Nomex honeycomb is a commonly used composite core material manufactured with aramid fiber paper, known as Nomex paper, dipped in a heat resistant resin. The material takes its name from bee's honeycomb, a hexagonal sheet structure. This structure provides an excellent combination of strength and efficiency while at the same time reduces the weight of the component. For this reason honeycomb materials are widely used where their high strength to weight ratio is valuable in industries like aerospace, marine, military, construction, sports and automotive.
Honeycomb can be manufactured with other materials too, such as metal (aluminum), plastic (polypropylene), fiberglass and carbon fiber reinforced plastic. Today, 'Nomex' honeycomb in prepreg constructions dominate the market. Other honeycomb products are continuously developed mainly to cover more price sensitive uses and needs in the sandwich construction field.
Recent studies show an estimated growth in the Nomex honeycomb market. At the same time an estimated growth rate of commercial passenger aircrafts ranges from 3.4% to 5.3% annually between 2012 and 2030, if the market trend remains the same. In addition, new uses of Nomex honeycomb as in UAVs (unmanned aircraft vehicles) appear. Also, there is major optimism in luxury yacht industry, where honeycombs are used to make yachts more light-weight for speed and stability. Finally, because energy saving concerns become greater, Nomex honeycomb use in transportation is expected to increase as well.
NOMEX HONEYCOMB HISTORY
It’s said that the first paper honeycomb structures have been made by the Chinese 2000 years ago for ornaments, but no reference for this has been found. Paper honeycombs and the expansion production process have been invented in Halle/Saale in Germany by Hans Heilbrun in 1901 for decorative applications. For decorative applications, the expanded honeycomb production reached a remarkable degree of automation in the first decade of the 20th century. The technique of three process stages is still used today for honeycomb production: expansion, corrugation and moulding. This technique was already developed by 1901 for non-sandwich applications. The first use for industrial honeycomb in sandwich structure was reported in 1915 by the German Hugo Junkers who owned an airplane company.
The widespread use of core materials and honeycomb in composite manufacturing began in the 1970s, when sandwich construction was first widely recognized as important means to provide a stiffer, stronger and lighter alternative to solid laminates. Nomex fiber material was first marketed by DuPont earlier, in 1967, and was then used in order to construct driving suits for race car drivers, as it protects against fire and heat. Nomex paper, the material that is mostly used as advanced composites honeycomb core today, was introduced with great success a bit later.
NOMEX HONEYCOMB STRUCTURE
Nomex honeycomb is made of nomex paper, a form of paper made of aromatic polyamide -aramid- fibers. Nomex paper provides high electrical, mechanical and chemical integrity, moisture insensitivity, radiation and flame resistance. These unique characteristics make it the perfect solution for many applications, especially those which need to be lightweight and fire retardant.
An initial unstable expanded paper honeycomb structure is dipped into phenolic resin to produce a honeycomb core which (after cure) becomes very strong. Subsequent dipping cycles can increase strength and weight of the resulting product. Honeycomb cells can also be filled with Fibermax 2 component rigid foam for greater bond area for the skins. This manufacturing technique increases the mechanical properties of the core by stabilizing the cell walls and increases thermal and acoustic insulation properties.
The behavior of the honeycomb structures is orthotropic, hence the panels react differently depending on the orientation of the structure. Therefore it is necessary to distinguish between the directions of symmetry, the so-called L or ribbon direction and W or transverse-to-ribbon direction. The shear modulus and strength in the L direction are roughly twice than this in the W direction.
The manufacturing process
Fibermax Composites honeycomb is manufactured by the expansion method which is a quite simple process. Honeycomb starts out as flat sheets of Nomex paper material. Strips of adhesive are “printed” on the Nomex paper in a staggered pattern. Next, the sheets of paper are stacked together and cured to form a “HOBE” (honeycomb before expansion) block.The HOBE is pulled apart from its sides (or “expanded”), much like an accordion, forming an expanded honeycomb block, that now incorporates the hexagon cell shapes. This initially unstable expanded paper honeycomb cell structure is dipped into phenolic resin. Once cured, the blocks are cut to the honeycomb sheets with the desired thickness.
