Metal fiber
Metal fibers are man-made fibers made of metal, metal alloys, plastic-coated metal, metal-coated plastic or a core completely covered with metal.
Metal fibers have their origins in clothing and textile technology: gold and silver fibers have been used as yarns for decorating fabrics since ancient times . More recently, aluminum , aluminum-coated plastic, and nylon yarns have taken the place of gold and silver.
Today, the metal fiber industry primarily offers fibers made of stainless steel, nickel, titanium, copper and aluminum for numerous applications. Metal filaments can be provided with a transparent coating to prevent tarnishing as much as possible.
Metal fibers can also be produced by shearing processes with wire (steel wool) or foil as the starting material, or they are drawn in bundles from wires with a larger diameter, drawn from a block, cast from molten metal or can be wrapped around a core (core fiber, often made of carbon) be formed spun sheath fibers.
history
Gold and silver have been used since ancient times to decorate the clothing and textiles of kings, leading and distinguished personalities and the nobility . Many of these elegant textiles can be seen in museums around the world. Historically, a metallic thread consisted of a metal strip wrapped around a fiber core (cotton or silk), whereby it was often ensured that the color of the fiber core shimmered through to give the ornament a better look. Ancient textiles and clothing that are partially or wholly woven with gold threads are sometimes referred to as gold cloth . From the 7th to 9th centuries the gold fabrics were woven on Byzantine looms, then in Sicily , Cyprus , Lucca and Venice . Weaving also flourished in the 12th century under the influence of the legacy of Genghis Khan , when the arts and trade flourished under Mongol rule in China and some areas in the Middle East. The first modern metal fiber was manufactured by the Dobeckmum company in 1946.
In the early 1960s, Brunswick Corp. carried out a research program to develop an economically viable process for the production of metal threads. It started with the production of metal threads on a laboratory-scale test facility. Until 1964 Brunswick produced fine metal fibers with a diameter of 1 μm from stainless steel (AISI 304). The first large-scale production facility located in the USA was then commissioned by Brunswick in 1966. Nowadays, metal fibers are produced in large quantities and used in a wide variety of technology industries. This is a technically mature sector with a large number of applications.
In the past, aluminum was often used as a starting material for the manufacture of metal fibers. More recently, however, stainless steel has become the material most commonly used for metal fibers. Depending on the alloy, the metal fibers have properties that enable them to be used in high-tech applications.
Fiber properties
Metal fibers come in different shapes and diameters. In general, metal fibers with diameters from 100 μm to 1 μm are offered.
Metal fibers are produced both as long continuous fibers and as short fibers (with a ratio of length and diameter of less than 100).
Compared to other types of fiber such as carbon, glass or natural fibers, metal fibers have a low electrical resistance, so they are suitable for all applications where electrical conductivity is required. Thanks to their excellent heat resistance, they can withstand extreme temperatures. Their corrosion resistance is achieved through the use of high quality stainless steel alloys or other metal alloys. Metal fibers also offer other advantageous mechanical properties, such as high elongation at break, ductility, impact resistance, fire resistance and sound absorption.
Sintered metal fiber structures and products are characterized by high porosity with a consistently stable and resilient structure. These properties benefit the function and structure of specific applications such as filters or electrodes.
By coating the metal threads, tarnishing of the metal (oxidation) can be minimized. If suitable adhesives and foils are used, they are resistant to salt water, chlorinated water in swimming pools or climatic influences. If there is no care label, all metal fiber products should be dry-cleaned if possible. Ironing can be particularly problematic at high temperatures as the heat generated can melt the fibers.
production method
There are various methods of fiber production for metals.
The most common method is the so-called bundle drawing process. Several thousand wires are drawn as a bundle at the same time, ie they are bundled in what is known as a composite wire, which is drawn through a drawing nozzle to further reduce its diameter. The outer sheath is later dissolved in acid and what remains are the individual endless metal fibers. The composite wire is pulled until the desired diameter of the individual filaments within the bundle is reached. With the bundle drawing process, endless metal fibers can be produced in lengths of up to several kilometers. Naturally, the cross-section of the fibers produced with this method is octagonal. This technology can be refined to produce high quality fibers. The end result is very fine fibers with a very small diameter spread. Thanks to special developments in recent years, this technology can now be used to manufacture fibers with a diameter of 200 nm and smaller.
During lamination , an aluminum layer is sealed between two sheets of acetate or polyester film . These fibers can then be cut lengthways into strips and wound onto bobbins for the production of yarn. The metal can be colored and sealed with a transparent foil, the adhesive can be colored or the foil can be colored before lamination. Many different colors and effects can be realized with metal fibers, so that many different designs are possible.
