Staple fiber formation

The advantageous properties of the man-made fibers can be utilized in better ways to reduce the unwanted properties of the man-made fibers. This can be done by a process, generally referred to as blending. The basic objective of fiber blending is to combine together exact the proportion of different fibers to enhance the ultimate properties of the blended yarn. The properties which can be enhanced are:

(a) Aesthetic or performance requirements like fiber stability, abrasion resistance, moisture absorption, bulkiness, etc.

(b) Mechanical properties

(c) Novelty effects

However, all the man-made fibers are generally obtained in continuous filament form. For blending, the man-made fiber should be cut into staple form i.e., the fiber with definite length. The staple fibers, apart from their own advantageous properties, offer the following advantages:

(a) Required staple length

(b) Determined fineness

(c) Perfect cleanliness

(d) No fluctuations in quality

(e) Easy availability

In the manufacture of staple fiber, the filaments after solidification is collected in a rope-like form of parallel filaments. The rope is referred to as tow. The tow is generally converted into staple fiber form depending upon the end-product, or the sequence of machinery. The process is referred to 3o as 'tow-to-top', 'tow-to-sliver' or 'tow-to-yarn' conversion system. In all the systems, the first process is the conversion of the tow into staple fiber

There are various systems of tow-to-staple conversion, which can be classified according to the basic methods used for severing the filaments. The methods are

(a) Cutting,

(b) Abrasion and

(C) stretch-breaking.

Of course, each method has its own advantages and disadvantages.

Staple fiber cutting method

The cutting method is the most commonly used for tow-to-top conversion. In this system, a flat sheet of tow in the tensioned condition is fed to a rotary cutter. The principle of operation is to cut ‘a uniform spreadsheet of filaments between a revolving spiral cutter and a hardened steel roller. The cutter is generally projected in an angular manner.

The actual staple length depends upon the helix angle of the cutter blade. The blade roller width is usually about 25 mm to 38 mm. The space between the cutting edges is lined with synthetic rubber to prevent lateral movement of the filaments during cutting.

Different rollers are required to produce different fiber lengths. In this way, the filaments are sheared at an acute angle without disturbing the parallel arrangements of the filaments.  Schematic diagram of a tow to staple fiber conversion by the cutting method. This method does not alter fiber characteristics such as strength, elasticity, extensibility or shrinkage characteristics. Also, the staple length and fiber length distribution are controlled positively. Also by redesigning the arrangement of the projected helical blades on the cutting roller, staple fibers having a varied staple length can be produced for fancy yam. On the other hand, the cutting method is not very effective for the fibers finer than. 2 deniers. The pacific converter converts all types of man-made fiber tows into a staple. 

Abrasion method

In this method, the filament tow is ruptured against an abrasive surface. This method is not popular and has only limited application because of the following reasons:

(a) It cannot be applied to fibers having higher abrasion resistance characteristics.

(b) There is no control over the fiber length. The length is generally varied greatly say, I cm to 25 cm.

(c) The presence of short fibers reduces the mechanical properties of the ultimate product.

The process is generally used to regenerated fibers and/or light tows and to a very special purpose.

Stretch breaking method

The stretch-breaking method can be utilized for any filament of any thickness. The system is based on the principle that if a filament is held between the nips of two sets of rollers, then under suitable conditions, the filament will be stretched and broken. The two sets of rollers are usually running at different speeds.

The delivery roller is always faster than the feeding roller. Depending upon the speed of the rollers and deformability of the fiber, the fiber will first be stretched ard then will be broken. The break takes place at the weakest point of the fiber which may be anywhere along its length.

The stretch breaking process gives a reasonably nap-free product. The load-elongation characteristics of the fiber after breakage differs in comparison with that of the same fibers before breakage. Mostly stretch breaking enhances tenacity and lowers the extensibility of the fiber. Simultaneously the filament is reduced and finer filaments are produced after stretch breaking. There are several machines available in stretch-breaking the principle, like Seydel stretch-breaking machine, Porlock machine, Turbo stapler.

Flow chart of the staple fiber production process

Each man-made fiber is manufactured in different principles and with different processing conditions. Accordingly, their processing also differs and they undergo a series of purifying and finishing stages after fiber formation. These post spinning treatment operations for staple fiber production are not the same for all the fibers. This section highlighted the post spinning treatment of individual staple fibers

Production and post-treatment of viscose staple fiber

Spinning → Drawing-- Stapling- Pre-opening Drying- Conditioning- Washing- - Intermediate opening Drying - Fleece formation - Fine opening - Packing

Production and post-treatment of polyester staple fiber

Spinning + Tow formation - Tow Collection- Drawing - Setting –Crimping – stapling -  packing

Production and post-treatment of polyacrylonitrile staple fiber

Spinning - Wet drawing – Washing - Finish Application - Drying- Crimping - Steaming - Cooling - Stapling - Baling