordance with an “umbrella” principle. This type of feed has three major defects:

• Fibre orientation in the groove is bad, and the yarn quality is correspondingly poor;

• A large rotor diameter is needed, and this limits rotor revclutions;

• The spun yarn has to be withdrawn through the rotor axis. These problems lad to the adoption of the currently almost-universal tangential-feed technique. Here, the rotation of the rotor, and a corresponding air circulation within the rotor, ensure ordered deposition of fibres in the groove.

YARN WITHDRAWAL AND WINDING Basically, yarn can be withdrawn opposite the rotor shaft or through it. In some circumstances, the latter arrangement gives a better self-cleaning effect because the yarn is dragged over the floor of the rotor(fig.79).However, this method cannot always be used owing to the associated larger shaft diameter(and for other reasons) and is in any event more expensive. Accordingly , the withdrawal direction shown is now the only one used.