Page 230 - Basic Principles of Textile Coloration

MACHINES FOR DYEING YARN 219

within the packed skeins. The machine will therefore usually be over-packed so
that after shrinkage has occurred the yarns just fill the machine with even
circulation. When shrinkage of high bulk acrylic yarns is likely, any bottom poles
are initially placed several centimetres above the bottom of the extended skeins.

There have been a number of refinements to the basic Hussong machine.
Invariant downward flow of the dye liquor through the hanks keeps them
extended so that bottom poles are not needed. In this case, the problem of contact
between the solution and the yarns touching the upper poles can be avoided by
pulsating the liquor flow. In another method, the dye liquor circulates through
upward-pointing holes in the poles holding the skeins. There may be occasional
problems of unlevel dyeing with dyes that do not migrate readily.

A major reason for the decline of hank dyeing is the problem of unwinding.
After dyeing, the wet hanks are centrifuged, hung on poles or hooks, and passed
through a hot air oven. They must then be mounted on a rotating frame to
unwind the yarn. After package dyeing, yarn can be more easily unwound at much
higher speed by pulling it over the top of a stationary bobbin.

12.3.2 Package dyeing machines

A package dyeing machine is typically a cylindrical vessel, about 2 m high and
2 m wide, with a rounded bottom and lid. The yarn is wound into cheeses, cones
or cakes using perforated former tubes. The formers may be rigid or compressible,
the latter allowing packages to be squeezed tightly together when mounted on top
of each other in the machine. Cheeses are cylindrical with parallel sides, with a
diameter usually larger than the length. Cones taper with a small angle. They
usually have the shape of the former tube onto which the yarn is wound and
uniform wall thickness. Cones allow easier over-the-top unwinding of the yarn
than cheeses. Cakes are wound on a former tube that is then removed so the
inside collapses. They are also produced by winding yarn or tow in a centrifuge or
Topham box. High bulk acrylic yarn can be dyed in cake form.

The packages of yarn are inserted onto vertical, perforated spindles in the
machine. Each spindle typically takes 8–10 packages but the vertical columns of
packages do not touch. The packages may have a stocking over them to protect
them and to act as a filter during dyeing. The spindles screw into holes in the base
of a hollow, circular frame, at the bottom of which is a connection fitting onto the
pump (Figure 12.2). The spacing of the spindles and hence the maximum load
depends on the frame diameter and package size. The frame, with its load, can be