Sizing in textile industry
Sizing is applied to lubricate and protect the warp yarn during weaving, sizing agents (in the form of water solutions or water dispersions) are applied after warping. Another aim is that to make stick to the body of yarn the superficial down (BAT for the Textiles Industry, July 2003).
2. FIELD OF APPLICATION
Sizing can be carried out on yarn. Sizing is applied on natural fibres and on technical fibres =(BAT for the Textiles Industry, July 2003).
3. DESCRIPTION OF TECHNIQUES, METHODS AND EQUIPMENT
The equipment necessary for sizing is (BAT for the Textiles Industry, July 2003):
- a size boiler to swell the polymers (Fig. l),
- a size trough with high-performance squeeze rolls (Fig. 2),
- a cylinder drier with optimum heat utilization (Fig. 3),
- in certain circumstances, a section warp division machine (Fig. 4),
- in certain circumstances, an assembler machine (Fig. 5).
For the classic warp sizing process, the size has to be cooked in a kettle after which the size liquor is transferred to a heated storage vessel from where it is finally delivered to one or several size boxes for application to the warp sheet. The wet yarn is subjected to "wet extension" whereby the individual yarn fibres slip against one another and the yarns are stretched. This wet extension in the process is often necessary in order to be able to control the behaviour of the yarns; it is, however, not desirable since the strength of the yarn is generally reduced as a result. Excessive extension of the yarns during sizing is a common cause of broken ends in weaving. The warp is squeezed between one or several pairs of rollers at pressures of 300 kg to (in high pressure size boxes) 10000 kg. The impregnated warp then passes over drying cylinders supplied with superheated steam. During this stage, water evaporates from the still wet yarns into the surrounding air which is normally collected under a hood and discharged by means of an extractor fan into the atmosphere through the roof. In order to expel the water quickly enough to achieve high processing speeds of, e.g. 100-125 m/min, the yarn is "cooked" on the drying cylinders. This rapid drying often leads to size bridging between individual yarns. The layer of warp yarns is peeled off the cylinders as a result of which individual fibres or hairs protrude from the fibre bundles. If the working speed changes, drying is either excessive or insufficient since the system inertia cannot be overcome quickly enough to compensate for changes in temperature/speed. After leaving the drier, the yarns are separated with the aid of lease rods. In some cases, waxes are recommended instead of sizing.
4. COMPETITIVE TECHNOLOGIES AND ENERGY SAVING POTENTIALS
- a) Changes in the process
- Recovery of sizes and heat from sizing machines: (BAT for the Textiles Industry, July 2003).
The efforts have been focussed on developing methods for the recovery of sizes and heat from sizing machines like ultrafiltration:
After sizing and weaving, sizing agents are removed during textile pretreatment by hot washing with water in a continuous washing machine (in order to minimise water consumption, the washing process may need to be optimised). Sizing agents concentration in the washing liquor is about 20 - 30 g/l. In the ultrafiltration plant, they are concentrated to 150 - 350 g/l. The concentrate is recovered and can be re-used for sizing, whereas the permeate can be recycled as water in the washing machine. Note that the concentrate is kept at high temperature (80 - 85°C) and does not need to be reheated.
- b) Changes in the energy distribution system
No information is available.
- c) Changes in the heat supply system
No information is available.