Henkel in collaboration with Benteler-SGL have made it possible to mass-produce lightweight, fibre-reinforced leaf springs using a polyurethane matrix resin system.
Lightweight composite construction technologies are steadily gaining ground in the automotive industry as the weight savings they achieve in modern cars help to significantly reduce fuel consumption and carbon emissions. Working with Benteler-SGL, Henkel has developed a process for resin transfer molding (RTM) of glass fibre reinforced leaf springs that uses a polyurethane matrix resin. Compared to conventional leaf springs made of steel, these composite leaf springs are up to 65 percent lighter.
Henkel says that its Loctite MAX 2 composite matrix resin is a composite matrix resin cures significantly faster than the epoxy products usually employed for the RTM process. Due to its low viscosity, the polyurethane resin penetrates and impregnates the fibre material more easily and less harshly, thus enabling very short injection times to be applied. One special feature of Loctite MAX 2 is its exceptionally high stress intensity factor, which is a measure of toughness. This excellent toughness also has a positive effect on the fatigue behavior under load. Leaf springs in cars are constantly subjected to dynamic loading under driving conditions, so the use of flexible materials with a high fatigue tolerance considerably prolongs the life of such components.
Resin injection processes such as RTM predominate in the manufacture of automotive composites for mass-produced automobiles because they make it possible to control the curing reaction more reliably, either by adjusting the temperature or adding an accelerator. Furthermore, the risk of local overheating and resulting shrinkage is reduced, as the polyurethane resin Loctite MAX 2 generates less heat overall during curing than epoxy resins do. As a result, even thick components with many fiber layers cure fast. The RTM process is especially attractive for volume production of cars as fast curing of the matrix resin permits short cycle times to be achieved.
The product range of Benteler-SGL includes body shell components such as side blades, doors and visible carbon components. The composite components, which are designed specifically for mass-production consist mainly of carbon and glass fibres in various textile forms such as stitched or woven fabrics.