With the " foil-shaving" technique (fibers are scraped off a foil), fiber diameters of up to 14 μm and a more rectangular cross-section are possible. This technique is used to produce “semi-endless” fiber bundles or staple fibers.
By machining solid metallic starting products, semi-endless bundles of fibers with a diameter of up to 10 μm can be produced. By optimizing the manufacturing process for staple fibers, the diameter spread for this type of fiber can be reduced and its geometry can be refined. This technique is unique due to the small diameter that can be achieved and the relatively small diameter spread compared to foil shaving or melt spinning
Another possibility for the production of metal fibers is metallization. In this process, the metal is heated until it evaporates , and then it is applied to a polyester film under high pressure. This process produces thinner, more flexible, more durable and easier to process fibers.
Metal fibers can also be produced by shearing processes using wire as the starting material (steel wool) or cast from molten metal or designed as jacket fibers spun around a core (core fiber, often made of carbon).
Types of metal fiber products
Sintered media
Metal fibers are processed either into a fleece or into sintered fiber structures with a fiber diameter of 1.5 to 80 μm. These porous filter media are used in very demanding applications because of their uniqueness. The advantage of a material with outstanding permeability (porosity of up to 90% for sintered fiber structures and up to 99% for non-woven structures) paired with high corrosion and temperature resistance is very much appreciated. The sintered porous structure has no binding agent, as the individual fibers are firmly bonded to one another through diffusion processes. Sintered 3D structures have also become standard. Some of the latest developments concern filter media, in which metallic and non-metallic fibers are combined and thus combine the best of "both worlds".
Short fibers
A specially developed process enables the production of individual, powder-like metal fibers, which are referred to as short fibers and have a length-to-diameter ratio of 100. These short fibers can be used alone or in combination with metal powders for the production of sintered filter structures with extremely high filtration performance and at the same time unique permeability.
Polymer pellets
Other metal fiber products are polymer pellets or granules made from metal fibers. Several fiber bundles are glued together, different sizes being possible and a correspondingly suitable extrusion coating being carried out. After these coated bundles have been cut into pellets, they can be used as additives in the production of technical, conductive / shielding plastic parts by means of injection molding or extrusion. The unique advantage of metal fibers is that a conductive composite can be formed with a relatively limited amount of conductive additives.
Nonwovens
As with conventional textile fibers, nonwovens or felts can also be made with metal fibers. In very few cases, the fibers can be intertwined by needling and thus the fleece can be consolidated.
Yarn
A bundle of endless stainless steel fibers can be used in textile spinning process to yarns to be processed. A distinction is made between yarn with a low proportion of metal fibers and yarn with a high proportion of metal fibers. The former can be processed into a filament yarn with a filament count of approximately 275 by twisting the bundle. Fiber bundles with several thousand fibers are typically processed further into spun yarns. For this purpose, the bundles are first stretched or stretched and then processed into a yarn using traditional spinning processes. The result is a yarn made from 100% metal fibers. During the spinning process, the cables can be mixed and mixed yarns can also be produced. Mixtures of the metal fibers with cotton, polyester and wool are possible. Accordingly, metal fibers can be further processed into various textile products using textile processes. Knitting (round and flat knitting as well as warp knitting) and weaving of textile surfaces are just as possible as braiding. Mixed fiber textiles can be produced by combining metal yarns with other yarns or by using yarns with two types of fibers, which are themselves a mixed yarn.
Electric cables
To produce cables , two or more filaments are twisted several times. During this process the torsion and straightness of the cables are monitored. The cable can be optimized for a specific application by combining filaments that differ in terms of strength, diameter or number of twists, or by preforming them.
Fiber composite materials
Metal fibers can be used as reinforcement fibers for composite materials and in this case lead to improved breaking behavior in the event of impact / shock loads and better electrical conductivity. The carbon or glass fibers traditionally used as reinforcement have a very limited elasticity, which leads to a brittle and explosive breaking behavior. Metal fibers counteract this perfectly: they can absorb significantly more energy before they break. The processing is no different from other fibers that are used for reinforcement in composite materials. It is even possible to combine metal fibers with other fibers in a “hybrid” composite structure that combines all the advantages of the individual materials carbon, glass and steel.
