Car body: From the Trabant to lightweight construction
Probably the best known example of alternative lightweight structure is the "Trabi", the Trabant 601, the standard vehicle in East Germany which still enjoys cult status. Its outer paneling consists of short cotton fibers (linters). Since they are not long enough for spin yarn, they are compressed to fleece mats, hardened with phenolic resin, and hot-pressed. Structural stability, weather resistance and especially the availability of raw material were the main benefits of this type of construction.
Changes to automobiles go hand in hand with growing requirements for the automotive industry, which is confronted with scarcer resources, rising raw-material prices and enormous price and competitive pressures, but also with growing vehicle production. In addition to appealing design, customers of automotive manufacturers furthermore expect ever more comfort, functions and safety, while at the same time reduced weight is required.
These demands have led to a trend to lightweight materials such as nonwovens. Already today, more than 35 square meters of textile fabric are used in an average of 40 applications per vehicle [Newsletter 4/2011]. According to experts, this comes to about 25 kilograms of technical textiles per new vehicle. The amount of fiber-based material should soon rise to between 30 and 35 kilograms. It is assumed that 50–60 percent of this will be made out of nonwovens and 40–50 percent of other textile fabrics.
The use of fiber-reinforced plastic (FRP) is a major improvement in component properties and, in particular, makes lightweight structures possible. Originally developed for aerospace, lightweight construction is also making inroads in traffic engineering. Carbon-fiber-reinforced plastics (CFRP) are finding ever more applications, for example as leaf springs, drive shafts, paneling and even as entire body components.
With a hybrid process (multi-material construction), door-panel weight can be reduced by up to 60 percent.
Compared to injection-molded parts, this translates to a weight reduction of 100 kilograms in a mid-class car, cutting fuel consumption by up to 0.3 liter per 100 kilometers of driving.
Carbon-fiber process – getting down to brass tacks
Nonwovens are used in body-making et al. as lightweight structures. But how is a component made from carbon-fiber, for example a car roof?
Pure carbon appears in nature as graphite and diamond, and both materials are insoluble and infusible and thus unsuited to direct production of fiber. Carbon-fiber initially exists as precursor fibers such aramide, viscose and polyarcrylnitrile fiber and is thermally processed in three-stages (immobilization – carbonization – graphitization) at gradually increasing temperature from 180°C up to 3,000°C.
Carbon-fiber made in this way displays high rigidity, tensile strength and vibration dampening, which is why it is popular in lightweight construction. In addition to its resistance to corrosion, carbon-fiber is also electroconductive and very refractory. For these reasons, nonwovens are seldom made directly from carbon-fiber. Instead, needle felts are produced from precursor fibers and subsequently undergo carbonization.
Similar to the manufacture of the Trabant, carbon-fiber mats are also then dipped in resin, shaped and hardened in order to give them their final dimensional stability as a body component.
In order to needle punch precursor fibers into high performance materials, Groz-Beckert administers its part in the form of powerful needles for flat needling. Needles from Groz-Beckert with a standard triangular point stand for high surface quality and uniform deflection in all stress directions, as well as long service life.
Inner life: masked nonwovens with a fairly large profile
Innovative materials and finishing procedures bestow automotive nonwovens with weight, function and design advantages. This applies to the vehicle exterior and interior, as well as to visible and masked applications. They can be decorative, but are also used subsurface, where they usually act as carrier material – for instance for synthetic leather and for damping and insulation. In the interior, environmentally-friendly and recyclable materials are increasingly used and usually reduce the mass of the vehicle. The proportion of masked nonwovens in automobiles comes to 90 percent. The areas of application in which nonwovens work behind the scenes include brakes, filters, exhaust systems and batteries.
The other visible ten percent includes door and side panels, rear shelves and the headliner. Surface quality is particularly important in visible nonwovens in automotive interiors. Groz-Beckert offers a needle for the best-possible surface quality in every field of application.
GEBECON® and EcoStar®
Higher stability and dense surface quality
Compared to standard felting needles, the newly developed EcoStar® style facilitates not only a denser surface quality but also provides a defined fiber transportation and an improved needle life.
GEBECON® and Twisted – efficiency
A typical area of application is the rear shelf. If efficiency in the manufacture of smooth products is priority, then it makes sense to use the twisted felting needle. The barbs are more defined while in use because of the twisted working part.
However, if a granular or velvety surface aspect is desired then structuring needles are called for.
The structuring process takes place on special-purpose machines and the nonwoven fabric has to be needle-punched before. The product surface can have a velours or rib character or even be structured in geometrical or linear patterns. Structuring needles are differentiated in fork and crown needles. A very uniform velvety surface structure is achieved with crown needles whereas fork needles give a more grainy aspect. In order to achieve a very dense and uniform velours surface a combination of fork and crown needles should be used.
The main areas of application for these products are usually floor coverings, foot mats, rear shelves, door and luggage-compartment panels, and headliners.
In order to achieve required features such as:
- best finish quality
- high surface uniformity
- optimum deep-draw behavior
- dimensional stability
Fork needles have a simple or multiple intermediate section with a cylindrical working part, as well as rounded fork geometry which ensures perfect interlocking and protection of fibers in the fork during the structuring process. Very high precision in the manufacturing process of the needle prevents needle breakage or bending thanks to the straightness of the needle. Configuring the fork position as a V or D allows the resulting loops to be aligned in the desired direction.
Fork needles are inserted into special structuring machines either with brush-conveyor or lamella plate. Brush-conveyor machines contain a rotating conveyor belt equipped with brush segments. The bristles of the brush segments serve to hold the fibers in place during the needling process so that a velours fabric with uniform loops without distortion results.
Example of use
The use of fine-gauge fork needles can achieve very high needling density. The combination with an intact brush conveyor ensures a pattern- and stripe-free product.
The interaction of these elements can lead to the following benefits:
- High uniformity during the structuring process
- Pronounced loops (granular structure)
- Very dense surface aspect thanks to high fiber transport capacity
- Optimum product quality from high process stability
- High surface quality from finest working-part cross sections (smaller penetration holes)
- Dimensional stability of the product
Crown needles are very similar to felting needles in their structure. The only difference consists in the arrangement of the barbs. Crown needles have a barb on each edge of the working part. It is important that the barbs have high dimensional accuracy with very dense and precise barb spacing. In the subsequent process, these properties enable the needle to produce an end product of high consistency and uniform quality. Furthermore, the structuring process requires a shorter disctance from the point of the needle to the barbs.
Crown needles are only installed in brush-conveyor machines, because they need the brush segments to form the loops. They make it possible to achieve an especially uniform, velvety surface texture. Another benefit is simultaneous fiber take-up during structuring, achieved with the high dimensional accuracy of the barbs and exact kick-up.