As the need for tubular knit goods finishing arose during the 70’s, a machine for the continuous mercerization of these fabrics, using patented circular expanders, was developed in cooperation with the Swiss company Terlinden, and was first marketed in 1979.

DORNIER thus responded to the market demand for the treatment of tubular knit goods in their natural form in order to maintain accuracy and consistency in finishing throughout the width and length of the fabric being processed. During subsequent years this system was developed into a family of machines covering singeing, mercerizing and a combined wet-in-wet finishing range for continuous mercerizing and bleaching.

Mercerization assures fabric luster and dimensional stability
Mercerized tubular knit goods produced from cotton, cotton blends, cotton/Lycra and more recently also Tencel are distinguished by such good qualities as: reduced tendency to skew and very little pilling effect after washing, permanent luster, brilliance and depth of color, soft and silk-like hand, high degree of elasticity, significant saving in dyestuffs (up to 30%) as well as excellent dimensional stability in length and width.

First and foremost, the impressive results achieved in the luster and dimensional stability of the finished fabric are primarily due to the precise control of fabric tension throughout the entire mercerizing process. The conditions created at each stage in the processing cycle are also significant, within the inlet and impregnation sections of the machine, and particularly in the critical stabilization process.

Due to the DORNIER concept based on patented circular expanders as already outlined, during every stage of processing the tubular knit fabric is evenly tensioned in its natural tubular form at all times. This results in a very reliable stabilization without selvedge marks. The following information emphasizes the technical features of the principle of circular expander technology.

The adjustment in the diameter of the circular expanders from 10 to 40 inches (254 to 1016 mm) is motorized. These circular expanders are freely suspended in the washing towers and are held in the vertical position by concave rolls. Conforming with the circumference of the circular expanders, the spray rings provide for an even spraying of the tubular knit fabric with water at a temperature value of approximately 80°C .

As a result of this unique concept, a very even stabilization and washing over the entire circumference of the tubular fabric is achieved. The arrangement of the respective stabilization, washing and neutralizing zones is constantly maintained at an angle of 90°, ensuring that there is no mesh distortion whatsoever in the knitted fabric during mercerization.

The complete range is modular in concept, enabling for example the number of circular expanders to be increased at any time through the addition of further modules. There are many advantages including the possibility on the part of the enduser to customize the dimension of the range to his own specific requirements.

Efficient linking of the mercerizing and bleaching processes
Particularly mid-size tubular knit goods finishers very often do not fully utilize their mercerizing equipment round the clock due to the relatively small amount of tubular knit goods to be finished. In order to be in a position to offer such customers a more economic solution, DORNIER developed a linked system. This is designed for alternatively mercerizing and bleaching with one and the same machine. As a result an ideal solution from the technical and commercial standpoints has been found, to install a range tailored to available capacities according to individual requirements.

The unique method of operation offered by this system ensures the treatment of the fabric without the danger of creasing, a high degree of whiteness and accurate reproducibility of previously attained results. In addition, environmentally friendly and harmless peroxide bleach is utilized in conjunction with the pad-steam process.

This combined wet-in-wet finishing range consists of an inlet section, the peroxide impregnation trough, a preheating chamber, the dwelling chamber, and in accordance with requirements two to four washing sections, the neutralizing bath and plaiter.

The goods pass via the inlet section into the impregnation trough and are soaked in the peroxide bath. Thereafter, the knitted fabric passes through the heating unit where it is heated to such an extent that the reaction process begins. The subsequent pad-steam operation in the dwelling chamber takes about 20 to 40 minutes. Washing out the chemical agents takes place with the use of two to four washing sections.

An optional module can be added for brightening and softening the fabric after processing in the washing towers. Furthermore, the possibility is provided for the addition of a demineralization process with impregnation and a reaction section prior to the peroxide impregnation process.

A circular singeing concept, providing exceptional productivity
Due to the mechanical handling of the knit goods during the processing cycle, a certain amount of yarn hairiness to one degree or another is inevitable. This hairiness increases as the count of the yarn becomes coarser. The same applies as regards modal fibers. In order to reliably prevent the yarn from pilling, even after a number of washings, the deployment of a singeing process for grey knit fabrics becomes a desirable feature.

On the basis of the mercerizing and bleaching ranges utilizing the patented circular expanders that have been tried and proven over many years, DORNIER has developed an efficient circular singeing concept. Using this concept, it has been possible for the first time to carry out the singeing process on tubular knit goods without selvedge marks.

The technical process begins with the goods being fed to the circular expander from a turntable and an automatic detwisting device. Located around the circumference of the circular expander are eight swivelling high efficiency burners in circular form. With this arrangement it is possible to direct the full width of each burner segment in the most ideal position in relation to the knit goods being processed, even when the diameter of the goods is changed from one lot to the next.

Utilizing this system of singeing, the end result is an absolutely even and constant surface of the knit goods, something that no other method of singeing has been able to achieve.

Since DORNIER is striving toward being a single supplier with a complete family of machines for the treatment of tubular knit goods, additional innovative machines will be developed for the finishing of such fabrics without selvedge marks.