Weaving is one of the oldest of humaninventions. Over time, it evolved frommanual craft methods to highly advanced,automated processes. The materials usedhave also evolved – from natural textilessuch as fibers of plant and animal originto synthetic polymers and even metals. In this context, it isn’t surprising thatstainless steel wire has made its way into current weaving processes. It is found inmany mesh applications, both spectacularand inconspicuous, but all essential toeveryday life. The many crevices formedby overlapping wires in mesh products areideal sites for crevice corrosion even inrelatively mild environments. It is thereforealso no surprise that molybdenum- containing stainless steel is the standard
material for such applications since moly improves resistance to corrosion,especially crevice corrosion.
Stainless steel mesh is traditionally usedfor filtering and screening in a wide rangeof industries from mining to processing,all the way to high-technology sectors. Architectural applications have emergedmore recently but are growing strongly,because stainless steel mesh offers bothaesthetic and functional benefits. Thecommon molybdenum grades, Types 316and 316L are the workhorses, but highermolybdenum grades such as 904L ornickel-based alloys are also used in moreaggressive environments.
Weaving techniques borrowed fromthe textile industry
The weaving of metallic mesh has employed the techniques and vocabularyof the textile industry. Fully automatedlooms for metal, like cloth looms, employshuttles, bobbins, and reels. Just as incloth looms, wires running along thelength of the mesh are called the warp;they wrap around stiffer cross wires orrods that are called the weft. Modern looms can weave single fibersless than one micron thick, tufts or strandscomposed of several braided fibers, cables, or solid wire of various shapeswith thicknesses up to 5 mm. Such loomscan produce mesh up to 20 meters longand 8 meters wide. Woven mesh is available as flat sheets or in rolls, in eitherstiff or supple form, depending upon thedimensions of the wire used to manu -facture the mesh and the details of themesh design.
Architectural applications
Stainless steel has long been used in architecture because of its aesthetic appeal and longevity. More recently stainless steel mesh made a strong entryinto the market because of its remarkablemix of properties. Mesh products can playmultiple roles, providing shading while allowing natural light to enter, ventilationwhile protecting from the elements, and safety while maintaining a pleasing appearance. Mesh offers the designercountless options for customization ofbuildings, structures and spaces. In manyinstances it is selected not only for its visual appeal but also for its contributionto energy-saving and sustainable design.The article on energy-saving stainless
Stainless steel wire and rod are used to manufacture a wide variety of woven steel mesh products. They are used in many applications ranging from the eye-catching and spectacular to the unobtrusive and utilitarian.Molybdenum contributes to their growing popularity and success by improving corrosion resistance.
steel facades in the January 2012 issueof MolyReview gives more detail on thissubject.
A second “skin” to encase buildings –A growing trend in modern architecture isto surround buildings in metal mesh toform a “second skin”. The mesh may beapplied as rigid flat panels, following thecontour of the building, or as flexiblemesh modifying its shape. In some casesthe “skin” can be used to dramatic effect,for example, in the Maison Folie of Lille,in northern France, where the spiralmesh takes on the appearance of a lightveil. But, at the same time, the mesh has the practical purpose of thermal insulation, reducing solar gain and windcooling, and therefore cutting the building’senergy requirements, while providing ameasure of privacy for the tenants.
The specific finish of the mesh (glossy or satin, darker or lighter color) and theever-changing play of clouds and sun, reflected by the stainless steel mesh,make a building come alive. At night, illumination can generate a transparent,colored or light-dimming effect. The meshcan also be fitted with an integrated
micro-LED lighting system to create programmed lighting effects used, for example, for advertising or for thescreening of a movie. Molybdenum containing stainless steel is nearly maintenance-free in these applicationsdue to its high corrosion resistance.
In high-rise parking garages – Meshallows escape of automotive exhaustgases, and allows sunlight to supplementinterior lighting, all the while securing the garage against intrusion and the elements, without leaving a closed-infeeling. Furthermore, woven metal sheetsare easy to install. They are simply secured along the perimeter, while solidsheet metal partitions require support and fixing substructures. Carefullythought-out screening on a garage facadecan transform the purely utilitarian andgenerally unsightly aspect of this type ofstructure to something visually pleasing.
Indoors – mesh from floor to ceiling –A tight weave that comes in rolls offers awear-resistant and unusually aestheticfloor covering. Metal mesh partitions divide spaces and provide a sense of privacy without completely closing them
off. Decorative and ornamental meshescan blend steel wires and cables withbuilt-in lighting or exotic materials to create specific ambiences that are highlyappreciated by hotel and restaurant de-signers. On the ceiling, stretched sheetsprovide good sound insulation and addan interesting decorative element. Thefire resistance of stainless steel mesh isanother strong point in its favor for architectural use, particularly in publicand commercial buildings.
