O o d h e a d p u b L i s h I n g L i m I t e d

6.2
Nonwoven processes and recent innovations
The nonwoven process can be broken down into several stages:
• web formation;
• bonding;
• finishing;
• coloration;
• converting.
6.2.1
Web formation
In synthetic fibre nonwovens the major web formation processes are:
• carding (with cross-lapping);
• air-lay;
• wet-laid;
• spunbond;
• melt-blown.
As wool is a staple fibre and not found in continuous form, web formation
for wool nonwovens can be achieved only by carding, air-lay or wet-laid
processes. These could be combined with non-staple fibre nonwovens, e.g.
spunbond or melt-blown processes; a less common alternative is the air-laid
process.
The wool inputs are usually similar to those chosen for woollen processing,
i.e. shorter fibre than for worsted and usually free of vegetable matter and so
carbonised wool or broken top is used. Broken top is shorter wools that have
been combed to remove vegetable matter (VM), very short fibres and neps
and is expensive compared with carbonised wool. As with woollen processing,
it is also possible to piece-carbonise the fabric having made it with low-VM
wools but this is rare and the VM may cause other problems in the nonwoven
plant if it is not dedicated to the wool process. Blends of wool and synthetic
fibres are also possible; a huge range of fibre blends are commonly used in
nonwovens processing. Web formation for staple fibres is usually via a carding
process a less common alternative is air-laid systems.
© 2009 Woodhead Publishing Limited

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Advances in wool technology
132
The schematic diagram of Fig. 6.1 shows carded web formation. The card
rollers are covered with card clothing (Fig. 6.1 inset) which carries the fibre
tufts through the machine. The workers rotate in the opposite direction to the
main cylinder with the card wire points are also opposed. The main cylinder
has high surface speed (1000 to 1500 m/min) while the workers have low
surface speed (20 to 100 m/min). This action opens the tufts and individualises
the fibres before forming them into webs on the workers. Stripper rollers
pass the fibres back onto the main cylinder. This recycling intimately blends
the fibres together. At the doffers a fraction of the fibres on the main cylinder
is transferred to each doffer to form the output webs. In double doffer cards
the two webs are combined by the take-off conveyors into a single web and
delivered forward for further processing. Some cards have only one doffer.
The double doffer allows higher productivity. The output speed is typically
around 30 m/min but may be as high as 100 m/min.
For lightweight fabrics, the web produced by the carding machine goes
directly into the bonding process. For heavier fabrics several cards can be
positioned in line and their webs combined by being laid one upon the other
onto a conveyor belt travelling beneath the machines. The fibre orientation
leaving a card is usually predominantly in the machine direction. This leads
to the strength being greater in the machine direction (MD) and weaker in
Workers
Strippers
Web output
Main
cylinder
Doffers
Fibre feed
Breast
Transfer rollers
6.1
 Basic non woven card. (This is the most common means of web
formation).
© 2009 Woodhead Publishing Limited

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Advances in the manufacture of nonwoven wool
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the cross-machine direction (CMD). This results in a high MD/CMD ratio,
which is undesirable for some applications such as wool apparel.
Condenser rollers such as those shown in Fig. 6.2 can improve the MD/
CMD ratio by reorienting the fibres. These rollers are clothed with special
wire and each one rotates at a slower speed than the prior roller so the web
is passed on to the next roller with greater areal density and with more fibres
oriented across the web. This also has the added effect of increasing the
doffer speed while keeping the output line speed the same. The higher doffer
speed takes more fibre from the card per revolution of the main cylinder and
so lowers the total fibre load of the card and can allow higher production
rates.
A recent development has been the random card. This card has an extra
roller between the doffers and the main cylinder with special wire; see
Fig. 6.3.
 This roller turns at high speed counter to the main cylinder and