1 Introduction

During IGATEX 2004 in Karachi Küsters was present together with its local representative KASH International (Pvt.) Ltd. A waterfall was shown which attracted many visitors. This highly aesthetic exhibit was created from parts of the Küsters washing machine TurboFlush. It showed in which way washing water is applied on a running web numerous times in the machine. Several visitors wanted to receive more information about the washing machine TurboFlush and its working principle. Therfore, in this article the TurboFlush and its working principle are explained.

2 Continuous washing of fabrics in open width

Washing is a very important process in fabric finishing. In most cases a fabric, particularly a cotton fabric, passes several washing processes in getting finished from the raw state to the completely finished state. The success of the washing process is responsible for the quality of the fabric as wahing determines textile properties like fastnesses as well as the amount of residual chemicals on a fabric which influences further finishing steps. Therefore, washing influences in a high degree the quality of a textile item as well as the cost of the finishing process.

Basically washing means to eliminate impurities from the textile. These impurities are of a chemical or of a physical nature or they are a combination of both. Characteristics of chemical impurities are:

· They are produced by chemical reactions during finishing, by treatment media or by additives.
· They are in most cases in liquid state.
· They are situated on the fabric surface, in spaces between yarns and fibres and they are enclosed in the fibres.

Physical impurities are:
· Particles like loose fibres, neps, pigments and others.
· In most cases dispersed in the treatment liquor.
· Situated on the fabric surface as well as in spaces between yarns and fibres.
The washing result is determined by the residual amount of impurities on the textile. The quantity of residual impurities influences further finishing processes. This quantity is also a sign for the quality of a finished textile material.

3 TurboFlush in general

Conventional washing machines make use of an up and down cloth guiding. For this reason they are called up-and-down-washers. In these washing machines the fabric is guided several times - depending on the number of rolls - into the washing bath. After pulling it out of the washing bath the water flows back on the textile surface which causes a surface washing. It depends on the production speed if some of the water adheres to the fabric up to an upper roll. At the upper roll this water is pressed through the fabric so that a typical "wash nip" results.

Several parameters influence the washing effect of an up-and-down-washer, but the strongest parameter is the production speed. At a production speed of 60 m/min reasonable washing starts in this kind of washing machines. This is based on an adhesion of washing liquor to the fabric surface and on the flow back along the fabric surface as well as a penetration at the wash nips. For washing a high turbulence in a washing machine is necessary, particularly to contact the fabric surface directly with the washing liquor. This is also achieved in up-and-down-washers above production speeds of 60 m/min.

Usually in up-and-down-washers the distances between the upper and the lower rolls are nearly 1000 mm long. The distance between two rolls is important for the cloth guiding properties of a washing machine. For this reason most up-and-down-washers are not suitable for the treatment of delicate fabrics or of fabrics which tend to crease. They need short distances between the rolls to avoid creases and deviations of the fabric.

The new washing machine TurboFlush (Figure 1) is designed to achieve high washing efficiencies, beginning at low production speeds. Furthermore, it is designed for optimized cloth guiding properties.

The machine comprises two compartments. In both compartments are troughs at the bottom of the machine. Furthermore they are equipped with a circulation system which works with circulation rates of up to 35 m³/h. By means of the circulation system the water is poured on the fabric and cascades downwards through three swivelling troughs, contacting the textile several times. By this a counterflow effect applies in every compartment of the machine. Furthermore the circulation systems are responsible for high washing turbulences and very intensive washing mechanics. These washing mechanics are independent of the production speed, so that best washing results are obtained already at low production speeds. Another counterflow exists which transfers the washing liquor from compartment 1 to compartment 2. All flow directions are shown in Figure 2.