Infrastructure applications –The Arganzuela walkway, spanning theManzaranes River in Madrid, designed byFrench architect Dominique Perrault,uses stainless steel mesh over the lengthof its double helix structure, serving asguardrails and a screen to protect walkersfrom the strong summer sun. In additionto these safety and protection functionsthe mesh’s semi-transparency preservesthe elegant design’s airiness. In Norwaystainless steel mesh protects users of the Holmenkollen ski-jump featured on the front cover. Over 7,000 m2 of Type 316L stainless steel mesh shroudthe spectacular flight of steel to protect athletes from the wind and reduce the
effects of the cold. By day, the sun’s raysplay on the metal mesh, while at night illumination creates an impressive rampof light.
Industrial applications
Architectural applications of stainless steelscreening and mesh are only the newest,and perhaps in some ways the most exciting uses of these products. However,mesh has long been used behind thescenes in industrial applications thathave underwritten our great technologicalprogress of the last century or more.
Screening, filtering, and sieving –These processes separate or removewet, humid or dry particles from their environment and are widely used inmany industries. A perfect illustration oftheir importance is in molybdenum mining, to use a close-to-home example.Winning molybdenite (MoS2) from theore in which it is entrapped requires converting hundreds of millions of tons oflarge rocks into micron-sized particles.They then have to be further treated toliberate and purify molybdenite so that it can be used in all the products that
support our society today. The processrequires many crushing and grindingsteps, each of which must also have ascreening step to separate smaller particles that can go on to the next stepof processing from larger ones that have to go through additional crushing andgrinding. The screens used in these stepsrequire materials having high strength,stability to maintain the proper openingsize, and in some steps resistance to corrosion from aggressive liquids.
Food, agricultural, pharmaceutical,metallurgical, pulp and paper, chemicaland petrochemical processing are otherindustries that depend on metal filters andscreens as do cars, trucks, airplanesand power plants. The wire material depends mainly on the corrosivity of theprocess. Materials include the austeniticstainless steels Type 316, Type 904L and 6% Mo grades, and the nickel-basedalloys Alloy 22 and Alloy 59, the latter forthe most corrosive fluids. There are many filter and sieve designs utilizing many different kinds of mesh. Filters can becylindrical (structured packs), flat, curvedor folded. Fine applications such as dyeand ink production may employ wire diameters and opening widths as smallas 0.02 mm. Coarse screens used in themining industry can have wire diametersup to 5 mm with opening widths as large as 18 mm. Large or small, industrialscreens, filters and sieves rely on moly-grade alloys because of their mechanicalstrength and their corrosion and abrasionresistance.
Belt conveyers – Metal belt conveyersare used in many industrial processes.For instance, they are used for the removal of liquids and moisture from solidwaste prior to burning in waste-to-energyplants. These belts must carry heavyloads at elevated temperatures, and beresistant to attack from the cocktail of fluids contained in such waste streams.
At the other end of the spectrum lie thestainless steel mesh belts used in foodprocessing. The food industry uses thesebelts extensively because they are easilycleaned, are resistant to aggressive sanitizing, and they work well in high andlow temperatures. Food processing belts are used to bake or toast foods attemperatures reaching 200°C; they arealso found in liquid-nitrogen spray-freezingtunnels that operate at temperatures aslow as -196°C.
Screen-printing mesh – from soda bottles to semiconductors –Metal mesh is frequently used for screen-printing because mechanical strength and abrasion resistance are essentialproperties for mesh materials in thisprocess. The mesh must support hightensile stresses arising from the fast passage of the squeegee as it forces thehigh-viscosity ink through the mesh. Forthis type of application, Type 316 wireshaving a diameter of 15 microns arecommonly used for the screen’s wefts.Type 316 stainless steel resists the corrosive inks and cleaning solvents thatare entrapped in the crevices where warp and weft wires cross. Screen-printingapplications range from conventional labeling for pharmaceutical and food bottles to advanced applications requiredby the semiconductor industry. Here, ultrafine woven metal meshes, for whichdimensional accuracy and printing sharp-ness are imperative, are used to print themasks of printed circuits and mark liquid
crystal displays and photovoltaic solarpanels. Molybdenum-containing stainlesssteel micromeshes are present in ink jetcartridges where they ensure the fluidityand proper distribution of inks ahead ofthe jets. Micromeshes made with wirehaving diameters smaller than one micronmay constitute the lower dimensionallimit that can be achieved in stainless steelwire meshes.
Summary
Just as woven fabrics evolved from simplenatural fibers woven by hand to producesimple items, woven metal mesh
has evolved from simple products using common materials to highly engineereddesigns that require sophisticated materials solutions for their successfuluse. Molybdenum-containing stainlesssteel and other moly-containing alloyssolve the problems posed by applicationsfor such new woven products, whether theneed is high strength, corrosion resistance,aesthetic properties, or heat resistance.We can expect to see more uses of these sophisticated materials systems as engineers and architects tackle ever more challenging problems and turn tomolybdenum containing materials for assistance. (Thierry Pierard)
