The choice of using two or three roll padders depends on:
the ability of the fabric to absorb water (hydrophilic = high absorption);
the speed you want for the treatment.
a) Normally, for a hydrophilic fabric that "foulards" at low speed, the two cylinders are used.
b) With a little absorbent fabric, or if you want to adopt a high speed, the three-cylinder is better,
remembering that in this case you need a tray with a greater volume of liquid.
Remember that:
a good impregnation of the fabric is essential for all padding procedures;
the amount of retained bath is always proportional to the weight of the fabric;
a rapid and uniform impregnation is obtained with an adequate pre-treatment that makes the
more absorbent fabric;
less fluidity of the padding liquid can cause less residual impregnation;
the degree of squeezing to be exerted on it is important for subsequent processing.
Examples:
in the presence of intense colors, an effect with a high watery residue on the fabric is sometimes required,
this allows lower concentrations of dye and avoids reaching the solubility limits of the
same;
if the padding is followed by drying, an effect with less water residue is preferable,
which also allows energy savings in that subsequent phase;
if the wet fabric passes to a second impregnation, for example of reactants, carried out
still with a foulard, a low aqueous residue is required.
In any case, a reduced residual of water on the fabric:
a) reduces the dangers of migration of dyes during drying;
b) allows easier corrections of the composition of the impregnating bath,
made necessary for example by preferential absorptions of the dye.
The high or low aqueous residue effect after squeezing also depends on the passage speed
of the fabric in the process and from the cylinders, in particular:
by the pressure exerted by the cylinders;
from the materials with which the cylinders are made, which determine their hardness;
the size or diameter of the cylinders, which determines the size of the squeezing area.