NEEDLE PUNCHED NONWOVENS
Updated: April, 2004 - M. G. Kamath, Atul Dahiya, Raghavendra R. Hegde
(Praveen Jana & Xinli Liu)
Worldwide, the needlepunching industry enjoys one of the greatest successes of any textile related process . The needlepunching industry around the world is a very exciting and diverse trade involving either natural or both natural and synthetic fibers.
The needlepunch process is illustrated in fig. 1. Needlepunched nonwovens are created by mechanically orienting and interlocking the fibers of a spunbonded or carded web. This mechanical interlocking is achieved with thousands of barbed felting needles repeatedly passing into and out of the web.
Fig. 1: Needle punching process
The major components of the needle loom and brief description of each are as follows:
2.1 THE NEEDLE LOOM (Fig-2 a & b)
Fig. 2a: Needle loom
Fig. 2b: Needle penetration
2.2 THE FELTING NEEDLE
The correct felting needle can make or break the needle punched product. The proper selection of gauge, barb, point type and blade shape (pinch blade, star blade, conical) can often give the needlepuncher the added edge needed in this competitive industry (fig. 3).
Fig. 2: Types of needles
The gauge of the needles is defined as the number of needles that can be fitted in a square inch area. Thus finer the needles, higher the gauge of the needles. Coarse fibers and crude products use the lower gauge needles, and fine fibers and delicate fibers use the higher gauge needls. For example, a sisal fiber product may use a 12 to 16 gauge needle and fine synthetics may use 25 to 40 gauge needle .
The major components of the basic felting needle are as follows :
As the needleloom beam moves up and down the blades of the needles penetrate the fiber batting. Barbs on the blade of the needle pick up fibers on the downward movement and carry these fibers the depth of the penetration. The draw roll pulls the batt through the needle loom as the needles reorient the fibers from a predominately horizontal to almost a vertical position. The more the needles penetrate the web the more dense and strong the web becomes generally See fig. 4 a & b. Beyond some point, fiber damage results from excessive penetration.
Fig. 4a: Needle Action - Schematic
Fig. 4b: Needle action
3. TYPES OF LOOMS
There are three basic types of needle looms in the needlepunching industry. They are:
The felting looms are the type just described. These needle looms may have one to four needle boards and needles from the top, bottom or top and bottom. The primary function of this type of loom is to do interlocking of fibers resulting in a flat, one dimension fabric. The types of products made with this process and needle loom are diverse and multifaceted. They exist in variety of industrial products, geotextileds, automotives, interlinings, home furnishings, etc. .
Structuring looms use what are called fork needles. Instead of carrying fibers into bedplate hole, the fork needles carry fiber tufts into lamella bars that extend from the entry to the exit of the needle loom (fig. 1). These fork needles carry large tufts of fibers into parallel lamella bars. These bars carry the tuft of fiber from the entry to the exit side of the loom. Depending on the orientation of the fork needle, a rib or velour surface is introduced (fig. 5). The most popular products made with structuring looms include home and commercial carpets and floor mats, automotive rib and velour products, wall covering and marine products.
Fig. 5: Structured needling
Random velour looms are the newest type of needle looms, having only been available since the mid 1980's. The random velour looms are used to produce velour surfaces. Unlike the structuring looms, the velour products produced by this loom are completely isotropic. It is almost impossible to distinguish the cross direction from the machine direction.
Unique to this type of needle loom is the
bristle-brush, bed-plate system. Special crown type needles or fork needles are
used in this loom design. The needles push fibers into a moving brush bed
plate. The fibers are carried in this brush from the entry to the exit of the
loom with zero draft. This allows for the completely non-linear look, perfect
for molded products. Random velour type products have been very popular in the
European and Japanese automotive industry. While almost all
3.1 Machine variable:
The most important machine variable is the depth of penetration and puncture density. The fiber travel through the web depends on the depth of penetration of the needle. The maximum penetration is fixed by the needle of the machine and depends on the length of the three sided shank, the distance between the needle plates, the height of stroke, and the angle of penetration. The greater the depth of penetration, greater is the entanglement of fibers within the fabric because more barbs are employed.
The puncture density i.e. number of punches on the surface of the feed in the web is a complex factor and depends on
· the density of needles in the needle board (Nd)
· the rate of material feed
· the frequency of punching
· the effective width of the needle board (Nb T)
· the number of runs
The puncture density per run Edpass = [n*F] / [V*W]
Where, n= number of needles within a needleboard
F = frequency of punching
V = rate of material feed
W = effective width of the needle board
The puncture density in the needled fabric Ed NV depends on the number of runs Npass; Ed NV = Edpass * Npass
The thickness, basis weight, bulking density and air permeability - which provide information about compactness of fabric are influenced by a number of factors. If the basis weight of the web and puncture density and depth are increased, the web density increases and air permeability is reduced (when finer needles and longer, finer and more tightly crimped fibers are used). Web density does not increase when finer fibers are needled with coarser needles. There is neither an increase nor a decrease in air permeability if the puncture density is increased.
As far as the strength of a needled nonwoven web, the situation is similar to that for compactness, namely that finer needles, finer and longer fibers, greater web basis weight and greater puncture depth and density, result in increased strength of the needled web. However, once a certain critical puncture depth or density has been reached, the rise in strength may be reversed. If the depth of the barb is decreased or the distance between the barbs is increased, the dimensional stability is improved during needling, and the web density and maximum tensile strength in relation to basis weight can be raised.
5. MARKET & PROSPECTS
Needled felts used for filtration forms only
about 10% of the total consumption, which accounts to approximately $400
million. The Pacific Rim countries like
Needlepunched nonwovens industries are rapidly