Magazine July 2011

All the latest information from the textile world

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Geotextile production methods

DescriptionBasic materialReinforcement toolEffect of reinforcementProduct structure
NeedlefeltTransversely oriented webBarbed hook needleBarbs catch and entangle the backing material to form a vertical fibre bundleCompacted fibre nonwoven with vertical fibre plug; fabric weight 100 - 2,000 gsm
Nonwoven stitch-bonded fabric

Transversely oriented webSlider needle closure wire systemFibres are clamped together with binder yarn via oversewingFlat nonwoven, the binder yarn system creates a fabric connection on the top and the underside; fabric weight 100 - 1500 gsm
Nonwoven stitch-bonded fabric

Transversely oriented webSlider needle closure wire systemTool is used to catch several fibres and form them into fibre bundlesFlat nonwoven, one side shows loops, the other has a flat and fluffy fibre arrangement; fabric weight 100 - 2,000 gsm
Agitated nonwovenChaotically oriented webHigh pressure water jetWater jet moves the fibres during collision and discharge; leads to entanglementCompacted fibre nonwoven with numerous fibre entanglements - fabric weight 30 - 500 gsm

The choice of fibre is decisive

Geotextiles filter, reinforce, separate, protect, drain and compensate stress. Because of these diverse characteristics, special requirements are placed on the choice of fibre and the physical properties of the textile.

Natural fibres are mainly used whenever a product has to rot completely, leaving no residue. Water absorption and water discharge capabilities are also important. Hemp and jute fibres are frequently found in geotextiles that can rot.

In addition to natural fibres, a large number of synthetic raw materials are also used, especially if the product needs to be resistant to environmental influences. This is why the fibre used must also be insensitive to water, soils, other construction materials or micro-organisms.

Physical properties

Depending on the function of the geotextile, differing requirements are placed on the physical properties of the nonwoven. This demands intensive and even needling, together with stability and gentleness on the fibres. The requirements placed on felting needles in the production of geotextiles are therefore enormous. For this reason, Groz-Beckert has needles in its product range that have been developed specifically for this sector: the Tri STAR® and the Cross STAR® needles.

Groz-Beckert Tri STAR®

Tri STAR® needles from Groz-Beckert, the result of a further design development of the standard working component and the barb shape, are distinctive for their even needling effect and their long service life. The needles, which are gentle on the fibres, increase product quality - and the sharply reduced machine downtimes guarantee reliable and economically efficient production processes. The needles are thus ideally suited to the production of typical geo-products. Examples include geo-nonwovens for highway construction, separation and filter felts, coating substrates, safety nonwovens and geo-membranes.

Concave-shaped working-component surfaces with narrower edge angles enable precisely defined fibre looping and better fibre support in the barb. Fibre transport thus increases, leading to more intensive needling and a compact integration of the fibres in the felt. The combination of Groz-Beckert RF barbs with rounded edges and the Tri STAR® working-component cross-section ensures that needling remains gentle on the fibres and simultaneously efficient.

The benefits of a Groz-Beckert Tri STAR® needle over a standard needle are many and varied:

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  • more compact felt
  • reduced material thickness with the same weights
  • economically efficient benefits due to longer-running rollers
  • higher line speeds
  • higher productivity
  • reduced downtimes
  • efficient needling even at low needle densities

Groz-Beckert Cross STAR®

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Cross STAR® needles are especially suitable with powerfully compacted geo-felts, also in high fabric-weight sectors. They enable constant material properties and highest tensile strengths to be achieved in the transversal and longitudinal direction.

Cross STAR® needles enable efficient and economical needling. They are successfully used in the production of numerous different applications in the geo-nonwovens sector, e.g. in landscaping, as drainage felts, or as heavyweight compaction mats. The use of the Cross STAR® needles enables the optimal puncture resistance of the product to be achieved.

The Cross STAR® needle has a working component that, in cross-section, resembles a star with four identical edges. The special geometry of the working component with its narrower edge widths enables more effective fibre transport. The use of Cross STAR® needles is thus especially effective during needling of geotextiles with high fabric weights. Apart from this, four edges are also advantageous where more even needling is concerned, especially with regard to isotropy.

Landfills – inconceivable without geotextiles

In contrast to other application sectors for geotextiles, in which they are needed and integrated as a basic supporting element, modern landfill construction is quite unthinkable without them. Here, geotextiles function as indispensable construction materials, guaranteeing effective watertightness in the lower as well as the upper section of the landfill. Here they fulfil a host of tasks, ranging from separation, filtration and drainage to reinforcement, protection and compaction. This basically involves a so-called "sandwich composite" whereby clay is spread onto a separately pre-needled single layer. After the layer has been spread, a further felt is added as a covering layer and finally needled together with the lower layer.

The separation web – how it is made

For the production of separation webs the main fibres used are PP, PES, PA with staple lengths of 60-90 mm, recycled fibres and spun-bonded fibres (PP). The fibre gauges lie in the region of 1.7-44 dtex, and in special cases up to 200 dtex. The weight area varies depending on the planned application from 80 to 2,000 gsm, and even higher in the sandwich composite. The needling takes place on both sides, whereby the felt is often stretched in the machine direction between the pre-needling and finish needling, in order to achieve optimal lateral and transverse strength conditions (almost 1:1) in the end-product. For the finish needling, the two specially developed Groz-Beckert needle types Tri STAR® and Cross STAR® are available.

Downstream tenter frames or calenders are used to fix the geotextile, to smooth it or to stretch it to the desired width. Generally, parameters between 50 and 250 E/cm2 and a penetration depth of 8-12 mm are selected.