Saminathan Ratnapandian

Circulating liquor machines
The fabric is wound onto a perforated beam and placed in the dyeing vessel. Dyeing is brought about by pumping dye liquor from the inside of the beam to the outside through the multiple layers of fabric. This ensures uniform contact between fabric and dye liquor [51]. Bi-directional pumping, periodically reversing the flow direction of the dye liquor, is used for yarn dyeing. Consistent packing density ensures level dyeing [52].


Circulating goods machines
Jiggers and winches are the traditional dyeing machines of this class. In the former, fabric is mounted in open width on a roller and guided back and forth through the dye bath. On a winch, the fabric is traversed in rope form through the dye bath. The lower fabric tension of winch dyeing favours its use for knitted and other delicate fabrics, while woven fabrics are mostly processed on jiggers. Pressurised jet dyeing machines are often used for lightweight fabrics because of shorter dyeing times and uniform dyeing. The liquor is injected into the fabric as it passes through the jet. The combination of pressure and injection of liquor permits dyeing at a typical low liquor ratio of 1:8 and in some cases even 1:4 [52].

2. Continuous dyeing

This is a method for open-width dyeing of fabric lengths in excess of 10,000 metres in a single colour [11]. It generally involves the use of a production line system where machines of consecutive processes, which may include pre- and post-dyeing treatments, are arranged sequentially and operated in a synchronised manner. The process can also be utilized in a semi-continuous manner for shorter lengths. Fabric running speed controls the dwell time in each process although dwell may be modified by the use of ‘festoon’ type fabric transport [12, 52]. A material to liquor ratio of 1:1 or even 1:0.5 is an advantage of this method [53]. Some of the key features of batch and continuous dyeing are compared in Table 1.2 [52, 54].

Table 1.2 Continuous dyeing vs. batch dyeing [52]