Page 244 - Basic Principles of Textile Coloration

DYEING MACHINES FOR SPECIFIC ARTICLES 233

12.5 DYEING MACHINES FOR SPECIFIC ARTICLES

12.5.1 The star frame

The star-frame has a central shaft with many horizontal radial arms with hooks on
the underside that hold the suspended fabric by the selvages as it winds around in
ever increasing circles. The dye liquor circulates over a perforated plate above the
frame and evenly distributes itself over the fabric. The frame may even be raised
and lowered in the bath during dyeing. The liquor ratio is often about 50:1. The
frame only takes about 200–250 m of fabric. Dyeing using the star-frame is fairly
expensive because of the time required for mounting the fabric on the frame. This
machine is usually reserved for dyeing expensive fabrics such as high quality
velvets.

12.5.2 Garment dyeing machines

In paddle dyeing machines, the goods pass around a central island as a rotating
paddle circulates the dye liquor. The walls of the island are perforated and the
central section is flooded. It serves for dye and chemical additions and for draining
the machine. The paddle is usually located along one of the straight sides of the
oval shaped vessel with its axle passing through the island above bath level. The
paddle blades dip to about half the depth of the bath and the paddle speed is about
5–10 rev min–1. This type of machine is used for dyeing loose articles such as
hose and small garments. These are preferably held in mesh bags made of a non-
dyeable material since this facilitates loading and unloading and minimises
tangling. The liquor ratio is fairly high, with a minimum value of about 25:1. Live
steam heats the bath, issuing from pipes in the bottom of the vessel.

Rotating drum machines are also useful for dyeing hose and garments. These
have an inner perforated drum that rotates in either direction inside a sealed drum
of slightly greater size. Baffles divide the inner drum into quadrants to ensure that
the goods move as it rotates. The rate of rotation is quite low, about 3–
4 rev min–1, with frequent reversals of direction. Again, the goods are preferably
bagged. As for all dyeing machines, a smooth interior is essential to avoid
snagging. A variety of tumbling machines have higher rotation speeds and can
spin dry at the end of the cycle. These are similar to dry-cleaning machines.
Rotating drum machines are more efficient and cleaner to operate than paddle
machines. The more vigorous mechanical action often promotes more shrinkage
and bulking, which may be desirable for some articles.