is a patented new technology of washing, which allows important savings
both in water consumption, energy and cycle time during dyeing
Machine manufacturers are constantly looking for advantages in productivity and
they develope new technologies for yarn dyeing machines. All
efforts have been directed to rationalise performance in order to reduce the possibility, or better, the necessity of expensive re-dye operations.
particular we will take into consideration in which way technical
evolutions have given the dyer the possibility of obtaining "first-time right" final results. This has been the result of
countless improvements; specific examples are the use of auxiliaries to
increase the general effectiveness of preparation treatments and a more
exact dyeing technology.
We can list the following:
- Lower bath-ratio machines
- better-developed dyeing cycle controllers
- efficient support structures such as dosing systems
- more refined process parameter controllers
All these elements have made a dyeing cycle simpler but, most of all, they have brought to a more predictable final result.
The Dyeing of Cotton
we take into consideration cotton dyeing, we can assert that all
above-described elements surely improved productivity, but, apart the newest
bath ratios, not one had a real impact on the reduction of production
costs. The reason is simple: all those innovations focused on improving just dyeing , but only few of them have
been introduced to improve treatments before or after dyeing.
it is possible to estimate that, during a complete cycle, the
operations of scouring, rinsing and final washing take up almost 80% of
the used water, 90% of the energy and about 70% of the needed time to
reach the final goal. We can say that before and after treatments in the
cycle are extremely important in order to reduce consumptions and,
Starting from the mid '90s, mainly in fabric dyeing extensive efforts have been directed towards lower water consumption
rates in order to manufacture machines with the best possible efficiency.
reduction of water usage is naturally linked to a reduction of the
energy costs and an overall reduction of the time needed to obtain a
Up to now the potential available
to reach the same goals In yarn dyeing is limited: most machines on the market today
use the following two standard ways of performing washing operations :
Drop & Fill Washing
- traditional washing based on the sequence: fill, circulation, drop
- continuous rinsing
after scouring and after dyeing is reached by subsequent dilution
of pollutants through the cyclic addition of clean water.
The efficiency of this operation is strictly linked to the combined effects of several factors:
- the quantity of bath circulating in the machine and the temperature
of the washing medium; this determines the dilution ability to remove
- the ratio of circulation which is created inside the machine ;
- the quantity of fluid remaining inside the machine (in the material) during discharge operations.
Another fundamental factor is the level of chemical bonding maintaining the pollutants on the material to be treated.
above variables are linked to other industrial conditions such as the
continuous availability of water, the capacity of distribution systems
to supply a sufficient quantity of thermal energy in the desired time, and the swiftness of all these operations.
disadvantage of performing washing operations through drop & fill
is the likelihood that a large quantity of pollutants may remain on the material during drain operations.
oxidation sensitive dyeing the contact with air let into the material
during drains after dyeing can cause differential oxidation states of
the material itself leading to "bronzing" defects.
The technology of
continuous rinsing has been introduced in order to avoid problems. At
the end of the dyeing operation water is introduced in the material to
be treated and, at the same time, the same quantity of water is
discharged after passing through the material; in this way pollutants are
SYNCHROWASH: THE INNOVATION
Both above-described methods have disadvantages from a chemical and physical point of view.
the first case, "DROP & FILL", the efficiency of the washing system is
naturally proportional to the difference of concentration between
washing fluid and pollutant quantity in the material, which is
deeply influenced by the bath ratio in the machine.
drop & fill has to be reiterated until the balance between
pollutant concentration in the material to be washed and fluid
concentration is acceptable.
Picture a : efficiency of washing operations
is proportional to differential concentrations
reactive-dye washing it is widely accepted that the higher the bath
ratio is, the lower the number of required washing operations is in order to obtain
an acceptable final result.
But both high bath ratio and high number of washings use a considerable amount of water.
the second case, i.e."CONTINUOUS RINSING", the mixing effect of the
circulated bath, charged with pollutants with the rest of the bath in the machine, makes the concentration of pollutants which can
be extracted from the system lower.
The following two graphs represent the concentration levels typical of the two cases (examples are referred to the extraction of electrolytes from a 100% cotton yarn in a reactive dye bath):
Picture b: continuous rinsing (bath concentration vs time)
Picture c: drop & fill washing
(bath concentration vs time)
On the other hand,
SYNCHROWASH is a new patented washing system which permits an
exceptional saving of water and energy during dyeing operations.
How Synchrowash works:
The concept of this new technology can be summed up as follows:
The optimisation of differential pollutant concentrations
- Each washing operation is fundamentally based on progressive pollutant dilution.
efficiency obtainable during the dilution operation is directly
proportional to the concentration difference which is dynamically
created during washing. Synchrowash permits to always obtain the
maximum washing efficiency concentrating the most pollutants in the bare minimum discharge water.
- Energy recovery in washing waters
the washing operation is more efficient if it is done with hot
water, but water heating brings a considerable increase of costs.
Synchrowash a continuous process, on its discharge piping it is
possible to install a heat recovery device which cancels this cost
increase. In addition, since the thermal needs of the machine are
reduced, the heat recovery device offers substantial economical
Even though at first sight the system recalls the
traditional "continuous rinsing", this new technology is based on a
different concept that, as we will see, offers superior advantages.
Picture d process schematics
created through the application on an air-cushion dye machine of a
special device which successfully splits the circulation flow. It
divides the bath in different flows on the base of their pollutant
This device, equipped with a sophisticated control
system, continually extracts from the circulating fluid only the most
polluted fraction, and at the same time it reintegrates the same
quantity of clean pre-heated water in the circulation flow before it
enters the material to be washed (image d).
The net result of this
operation is to obtain a continuous, very polluted discharge flow,
maintaining always at the maximum level the difference of pollutant
concentration between the fluid entering the material and the one
contained in the material itself.
Picture e : SYNCHROWASH washing results
Picture e underlines that, with
similar flow rate characteristics, with the use of Synchrowash the decrease of pollutants concentration in the material is remarkably
quicker than with a traditional continuous rinsing (see Picture b).
curve shape and the related mathematic model are very similar to the
continuous rinsing data , but, since with Synchrowash the separation of
pollutants in the washing bath is effective , the operation time and
consequently the used amount of water are lower.
Synchrowash technology can be applied to every washing operation performed during a dyeing cycle:
the after-scouring washing operations Synchrowash maintains the
circulation flow inside the material constant, thus preventing the
deposit of grease and wax emulsions in scouring foams on the yarn, which is
typical in standard operations of drop & fill washing.
the after-dyeing washing, the efficacy of Synchrowash permits to obtain
the complete removal of not-fixed dye which is contained in the
interstices of the yarn to be treated.
A high difference of
concentration between the hydrolysed dye solution inside the yarn and
the circulation fluid permits a quicker diffusion of hydrolysed dye out
of the yarn, and consequently its removal during soaping is easier. This
is the reason why Synchrowash drastically reduces the number of soaping
operations necessary to obtain higher fastness.
Synchrowash in washing after soaping moves the hydrolysed dye on the
yarn surface faster and its removal needs much less water.
The advantage of using Synchrowash is evident: the washing operation is more efficient and thus the needed water is reduced.
following graphs (Image f) shows the different operation conditions of
traditional washing systems such as drop & fill and continuous
rinsing in a comparison with the results obtainable with Synchrowash.