Roving
A roving is a bundle, strand or multifilament yarn made of parallel filaments (continuous fibers), which is mainly used in the manufacture of fiber- reinforced plastics (FRP) or fiber-reinforced plastics, a subgroup of composite materials . The cross-section of a roving is usually elliptical or rectangular. However, there are also rovings with a slight protective twist (e.g. 10 turns / m), which makes the cross-section more rounded. Most often, filaments made of glass , aramid or carbon are combined into rovings.
Type and structure
A basic distinction is made between direct rovings and assembled (plied) rovings .
Direct rovings are formed directly in the primary spinning mill through the parallel combination of the spun filaments after a size has been applied. By applying the size, a certain cohesion of the filaments in the roving is achieved. The chemical composition of the size is matched to the chemical composition of the plastic matrix into which the rovings are to be incorporated so that optimal adhesion of the two structural elements is achieved. Direct rovings are used from a fineness of> 300 tex , i.e. i.e. 1000 m of this roving weighs more than 300 g.
Assembled rovings are made from a predetermined number of tension equal direct rovings or multifilament yarns depending on the desired total number of filaments by plying.
Both types of roving are supplied either on roving spools with an external take-off or as a support-free pack with an internal take-off for further processing.
Usually rovings are sorted by type, i. H. produced from one type of fiber. However, there are also hybrid rovings made of filaments of different materials. The reinforcing fibers are usually mixed with thermoplastic fibers. Depending on the fiber volume , these hybrid rovings can be used directly, e.g. B. in the hot pressing process, without adding a matrix material. The mixture with fine thermoplastic fibers ensures good micro-impregnation. Another way to produce hybrid rovings is to coat them with powdered thermoplastic. Compared to unidirectional semi-finished products, the hybrid rovings have the advantage that they have not yet been consolidated. As a result, they remain just as malleable as pure fiber roving.
designation
Rovings are named after their number of individual filaments and / or their fineness (length-related mass in tex; 1 tex = 1 g / 1000 m). The number of individual filaments is given in full 1000 filaments (K). Usual forms of delivery are:
- 1 K (1000 filaments)
- 3 K (3000 filaments)
- 6 K (6000 filaments)
- 12 K (12000 filaments)
- 24 K (24000 filaments)
Rovings with a filament count of more than 24 K, e.g. B. 50 K or 100 K are referred to as Heavy Tows, the z. Currently only made of carbon filaments and are offered at a lower price than conventional rovings. These cables have to be spread apart when they are further processed into textile fabrics.
The fineness of the rovings depends on the number of combined individual filaments and their fineness and thus on the diameter or cross-sectional area and the density of these filaments. A 12 K carbon filament roving is specified with a fineness of 800 tex and a 24 K roving corresponding to 1600 tex.
properties
The roving can practically only be used in conjunction with a matrix. It has high strength and rigidity in the longitudinal direction of the fibers. Mechanically speaking, it is a unidirectional layer . The mechanical properties across the fiber are mostly poor. Therefore rovings are laid along the main load paths (main normal stresses). Composites made from unidirectional stretched rovings have a higher strength / stiffness than those made from roving fabrics, since the rovings in fabrics are corrugated, which puts a complex strain on the fibers when loaded.
Processing and application
Rovings are laid by hand in manual manufacturing processes, with the impregnation and fixation of the roving being a difficulty. For these reasons, roving tapes are often used. These tapes are loosely bonded (e.g. made of paper) so that the rovings can be processed more effectively.
Rovings can be machined directly when manufacturing rotationally symmetrical bodies from fiber-reinforced plastics such as containers, pipes, axles, rollers and shafts using the winding method and when manufacturing them using the profile drawing method or pultrusion method. In addition, two- and three-dimensional semi-finished fiber products for further processing into FRP components are manufactured from rovings by weaving, braiding or knitting. In fiber spray technology and in the production of fiber matrix semi-finished products such as sheet molding compounds , bulk molding compounds or LFT , so-called cutting rovings, equipped with a stiffer size to improve the cutting behavior, are only fed and cut directly into long or short fibers. In prepreg production, they serve as the starting material for unidirectional prepreg tapes or prepreg fabrics. With the help of laying heads, robots can lay roving tapes on curved surfaces.
In particular, components that are mainly stressed in a preferred direction can be made from rovings. Because of the orientation of the fibers, one speaks of a unidirectional layer . Examples of such components are leaf springs , rotor blades or wing spars . Rovings can be used in drive belts as local reinforcement. They are also used for local reinforcement and stiffening of cutouts and borders. Another important application is the ring reinforcement of components such. B. from high-speed runners, pressure vessels or concrete supports.
The roving can be used in loop form to introduce concentrated tensile forces into a component. In strand form it can be found in suspension ropes and cables, e.g. B. in bridge construction. Ropes with a high dynamic load capacity are made from aramid fiber rovings. Fiberglass rovings are also used as rodent protection for cables.
Individual evidence
- ↑ Note: based on DIN 60 001, Part 2: Textile fibers, fiber and production forms, October 1990, in which a cable is referred to as a multitude of filaments without any significant twist. Sometimes also known as continuous fiber cable
- ↑ Chokri Cherif (Ed.): Textile materials for lightweight construction - Techniques - Process - Materials - Properties. Springer-Verlag, Berlin / Heidelberg 2011, ISBN 978-3-642-17991-4 , p. 122.
- ^ Fabia Denninger: Lexicon of technical textiles. Deutscher Fachverlag GmbH, Frankfurt am Main 2009, ISBN 978-3-86641-093-0 , p. 354.
- ↑ Chokri Cherif (Ed.): Textile materials for lightweight construction - Techniques - Process - Materials - Properties. Springer-Verlag, Berlin / Heidelberg 2011, ISBN 978-3-642-17991-4 , p. 120.
- ↑ Chokri Cherif (Ed.): Textile materials for lightweight construction - Techniques - Process - Materials - Properties. Springer-Verlag, Berlin / Heidelberg 2011, ISBN 978-3-642-17991-4 , p. 123.
- ↑ Product information on a 12 K roving. Carbon-Werke, accessed on May 24, 2020 .
- ↑ AVK - Industrial Association for Reinforced Plastics eV (Ed.): Handbook fiber composite plastics - Basics, processing, application. 3rd, completely revised edition, Vieweg + Teubner | GWV Fachverlage GmbH, Wiesbaden 2010, ISBN 978-3-8348-0881-3 , pp. 346-347.
- ↑ Manfred Neitzel, Peter Mitschang: Handbook composite materials - materials, processing, application. Carl Hanser Verlag, Munich / Vienna 2004, ISBN 3-446-22041-0 , p. 237.
- ↑ AVK - Industrial Association for Reinforced Plastics eV (Ed.): Handbook fiber composite plastics - Basics, processing, application. 3rd, completely revised edition, Vieweg + Teubner | GWV Fachverlage GmbH, Wiesbaden 2010, ISBN 978-3-8348-0881-3 , pp. 313-314.