For a further explanation of the high washing efficiency of the TurboFlush an example is given: If the washing process works at a counterflow rate of 5 m³/h and the circulation rate in each compartment is 35 m³/h, then each part of the water in compartment 2 is circulated 7 times before leaving the compartment 2 and being transferred by means of counterflow to compartment 1. There again the water is circulated 7 times before leaving the compartment and the machine. That means that every part of the water contacts the fabric several times in the TurboFlush. The water is applied to the fabric by means of an application pipe. Then it cascades through three troughs to the bottom trough of the machine. By each overflow of one of the troughs it is applied on the fabric surface again. That means that in every compartment of the machine four application situations exist, so that in this example in every compartment of the machine the water is applied 28 times on the textile. As a result the water is applied 56 times on the fabric in this example.
The liquor content of this machine is very small. It is only about 570 l at a working width of 1800 mm. The fabric content of the TurboFlush is 20 m.

4 TurboFlush and its washing principles

The TurboFlush uses different washing principles. By the combination of this washing principle it achieves its full properties. The first principle is a turbulent washing in the single trough (Figure 3). This is comparable to the washing in the lower trough of a conventional washing machine. The geometry of the trough is adapted to the roll diameter so that the water content is very small. Furthermore, this leads to an intensive liquor exchange and an excellent washing performance.
By the circulation system the troughs are filled and an overflow occurs. This overflow is poured on the next web path again, so that there is another application of washing liquor on the fabric surface. This leads to a liquor exchange and improves thereby the washing properties (Figure 4).

In the area of liquor application the fabric runs upwards. The applied washing liquor and the gathered washing liquor tend to flow downwards by means of gravity. Thereby, a high turbulence is caused on the fabric surface which improves the washing properties (Figure 5).

Due to the slanted cloth guiding some of the wash liquor penetrates the fabric by means of gravity (Figure 6). The penetration is important as it improves the liquor exchange also at the inner parts of the textile web.

Furthermore the washing liquor is pressed through the fabric at the rolls (Figure 7). This also causes an intensive washing effect which is similar to the washing effect in up-and-down-washers. However, in Turbo-Flush this effect is active already at low production speeds because of the slanted cloth guiding and the short distances between the rolls.

In total this shows that several washing effects are combined in the TurboFlush (Figure 8) which lead in this combination to excellent washing properties. Based on the circulation systems these effects are achieved already at low production speeds.

5 Properties of TurboFlush

Based on the above described washing principles the TurboFlush washing machines show some properties which are outstanding.

5.1 Cloth guiding

The fabric path is characterized by short distances from roll to roll and by a slanting cloth guiding. These short distances from roll to roll are responsible for excellent cloth guiding properties. Fabrics which show difficult cloth guiding properties, like delicate fabrics, fabrics which tend to crease and elastic fabrics, are guided through the machine without any problems. It is possible to equip the fabric path with additional expander rolls if this is necessary. Tensions in the machine are low, however it is possible to add drives to some rolls of the machine. Complete tension control loops are possible which allow to operate at limited tension levels. Furthermore, as an option jockey rollers are available for the driven rolls.

5.2 Washing performance & water consumption

Trials were done to compare the washing properties of the TurboFlush with washing properties of conventional up-and-down-washers. These trials and the installed base show clearly that the high washing performance of TurboFlush washing machines is available already at low production speeds. It remains nearly the same all over the range of production speeds which is up to 200 m/min. In some trials the water consumption could be reduced heavily. The washing properties were compared between a range of three up-and-down-washers with a cloth content of 30 m each and intermediate squeezers and another range consisting of three TurboFlush with a cloth content of 20 m each, also equipped with intermediate squeezers between the washing machines. Cotton fabric was impregnated with a caustic soda lye.

The impregnation took place 8 h before the washing trials were done. In this trial it was observed that the same washing results could be achieved in the TurboFlush range with half of the water consumption compared to the range with up-and-down-washers. Of course this result cannot be generalized for every kind of washing process, every kind of fabric and of fibre material, but in general it shows that the dust absorbing capacities of the water are used in a higher degree in the TurboFlush compared to up-and-down-washer - and this leads to a lower water consumption as well as to a lower steam and energy consumption as well.

5.3 Further properties

Besides the excellent cloth guiding and washing properties some other characteristics are important as well. One of these characteristics is simple cleaning. For the change of the water content the troughs swivel down and get emptied by this.