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In today’s society we are always striving to be the biggest, fastest, strongest and most importantly loudest at everything we do. Now with the invention of the composite Hexacone the latter is certain to be achieved. Many audio engineers have now decided to manufacture speaker cones out of the aforementioned Hexacone in order to reach volumes which are unable to be achieved by paper, aluminium or polypropylene which are the commonly found in speakers today. Hexacone is used because of its very stiff and rigid properties. This is due to the fact that it is a composite made from two very strong materials in their own right. Hexacone is composed of two layers of Kevlar sandwiching a honeycomb core of Nomex.
Firstly Kevlar is an incredible material. Its combination of strength, lightness and flexibility means that it is extremely versatile and can out perform other materials in many different uses. Elsewhere Kevlar is used for bullet-proof jackets, sports equipment such as kayaks and skis and the ropes used in the landing of the Mars Pathfinder were made from Kevlar. When measured in a laboratory Kevlar was found to be up to five times the strength of steel on an equal weight basis. The reason for the strength is a combination of its chemical structure and the way it has been processed. Kevlar is an aromatic polymer or aramid, which could be described as a nylon and it is only manufactured as a fibre.
Its chemical name is paraphenylene terephthalamide and is made up from benzene rings, which are rings of carbon atoms joined by hydrogen molecules. Half the bonds in the rings are double bonded creating very strong strings of atoms. Kevlar’s structure consists of copolymer chains that are hydrogen bonded in a plane that is pleated and aligned radially. When the fibre is pulled along its axis it stretches before the load is applied directly to the bonds in the sheet plane. Another reason for Kevlar’s high strength and stiffness is in the way the material is spun, during the process of wet spinning liquid crystals form in the spinning solution and with its stiff linear molecules it causes a high degree of molecular orientation.
The other material used in Hexacone is Nomex, this is a chemical isomer of Kevlar, this means the molecules, the bonds between the atoms and the chemical formula is the same but they are just arranged in a different way. Nomex has slightly different properties, on the downside it is not as strong as Kevlar because the connections between the benzene rings are meta not para, and these meta links are kinked and this causes the polymer not to be as stiff but on the other hand Nomex has outstanding thermal stability and resistance to fire and along with the fact that it is comfortable to wear it means that it is the choice material for fire fighters, racing drivers and other high performance applications. This is because when the material is exposed to flame, it expands and thickens creating a protective barrier between the skin and the flame.
In the context of Hexacone, Nomex is manufactured as a honeycomb core and is made from Nomex paper. Honeycomb structures are the choice core in many different applications and most famously in aviation. The interior of body on planes use honeycomb structures because it can maintain high stiffness while being very lightweight at the same time, and they are used in speaker cones to prevent any deformation at high volumes. The honeycomb is saturated with a synthetic resin called phenolic resin. This saturation process creates a crystalline cell structure within the aramid paper that improves its mechanical properties.