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Fleissner solves powder bonding challenge with novel combination process.

Fleissner Solves Powder Bonding Challenge With Novel Combination Process

machinery producer shipped first powder bonding unit this fall

As market demand for webs bonded with fusible fibers and powders has increased in recent years, Fleissner GmbH, Egelsbach, West Germany, has introduced a system combining a thru-flow drum dryer with powder bonding techniques. Advantages of the new line include less energy expended for bonding thermobonded webs, faster processing and shorter production lines. The first production line was recently delivered, according to the company.

While powders are more desirable than fibers because of the less expensive cost and many more bonding points, until now it had not been technically possible to use powder bonding in connection with the suction drum dryer simply because the powder and part of the fibers stuck to the drums and became soiled. In addition, the binder powder was blown into the air flow and partially lost during the hot air jetting in the suction dryer.

The Answer To The Problem

Fleissner claims to have discovered a way to combat the problems associated with powder bonders and thru-air drying while utilizing the advantages, such as high evaporation capacity per sq. meter drying surface, high drying speed, small migration tendency and a compact design.

The company's answer lies in presteaming the polyamide web prior to thermobonding. The steam application prevents the polyamide fibers from turning yellow during thermobonding. Trials at Fleissner also determined that webs treated with steam do not possess the negative sticking properties and binder substances do not settle on the transport devices any longer. Also, separating agents are no longer needed for the individual transport devices.

Finally, bonding powders made of phenolic resin melt will not be sucked out of the web during the pre-steaming process or, even in the case of strong suction drafts, in the suction drum dryer. However, bonding of webs with powder at temperatures under 200 [degrees]C is not recommended, as the steam condenses on the fibers and makes further drying necessary.

The steaming unit is arranged in front of the intake belt of the drum dryer and can be one or two-sided or the steam can be blown through the web. The web then passes through the drum dryer, where hot air is sucked through at a high speed. Usually dryers with two suction drums are used for alternating the flow through the material.

A calibrating unit, installed after the second drum, squeezes the web to the desired thickness and density. The roll gap of the calibrating unit can be adjusted with an accuracy of 2/100 mm and the squeezing pressure can reach up to 20 [] Lastly, the web is cooled by means of a cooling belt or drum.

In Fleissner's trials to determine production speed, the company told Non-wovens Industry it used a double-drum suction drum dryer with a treatment length of 4.4 meters. The trials were run at 20 meters a minute and the weight of the web used was 1000 grams sq. meter. Despite the high speed, the phenolic resin bonding powder was completely cured.

Other advantages include no contamination of the web, equal distribution of the bonding powder in the web and none of the disadvantages of liquid impregnation such as high quantities of water to be evaporated and squeezing of the web due to padder impregnation.

The new process also allows the bonding of light, cotton-type webs that up until now had to be bonded by means of bonding fibers or spray bonding.

PHOTO : Fleissner shipped its first powder bonder this fall.
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Author:Noonan, Ellen
Publication:Nonwovens Industry
Date:Oct 1, 1989
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