Short staple fibres

ICI Co. uses a sol-gel method to produce silica-stabilized alumina (Saffil) and calcia-stabilized zirconia fibre [15], The saffil fibre is a 8-alumina short staple fibre that has about 4% Si02 and a very fine diameter (3 pm). 

Filter fabrics, especially nonwoven fabrics, which are produced from short staple fibres, invariably possess surfaces with protruding fibre ends. Since such protrusions may inhibit the cake release by clinging to the dust, it is a common practice to remove them. This is achieved by singeing, a process in which the fabric is passed, at relatively high speed, over a naked gas flame, or, in another technique, over a heated copper plate. The heat of the flame causes the fibres to contract to the surface of the fabric where, in the case of thermoplastic fibres, they form small hard polymer beads (Fig. 3.8). Singeing conditions (i.e. speed and gas pressure) will normally be adjusted according to polymer type and the intensity required by either the end-use application or the individual manufacturer s preference. 

This is the most basic weave of all woven stractures that provides the framework for the tightest and most rigid of all single-layer filter fabrics (see Fig. 3.19). Because of the sinusoidal path that the yams follow, this weave is particularly suitable for flexible yams of the multifilament and short staple-fibre types. The weave is also ideally suited to applications where thread displacement, due for example to high internal pressures, may otherwise be experienced. 

Short (staple) fibres. Filaments are chopped into short lengths ranging from 2 to 10 cm, which are known as staple fibres. These staple fibres are then twisted together to form a yam. 

Fabrics produced from short staple fibres have a natural fibrous surface (an example can be seen in Figure 2.4) that can impede cake discharge this is overcome by singeing the fabric by passing it over a gas flame or a hot metal strip, which is usually followed by contact with a wet surface in order to stop any smouldering. 

Wet laid media are derived from paper manufacturing processes and are composed of short staple fibres dispersed in water to form a slurry that is fed to a moving wire screen on which it is dewatered. The randomly orientated fibres form a web which is dried by a sequence of heated rollers. An adhesive or binding agent may be dispersed in the original slurry or sprayed onto the web during or after dewatering. 

The dimension of the fibre, yam or filament has a direct impact on the mechanical and hydraulic properties of the geotextile. Fibre dimension is expressed according to its diameter, described in deniers or dtex, depending on the measuring system used (American or International System). Thread dimension is generally defined by its yam density. In the case of nonwoven geotextiles made from short staple fibres, fibre dimension is completed by the length of the cut fibres. 

Nonwoven made from short staple fibres... 

The process of heat bonding using hot calendering is sometimes used in the production of short staple fibre geotextiles. However, this method is more often used for continuous filament—based geotextiles. This process will be explained in detail in the next section covering the continuous filament process. 

The first step in this process involves the creation of a filament from the polymer pellets. This step is identical to that used to produce the filament used for the production of short staple fibres. The difference is that the filament will not be crimped, cut or baled. Here are the main operations in this process of making the filament ... 

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