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Colour Kitchens
Colour kitchens were once manual systems used for weighing dyestuffs and auxiliaries and dye bath preparation (dyestuff dissolving) carried out by operators who manipulated the colour kitchen directly.
However, this created several problems, both in terms of reproducibility (matching and consistency of the dye, weight, dissolving procedure) and operator’s safety and health. The first development, concerning the second problem, was the use of special hoods (protective coverings, usually providing special ventilation to evacuate noxious vapours, dusts, and gases) introduced by manufacturers of granule or liquid dyestuffs. Wrong results due to human mistakes (or even to the actions of different operators) have been then corrected by introducing automated colour kitchens equipped with dispenser systems which can reproduce the recipes established by the operator by means of a computer-controlled system which weights, mixes and dissolves the dyes and auxiliaries.
The second development instead concerned the production of semi-automated colour kitchens, which retrieve the recipe to be reproduced, move the dye bins automatically and send the operator the required mix.
Another step forward has been brought about by automated colour kitchens: the dyestuffs are stored inside special containers and the operator, using a keyboard and a computer, retrieves the recipe to be sent to the production process. A container on a special weighing device moves every time under the screw conveyor, distributing the powders of the various dyes taken from the relevant container; this process is controlled by a PLC. Once the weighing operation has finished, the necessary quantity of water is added at the temperature established by the dissolving procedure, the dyes are dissolved by agitation and the solution is sent to a special stand-by vat, before being poured into the dyeing machine. The container where the dissolving process is carried out is washed and dried automatically for the next cycle.
Modern vacuum systems halve the powder dyestuff treatment and dissolving times (previously, 20 to 25 minutes were necessary to prepare 200-300 litres of dyeing liquor): the previously weighed container (three or four dyestuffs) is sent to the vat for dissolving (the capacity ranges from 30 to 100 litres) by means of a liquid piston rotary vacuum pump, which can deliver from 150 to 350 g/sec of products. The vacuum effect makes the dye dissolve and avoids the formation of undesired adhesion of granular particles. This technique requires extremely reduced water volumes (the remaining quantity is added afterward), the mixing does not produce foams and is carried out at low temperatures and in half the time required by traditional systems. The vacuum effect facilitates the tube and hose cleaning.
By using a 10 kW pump; it is possible to feed a system of four dissolving devices feeding twenty dyeing machines.
Dyeing machines can be fed directly by automatic systems, which dose and forward chemicals and auxiliaries; these systems are controlled by microprocessors using only one line for transferring operations, with distribution mistakes ranging between 10 and 15 ml. The pump motors are equipped
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