Apparel Online Bangladesh Magazine October Issue 2018 | Page 45

achievable with Airflow-type
dyeing machines).
The typical process cycle of a 500 kg
machine on medium shades include:
l Loading: 10 minutes
l Bleaching: 80 minutes (at 110 0 C)
l Dyeing: 120 minutes
l Washing off: 70 minutes
l Unloading: 10 minutes
This adds up to a total time of 290
minutes, assuming a load of 450 kg.
Water consumption per kg of fabric
is 31 litres. (Data based on THEN-
AIRFLOW™ machine).
From the above, we see that almost
30% of the time spent for this is
dedicated to bleaching. Conversely,
if the bleaching processes were to
be continuous, the daily dye house
production would increase by 38%,
i.e. from the current theoretical batch
rate of 4.96 to 6.85. In tonnes per day,
we would see an output of more than
15 tonnes – without the addition of a
single dyeing machine. In fact, adding
another 5 tonnes of daily capacity
would necessitate adding at least 2
dyeing vessels with 500 kg capacity
and one with 250 kg (again based on
THEN-AIRFLOW™ productivity).
Bio-polishing can reduce dyeing
output by 30% or more
RIGHT
Bio-polishing has become extremely
popular over the last few years,
possibly so without anyone in the
value-addition chain working out
the true cost of the process. Its main
purpose is to achieve a smooth
fabric surface even when lower
quality yarn with a high content
of short fibres has been used in
knitting. Usually, this type of enzyme
treatment is carried out as part of
the piece dyeing process and slotted
in-between bleaching and dyeing or
between dyeing and washing off. (The
advantage of bio-polishing between
bleaching and dyeing is that the
subsequent dyeing is carried out on
the fabric post-weight loss).
Logically, and
proving the point
that nothing
in life is free,
poorer quality
yarn needs more
bio-polishing
than better
quality yarn,
often offsetting
the lower yarn
price of the
former.
on a continuous line, such as the
SINTENSA and COMPLEXA ranges
by GOLLER. These can be used for
either RFD or for optical white. As
opposed to even the most advanced
piece dyeing machines using Airflow
technology, this will result in a
reduced specific water consumption
of around 1 litre per kg of fabric on
both RFD and on optical white.
Coming back to the issue of bio-
polishing, the alternative is to singe
and/or mercerize the cotton as part
of the same continuous washing
and bleaching process. For this
an additional mercerizing module
(e.g. CADENA) can be added to the
washing/bleaching range mentioned
above. For higher-quality fabrics,
this process can be combined with a
singeing unit.
Embedding the enzyme treatment
in the overall dyeing process sounds
convenient and cost-effective.
However, the fact is that depending
on the desired intensity of the bio-
polishing, this additional process
step adds 60 to even 90 minutes to the
batch time or, in other words, some
20-30% in terms of time.
Logically, and proving the point that
nothing in life is free, poorer quality
yarn needs more bio-polishing than
better quality yarn, often offsetting
the lower yarn price of the former.
But, coming back to our example of
a 10-tonne-per-day dye house, bio
polishing costs us between 2 and 3
tonnes of daily output! Looking at
the loss of dyeing capacity caused
by bleaching and bio-polishing, we
see that these two processes – when
integrated into the exhaust dyeing
process – reduce our dyeing output
by 50%!
Considering only bleaching of knitted
fabrics for the moment, one solution
is to handle washing and bleaching
www.apparelresources.com | October 2018 | Apparel Online Bangladesh
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