Operation Techniques of Decatising Machine in Textile

Operation Techniques of Decatising Machine in Textile

Sameer Mubarak Pinjari
Department of Textiles (Textile Chemistry)
DKTE’S Textile & Engineering Institute, Ichalkaranji, India
Intern at Textile Learner
Email: samirpinjari2021@gmail.com


Decatising in Textile:
This process is mainly carried out on wool by exploiting its elastic properties in hot and wet conditions by the direct action of the steam on the fabric. This treatment gives the processed fabric the following characteristics:

  1. Dimensional stability;
  2. Setting of pile after raising;
  3. Reduction of possible glazing effect after calendering, thank to the swelling caused by steam blown on fibers;
  4. Modification of the hand, which is much more consistent after the treatment;
  5. Pre-stabilization to autoclave dyeing.

This category  of  treatments  does  not  include  the  stabilization  of  wool fabrics such as potting,  where  the  dimensional  stabilization  is  obtained thanks to the “plasticization” phenomenon occurring when the wool fabric is immersed in hot water. On fabrics made with other fibers, the same treatment can be carried out as “steam ironing” alternatively to the calendering treatment, when an excessive “glazing effect” could result from the treatment.

The  steam  decatising,  which  is  also  referred  to  as  dry  decatising,  is carried out on decatising machines in one continuous treatment or two discontinuous ones.

Operation Techniques of Decatising Machine in Textile:
Operating techniques of decatising machine are given below:

  1. Drum decatising (alternated at atmospheric pressure);
  2. Autoclave vacuum decatising (KD);
  3. Continuous decatising.

Above operation techniques of textile decatising machine are described below:

1. Drum decatising (alternated at atmospheric pressure):
In discontinuous decatising processes, the fabric is wound, together with the satin or blanket on a large perforated drum (90 cm) on which some meters of blanket or similar cloth have been previously rolled. By using large rollers, it is possible to wind the same quantity of cloth with a thinner density of the roller, to allow the steam imparting a more uniform effect and reducing the differences between the tail and the head. The steam, at a temperature that can reach 130°C and a pressure of up to 6 bars, is forced into the cylinder through the fabric roll (i.e. it is forced through both fabric and blanket) for an interval of time that can range from 1 and 3-4 minutes, according to the desired effect. The steam is then exhausted by means of a pump.

2. Autoclave vacuum decatising (Kessel-Dekatur):
The possibility of reaching higher temperatures (130°C) and greater pressures (up to 6 bar), the setting effect is markedly more durable than when working at atmospheric pressure. This treatment is now well appreciated and commonly used to give dimensional stability to all combed fabrics and also to some carded ones. The machine can be divided into two main compartments: the fabric taking up area and the horizontal autoclave. Recently, semi-automatic systems have been successfully developed and improved multiple-position stations, which allow preparing a new roller and unloading the treated one while a third roller is undergoing the decatising treatment. It is worth considering that the setting effect is directly proportional to the increase of process time and steam pressure and consequently to temperature. The increase of both factors causes a marked yellowing of the wool together with a progressive deterioration of the peculiar qualities of the fiber (resistance, elasticity and soft hand).

Autoclave Vacuum Decatising
Figure 1: Autoclave Vacuum Decatising

3. Continuous decatising:
The need to speed up the processing cycles has led to the development of continuous systems, which give better output rates, no head-tails differences, no marks on the fabrics due to seams necessary to sew the heads and sometimes moiré effects (surface pattern resembling water ripples). The only disadvantage is a less powerful effect given by the treatment; in particular an unsuitable stabilization for all products. The continuous decatising process carried out under pressure allows a permanent setting of the wool fabric, which is obtained through a first processing step with saturated vapour under pressure (which can reach a temperature exceeding 135°C), while a second cooling step grants the surface and dimensional stabilization. For handling purposes, the fabric is compressed between a large perforated roller, coated with a heavy textile coat and a thick endless layer made of dense cotton/polyester felting material. All along its path the fabric is treated (using different systems) with steam supplied by means of special delivering units assembled under the conveyor belt in the lower part of the cylinder, and subsequently cooled with air. The intensity of the treatment can be adjusted by adjusting the process speed, the pressure between the cylinder and the conveyor belt, the moisture degree and the steam pressure.

Continuous Pressure Decatising Process
Figure 2: Continuous Pressure Decatising Process

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