JEC COMPOSITES MAGAZINE - Issue #39 - March/April 2008 - 114

Process g…/… Liquid composite moulding with honeycomb More information The EC group is a globally leading manufacturer of honeycombs based on Kevlar® and Nomex® paper. In 2006, the group had already foreseen the current developments in the composite industry, increasing its capacity by 30% with a new production line. Additional measures are underway to meet the growing market demand for honeycomb products. The group’s vision is to become the leading full-service solutions provider for advanced composites in all areas of transportation (air, space, land, sea) and in specialized fields like machine building and architecture. Therefore, EC can now offer any product from a preassembly over milled and formed panel and core details down to the plain sheet of honeycomb. Honeycomb is where it starts, not where it ends! aircraft industry have proved the claims of the EC-HLM technology as far as mechanical and bonding behavior (see table 1), surface quality, impact behavior (see table 2) and the prevention of water migration are concerned (Water tightness test according to AITM 2.0037, Test results: water tightness, no air bubbles during immersion Table 1: Test material of ECK Kevlar® honeycomb, carbon fabric 5H satin, 6 layers (0°/90°/+45°/-45°/90°/0°) on each side, Infusion with structural epoxy resin Test Method 4-Point-Bending (5 samples per testing) Reinforcement Test Result Panel 1 in W-Direction: 3202 N in L-Direction: 4930 N Panel 2 in W-Direction: 3238 N in L-Direction: 4739 N Panel 1 in W-Direction: 3657 N in L-Direction: 5198 N Panel 2 in W-Direction: 3509 N in L-Direction: 5181 N Panel 1 4,35 N/mm2 Panel 2 4,26 N/mm2 Behavior of Honeycomb Core failure New fields of application for honeycomb The EC-HLM technology will improve existing applications and introduce honeycomb to new fields of use. The cost-efficient, onestep process can be used with all types of EC honeycomb cores (Nomex®, Kevlar®, aluminium). It seals the honeycomb and prevents resin fill of the cells during the impregnation process. In comparison to parts manufactured with conventional prepreg/autoclave technology, the process offers the following advantages: - reduced material cost (dry fabric and pure resin instead of prepregs; less adhesive layers); - up to 10-15% weight saving (less adhesive films); - out-of-autoclave processing: lower process cost, 30% time reduction; - reduced outgoing inspection cost because of improved water tightness (no longer needs to be controlled); - improved operating properties (minimized porosity and sealed honeycomb), and therefore fewer problems with water condensing into the honeycomb cells. It was important to reach the following goals during the development of the infusion process: - making honeycomb core available for liquid moulding processes without filling the honeycomb cells with resin; - easy processing of flat and formed honeycomb parts; - core sealing with no need for thermal pre-treatment; - impermeability to liquid resin up to 180°C; - integrating a core sealing to reduce or prevent liquid ingress in service (due to water exposure or climatic changes); - compatibility with different types of resin systems and fabrics; - stabilizing the honeycomb/sealing in an integrated one-step process (during the curing process); - possibility to integrate fasteners and reinforcements into the sandwich structure despite core sealing. Tests performed in cooperation with customers from the European 3-Point-Bending (5 samples per testing) Core failure Flat wise tensile (22°C/75% RH) (6 samples per testing) Flat wise tensile (80°C) (2 samples per testing) Core failure Panel 1 3,47 N/mm2 Panel 2 3,38 N/mm2 Core failure Table 2: Process comparison between EC-HLM and conventional autoclave/prepreg process for impact test according to AITM 1-0057 Production method Materials Part made with EC-HLM Part made with autoclave/prepreg process ECA-4.8-96 (Nomex), 12 mm ECA-4.8-96 (Nomex), 12 mm 2 layers carbon fabric (twill 2/2) 2 layers carbon prepreg infused with structural (twill 2/2) + epoxy adhesive film epoxy resin Test Results Passed: 3.3 Joule Passed: 3.0 Joule Beside its activities in structural applications, EC formulated a resin which is especially focused on the EC-HLM technology, but can also be used in laminate parts for interior applications. For interior parts, weight and flame-retardancy are the most important requirements. The EC-RI-FST resin, which is filler free and exhibits very low viscosity (< 80 mPas), fulfils the requirements for aircraft interior parts either as a pure infusion laminate or in combination with honeycomb processed with the EC–HLM technology. Contact: bottler@euro-composites.com (technical) willkomm@euro-composites.com (commercial) JEC Composites Magazine / No39 March - April 2008
JEC COMPOSITES MAGAZINE - Issue #39 - March/April 2008

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #39 - March/April 2008
