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

12.4
Spinning wool blend on the long staple
worsted system
Long staple synthetic fibres are often processed into tops first and then
blended with wool in top form on gilling machines. The number of gilling
operations should be sufficiently large so that good fibre mixing is achieved.
The blended slivers are then processed into rovings and yarns in much the
same way as pure wool slivers.
Fibre diameter and length distributions of the blend are important for the
spinners to determine the final yarn count that can be made from the blend
and to set the roller drafting system during the process from top to yarn.
Spinners are well aware of the relationship between the mean number of
fibres in a yarn cross-section and the theoretical minimum mass irregularity
that the yarn can achieve. The theoretical irregularity of a pure wool yarns
can be predicted from the mean fibre diameter and its coefficient of variation.
The fineness of synthetic fibres, on the other hand, is commonly measured
in terms of linear density (denier, or decitex). The minimum mass irregularity
of a two-component wool/synthetic fibre blend yarn (Rae and Bruce, 1973)
can be calculated using
CV% = 
1
10 [
(1 + 4 CVD ) + 
]   100%
w
w
w
2
s
s
T
w p
w p
×
12.1
where T is the linear density of the blended yarn in tex, w
w
 and w
s
 are the
ratios of the wool and synthetic fibres by weight in the blend yarn, p
w
 and p
s
are the mean linear densities of the wool fibre and the synthetic fibre expressed
in decitex, and CVD
w
 is the fractional coefficient of variation of wool fibre
© 2009 Woodhead Publishing Limited

---

Advances in wool technology
298
diameter. The mean wool fibre diameter in micron, d, can be converted into
mean linear density in tex using p
w
 = 0.01 062 5d
2
.
The fibre length of long staple fibre tops may be expressed in terms of
barbe or hauteur. Most woollen spinners prefer to use barbe (mm) while
worsted spinners tend to use hauteur. If a number of wool batches with barbe
values of B
1
, B
2
, …, B
n
 are blended according to their proportions by weight
w
1
,  w
2
, …, w
n
, the barbe value of the resultant wool batch will be the
weighted average of the components:
B = w
1
B
1
 + w
2
B
2
 + … + w
n
B
n
12.2
Hauteur of a resultant wool sliver (H), on the other hand, follows a harmonic
relationship with its components (H
1
, H
2
, …, H
n
) (Miao, 1998):
1
 = 
 + 
 +   + 
1
1
2
2
H
w
H
w
H
w
H
n
n
…
12.3
When using the above formula on blends of wool and other types of
fibres, the fibre weight-based blend ratio may need to be replaced by a fibre
volume-based blend ratio or a dielectric constant-based blend ratio, depending
on the fibre length measurement method adopted.