Manufacturer
Metal fibers are currently mainly manufactured in Europe. The largest and most integrated manufacturer of metal fibers in the world is the multinational Bekaert , headquartered in Belgium, with production facilities in Europe, Asia and America. There are still three manufacturers of metal thread in the USA. Metlon Corporation is one of the remaining manufacturers in the US that stocks a wide variety of laminated and non-laminated metal yarns. The Brightex Corporation (Japan) and Hwa Young (South Korea) also produce metal fibers. Metal fibers are also manufactured in China: there are more than 100 factories in the city of Dongyang, although some of these are more local than traditional factories. Two of the better known factories are Salu Metallic Yarn and Aoqi Textile.
Trademarks
Bekaert manufactures metal fibers and many related products such as continuous fibers, sintered media, nonwovens, polymer pellets, braided structures, fabrics, cables, yarns and short fibers. Established brand names are Bekipor, Beki-shield and Bekinox.
The company Lurex up in Europe for more than fifty years ago metallic fibers. It produces a wide variety of metal fiber products, including metal fibers used in clothing fabrics, embroidery , plaiting , knitwear, military uniforms, decorations, cords and cords. Most Lurex fibers consist of a metal ribbon that is laminated onto a polyamide film, but films made of polyester and viscose are also used. The fibers are also treated with a mineral-based lubricating oil called PW to make them easier to use and process.
Metlon Corporation is a metallic yarn manufacturer in the United States that has been making metallic yarn for more than sixty years. The metal yarns manufactured by Metlon consist of fibers cut into lengthwise strips that are wrapped with nylon. One end of the nylon thread is wound clockwise and the other counterclockwise around the metal thread. The most commonly used nylon material is 15 or 20 denier nylon, but higher denier materials are also used for special purposes.
use
Metal fibers are used in numerous industries and market segments.
Automobile manufacturing
Sintered parts based on metal fiber technology are used for diesel and gasoline particle filters as well as filters for crankcase ventilation .
Heat-resistant textile materials are made from metal fibers for glass bending processes in the automotive industry. These metal fiber fabrics protect the glass during the bending process, which is associated with very high temperatures and pressures.
Metal fibers are also used in heating cables for seat heating, in pipelines for selective catalytic reduction and in Adblue tanks . Metal fiber heating cables offer extremely high flexibility and durability compared to copper wire.
Aerospace
Metal fiber filters are used to filter the hydraulic fluid in the hydraulic systems of aircraft. In comparison to filter media made of glass fiber, metal fibers show excellent durability, as these fibers are metallically connected by a sintering process and no binding agent has to be used.
Metal fibers, which are processed into porous components or sheets by sintering, are used in the aircraft cabin as sound-absorbing elements and reduce the noise emissions of the heating, ventilation and air conditioning systems and the auxiliary engines .
Technical Textiles
Metal fibers can be used in textiles as antistatic fibers and in this capacity can be used in electrically insulating protective clothing or antistatic big bags.
Metal fiber textiles offer not only antistatic properties, but also a shielding effect against electromagnetic interference (EMI).
Textiles made from stainless steel fibers can be heated with electricity. In addition, stainless steel fibers can also be used for cut-resistant clothing (gloves). You could say that they are the chain armor of today.
Power generation
Metal fiber filters can achieve a very high porosity with very small pore sizes, which makes them suitable for high efficiency particulate air filters (HEPA) and high performance particulate filters (ultra low penetration air filters, ULPA). These filters are used, among other things, in nuclear power plants as a safety device to prevent a possible release of radioactive vapor.
marine
Metal fiber filters are used to clean marine fuel and lubricating oil.
Other uses of metal fibers
Another common area of application for metal fibers is upholstery and upholstery fabrics, such as lamé and brocade . Metal fibers are also widely used in weaving and embroidery . Nowadays, metal fibers are also increasingly used in the manufacture of clothing: from party and evening wear to sportswear for clubs to clothing for cold weather, survival clothing and everyday clothing. Metal yarns are processed into many fashionable fabrics and decorative elements (by weaving, braiding and knitting). For an even greater variety, metal yarns are twisted with other fibers such as wool, nylon, cotton and synthetic fibers to create new effects in clothing or decorative elements.
Stainless steel fibers and other metal fibers are used for communication lines such as telephone lines and lines for cable television.
Stainless steel fibers are also used in carpets . They are used as an admixture with other fibers so that they cannot be recognized. Their use increases the electrical conductivity of the carpets and thus reduces static charges. These types of carpets are often used in computer rooms where there is a much higher risk of static electricity. Other possible areas of application are tire cord, rocket tips, work clothing such as protective suits, space suits and cut-resistant gloves for butchers and other people who work in the area of cutting tools or other machines with cutting hazards.
Metal fibers can be used as reinforcement or to increase the electrical conductivity in fiber composite materials .