Fibermax Composites honeycomb is manufactured by the expansion method which is a quite simple process. Honeycomb starts out as flat sheets of Nomex paper material. Strips of adhesive are “printed” on the Nomex paper in a staggered pattern. Next, the sheets of paper are stacked together and cured to form a “HOBE” (honeycomb before expansion) block.The HOBE is pulled apart from its sides (or “expanded”), much like an accordion, forming an expanded honeycomb block, that now incorporates the hexagon cell shapes. This initially unstable expanded paper honeycomb cell structure is dipped into phenolic resin. Once cured, the blocks are cut to the honeycomb sheets with the desired thickness.
Cell configuration
Honeycomb can be made and cut to the standard hexagonal style which is and the most common cellular configuration, or it can be over-expanded in the W direction to form the corrugated or over-expanded (OX) configuration, where the cells look rectangular. The OX process tends to increase W sheer properties and slightly reduce L shear properties compared to hexagonal honeycomb core. There are also other configurations that Fibermax Composites can design depending customers specific needs.
Honeycomb can be made and cut to the standard hexagonal style which is and the most common cellular configuration, or it can be over-expanded in the W direction to form the corrugated or over-expanded (OX) configuration, where the cells look rectangular. The OX process tends to increase W sheer properties and slightly reduce L shear properties compared to hexagonal honeycomb core. There are also other configurations that Fibermax Composites can design depending customers specific needs.
MAIN ADVANTAGES
Fibermax Nomex honeycomb is used in numerous engineering and scientific applications in industries including the aerospace, marine, military, sports, construction and automotive markets. Because it is characterized by great stiffness to weight ratio, all the applications are structural. More specifically:
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Aircraft parts including sidewalls, galleys, seating, ailerons, flooring and ceiling
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Aircraft leading and trailing edges
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Protective structures in race cars
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Crash testing barriers
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Rail parts (doors, floors, ceilings)
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Hull composites
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Navy bulkhead joiner panels
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Military shelters
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Snowboards and skis
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Racing shells
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Energy absorption protective structures
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Radar and telecommunication industry (antennas, radomes)
Nomex honeycomb has been the first choice for composite aircraft structures, but moisture accumulation, because of the open cells has been a crucial matter. That's why aircraft manufacturers are looking for new closed-cell foam products, suitable for sandwich applications that overcome this weakness.
Fibermax honeycomb products are available in different cell size, thickness and strength. In order to determine the most appropriate type for an application some attributes should be considered including: cost against performance, size, density, stiffness, facings, color, mechanical-electrical properties, moisture absorption. Some readily available Nomex honeycomb products are:
| Type | Thickness | Cell size | Density | Strength | Modulus |
| 1 | 1.5 mm | 3.2 mm | 48Kg/m3 | 300 PSI | 18.5 KSI |
| 2 | 2 mm | 3.2 mm | 48Kg/m3 | 300 PSI | 18.5 KSI |
| 3 | 3 mm | 3.2 mm | 48Kg/m3 | 300 PSI | 18.5 KSI |
| 4 | 4 mm | 3.2 mm | 48Kg/m3 | 300 PSI | 18.5 KSI |
| 5 | 5 mm | 3.2 mm | 48Kg/m3 | 300 PSI | 18.5 KSI |
| 6 | 7 mm | 3.2 mm | 48Kg/m3 | 150 PSI | 11 KSI |
| 7 | 10 mm | 3.2 mm | 48Kg/m3 | 300 PSI | 18.5 KSI |
| 8 | 15 mm | 3.2 mm | 48Kg/m3 | 150 PSI | 11 KSI |
| 9 | 20 mm | 3.2 mm | 48Kg/m3 | 150 PSI | 11 KSI |
| 10 | 25 mm | 3.2 mm | 48Kg/m3 | 150 PSI | 11 KSI |
| 11 | 30 mm | 3.2 mm | 48Kg/m3 | 150 PSI | 11 KSI |
For any other type of Nomex honeycomb products and special orders (different thickness, weight, cell size) please contact. However, those special products maybe subject to minimum order level.