Bumpers for trucks and HGVs are being increasingly manufactured from thermoplastics. The latest examples are the new models from Man’s TGX, TGS, TGL and TGM series. Unlike the previous models, their bumpers are no longer produced in one part from sheet moulding compounds (SMC). Instead, they are manufactured on a modular basis from several components, consisting of, for example, polyamide and polyester compounds from the Lanxess company, and have the advantage of being easier to repair. These materials are said to offer higher surface quality than SMC and are also tougher and easier to coat and do not require any post-finishing.
Alexander Büchler talks to Frank Krause, Lanxess at the Lanxess VDI booth in Mannheim
The headlamp supports of all four model series are made of Durethan DP BKV 60 H2.0 EF, a reinforced polyamide (PA) 6 with 60% glass fibres. The supports hold the headlamps and the light strips. They not only have to bear their weight which, in the case of the TGX and TGS, together amounts to around 8.5kg per headlight, they must also withstand high static and dynamic loads. For instance, they must not fracture even under severe dynamic acceleration of up to ten times the force of gravity. The high stiffness of PA6 helps ensure that there is no fluttering of the headlamps when driving in the dark, it is said.
Centre front step with high strength and stiffness
The U-shaped centre front step of the TGX and TGS, which is connected to the headlamp supports, is injection-moulded from the PET+PBT blend Pocan TS 3220, reinforced with 20% glass fibres. The part is provided with numerous ribs and designed for a static load of 2kN as it has to bear the weight of the driver as he climbs on to the front to clean the windscreen. The blend has adequate flexural stiffness for this, making steel reinforcement unnecessary. In addition, it provides good UV and weather-resistant surfaces that are easy to coat. The centre front step for the TGL and TGM, on the other hand, is made of highly reinforced Durethan DP BKV 60 H2.0 EF. The step is partly concealed by other components and in visible areas is provided with a cover of Pocan C 1206, an unreinforced PET+PC blend which features good surface quality, UV and weather stability. The cover can therefore be used either with or without a coating.
The headlamp supports of the TGX and TGS are made of a highly reinforced PA6. The U-shaped centre front step, which is connected to the headlamp supports, is injection-moulded from a PET+PBT blend. (photo: Lanxess)
Superior finish with PET+PC blend
With the bumpers of the TGL and TGM series, both the centre cover and the headlamp covers are also made of Pocan C 1206. The material features low shrinkage, high heat resistance and good low-temperature impact strength. The good surface quality and UV and weather resistance mean that the parts can also be used without a coating. The side covers of the headlamp supports must be easy to disassemble to ensure quick and easy lamp changes. A single-shell design with ribs and retainers on the back would have led to unsightly marks on the visible surfaces. For this reason, the covers were designed with twin walls and also provided with a fixing frame of Pocan C 1206 by ultrasonic welding.
The bumpers for the TGX and TGS series are produced by Mei Liberec, a production site of the Magna Exteriors & Interiors (Mei) Group belonging to the supplier Magna. The bumper systems for the TGL and TGM are made by Werkzeugbau Karl Krumpholz – Kunststofftechnik based in Redwitz, Germany.
www.lanxess.com
