is a patented new technology of washing, which allows important savings both in water consumption, energy and cycle time during dyeing operations.
Recent Developments
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.
In 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
If 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.
Nowadays 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, consequently, costs.
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.
The 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 finished product.
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 :
  • traditional washing based on the sequence: fill, circulation, drop
  • continuous rinsing
Drop & Fill Washing
Washing 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 hydrolysed dye;
  • 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.
All 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.

Continuous Washing
A 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.
Furthermore, in 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 continuously diluted.

Both above-described methods  have disadvantages from a chemical and physical point of view.
In 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.
In fact, 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

In 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.
In 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.
The 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
Generally, the washing operation is more efficient if it is done with hot water, but water heating brings a considerable increase of costs.
Being 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 advantages.
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

SYNCHROWASH has been 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 concentrations.
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).
The 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:
During 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.
During 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.
Naturally, 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.
The 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.