|Needlepunched nonwovens are created by mechanically interlocking the fibers of a carded or an air laid batt (web), or of a spun bond material. This mechanical interlocking is achieved with thousands of felting needles repeatedly penetrating the web or spun bond.
Figure 1 helps illustrate the needle felting process. As the needle beam raises and lowers the felting needles, the blades of these barbed needles repeatedly pass into and out of the fiber batt (web). Each barb fills with fibers on the downward movement and carries these fibers the depth of the penetration. When the needle beam retreats upward, the fibers are released from the barbs. Reorientation of these carried fibers from a horizontal to a vertical plane within the web will result as this motion is repeated. Generally speaking, as the number of penetrations per square inch is increased, as are fabric dimensional stability and density.
The batt is pulled through the needle loom by what are called draw rolls. The material passes through the needle loom between two plates: a stripper plate which is on the top and a bed plate which is on the bottom. Needles go through corresponding holes located in the stripper and bed plates. As the needle beam moves up and down, the draw rolls pull the material through the loom while the needles penetrate the batt and perform the interlocking process.
Although there are more than 1000 types, sizes and variations, all felting needles will fit the shape of those shown in Figure 2. All will have most of the six common features:
The Crank is the 90 degree bend on the top of the needle. The crank provides for needle location in the board of the loom. Perhaps more importantly, each barb will have a precise distance from the crank. When making penetration depth adjustments, barb to crank distances must be equal from needle to needle.
The Shank is that portion of the needle that fits directly into the needle board.
The Intermediate Blade is used on double reduced needles. This section makes them more flexible and somewhat easier to place into the boards.
The Blade is the working part of the needle. It is the blade of the needle that penetrates the fiber batt. The most common shape of the blade is triangular, with three edges into which barbs can be formed.
The Barbs are the most important part of the needle. It is the barbs which engage fibers during penetration through the batt and perform the interlocking function. Felting needles can have one, two or as many as 36 barbs. There are many variations in barb placements and spacing. Most felting needles will have two or three barbs per edge.
The Points seem self explanatory. But there are long points, short points, polished points, ball points, chisel points and beveled points. Each can offer a different effect for a given application.
Needlepunching is no newcomer to the nonwovens industry. The process itself was established before the turn of the century. However, early felting needle looms and the fabrics they produced were extremely crude in their design and engineering. The early needle looms were also quite slow, capable of only 100 strokes a minute. The main products produced during those early years were paddings and waddings made of jute, sisal and animal hair. These pads were used primarily for spring insulators in the mattress and furniture industry and for carpet underlay in commercial applications or for the home furnishings industry.
Since these early days, however, needle felting technology has advanced greatly. Todays modern felting needle looms have the capability of 2000 strokes a minute.
The felting needles that produce todays highly technical felts have also become more engineered and advanced. Uses for todays highly technical needlepunched fabrics include space shuttle exterior tiles, geotextiles, filtration, papermaker felt and synthetic leather.
The fibers used in the needling process have also become more advanced over the years. In the 1940s and 1950s natural fiber such as coir, sisal, wool and animal hair were the predominant fibers being needled. Today, man-made fibers such as polyester, polypropylene, aramid fibers, glass fibers, teflon fibers, ceramic fibers, mineral fibers and nylon have replaced many of the natural fibers used years ago.
Let us now take a closer look at some of these features and their variations that have a relationship to various nonwoven physical properties.
Click on the "Rounded Barb Styles" link below to continue: